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# SOME DESCRIPTIVE TITLE # Copyright (C) YEAR The FreeBSD Project # This file is distributed under the same license as the FreeBSD Documentation package. # FIRST AUTHOR <EMAIL@ADDRESS>, YEAR. # #, fuzzy msgid "" msgstr "" "Project-Id-Version: FreeBSD Documentation VERSION\n" "POT-Creation-Date: 2026-05-19 11:05-0300\n" "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n" "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n" "Language-Team: LANGUAGE <[email protected]>\n" "Language: \n" "MIME-Version: 1.0\n" "Content-Type: text/plain; charset=UTF-8\n" "Content-Transfer-Encoding: 8bit\n" #. type: YAML Front Matter: description #: documentation/content/en/articles/x86-assembly/_index.adoc:1 #, no-wrap msgid "A tutorial on writing programs for FreeBSD in x86 assembly language" msgstr "" #. type: Title = #: documentation/content/en/articles/x86-assembly/_index.adoc:1 #: documentation/content/en/articles/x86-assembly/_index.adoc:11 #, no-wrap msgid "x86 Assembly Language Programming" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:46 msgid "" "_This article was written by {stanislav} (2001), and adjusted by {mhorne} " "(2026)._" msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:50 msgid "The content in this article is historical." msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:53 #, no-wrap msgid "Synopsis" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:57 msgid "" "Assembly language programming under UNIX(R) is highly undocumented. It is " "generally assumed that no one would ever want to use it because various UNIX " "systems run on different microprocessors, so everything should be written in " "C for portability." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:61 msgid "" "In reality, C portability is quite a myth. Even C programs need to be " "modified when ported from one UNIX to another, regardless of what processor " "each runs on. Typically, such a program is full of conditional statements " "depending on the system it is compiled for." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:63 msgid "" "Even if we believe that all of UNIX software should be written in C, or some " "other high-level language, we still need assembly language programmers: Who " "else would write the section of C library that accesses the kernel?" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:65 msgid "" "In this article I will attempt to show you how you can use assembly language " "writing UNIX programs, specifically under FreeBSD." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:70 msgid "" "This article does not explain the basics of assembly language. There are " "enough resources about that (for a complete online course in assembly " "language, see Randall Hyde's http://webster.cs.ucr.edu/[Art of Assembly " "Language]; or if you prefer a printed book, take a look at Jeff Duntemann's " "Assembly Language Step-by-Step (ISBN: 0471375233). However, once the " "article is finished, any assembly language programmer will be able to write " "programs for FreeBSD quickly and efficiently." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:72 #: documentation/content/en/articles/x86-assembly/_index.adoc:4287 msgid "Copyright (R) 2000-2001 G. Adam Stanislav. All rights reserved." msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:74 #, no-wrap msgid "The Tools" msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:77 #, no-wrap msgid "The Assembler" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:81 msgid "" "The most important tool for assembly language programming is the assembler, " "the software that converts assembly language code into machine language. " "Two very different types of assemblers are available for FreeBSD." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:84 msgid "" "The first is the GNU man:as[1] (package:devel/binutils[]), which uses the " "traditional UNIX assembly language syntax. Alternatively, one can use " "man:clang[1], which is a compatible replacement for the GNU assembler and " "comes with the system." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:87 msgid "" "The other is man:nasm[1] (package:devel/nasm[]). This assembler uses the " "Intel syntax, and its main advantage is that it can assemble code for many " "operating systems." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:90 msgid "" "This article uses nasm syntax because most assembly language programmers " "coming to FreeBSD from other operating systems will find it easier to " "understand. And, because, quite frankly, that is what I am used to." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:92 #, no-wrap msgid "The Linker" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:95 msgid "" "The output of the assembler, like that of any compiler, needs to be linked " "to form an executable file." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:98 msgid "" "The standard man:ld[1] linker comes with FreeBSD. It works with the code " "assembled with either assembler." msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:100 #, no-wrap msgid "System Calls" msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:103 #, no-wrap msgid "Default Calling Convention" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:107 msgid "" "By default, the FreeBSD kernel uses the C calling convention. Further, " "although the kernel is accessed using `int 80h`, it is assumed the program " "will call a function that issues `int 80h`, rather than issuing `int 80h` " "directly." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:110 msgid "" "This convention is very convenient, and quite superior to the Microsoft(R) " "convention used by MS-DOS(R). Why? Because the UNIX convention allows any " "program written in any language to access the kernel." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:113 msgid "" "An assembly language program can do that as well. For example, we could " "open a file:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:119 #, no-wrap msgid "" "kernel:\n" "\tint\t80h\t; Call kernel\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:128 #, no-wrap msgid "" "open:\n" "\tpush\tdword mode\n" "\tpush\tdword flags\n" "\tpush\tdword path\n" "\tmov\teax, 5\n" "\tcall\tkernel\n" "\tadd\tesp, byte 12\n" "\tret\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:132 msgid "" "This is a very clean and portable way of coding. If you need to port the " "code to a UNIX system which uses a different interrupt, or a different way " "of passing parameters, all you need to change is the kernel procedure." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:136 msgid "" "But assembly language programmers like to shave off cycles. The above " "example requires a `call/ret` combination. We can eliminate it by " "``push``ing an extra dword:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:147 #, no-wrap msgid "" "open:\n" "\tpush\tdword mode\n" "\tpush\tdword flags\n" "\tpush\tdword path\n" "\tmov\teax, 5\n" "\tpush\teax\t\t; Or any other dword\n" "\tint\t80h\n" "\tadd\tesp, byte 16\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:150 msgid "" "The `5` that we have placed in `EAX` identifies the kernel function, in this " "case `open`." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:152 #, no-wrap msgid "Alternate Calling Convention" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:157 msgid "" "FreeBSD is an extremely flexible system. It offers other ways of calling " "the kernel. For it to work, however, the system must have Linux(R) " "emulation installed." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:162 msgid "" "Linux is a UNIX-like system. However, its kernel uses the same system-call " "convention of passing parameters in registers MS-DOS does. As with the UNIX " "convention, the function number is placed in `EAX`. The parameters, " "however, are not passed on the stack but in `EBX, ECX, EDX, ESI, EDI, EBP`:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:171 #, no-wrap msgid "" "open:\n" "\tmov\teax, 5\n" "\tmov\tebx, path\n" "\tmov\tecx, flags\n" "\tmov\tedx, mode\n" "\tint\t80h\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:177 msgid "" "This convention has a great disadvantage over the UNIX(R) way, at least as " "far as assembly language programming is concerned: Every time you make a " "kernel call you must `push` the registers, then `pop` them later. This " "makes your code bulkier and slower. Nevertheless, FreeBSD gives you a " "choice." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:180 msgid "" "If you do choose the Linux convention, you must let the system know about " "it. After your program is assembled and linked, you need to brand the " "executable:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:184 #, no-wrap msgid "% brandelf -t Linux filename\n" msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:187 #, no-wrap msgid "Which Convention Should You Use?" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:192 msgid "" "If you are coding specifically for FreeBSD, you should always use the UNIX " "convention: It is faster, you can store global variables in registers, you " "do not have to brand the executable, and you do not impose the installation " "of the Linux emulation package on the target system." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:195 msgid "" "If you want to create portable code that can also run on Linux, you will " "probably still want to give the FreeBSD users as efficient a code as " "possible. I will show you how you can accomplish that after I have " "explained the basics." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:197 #, no-wrap msgid "Call Numbers" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:201 msgid "" "To tell the kernel which system service you are calling, place its number in " "`EAX`. Of course, you need to know what the number is." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:203 #, no-wrap msgid "The [.filename]#syscalls# File" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:207 msgid "" "The numbers are listed in [.filename]#syscalls#. `locate syscalls` finds " "this file in several different formats, all produced automatically from " "[.filename]#syscalls.master#." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:210 msgid "" "You can find the master file for the default UNIX calling convention in " "[.filename]#/usr/src/sys/kern/syscalls.master#. If you need to use the " "other convention implemented in the Linux emulation mode, read [.filename]#/" "usr/src/sys/i386/linux/syscalls.master#." msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:214 msgid "" "Not only do FreeBSD and Linux use different calling conventions, they " "sometimes use different numbers for the same functions." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:217 msgid "[.filename]#syscalls.master# describes how the call is to be made:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:228 #, no-wrap msgid "" "0\tSTD\tNOHIDE\t{ int nosys(void); } syscall nosys_args int\n" "1\tSTD\tNOHIDE\t{ void exit(int rval); } exit rexit_args void\n" "2\tSTD\tPOSIX\t{ int fork(void); }\n" "3\tSTD\tPOSIX\t{ ssize_t read(int fd, void *buf, size_t nbyte); }\n" "4\tSTD\tPOSIX\t{ ssize_t write(int fd, const void *buf, size_t nbyte); }\n" "5\tSTD\tPOSIX\t{ int open(char *path, int flags, int mode); }\n" "6\tSTD\tPOSIX\t{ int close(int fd); }\n" "etc...\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:231 msgid "It is the leftmost column that tells us the number to place in `EAX`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:234 msgid "" "The rightmost column tells us what parameters to `push`. They are " "``push``ed _from right to left_." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:236 msgid "" "For example, to `open` a file, we need to `push` the `mode` first, then " "`flags`, then the address at which the `path` is stored." msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:238 #, no-wrap msgid "Return Values" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:242 msgid "" "A system call would not be useful most of the time if it did not return some " "kind of a value: The file descriptor of an open file, the number of bytes " "read to a buffer, the system time, etc." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:245 msgid "" "Additionally, the system needs to inform us if an error occurs: A file does " "not exist, system resources are exhausted, we passed an invalid parameter, " "etc." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:247 #, no-wrap msgid "Man Pages" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:251 msgid "" "The traditional place to look for information about various system calls " "under UNIX systems are the manual pages. FreeBSD describes its system calls " "in section 2, sometimes in section 3." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:253 msgid "For example, man:open[2] says:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:257 msgid "" "If successful, `open()` returns a non-negative integer, termed a file " "descriptor. It returns `-1` on failure, and sets `errno` to indicate the " "error." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:259 msgid "" "The assembly language programmer new to UNIX and FreeBSD will immediately " "ask the puzzling question: Where is `errno` and how do I get to it?" msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:264 msgid "" "The information presented in the manual pages applies to C programs. The " "assembly language programmer needs additional information." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:267 #, no-wrap msgid "Where Are the Return Values?" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:272 msgid "" "Unfortunately, it depends... For most system calls it is in `EAX`, but not " "for all. A good rule of thumb, when working with a system call for the " "first time, is to look for the return value in `EAX`. If it is not there, " "you need further research." msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:278 msgid "" "I am aware of one system call that returns the value in `EDX`: `SYS_fork`. " "All others I have worked with use `EAX`. But I have not worked with them " "all yet." msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:283 msgid "" "If you cannot find the answer here or anywhere else, study libc source code " "and see how it interfaces with the kernel." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:286 #, no-wrap msgid "Where Is `errno`?" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:289 msgid "Actually, nowhere..." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:292 msgid "" "`errno` is part of the C language, not the UNIX kernel. When accessing " "kernel services directly, the error code is returned in `EAX`, the same " "register the proper return value generally ends up in." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:296 msgid "" "This makes perfect sense. If there is no error, there is no error code. If " "there is an error, there is no return value. One register can contain " "either." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:298 #, no-wrap msgid "Determining an Error Occurred" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:301 msgid "" "When using the standard FreeBSD calling convention, the `carry flag` is " "cleared upon success, set upon failure." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:304 msgid "" "When using the Linux emulation mode, the signed value in `EAX` is non-" "negative upon success, and contains the return value. In case of an error, " "the value is negative, i.e., `-errno`." msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:306 #, no-wrap msgid "Creating Portable Code" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:311 msgid "" "Portability is generally not one of the strengths of assembly language. " "Yet, writing assembly language programs for different platforms is possible, " "especially with nasm. I have written assembly language libraries that can " "be assembled for such different operating systems as Windows(R) and FreeBSD." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:313 msgid "" "It is all the more possible when you want your code to run on two platforms " "which, while different, are based on similar architectures." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:317 msgid "" "For example, FreeBSD is UNIX, Linux is UNIX-like. I only mentioned three " "differences between them (from an assembly language programmer's " "perspective): The calling convention, the function numbers, and the way of " "returning values." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:319 #, no-wrap msgid "Dealing with Function Numbers" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:324 msgid "" "In many cases the function numbers are the same. However, even when they " "are not, the problem is easy to deal with: Instead of using numbers in your " "code, use constants which you have declared differently depending on the " "target architecture:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:332 #, no-wrap msgid "" "%ifdef\tLINUX\n" "%define\tSYS_execve\t11\n" "%else\n" "%define\tSYS_execve\t59\n" "%endif\n" msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:335 #, no-wrap msgid "Dealing with Conventions" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:338 msgid "" "Both, the calling convention, and the return value (the `errno` problem) can " "be resolved with macros:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:342 #, no-wrap msgid "%ifdef\tLINUX\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:346 #, no-wrap msgid "" "%macro\tsystem\t0\n" "\tcall\tkernel\n" "%endmacro\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:355 #, no-wrap msgid "" "align 4\n" "kernel:\n" "\tpush\tebx\n" "\tpush\tecx\n" "\tpush\tedx\n" "\tpush\tesi\n" "\tpush\tedi\n" "\tpush\tebp\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:362 #, no-wrap msgid "" "\tmov\tebx, [esp+32]\n" "\tmov\tecx, [esp+36]\n" "\tmov\tedx, [esp+40]\n" "\tmov\tesi, [esp+44]\n" "\tmov\tebp, [esp+48]\n" "\tint\t80h\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:369 #, no-wrap msgid "" "\tpop\tebp\n" "\tpop\tedi\n" "\tpop\tesi\n" "\tpop\tedx\n" "\tpop\tecx\n" "\tpop\tebx\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:374 #, no-wrap msgid "" "\tor\teax, eax\n" "\tjs\t.errno\n" "\tclc\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:379 #, no-wrap msgid "" ".errno:\n" "\tneg\teax\n" "\tstc\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:381 #, no-wrap msgid "%else\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:385 #, no-wrap msgid "" "%macro\tsystem\t0\n" "\tint\t80h\n" "%endmacro\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:387 #, no-wrap msgid "%endif\n" msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:390 #, no-wrap msgid "Dealing with Other Portability Issues" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:394 msgid "" "The above solutions can handle most cases of writing code portable between " "FreeBSD and Linux. Nevertheless, with some kernel services the differences " "are deeper." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:397 msgid "" "In that case, you need to write two different handlers for those particular " "system calls, and use conditional assembly. Luckily, most of your code does " "something other than calling the kernel, so usually you will only need a few " "such conditional sections in your code." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:399 #, no-wrap msgid "Using a Library" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:403 msgid "" "You can avoid portability issues in your main code altogether by writing a " "library of system calls. Create a separate library for FreeBSD, a different " "one for Linux, and yet other libraries for more operating systems." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:408 msgid "" "In your library, write a separate function (or procedure, if you prefer the " "traditional assembly language terminology) for each system call. Use the C " "calling convention of passing parameters. But still use `EAX` to pass the " "call number in. In that case, your FreeBSD library can be very simple, as " "many seemingly different functions can be just labels to the same code:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:416 #, no-wrap msgid "" "sys.open:\n" "sys.close:\n" "[etc...]\n" "\tint\t80h\n" "\tret\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:420 msgid "" "Your Linux library will require more different functions. But even here you " "can group system calls using the same number of parameters:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:431 #, no-wrap msgid "" "sys.exit:\n" "sys.close:\n" "[etc... one-parameter functions]\n" "\tpush\tebx\n" "\tmov\tebx, [esp+12]\n" "\tint\t80h\n" "\tpop\tebx\n" "\tjmp\tsys.return\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:433 #, no-wrap msgid "...\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:439 #, no-wrap msgid "" "sys.return:\n" "\tor\teax, eax\n" "\tjs\tsys.err\n" "\tclc\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:444 #, no-wrap msgid "" "sys.err:\n" "\tneg\teax\n" "\tstc\n" "\tret\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:451 msgid "" "The library approach may seem inconvenient at first because it requires you " "to produce a separate file your code depends on. But it has many " "advantages: For one, you only need to write it once and can use it for all " "your programs. You can even let other assembly language programmers use it, " "or perhaps use one written by someone else. But perhaps the greatest " "advantage of the library is that your code can be ported to other systems, " "even by other programmers, by simply writing a new library without any " "changes to your code." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:453 msgid "" "If you do not like the idea of having a library, you can at least place all " "your system calls in a separate assembly language file and link it with your " "main program. Here, again, all porters have to do is create a new object " "file to link with your main program." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:455 #, no-wrap msgid "Using an Include File" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:458 msgid "" "If you are releasing your software as (or with) source code, you can use " "macros and place them in a separate file, which you include in your code." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:461 msgid "" "Porters of your software will simply write a new include file. No library " "or external object file is necessary, yet your code is portable without any " "need to edit the code." msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:466 msgid "" "This is the approach we will use throughout this article. We will name our " "include file [.filename]#system.inc#, and add to it whenever we deal with a " "new system call." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:469 msgid "" "We can start our [.filename]#system.inc# by declaring the standard file " "descriptors:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:475 #, no-wrap msgid "" "%define\tstdin\t0\n" "%define\tstdout\t1\n" "%define\tstderr\t2\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:478 msgid "Next, we create a symbolic name for each system call:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:487 #, no-wrap msgid "" "%define\tSYS_nosys\t0\n" "%define\tSYS_exit\t1\n" "%define\tSYS_fork\t2\n" "%define\tSYS_read\t3\n" "%define\tSYS_write\t4\n" "; [etc...]\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:490 msgid "" "We add a short, non-global procedure with a long name, so we do not " "accidentally reuse the name in our code:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:498 #, no-wrap msgid "" "section\t.text\n" "align 4\n" "access.the.bsd.kernel:\n" "\tint\t80h\n" "\tret\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:501 msgid "We create a macro which takes one argument, the syscall number:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:508 #, no-wrap msgid "" "%macro\tsystem\t1\n" "\tmov\teax, %1\n" "\tcall\taccess.the.bsd.kernel\n" "%endmacro\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:512 msgid "" "Finally, we create macros for each syscall. These macros take no arguments." msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:518 #, no-wrap msgid "" "%macro\tsys.exit\t0\n" "\tsystem\tSYS_exit\n" "%endmacro\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:522 #, no-wrap msgid "" "%macro\tsys.fork\t0\n" "\tsystem\tSYS_fork\n" "%endmacro\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:526 #, no-wrap msgid "" "%macro\tsys.read\t0\n" "\tsystem\tSYS_read\n" "%endmacro\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:530 #, no-wrap msgid "" "%macro\tsys.write\t0\n" "\tsystem\tSYS_write\n" "%endmacro\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:532 #, no-wrap msgid "; [etc...]\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:536 msgid "" "Go ahead, enter it into your editor and save it as [.filename]#system.inc#. " "We will add more to it as we discuss more syscalls." msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:538 #, no-wrap msgid "Our First Program" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:541 msgid "We are now ready for our first program, the mandatory Hello, World!" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:545 #, no-wrap msgid "\t%include\t'system.inc'\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:549 #, no-wrap msgid "" "\tsection\t.data\n" "\thello\tdb\t'Hello, World!', 0Ah\n" "\thbytes\tequ\t$-hello\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:557 #, no-wrap msgid "" "\tsection\t.text\n" "\tglobal\t_start\n" "_start:\n" "\tpush\tdword hbytes\n" "\tpush\tdword hello\n" "\tpush\tdword stdout\n" "\tsys.write\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:560 #, no-wrap msgid "" "\tpush\tdword 0\n" "\tsys.exit\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:563 msgid "" "Here is what it does: Line 1 includes the defines, the macros, and the code " "from [.filename]#system.inc#." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:567 msgid "" "Lines 3-5 are the data: Line 3 starts the data section/segment. Line 4 " "contains the string \"Hello, World!\" followed by a new line (`0Ah`). Line " "5 creates a constant that contains the length of the string from line 4 in " "bytes." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:571 msgid "" "Lines 7-16 contain the code. Note that FreeBSD uses the _elf_ file format " "for its executables, which requires every program to start at the point " "labeled `_start` (or, more precisely, the linker expects that). This label " "has to be global." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:573 msgid "" "Lines 10-13 ask the system to write `hbytes` bytes of the `hello` string to " "`stdout`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:576 msgid "" "Lines 15-16 ask the system to end the program with the return value of `0`. " "The `SYS_exit` syscall never returns, so the code ends there." msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:584 msgid "" "If you have come to UNIX from MS-DOS assembly language background, you may " "be used to writing directly to the video hardware. You will never have to " "worry about this in FreeBSD, or any other flavor of UNIX. As far as you are " "concerned, you are writing to a file known as [.filename]#stdout#. This can " "be the video screen, or a telnet terminal, or an actual file, or even the " "input of another program. Which one it is, is for the system to figure out." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:587 #, no-wrap msgid "Assembling the Code" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:591 msgid "" "Type the code in an editor, and save it in a file named " "[.filename]#hello.asm#. You need package:devel/nasm[] to assemble it." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:593 msgid "Now you can assemble, link, and run the code:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:601 #, no-wrap msgid "" "% nasm -f elf hello.asm\n" "% ld -s -o hello hello.o\n" "% ./hello\n" "Hello, World!\n" "%\n" msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:604 #, no-wrap msgid "Writing UNIX Filters" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:607 msgid "" "A common type of UNIX application is a filter-a program that reads data from " "the [.filename]#stdin#, processes it somehow, then writes the result to " "[.filename]#stdout#." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:610 msgid "" "In this chapter, we shall develop a simple filter, and learn how to read " "from [.filename]#stdin# and write to [.filename]#stdout#. This filter will " "convert each byte of its input into a hexadecimal number followed by a blank " "space." msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:614 #: documentation/content/en/articles/x86-assembly/_index.adoc:708 #: documentation/content/en/articles/x86-assembly/_index.adoc:798 #: documentation/content/en/articles/x86-assembly/_index.adoc:926 #: documentation/content/en/articles/x86-assembly/_index.adoc:1193 #: documentation/content/en/articles/x86-assembly/_index.adoc:2313 #: documentation/content/en/articles/x86-assembly/_index.adoc:3311 #, no-wrap msgid "%include\t'system.inc'\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:618 #: documentation/content/en/articles/x86-assembly/_index.adoc:712 #, no-wrap msgid "" "section\t.data\n" "hex\tdb\t'0123456789ABCDEF'\n" "buffer\tdb\t0, 0, ' '\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:630 #, no-wrap msgid "" "section\t.text\n" "global\t_start\n" "_start:\n" "\t; read a byte from stdin\n" "\tpush\tdword 1\n" "\tpush\tdword buffer\n" "\tpush\tdword stdin\n" "\tsys.read\n" "\tadd\tesp, byte 12\n" "\tor\teax, eax\n" "\tje\t.done\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:640 #, no-wrap msgid "" "\t; convert it to hex\n" "\tmovzx\teax, byte [buffer]\n" "\tmov\tedx, eax\n" "\tshr\tdl, 4\n" "\tmov\tdl, [hex+edx]\n" "\tmov\t[buffer], dl\n" "\tand\tal, 0Fh\n" "\tmov\tal, [hex+eax]\n" "\tmov\t[buffer+1], al\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:648 #, no-wrap msgid "" "\t; print it\n" "\tpush\tdword 3\n" "\tpush\tdword buffer\n" "\tpush\tdword stdout\n" "\tsys.write\n" "\tadd\tesp, byte 12\n" "\tjmp\tshort _start\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:652 #: documentation/content/en/articles/x86-assembly/_index.adoc:755 #, no-wrap msgid "" ".done:\n" "\tpush\tdword 0\n" "\tsys.exit\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:660 msgid "" "In the data section we create an array called `hex`. It contains the 16 " "hexadecimal digits in ascending order. The array is followed by a buffer " "which we will use for both input and output. The first two bytes of the " "buffer are initially set to `0`. This is where we will write the two " "hexadecimal digits (the first byte also is where we will read the input). " "The third byte is a space." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:662 msgid "" "The code section consists of four parts: Reading the byte, converting it to " "a hexadecimal number, writing the result, and eventually exiting the program." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:668 msgid "" "To read the byte, we ask the system to read one byte from " "[.filename]#stdin#, and store it in the first byte of the `buffer`. The " "system returns the number of bytes read in `EAX`. This will be `1` while " "data is coming, or `0`, when no more input data is available. Therefore, we " "check the value of `EAX`. If it is `0`, we jump to `.done`, otherwise we " "continue." msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:672 msgid "" "For simplicity sake, we are ignoring the possibility of an error condition " "at this time." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:677 msgid "" "The hexadecimal conversion reads the byte from the `buffer` into `EAX`, or " "actually just `AL`, while clearing the remaining bits of `EAX` to zeros. We " "also copy the byte to `EDX` because we need to convert the upper four bits " "(nibble) separately from the lower four bits. We store the result in the " "first two bytes of the buffer." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:680 msgid "" "Next, we ask the system to write the three bytes of the buffer, i.e., the " "two hexadecimal digits and the blank space, to [.filename]#stdout#. We then " "jump back to the beginning of the program and process the next byte." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:682 msgid "" "Once there is no more input left, we ask the system to exit our program, " "returning a zero, which is the traditional value meaning the program was " "successful." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:684 msgid "" "Go ahead, and save the code in a file named [.filename]#hex.asm#, then type " "the following (the `^D` means press the control key and type `D` while " "holding the control key down):" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:693 #, no-wrap msgid "" "% nasm -f elf hex.asm\n" "% ld -s -o hex hex.o\n" "% ./hex\n" "Hello, World!\n" "48 65 6C 6C 6F 2C 20 57 6F 72 6C 64 21 0A Here I come!\n" "48 65 72 65 20 49 20 63 6F 6D 65 21 0A ^D %\n" msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:699 msgid "" "If you are migrating to UNIX from MS-DOS, you may be wondering why each line " "ends with `0A` instead of `0D 0A`. This is because UNIX does not use the cr/" "lf convention, but a \"new line\" convention, which is `0A` in hexadecimal." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:704 msgid "" "Can we improve this? Well, for one, it is a bit confusing because once we " "have converted a line of text, our input no longer starts at the beginning " "of the line. We can modify it to print a new line instead of a space after " "each `0A`:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:717 #, no-wrap msgid "" "section\t.text\n" "global\t_start\n" "_start:\n" "\tmov\tcl, ' '\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:727 #, no-wrap msgid "" ".loop:\n" "\t; read a byte from stdin\n" "\tpush\tdword 1\n" "\tpush\tdword buffer\n" "\tpush\tdword stdin\n" "\tsys.read\n" "\tadd\tesp, byte 12\n" "\tor\teax, eax\n" "\tje\t.done\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:734 #, no-wrap msgid "" "\t; convert it to hex\n" "\tmovzx\teax, byte [buffer]\n" "\tmov\t[buffer+2], cl\n" "\tcmp\tal, 0Ah\n" "\tjne\t.hex\n" "\tmov\t[buffer+2], al\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:743 #, no-wrap msgid "" ".hex:\n" "\tmov\tedx, eax\n" "\tshr\tdl, 4\n" "\tmov\tdl, [hex+edx]\n" "\tmov\t[buffer], dl\n" "\tand\tal, 0Fh\n" "\tmov\tal, [hex+eax]\n" "\tmov\t[buffer+1], al\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:751 #, no-wrap msgid "" "\t; print it\n" "\tpush\tdword 3\n" "\tpush\tdword buffer\n" "\tpush\tdword stdout\n" "\tsys.write\n" "\tadd\tesp, byte 12\n" "\tjmp\tshort .loop\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:759 msgid "" "We have stored the space in the `CL` register. We can do this safely " "because, unlike Microsoft Windows, UNIX system calls do not modify the value " "of any register they do not use to return a value in." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:763 msgid "" "That means we only need to set `CL` once. We have, therefore, added a new " "label `.loop` and jump to it for the next byte instead of jumping at " "`_start`. We have also added the `.hex` label so we can either have a blank " "space or a new line as the third byte of the `buffer`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:765 msgid "" "Once you have changed [.filename]#hex.asm# to reflect these changes, type:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:776 #: documentation/content/en/articles/x86-assembly/_index.adoc:1035 #, no-wrap msgid "" "% nasm -f elf hex.asm\n" "% ld -s -o hex hex.o\n" "% ./hex\n" "Hello, World!\n" "48 65 6C 6C 6F 2C 20 57 6F 72 6C 64 21 0A\n" "Here I come!\n" "48 65 72 65 20 49 20 63 6F 6D 65 21 0A\n" "^D %\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:780 msgid "" "That looks better. But this code is quite inefficient! We are making a " "system call for every single byte twice (once to read it, another time to " "write the output)." msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:782 #, no-wrap msgid "Buffered Input and Output" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:787 msgid "" "We can improve the efficiency of our code by buffering our input and " "output. We create an input buffer and read a whole sequence of bytes at one " "time. Then we fetch them one by one from the buffer." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:790 msgid "" "We also create an output buffer. We store our output in it until it is " "full. At that time we ask the kernel to write the contents of the buffer to " "[.filename]#stdout#." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:794 msgid "" "The program ends when there is no more input. But we still need to ask the " "kernel to write the contents of our output buffer to [.filename]#stdout# one " "last time, otherwise some of our output would make it to the output buffer, " "but never be sent out. Do not forget that, or you will be wondering why " "some of your output is missing." msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:800 #: documentation/content/en/articles/x86-assembly/_index.adoc:928 #: documentation/content/en/articles/x86-assembly/_index.adoc:1195 #: documentation/content/en/articles/x86-assembly/_index.adoc:2315 #: documentation/content/en/articles/x86-assembly/_index.adoc:3313 #, no-wrap msgid "%define\tBUFSIZE\t2048\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:803 #: documentation/content/en/articles/x86-assembly/_index.adoc:931 #, no-wrap msgid "" "section\t.data\n" "hex\tdb\t'0123456789ABCDEF'\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:807 #: documentation/content/en/articles/x86-assembly/_index.adoc:935 #: documentation/content/en/articles/x86-assembly/_index.adoc:1204 #: documentation/content/en/articles/x86-assembly/_index.adoc:2329 #, no-wrap msgid "" "section .bss\n" "ibuffer\tresb\tBUFSIZE\n" "obuffer\tresb\tBUFSIZE\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:815 #: documentation/content/en/articles/x86-assembly/_index.adoc:943 #, no-wrap msgid "" "section\t.text\n" "global\t_start\n" "_start:\n" "\tsub\teax, eax\n" "\tsub\tebx, ebx\n" "\tsub\tecx, ecx\n" "\tmov\tedi, obuffer\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:819 #: documentation/content/en/articles/x86-assembly/_index.adoc:947 #: documentation/content/en/articles/x86-assembly/_index.adoc:2477 #, no-wrap msgid "" ".loop:\n" "\t; read a byte from stdin\n" "\tcall\tgetchar\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:825 #: documentation/content/en/articles/x86-assembly/_index.adoc:953 #: documentation/content/en/articles/x86-assembly/_index.adoc:1257 #, no-wrap msgid "" "\t; convert it to hex\n" "\tmov\tdl, al\n" "\tshr\tal, 4\n" "\tmov\tal, [hex+eax]\n" "\tcall\tputchar\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:830 #: documentation/content/en/articles/x86-assembly/_index.adoc:958 #: documentation/content/en/articles/x86-assembly/_index.adoc:1262 #, no-wrap msgid "" "\tmov\tal, dl\n" "\tand\tal, 0Fh\n" "\tmov\tal, [hex+eax]\n" "\tcall\tputchar\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:835 #: documentation/content/en/articles/x86-assembly/_index.adoc:963 #: documentation/content/en/articles/x86-assembly/_index.adoc:1267 #, no-wrap msgid "" "\tmov\tal, ' '\n" "\tcmp\tdl, 0Ah\n" "\tjne\t.put\n" "\tmov\tal, dl\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:839 #: documentation/content/en/articles/x86-assembly/_index.adoc:2488 #, no-wrap msgid "" ".put:\n" "\tcall\tputchar\n" "\tjmp\tshort .loop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:844 #: documentation/content/en/articles/x86-assembly/_index.adoc:975 #: documentation/content/en/articles/x86-assembly/_index.adoc:1279 #: documentation/content/en/articles/x86-assembly/_index.adoc:2510 #: documentation/content/en/articles/x86-assembly/_index.adoc:3824 #, no-wrap msgid "" "align 4\n" "getchar:\n" "\tor\tebx, ebx\n" "\tjne\t.fetch\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:846 #: documentation/content/en/articles/x86-assembly/_index.adoc:977 #: documentation/content/en/articles/x86-assembly/_index.adoc:1281 #: documentation/content/en/articles/x86-assembly/_index.adoc:2512 #: documentation/content/en/articles/x86-assembly/_index.adoc:3826 #, no-wrap msgid "\tcall\tread\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:851 #: documentation/content/en/articles/x86-assembly/_index.adoc:982 #: documentation/content/en/articles/x86-assembly/_index.adoc:1286 #: documentation/content/en/articles/x86-assembly/_index.adoc:2517 #, no-wrap msgid "" ".fetch:\n" "\tlodsb\n" "\tdec\tebx\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:864 #: documentation/content/en/articles/x86-assembly/_index.adoc:995 #, no-wrap msgid "" "read:\n" "\tpush\tdword BUFSIZE\n" "\tmov\tesi, ibuffer\n" "\tpush\tesi\n" "\tpush\tdword stdin\n" "\tsys.read\n" "\tadd\tesp, byte 12\n" "\tmov\tebx, eax\n" "\tor\teax, eax\n" "\tje\t.done\n" "\tsub\teax, eax\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:870 #: documentation/content/en/articles/x86-assembly/_index.adoc:1001 #, no-wrap msgid "" "align 4\n" ".done:\n" "\tcall\twrite\t\t; flush output buffer\n" "\tpush\tdword 0\n" "\tsys.exit\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:878 #: documentation/content/en/articles/x86-assembly/_index.adoc:1009 #: documentation/content/en/articles/x86-assembly/_index.adoc:1322 #: documentation/content/en/articles/x86-assembly/_index.adoc:2557 #: documentation/content/en/articles/x86-assembly/_index.adoc:3863 #, no-wrap msgid "" "align 4\n" "putchar:\n" "\tstosb\n" "\tinc\tecx\n" "\tcmp\tecx, BUFSIZE\n" "\tje\twrite\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:890 #: documentation/content/en/articles/x86-assembly/_index.adoc:1021 #, no-wrap msgid "" "align 4\n" "write:\n" "\tsub\tedi, ecx\t; start of buffer\n" "\tpush\tecx\n" "\tpush\tedi\n" "\tpush\tdword stdout\n" "\tsys.write\n" "\tadd\tesp, byte 12\n" "\tsub\teax, eax\n" "\tsub\tecx, ecx\t; buffer is empty now\n" "\tret\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:896 msgid "" "We now have a third section in the source code, named `.bss`. This section " "is not included in our executable file, and, therefore, cannot be " "initialized. We use `resb` instead of `db`. It simply reserves the " "requested size of uninitialized memory for our use." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:900 msgid "" "We take advantage of the fact that the system does not modify the registers: " "We use registers for what, otherwise, would have to be global variables " "stored in the `.data` section. This is also why the UNIX convention of " "passing parameters to system calls on the stack is superior to the Microsoft " "convention of passing them in the registers: We can keep the registers for " "our own use." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:904 msgid "" "We use `EDI` and `ESI` as pointers to the next byte to be read from or " "written to. We use `EBX` and `ECX` to keep count of the number of bytes in " "the two buffers, so we know when to dump the output to, or read more input " "from, the system." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:906 msgid "Let us see how it works now:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:917 #, no-wrap msgid "" "% nasm -f elf hex.asm\n" "% ld -s -o hex hex.o\n" "% ./hex\n" "Hello, World!\n" "Here I come!\n" "48 65 6C 6C 6F 2C 20 57 6F 72 6C 64 21 0A\n" "48 65 72 65 20 49 20 63 6F 6D 65 21 0A\n" "^D %\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:922 msgid "" "Not what you expected? The program did not print the output until we pressed " "`^D`. That is easy to fix by inserting three lines of code to write the " "output every time we have converted a new line to `0A`. I have marked the " "three lines with > (do not copy the > in your [.filename]#hex.asm#)." msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:970 #, no-wrap msgid "" ".put:\n" "\tcall\tputchar\n" ">\tcmp\tal, 0Ah\n" ">\tjne\t.loop\n" ">\tcall\twrite\n" "\tjmp\tshort .loop\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1024 msgid "Now, let us see how it works:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1038 msgid "Not bad for a 644-byte executable, is it!" msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1043 msgid "" "This approach to buffered input/output still contains a hidden danger. I " "will discuss-and fix-it later, when I talk about the crossref:x86[x86-" "buffered-dark-side,dark side of buffering]." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:1046 #, no-wrap msgid "How to Unread a Character" msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1052 msgid "" "This may be a somewhat advanced topic, mostly of interest to programmers " "familiar with the theory of compilers. If you wish, you may " "crossref:x86[x86-command-line,skip to the next section], and perhaps read " "this later." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1058 msgid "" "While our sample program does not require it, more sophisticated filters " "often need to look ahead. In other words, they may need to see what the " "next character is (or even several characters). If the next character is of " "a certain value, it is part of the token currently being processed. " "Otherwise, it is not." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1062 msgid "" "For example, you may be parsing the input stream for a textual string (e.g., " "when implementing a language compiler): If a character is followed by " "another character, or perhaps a digit, it is part of the token you are " "processing. If it is followed by white space, or some other value, then it " "is not part of the current token." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1064 msgid "" "This presents an interesting problem: How to return the next character back " "to the input stream, so it can be read again later?" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1068 msgid "" "One possible solution is to store it in a character variable, then set a " "flag. We can modify `getchar` to check the flag, and if it is set, fetch " "the byte from that variable instead of the input buffer, and reset the " "flag. But, of course, that slows us down." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1073 msgid "" "The C language has an `ungetc()` function, just for that purpose. Is there " "a quick way to implement it in our code? I would like you to scroll back up " "and take a look at the `getchar` procedure and see if you can find a nice " "and fast solution before reading the next paragraph. Then come back here " "and see my own solution." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1075 msgid "" "The key to returning a character back to the stream is in how we are getting " "the characters to start with:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1078 msgid "" "First we check if the buffer is empty by testing the value of `EBX`. If it " "is zero, we call the `read` procedure." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1081 msgid "" "If we do have a character available, we use `lodsb`, then decrease the value " "of `EBX`. The `lodsb` instruction is effectively identical to:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1086 #, no-wrap msgid "" "mov\tal, [esi]\n" "\tinc\tesi\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1091 msgid "" "The byte we have fetched remains in the buffer until the next time `read` is " "called. We do not know when that happens, but we do know it will not happen " "until the next call to `getchar`. Hence, to \"return\" the last-read byte " "back to the stream, all we have to do is decrease the value of `ESI` and " "increase the value of `EBX`:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1098 #, no-wrap msgid "" "ungetc:\n" "\tdec\tesi\n" "\tinc\tebx\n" "\tret\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1102 msgid "" "But, be careful! We are perfectly safe doing this if our look-ahead is at " "most one character at a time. If we are examining more than one upcoming " "character and call `ungetc` several times in a row, it will work most of the " "time, but not all the time (and will be tough to debug). Why?" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1105 msgid "" "Because as long as `getchar` does not have to call `read`, all of the pre-" "read bytes are still in the buffer, and our `ungetc` works without a " "glitch. But the moment `getchar` calls `read`, the contents of the buffer " "change." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1107 msgid "" "We can always rely on `ungetc` working properly on the last character we " "have read with `getchar`, but not on anything we have read before that." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1109 msgid "" "If your program reads more than one byte ahead, you have at least two " "choices:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1112 msgid "" "If possible, modify the program so it only reads one byte ahead. This is " "the simplest solution." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1116 msgid "" "If that option is not available, first of all determine the maximum number " "of characters your program needs to return to the input stream at one time. " "Increase that number slightly, just to be sure, preferably to a multiple of " "16-so it aligns nicely. Then modify the `.bss` section of your code, and " "create a small \"spare\" buffer right before your input buffer, something " "like this:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1123 #, no-wrap msgid "" "section\t.bss\n" "\tresb\t16\t; or whatever the value you came up with\n" "ibuffer\tresb\tBUFSIZE\n" "obuffer\tresb\tBUFSIZE\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1126 msgid "" "You also need to modify your `ungetc` to pass the value of the byte to unget " "in `AL`:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1134 #, no-wrap msgid "" "ungetc:\n" "\tdec\tesi\n" "\tinc\tebx\n" "\tmov\t[esi], al\n" "\tret\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1137 msgid "" "With this modification, you can call `ungetc` up to 17 times in a row safely " "(the first call will still be within the buffer, the remaining 16 may be " "either within the buffer or within the \"spare\")." msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:1139 #, no-wrap msgid "Command Line Arguments" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1143 msgid "" "Our hex program will be more useful if it can read the names of an input and " "output file from its command line, i.e., if it can process the command line " "arguments. But... Where are they?" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1147 msgid "" "Before a UNIX system starts a program, it ``push``es some data on the stack, " "then jumps at the `_start` label of the program. Yes, I said jumps, not " "calls. That means the data can be accessed by reading `[esp+offset]`, or by " "simply ``pop``ping it." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1150 msgid "" "The value at the top of the stack contains the number of command line " "arguments. It is traditionally called `argc`, for \"argument count.\"" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1155 msgid "" "Command line arguments follow next, all `argc` of them. These are typically " "referred to as `argv`, for \"argument value(s).\" That is, we get `argv[0]`, " "`argv[1]`, `...`, `argv[argc-1]`. These are not the actual arguments, but " "pointers to arguments, i.e., memory addresses of the actual arguments. The " "arguments themselves are NUL-terminated character strings." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1157 msgid "" "The `argv` list is followed by a NULL pointer, which is simply a `0`. There " "is more, but this is enough for our purposes right now." msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1162 msgid "" "If you have come from the MS-DOS programming environment, the main " "difference is that each argument is in a separate string. The second " "difference is that there is no practical limit on how many arguments there " "can be." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1166 msgid "" "Armed with this knowledge, we are almost ready for the next version of " "[.filename]#hex.asm#. First, however, we need to add a few lines to " "[.filename]#system.inc#:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1168 msgid "" "First, we need to add two new entries to our list of system call numbers:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1173 #, no-wrap msgid "" "%define\tSYS_open\t5\n" "%define\tSYS_close\t6\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1176 msgid "Then we add two new macros at the end of the file:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1182 #, no-wrap msgid "" "%macro\tsys.open\t0\n" "\tsystem\tSYS_open\n" "%endmacro\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1186 #, no-wrap msgid "" "%macro\tsys.close\t0\n" "\tsystem\tSYS_close\n" "%endmacro\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1189 msgid "Here, then, is our modified source code:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1200 #, no-wrap msgid "" "section\t.data\n" "fd.in\tdd\tstdin\n" "fd.out\tdd\tstdout\n" "hex\tdb\t'0123456789ABCDEF'\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1210 #, no-wrap msgid "" "section\t.text\n" "align 4\n" "err:\n" "\tpush\tdword 1\t\t; return failure\n" "\tsys.exit\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1215 #, no-wrap msgid "" "align 4\n" "global\t_start\n" "_start:\n" "\tadd\tesp, byte 8\t; discard argc and argv[0]\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1218 #: documentation/content/en/articles/x86-assembly/_index.adoc:1230 #, no-wrap msgid "" "\tpop\tecx\n" "\tjecxz\t.init\t\t; no more arguments\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1224 #, no-wrap msgid "" "\t; ECX contains the path to input file\n" "\tpush\tdword 0\t\t; O_RDONLY\n" "\tpush\tecx\n" "\tsys.open\n" "\tjc\terr\t\t; open failed\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1227 #, no-wrap msgid "" "\tadd\tesp, byte 8\n" "\tmov\t[fd.in], eax\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1238 #, no-wrap msgid "" "\t; ECX contains the path to output file\n" "\tpush\tdword 420\t; file mode (644 octal)\n" "\tpush\tdword 0200h | 0400h | 01h\n" "\t; O_CREAT | O_TRUNC | O_WRONLY\n" "\tpush\tecx\n" "\tsys.open\n" "\tjc\terr\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1241 #, no-wrap msgid "" "\tadd\tesp, byte 12\n" "\tmov\t[fd.out], eax\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1247 #, no-wrap msgid "" ".init:\n" "\tsub\teax, eax\n" "\tsub\tebx, ebx\n" "\tsub\tecx, ecx\n" "\tmov\tedi, obuffer\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1251 #, no-wrap msgid "" ".loop:\n" "\t; read a byte from input file or stdin\n" "\tcall\tgetchar\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1274 #, no-wrap msgid "" ".put:\n" "\tcall\tputchar\n" "\tcmp\tal, dl\n" "\tjne\t.loop\n" "\tcall\twrite\n" "\tjmp\tshort .loop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1299 #, no-wrap msgid "" "read:\n" "\tpush\tdword BUFSIZE\n" "\tmov\tesi, ibuffer\n" "\tpush\tesi\n" "\tpush\tdword [fd.in]\n" "\tsys.read\n" "\tadd\tesp, byte 12\n" "\tmov\tebx, eax\n" "\tor\teax, eax\n" "\tje\t.done\n" "\tsub\teax, eax\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1303 #: documentation/content/en/articles/x86-assembly/_index.adoc:2538 #, no-wrap msgid "" "align 4\n" ".done:\n" "\tcall\twrite\t\t; flush output buffer\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1307 #: documentation/content/en/articles/x86-assembly/_index.adoc:2542 #: documentation/content/en/articles/x86-assembly/_index.adoc:3796 #, no-wrap msgid "" "\t; close files\n" "\tpush\tdword [fd.in]\n" "\tsys.close\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1310 #: documentation/content/en/articles/x86-assembly/_index.adoc:2545 #: documentation/content/en/articles/x86-assembly/_index.adoc:3799 #, no-wrap msgid "" "\tpush\tdword [fd.out]\n" "\tsys.close\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1314 #: documentation/content/en/articles/x86-assembly/_index.adoc:2549 #: documentation/content/en/articles/x86-assembly/_index.adoc:3805 #, no-wrap msgid "" "\t; return success\n" "\tpush\tdword 0\n" "\tsys.exit\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1334 #, no-wrap msgid "" "align 4\n" "write:\n" "\tsub\tedi, ecx\t; start of buffer\n" "\tpush\tecx\n" "\tpush\tedi\n" "\tpush\tdword [fd.out]\n" "\tsys.write\n" "\tadd\tesp, byte 12\n" "\tsub\teax, eax\n" "\tsub\tecx, ecx\t; buffer is empty now\n" "\tret\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1338 msgid "" "In our `.data` section we now have two new variables, `fd.in` and `fd.out`. " "We store the input and output file descriptors here." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1340 msgid "" "In the `.text` section we have replaced the references to `stdin` and " "`stdout` with `[fd.in]` and `[fd.out]`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1343 msgid "" "The `.text` section now starts with a simple error handler, which does " "nothing but exit the program with a return value of `1`. The error handler " "is before `_start` so we are within a short distance from where the errors " "occur." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1346 msgid "" "Naturally, the program execution still begins at `_start`. First, we remove " "`argc` and `argv[0]` from the stack: They are of no interest to us (in this " "program, that is)." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1352 msgid "" "We pop `argv[1]` to `ECX`. This register is particularly suited for " "pointers, as we can handle NULL pointers with `jecxz`. If `argv[1]` is not " "NULL, we try to open the file named in the first argument. Otherwise, we " "continue the program as before: Reading from `stdin`, writing to `stdout`. " "If we fail to open the input file (e.g., it does not exist), we jump to the " "error handler and quit." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1357 msgid "" "If all went well, we now check for the second argument. If it is there, we " "open the output file. Otherwise, we send the output to `stdout`. If we " "fail to open the output file (e.g., it exists and we do not have the write " "permission), we, again, jump to the error handler." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1359 msgid "" "The rest of the code is the same as before, except we close the input and " "output files before exiting, and, as mentioned, we use `[fd.in]` and " "`[fd.out]`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1361 msgid "Our executable is now a whopping 768 bytes long." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1364 msgid "" "Can we still improve it? Of course! Every program can be improved. Here are " "a few ideas of what we could do:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1366 msgid "Have our error handler print a message to `stderr`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1367 msgid "Add error handlers to the `read` and `write` functions." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1368 msgid "" "Close `stdin` when we open an input file, `stdout` when we open an output " "file." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1369 msgid "" "Add command line switches, such as `-i` and `-o`, so we can list the input " "and output files in any order, or perhaps read from `stdin` and write to a " "file." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1370 msgid "Print a usage message if command line arguments are incorrect." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1372 msgid "" "I shall leave these enhancements as an exercise to the reader: You already " "know everything you need to know to implement them." msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:1374 #, no-wrap msgid "UNIX Environment" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1378 msgid "" "An important UNIX concept is the environment, which is defined by " "_environment variables_. Some are set by the system, others by you, yet " "others by the shell, or any program that loads another program." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:1380 #, no-wrap msgid "How to Find Environment Variables" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1385 msgid "" "I said earlier that when a program starts executing, the stack contains " "`argc` followed by the NULL-terminated `argv` array, followed by something " "else. The \"something else\" is the _environment_, or, to be more precise, " "a NULL-terminated array of pointers to _environment variables_. This is " "often referred to as `env`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1388 msgid "" "The structure of `env` is the same as that of `argv`, a list of memory " "addresses followed by a NULL (`0`). In this case, there is no `\"envc\"`-we " "figure out where the array ends by searching for the final NULL." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1391 msgid "" "The variables usually come in the `name=value` format, but sometimes the " "`=value` part may be missing. We need to account for that possibility." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:1393 #, no-wrap msgid "webvars" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1397 msgid "" "I could just show you some code that prints the environment the same way the " "UNIX env command does. But I thought it would be more interesting to write " "a simple assembly language CGI utility." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:1399 #, no-wrap msgid "CGI: a Quick Overview" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1404 msgid "" "I have a link:https://web.archive.org/web/20230612082452/http://" "www.whizkidtech.redprince.net/cgi-bin/tutorial[detailed CGI tutorial] on my " "web site, but here is a very quick overview of CGI:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1406 msgid "" "The web server communicates with the CGI program by setting _environment " "variables_." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1407 msgid "" "The CGI program sends its output to [.filename]#stdout#. The web server " "reads it from there." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1408 msgid "It must start with an HTTP header followed by two blank lines." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1409 msgid "" "It then prints the HTML code, or whatever other type of data it is producing." msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1414 msgid "" "While certain _environment variables_ use standard names, others vary, " "depending on the web server. That makes webvars quite a useful diagnostic " "tool." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:1417 #, no-wrap msgid "The Code" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1421 msgid "" "Our webvars program, then, must send out the HTTP header followed by some " "HTML mark-up. It then must read the _environment variables_ one by one and " "send them out as part of the HTML page." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1424 msgid "" "The code follows. I placed comments and explanations right inside the code:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1461 #, no-wrap msgid "" ";;;;;;; webvars.asm ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;\n" ";\n" "; Copyright (c) 2000 G. Adam Stanislav\n" "; All rights reserved.\n" ";\n" "; Redistribution and use in source and binary forms, with or without\n" "; modification, are permitted provided that the following conditions\n" "; are met:\n" "; 1. Redistributions of source code must retain the above copyright\n" "; notice, this list of conditions and the following disclaimer.\n" "; 2. Redistributions in binary form must reproduce the above copyright\n" "; notice, this list of conditions and the following disclaimer in the\n" "; documentation and/or other materials provided with the distribution.\n" ";\n" "; THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND\n" "; ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE\n" "; IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE\n" "; ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE\n" "; FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL\n" "; DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS\n" "; OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)\n" "; HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT\n" "; LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY\n" "; OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF\n" "; SUCH DAMAGE.\n" ";;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;\n" ";\n" "; Version 1.0\n" ";\n" "; Started:\t 8-Dec-2000\n" "; Updated:\t 8-Dec-2000\n" ";\n" ";;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;\n" "%include\t'system.inc'\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1498 #, no-wrap msgid "" "section\t.data\n" "http\tdb\t'Content-type: text/html', 0Ah, 0Ah\n" "\tdb\t'<?xml version=\"1.0\" encoding=\"utf-8\"?>', 0Ah\n" "\tdb\t'<!DOCTYPE html PUBLIC \"-//W3C/DTD XHTML Strict//EN\" '\n" "\tdb\t'\"DTD/xhtml1-strict.dtd\">', 0Ah\n" "\tdb\t'<html xmlns=\"http://www.w3.org/1999/xhtml\" '\n" "\tdb\t'xml.lang=\"en\" lang=\"en\">', 0Ah\n" "\tdb\t'<head>', 0Ah\n" "\tdb\t'<title>Web Environment</title>', 0Ah\n" "\tdb\t'<meta name=\"author\" content=\"G. Adam Stanislav\" />', 0Ah\n" "\tdb\t'</head>', 0Ah, 0Ah\n" "\tdb\t'<body bgcolor=\"#ffffff\" text=\"#000000\" link=\"#0000ff\" '\n" "\tdb\t'vlink=\"#840084\" alink=\"#0000ff\">', 0Ah\n" "\tdb\t'<div class=\"webvars\">', 0Ah\n" "\tdb\t'<h1>Web Environment</h1>', 0Ah\n" "\tdb\t'<p>The following <b>environment variables</b> are defined '\n" "\tdb\t'on this web server:</p>', 0Ah, 0Ah\n" "\tdb\t'<table align=\"center\" width=\"80\" border=\"0\" cellpadding=\"10\" '\n" "\tdb\t'cellspacing=\"0\" class=\"webvars\">', 0Ah\n" "httplen\tequ\t$-http\n" "left\tdb\t'<tr>', 0Ah\n" "\tdb\t'<td class=\"name\"><tt>'\n" "leftlen\tequ\t$-left\n" "middle\tdb\t'</tt></td>', 0Ah\n" "\tdb\t'<td class=\"value\"><tt><b>'\n" "midlen\tequ\t$-middle\n" "undef\tdb\t'<i>(undefined)</i>'\n" "undeflen\tequ\t$-undef\n" "right\tdb\t'</b></tt></td>', 0Ah\n" "\tdb\t'</tr>', 0Ah\n" "rightlen\tequ\t$-right\n" "wrap\tdb\t'</table>', 0Ah\n" "\tdb\t'</div>', 0Ah\n" "\tdb\t'</body>', 0Ah\n" "\tdb\t'</html>', 0Ah, 0Ah\n" "wraplen\tequ\t$-wrap\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1508 #, no-wrap msgid "" "section\t.text\n" "global\t_start\n" "_start:\n" "\t; First, send out all the http and xhtml stuff that is\n" "\t; needed before we start showing the environment\n" "\tpush\tdword httplen\n" "\tpush\tdword http\n" "\tpush\tdword stdout\n" "\tsys.write\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1512 #, no-wrap msgid "" "\t; Now find how far on the stack the environment pointers\n" "\t; are. We have 12 bytes we have pushed before \"argc\"\n" "\tmov\teax, [esp+12]\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1527 #, no-wrap msgid "" "\t; We need to remove the following from the stack:\n" "\t;\n" "\t;\tThe 12 bytes we pushed for sys.write\n" "\t;\tThe 4 bytes of argc\n" "\t;\tThe EAX*4 bytes of argv\n" "\t;\tThe 4 bytes of the NULL after argv\n" "\t;\n" "\t; Total:\n" "\t;\t20 + eax * 4\n" "\t;\n" "\t; Because stack grows down, we need to ADD that many bytes\n" "\t; to ESP.\n" "\tlea\tesp, [esp+20+eax*4]\n" "\tcld\t\t; This should already be the case, but let's be sure.\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1533 #, no-wrap msgid "" "\t; Loop through the environment, printing it out\n" ".loop:\n" "\tpop\tedi\n" "\tor\tedi, edi\t; Done yet?\n" "\tje\tnear .wrap\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1539 #, no-wrap msgid "" "\t; Print the left part of HTML\n" "\tpush\tdword leftlen\n" "\tpush\tdword left\n" "\tpush\tdword stdout\n" "\tsys.write\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1550 #, no-wrap msgid "" "\t; It may be tempting to search for the '=' in the env string next.\n" "\t; But it is possible there is no '=', so we search for the\n" "\t; terminating NUL first.\n" "\tmov\tesi, edi\t; Save start of string\n" "\tsub\tecx, ecx\n" "\tnot\tecx\t\t; ECX = FFFFFFFF\n" "\tsub\teax, eax\n" "repne\tscasb\n" "\tnot\tecx\t\t; ECX = string length + 1\n" "\tmov\tebx, ecx\t; Save it in EBX\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1557 #, no-wrap msgid "" "\t; Now is the time to find '='\n" "\tmov\tedi, esi\t; Start of string\n" "\tmov\tal, '='\n" "repne\tscasb\n" "\tnot\tecx\n" "\tadd\tecx, ebx\t; Length of name\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1562 #, no-wrap msgid "" "\tpush\tecx\n" "\tpush\tesi\n" "\tpush\tdword stdout\n" "\tsys.write\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1568 #, no-wrap msgid "" "\t; Print the middle part of HTML table code\n" "\tpush\tdword midlen\n" "\tpush\tdword middle\n" "\tpush\tdword stdout\n" "\tsys.write\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1572 #, no-wrap msgid "" "\t; Find the length of the value\n" "\tnot\tecx\n" "\tlea\tebx, [ebx+ecx-1]\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1576 #, no-wrap msgid "" "\t; Print \"undefined\" if 0\n" "\tor\tebx, ebx\n" "\tjne\t.value\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1579 #, no-wrap msgid "" "\tmov\tebx, undeflen\n" "\tmov\tedi, undef\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1585 #, no-wrap msgid "" ".value:\n" "\tpush\tebx\n" "\tpush\tedi\n" "\tpush\tdword stdout\n" "\tsys.write\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1591 #, no-wrap msgid "" "\t; Print the right part of the table row\n" "\tpush\tdword rightlen\n" "\tpush\tdword right\n" "\tpush\tdword stdout\n" "\tsys.write\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1594 #, no-wrap msgid "" "\t; Get rid of the 60 bytes we have pushed\n" "\tadd\tesp, byte 60\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1597 #, no-wrap msgid "" "\t; Get the next variable\n" "\tjmp\t.loop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1604 #, no-wrap msgid "" ".wrap:\n" "\t; Print the rest of HTML\n" "\tpush\tdword wraplen\n" "\tpush\tdword wrap\n" "\tpush\tdword stdout\n" "\tsys.write\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1608 #, no-wrap msgid "" "\t; Return success\n" "\tpush\tdword 0\n" "\tsys.exit\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1612 msgid "" "This code produces a 1,396-byte executable. Most of it is data, i.e., the " "HTML mark-up we need to send out." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1614 msgid "Assemble and link it as usual:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1619 #, no-wrap msgid "" "% nasm -f elf webvars.asm\n" "% ld -s -o webvars webvars.o\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1623 msgid "" "To use it, you need to upload [.filename]#webvars# to your web server. " "Depending on how your web server is set up, you may have to store it in a " "special [.filename]#cgi-bin# directory, or perhaps rename it with a " "[.filename]#.cgi# extension." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1627 msgid "" "Then you need to use your browser to view its output. To see its output on " "my web server, please go to link:https://web.archive.org/web/20100818031015/" "http://www.int80h.org/webvars/[http://www.int80h.org/webvars]." msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:1629 #, no-wrap msgid "Working with Files" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1634 msgid "" "We have already done some basic file work: We know how to open and close " "them, how to read and write them using buffers. But UNIX offers much more " "functionality when it comes to files. We will examine some of it in this " "section, and end up with a nice file conversion utility." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1637 msgid "" "Indeed, let us start at the end, that is, with the file conversion utility. " "It always makes programming easier when we know from the start what the end " "product is supposed to do." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1643 msgid "" "One of the first programs I wrote for UNIX was package:converters/" "tuc[tuc(1)], a text-to-UNIX file converter. It converts a text file from " "other operating systems to a UNIX text file. In other words, it changes " "from different kind of line endings to the newline convention of UNIX. It " "saves the output in a different file. Optionally, it converts a UNIX text " "file to a DOS text file." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1647 msgid "" "I have used tuc extensively, but always only to convert from some other OS " "to UNIX, never the other way. I have always wished it would just overwrite " "the file instead of me having to send the output to a different file. Most " "of the time, I end up using it like this:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1652 #, no-wrap msgid "" "% tuc myfile tempfile\n" "% mv tempfile myfile\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1655 msgid "" "It would be nice to have a ftuc, i.e., _fast tuc_, and use it like this:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1659 #, no-wrap msgid "% ftuc myfile\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1662 msgid "" "In this article, then, we will write ftuc in assembly language (the original " "tuc is in C), and study various file-oriented kernel services in the process." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1664 msgid "" "At first sight, such a file conversion is very simple: All you have to do is " "strip the carriage returns, right?" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1666 msgid "" "If you answered yes, think again: That approach will work most of the time " "(at least with MS DOS text files), but will fail occasionally." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1671 msgid "" "The problem is that not all non-UNIX text files end their line with the " "carriage return / line feed sequence. Some use carriage returns without " "line feeds. Others combine several blank lines into a single carriage " "return followed by several line feeds. And so on." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1673 msgid "" "A text file converter, then, must be able to handle any possible line " "endings:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1675 msgid "carriage return / line feed" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1676 msgid "carriage return" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1677 msgid "line feed / carriage return" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1678 msgid "line feed" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1680 msgid "" "It should also handle files that use some kind of a combination of the above " "(e.g., carriage return followed by several line feeds)." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:1682 #, no-wrap msgid "Finite State Machine" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1689 msgid "" "The problem is easily solved by the use of a technique called _finite state " "machine_, originally developed by the designers of digital electronic " "circuits. A _finite state machine_ is a digital circuit whose output is " "dependent not only on its input but on its previous input, i.e., on its " "state. The microprocessor is an example of a _finite state machine_: Our " "assembly language code is assembled to machine language in which some " "assembly language code produces a single byte of machine language, while " "others produce several bytes. As the microprocessor fetches the bytes from " "the memory one by one, some of them simply change its state rather than " "produce some output. When all the bytes of the op code are fetched, the " "microprocessor produces some output, or changes the value of a register, etc." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1692 msgid "" "Because of that, all software is essentially a sequence of state " "instructions for the microprocessor. Nevertheless, the concept of _finite " "state machine_ is useful in software design as well." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1695 msgid "" "Our text file converter can be designer as a _finite state machine_ with " "three possible states. We could call them states 0-2, but it will make our " "life easier if we give them symbolic names:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1697 msgid "ordinary" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1698 msgid "cr" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1699 msgid "lf" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1701 msgid "" "Our program will start in the ordinary state. During this state, the program " "action depends on its input as follows:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1704 msgid "" "If the input is anything other than a carriage return or line feed, the " "input is simply passed on to the output. The state remains unchanged." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1706 msgid "" "If the input is a carriage return, the state is changed to cr. The input is " "then discarded, i.e., no output is made." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1708 msgid "" "If the input is a line feed, the state is changed to lf. The input is then " "discarded." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1711 msgid "" "Whenever we are in the cr state, it is because the last input was a carriage " "return, which was unprocessed. What our software does in this state again " "depends on the current input:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1713 msgid "" "If the input is anything other than a carriage return or line feed, output a " "line feed, then output the input, then change the state to ordinary." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1714 msgid "" "If the input is a carriage return, we have received two (or more) carriage " "returns in a row. We discard the input, we output a line feed, and leave the " "state unchanged." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1715 msgid "" "If the input is a line feed, we output the line feed and change the state to " "ordinary. Note that this is not the same as the first case above - if we " "tried to combine them, we would be outputting two line feeds instead of one." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1719 msgid "" "Finally, we are in the lf state after we have received a line feed that was " "not preceded by a carriage return. This will happen when our file already " "is in UNIX format, or whenever several lines in a row are expressed by a " "single carriage return followed by several line feeds, or when line ends " "with a line feed / carriage return sequence. Here is how we need to handle " "our input in this state:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1721 msgid "" "If the input is anything other than a carriage return or line feed, we " "output a line feed, then output the input, then change the state to " "ordinary. This is exactly the same action as in the cr state upon receiving " "the same kind of input." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1722 msgid "" "If the input is a carriage return, we discard the input, we output a line " "feed, then change the state to ordinary." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1723 msgid "" "If the input is a line feed, we output the line feed, and leave the state " "unchanged." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:1725 #, no-wrap msgid "The Final State" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1730 msgid "" "The above _finite state machine_ works for the entire file, but leaves the " "possibility that the final line end will be ignored. That will happen " "whenever the file ends with a single carriage return or a single line feed. " "I did not think of it when I wrote tuc, just to discover that occasionally " "it strips the last line ending." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1733 msgid "" "This problem is easily fixed by checking the state after the entire file was " "processed. If the state is not ordinary, we simply need to output one last " "line feed." msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1739 msgid "" "Now that we have expressed our algorithm as a _finite state machine_, we " "could easily design a dedicated digital electronic circuit (a \"chip\") to " "do the conversion for us. Of course, doing so would be considerably more " "expensive than writing an assembly language program." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:1742 #, no-wrap msgid "The Output Counter" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1747 msgid "" "Because our file conversion program may be combining two characters into " "one, we need to use an output counter. We initialize it to `0`, and " "increase it every time we send a character to the output. At the end of the " "program, the counter will tell us what size we need to set the file to." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:1749 #, no-wrap msgid "Implementing FSM in Software" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1753 msgid "" "The hardest part of working with a _finite state machine_ is analyzing the " "problem and expressing it as a _finite state machine_. That accomplished, " "the software almost writes itself." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1756 msgid "" "In a high-level language, such as C, there are several main approaches. One " "is to use a `switch` statement which chooses what function should be run. " "For example," msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1771 #, no-wrap msgid "" "switch (state) {\n" "\tdefault:\n" "\tcase REGULAR:\n" "\t\tregular(inputchar);\n" "\t\tbreak;\n" "\tcase CR:\n" "\t\tcr(inputchar);\n" "\t\tbreak;\n" "\tcase LF:\n" "\t\tlf(inputchar);\n" "\t\tbreak;\n" "\t}\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1774 msgid "" "Another approach is by using an array of function pointers, something like " "this:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1778 #, no-wrap msgid "(output[state])(inputchar);\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1781 msgid "" "Yet another is to have `state` be a function pointer, set to point at the " "appropriate function:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1785 #, no-wrap msgid "(*state)(inputchar);\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1789 msgid "" "This is the approach we will use in our program because it is very easy to " "do in assembly language, and very fast, too. We will simply keep the " "address of the right procedure in `EBX`, and then just issue:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1793 #, no-wrap msgid "call\tebx\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1797 msgid "" "This is possibly faster than hardcoding the address in the code because the " "microprocessor does not have to fetch the address from the memory-it is " "already stored in one of its registers. I said _possibly_ because with the " "caching modern microprocessors do, either way may be equally fast." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:1799 #, no-wrap msgid "Memory Mapped Files" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1803 msgid "" "Because our program works on a single file, we cannot use the approach that " "worked for us before, i.e., to read from an input file and to write to an " "output file." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1811 msgid "" "UNIX allows us to map a file, or a section of a file, into memory. To do " "that, we first need to open the file with the appropriate read/write flags. " "Then we use the `mmap` system call to map it into the memory. One nice " "thing about `mmap` is that it automatically works with virtual memory: We " "can map more of the file into the memory than we have physical memory " "available, yet still access it through regular memory op codes, such as " "`mov`, `lods`, and `stos`. Whatever changes we make to the memory image of " "the file will be written to the file by the system. We do not even have to " "keep the file open: As long as it stays mapped, we can read from it and " "write to it." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1814 msgid "" "The 32-bit Intel microprocessors can access up to four gigabytes of memory - " "physical or virtual. The FreeBSD system allows us to use up to a half of it " "for file mapping." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1818 msgid "" "For simplicity sake, in this tutorial we will only convert files that can be " "mapped into the memory in their entirety. There are probably not too many " "text files that exceed two gigabytes in size. If our program encounters " "one, it will simply display a message suggesting we use the original tuc " "instead." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1824 msgid "" "If you examine your copy of [.filename]#syscalls.master#, you will find two " "separate syscalls named `mmap`. This is because of evolution of UNIX: There " "was the traditional BSD `mmap`, syscall 71. That one was superseded by the " "POSIX(R) `mmap`, syscall 197. The FreeBSD system supports both because " "older programs were written by using the original BSD version. But new " "software uses the POSIX version, which is what we will use." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1826 msgid "The [.filename]#syscalls.master# lists the POSIX version like this:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1831 #, no-wrap msgid "" "197\tSTD\tBSD\t{ caddr_t mmap(caddr_t addr, size_t len, int prot, \\\n" "\t\t\t int flags, int fd, long pad, off_t pos); }\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1835 msgid "" "This differs slightly from what man:mmap[2] says. That is because " "man:mmap[2] describes the C version." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1839 msgid "" "The difference is in the `long pad` argument, which is not present in the C " "version. However, the FreeBSD syscalls add a 32-bit pad after ``push``ing a " "64-bit argument. In this case, `off_t` is a 64-bit value." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1841 msgid "" "When we are finished working with a memory-mapped file, we unmap it with the " "`munmap` syscall:" msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1845 msgid "" "For an in-depth treatment of `mmap`, see W. Richard Stevens' _Unix Network " "Programming_, Volume 2, Chapter 12." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:1848 #, no-wrap msgid "Determining File Size" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1851 msgid "" "Because we need to tell `mmap` how many bytes of the file to map into the " "memory, and because we want to map the entire file, we need to determine the " "size of the file." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1854 msgid "" "We can use the `fstat` syscall to get all the information about an open file " "that the system can give us. That includes the file size." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1857 msgid "" "Again, [.filename]#syscalls.master# lists two versions of `fstat`, a " "traditional one (syscall 62), and a POSIX one (syscall 189). Naturally, we " "will use the POSIX version:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1861 #, no-wrap msgid "189\tSTD\tPOSIX\t{ int fstat(int fd, struct stat *sb); }\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1865 msgid "" "This is a very straightforward call: We pass to it the address of a `stat` " "structure and the descriptor of an open file. It will fill out the contents " "of the `stat` structure." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1868 msgid "" "I do, however, have to say that I tried to declare the `stat` structure in " "the `.bss` section, and `fstat` did not like it: It set the carry flag " "indicating an error. After I changed the code to allocate the structure on " "the stack, everything was working fine." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:1870 #, no-wrap msgid "Changing the File Size" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1874 msgid "" "Because our program may combine carriage return / line feed sequences into " "straight line feeds, our output may be smaller than our input. However, " "since we are placing our output into the same file we read the input from, " "we may have to change the size of the file." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1877 msgid "" "The `ftruncate` system call allows us to do just that. Despite its somewhat " "misleading name, the `ftruncate` system call can be used to both truncate " "the file (make it smaller) and to grow it." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1880 msgid "" "And yes, we will find two versions of `ftruncate` in " "[.filename]#syscalls.master#, an older one (130), and a newer one (201). We " "will use the newer one:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1884 #, no-wrap msgid "201\tSTD\tBSD\t{ int ftruncate(int fd, int pad, off_t length); }\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1887 msgid "Please note that this one contains a `int pad` again." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:1889 #, no-wrap msgid "ftuc" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1894 msgid "" "We now know everything we need to write ftuc. We start by adding some new " "lines in [.filename]#system.inc#. First, we define some constants and " "structures, somewhere at or near the beginning of the file:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1901 #, no-wrap msgid "" ";;;;;;; open flags\n" "%define\tO_RDONLY\t0\n" "%define\tO_WRONLY\t1\n" "%define\tO_RDWR\t2\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1910 #, no-wrap msgid "" ";;;;;;; mmap flags\n" "%define\tPROT_NONE\t0\n" "%define\tPROT_READ\t1\n" "%define\tPROT_WRITE\t2\n" "%define\tPROT_EXEC\t4\n" ";;\n" "%define\tMAP_SHARED\t0001h\n" "%define\tMAP_PRIVATE\t0002h\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1934 #, no-wrap msgid "" ";;;;;;; stat structure\n" "struc\tstat\n" "st_dev\t\tresd\t1\t; = 0\n" "st_ino\t\tresd\t1\t; = 4\n" "st_mode\t\tresw\t1\t; = 8, size is 16 bits\n" "st_nlink\tresw\t1\t; = 10, ditto\n" "st_uid\t\tresd\t1\t; = 12\n" "st_gid\t\tresd\t1\t; = 16\n" "st_rdev\t\tresd\t1\t; = 20\n" "st_atime\tresd\t1\t; = 24\n" "st_atimensec\tresd\t1\t; = 28\n" "st_mtime\tresd\t1\t; = 32\n" "st_mtimensec\tresd\t1\t; = 36\n" "st_ctime\tresd\t1\t; = 40\n" "st_ctimensec\tresd\t1\t; = 44\n" "st_size\t\tresd\t2\t; = 48, size is 64 bits\n" "st_blocks\tresd\t2\t; = 56, ditto\n" "st_blksize\tresd\t1\t; = 64\n" "st_flags\tresd\t1\t; = 68\n" "st_gen\t\tresd\t1\t; = 72\n" "st_lspare\tresd\t1\t; = 76\n" "st_qspare\tresd\t4\t; = 80\n" "endstruc\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1937 msgid "We define the new syscalls:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1944 #, no-wrap msgid "" "%define\tSYS_mmap\t197\n" "%define\tSYS_munmap\t73\n" "%define\tSYS_fstat\t189\n" "%define\tSYS_ftruncate\t201\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1947 msgid "We add the macros for their use:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1953 #, no-wrap msgid "" "%macro\tsys.mmap\t0\n" "\tsystem\tSYS_mmap\n" "%endmacro\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1957 #, no-wrap msgid "" "%macro\tsys.munmap\t0\n" "\tsystem\tSYS_munmap\n" "%endmacro\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1961 #, no-wrap msgid "" "%macro\tsys.ftruncate\t0\n" "\tsystem\tSYS_ftruncate\n" "%endmacro\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1965 #, no-wrap msgid "" "%macro\tsys.fstat\t0\n" "\tsystem\tSYS_fstat\n" "%endmacro\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:1968 msgid "And here is our code:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1981 #, no-wrap msgid "" ";;;;;;; Fast Text-to-Unix Conversion (ftuc.asm) ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;\n" ";;\n" ";; Started:\t21-Dec-2000\n" ";; Updated:\t22-Dec-2000\n" ";;\n" ";; Copyright 2000 G. Adam Stanislav.\n" ";; All rights reserved.\n" ";;\n" ";;;;;;; v.1 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;\n" "%include\t'system.inc'\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1995 #, no-wrap msgid "" "section\t.data\n" "\tdb\t'Copyright 2000 G. Adam Stanislav.', 0Ah\n" "\tdb\t'All rights reserved.', 0Ah\n" "usg\tdb\t'Usage: ftuc filename', 0Ah\n" "usglen\tequ\t$-usg\n" "co\tdb\t\"ftuc: Can't open file.\", 0Ah\n" "colen\tequ\t$-co\n" "fae\tdb\t'ftuc: File access error.', 0Ah\n" "faelen\tequ\t$-fae\n" "ftl\tdb\t'ftuc: File too long, use regular tuc instead.', 0Ah\n" "ftllen\tequ\t$-ftl\n" "mae\tdb\t'ftuc: Memory allocation error.', 0Ah\n" "maelen\tequ\t$-mae\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:1997 #, no-wrap msgid "section\t.text\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2003 #, no-wrap msgid "" "align 4\n" "memerr:\n" "\tpush\tdword maelen\n" "\tpush\tdword mae\n" "\tjmp\tshort error\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2009 #, no-wrap msgid "" "align 4\n" "toolong:\n" "\tpush\tdword ftllen\n" "\tpush\tdword ftl\n" "\tjmp\tshort error\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2015 #, no-wrap msgid "" "align 4\n" "facerr:\n" "\tpush\tdword faelen\n" "\tpush\tdword fae\n" "\tjmp\tshort error\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2021 #, no-wrap msgid "" "align 4\n" "cantopen:\n" "\tpush\tdword colen\n" "\tpush\tdword co\n" "\tjmp\tshort error\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2026 #, no-wrap msgid "" "align 4\n" "usage:\n" "\tpush\tdword usglen\n" "\tpush\tdword usg\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2030 #, no-wrap msgid "" "error:\n" "\tpush\tdword stderr\n" "\tsys.write\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2033 #, no-wrap msgid "" "\tpush\tdword 1\n" "\tsys.exit\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2041 #, no-wrap msgid "" "align 4\n" "global\t_start\n" "_start:\n" "\tpop\teax\t\t; argc\n" "\tpop\teax\t\t; program name\n" "\tpop\tecx\t\t; file to convert\n" "\tjecxz\tusage\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2045 #, no-wrap msgid "" "\tpop\teax\n" "\tor\teax, eax\t; Too many arguments?\n" "\tjne\tusage\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2051 #, no-wrap msgid "" "\t; Open the file\n" "\tpush\tdword O_RDWR\n" "\tpush\tecx\n" "\tsys.open\n" "\tjc\tcantopen\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2053 #, no-wrap msgid "\tmov\tebp, eax\t; Save fd\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2056 #, no-wrap msgid "" "\tsub\tesp, byte stat_size\n" "\tmov\tebx, esp\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2062 #, no-wrap msgid "" "\t; Find file size\n" "\tpush\tebx\n" "\tpush\tebp\t\t; fd\n" "\tsys.fstat\n" "\tjc\tfacerr\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2064 #, no-wrap msgid "\tmov\tedx, [ebx + st_size + 4]\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2072 #, no-wrap msgid "" "\t; File is too long if EDX != 0 ...\n" "\tor\tedx, edx\n" "\tjne\tnear toolong\n" "\tmov\tecx, [ebx + st_size]\n" "\t; ... or if it is above 2 GB\n" "\tor\tecx, ecx\n" "\tjs\tnear toolong\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2075 #, no-wrap msgid "" "\t; Do nothing if the file is 0 bytes in size\n" "\tjecxz\t.quit\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2087 #, no-wrap msgid "" "\t; Map the entire file in memory\n" "\tpush\tedx\n" "\tpush\tedx\t\t; starting at offset 0\n" "\tpush\tedx\t\t; pad\n" "\tpush\tebp\t\t; fd\n" "\tpush\tdword MAP_SHARED\n" "\tpush\tdword PROT_READ | PROT_WRITE\n" "\tpush\tecx\t\t; entire file size\n" "\tpush\tedx\t\t; let system decide on the address\n" "\tsys.mmap\n" "\tjc\tnear memerr\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2092 #, no-wrap msgid "" "\tmov\tedi, eax\n" "\tmov\tesi, eax\n" "\tpush\tecx\t\t; for SYS_munmap\n" "\tpush\tedi\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2097 #, no-wrap msgid "" "\t; Use EBX for state machine\n" "\tmov\tebx, ordinary\n" "\tmov\tah, 0Ah\n" "\tcld\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2102 #, no-wrap msgid "" ".loop:\n" "\tlodsb\n" "\tcall\tebx\n" "\tloop\t.loop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2105 #, no-wrap msgid "" "\tcmp\tebx, ordinary\n" "\tje\t.filesize\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2110 #, no-wrap msgid "" "\t; Output final lf\n" "\tmov\tal, ah\n" "\tstosb\n" "\tinc\tedx\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2118 #, no-wrap msgid "" ".filesize:\n" "\t; truncate file to new size\n" "\tpush\tdword 0\t\t; high dword\n" "\tpush\tedx\t\t; low dword\n" "\tpush\teax\t\t; pad\n" "\tpush\tebp\n" "\tsys.ftruncate\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2121 #, no-wrap msgid "" "\t; close it (ebp still pushed)\n" "\tsys.close\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2124 #, no-wrap msgid "" "\tadd\tesp, byte 16\n" "\tsys.munmap\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2128 #, no-wrap msgid "" ".quit:\n" "\tpush\tdword 0\n" "\tsys.exit\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2133 #, no-wrap msgid "" "align 4\n" "ordinary:\n" "\tcmp\tal, 0Dh\n" "\tje\t.cr\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2136 #: documentation/content/en/articles/x86-assembly/_index.adoc:2158 #, no-wrap msgid "" "\tcmp\tal, ah\n" "\tje\t.lf\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2140 #, no-wrap msgid "" "\tstosb\n" "\tinc\tedx\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2145 #, no-wrap msgid "" "align 4\n" ".cr:\n" "\tmov\tebx, cr\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2150 #, no-wrap msgid "" "align 4\n" ".lf:\n" "\tmov\tebx, lf\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2155 #, no-wrap msgid "" "align 4\n" "cr:\n" "\tcmp\tal, 0Dh\n" "\tje\t.cr\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2162 #: documentation/content/en/articles/x86-assembly/_index.adoc:2190 #, no-wrap msgid "" "\txchg\tal, ah\n" "\tstosb\n" "\tinc\tedx\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2165 #, no-wrap msgid "" "\txchg\tal, ah\n" "\t; fall through\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2171 #, no-wrap msgid "" ".lf:\n" "\tstosb\n" "\tinc\tedx\n" "\tmov\tebx, ordinary\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2178 #, no-wrap msgid "" "align 4\n" ".cr:\n" "\tmov\tal, ah\n" "\tstosb\n" "\tinc\tedx\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2183 #, no-wrap msgid "" "align 4\n" "lf:\n" "\tcmp\tal, ah\n" "\tje\t.lf\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2186 #, no-wrap msgid "" "\tcmp\tal, 0Dh\n" "\tje\t.cr\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2196 #, no-wrap msgid "" "\txchg\tal, ah\n" "\tstosb\n" "\tinc\tedx\n" "\tmov\tebx, ordinary\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2202 #, no-wrap msgid "" "align 4\n" ".cr:\n" "\tmov\tebx, ordinary\n" "\tmov\tal, ah\n" "\t; fall through\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2207 #, no-wrap msgid "" ".lf:\n" "\tstosb\n" "\tinc\tedx\n" "\tret\n" msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2214 msgid "" "Do not use this program on files stored on a disk formatted by MS-DOS or " "Windows. There seems to be a subtle bug in the FreeBSD code when using " "`mmap` on these drives mounted under FreeBSD: If the file is over a certain " "size, `mmap` will just fill the memory with zeros, and then copy them to the " "file overwriting its contents." msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:2217 #, no-wrap msgid "One-Pointed Mind" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2220 msgid "" "As a student of Zen, I like the idea of a one-pointed mind: Do one thing at " "a time, and do it well." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2223 msgid "" "This, indeed, is very much how UNIX works as well. While a typical Windows " "application is attempting to do everything imaginable (and is, therefore, " "riddled with bugs), a typical UNIX program does only one thing, and it does " "it well." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2225 msgid "" "The typical UNIX user then essentially assembles his own applications by " "writing a shell script which combines the various existing programs by " "piping the output of one program to the input of another." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2227 msgid "" "When writing your own UNIX software, it is generally a good idea to see what " "parts of the problem you need to solve can be handled by existing programs, " "and only write your own programs for that part of the problem that you do " "not have an existing solution for." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:2229 #, no-wrap msgid "CSV" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2232 msgid "" "I will illustrate this principle with a specific real-life example I was " "faced with recently:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2236 msgid "" "I needed to extract the 11th field of each record from a database I " "downloaded from a web site. The database was a CSV file, i.e., a list of " "_comma-separated values_. That is quite a standard format for sharing data " "among people who may be using different database software." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2239 msgid "" "The first line of the file contains the list of various fields separated by " "commas. The rest of the file contains the data listed line by line, with " "values separated by commas." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2241 msgid "" "I tried awk, using the comma as a separator. But because several lines " "contained a quoted comma, awk was extracting the wrong field from those " "lines." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2244 msgid "" "Therefore, I needed to write my own software to extract the 11th field from " "the CSV file. However, going with the UNIX spirit, I only needed to write a " "simple filter that would do the following:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2246 msgid "Remove the first line from the file;" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2247 msgid "Change all unquoted commas to a different character;" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2248 msgid "Remove all quotation marks." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2250 msgid "" "Strictly speaking, I could use sed to remove the first line from the file, " "but doing so in my own program was very easy, so I decided to do it and " "reduce the size of the pipeline." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2254 msgid "" "At any rate, writing a program like this took me about 20 minutes. Writing " "a program that extracts the 11th field from the CSV file would take a lot " "longer, and I could not reuse it to extract some other field from some other " "database." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2256 msgid "" "This time I decided to let it do a little more work than a typical tutorial " "program would:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2258 msgid "It parses its command line for options;" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2259 msgid "It displays proper usage if it finds wrong arguments;" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2260 msgid "It produces meaningful error messages." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2262 msgid "Here is its usage message:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2266 #, no-wrap msgid "Usage: csv [-t<delim>] [-c<comma>] [-p] [-o <outfile>] [-i <infile>]\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2269 msgid "All parameters are optional, and can appear in any order." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2273 msgid "" "The `-t` parameter declares what to replace the commas with. The `tab` is " "the default here. For example, `-t;` will replace all unquoted commas with " "semicolons." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2277 msgid "" "I did not need the `-c` option, but it may come in handy in the future. It " "lets me declare that I want a character other than a comma replaced with " "something else. For example, `-c@` will replace all at signs (useful if you " "want to split a list of email addresses to their user names and domains)." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2280 msgid "" "The `-p` option preserves the first line, i.e., it does not delete it. By " "default, we delete the first line because in a CSV file it contains the " "field names rather than data." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2283 msgid "" "The `-i` and `-o` options let me specify the input and the output files. " "Defaults are [.filename]#stdin# and [.filename]#stdout#, so this is a " "regular UNIX filter." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2286 msgid "" "I made sure that both `-i filename` and `-ifilename` are accepted. I also " "made sure that only one input and one output files may be specified." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2288 msgid "To get the 11th field of each record, I can now do:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2292 #, no-wrap msgid "% csv '-t;' data.csv | awk '-F;' '{print $11}'\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2295 msgid "" "The code stores the options (except for the file descriptors) in `EDX`: The " "comma in `DH`, the new separator in `DL`, and the flag for the `-p` option " "in the highest bit of `EDX`, so a check for its sign will give us a quick " "decision what to do." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2297 msgid "Here is the code:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2311 #, no-wrap msgid "" ";;;;;;; csv.asm ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;\n" ";\n" "; Convert a comma-separated file to a something-else separated file.\n" ";\n" "; Started:\t31-May-2001\n" "; Updated:\t 1-Jun-2001\n" ";\n" "; Copyright (c) 2001 G. Adam Stanislav\n" "; All rights reserved.\n" ";\n" ";;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2325 #, no-wrap msgid "" "section\t.data\n" "fd.in\tdd\tstdin\n" "fd.out\tdd\tstdout\n" "usg\tdb\t'Usage: csv [-t<delim>] [-c<comma>] [-p] [-o <outfile>] [-i <infile>]', 0Ah\n" "usglen\tequ\t$-usg\n" "iemsg\tdb\t\"csv: Can't open input file\", 0Ah\n" "iemlen\tequ\t$-iemsg\n" "oemsg\tdb\t\"csv: Can't create output file\", 0Ah\n" "oemlen\tequ\t$-oemsg\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2339 #, no-wrap msgid "" "section\t.text\n" "align 4\n" "ierr:\n" "\tpush\tdword iemlen\n" "\tpush\tdword iemsg\n" "\tpush\tdword stderr\n" "\tsys.write\n" "\tpush\tdword 1\t\t; return failure\n" "\tsys.exit\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2348 #: documentation/content/en/articles/x86-assembly/_index.adoc:3397 #, no-wrap msgid "" "align 4\n" "oerr:\n" "\tpush\tdword oemlen\n" "\tpush\tdword oemsg\n" "\tpush\tdword stderr\n" "\tsys.write\n" "\tpush\tdword 2\n" "\tsys.exit\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2357 #: documentation/content/en/articles/x86-assembly/_index.adoc:3406 #, no-wrap msgid "" "align 4\n" "usage:\n" "\tpush\tdword usglen\n" "\tpush\tdword usg\n" "\tpush\tdword stderr\n" "\tsys.write\n" "\tpush\tdword 3\n" "\tsys.exit\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2363 #, no-wrap msgid "" "align 4\n" "global\t_start\n" "_start:\n" "\tadd\tesp, byte 8\t; discard argc and argv[0]\n" "\tmov\tedx, (',' << 8) | 9\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2368 #, no-wrap msgid "" ".arg:\n" "\tpop\tecx\n" "\tor\tecx, ecx\n" "\tje\tnear .init\t\t; no more arguments\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2372 #: documentation/content/en/articles/x86-assembly/_index.adoc:3421 #, no-wrap msgid "" "\t; ECX contains the pointer to an argument\n" "\tcmp\tbyte [ecx], '-'\n" "\tjne\tusage\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2375 #, no-wrap msgid "" "\tinc\tecx\n" "\tmov\tax, [ecx]\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2379 #: documentation/content/en/articles/x86-assembly/_index.adoc:3429 #, no-wrap msgid "" ".o:\n" "\tcmp\tal, 'o'\n" "\tjne\t.i\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2383 #: documentation/content/en/articles/x86-assembly/_index.adoc:3433 #, no-wrap msgid "" "\t; Make sure we are not asked for the output file twice\n" "\tcmp\tdword [fd.out], stdout\n" "\tjne\tusage\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2388 #: documentation/content/en/articles/x86-assembly/_index.adoc:3438 #, no-wrap msgid "" "\t; Find the path to output file - it is either at [ECX+1],\n" "\t; i.e., -ofile --\n" "\t; or in the next argument,\n" "\t; i.e., -o file\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2394 #, no-wrap msgid "" "\tinc\tecx\n" "\tor\tah, ah\n" "\tjne\t.openoutput\n" "\tpop\tecx\n" "\tjecxz\tusage\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2402 #: documentation/content/en/articles/x86-assembly/_index.adoc:3451 #, no-wrap msgid "" ".openoutput:\n" "\tpush\tdword 420\t; file mode (644 octal)\n" "\tpush\tdword 0200h | 0400h | 01h\n" "\t; O_CREAT | O_TRUNC | O_WRONLY\n" "\tpush\tecx\n" "\tsys.open\n" "\tjc\tnear oerr\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2406 #: documentation/content/en/articles/x86-assembly/_index.adoc:3455 #, no-wrap msgid "" "\tadd\tesp, byte 12\n" "\tmov\t[fd.out], eax\n" "\tjmp\tshort .arg\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2410 #: documentation/content/en/articles/x86-assembly/_index.adoc:3459 #, no-wrap msgid "" ".i:\n" "\tcmp\tal, 'i'\n" "\tjne\t.p\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2414 #: documentation/content/en/articles/x86-assembly/_index.adoc:3463 #, no-wrap msgid "" "\t; Make sure we are not asked twice\n" "\tcmp\tdword [fd.in], stdin\n" "\tjne\tnear usage\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2422 #, no-wrap msgid "" "\t; Find the path to the input file\n" "\tinc\tecx\n" "\tor\tah, ah\n" "\tjne\t.openinput\n" "\tpop\tecx\n" "\tor\tecx, ecx\n" "\tje near usage\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2428 #: documentation/content/en/articles/x86-assembly/_index.adoc:3476 #, no-wrap msgid "" ".openinput:\n" "\tpush\tdword 0\t\t; O_RDONLY\n" "\tpush\tecx\n" "\tsys.open\n" "\tjc\tnear ierr\t\t; open failed\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2432 #: documentation/content/en/articles/x86-assembly/_index.adoc:3480 #, no-wrap msgid "" "\tadd\tesp, byte 8\n" "\tmov\t[fd.in], eax\n" "\tjmp\t.arg\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2440 #, no-wrap msgid "" ".p:\n" "\tcmp\tal, 'p'\n" "\tjne\t.t\n" "\tor\tah, ah\n" "\tjne\tnear usage\n" "\tor\tedx, 1 << 31\n" "\tjmp\t.arg\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2448 #, no-wrap msgid "" ".t:\n" "\tcmp\tal, 't'\t\t; redefine output delimiter\n" "\tjne\t.c\n" "\tor\tah, ah\n" "\tje\tnear usage\n" "\tmov\tdl, ah\n" "\tjmp\t.arg\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2456 #, no-wrap msgid "" ".c:\n" "\tcmp\tal, 'c'\n" "\tjne\tnear usage\n" "\tor\tah, ah\n" "\tje\tnear usage\n" "\tmov\tdh, ah\n" "\tjmp\t.arg\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2463 #, no-wrap msgid "" "align 4\n" ".init:\n" "\tsub\teax, eax\n" "\tsub\tebx, ebx\n" "\tsub\tecx, ecx\n" "\tmov\tedi, obuffer\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2467 #, no-wrap msgid "" "\t; See if we are to preserve the first line\n" "\tor\tedx, edx\n" "\tjs\t.loop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2473 #, no-wrap msgid "" ".firstline:\n" "\t; get rid of the first line\n" "\tcall\tgetchar\n" "\tcmp\tal, 0Ah\n" "\tjne\t.firstline\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2481 #, no-wrap msgid "" "\t; is it a comma (or whatever the user asked for)?\n" "\tcmp\tal, dh\n" "\tjne\t.quote\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2484 #, no-wrap msgid "" "\t; Replace the comma with a tab (or whatever the user wants)\n" "\tmov\tal, dl\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2492 #, no-wrap msgid "" ".quote:\n" "\tcmp\tal, '\"'\n" "\tjne\t.put\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2499 #, no-wrap msgid "" "\t; Print everything until you get another quote or EOL. If it\n" "\t; is a quote, skip it. If it is EOL, print it.\n" ".qloop:\n" "\tcall\tgetchar\n" "\tcmp\tal, '\"'\n" "\tje\t.loop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2502 #, no-wrap msgid "" "\tcmp\tal, 0Ah\n" "\tje\t.put\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2505 #, no-wrap msgid "" "\tcall\tputchar\n" "\tjmp\tshort .qloop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2521 #: documentation/content/en/articles/x86-assembly/_index.adoc:3836 #, no-wrap msgid "" "read:\n" "\tjecxz\t.read\n" "\tcall\twrite\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2534 #, no-wrap msgid "" ".read:\n" "\tpush\tdword BUFSIZE\n" "\tmov\tesi, ibuffer\n" "\tpush\tesi\n" "\tpush\tdword [fd.in]\n" "\tsys.read\n" "\tadd\tesp, byte 12\n" "\tmov\tebx, eax\n" "\tor\teax, eax\n" "\tje\t.done\n" "\tsub\teax, eax\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2571 #: documentation/content/en/articles/x86-assembly/_index.adoc:3877 #, no-wrap msgid "" "align 4\n" "write:\n" "\tjecxz\t.ret\t; nothing to write\n" "\tsub\tedi, ecx\t; start of buffer\n" "\tpush\tecx\n" "\tpush\tedi\n" "\tpush\tdword [fd.out]\n" "\tsys.write\n" "\tadd\tesp, byte 12\n" "\tsub\teax, eax\n" "\tsub\tecx, ecx\t; buffer is empty now\n" ".ret:\n" "\tret\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2576 msgid "" "Much of it is taken from [.filename]#hex.asm# above. But there is one " "important difference: I no longer call `write` whenever I am outputting a " "line feed. Yet, the code can be used interactively." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2580 msgid "" "I have found a better solution for the interactive problem since I first " "started writing this article. I wanted to make sure each line is printed " "out separately only when needed. After all, there is no need to flush out " "every line when used non-interactively." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2584 msgid "" "The new solution I use now is to call `write` every time I find the input " "buffer empty. That way, when running in the interactive mode, the program " "reads one line from the user's keyboard, processes it, and sees its input " "buffer is empty. It flushes its output and reads the next line." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:2586 #, no-wrap msgid "The Dark Side of Buffering" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2590 msgid "" "This change prevents a mysterious lockup in a very specific case. I refer " "to it as the _dark side of buffering_, mostly because it presents a danger " "that is not quite obvious." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2594 msgid "" "It is unlikely to happen with a program like the csv above, so let us " "consider yet another filter: In this case we expect our input to be raw data " "representing color values, such as the _red_, _green_, and _blue_ " "intensities of a pixel. Our output will be the negative of our input." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2597 msgid "" "Such a filter would be very simple to write. Most of it would look just " "like all the other filters we have written so far, so I am only going to " "show you its inner loop:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2605 #, no-wrap msgid "" ".loop:\n" "\tcall\tgetchar\n" "\tnot\tal\t\t; Create a negative\n" "\tcall\tputchar\n" "\tjmp\tshort .loop\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2608 msgid "" "Because this filter works with raw data, it is unlikely to be used " "interactively." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2611 msgid "" "But it could be called by image manipulation software. And, unless it calls " "`write` before each call to `read`, chances are it will lock up." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2613 msgid "Here is what might happen:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2616 msgid "The image editor will load our filter using the C function `popen()`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2617 msgid "It will read the first row of pixels from a bitmap or pixmap." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2618 msgid "" "It will write the first row of pixels to the _pipe_ leading to the `fd.in` " "of our filter." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2619 msgid "" "Our filter will read each pixel from its input, turn it to a negative, and " "write it to its output buffer." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2620 msgid "Our filter will call `getchar` to fetch the next pixel." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2621 msgid "`getchar` will find an empty input buffer, so it will call `read`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2622 msgid "`read` will call the `SYS_read` system call." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2623 msgid "" "The _kernel_ will suspend our filter until the image editor sends more data " "to the pipe." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2624 msgid "" "The image editor will read from the other pipe, connected to the `fd.out` of " "our filter so it can set the first row of the output image _before_ it sends " "us the second row of the input." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2625 msgid "" "The _kernel_ suspends the image editor until it receives some output from " "our filter, so it can pass it on to the image editor." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2629 msgid "" "At this point our filter waits for the image editor to send it more data to " "process, while the image editor is waiting for our filter to send it the " "result of the processing of the first row. But the result sits in our " "output buffer." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2632 msgid "" "The filter and the image editor will continue waiting for each other forever " "(or, at least, until they are killed). Our software has just entered a " "crossref:secure[secure-race-conditions,race condition]." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2634 msgid "" "This problem does not exist if our filter flushes its output buffer _before_ " "asking the _kernel_ for more input data." msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:2636 #, no-wrap msgid "Using the FPU" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2639 msgid "" "Strangely enough, most of assembly language literature does not even mention " "the existence of the FPU, or _floating point unit_, let alone discuss " "programming it." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2641 msgid "" "Yet, never does assembly language shine more than when we create highly " "optimized FPU code by doing things that can be done _only_ in assembly " "language." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:2643 #, no-wrap msgid "Organization of the FPU" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2647 msgid "" "The FPU consists of 8 80-bit floating-point registers. These are organized " "in a stack fashion-you can `push` a value on TOS (_top of stack_) and you " "can `pop` it." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2649 msgid "" "That said, the assembly language op codes are not `push` and `pop` because " "those are already taken." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2652 msgid "" "You can `push` a value on TOS by using `fld`, `fild`, and `fbld`. Several " "other op codes let you `push` many common _constants_-such as _pi_-on the " "TOS." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2655 msgid "" "Similarly, you can `pop` a value by using `fst`, `fstp`, `fist`, `fistp`, " "and `fbstp`. Actually, only the op codes that end with a _p_ will literally " "`pop` the value, the rest will `store` it somewhere else without removing it " "from the TOS." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2657 msgid "" "We can transfer the data between the TOS and the computer memory either as a " "32-bit, 64-bit, or 80-bit _real_, a 16-bit, 32-bit, or 64-bit _integer_, or " "an 80-bit _packed decimal_." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2660 msgid "" "The 80-bit _packed decimal_ is a special case of _binary coded decimal_ " "which is very convenient when converting between the ASCII representation of " "data and the internal data of the FPU. It allows us to use 18 significant " "digits." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2662 msgid "" "No matter how we represent data in the memory, the FPU always stores it in " "the 80-bit _real_ format in its registers." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2664 msgid "" "Its internal precision is at least 19 decimal digits, so even if we choose " "to display results as ASCII in the full 18-digit precision, we are still " "showing correct results." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2666 msgid "" "We can perform mathematical operations on the TOS: We can calculate its " "_sine_, we can _scale_ it (i.e., we can multiply or divide it by a power of " "2), we can calculate its base-2 _logarithm_, and many other things." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2668 msgid "" "We can also _multiply_ or _divide_ it by, _add_ it to, or _subtract_ it " "from, any of the FPU registers (including itself)." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2671 msgid "" "The official Intel op code for the TOS is `st`, and for the _registers_ " "`st(0)`-`st(7)`. `st` and `st(0)`, then, refer to the same register." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2674 msgid "" "For whatever reasons, the original author of nasm has decided to use " "different op codes, namely `st0`-`st7`. In other words, there are no " "parentheses, and the TOS is always `st0`, never just `st`." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:2676 #, no-wrap msgid "The Packed Decimal Format" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2680 msgid "" "The _packed decimal_ format uses 10 bytes (80 bits) of memory to represent " "18 digits. The number represented there is always an _integer_." msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2684 msgid "" "You can use it to get decimal places by multiplying the TOS by a power of 10 " "first." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2688 msgid "" "The highest bit of the highest byte (byte 9) is the _sign bit_: If it is " "set, the number is _negative_, otherwise, it is _positive_. The rest of the " "bits of this byte are unused/ignored." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2690 msgid "" "The remaining 9 bytes store the 18 digits of the number: 2 digits per byte." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2692 msgid "" "The _more significant digit_ is stored in the high _nibble_ (4 bits), the " "_less significant digit_ in the low _nibble_." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2694 msgid "" "That said, you might think that `-1234567` would be stored in the memory " "like this (using hexadecimal notation):" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2698 #, no-wrap msgid "80 00 00 00 00 00 01 23 45 67\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2701 msgid "" "Alas it is not! As with everything else of Intel make, even the _packed " "decimal_ is _little-endian_." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2703 msgid "That means our `-1234567` is stored like this:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2707 #, no-wrap msgid "67 45 23 01 00 00 00 00 00 80\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2710 msgid "Remember that, or you will be pulling your hair out in desperation!" msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2716 msgid "" "The book to read-if you can find it-is Richard Startz' http://www.amazon.com/" "exec/obidos/ASIN/013246604X/whizkidtechnomag[8087/80287/80387 for the IBM PC " "& Compatibles]. Though it does seem to take the fact about the little-" "endian storage of the _packed decimal_ for granted. I kid you not about the " "desperation of trying to figure out what was wrong with the filter I show " "below _before_ it occurred to me I should try the little-endian order even " "for this type of data." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:2719 #, no-wrap msgid "Excursion to Pinhole Photography" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2722 msgid "" "To write meaningful software, we must not only understand our programming " "tools, but also the field we are creating software for." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2724 msgid "" "Our next filter will help us whenever we want to build a _pinhole camera_, " "so, we need some background in _pinhole photography_ before we can continue." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:2726 #, no-wrap msgid "The Camera" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2729 msgid "" "The easiest way to describe any camera ever built is as some empty space " "enclosed in some lightproof material, with a small hole in the enclosure." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2734 msgid "" "The enclosure is usually sturdy (e.g., a box), though sometimes it is " "flexible (the bellows). It is quite dark inside the camera. However, the " "hole lets light rays in through a single point (though in some cases there " "may be several). These light rays form an image, a representation of " "whatever is outside the camera, in front of the hole." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2736 msgid "" "If some light sensitive material (such as film) is placed inside the camera, " "it can capture the image." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2738 msgid "" "The hole often contains a _lens_, or a lens assembly, often called the " "_objective_." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:2740 #, no-wrap msgid "The Pinhole" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2744 msgid "" "But, strictly speaking, the lens is not necessary: The original cameras did " "not use a lens but a _pinhole_. Even today, _pinholes_ are used, both as a " "tool to study how cameras work, and to achieve a special kind of image." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2748 msgid "" "The image produced by the _pinhole_ is all equally sharp. Or _blurred_. " "There is an ideal size for a pinhole: If it is either larger or smaller, the " "image loses its sharpness." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:2750 #, no-wrap msgid "Focal Length" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2753 msgid "" "This ideal pinhole diameter is a function of the square root of _focal " "length_, which is the distance of the pinhole from the film." msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2757 #, no-wrap msgid "D = PC * sqrt(FL)\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2763 msgid "" "In here, `D` is the ideal diameter of the pinhole, `FL` is the focal length, " "and `PC` is a pinhole constant. According to Jay Bender, its value is " "`0.04`, while Kenneth Connors has determined it to be `0.037`. Others have " "proposed other values. Plus, this value is for the daylight only: Other " "types of light will require a different constant, whose value can only be " "determined by experimentation." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:2765 #, no-wrap msgid "The F-Number" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2769 msgid "" "The f-number is a very useful measure of how much light reaches the film. A " "light meter can determine that, for example, to expose a film of specific " "sensitivity with f/5.6 may require the exposure to last 1/1000 sec." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2772 msgid "" "It does not matter whether it is a 35-mm camera, or a 6x9cm camera, etc. As " "long as we know the f-number, we can determine the proper exposure." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2774 msgid "The f-number is easy to calculate:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2778 #, no-wrap msgid "F = FL / D\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2783 msgid "" "In other words, the f-number equals the focal length divided by the diameter " "of the pinhole. It also means a higher f-number either implies a smaller " "pinhole or a larger focal distance, or both. That, in turn, implies, the " "higher the f-number, the longer the exposure has to be." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2786 msgid "" "Furthermore, while pinhole diameter and focal distance are one-dimensional " "measurements, both, the film and the pinhole, are two-dimensional. That " "means that if you have measured the exposure at f-number `A` as `t`, then " "the exposure at f-number `B` is:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2790 #, no-wrap msgid "t * (B / A)²\n" msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:2793 #, no-wrap msgid "Normalized F-Number" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2796 msgid "" "While many modern cameras can change the diameter of their pinhole, and thus " "their f-number, quite smoothly and gradually, such was not always the case." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2798 msgid "" "To allow for different f-numbers, cameras typically contained a metal plate " "with several holes of different sizes drilled to them." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2801 msgid "" "Their sizes were chosen according to the above formula in such a way that " "the resultant f-number was one of standard f-numbers used on all cameras " "everywhere. For example, a very old Kodak Duaflex IV camera in my " "possession has three such holes for f-numbers 8, 11, and 16." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2804 msgid "" "A more recently made camera may offer f-numbers of 2.8, 4, 5.6, 8, 11, 16, " "22, and 32 (as well as others). These numbers were not chosen arbitrarily: " "They all are powers of the square root of 2, though they may be rounded " "somewha." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:2806 #, no-wrap msgid "The F-Stop" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2810 msgid "" "A typical camera is designed in such a way that setting any of the " "normalized f-numbers changes the feel of the dial. It will naturally _stop_ " "in that position. Because of that, these positions of the dial are called f-" "stops." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2814 msgid "" "Since the f-numbers at each stop are powers of the square root of 2, moving " "the dial by 1 stop will double the amount of light required for proper " "exposure. Moving it by 2 stops will quadruple the required exposure. " "Moving the dial by 3 stops will require the increase in exposure 8 times, " "etc." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:2816 #, no-wrap msgid "Designing the Pinhole Software" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2819 msgid "" "We are now ready to decide what exactly we want our pinhole software to do." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:2821 #, no-wrap msgid "Processing Program Input" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2825 msgid "" "Since its main purpose is to help us design a working pinhole camera, we " "will use the _focal length_ as the input to the program. This is something " "we can determine without software: Proper focal length is determined by the " "size of the film and by the need to shoot \"regular\" pictures, wide angle " "pictures, or telephoto pictures." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2827 msgid "" "Most of the programs we have written so far worked with individual " "characters, or bytes, as their input: The hex program converted individual " "bytes into a hexadecimal number, the csv program either let a character " "through, or deleted it, or changed it to a different character, etc." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2829 msgid "" "One program, ftuc used the state machine to consider at most two input bytes " "at a time." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2831 msgid "" "But our pinhole program cannot just work with individual characters, it has " "to deal with larger syntactic units." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2833 msgid "" "For example, if we want the program to calculate the pinhole diameter (and " "other values we will discuss later) at the focal lengths of `100 mm`, `150 " "mm`, and `210 mm`, we may want to enter something like this:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2837 #, no-wrap msgid " 100, 150, 210\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2842 msgid "" "Our program needs to consider more than a single byte of input at a time. " "When it sees the first `1`, it must understand it is seeing the first digit " "of a decimal number. When it sees the `0` and the other `0`, it must know " "it is seeing more digits of the same number." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2847 msgid "" "When it encounters the first comma, it must know it is no longer receiving " "the digits of the first number. It must be able to convert the digits of " "the first number into the value of `100`. And the digits of the second " "number into the value of `150`. And, of course, the digits of the third " "number into the numeric value of `210`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2849 msgid "" "We need to decide what delimiters to accept: Do the input numbers have to be " "separated by a comma? If so, how do we treat two numbers separated by " "something else?" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2854 msgid "" "Personally, I like to keep it simple. Something either is a number, so I " "process it. Or it is not a number, so I discard it. I do not like the " "computer complaining about me typing in an extra character when it is " "_obvious_ that it is an extra character. Duh!" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2856 msgid "" "Plus, it allows me to break up the monotony of computing and type in a query " "instead of just a number:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2861 #, no-wrap msgid "" "What is the best pinhole diameter for the\n" "\t focal length of 150?\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2864 msgid "There is no reason for the computer to spit out a number of complaints:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2871 #, no-wrap msgid "" "Syntax error: What\n" "Syntax error: is\n" "Syntax error: the\n" "Syntax error: best\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2874 msgid "Et cetera, et cetera, et cetera." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2877 msgid "" "Secondly, I like the `+#+` character to denote the start of a comment which " "extends to the end of the line. This does not take too much effort to code, " "and lets me treat input files for my software as executable scripts." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2879 msgid "" "In our case, we also need to decide what units the input should come in: We " "choose _millimeters_ because that is how most photographers measure the " "focus length." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2881 msgid "" "Finally, we need to decide whether to allow the use of the decimal point (in " "which case we must also consider the fact that much of the world uses a " "decimal _comma_)." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2885 msgid "" "In our case allowing for the decimal point/comma would offer a false sense " "of precision: There is little if any noticeable difference between the focus " "lengths of `50` and `51`, so allowing the user to input something like " "`50.5` is not a good idea. This is my opinion, mind you, but I am the one " "writing this program. You can make other choices in yours, of course." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:2887 #, no-wrap msgid "Offering Options" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2892 msgid "" "The most important thing we need to know when building a pinhole camera is " "the diameter of the pinhole. Since we want to shoot sharp images, we will " "use the above formula to calculate the pinhole diameter from focal length. " "As experts are offering several different values for the `PC` constant, we " "will need to have the choice." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2894 msgid "" "It is traditional in UNIX programming to have two main ways of choosing " "program parameters, plus to have a default for the time the user does not " "make a choice." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2896 msgid "Why have two ways of choosing?" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2898 msgid "" "One is to allow a (relatively) _permanent_ choice that applies automatically " "each time the software is run without us having to tell it over and over " "what we want it to do." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2903 msgid "" "The permanent choices may be stored in a configuration file, typically found " "in the user's home directory. The file usually has the same name as the " "application but is started with a dot. Often _\"rc\"_ is added to the file " "name. So, ours could be [.filename]#~/.pinhole# or " "[.filename]#~/.pinholerc#. (The [.filename]#~/# means current user's home " "directory.)" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2908 msgid "" "The configuration file is used mostly by programs that have many " "configurable parameters. Those that have only one (or a few) often use a " "different method: They expect to find the parameter in an _environment " "variable_. In our case, we might look at an environment variable named " "`PINHOLE`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2911 msgid "" "Usually, a program uses one or the other of the above methods. Otherwise, " "if a configuration file said one thing, but an environment variable another, " "the program might get confused (or just too complicated)." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2913 msgid "" "Because we only need to choose _one_ such parameter, we will go with the " "second method and search the environment for a variable named `PINHOLE`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2916 msgid "" "The other way allows us to make _ad hoc_ decisions: _\"Though I usually want " "you to use 0.039, this time I want 0.03872.\"_ In other words, it allows us " "to _override_ the permanent choice." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2918 msgid "This type of choice is usually done with command line parameters." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2926 msgid "" "Finally, a program _always_ needs a _default_. The user may not make any " "choices. Perhaps he does not know what to choose. Perhaps he is \"just " "browsing.\" Preferably, the default will be the value most users would " "choose anyway. That way they do not need to choose. Or, rather, they can " "choose the default without an additional effort." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2928 msgid "" "Given this system, the program may find conflicting options, and handle them " "this way:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2931 msgid "" "If it finds an _ad hoc_ choice (e.g., command line parameter), it should " "accept that choice. It must ignore any permanent choice and any default." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2932 msgid "" "_Otherwise_, if it finds a permanent option (e.g., an environment variable), " "it should accept it, and ignore the default." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2933 msgid "_Otherwise_, it should use the default." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2935 msgid "We also need to decide what _format_ our `PC` option should have." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2937 msgid "" "At first site, it seems obvious to use the `PINHOLE=0.04` format for the " "environment variable, and `-p0.04` for the command line." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2941 msgid "" "Allowing that is actually a security risk. The `PC` constant is a very small " "number. Naturally, we will test our software using various small values of " "`PC`. But what will happen if someone runs the program choosing a huge " "value?" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2943 msgid "" "It may crash the program because we have not designed it to handle huge " "numbers." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2946 msgid "" "Or, we may spend more time on the program so it can handle huge numbers. We " "might do that if we were writing commercial software for computer illiterate " "audience." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2948 msgid "Or, we might say, _\"Tough! The user should know better.\"\"_" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2951 msgid "" "Or, we just may make it impossible for the user to enter a huge number. " "This is the approach we will take: We will use an _implied 0._ prefix." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2954 msgid "" "In other words, if the user wants `0.04`, we will expect him to type `-p04`, " "or set `PINHOLE=04` in his environment. So, if he says `-p9999999`, we will " "interpret it as ``0.9999999``-still ridiculous but at least safer." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2957 msgid "" "Secondly, many users will just want to go with either Bender's constant or " "Connors' constant. To make it easier on them, we will interpret `-b` as " "identical to `-p04`, and `-c` as identical to `-p037`." msgstr "" #. type: Title ==== #: documentation/content/en/articles/x86-assembly/_index.adoc:2959 #, no-wrap msgid "The Output" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2962 msgid "" "We need to decide what we want our software to send to the output, and in " "what format." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2964 msgid "" "Since our input allows for an unspecified number of focal length entries, it " "makes sense to use a traditional database-style output of showing the result " "of the calculation for each focal length on a separate line, while " "separating all values on one line by a `tab` character." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2967 msgid "" "Optionally, we should also allow the user to specify the use of the CSV " "format we have studied earlier. In this case, we will print out a line of " "comma-separated names describing each field of every line, then show our " "results as before, but substituting a `comma` for the `tab`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2972 msgid "" "We need a command line option for the CSV format. We cannot use `-c` " "because that already means _use Connors' constant_. For some strange " "reason, many web sites refer to CSV files as _\"Excel spreadsheet\"_ (though " "the CSV format predates Excel). We will, therefore, use the `-e` switch to " "inform our software we want the output in the CSV format." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2976 msgid "" "We will start each line of the output with the focal length. This may sound " "repetitious at first, especially in the interactive mode: The user types in " "the focal length, and we are repeating it." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2980 msgid "" "But the user can type several focal lengths on one line. The input can also " "come in from a file or from the output of another program. In that case the " "user does not see the input at all." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2982 msgid "" "By the same token, the output can go to a file which we will want to examine " "later, or it could go to the printer, or become the input of another program." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2984 msgid "" "So, it makes perfect sense to start each line with the focal length as " "entered by the user." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2987 msgid "" "No, wait! Not as entered by the user. What if the user types in something " "like this:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:2991 #, no-wrap msgid " 00000000150\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2994 msgid "Clearly, we need to strip those leading zeros." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2996 msgid "" "So, we might consider reading the user input as is, converting it to binary " "inside the FPU, and printing it out from there." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:2998 #: documentation/content/en/articles/x86-assembly/_index.adoc:3183 msgid "But..." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3000 msgid "What if the user types something like this:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3004 #, no-wrap msgid " 17459765723452353453534535353530530534563507309676764423\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3009 msgid "" "Ha! The packed decimal FPU format lets us input 18-digit numbers. But the " "user has entered more than 18 digits. How do we handle that?" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3011 msgid "" "Well, we _could_ modify our code to read the first 18 digits, enter it to " "the FPU, then read more, multiply what we already have on the TOS by 10 " "raised to the number of additional digits, then `add` to it." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3015 msgid "" "Yes, we could do that. But in _this_ program it would be ridiculous (in a " "different one it may be just the thing to do): Even the circumference of the " "Earth expressed in millimeters only takes 11 digits. Clearly, we cannot " "build a camera that large (not yet, anyway)." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3017 msgid "" "So, if the user enters such a huge number, he is either bored, or testing " "us, or trying to break into the system, or playing games-doing anything but " "designing a pinhole camera." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3019 msgid "What will we do?" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3021 msgid "We will slap him in the face, in a manner of speaking:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3025 #, no-wrap msgid "17459765723452353453534535353530530534563507309676764423\t???\t???\t???\t???\t???\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3029 msgid "" "To achieve that, we will simply ignore any leading zeros. Once we find a " "non-zero digit, we will initialize a counter to `0` and start taking three " "steps:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3032 msgid "Send the digit to the output." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3033 msgid "" "Append the digit to a buffer we will use later to produce the packed decimal " "we can send to the FPU." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3034 msgid "Increase the counter." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3036 msgid "" "Now, while we are taking these three steps, we also need to watch out for " "one of two conditions:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3038 msgid "" "If the counter grows above 18, we stop appending to the buffer. We continue " "reading the digits and sending them to the output." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3039 msgid "" "If, or rather _when_, the next input character is not a digit, we are done " "inputting for now." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3042 msgid "" "Incidentally, we can simply discard the non-digit, unless it is a `+#+`, " "which we must return to the input stream. It starts a comment, so we must " "see it after we are done producing output and start looking for more input." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3044 msgid "" "That still leaves one possibility uncovered: If all the user enters is a " "zero (or several zeros), we will never find a non-zero to display." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3047 msgid "" "We can determine this has happened whenever our counter stays at `0`. In " "that case we need to send `0` to the output, and perform another \"slap in " "the face\":" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3051 #, no-wrap msgid "0\t???\t???\t???\t???\t???\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3054 msgid "" "Once we have displayed the focal length and determined it is valid (greater " "than `0` but not exceeding 18 digits), we can calculate the pinhole diameter." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3057 msgid "" "It is not by coincidence that _pinhole_ contains the word _pin_. Indeed, " "many a pinhole literally is a _pin hole_, a hole carefully punched with the " "tip of a pin." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3060 msgid "" "That is because a typical pinhole is very small. Our formula gets the result " "in millimeters. We will multiply it by `1000`, so we can output the result " "in _microns_." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3062 msgid "At this point we have yet another trap to face: _Too much precision._" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3066 msgid "" "Yes, the FPU was designed for high precision mathematics. But we are not " "dealing with high precision mathematics. We are dealing with physics " "(optics, specifically)." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3070 msgid "" "Suppose we want to convert a truck into a pinhole camera (we would not be " "the first ones to do that!). Suppose its box is `12` meters long, so we " "have the focal length of `12000`. Well, using Bender's constant, it gives " "us square root of `12000` multiplied by `0.04`, which is `4.381780460` " "millimeters, or `4381.780460` microns." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3075 msgid "" "Put either way, the result is absurdly precise. Our truck is not _exactly_ " "`12000` millimeters long. We did not measure its length with such a " "precision, so stating we need a pinhole with the diameter of `4.381780460` " "millimeters is, well, deceiving. `4.4` millimeters would do just fine." msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3080 msgid "" "I \"only\" used ten digits in the above example. Imagine the absurdity of " "going for all 18!" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3086 msgid "" "We need to limit the number of significant digits of our result. One way of " "doing it is by using an integer representing microns. So, our truck would " "need a pinhole with the diameter of `4382` microns. Looking at that number, " "we still decide that `4400` microns, or `4.4` millimeters is close enough." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3089 msgid "" "Additionally, we can decide that no matter how big a result we get, we only " "want to display four significant digits (or any other number of them, of " "course). Alas, the FPU does not offer rounding to a specific number of " "digits (after all, it does not view the numbers as decimal but as binary)." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3091 msgid "" "We, therefore, must devise an algorithm to reduce the number of significant " "digits." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3093 msgid "" "Here is mine (I think it is awkward-if you know a better one, _please_, let " "me know):" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3096 msgid "Initialize a counter to `0`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3097 msgid "" "While the number is greater than or equal to `10000`, divide it by `10` and " "increase the counter." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3098 msgid "Output the result." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3099 msgid "" "While the counter is greater than `0`, output `0` and decrease the counter." msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3104 msgid "" "The `10000` is only good if you want _four_ significant digits. For any " "other number of significant digits, replace `10000` with `10` raised to the " "number of significant digits." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3107 msgid "" "We will, then, output the pinhole diameter in microns, rounded off to four " "significant digits." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3110 msgid "" "At this point, we know the _focal length_ and the _pinhole diameter_. That " "means we have enough information to also calculate the _f-number_." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3114 msgid "" "We will display the f-number, rounded to four significant digits. Chances " "are the f-number will tell us very little. To make it more meaningful, we " "can find the nearest _normalized f-number_, i.e., the nearest power of the " "square root of 2." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3120 msgid "" "We do that by multiplying the actual f-number by itself, which, of course, " "will give us its `square`. We will then calculate its base-2 logarithm, " "which is much easier to do than calculating the base-square-root-of-2 " "logarithm! We will round the result to the nearest integer. Next, we will " "raise 2 to the result. Actually, the FPU gives us a good shortcut to do " "that: We can use the `fscale` op code to \"scale\" 1, which is analogous to " "``shift``ing an integer left. Finally, we calculate the square root of it " "all, and we have the nearest normalized f-number." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3123 msgid "" "If all that sounds overwhelming-or too much work, perhaps-it may become much " "clearer if you see the code. It takes 9 op codes altogether:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3135 #, no-wrap msgid "" "fmul\tst0, st0\n" "\tfld1\n" "\tfld\tst1\n" "\tfyl2x\n" "\tfrndint\n" "\tfld1\n" "\tfscale\n" "\tfsqrt\n" "\tfstp\tst1\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3139 msgid "" "The first line, `fmul st0, st0`, squares the contents of the TOS (top of the " "stack, same as `st`, called `st0` by nasm). The `fld1` pushes `1` on the " "TOS." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3143 msgid "" "The next line, `fld st1`, pushes the square back to the TOS. At this point " "the square is both in `st` and `st(2)` (it will become clear why we leave a " "second copy on the stack in a moment). `st(1)` contains `1`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3146 msgid "" "Next, `fyl2x` calculates base-2 logarithm of `st` multiplied by `st(1)`. " "That is why we placed `1` on `st(1)` before." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3148 msgid "" "At this point, `st` contains the logarithm we have just calculated, `st(1)` " "contains the square of the actual f-number we saved for later." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3152 msgid "" "`frndint` rounds the TOS to the nearest integer. `fld1` pushes a `1`. " "`fscale` shifts the `1` we have on the TOS by the value in `st(1)`, " "effectively raising 2 to `st(1)`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3154 msgid "" "Finally, `fsqrt` calculates the square root of the result, i.e., the nearest " "normalized f-number." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3157 msgid "" "We now have the nearest normalized f-number on the TOS, the base-2 logarithm " "rounded to the nearest integer in `st(1)`, and the square of the actual f-" "number in `st(2)`. We are saving the value in `st(2)` for later." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3163 msgid "" "But we do not need the contents of `st(1)` anymore. The last line, `fstp " "st1`, places the contents of `st` to `st(1)`, and pops. As a result, what " "was `st(1)` is now `st`, what was `st(2)` is now `st(1)`, etc. The new `st` " "contains the normalized f-number. The new `st(1)` contains the square of " "the actual f-number we have stored there for posterity." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3166 msgid "" "At this point, we are ready to output the normalized f-number. Because it " "is normalized, we will not round it off to four significant digits, but will " "send it out in its full precision." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3169 msgid "" "The normalized f-number is useful as long as it is reasonably small and can " "be found on our light meter. Otherwise we need a different method of " "determining proper exposure." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3171 msgid "" "Earlier we have figured out the formula of calculating proper exposure at an " "arbitrary f-number from that measured at a different f-number." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3174 msgid "" "Every light meter I have ever seen can determine proper exposure at f5.6. " "We will, therefore, calculate an _\"f5.6 multiplier,\"_ i.e., by how much we " "need to multiply the exposure measured at f5.6 to determine the proper " "exposure for our pinhole camera." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3176 msgid "" "From the above formula we know this factor can be calculated by dividing our " "f-number (the actual one, not the normalized one) by `5.6`, and squaring the " "result." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3178 msgid "" "Mathematically, dividing the square of our f-number by the square of `5.6` " "will give us the same result." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3181 msgid "" "Computationally, we do not want to square two numbers when we can only " "square one. So, the first solution seems better at first." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3189 msgid "" "`5.6` is a _constant_. We do not have to have our FPU waste precious " "cycles. We can just tell it to divide the square of the f-number by " "whatever `5.6²` equals to. Or we can divide the f-number by `5.6`, and then " "square the result. The two ways now seem equal." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3191 msgid "But, they are not!" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3195 msgid "" "Having studied the principles of photography above, we remember that the " "`5.6` is actually square root of 2 raised to the fifth power. An " "_irrational_ number. The square of this number is _exactly_ `32`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3201 msgid "" "Not only is `32` an integer, it is a power of 2. We do not need to divide " "the square of the f-number by `32`. We only need to use `fscale` to shift " "it right by five positions. In the FPU lingo it means we will `fscale` it " "with `st(1)` equal to `-5`. That is _much faster_ than a division." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3204 msgid "" "So, now it has become clear why we have saved the square of the f-number on " "the top of the FPU stack. The calculation of the f5.6 multiplier is the " "easiest calculation of this entire program! We will output it rounded to " "four significant digits." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3207 msgid "" "There is one more useful number we can calculate: The number of stops our f-" "number is from f5.6. This may help us if our f-number is just outside the " "range of our light meter, but we have a shutter which lets us set various " "speeds, and this shutter uses stops." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3210 msgid "" "Say, our f-number is 5 stops from f5.6, and the light meter says we should " "use 1/1000 sec. Then we can set our shutter speed to 1/1000 first, then " "move the dial by 5 stops." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3215 msgid "" "This calculation is quite easy as well. All we have to do is to calculate " "the base-2 logarithm of the f5.6 multiplier we had just calculated (though " "we need its value from before we rounded it off). We then output the result " "rounded to the nearest integer. We do not need to worry about having more " "than four significant digits in this one: The result is most likely to have " "only one or two digits anyway." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:3217 #, no-wrap msgid "FPU Optimizations" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3220 msgid "" "In assembly language we can optimize the FPU code in ways impossible in high " "languages, including C." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3224 msgid "" "Whenever a C function needs to calculate a floating-point value, it loads " "all necessary variables and constants into FPU registers. It then does " "whatever calculation is required to get the correct result. Good C " "compilers can optimize that part of the code really well." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3228 msgid "" "It \"returns\" the value by leaving the result on the TOS. However, before " "it returns, it cleans up. Any variables and constants it used in its " "calculation are now gone from the FPU." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3230 msgid "" "It cannot do what we just did above: We calculated the square of the f-" "number and kept it on the stack for later use by another function." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3233 msgid "" "We _knew_ we would need that value later on. We also knew we had enough " "room on the stack (which only has room for 8 numbers) to store it there." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3235 msgid "" "A C compiler has no way of knowing that a value it has on the stack will be " "required again in the very near future." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3238 msgid "" "Of course, the C programmer may know it. But the only recourse he has is to " "store the value in a memory variable." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3240 msgid "" "That means, for one, the value will be changed from the 80-bit precision " "used internally by the FPU to a C _double_ (64 bits) or even _single_ (32 " "bits)." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3243 msgid "" "That also means that the value must be moved from the TOS into the memory, " "and then back again. Alas, of all FPU operations, the ones that access the " "computer memory are the slowest." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3245 msgid "" "So, whenever programming the FPU in assembly language, look for the ways of " "keeping intermediate results on the FPU stack." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3247 msgid "" "We can take that idea even further! In our program we are using a _constant_ " "(the one we named `PC`)." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3250 msgid "" "It does not matter how many pinhole diameters we are calculating: 1, 10, 20, " "1000, we are always using the same constant. Therefore, we can optimize our " "program by keeping the constant on the stack all the time." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3253 msgid "" "Early on in our program, we are calculating the value of the above " "constant. We need to divide our input by `10` for every digit in the " "constant." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3256 msgid "" "It is much faster to multiply than to divide. So, at the start of our " "program, we divide `10` into `1` to obtain `0.1`, which we then keep on the " "stack: Instead of dividing the input by `10` for every digit, we multiply it " "by `0.1`." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3260 msgid "" "By the way, we do not input `0.1` directly, even though we could. We have a " "reason for that: While `0.1` can be expressed with just one decimal place, " "we do not know how many _binary_ places it takes. We, therefore, let the " "FPU calculate its binary value to its own high precision." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3265 msgid "" "We are using other constants: We multiply the pinhole diameter by `1000` to " "convert it from millimeters to microns. We compare numbers to `10000` when " "we are rounding them off to four significant digits. So, we keep both, " "`1000` and `10000`, on the stack. And, of course, we reuse the `0.1` when " "rounding off numbers to four digits." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3271 msgid "" "Last but not least, we keep `-5` on the stack. We need it to scale the " "square of the f-number, instead of dividing it by `32`. It is not by " "coincidence we load this constant last. That makes it the top of the stack " "when only the constants are on it. So, when the square of the f-number is " "being scaled, the `-5` is at `st(1)`, precisely where `fscale` expects it to " "be." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3274 msgid "" "It is common to create certain constants from scratch instead of loading " "them from the memory. That is what we are doing with `-5`:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3283 #, no-wrap msgid "" "\tfld1\t\t\t; TOS = 1\n" "\tfadd\tst0, st0\t; TOS = 2\n" "\tfadd\tst0, st0\t; TOS = 4\n" "\tfld1\t\t\t; TOS = 1\n" "\tfaddp\tst1, st0\t; TOS = 5\n" "\tfchs\t\t\t; TOS = -5\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3286 msgid "" "We can generalize all these optimizations into one rule: _Keep repeat values " "on the stack!_" msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3291 msgid "" "_PostScript(R)_ is a stack-oriented programming language. There are many " "more books available about PostScript(R) than about the FPU assembly " "language: Mastering PostScript(R) will help you master the FPU." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:3294 #, no-wrap msgid "pinhole-The Code" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3309 #, no-wrap msgid "" ";;;;;;; pinhole.asm ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;\n" ";\n" "; Find various parameters of a pinhole camera construction and use\n" ";\n" "; Started:\t 9-Jun-2001\n" "; Updated:\t10-Jun-2001\n" ";\n" "; Copyright (c) 2001 G. Adam Stanislav\n" "; All rights reserved.\n" ";\n" ";;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3344 #, no-wrap msgid "" "section\t.data\n" "align 4\n" "ten\tdd\t10\n" "thousand\tdd\t1000\n" "tthou\tdd\t10000\n" "fd.in\tdd\tstdin\n" "fd.out\tdd\tstdout\n" "envar\tdb\t'PINHOLE='\t; Exactly 8 bytes, or 2 dwords long\n" "pinhole\tdb\t'04,', \t\t; Bender's constant (0.04)\n" "connors\tdb\t'037', 0Ah\t; Connors' constant\n" "usg\tdb\t'Usage: pinhole [-b] [-c] [-e] [-p <value>] [-o <outfile>] [-i <infile>]', 0Ah\n" "usglen\tequ\t$-usg\n" "iemsg\tdb\t\"pinhole: Can't open input file\", 0Ah\n" "iemlen\tequ\t$-iemsg\n" "oemsg\tdb\t\"pinhole: Can't create output file\", 0Ah\n" "oemlen\tequ\t$-oemsg\n" "pinmsg\tdb\t\"pinhole: The PINHOLE constant must not be 0\", 0Ah\n" "pinlen\tequ\t$-pinmsg\n" "toobig\tdb\t\"pinhole: The PINHOLE constant may not exceed 18 decimal places\", 0Ah\n" "biglen\tequ\t$-toobig\n" "huhmsg\tdb\t9, '???'\n" "separ\tdb\t9, '???'\n" "sep2\tdb\t9, '???'\n" "sep3\tdb\t9, '???'\n" "sep4\tdb\t9, '???', 0Ah\n" "huhlen\tequ\t$-huhmsg\n" "header\tdb\t'focal length in millimeters,pinhole diameter in microns,'\n" "\tdb\t'F-number,normalized F-number,F-5.6 multiplier,stops '\n" "\tdb\t'from F-5.6', 0Ah\n" "headlen\tequ\t$-header\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3350 #, no-wrap msgid "" "section .bss\n" "ibuffer\tresb\tBUFSIZE\n" "obuffer\tresb\tBUFSIZE\n" "dbuffer\tresb\t20\t\t; decimal input buffer\n" "bbuffer\tresb\t10\t\t; BCD buffer\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3361 #, no-wrap msgid "" "section\t.text\n" "align 4\n" "huh:\n" "\tcall\twrite\n" "\tpush\tdword huhlen\n" "\tpush\tdword huhmsg\n" "\tpush\tdword [fd.out]\n" "\tsys.write\n" "\tadd\tesp, byte 12\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3370 #, no-wrap msgid "" "align 4\n" "perr:\n" "\tpush\tdword pinlen\n" "\tpush\tdword pinmsg\n" "\tpush\tdword stderr\n" "\tsys.write\n" "\tpush\tdword 4\t\t; return failure\n" "\tsys.exit\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3379 #, no-wrap msgid "" "align 4\n" "consttoobig:\n" "\tpush\tdword biglen\n" "\tpush\tdword toobig\n" "\tpush\tdword stderr\n" "\tsys.write\n" "\tpush\tdword 5\t\t; return failure\n" "\tsys.exit\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3388 #, no-wrap msgid "" "align 4\n" "ierr:\n" "\tpush\tdword iemlen\n" "\tpush\tdword iemsg\n" "\tpush\tdword stderr\n" "\tsys.write\n" "\tpush\tdword 1\t\t; return failure\n" "\tsys.exit\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3412 #, no-wrap msgid "" "align 4\n" "global\t_start\n" "_start:\n" "\tadd\tesp, byte 8\t; discard argc and argv[0]\n" "\tsub\tesi, esi\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3417 #, no-wrap msgid "" ".arg:\n" "\tpop\tecx\n" "\tor\tecx, ecx\n" "\tje\tnear .getenv\t\t; no more arguments\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3425 #, no-wrap msgid "" "\tinc\tecx\n" "\tmov\tax, [ecx]\n" "\tinc\tecx\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3443 #, no-wrap msgid "" "\tor\tah, ah\n" "\tjne\t.openoutput\n" "\tpop\tecx\n" "\tjecxz\tusage\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3470 #, no-wrap msgid "" "\t; Find the path to the input file\n" "\tor\tah, ah\n" "\tjne\t.openinput\n" "\tpop\tecx\n" "\tor\tecx, ecx\n" "\tje near usage\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3486 #, no-wrap msgid "" ".p:\n" "\tcmp\tal, 'p'\n" "\tjne\t.c\n" "\tor\tah, ah\n" "\tjne\t.pcheck\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3490 #, no-wrap msgid "" "\tpop\tecx\n" "\tor\tecx, ecx\n" "\tje\tnear usage\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3492 #, no-wrap msgid "\tmov\tah, [ecx]\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3500 #, no-wrap msgid "" ".pcheck:\n" "\tcmp\tah, '0'\n" "\tjl\tnear usage\n" "\tcmp\tah, '9'\n" "\tja\tnear usage\n" "\tmov\tesi, ecx\n" "\tjmp\t.arg\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3508 #, no-wrap msgid "" ".c:\n" "\tcmp\tal, 'c'\n" "\tjne\t.b\n" "\tor\tah, ah\n" "\tjne\tnear usage\n" "\tmov\tesi, connors\n" "\tjmp\t.arg\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3516 #, no-wrap msgid "" ".b:\n" "\tcmp\tal, 'b'\n" "\tjne\t.e\n" "\tor\tah, ah\n" "\tjne\tnear usage\n" "\tmov\tesi, pinhole\n" "\tjmp\t.arg\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3529 #, no-wrap msgid "" ".e:\n" "\tcmp\tal, 'e'\n" "\tjne\tnear usage\n" "\tor\tah, ah\n" "\tjne\tnear usage\n" "\tmov\tal, ','\n" "\tmov\t[huhmsg], al\n" "\tmov\t[separ], al\n" "\tmov\t[sep2], al\n" "\tmov\t[sep3], al\n" "\tmov\t[sep4], al\n" "\tjmp\t.arg\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3536 #, no-wrap msgid "" "align 4\n" ".getenv:\n" "\t; If ESI = 0, we did not have a -p argument,\n" "\t; and need to check the environment for \"PINHOLE=\"\n" "\tor\tesi, esi\n" "\tjne\t.init\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3538 #, no-wrap msgid "\tsub\tecx, ecx\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3543 #, no-wrap msgid "" ".nextenv:\n" "\tpop\tesi\n" "\tor\tesi, esi\n" "\tje\t.default\t; no PINHOLE envar found\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3549 #, no-wrap msgid "" "\t; check if this envar starts with 'PINHOLE='\n" "\tmov\tedi, envar\n" "\tmov\tcl, 2\t\t; 'PINHOLE=' is 2 dwords long\n" "rep\tcmpsd\n" "\tjne\t.nextenv\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3557 #, no-wrap msgid "" "\t; Check if it is followed by a digit\n" "\tmov\tal, [esi]\n" "\tcmp\tal, '0'\n" "\tjl\t.default\n" "\tcmp\tal, '9'\n" "\tjbe\t.init\n" "\t; fall through\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3564 #, no-wrap msgid "" "align 4\n" ".default:\n" "\t; We got here because we had no -p argument,\n" "\t; and did not find the PINHOLE envar.\n" "\tmov\tesi, pinhole\n" "\t; fall through\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3573 #, no-wrap msgid "" "align 4\n" ".init:\n" "\tsub\teax, eax\n" "\tsub\tebx, ebx\n" "\tsub\tecx, ecx\n" "\tsub\tedx, edx\n" "\tmov\tedi, dbuffer+1\n" "\tmov\tbyte [dbuffer], '0'\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3582 #, no-wrap msgid "" "\t; Convert the pinhole constant to real\n" ".constloop:\n" "\tlodsb\n" "\tcmp\tal, '9'\n" "\tja\t.setconst\n" "\tcmp\tal, '0'\n" "\tje\t.processconst\n" "\tjb\t.setconst\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3584 #, no-wrap msgid "\tinc\tdl\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3591 #, no-wrap msgid "" ".processconst:\n" "\tinc\tcl\n" "\tcmp\tcl, 18\n" "\tja\tnear consttoobig\n" "\tstosb\n" "\tjmp\tshort .constloop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3596 #, no-wrap msgid "" "align 4\n" ".setconst:\n" "\tor\tdl, dl\n" "\tje\tnear perr\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3599 #, no-wrap msgid "" "\tfinit\n" "\tfild\tdword [tthou]\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3603 #, no-wrap msgid "" "\tfld1\n" "\tfild\tdword [ten]\n" "\tfdivp\tst1, st0\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3606 #, no-wrap msgid "" "\tfild\tdword [thousand]\n" "\tmov\tedi, obuffer\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3609 #, no-wrap msgid "" "\tmov\tebp, ecx\n" "\tcall\tbcdload\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3613 #, no-wrap msgid "" ".constdiv:\n" "\tfmul\tst0, st2\n" "\tloop\t.constdiv\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3620 #, no-wrap msgid "" "\tfld1\n" "\tfadd\tst0, st0\n" "\tfadd\tst0, st0\n" "\tfld1\n" "\tfaddp\tst1, st0\n" "\tfchs\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3625 #, no-wrap msgid "" "\t; If we are creating a CSV file,\n" "\t; print header\n" "\tcmp\tbyte [separ], ','\n" "\tjne\t.bigloop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3630 #, no-wrap msgid "" "\tpush\tdword headlen\n" "\tpush\tdword header\n" "\tpush\tdword [fd.out]\n" "\tsys.write\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3634 #, no-wrap msgid "" ".bigloop:\n" "\tcall\tgetchar\n" "\tjc\tnear done\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3640 #, no-wrap msgid "" "\t; Skip to the end of the line if you got '#'\n" "\tcmp\tal, '#'\n" "\tjne\t.num\n" "\tcall\tskiptoeol\n" "\tjmp\tshort .bigloop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3647 #, no-wrap msgid "" ".num:\n" "\t; See if you got a number\n" "\tcmp\tal, '0'\n" "\tjl\t.bigloop\n" "\tcmp\tal, '9'\n" "\tja\t.bigloop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3651 #, no-wrap msgid "" "\t; Yes, we have a number\n" "\tsub\tebp, ebp\n" "\tsub\tedx, edx\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3656 #, no-wrap msgid "" ".number:\n" "\tcmp\tal, '0'\n" "\tje\t.number0\n" "\tmov\tdl, 1\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3667 #, no-wrap msgid "" ".number0:\n" "\tor\tdl, dl\t\t; Skip leading 0's\n" "\tje\t.nextnumber\n" "\tpush\teax\n" "\tcall\tputchar\n" "\tpop\teax\n" "\tinc\tebp\n" "\tcmp\tebp, 19\n" "\tjae\t.nextnumber\n" "\tmov\t[dbuffer+ebp], al\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3678 #, no-wrap msgid "" ".nextnumber:\n" "\tcall\tgetchar\n" "\tjc\t.work\n" "\tcmp\tal, '#'\n" "\tje\t.ungetc\n" "\tcmp\tal, '0'\n" "\tjl\t.work\n" "\tcmp\tal, '9'\n" "\tja\t.work\n" "\tjmp\tshort .number\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3682 #, no-wrap msgid "" ".ungetc:\n" "\tdec\tesi\n" "\tinc\tebx\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3687 #, no-wrap msgid "" ".work:\n" "\t; Now, do all the work\n" "\tor\tdl, dl\n" "\tje\tnear .work0\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3690 #, no-wrap msgid "" "\tcmp\tebp, 19\n" "\tjae\tnear .toobig\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3692 #, no-wrap msgid "\tcall\tbcdload\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3694 #, no-wrap msgid "\t; Calculate pinhole diameter\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3701 #, no-wrap msgid "" "\tfld\tst0\t; save it\n" "\tfsqrt\n" "\tfmul\tst0, st3\n" "\tfld\tst0\n" "\tfmul\tst5\n" "\tsub\tebp, ebp\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3711 #, no-wrap msgid "" "\t; Round off to 4 significant digits\n" ".diameter:\n" "\tfcom\tst0, st7\n" "\tfstsw\tax\n" "\tsahf\n" "\tjb\t.printdiameter\n" "\tfmul\tst0, st6\n" "\tinc\tebp\n" "\tjmp\tshort .diameter\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3714 #, no-wrap msgid "" ".printdiameter:\n" "\tcall\tprintnumber\t; pinhole diameter\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3716 #, no-wrap msgid "\t; Calculate F-number\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3719 #, no-wrap msgid "" "\tfdivp\tst1, st0\n" "\tfld\tst0\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3721 #, no-wrap msgid "\tsub\tebp, ebp\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3730 #, no-wrap msgid "" ".fnumber:\n" "\tfcom\tst0, st6\n" "\tfstsw\tax\n" "\tsahf\n" "\tjb\t.printfnumber\n" "\tfmul\tst0, st5\n" "\tinc\tebp\n" "\tjmp\tshort .fnumber\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3733 #, no-wrap msgid "" ".printfnumber:\n" "\tcall\tprintnumber\t; F number\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3744 #, no-wrap msgid "" "\t; Calculate normalized F-number\n" "\tfmul\tst0, st0\n" "\tfld1\n" "\tfld\tst1\n" "\tfyl2x\n" "\tfrndint\n" "\tfld1\n" "\tfscale\n" "\tfsqrt\n" "\tfstp\tst1\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3747 #: documentation/content/en/articles/x86-assembly/_index.adoc:3775 #, no-wrap msgid "" "\tsub\tebp, ebp\n" "\tcall\tprintnumber\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3749 #, no-wrap msgid "\t; Calculate time multiplier from F-5.6\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3752 #, no-wrap msgid "" "\tfscale\n" "\tfld\tst0\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3758 #, no-wrap msgid "" "\t; Round off to 4 significant digits\n" ".fmul:\n" "\tfcom\tst0, st6\n" "\tfstsw\tax\n" "\tsahf\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3763 #, no-wrap msgid "" "\tjb\t.printfmul\n" "\tinc\tebp\n" "\tfmul\tst0, st5\n" "\tjmp\tshort .fmul\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3766 #, no-wrap msgid "" ".printfmul:\n" "\tcall\tprintnumber\t; F multiplier\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3768 #, no-wrap msgid "\t; Calculate F-stops from 5.6\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3772 #, no-wrap msgid "" "\tfld1\n" "\tfxch\tst1\n" "\tfyl2x\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3779 #, no-wrap msgid "" "\tmov\tal, 0Ah\n" "\tcall\tputchar\n" "\tjmp\t.bigloop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3783 #, no-wrap msgid "" ".work0:\n" "\tmov\tal, '0'\n" "\tcall\tputchar\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3788 #, no-wrap msgid "" "align 4\n" ".toobig:\n" "\tcall\thuh\n" "\tjmp\t.bigloop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3792 #, no-wrap msgid "" "align 4\n" "done:\n" "\tcall\twrite\t\t; flush output buffer\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3801 #, no-wrap msgid "\tfinit\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3814 #, no-wrap msgid "" "align 4\n" "skiptoeol:\n" "\t; Keep reading until you come to cr, lf, or eof\n" "\tcall\tgetchar\n" "\tjc\tdone\n" "\tcmp\tal, 0Ah\n" "\tjne\t.cr\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3819 #, no-wrap msgid "" ".cr:\n" "\tcmp\tal, 0Dh\n" "\tjne\tskiptoeol\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3832 #, no-wrap msgid "" ".fetch:\n" "\tlodsb\n" "\tdec\tebx\n" "\tclc\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3849 #, no-wrap msgid "" ".read:\n" "\tpush\tdword BUFSIZE\n" "\tmov\tesi, ibuffer\n" "\tpush\tesi\n" "\tpush\tdword [fd.in]\n" "\tsys.read\n" "\tadd\tesp, byte 12\n" "\tmov\tebx, eax\n" "\tor\teax, eax\n" "\tje\t.empty\n" "\tsub\teax, eax\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3855 #, no-wrap msgid "" "align 4\n" ".empty:\n" "\tadd\tesp, byte 4\n" "\tstc\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3884 #, no-wrap msgid "" "align 4\n" "bcdload:\n" "\t; EBP contains the number of chars in dbuffer\n" "\tpush\tecx\n" "\tpush\tesi\n" "\tpush\tedi\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3888 #, no-wrap msgid "" "\tlea\tecx, [ebp+1]\n" "\tlea\tesi, [dbuffer+ebp-1]\n" "\tshr\tecx, 1\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3890 #, no-wrap msgid "\tstd\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3896 #, no-wrap msgid "" "\tmov\tedi, bbuffer\n" "\tsub\teax, eax\n" "\tmov\t[edi], eax\n" "\tmov\t[edi+4], eax\n" "\tmov\t[edi+2], ax\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3905 #, no-wrap msgid "" ".loop:\n" "\tlodsw\n" "\tsub\tax, 3030h\n" "\tshl\tal, 4\n" "\tor\tal, ah\n" "\tmov\t[edi], al\n" "\tinc\tedi\n" "\tloop\t.loop\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3907 #, no-wrap msgid "\tfbld\t[bbuffer]\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3914 #, no-wrap msgid "" "\tcld\n" "\tpop\tedi\n" "\tpop\tesi\n" "\tpop\tecx\n" "\tsub\teax, eax\n" "\tret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3920 #, no-wrap msgid "" "align 4\n" "printnumber:\n" "\tpush\tebp\n" "\tmov\tal, [separ]\n" "\tcall\tputchar\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3924 #, no-wrap msgid "" "\t; Print the integer at the TOS\n" "\tmov\tebp, bbuffer+9\n" "\tfbstp\t[bbuffer]\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3930 #, no-wrap msgid "" "\t; Check the sign\n" "\tmov\tal, [ebp]\n" "\tdec\tebp\n" "\tor\tal, al\n" "\tjns\t.leading\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3934 #, no-wrap msgid "" "\t; We got a negative number (should never happen)\n" "\tmov\tal, '-'\n" "\tcall\tputchar\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3943 #, no-wrap msgid "" ".leading:\n" "\t; Skip leading zeros\n" "\tmov\tal, [ebp]\n" "\tdec\tebp\n" "\tor\tal, al\n" "\tjne\t.first\n" "\tcmp\tebp, bbuffer\n" "\tjae\t.leading\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3948 #, no-wrap msgid "" "\t; We are here because the result was 0.\n" "\t; Print '0' and return\n" "\tmov\tal, '0'\n" "\tjmp\tputchar\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3960 #, no-wrap msgid "" ".first:\n" "\t; We have found the first non-zero.\n" "\t; But it is still packed\n" "\ttest\tal, 0F0h\n" "\tjz\t.second\n" "\tpush\teax\n" "\tshr\tal, 4\n" "\tadd\tal, '0'\n" "\tcall\tputchar\n" "\tpop\teax\n" "\tand\tal, 0Fh\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3964 #, no-wrap msgid "" ".second:\n" "\tadd\tal, '0'\n" "\tcall\tputchar\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3968 #, no-wrap msgid "" ".next:\n" "\tcmp\tebp, bbuffer\n" "\tjb\t.done\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3978 #, no-wrap msgid "" "\tmov\tal, [ebp]\n" "\tpush\teax\n" "\tshr\tal, 4\n" "\tadd\tal, '0'\n" "\tcall\tputchar\n" "\tpop\teax\n" "\tand\tal, 0Fh\n" "\tadd\tal, '0'\n" "\tcall\tputchar\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3981 #, no-wrap msgid "" "\tdec\tebp\n" "\tjmp\tshort .next\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3986 #, no-wrap msgid "" ".done:\n" "\tpop\tebp\n" "\tor\tebp, ebp\n" "\tje\t.ret\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3992 #, no-wrap msgid "" ".zeros:\n" "\tmov\tal, '0'\n" "\tcall\tputchar\n" "\tdec\tebp\n" "\tjne\t.zeros\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:3995 #, no-wrap msgid "" ".ret:\n" "\tret\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:3998 msgid "" "The code follows the same format as all the other filters we have seen " "before, with one subtle exception:" msgstr "" #. type: delimited block _ 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4001 msgid "" "We are no longer assuming that the end of input implies the end of things to " "do, something we took for granted in the _character-oriented_ filters." msgstr "" #. type: delimited block _ 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4003 msgid "" "This filter does not process characters. It processes a _language_ (albeit a " "very simple one, consisting only of numbers)." msgstr "" #. type: delimited block _ 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4005 msgid "When we have no more input, it can mean one of two things:" msgstr "" #. type: delimited block _ 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4007 msgid "We are done and can quit. This is the same as before." msgstr "" #. type: delimited block _ 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4008 msgid "" "The last character we have read was a digit. We have stored it at the end of " "our ASCII-to-float conversion buffer. We now need to convert the contents of " "that buffer into a number and write the last line of our output." msgstr "" #. type: delimited block _ 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4010 msgid "" "For that reason, we have modified our `getchar` and our `read` routines to " "return with the `carry flag` _clear_ whenever we are fetching another " "character from the input, or the `carry flag` _set_ whenever there is no " "more input." msgstr "" #. type: delimited block _ 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4013 msgid "" "Of course, we are still using assembly language magic to do that! Take a " "good look at `getchar`. It _always_ returns with the `carry flag` _clear_." msgstr "" #. type: delimited block _ 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4015 msgid "" "Yet, our main code relies on the `carry flag` to tell it when to quit-and it " "works." msgstr "" #. type: delimited block _ 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4018 msgid "" "The magic is in `read`. Whenever it receives more input from the system, it " "just returns to `getchar`, which fetches a character from the input buffer, " "_clears_ the `carry flag` and returns." msgstr "" #. type: delimited block _ 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4021 msgid "" "But when `read` receives no more input from the system, it does _not_ return " "to `getchar` at all. Instead, the `add esp, byte 4` op code adds `4` to " "`ESP`, _sets_ the `carry flag`, and returns." msgstr "" #. type: delimited block _ 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4025 msgid "" "So, where does it return to? Whenever a program uses the `call` op code, the " "microprocessor ``push``es the return address, i.e., it stores it on the top " "of the stack (not the FPU stack, the system stack, which is in the memory). " "When a program uses the `ret` op code, the microprocessor ``pop``s the " "return value from the stack, and jumps to the address that was stored there." msgstr "" #. type: delimited block _ 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4027 msgid "" "But since we added `4` to `ESP` (which is the stack pointer register), we " "have effectively given the microprocessor a minor case of _amnesia_: It no " "longer remembers it was `getchar` that ``call``ed `read`." msgstr "" #. type: delimited block _ 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4029 msgid "" "And since `getchar` never ``push``ed anything before ``call``ing `read`, the " "top of the stack now contains the return address to whatever or whoever " "``call``ed `getchar`. As far as that caller is concerned, he ``call``ed " "`getchar`, which ``ret``urned with the `carry flag` set!" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4032 msgid "" "Other than that, the `bcdload` routine is caught up in the middle of a " "Lilliputian conflict between the Big-Endians and the Little-Endians." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4034 msgid "" "It is converting the text representation of a number into that number: The " "text is stored in the big-endian order, but the _packed decimal_ is little-" "endian." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4037 msgid "" "To solve the conflict, we use the `std` op code early on. We cancel it with " "`cld` later on: It is quite important we do not `call` anything that may " "depend on the default setting of the _direction flag_ while `std` is active." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4039 msgid "" "Everything else in this code should be quit eclear, providing you have read " "the entire article that precedes it." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4042 msgid "" "It is a classical example of the adage that programming requires a lot of " "thought and only a little coding. Once we have thought through every tiny " "detail, the code almost writes itself." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:4044 #, no-wrap msgid "Using pinhole" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4048 msgid "" "Because we have decided to make the program _ignore_ any input except for " "numbers (and even those inside a comment), we can actually perform _textual " "queries_. We do not _have to_, but we _can_." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4050 msgid "" "In my humble opinion, forming a textual query, instead of having to follow a " "very strict syntax, makes software much more user friendly." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4056 msgid "" "Suppose we want to build a pinhole camera to use the 4x5 inch film. The " "standard focal length for that film is about 150mm. We want to _fine-tune_ " "our focal length so the pinhole diameter is as round a number as possible. " "Let us also suppose we are quite comfortable with cameras but somewhat " "intimidated by computers. Rather than just have to type in a bunch of " "numbers, we want to _ask_ a couple of questions." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4058 msgid "Our session might look like this:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4062 #, no-wrap msgid "% pinhole\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4064 #, no-wrap msgid "Computer,\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4077 #, no-wrap msgid "" "What size pinhole do I need for the focal length of 150?\n" "150\t490\t306\t362\t2930\t12\n" "Hmmm... How about 160?\n" "160\t506\t316\t362\t3125\t12\n" "Let's make it 155, please.\n" "155\t498\t311\t362\t3027\t12\n" "Ah, let's try 157...\n" "157\t501\t313\t362\t3066\t12\n" "156?\n" "156\t500\t312\t362\t3047\t12\n" "That's it! Perfect! Thank you very much!\n" "^D\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4080 msgid "" "We have found that while for the focal length of 150, our pinhole diameter " "should be 490 microns, or 0.49 mm, if we go with the almost identical focal " "length of 156 mm, we can get away with a pinhole diameter of exactly one " "half of a millimeter." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:4082 #, no-wrap msgid "Scripting" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4085 msgid "" "Because we have chosen the `+#+` character to denote the start of a comment, " "we can treat our pinhole software as a _scripting language_." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4087 msgid "You have probably seen shell _scripts_ that start with:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4091 #, no-wrap msgid "#! /bin/sh\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4094 msgid "...or..." msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4098 #, no-wrap msgid "#!/bin/sh\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4101 msgid "...because the blank space after the `#!` is optional." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4104 msgid "" "Whenever UNIX is asked to run an executable file which starts with the `#!`, " "it assumes the file is a script. It adds the command to the rest of the " "first line of the script, and tries to execute that." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4106 msgid "" "Suppose now that we have installed pinhole in /usr/local/bin/, we can now " "write a script to calculate various pinhole diameters suitable for various " "focal lengths commonly used with the 120 film." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4108 msgid "The script might look something like this:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4114 #, no-wrap msgid "" "#! /usr/local/bin/pinhole -b -i\n" "# Find the best pinhole diameter\n" "# for the 120 film\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4117 #, no-wrap msgid "" "### Standard\n" "80\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4120 #, no-wrap msgid "" "### Wide angle\n" "30, 40, 50, 60, 70\n" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4123 #, no-wrap msgid "" "### Telephoto\n" "100, 120, 140\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4126 msgid "Because 120 is a medium size film, we may name this file medium." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4128 msgid "" "We can set its permissions to execute, and run it as if it were a program:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4133 #, no-wrap msgid "" "% chmod 755 medium\n" "% ./medium\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4136 msgid "UNIX will interpret that last command as:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4140 #, no-wrap msgid "% /usr/local/bin/pinhole -b -i ./medium\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4143 msgid "It will run that command and display:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4155 #, no-wrap msgid "" "80\t358\t224\t256\t1562\t11\n" "30\t219\t137\t128\t586\t9\n" "40\t253\t158\t181\t781\t10\n" "50\t283\t177\t181\t977\t10\n" "60\t310\t194\t181\t1172\t10\n" "70\t335\t209\t181\t1367\t10\n" "100\t400\t250\t256\t1953\t11\n" "120\t438\t274\t256\t2344\t11\n" "140\t473\t296\t256\t2734\t11\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4158 msgid "Now, let us enter:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4162 #, no-wrap msgid "% ./medium -c\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4165 msgid "UNIX will treat that as:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4169 #, no-wrap msgid "% /usr/local/bin/pinhole -b -i ./medium -c\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4173 msgid "" "That gives it two conflicting options: `-b` and `-c` (Use Bender's constant " "and use Connors' constant). We have programmed it so later options override " "early ones-our program will calculate everything using Connors' constant:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4185 #, no-wrap msgid "" "80\t331\t242\t256\t1826\t11\n" "30\t203\t148\t128\t685\t9\n" "40\t234\t171\t181\t913\t10\n" "50\t262\t191\t181\t1141\t10\n" "60\t287\t209\t181\t1370\t10\n" "70\t310\t226\t256\t1598\t11\n" "100\t370\t270\t256\t2283\t11\n" "120\t405\t296\t256\t2739\t11\n" "140\t438\t320\t362\t3196\t12\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4189 msgid "" "We decide we want to go with Bender's constant after all. We want to save " "its values as a comma-separated file:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4205 #, no-wrap msgid "" "% ./medium -b -e > bender\n" "% cat bender\n" "focal length in millimeters,pinhole diameter in microns,F-number,normalized F-number,F-5.6 multiplier,stops from F-5.6\n" "80,358,224,256,1562,11\n" "30,219,137,128,586,9\n" "40,253,158,181,781,10\n" "50,283,177,181,977,10\n" "60,310,194,181,1172,10\n" "70,335,209,181,1367,10\n" "100,400,250,256,1953,11\n" "120,438,274,256,2344,11\n" "140,473,296,256,2734,11\n" "%\n" msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:4208 #, no-wrap msgid "Caveats" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4212 msgid "" "Assembly language programmers who \"grew up\" under MS-DOS and Windows often " "tend to take shortcuts. Reading the keyboard scan codes and writing " "directly to video memory are two classical examples of practices which, " "under MS-DOS are not frowned upon but considered the right thing to do." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4214 msgid "" "The reason? Both the PC BIOS and MS-DOS are notoriously slow when performing " "these operations." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4217 msgid "" "You may be tempted to continue similar practices in the UNIX environment. " "For example, I have seen a web site which explains how to access the " "keyboard scan codes on a popular UNIX clone." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4219 msgid "" "That is generally a _very bad idea_ in UNIX environment! Let me explain why." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:4221 #, no-wrap msgid "UNIX Is Protected" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4228 msgid "" "For one thing, it may simply not be possible. UNIX runs in protected mode. " "Only the kernel and device drivers are allowed to access hardware directly. " "Perhaps a particular UNIX clone will let you read the keyboard scan codes, " "but chances are a real UNIX operating system will not. And even if one " "version may let you do it, the next one may not, so your carefully crafted " "software may become a dinosaur overnight." msgstr "" #. type: Title === #: documentation/content/en/articles/x86-assembly/_index.adoc:4230 #, no-wrap msgid "UNIX Is an Abstraction" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4233 msgid "" "But there is a much more important reason not to try accessing the hardware " "directly (unless, of course, you are writing a device driver), even on the " "UNIX like systems that let you do it:" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4235 msgid "_UNIX is an abstraction!_" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4241 msgid "" "There is a major difference in the philosophy of design between MS-DOS and " "UNIX. MS-DOS was designed as a single-user system. It is run on a computer " "with a keyboard and a video screen attached directly to that computer. User " "input is almost guaranteed to come from that keyboard. Your program's " "output virtually always ends up on that screen." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4244 msgid "" "This is NEVER guaranteed under UNIX. It is quite common for a UNIX user to " "pipe and redirect program input and output:" msgstr "" #. type: delimited block . 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4248 #, no-wrap msgid "% program1 | program2 | program3 > file1\n" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4252 msgid "" "If you have written program2, your input does not come from the keyboard but " "from the output of program1. Similarly, your output does not go to the " "screen but becomes the input for program3 whose output, in turn, goes to " "[.filename]#file1#." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4255 msgid "" "But there is more! Even if you made sure that your input comes from, and " "your output goes to, the terminal, there is no guarantee the terminal is a " "PC: It may not have its video memory where you expect it, nor may its " "keyboard be producing PC-style scan codes. It may be a Macintosh, or any " "other computer." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4257 msgid "" "Now you may be shaking your head: My software is in PC assembly language, " "how can it run on a Macintosh? But I did not say your software would be " "running on a Macintosh, only that its terminal may be a Macintosh." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4261 msgid "" "Under UNIX, the terminal does not have to be directly attached to the " "computer that runs your software, it can even be on another continent, or, " "for that matter, on another planet. It is perfectly possible that a " "Macintosh user in Australia connects to a UNIX system in North America (or " "anywhere else) via telnet. The software then runs on one computer, while " "the terminal is on a different computer: If you try to read the scan codes, " "you will get the wrong input!" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4264 msgid "" "Same holds true about any other hardware: A file you are reading may be on a " "disk you have no direct access to. A camera you are reading images from may " "be on a space shuttle, connected to you via satellites." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4267 msgid "" "That is why under UNIX you must never make any assumptions about where your " "data is coming from and going to. Always let the system handle the physical " "access to the hardware." msgstr "" #. type: delimited block = 4 #: documentation/content/en/articles/x86-assembly/_index.adoc:4275 msgid "" "These are caveats, not absolute rules. Exceptions are possible. For " "example, if a text editor has determined it is running on a local machine, " "it may want to read the scan codes directly for improved control. I am not " "mentioning these caveats to tell you what to do or what not to do, just to " "make you aware of certain pitfalls that await you if you have just arrived " "to UNIX form MS-DOS. Of course, creative people often break rules, and it " "is OK as long as they know they are breaking them and why." msgstr "" #. type: Title == #: documentation/content/en/articles/x86-assembly/_index.adoc:4278 #, no-wrap msgid "Acknowledgements" msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4281 msgid "" "This tutorial would never have been possible without the help of many " "experienced FreeBSD programmers from the {freebsd-hackers}, many of whom " "have patiently answered my questions, and pointed me in the right direction " "in my attempts to explore the inner workings of UNIX system programming in " "general and FreeBSD in particular." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4284 msgid "" "Thomas M. Sommers opened the door for me. His link:https://web.archive.org/" "web/20090914064615/http://www.codebreakers-journal.com/content/view/" "262/27[How do I write \"Hello, world\" in FreeBSD assembler?] web page was " "my first encounter with an example of assembly language programming under " "FreeBSD." msgstr "" #. type: Plain text #: documentation/content/en/articles/x86-assembly/_index.adoc:4286 msgid "" "Jake Burkholder has kept the door open by willingly answering all of my " "questions and supplying me with example assembly language source code." msgstr ""