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freebsd
GitHub Repository: freebsd/freebsd-src
 Path: blob/main/lib/libc/i386/string/swab.S
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/*

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 * Copyright (c) 1993,94 Winning Strategies, Inc.

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 * All rights reserved.

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 *

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 * Redistribution and use in source and binary forms, with or without

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 * modification, are permitted provided that the following conditions

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 * are met:

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 * 1. Redistributions of source code must retain the above copyright

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 *    notice, this list of conditions and the following disclaimer.

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 * 2. Redistributions in binary form must reproduce the above copyright

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 *    notice, this list of conditions and the following disclaimer in the

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 *    documentation and/or other materials provided with the distribution.

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 * 3. All advertising materials mentioning features or use of this software

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 *    must display the following acknowledgement:

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 *      This product includes software developed by Winning Strategies, Inc.

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 * 4. The name of the author may not be used to endorse or promote products

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 *    derived from this software without specific prior written permission

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 *

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 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

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 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

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 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

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 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

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 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

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 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

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 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

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 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

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 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

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 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

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 */

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#include <machine/asm.h>

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/*

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 * void

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 * swab (const void *src, void *dst, size_t len)

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 *	copy len bytes from src to dst, swapping adjacent bytes

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 *

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 * On the i486, this code is negligibly faster than the code generated

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 * by gcc at about half the size.  If my i386 databook is correct, it

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 * should be considerably faster than the gcc code on an i386.

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 *

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 * Written by:

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 *	J.T. Conklin ([email protected]), Winning Strategies, Inc.

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 */

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ENTRY(swab)

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	pushl	%esi

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	pushl	%edi

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	movl	12(%esp),%esi

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	movl	16(%esp),%edi

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	movl	20(%esp),%ecx

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	cld				# set direction forward

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	shrl	$1,%ecx

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	testl	$7,%ecx			# copy first group of 1 to 7 words

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	jz	L2			# while swaping alternate bytes.

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	.align	2,0x90

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L1:	lodsw

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	rorw	$8,%ax

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	stosw

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	decl	%ecx

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	testl	$7,%ecx

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	jnz	L1

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L2:	shrl	$3,%ecx			# copy remainder 8 words at a time

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	jz	L4			# while swapping alternate bytes.

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	.align	2,0x90

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L3:	lodsw

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	rorw	$8,%ax

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	stosw

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	lodsw

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	rorw	$8,%ax

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	stosw

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	lodsw

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	rorw	$8,%ax

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	stosw

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	lodsw

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	rorw	$8,%ax

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	stosw

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	lodsw

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	rorw	$8,%ax

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	stosw

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	lodsw

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	rorw	$8,%ax

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	stosw

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	lodsw

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	rorw	$8,%ax

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	stosw

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	lodsw

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	rorw	$8,%ax

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	stosw

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	decl	%ecx

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	jnz	L3

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L4:	popl	%edi

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	popl	%esi

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	ret

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END(swab)

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	.section .note.GNU-stack,"",%progbits

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