inffast.js

'use strict';

// See state defs from inflate.js
var BAD = 30;       /* got a data error -- remain here until reset */
var TYPE = 12;      /* i: waiting for type bits, including last-flag bit */

/*
   Decode literal, length, and distance codes and write out the resulting
   literal and match bytes until either not enough input or output is
   available, an end-of-block is encountered, or a data error is encountered.
   When large enough input and output buffers are supplied to inflate(), for
   example, a 16K input buffer and a 64K output buffer, more than 95% of the
   inflate execution time is spent in this routine.

   Entry assumptions:

        state.mode === LEN
        strm.avail_in >= 6
        strm.avail_out >= 258
        start >= strm.avail_out
        state.bits < 8

   On return, state.mode is one of:

        LEN -- ran out of enough output space or enough available input
        TYPE -- reached end of block code, inflate() to interpret next block
        BAD -- error in block data

   Notes:

    - The maximum input bits used by a length/distance pair is 15 bits for the
      length code, 5 bits for the length extra, 15 bits for the distance code,
      and 13 bits for the distance extra.  This totals 48 bits, or six bytes.
      Therefore if strm.avail_in >= 6, then there is enough input to avoid
      checking for available input while decoding.

    - The maximum bytes that a single length/distance pair can output is 258
      bytes, which is the maximum length that can be coded.  inflate_fast()
      requires strm.avail_out >= 258 for each loop to avoid checking for
      output space.
 */
module.exports = function inflate_fast(strm, start) {
  var state;
  var _in;                    /* local strm.input */
  var last;                   /* have enough input while in < last */
  var _out;                   /* local strm.output */
  var beg;                    /* inflate()'s initial strm.output */
  var end;                    /* while out < end, enough space available */
//#ifdef INFLATE_STRICT
  var dmax;                   /* maximum distance from zlib header */
//#endif
  var wsize;                  /* window size or zero if not using window */
  var whave;                  /* valid bytes in the window */
  var wnext;                  /* window write index */
  var window;                 /* allocated sliding window, if wsize != 0 */
  var hold;                   /* local strm.hold */
  var bits;                   /* local strm.bits */
  var lcode;                  /* local strm.lencode */
  var dcode;                  /* local strm.distcode */
  var lmask;                  /* mask for first level of length codes */
  var dmask;                  /* mask for first level of distance codes */
  var here;                   /* retrieved table entry */
  var op;                     /* code bits, operation, extra bits, or */
                              /*  window position, window bytes to copy */
  var len;                    /* match length, unused bytes */
  var dist;                   /* match distance */
  var from;                   /* where to copy match from */
  var from_source;


  var input, output; // JS specific, because we have no pointers

  /* copy state to local variables */
  state = strm.state;
  //here = state.here;
  _in = strm.next_in;
  input = strm.input;
  last = _in + (strm.avail_in - 5);
  _out = strm.next_out;
  output = strm.output;
  beg = _out - (start - strm.avail_out);
  end = _out + (strm.avail_out - 257);
//#ifdef INFLATE_STRICT
  dmax = state.dmax;
//#endif
  wsize = state.wsize;
  whave = state.whave;
  wnext = state.wnext;
  window = state.window;
  hold = state.hold;
  bits = state.bits;
  lcode = state.lencode;
  dcode = state.distcode;
  lmask = (1 << state.lenbits) - 1;
  dmask = (1 << state.distbits) - 1;


  /* decode literals and length/distances until end-of-block or not enough
     input data or output space */

  top:
  do {
    if (bits < 15) {
      hold += input[_in++] << bits;
      bits += 8;
      hold += input[_in++] << bits;
      bits += 8;
    }

    here = lcode[hold & lmask];

    dolen:
    for (;;) { // Goto emulation
      op = here >>> 24/*here.bits*/;
      hold >>>= op;
      bits -= op;
      op = (here >>> 16) & 0xff/*here.op*/;
      if (op === 0) {                          /* literal */
        //Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ?
        //        "inflate:         literal '%c'\n" :
        //        "inflate:         literal 0x%02x\n", here.val));
        output[_out++] = here & 0xffff/*here.val*/;
      }
      else if (op & 16) {                     /* length base */
        len = here & 0xffff/*here.val*/;
        op &= 15;                           /* number of extra bits */
        if (op) {
          if (bits < op) {
            hold += input[_in++] << bits;
            bits += 8;
          }
          len += hold & ((1 << op) - 1);
          hold >>>= op;
          bits -= op;
        }
        //Tracevv((stderr, "inflate:         length %u\n", len));
        if (bits < 15) {
          hold += input[_in++] << bits;
          bits += 8;
          hold += input[_in++] << bits;
          bits += 8;
        }
        here = dcode[hold & dmask];

        dodist:
        for (;;) { // goto emulation
          op = here >>> 24/*here.bits*/;
          hold >>>= op;
          bits -= op;
          op = (here >>> 16) & 0xff/*here.op*/;

          if (op & 16) {                      /* distance base */
            dist = here & 0xffff/*here.val*/;
            op &= 15;                       /* number of extra bits */
            if (bits < op) {
              hold += input[_in++] << bits;
              bits += 8;
              if (bits < op) {
                hold += input[_in++] << bits;
                bits += 8;
              }
            }
            dist += hold & ((1 << op) - 1);
//#ifdef INFLATE_STRICT
            if (dist > dmax) {
              strm.msg = 'invalid distance too far back';
              state.mode = BAD;
              break top;
            }
//#endif
            hold >>>= op;
            bits -= op;
            //Tracevv((stderr, "inflate:         distance %u\n", dist));
            op = _out - beg;                /* max distance in output */
            if (dist > op) {                /* see if copy from window */
              op = dist - op;               /* distance back in window */
              if (op > whave) {
                if (state.sane) {
                  strm.msg = 'invalid distance too far back';
                  state.mode = BAD;
                  break top;
                }

// (!) This block is disabled in zlib defailts,
// don't enable it for binary compatibility
//#ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
//                if (len <= op - whave) {
//                  do {
//                    output[_out++] = 0;
//                  } while (--len);
//                  continue top;
//                }
//                len -= op - whave;
//                do {
//                  output[_out++] = 0;
//                } while (--op > whave);
//                if (op === 0) {
//                  from = _out - dist;
//                  do {
//                    output[_out++] = output[from++];
//                  } while (--len);
//                  continue top;
//                }
//#endif
              }
              from = 0; // window index
              from_source = window;
              if (wnext === 0) {           /* very common case */
                from += wsize - op;
                if (op < len) {         /* some from window */
                  len -= op;
                  do {
                    output[_out++] = window[from++];
                  } while (--op);
                  from = _out - dist;  /* rest from output */
                  from_source = output;
                }
              }
              else if (wnext < op) {      /* wrap around window */
                from += wsize + wnext - op;
                op -= wnext;
                if (op < len) {         /* some from end of window */
                  len -= op;
                  do {
                    output[_out++] = window[from++];
                  } while (--op);
                  from = 0;
                  if (wnext < len) {  /* some from start of window */
                    op = wnext;
                    len -= op;
                    do {
                      output[_out++] = window[from++];
                    } while (--op);
                    from = _out - dist;      /* rest from output */
                    from_source = output;
                  }
                }
              }
              else {                      /* contiguous in window */
                from += wnext - op;
                if (op < len) {         /* some from window */
                  len -= op;
                  do {
                    output[_out++] = window[from++];
                  } while (--op);
                  from = _out - dist;  /* rest from output */
                  from_source = output;
                }
              }
              while (len > 2) {
                output[_out++] = from_source[from++];
                output[_out++] = from_source[from++];
                output[_out++] = from_source[from++];
                len -= 3;
              }
              if (len) {
                output[_out++] = from_source[from++];
                if (len > 1) {
                  output[_out++] = from_source[from++];
                }
              }
            }
            else {
              from = _out - dist;          /* copy direct from output */
              do {                        /* minimum length is three */
                output[_out++] = output[from++];
                output[_out++] = output[from++];
                output[_out++] = output[from++];
                len -= 3;
              } while (len > 2);
              if (len) {
                output[_out++] = output[from++];
                if (len > 1) {
                  output[_out++] = output[from++];
                }
              }
            }
          }
          else if ((op & 64) === 0) {          /* 2nd level distance code */
            here = dcode[(here & 0xffff)/*here.val*/ + (hold & ((1 << op) - 1))];
            continue dodist;
          }
          else {
            strm.msg = 'invalid distance code';
            state.mode = BAD;
            break top;
          }

          break; // need to emulate goto via "continue"
        }
      }
      else if ((op & 64) === 0) {              /* 2nd level length code */
        here = lcode[(here & 0xffff)/*here.val*/ + (hold & ((1 << op) - 1))];
        continue dolen;
      }
      else if (op & 32) {                     /* end-of-block */
        //Tracevv((stderr, "inflate:         end of block\n"));
        state.mode = TYPE;
        break top;
      }
      else {
        strm.msg = 'invalid literal/length code';
        state.mode = BAD;
        break top;
      }

      break; // need to emulate goto via "continue"
    }
  } while (_in < last && _out < end);

  /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
  len = bits >> 3;
  _in -= len;
  bits -= len << 3;
  hold &= (1 << bits) - 1;

  /* update state and return */
  strm.next_in = _in;
  strm.next_out = _out;
  strm.avail_in = (_in < last ? 5 + (last - _in) : 5 - (_in - last));
  strm.avail_out = (_out < end ? 257 + (end - _out) : 257 - (_out - end));
  state.hold = hold;
  state.bits = bits;
  return;
};