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cycrow |
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/* inffast.c -- fast decoding
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* Copyright (C) 1995-2008, 2010 Mark Adler
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* For conditions of distribution and use, see copyright notice in zlib.h
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*/
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#include "zutil.h"
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#include "inftrees.h"
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#include "inflate.h"
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#include "inffast.h"
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#ifndef ASMINF
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/* Allow machine dependent optimization for post-increment or pre-increment.
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Based on testing to date,
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Pre-increment preferred for:
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- PowerPC G3 (Adler)
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- MIPS R5000 (Randers-Pehrson)
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Post-increment preferred for:
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- none
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No measurable difference:
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- Pentium III (Anderson)
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- M68060 (Nikl)
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*/
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#ifdef POSTINC
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# define OFF 0
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# define PUP(a) *(a)++
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#else
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# define OFF 1
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# define PUP(a) *++(a)
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#endif
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/*
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Decode literal, length, and distance codes and write out the resulting
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literal and match bytes until either not enough input or output is
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available, an end-of-block is encountered, or a data error is encountered.
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When large enough input and output buffers are supplied to inflate(), for
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example, a 16K input buffer and a 64K output buffer, more than 95% of the
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inflate execution time is spent in this routine.
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Entry assumptions:
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state->mode == LEN
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strm->avail_in >= 6
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strm->avail_out >= 258
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start >= strm->avail_out
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state->bits < 8
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On return, state->mode is one of:
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LEN -- ran out of enough output space or enough available input
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TYPE -- reached end of block code, inflate() to interpret next block
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BAD -- error in block data
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Notes:
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- The maximum input bits used by a length/distance pair is 15 bits for the
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length code, 5 bits for the length extra, 15 bits for the distance code,
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and 13 bits for the distance extra. This totals 48 bits, or six bytes.
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Therefore if strm->avail_in >= 6, then there is enough input to avoid
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checking for available input while decoding.
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- The maximum bytes that a single length/distance pair can output is 258
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bytes, which is the maximum length that can be coded. inflate_fast()
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requires strm->avail_out >= 258 for each loop to avoid checking for
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output space.
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*/
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void ZLIB_INTERNAL inflate_fast(strm, start)
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z_streamp strm;
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unsigned start; /* inflate()'s starting value for strm->avail_out */
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{
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struct inflate_state FAR *state;
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unsigned char FAR *in; /* local strm->next_in */
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unsigned char FAR *last; /* while in < last, enough input available */
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unsigned char FAR *out; /* local strm->next_out */
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unsigned char FAR *beg; /* inflate()'s initial strm->next_out */
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unsigned char FAR *end; /* while out < end, enough space available */
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#ifdef INFLATE_STRICT
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unsigned dmax; /* maximum distance from zlib header */
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#endif
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unsigned wsize; /* window size or zero if not using window */
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unsigned whave; /* valid bytes in the window */
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unsigned wnext; /* window write index */
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unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */
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unsigned long hold; /* local strm->hold */
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unsigned bits; /* local strm->bits */
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code const FAR *lcode; /* local strm->lencode */
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code const FAR *dcode; /* local strm->distcode */
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unsigned lmask; /* mask for first level of length codes */
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unsigned dmask; /* mask for first level of distance codes */
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code here; /* retrieved table entry */
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unsigned op; /* code bits, operation, extra bits, or */
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/* window position, window bytes to copy */
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unsigned len; /* match length, unused bytes */
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unsigned dist; /* match distance */
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unsigned char FAR *from; /* where to copy match from */
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/* copy state to local variables */
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state = (struct inflate_state FAR *)strm->state;
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in = strm->next_in - OFF;
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last = in + (strm->avail_in - 5);
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out = strm->next_out - OFF;
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beg = out - (start - strm->avail_out);
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end = out + (strm->avail_out - 257);
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#ifdef INFLATE_STRICT
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dmax = state->dmax;
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#endif
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wsize = state->wsize;
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whave = state->whave;
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wnext = state->wnext;
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window = state->window;
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hold = state->hold;
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bits = state->bits;
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lcode = state->lencode;
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dcode = state->distcode;
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lmask = (1U << state->lenbits) - 1;
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dmask = (1U << state->distbits) - 1;
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/* decode literals and length/distances until end-of-block or not enough
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input data or output space */
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do {
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if (bits < 15) {
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hold += (unsigned long)(PUP(in)) << bits;
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bits += 8;
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hold += (unsigned long)(PUP(in)) << bits;
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bits += 8;
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}
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here = lcode[hold & lmask];
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dolen:
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op = (unsigned)(here.bits);
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hold >>= op;
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bits -= op;
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op = (unsigned)(here.op);
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if (op == 0) { /* literal */
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Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ?
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"inflate: literal '%c'\n" :
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"inflate: literal 0x%02x\n", here.val));
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PUP(out) = (unsigned char)(here.val);
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}
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else if (op & 16) { /* length base */
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len = (unsigned)(here.val);
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op &= 15; /* number of extra bits */
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if (op) {
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if (bits < op) {
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hold += (unsigned long)(PUP(in)) << bits;
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bits += 8;
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}
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len += (unsigned)hold & ((1U << op) - 1);
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hold >>= op;
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bits -= op;
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}
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Tracevv((stderr, "inflate: length %u\n", len));
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if (bits < 15) {
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hold += (unsigned long)(PUP(in)) << bits;
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bits += 8;
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hold += (unsigned long)(PUP(in)) << bits;
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bits += 8;
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}
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here = dcode[hold & dmask];
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dodist:
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op = (unsigned)(here.bits);
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hold >>= op;
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bits -= op;
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op = (unsigned)(here.op);
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if (op & 16) { /* distance base */
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dist = (unsigned)(here.val);
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op &= 15; /* number of extra bits */
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if (bits < op) {
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hold += (unsigned long)(PUP(in)) << bits;
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bits += 8;
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if (bits < op) {
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hold += (unsigned long)(PUP(in)) << bits;
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bits += 8;
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}
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}
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dist += (unsigned)hold & ((1U << op) - 1);
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#ifdef INFLATE_STRICT
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if (dist > dmax) {
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strm->msg = (char *)"invalid distance too far back";
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state->mode = BAD;
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break;
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}
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#endif
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hold >>= op;
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bits -= op;
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Tracevv((stderr, "inflate: distance %u\n", dist));
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op = (unsigned)(out - beg); /* max distance in output */
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if (dist > op) { /* see if copy from window */
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op = dist - op; /* distance back in window */
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if (op > whave) {
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if (state->sane) {
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strm->msg =
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(char *)"invalid distance too far back";
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state->mode = BAD;
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break;
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}
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#ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
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if (len <= op - whave) {
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do {
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PUP(out) = 0;
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} while (--len);
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continue;
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}
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len -= op - whave;
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do {
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PUP(out) = 0;
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} while (--op > whave);
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if (op == 0) {
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from = out - dist;
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do {
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PUP(out) = PUP(from);
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} while (--len);
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continue;
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}
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#endif
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}
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from = window - OFF;
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if (wnext == 0) { /* very common case */
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from += wsize - op;
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if (op < len) { /* some from window */
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len -= op;
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do {
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PUP(out) = PUP(from);
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} while (--op);
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from = out - dist; /* rest from output */
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}
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}
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else if (wnext < op) { /* wrap around window */
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from += wsize + wnext - op;
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op -= wnext;
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if (op < len) { /* some from end of window */
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len -= op;
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do {
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PUP(out) = PUP(from);
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} while (--op);
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from = window - OFF;
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if (wnext < len) { /* some from start of window */
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op = wnext;
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len -= op;
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do {
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PUP(out) = PUP(from);
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} while (--op);
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from = out - dist; /* rest from output */
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}
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}
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}
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else { /* contiguous in window */
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from += wnext - op;
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if (op < len) { /* some from window */
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len -= op;
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do {
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PUP(out) = PUP(from);
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} while (--op);
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from = out - dist; /* rest from output */
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}
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}
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while (len > 2) {
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PUP(out) = PUP(from);
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PUP(out) = PUP(from);
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PUP(out) = PUP(from);
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len -= 3;
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}
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if (len) {
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PUP(out) = PUP(from);
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if (len > 1)
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PUP(out) = PUP(from);
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}
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}
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else {
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from = out - dist; /* copy direct from output */
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do { /* minimum length is three */
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PUP(out) = PUP(from);
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PUP(out) = PUP(from);
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PUP(out) = PUP(from);
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len -= 3;
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} while (len > 2);
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if (len) {
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PUP(out) = PUP(from);
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if (len > 1)
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PUP(out) = PUP(from);
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}
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}
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}
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else if ((op & 64) == 0) { /* 2nd level distance code */
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here = dcode[here.val + (hold & ((1U << op) - 1))];
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goto dodist;
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}
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else {
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strm->msg = (char *)"invalid distance code";
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state->mode = BAD;
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break;
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}
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}
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else if ((op & 64) == 0) { /* 2nd level length code */
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here = lcode[here.val + (hold & ((1U << op) - 1))];
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goto dolen;
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}
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else if (op & 32) { /* end-of-block */
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Tracevv((stderr, "inflate: end of block\n"));
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state->mode = TYPE;
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break;
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}
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else {
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strm->msg = (char *)"invalid literal/length code";
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state->mode = BAD;
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break;
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}
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} while (in < last && out < end);
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/* return unused bytes (on entry, bits < 8, so in won't go too far back) */
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len = bits >> 3;
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in -= len;
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bits -= len << 3;
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hold &= (1U << bits) - 1;
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/* update state and return */
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strm->next_in = in + OFF;
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strm->next_out = out + OFF;
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318 |
strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
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319 |
strm->avail_out = (unsigned)(out < end ?
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320 |
257 + (end - out) : 257 - (out - end));
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321 |
state->hold = hold;
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322 |
state->bits = bits;
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323 |
return;
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324 |
}
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325 |
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326 |
/*
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327 |
inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
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328 |
- Using bit fields for code structure
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329 |
- Different op definition to avoid & for extra bits (do & for table bits)
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330 |
- Three separate decoding do-loops for direct, window, and wnext == 0
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331 |
- Special case for distance > 1 copies to do overlapped load and store copy
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332 |
- Explicit branch predictions (based on measured branch probabilities)
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- Deferring match copy and interspersed it with decoding subsequent codes
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- Swapping literal/length else
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- Swapping window/direct else
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- Larger unrolled copy loops (three is about right)
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- Moving len -= 3 statement into middle of loop
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338 |
*/
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339 |
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340 |
#endif /* !ASMINF */
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