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0de26fd78e
Zlib-ng is zlib replacement with optimizations for "next generation" systems. Its optimization may benifits image library decode and encode speed such as libpng. In our tests, if using zlib-ng and libpng combination on a x86_64 machine with AVX2, the time of `imdecode` amd `imencode` will drop 20% approximately. This patch enables zlib-ng's optimization if `CV_DISABLE_OPTIMIZATION` is OFF. Since Zlib-ng can dispatch intrinsics on the fly, port work is much easier. Related discussion: https://github.com/opencv/opencv/issues/22573
327 lines
14 KiB
C
327 lines
14 KiB
C
/* inffast.c -- fast decoding
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* Copyright (C) 1995-2017 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 "zbuild.h"
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#include "zendian.h"
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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 "inflate_p.h"
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#include "functable.h"
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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 >= INFLATE_FAST_MIN_HAVE
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strm->avail_out >= INFLATE_FAST_MIN_LEFT
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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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- On some architectures, it can be significantly faster (e.g. up to 1.2x
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faster on x86_64) to load from strm->next_in 64 bits, or 8 bytes, at a
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time, so INFLATE_FAST_MIN_HAVE == 8.
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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 Z_INTERNAL INFLATE_FAST(PREFIX3(stream) *strm, uint32_t start) {
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/* start: inflate()'s starting value for strm->avail_out */
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struct inflate_state *state;
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z_const unsigned char *in; /* local strm->next_in */
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const unsigned char *last; /* have enough input while in < last */
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unsigned char *out; /* local strm->next_out */
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unsigned char *beg; /* inflate()'s initial strm->next_out */
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unsigned char *end; /* while out < end, enough space available */
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unsigned char *safe; /* can use chunkcopy provided out < safe */
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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 *window; /* allocated sliding window, if wsize != 0 */
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/* hold is a local copy of strm->hold. By default, hold satisfies the same
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invariants that strm->hold does, namely that (hold >> bits) == 0. This
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invariant is kept by loading bits into hold one byte at a time, like:
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hold |= next_byte_of_input << bits; in++; bits += 8;
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If we need to ensure that bits >= 15 then this code snippet is simply
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repeated. Over one iteration of the outermost do/while loop, this
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happens up to six times (48 bits of input), as described in the NOTES
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above.
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However, on some little endian architectures, it can be significantly
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faster to load 64 bits once instead of 8 bits six times:
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if (bits <= 16) {
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hold |= next_8_bytes_of_input << bits; in += 6; bits += 48;
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}
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Unlike the simpler one byte load, shifting the next_8_bytes_of_input
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by bits will overflow and lose those high bits, up to 2 bytes' worth.
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The conservative estimate is therefore that we have read only 6 bytes
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(48 bits). Again, as per the NOTES above, 48 bits is sufficient for the
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rest of the iteration, and we will not need to load another 8 bytes.
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Inside this function, we no longer satisfy (hold >> bits) == 0, but
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this is not problematic, even if that overflow does not land on an 8 bit
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byte boundary. Those excess bits will eventually shift down lower as the
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Huffman decoder consumes input, and when new input bits need to be loaded
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into the bits variable, the same input bits will be or'ed over those
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existing bits. A bitwise or is idempotent: (a | b | b) equals (a | b).
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Note that we therefore write that load operation as "hold |= etc" and not
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"hold += etc".
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Outside that loop, at the end of the function, hold is bitwise and'ed
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with (1<<bits)-1 to drop those excess bits so that, on function exit, we
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keep the invariant that (state->hold >> state->bits) == 0.
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*/
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uint64_t hold; /* local strm->hold */
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unsigned bits; /* local strm->bits */
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code const *lcode; /* local strm->lencode */
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code const *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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const 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 *from; /* where to copy match from */
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unsigned extra_safe; /* copy chunks safely in all cases */
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/* copy state to local variables */
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state = (struct inflate_state *)strm->state;
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in = strm->next_in;
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last = in + (strm->avail_in - (INFLATE_FAST_MIN_HAVE - 1));
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out = strm->next_out;
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beg = out - (start - strm->avail_out);
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end = out + (strm->avail_out - (INFLATE_FAST_MIN_LEFT - 1));
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safe = out + strm->avail_out;
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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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/* Detect if out and window point to the same memory allocation. In this instance it is
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necessary to use safe chunk copy functions to prevent overwriting the window. If the
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window is overwritten then future matches with far distances will fail to copy correctly. */
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extra_safe = (wsize != 0 && out >= window && out + INFLATE_FAST_MIN_LEFT <= window + wsize);
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#define REFILL() do { \
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hold |= load_64_bits(in, bits); \
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in += 7; \
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in -= ((bits >> 3) & 7); \
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bits |= 56; \
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} while (0)
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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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REFILL();
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here = lcode + (hold & lmask);
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if (here->op == 0) {
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*out++ = (unsigned char)(here->val);
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DROPBITS(here->bits);
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here = lcode + (hold & lmask);
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if (here->op == 0) {
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*out++ = (unsigned char)(here->val);
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DROPBITS(here->bits);
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here = lcode + (hold & lmask);
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}
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}
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dolen:
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DROPBITS(here->bits);
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op = 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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*out++ = (unsigned char)(here->val);
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} else if (op & 16) { /* length base */
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len = here->val;
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op &= MAX_BITS; /* number of extra bits */
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len += BITS(op);
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DROPBITS(op);
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Tracevv((stderr, "inflate: length %u\n", len));
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here = dcode + (hold & dmask);
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if (bits < MAX_BITS + MAX_DIST_EXTRA_BITS) {
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REFILL();
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}
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dodist:
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DROPBITS(here->bits);
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op = here->op;
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if (op & 16) { /* distance base */
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dist = here->val;
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op &= MAX_BITS; /* number of extra bits */
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dist += BITS(op);
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#ifdef INFLATE_STRICT
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if (dist > dmax) {
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SET_BAD("invalid distance too far back");
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break;
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}
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#endif
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DROPBITS(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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SET_BAD("invalid distance too far back");
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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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*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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*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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*out++ = *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;
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if (wnext == 0) { /* very common case */
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from += wsize - op;
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} else if (wnext >= op) { /* contiguous in window */
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from += wnext - op;
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} else { /* wrap around window */
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op -= wnext;
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from += wsize - op;
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if (op < len) { /* some from end of window */
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len -= op;
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out = chunkcopy_safe(out, from, op, safe);
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from = window; /* more from start of window */
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op = wnext;
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/* This (rare) case can create a situation where
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the first chunkcopy below must be checked.
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*/
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}
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}
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if (op < len) { /* still need some from output */
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len -= op;
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out = chunkcopy_safe(out, from, op, safe);
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out = CHUNKUNROLL(out, &dist, &len);
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out = chunkcopy_safe(out, out - dist, len, safe);
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} else {
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out = chunkcopy_safe(out, from, len, safe);
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}
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} else if (extra_safe) {
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/* Whole reference is in range of current output. */
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if (dist >= len || dist >= state->chunksize)
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out = chunkcopy_safe(out, out - dist, len, safe);
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else
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out = CHUNKMEMSET_SAFE(out, dist, len, (unsigned)((safe - out) + 1));
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} else {
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/* Whole reference is in range of current output. No range checks are
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necessary because we start with room for at least 258 bytes of output,
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so unroll and roundoff operations can write beyond `out+len` so long
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as they stay within 258 bytes of `out`.
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*/
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if (dist >= len || dist >= state->chunksize)
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out = CHUNKCOPY(out, out - dist, len);
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else
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out = CHUNKMEMSET(out, dist, len);
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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 + BITS(op);
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goto dodist;
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} else {
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SET_BAD("invalid distance code");
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break;
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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 + BITS(op);
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goto dolen;
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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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} else {
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SET_BAD("invalid literal/length code");
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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 &= (UINT64_C(1) << bits) - 1;
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/* update state and return */
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strm->next_in = in;
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strm->next_out = out;
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strm->avail_in = (unsigned)(in < last ? (INFLATE_FAST_MIN_HAVE - 1) + (last - in)
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: (INFLATE_FAST_MIN_HAVE - 1) - (in - last));
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strm->avail_out = (unsigned)(out < end ? (INFLATE_FAST_MIN_LEFT - 1) + (end - out)
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: (INFLATE_FAST_MIN_LEFT - 1) - (out - end));
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Assert(bits <= 32, "Remaining bits greater than 32");
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state->hold = (uint32_t)hold;
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state->bits = bits;
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return;
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}
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/*
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inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
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- Using bit fields for code structure
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- Different op definition to avoid & for extra bits (do & for table bits)
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- Three separate decoding do-loops for direct, window, and wnext == 0
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- Special case for distance > 1 copies to do overlapped load and store copy
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- 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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*/
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