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inffast.c
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inffast.c
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/* inffast.c -- fast decoding
* Copyright (C) 1995-2017 Mark Adler
* For conditions of distribution and use, see copyright notice in zlib.h
*/
#include "zutil.h"
#include "inftrees.h"
#include "inflate.h"
#include "inffast.h"
#ifdef ASMINF
# pragma message("Assembler code may have bugs -- use at your own risk")
#else
/*
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.
*/
void ZLIB_INTERNAL inflate_fast(z_streamp strm, unsigned start) {
struct inflate_state FAR *state;
z_const unsigned char FAR *in; /* local strm->next_in */
z_const unsigned char FAR *last; /* have enough input while in < last */
unsigned char FAR *out; /* local strm->next_out */
unsigned char FAR *beg; /* inflate()'s initial strm->next_out */
unsigned char FAR *end; /* while out < end, enough space available */
#ifdef INFLATE_STRICT
unsigned dmax; /* maximum distance from zlib header */
#endif
unsigned wsize; /* window size or zero if not using window */
unsigned whave; /* valid bytes in the window */
unsigned wnext; /* window write index */
unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */
unsigned long hold; /* local strm->hold */
unsigned bits; /* local strm->bits */
code const FAR *lcode; /* local strm->lencode */
code const FAR *dcode; /* local strm->distcode */
unsigned lmask; /* mask for first level of length codes */
unsigned dmask; /* mask for first level of distance codes */
code const *here; /* retrieved table entry */
unsigned op; /* code bits, operation, extra bits, or */
/* window position, window bytes to copy */
unsigned len; /* match length, unused bytes */
unsigned dist; /* match distance */
unsigned char FAR *from; /* where to copy match from */
/* copy state to local variables */
state = (struct inflate_state FAR *)strm->state;
in = strm->next_in;
last = in + (strm->avail_in - 5);
out = strm->next_out;
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 = (1U << state->lenbits) - 1;
dmask = (1U << state->distbits) - 1;
/* decode literals and length/distances until end-of-block or not enough
input data or output space */
do {
if (bits < 15) {
hold += (unsigned long)(*in++) << bits;
bits += 8;
hold += (unsigned long)(*in++) << bits;
bits += 8;
}
here = lcode + (hold & lmask);
dolen:
op = (unsigned)(here->bits);
hold >>= op;
bits -= op;
op = (unsigned)(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));
*out++ = (unsigned char)(here->val);
}
else if (op & 16) { /* length base */
len = (unsigned)(here->val);
op &= 15; /* number of extra bits */
if (op) {
if (bits < op) {
hold += (unsigned long)(*in++) << bits;
bits += 8;
}
len += (unsigned)hold & ((1U << op) - 1);
hold >>= op;
bits -= op;
}
Tracevv((stderr, "inflate: length %u\n", len));
if (bits < 15) {
hold += (unsigned long)(*in++) << bits;
bits += 8;
hold += (unsigned long)(*in++) << bits;
bits += 8;
}
here = dcode + (hold & dmask);
dodist:
op = (unsigned)(here->bits);
hold >>= op;
bits -= op;
op = (unsigned)(here->op);
if (op & 16) { /* distance base */
dist = (unsigned)(here->val);
op &= 15; /* number of extra bits */
if (bits < op) {
hold += (unsigned long)(*in++) << bits;
bits += 8;
if (bits < op) {
hold += (unsigned long)(*in++) << bits;
bits += 8;
}
}
dist += (unsigned)hold & ((1U << op) - 1);
#ifdef INFLATE_STRICT
if (dist > dmax) {
strm->msg = (char *)"invalid distance too far back";
state->mode = BAD;
break;
}
#endif
hold >>= op;
bits -= op;
Tracevv((stderr, "inflate: distance %u\n", dist));
op = (unsigned)(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 ( ! inflate_allow_distance_too_far_back ) {
if (state->sane) {
strm->msg =
(char *)"invalid distance too far back";
state->mode = BAD;
break;
}
}
else {
if (len <= op - whave) {
do {
*out++ = 0;
} while (--len);
continue;
}
len -= op - whave;
do {
*out++ = 0;
} while (--op > whave);
if (op == 0) {
from = out - dist;
do {
*out++ = *from++;
} while (--len);
continue;
}
}
}
from = window;
if (wnext == 0) { /* very common case */
from += wsize - op;
if (op < len) { /* some from window */
len -= op;
do {
*out++ = *from++;
} while (--op);
from = out - dist; /* rest from 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 {
*out++ = *from++;
} while (--op);
from = window;
if (wnext < len) { /* some from start of window */
op = wnext;
len -= op;
do {
*out++ = *from++;
} while (--op);
from = out - dist; /* rest from output */
}
}
}
else { /* contiguous in window */
from += wnext - op;
if (op < len) { /* some from window */
len -= op;
do {
*out++ = *from++;
} while (--op);
from = out - dist; /* rest from output */
}
}
while (len > 2) {
*out++ = *from++;
*out++ = *from++;
*out++ = *from++;
len -= 3;
}
if (len) {
*out++ = *from++;
if (len > 1)
*out++ = *from++;
}
}
else {
from = out - dist; /* copy direct from output */
do { /* minimum length is three */
*out++ = *from++;
*out++ = *from++;
*out++ = *from++;
len -= 3;
} while (len > 2);
if (len) {
*out++ = *from++;
if (len > 1)
*out++ = *from++;
}
}
}
else if ((op & 64) == 0) { /* 2nd level distance code */
here = dcode + here->val + (hold & ((1U << op) - 1));
goto dodist;
}
else {
strm->msg = (char *)"invalid distance code";
state->mode = BAD;
break;
}
}
else if ((op & 64) == 0) { /* 2nd level length code */
here = lcode + here->val + (hold & ((1U << op) - 1));
goto dolen;
}
else if (op & 32) { /* end-of-block */
Tracevv((stderr, "inflate: end of block\n"));
state->mode = TYPE;
break;
}
else {
strm->msg = (char *)"invalid literal/length code";
state->mode = BAD;
break;
}
} 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 &= (1U << bits) - 1;
/* update state and return */
strm->next_in = in;
strm->next_out = out;
strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
strm->avail_out = (unsigned)(out < end ?
257 + (end - out) : 257 - (out - end));
state->hold = hold;
state->bits = bits;
return;
}
/*
inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
- Using bit fields for code structure
- Different op definition to avoid & for extra bits (do & for table bits)
- Three separate decoding do-loops for direct, window, and wnext == 0
- Special case for distance > 1 copies to do overlapped load and store copy
- Explicit branch predictions (based on measured branch probabilities)
- Deferring match copy and interspersed it with decoding subsequent codes
- Swapping literal/length else
- Swapping window/direct else
- Larger unrolled copy loops (three is about right)
- Moving len -= 3 statement into middle of loop
*/
#endif /* !ASMINF */