0,0 → 1,340 |
/* inffast.c -- fast decoding |
* Copyright (C) 1995-2008, 2010, 2013 Mark Adler |
* For conditions of distribution and use, see copyright notice in zlib.h |
*/ |
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#include "zutil.h" |
#include "inftrees.h" |
#include "inflate.h" |
#include "inffast.h" |
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#ifndef ASMINF |
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/* Allow machine dependent optimization for post-increment or pre-increment. |
Based on testing to date, |
Pre-increment preferred for: |
- PowerPC G3 (Adler) |
- MIPS R5000 (Randers-Pehrson) |
Post-increment preferred for: |
- none |
No measurable difference: |
- Pentium III (Anderson) |
- M68060 (Nikl) |
*/ |
#ifdef POSTINC |
# define OFF 0 |
# define PUP(a) *(a)++ |
#else |
# define OFF 1 |
# define PUP(a) *++(a) |
#endif |
|
/* |
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. |
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Entry assumptions: |
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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: |
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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: |
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- 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(strm, start) |
z_streamp strm; |
unsigned start; /* inflate()'s starting value for strm->avail_out */ |
{ |
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 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 - OFF; |
last = in + (strm->avail_in - 5); |
out = strm->next_out - OFF; |
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)(PUP(in)) << bits; |
bits += 8; |
hold += (unsigned long)(PUP(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)); |
PUP(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)(PUP(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)(PUP(in)) << bits; |
bits += 8; |
hold += (unsigned long)(PUP(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)(PUP(in)) << bits; |
bits += 8; |
if (bits < op) { |
hold += (unsigned long)(PUP(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 (state->sane) { |
strm->msg = |
(char *)"invalid distance too far back"; |
state->mode = BAD; |
break; |
} |
#ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR |
if (len <= op - whave) { |
do { |
PUP(out) = 0; |
} while (--len); |
continue; |
} |
len -= op - whave; |
do { |
PUP(out) = 0; |
} while (--op > whave); |
if (op == 0) { |
from = out - dist; |
do { |
PUP(out) = PUP(from); |
} while (--len); |
continue; |
} |
#endif |
} |
from = window - OFF; |
if (wnext == 0) { /* very common case */ |
from += wsize - op; |
if (op < len) { /* some from window */ |
len -= op; |
do { |
PUP(out) = PUP(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 { |
PUP(out) = PUP(from); |
} while (--op); |
from = window - OFF; |
if (wnext < len) { /* some from start of window */ |
op = wnext; |
len -= op; |
do { |
PUP(out) = PUP(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 { |
PUP(out) = PUP(from); |
} while (--op); |
from = out - dist; /* rest from output */ |
} |
} |
while (len > 2) { |
PUP(out) = PUP(from); |
PUP(out) = PUP(from); |
PUP(out) = PUP(from); |
len -= 3; |
} |
if (len) { |
PUP(out) = PUP(from); |
if (len > 1) |
PUP(out) = PUP(from); |
} |
} |
else { |
from = out - dist; /* copy direct from output */ |
do { /* minimum length is three */ |
PUP(out) = PUP(from); |
PUP(out) = PUP(from); |
PUP(out) = PUP(from); |
len -= 3; |
} while (len > 2); |
if (len) { |
PUP(out) = PUP(from); |
if (len > 1) |
PUP(out) = PUP(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 + OFF; |
strm->next_out = out + OFF; |
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; |
} |
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/* |
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 |
*/ |
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#endif /* !ASMINF */ |