chromium / chromium / src / e4d2c607d6450e220fa4ca2af00746632ecb5bf1 / . / third_party / zlib / inffast.c

/* 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 >= INFLATE_FAST_MIN_INPUT (6 bytes) | |

strm->avail_out >= INFLATE_FAST_MIN_OUTPUT (258 bytes) | |

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: | |

INFLATE_FAST_MIN_INPUT: 6 bytes | |

- 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. | |

INFLATE_FAST_MIN_OUTPUT: 258 bytes | |

- 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 | |

available output space while decoding. | |

*/ | |

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; | |

last = in + (strm->avail_in - (INFLATE_FAST_MIN_INPUT - 1)); | |

out = strm->next_out; | |

beg = out - (start - strm->avail_out); | |

end = out + (strm->avail_out - (INFLATE_FAST_MIN_OUTPUT - 1)); | |

#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 (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 { | |

*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; | |

} | |

#endif | |

} | |

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 ? | |

(INFLATE_FAST_MIN_INPUT - 1) + (last - in) : | |

(INFLATE_FAST_MIN_INPUT - 1) - (in - last)); | |

strm->avail_out = (unsigned)(out < end ? | |

(INFLATE_FAST_MIN_OUTPUT - 1) + (end - out) : | |

(INFLATE_FAST_MIN_OUTPUT - 1) - (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 */ |