/* 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(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 - (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 */