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/* inffast.c -- fast decoding* Copyright (C) 1995-2008, 2010 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"#ifndef ASMINF/* 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:- noneNo 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 resultingliteral and match bytes until either not enough input or output isavailable, an end-of-block is encountered, or a data error is encountered.When large enough input and output buffers are supplied to inflate(), forexample, a 16K input buffer and a 64K output buffer, more than 95% of theinflate execution time is spent in this routine.Entry assumptions:state->mode == LENstrm->avail_in >= 6strm->avail_out >= 258start >= strm->avail_outstate->bits < 8On return, state->mode is one of:LEN -- ran out of enough output space or enough available inputTYPE -- reached end of block code, inflate() to interpret next blockBAD -- error in block dataNotes:- The maximum input bits used by a length/distance pair is 15 bits for thelength 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 avoidchecking for available input while decoding.- The maximum bytes that a single length/distance pair can output is 258bytes, which is the maximum length that can be coded. inflate_fast()requires strm->avail_out >= 258 for each loop to avoid checking foroutput 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;unsigned char FAR *in; /* local strm->next_in */unsigned char FAR *last; /* while in < last, enough input available */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_STRICTunsigned dmax; /* maximum distance from zlib header */#endifunsigned 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_STRICTdmax = state->dmax;#endifwsize = 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 enoughinput 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_STRICTif (dist > dmax) {strm->msg = (char *)"invalid distance too far back";state->mode = BAD;break;}#endifhold >>= 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_ARRRif (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;}/*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 */