inffast.c revision 347244
1203134Sthompsa/* inffast.c -- fast decoding 2203134Sthompsa * Copyright (C) 1995-2017 Mark Adler 3203134Sthompsa * For conditions of distribution and use, see copyright notice in zlib.h 4203134Sthompsa */ 5203134Sthompsa 6203134Sthompsa#include "zutil.h" 7203134Sthompsa#include "inftrees.h" 8203134Sthompsa#include "inflate.h" 9203134Sthompsa#include "inffast.h" 10203134Sthompsa 11203134Sthompsa#ifdef ASMINF 12203134Sthompsa# pragma message("Assembler code may have bugs -- use at your own risk") 13203134Sthompsa#else 14203134Sthompsa 15203134Sthompsa/* 16203134Sthompsa Decode literal, length, and distance codes and write out the resulting 17203134Sthompsa literal and match bytes until either not enough input or output is 18203134Sthompsa available, an end-of-block is encountered, or a data error is encountered. 19203134Sthompsa When large enough input and output buffers are supplied to inflate(), for 20203134Sthompsa example, a 16K input buffer and a 64K output buffer, more than 95% of the 21203134Sthompsa inflate execution time is spent in this routine. 22203134Sthompsa 23203134Sthompsa Entry assumptions: 24203134Sthompsa 25259546Skevlo state->mode == LEN 26259546Skevlo strm->avail_in >= 6 27203134Sthompsa strm->avail_out >= 258 28259546Skevlo start >= strm->avail_out 29203134Sthompsa state->bits < 8 30203134Sthompsa 31259546Skevlo On return, state->mode is one of: 32259546Skevlo 33259546Skevlo LEN -- ran out of enough output space or enough available input 34259546Skevlo TYPE -- reached end of block code, inflate() to interpret next block 35259546Skevlo BAD -- error in block data 36259546Skevlo 37259546Skevlo Notes: 38259546Skevlo 39259546Skevlo - The maximum input bits used by a length/distance pair is 15 bits for the 40259546Skevlo length code, 5 bits for the length extra, 15 bits for the distance code, 41259546Skevlo and 13 bits for the distance extra. This totals 48 bits, or six bytes. 42259546Skevlo Therefore if strm->avail_in >= 6, then there is enough input to avoid 43259546Skevlo checking for available input while decoding. 44259546Skevlo 45259546Skevlo - The maximum bytes that a single length/distance pair can output is 258 46259546Skevlo bytes, which is the maximum length that can be coded. inflate_fast() 47259546Skevlo requires strm->avail_out >= 258 for each loop to avoid checking for 48259546Skevlo output space. 49259546Skevlo */ 50259546Skevlovoid ZLIB_INTERNAL inflate_fast(strm, start) 51259546Skevloz_streamp strm; 52259546Skevlounsigned start; /* inflate()'s starting value for strm->avail_out */ 53203134Sthompsa{ 54203134Sthompsa struct inflate_state FAR *state; 55259546Skevlo z_const unsigned char FAR *in; /* local strm->next_in */ 56259546Skevlo z_const unsigned char FAR *last; /* have enough input while in < last */ 57259546Skevlo unsigned char FAR *out; /* local strm->next_out */ 58259546Skevlo unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ 59259546Skevlo unsigned char FAR *end; /* while out < end, enough space available */ 60259546Skevlo#ifdef INFLATE_STRICT 61259546Skevlo unsigned dmax; /* maximum distance from zlib header */ 62259546Skevlo#endif 63259546Skevlo unsigned wsize; /* window size or zero if not using window */ 64259546Skevlo unsigned whave; /* valid bytes in the window */ 65259546Skevlo unsigned wnext; /* window write index */ 66259546Skevlo unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ 67259546Skevlo unsigned long hold; /* local strm->hold */ 68259546Skevlo unsigned bits; /* local strm->bits */ 69259546Skevlo code const FAR *lcode; /* local strm->lencode */ 70203134Sthompsa code const FAR *dcode; /* local strm->distcode */ 71203134Sthompsa unsigned lmask; /* mask for first level of length codes */ 72259546Skevlo unsigned dmask; /* mask for first level of distance codes */ 73259546Skevlo code here; /* retrieved table entry */ 74259546Skevlo unsigned op; /* code bits, operation, extra bits, or */ 75259546Skevlo /* window position, window bytes to copy */ 76259546Skevlo unsigned len; /* match length, unused bytes */ 77259546Skevlo unsigned dist; /* match distance */ 78259546Skevlo unsigned char FAR *from; /* where to copy match from */ 79259546Skevlo 80203134Sthompsa /* copy state to local variables */ 81259032Skevlo state = (struct inflate_state FAR *)strm->state; 82259546Skevlo in = strm->next_in; 83259032Skevlo last = in + (strm->avail_in - 5); 84203134Sthompsa out = strm->next_out; 85259546Skevlo beg = out - (start - strm->avail_out); 86259546Skevlo end = out + (strm->avail_out - 257); 87259546Skevlo#ifdef INFLATE_STRICT 88259546Skevlo dmax = state->dmax; 89259546Skevlo#endif 90259546Skevlo wsize = state->wsize; 91259546Skevlo whave = state->whave; 92259546Skevlo wnext = state->wnext; 93259546Skevlo window = state->window; 94259546Skevlo hold = state->hold; 95259546Skevlo bits = state->bits; 96259546Skevlo lcode = state->lencode; 97203134Sthompsa dcode = state->distcode; 98203134Sthompsa lmask = (1U << state->lenbits) - 1; 99259546Skevlo dmask = (1U << state->distbits) - 1; 100203134Sthompsa 101203134Sthompsa /* decode literals and length/distances until end-of-block or not enough 102259546Skevlo input data or output space */ 103259546Skevlo do { 104259546Skevlo if (bits < 15) { 105259546Skevlo hold += (unsigned long)(*in++) << bits; 106259546Skevlo bits += 8; 107259546Skevlo hold += (unsigned long)(*in++) << bits; 108259546Skevlo bits += 8; 109259546Skevlo } 110259546Skevlo here = lcode[hold & lmask]; 111259546Skevlo dolen: 112259546Skevlo op = (unsigned)(here.bits); 113259546Skevlo hold >>= op; 114259546Skevlo bits -= op; 115203134Sthompsa op = (unsigned)(here.op); 116203134Sthompsa if (op == 0) { /* literal */ 117259546Skevlo Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ? 118259546Skevlo "inflate: literal '%c'\n" : 119259546Skevlo "inflate: literal 0x%02x\n", here.val)); 120203134Sthompsa *out++ = (unsigned char)(here.val); 121203134Sthompsa } 122259546Skevlo else if (op & 16) { /* length base */ 123259546Skevlo len = (unsigned)(here.val); 124259546Skevlo op &= 15; /* number of extra bits */ 125259546Skevlo if (op) { 126259546Skevlo if (bits < op) { 127259546Skevlo hold += (unsigned long)(*in++) << bits; 128259546Skevlo bits += 8; 129259546Skevlo } 130259546Skevlo len += (unsigned)hold & ((1U << op) - 1); 131259546Skevlo hold >>= op; 132259546Skevlo bits -= op; 133259546Skevlo } 134259546Skevlo Tracevv((stderr, "inflate: length %u\n", len)); 135259546Skevlo if (bits < 15) { 136259546Skevlo hold += (unsigned long)(*in++) << bits; 137259546Skevlo bits += 8; 138259546Skevlo hold += (unsigned long)(*in++) << bits; 139259546Skevlo bits += 8; 140259546Skevlo } 141259546Skevlo here = dcode[hold & dmask]; 142259546Skevlo dodist: 143259546Skevlo op = (unsigned)(here.bits); 144259546Skevlo hold >>= op; 145259546Skevlo bits -= op; 146259546Skevlo op = (unsigned)(here.op); 147259546Skevlo if (op & 16) { /* distance base */ 148203134Sthompsa dist = (unsigned)(here.val); 149203134Sthompsa op &= 15; /* number of extra bits */ 150259546Skevlo if (bits < op) { 151259546Skevlo hold += (unsigned long)(*in++) << bits; 152259546Skevlo bits += 8; 153259546Skevlo if (bits < op) { 154259546Skevlo hold += (unsigned long)(*in++) << bits; 155259546Skevlo bits += 8; 156259546Skevlo } 157203134Sthompsa } 158203134Sthompsa dist += (unsigned)hold & ((1U << op) - 1); 159259546Skevlo#ifdef INFLATE_STRICT 160259546Skevlo if (dist > dmax) { 161259546Skevlo strm->msg = (char *)"invalid distance too far back"; 162203134Sthompsa state->mode = BAD; 163203134Sthompsa break; 164259546Skevlo } 165259546Skevlo#endif 166259546Skevlo hold >>= op; 167259546Skevlo bits -= op; 168259546Skevlo Tracevv((stderr, "inflate: distance %u\n", dist)); 169259546Skevlo op = (unsigned)(out - beg); /* max distance in output */ 170203134Sthompsa if (dist > op) { /* see if copy from window */ 171203134Sthompsa op = dist - op; /* distance back in window */ 172259546Skevlo if (op > whave) { 173259546Skevlo if (state->sane) { 174259546Skevlo strm->msg = 175259546Skevlo (char *)"invalid distance too far back"; 176259546Skevlo state->mode = BAD; 177259546Skevlo break; 178259546Skevlo } 179203134Sthompsa#ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR 180203134Sthompsa if (len <= op - whave) { 181259546Skevlo do { 182203134Sthompsa *out++ = 0; 183259546Skevlo } while (--len); 184259546Skevlo continue; 185203134Sthompsa } 186203134Sthompsa len -= op - whave; 187259546Skevlo do { 188203134Sthompsa *out++ = 0; 189203134Sthompsa } while (--op > whave); 190259546Skevlo if (op == 0) { 191203134Sthompsa from = out - dist; 192203134Sthompsa do { 193259546Skevlo *out++ = *from++; 194203134Sthompsa } while (--len); 195203134Sthompsa continue; 196259546Skevlo } 197203134Sthompsa#endif 198203134Sthompsa } 199259546Skevlo from = window; 200259546Skevlo if (wnext == 0) { /* very common case */ 201259546Skevlo from += wsize - op; 202259546Skevlo if (op < len) { /* some from window */ 203203134Sthompsa len -= op; 204203134Sthompsa do { 205259546Skevlo *out++ = *from++; 206259546Skevlo } while (--op); 207259546Skevlo from = out - dist; /* rest from output */ 208259546Skevlo } 209259546Skevlo } 210259546Skevlo else if (wnext < op) { /* wrap around window */ 211203134Sthompsa from += wsize + wnext - op; 212203134Sthompsa op -= wnext; 213203134Sthompsa if (op < len) { /* some from end of window */ 214259546Skevlo len -= op; 215259546Skevlo do { 216259546Skevlo *out++ = *from++; 217259546Skevlo } while (--op); 218259546Skevlo from = window; 219259546Skevlo if (wnext < len) { /* some from start of window */ 220203134Sthompsa op = wnext; 221203134Sthompsa len -= op; 222259546Skevlo do { 223259546Skevlo *out++ = *from++; 224259546Skevlo } while (--op); 225259546Skevlo from = out - dist; /* rest from output */ 226259546Skevlo } 227259546Skevlo } 228259546Skevlo } 229259546Skevlo else { /* contiguous in window */ 230259546Skevlo from += wnext - op; 231259546Skevlo if (op < len) { /* some from window */ 232259546Skevlo len -= op; 233259546Skevlo do { 234259546Skevlo *out++ = *from++; 235259546Skevlo } while (--op); 236259546Skevlo from = out - dist; /* rest from output */ 237259546Skevlo } 238259546Skevlo } 239259546Skevlo while (len > 2) { 240203134Sthompsa *out++ = *from++; 241203134Sthompsa *out++ = *from++; 242259546Skevlo *out++ = *from++; 243259546Skevlo len -= 3; 244259546Skevlo } 245259546Skevlo if (len) { 246259546Skevlo *out++ = *from++; 247259546Skevlo if (len > 1) 248259546Skevlo *out++ = *from++; 249259546Skevlo } 250259546Skevlo } 251259546Skevlo else { 252259546Skevlo from = out - dist; /* copy direct from output */ 253259546Skevlo do { /* minimum length is three */ 254203134Sthompsa *out++ = *from++; 255203134Sthompsa *out++ = *from++; 256259546Skevlo *out++ = *from++; 257259546Skevlo len -= 3; 258259546Skevlo } while (len > 2); 259259546Skevlo if (len) { 260259546Skevlo *out++ = *from++; 261259546Skevlo if (len > 1) 262203134Sthompsa *out++ = *from++; 263203134Sthompsa } 264259546Skevlo } 265259546Skevlo } 266203134Sthompsa else if ((op & 64) == 0) { /* 2nd level distance code */ 267203134Sthompsa here = dcode[here.val + (hold & ((1U << op) - 1))]; 268259546Skevlo goto dodist; 269259546Skevlo } 270259546Skevlo else { 271259546Skevlo strm->msg = (char *)"invalid distance code"; 272259546Skevlo state->mode = BAD; 273259546Skevlo break; 274259546Skevlo } 275259546Skevlo } 276259546Skevlo else if ((op & 64) == 0) { /* 2nd level length code */ 277259546Skevlo here = lcode[here.val + (hold & ((1U << op) - 1))]; 278259546Skevlo goto dolen; 279203134Sthompsa } 280203134Sthompsa else if (op & 32) { /* end-of-block */ 281259546Skevlo Tracevv((stderr, "inflate: end of block\n")); 282259546Skevlo state->mode = TYPE; 283259546Skevlo break; 284259546Skevlo } 285203134Sthompsa else { 286203134Sthompsa strm->msg = (char *)"invalid literal/length code"; 287259546Skevlo state->mode = BAD; 288259546Skevlo break; 289259546Skevlo } 290259546Skevlo } while (in < last && out < end); 291259546Skevlo 292259546Skevlo /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 293259546Skevlo len = bits >> 3; 294259546Skevlo in -= len; 295259546Skevlo bits -= len << 3; 296259546Skevlo hold &= (1U << bits) - 1; 297259546Skevlo 298259546Skevlo /* update state and return */ 299259546Skevlo strm->next_in = in; 300203134Sthompsa strm->next_out = out; 301203134Sthompsa strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 302259546Skevlo strm->avail_out = (unsigned)(out < end ? 303259546Skevlo 257 + (end - out) : 257 - (out - end)); 304259546Skevlo state->hold = hold; 305259546Skevlo state->bits = bits; 306259546Skevlo return; 307259546Skevlo} 308259546Skevlo 309259546Skevlo/* 310259546Skevlo inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 311259546Skevlo - Using bit fields for code structure 312259546Skevlo - Different op definition to avoid & for extra bits (do & for table bits) 313203134Sthompsa - Three separate decoding do-loops for direct, window, and wnext == 0 314203134Sthompsa - Special case for distance > 1 copies to do overlapped load and store copy 315259546Skevlo - Explicit branch predictions (based on measured branch probabilities) 316259546Skevlo - Deferring match copy and interspersed it with decoding subsequent codes 317259546Skevlo - Swapping literal/length else 318259546Skevlo - Swapping window/direct else 319259546Skevlo - Larger unrolled copy loops (three is about right) 320259546Skevlo - Moving len -= 3 statement into middle of loop 321259546Skevlo */ 322259546Skevlo 323259546Skevlo#endif /* !ASMINF */ 324259546Skevlo