inffast.c revision 146081
1193323Sed/* inffast.c -- fast decoding 2193323Sed * Copyright (C) 1995-2004 Mark Adler 3193323Sed * For conditions of distribution and use, see copyright notice in zlib.h 4193323Sed */ 5193323Sed 6193323Sed#include "zutil.h" 7193323Sed#include "inftrees.h" 8193323Sed#include "inflate.h" 9193323Sed#include "inffast.h" 10193323Sed 11193323Sed#ifndef ASMINF 12193323Sed 13193323Sed/* Allow machine dependent optimization for post-increment or pre-increment. 14193323Sed Based on testing to date, 15193323Sed Pre-increment preferred for: 16193323Sed - PowerPC G3 (Adler) 17193323Sed - MIPS R5000 (Randers-Pehrson) 18193323Sed Post-increment preferred for: 19193323Sed - none 20193323Sed No measurable difference: 21193323Sed - Pentium III (Anderson) 22193323Sed - M68060 (Nikl) 23193323Sed */ 24198090Srdivacky#ifdef POSTINC 25251662Sdim# define OFF 0 26249423Sdim# define PUP(a) *(a)++ 27249423Sdim#else 28193323Sed# define OFF 1 29193323Sed# define PUP(a) *++(a) 30193323Sed#endif 31193323Sed 32193323Sed/* 33193323Sed Decode literal, length, and distance codes and write out the resulting 34193323Sed literal and match bytes until either not enough input or output is 35212904Sdim available, an end-of-block is encountered, or a data error is encountered. 36193323Sed When large enough input and output buffers are supplied to inflate(), for 37193323Sed example, a 16K input buffer and a 64K output buffer, more than 95% of the 38193323Sed inflate execution time is spent in this routine. 39193323Sed 40193323Sed Entry assumptions: 41193323Sed 42193323Sed state->mode == LEN 43193323Sed strm->avail_in >= 6 44234353Sdim strm->avail_out >= 258 45243830Sdim start >= strm->avail_out 46193323Sed state->bits < 8 47193323Sed 48193323Sed On return, state->mode is one of: 49193323Sed 50193323Sed LEN -- ran out of enough output space or enough available input 51193323Sed TYPE -- reached end of block code, inflate() to interpret next block 52243830Sdim BAD -- error in block data 53193323Sed 54193323Sed Notes: 55193323Sed 56193323Sed - The maximum input bits used by a length/distance pair is 15 bits for the 57193323Sed length code, 5 bits for the length extra, 15 bits for the distance code, 58193323Sed and 13 bits for the distance extra. This totals 48 bits, or six bytes. 59193323Sed Therefore if strm->avail_in >= 6, then there is enough input to avoid 60193323Sed checking for available input while decoding. 61226633Sdim 62226633Sdim - The maximum bytes that a single length/distance pair can output is 258 63226633Sdim bytes, which is the maximum length that can be coded. inflate_fast() 64226633Sdim requires strm->avail_out >= 258 for each loop to avoid checking for 65226633Sdim output space. 66226633Sdim */ 67226633Sdimvoid inflate_fast(strm, start) 68226633Sdimz_streamp strm; 69193323Sedunsigned start; /* inflate()'s starting value for strm->avail_out */ 70226633Sdim{ 71221345Sdim struct inflate_state FAR *state; 72221345Sdim unsigned char FAR *in; /* local strm->next_in */ 73221345Sdim unsigned char FAR *last; /* while in < last, enough input available */ 74221345Sdim unsigned char FAR *out; /* local strm->next_out */ 75221345Sdim unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ 76221345Sdim unsigned char FAR *end; /* while out < end, enough space available */ 77193323Sed unsigned wsize; /* window size or zero if not using window */ 78193323Sed unsigned whave; /* valid bytes in the window */ 79193323Sed unsigned write; /* window write index */ 80193323Sed unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ 81193323Sed unsigned long hold; /* local strm->hold */ 82193323Sed unsigned bits; /* local strm->bits */ 83193323Sed code const FAR *lcode; /* local strm->lencode */ 84198090Srdivacky code const FAR *dcode; /* local strm->distcode */ 85234353Sdim unsigned lmask; /* mask for first level of length codes */ 86234353Sdim unsigned dmask; /* mask for first level of distance codes */ 87234353Sdim code this; /* retrieved table entry */ 88234353Sdim unsigned op; /* code bits, operation, extra bits, or */ 89193323Sed /* window position, window bytes to copy */ 90193323Sed unsigned len; /* match length, unused bytes */ 91193323Sed unsigned dist; /* match distance */ 92193323Sed unsigned char FAR *from; /* where to copy match from */ 93193323Sed 94193323Sed /* copy state to local variables */ 95193323Sed state = (struct inflate_state FAR *)strm->state; 96193323Sed in = strm->next_in - OFF; 97234353Sdim last = in + (strm->avail_in - 5); 98193323Sed out = strm->next_out - OFF; 99193323Sed beg = out - (start - strm->avail_out); 100193323Sed end = out + (strm->avail_out - 257); 101234353Sdim wsize = state->wsize; 102234353Sdim whave = state->whave; 103234353Sdim write = state->write; 104234353Sdim window = state->window; 105193323Sed hold = state->hold; 106193323Sed bits = state->bits; 107193323Sed lcode = state->lencode; 108234353Sdim dcode = state->distcode; 109234353Sdim lmask = (1U << state->lenbits) - 1; 110234353Sdim dmask = (1U << state->distbits) - 1; 111193323Sed 112193323Sed /* decode literals and length/distances until end-of-block or not enough 113193323Sed input data or output space */ 114193323Sed do { 115193323Sed if (bits < 15) { 116193323Sed hold += (unsigned long)(PUP(in)) << bits; 117193323Sed bits += 8; 118193323Sed hold += (unsigned long)(PUP(in)) << bits; 119193323Sed bits += 8; 120193323Sed } 121193323Sed this = lcode[hold & lmask]; 122193323Sed dolen: 123193323Sed op = (unsigned)(this.bits); 124193323Sed hold >>= op; 125193323Sed bits -= op; 126193323Sed op = (unsigned)(this.op); 127193323Sed if (op == 0) { /* literal */ 128193323Sed Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ? 129234353Sdim "inflate: literal '%c'\n" : 130234353Sdim "inflate: literal 0x%02x\n", this.val)); 131234353Sdim PUP(out) = (unsigned char)(this.val); 132234353Sdim } 133193323Sed else if (op & 16) { /* length base */ 134193323Sed len = (unsigned)(this.val); 135193323Sed op &= 15; /* number of extra bits */ 136234353Sdim if (op) { 137234353Sdim if (bits < op) { 138234353Sdim hold += (unsigned long)(PUP(in)) << bits; 139193323Sed bits += 8; 140193323Sed } 141251662Sdim len += (unsigned)hold & ((1U << op) - 1); 142251662Sdim hold >>= op; 143251662Sdim bits -= op; 144251662Sdim } 145251662Sdim Tracevv((stderr, "inflate: length %u\n", len)); 146251662Sdim if (bits < 15) { 147251662Sdim hold += (unsigned long)(PUP(in)) << bits; 148251662Sdim bits += 8; 149251662Sdim hold += (unsigned long)(PUP(in)) << bits; 150251662Sdim bits += 8; 151251662Sdim } 152251662Sdim this = dcode[hold & dmask]; 153251662Sdim dodist: 154251662Sdim op = (unsigned)(this.bits); 155193323Sed hold >>= op; 156251662Sdim bits -= op; 157251662Sdim op = (unsigned)(this.op); 158193323Sed if (op & 16) { /* distance base */ 159193323Sed dist = (unsigned)(this.val); 160193323Sed op &= 15; /* number of extra bits */ 161193323Sed if (bits < op) { 162193323Sed hold += (unsigned long)(PUP(in)) << bits; 163193323Sed bits += 8; 164193323Sed if (bits < op) { 165193323Sed hold += (unsigned long)(PUP(in)) << bits; 166193323Sed bits += 8; 167193323Sed } 168193323Sed } 169193323Sed dist += (unsigned)hold & ((1U << op) - 1); 170198090Srdivacky hold >>= op; 171198090Srdivacky bits -= op; 172193323Sed Tracevv((stderr, "inflate: distance %u\n", dist)); 173193323Sed op = (unsigned)(out - beg); /* max distance in output */ 174193323Sed if (dist > op) { /* see if copy from window */ 175193323Sed op = dist - op; /* distance back in window */ 176193323Sed if (op > whave) { 177193323Sed strm->msg = (char *)"invalid distance too far back"; 178193323Sed state->mode = BAD; 179193323Sed break; 180193323Sed } 181234353Sdim from = window - OFF; 182234353Sdim if (write == 0) { /* very common case */ 183234353Sdim from += wsize - op; 184234353Sdim if (op < len) { /* some from window */ 185234353Sdim len -= op; 186234353Sdim do { 187234353Sdim PUP(out) = PUP(from); 188234353Sdim } while (--op); 189234353Sdim from = out - dist; /* rest from output */ 190193323Sed } 191193323Sed } 192193323Sed else if (write < op) { /* wrap around window */ 193251662Sdim from += wsize + write - op; 194193323Sed op -= write; 195251662Sdim if (op < len) { /* some from end of window */ 196251662Sdim len -= op; 197251662Sdim do { 198251662Sdim PUP(out) = PUP(from); 199193323Sed } while (--op); 200198090Srdivacky from = window - OFF; 201234353Sdim if (write < len) { /* some from start of window */ 202193323Sed op = write; 203193323Sed len -= op; 204234353Sdim do { 205193323Sed PUP(out) = PUP(from); 206193323Sed } while (--op); 207193323Sed from = out - dist; /* rest from output */ 208234353Sdim } 209193323Sed } 210193323Sed } 211234353Sdim else { /* contiguous in window */ 212193323Sed from += write - op; 213193323Sed if (op < len) { /* some from window */ 214234353Sdim len -= op; 215193323Sed do { 216193323Sed PUP(out) = PUP(from); 217193323Sed } while (--op); 218193323Sed from = out - dist; /* rest from output */ 219193323Sed } 220193323Sed } 221193323Sed while (len > 2) { 222193323Sed PUP(out) = PUP(from); 223193323Sed PUP(out) = PUP(from); 224193323Sed PUP(out) = PUP(from); 225193323Sed len -= 3; 226193323Sed } 227193323Sed if (len) { 228198090Srdivacky PUP(out) = PUP(from); 229234353Sdim if (len > 1) 230193323Sed PUP(out) = PUP(from); 231234353Sdim } 232234353Sdim } 233234353Sdim else { 234234353Sdim from = out - dist; /* copy direct from output */ 235193323Sed do { /* minimum length is three */ 236251662Sdim PUP(out) = PUP(from); 237193323Sed PUP(out) = PUP(from); 238239462Sdim PUP(out) = PUP(from); 239234353Sdim len -= 3; 240239462Sdim } while (len > 2); 241239462Sdim if (len) { 242239462Sdim PUP(out) = PUP(from); 243251662Sdim if (len > 1) 244193323Sed PUP(out) = PUP(from); 245193323Sed } 246198090Srdivacky } 247193323Sed } 248193323Sed else if ((op & 64) == 0) { /* 2nd level distance code */ 249193323Sed this = dcode[this.val + (hold & ((1U << op) - 1))]; 250193323Sed goto dodist; 251193323Sed } 252193323Sed else { 253193323Sed strm->msg = (char *)"invalid distance code"; 254193323Sed state->mode = BAD; 255193323Sed break; 256193323Sed } 257193323Sed } 258193323Sed else if ((op & 64) == 0) { /* 2nd level length code */ 259193323Sed this = lcode[this.val + (hold & ((1U << op) - 1))]; 260193323Sed goto dolen; 261193323Sed } 262221345Sdim else if (op & 32) { /* end-of-block */ 263221345Sdim Tracevv((stderr, "inflate: end of block\n")); 264198090Srdivacky state->mode = TYPE; 265193323Sed break; 266198090Srdivacky } 267193323Sed else { 268198090Srdivacky strm->msg = (char *)"invalid literal/length code"; 269198090Srdivacky state->mode = BAD; 270193323Sed break; 271193323Sed } 272198090Srdivacky } while (in < last && out < end); 273193323Sed 274193323Sed /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 275193323Sed len = bits >> 3; 276193323Sed in -= len; 277193323Sed bits -= len << 3; 278193323Sed hold &= (1U << bits) - 1; 279193323Sed 280193323Sed /* update state and return */ 281193323Sed strm->next_in = in + OFF; 282193323Sed strm->next_out = out + OFF; 283193323Sed strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 284193323Sed strm->avail_out = (unsigned)(out < end ? 285204642Srdivacky 257 + (end - out) : 257 - (out - end)); 286193323Sed state->hold = hold; 287193323Sed state->bits = bits; 288193323Sed return; 289193323Sed} 290193323Sed 291193323Sed/* 292204642Srdivacky inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 293193323Sed - Using bit fields for code structure 294193323Sed - Different op definition to avoid & for extra bits (do & for table bits) 295193323Sed - Three separate decoding do-loops for direct, window, and write == 0 296193323Sed - Special case for distance > 1 copies to do overlapped load and store copy 297193323Sed - Explicit branch predictions (based on measured branch probabilities) 298193323Sed - Deferring match copy and interspersed it with decoding subsequent codes 299193323Sed - Swapping literal/length else 300193323Sed - Swapping window/direct else 301193323Sed - Larger unrolled copy loops (three is about right) 302193323Sed - Moving len -= 3 statement into middle of loop 303193323Sed */ 304193323Sed 305193323Sed#endif /* !ASMINF */ 306193323Sed