inffast.c revision 157046
1131380Stjr/* inffast.c -- fast decoding 2146081Skientzle * Copyright (C) 1995-2004 Mark Adler 3131380Stjr * For conditions of distribution and use, see copyright notice in zlib.h 417651Speter */ 517651Speter 617651Speter#include "zutil.h" 717651Speter#include "inftrees.h" 8131380Stjr#include "inflate.h" 917651Speter#include "inffast.h" 1017651Speter 11131380Stjr#ifndef ASMINF 1217651Speter 13131380Stjr/* Allow machine dependent optimization for post-increment or pre-increment. 14131380Stjr Based on testing to date, 15131380Stjr Pre-increment preferred for: 16131380Stjr - PowerPC G3 (Adler) 17131380Stjr - MIPS R5000 (Randers-Pehrson) 18131380Stjr Post-increment preferred for: 19131380Stjr - none 20131380Stjr No measurable difference: 21131380Stjr - Pentium III (Anderson) 22146081Skientzle - M68060 (Nikl) 23131380Stjr */ 24131380Stjr#ifdef POSTINC 25131380Stjr# define OFF 0 26131380Stjr# define PUP(a) *(a)++ 27131380Stjr#else 28131380Stjr# define OFF 1 29131380Stjr# define PUP(a) *++(a) 30131380Stjr#endif 3117651Speter 32131380Stjr/* 33131380Stjr Decode literal, length, and distance codes and write out the resulting 34131380Stjr literal and match bytes until either not enough input or output is 35131380Stjr available, an end-of-block is encountered, or a data error is encountered. 36131380Stjr When large enough input and output buffers are supplied to inflate(), for 37131380Stjr example, a 16K input buffer and a 64K output buffer, more than 95% of the 38131380Stjr inflate execution time is spent in this routine. 3917651Speter 40131380Stjr Entry assumptions: 4117651Speter 42131380Stjr state->mode == LEN 43131380Stjr strm->avail_in >= 6 44131380Stjr strm->avail_out >= 258 45131380Stjr start >= strm->avail_out 46131380Stjr state->bits < 8 4717651Speter 48131380Stjr On return, state->mode is one of: 4917651Speter 50131380Stjr LEN -- ran out of enough output space or enough available input 51131380Stjr TYPE -- reached end of block code, inflate() to interpret next block 52131380Stjr BAD -- error in block data 5317651Speter 54131380Stjr Notes: 5517651Speter 56131380Stjr - The maximum input bits used by a length/distance pair is 15 bits for the 57131380Stjr length code, 5 bits for the length extra, 15 bits for the distance code, 58131380Stjr and 13 bits for the distance extra. This totals 48 bits, or six bytes. 59131380Stjr Therefore if strm->avail_in >= 6, then there is enough input to avoid 60131380Stjr checking for available input while decoding. 6117651Speter 62131380Stjr - The maximum bytes that a single length/distance pair can output is 258 63131380Stjr bytes, which is the maximum length that can be coded. inflate_fast() 64131380Stjr requires strm->avail_out >= 258 for each loop to avoid checking for 65131380Stjr output space. 66131380Stjr */ 67131380Stjrvoid inflate_fast(strm, start) 68131380Stjrz_streamp strm; 69131380Stjrunsigned start; /* inflate()'s starting value for strm->avail_out */ 70131380Stjr{ 71131380Stjr struct inflate_state FAR *state; 72131380Stjr unsigned char FAR *in; /* local strm->next_in */ 73131380Stjr unsigned char FAR *last; /* while in < last, enough input available */ 74131380Stjr unsigned char FAR *out; /* local strm->next_out */ 75131380Stjr unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ 76131380Stjr unsigned char FAR *end; /* while out < end, enough space available */ 77157046Sdes#ifdef INFLATE_STRICT 78157046Sdes unsigned dmax; /* maximum distance from zlib header */ 79157046Sdes#endif 80131380Stjr unsigned wsize; /* window size or zero if not using window */ 81131380Stjr unsigned whave; /* valid bytes in the window */ 82131380Stjr unsigned write; /* window write index */ 83131380Stjr unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ 84131380Stjr unsigned long hold; /* local strm->hold */ 85131380Stjr unsigned bits; /* local strm->bits */ 86131380Stjr code const FAR *lcode; /* local strm->lencode */ 87131380Stjr code const FAR *dcode; /* local strm->distcode */ 88131380Stjr unsigned lmask; /* mask for first level of length codes */ 89131380Stjr unsigned dmask; /* mask for first level of distance codes */ 90131380Stjr code this; /* retrieved table entry */ 91131380Stjr unsigned op; /* code bits, operation, extra bits, or */ 92131380Stjr /* window position, window bytes to copy */ 93131380Stjr unsigned len; /* match length, unused bytes */ 94131380Stjr unsigned dist; /* match distance */ 95131380Stjr unsigned char FAR *from; /* where to copy match from */ 96131380Stjr 97131380Stjr /* copy state to local variables */ 98131380Stjr state = (struct inflate_state FAR *)strm->state; 99131380Stjr in = strm->next_in - OFF; 100131380Stjr last = in + (strm->avail_in - 5); 101131380Stjr out = strm->next_out - OFF; 102131380Stjr beg = out - (start - strm->avail_out); 103131380Stjr end = out + (strm->avail_out - 257); 104157046Sdes#ifdef INFLATE_STRICT 105157046Sdes dmax = state->dmax; 106157046Sdes#endif 107131380Stjr wsize = state->wsize; 108131380Stjr whave = state->whave; 109131380Stjr write = state->write; 110131380Stjr window = state->window; 111131380Stjr hold = state->hold; 112131380Stjr bits = state->bits; 113131380Stjr lcode = state->lencode; 114131380Stjr dcode = state->distcode; 115131380Stjr lmask = (1U << state->lenbits) - 1; 116131380Stjr dmask = (1U << state->distbits) - 1; 117131380Stjr 118131380Stjr /* decode literals and length/distances until end-of-block or not enough 119131380Stjr input data or output space */ 120131380Stjr do { 121131380Stjr if (bits < 15) { 122131380Stjr hold += (unsigned long)(PUP(in)) << bits; 123131380Stjr bits += 8; 124131380Stjr hold += (unsigned long)(PUP(in)) << bits; 125131380Stjr bits += 8; 126131380Stjr } 127131380Stjr this = lcode[hold & lmask]; 128131380Stjr dolen: 129131380Stjr op = (unsigned)(this.bits); 130131380Stjr hold >>= op; 131131380Stjr bits -= op; 132131380Stjr op = (unsigned)(this.op); 133131380Stjr if (op == 0) { /* literal */ 134131380Stjr Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ? 135131380Stjr "inflate: literal '%c'\n" : 136131380Stjr "inflate: literal 0x%02x\n", this.val)); 137131380Stjr PUP(out) = (unsigned char)(this.val); 138131380Stjr } 139131380Stjr else if (op & 16) { /* length base */ 140131380Stjr len = (unsigned)(this.val); 141131380Stjr op &= 15; /* number of extra bits */ 142131380Stjr if (op) { 143131380Stjr if (bits < op) { 144131380Stjr hold += (unsigned long)(PUP(in)) << bits; 145131380Stjr bits += 8; 146131380Stjr } 147131380Stjr len += (unsigned)hold & ((1U << op) - 1); 148131380Stjr hold >>= op; 149131380Stjr bits -= op; 15017651Speter } 151131380Stjr Tracevv((stderr, "inflate: length %u\n", len)); 152131380Stjr if (bits < 15) { 153131380Stjr hold += (unsigned long)(PUP(in)) << bits; 154131380Stjr bits += 8; 155131380Stjr hold += (unsigned long)(PUP(in)) << bits; 156131380Stjr bits += 8; 15792114Sgreen } 158131380Stjr this = dcode[hold & dmask]; 159131380Stjr dodist: 160131380Stjr op = (unsigned)(this.bits); 161131380Stjr hold >>= op; 162131380Stjr bits -= op; 163131380Stjr op = (unsigned)(this.op); 164131380Stjr if (op & 16) { /* distance base */ 165131380Stjr dist = (unsigned)(this.val); 166131380Stjr op &= 15; /* number of extra bits */ 167131380Stjr if (bits < op) { 168131380Stjr hold += (unsigned long)(PUP(in)) << bits; 169131380Stjr bits += 8; 170131380Stjr if (bits < op) { 171131380Stjr hold += (unsigned long)(PUP(in)) << bits; 172131380Stjr bits += 8; 173131380Stjr } 174131380Stjr } 175131380Stjr dist += (unsigned)hold & ((1U << op) - 1); 176157046Sdes#ifdef INFLATE_STRICT 177157046Sdes if (dist > dmax) { 178157046Sdes strm->msg = (char *)"invalid distance too far back"; 179157046Sdes state->mode = BAD; 180157046Sdes break; 181157046Sdes } 182157046Sdes#endif 183131380Stjr hold >>= op; 184131380Stjr bits -= op; 185131380Stjr Tracevv((stderr, "inflate: distance %u\n", dist)); 186131380Stjr op = (unsigned)(out - beg); /* max distance in output */ 187131380Stjr if (dist > op) { /* see if copy from window */ 188131380Stjr op = dist - op; /* distance back in window */ 189131380Stjr if (op > whave) { 190131380Stjr strm->msg = (char *)"invalid distance too far back"; 191131380Stjr state->mode = BAD; 192131380Stjr break; 193131380Stjr } 194131380Stjr from = window - OFF; 195131380Stjr if (write == 0) { /* very common case */ 196131380Stjr from += wsize - op; 197131380Stjr if (op < len) { /* some from window */ 198131380Stjr len -= op; 199131380Stjr do { 200131380Stjr PUP(out) = PUP(from); 201131380Stjr } while (--op); 202131380Stjr from = out - dist; /* rest from output */ 203131380Stjr } 204131380Stjr } 205131380Stjr else if (write < op) { /* wrap around window */ 206131380Stjr from += wsize + write - op; 207131380Stjr op -= write; 208131380Stjr if (op < len) { /* some from end of window */ 209131380Stjr len -= op; 210131380Stjr do { 211131380Stjr PUP(out) = PUP(from); 212131380Stjr } while (--op); 213131380Stjr from = window - OFF; 214131380Stjr if (write < len) { /* some from start of window */ 215131380Stjr op = write; 216131380Stjr len -= op; 217131380Stjr do { 218131380Stjr PUP(out) = PUP(from); 219131380Stjr } while (--op); 220131380Stjr from = out - dist; /* rest from output */ 221131380Stjr } 222131380Stjr } 223131380Stjr } 224131380Stjr else { /* contiguous in window */ 225131380Stjr from += write - op; 226131380Stjr if (op < len) { /* some from window */ 227131380Stjr len -= op; 228131380Stjr do { 229131380Stjr PUP(out) = PUP(from); 230131380Stjr } while (--op); 231131380Stjr from = out - dist; /* rest from output */ 232131380Stjr } 233131380Stjr } 234131380Stjr while (len > 2) { 235131380Stjr PUP(out) = PUP(from); 236131380Stjr PUP(out) = PUP(from); 237131380Stjr PUP(out) = PUP(from); 238131380Stjr len -= 3; 239131380Stjr } 240131380Stjr if (len) { 241131380Stjr PUP(out) = PUP(from); 242131380Stjr if (len > 1) 243131380Stjr PUP(out) = PUP(from); 244131380Stjr } 245131380Stjr } 246131380Stjr else { 247131380Stjr from = out - dist; /* copy direct from output */ 248131380Stjr do { /* minimum length is three */ 249131380Stjr PUP(out) = PUP(from); 250131380Stjr PUP(out) = PUP(from); 251131380Stjr PUP(out) = PUP(from); 252131380Stjr len -= 3; 253131380Stjr } while (len > 2); 254131380Stjr if (len) { 255131380Stjr PUP(out) = PUP(from); 256131380Stjr if (len > 1) 257131380Stjr PUP(out) = PUP(from); 258131380Stjr } 259131380Stjr } 260131380Stjr } 261131380Stjr else if ((op & 64) == 0) { /* 2nd level distance code */ 262131380Stjr this = dcode[this.val + (hold & ((1U << op) - 1))]; 263131380Stjr goto dodist; 264131380Stjr } 265131380Stjr else { 266131380Stjr strm->msg = (char *)"invalid distance code"; 267131380Stjr state->mode = BAD; 268131380Stjr break; 269131380Stjr } 270131380Stjr } 271131380Stjr else if ((op & 64) == 0) { /* 2nd level length code */ 272131380Stjr this = lcode[this.val + (hold & ((1U << op) - 1))]; 273131380Stjr goto dolen; 274131380Stjr } 275131380Stjr else if (op & 32) { /* end-of-block */ 276131380Stjr Tracevv((stderr, "inflate: end of block\n")); 277131380Stjr state->mode = TYPE; 27817651Speter break; 27917651Speter } 280131380Stjr else { 281131380Stjr strm->msg = (char *)"invalid literal/length code"; 282131380Stjr state->mode = BAD; 283131380Stjr break; 284131380Stjr } 285131380Stjr } while (in < last && out < end); 28617651Speter 287131380Stjr /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 288131380Stjr len = bits >> 3; 289131380Stjr in -= len; 290131380Stjr bits -= len << 3; 291131380Stjr hold &= (1U << bits) - 1; 292131380Stjr 293131380Stjr /* update state and return */ 294131380Stjr strm->next_in = in + OFF; 295131380Stjr strm->next_out = out + OFF; 296131380Stjr strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 297131380Stjr strm->avail_out = (unsigned)(out < end ? 298131380Stjr 257 + (end - out) : 257 - (out - end)); 299131380Stjr state->hold = hold; 300131380Stjr state->bits = bits; 301131380Stjr return; 30217651Speter} 303131380Stjr 304131380Stjr/* 305131380Stjr inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 306131380Stjr - Using bit fields for code structure 307131380Stjr - Different op definition to avoid & for extra bits (do & for table bits) 308131380Stjr - Three separate decoding do-loops for direct, window, and write == 0 309131380Stjr - Special case for distance > 1 copies to do overlapped load and store copy 310131380Stjr - Explicit branch predictions (based on measured branch probabilities) 311131380Stjr - Deferring match copy and interspersed it with decoding subsequent codes 312131380Stjr - Swapping literal/length else 313131380Stjr - Swapping window/direct else 314131380Stjr - Larger unrolled copy loops (three is about right) 315131380Stjr - Moving len -= 3 statement into middle of loop 316131380Stjr */ 317131380Stjr 318131380Stjr#endif /* !ASMINF */ 319