inffast.c revision 131377
153024Sguido/* inffast.c -- fast decoding 253024Sguido * Copyright (C) 1995-2003 Mark Adler 353024Sguido * For conditions of distribution and use, see copyright notice in zlib.h 453024Sguido */ 553024Sguido 653024Sguido#include "zutil.h" 753024Sguido#include "inftrees.h" 853024Sguido#include "inflate.h" 953024Sguido#include "inffast.h" 1053024Sguido 1153024Sguido#ifndef ASMINF 1253024Sguido 1353024Sguido/* Allow machine dependent optimization for post-increment or pre-increment. 1453024Sguido Based on testing to date, 1553024Sguido Pre-increment preferred for: 1653024Sguido - PowerPC G3 (Adler) 1753024Sguido - MIPS R5000 (Randers-Pehrson) 1853024Sguido Post-increment preferred for: 1953024Sguido - none 2053024Sguido No measurable difference: 2153024Sguido - Pentium III (Anderson) 2253024Sguido - 68060 (Nikl) 2353024Sguido */ 2453024Sguido#ifdef POSTINC 2553024Sguido# define OFF 0 2653024Sguido# define PUP(a) *(a)++ 2753024Sguido#else 2853024Sguido# define OFF 1 2953024Sguido# define PUP(a) *++(a) 3053024Sguido#endif 3153024Sguido 3253024Sguido/* 3353024Sguido Decode literal, length, and distance codes and write out the resulting 3453024Sguido literal and match bytes until either not enough input or output is 3553024Sguido available, an end-of-block is encountered, or a data error is encountered. 3653024Sguido When large enough input and output buffers are supplied to inflate(), for 3753024Sguido example, a 16K input buffer and a 64K output buffer, more than 95% of the 3853024Sguido inflate execution time is spent in this routine. 3953024Sguido 4053024Sguido Entry assumptions: 4153024Sguido 4253024Sguido state->mode == LEN 4353024Sguido strm->avail_in >= 6 4453024Sguido strm->avail_out >= 258 4553024Sguido start >= strm->avail_out 4653024Sguido state->bits < 8 4753024Sguido 4853024Sguido On return, state->mode is one of: 4953024Sguido 50 LEN -- ran out of enough output space or enough available input 51 TYPE -- reached end of block code, inflate() to interpret next block 52 BAD -- error in block data 53 54 Notes: 55 56 - The maximum input bits used by a length/distance pair is 15 bits for the 57 length code, 5 bits for the length extra, 15 bits for the distance code, 58 and 13 bits for the distance extra. This totals 48 bits, or six bytes. 59 Therefore if strm->avail_in >= 6, then there is enough input to avoid 60 checking for available input while decoding. 61 62 - The maximum bytes that a single length/distance pair can output is 258 63 bytes, which is the maximum length that can be coded. inflate_fast() 64 requires strm->avail_out >= 258 for each loop to avoid checking for 65 output space. 66 */ 67void inflate_fast(strm, start) 68z_streamp strm; 69unsigned start; /* inflate()'s starting value for strm->avail_out */ 70{ 71 struct inflate_state FAR *state; 72 unsigned char FAR *in; /* local strm->next_in */ 73 unsigned char FAR *last; /* while in < last, enough input available */ 74 unsigned char FAR *out; /* local strm->next_out */ 75 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ 76 unsigned char FAR *end; /* while out < end, enough space available */ 77 unsigned wsize; /* window size or zero if not using window */ 78 unsigned whave; /* valid bytes in the window */ 79 unsigned write; /* window write index */ 80 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ 81 unsigned long hold; /* local strm->hold */ 82 unsigned bits; /* local strm->bits */ 83 code const FAR *lcode; /* local strm->lencode */ 84 code const FAR *dcode; /* local strm->distcode */ 85 unsigned lmask; /* mask for first level of length codes */ 86 unsigned dmask; /* mask for first level of distance codes */ 87 code this; /* retrieved table entry */ 88 unsigned op; /* code bits, operation, extra bits, or */ 89 /* window position, window bytes to copy */ 90 unsigned len; /* match length, unused bytes */ 91 unsigned dist; /* match distance */ 92 unsigned char FAR *from; /* where to copy match from */ 93 94 /* copy state to local variables */ 95 state = (struct inflate_state FAR *)strm->state; 96 in = strm->next_in - OFF; 97 last = in + (strm->avail_in - 5); 98 out = strm->next_out - OFF; 99 beg = out - (start - strm->avail_out); 100 end = out + (strm->avail_out - 257); 101 wsize = state->wsize; 102 whave = state->whave; 103 write = state->write; 104 window = state->window; 105 hold = state->hold; 106 bits = state->bits; 107 lcode = state->lencode; 108 dcode = state->distcode; 109 lmask = (1U << state->lenbits) - 1; 110 dmask = (1U << state->distbits) - 1; 111 112 /* decode literals and length/distances until end-of-block or not enough 113 input data or output space */ 114 do { 115 if (bits < 15) { 116 hold += (unsigned long)(PUP(in)) << bits; 117 bits += 8; 118 hold += (unsigned long)(PUP(in)) << bits; 119 bits += 8; 120 } 121 this = lcode[hold & lmask]; 122 dolen: 123 op = (unsigned)(this.bits); 124 hold >>= op; 125 bits -= op; 126 op = (unsigned)(this.op); 127 if (op == 0) { /* literal */ 128 Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ? 129 "inflate: literal '%c'\n" : 130 "inflate: literal 0x%02x\n", this.val)); 131 PUP(out) = (unsigned char)(this.val); 132 } 133 else if (op & 16) { /* length base */ 134 len = (unsigned)(this.val); 135 op &= 15; /* number of extra bits */ 136 if (op) { 137 if (bits < op) { 138 hold += (unsigned long)(PUP(in)) << bits; 139 bits += 8; 140 } 141 len += (unsigned)hold & ((1U << op) - 1); 142 hold >>= op; 143 bits -= op; 144 } 145 Tracevv((stderr, "inflate: length %u\n", len)); 146 if (bits < 15) { 147 hold += (unsigned long)(PUP(in)) << bits; 148 bits += 8; 149 hold += (unsigned long)(PUP(in)) << bits; 150 bits += 8; 151 } 152 this = dcode[hold & dmask]; 153 dodist: 154 op = (unsigned)(this.bits); 155 hold >>= op; 156 bits -= op; 157 op = (unsigned)(this.op); 158 if (op & 16) { /* distance base */ 159 dist = (unsigned)(this.val); 160 op &= 15; /* number of extra bits */ 161 if (bits < op) { 162 hold += (unsigned long)(PUP(in)) << bits; 163 bits += 8; 164 if (bits < op) { 165 hold += (unsigned long)(PUP(in)) << bits; 166 bits += 8; 167 } 168 } 169 dist += (unsigned)hold & ((1U << op) - 1); 170 hold >>= op; 171 bits -= op; 172 Tracevv((stderr, "inflate: distance %u\n", dist)); 173 op = (unsigned)(out - beg); /* max distance in output */ 174 if (dist > op) { /* see if copy from window */ 175 op = dist - op; /* distance back in window */ 176 if (op > whave) { 177 strm->msg = (char *)"invalid distance too far back"; 178 state->mode = BAD; 179 break; 180 } 181 from = window - OFF; 182 if (write == 0) { /* very common case */ 183 from += wsize - op; 184 if (op < len) { /* some from window */ 185 len -= op; 186 do { 187 PUP(out) = PUP(from); 188 } while (--op); 189 from = out - dist; /* rest from output */ 190 } 191 } 192 else if (write < op) { /* wrap around window */ 193 from += wsize + write - op; 194 op -= write; 195 if (op < len) { /* some from end of window */ 196 len -= op; 197 do { 198 PUP(out) = PUP(from); 199 } while (--op); 200 from = window - OFF; 201 if (write < len) { /* some from start of window */ 202 op = write; 203 len -= op; 204 do { 205 PUP(out) = PUP(from); 206 } while (--op); 207 from = out - dist; /* rest from output */ 208 } 209 } 210 } 211 else { /* contiguous in window */ 212 from += write - op; 213 if (op < len) { /* some from window */ 214 len -= op; 215 do { 216 PUP(out) = PUP(from); 217 } while (--op); 218 from = out - dist; /* rest from output */ 219 } 220 } 221 while (len > 2) { 222 PUP(out) = PUP(from); 223 PUP(out) = PUP(from); 224 PUP(out) = PUP(from); 225 len -= 3; 226 } 227 if (len) { 228 PUP(out) = PUP(from); 229 if (len > 1) 230 PUP(out) = PUP(from); 231 } 232 } 233 else { 234 from = out - dist; /* copy direct from output */ 235 do { /* minimum length is three */ 236 PUP(out) = PUP(from); 237 PUP(out) = PUP(from); 238 PUP(out) = PUP(from); 239 len -= 3; 240 } while (len > 2); 241 if (len) { 242 PUP(out) = PUP(from); 243 if (len > 1) 244 PUP(out) = PUP(from); 245 } 246 } 247 } 248 else if ((op & 64) == 0) { /* 2nd level distance code */ 249 this = dcode[this.val + (hold & ((1U << op) - 1))]; 250 goto dodist; 251 } 252 else { 253 strm->msg = (char *)"invalid distance code"; 254 state->mode = BAD; 255 break; 256 } 257 } 258 else if ((op & 64) == 0) { /* 2nd level length code */ 259 this = lcode[this.val + (hold & ((1U << op) - 1))]; 260 goto dolen; 261 } 262 else if (op & 32) { /* end-of-block */ 263 Tracevv((stderr, "inflate: end of block\n")); 264 state->mode = TYPE; 265 break; 266 } 267 else { 268 strm->msg = (char *)"invalid literal/length code"; 269 state->mode = BAD; 270 break; 271 } 272 } while (in < last && out < end); 273 274 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 275 len = bits >> 3; 276 in -= len; 277 bits -= len << 3; 278 hold &= (1U << bits) - 1; 279 280 /* update state and return */ 281 strm->next_in = in + OFF; 282 strm->next_out = out + OFF; 283 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 284 strm->avail_out = (unsigned)(out < end ? 285 257 + (end - out) : 257 - (out - end)); 286 state->hold = hold; 287 state->bits = bits; 288 return; 289} 290 291/* 292 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 293 - Using bit fields for code structure 294 - Different op definition to avoid & for extra bits (do & for table bits) 295 - Three separate decoding do-loops for direct, window, and write == 0 296 - Special case for distance > 1 copies to do overlapped load and store copy 297 - Explicit branch predictions (based on measured branch probabilities) 298 - Deferring match copy and interspersed it with decoding subsequent codes 299 - Swapping literal/length else 300 - Swapping window/direct else 301 - Larger unrolled copy loops (three is about right) 302 - Moving len -= 3 statement into middle of loop 303 */ 304 305#endif /* !ASMINF */ 306