inffast.c revision 1.3
1 /* $NetBSD: inffast.c,v 1.3 2006/01/27 00:45:27 christos Exp $ */ 2 3 /* inffast.c -- fast decoding 4 * Copyright (C) 1995-2004 Mark Adler 5 * For conditions of distribution and use, see copyright notice in zlib.h 6 */ 7 8 #include "zutil.h" 9 #include "inftrees.h" 10 #include "inflate.h" 11 #include "inffast.h" 12 13 #ifndef ASMINF 14 15 /* Allow machine dependent optimization for post-increment or pre-increment. 16 Based on testing to date, 17 Pre-increment preferred for: 18 - PowerPC G3 (Adler) 19 - MIPS R5000 (Randers-Pehrson) 20 Post-increment preferred for: 21 - none 22 No measurable difference: 23 - Pentium III (Anderson) 24 - M68060 (Nikl) 25 */ 26 #ifdef POSTINC 27 # define OFF 0 28 # define PUP(a) *(a)++ 29 #else 30 # define OFF 1 31 # define PUP(a) *++(a) 32 #endif 33 34 /* 35 Decode literal, length, and distance codes and write out the resulting 36 literal and match bytes until either not enough input or output is 37 available, an end-of-block is encountered, or a data error is encountered. 38 When large enough input and output buffers are supplied to inflate(), for 39 example, a 16K input buffer and a 64K output buffer, more than 95% of the 40 inflate execution time is spent in this routine. 41 42 Entry assumptions: 43 44 state->mode == LEN 45 strm->avail_in >= 6 46 strm->avail_out >= 258 47 start >= strm->avail_out 48 state->bits < 8 49 50 On return, state->mode is one of: 51 52 LEN -- ran out of enough output space or enough available input 53 TYPE -- reached end of block code, inflate() to interpret next block 54 BAD -- error in block data 55 56 Notes: 57 58 - The maximum input bits used by a length/distance pair is 15 bits for the 59 length code, 5 bits for the length extra, 15 bits for the distance code, 60 and 13 bits for the distance extra. This totals 48 bits, or six bytes. 61 Therefore if strm->avail_in >= 6, then there is enough input to avoid 62 checking for available input while decoding. 63 64 - The maximum bytes that a single length/distance pair can output is 258 65 bytes, which is the maximum length that can be coded. inflate_fast() 66 requires strm->avail_out >= 258 for each loop to avoid checking for 67 output space. 68 */ 69 void inflate_fast(strm, start) 70 z_streamp strm; 71 unsigned start; /* inflate()'s starting value for strm->avail_out */ 72 { 73 struct inflate_state FAR *state; 74 unsigned char FAR *in; /* local strm->next_in */ 75 unsigned char FAR *last; /* while in < last, enough input available */ 76 unsigned char FAR *out; /* local strm->next_out */ 77 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ 78 unsigned char FAR *end; /* while out < end, enough space available */ 79 #ifdef INFLATE_STRICT 80 unsigned dmax; /* maximum distance from zlib header */ 81 #endif 82 unsigned wsize; /* window size or zero if not using window */ 83 unsigned whave; /* valid bytes in the window */ 84 unsigned wwrite; /* window write index */ 85 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ 86 unsigned long hold; /* local strm->hold */ 87 unsigned bits; /* local strm->bits */ 88 code const FAR *lcode; /* local strm->lencode */ 89 code const FAR *dcode; /* local strm->distcode */ 90 unsigned lmask; /* mask for first level of length codes */ 91 unsigned dmask; /* mask for first level of distance codes */ 92 code this; /* retrieved table entry */ 93 unsigned op; /* code bits, operation, extra bits, or */ 94 /* window position, window bytes to copy */ 95 unsigned len; /* match length, unused bytes */ 96 unsigned dist; /* match distance */ 97 unsigned char FAR *from; /* where to copy match from */ 98 99 /* copy state to local variables */ 100 state = (struct inflate_state FAR *)strm->state; 101 in = strm->next_in - OFF; 102 last = in + (strm->avail_in - 5); 103 out = strm->next_out - OFF; 104 beg = out - (start - strm->avail_out); 105 end = out + (strm->avail_out - 257); 106 #ifdef INFLATE_STRICT 107 dmax = state->dmax; 108 #endif 109 wsize = state->wsize; 110 whave = state->whave; 111 wwrite = state->write; 112 window = state->window; 113 hold = state->hold; 114 bits = state->bits; 115 lcode = state->lencode; 116 dcode = state->distcode; 117 lmask = (1U << state->lenbits) - 1; 118 dmask = (1U << state->distbits) - 1; 119 120 /* decode literals and length/distances until end-of-block or not enough 121 input data or output space */ 122 do { 123 if (bits < 15) { 124 hold += (unsigned long)(PUP(in)) << bits; 125 bits += 8; 126 hold += (unsigned long)(PUP(in)) << bits; 127 bits += 8; 128 } 129 this = lcode[hold & lmask]; 130 dolen: 131 op = (unsigned)(this.bits); 132 hold >>= op; 133 bits -= op; 134 op = (unsigned)(this.op); 135 if (op == 0) { /* literal */ 136 Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ? 137 "inflate: literal '%c'\n" : 138 "inflate: literal 0x%02x\n", this.val)); 139 PUP(out) = (unsigned char)(this.val); 140 } 141 else if (op & 16) { /* length base */ 142 len = (unsigned)(this.val); 143 op &= 15; /* number of extra bits */ 144 if (op) { 145 if (bits < op) { 146 hold += (unsigned long)(PUP(in)) << bits; 147 bits += 8; 148 } 149 len += (unsigned)hold & ((1U << op) - 1); 150 hold >>= op; 151 bits -= op; 152 } 153 Tracevv((stderr, "inflate: length %u\n", len)); 154 if (bits < 15) { 155 hold += (unsigned long)(PUP(in)) << bits; 156 bits += 8; 157 hold += (unsigned long)(PUP(in)) << bits; 158 bits += 8; 159 } 160 this = dcode[hold & dmask]; 161 dodist: 162 op = (unsigned)(this.bits); 163 hold >>= op; 164 bits -= op; 165 op = (unsigned)(this.op); 166 if (op & 16) { /* distance base */ 167 dist = (unsigned)(this.val); 168 op &= 15; /* number of extra bits */ 169 if (bits < op) { 170 hold += (unsigned long)(PUP(in)) << bits; 171 bits += 8; 172 if (bits < op) { 173 hold += (unsigned long)(PUP(in)) << bits; 174 bits += 8; 175 } 176 } 177 dist += (unsigned)hold & ((1U << op) - 1); 178 #ifdef INFLATE_STRICT 179 if (dist > dmax) { 180 strm->msg = (char *)"invalid distance too far back"; 181 state->mode = BAD; 182 break; 183 } 184 #endif 185 hold >>= op; 186 bits -= op; 187 Tracevv((stderr, "inflate: distance %u\n", dist)); 188 op = (unsigned)(out - beg); /* max distance in output */ 189 if (dist > op) { /* see if copy from window */ 190 op = dist - op; /* distance back in window */ 191 if (op > whave) { 192 strm->msg = __UNCONST("invalid distance too far back"); 193 state->mode = BAD; 194 break; 195 } 196 from = window - OFF; 197 if (wwrite == 0) { /* very common case */ 198 from += wsize - op; 199 if (op < len) { /* some from window */ 200 len -= op; 201 do { 202 PUP(out) = PUP(from); 203 } while (--op); 204 from = out - dist; /* rest from output */ 205 } 206 } 207 else if (wwrite < op) { /* wrap around window */ 208 from += wsize + wwrite - op; 209 op -= wwrite; 210 if (op < len) { /* some from end of window */ 211 len -= op; 212 do { 213 PUP(out) = PUP(from); 214 } while (--op); 215 from = window - OFF; 216 if (wwrite < len) { /* some from start of window */ 217 op = wwrite; 218 len -= op; 219 do { 220 PUP(out) = PUP(from); 221 } while (--op); 222 from = out - dist; /* rest from output */ 223 } 224 } 225 } 226 else { /* contiguous in window */ 227 from += wwrite - op; 228 if (op < len) { /* some from window */ 229 len -= op; 230 do { 231 PUP(out) = PUP(from); 232 } while (--op); 233 from = out - dist; /* rest from output */ 234 } 235 } 236 while (len > 2) { 237 PUP(out) = PUP(from); 238 PUP(out) = PUP(from); 239 PUP(out) = PUP(from); 240 len -= 3; 241 } 242 if (len) { 243 PUP(out) = PUP(from); 244 if (len > 1) 245 PUP(out) = PUP(from); 246 } 247 } 248 else { 249 from = out - dist; /* copy direct from output */ 250 do { /* minimum length is three */ 251 PUP(out) = PUP(from); 252 PUP(out) = PUP(from); 253 PUP(out) = PUP(from); 254 len -= 3; 255 } while (len > 2); 256 if (len) { 257 PUP(out) = PUP(from); 258 if (len > 1) 259 PUP(out) = PUP(from); 260 } 261 } 262 } 263 else if ((op & 64) == 0) { /* 2nd level distance code */ 264 this = dcode[this.val + (hold & ((1U << op) - 1))]; 265 goto dodist; 266 } 267 else { 268 strm->msg = __UNCONST("invalid distance code"); 269 state->mode = BAD; 270 break; 271 } 272 } 273 else if ((op & 64) == 0) { /* 2nd level length code */ 274 this = lcode[this.val + (hold & ((1U << op) - 1))]; 275 goto dolen; 276 } 277 else if (op & 32) { /* end-of-block */ 278 Tracevv((stderr, "inflate: end of block\n")); 279 state->mode = TYPE; 280 break; 281 } 282 else { 283 strm->msg = __UNCONST("invalid literal/length code"); 284 state->mode = BAD; 285 break; 286 } 287 } while (in < last && out < end); 288 289 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 290 len = bits >> 3; 291 in -= len; 292 bits -= len << 3; 293 hold &= (1U << bits) - 1; 294 295 /* update state and return */ 296 strm->next_in = in + OFF; 297 strm->next_out = out + OFF; 298 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 299 strm->avail_out = (unsigned)(out < end ? 300 257 + (end - out) : 257 - (out - end)); 301 state->hold = hold; 302 state->bits = bits; 303 return; 304 } 305 306 /* 307 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 308 - Using bit fields for code structure 309 - Different op definition to avoid & for extra bits (do & for table bits) 310 - Three separate decoding do-loops for direct, window, and write == 0 311 - Special case for distance > 1 copies to do overlapped load and store copy 312 - Explicit branch predictions (based on measured branch probabilities) 313 - Deferring match copy and interspersed it with decoding subsequent codes 314 - Swapping literal/length else 315 - Swapping window/direct else 316 - Larger unrolled copy loops (three is about right) 317 - Moving len -= 3 statement into middle of loop 318 */ 319 320 #endif /* !ASMINF */ 321
Indexes created Mon Sep 22 13:09:51 GMT 2025