inffast.c revision 1.6
1 /* $NetBSD: inffast.c,v 1.6 2024/09/22 19:12:27 christos Exp $ */ 2 3 /* inffast.c -- fast decoding 4 * Copyright (C) 1995-2017 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 #ifdef ASMINF 14 # pragma message("Assembler code may have bugs -- use at your own risk") 15 #else 16 17 /* 18 Decode literal, length, and distance codes and write out the resulting 19 literal and match bytes until either not enough input or output is 20 available, an end-of-block is encountered, or a data error is encountered. 21 When large enough input and output buffers are supplied to inflate(), for 22 example, a 16K input buffer and a 64K output buffer, more than 95% of the 23 inflate execution time is spent in this routine. 24 25 Entry assumptions: 26 27 state->mode == LEN 28 strm->avail_in >= 6 29 strm->avail_out >= 258 30 start >= strm->avail_out 31 state->bits < 8 32 33 On return, state->mode is one of: 34 35 LEN -- ran out of enough output space or enough available input 36 TYPE -- reached end of block code, inflate() to interpret next block 37 BAD -- error in block data 38 39 Notes: 40 41 - The maximum input bits used by a length/distance pair is 15 bits for the 42 length code, 5 bits for the length extra, 15 bits for the distance code, 43 and 13 bits for the distance extra. This totals 48 bits, or six bytes. 44 Therefore if strm->avail_in >= 6, then there is enough input to avoid 45 checking for available input while decoding. 46 47 - The maximum bytes that a single length/distance pair can output is 258 48 bytes, which is the maximum length that can be coded. inflate_fast() 49 requires strm->avail_out >= 258 for each loop to avoid checking for 50 output space. 51 */ 52 void ZLIB_INTERNAL inflate_fast(z_streamp strm, unsigned start) { 53 struct inflate_state FAR *state; 54 z_const unsigned char FAR *in; /* local strm->next_in */ 55 z_const unsigned char FAR *last; /* have enough input while in < last */ 56 unsigned char FAR *out; /* local strm->next_out */ 57 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ 58 unsigned char FAR *end; /* while out < end, enough space available */ 59 #ifdef INFLATE_STRICT 60 unsigned dmax; /* maximum distance from zlib header */ 61 #endif 62 unsigned wsize; /* window size or zero if not using window */ 63 unsigned whave; /* valid bytes in the window */ 64 unsigned wnext; /* window write index */ 65 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ 66 unsigned long hold; /* local strm->hold */ 67 unsigned bits; /* local strm->bits */ 68 code const FAR *lcode; /* local strm->lencode */ 69 code const FAR *dcode; /* local strm->distcode */ 70 unsigned lmask; /* mask for first level of length codes */ 71 unsigned dmask; /* mask for first level of distance codes */ 72 code const *here; /* retrieved table entry */ 73 unsigned op; /* code bits, operation, extra bits, or */ 74 /* window position, window bytes to copy */ 75 unsigned len; /* match length, unused bytes */ 76 unsigned dist; /* match distance */ 77 unsigned char FAR *from; /* where to copy match from */ 78 79 /* copy state to local variables */ 80 state = (struct inflate_state FAR *)strm->state; 81 in = strm->next_in; 82 last = in + (strm->avail_in - 5); 83 out = strm->next_out; 84 beg = out - (start - strm->avail_out); 85 end = out + (strm->avail_out - 257); 86 #ifdef INFLATE_STRICT 87 dmax = state->dmax; 88 #endif 89 wsize = state->wsize; 90 whave = state->whave; 91 wnext = state->wnext; 92 window = state->window; 93 hold = state->hold; 94 bits = state->bits; 95 lcode = state->lencode; 96 dcode = state->distcode; 97 lmask = (1U << state->lenbits) - 1; 98 dmask = (1U << state->distbits) - 1; 99 100 /* decode literals and length/distances until end-of-block or not enough 101 input data or output space */ 102 do { 103 if (bits < 15) { 104 hold += (unsigned long)(*in++) << bits; 105 bits += 8; 106 hold += (unsigned long)(*in++) << bits; 107 bits += 8; 108 } 109 here = lcode + (hold & lmask); 110 dolen: 111 op = (unsigned)(here->bits); 112 hold >>= op; 113 bits -= op; 114 op = (unsigned)(here->op); 115 if (op == 0) { /* literal */ 116 Tracevv((stderr, here->val >= 0x20 && here->val < 0x7f ? 117 "inflate: literal '%c'\n" : 118 "inflate: literal 0x%02x\n", here->val)); 119 *out++ = (unsigned char)(here->val); 120 } 121 else if (op & 16) { /* length base */ 122 len = (unsigned)(here->val); 123 op &= 15; /* number of extra bits */ 124 if (op) { 125 if (bits < op) { 126 hold += (unsigned long)(*in++) << bits; 127 bits += 8; 128 } 129 len += (unsigned)hold & ((1U << op) - 1); 130 hold >>= op; 131 bits -= op; 132 } 133 Tracevv((stderr, "inflate: length %u\n", len)); 134 if (bits < 15) { 135 hold += (unsigned long)(*in++) << bits; 136 bits += 8; 137 hold += (unsigned long)(*in++) << bits; 138 bits += 8; 139 } 140 here = dcode + (hold & dmask); 141 dodist: 142 op = (unsigned)(here->bits); 143 hold >>= op; 144 bits -= op; 145 op = (unsigned)(here->op); 146 if (op & 16) { /* distance base */ 147 dist = (unsigned)(here->val); 148 op &= 15; /* number of extra bits */ 149 if (bits < op) { 150 hold += (unsigned long)(*in++) << bits; 151 bits += 8; 152 if (bits < op) { 153 hold += (unsigned long)(*in++) << bits; 154 bits += 8; 155 } 156 } 157 dist += (unsigned)hold & ((1U << op) - 1); 158 #ifdef INFLATE_STRICT 159 if (dist > dmax) { 160 strm->msg = (char *)"invalid distance too far back"; 161 state->mode = BAD; 162 break; 163 } 164 #endif 165 hold >>= op; 166 bits -= op; 167 Tracevv((stderr, "inflate: distance %u\n", dist)); 168 op = (unsigned)(out - beg); /* max distance in output */ 169 if (dist > op) { /* see if copy from window */ 170 op = dist - op; /* distance back in window */ 171 if (op > whave) { 172 if (state->sane) { 173 strm->msg = 174 __UNCONST("invalid distance too far back"); 175 state->mode = BAD; 176 break; 177 } 178 #ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR 179 if (len <= op - whave) { 180 do { 181 *out++ = 0; 182 } while (--len); 183 continue; 184 } 185 len -= op - whave; 186 do { 187 *out++ = 0; 188 } while (--op > whave); 189 if (op == 0) { 190 from = out - dist; 191 do { 192 *out++ = *from++; 193 } while (--len); 194 continue; 195 } 196 #endif 197 } 198 from = window; 199 if (wnext == 0) { /* very common case */ 200 from += wsize - op; 201 if (op < len) { /* some from window */ 202 len -= op; 203 do { 204 *out++ = *from++; 205 } while (--op); 206 from = out - dist; /* rest from output */ 207 } 208 } 209 else if (wnext < op) { /* wrap around window */ 210 from += wsize + wnext - op; 211 op -= wnext; 212 if (op < len) { /* some from end of window */ 213 len -= op; 214 do { 215 *out++ = *from++; 216 } while (--op); 217 from = window; 218 if (wnext < len) { /* some from start of window */ 219 op = wnext; 220 len -= op; 221 do { 222 *out++ = *from++; 223 } while (--op); 224 from = out - dist; /* rest from output */ 225 } 226 } 227 } 228 else { /* contiguous in window */ 229 from += wnext - op; 230 if (op < len) { /* some from window */ 231 len -= op; 232 do { 233 *out++ = *from++; 234 } while (--op); 235 from = out - dist; /* rest from output */ 236 } 237 } 238 while (len > 2) { 239 *out++ = *from++; 240 *out++ = *from++; 241 *out++ = *from++; 242 len -= 3; 243 } 244 if (len) { 245 *out++ = *from++; 246 if (len > 1) 247 *out++ = *from++; 248 } 249 } 250 else { 251 from = out - dist; /* copy direct from output */ 252 do { /* minimum length is three */ 253 *out++ = *from++; 254 *out++ = *from++; 255 *out++ = *from++; 256 len -= 3; 257 } while (len > 2); 258 if (len) { 259 *out++ = *from++; 260 if (len > 1) 261 *out++ = *from++; 262 } 263 } 264 } 265 else if ((op & 64) == 0) { /* 2nd level distance code */ 266 here = dcode + here->val + (hold & ((1U << op) - 1)); 267 goto dodist; 268 } 269 else { 270 strm->msg = __UNCONST("invalid distance code"); 271 state->mode = BAD; 272 break; 273 } 274 } 275 else if ((op & 64) == 0) { /* 2nd level length code */ 276 here = lcode + here->val + (hold & ((1U << op) - 1)); 277 goto dolen; 278 } 279 else if (op & 32) { /* end-of-block */ 280 Tracevv((stderr, "inflate: end of block\n")); 281 state->mode = TYPE; 282 break; 283 } 284 else { 285 strm->msg = __UNCONST("invalid literal/length code"); 286 state->mode = BAD; 287 break; 288 } 289 } while (in < last && out < end); 290 291 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 292 len = bits >> 3; 293 in -= len; 294 bits -= len << 3; 295 hold &= (1U << bits) - 1; 296 297 /* update state and return */ 298 strm->next_in = in; 299 strm->next_out = out; 300 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 301 strm->avail_out = (unsigned)(out < end ? 302 257 + (end - out) : 257 - (out - end)); 303 state->hold = hold; 304 state->bits = bits; 305 return; 306 } 307 308 /* 309 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 310 - Using bit fields for code structure 311 - Different op definition to avoid & for extra bits (do & for table bits) 312 - Three separate decoding do-loops for direct, window, and wnext == 0 313 - Special case for distance > 1 copies to do overlapped load and store copy 314 - Explicit branch predictions (based on measured branch probabilities) 315 - Deferring match copy and interspersed it with decoding subsequent codes 316 - Swapping literal/length else 317 - Swapping window/direct else 318 - Larger unrolled copy loops (three is about right) 319 - Moving len -= 3 statement into middle of loop 320 */ 321 322 #endif /* !ASMINF */ 323
Indexes created Tue Sep 23 23:09:58 GMT 2025