1 /* inffast.c -- fast decoding 2 * Copyright (C) 1995-2017 Mark Adler 3 * For conditions of distribution and use, see copyright notice in zlib.h 4 */ 5 6 #include "zutil.h" 7 #include "inftrees.h" 8 #include "inflate.h" 9 #include "inffast.h" 10 11 #ifdef ASMINF 12 # pragma message("Assembler code may have bugs -- use at your own risk") 13 #else 14 15 /* 16 Decode literal, length, and distance codes and write out the resulting 17 literal and match bytes until either not enough input or output is 18 available, an end-of-block is encountered, or a data error is encountered. 19 When large enough input and output buffers are supplied to inflate(), for 20 example, a 16K input buffer and a 64K output buffer, more than 95% of the 21 inflate execution time is spent in this routine. 22 23 Entry assumptions: 24 25 state->mode == LEN 26 strm->avail_in >= 6 27 strm->avail_out >= 258 28 start >= strm->avail_out 29 state->bits < 8 30 31 On return, state->mode is one of: 32 33 LEN -- ran out of enough output space or enough available input 34 TYPE -- reached end of block code, inflate() to interpret next block 35 BAD -- error in block data 36 37 Notes: 38 39 - The maximum input bits used by a length/distance pair is 15 bits for the 40 length code, 5 bits for the length extra, 15 bits for the distance code, 41 and 13 bits for the distance extra. This totals 48 bits, or six bytes. 42 Therefore if strm->avail_in >= 6, then there is enough input to avoid 43 checking for available input while decoding. 44 45 - The maximum bytes that a single length/distance pair can output is 258 46 bytes, which is the maximum length that can be coded. inflate_fast() 47 requires strm->avail_out >= 258 for each loop to avoid checking for 48 output space. 49 */ 50 void ZLIB_INTERNAL inflate_fast(strm, start) 51 z_streamp strm; 52 unsigned start; /* inflate()'s starting value for strm->avail_out */ 53 { 54 struct inflate_state FAR *state; 55 z_const unsigned char FAR *in; /* local strm->next_in */ 56 z_const unsigned char FAR *last; /* have enough input while in < last */ 57 unsigned char FAR *out; /* local strm->next_out */ 58 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ 59 unsigned char FAR *end; /* while out < end, enough space available */ 60 #ifdef INFLATE_STRICT 61 unsigned dmax; /* maximum distance from zlib header */ 62 #endif 63 unsigned wsize; /* window size or zero if not using window */ 64 unsigned whave; /* valid bytes in the window */ 65 unsigned wnext; /* window write index */ 66 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ 67 unsigned long hold; /* local strm->hold */ 68 unsigned bits; /* local strm->bits */ 69 code const FAR *lcode; /* local strm->lencode */ 70 code const FAR *dcode; /* local strm->distcode */ 71 unsigned lmask; /* mask for first level of length codes */ 72 unsigned dmask; /* mask for first level of distance codes */ 73 code const *here; /* retrieved table entry */ 74 unsigned op; /* code bits, operation, extra bits, or */ 75 /* window position, window bytes to copy */ 76 unsigned len; /* match length, unused bytes */ 77 unsigned dist; /* match distance */ 78 unsigned char FAR *from; /* where to copy match from */ 79 80 /* copy state to local variables */ 81 state = (struct inflate_state FAR *)strm->state; 82 in = strm->next_in; 83 last = in + (strm->avail_in - 5); 84 out = strm->next_out; 85 beg = out - (start - strm->avail_out); 86 end = out + (strm->avail_out - 257); 87 #ifdef INFLATE_STRICT 88 dmax = state->dmax; 89 #endif 90 wsize = state->wsize; 91 whave = state->whave; 92 wnext = state->wnext; 93 window = state->window; 94 hold = state->hold; 95 bits = state->bits; 96 lcode = state->lencode; 97 dcode = state->distcode; 98 lmask = (1U << state->lenbits) - 1; 99 dmask = (1U << state->distbits) - 1; 100 101 /* decode literals and length/distances until end-of-block or not enough 102 input data or output space */ 103 do { 104 if (bits < 15) { 105 hold += (unsigned long)(*in++) << bits; 106 bits += 8; 107 hold += (unsigned long)(*in++) << bits; 108 bits += 8; 109 } 110 here = lcode + (hold & lmask); 111 dolen: 112 op = (unsigned)(here->bits); 113 hold >>= op; 114 bits -= op; 115 op = (unsigned)(here->op); 116 if (op == 0) { /* literal */ 117 Tracevv((stderr, here->val >= 0x20 && here->val < 0x7f ? 118 "inflate: literal '%c'\n" : 119 "inflate: literal 0x%02x\n", here->val)); 120 *out++ = (unsigned char)(here->val); 121 } 122 else if (op & 16) { /* length base */ 123 len = (unsigned)(here->val); 124 op &= 15; /* number of extra bits */ 125 if (op) { 126 if (bits < op) { 127 hold += (unsigned long)(*in++) << bits; 128 bits += 8; 129 } 130 len += (unsigned)hold & ((1U << op) - 1); 131 hold >>= op; 132 bits -= op; 133 } 134 Tracevv((stderr, "inflate: length %u\n", len)); 135 if (bits < 15) { 136 hold += (unsigned long)(*in++) << bits; 137 bits += 8; 138 hold += (unsigned long)(*in++) << bits; 139 bits += 8; 140 } 141 here = dcode + (hold & dmask); 142 dodist: 143 op = (unsigned)(here->bits); 144 hold >>= op; 145 bits -= op; 146 op = (unsigned)(here->op); 147 if (op & 16) { /* distance base */ 148 dist = (unsigned)(here->val); 149 op &= 15; /* number of extra bits */ 150 if (bits < op) { 151 hold += (unsigned long)(*in++) << bits; 152 bits += 8; 153 if (bits < op) { 154 hold += (unsigned long)(*in++) << bits; 155 bits += 8; 156 } 157 } 158 dist += (unsigned)hold & ((1U << op) - 1); 159 #ifdef INFLATE_STRICT 160 if (dist > dmax) { 161 strm->msg = (char *)"invalid distance too far back"; 162 state->mode = BAD; 163 break; 164 } 165 #endif 166 hold >>= op; 167 bits -= op; 168 Tracevv((stderr, "inflate: distance %u\n", dist)); 169 op = (unsigned)(out - beg); /* max distance in output */ 170 if (dist > op) { /* see if copy from window */ 171 op = dist - op; /* distance back in window */ 172 if (op > whave) { 173 if (state->sane) { 174 #ifdef SMALL 175 strm->msg = "error"; 176 #else 177 strm->msg = 178 (char *)"invalid distance too far back"; 179 #endif 180 state->mode = BAD; 181 break; 182 } 183 #ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR 184 if (len <= op - whave) { 185 do { 186 *out++ = 0; 187 } while (--len); 188 continue; 189 } 190 len -= op - whave; 191 do { 192 *out++ = 0; 193 } while (--op > whave); 194 if (op == 0) { 195 from = out - dist; 196 do { 197 *out++ = *from++; 198 } while (--len); 199 continue; 200 } 201 #endif 202 } 203 from = window; 204 if (wnext == 0) { /* very common case */ 205 from += wsize - op; 206 if (op < len) { /* some from window */ 207 len -= op; 208 do { 209 *out++ = *from++; 210 } while (--op); 211 from = out - dist; /* rest from output */ 212 } 213 } 214 else if (wnext < op) { /* wrap around window */ 215 from += wsize + wnext - op; 216 op -= wnext; 217 if (op < len) { /* some from end of window */ 218 len -= op; 219 do { 220 *out++ = *from++; 221 } while (--op); 222 from = window; 223 if (wnext < len) { /* some from start of window */ 224 op = wnext; 225 len -= op; 226 do { 227 *out++ = *from++; 228 } while (--op); 229 from = out - dist; /* rest from output */ 230 } 231 } 232 } 233 else { /* contiguous in window */ 234 from += wnext - op; 235 if (op < len) { /* some from window */ 236 len -= op; 237 do { 238 *out++ = *from++; 239 } while (--op); 240 from = out - dist; /* rest from output */ 241 } 242 } 243 while (len > 2) { 244 *out++ = *from++; 245 *out++ = *from++; 246 *out++ = *from++; 247 len -= 3; 248 } 249 if (len) { 250 *out++ = *from++; 251 if (len > 1) 252 *out++ = *from++; 253 } 254 } 255 else { 256 from = out - dist; /* copy direct from output */ 257 do { /* minimum length is three */ 258 *out++ = *from++; 259 *out++ = *from++; 260 *out++ = *from++; 261 len -= 3; 262 } while (len > 2); 263 if (len) { 264 *out++ = *from++; 265 if (len > 1) 266 *out++ = *from++; 267 } 268 } 269 } 270 else if ((op & 64) == 0) { /* 2nd level distance code */ 271 here = dcode + here->val + (hold & ((1U << op) - 1)); 272 goto dodist; 273 } 274 else { 275 #ifdef SMALL 276 strm->msg = "error"; 277 #else 278 strm->msg = (char *)"invalid distance code"; 279 #endif 280 state->mode = BAD; 281 break; 282 } 283 } 284 else if ((op & 64) == 0) { /* 2nd level length code */ 285 here = lcode + here->val + (hold & ((1U << op) - 1)); 286 goto dolen; 287 } 288 else if (op & 32) { /* end-of-block */ 289 Tracevv((stderr, "inflate: end of block\n")); 290 state->mode = TYPE; 291 break; 292 } 293 else { 294 #ifdef SMALL 295 strm->msg = "error"; 296 #else 297 strm->msg = (char *)"invalid literal/length code"; 298 #endif 299 state->mode = BAD; 300 break; 301 } 302 } while (in < last && out < end); 303 304 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 305 len = bits >> 3; 306 in -= len; 307 bits -= len << 3; 308 hold &= (1U << bits) - 1; 309 310 /* update state and return */ 311 strm->next_in = in; 312 strm->next_out = out; 313 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 314 strm->avail_out = (unsigned)(out < end ? 315 257 + (end - out) : 257 - (out - end)); 316 state->hold = hold; 317 state->bits = bits; 318 return; 319 } 320 321 /* 322 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 323 - Using bit fields for code structure 324 - Different op definition to avoid & for extra bits (do & for table bits) 325 - Three separate decoding do-loops for direct, window, and wnext == 0 326 - Special case for distance > 1 copies to do overlapped load and store copy 327 - Explicit branch predictions (based on measured branch probabilities) 328 - Deferring match copy and interspersed it with decoding subsequent codes 329 - Swapping literal/length else 330 - Swapping window/direct else 331 - Larger unrolled copy loops (three is about right) 332 - Moving len -= 3 statement into middle of loop 333 */ 334 335 #endif /* !ASMINF */ 336