1 /* inffast.c -- fast decoding 2 * Copyright (C) 1995-2008, 2010 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 #ifndef ASMINF 12 13 /* Allow machine dependent optimization for post-increment or pre-increment. 14 Based on testing to date, 15 Pre-increment preferred for: 16 - PowerPC G3 (Adler) 17 - MIPS R5000 (Randers-Pehrson) 18 Post-increment preferred for: 19 - none 20 No measurable difference: 21 - Pentium III (Anderson) 22 - M68060 (Nikl) 23 */ 24 #ifdef POSTINC 25 # define OFF 0 26 # define PUP(a) *(a)++ 27 #else 28 # define OFF 1 29 # define PUP(a) *++(a) 30 #endif 31 32 /* 33 Decode literal, length, and distance codes and write out the resulting 34 literal and match bytes until either not enough input or output is 35 available, an end-of-block is encountered, or a data error is encountered. 36 When large enough input and output buffers are supplied to inflate(), for 37 example, a 16K input buffer and a 64K output buffer, more than 95% of the 38 inflate execution time is spent in this routine. 39 40 Entry assumptions: 41 42 state->mode == LEN 43 strm->avail_in >= 6 44 strm->avail_out >= 258 45 start >= strm->avail_out 46 state->bits < 8 47 48 On return, state->mode is one of: 49 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 */ 67 void ZLIB_INTERNAL inflate_fast(strm, start) 68 z_streamp strm; 69 unsigned 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 #ifdef INFLATE_STRICT 78 unsigned dmax; /* maximum distance from zlib header */ 79 #endif 80 unsigned wsize; /* window size or zero if not using window */ 81 unsigned whave; /* valid bytes in the window */ 82 unsigned wnext; /* window write index */ 83 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ 84 unsigned long hold; /* local strm->hold */ 85 unsigned bits; /* local strm->bits */ 86 code const FAR *lcode; /* local strm->lencode */ 87 code const FAR *dcode; /* local strm->distcode */ 88 unsigned lmask; /* mask for first level of length codes */ 89 unsigned dmask; /* mask for first level of distance codes */ 90 code here; /* retrieved table entry */ 91 unsigned op; /* code bits, operation, extra bits, or */ 92 /* window position, window bytes to copy */ 93 unsigned len; /* match length, unused bytes */ 94 unsigned dist; /* match distance */ 95 unsigned char FAR *from; /* where to copy match from */ 96 97 /* copy state to local variables */ 98 state = (struct inflate_state FAR *)strm->state; 99 in = strm->next_in - OFF; 100 last = in + (strm->avail_in - 5); 101 out = strm->next_out - OFF; 102 beg = out - (start - strm->avail_out); 103 end = out + (strm->avail_out - 257); 104 #ifdef INFLATE_STRICT 105 dmax = state->dmax; 106 #endif 107 wsize = state->wsize; 108 whave = state->whave; 109 wnext = state->wnext; 110 window = state->window; 111 hold = state->hold; 112 bits = state->bits; 113 lcode = state->lencode; 114 dcode = state->distcode; 115 lmask = (1U << state->lenbits) - 1; 116 dmask = (1U << state->distbits) - 1; 117 118 /* decode literals and length/distances until end-of-block or not enough 119 input data or output space */ 120 do { 121 if (bits < 15) { 122 hold += (unsigned long)(PUP(in)) << bits; 123 bits += 8; 124 hold += (unsigned long)(PUP(in)) << bits; 125 bits += 8; 126 } 127 here = lcode[hold & lmask]; 128 dolen: 129 op = (unsigned)(here.bits); 130 hold >>= op; 131 bits -= op; 132 op = (unsigned)(here.op); 133 if (op == 0) { /* literal */ 134 Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ? 135 "inflate: literal '%c'\n" : 136 "inflate: literal 0x%02x\n", here.val)); 137 PUP(out) = (unsigned char)(here.val); 138 } 139 else if (op & 16) { /* length base */ 140 len = (unsigned)(here.val); 141 op &= 15; /* number of extra bits */ 142 if (op) { 143 if (bits < op) { 144 hold += (unsigned long)(PUP(in)) << bits; 145 bits += 8; 146 } 147 len += (unsigned)hold & ((1U << op) - 1); 148 hold >>= op; 149 bits -= op; 150 } 151 Tracevv((stderr, "inflate: length %u\n", len)); 152 if (bits < 15) { 153 hold += (unsigned long)(PUP(in)) << bits; 154 bits += 8; 155 hold += (unsigned long)(PUP(in)) << bits; 156 bits += 8; 157 } 158 here = dcode[hold & dmask]; 159 dodist: 160 op = (unsigned)(here.bits); 161 hold >>= op; 162 bits -= op; 163 op = (unsigned)(here.op); 164 if (op & 16) { /* distance base */ 165 dist = (unsigned)(here.val); 166 op &= 15; /* number of extra bits */ 167 if (bits < op) { 168 hold += (unsigned long)(PUP(in)) << bits; 169 bits += 8; 170 if (bits < op) { 171 hold += (unsigned long)(PUP(in)) << bits; 172 bits += 8; 173 } 174 } 175 dist += (unsigned)hold & ((1U << op) - 1); 176 #ifdef INFLATE_STRICT 177 if (dist > dmax) { 178 strm->msg = (char *)"invalid distance too far back"; 179 state->mode = BAD; 180 break; 181 } 182 #endif 183 hold >>= op; 184 bits -= op; 185 Tracevv((stderr, "inflate: distance %u\n", dist)); 186 op = (unsigned)(out - beg); /* max distance in output */ 187 if (dist > op) { /* see if copy from window */ 188 op = dist - op; /* distance back in window */ 189 if (op > whave) { 190 if (state->sane) { 191 strm->msg = 192 (char *)"invalid distance too far back"; 193 state->mode = BAD; 194 break; 195 } 196 #ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR 197 if (len <= op - whave) { 198 do { 199 PUP(out) = 0; 200 } while (--len); 201 continue; 202 } 203 len -= op - whave; 204 do { 205 PUP(out) = 0; 206 } while (--op > whave); 207 if (op == 0) { 208 from = out - dist; 209 do { 210 PUP(out) = PUP(from); 211 } while (--len); 212 continue; 213 } 214 #endif 215 } 216 from = window - OFF; 217 if (wnext == 0) { /* very common case */ 218 from += wsize - op; 219 if (op < len) { /* some from window */ 220 len -= op; 221 do { 222 PUP(out) = PUP(from); 223 } while (--op); 224 from = out - dist; /* rest from output */ 225 } 226 } 227 else if (wnext < op) { /* wrap around window */ 228 from += wsize + wnext - op; 229 op -= wnext; 230 if (op < len) { /* some from end of window */ 231 len -= op; 232 do { 233 PUP(out) = PUP(from); 234 } while (--op); 235 from = window - OFF; 236 if (wnext < len) { /* some from start of window */ 237 op = wnext; 238 len -= op; 239 do { 240 PUP(out) = PUP(from); 241 } while (--op); 242 from = out - dist; /* rest from output */ 243 } 244 } 245 } 246 else { /* contiguous in window */ 247 from += wnext - op; 248 if (op < len) { /* some from window */ 249 len -= op; 250 do { 251 PUP(out) = PUP(from); 252 } while (--op); 253 from = out - dist; /* rest from output */ 254 } 255 } 256 while (len > 2) { 257 PUP(out) = PUP(from); 258 PUP(out) = PUP(from); 259 PUP(out) = PUP(from); 260 len -= 3; 261 } 262 if (len) { 263 PUP(out) = PUP(from); 264 if (len > 1) 265 PUP(out) = PUP(from); 266 } 267 } 268 else { 269 from = out - dist; /* copy direct from output */ 270 do { /* minimum length is three */ 271 PUP(out) = PUP(from); 272 PUP(out) = PUP(from); 273 PUP(out) = PUP(from); 274 len -= 3; 275 } while (len > 2); 276 if (len) { 277 PUP(out) = PUP(from); 278 if (len > 1) 279 PUP(out) = PUP(from); 280 } 281 } 282 } 283 else if ((op & 64) == 0) { /* 2nd level distance code */ 284 here = dcode[here.val + (hold & ((1U << op) - 1))]; 285 goto dodist; 286 } 287 else { 288 strm->msg = (char *)"invalid distance code"; 289 state->mode = BAD; 290 break; 291 } 292 } 293 else if ((op & 64) == 0) { /* 2nd level length code */ 294 here = lcode[here.val + (hold & ((1U << op) - 1))]; 295 goto dolen; 296 } 297 else if (op & 32) { /* end-of-block */ 298 Tracevv((stderr, "inflate: end of block\n")); 299 state->mode = TYPE; 300 break; 301 } 302 else { 303 strm->msg = (char *)"invalid literal/length code"; 304 state->mode = BAD; 305 break; 306 } 307 } while (in < last && out < end); 308 309 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 310 len = bits >> 3; 311 in -= len; 312 bits -= len << 3; 313 hold &= (1U << bits) - 1; 314 315 /* update state and return */ 316 strm->next_in = in + OFF; 317 strm->next_out = out + OFF; 318 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 319 strm->avail_out = (unsigned)(out < end ? 320 257 + (end - out) : 257 - (out - end)); 321 state->hold = hold; 322 state->bits = bits; 323 return; 324 } 325 326 /* 327 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 328 - Using bit fields for code structure 329 - Different op definition to avoid & for extra bits (do & for table bits) 330 - Three separate decoding do-loops for direct, window, and wnext == 0 331 - Special case for distance > 1 copies to do overlapped load and store copy 332 - Explicit branch predictions (based on measured branch probabilities) 333 - Deferring match copy and interspersed it with decoding subsequent codes 334 - Swapping literal/length else 335 - Swapping window/direct else 336 - Larger unrolled copy loops (three is about right) 337 - Moving len -= 3 statement into middle of loop 338 */ 339 340 #endif /* !ASMINF */ 341
