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 >= INFLATE_FAST_MIN_INPUT (6 bytes) 27 strm->avail_out >= INFLATE_FAST_MIN_OUTPUT (258 bytes) 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 INFLATE_FAST_MIN_INPUT: 6 bytes 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 INFLATE_FAST_MIN_OUTPUT: 258 bytes 48 49 - The maximum bytes that a single length/distance pair can output is 258 50 bytes, which is the maximum length that can be coded. inflate_fast() 51 requires strm->avail_out >= 258 for each loop to avoid checking for 52 available output space while decoding. 53 */ 54 void ZLIB_INTERNAL inflate_fast(strm, start) 55 z_streamp strm; 56 unsigned start; /* inflate()'s starting value for strm->avail_out */ 57 { 58 struct inflate_state FAR *state; 59 z_const unsigned char FAR *in; /* local strm->next_in */ 60 z_const unsigned char FAR *last; /* have enough input while in < last */ 61 unsigned char FAR *out; /* local strm->next_out */ 62 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ 63 unsigned char FAR *end; /* while out < end, enough space available */ 64 #ifdef INFLATE_STRICT 65 unsigned dmax; /* maximum distance from zlib header */ 66 #endif 67 unsigned wsize; /* window size or zero if not using window */ 68 unsigned whave; /* valid bytes in the window */ 69 unsigned wnext; /* window write index */ 70 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ 71 unsigned long hold; /* local strm->hold */ 72 unsigned bits; /* local strm->bits */ 73 code const FAR *lcode; /* local strm->lencode */ 74 code const FAR *dcode; /* local strm->distcode */ 75 unsigned lmask; /* mask for first level of length codes */ 76 unsigned dmask; /* mask for first level of distance codes */ 77 code here; /* retrieved table entry */ 78 unsigned op; /* code bits, operation, extra bits, or */ 79 /* window position, window bytes to copy */ 80 unsigned len; /* match length, unused bytes */ 81 unsigned dist; /* match distance */ 82 unsigned char FAR *from; /* where to copy match from */ 83 84 /* copy state to local variables */ 85 state = (struct inflate_state FAR *)strm->state; 86 in = strm->next_in; 87 last = in + (strm->avail_in - (INFLATE_FAST_MIN_INPUT - 1)); 88 out = strm->next_out; 89 beg = out - (start - strm->avail_out); 90 end = out + (strm->avail_out - (INFLATE_FAST_MIN_OUTPUT - 1)); 91 #ifdef INFLATE_STRICT 92 dmax = state->dmax; 93 #endif 94 wsize = state->wsize; 95 whave = state->whave; 96 wnext = state->wnext; 97 window = state->window; 98 hold = state->hold; 99 bits = state->bits; 100 lcode = state->lencode; 101 dcode = state->distcode; 102 lmask = (1U << state->lenbits) - 1; 103 dmask = (1U << state->distbits) - 1; 104 105 /* decode literals and length/distances until end-of-block or not enough 106 input data or output space */ 107 do { 108 if (bits < 15) { 109 hold += (unsigned long)(*in++) << bits; 110 bits += 8; 111 hold += (unsigned long)(*in++) << bits; 112 bits += 8; 113 } 114 here = lcode[hold & lmask]; 115 dolen: 116 op = (unsigned)(here.bits); 117 hold >>= op; 118 bits -= op; 119 op = (unsigned)(here.op); 120 if (op == 0) { /* literal */ 121 Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ? 122 "inflate: literal '%c'\n" : 123 "inflate: literal 0x%02x\n", here.val)); 124 *out++ = (unsigned char)(here.val); 125 } 126 else if (op & 16) { /* length base */ 127 len = (unsigned)(here.val); 128 op &= 15; /* number of extra bits */ 129 if (op) { 130 if (bits < op) { 131 hold += (unsigned long)(*in++) << bits; 132 bits += 8; 133 } 134 len += (unsigned)hold & ((1U << op) - 1); 135 hold >>= op; 136 bits -= op; 137 } 138 Tracevv((stderr, "inflate: length %u\n", len)); 139 if (bits < 15) { 140 hold += (unsigned long)(*in++) << bits; 141 bits += 8; 142 hold += (unsigned long)(*in++) << bits; 143 bits += 8; 144 } 145 here = dcode[hold & dmask]; 146 dodist: 147 op = (unsigned)(here.bits); 148 hold >>= op; 149 bits -= op; 150 op = (unsigned)(here.op); 151 if (op & 16) { /* distance base */ 152 dist = (unsigned)(here.val); 153 op &= 15; /* number of extra bits */ 154 if (bits < op) { 155 hold += (unsigned long)(*in++) << bits; 156 bits += 8; 157 if (bits < op) { 158 hold += (unsigned long)(*in++) << bits; 159 bits += 8; 160 } 161 } 162 dist += (unsigned)hold & ((1U << op) - 1); 163 #ifdef INFLATE_STRICT 164 if (dist > dmax) { 165 strm->msg = (char *)"invalid distance too far back"; 166 state->mode = BAD; 167 break; 168 } 169 #endif 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 if (state->sane) { 178 strm->msg = 179 (char *)"invalid distance too far back"; 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 strm->msg = (char *)"invalid distance code"; 276 state->mode = BAD; 277 break; 278 } 279 } 280 else if ((op & 64) == 0) { /* 2nd level length code */ 281 here = lcode[here.val + (hold & ((1U << op) - 1))]; 282 goto dolen; 283 } 284 else if (op & 32) { /* end-of-block */ 285 Tracevv((stderr, "inflate: end of block\n")); 286 state->mode = TYPE; 287 break; 288 } 289 else { 290 strm->msg = (char *)"invalid literal/length code"; 291 state->mode = BAD; 292 break; 293 } 294 } while (in < last && out < end); 295 296 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 297 len = bits >> 3; 298 in -= len; 299 bits -= len << 3; 300 hold &= (1U << bits) - 1; 301 302 /* update state and return */ 303 strm->next_in = in; 304 strm->next_out = out; 305 strm->avail_in = (unsigned)(in < last ? 306 (INFLATE_FAST_MIN_INPUT - 1) + (last - in) : 307 (INFLATE_FAST_MIN_INPUT - 1) - (in - last)); 308 strm->avail_out = (unsigned)(out < end ? 309 (INFLATE_FAST_MIN_OUTPUT - 1) + (end - out) : 310 (INFLATE_FAST_MIN_OUTPUT - 1) - (out - end)); 311 state->hold = hold; 312 state->bits = bits; 313 return; 314 } 315 316 /* 317 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 318 - Using bit fields for code structure 319 - Different op definition to avoid & for extra bits (do & for table bits) 320 - Three separate decoding do-loops for direct, window, and wnext == 0 321 - Special case for distance > 1 copies to do overlapped load and store copy 322 - Explicit branch predictions (based on measured branch probabilities) 323 - Deferring match copy and interspersed it with decoding subsequent codes 324 - Swapping literal/length else 325 - Swapping window/direct else 326 - Larger unrolled copy loops (three is about right) 327 - Moving len -= 3 statement into middle of loop 328 */ 329 330 #endif /* !ASMINF */ 331