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 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 strm->msg = 175 (char *)"invalid distance too far back"; 176 state->mode = BAD; 177 break; 178 } 179 #ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR 180 if (len <= op - whave) { 181 do { 182 *out++ = 0; 183 } while (--len); 184 continue; 185 } 186 len -= op - whave; 187 do { 188 *out++ = 0; 189 } while (--op > whave); 190 if (op == 0) { 191 from = out - dist; 192 do { 193 *out++ = *from++; 194 } while (--len); 195 continue; 196 } 197 #endif 198 } 199 from = window; 200 if (wnext == 0) { /* very common case */ 201 from += wsize - op; 202 if (op < len) { /* some from window */ 203 len -= op; 204 do { 205 *out++ = *from++; 206 } while (--op); 207 from = out - dist; /* rest from output */ 208 } 209 } 210 else if (wnext < op) { /* wrap around window */ 211 from += wsize + wnext - op; 212 op -= wnext; 213 if (op < len) { /* some from end of window */ 214 len -= op; 215 do { 216 *out++ = *from++; 217 } while (--op); 218 from = window; 219 if (wnext < len) { /* some from start of window */ 220 op = wnext; 221 len -= op; 222 do { 223 *out++ = *from++; 224 } while (--op); 225 from = out - dist; /* rest from output */ 226 } 227 } 228 } 229 else { /* contiguous in window */ 230 from += wnext - op; 231 if (op < len) { /* some from window */ 232 len -= op; 233 do { 234 *out++ = *from++; 235 } while (--op); 236 from = out - dist; /* rest from output */ 237 } 238 } 239 while (len > 2) { 240 *out++ = *from++; 241 *out++ = *from++; 242 *out++ = *from++; 243 len -= 3; 244 } 245 if (len) { 246 *out++ = *from++; 247 if (len > 1) 248 *out++ = *from++; 249 } 250 } 251 else { 252 from = out - dist; /* copy direct from output */ 253 do { /* minimum length is three */ 254 *out++ = *from++; 255 *out++ = *from++; 256 *out++ = *from++; 257 len -= 3; 258 } while (len > 2); 259 if (len) { 260 *out++ = *from++; 261 if (len > 1) 262 *out++ = *from++; 263 } 264 } 265 } 266 else if ((op & 64) == 0) { /* 2nd level distance code */ 267 here = dcode[here.val + (hold & ((1U << op) - 1))]; 268 goto dodist; 269 } 270 else { 271 strm->msg = (char *)"invalid distance code"; 272 state->mode = BAD; 273 break; 274 } 275 } 276 else if ((op & 64) == 0) { /* 2nd level length code */ 277 here = lcode[here.val + (hold & ((1U << op) - 1))]; 278 goto dolen; 279 } 280 else if (op & 32) { /* end-of-block */ 281 Tracevv((stderr, "inflate: end of block\n")); 282 state->mode = TYPE; 283 break; 284 } 285 else { 286 strm->msg = (char *)"invalid literal/length code"; 287 state->mode = BAD; 288 break; 289 } 290 } while (in < last && out < end); 291 292 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 293 len = bits >> 3; 294 in -= len; 295 bits -= len << 3; 296 hold &= (1U << bits) - 1; 297 298 /* update state and return */ 299 strm->next_in = in; 300 strm->next_out = out; 301 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 302 strm->avail_out = (unsigned)(out < end ? 303 257 + (end - out) : 257 - (out - end)); 304 state->hold = hold; 305 state->bits = bits; 306 return; 307 } 308 309 /* 310 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 311 - Using bit fields for code structure 312 - Different op definition to avoid & for extra bits (do & for table bits) 313 - Three separate decoding do-loops for direct, window, and wnext == 0 314 - Special case for distance > 1 copies to do overlapped load and store copy 315 - Explicit branch predictions (based on measured branch probabilities) 316 - Deferring match copy and interspersed it with decoding subsequent codes 317 - Swapping literal/length else 318 - Swapping window/direct else 319 - Larger unrolled copy loops (three is about right) 320 - Moving len -= 3 statement into middle of loop 321 */ 322 323 #endif /* !ASMINF */ 324
