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