inffast.c (12568B)
1 /* inffast.c -- fast decoding 2 * Copyright (C) 1995-2004 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 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 write; /* 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 this; /* 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 write = state->write; 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 this = lcode[hold & lmask]; 128 dolen: 129 op = (unsigned)(this.bits); 130 hold >>= op; 131 bits -= op; 132 op = (unsigned)(this.op); 133 if (op == 0) { /* literal */ 134 Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ? 135 "inflate: literal '%c'\n" : 136 "inflate: literal 0x%02x\n", this.val)); 137 PUP(out) = (unsigned char)(this.val); 138 } 139 else if (op & 16) { /* length base */ 140 len = (unsigned)(this.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 this = dcode[hold & dmask]; 159 dodist: 160 op = (unsigned)(this.bits); 161 hold >>= op; 162 bits -= op; 163 op = (unsigned)(this.op); 164 if (op & 16) { /* distance base */ 165 dist = (unsigned)(this.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 strm->msg = (char *)"invalid distance too far back"; 191 state->mode = BAD; 192 break; 193 } 194 from = window - OFF; 195 if (write == 0) { /* very common case */ 196 from += wsize - op; 197 if (op < len) { /* some from window */ 198 len -= op; 199 do { 200 PUP(out) = PUP(from); 201 } while (--op); 202 from = out - dist; /* rest from output */ 203 } 204 } 205 else if (write < op) { /* wrap around window */ 206 from += wsize + write - op; 207 op -= write; 208 if (op < len) { /* some from end of window */ 209 len -= op; 210 do { 211 PUP(out) = PUP(from); 212 } while (--op); 213 from = window - OFF; 214 if (write < len) { /* some from start of window */ 215 op = write; 216 len -= op; 217 do { 218 PUP(out) = PUP(from); 219 } while (--op); 220 from = out - dist; /* rest from output */ 221 } 222 } 223 } 224 else { /* contiguous in window */ 225 from += write - op; 226 if (op < len) { /* some from window */ 227 len -= op; 228 do { 229 PUP(out) = PUP(from); 230 } while (--op); 231 from = out - dist; /* rest from output */ 232 } 233 } 234 while (len > 2) { 235 PUP(out) = PUP(from); 236 PUP(out) = PUP(from); 237 PUP(out) = PUP(from); 238 len -= 3; 239 } 240 if (len) { 241 PUP(out) = PUP(from); 242 if (len > 1) 243 PUP(out) = PUP(from); 244 } 245 } 246 else { 247 from = out - dist; /* copy direct from output */ 248 do { /* minimum length is three */ 249 PUP(out) = PUP(from); 250 PUP(out) = PUP(from); 251 PUP(out) = PUP(from); 252 len -= 3; 253 } while (len > 2); 254 if (len) { 255 PUP(out) = PUP(from); 256 if (len > 1) 257 PUP(out) = PUP(from); 258 } 259 } 260 } 261 else if ((op & 64) == 0) { /* 2nd level distance code */ 262 this = dcode[this.val + (hold & ((1U << op) - 1))]; 263 goto dodist; 264 } 265 else { 266 strm->msg = (char *)"invalid distance code"; 267 state->mode = BAD; 268 break; 269 } 270 } 271 else if ((op & 64) == 0) { /* 2nd level length code */ 272 this = lcode[this.val + (hold & ((1U << op) - 1))]; 273 goto dolen; 274 } 275 else if (op & 32) { /* end-of-block */ 276 Tracevv((stderr, "inflate: end of block\n")); 277 state->mode = TYPE; 278 break; 279 } 280 else { 281 strm->msg = (char *)"invalid literal/length code"; 282 state->mode = BAD; 283 break; 284 } 285 } while (in < last && out < end); 286 287 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 288 len = bits >> 3; 289 in -= len; 290 bits -= len << 3; 291 hold &= (1U << bits) - 1; 292 293 /* update state and return */ 294 strm->next_in = in + OFF; 295 strm->next_out = out + OFF; 296 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 297 strm->avail_out = (unsigned)(out < end ? 298 257 + (end - out) : 257 - (out - end)); 299 state->hold = hold; 300 state->bits = bits; 301 return; 302 } 303 304 /* 305 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 306 - Using bit fields for code structure 307 - Different op definition to avoid & for extra bits (do & for table bits) 308 - Three separate decoding do-loops for direct, window, and write == 0 309 - Special case for distance > 1 copies to do overlapped load and store copy 310 - Explicit branch predictions (based on measured branch probabilities) 311 - Deferring match copy and interspersed it with decoding subsequent codes 312 - Swapping literal/length else 313 - Swapping window/direct else 314 - Larger unrolled copy loops (three is about right) 315 - Moving len -= 3 statement into middle of loop 316 */ 317 318 #endif /* !ASMINF */