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 */ 70 185 { 71 185 struct inflate_state FAR *state; 72 185 unsigned char FAR *in; /* local strm->next_in */ 73 185 unsigned char FAR *last; /* while in < last, enough input available */ 74 185 unsigned char FAR *out; /* local strm->next_out */ 75 185 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ 76 185 unsigned char FAR *end; /* while out < end, enough space available */ 77 185 unsigned wsize; /* window size or zero if not using window */ 78 185 unsigned whave; /* valid bytes in the window */ 79 185 unsigned write; /* window write index */ 80 185 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ 81 185 unsigned long hold; /* local strm->hold */ 82 185 unsigned bits; /* local strm->bits */ 83 185 code const FAR *lcode; /* local strm->lencode */ 84 185 code const FAR *dcode; /* local strm->distcode */ 85 185 unsigned lmask; /* mask for first level of length codes */ 86 185 unsigned dmask; /* mask for first level of distance codes */ 87 185 code this; /* retrieved table entry */ 88 185 unsigned op; /* code bits, operation, extra bits, or */ 89 /* window position, window bytes to copy */ 90 185 unsigned len; /* match length, unused bytes */ 91 185 unsigned dist; /* match distance */ 92 185 unsigned char FAR *from; /* where to copy match from */ 93 94 /* copy state to local variables */ 95 185 state = (struct inflate_state FAR *)strm->state; 96 185 in = strm->next_in - OFF; 97 185 last = in + (strm->avail_in - 5); 98 185 out = strm->next_out - OFF; 99 185 beg = out - (start - strm->avail_out); 100 185 end = out + (strm->avail_out - 257); 101 185 wsize = state->wsize; 102 185 whave = state->whave; 103 185 write = state->write; 104 185 window = state->window; 105 185 hold = state->hold; 106 185 bits = state->bits; 107 185 lcode = state->lencode; 108 185 dcode = state->distcode; 109 185 lmask = (1U << state->lenbits) - 1; 110 185 dmask = (1U << state->distbits) - 1; 111 112 /* decode literals and length/distances until end-of-block or not enough 113 input data or output space */ 114 82156 do { 115 82156 if (bits < 15) { 116 30470 hold += (unsigned long)(PUP(in)) << bits; 117 30470 bits += 8; 118 30470 hold += (unsigned long)(PUP(in)) << bits; 119 30470 bits += 8; 120 } 121 82156 this = lcode[hold & lmask]; 122 dolen: 123 82783 op = (unsigned)(this.bits); 124 82783 hold >>= op; 125 82783 bits -= op; 126 82783 op = (unsigned)(this.op); 127 82783 if (op == 0) { /* literal */ 128 Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ? 129 "inflate: literal '%c'\n" : 130 "inflate: literal 0x%02x\n", this.val)); 131 64107 PUP(out) = (unsigned char)(this.val); 132 } 133 18676 else if (op & 16) { /* length base */ 134 18011 len = (unsigned)(this.val); 135 18011 op &= 15; /* number of extra bits */ 136 18011 if (op) { 137 3504 if (bits < op) { 138 ###### hold += (unsigned long)(PUP(in)) << bits; 139 ###### bits += 8; 140 } 141 3504 len += (unsigned)hold & ((1U << op) - 1); 142 3504 hold >>= op; 143 3504 bits -= op; 144 } 145 Tracevv((stderr, "inflate: length %u\n", len)); 146 18011 if (bits < 15) { 147 5192 hold += (unsigned long)(PUP(in)) << bits; 148 5192 bits += 8; 149 5192 hold += (unsigned long)(PUP(in)) << bits; 150 5192 bits += 8; 151 } 152 18011 this = dcode[hold & dmask]; 153 dodist: 154 18502 op = (unsigned)(this.bits); 155 18502 hold >>= op; 156 18502 bits -= op; 157 18502 op = (unsigned)(this.op); 158 18502 if (op & 16) { /* distance base */ 159 18011 dist = (unsigned)(this.val); 160 18011 op &= 15; /* number of extra bits */ 161 18011 if (bits < op) { 162 231 hold += (unsigned long)(PUP(in)) << bits; 163 231 bits += 8; 164 231 if (bits < op) { 165 ###### hold += (unsigned long)(PUP(in)) << bits; 166 ###### bits += 8; 167 } 168 } 169 18011 dist += (unsigned)hold & ((1U << op) - 1); 170 18011 hold >>= op; 171 18011 bits -= op; 172 Tracevv((stderr, "inflate: distance %u\n", dist)); 173 18011 op = (unsigned)(out - beg); /* max distance in output */ 174 18011 if (dist > op) { /* see if copy from window */ 175 3259 op = dist - op; /* distance back in window */ 176 3259 if (op > whave) { 177 ###### strm->msg = (char *)"invalid distance too far back"; 178 ###### state->mode = BAD; 179 ###### break; 180 } 181 3259 from = window - OFF; 182 3259 if (write == 0) { /* very common case */ 183 1 from += wsize - op; 184 1 if (op < len) { /* some from window */ 185 1 len -= op; 186 1 do { 187 1 PUP(out) = PUP(from); 188 1 } while (--op); 189 1 from = out - dist; /* rest from output */ 190 } 191 } 192 3258 else if (write < op) { /* wrap around window */ 193 ###### from += wsize + write - op; 194 ###### op -= write; 195 ###### if (op < len) { /* some from end of window */ 196 ###### len -= op; 197 ###### do { 198 ###### PUP(out) = PUP(from); 199 ###### } while (--op); 200 ###### from = window - OFF; 201 ###### if (write < len) { /* some from start of window */ 202 ###### op = write; 203 ###### len -= op; 204 ###### do { 205 ###### PUP(out) = PUP(from); 206 ###### } while (--op); 207 ###### from = out - dist; /* rest from output */ 208 } 209 } 210 } 211 else { /* contiguous in window */ 212 3258 from += write - op; 213 3258 if (op < len) { /* some from window */ 214 18 len -= op; 215 2130 do { 216 2130 PUP(out) = PUP(from); 217 2130 } while (--op); 218 18 from = out - dist; /* rest from output */ 219 } 220 } 221 14885 while (len > 2) { 222 11626 PUP(out) = PUP(from); 223 11626 PUP(out) = PUP(from); 224 11626 PUP(out) = PUP(from); 225 11626 len -= 3; 226 } 227 3259 if (len) { 228 1831 PUP(out) = PUP(from); 229 1831 if (len > 1) 230 735 PUP(out) = PUP(from); 231 } 232 } 233 else { 234 14752 from = out - dist; /* copy direct from output */ 235 95777 do { /* minimum length is three */ 236 95777 PUP(out) = PUP(from); 237 95777 PUP(out) = PUP(from); 238 95777 PUP(out) = PUP(from); 239 95777 len -= 3; 240 95777 } while (len > 2); 241 14752 if (len) { 242 8874 PUP(out) = PUP(from); 243 8874 if (len > 1) 244 3674 PUP(out) = PUP(from); 245 } 246 } 247 } 248 491 else if ((op & 64) == 0) { /* 2nd level distance code */ 249 491 this = dcode[this.val + (hold & ((1U << op) - 1))]; 250 491 goto dodist; 251 } 252 else { 253 ###### strm->msg = (char *)"invalid distance code"; 254 ###### state->mode = BAD; 255 ###### break; 256 } 257 } 258 665 else if ((op & 64) == 0) { /* 2nd level length code */ 259 627 this = lcode[this.val + (hold & ((1U << op) - 1))]; 260 627 goto dolen; 261 } 262 38 else if (op & 32) { /* end-of-block */ 263 Tracevv((stderr, "inflate: end of block\n")); 264 38 state->mode = TYPE; 265 38 break; 266 } 267 else { 268 ###### strm->msg = (char *)"invalid literal/length code"; 269 ###### state->mode = BAD; 270 ###### break; 271 } 272 82118 } while (in < last && out < end); 273 274 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 275 185 len = bits >> 3; 276 185 in -= len; 277 185 bits -= len << 3; 278 185 hold &= (1U << bits) - 1; 279 280 /* update state and return */ 281 185 strm->next_in = in + OFF; 282 185 strm->next_out = out + OFF; 283 185 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 284 185 strm->avail_out = (unsigned)(out < end ? 285 257 + (end - out) : 257 - (out - end)); 286 185 state->hold = hold; 287 185 state->bits = bits; 288 return; 289 } 290 291 /* 292 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 293 - Using bit fields for code structure 294 - Different op definition to avoid & for extra bits (do & for table bits) 295 - Three separate decoding do-loops for direct, window, and write == 0 296 - Special case for distance > 1 copies to do overlapped load and store copy 297 - Explicit branch predictions (based on measured branch probabilities) 298 - Deferring match copy and interspersed it with decoding subsequent codes 299 - Swapping literal/length else 300 - Swapping window/direct else 301 - Larger unrolled copy loops (three is about right) 302 - Moving len -= 3 statement into middle of loop 303 */ 304 305 #endif /* !ASMINF */