inffast.c revision 131380
1/* inffast.c -- fast decoding 2 * Copyright (C) 1995-2003 Mark Adler 3 * For conditions of distribution and use, see copyright notice in zlib.h 4 */ 5 6#include <sys/cdefs.h> 7__FBSDID("$FreeBSD: head/lib/libz/inffast.c 131380 2004-06-30 23:54:46Z tjr $"); 8 9#include "zutil.h" 10#include "inftrees.h" 11#include "inflate.h" 12#include "inffast.h" 13 14#ifndef ASMINF 15 16/* Allow machine dependent optimization for post-increment or pre-increment. 17 Based on testing to date, 18 Pre-increment preferred for: 19 - PowerPC G3 (Adler) 20 - MIPS R5000 (Randers-Pehrson) 21 Post-increment preferred for: 22 - none 23 No measurable difference: 24 - Pentium III (Anderson) 25 - 68060 (Nikl) 26 */ 27#ifdef POSTINC 28# define OFF 0 29# define PUP(a) *(a)++ 30#else 31# define OFF 1 32# define PUP(a) *++(a) 33#endif 34 35/* 36 Decode literal, length, and distance codes and write out the resulting 37 literal and match bytes until either not enough input or output is 38 available, an end-of-block is encountered, or a data error is encountered. 39 When large enough input and output buffers are supplied to inflate(), for 40 example, a 16K input buffer and a 64K output buffer, more than 95% of the 41 inflate execution time is spent in this routine. 42 43 Entry assumptions: 44 45 state->mode == LEN 46 strm->avail_in >= 6 47 strm->avail_out >= 258 48 start >= strm->avail_out 49 state->bits < 8 50 51 On return, state->mode is one of: 52 53 LEN -- ran out of enough output space or enough available input 54 TYPE -- reached end of block code, inflate() to interpret next block 55 BAD -- error in block data 56 57 Notes: 58 59 - The maximum input bits used by a length/distance pair is 15 bits for the 60 length code, 5 bits for the length extra, 15 bits for the distance code, 61 and 13 bits for the distance extra. This totals 48 bits, or six bytes. 62 Therefore if strm->avail_in >= 6, then there is enough input to avoid 63 checking for available input while decoding. 64 65 - The maximum bytes that a single length/distance pair can output is 258 66 bytes, which is the maximum length that can be coded. inflate_fast() 67 requires strm->avail_out >= 258 for each loop to avoid checking for 68 output space. 69 */ 70void inflate_fast(strm, start) 71z_streamp strm; 72unsigned start; /* inflate()'s starting value for strm->avail_out */ 73{ 74 struct inflate_state FAR *state; 75 unsigned char FAR *in; /* local strm->next_in */ 76 unsigned char FAR *last; /* while in < last, enough input available */ 77 unsigned char FAR *out; /* local strm->next_out */ 78 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ 79 unsigned char FAR *end; /* while out < end, enough space available */ 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 wsize = state->wsize; 105 whave = state->whave; 106 write = state->write; 107 window = state->window; 108 hold = state->hold; 109 bits = state->bits; 110 lcode = state->lencode; 111 dcode = state->distcode; 112 lmask = (1U << state->lenbits) - 1; 113 dmask = (1U << state->distbits) - 1; 114 115 /* decode literals and length/distances until end-of-block or not enough 116 input data or output space */ 117 do { 118 if (bits < 15) { 119 hold += (unsigned long)(PUP(in)) << bits; 120 bits += 8; 121 hold += (unsigned long)(PUP(in)) << bits; 122 bits += 8; 123 } 124 this = lcode[hold & lmask]; 125 dolen: 126 op = (unsigned)(this.bits); 127 hold >>= op; 128 bits -= op; 129 op = (unsigned)(this.op); 130 if (op == 0) { /* literal */ 131 Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ? 132 "inflate: literal '%c'\n" : 133 "inflate: literal 0x%02x\n", this.val)); 134 PUP(out) = (unsigned char)(this.val); 135 } 136 else if (op & 16) { /* length base */ 137 len = (unsigned)(this.val); 138 op &= 15; /* number of extra bits */ 139 if (op) { 140 if (bits < op) { 141 hold += (unsigned long)(PUP(in)) << bits; 142 bits += 8; 143 } 144 len += (unsigned)hold & ((1U << op) - 1); 145 hold >>= op; 146 bits -= op; 147 } 148 Tracevv((stderr, "inflate: length %u\n", len)); 149 if (bits < 15) { 150 hold += (unsigned long)(PUP(in)) << bits; 151 bits += 8; 152 hold += (unsigned long)(PUP(in)) << bits; 153 bits += 8; 154 } 155 this = dcode[hold & dmask]; 156 dodist: 157 op = (unsigned)(this.bits); 158 hold >>= op; 159 bits -= op; 160 op = (unsigned)(this.op); 161 if (op & 16) { /* distance base */ 162 dist = (unsigned)(this.val); 163 op &= 15; /* number of extra bits */ 164 if (bits < op) { 165 hold += (unsigned long)(PUP(in)) << bits; 166 bits += 8; 167 if (bits < op) { 168 hold += (unsigned long)(PUP(in)) << bits; 169 bits += 8; 170 } 171 } 172 dist += (unsigned)hold & ((1U << op) - 1); 173 hold >>= op; 174 bits -= op; 175 Tracevv((stderr, "inflate: distance %u\n", dist)); 176 op = (unsigned)(out - beg); /* max distance in output */ 177 if (dist > op) { /* see if copy from window */ 178 op = dist - op; /* distance back in window */ 179 if (op > whave) { 180 strm->msg = (char *)"invalid distance too far back"; 181 state->mode = BAD; 182 break; 183 } 184 from = window - OFF; 185 if (write == 0) { /* very common case */ 186 from += wsize - op; 187 if (op < len) { /* some from window */ 188 len -= op; 189 do { 190 PUP(out) = PUP(from); 191 } while (--op); 192 from = out - dist; /* rest from output */ 193 } 194 } 195 else if (write < op) { /* wrap around window */ 196 from += wsize + write - op; 197 op -= write; 198 if (op < len) { /* some from end of window */ 199 len -= op; 200 do { 201 PUP(out) = PUP(from); 202 } while (--op); 203 from = window - OFF; 204 if (write < len) { /* some from start of window */ 205 op = write; 206 len -= op; 207 do { 208 PUP(out) = PUP(from); 209 } while (--op); 210 from = out - dist; /* rest from output */ 211 } 212 } 213 } 214 else { /* contiguous in window */ 215 from += write - op; 216 if (op < len) { /* some from window */ 217 len -= op; 218 do { 219 PUP(out) = PUP(from); 220 } while (--op); 221 from = out - dist; /* rest from output */ 222 } 223 } 224 while (len > 2) { 225 PUP(out) = PUP(from); 226 PUP(out) = PUP(from); 227 PUP(out) = PUP(from); 228 len -= 3; 229 } 230 if (len) { 231 PUP(out) = PUP(from); 232 if (len > 1) 233 PUP(out) = PUP(from); 234 } 235 } 236 else { 237 from = out - dist; /* copy direct from output */ 238 do { /* minimum length is three */ 239 PUP(out) = PUP(from); 240 PUP(out) = PUP(from); 241 PUP(out) = PUP(from); 242 len -= 3; 243 } while (len > 2); 244 if (len) { 245 PUP(out) = PUP(from); 246 if (len > 1) 247 PUP(out) = PUP(from); 248 } 249 } 250 } 251 else if ((op & 64) == 0) { /* 2nd level distance code */ 252 this = dcode[this.val + (hold & ((1U << op) - 1))]; 253 goto dodist; 254 } 255 else { 256 strm->msg = (char *)"invalid distance code"; 257 state->mode = BAD; 258 break; 259 } 260 } 261 else if ((op & 64) == 0) { /* 2nd level length code */ 262 this = lcode[this.val + (hold & ((1U << op) - 1))]; 263 goto dolen; 264 } 265 else if (op & 32) { /* end-of-block */ 266 Tracevv((stderr, "inflate: end of block\n")); 267 state->mode = TYPE; 268 break; 269 } 270 else { 271 strm->msg = (char *)"invalid literal/length code"; 272 state->mode = BAD; 273 break; 274 } 275 } while (in < last && out < end); 276 277 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 278 len = bits >> 3; 279 in -= len; 280 bits -= len << 3; 281 hold &= (1U << bits) - 1; 282 283 /* update state and return */ 284 strm->next_in = in + OFF; 285 strm->next_out = out + OFF; 286 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 287 strm->avail_out = (unsigned)(out < end ? 288 257 + (end - out) : 257 - (out - end)); 289 state->hold = hold; 290 state->bits = bits; 291 return; 292} 293 294/* 295 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 296 - Using bit fields for code structure 297 - Different op definition to avoid & for extra bits (do & for table bits) 298 - Three separate decoding do-loops for direct, window, and write == 0 299 - Special case for distance > 1 copies to do overlapped load and store copy 300 - Explicit branch predictions (based on measured branch probabilities) 301 - Deferring match copy and interspersed it with decoding subsequent codes 302 - Swapping literal/length else 303 - Swapping window/direct else 304 - Larger unrolled copy loops (three is about right) 305 - Moving len -= 3 statement into middle of loop 306 */ 307 308#endif /* !ASMINF */ 309