1 /* $OpenBSD: inffast.c,v 1.8 2019/06/01 11:39:57 jca Exp $ */ 2 /* inffast.c -- fast decoding 3 * Copyright (C) 1995-2004 Mark Adler 4 * For conditions of distribution and use, see copyright notice in zlib.h 5 */ 6 7 #include "zutil.h" 8 #include "inftrees.h" 9 #include "inflate.h" 10 #include "inffast.h" 11 12 #ifndef ASMINF 13 14 /* Allow machine dependent optimization for post-increment or pre-increment. 15 Based on testing to date, 16 Pre-increment preferred for: 17 - PowerPC G3 (Adler) 18 - MIPS R5000 (Randers-Pehrson) 19 Post-increment preferred for: 20 - none 21 No measurable difference: 22 - Pentium III (Anderson) 23 - M68060 (Nikl) 24 */ 25 #ifdef POSTINC 26 # define OFF 0 27 # define PUP(a) *(a)++ 28 #else 29 # define OFF 1 30 # define PUP(a) *++(a) 31 #endif 32 33 /* 34 Decode literal, length, and distance codes and write out the resulting 35 literal and match bytes until either not enough input or output is 36 available, an end-of-block is encountered, or a data error is encountered. 37 When large enough input and output buffers are supplied to inflate(), for 38 example, a 16K input buffer and a 64K output buffer, more than 95% of the 39 inflate execution time is spent in this routine. 40 41 Entry assumptions: 42 43 state->mode == LEN 44 strm->avail_in >= 6 45 strm->avail_out >= 258 46 start >= strm->avail_out 47 state->bits < 8 48 49 On return, state->mode is one of: 50 51 LEN -- ran out of enough output space or enough available input 52 TYPE -- reached end of block code, inflate() to interpret next block 53 BAD -- error in block data 54 55 Notes: 56 57 - The maximum input bits used by a length/distance pair is 15 bits for the 58 length code, 5 bits for the length extra, 15 bits for the distance code, 59 and 13 bits for the distance extra. This totals 48 bits, or six bytes. 60 Therefore if strm->avail_in >= 6, then there is enough input to avoid 61 checking for available input while decoding. 62 63 - The maximum bytes that a single length/distance pair can output is 258 64 bytes, which is the maximum length that can be coded. inflate_fast() 65 requires strm->avail_out >= 258 for each loop to avoid checking for 66 output space. 67 */ 68 void inflate_fast(strm, start) 69 z_streamp strm; 70 unsigned start; /* inflate()'s starting value for strm->avail_out */ 71 { 72 struct inflate_state FAR *state; 73 z_const unsigned char FAR *in; /* local strm->next_in */ 74 z_const unsigned char FAR *last; /* while in < last, enough input available */ 75 unsigned char FAR *out; /* local strm->next_out */ 76 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ 77 unsigned char FAR *end; /* while out < end, enough space available */ 78 #ifdef INFLATE_STRICT 79 unsigned dmax; /* maximum distance from zlib header */ 80 #endif 81 unsigned wsize; /* window size or zero if not using window */ 82 unsigned whave; /* valid bytes in the window */ 83 unsigned write; /* window write index */ 84 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ 85 unsigned long hold; /* local strm->hold */ 86 unsigned bits; /* local strm->bits */ 87 code const FAR *lcode; /* local strm->lencode */ 88 code const FAR *dcode; /* local strm->distcode */ 89 unsigned lmask; /* mask for first level of length codes */ 90 unsigned dmask; /* mask for first level of distance codes */ 91 code this; /* retrieved table entry */ 92 unsigned op; /* code bits, operation, extra bits, or */ 93 /* window position, window bytes to copy */ 94 unsigned len; /* match length, unused bytes */ 95 unsigned dist; /* match distance */ 96 unsigned char FAR *from; /* where to copy match from */ 97 98 /* copy state to local variables */ 99 state = (struct inflate_state FAR *)strm->state; 100 in = strm->next_in - OFF; 101 last = in + (strm->avail_in - 5); 102 out = strm->next_out - OFF; 103 beg = out - (start - strm->avail_out); 104 end = out + (strm->avail_out - 257); 105 #ifdef INFLATE_STRICT 106 dmax = state->dmax; 107 #endif 108 wsize = state->wsize; 109 whave = state->whave; 110 write = state->write; 111 window = state->window; 112 hold = state->hold; 113 bits = state->bits; 114 lcode = state->lencode; 115 dcode = state->distcode; 116 lmask = (1U << state->lenbits) - 1; 117 dmask = (1U << state->distbits) - 1; 118 119 /* decode literals and length/distances until end-of-block or not enough 120 input data or output space */ 121 do { 122 if (bits < 15) { 123 hold += (unsigned long)(PUP(in)) << bits; 124 bits += 8; 125 hold += (unsigned long)(PUP(in)) << bits; 126 bits += 8; 127 } 128 this = lcode[hold & lmask]; 129 dolen: 130 op = (unsigned)(this.bits); 131 hold >>= op; 132 bits -= op; 133 op = (unsigned)(this.op); 134 if (op == 0) { /* literal */ 135 Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ? 136 "inflate: literal '%c'\n" : 137 "inflate: literal 0x%02x\n", this.val)); 138 PUP(out) = (unsigned char)(this.val); 139 } 140 else if (op & 16) { /* length base */ 141 len = (unsigned)(this.val); 142 op &= 15; /* number of extra bits */ 143 if (op) { 144 if (bits < op) { 145 hold += (unsigned long)(PUP(in)) << bits; 146 bits += 8; 147 } 148 len += (unsigned)hold & ((1U << op) - 1); 149 hold >>= op; 150 bits -= op; 151 } 152 Tracevv((stderr, "inflate: length %u\n", len)); 153 if (bits < 15) { 154 hold += (unsigned long)(PUP(in)) << bits; 155 bits += 8; 156 hold += (unsigned long)(PUP(in)) << bits; 157 bits += 8; 158 } 159 this = dcode[hold & dmask]; 160 dodist: 161 op = (unsigned)(this.bits); 162 hold >>= op; 163 bits -= op; 164 op = (unsigned)(this.op); 165 if (op & 16) { /* distance base */ 166 dist = (unsigned)(this.val); 167 op &= 15; /* number of extra bits */ 168 if (bits < op) { 169 hold += (unsigned long)(PUP(in)) << bits; 170 bits += 8; 171 if (bits < op) { 172 hold += (unsigned long)(PUP(in)) << bits; 173 bits += 8; 174 } 175 } 176 dist += (unsigned)hold & ((1U << op) - 1); 177 #ifdef INFLATE_STRICT 178 if (dist > dmax) { 179 strm->msg = (char *)"invalid distance too far back"; 180 state->mode = BAD; 181 break; 182 } 183 #endif 184 hold >>= op; 185 bits -= op; 186 Tracevv((stderr, "inflate: distance %u\n", dist)); 187 op = (unsigned)(out - beg); /* max distance in output */ 188 if (dist > op) { /* see if copy from window */ 189 op = dist - op; /* distance back in window */ 190 if (op > whave) { 191 #ifdef SMALL 192 strm->msg = "error"; 193 #else 194 strm->msg = (char *)"invalid distance too far back"; 195 #endif 196 state->mode = BAD; 197 break; 198 } 199 from = window - OFF; 200 if (write == 0) { /* very common case */ 201 from += wsize - op; 202 if (op < len) { /* some from window */ 203 len -= op; 204 do { 205 PUP(out) = PUP(from); 206 } while (--op); 207 from = out - dist; /* rest from output */ 208 } 209 } 210 else if (write < op) { /* wrap around window */ 211 from += wsize + write - op; 212 op -= write; 213 if (op < len) { /* some from end of window */ 214 len -= op; 215 do { 216 PUP(out) = PUP(from); 217 } while (--op); 218 from = window - OFF; 219 if (write < len) { /* some from start of window */ 220 op = write; 221 len -= op; 222 do { 223 PUP(out) = PUP(from); 224 } while (--op); 225 from = out - dist; /* rest from output */ 226 } 227 } 228 } 229 else { /* contiguous in window */ 230 from += write - op; 231 if (op < len) { /* some from window */ 232 len -= op; 233 do { 234 PUP(out) = PUP(from); 235 } while (--op); 236 from = out - dist; /* rest from output */ 237 } 238 } 239 while (len > 2) { 240 PUP(out) = PUP(from); 241 PUP(out) = PUP(from); 242 PUP(out) = PUP(from); 243 len -= 3; 244 } 245 if (len) { 246 PUP(out) = PUP(from); 247 if (len > 1) 248 PUP(out) = PUP(from); 249 } 250 } 251 else { 252 from = out - dist; /* copy direct from output */ 253 do { /* minimum length is three */ 254 PUP(out) = PUP(from); 255 PUP(out) = PUP(from); 256 PUP(out) = PUP(from); 257 len -= 3; 258 } while (len > 2); 259 if (len) { 260 PUP(out) = PUP(from); 261 if (len > 1) 262 PUP(out) = PUP(from); 263 } 264 } 265 } 266 else if ((op & 64) == 0) { /* 2nd level distance code */ 267 this = dcode[this.val + (hold & ((1U << op) - 1))]; 268 goto dodist; 269 } 270 else { 271 #ifdef SMALL 272 strm->msg = "error"; 273 #else 274 strm->msg = (char *)"invalid distance code"; 275 #endif 276 state->mode = BAD; 277 break; 278 } 279 } 280 else if ((op & 64) == 0) { /* 2nd level length code */ 281 this = lcode[this.val + (hold & ((1U << op) - 1))]; 282 goto dolen; 283 } 284 else if (op & 32) { /* end-of-block */ 285 Tracevv((stderr, "inflate: end of block\n")); 286 state->mode = TYPE; 287 break; 288 } 289 else { 290 #ifdef SMALL 291 strm->msg = "error"; 292 #else 293 strm->msg = (char *)"invalid literal/length code"; 294 #endif 295 state->mode = BAD; 296 break; 297 } 298 } while (in < last && out < end); 299 300 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 301 len = bits >> 3; 302 in -= len; 303 bits -= len << 3; 304 hold &= (1U << bits) - 1; 305 306 /* update state and return */ 307 strm->next_in = in + OFF; 308 strm->next_out = out + OFF; 309 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 310 strm->avail_out = (unsigned)(out < end ? 311 257 + (end - out) : 257 - (out - end)); 312 state->hold = hold; 313 state->bits = bits; 314 return; 315 } 316 317 /* 318 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 319 - Using bit fields for code structure 320 - Different op definition to avoid & for extra bits (do & for table bits) 321 - Three separate decoding do-loops for direct, window, and write == 0 322 - Special case for distance > 1 copies to do overlapped load and store copy 323 - Explicit branch predictions (based on measured branch probabilities) 324 - Deferring match copy and interspersed it with decoding subsequent codes 325 - Swapping literal/length else 326 - Swapping window/direct else 327 - Larger unrolled copy loops (three is about right) 328 - Moving len -= 3 statement into middle of loop 329 */ 330 331 #endif /* !ASMINF */ 332