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 <linux/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 - @start: inflate()'s starting value for strm->avail_out 68 */ 69 void inflate_fast(z_streamp strm, unsigned start) 70 { 71 struct inflate_state *state; 72 const unsigned char *in; /* local strm->next_in */ 73 const unsigned char *last; /* while in < last, enough input available */ 74 unsigned char *out; /* local strm->next_out */ 75 unsigned char *beg; /* inflate()'s initial strm->next_out */ 76 unsigned char *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 *window; /* allocated sliding window, if wsize != 0 */ 84 unsigned long hold; /* local strm->hold */ 85 unsigned bits; /* local strm->bits */ 86 code const *lcode; /* local strm->lencode */ 87 code const *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 *from; /* where to copy match from */ 96 97 /* copy state to local variables */ 98 state = (struct inflate_state *)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 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 if (bits < 15) { 149 hold += (unsigned long)(PUP(in)) << bits; 150 bits += 8; 151 hold += (unsigned long)(PUP(in)) << bits; 152 bits += 8; 153 } 154 this = dcode[hold & dmask]; 155 dodist: 156 op = (unsigned)(this.bits); 157 hold >>= op; 158 bits -= op; 159 op = (unsigned)(this.op); 160 if (op & 16) { /* distance base */ 161 dist = (unsigned)(this.val); 162 op &= 15; /* number of extra bits */ 163 if (bits < op) { 164 hold += (unsigned long)(PUP(in)) << bits; 165 bits += 8; 166 if (bits < op) { 167 hold += (unsigned long)(PUP(in)) << bits; 168 bits += 8; 169 } 170 } 171 dist += (unsigned)hold & ((1U << op) - 1); 172 #ifdef INFLATE_STRICT 173 if (dist > dmax) { 174 strm->msg = (char *)"invalid distance too far back"; 175 state->mode = BAD; 176 break; 177 } 178 #endif 179 hold >>= op; 180 bits -= op; 181 op = (unsigned)(out - beg); /* max distance in output */ 182 if (dist > op) { /* see if copy from window */ 183 op = dist - op; /* distance back in window */ 184 if (op > whave) { 185 strm->msg = (char *)"invalid distance too far back"; 186 state->mode = BAD; 187 break; 188 } 189 from = window - OFF; 190 if (write == 0) { /* very common case */ 191 from += wsize - op; 192 if (op < len) { /* some from window */ 193 len -= op; 194 do { 195 PUP(out) = PUP(from); 196 } while (--op); 197 from = out - dist; /* rest from output */ 198 } 199 } 200 else if (write < op) { /* wrap around window */ 201 from += wsize + write - op; 202 op -= write; 203 if (op < len) { /* some from end of window */ 204 len -= op; 205 do { 206 PUP(out) = PUP(from); 207 } while (--op); 208 from = window - OFF; 209 if (write < len) { /* some from start of window */ 210 op = write; 211 len -= op; 212 do { 213 PUP(out) = PUP(from); 214 } while (--op); 215 from = out - dist; /* rest from output */ 216 } 217 } 218 } 219 else { /* contiguous in window */ 220 from += write - op; 221 if (op < len) { /* some from window */ 222 len -= op; 223 do { 224 PUP(out) = PUP(from); 225 } while (--op); 226 from = out - dist; /* rest from output */ 227 } 228 } 229 while (len > 2) { 230 PUP(out) = PUP(from); 231 PUP(out) = PUP(from); 232 PUP(out) = PUP(from); 233 len -= 3; 234 } 235 if (len) { 236 PUP(out) = PUP(from); 237 if (len > 1) 238 PUP(out) = PUP(from); 239 } 240 } 241 else { 242 from = out - dist; /* copy direct from output */ 243 do { /* minimum length is three */ 244 PUP(out) = PUP(from); 245 PUP(out) = PUP(from); 246 PUP(out) = PUP(from); 247 len -= 3; 248 } while (len > 2); 249 if (len) { 250 PUP(out) = PUP(from); 251 if (len > 1) 252 PUP(out) = PUP(from); 253 } 254 } 255 } 256 else if ((op & 64) == 0) { /* 2nd level distance code */ 257 this = dcode[this.val + (hold & ((1U << op) - 1))]; 258 goto dodist; 259 } 260 else { 261 strm->msg = (char *)"invalid distance code"; 262 state->mode = BAD; 263 break; 264 } 265 } 266 else if ((op & 64) == 0) { /* 2nd level length code */ 267 this = lcode[this.val + (hold & ((1U << op) - 1))]; 268 goto dolen; 269 } 270 else if (op & 32) { /* end-of-block */ 271 state->mode = TYPE; 272 break; 273 } 274 else { 275 strm->msg = (char *)"invalid literal/length code"; 276 state->mode = BAD; 277 break; 278 } 279 } while (in < last && out < end); 280 281 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 282 len = bits >> 3; 283 in -= len; 284 bits -= len << 3; 285 hold &= (1U << bits) - 1; 286 287 /* update state and return */ 288 strm->next_in = in + OFF; 289 strm->next_out = out + OFF; 290 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 291 strm->avail_out = (unsigned)(out < end ? 292 257 + (end - out) : 257 - (out - end)); 293 state->hold = hold; 294 state->bits = bits; 295 return; 296 } 297 298 /* 299 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 300 - Using bit fields for code structure 301 - Different op definition to avoid & for extra bits (do & for table bits) 302 - Three separate decoding do-loops for direct, window, and write == 0 303 - Special case for distance > 1 copies to do overlapped load and store copy 304 - Explicit branch predictions (based on measured branch probabilities) 305 - Deferring match copy and interspersed it with decoding subsequent codes 306 - Swapping literal/length else 307 - Swapping window/direct else 308 - Larger unrolled copy loops (three is about right) 309 - Moving len -= 3 statement into middle of loop 310 */ 311 312 #endif /* !ASMINF */ 313