Masahiro Yamada | 221b163 | 2018-01-26 11:42:01 +0900 | [diff] [blame] | 1 | /* inffast.c -- fast decoding |
| 2 | * Copyright (C) 1995-2017 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 | #ifdef ASMINF |
| 12 | # pragma message("Assembler code may have bugs -- use at your own risk") |
| 13 | #else |
| 14 | |
| 15 | /* |
| 16 | Decode literal, length, and distance codes and write out the resulting |
| 17 | literal and match bytes until either not enough input or output is |
| 18 | available, an end-of-block is encountered, or a data error is encountered. |
| 19 | When large enough input and output buffers are supplied to inflate(), for |
| 20 | example, a 16K input buffer and a 64K output buffer, more than 95% of the |
| 21 | inflate execution time is spent in this routine. |
| 22 | |
| 23 | Entry assumptions: |
| 24 | |
| 25 | state->mode == LEN |
| 26 | strm->avail_in >= 6 |
| 27 | strm->avail_out >= 258 |
| 28 | start >= strm->avail_out |
| 29 | state->bits < 8 |
| 30 | |
| 31 | On return, state->mode is one of: |
| 32 | |
| 33 | LEN -- ran out of enough output space or enough available input |
| 34 | TYPE -- reached end of block code, inflate() to interpret next block |
| 35 | BAD -- error in block data |
| 36 | |
| 37 | Notes: |
| 38 | |
| 39 | - The maximum input bits used by a length/distance pair is 15 bits for the |
| 40 | length code, 5 bits for the length extra, 15 bits for the distance code, |
| 41 | and 13 bits for the distance extra. This totals 48 bits, or six bytes. |
| 42 | Therefore if strm->avail_in >= 6, then there is enough input to avoid |
| 43 | checking for available input while decoding. |
| 44 | |
| 45 | - The maximum bytes that a single length/distance pair can output is 258 |
| 46 | bytes, which is the maximum length that can be coded. inflate_fast() |
| 47 | requires strm->avail_out >= 258 for each loop to avoid checking for |
| 48 | output space. |
| 49 | */ |
| 50 | void ZLIB_INTERNAL inflate_fast(strm, start) |
| 51 | z_streamp strm; |
| 52 | unsigned start; /* inflate()'s starting value for strm->avail_out */ |
| 53 | { |
| 54 | struct inflate_state FAR *state; |
| 55 | z_const unsigned char FAR *in; /* local strm->next_in */ |
| 56 | z_const unsigned char FAR *last; /* have enough input while in < last */ |
| 57 | unsigned char FAR *out; /* local strm->next_out */ |
| 58 | unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ |
| 59 | unsigned char FAR *end; /* while out < end, enough space available */ |
| 60 | #ifdef INFLATE_STRICT |
| 61 | unsigned dmax; /* maximum distance from zlib header */ |
| 62 | #endif |
| 63 | unsigned wsize; /* window size or zero if not using window */ |
| 64 | unsigned whave; /* valid bytes in the window */ |
| 65 | unsigned wnext; /* window write index */ |
| 66 | unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ |
| 67 | unsigned long hold; /* local strm->hold */ |
| 68 | unsigned bits; /* local strm->bits */ |
| 69 | code const FAR *lcode; /* local strm->lencode */ |
| 70 | code const FAR *dcode; /* local strm->distcode */ |
| 71 | unsigned lmask; /* mask for first level of length codes */ |
| 72 | unsigned dmask; /* mask for first level of distance codes */ |
| 73 | code here; /* retrieved table entry */ |
| 74 | unsigned op; /* code bits, operation, extra bits, or */ |
| 75 | /* window position, window bytes to copy */ |
| 76 | unsigned len; /* match length, unused bytes */ |
| 77 | unsigned dist; /* match distance */ |
| 78 | unsigned char FAR *from; /* where to copy match from */ |
| 79 | |
| 80 | /* copy state to local variables */ |
| 81 | state = (struct inflate_state FAR *)strm->state; |
| 82 | in = strm->next_in; |
| 83 | last = in + (strm->avail_in - 5); |
| 84 | out = strm->next_out; |
| 85 | beg = out - (start - strm->avail_out); |
| 86 | end = out + (strm->avail_out - 257); |
| 87 | #ifdef INFLATE_STRICT |
| 88 | dmax = state->dmax; |
| 89 | #endif |
| 90 | wsize = state->wsize; |
| 91 | whave = state->whave; |
| 92 | wnext = state->wnext; |
| 93 | window = state->window; |
| 94 | hold = state->hold; |
| 95 | bits = state->bits; |
| 96 | lcode = state->lencode; |
| 97 | dcode = state->distcode; |
| 98 | lmask = (1U << state->lenbits) - 1; |
| 99 | dmask = (1U << state->distbits) - 1; |
| 100 | |
| 101 | /* decode literals and length/distances until end-of-block or not enough |
| 102 | input data or output space */ |
| 103 | do { |
| 104 | if (bits < 15) { |
| 105 | hold += (unsigned long)(*in++) << bits; |
| 106 | bits += 8; |
| 107 | hold += (unsigned long)(*in++) << bits; |
| 108 | bits += 8; |
| 109 | } |
| 110 | here = lcode[hold & lmask]; |
| 111 | dolen: |
| 112 | op = (unsigned)(here.bits); |
| 113 | hold >>= op; |
| 114 | bits -= op; |
| 115 | op = (unsigned)(here.op); |
| 116 | if (op == 0) { /* literal */ |
| 117 | Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ? |
| 118 | "inflate: literal '%c'\n" : |
| 119 | "inflate: literal 0x%02x\n", here.val)); |
| 120 | *out++ = (unsigned char)(here.val); |
| 121 | } |
| 122 | else if (op & 16) { /* length base */ |
| 123 | len = (unsigned)(here.val); |
| 124 | op &= 15; /* number of extra bits */ |
| 125 | if (op) { |
| 126 | if (bits < op) { |
| 127 | hold += (unsigned long)(*in++) << bits; |
| 128 | bits += 8; |
| 129 | } |
| 130 | len += (unsigned)hold & ((1U << op) - 1); |
| 131 | hold >>= op; |
| 132 | bits -= op; |
| 133 | } |
| 134 | Tracevv((stderr, "inflate: length %u\n", len)); |
| 135 | if (bits < 15) { |
| 136 | hold += (unsigned long)(*in++) << bits; |
| 137 | bits += 8; |
| 138 | hold += (unsigned long)(*in++) << bits; |
| 139 | bits += 8; |
| 140 | } |
| 141 | here = dcode[hold & dmask]; |
| 142 | dodist: |
| 143 | op = (unsigned)(here.bits); |
| 144 | hold >>= op; |
| 145 | bits -= op; |
| 146 | op = (unsigned)(here.op); |
| 147 | if (op & 16) { /* distance base */ |
| 148 | dist = (unsigned)(here.val); |
| 149 | op &= 15; /* number of extra bits */ |
| 150 | if (bits < op) { |
| 151 | hold += (unsigned long)(*in++) << bits; |
| 152 | bits += 8; |
| 153 | if (bits < op) { |
| 154 | hold += (unsigned long)(*in++) << bits; |
| 155 | bits += 8; |
| 156 | } |
| 157 | } |
| 158 | dist += (unsigned)hold & ((1U << op) - 1); |
| 159 | #ifdef INFLATE_STRICT |
| 160 | if (dist > dmax) { |
| 161 | strm->msg = (char *)"invalid distance too far back"; |
| 162 | state->mode = BAD; |
| 163 | break; |
| 164 | } |
| 165 | #endif |
| 166 | hold >>= op; |
| 167 | bits -= op; |
| 168 | Tracevv((stderr, "inflate: distance %u\n", dist)); |
| 169 | op = (unsigned)(out - beg); /* max distance in output */ |
| 170 | if (dist > op) { /* see if copy from window */ |
| 171 | op = dist - op; /* distance back in window */ |
| 172 | if (op > whave) { |
| 173 | if (state->sane) { |
| 174 | strm->msg = |
| 175 | (char *)"invalid distance too far back"; |
| 176 | state->mode = BAD; |
| 177 | break; |
| 178 | } |
| 179 | #ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR |
| 180 | if (len <= op - whave) { |
| 181 | do { |
| 182 | *out++ = 0; |
| 183 | } while (--len); |
| 184 | continue; |
| 185 | } |
| 186 | len -= op - whave; |
| 187 | do { |
| 188 | *out++ = 0; |
| 189 | } while (--op > whave); |
| 190 | if (op == 0) { |
| 191 | from = out - dist; |
| 192 | do { |
| 193 | *out++ = *from++; |
| 194 | } while (--len); |
| 195 | continue; |
| 196 | } |
| 197 | #endif |
| 198 | } |
| 199 | from = window; |
| 200 | if (wnext == 0) { /* very common case */ |
| 201 | from += wsize - op; |
| 202 | if (op < len) { /* some from window */ |
| 203 | len -= op; |
| 204 | do { |
| 205 | *out++ = *from++; |
| 206 | } while (--op); |
| 207 | from = out - dist; /* rest from output */ |
| 208 | } |
| 209 | } |
| 210 | else if (wnext < op) { /* wrap around window */ |
| 211 | from += wsize + wnext - op; |
| 212 | op -= wnext; |
| 213 | if (op < len) { /* some from end of window */ |
| 214 | len -= op; |
| 215 | do { |
| 216 | *out++ = *from++; |
| 217 | } while (--op); |
| 218 | from = window; |
| 219 | if (wnext < len) { /* some from start of window */ |
| 220 | op = wnext; |
| 221 | len -= op; |
| 222 | do { |
| 223 | *out++ = *from++; |
| 224 | } while (--op); |
| 225 | from = out - dist; /* rest from output */ |
| 226 | } |
| 227 | } |
| 228 | } |
| 229 | else { /* contiguous in window */ |
| 230 | from += wnext - op; |
| 231 | if (op < len) { /* some from window */ |
| 232 | len -= op; |
| 233 | do { |
| 234 | *out++ = *from++; |
| 235 | } while (--op); |
| 236 | from = out - dist; /* rest from output */ |
| 237 | } |
| 238 | } |
| 239 | while (len > 2) { |
| 240 | *out++ = *from++; |
| 241 | *out++ = *from++; |
| 242 | *out++ = *from++; |
| 243 | len -= 3; |
| 244 | } |
| 245 | if (len) { |
| 246 | *out++ = *from++; |
| 247 | if (len > 1) |
| 248 | *out++ = *from++; |
| 249 | } |
| 250 | } |
| 251 | else { |
| 252 | from = out - dist; /* copy direct from output */ |
| 253 | do { /* minimum length is three */ |
| 254 | *out++ = *from++; |
| 255 | *out++ = *from++; |
| 256 | *out++ = *from++; |
| 257 | len -= 3; |
| 258 | } while (len > 2); |
| 259 | if (len) { |
| 260 | *out++ = *from++; |
| 261 | if (len > 1) |
| 262 | *out++ = *from++; |
| 263 | } |
| 264 | } |
| 265 | } |
| 266 | else if ((op & 64) == 0) { /* 2nd level distance code */ |
| 267 | here = dcode[here.val + (hold & ((1U << op) - 1))]; |
| 268 | goto dodist; |
| 269 | } |
| 270 | else { |
| 271 | strm->msg = (char *)"invalid distance code"; |
| 272 | state->mode = BAD; |
| 273 | break; |
| 274 | } |
| 275 | } |
| 276 | else if ((op & 64) == 0) { /* 2nd level length code */ |
| 277 | here = lcode[here.val + (hold & ((1U << op) - 1))]; |
| 278 | goto dolen; |
| 279 | } |
| 280 | else if (op & 32) { /* end-of-block */ |
| 281 | Tracevv((stderr, "inflate: end of block\n")); |
| 282 | state->mode = TYPE; |
| 283 | break; |
| 284 | } |
| 285 | else { |
| 286 | strm->msg = (char *)"invalid literal/length code"; |
| 287 | state->mode = BAD; |
| 288 | break; |
| 289 | } |
| 290 | } while (in < last && out < end); |
| 291 | |
| 292 | /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ |
| 293 | len = bits >> 3; |
| 294 | in -= len; |
| 295 | bits -= len << 3; |
| 296 | hold &= (1U << bits) - 1; |
| 297 | |
| 298 | /* update state and return */ |
| 299 | strm->next_in = in; |
| 300 | strm->next_out = out; |
| 301 | strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); |
| 302 | strm->avail_out = (unsigned)(out < end ? |
| 303 | 257 + (end - out) : 257 - (out - end)); |
| 304 | state->hold = hold; |
| 305 | state->bits = bits; |
| 306 | return; |
| 307 | } |
| 308 | |
| 309 | /* |
| 310 | inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): |
| 311 | - Using bit fields for code structure |
| 312 | - Different op definition to avoid & for extra bits (do & for table bits) |
| 313 | - Three separate decoding do-loops for direct, window, and wnext == 0 |
| 314 | - Special case for distance > 1 copies to do overlapped load and store copy |
| 315 | - Explicit branch predictions (based on measured branch probabilities) |
| 316 | - Deferring match copy and interspersed it with decoding subsequent codes |
| 317 | - Swapping literal/length else |
| 318 | - Swapping window/direct else |
| 319 | - Larger unrolled copy loops (three is about right) |
| 320 | - Moving len -= 3 statement into middle of loop |
| 321 | */ |
| 322 | |
| 323 | #endif /* !ASMINF */ |