1 /* 2 * puff.c 3 * Copyright (C) 2002-2004 Mark Adler 4 * For conditions of distribution and use, see copyright notice in puff.h 5 * version 1.8, 9 Jan 2004 6 * 7 * puff.c is a simple inflate written to be an unambiguous way to specify the 8 * deflate format. It is not written for speed but rather simplicity. As a 9 * side benefit, this code might actually be useful when small code is more 10 * important than speed, such as bootstrap applications. For typical deflate 11 * data, zlib's inflate() is about four times as fast as puff(). zlib's 12 * inflate compiles to around 20K on my machine, whereas puff.c compiles to 13 * around 4K on my machine (a PowerPC using GNU cc). If the faster decode() 14 * function here is used, then puff() is only twice as slow as zlib's 15 * inflate(). 16 * 17 * All dynamically allocated memory comes from the stack. The stack required 18 * is less than 2K bytes. This code is compatible with 16-bit int's and 19 * assumes that long's are at least 32 bits. puff.c uses the short data type, 20 * assumed to be 16 bits, for arrays in order to to conserve memory. The code 21 * works whether integers are stored big endian or little endian. 22 * 23 * In the comments below are "Format notes" that describe the inflate process 24 * and document some of the less obvious aspects of the format. This source 25 * code is meant to supplement RFC 1951, which formally describes the deflate 26 * format: 27 * 28 * http://www.zlib.org/rfc-deflate.html 29 */ 30 31 /* 32 * Change history: 33 * 34 * 1.0 10 Feb 2002 - First version 35 * 1.1 17 Feb 2002 - Clarifications of some comments and notes 36 * - Update puff() dest and source pointers on negative 37 * errors to facilitate debugging deflators 38 * - Remove longest from struct huffman -- not needed 39 * - Simplify offs[] index in construct() 40 * - Add input size and checking, using longjmp() to 41 * maintain easy readability 42 * - Use short data type for large arrays 43 * - Use pointers instead of long to specify source and 44 * destination sizes to avoid arbitrary 4 GB limits 45 * 1.2 17 Mar 2002 - Add faster version of decode(), doubles speed (!), 46 * but leave simple version for readabilty 47 * - Make sure invalid distances detected if pointers 48 * are 16 bits 49 * - Fix fixed codes table error 50 * - Provide a scanning mode for determining size of 51 * uncompressed data 52 * 1.3 20 Mar 2002 - Go back to lengths for puff() parameters [Jean-loup] 53 * - Add a puff.h file for the interface 54 * - Add braces in puff() for else do [Jean-loup] 55 * - Use indexes instead of pointers for readability 56 * 1.4 31 Mar 2002 - Simplify construct() code set check 57 * - Fix some comments 58 * - Add FIXLCODES #define 59 * 1.5 6 Apr 2002 - Minor comment fixes 60 * 1.6 7 Aug 2002 - Minor format changes 61 * 1.7 3 Mar 2003 - Added test code for distribution 62 * - Added zlib-like license 63 * 1.8 9 Jan 2004 - Added some comments on no distance codes case 64 */ 65 66 #include <setjmp.h> /* for setjmp(), longjmp(), and jmp_buf */ 67 #include "puff.h" /* prototype for puff() */ 68 69 #define local static /* for local function definitions */ 70 #define NIL ((unsigned char *)0) /* for no output option */ 71 72 /* 73 * Maximums for allocations and loops. It is not useful to change these -- 74 * they are fixed by the deflate format. 75 */ 76 #define MAXBITS 15 /* maximum bits in a code */ 77 #define MAXLCODES 286 /* maximum number of literal/length codes */ 78 #define MAXDCODES 30 /* maximum number of distance codes */ 79 #define MAXCODES (MAXLCODES+MAXDCODES) /* maximum codes lengths to read */ 80 #define FIXLCODES 288 /* number of fixed literal/length codes */ 81 82 /* input and output state */ 83 struct state { 84 /* output state */ 85 unsigned char *out; /* output buffer */ 86 unsigned long outlen; /* available space at out */ 87 unsigned long outcnt; /* bytes written to out so far */ 88 89 /* input state */ 90 unsigned char *in; /* input buffer */ 91 unsigned long inlen; /* available input at in */ 92 unsigned long incnt; /* bytes read so far */ 93 int bitbuf; /* bit buffer */ 94 int bitcnt; /* number of bits in bit buffer */ 95 96 /* input limit error return state for bits() and decode() */ 97 jmp_buf env; 98 }; 99 100 /* 101 * Return need bits from the input stream. This always leaves less than 102 * eight bits in the buffer. bits() works properly for need == 0. 103 * 104 * Format notes: 105 * 106 * - Bits are stored in bytes from the least significant bit to the most 107 * significant bit. Therefore bits are dropped from the bottom of the bit 108 * buffer, using shift right, and new bytes are appended to the top of the 109 * bit buffer, using shift left. 110 */ 111 local int bits(struct state *s, int need) 112 { 113 long val; /* bit accumulator (can use up to 20 bits) */ 114 115 /* load at least need bits into val */ 116 val = s->bitbuf; 117 while (s->bitcnt < need) { 118 if (s->incnt == s->inlen) longjmp(s->env, 1); /* out of input */ 119 val |= (long)(s->in[s->incnt++]) << s->bitcnt; /* load eight bits */ 120 s->bitcnt += 8; 121 } 122 123 /* drop need bits and update buffer, always zero to seven bits left */ 124 s->bitbuf = (int)(val >> need); 125 s->bitcnt -= need; 126 127 /* return need bits, zeroing the bits above that */ 128 return (int)(val & ((1L << need) - 1)); 129 } 130 131 /* 132 * Process a stored block. 133 * 134 * Format notes: 135 * 136 * - After the two-bit stored block type (00), the stored block length and 137 * stored bytes are byte-aligned for fast copying. Therefore any leftover 138 * bits in the byte that has the last bit of the type, as many as seven, are 139 * discarded. The value of the discarded bits are not defined and should not 140 * be checked against any expectation. 141 * 142 * - The second inverted copy of the stored block length does not have to be 143 * checked, but it's probably a good idea to do so anyway. 144 * 145 * - A stored block can have zero length. This is sometimes used to byte-align 146 * subsets of the compressed data for random access or partial recovery. 147 */ 148 local int stored(struct state *s) 149 { 150 unsigned len; /* length of stored block */ 151 152 /* discard leftover bits from current byte (assumes s->bitcnt < 8) */ 153 s->bitbuf = 0; 154 s->bitcnt = 0; 155 156 /* get length and check against its one's complement */ 157 if (s->incnt + 4 > s->inlen) return 2; /* not enough input */ 158 len = s->in[s->incnt++]; 159 len |= s->in[s->incnt++] << 8; 160 if (s->in[s->incnt++] != (~len & 0xff) || 161 s->in[s->incnt++] != ((~len >> 8) & 0xff)) 162 return -2; /* didn't match complement! */ 163 164 /* copy len bytes from in to out */ 165 if (s->incnt + len > s->inlen) return 2; /* not enough input */ 166 if (s->out != NIL) { 167 if (s->outcnt + len > s->outlen) 168 return 1; /* not enough output space */ 169 while (len--) 170 s->out[s->outcnt++] = s->in[s->incnt++]; 171 } 172 else { /* just scanning */ 173 s->outcnt += len; 174 s->incnt += len; 175 } 176 177 /* done with a valid stored block */ 178 return 0; 179 } 180 181 /* 182 * Huffman code decoding tables. count[1..MAXBITS] is the number of symbols of 183 * each length, which for a canonical code are stepped through in order. 184 * symbol[] are the symbol values in canonical order, where the number of 185 * entries is the sum of the counts in count[]. The decoding process can be 186 * seen in the function decode() below. 187 */ 188 struct huffman { 189 short *count; /* number of symbols of each length */ 190 short *symbol; /* canonically ordered symbols */ 191 }; 192 193 /* 194 * Decode a code from the stream s using huffman table h. Return the symbol or 195 * a negative value if there is an error. If all of the lengths are zero, i.e. 196 * an empty code, or if the code is incomplete and an invalid code is received, 197 * then -9 is returned after reading MAXBITS bits. 198 * 199 * Format notes: 200 * 201 * - The codes as stored in the compressed data are bit-reversed relative to 202 * a simple integer ordering of codes of the same lengths. Hence below the 203 * bits are pulled from the compressed data one at a time and used to 204 * build the code value reversed from what is in the stream in order to 205 * permit simple integer comparisons for decoding. A table-based decoding 206 * scheme (as used in zlib) does not need to do this reversal. 207 * 208 * - The first code for the shortest length is all zeros. Subsequent codes of 209 * the same length are simply integer increments of the previous code. When 210 * moving up a length, a zero bit is appended to the code. For a complete 211 * code, the last code of the longest length will be all ones. 212 * 213 * - Incomplete codes are handled by this decoder, since they are permitted 214 * in the deflate format. See the format notes for fixed() and dynamic(). 215 */ 216 #ifdef SLOW 217 local int decode(struct state *s, struct huffman *h) 218 { 219 int len; /* current number of bits in code */ 220 int code; /* len bits being decoded */ 221 int first; /* first code of length len */ 222 int count; /* number of codes of length len */ 223 int index; /* index of first code of length len in symbol table */ 224 225 code = first = index = 0; 226 for (len = 1; len <= MAXBITS; len++) { 227 code |= bits(s, 1); /* get next bit */ 228 count = h->count[len]; 229 if (code < first + count) /* if length len, return symbol */ 230 return h->symbol[index + (code - first)]; 231 index += count; /* else update for next length */ 232 first += count; 233 first <<= 1; 234 code <<= 1; 235 } 236 return -9; /* ran out of codes */ 237 } 238 239 /* 240 * A faster version of decode() for real applications of this code. It's not 241 * as readable, but it makes puff() twice as fast. And it only makes the code 242 * a few percent larger. 243 */ 244 #else /* !SLOW */ 245 local int decode(struct state *s, struct huffman *h) 246 { 247 int len; /* current number of bits in code */ 248 int code; /* len bits being decoded */ 249 int first; /* first code of length len */ 250 int count; /* number of codes of length len */ 251 int index; /* index of first code of length len in symbol table */ 252 int bitbuf; /* bits from stream */ 253 int left; /* bits left in next or left to process */ 254 short *next; /* next number of codes */ 255 256 bitbuf = s->bitbuf; 257 left = s->bitcnt; 258 code = first = index = 0; 259 len = 1; 260 next = h->count + 1; 261 while (1) { 262 while (left--) { 263 code |= bitbuf & 1; 264 bitbuf >>= 1; 265 count = *next++; 266 if (code < first + count) { /* if length len, return symbol */ 267 s->bitbuf = bitbuf; 268 s->bitcnt = (s->bitcnt - len) & 7; 269 return h->symbol[index + (code - first)]; 270 } 271 index += count; /* else update for next length */ 272 first += count; 273 first <<= 1; 274 code <<= 1; 275 len++; 276 } 277 left = (MAXBITS+1) - len; 278 if (left == 0) break; 279 if (s->incnt == s->inlen) longjmp(s->env, 1); /* out of input */ 280 bitbuf = s->in[s->incnt++]; 281 if (left > 8) left = 8; 282 } 283 return -9; /* ran out of codes */ 284 } 285 #endif /* SLOW */ 286 287 /* 288 * Given the list of code lengths length[0..n-1] representing a canonical 289 * Huffman code for n symbols, construct the tables required to decode those 290 * codes. Those tables are the number of codes of each length, and the symbols 291 * sorted by length, retaining their original order within each length. The 292 * return value is zero for a complete code set, negative for an over- 293 * subscribed code set, and positive for an incomplete code set. The tables 294 * can be used if the return value is zero or positive, but they cannot be used 295 * if the return value is negative. If the return value is zero, it is not 296 * possible for decode() using that table to return an error--any stream of 297 * enough bits will resolve to a symbol. If the return value is positive, then 298 * it is possible for decode() using that table to return an error for received 299 * codes past the end of the incomplete lengths. 300 * 301 * Not used by decode(), but used for error checking, h->count[0] is the number 302 * of the n symbols not in the code. So n - h->count[0] is the number of 303 * codes. This is useful for checking for incomplete codes that have more than 304 * one symbol, which is an error in a dynamic block. 305 * 306 * Assumption: for all i in 0..n-1, 0 <= length[i] <= MAXBITS 307 * This is assured by the construction of the length arrays in dynamic() and 308 * fixed() and is not verified by construct(). 309 * 310 * Format notes: 311 * 312 * - Permitted and expected examples of incomplete codes are one of the fixed 313 * codes and any code with a single symbol which in deflate is coded as one 314 * bit instead of zero bits. See the format notes for fixed() and dynamic(). 315 * 316 * - Within a given code length, the symbols are kept in ascending order for 317 * the code bits definition. 318 */ 319 local int construct(struct huffman *h, short *length, int n) 320 { 321 int symbol; /* current symbol when stepping through length[] */ 322 int len; /* current length when stepping through h->count[] */ 323 int left; /* number of possible codes left of current length */ 324 short offs[MAXBITS+1]; /* offsets in symbol table for each length */ 325 326 /* count number of codes of each length */ 327 for (len = 0; len <= MAXBITS; len++) 328 h->count[len] = 0; 329 for (symbol = 0; symbol < n; symbol++) 330 (h->count[length[symbol]])++; /* assumes lengths are within bounds */ 331 if (h->count[0] == n) /* no codes! */ 332 return 0; /* complete, but decode() will fail */ 333 334 /* check for an over-subscribed or incomplete set of lengths */ 335 left = 1; /* one possible code of zero length */ 336 for (len = 1; len <= MAXBITS; len++) { 337 left <<= 1; /* one more bit, double codes left */ 338 left -= h->count[len]; /* deduct count from possible codes */ 339 if (left < 0) return left; /* over-subscribed--return negative */ 340 } /* left > 0 means incomplete */ 341 342 /* generate offsets into symbol table for each length for sorting */ 343 offs[1] = 0; 344 for (len = 1; len < MAXBITS; len++) 345 offs[len + 1] = offs[len] + h->count[len]; 346 347 /* 348 * put symbols in table sorted by length, by symbol order within each 349 * length 350 */ 351 for (symbol = 0; symbol < n; symbol++) 352 if (length[symbol] != 0) 353 h->symbol[offs[length[symbol]]++] = symbol; 354 355 /* return zero for complete set, positive for incomplete set */ 356 return left; 357 } 358 359 /* 360 * Decode literal/length and distance codes until an end-of-block code. 361 * 362 * Format notes: 363 * 364 * - Compressed data that is after the block type if fixed or after the code 365 * description if dynamic is a combination of literals and length/distance 366 * pairs terminated by and end-of-block code. Literals are simply Huffman 367 * coded bytes. A length/distance pair is a coded length followed by a 368 * coded distance to represent a string that occurs earlier in the 369 * uncompressed data that occurs again at the current location. 370 * 371 * - Literals, lengths, and the end-of-block code are combined into a single 372 * code of up to 286 symbols. They are 256 literals (0..255), 29 length 373 * symbols (257..285), and the end-of-block symbol (256). 374 * 375 * - There are 256 possible lengths (3..258), and so 29 symbols are not enough 376 * to represent all of those. Lengths 3..10 and 258 are in fact represented 377 * by just a length symbol. Lengths 11..257 are represented as a symbol and 378 * some number of extra bits that are added as an integer to the base length 379 * of the length symbol. The number of extra bits is determined by the base 380 * length symbol. These are in the static arrays below, lens[] for the base 381 * lengths and lext[] for the corresponding number of extra bits. 382 * 383 * - The reason that 258 gets its own symbol is that the longest length is used 384 * often in highly redundant files. Note that 258 can also be coded as the 385 * base value 227 plus the maximum extra value of 31. While a good deflate 386 * should never do this, it is not an error, and should be decoded properly. 387 * 388 * - If a length is decoded, including its extra bits if any, then it is 389 * followed a distance code. There are up to 30 distance symbols. Again 390 * there are many more possible distances (1..32768), so extra bits are added 391 * to a base value represented by the symbol. The distances 1..4 get their 392 * own symbol, but the rest require extra bits. The base distances and 393 * corresponding number of extra bits are below in the static arrays dist[] 394 * and dext[]. 395 * 396 * - Literal bytes are simply written to the output. A length/distance pair is 397 * an instruction to copy previously uncompressed bytes to the output. The 398 * copy is from distance bytes back in the output stream, copying for length 399 * bytes. 400 * 401 * - Distances pointing before the beginning of the output data are not 402 * permitted. 403 * 404 * - Overlapped copies, where the length is greater than the distance, are 405 * allowed and common. For example, a distance of one and a length of 258 406 * simply copies the last byte 258 times. A distance of four and a length of 407 * twelve copies the last four bytes three times. A simple forward copy 408 * ignoring whether the length is greater than the distance or not implements 409 * this correctly. You should not use memcpy() since its behavior is not 410 * defined for overlapped arrays. You should not use memmove() or bcopy() 411 * since though their behavior -is- defined for overlapping arrays, it is 412 * defined to do the wrong thing in this case. 413 */ 414 local int codes(struct state *s, 415 struct huffman *lencode, 416 struct huffman *distcode) 417 { 418 int symbol; /* decoded symbol */ 419 int len; /* length for copy */ 420 unsigned dist; /* distance for copy */ 421 static const short lens[29] = { /* Size base for length codes 257..285 */ 422 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, 423 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258}; 424 static const short lext[29] = { /* Extra bits for length codes 257..285 */ 425 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 426 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0}; 427 static const short dists[30] = { /* Offset base for distance codes 0..29 */ 428 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, 429 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 430 8193, 12289, 16385, 24577}; 431 static const short dext[30] = { /* Extra bits for distance codes 0..29 */ 432 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 433 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 434 12, 12, 13, 13}; 435 436 /* decode literals and length/distance pairs */ 437 do { 438 symbol = decode(s, lencode); 439 if (symbol < 0) return symbol; /* invalid symbol */ 440 if (symbol < 256) { /* literal: symbol is the byte */ 441 /* write out the literal */ 442 if (s->out != NIL) { 443 if (s->outcnt == s->outlen) return 1; 444 s->out[s->outcnt] = symbol; 445 } 446 s->outcnt++; 447 } 448 else if (symbol > 256) { /* length */ 449 /* get and compute length */ 450 symbol -= 257; 451 if (symbol >= 29) return -9; /* invalid fixed code */ 452 len = lens[symbol] + bits(s, lext[symbol]); 453 454 /* get and check distance */ 455 symbol = decode(s, distcode); 456 if (symbol < 0) return symbol; /* invalid symbol */ 457 dist = dists[symbol] + bits(s, dext[symbol]); 458 if (dist > s->outcnt) 459 return -10; /* distance too far back */ 460 461 /* copy length bytes from distance bytes back */ 462 if (s->out != NIL) { 463 if (s->outcnt + len > s->outlen) return 1; 464 while (len--) { 465 s->out[s->outcnt] = s->out[s->outcnt - dist]; 466 s->outcnt++; 467 } 468 } 469 else 470 s->outcnt += len; 471 } 472 } while (symbol != 256); /* end of block symbol */ 473 474 /* done with a valid fixed or dynamic block */ 475 return 0; 476 } 477 478 /* 479 * Process a fixed codes block. 480 * 481 * Format notes: 482 * 483 * - This block type can be useful for compressing small amounts of data for 484 * which the size of the code descriptions in a dynamic block exceeds the 485 * benefit of custom codes for that block. For fixed codes, no bits are 486 * spent on code descriptions. Instead the code lengths for literal/length 487 * codes and distance codes are fixed. The specific lengths for each symbol 488 * can be seen in the "for" loops below. 489 * 490 * - The literal/length code is complete, but has two symbols that are invalid 491 * and should result in an error if received. This cannot be implemented 492 * simply as an incomplete code since those two symbols are in the "middle" 493 * of the code. They are eight bits long and the longest literal/length\ 494 * code is nine bits. Therefore the code must be constructed with those 495 * symbols, and the invalid symbols must be detected after decoding. 496 * 497 * - The fixed distance codes also have two invalid symbols that should result 498 * in an error if received. Since all of the distance codes are the same 499 * length, this can be implemented as an incomplete code. Then the invalid 500 * codes are detected while decoding. 501 */ 502 local int fixed(struct state *s) 503 { 504 static int virgin = 1; 505 static short lencnt[MAXBITS+1], lensym[FIXLCODES]; 506 static short distcnt[MAXBITS+1], distsym[MAXDCODES]; 507 static struct huffman lencode = {lencnt, lensym}; 508 static struct huffman distcode = {distcnt, distsym}; 509 510 /* build fixed huffman tables if first call (may not be thread safe) */ 511 if (virgin) { 512 int symbol; 513 short lengths[FIXLCODES]; 514 515 /* literal/length table */ 516 for (symbol = 0; symbol < 144; symbol++) 517 lengths[symbol] = 8; 518 for (; symbol < 256; symbol++) 519 lengths[symbol] = 9; 520 for (; symbol < 280; symbol++) 521 lengths[symbol] = 7; 522 for (; symbol < FIXLCODES; symbol++) 523 lengths[symbol] = 8; 524 construct(&lencode, lengths, FIXLCODES); 525 526 /* distance table */ 527 for (symbol = 0; symbol < MAXDCODES; symbol++) 528 lengths[symbol] = 5; 529 construct(&distcode, lengths, MAXDCODES); 530 531 /* do this just once */ 532 virgin = 0; 533 } 534 535 /* decode data until end-of-block code */ 536 return codes(s, &lencode, &distcode); 537 } 538 539 /* 540 * Process a dynamic codes block. 541 * 542 * Format notes: 543 * 544 * - A dynamic block starts with a description of the literal/length and 545 * distance codes for that block. New dynamic blocks allow the compressor to 546 * rapidly adapt to changing data with new codes optimized for that data. 547 * 548 * - The codes used by the deflate format are "canonical", which means that 549 * the actual bits of the codes are generated in an unambiguous way simply 550 * from the number of bits in each code. Therefore the code descriptions 551 * are simply a list of code lengths for each symbol. 552 * 553 * - The code lengths are stored in order for the symbols, so lengths are 554 * provided for each of the literal/length symbols, and for each of the 555 * distance symbols. 556 * 557 * - If a symbol is not used in the block, this is represented by a zero as 558 * as the code length. This does not mean a zero-length code, but rather 559 * that no code should be created for this symbol. There is no way in the 560 * deflate format to represent a zero-length code. 561 * 562 * - The maximum number of bits in a code is 15, so the possible lengths for 563 * any code are 1..15. 564 * 565 * - The fact that a length of zero is not permitted for a code has an 566 * interesting consequence. Normally if only one symbol is used for a given 567 * code, then in fact that code could be represented with zero bits. However 568 * in deflate, that code has to be at least one bit. So for example, if 569 * only a single distance base symbol appears in a block, then it will be 570 * represented by a single code of length one, in particular one 0 bit. This 571 * is an incomplete code, since if a 1 bit is received, it has no meaning, 572 * and should result in an error. So incomplete distance codes of one symbol 573 * should be permitted, and the receipt of invalid codes should be handled. 574 * 575 * - It is also possible to have a single literal/length code, but that code 576 * must be the end-of-block code, since every dynamic block has one. This 577 * is not the most efficient way to create an empty block (an empty fixed 578 * block is fewer bits), but it is allowed by the format. So incomplete 579 * literal/length codes of one symbol should also be permitted. 580 * 581 * - If there are only literal codes and no lengths, then there are no distance 582 * codes. This is represented by one distance code with zero bits. 583 * 584 * - The list of up to 286 length/literal lengths and up to 30 distance lengths 585 * are themselves compressed using Huffman codes and run-length encoding. In 586 * the list of code lengths, a 0 symbol means no code, a 1..15 symbol means 587 * that length, and the symbols 16, 17, and 18 are run-length instructions. 588 * Each of 16, 17, and 18 are follwed by extra bits to define the length of 589 * the run. 16 copies the last length 3 to 6 times. 17 represents 3 to 10 590 * zero lengths, and 18 represents 11 to 138 zero lengths. Unused symbols 591 * are common, hence the special coding for zero lengths. 592 * 593 * - The symbols for 0..18 are Huffman coded, and so that code must be 594 * described first. This is simply a sequence of up to 19 three-bit values 595 * representing no code (0) or the code length for that symbol (1..7). 596 * 597 * - A dynamic block starts with three fixed-size counts from which is computed 598 * the number of literal/length code lengths, the number of distance code 599 * lengths, and the number of code length code lengths (ok, you come up with 600 * a better name!) in the code descriptions. For the literal/length and 601 * distance codes, lengths after those provided are considered zero, i.e. no 602 * code. The code length code lengths are received in a permuted order (see 603 * the order[] array below) to make a short code length code length list more 604 * likely. As it turns out, very short and very long codes are less likely 605 * to be seen in a dynamic code description, hence what may appear initially 606 * to be a peculiar ordering. 607 * 608 * - Given the number of literal/length code lengths (nlen) and distance code 609 * lengths (ndist), then they are treated as one long list of nlen + ndist 610 * code lengths. Therefore run-length coding can and often does cross the 611 * boundary between the two sets of lengths. 612 * 613 * - So to summarize, the code description at the start of a dynamic block is 614 * three counts for the number of code lengths for the literal/length codes, 615 * the distance codes, and the code length codes. This is followed by the 616 * code length code lengths, three bits each. This is used to construct the 617 * code length code which is used to read the remainder of the lengths. Then 618 * the literal/length code lengths and distance lengths are read as a single 619 * set of lengths using the code length codes. Codes are constructed from 620 * the resulting two sets of lengths, and then finally you can start 621 * decoding actual compressed data in the block. 622 * 623 * - For reference, a "typical" size for the code description in a dynamic 624 * block is around 80 bytes. 625 */ 626 local int dynamic(struct state *s) 627 { 628 int nlen, ndist, ncode; /* number of lengths in descriptor */ 629 int index; /* index of lengths[] */ 630 int err; /* construct() return value */ 631 short lengths[MAXCODES]; /* descriptor code lengths */ 632 short lencnt[MAXBITS+1], lensym[MAXLCODES]; /* lencode memory */ 633 short distcnt[MAXBITS+1], distsym[MAXDCODES]; /* distcode memory */ 634 struct huffman lencode = {lencnt, lensym}; /* length code */ 635 struct huffman distcode = {distcnt, distsym}; /* distance code */ 636 static const short order[19] = /* permutation of code length codes */ 637 {16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15}; 638 639 /* get number of lengths in each table, check lengths */ 640 nlen = bits(s, 5) + 257; 641 ndist = bits(s, 5) + 1; 642 ncode = bits(s, 4) + 4; 643 if (nlen > MAXLCODES || ndist > MAXDCODES) 644 return -3; /* bad counts */ 645 646 /* read code length code lengths (really), missing lengths are zero */ 647 for (index = 0; index < ncode; index++) 648 lengths[order[index]] = bits(s, 3); 649 for (; index < 19; index++) 650 lengths[order[index]] = 0; 651 652 /* build huffman table for code lengths codes (use lencode temporarily) */ 653 err = construct(&lencode, lengths, 19); 654 if (err != 0) return -4; /* require complete code set here */ 655 656 /* read length/literal and distance code length tables */ 657 index = 0; 658 while (index < nlen + ndist) { 659 int symbol; /* decoded value */ 660 int len; /* last length to repeat */ 661 662 symbol = decode(s, &lencode); 663 if (symbol < 16) /* length in 0..15 */ 664 lengths[index++] = symbol; 665 else { /* repeat instruction */ 666 len = 0; /* assume repeating zeros */ 667 if (symbol == 16) { /* repeat last length 3..6 times */ 668 if (index == 0) return -5; /* no last length! */ 669 len = lengths[index - 1]; /* last length */ 670 symbol = 3 + bits(s, 2); 671 } 672 else if (symbol == 17) /* repeat zero 3..10 times */ 673 symbol = 3 + bits(s, 3); 674 else /* == 18, repeat zero 11..138 times */ 675 symbol = 11 + bits(s, 7); 676 if (index + symbol > nlen + ndist) 677 return -6; /* too many lengths! */ 678 while (symbol--) /* repeat last or zero symbol times */ 679 lengths[index++] = len; 680 } 681 } 682 683 /* build huffman table for literal/length codes */ 684 err = construct(&lencode, lengths, nlen); 685 if (err < 0 || (err > 0 && nlen - lencode.count[0] != 1)) 686 return -7; /* only allow incomplete codes if just one code */ 687 688 /* build huffman table for distance codes */ 689 err = construct(&distcode, lengths + nlen, ndist); 690 if (err < 0 || (err > 0 && ndist - distcode.count[0] != 1)) 691 return -8; /* only allow incomplete codes if just one code */ 692 693 /* decode data until end-of-block code */ 694 return codes(s, &lencode, &distcode); 695 } 696 697 /* 698 * Inflate source to dest. On return, destlen and sourcelen are updated to the 699 * size of the uncompressed data and the size of the deflate data respectively. 700 * On success, the return value of puff() is zero. If there is an error in the 701 * source data, i.e. it is not in the deflate format, then a negative value is 702 * returned. If there is not enough input available or there is not enough 703 * output space, then a positive error is returned. In that case, destlen and 704 * sourcelen are not updated to facilitate retrying from the beginning with the 705 * provision of more input data or more output space. In the case of invalid 706 * inflate data (a negative error), the dest and source pointers are updated to 707 * facilitate the debugging of deflators. 708 * 709 * puff() also has a mode to determine the size of the uncompressed output with 710 * no output written. For this dest must be (unsigned char *)0. In this case, 711 * the input value of *destlen is ignored, and on return *destlen is set to the 712 * size of the uncompressed output. 713 * 714 * The return codes are: 715 * 716 * 2: available inflate data did not terminate 717 * 1: output space exhausted before completing inflate 718 * 0: successful inflate 719 * -1: invalid block type (type == 3) 720 * -2: stored block length did not match one's complement 721 * -3: dynamic block code description: too many length or distance codes 722 * -4: dynamic block code description: code lengths codes incomplete 723 * -5: dynamic block code description: repeat lengths with no first length 724 * -6: dynamic block code description: repeat more than specified lengths 725 * -7: dynamic block code description: invalid literal/length code lengths 726 * -8: dynamic block code description: invalid distance code lengths 727 * -9: invalid literal/length or distance code in fixed or dynamic block 728 * -10: distance is too far back in fixed or dynamic block 729 * 730 * Format notes: 731 * 732 * - Three bits are read for each block to determine the kind of block and 733 * whether or not it is the last block. Then the block is decoded and the 734 * process repeated if it was not the last block. 735 * 736 * - The leftover bits in the last byte of the deflate data after the last 737 * block (if it was a fixed or dynamic block) are undefined and have no 738 * expected values to check. 739 */ 740 int puff(unsigned char *dest, /* pointer to destination pointer */ 741 unsigned long *destlen, /* amount of output space */ 742 unsigned char *source, /* pointer to source data pointer */ 743 unsigned long *sourcelen) /* amount of input available */ 744 { 745 struct state s; /* input/output state */ 746 int last, type; /* block information */ 747 int err; /* return value */ 748 749 /* initialize output state */ 750 s.out = dest; 751 s.outlen = *destlen; /* ignored if dest is NIL */ 752 s.outcnt = 0; 753 754 /* initialize input state */ 755 s.in = source; 756 s.inlen = *sourcelen; 757 s.incnt = 0; 758 s.bitbuf = 0; 759 s.bitcnt = 0; 760 761 /* return if bits() or decode() tries to read past available input */ 762 if (setjmp(s.env) != 0) /* if came back here via longjmp() */ 763 err = 2; /* then skip do-loop, return error */ 764 else { 765 /* process blocks until last block or error */ 766 do { 767 last = bits(&s, 1); /* one if last block */ 768 type = bits(&s, 2); /* block type 0..3 */ 769 err = type == 0 ? stored(&s) : 770 (type == 1 ? fixed(&s) : 771 (type == 2 ? dynamic(&s) : 772 -1)); /* type == 3, invalid */ 773 if (err != 0) break; /* return with error */ 774 } while (!last); 775 } 776 777 /* update the lengths and return */ 778 if (err <= 0) { 779 *destlen = s.outcnt; 780 *sourcelen = s.incnt; 781 } 782 return err; 783 } 784 785 #ifdef TEST 786 /* Example of how to use puff() */ 787 #include <stdio.h> 788 #include <stdlib.h> 789 #include <sys/types.h> 790 #include <sys/stat.h> 791 792 local unsigned char *yank(char *name, unsigned long *len) 793 { 794 unsigned long size; 795 unsigned char *buf; 796 FILE *in; 797 struct stat s; 798 799 *len = 0; 800 if (stat(name, &s)) return NULL; 801 if ((s.st_mode & S_IFMT) != S_IFREG) return NULL; 802 size = (unsigned long)(s.st_size); 803 if (size == 0 || (off_t)size != s.st_size) return NULL; 804 in = fopen(name, "r"); 805 if (in == NULL) return NULL; 806 buf = malloc(size); 807 if (buf != NULL && fread(buf, 1, size, in) != size) { 808 free(buf); 809 buf = NULL; 810 } 811 fclose(in); 812 *len = size; 813 return buf; 814 } 815 816 int main(int argc, char **argv) 817 { 818 int ret; 819 unsigned char *source; 820 unsigned long len, sourcelen, destlen; 821 822 if (argc < 2) return 2; 823 source = yank(argv[1], &len); 824 if (source == NULL) return 2; 825 sourcelen = len; 826 ret = puff(NIL, &destlen, source, &sourcelen); 827 if (ret) 828 printf("puff() failed with return code %d\n", ret); 829 else { 830 printf("puff() succeeded uncompressing %lu bytes\n", destlen); 831 if (sourcelen < len) printf("%lu compressed bytes unused\n", 832 len - sourcelen); 833 } 834 free(source); 835 return ret; 836 } 837 #endif 838
