1 /*
2 * puff.c
3 * Copyright (C) 2002-2013 Mark Adler
4 * For conditions of distribution and use, see copyright notice in puff.h
5 * version 2.3, 21 Jan 2013
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 [Gailly]
53 * - Add a puff.h file for the interface
54 * - Add braces in puff() for else do [Gailly]
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 * 1.9 21 Feb 2008 - Fix bug on 16-bit integer architectures [Pohland]
65 * - Catch missing end-of-block symbol error
66 * 2.0 25 Jul 2008 - Add #define to permit distance too far back
67 * - Add option in TEST code for puff to write the data
68 * - Add option in TEST code to skip input bytes
69 * - Allow TEST code to read from piped stdin
70 * 2.1 4 Apr 2010 - Avoid variable initialization for happier compilers
71 * - Avoid unsigned comparisons for even happier compilers
72 * 2.2 25 Apr 2010 - Fix bug in variable initializations [Oberhumer]
73 * - Add const where appropriate [Oberhumer]
74 * - Split if's and ?'s for coverage testing
75 * - Break out test code to separate file
76 * - Move NIL to puff.h
77 * - Allow incomplete code only if single code length is 1
78 * - Add full code coverage test to Makefile
79 * 2.3 21 Jan 2013 - Check for invalid code length codes in dynamic blocks
80 */
81
82 #include <setjmp.h> /* for setjmp(), longjmp(), and jmp_buf */
83 #include "puff.h" /* prototype for puff() */
84
85 #define local static /* for local function definitions */
86
87 /*
88 * Maximums for allocations and loops. It is not useful to change these --
89 * they are fixed by the deflate format.
90 */
91 #define MAXBITS 15 /* maximum bits in a code */
92 #define MAXLCODES 286 /* maximum number of literal/length codes */
93 #define MAXDCODES 30 /* maximum number of distance codes */
94 #define MAXCODES (MAXLCODES+MAXDCODES) /* maximum codes lengths to read */
95 #define FIXLCODES 288 /* number of fixed literal/length codes */
96
97 /* input and output state */
98 struct state {
99 /* output state */
100 unsigned char *out; /* output buffer */
101 unsigned long outlen; /* available space at out */
102 unsigned long outcnt; /* bytes written to out so far */
103
104 /* input state */
105 const unsigned char *in; /* input buffer */
106 unsigned long inlen; /* available input at in */
107 unsigned long incnt; /* bytes read so far */
108 int bitbuf; /* bit buffer */
109 int bitcnt; /* number of bits in bit buffer */
110
111 /* input limit error return state for bits() and decode() */
112 jmp_buf env;
113 };
114
115 /*
116 * Return need bits from the input stream. This always leaves less than
117 * eight bits in the buffer. bits() works properly for need == 0.
118 *
119 * Format notes:
120 *
121 * - Bits are stored in bytes from the least significant bit to the most
122 * significant bit. Therefore bits are dropped from the bottom of the bit
123 * buffer, using shift right, and new bytes are appended to the top of the
124 * bit buffer, using shift left.
125 */
126 local int bits(struct state *s, int need)
127 {
128 long val; /* bit accumulator (can use up to 20 bits) */
129
130 /* load at least need bits into val */
131 val = s->bitbuf;
132 while (s->bitcnt < need) {
133 if (s->incnt == s->inlen)
134 longjmp(s->env, 1); /* out of input */
135 val |= (long)(s->in[s->incnt++]) << s->bitcnt; /* load eight bits */
136 s->bitcnt += 8;
137 }
138
139 /* drop need bits and update buffer, always zero to seven bits left */
140 s->bitbuf = (int)(val >> need);
141 s->bitcnt -= need;
142
143 /* return need bits, zeroing the bits above that */
144 return (int)(val & ((1L << need) - 1));
145 }
146
147 /*
148 * Process a stored block.
149 *
150 * Format notes:
151 *
152 * - After the two-bit stored block type (00), the stored block length and
153 * stored bytes are byte-aligned for fast copying. Therefore any leftover
154 * bits in the byte that has the last bit of the type, as many as seven, are
155 * discarded. The value of the discarded bits are not defined and should not
156 * be checked against any expectation.
157 *
158 * - The second inverted copy of the stored block length does not have to be
159 * checked, but it's probably a good idea to do so anyway.
160 *
161 * - A stored block can have zero length. This is sometimes used to byte-align
162 * subsets of the compressed data for random access or partial recovery.
163 */
164 local int stored(struct state *s)
165 {
166 unsigned len; /* length of stored block */
167
168 /* discard leftover bits from current byte (assumes s->bitcnt < 8) */
169 s->bitbuf = 0;
170 s->bitcnt = 0;
171
172 /* get length and check against its one's complement */
173 if (s->incnt + 4 > s->inlen)
174 return 2; /* not enough input */
175 len = s->in[s->incnt++];
176 len |= s->in[s->incnt++] << 8;
177 if (s->in[s->incnt++] != (~len & 0xff) ||
178 s->in[s->incnt++] != ((~len >> 8) & 0xff))
179 return -2; /* didn't match complement! */
180
181 /* copy len bytes from in to out */
182 if (s->incnt + len > s->inlen)
183 return 2; /* not enough input */
184 if (s->out != NIL) {
185 if (s->outcnt + len > s->outlen)
186 return 1; /* not enough output space */
187 while (len--)
188 s->out[s->outcnt++] = s->in[s->incnt++];
189 }
190 else { /* just scanning */
191 s->outcnt += len;
192 s->incnt += len;
193 }
194
195 /* done with a valid stored block */
196 return 0;
197 }
198
199 /*
200 * Huffman code decoding tables. count[1..MAXBITS] is the number of symbols of
201 * each length, which for a canonical code are stepped through in order.
202 * symbol[] are the symbol values in canonical order, where the number of
203 * entries is the sum of the counts in count[]. The decoding process can be
204 * seen in the function decode() below.
205 */
206 struct huffman {
207 short *count; /* number of symbols of each length */
208 short *symbol; /* canonically ordered symbols */
209 };
210
211 /*
212 * Decode a code from the stream s using huffman table h. Return the symbol or
213 * a negative value if there is an error. If all of the lengths are zero, i.e.
214 * an empty code, or if the code is incomplete and an invalid code is received,
215 * then -10 is returned after reading MAXBITS bits.
216 *
217 * Format notes:
218 *
219 * - The codes as stored in the compressed data are bit-reversed relative to
220 * a simple integer ordering of codes of the same lengths. Hence below the
221 * bits are pulled from the compressed data one at a time and used to
222 * build the code value reversed from what is in the stream in order to
223 * permit simple integer comparisons for decoding. A table-based decoding
224 * scheme (as used in zlib) does not need to do this reversal.
225 *
226 * - The first code for the shortest length is all zeros. Subsequent codes of
227 * the same length are simply integer increments of the previous code. When
228 * moving up a length, a zero bit is appended to the code. For a complete
229 * code, the last code of the longest length will be all ones.
230 *
231 * - Incomplete codes are handled by this decoder, since they are permitted
232 * in the deflate format. See the format notes for fixed() and dynamic().
233 */
234 #ifdef SLOW
235 local int decode(struct state *s, const struct huffman *h)
236 {
237 int len; /* current number of bits in code */
238 int code; /* len bits being decoded */
239 int first; /* first code of length len */
240 int count; /* number of codes of length len */
241 int index; /* index of first code of length len in symbol table */
242
243 code = first = index = 0;
244 for (len = 1; len <= MAXBITS; len++) {
245 code |= bits(s, 1); /* get next bit */
246 count = h->count[len];
247 if (code - count < first) /* if length len, return symbol */
248 return h->symbol[index + (code - first)];
249 index += count; /* else update for next length */
250 first += count;
251 first <<= 1;
252 code <<= 1;
253 }
254 return -10; /* ran out of codes */
255 }
256
257 /*
258 * A faster version of decode() for real applications of this code. It's not
259 * as readable, but it makes puff() twice as fast. And it only makes the code
260 * a few percent larger.
261 */
262 #else /* !SLOW */
263 local int decode(struct state *s, const struct huffman *h)
264 {
265 int len; /* current number of bits in code */
266 int code; /* len bits being decoded */
267 int first; /* first code of length len */
268 int count; /* number of codes of length len */
269 int index; /* index of first code of length len in symbol table */
270 int bitbuf; /* bits from stream */
271 int left; /* bits left in next or left to process */
272 short *next; /* next number of codes */
273
274 bitbuf = s->bitbuf;
275 left = s->bitcnt;
276 code = first = index = 0;
277 len = 1;
278 next = h->count + 1;
279 while (1) {
280 while (left--) {
281 code |= bitbuf & 1;
282 bitbuf >>= 1;
283 count = *next++;
284 if (code - count < first) { /* if length len, return symbol */
285 s->bitbuf = bitbuf;
286 s->bitcnt = (s->bitcnt - len) & 7;
287 return h->symbol[index + (code - first)];
288 }
289 index += count; /* else update for next length */
290 first += count;
291 first <<= 1;
292 code <<= 1;
293 len++;
294 }
295 left = (MAXBITS+1) - len;
296 if (left == 0)
297 break;
298 if (s->incnt == s->inlen)
299 longjmp(s->env, 1); /* out of input */
300 bitbuf = s->in[s->incnt++];
301 if (left > 8)
302 left = 8;
303 }
304 return -10; /* ran out of codes */
305 }
306 #endif /* SLOW */
307
308 /*
309 * Given the list of code lengths length[0..n-1] representing a canonical
310 * Huffman code for n symbols, construct the tables required to decode those
311 * codes. Those tables are the number of codes of each length, and the symbols
312 * sorted by length, retaining their original order within each length. The
313 * return value is zero for a complete code set, negative for an over-
314 * subscribed code set, and positive for an incomplete code set. The tables
315 * can be used if the return value is zero or positive, but they cannot be used
316 * if the return value is negative. If the return value is zero, it is not
317 * possible for decode() using that table to return an error--any stream of
318 * enough bits will resolve to a symbol. If the return value is positive, then
319 * it is possible for decode() using that table to return an error for received
320 * codes past the end of the incomplete lengths.
321 *
322 * Not used by decode(), but used for error checking, h->count[0] is the number
323 * of the n symbols not in the code. So n - h->count[0] is the number of
324 * codes. This is useful for checking for incomplete codes that have more than
325 * one symbol, which is an error in a dynamic block.
326 *
327 * Assumption: for all i in 0..n-1, 0 <= length[i] <= MAXBITS
328 * This is assured by the construction of the length arrays in dynamic() and
329 * fixed() and is not verified by construct().
330 *
331 * Format notes:
332 *
333 * - Permitted and expected examples of incomplete codes are one of the fixed
334 * codes and any code with a single symbol which in deflate is coded as one
335 * bit instead of zero bits. See the format notes for fixed() and dynamic().
336 *
337 * - Within a given code length, the symbols are kept in ascending order for
338 * the code bits definition.
339 */
340 local int construct(struct huffman *h, const short *length, int n)
341 {
342 int symbol; /* current symbol when stepping through length[] */
343 int len; /* current length when stepping through h->count[] */
344 int left; /* number of possible codes left of current length */
345 short offs[MAXBITS+1]; /* offsets in symbol table for each length */
346
347 /* count number of codes of each length */
348 for (len = 0; len <= MAXBITS; len++)
349 h->count[len] = 0;
350 for (symbol = 0; symbol < n; symbol++)
351 (h->count[length[symbol]])++; /* assumes lengths are within bounds */
352 if (h->count[0] == n) /* no codes! */
353 return 0; /* complete, but decode() will fail */
354
355 /* check for an over-subscribed or incomplete set of lengths */
356 left = 1; /* one possible code of zero length */
357 for (len = 1; len <= MAXBITS; len++) {
358 left <<= 1; /* one more bit, double codes left */
359 left -= h->count[len]; /* deduct count from possible codes */
360 if (left < 0)
361 return left; /* over-subscribed--return negative */
362 } /* left > 0 means incomplete */
363
364 /* generate offsets into symbol table for each length for sorting */
365 offs[1] = 0;
366 for (len = 1; len < MAXBITS; len++)
367 offs[len + 1] = offs[len] + h->count[len];
368
369 /*
370 * put symbols in table sorted by length, by symbol order within each
371 * length
372 */
373 for (symbol = 0; symbol < n; symbol++)
374 if (length[symbol] != 0)
375 h->symbol[offs[length[symbol]]++] = symbol;
376
377 /* return zero for complete set, positive for incomplete set */
378 return left;
379 }
380
381 /*
382 * Decode literal/length and distance codes until an end-of-block code.
383 *
384 * Format notes:
385 *
386 * - Compressed data that is after the block type if fixed or after the code
387 * description if dynamic is a combination of literals and length/distance
388 * pairs terminated by and end-of-block code. Literals are simply Huffman
389 * coded bytes. A length/distance pair is a coded length followed by a
390 * coded distance to represent a string that occurs earlier in the
391 * uncompressed data that occurs again at the current location.
392 *
393 * - Literals, lengths, and the end-of-block code are combined into a single
394 * code of up to 286 symbols. They are 256 literals (0..255), 29 length
395 * symbols (257..285), and the end-of-block symbol (256).
396 *
397 * - There are 256 possible lengths (3..258), and so 29 symbols are not enough
398 * to represent all of those. Lengths 3..10 and 258 are in fact represented
399 * by just a length symbol. Lengths 11..257 are represented as a symbol and
400 * some number of extra bits that are added as an integer to the base length
401 * of the length symbol. The number of extra bits is determined by the base
402 * length symbol. These are in the static arrays below, lens[] for the base
403 * lengths and lext[] for the corresponding number of extra bits.
404 *
405 * - The reason that 258 gets its own symbol is that the longest length is used
406 * often in highly redundant files. Note that 258 can also be coded as the
407 * base value 227 plus the maximum extra value of 31. While a good deflate
408 * should never do this, it is not an error, and should be decoded properly.
409 *
410 * - If a length is decoded, including its extra bits if any, then it is
411 * followed a distance code. There are up to 30 distance symbols. Again
412 * there are many more possible distances (1..32768), so extra bits are added
413 * to a base value represented by the symbol. The distances 1..4 get their
414 * own symbol, but the rest require extra bits. The base distances and
415 * corresponding number of extra bits are below in the static arrays dist[]
416 * and dext[].
417 *
418 * - Literal bytes are simply written to the output. A length/distance pair is
419 * an instruction to copy previously uncompressed bytes to the output. The
420 * copy is from distance bytes back in the output stream, copying for length
421 * bytes.
422 *
423 * - Distances pointing before the beginning of the output data are not
424 * permitted.
425 *
426 * - Overlapped copies, where the length is greater than the distance, are
427 * allowed and common. For example, a distance of one and a length of 258
428 * simply copies the last byte 258 times. A distance of four and a length of
429 * twelve copies the last four bytes three times. A simple forward copy
430 * ignoring whether the length is greater than the distance or not implements
431 * this correctly. You should not use memcpy() since its behavior is not
432 * defined for overlapped arrays. You should not use memmove() or bcopy()
433 * since though their behavior -is- defined for overlapping arrays, it is
434 * defined to do the wrong thing in this case.
435 */
436 local int codes(struct state *s,
437 const struct huffman *lencode,
438 const struct huffman *distcode)
439 {
440 int symbol; /* decoded symbol */
441 int len; /* length for copy */
442 unsigned dist; /* distance for copy */
443 static const short lens[29] = { /* Size base for length codes 257..285 */
444 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
445 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258};
446 static const short lext[29] = { /* Extra bits for length codes 257..285 */
447 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2,
448 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0};
449 static const short dists[30] = { /* Offset base for distance codes 0..29 */
450 1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
451 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
452 8193, 12289, 16385, 24577};
453 static const short dext[30] = { /* Extra bits for distance codes 0..29 */
454 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6,
455 7, 7, 8, 8, 9, 9, 10, 10, 11, 11,
456 12, 12, 13, 13};
457
458 /* decode literals and length/distance pairs */
459 do {
460 symbol = decode(s, lencode);
461 if (symbol < 0)
462 return symbol; /* invalid symbol */
463 if (symbol < 256) { /* literal: symbol is the byte */
464 /* write out the literal */
465 if (s->out != NIL) {
466 if (s->outcnt == s->outlen)
467 return 1;
468 s->out[s->outcnt] = symbol;
469 }
470 s->outcnt++;
471 }
472 else if (symbol > 256) { /* length */
473 /* get and compute length */
474 symbol -= 257;
475 if (symbol >= 29)
476 return -10; /* invalid fixed code */
477 len = lens[symbol] + bits(s, lext[symbol]);
478
479 /* get and check distance */
480 symbol = decode(s, distcode);
481 if (symbol < 0)
482 return symbol; /* invalid symbol */
483 dist = dists[symbol] + bits(s, dext[symbol]);
484 #ifndef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
485 if (dist > s->outcnt)
486 return -11; /* distance too far back */
487 #endif
488
489 /* copy length bytes from distance bytes back */
490 if (s->out != NIL) {
491 if (s->outcnt + len > s->outlen)
492 return 1;
493 while (len--) {
494 s->out[s->outcnt] =
495 #ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
496 dist > s->outcnt ?
497 0 :
498 #endif
499 s->out[s->outcnt - dist];
500 s->outcnt++;
501 }
502 }
503 else
504 s->outcnt += len;
505 }
506 } while (symbol != 256); /* end of block symbol */
507
508 /* done with a valid fixed or dynamic block */
509 return 0;
510 }
511
512 /*
513 * Process a fixed codes block.
514 *
515 * Format notes:
516 *
517 * - This block type can be useful for compressing small amounts of data for
518 * which the size of the code descriptions in a dynamic block exceeds the
519 * benefit of custom codes for that block. For fixed codes, no bits are
520 * spent on code descriptions. Instead the code lengths for literal/length
521 * codes and distance codes are fixed. The specific lengths for each symbol
522 * can be seen in the "for" loops below.
523 *
524 * - The literal/length code is complete, but has two symbols that are invalid
525 * and should result in an error if received. This cannot be implemented
526 * simply as an incomplete code since those two symbols are in the "middle"
527 * of the code. They are eight bits long and the longest literal/length\
528 * code is nine bits. Therefore the code must be constructed with those
529 * symbols, and the invalid symbols must be detected after decoding.
530 *
531 * - The fixed distance codes also have two invalid symbols that should result
532 * in an error if received. Since all of the distance codes are the same
533 * length, this can be implemented as an incomplete code. Then the invalid
534 * codes are detected while decoding.
535 */
536 local int fixed(struct state *s)
537 {
538 static int virgin = 1;
539 static short lencnt[MAXBITS+1], lensym[FIXLCODES];
540 static short distcnt[MAXBITS+1], distsym[MAXDCODES];
541 static struct huffman lencode, distcode;
542
543 /* build fixed huffman tables if first call (may not be thread safe) */
544 if (virgin) {
545 int symbol;
546 short lengths[FIXLCODES];
547
548 /* construct lencode and distcode */
549 lencode.count = lencnt;
550 lencode.symbol = lensym;
551 distcode.count = distcnt;
552 distcode.symbol = distsym;
553
554 /* literal/length table */
555 for (symbol = 0; symbol < 144; symbol++)
556 lengths[symbol] = 8;
557 for (; symbol < 256; symbol++)
558 lengths[symbol] = 9;
559 for (; symbol < 280; symbol++)
560 lengths[symbol] = 7;
561 for (; symbol < FIXLCODES; symbol++)
562 lengths[symbol] = 8;
563 construct(&lencode, lengths, FIXLCODES);
564
565 /* distance table */
566 for (symbol = 0; symbol < MAXDCODES; symbol++)
567 lengths[symbol] = 5;
568 construct(&distcode, lengths, MAXDCODES);
569
570 /* do this just once */
571 virgin = 0;
572 }
573
574 /* decode data until end-of-block code */
575 return codes(s, &lencode, &distcode);
576 }
577
578 /*
579 * Process a dynamic codes block.
580 *
581 * Format notes:
582 *
583 * - A dynamic block starts with a description of the literal/length and
584 * distance codes for that block. New dynamic blocks allow the compressor to
585 * rapidly adapt to changing data with new codes optimized for that data.
586 *
587 * - The codes used by the deflate format are "canonical", which means that
588 * the actual bits of the codes are generated in an unambiguous way simply
589 * from the number of bits in each code. Therefore the code descriptions
590 * are simply a list of code lengths for each symbol.
591 *
592 * - The code lengths are stored in order for the symbols, so lengths are
593 * provided for each of the literal/length symbols, and for each of the
594 * distance symbols.
595 *
596 * - If a symbol is not used in the block, this is represented by a zero as
597 * as the code length. This does not mean a zero-length code, but rather
598 * that no code should be created for this symbol. There is no way in the
599 * deflate format to represent a zero-length code.
600 *
601 * - The maximum number of bits in a code is 15, so the possible lengths for
602 * any code are 1..15.
603 *
604 * - The fact that a length of zero is not permitted for a code has an
605 * interesting consequence. Normally if only one symbol is used for a given
606 * code, then in fact that code could be represented with zero bits. However
607 * in deflate, that code has to be at least one bit. So for example, if
608 * only a single distance base symbol appears in a block, then it will be
609 * represented by a single code of length one, in particular one 0 bit. This
610 * is an incomplete code, since if a 1 bit is received, it has no meaning,
611 * and should result in an error. So incomplete distance codes of one symbol
612 * should be permitted, and the receipt of invalid codes should be handled.
613 *
614 * - It is also possible to have a single literal/length code, but that code
615 * must be the end-of-block code, since every dynamic block has one. This
616 * is not the most efficient way to create an empty block (an empty fixed
617 * block is fewer bits), but it is allowed by the format. So incomplete
618 * literal/length codes of one symbol should also be permitted.
619 *
620 * - If there are only literal codes and no lengths, then there are no distance
621 * codes. This is represented by one distance code with zero bits.
622 *
623 * - The list of up to 286 length/literal lengths and up to 30 distance lengths
624 * are themselves compressed using Huffman codes and run-length encoding. In
625 * the list of code lengths, a 0 symbol means no code, a 1..15 symbol means
626 * that length, and the symbols 16, 17, and 18 are run-length instructions.
627 * Each of 16, 17, and 18 are follwed by extra bits to define the length of
628 * the run. 16 copies the last length 3 to 6 times. 17 represents 3 to 10
629 * zero lengths, and 18 represents 11 to 138 zero lengths. Unused symbols
630 * are common, hence the special coding for zero lengths.
631 *
632 * - The symbols for 0..18 are Huffman coded, and so that code must be
633 * described first. This is simply a sequence of up to 19 three-bit values
634 * representing no code (0) or the code length for that symbol (1..7).
635 *
636 * - A dynamic block starts with three fixed-size counts from which is computed
637 * the number of literal/length code lengths, the number of distance code
638 * lengths, and the number of code length code lengths (ok, you come up with
639 * a better name!) in the code descriptions. For the literal/length and
640 * distance codes, lengths after those provided are considered zero, i.e. no
641 * code. The code length code lengths are received in a permuted order (see
642 * the order[] array below) to make a short code length code length list more
643 * likely. As it turns out, very short and very long codes are less likely
644 * to be seen in a dynamic code description, hence what may appear initially
645 * to be a peculiar ordering.
646 *
647 * - Given the number of literal/length code lengths (nlen) and distance code
648 * lengths (ndist), then they are treated as one long list of nlen + ndist
649 * code lengths. Therefore run-length coding can and often does cross the
650 * boundary between the two sets of lengths.
651 *
652 * - So to summarize, the code description at the start of a dynamic block is
653 * three counts for the number of code lengths for the literal/length codes,
654 * the distance codes, and the code length codes. This is followed by the
655 * code length code lengths, three bits each. This is used to construct the
656 * code length code which is used to read the remainder of the lengths. Then
657 * the literal/length code lengths and distance lengths are read as a single
658 * set of lengths using the code length codes. Codes are constructed from
659 * the resulting two sets of lengths, and then finally you can start
660 * decoding actual compressed data in the block.
661 *
662 * - For reference, a "typical" size for the code description in a dynamic
663 * block is around 80 bytes.
664 */
665 local int dynamic(struct state *s)
666 {
667 int nlen, ndist, ncode; /* number of lengths in descriptor */
668 int index; /* index of lengths[] */
669 int err; /* construct() return value */
670 short lengths[MAXCODES]; /* descriptor code lengths */
671 short lencnt[MAXBITS+1], lensym[MAXLCODES]; /* lencode memory */
672 short distcnt[MAXBITS+1], distsym[MAXDCODES]; /* distcode memory */
673 struct huffman lencode, distcode; /* length and distance codes */
674 static const short order[19] = /* permutation of code length codes */
675 {16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};
676
677 /* construct lencode and distcode */
678 lencode.count = lencnt;
679 lencode.symbol = lensym;
680 distcode.count = distcnt;
681 distcode.symbol = distsym;
682
683 /* get number of lengths in each table, check lengths */
684 nlen = bits(s, 5) + 257;
685 ndist = bits(s, 5) + 1;
686 ncode = bits(s, 4) + 4;
687 if (nlen > MAXLCODES || ndist > MAXDCODES)
688 return -3; /* bad counts */
689
690 /* read code length code lengths (really), missing lengths are zero */
691 for (index = 0; index < ncode; index++)
692 lengths[order[index]] = bits(s, 3);
693 for (; index < 19; index++)
694 lengths[order[index]] = 0;
695
696 /* build huffman table for code lengths codes (use lencode temporarily) */
697 err = construct(&lencode, lengths, 19);
698 if (err != 0) /* require complete code set here */
699 return -4;
700
701 /* read length/literal and distance code length tables */
702 index = 0;
703 while (index < nlen + ndist) {
704 int symbol; /* decoded value */
705 int len; /* last length to repeat */
706
707 symbol = decode(s, &lencode);
708 if (symbol < 0)
709 return symbol; /* invalid symbol */
710 if (symbol < 16) /* length in 0..15 */
711 lengths[index++] = symbol;
712 else { /* repeat instruction */
713 len = 0; /* assume repeating zeros */
714 if (symbol == 16) { /* repeat last length 3..6 times */
715 if (index == 0)
716 return -5; /* no last length! */
717 len = lengths[index - 1]; /* last length */
718 symbol = 3 + bits(s, 2);
719 }
720 else if (symbol == 17) /* repeat zero 3..10 times */
721 symbol = 3 + bits(s, 3);
722 else /* == 18, repeat zero 11..138 times */
723 symbol = 11 + bits(s, 7);
724 if (index + symbol > nlen + ndist)
725 return -6; /* too many lengths! */
726 while (symbol--) /* repeat last or zero symbol times */
727 lengths[index++] = len;
728 }
729 }
730
731 /* check for end-of-block code -- there better be one! */
732 if (lengths[256] == 0)
733 return -9;
734
735 /* build huffman table for literal/length codes */
736 err = construct(&lencode, lengths, nlen);
737 if (err && (err < 0 || nlen != lencode.count[0] + lencode.count[1]))
738 return -7; /* incomplete code ok only for single length 1 code */
739
740 /* build huffman table for distance codes */
741 err = construct(&distcode, lengths + nlen, ndist);
742 if (err && (err < 0 || ndist != distcode.count[0] + distcode.count[1]))
743 return -8; /* incomplete code ok only for single length 1 code */
744
745 /* decode data until end-of-block code */
746 return codes(s, &lencode, &distcode);
747 }
748
749 /*
750 * Inflate source to dest. On return, destlen and sourcelen are updated to the
751 * size of the uncompressed data and the size of the deflate data respectively.
752 * On success, the return value of puff() is zero. If there is an error in the
753 * source data, i.e. it is not in the deflate format, then a negative value is
754 * returned. If there is not enough input available or there is not enough
755 * output space, then a positive error is returned. In that case, destlen and
756 * sourcelen are not updated to facilitate retrying from the beginning with the
757 * provision of more input data or more output space. In the case of invalid
758 * inflate data (a negative error), the dest and source pointers are updated to
759 * facilitate the debugging of deflators.
760 *
761 * puff() also has a mode to determine the size of the uncompressed output with
762 * no output written. For this dest must be (unsigned char *)0. In this case,
763 * the input value of *destlen is ignored, and on return *destlen is set to the
764 * size of the uncompressed output.
765 *
766 * The return codes are:
767 *
768 * 2: available inflate data did not terminate
769 * 1: output space exhausted before completing inflate
770 * 0: successful inflate
771 * -1: invalid block type (type == 3)
772 * -2: stored block length did not match one's complement
773 * -3: dynamic block code description: too many length or distance codes
774 * -4: dynamic block code description: code lengths codes incomplete
775 * -5: dynamic block code description: repeat lengths with no first length
776 * -6: dynamic block code description: repeat more than specified lengths
777 * -7: dynamic block code description: invalid literal/length code lengths
778 * -8: dynamic block code description: invalid distance code lengths
779 * -9: dynamic block code description: missing end-of-block code
780 * -10: invalid literal/length or distance code in fixed or dynamic block
781 * -11: distance is too far back in fixed or dynamic block
782 *
783 * Format notes:
784 *
785 * - Three bits are read for each block to determine the kind of block and
786 * whether or not it is the last block. Then the block is decoded and the
787 * process repeated if it was not the last block.
788 *
789 * - The leftover bits in the last byte of the deflate data after the last
790 * block (if it was a fixed or dynamic block) are undefined and have no
791 * expected values to check.
792 */
793 int puff(unsigned char *dest, /* pointer to destination pointer */
794 unsigned long *destlen, /* amount of output space */
795 const unsigned char *source, /* pointer to source data pointer */
796 unsigned long *sourcelen) /* amount of input available */
797 {
798 struct state s; /* input/output state */
799 int last, type; /* block information */
800 int err; /* return value */
801
802 /* initialize output state */
803 s.out = dest;
804 s.outlen = *destlen; /* ignored if dest is NIL */
805 s.outcnt = 0;
806
807 /* initialize input state */
808 s.in = source;
809 s.inlen = *sourcelen;
810 s.incnt = 0;
811 s.bitbuf = 0;
812 s.bitcnt = 0;
813
814 /* return if bits() or decode() tries to read past available input */
815 if (setjmp(s.env) != 0) /* if came back here via longjmp() */
816 err = 2; /* then skip do-loop, return error */
817 else {
818 /* process blocks until last block or error */
819 do {
820 last = bits(&s, 1); /* one if last block */
821 type = bits(&s, 2); /* block type 0..3 */
822 err = type == 0 ?
823 stored(&s) :
824 (type == 1 ?
825 fixed(&s) :
826 (type == 2 ?
827 dynamic(&s) :
828 -1)); /* type == 3, invalid */
829 if (err != 0)
830 break; /* return with error */
831 } while (!last);
832 }
833
834 /* update the lengths and return */
835 if (err <= 0) {
836 *destlen = s.outcnt;
837 *sourcelen = s.incnt;
838 }
839 return err;
840 }