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 */
bits(struct state * s,int need)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 */
stored(struct state * s)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
decode(struct state * s,struct huffman * h)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 */
decode(struct state * s,struct huffman * h)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 */
construct(struct huffman * h,short * length,int n)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 */
codes(struct state * s,struct huffman * lencode,struct huffman * distcode)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 */
fixed(struct state * s)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 */
dynamic(struct state * s)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 */
puff(unsigned char * dest,unsigned long * destlen,unsigned char * source,unsigned long * sourcelen)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
yank(char * name,unsigned long * len)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
main(int argc,char ** argv)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