2
* Copyright (C) 2003 Mark Adler
3
* For conditions of distribution and use, see copyright notice in blast.h
4
* version 1.1, 16 Feb 2003
6
* blast.c decompresses data compressed by the PKWare Compression Library.
7
* This function provides functionality similar to the explode() function of
8
* the PKWare library, hence the name "blast".
10
* This decompressor is based on the excellent format description provided by
11
* Ben Rudiak-Gould in comp.compression on August 13, 2001. Interestingly, the
12
* example Ben provided in the post is incorrect. The distance 110001 should
13
* instead be 111000. When corrected, the example byte stream becomes:
15
* 00 04 82 24 25 8f 80 7f
17
* which decompresses to "AIAIAIAIAIAIA" (without the quotes).
23
* 1.0 12 Feb 2003 - First version
24
* 1.1 16 Feb 2003 - Fixed distance check for > 4 GB uncompressed data
27
#include <setjmp.h> /* for setjmp(), longjmp(), and jmp_buf */
28
#include "blast.h" /* prototype for blast() */
30
#define local static /* for local function definitions */
31
#define MAXBITS 13 /* maximum code length */
32
#define MAXWIN 4096 /* maximum window size */
34
/* input and output state */
37
blast_in infun; /* input function provided by user */
38
void *inhow; /* opaque information passed to infun() */
39
unsigned char *in; /* next input location */
40
unsigned left; /* available input at in */
41
int bitbuf; /* bit buffer */
42
int bitcnt; /* number of bits in bit buffer */
44
/* input limit error return state for bits() and decode() */
48
blast_out outfun; /* output function provided by user */
49
void *outhow; /* opaque information passed to outfun() */
50
unsigned next; /* index of next write location in out[] */
51
int first; /* true to check distances (for first 4K) */
52
unsigned char out[MAXWIN]; /* output buffer and sliding window */
56
* Return need bits from the input stream. This always leaves less than
57
* eight bits in the buffer. bits() works properly for need == 0.
61
* - Bits are stored in bytes from the least significant bit to the most
62
* significant bit. Therefore bits are dropped from the bottom of the bit
63
* buffer, using shift right, and new bytes are appended to the top of the
64
* bit buffer, using shift left.
66
local int bits(struct state *s, int need)
68
int val; /* bit accumulator */
70
/* load at least need bits into val */
72
while (s->bitcnt < need) {
74
s->left = s->infun(s->inhow, &(s->in));
75
if (s->left == 0) longjmp(s->env, 1); /* out of input */
77
val |= (int)(*(s->in)++) << s->bitcnt; /* load eight bits */
82
/* drop need bits and update buffer, always zero to seven bits left */
83
s->bitbuf = val >> need;
86
/* return need bits, zeroing the bits above that */
87
return val & ((1 << need) - 1);
91
* Huffman code decoding tables. count[1..MAXBITS] is the number of symbols of
92
* each length, which for a canonical code are stepped through in order.
93
* symbol[] are the symbol values in canonical order, where the number of
94
* entries is the sum of the counts in count[]. The decoding process can be
95
* seen in the function decode() below.
98
short *count; /* number of symbols of each length */
99
short *symbol; /* canonically ordered symbols */
103
* Decode a code from the stream s using huffman table h. Return the symbol or
104
* a negative value if there is an error. If all of the lengths are zero, i.e.
105
* an empty code, or if the code is incomplete and an invalid code is received,
106
* then -9 is returned after reading MAXBITS bits.
110
* - The codes as stored in the compressed data are bit-reversed relative to
111
* a simple integer ordering of codes of the same lengths. Hence below the
112
* bits are pulled from the compressed data one at a time and used to
113
* build the code value reversed from what is in the stream in order to
114
* permit simple integer comparisons for decoding.
116
* - The first code for the shortest length is all ones. Subsequent codes of
117
* the same length are simply integer decrements of the previous code. When
118
* moving up a length, a one bit is appended to the code. For a complete
119
* code, the last code of the longest length will be all zeros. To support
120
* this ordering, the bits pulled during decoding are inverted to apply the
121
* more "natural" ordering starting with all zeros and incrementing.
123
local int decode(struct state *s, struct huffman *h)
125
int len; /* current number of bits in code */
126
int code; /* len bits being decoded */
127
int first; /* first code of length len */
128
int count; /* number of codes of length len */
129
int index; /* index of first code of length len in symbol table */
130
int bitbuf; /* bits from stream */
131
int left; /* bits left in next or left to process */
132
short *next; /* next number of codes */
136
code = first = index = 0;
141
code |= (bitbuf & 1) ^ 1; /* invert code */
144
if (code < first + count) { /* if length len, return symbol */
146
s->bitcnt = (s->bitcnt - len) & 7;
147
return h->symbol[index + (code - first)];
149
index += count; /* else update for next length */
155
left = (MAXBITS+1) - len;
156
if (left == 0) break;
158
s->left = s->infun(s->inhow, &(s->in));
159
if (s->left == 0) longjmp(s->env, 1); /* out of input */
163
if (left > 8) left = 8;
165
return -9; /* ran out of codes */
169
* Given a list of repeated code lengths rep[0..n-1], where each byte is a
170
* count (high four bits + 1) and a code length (low four bits), generate the
171
* list of code lengths. This compaction reduces the size of the object code.
172
* Then given the list of code lengths length[0..n-1] representing a canonical
173
* Huffman code for n symbols, construct the tables required to decode those
174
* codes. Those tables are the number of codes of each length, and the symbols
175
* sorted by length, retaining their original order within each length. The
176
* return value is zero for a complete code set, negative for an over-
177
* subscribed code set, and positive for an incomplete code set. The tables
178
* can be used if the return value is zero or positive, but they cannot be used
179
* if the return value is negative. If the return value is zero, it is not
180
* possible for decode() using that table to return an error--any stream of
181
* enough bits will resolve to a symbol. If the return value is positive, then
182
* it is possible for decode() using that table to return an error for received
183
* codes past the end of the incomplete lengths.
185
local int construct(struct huffman *h, const unsigned char *rep, int n)
187
int symbol; /* current symbol when stepping through length[] */
188
int len; /* current length when stepping through h->count[] */
189
int left; /* number of possible codes left of current length */
190
short offs[MAXBITS+1]; /* offsets in symbol table for each length */
191
short length[256]; /* code lengths */
193
/* convert compact repeat counts into symbol bit length list */
197
left = (len >> 4) + 1;
200
length[symbol++] = len;
205
/* count number of codes of each length */
206
for (len = 0; len <= MAXBITS; len++)
208
for (symbol = 0; symbol < n; symbol++)
209
(h->count[length[symbol]])++; /* assumes lengths are within bounds */
210
if (h->count[0] == n) /* no codes! */
211
return 0; /* complete, but decode() will fail */
213
/* check for an over-subscribed or incomplete set of lengths */
214
left = 1; /* one possible code of zero length */
215
for (len = 1; len <= MAXBITS; len++) {
216
left <<= 1; /* one more bit, double codes left */
217
left -= h->count[len]; /* deduct count from possible codes */
218
if (left < 0) return left; /* over-subscribed--return negative */
219
} /* left > 0 means incomplete */
221
/* generate offsets into symbol table for each length for sorting */
223
for (len = 1; len < MAXBITS; len++)
224
offs[len + 1] = offs[len] + h->count[len];
227
* put symbols in table sorted by length, by symbol order within each
230
for (symbol = 0; symbol < n; symbol++)
231
if (length[symbol] != 0)
232
h->symbol[offs[length[symbol]]++] = symbol;
234
/* return zero for complete set, positive for incomplete set */
239
* Decode PKWare Compression Library stream.
243
* - First byte is 0 if literals are uncoded or 1 if they are coded. Second
244
* byte is 4, 5, or 6 for the number of extra bits in the distance code.
245
* This is the base-2 logarithm of the dictionary size minus six.
247
* - Compressed data is a combination of literals and length/distance pairs
248
* terminated by an end code. Literals are either Huffman coded or
249
* uncoded bytes. A length/distance pair is a coded length followed by a
250
* coded distance to represent a string that occurs earlier in the
251
* uncompressed data that occurs again at the current location.
253
* - A bit preceding a literal or length/distance pair indicates which comes
254
* next, 0 for literals, 1 for length/distance.
256
* - If literals are uncoded, then the next eight bits are the literal, in the
257
* normal bit order in th stream, i.e. no bit-reversal is needed. Similarly,
258
* no bit reversal is needed for either the length extra bits or the distance
261
* - Literal bytes are simply written to the output. A length/distance pair is
262
* an instruction to copy previously uncompressed bytes to the output. The
263
* copy is from distance bytes back in the output stream, copying for length
266
* - Distances pointing before the beginning of the output data are not
269
* - Overlapped copies, where the length is greater than the distance, are
270
* allowed and common. For example, a distance of one and a length of 518
271
* simply copies the last byte 518 times. A distance of four and a length of
272
* twelve copies the last four bytes three times. A simple forward copy
273
* ignoring whether the length is greater than the distance or not implements
276
local int decomp(struct state *s)
278
int lit; /* true if literals are coded */
279
int dict; /* log2(dictionary size) - 6 */
280
int symbol; /* decoded symbol, extra bits for distance */
281
int len; /* length for copy */
282
int dist; /* distance for copy */
283
int copy; /* copy counter */
284
unsigned char *from, *to; /* copy pointers */
285
static int virgin = 1; /* build tables once */
286
static short litcnt[MAXBITS+1], litsym[256]; /* litcode memory */
287
static short lencnt[MAXBITS+1], lensym[16]; /* lencode memory */
288
static short distcnt[MAXBITS+1], distsym[64]; /* distcode memory */
289
static struct huffman litcode = {litcnt, litsym}; /* length code */
290
static struct huffman lencode = {lencnt, lensym}; /* length code */
291
static struct huffman distcode = {distcnt, distsym};/* distance code */
292
/* bit lengths of literal codes */
293
static const unsigned char litlen[] = {
294
11, 124, 8, 7, 28, 7, 188, 13, 76, 4, 10, 8, 12, 10, 12, 10, 8, 23, 8,
295
9, 7, 6, 7, 8, 7, 6, 55, 8, 23, 24, 12, 11, 7, 9, 11, 12, 6, 7, 22, 5,
296
7, 24, 6, 11, 9, 6, 7, 22, 7, 11, 38, 7, 9, 8, 25, 11, 8, 11, 9, 12,
297
8, 12, 5, 38, 5, 38, 5, 11, 7, 5, 6, 21, 6, 10, 53, 8, 7, 24, 10, 27,
298
44, 253, 253, 253, 252, 252, 252, 13, 12, 45, 12, 45, 12, 61, 12, 45,
300
/* bit lengths of length codes 0..15 */
301
static const unsigned char lenlen[] = {2, 35, 36, 53, 38, 23};
302
/* bit lengths of distance codes 0..63 */
303
static const unsigned char distlen[] = {2, 20, 53, 230, 247, 151, 248};
304
static const short base[16] = { /* base for length codes */
305
3, 2, 4, 5, 6, 7, 8, 9, 10, 12, 16, 24, 40, 72, 136, 264};
306
static const char extra[16] = { /* extra bits for length codes */
307
0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8};
309
/* set up decoding tables (once--might not be thread-safe) */
311
construct(&litcode, litlen, sizeof(litlen));
312
construct(&lencode, lenlen, sizeof(lenlen));
313
construct(&distcode, distlen, sizeof(distlen));
319
if (lit > 1) return -1;
321
if (dict < 4 || dict > 6) return -2;
323
/* decode literals and length/distance pairs */
327
symbol = decode(s, &lencode);
328
len = base[symbol] + bits(s, extra[symbol]);
329
if (len == 519) break; /* end code */
332
symbol = len == 2 ? 2 : dict;
333
dist = decode(s, &distcode) << symbol;
334
dist += bits(s, symbol);
336
if (s->first && dist > s->next)
337
return -3; /* distance too far back */
339
/* copy length bytes from distance bytes back */
341
to = s->out + s->next;
344
if (s->next < dist) {
349
if (copy > len) copy = len;
355
if (s->next == MAXWIN) {
356
if (s->outfun(s->outhow, s->out, s->next)) return 1;
363
/* get literal and write it */
364
symbol = lit ? decode(s, &litcode) : bits(s, 8);
365
s->out[s->next++] = symbol;
366
if (s->next == MAXWIN) {
367
if (s->outfun(s->outhow, s->out, s->next)) return 1;
376
/* See comments in blast.h */
377
int blast(blast_in infun, void *inhow, blast_out outfun, void *outhow)
379
struct state s; /* input/output state */
380
int err; /* return value */
382
/* initialize input state */
389
/* initialize output state */
395
/* return if bits() or decode() tries to read past available input */
396
if (setjmp(s.env) != 0) /* if came back here via longjmp(), */
397
err = 2; /* then skip decomp(), return error */
399
err = decomp(&s); /* decompress */
401
/* write any leftover output and update the error code if needed */
402
if (err != 1 && s.next && s.outfun(s.outhow, s.out, s.next) && err == 0)
408
/* Example of how to use blast() */
414
local unsigned inf(void *how, unsigned char **buf)
416
static unsigned char hold[CHUNK];
419
return fread(hold, 1, CHUNK, (FILE *)how);
422
local int outf(void *how, unsigned char *buf, unsigned len)
424
return fwrite(buf, 1, len, (FILE *)how) != len;
427
/* Decompress a PKWare Compression Library stream from stdin to stdout */
432
/* decompress to stdout */
433
ret = blast(inf, stdin, outf, stdout);
434
if (ret != 0) fprintf(stderr, "blast error: %d\n", ret);
436
/* see if there are any leftover bytes */
438
while (getchar() != EOF) n++;
439
if (n) fprintf(stderr, "blast warning: %d unused bytes of input\n", n);
441
/* return blast() error code */