00001 /* blast.c 00002 * Copyright (C) 2003 Mark Adler 00003 * For conditions of distribution and use, see copyright notice in blast.h 00004 * version 1.1, 16 Feb 2003 00005 * 00006 * blast.c decompresses data compressed by the PKWare Compression Library. 00007 * This function provides functionality similar to the explode() function of 00008 * the PKWare library, hence the name "blast". 00009 * 00010 * This decompressor is based on the excellent format description provided by 00011 * Ben Rudiak-Gould in comp.compression on August 13, 2001. Interestingly, the 00012 * example Ben provided in the post is incorrect. The distance 110001 should 00013 * instead be 111000. When corrected, the example byte stream becomes: 00014 * 00015 * 00 04 82 24 25 8f 80 7f 00016 * 00017 * which decompresses to "AIAIAIAIAIAIA" (without the quotes). 00018 */ 00019 00020 /* 00021 * Change history: 00022 * 00023 * 1.0 12 Feb 2003 - First version 00024 * 1.1 16 Feb 2003 - Fixed distance check for > 4 GB uncompressed data 00025 */ 00026 00027 #include <setjmp.h> /* for setjmp(), longjmp(), and jmp_buf */ 00028 #include "blast.h" /* prototype for blast() */ 00029 00030 #define local static /* for local function definitions */ 00031 #define MAXBITS 13 /* maximum code length */ 00032 #define MAXWIN 4096 /* maximum window size */ 00033 00034 /* input and output state */ 00035 struct state { 00036 /* input state */ 00037 blast_in infun; /* input function provided by user */ 00038 void *inhow; /* opaque information passed to infun() */ 00039 unsigned char *in; /* next input location */ 00040 unsigned left; /* available input at in */ 00041 int bitbuf; /* bit buffer */ 00042 int bitcnt; /* number of bits in bit buffer */ 00043 00044 /* input limit error return state for bits() and decode() */ 00045 jmp_buf env; 00046 00047 /* output state */ 00048 blast_out outfun; /* output function provided by user */ 00049 void *outhow; /* opaque information passed to outfun() */ 00050 unsigned next; /* index of next write location in out[] */ 00051 int first; /* true to check distances (for first 4K) */ 00052 unsigned char out[MAXWIN]; /* output buffer and sliding window */ 00053 }; 00054 00055 /* 00056 * Return need bits from the input stream. This always leaves less than 00057 * eight bits in the buffer. bits() works properly for need == 0. 00058 * 00059 * Format notes: 00060 * 00061 * - Bits are stored in bytes from the least significant bit to the most 00062 * significant bit. Therefore bits are dropped from the bottom of the bit 00063 * buffer, using shift right, and new bytes are appended to the top of the 00064 * bit buffer, using shift left. 00065 */ 00066 local int bits(struct state *s, int need) 00067 { 00068 int val; /* bit accumulator */ 00069 00070 /* load at least need bits into val */ 00071 val = s->bitbuf; 00072 while (s->bitcnt < need) { 00073 if (s->left == 0) { 00074 s->left = s->infun(s->inhow, &(s->in)); 00075 if (s->left == 0) longjmp(s->env, 1); /* out of input */ 00076 } 00077 val |= (int)(*(s->in)++) << s->bitcnt; /* load eight bits */ 00078 s->left--; 00079 s->bitcnt += 8; 00080 } 00081 00082 /* drop need bits and update buffer, always zero to seven bits left */ 00083 s->bitbuf = val >> need; 00084 s->bitcnt -= need; 00085 00086 /* return need bits, zeroing the bits above that */ 00087 return val & ((1 << need) - 1); 00088 } 00089 00090 /* 00091 * Huffman code decoding tables. count[1..MAXBITS] is the number of symbols of 00092 * each length, which for a canonical code are stepped through in order. 00093 * symbol[] are the symbol values in canonical order, where the number of 00094 * entries is the sum of the counts in count[]. The decoding process can be 00095 * seen in the function decode() below. 00096 */ 00097 struct huffman { 00098 short *count; /* number of symbols of each length */ 00099 short *symbol; /* canonically ordered symbols */ 00100 }; 00101 00102 /* 00103 * Decode a code from the stream s using huffman table h. Return the symbol or 00104 * a negative value if there is an error. If all of the lengths are zero, i.e. 00105 * an empty code, or if the code is incomplete and an invalid code is received, 00106 * then -9 is returned after reading MAXBITS bits. 00107 * 00108 * Format notes: 00109 * 00110 * - The codes as stored in the compressed data are bit-reversed relative to 00111 * a simple integer ordering of codes of the same lengths. Hence below the 00112 * bits are pulled from the compressed data one at a time and used to 00113 * build the code value reversed from what is in the stream in order to 00114 * permit simple integer comparisons for decoding. 00115 * 00116 * - The first code for the shortest length is all ones. Subsequent codes of 00117 * the same length are simply integer decrements of the previous code. When 00118 * moving up a length, a one bit is appended to the code. For a complete 00119 * code, the last code of the longest length will be all zeros. To support 00120 * this ordering, the bits pulled during decoding are inverted to apply the 00121 * more "natural" ordering starting with all zeros and incrementing. 00122 */ 00123 local int decode(struct state *s, struct huffman *h) 00124 { 00125 int len; /* current number of bits in code */ 00126 int code; /* len bits being decoded */ 00127 int first; /* first code of length len */ 00128 int count; /* number of codes of length len */ 00129 int index; /* index of first code of length len in symbol table */ 00130 int bitbuf; /* bits from stream */ 00131 int left; /* bits left in next or left to process */ 00132 short *next; /* next number of codes */ 00133 00134 bitbuf = s->bitbuf; 00135 left = s->bitcnt; 00136 code = first = index = 0; 00137 len = 1; 00138 next = h->count + 1; 00139 while (1) { 00140 while (left--) { 00141 code |= (bitbuf & 1) ^ 1; /* invert code */ 00142 bitbuf >>= 1; 00143 count = *next++; 00144 if (code < first + count) { /* if length len, return symbol */ 00145 s->bitbuf = bitbuf; 00146 s->bitcnt = (s->bitcnt - len) & 7; 00147 return h->symbol[index + (code - first)]; 00148 } 00149 index += count; /* else update for next length */ 00150 first += count; 00151 first <<= 1; 00152 code <<= 1; 00153 len++; 00154 } 00155 left = (MAXBITS+1) - len; 00156 if (left == 0) break; 00157 if (s->left == 0) { 00158 s->left = s->infun(s->inhow, &(s->in)); 00159 if (s->left == 0) longjmp(s->env, 1); /* out of input */ 00160 } 00161 bitbuf = *(s->in)++; 00162 s->left--; 00163 if (left > 8) left = 8; 00164 } 00165 return -9; /* ran out of codes */ 00166 } 00167 00168 /* 00169 * Given a list of repeated code lengths rep[0..n-1], where each byte is a 00170 * count (high four bits + 1) and a code length (low four bits), generate the 00171 * list of code lengths. This compaction reduces the size of the object code. 00172 * Then given the list of code lengths length[0..n-1] representing a canonical 00173 * Huffman code for n symbols, construct the tables required to decode those 00174 * codes. Those tables are the number of codes of each length, and the symbols 00175 * sorted by length, retaining their original order within each length. The 00176 * return value is zero for a complete code set, negative for an over- 00177 * subscribed code set, and positive for an incomplete code set. The tables 00178 * can be used if the return value is zero or positive, but they cannot be used 00179 * if the return value is negative. If the return value is zero, it is not 00180 * possible for decode() using that table to return an error--any stream of 00181 * enough bits will resolve to a symbol. If the return value is positive, then 00182 * it is possible for decode() using that table to return an error for received 00183 * codes past the end of the incomplete lengths. 00184 */ 00185 local int construct(struct huffman *h, const unsigned char *rep, int n) 00186 { 00187 int symbol; /* current symbol when stepping through length[] */ 00188 int len; /* current length when stepping through h->count[] */ 00189 int left; /* number of possible codes left of current length */ 00190 short offs[MAXBITS+1]; /* offsets in symbol table for each length */ 00191 short length[256]; /* code lengths */ 00192 00193 /* convert compact repeat counts into symbol bit length list */ 00194 symbol = 0; 00195 do { 00196 len = *rep++; 00197 left = (len >> 4) + 1; 00198 len &= 15; 00199 do { 00200 length[symbol++] = len; 00201 } while (--left); 00202 } while (--n); 00203 n = symbol; 00204 00205 /* count number of codes of each length */ 00206 for (len = 0; len <= MAXBITS; len++) 00207 h->count[len] = 0; 00208 for (symbol = 0; symbol < n; symbol++) 00209 (h->count[length[symbol]])++; /* assumes lengths are within bounds */ 00210 if (h->count[0] == n) /* no codes! */ 00211 return 0; /* complete, but decode() will fail */ 00212 00213 /* check for an over-subscribed or incomplete set of lengths */ 00214 left = 1; /* one possible code of zero length */ 00215 for (len = 1; len <= MAXBITS; len++) { 00216 left <<= 1; /* one more bit, double codes left */ 00217 left -= h->count[len]; /* deduct count from possible codes */ 00218 if (left < 0) return left; /* over-subscribed--return negative */ 00219 } /* left > 0 means incomplete */ 00220 00221 /* generate offsets into symbol table for each length for sorting */ 00222 offs[1] = 0; 00223 for (len = 1; len < MAXBITS; len++) 00224 offs[len + 1] = offs[len] + h->count[len]; 00225 00226 /* 00227 * put symbols in table sorted by length, by symbol order within each 00228 * length 00229 */ 00230 for (symbol = 0; symbol < n; symbol++) 00231 if (length[symbol] != 0) 00232 h->symbol[offs[length[symbol]]++] = symbol; 00233 00234 /* return zero for complete set, positive for incomplete set */ 00235 return left; 00236 } 00237 00238 /* 00239 * Decode PKWare Compression Library stream. 00240 * 00241 * Format notes: 00242 * 00243 * - First byte is 0 if literals are uncoded or 1 if they are coded. Second 00244 * byte is 4, 5, or 6 for the number of extra bits in the distance code. 00245 * This is the base-2 logarithm of the dictionary size minus six. 00246 * 00247 * - Compressed data is a combination of literals and length/distance pairs 00248 * terminated by an end code. Literals are either Huffman coded or 00249 * uncoded bytes. A length/distance pair is a coded length followed by a 00250 * coded distance to represent a string that occurs earlier in the 00251 * uncompressed data that occurs again at the current location. 00252 * 00253 * - A bit preceding a literal or length/distance pair indicates which comes 00254 * next, 0 for literals, 1 for length/distance. 00255 * 00256 * - If literals are uncoded, then the next eight bits are the literal, in the 00257 * normal bit order in th stream, i.e. no bit-reversal is needed. Similarly, 00258 * no bit reversal is needed for either the length extra bits or the distance 00259 * extra bits. 00260 * 00261 * - Literal bytes are simply written to the output. A length/distance pair is 00262 * an instruction to copy previously uncompressed bytes to the output. The 00263 * copy is from distance bytes back in the output stream, copying for length 00264 * bytes. 00265 * 00266 * - Distances pointing before the beginning of the output data are not 00267 * permitted. 00268 * 00269 * - Overlapped copies, where the length is greater than the distance, are 00270 * allowed and common. For example, a distance of one and a length of 518 00271 * simply copies the last byte 518 times. A distance of four and a length of 00272 * twelve copies the last four bytes three times. A simple forward copy 00273 * ignoring whether the length is greater than the distance or not implements 00274 * this correctly. 00275 */ 00276 local int decomp(struct state *s) 00277 { 00278 int lit; /* true if literals are coded */ 00279 int dict; /* log2(dictionary size) - 6 */ 00280 int symbol; /* decoded symbol, extra bits for distance */ 00281 int len; /* length for copy */ 00282 int dist; /* distance for copy */ 00283 int copy; /* copy counter */ 00284 unsigned char *from, *to; /* copy pointers */ 00285 static int virgin = 1; /* build tables once */ 00286 static short litcnt[MAXBITS+1], litsym[256]; /* litcode memory */ 00287 static short lencnt[MAXBITS+1], lensym[16]; /* lencode memory */ 00288 static short distcnt[MAXBITS+1], distsym[64]; /* distcode memory */ 00289 static struct huffman litcode = {litcnt, litsym}; /* length code */ 00290 static struct huffman lencode = {lencnt, lensym}; /* length code */ 00291 static struct huffman distcode = {distcnt, distsym};/* distance code */ 00292 /* bit lengths of literal codes */ 00293 static const unsigned char litlen[] = { 00294 11, 124, 8, 7, 28, 7, 188, 13, 76, 4, 10, 8, 12, 10, 12, 10, 8, 23, 8, 00295 9, 7, 6, 7, 8, 7, 6, 55, 8, 23, 24, 12, 11, 7, 9, 11, 12, 6, 7, 22, 5, 00296 7, 24, 6, 11, 9, 6, 7, 22, 7, 11, 38, 7, 9, 8, 25, 11, 8, 11, 9, 12, 00297 8, 12, 5, 38, 5, 38, 5, 11, 7, 5, 6, 21, 6, 10, 53, 8, 7, 24, 10, 27, 00298 44, 253, 253, 253, 252, 252, 252, 13, 12, 45, 12, 45, 12, 61, 12, 45, 00299 44, 173}; 00300 /* bit lengths of length codes 0..15 */ 00301 static const unsigned char lenlen[] = {2, 35, 36, 53, 38, 23}; 00302 /* bit lengths of distance codes 0..63 */ 00303 static const unsigned char distlen[] = {2, 20, 53, 230, 247, 151, 248}; 00304 static const short base[16] = { /* base for length codes */ 00305 3, 2, 4, 5, 6, 7, 8, 9, 10, 12, 16, 24, 40, 72, 136, 264}; 00306 static const char extra[16] = { /* extra bits for length codes */ 00307 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8}; 00308 00309 /* set up decoding tables (once--might not be thread-safe) */ 00310 if (virgin) { 00311 construct(&litcode, litlen, sizeof(litlen)); 00312 construct(&lencode, lenlen, sizeof(lenlen)); 00313 construct(&distcode, distlen, sizeof(distlen)); 00314 virgin = 0; 00315 } 00316 00317 /* read header */ 00318 lit = bits(s, 8); 00319 if (lit > 1) return -1; 00320 dict = bits(s, 8); 00321 if (dict < 4 || dict > 6) return -2; 00322 00323 /* decode literals and length/distance pairs */ 00324 do { 00325 if (bits(s, 1)) { 00326 /* get length */ 00327 symbol = decode(s, &lencode); 00328 len = base[symbol] + bits(s, extra[symbol]); 00329 if (len == 519) break; /* end code */ 00330 00331 /* get distance */ 00332 symbol = len == 2 ? 2 : dict; 00333 dist = decode(s, &distcode) << symbol; 00334 dist += bits(s, symbol); 00335 dist++; 00336 if (s->first && dist > s->next) 00337 return -3; /* distance too far back */ 00338 00339 /* copy length bytes from distance bytes back */ 00340 do { 00341 to = s->out + s->next; 00342 from = to - dist; 00343 copy = MAXWIN; 00344 if (s->next < dist) { 00345 from += copy; 00346 copy = dist; 00347 } 00348 copy -= s->next; 00349 if (copy > len) copy = len; 00350 len -= copy; 00351 s->next += copy; 00352 do { 00353 *to++ = *from++; 00354 } while (--copy); 00355 if (s->next == MAXWIN) { 00356 if (s->outfun(s->outhow, s->out, s->next)) return 1; 00357 s->next = 0; 00358 s->first = 0; 00359 } 00360 } while (len != 0); 00361 } 00362 else { 00363 /* get literal and write it */ 00364 symbol = lit ? decode(s, &litcode) : bits(s, 8); 00365 s->out[s->next++] = symbol; 00366 if (s->next == MAXWIN) { 00367 if (s->outfun(s->outhow, s->out, s->next)) return 1; 00368 s->next = 0; 00369 s->first = 0; 00370 } 00371 } 00372 } while (1); 00373 return 0; 00374 } 00375 00376 /* See comments in blast.h */ 00377 int blast(blast_in infun, void *inhow, blast_out outfun, void *outhow) 00378 { 00379 struct state s; /* input/output state */ 00380 int err; /* return value */ 00381 00382 /* initialize input state */ 00383 s.infun = infun; 00384 s.inhow = inhow; 00385 s.left = 0; 00386 s.bitbuf = 0; 00387 s.bitcnt = 0; 00388 00389 /* initialize output state */ 00390 s.outfun = outfun; 00391 s.outhow = outhow; 00392 s.next = 0; 00393 s.first = 1; 00394 00395 /* return if bits() or decode() tries to read past available input */ 00396 if (setjmp(s.env) != 0) /* if came back here via longjmp(), */ 00397 err = 2; /* then skip decomp(), return error */ 00398 else 00399 err = decomp(&s); /* decompress */ 00400 00401 /* write any leftover output and update the error code if needed */ 00402 if (err != 1 && s.next && s.outfun(s.outhow, s.out, s.next) && err == 0) 00403 err = 1; 00404 return err; 00405 } 00406 00407 #ifdef TEST 00408 /* Example of how to use blast() */ 00409 #include <stdio.h> 00410 #include <stdlib.h> 00411 00412 #define CHUNK 16384 00413 00414 local unsigned inf(void *how, unsigned char **buf) 00415 { 00416 static unsigned char hold[CHUNK]; 00417 00418 *buf = hold; 00419 return fread(hold, 1, CHUNK, (FILE *)how); 00420 } 00421 00422 local int outf(void *how, unsigned char *buf, unsigned len) 00423 { 00424 return fwrite(buf, 1, len, (FILE *)how) != len; 00425 } 00426 00427 /* Decompress a PKWare Compression Library stream from stdin to stdout */ 00428 int main(void) 00429 { 00430 int ret, n; 00431 00432 /* decompress to stdout */ 00433 ret = blast(inf, stdin, outf, stdout); 00434 if (ret != 0) fprintf(stderr, "blast error: %d\n", ret); 00435 00436 /* see if there are any leftover bytes */ 00437 n = 0; 00438 while (getchar() != EOF) n++; 00439 if (n) fprintf(stderr, "blast warning: %d unused bytes of input\n", n); 00440 00441 /* return blast() error code */ 00442 return ret; 00443 } 00444 #endif