/* blast.c * Copyright (C) 2003 Mark Adler * For conditions of distribution and use, see copyright notice in blast.h * version 1.1, 16 Feb 2003 * * blast.c decompresses data compressed by the PKWare Compression Library. * This function provides functionality similar to the explode() function of * the PKWare library, hence the name "blast". * * This decompressor is based on the excellent format description provided by * Ben Rudiak-Gould in comp.compression on August 13, 2001. Interestingly, the * example Ben provided in the post is incorrect. The distance 110001 should * instead be 111000. When corrected, the example byte stream becomes: * * 00 04 82 24 25 8f 80 7f * * which decompresses to "AIAIAIAIAIAIA" (without the quotes). */ /* * Change history: * * 1.0 12 Feb 2003 - First version * 1.1 16 Feb 2003 - Fixed distance check for > 4 GB uncompressed data */ #include <setjmp.h> /* for setjmp(), longjmp(), and jmp_buf */ #include "blast.h" /* prototype for blast() */ #define local static /* for local function definitions */ #define MAXBITS 13 /* maximum code length */ #define MAXWIN 4096 /* maximum window size */ /* input and output state */ struct state { /* input state */ blast_in infun; /* input function provided by user */ void *inhow; /* opaque information passed to infun() */ unsigned char *in; /* next input location */ unsigned left; /* available input at in */ int bitbuf; /* bit buffer */ int bitcnt; /* number of bits in bit buffer */ /* input limit error return state for bits() and decode() */ jmp_buf env; /* output state */ blast_out outfun; /* output function provided by user */ void *outhow; /* opaque information passed to outfun() */ unsigned next; /* index of next write location in out[] */ int first; /* true to check distances (for first 4K) */ unsigned char out[MAXWIN]; /* output buffer and sliding window */ }; /* * Return need bits from the input stream. This always leaves less than * eight bits in the buffer. bits() works properly for need == 0. * * Format notes: * * - Bits are stored in bytes from the least significant bit to the most * significant bit. Therefore bits are dropped from the bottom of the bit * buffer, using shift right, and new bytes are appended to the top of the * bit buffer, using shift left. */ local int bits(struct state *s, int need) { int val; /* bit accumulator */ /* load at least need bits into val */ val = s->bitbuf; while (s->bitcnt < need) { if (s->left == 0) { s->left = s->infun(s->inhow, &(s->in)); if (s->left == 0) longjmp(s->env, 1); /* out of input */ } val |= (int)(*(s->in)++) << s->bitcnt; /* load eight bits */ s->left--; s->bitcnt += 8; } /* drop need bits and update buffer, always zero to seven bits left */ s->bitbuf = val >> need; s->bitcnt -= need; /* return need bits, zeroing the bits above that */ return val & ((1 << need) - 1); } /* * Huffman code decoding tables. count[1..MAXBITS] is the number of symbols of * each length, which for a canonical code are stepped through in order. * symbol[] are the symbol values in canonical order, where the number of * entries is the sum of the counts in count[]. The decoding process can be * seen in the function decode() below. */ struct huffman { short *count; /* number of symbols of each length */ short *symbol; /* canonically ordered symbols */ }; /* * Decode a code from the stream s using huffman table h. Return the symbol or * a negative value if there is an error. If all of the lengths are zero, i.e. * an empty code, or if the code is incomplete and an invalid code is received, * then -9 is returned after reading MAXBITS bits. * * Format notes: * * - The codes as stored in the compressed data are bit-reversed relative to * a simple integer ordering of codes of the same lengths. Hence below the * bits are pulled from the compressed data one at a time and used to * build the code value reversed from what is in the stream in order to * permit simple integer comparisons for decoding. * * - The first code for the shortest length is all ones. Subsequent codes of * the same length are simply integer decrements of the previous code. When * moving up a length, a one bit is appended to the code. For a complete * code, the last code of the longest length will be all zeros. To support * this ordering, the bits pulled during decoding are inverted to apply the * more "natural" ordering starting with all zeros and incrementing. */ local int decode(struct state *s, struct huffman *h) { int len; /* current number of bits in code */ int code; /* len bits being decoded */ int first; /* first code of length len */ int count; /* number of codes of length len */ int index; /* index of first code of length len in symbol table */ int bitbuf; /* bits from stream */ int left; /* bits left in next or left to process */ short *next; /* next number of codes */ bitbuf = s->bitbuf; left = s->bitcnt; code = first = index = 0; len = 1; next = h->count + 1; while (1) { while (left--) { code |= (bitbuf & 1) ^ 1; /* invert code */ bitbuf >>= 1; count = *next++; if (code < first + count) { /* if length len, return symbol */ s->bitbuf = bitbuf; s->bitcnt = (s->bitcnt - len) & 7; return h->symbol[index + (code - first)]; } index += count; /* else update for next length */ first += count; first <<= 1; code <<= 1; len++; } left = (MAXBITS+1) - len; if (left == 0) break; if (s->left == 0) { s->left = s->infun(s->inhow, &(s->in)); if (s->left == 0) longjmp(s->env, 1); /* out of input */ } bitbuf = *(s->in)++; s->left--; if (left > 8) left = 8; } return -9; /* ran out of codes */ } /* * Given a list of repeated code lengths rep[0..n-1], where each byte is a * count (high four bits + 1) and a code length (low four bits), generate the * list of code lengths. This compaction reduces the size of the object code. * Then given the list of code lengths length[0..n-1] representing a canonical * Huffman code for n symbols, construct the tables required to decode those * codes. Those tables are the number of codes of each length, and the symbols * sorted by length, retaining their original order within each length. The * return value is zero for a complete code set, negative for an over- * subscribed code set, and positive for an incomplete code set. The tables * can be used if the return value is zero or positive, but they cannot be used * if the return value is negative. If the return value is zero, it is not * possible for decode() using that table to return an error--any stream of * enough bits will resolve to a symbol. If the return value is positive, then * it is possible for decode() using that table to return an error for received * codes past the end of the incomplete lengths. */ local int construct(struct huffman *h, const unsigned char *rep, int n) { int symbol; /* current symbol when stepping through length[] */ int len; /* current length when stepping through h->count[] */ int left; /* number of possible codes left of current length */ short offs[MAXBITS+1]; /* offsets in symbol table for each length */ short length[256]; /* code lengths */ /* convert compact repeat counts into symbol bit length list */ symbol = 0; do { len = *rep++; left = (len >> 4) + 1; len &= 15; do { length[symbol++] = len; } while (--left); } while (--n); n = symbol; /* count number of codes of each length */ for (len = 0; len <= MAXBITS; len++) h->count[len] = 0; for (symbol = 0; symbol < n; symbol++) (h->count[length[symbol]])++; /* assumes lengths are within bounds */ if (h->count[0] == n) /* no codes! */ return 0; /* complete, but decode() will fail */ /* check for an over-subscribed or incomplete set of lengths */ left = 1; /* one possible code of zero length */ for (len = 1; len <= MAXBITS; len++) { left <<= 1; /* one more bit, double codes left */ left -= h->count[len]; /* deduct count from possible codes */ if (left < 0) return left; /* over-subscribed--return negative */ } /* left > 0 means incomplete */ /* generate offsets into symbol table for each length for sorting */ offs[1] = 0; for (len = 1; len < MAXBITS; len++) offs[len + 1] = offs[len] + h->count[len]; /* * put symbols in table sorted by length, by symbol order within each * length */ for (symbol = 0; symbol < n; symbol++) if (length[symbol] != 0) h->symbol[offs[length[symbol]]++] = symbol; /* return zero for complete set, positive for incomplete set */ return left; } /* * Decode PKWare Compression Library stream. * * Format notes: * * - First byte is 0 if literals are uncoded or 1 if they are coded. Second * byte is 4, 5, or 6 for the number of extra bits in the distance code. * This is the base-2 logarithm of the dictionary size minus six. * * - Compressed data is a combination of literals and length/distance pairs * terminated by an end code. Literals are either Huffman coded or * uncoded bytes. A length/distance pair is a coded length followed by a * coded distance to represent a string that occurs earlier in the * uncompressed data that occurs again at the current location. * * - A bit preceding a literal or length/distance pair indicates which comes * next, 0 for literals, 1 for length/distance. * * - If literals are uncoded, then the next eight bits are the literal, in the * normal bit order in th stream, i.e. no bit-reversal is needed. Similarly, * no bit reversal is needed for either the length extra bits or the distance * extra bits. * * - Literal bytes are simply written to the output. A length/distance pair is * an instruction to copy previously uncompressed bytes to the output. The * copy is from distance bytes back in the output stream, copying for length * bytes. * * - Distances pointing before the beginning of the output data are not * permitted. * * - Overlapped copies, where the length is greater than the distance, are * allowed and common. For example, a distance of one and a length of 518 * simply copies the last byte 518 times. A distance of four and a length of * twelve copies the last four bytes three times. A simple forward copy * ignoring whether the length is greater than the distance or not implements * this correctly. */ local int decomp(struct state *s) { int lit; /* true if literals are coded */ int dict; /* log2(dictionary size) - 6 */ int symbol; /* decoded symbol, extra bits for distance */ int len; /* length for copy */ int dist; /* distance for copy */ int copy; /* copy counter */ unsigned char *from, *to; /* copy pointers */ static int virgin = 1; /* build tables once */ static short litcnt[MAXBITS+1], litsym[256]; /* litcode memory */ static short lencnt[MAXBITS+1], lensym[16]; /* lencode memory */ static short distcnt[MAXBITS+1], distsym[64]; /* distcode memory */ static struct huffman litcode = {litcnt, litsym}; /* length code */ static struct huffman lencode = {lencnt, lensym}; /* length code */ static struct huffman distcode = {distcnt, distsym};/* distance code */ /* bit lengths of literal codes */ static const unsigned char litlen[] = { 11, 124, 8, 7, 28, 7, 188, 13, 76, 4, 10, 8, 12, 10, 12, 10, 8, 23, 8, 9, 7, 6, 7, 8, 7, 6, 55, 8, 23, 24, 12, 11, 7, 9, 11, 12, 6, 7, 22, 5, 7, 24, 6, 11, 9, 6, 7, 22, 7, 11, 38, 7, 9, 8, 25, 11, 8, 11, 9, 12, 8, 12, 5, 38, 5, 38, 5, 11, 7, 5, 6, 21, 6, 10, 53, 8, 7, 24, 10, 27, 44, 253, 253, 253, 252, 252, 252, 13, 12, 45, 12, 45, 12, 61, 12, 45, 44, 173}; /* bit lengths of length codes 0..15 */ static const unsigned char lenlen[] = {2, 35, 36, 53, 38, 23}; /* bit lengths of distance codes 0..63 */ static const unsigned char distlen[] = {2, 20, 53, 230, 247, 151, 248}; static const short base[16] = { /* base for length codes */ 3, 2, 4, 5, 6, 7, 8, 9, 10, 12, 16, 24, 40, 72, 136, 264}; static const char extra[16] = { /* extra bits for length codes */ 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8}; /* set up decoding tables (once--might not be thread-safe) */ if (virgin) { construct(&litcode, litlen, sizeof(litlen)); construct(&lencode, lenlen, sizeof(lenlen)); construct(&distcode, distlen, sizeof(distlen)); virgin = 0; } /* read header */ lit = bits(s, 8); if (lit > 1) return -1; dict = bits(s, 8); if (dict < 4 || dict > 6) return -2; /* decode literals and length/distance pairs */ do { if (bits(s, 1)) { /* get length */ symbol = decode(s, &lencode); len = base[symbol] + bits(s, extra[symbol]); if (len == 519) break; /* end code */ /* get distance */ symbol = len == 2 ? 2 : dict; dist = decode(s, &distcode) << symbol; dist += bits(s, symbol); dist++; if (s->first && dist > s->next) return -3; /* distance too far back */ /* copy length bytes from distance bytes back */ do { to = s->out + s->next; from = to - dist; copy = MAXWIN; if (s->next < dist) { from += copy; copy = dist; } copy -= s->next; if (copy > len) copy = len; len -= copy; s->next += copy; do { *to++ = *from++; } while (--copy); if (s->next == MAXWIN) { if (s->outfun(s->outhow, s->out, s->next)) return 1; s->next = 0; s->first = 0; } } while (len != 0); } else { /* get literal and write it */ symbol = lit ? decode(s, &litcode) : bits(s, 8); s->out[s->next++] = symbol; if (s->next == MAXWIN) { if (s->outfun(s->outhow, s->out, s->next)) return 1; s->next = 0; s->first = 0; } } } while (1); return 0; } /* See comments in blast.h */ int blast(blast_in infun, void *inhow, blast_out outfun, void *outhow) { struct state s; /* input/output state */ int err; /* return value */ /* initialize input state */ s.infun = infun; s.inhow = inhow; s.left = 0; s.bitbuf = 0; s.bitcnt = 0; /* initialize output state */ s.outfun = outfun; s.outhow = outhow; s.next = 0; s.first = 1; /* return if bits() or decode() tries to read past available input */ if (setjmp(s.env) != 0) /* if came back here via longjmp(), */ err = 2; /* then skip decomp(), return error */ else err = decomp(&s); /* decompress */ /* write any leftover output and update the error code if needed */ if (err != 1 && s.next && s.outfun(s.outhow, s.out, s.next) && err == 0) err = 1; return err; } #ifdef TEST /* Example of how to use blast() */ #include <stdio.h> #include <stdlib.h> #define CHUNK 16384 local unsigned inf(void *how, unsigned char **buf) { static unsigned char hold[CHUNK]; *buf = hold; return fread(hold, 1, CHUNK, (FILE *)how); } local int outf(void *how, unsigned char *buf, unsigned len) { return fwrite(buf, 1, len, (FILE *)how) != len; } /* Decompress a PKWare Compression Library stream from stdin to stdout */ int main(void) { int ret, n; /* decompress to stdout */ ret = blast(inf, stdin, outf, stdout); if (ret != 0) fprintf(stderr, "blast error: %d\n", ret); /* see if there are any leftover bytes */ n = 0; while (getchar() != EOF) n++; if (n) fprintf(stderr, "blast warning: %d unused bytes of input\n", n); /* return blast() error code */ return ret; } #endif

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