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+/* 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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