/* 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
Submit an article or tip