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