240 lines
8.0 KiB
C
240 lines
8.0 KiB
C
/* unpack.c -- decompress files in pack format.
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* Copyright (C) 1992-1993 Jean-loup Gailly
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* This is free software; you can redistribute it and/or modify it under the
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* terms of the GNU General Public License, see the file COPYING.
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*/
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#ifdef RCSID
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static char rcsid[] = "$Id: unpack.c,v 1.4 1993/06/11 19:25:36 jloup Exp $";
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#endif
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#include "tailor.h"
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#include "gzip.h"
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#include "crypt.h"
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#define MIN(a,b) ((a) <= (b) ? (a) : (b))
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/* The arguments must not have side effects. */
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#define MAX_BITLEN 25
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/* Maximum length of Huffman codes. (Minor modifications to the code
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* would be needed to support 32 bits codes, but pack never generates
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* more than 24 bits anyway.)
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*/
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#define LITERALS 256
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/* Number of literals, excluding the End of Block (EOB) code */
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#define MAX_PEEK 12
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/* Maximum number of 'peek' bits used to optimize traversal of the
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* Huffman tree.
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*/
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local ulg orig_len; /* original uncompressed length */
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local int max_len; /* maximum bit length of Huffman codes */
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local uch literal[LITERALS];
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/* The literal bytes present in the Huffman tree. The EOB code is not
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* represented.
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*/
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local int lit_base[MAX_BITLEN+1];
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/* All literals of a given bit length are contiguous in literal[] and
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* have contiguous codes. literal[code+lit_base[len]] is the literal
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* for a code of len bits.
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*/
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local int leaves [MAX_BITLEN+1]; /* Number of leaves for each bit length */
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local int parents[MAX_BITLEN+1]; /* Number of parents for each bit length */
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local int peek_bits; /* Number of peek bits currently used */
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/* local uch prefix_len[1 << MAX_PEEK]; */
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#define prefix_len outbuf
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/* For each bit pattern b of peek_bits bits, prefix_len[b] is the length
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* of the Huffman code starting with a prefix of b (upper bits), or 0
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* if all codes of prefix b have more than peek_bits bits. It is not
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* necessary to have a huge table (large MAX_PEEK) because most of the
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* codes encountered in the input stream are short codes (by construction).
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* So for most codes a single lookup will be necessary.
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*/
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#if (1<<MAX_PEEK) > OUTBUFSIZ
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error cannot overlay prefix_len and outbuf
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#endif
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local ulg bitbuf;
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/* Bits are added on the low part of bitbuf and read from the high part. */
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local int valid; /* number of valid bits in bitbuf */
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/* all bits above the last valid bit are always zero */
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/* Set code to the next 'bits' input bits without skipping them. code
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* must be the name of a simple variable and bits must not have side effects.
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* IN assertions: bits <= 25 (so that we still have room for an extra byte
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* when valid is only 24), and mask = (1<<bits)-1.
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*/
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#define look_bits(code,bits,mask) \
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{ \
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while (valid < (bits)) bitbuf = (bitbuf<<8) | (ulg)get_byte(), valid += 8; \
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code = (bitbuf >> (valid-(bits))) & (mask); \
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}
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/* Skip the given number of bits (after having peeked at them): */
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#define skip_bits(bits) (valid -= (bits))
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#define clear_bitbuf() (valid = 0, bitbuf = 0)
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/* Local functions */
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local void read_tree OF((void));
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local void build_tree OF((void));
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/* ===========================================================================
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* Read the Huffman tree.
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*/
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local void read_tree()
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{
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int len; /* bit length */
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int base; /* base offset for a sequence of leaves */
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int n;
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/* Read the original input size, MSB first */
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orig_len = 0;
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for (n = 1; n <= 4; n++) orig_len = (orig_len << 8) | (ulg)get_byte();
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max_len = (int)get_byte(); /* maximum bit length of Huffman codes */
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if (max_len > MAX_BITLEN) {
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error("invalid compressed data -- Huffman code > 32 bits");
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}
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/* Get the number of leaves at each bit length */
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n = 0;
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for (len = 1; len <= max_len; len++) {
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leaves[len] = (int)get_byte();
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n += leaves[len];
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}
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if (n > LITERALS) {
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error("too many leaves in Huffman tree");
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}
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Trace((stderr, "orig_len %ld, max_len %d, leaves %d\n",
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orig_len, max_len, n));
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/* There are at least 2 and at most 256 leaves of length max_len.
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* (Pack arbitrarily rejects empty files and files consisting of
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* a single byte even repeated.) To fit the last leaf count in a
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* byte, it is offset by 2. However, the last literal is the EOB
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* code, and is not transmitted explicitly in the tree, so we must
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* adjust here by one only.
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*/
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leaves[max_len]++;
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/* Now read the leaves themselves */
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base = 0;
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for (len = 1; len <= max_len; len++) {
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/* Remember where the literals of this length start in literal[] : */
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lit_base[len] = base;
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/* And read the literals: */
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for (n = leaves[len]; n > 0; n--) {
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literal[base++] = (uch)get_byte();
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}
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}
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leaves[max_len]++; /* Now include the EOB code in the Huffman tree */
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}
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/* ===========================================================================
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* Build the Huffman tree and the prefix table.
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*/
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local void build_tree()
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{
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int nodes = 0; /* number of nodes (parents+leaves) at current bit length */
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int len; /* current bit length */
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uch *prefixp; /* pointer in prefix_len */
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for (len = max_len; len >= 1; len--) {
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/* The number of parent nodes at this level is half the total
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* number of nodes at parent level:
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*/
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nodes >>= 1;
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parents[len] = nodes;
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/* Update lit_base by the appropriate bias to skip the parent nodes
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* (which are not represented in the literal array):
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*/
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lit_base[len] -= nodes;
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/* Restore nodes to be parents+leaves: */
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nodes += leaves[len];
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}
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/* Construct the prefix table, from shortest leaves to longest ones.
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* The shortest code is all ones, so we start at the end of the table.
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*/
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peek_bits = MIN(max_len, MAX_PEEK);
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prefixp = &prefix_len[1<<peek_bits];
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for (len = 1; len <= peek_bits; len++) {
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int prefixes = leaves[len] << (peek_bits-len); /* may be 0 */
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while (prefixes--) *--prefixp = (uch)len;
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}
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/* The length of all other codes is unknown: */
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while (prefixp > prefix_len) *--prefixp = 0;
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}
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/* ===========================================================================
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* Unpack in to out. This routine does not support the old pack format
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* with magic header \037\037.
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*
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* IN assertions: the buffer inbuf contains already the beginning of
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* the compressed data, from offsets inptr to insize-1 included.
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* The magic header has already been checked. The output buffer is cleared.
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*/
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int unpack(in, out)
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int in, out; /* input and output file descriptors */
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{
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int len; /* Bit length of current code */
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unsigned eob; /* End Of Block code */
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register unsigned peek; /* lookahead bits */
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unsigned peek_mask; /* Mask for peek_bits bits */
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ifd = in;
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ofd = out;
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read_tree(); /* Read the Huffman tree */
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build_tree(); /* Build the prefix table */
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clear_bitbuf(); /* Initialize bit input */
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peek_mask = (1<<peek_bits)-1;
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/* The eob code is the largest code among all leaves of maximal length: */
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eob = leaves[max_len]-1;
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Trace((stderr, "eob %d %x\n", max_len, eob));
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/* Decode the input data: */
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for (;;) {
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/* Since eob is the longest code and not shorter than max_len,
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* we can peek at max_len bits without having the risk of reading
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* beyond the end of file.
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*/
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look_bits(peek, peek_bits, peek_mask);
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len = prefix_len[peek];
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if (len > 0) {
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peek >>= peek_bits - len; /* discard the extra bits */
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} else {
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/* Code of more than peek_bits bits, we must traverse the tree */
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ulg mask = peek_mask;
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len = peek_bits;
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do {
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len++, mask = (mask<<1)+1;
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look_bits(peek, len, mask);
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} while (peek < (unsigned)parents[len]);
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/* loop as long as peek is a parent node */
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}
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/* At this point, peek is the next complete code, of len bits */
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if (peek == eob && len == max_len) break; /* end of file? */
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put_ubyte(literal[peek+lit_base[len]]);
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Tracev((stderr,"%02d %04x %c\n", len, peek,
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literal[peek+lit_base[len]]));
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skip_bits(len);
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} /* for (;;) */
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flush_window();
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Trace((stderr, "bytes_out %ld\n", bytes_out));
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if (orig_len != (ulg)bytes_out) {
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error("invalid compressed data--length error");
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}
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return OK;
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}
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