1 /* unpack.c -- decompress files in pack format.
2 * Copyright (C) 1992-1993 Jean-loup Gailly
3 * This is free software; you can redistribute it and/or modify it under the
4 * terms of the GNU General Public License, see the file COPYING.
8 static char rcsid[] = "$Id$";
15 #define MIN(a,b) ((a) <= (b) ? (a) : (b))
16 /* The arguments must not have side effects. */
19 /* Maximum length of Huffman codes. (Minor modifications to the code
20 * would be needed to support 32 bits codes, but pack never generates
21 * more than 24 bits anyway.)
25 /* Number of literals, excluding the End of Block (EOB) code */
28 /* Maximum number of 'peek' bits used to optimize traversal of the
32 local ulg orig_len; /* original uncompressed length */
33 local int max_len; /* maximum bit length of Huffman codes */
35 local uch literal[LITERALS];
36 /* The literal bytes present in the Huffman tree. The EOB code is not
40 local int lit_base[MAX_BITLEN+1];
41 /* All literals of a given bit length are contiguous in literal[] and
42 * have contiguous codes. literal[code+lit_base[len]] is the literal
43 * for a code of len bits.
46 local int leaves [MAX_BITLEN+1]; /* Number of leaves for each bit length */
47 local int parents[MAX_BITLEN+1]; /* Number of parents for each bit length */
49 local int peek_bits; /* Number of peek bits currently used */
51 /* local uch prefix_len[1 << MAX_PEEK]; */
52 #define prefix_len outbuf
53 /* For each bit pattern b of peek_bits bits, prefix_len[b] is the length
54 * of the Huffman code starting with a prefix of b (upper bits), or 0
55 * if all codes of prefix b have more than peek_bits bits. It is not
56 * necessary to have a huge table (large MAX_PEEK) because most of the
57 * codes encountered in the input stream are short codes (by construction).
58 * So for most codes a single lookup will be necessary.
60 #if (1<<MAX_PEEK) > OUTBUFSIZ
61 error cannot overlay prefix_len and outbuf
65 /* Bits are added on the low part of bitbuf and read from the high part. */
67 local int valid; /* number of valid bits in bitbuf */
68 /* all bits above the last valid bit are always zero */
70 /* Set code to the next 'bits' input bits without skipping them. code
71 * must be the name of a simple variable and bits must not have side effects.
72 * IN assertions: bits <= 25 (so that we still have room for an extra byte
73 * when valid is only 24), and mask = (1<<bits)-1.
75 #define look_bits(code,bits,mask) \
77 while (valid < (bits)) bitbuf = (bitbuf<<8) | (ulg)get_byte(), valid += 8; \
78 code = (bitbuf >> (valid-(bits))) & (mask); \
81 /* Skip the given number of bits (after having peeked at them): */
82 #define skip_bits(bits) (valid -= (bits))
84 #define clear_bitbuf() (valid = 0, bitbuf = 0)
88 local void read_tree OF((void));
89 local void build_tree OF((void));
91 /* ===========================================================================
92 * Read the Huffman tree.
94 local void read_tree()
96 int len; /* bit length */
97 int base; /* base offset for a sequence of leaves */
100 /* Read the original input size, MSB first */
102 for (n = 1; n <= 4; n++) orig_len = (orig_len << 8) | (ulg)get_byte();
104 max_len = (int)get_byte(); /* maximum bit length of Huffman codes */
105 if (max_len > MAX_BITLEN) {
106 error("invalid compressed data -- Huffman code > 32 bits");
109 /* Get the number of leaves at each bit length */
111 for (len = 1; len <= max_len; len++) {
112 leaves[len] = (int)get_byte();
116 error("too many leaves in Huffman tree");
118 Trace((stderr, "orig_len %ld, max_len %d, leaves %d\n",
119 orig_len, max_len, n));
120 /* There are at least 2 and at most 256 leaves of length max_len.
121 * (Pack arbitrarily rejects empty files and files consisting of
122 * a single byte even repeated.) To fit the last leaf count in a
123 * byte, it is offset by 2. However, the last literal is the EOB
124 * code, and is not transmitted explicitly in the tree, so we must
125 * adjust here by one only.
129 /* Now read the leaves themselves */
131 for (len = 1; len <= max_len; len++) {
132 /* Remember where the literals of this length start in literal[] : */
133 lit_base[len] = base;
134 /* And read the literals: */
135 for (n = leaves[len]; n > 0; n--) {
136 literal[base++] = (uch)get_byte();
139 leaves[max_len]++; /* Now include the EOB code in the Huffman tree */
142 /* ===========================================================================
143 * Build the Huffman tree and the prefix table.
145 local void build_tree()
147 int nodes = 0; /* number of nodes (parents+leaves) at current bit length */
148 int len; /* current bit length */
149 uch *prefixp; /* pointer in prefix_len */
151 for (len = max_len; len >= 1; len--) {
152 /* The number of parent nodes at this level is half the total
153 * number of nodes at parent level:
156 parents[len] = nodes;
157 /* Update lit_base by the appropriate bias to skip the parent nodes
158 * (which are not represented in the literal array):
160 lit_base[len] -= nodes;
161 /* Restore nodes to be parents+leaves: */
162 nodes += leaves[len];
164 /* Construct the prefix table, from shortest leaves to longest ones.
165 * The shortest code is all ones, so we start at the end of the table.
167 peek_bits = MIN(max_len, MAX_PEEK);
168 prefixp = &prefix_len[1<<peek_bits];
169 for (len = 1; len <= peek_bits; len++) {
170 int prefixes = leaves[len] << (peek_bits-len); /* may be 0 */
171 while (prefixes--) *--prefixp = (uch)len;
173 /* The length of all other codes is unknown: */
174 while (prefixp > prefix_len) *--prefixp = 0;
177 /* ===========================================================================
178 * Unpack in to out. This routine does not support the old pack format
179 * with magic header \037\037.
181 * IN assertions: the buffer inbuf contains already the beginning of
182 * the compressed data, from offsets inptr to insize-1 included.
183 * The magic header has already been checked. The output buffer is cleared.
186 int in, out; /* input and output file descriptors */
188 int len; /* Bit length of current code */
189 unsigned eob; /* End Of Block code */
190 register unsigned peek; /* lookahead bits */
191 unsigned peek_mask; /* Mask for peek_bits bits */
196 read_tree(); /* Read the Huffman tree */
197 build_tree(); /* Build the prefix table */
198 clear_bitbuf(); /* Initialize bit input */
199 peek_mask = (1<<peek_bits)-1;
201 /* The eob code is the largest code among all leaves of maximal length: */
202 eob = leaves[max_len]-1;
203 Trace((stderr, "eob %d %x\n", max_len, eob));
205 /* Decode the input data: */
207 /* Since eob is the longest code and not shorter than max_len,
208 * we can peek at max_len bits without having the risk of reading
209 * beyond the end of file.
211 look_bits(peek, peek_bits, peek_mask);
212 len = prefix_len[peek];
214 peek >>= peek_bits - len; /* discard the extra bits */
216 /* Code of more than peek_bits bits, we must traverse the tree */
217 ulg mask = peek_mask;
220 len++, mask = (mask<<1)+1;
221 look_bits(peek, len, mask);
222 } while (peek < (unsigned)parents[len]);
223 /* loop as long as peek is a parent node */
225 /* At this point, peek is the next complete code, of len bits */
226 if (peek == eob && len == max_len) break; /* end of file? */
227 put_ubyte(literal[peek+lit_base[len]]);
228 Tracev((stderr,"%02d %04x %c\n", len, peek,
229 literal[peek+lit_base[len]]));
234 Trace((stderr, "bytes_out %ld\n", bytes_out));
235 if (orig_len != (ulg)bytes_out) {
236 error("invalid compressed data--length error");