4 * XPRESS compression routines.
6 * See the comments in xpress-decompress.c about the XPRESS format.
10 * Copyright (C) 2012, 2013 Eric Biggers
12 * This file is part of wimlib, a library for working with WIM files.
14 * wimlib is free software; you can redistribute it and/or modify it under the
15 * terms of the GNU General Public License as published by the Free
16 * Software Foundation; either version 3 of the License, or (at your option)
19 * wimlib is distributed in the hope that it will be useful, but WITHOUT ANY
20 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
21 * A PARTICULAR PURPOSE. See the GNU General Public License for more
24 * You should have received a copy of the GNU General Public License
25 * along with wimlib; if not, see http://www.gnu.org/licenses/.
33 #include "wimlib/assert.h"
34 #include "wimlib/compress.h"
35 #include "wimlib/util.h"
36 #include "wimlib/xpress.h"
42 * Writes @match, which is a match given in the intermediate representation for
43 * XPRESS matches, to the output stream @ostream.
45 * @codewords and @lens provide the Huffman code that is being used.
48 xpress_write_match(struct output_bitstream *ostream, u32 match,
49 const u16 codewords[], const u8 lens[])
51 u32 adjusted_match_len = match & 0xffff;
52 u32 match_offset = match >> 16;
53 u32 len_hdr = min(adjusted_match_len, 0xf);
54 u32 offset_bsr = bsr32(match_offset);
55 u32 sym = len_hdr | (offset_bsr << 4) | XPRESS_NUM_CHARS;
58 ret = bitstream_put_bits(ostream, codewords[sym], lens[sym]);
62 if (adjusted_match_len >= 0xf) {
63 u8 byte1 = min(adjusted_match_len - 0xf, 0xff);
64 ret = bitstream_put_byte(ostream, byte1);
68 ret = bitstream_put_two_bytes(ostream, adjusted_match_len);
73 return bitstream_put_bits(ostream,
74 match_offset ^ (1 << offset_bsr), offset_bsr);
78 xpress_write_compressed_literals(struct output_bitstream *ostream,
79 const u32 match_tab[],
81 const u16 codewords[],
84 for (unsigned i = 0; i < num_matches; i++) {
86 u32 match = match_tab[i];
88 if (match >= XPRESS_NUM_CHARS) /* match */
89 ret = xpress_write_match(ostream, match, codewords,
91 else /* literal byte */
92 ret = bitstream_put_bits(ostream, codewords[match],
97 return bitstream_put_bits(ostream, codewords[XPRESS_END_OF_DATA],
98 lens[XPRESS_END_OF_DATA]);
102 xpress_record_literal(u8 literal, void *__freq_tab)
104 freq_t *freq_tab = __freq_tab;
110 xpress_record_match(unsigned match_offset, unsigned match_len,
111 void *freq_tab, void *ignore)
113 wimlib_assert(match_len >= XPRESS_MIN_MATCH &&
114 match_len <= XPRESS_MAX_MATCH);
115 wimlib_assert(match_offset >= XPRESS_MIN_OFFSET &&
116 match_offset <= XPRESS_MAX_OFFSET);
119 * The intermediate representation of XPRESS matches is as follows:
122 * ---- -----------------------------------------------------------
124 * 16-31 match offset (XPRESS_MIN_OFFSET < x < XPRESS_MAX_OFFSET)
126 * 0-15 adjusted match length (0 <= x <= XPRESS_MAX_MATCH - XPRESS_MIN_MATCH)
128 * Literals are simply represented as themselves and can be
129 * distinguished from matches by the fact that only literals will have
130 * the upper three bytes completely clear. */
132 u32 adjusted_match_len = match_len - XPRESS_MIN_MATCH;
133 u32 len_hdr = min(adjusted_match_len, 0xf);
134 u32 offset_bsr = bsr32(match_offset);
135 u32 sym = len_hdr | (offset_bsr << 4) | XPRESS_NUM_CHARS;
136 ((freq_t*)freq_tab)[sym]++;
137 return adjusted_match_len | (match_offset << 16);
140 static const struct lz_params xpress_lz_params = {
141 .min_match = XPRESS_MIN_MATCH,
142 .max_match = XPRESS_MAX_MATCH,
146 .max_lazy_match = 16,
150 /* Documented in wimlib.h */
152 wimlib_xpress_compress(const void *__uncompressed_data,
153 unsigned uncompressed_len, void *__compressed_data)
155 u8 *compressed_data = __compressed_data;
156 struct output_bitstream ostream;
157 u32 match_tab[uncompressed_len];
158 freq_t freq_tab[XPRESS_NUM_SYMBOLS];
159 u16 codewords[XPRESS_NUM_SYMBOLS];
160 u8 lens[XPRESS_NUM_SYMBOLS];
161 unsigned num_matches;
162 unsigned compressed_len;
165 u8 uncompressed_data[uncompressed_len + 8];
167 memcpy(uncompressed_data, __uncompressed_data, uncompressed_len);
168 memset(uncompressed_data + uncompressed_len, 0, 8);
170 wimlib_assert(uncompressed_len <= 32768);
172 /* XPRESS requires 256 bytes of overhead for the Huffman tables, so it's
173 * impossible cannot compress 256 bytes or less of data to less than the
176 * +1 to take into account that the buffer for compressed data is 1 byte
177 * smaller than the buffer for uncompressed data.
179 * +4 to take into account that init_output_bitstream() requires at
180 * least 4 bytes of data. */
181 if (uncompressed_len < XPRESS_NUM_SYMBOLS / 2 + 1 + 4)
184 ZERO_ARRAY(freq_tab);
185 num_matches = lz_analyze_block(uncompressed_data, uncompressed_len,
186 match_tab, xpress_record_match,
187 xpress_record_literal, freq_tab,
191 freq_tab[XPRESS_END_OF_DATA]++;
193 make_canonical_huffman_code(XPRESS_NUM_SYMBOLS, XPRESS_MAX_CODEWORD_LEN,
194 freq_tab, lens, codewords);
198 * It's tempting to output the 512 Huffman codeword lengths using the
199 * bitstream_put_bits() function. However, this is NOT correct because
200 * bitstream_put_bits() will output 2 bytes at a time in little-endian
201 * order, which is the order that is needed for the compressed literals.
202 * However, the bytes in the lengths table are in order, so they need to
203 * be written one at a time without using bitstream_put_bits().
205 * Because of this, init_output_bitstream() is not called until after
206 * the lengths table is output.
208 for (i = 0; i < XPRESS_NUM_SYMBOLS; i += 2)
209 *compressed_data++ = (lens[i] & 0xf) | (lens[i + 1] << 4);
211 init_output_bitstream(&ostream, compressed_data,
212 uncompressed_len - XPRESS_NUM_SYMBOLS / 2 - 1);
214 ret = xpress_write_compressed_literals(&ostream, match_tab,
215 num_matches, codewords, lens);
219 /* Flush any bits that are buffered. */
220 ret = flush_output_bitstream(&ostream);
224 /* Assert that there are no output bytes between the ostream.output
225 * pointer and the ostream.next_bit_output pointer. This can only
226 * happen if bytes had been written at the ostream.output pointer before
227 * the last bit word was written to the stream. But, this does not
228 * occur since xpress_write_match() always finishes by writing some bits
229 * (a Huffman symbol), and the bitstream was just flushed. */
230 wimlib_assert(ostream.output - ostream.next_bit_output == 2);
232 /* The length of the compressed data is supposed to be the value of the
233 * ostream.output pointer before flushing, which is now the
234 * output.next_bit_output pointer after flushing.
236 * There will be an extra 2 bytes at the ostream.bit_output pointer,
237 * which is zeroed out. (These 2 bytes may be either the last bytes in
238 * the compressed data, in which case they are actually unnecessary, or
239 * they may precede a number of bytes embedded into the bitstream.) */
240 if (ostream.bit_output >
241 (const u8*)__compressed_data + uncompressed_len - 3)
243 *(u16*)ostream.bit_output = cpu_to_le16(0);
244 compressed_len = ostream.next_bit_output - (const u8*)__compressed_data;
246 wimlib_assert(compressed_len <= uncompressed_len - 1);
248 #if defined(ENABLE_VERIFY_COMPRESSION)
249 /* Verify that we really get the same thing back when decompressing. */
251 u8 buf[uncompressed_len];
252 ret = wimlib_xpress_decompress(__compressed_data, compressed_len,
253 buf, uncompressed_len);
255 ERROR("xpress_compress(): Failed to decompress data we "
259 for (i = 0; i < uncompressed_len; i++) {
260 if (buf[i] != uncompressed_data[i]) {
261 ERROR("xpress_compress(): Data we compressed didn't "
262 "decompress to the original data (difference at "
263 "byte %u of %u)", i + 1, uncompressed_len);
269 return compressed_len;