wimlib.net Git - wimlib/blob - src/xpress-compress.c

   1 /*
   2  * xpress-compress.c
   3  *
   4  * XPRESS compression routines.
   5  *
   6  * See the comments in xpress-decompress.c about the XPRESS format.
   7  */
   8
   9 /*
  10  * Copyright (C) 2012, 2013 Eric Biggers
  11  *
  12  * This file is part of wimlib, a library for working with WIM files.
  13  *
  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)
  17  * any later version.
  18  *
  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
  22  * details.
  23  *
  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/.
  26  */
  27
  28 #include "xpress.h"
  29 #include "wimlib.h"
  30 #include "compress.h"
  31
  32 #include <stdlib.h>
  33 #include <string.h>
  34
  35 /*
  36  * Writes @match, which is a match given in the intermediate representation for
  37  * XPRESS matches, to the output stream @ostream.
  38  *
  39  * @codewords and @lens provide the Huffman code that is being used.
  40  */
  41 static int
  42 xpress_write_match(struct output_bitstream *ostream, u32 match,
  43                    const u16 codewords[], const u8 lens[])
  44 {
  45         u32 adjusted_match_len = match & 0xffff;
  46         u32 match_offset = match >> 16;
  47         u32 len_hdr = min(adjusted_match_len, 0xf);
  48         u32 offset_bsr = bsr32(match_offset);
  49         u32 sym = len_hdr | (offset_bsr << 4) | XPRESS_NUM_CHARS;
  50         int ret;
  51
  52         ret = bitstream_put_bits(ostream, codewords[sym], lens[sym]);
  53         if (ret != 0)
  54                 return ret;
  55
  56         if (adjusted_match_len >= 0xf) {
  57                 u8 byte1 = min(adjusted_match_len - 0xf, 0xff);
  58                 ret = bitstream_put_byte(ostream, byte1);
  59                 if (ret != 0)
  60                         return ret;
  61                 if (byte1 == 0xff) {
  62                         ret = bitstream_put_two_bytes(ostream, adjusted_match_len);
  63                         if (ret != 0)
  64                                 return ret;
  65                 }
  66         }
  67         return bitstream_put_bits(ostream,
  68                                   match_offset ^ (1 << offset_bsr), offset_bsr);
  69 }
  70
  71 static int
  72 xpress_write_compressed_literals(struct output_bitstream *ostream,
  73                                  const u32 match_tab[],
  74                                  unsigned num_matches,
  75                                  const u16 codewords[],
  76                                  const u8 lens[])
  77 {
  78         for (unsigned i = 0; i < num_matches; i++) {
  79                 int ret;
  80                 u32 match = match_tab[i];
  81
  82                 if (match >= XPRESS_NUM_CHARS) /* match */
  83                         ret = xpress_write_match(ostream, match, codewords,
  84                                                  lens);
  85                 else /* literal byte */
  86                         ret = bitstream_put_bits(ostream, codewords[match],
  87                                                  lens[match]);
  88                 if (ret != 0)
  89                         return ret;
  90         }
  91         return bitstream_put_bits(ostream, codewords[XPRESS_END_OF_DATA],
  92                                   lens[XPRESS_END_OF_DATA]);
  93 }
  94
  95 static u32
  96 xpress_record_literal(u8 literal, void *__freq_tab)
  97 {
  98         freq_t *freq_tab = __freq_tab;
  99         freq_tab[literal]++;
 100         return literal;
 101 }
 102
 103 static u32
 104 xpress_record_match(unsigned match_offset, unsigned match_len,
 105                     void *freq_tab, void *ignore)
 106 {
 107         wimlib_assert(match_len >= XPRESS_MIN_MATCH &&
 108                       match_len <= XPRESS_MAX_MATCH);
 109         wimlib_assert(match_offset >= XPRESS_MIN_OFFSET &&
 110                       match_offset <= XPRESS_MAX_OFFSET);
 111
 112         /*
 113          * The intermediate representation of XPRESS matches is as follows:
 114          *
 115          * bits    description
 116          * ----    -----------------------------------------------------------
 117          *
 118          * 16-31   match offset (XPRESS_MIN_OFFSET < x < XPRESS_MAX_OFFSET)
 119          *
 120          * 0-15    adjusted match length (0 <= x <= XPRESS_MAX_MATCH - XPRESS_MIN_MATCH)
 121          *
 122          * Literals are simply represented as themselves and can be
 123          * distinguished from matches by the fact that only literals will have
 124          * the upper three bytes completely clear. */
 125
 126         u32 adjusted_match_len = match_len - XPRESS_MIN_MATCH;
 127         u32 len_hdr = min(adjusted_match_len, 0xf);
 128         u32 offset_bsr = bsr32(match_offset);
 129         u32 sym = len_hdr | (offset_bsr << 4) | XPRESS_NUM_CHARS;
 130         ((freq_t*)freq_tab)[sym]++;
 131         return adjusted_match_len | (match_offset << 16);
 132 }
 133
 134 static const struct lz_params xpress_lz_params = {
 135         .min_match      = XPRESS_MIN_MATCH,
 136         .max_match      = XPRESS_MAX_MATCH,
 137         .good_match     = 16,
 138         .nice_match     = 32,
 139         .max_chain_len  = 16,
 140         .max_lazy_match = 16,
 141         .too_far        = 4096,
 142 };
 143
 144 /* Documented in wimlib.h */
 145 WIMLIBAPI unsigned
 146 wimlib_xpress_compress(const void *__uncompressed_data,
 147                        unsigned uncompressed_len, void *__compressed_data)
 148 {
 149         u8 *compressed_data = __compressed_data;
 150         struct output_bitstream ostream;
 151         u32 match_tab[uncompressed_len];
 152         freq_t freq_tab[XPRESS_NUM_SYMBOLS];
 153         u16 codewords[XPRESS_NUM_SYMBOLS];
 154         u8 lens[XPRESS_NUM_SYMBOLS];
 155         unsigned num_matches;
 156         unsigned compressed_len;
 157         unsigned i;
 158         int ret;
 159         u8 uncompressed_data[uncompressed_len + 8];
 160
 161         memcpy(uncompressed_data, __uncompressed_data, uncompressed_len);
 162         memset(uncompressed_data + uncompressed_len, 0, 8);
 163
 164         wimlib_assert(uncompressed_len <= 32768);
 165
 166         /* XPRESS requires 256 bytes of overhead for the Huffman tables, so it's
 167          * impossible cannot compress 256 bytes or less of data to less than the
 168          * input size.
 169          *
 170          * +1 to take into account that the buffer for compressed data is 1 byte
 171          * smaller than the buffer for uncompressed data.
 172          *
 173          * +4 to take into account that init_output_bitstream() requires at
 174          * least 4 bytes of data. */
 175         if (uncompressed_len < XPRESS_NUM_SYMBOLS / 2 + 1 + 4)
 176                 return 0;
 177
 178         ZERO_ARRAY(freq_tab);
 179         num_matches = lz_analyze_block(uncompressed_data, uncompressed_len,
 180                                        match_tab, xpress_record_match,
 181                                        xpress_record_literal, freq_tab,
 182                                        NULL, freq_tab,
 183                                        &xpress_lz_params);
 184
 185         freq_tab[XPRESS_END_OF_DATA]++;
 186
 187         make_canonical_huffman_code(XPRESS_NUM_SYMBOLS, XPRESS_MAX_CODEWORD_LEN,
 188                                     freq_tab, lens, codewords);
 189
 190         /* IMPORTANT NOTE:
 191          *
 192          * It's tempting to output the 512 Huffman codeword lengths using the
 193          * bitstream_put_bits() function.  However, this is NOT correct because
 194          * bitstream_put_bits() will output 2 bytes at a time in little-endian
 195          * order, which is the order that is needed for the compressed literals.
 196          * However, the bytes in the lengths table are in order, so they need to
 197          * be written one at a time without using bitstream_put_bits().
 198          *
 199          * Because of this, init_output_bitstream() is not called until after
 200          * the lengths table is output.
 201          */
 202         for (i = 0; i < XPRESS_NUM_SYMBOLS; i += 2)
 203                 *compressed_data++ = (lens[i] & 0xf) | (lens[i + 1] << 4);
 204
 205         init_output_bitstream(&ostream, compressed_data,
 206                               uncompressed_len - XPRESS_NUM_SYMBOLS / 2 - 1);
 207
 208         ret = xpress_write_compressed_literals(&ostream, match_tab,
 209                                                num_matches, codewords, lens);
 210         if (ret)
 211                 return 0;
 212
 213         /* Flush any bits that are buffered. */
 214         ret = flush_output_bitstream(&ostream);
 215         if (ret)
 216                 return 0;
 217
 218         /* Assert that there are no output bytes between the ostream.output
 219          * pointer and the ostream.next_bit_output pointer.  This can only
 220          * happen if bytes had been written at the ostream.output pointer before
 221          * the last bit word was written to the stream.  But, this does not
 222          * occur since xpress_write_match() always finishes by writing some bits
 223          * (a Huffman symbol), and the bitstream was just flushed. */
 224         wimlib_assert(ostream.output - ostream.next_bit_output == 2);
 225
 226         /* The length of the compressed data is supposed to be the value of the
 227          * ostream.output pointer before flushing, which is now the
 228          * output.next_bit_output pointer after flushing.
 229          *
 230          * There will be an extra 2 bytes at the ostream.bit_output pointer,
 231          * which is zeroed out.  (These 2 bytes may be either the last bytes in
 232          * the compressed data, in which case they are actually unnecessary, or
 233          * they may precede a number of bytes embedded into the bitstream.) */
 234         if (ostream.bit_output >
 235             (const u8*)__compressed_data + uncompressed_len - 3)
 236                 return 0;
 237         *(u16*)ostream.bit_output = cpu_to_le16(0);
 238         compressed_len = ostream.next_bit_output - (const u8*)__compressed_data;
 239
 240         wimlib_assert(compressed_len <= uncompressed_len - 1);
 241
 242 #if defined(ENABLE_VERIFY_COMPRESSION)
 243         /* Verify that we really get the same thing back when decompressing. */
 244         {
 245                 u8 buf[uncompressed_len];
 246                 ret = wimlib_xpress_decompress(__compressed_data, compressed_len,
 247                                                buf, uncompressed_len);
 248                 if (ret) {
 249                         ERROR("xpress_compress(): Failed to decompress data we "
 250                               "compressed");
 251                         abort();
 252                 }
 253                 for (i = 0; i < uncompressed_len; i++) {
 254                         if (buf[i] != uncompressed_data[i]) {
 255                                 ERROR("xpress_compress(): Data we compressed didn't "
 256                                       "decompress to the original data (difference at "
 257                                       "byte %u of %u)", i + 1, uncompressed_len);
 258                                 abort();
 259                         }
 260                 }
 261         }
 262 #endif
 263         return compressed_len;
 264 }