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   1 /*
   2  * lzx-decompress.c
   3  *
   4  * A very fast decompressor for LZX, as used in WIM files.
   5  */
   6
   7 /*
   8  * Copyright (C) 2012, 2013, 2014 Eric Biggers
   9  *
  10  * This file is part of wimlib, a library for working with WIM files.
  11  *
  12  * wimlib is free software; you can redistribute it and/or modify it under the
  13  * terms of the GNU General Public License as published by the Free
  14  * Software Foundation; either version 3 of the License, or (at your option)
  15  * any later version.
  16  *
  17  * wimlib is distributed in the hope that it will be useful, but WITHOUT ANY
  18  * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  19  * A PARTICULAR PURPOSE. See the GNU General Public License for more
  20  * details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with wimlib; if not, see http://www.gnu.org/licenses/.
  24  */
  25
  26 /*
  27  * LZX is an LZ77 and Huffman-code based compression format that has many
  28  * similarities to DEFLATE (the format used by zlib/gzip).  The compression
  29  * ratio is as good or better than DEFLATE.  See lzx-compress.c for a format
  30  * overview, and see https://en.wikipedia.org/wiki/LZX_(algorithm) for a
  31  * historical overview.  Here I make some pragmatic notes.
  32  *
  33  * The old specification for LZX is the document "Microsoft LZX Data Compression
  34  * Format" (1997).  It defines the LZX format as used in cabinet files.  Allowed
  35  * window sizes are 2^n where 15 <= n <= 21.  However, this document contains
  36  * several errors, so don't read too much into it...
  37  *
  38  * The new specification for LZX is the document "[MS-PATCH]: LZX DELTA
  39  * Compression and Decompression" (2014).  It defines the LZX format as used by
  40  * Microsoft's binary patcher.  It corrects several errors in the 1997 document
  41  * and extends the format in several ways --- namely, optional reference data,
  42  * up to 2^25 byte windows, and longer match lengths.
  43  *
  44  * WIM files use a more restricted form of LZX.  No LZX DELTA extensions are
  45  * present, the window is not "sliding", E8 preprocessing is done
  46  * unconditionally with a fixed file size, and the maximum window size is always
  47  * 2^15 bytes (equal to the size of each "chunk" in a compressed WIM resource).
  48  * This code is primarily intended to implement this form of LZX.  But although
  49  * not compatible with WIMGAPI, this code also supports maximum window sizes up
  50  * to 2^21 bytes.
  51  *
  52  * TODO: Add support for window sizes up to 2^25 bytes.
  53  */
  54
  55 #ifdef HAVE_CONFIG_H
  56 #  include "config.h"
  57 #endif
  58
  59 #include "wimlib/decompressor_ops.h"
  60 #include "wimlib/decompress_common.h"
  61 #include "wimlib/error.h"
  62 #include "wimlib/lzx.h"
  63 #include "wimlib/util.h"
  64
  65 #include <string.h>
  66
  67 /* These values are chosen for fast decompression.  */
  68 #define LZX_MAINCODE_TABLEBITS          11
  69 #define LZX_LENCODE_TABLEBITS           10
  70 #define LZX_PRECODE_TABLEBITS           6
  71 #define LZX_ALIGNEDCODE_TABLEBITS       7
  72
  73 /* Huffman decoding tables, and arrays that map symbols to codeword lengths.  */
  74 struct lzx_tables {
  75
  76         u16 maincode_decode_table[(1 << LZX_MAINCODE_TABLEBITS) +
  77                                         (LZX_MAINCODE_MAX_NUM_SYMBOLS * 2)]
  78                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
  79         u8 maincode_lens[LZX_MAINCODE_MAX_NUM_SYMBOLS];
  80
  81
  82         u16 lencode_decode_table[(1 << LZX_LENCODE_TABLEBITS) +
  83                                         (LZX_LENCODE_NUM_SYMBOLS * 2)]
  84                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
  85         u8 lencode_lens[LZX_LENCODE_NUM_SYMBOLS];
  86
  87
  88         u16 alignedcode_decode_table[(1 << LZX_ALIGNEDCODE_TABLEBITS) +
  89                                         (LZX_ALIGNEDCODE_NUM_SYMBOLS * 2)]
  90                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
  91         u8 alignedcode_lens[LZX_ALIGNEDCODE_NUM_SYMBOLS];
  92 } _aligned_attribute(DECODE_TABLE_ALIGNMENT);
  93
  94 /* The main LZX decompressor structure.
  95  *
  96  * Note: we keep track of most of the decompression state outside this
  97  * structure.  This structure only exists so that (1) we can store
  98  * @max_window_size and @num_main_syms for multiple calls to lzx_decompress();
  99  * and (2) so that we don't have to allocate the large 'struct lzx_tables' on
 100  * the stack.  */
 101 struct lzx_decompressor {
 102         u32 max_window_size;
 103         unsigned num_main_syms;
 104         struct lzx_tables tables;
 105 };
 106
 107 /* Read a Huffman-encoded symbol using the precode.  */
 108 static inline u16
 109 read_huffsym_using_precode(struct input_bitstream *istream,
 110                            const u16 precode_decode_table[])
 111 {
 112         return read_huffsym(istream, precode_decode_table,
 113                             LZX_PRECODE_TABLEBITS, LZX_MAX_PRE_CODEWORD_LEN);
 114 }
 115
 116 /* Read a Huffman-encoded symbol using the main code.  */
 117 static inline u16
 118 read_huffsym_using_maincode(struct input_bitstream *istream,
 119                             const struct lzx_tables *tables)
 120 {
 121         return read_huffsym(istream, tables->maincode_decode_table,
 122                             LZX_MAINCODE_TABLEBITS, LZX_MAX_MAIN_CODEWORD_LEN);
 123 }
 124
 125 /* Read a Huffman-encoded symbol using the length code.  */
 126 static inline u16
 127 read_huffsym_using_lencode(struct input_bitstream *istream,
 128                            const struct lzx_tables *tables)
 129 {
 130         return read_huffsym(istream, tables->lencode_decode_table,
 131                             LZX_LENCODE_TABLEBITS, LZX_MAX_LEN_CODEWORD_LEN);
 132 }
 133
 134 /* Read a Huffman-encoded symbol using the aligned offset code.  */
 135 static inline u16
 136 read_huffsym_using_alignedcode(struct input_bitstream *istream,
 137                                const struct lzx_tables *tables)
 138 {
 139         return read_huffsym(istream, tables->alignedcode_decode_table,
 140                             LZX_ALIGNEDCODE_TABLEBITS, LZX_MAX_ALIGNED_CODEWORD_LEN);
 141 }
 142
 143 /*
 144  * Read the precode from the compressed input bitstream, then use it to decode
 145  * @num_lens codeword length values.
 146  *
 147  * @istream:
 148  *      The input bitstream.
 149  *
 150  * @lens:
 151  *      An array that contains the length values from the previous time the
 152  *      codeword lengths for this Huffman code were read, or all 0's if this is
 153  *      the first time.
 154  *
 155  * @num_lens:
 156  *      Number of length values to decode.
 157  *
 158  * Returns 0 on success, or -1 if the data was invalid.
 159  */
 160 static int
 161 lzx_read_codeword_lens(struct input_bitstream *istream, u8 lens[], unsigned num_lens)
 162 {
 163         /* Declare the decoding table and length table for the precode.  */
 164         u16 precode_decode_table[(1 << LZX_PRECODE_TABLEBITS) +
 165                                         (LZX_PRECODE_NUM_SYMBOLS * 2)]
 166                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
 167         u8 precode_lens[LZX_PRECODE_NUM_SYMBOLS];
 168         int ret;
 169
 170         /* Read the lengths of the precode codewords.  These are given
 171          * explicitly.  */
 172         for (int i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++) {
 173                 precode_lens[i] = bitstream_read_bits(istream,
 174                                                       LZX_PRECODE_ELEMENT_SIZE);
 175         }
 176
 177         /* Make the decoding table for the precode.  */
 178         ret = make_huffman_decode_table(precode_decode_table,
 179                                         LZX_PRECODE_NUM_SYMBOLS,
 180                                         LZX_PRECODE_TABLEBITS,
 181                                         precode_lens,
 182                                         LZX_MAX_PRE_CODEWORD_LEN);
 183         if (ret)
 184                 return ret;
 185
 186         /* Pointer past the last length value that needs to be filled in.  */
 187         u8 *lens_end = lens + num_lens;
 188
 189         for (;;) {
 190
 191                 unsigned presym;
 192                 unsigned run_len;
 193                 signed char value;
 194
 195                 /* Decode a symbol from the input.
 196                  *
 197                  * If the symbol is between 0 and 16, it is the difference from
 198                  * the old length, modulo 17.
 199                  *
 200                  * If the symbol is between 17 and 19, it is a special symbol
 201                  * that indicates that some number of the next lengths are all
 202                  * 0, or that some number of the next lengths are all equal to
 203                  * the next symbol.  */
 204
 205                 presym = read_huffsym_using_precode(istream,
 206                                                     precode_decode_table);
 207                 switch (presym) {
 208
 209                 case 17: /* Run of 0's  */
 210                         run_len = 4 + bitstream_read_bits(istream, 4);
 211                         do {
 212                                 *lens = 0;
 213                                 if (++lens == lens_end)
 214                                         return 0;
 215                         } while (--run_len);
 216                         break;
 217
 218                 case 18: /* Longer run of 0's  */
 219                         run_len = 20 + bitstream_read_bits(istream, 5);
 220                         do {
 221                                 *lens = 0;
 222                                 if (++lens == lens_end)
 223                                         return 0;
 224                         } while (--run_len);
 225                         break;
 226
 227                 case 19: /* Run of identical lengths  */
 228                         run_len = 4 + bitstream_read_bits(istream, 1);
 229                         presym = read_huffsym_using_precode(istream,
 230                                                             precode_decode_table);
 231                         value = (signed char)*lens - (signed char)presym;
 232                         if (value < 0)
 233                                 value += 17;
 234                         do {
 235                                 *lens = value;
 236                                 if (++lens == lens_end)
 237                                         return 0;
 238                         } while (--run_len);
 239                         break;
 240
 241                 default: /* Difference from old length  */
 242                         value = (signed char)*lens - (signed char)presym;
 243                         if (value < 0)
 244                                 value += 17;
 245                         *lens = value;
 246                         if (++lens == lens_end)
 247                                 return 0;
 248                         break;
 249                 }
 250         }
 251 }
 252
 253 /*
 254  * Read the header of an LZX block and save the block type and size in
 255  * *block_type_ret and *block_size_ret, respectively.
 256  *
 257  * If the block is compressed, also update the Huffman decode @tables with the
 258  * new Huffman codes.
 259  *
 260  * If the block is uncompressed, also update the match offset @queue with the
 261  * new match offsets.
 262  *
 263  * Return 0 on success, or -1 if the data was invalid.
 264  */
 265 static int
 266 lzx_read_block_header(struct input_bitstream *istream,
 267                       unsigned num_main_syms,
 268                       u32 max_window_size,
 269                       int *block_type_ret,
 270                       u32 *block_size_ret,
 271                       struct lzx_tables *tables,
 272                       struct lzx_lru_queue *queue)
 273 {
 274         int block_type;
 275         u32 block_size;
 276         int ret;
 277
 278         bitstream_ensure_bits(istream, 4);
 279
 280         /* The first three bits tell us what kind of block it is, and should be
 281          * one of the LZX_BLOCKTYPE_* values.  */
 282         block_type = bitstream_pop_bits(istream, 3);
 283
 284         /* Read the block size.  This mirrors the behavior of
 285          * lzx_write_compressed_block() in lzx-compress.c; see that for more
 286          * details.  */
 287         if (bitstream_pop_bits(istream, 1)) {
 288                 block_size = LZX_DEFAULT_BLOCK_SIZE;
 289         } else {
 290                 u32 tmp;
 291                 block_size = 0;
 292
 293                 tmp = bitstream_read_bits(istream, 8);
 294                 block_size |= tmp;
 295                 tmp = bitstream_read_bits(istream, 8);
 296                 block_size <<= 8;
 297                 block_size |= tmp;
 298
 299                 if (max_window_size >= 65536) {
 300                         tmp = bitstream_read_bits(istream, 8);
 301                         block_size <<= 8;
 302                         block_size |= tmp;
 303                 }
 304         }
 305
 306         switch (block_type) {
 307
 308         case LZX_BLOCKTYPE_ALIGNED:
 309
 310                 /* Read the aligned offset code and prepare its decode table.
 311                  */
 312
 313                 for (int i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
 314                         tables->alignedcode_lens[i] =
 315                                 bitstream_read_bits(istream,
 316                                                     LZX_ALIGNEDCODE_ELEMENT_SIZE);
 317                 }
 318
 319                 ret = make_huffman_decode_table(tables->alignedcode_decode_table,
 320                                                 LZX_ALIGNEDCODE_NUM_SYMBOLS,
 321                                                 LZX_ALIGNEDCODE_TABLEBITS,
 322                                                 tables->alignedcode_lens,
 323                                                 LZX_MAX_ALIGNED_CODEWORD_LEN);
 324                 if (ret)
 325                         return ret;
 326
 327                 /* Fall though, since the rest of the header for aligned offset
 328                  * blocks is the same as that for verbatim blocks.  */
 329
 330         case LZX_BLOCKTYPE_VERBATIM:
 331
 332                 /* Read the main code and prepare its decode table.
 333                  *
 334                  * Note that the codeword lengths in the main code are encoded
 335                  * in two parts: one part for literal symbols, and one part for
 336                  * match symbols.  */
 337
 338                 ret = lzx_read_codeword_lens(istream, tables->maincode_lens,
 339                                              LZX_NUM_CHARS);
 340                 if (ret)
 341                         return ret;
 342
 343                 ret = lzx_read_codeword_lens(istream,
 344                                              tables->maincode_lens + LZX_NUM_CHARS,
 345                                              num_main_syms - LZX_NUM_CHARS);
 346                 if (ret)
 347                         return ret;
 348
 349                 ret = make_huffman_decode_table(tables->maincode_decode_table,
 350                                                 num_main_syms,
 351                                                 LZX_MAINCODE_TABLEBITS,
 352                                                 tables->maincode_lens,
 353                                                 LZX_MAX_MAIN_CODEWORD_LEN);
 354                 if (ret)
 355                         return ret;
 356
 357                 /* Read the length code and prepare its decode table.  */
 358
 359                 ret = lzx_read_codeword_lens(istream, tables->lencode_lens,
 360                                              LZX_LENCODE_NUM_SYMBOLS);
 361                 if (ret)
 362                         return ret;
 363
 364                 ret = make_huffman_decode_table(tables->lencode_decode_table,
 365                                                 LZX_LENCODE_NUM_SYMBOLS,
 366                                                 LZX_LENCODE_TABLEBITS,
 367                                                 tables->lencode_lens,
 368                                                 LZX_MAX_LEN_CODEWORD_LEN);
 369                 if (ret)
 370                         return ret;
 371
 372                 break;
 373
 374         case LZX_BLOCKTYPE_UNCOMPRESSED:
 375
 376                 /* Before reading the three LRU match offsets from the
 377                  * uncompressed block header, the stream must be aligned on a
 378                  * 16-bit boundary.  But, unexpectedly, if the stream is
 379                  * *already* aligned, the correct thing to do is to throw away
 380                  * the next 16 bits.  */
 381
 382                 if (istream->bitsleft == 0) {
 383                         if (istream->data_bytes_left < 14)
 384                                 return -1;
 385                         istream->data += 2;
 386                         istream->data_bytes_left -= 2;
 387                 } else {
 388                         if (istream->data_bytes_left < 12)
 389                                 return -1;
 390                         istream->bitsleft = 0;
 391                         istream->bitbuf = 0;
 392                 }
 393                 queue->R[0] = le32_to_cpu(*(le32*)(istream->data + 0));
 394                 queue->R[1] = le32_to_cpu(*(le32*)(istream->data + 4));
 395                 queue->R[2] = le32_to_cpu(*(le32*)(istream->data + 8));
 396                 istream->data += 12;
 397                 istream->data_bytes_left -= 12;
 398                 break;
 399
 400         default:
 401                 /* Unrecognized block type.  */
 402                 return -1;
 403         }
 404
 405         *block_type_ret = block_type;
 406         *block_size_ret = block_size;
 407         return 0;
 408 }
 409
 410 /*
 411  * Decode a match and copy its bytes into the decompression window.
 412  *
 413  * Return the length of the match in bytes, or 0 if the match underflowed the
 414  * window or overflowed the current block.
 415  */
 416 static u32
 417 lzx_decode_match(unsigned main_symbol, int block_type,
 418                  u32 bytes_remaining, u8 *window, u32 window_pos,
 419                  const struct lzx_tables *tables,
 420                  struct lzx_lru_queue *queue,
 421                  struct input_bitstream *istream)
 422 {
 423         unsigned length_header;
 424         unsigned position_slot;
 425         u32 match_len;
 426         u32 match_offset;
 427         unsigned num_extra_bits;
 428         u32 verbatim_bits;
 429         u32 aligned_bits;
 430
 431         /* The main symbol is offset by 256 because values under 256 indicate a
 432          * literal value.  */
 433         main_symbol -= LZX_NUM_CHARS;
 434
 435         /* The length header consists of the lower 3 bits of the main element.
 436          * The position slot is the rest of it. */
 437         length_header = main_symbol & LZX_NUM_PRIMARY_LENS;
 438         position_slot = main_symbol >> 3;
 439
 440         /* If the length_header is less than LZX_NUM_PRIMARY_LENS (= 7), it
 441          * gives the match length as the offset from LZX_MIN_MATCH_LEN.
 442          * Otherwise, the length is given by an additional symbol encoded using
 443          * the length code, offset by 9 (LZX_MIN_MATCH_LEN +
 444          * LZX_NUM_PRIMARY_LENS) */
 445         match_len = LZX_MIN_MATCH_LEN + length_header;
 446         if (length_header == LZX_NUM_PRIMARY_LENS)
 447                 match_len += read_huffsym_using_lencode(istream, tables);
 448
 449         /* If the position_slot is 0, 1, or 2, the match offset is retrieved
 450          * from the LRU queue.  Otherwise, the match offset is not in the LRU
 451          * queue. */
 452         if (position_slot <= 2) {
 453                 /* Note: This isn't a real LRU queue, since using the R2 offset
 454                  * doesn't bump the R1 offset down to R2.  This quirk allows all
 455                  * 3 recent offsets to be handled by the same code.  (For R0,
 456                  * the swap is a no-op.)  */
 457                 match_offset = queue->R[position_slot];
 458                 queue->R[position_slot] = queue->R[0];
 459                 queue->R[0] = match_offset;
 460         } else {
 461                 /* Otherwise, the offset was not encoded as one the offsets in
 462                  * the queue.  Depending on the position slot, there is a
 463                  * certain number of extra bits that need to be read to fully
 464                  * decode the match offset. */
 465
 466                 /* Look up the number of extra bits that need to be read. */
 467                 num_extra_bits = lzx_get_num_extra_bits(position_slot);
 468
 469                 /* For aligned blocks, if there are at least 3 extra bits, the
 470                  * actual number of extra bits is 3 less, and they encode a
 471                  * number of 8-byte words that are added to the offset; there
 472                  * is then an additional symbol read using the aligned offset
 473                  * code that specifies the actual byte alignment. */
 474                 if (block_type == LZX_BLOCKTYPE_ALIGNED && num_extra_bits >= 3) {
 475
 476                         /* There is an error in the LZX "specification" at this
 477                          * point; it indicates that a Huffman symbol is to be
 478                          * read only if num_extra_bits is greater than 3, but
 479                          * actually it is if num_extra_bits is greater than or
 480                          * equal to 3.  (Note that in the case with
 481                          * num_extra_bits == 3, the assignment to verbatim_bits
 482                          * will just set it to 0. ) */
 483                         verbatim_bits = bitstream_read_bits(istream,
 484                                                             num_extra_bits - 3);
 485                         verbatim_bits <<= 3;
 486                         aligned_bits = read_huffsym_using_alignedcode(istream,
 487                                                                       tables);
 488                 } else {
 489                         /* For non-aligned blocks, or for aligned blocks with
 490                          * less than 3 extra bits, the extra bits are added
 491                          * directly to the match offset, and the correction for
 492                          * the alignment is taken to be 0. */
 493                         verbatim_bits = bitstream_read_bits(istream, num_extra_bits);
 494                         aligned_bits = 0;
 495                 }
 496
 497                 /* Calculate the match offset. */
 498                 match_offset = lzx_position_base[position_slot] +
 499                                verbatim_bits + aligned_bits - LZX_OFFSET_OFFSET;
 500
 501                 /* Update the LRU queue. */
 502                 queue->R[2] = queue->R[1];
 503                 queue->R[1] = queue->R[0];
 504                 queue->R[0] = match_offset;
 505         }
 506
 507         /* Validate the match, then copy it to the current position.  */
 508
 509         if (unlikely(match_len > bytes_remaining))
 510                 return 0;
 511
 512         if (unlikely(match_offset > window_pos))
 513                 return 0;
 514
 515         lz_copy(&window[window_pos], match_len, match_offset,
 516                 &window[window_pos + bytes_remaining]);
 517
 518         return match_len;
 519 }
 520
 521 /*
 522  * Decompress an LZX-compressed block of data.
 523  *
 524  * @block_type:
 525  *      The type of the block (LZX_BLOCKTYPE_VERBATIM or LZX_BLOCKTYPE_ALIGNED).
 526  *
 527  * @block_size:
 528  *      The size of the block, in bytes.
 529  *
 530  * @window:
 531  *      Pointer to the beginning of the decompression window.
 532  *
 533  * @window_pos:
 534  *      The position in the window at which the block starts.
 535  *
 536  * @tables:
 537  *      The Huffman decoding tables for the block.
 538  *
 539  * @queue:
 540  *      The least-recently-used queue for match offsets.
 541  *
 542  * @istream:
 543  *      The input bitstream, positioned at the start of the block data.
 544  *
 545  * Returns 0 on success, or -1 if the data was invalid.
 546  */
 547 static int
 548 lzx_decompress_block(int block_type, u32 block_size,
 549                      u8 *window, u32 window_pos,
 550                      const struct lzx_tables *tables,
 551                      struct lzx_lru_queue *queue,
 552                      struct input_bitstream *istream)
 553 {
 554         u32 block_end;
 555         unsigned main_symbol;
 556         u32 match_len;
 557
 558         block_end = window_pos + block_size;
 559         while (window_pos < block_end) {
 560                 main_symbol = read_huffsym_using_maincode(istream, tables);
 561                 if (main_symbol < LZX_NUM_CHARS) {
 562                         /* Literal  */
 563                         window[window_pos++] = main_symbol;
 564                 } else {
 565                         /* Match  */
 566                         match_len = lzx_decode_match(main_symbol,
 567                                                      block_type,
 568                                                      block_end - window_pos,
 569                                                      window,
 570                                                      window_pos,
 571                                                      tables,
 572                                                      queue,
 573                                                      istream);
 574                         if (unlikely(match_len == 0))
 575                                 return -1;
 576                         window_pos += match_len;
 577                 }
 578         }
 579         return 0;
 580 }
 581
 582 static int
 583 lzx_decompress(const void *compressed_data, size_t compressed_size,
 584                void *uncompressed_data, size_t uncompressed_size,
 585                void *_dec)
 586 {
 587         struct lzx_decompressor *dec = _dec;
 588         struct input_bitstream istream;
 589         struct lzx_lru_queue queue;
 590         u32 window_pos;
 591         int block_type;
 592         u32 block_size;
 593         bool may_have_e8_byte;
 594         int ret;
 595
 596         if (uncompressed_size > dec->max_window_size)
 597                 return -1;
 598
 599         init_input_bitstream(&istream, compressed_data, compressed_size);
 600
 601         /* Initialize the recent offsets queue.  */
 602         lzx_lru_queue_init(&queue);
 603
 604         /* Codeword lengths begin as all 0's for delta encoding purposes.  */
 605         memset(dec->tables.maincode_lens, 0, sizeof(dec->tables.maincode_lens));
 606         memset(dec->tables.lencode_lens, 0, sizeof(dec->tables.lencode_lens));
 607
 608         /* Set this to true if there may be 0xe8 bytes in the uncompressed data.
 609          */
 610         may_have_e8_byte = false;
 611
 612         /* The compressed data will consist of one or more blocks.  The
 613          * following loop decompresses one block, and it runs until there all
 614          * the compressed data has been decompressed, so there are no more
 615          * blocks.  */
 616
 617         for (window_pos = 0;
 618              window_pos < uncompressed_size;
 619              window_pos += block_size)
 620         {
 621                 ret = lzx_read_block_header(&istream, dec->num_main_syms,
 622                                             dec->max_window_size, &block_type,
 623                                             &block_size, &dec->tables, &queue);
 624                 if (ret)
 625                         return ret;
 626
 627                 if (block_size > uncompressed_size - window_pos)
 628                         return -1;
 629
 630                 if (block_type != LZX_BLOCKTYPE_UNCOMPRESSED) {
 631
 632                         /* Compressed block.  */
 633
 634                         ret = lzx_decompress_block(block_type,
 635                                                    block_size,
 636                                                    uncompressed_data,
 637                                                    window_pos,
 638                                                    &dec->tables,
 639                                                    &queue,
 640                                                    &istream);
 641                         if (ret)
 642                                 return ret;
 643
 644                         /* If the first 0xe8 byte was in this block, it must
 645                          * have been encoded as a literal using mainsym 0xe8. */
 646                         if (dec->tables.maincode_lens[0xe8] != 0)
 647                                 may_have_e8_byte = true;
 648                 } else {
 649
 650                         /* Uncompressed block.  */
 651
 652                         if (istream.data_bytes_left < block_size)
 653                                 return -1;
 654
 655                         memcpy(&((u8*)uncompressed_data)[window_pos], istream.data,
 656                                block_size);
 657                         istream.data += block_size;
 658                         istream.data_bytes_left -= block_size;
 659
 660                         /* Re-align the bitstream if an odd number of bytes was
 661                          * read.  */
 662                         if (istream.data_bytes_left && (block_size & 1)) {
 663                                 istream.data_bytes_left--;
 664                                 istream.data++;
 665                         }
 666                         may_have_e8_byte = true;
 667                 }
 668         }
 669
 670         /* Postprocess the data unless it cannot possibly contain 0xe8 bytes  */
 671         if (may_have_e8_byte)
 672                 lzx_undo_e8_preprocessing(uncompressed_data, uncompressed_size);
 673
 674         return 0;
 675 }
 676
 677 static void
 678 lzx_free_decompressor(void *_dec)
 679 {
 680         struct lzx_decompressor *dec = _dec;
 681
 682         ALIGNED_FREE(dec);
 683 }
 684
 685 static int
 686 lzx_create_decompressor(size_t max_window_size, void **dec_ret)
 687 {
 688         struct lzx_decompressor *dec;
 689
 690         if (!lzx_window_size_valid(max_window_size))
 691                 return WIMLIB_ERR_INVALID_PARAM;
 692
 693         /* The aligned allocation is needed to ensure that the lzx_tables are
 694          * aligned properly.  */
 695         dec = ALIGNED_MALLOC(sizeof(struct lzx_decompressor),
 696                              DECODE_TABLE_ALIGNMENT);
 697         if (!dec)
 698                 return WIMLIB_ERR_NOMEM;
 699
 700         dec->max_window_size = max_window_size;
 701         dec->num_main_syms = lzx_get_num_main_syms(max_window_size);
 702
 703         *dec_ret = dec;
 704         return 0;
 705 }
 706
 707 const struct decompressor_ops lzx_decompressor_ops = {
 708         .create_decompressor = lzx_create_decompressor,
 709         .decompress          = lzx_decompress,
 710         .free_decompressor   = lzx_free_decompressor,
 711 };