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   1 /*
   2  * lzx_decompress.c
   3  *
   4  * A decompressor for the LZX compression format, as used in WIM files.
   5  */
   6
   7 /*
   8  * Copyright (C) 2012, 2013, 2014 Eric Biggers
   9  *
  10  * This file is free software; you can redistribute it and/or modify it under
  11  * the terms of the GNU Lesser General Public License as published by the Free
  12  * Software Foundation; either version 3 of the License, or (at your option) any
  13  * later version.
  14  *
  15  * This file is distributed in the hope that it will be useful, but WITHOUT
  16  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  17  * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
  18  * details.
  19  *
  20  * You should have received a copy of the GNU Lesser General Public License
  21  * along with this file; if not, see http://www.gnu.org/licenses/.
  22  */
  23
  24 /*
  25  * LZX is an LZ77 and Huffman-code based compression format that has many
  26  * similarities to DEFLATE (the format used by zlib/gzip).  The compression
  27  * ratio is as good or better than DEFLATE.  See lzx_compress.c for a format
  28  * overview, and see https://en.wikipedia.org/wiki/LZX_(algorithm) for a
  29  * historical overview.  Here I make some pragmatic notes.
  30  *
  31  * The old specification for LZX is the document "Microsoft LZX Data Compression
  32  * Format" (1997).  It defines the LZX format as used in cabinet files.  Allowed
  33  * window sizes are 2^n where 15 <= n <= 21.  However, this document contains
  34  * several errors, so don't read too much into it...
  35  *
  36  * The new specification for LZX is the document "[MS-PATCH]: LZX DELTA
  37  * Compression and Decompression" (2014).  It defines the LZX format as used by
  38  * Microsoft's binary patcher.  It corrects several errors in the 1997 document
  39  * and extends the format in several ways --- namely, optional reference data,
  40  * up to 2^25 byte windows, and longer match lengths.
  41  *
  42  * WIM files use a more restricted form of LZX.  No LZX DELTA extensions are
  43  * present, the window is not "sliding", E8 preprocessing is done
  44  * unconditionally with a fixed file size, and the maximum window size is always
  45  * 2^15 bytes (equal to the size of each "chunk" in a compressed WIM resource).
  46  * This code is primarily intended to implement this form of LZX.  But although
  47  * not compatible with WIMGAPI, this code also supports maximum window sizes up
  48  * to 2^21 bytes.
  49  *
  50  * TODO: Add support for window sizes up to 2^25 bytes.
  51  */
  52
  53 #ifdef HAVE_CONFIG_H
  54 #  include "config.h"
  55 #endif
  56
  57 #include "wimlib/decompressor_ops.h"
  58 #include "wimlib/decompress_common.h"
  59 #include "wimlib/error.h"
  60 #include "wimlib/lzx_common.h"
  61 #include "wimlib/util.h"
  62
  63 #include <string.h>
  64
  65 /* These values are chosen for fast decompression.  */
  66 #define LZX_MAINCODE_TABLEBITS          11
  67 #define LZX_LENCODE_TABLEBITS           10
  68 #define LZX_PRECODE_TABLEBITS           6
  69 #define LZX_ALIGNEDCODE_TABLEBITS       7
  70
  71 #define LZX_READ_LENS_MAX_OVERRUN 50
  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 + LZX_READ_LENS_MAX_OVERRUN];
  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 + LZX_READ_LENS_MAX_OVERRUN];
  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 @window_order
  98  * and @num_main_syms for multiple calls to lzx_decompress(); and (2) so that we
  99  * don't have to allocate the large 'struct lzx_tables' on the stack.  */
 100 struct lzx_decompressor {
 101         unsigned window_order;
 102         unsigned num_main_syms;
 103         struct lzx_tables tables;
 104 };
 105
 106 /* Read a Huffman-encoded symbol using the precode.  */
 107 static inline u16
 108 read_huffsym_using_precode(struct input_bitstream *istream,
 109                            const u16 precode_decode_table[])
 110 {
 111         return read_huffsym(istream, precode_decode_table,
 112                             LZX_PRECODE_TABLEBITS, LZX_MAX_PRE_CODEWORD_LEN);
 113 }
 114
 115 /* Read a Huffman-encoded symbol using the main code.  */
 116 static inline u16
 117 read_huffsym_using_maincode(struct input_bitstream *istream,
 118                             const struct lzx_tables *tables)
 119 {
 120         return read_huffsym(istream, tables->maincode_decode_table,
 121                             LZX_MAINCODE_TABLEBITS, LZX_MAX_MAIN_CODEWORD_LEN);
 122 }
 123
 124 /* Read a Huffman-encoded symbol using the length code.  */
 125 static inline u16
 126 read_huffsym_using_lencode(struct input_bitstream *istream,
 127                            const struct lzx_tables *tables)
 128 {
 129         return read_huffsym(istream, tables->lencode_decode_table,
 130                             LZX_LENCODE_TABLEBITS, LZX_MAX_LEN_CODEWORD_LEN);
 131 }
 132
 133 /* Read a Huffman-encoded symbol using the aligned offset code.  */
 134 static inline u16
 135 read_huffsym_using_alignedcode(struct input_bitstream *istream,
 136                                const struct lzx_tables *tables)
 137 {
 138         return read_huffsym(istream, tables->alignedcode_decode_table,
 139                             LZX_ALIGNEDCODE_TABLEBITS, LZX_MAX_ALIGNED_CODEWORD_LEN);
 140 }
 141
 142 /*
 143  * Read the precode from the compressed input bitstream, then use it to decode
 144  * @num_lens codeword length values.
 145  *
 146  * @istream:
 147  *      The input bitstream.
 148  *
 149  * @lens:
 150  *      An array that contains the length values from the previous time the
 151  *      codeword lengths for this Huffman code were read, or all 0's if this is
 152  *      the first time.  This array must have at least (@num_lens +
 153  *      LZX_READ_LENS_MAX_OVERRUN) entries.
 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         u16 precode_decode_table[(1 << LZX_PRECODE_TABLEBITS) +
 164                                         (LZX_PRECODE_NUM_SYMBOLS * 2)]
 165                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
 166         u8 precode_lens[LZX_PRECODE_NUM_SYMBOLS];
 167         u8 *len_ptr = lens;
 168         u8 *lens_end = lens + num_lens;
 169         int ret;
 170
 171         /* Read the lengths of the precode codewords.  These are given
 172          * explicitly.  */
 173         for (int i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++) {
 174                 precode_lens[i] = bitstream_read_bits(istream,
 175                                                       LZX_PRECODE_ELEMENT_SIZE);
 176         }
 177
 178         /* Make the decoding table for the precode.  */
 179         ret = make_huffman_decode_table(precode_decode_table,
 180                                         LZX_PRECODE_NUM_SYMBOLS,
 181                                         LZX_PRECODE_TABLEBITS,
 182                                         precode_lens,
 183                                         LZX_MAX_PRE_CODEWORD_LEN);
 184         if (ret)
 185                 return ret;
 186
 187         /* Decode the codeword lengths.  */
 188         do {
 189                 unsigned presym;
 190                 u8 len;
 191
 192                 /* Read the next precode symbol.  */
 193                 presym = read_huffsym_using_precode(istream,
 194                                                     precode_decode_table);
 195                 if (presym < 17) {
 196                         /* Difference from old length  */
 197                         len = *len_ptr - presym;
 198                         if ((s8)len < 0)
 199                                 len += 17;
 200                         *len_ptr++ = len;
 201                 } else {
 202                         /* Special RLE values  */
 203
 204                         unsigned run_len;
 205
 206                         if (presym == 17) {
 207                                 /* Run of 0's  */
 208                                 run_len = 4 + bitstream_read_bits(istream, 4);
 209                                 len = 0;
 210                         } else if (presym == 18) {
 211                                 /* Longer run of 0's  */
 212                                 run_len = 20 + bitstream_read_bits(istream, 5);
 213                                 len = 0;
 214                         } else {
 215                                 /* Run of identical lengths  */
 216                                 run_len = 4 + bitstream_read_bits(istream, 1);
 217                                 presym = read_huffsym_using_precode(istream,
 218                                                                     precode_decode_table);
 219                                 len = *len_ptr - presym;
 220                                 if ((s8)len < 0)
 221                                         len += 17;
 222                         }
 223
 224                         do {
 225                                 *len_ptr++ = len;
 226                         } while (--run_len);
 227                         /* Worst case overrun is when presym == 18,
 228                          * run_len == 20 + 31, and only 1 length was remaining.
 229                          * So LZX_READ_LENS_MAX_OVERRUN == 50.
 230                          *
 231                          * Overrun while reading the first half of maincode_lens
 232                          * can corrupt the previous values in the second half.
 233                          * This doesn't really matter because the resulting
 234                          * lengths will still be in range, and data that
 235                          * generates overruns is invalid anyway.  */
 236                 }
 237         } while (len_ptr < lens_end);
 238         return 0;
 239 }
 240
 241 /*
 242  * Read the header of an LZX block and save the block type and size in
 243  * *block_type_ret and *block_size_ret, respectively.
 244  *
 245  * If the block is compressed, also update the Huffman decode @tables with the
 246  * new Huffman codes.
 247  *
 248  * If the block is uncompressed, also update the match offset @queue with the
 249  * new match offsets.
 250  *
 251  * Return 0 on success, or -1 if the data was invalid.
 252  */
 253 static int
 254 lzx_read_block_header(struct input_bitstream *istream,
 255                       unsigned num_main_syms,
 256                       unsigned window_order,
 257                       int *block_type_ret,
 258                       u32 *block_size_ret,
 259                       struct lzx_tables *tables,
 260                       struct lzx_lru_queue *queue)
 261 {
 262         int block_type;
 263         u32 block_size;
 264         int ret;
 265
 266         bitstream_ensure_bits(istream, 4);
 267
 268         /* The first three bits tell us what kind of block it is, and should be
 269          * one of the LZX_BLOCKTYPE_* values.  */
 270         block_type = bitstream_pop_bits(istream, 3);
 271
 272         /* Read the block size.  This mirrors the behavior of
 273          * lzx_write_compressed_block() in lzx_compress.c; see that for more
 274          * details.  */
 275         if (bitstream_pop_bits(istream, 1)) {
 276                 block_size = LZX_DEFAULT_BLOCK_SIZE;
 277         } else {
 278                 u32 tmp;
 279                 block_size = 0;
 280
 281                 tmp = bitstream_read_bits(istream, 8);
 282                 block_size |= tmp;
 283                 tmp = bitstream_read_bits(istream, 8);
 284                 block_size <<= 8;
 285                 block_size |= tmp;
 286
 287                 if (window_order >= 16) {
 288                         tmp = bitstream_read_bits(istream, 8);
 289                         block_size <<= 8;
 290                         block_size |= tmp;
 291                 }
 292         }
 293
 294         switch (block_type) {
 295
 296         case LZX_BLOCKTYPE_ALIGNED:
 297
 298                 /* Read the aligned offset code and prepare its decode table.
 299                  */
 300
 301                 for (int i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
 302                         tables->alignedcode_lens[i] =
 303                                 bitstream_read_bits(istream,
 304                                                     LZX_ALIGNEDCODE_ELEMENT_SIZE);
 305                 }
 306
 307                 ret = make_huffman_decode_table(tables->alignedcode_decode_table,
 308                                                 LZX_ALIGNEDCODE_NUM_SYMBOLS,
 309                                                 LZX_ALIGNEDCODE_TABLEBITS,
 310                                                 tables->alignedcode_lens,
 311                                                 LZX_MAX_ALIGNED_CODEWORD_LEN);
 312                 if (ret)
 313                         return ret;
 314
 315                 /* Fall though, since the rest of the header for aligned offset
 316                  * blocks is the same as that for verbatim blocks.  */
 317
 318         case LZX_BLOCKTYPE_VERBATIM:
 319
 320                 /* Read the main code and prepare its decode table.
 321                  *
 322                  * Note that the codeword lengths in the main code are encoded
 323                  * in two parts: one part for literal symbols, and one part for
 324                  * match symbols.  */
 325
 326                 ret = lzx_read_codeword_lens(istream, tables->maincode_lens,
 327                                              LZX_NUM_CHARS);
 328                 if (ret)
 329                         return ret;
 330
 331                 ret = lzx_read_codeword_lens(istream,
 332                                              tables->maincode_lens + LZX_NUM_CHARS,
 333                                              num_main_syms - LZX_NUM_CHARS);
 334                 if (ret)
 335                         return ret;
 336
 337                 ret = make_huffman_decode_table(tables->maincode_decode_table,
 338                                                 num_main_syms,
 339                                                 LZX_MAINCODE_TABLEBITS,
 340                                                 tables->maincode_lens,
 341                                                 LZX_MAX_MAIN_CODEWORD_LEN);
 342                 if (ret)
 343                         return ret;
 344
 345                 /* Read the length code and prepare its decode table.  */
 346
 347                 ret = lzx_read_codeword_lens(istream, tables->lencode_lens,
 348                                              LZX_LENCODE_NUM_SYMBOLS);
 349                 if (ret)
 350                         return ret;
 351
 352                 ret = make_huffman_decode_table(tables->lencode_decode_table,
 353                                                 LZX_LENCODE_NUM_SYMBOLS,
 354                                                 LZX_LENCODE_TABLEBITS,
 355                                                 tables->lencode_lens,
 356                                                 LZX_MAX_LEN_CODEWORD_LEN);
 357                 if (ret)
 358                         return ret;
 359
 360                 break;
 361
 362         case LZX_BLOCKTYPE_UNCOMPRESSED:
 363
 364                 /* Before reading the three LRU match offsets from the
 365                  * uncompressed block header, the stream must be aligned on a
 366                  * 16-bit boundary.  But, unexpectedly, if the stream is
 367                  * *already* aligned, the correct thing to do is to throw away
 368                  * the next 16 bits.  */
 369
 370                 bitstream_ensure_bits(istream, 1);
 371                 bitstream_align(istream);
 372                 queue->R[0] = bitstream_read_u32(istream);
 373                 queue->R[1] = bitstream_read_u32(istream);
 374                 queue->R[2] = bitstream_read_u32(istream);
 375
 376                 /* Offsets of 0 are invalid.  */
 377                 if (queue->R[0] == 0 || queue->R[1] == 0 || queue->R[2] == 0)
 378                         return -1;
 379                 break;
 380
 381         default:
 382                 /* Unrecognized block type.  */
 383                 return -1;
 384         }
 385
 386         *block_type_ret = block_type;
 387         *block_size_ret = block_size;
 388         return 0;
 389 }
 390
 391 /*
 392  * Decompress an LZX-compressed block of data.
 393  *
 394  * @block_type:
 395  *      The type of the block (LZX_BLOCKTYPE_VERBATIM or LZX_BLOCKTYPE_ALIGNED).
 396  *
 397  * @block_size:
 398  *      The size of the block, in bytes.
 399  *
 400  * @window:
 401  *      Pointer to the beginning of the decompression window.
 402  *
 403  * @window_pos:
 404  *      The position in the window at which the block starts.
 405  *
 406  * @tables:
 407  *      The Huffman decoding tables for the block.
 408  *
 409  * @queue:
 410  *      The least-recently-used queue for match offsets.
 411  *
 412  * @istream:
 413  *      The input bitstream, positioned at the start of the block data.
 414  *
 415  * Returns 0 on success, or -1 if the data was invalid.
 416  */
 417 static int
 418 lzx_decompress_block(int block_type, u32 block_size,
 419                      u8 *window, u32 window_pos,
 420                      const struct lzx_tables *tables,
 421                      struct lzx_lru_queue *queue,
 422                      struct input_bitstream *istream)
 423 {
 424         u8 *window_ptr = &window[window_pos];
 425         u8 *window_end = window_ptr + block_size;
 426         unsigned mainsym;
 427         u32 match_len;
 428         unsigned offset_slot;
 429         u32 match_offset;
 430         unsigned num_extra_bits;
 431         unsigned ones_if_aligned = 0U - (block_type == LZX_BLOCKTYPE_ALIGNED);
 432
 433         while (window_ptr != window_end) {
 434
 435                 mainsym = read_huffsym_using_maincode(istream, tables);
 436                 if (mainsym < LZX_NUM_CHARS) {
 437                         /* Literal  */
 438                         *window_ptr++ = mainsym;
 439                         continue;
 440                 }
 441
 442                 /* Match  */
 443
 444                 /* Decode the length header and offset slot.  */
 445                 mainsym -= LZX_NUM_CHARS;
 446                 match_len = mainsym & 0x7;
 447                 offset_slot = mainsym >> 3;
 448
 449                 /* If needed, read a length symbol to decode the full length. */
 450                 if (match_len == 0x7)
 451                         match_len += read_huffsym_using_lencode(istream, tables);
 452                 match_len += LZX_MIN_MATCH_LEN;
 453
 454                 if (offset_slot <= 2) {
 455                         /* Repeat offset  */
 456
 457                         /* Note: This isn't a real LRU queue, since using the R2
 458                          * offset doesn't bump the R1 offset down to R2.  This
 459                          * quirk allows all 3 recent offsets to be handled by
 460                          * the same code.  (For R0, the swap is a no-op.)  */
 461                         match_offset = queue->R[offset_slot];
 462                         queue->R[offset_slot] = queue->R[0];
 463                         queue->R[0] = match_offset;
 464                 } else {
 465                         /* Explicit offset  */
 466
 467                         /* Look up the number of extra bits that need to be read
 468                          * to decode offsets with this offset slot.  */
 469                         num_extra_bits = lzx_extra_offset_bits[offset_slot];
 470
 471                         /* Start with the offset slot base value.  */
 472                         match_offset = lzx_offset_slot_base[offset_slot];
 473
 474                         /* In aligned offset blocks, the low-order 3 bits of
 475                          * each offset are encoded using the aligned offset
 476                          * code.  Otherwise, all the extra bits are literal.  */
 477
 478                         /*if (block_type == LZX_BLOCKTYPE_ALIGNED && num_extra_bits >= 3) {*/
 479                         if ((num_extra_bits & ones_if_aligned) >= 3) {
 480                                 match_offset += bitstream_read_bits(istream, num_extra_bits - 3) << 3;
 481                                 match_offset += read_huffsym_using_alignedcode(istream, tables);
 482                         } else {
 483                                 match_offset += bitstream_read_bits(istream, num_extra_bits);
 484                         }
 485
 486                         /* Adjust the offset.  */
 487                         match_offset -= LZX_OFFSET_OFFSET;
 488
 489                         /* Update the match offset LRU queue.  */
 490                         queue->R[2] = queue->R[1];
 491                         queue->R[1] = queue->R[0];
 492                         queue->R[0] = match_offset;
 493                 }
 494
 495                 /* Validate the match, then copy it to the current position.  */
 496
 497                 if (unlikely(match_len > window_end - window_ptr))
 498                         return -1;
 499
 500                 if (unlikely(match_offset > window_ptr - window))
 501                         return -1;
 502
 503                 lz_copy(window_ptr, match_len, match_offset, window_end,
 504                         LZX_MIN_MATCH_LEN);
 505
 506                 window_ptr += match_len;
 507         }
 508         return 0;
 509 }
 510
 511 static int
 512 lzx_decompress(const void *compressed_data, size_t compressed_size,
 513                void *uncompressed_data, size_t uncompressed_size,
 514                void *_dec)
 515 {
 516         struct lzx_decompressor *dec = _dec;
 517         struct input_bitstream istream;
 518         struct lzx_lru_queue queue;
 519         u32 window_pos;
 520         int block_type;
 521         u32 block_size;
 522         bool may_have_e8_byte;
 523         int ret;
 524
 525         init_input_bitstream(&istream, compressed_data, compressed_size);
 526
 527         /* Initialize the recent offsets queue.  */
 528         lzx_lru_queue_init(&queue);
 529
 530         /* Codeword lengths begin as all 0's for delta encoding purposes.  */
 531         memset(dec->tables.maincode_lens, 0, dec->num_main_syms);
 532         memset(dec->tables.lencode_lens, 0, LZX_LENCODE_NUM_SYMBOLS);
 533
 534         /* Set this to true if there may be 0xe8 bytes in the uncompressed data.
 535          */
 536         may_have_e8_byte = false;
 537
 538         /* The compressed data will consist of one or more blocks.  The
 539          * following loop decompresses one block, and it runs until there all
 540          * the compressed data has been decompressed, so there are no more
 541          * blocks.  */
 542
 543         for (window_pos = 0;
 544              window_pos < uncompressed_size;
 545              window_pos += block_size)
 546         {
 547                 ret = lzx_read_block_header(&istream, dec->num_main_syms,
 548                                             dec->window_order, &block_type,
 549                                             &block_size, &dec->tables, &queue);
 550                 if (ret)
 551                         return ret;
 552
 553                 if (block_size > uncompressed_size - window_pos)
 554                         return -1;
 555
 556                 if (block_type != LZX_BLOCKTYPE_UNCOMPRESSED) {
 557
 558                         /* Compressed block.  */
 559
 560                         ret = lzx_decompress_block(block_type,
 561                                                    block_size,
 562                                                    uncompressed_data,
 563                                                    window_pos,
 564                                                    &dec->tables,
 565                                                    &queue,
 566                                                    &istream);
 567                         if (ret)
 568                                 return ret;
 569
 570                         /* If the first 0xe8 byte was in this block, it must
 571                          * have been encoded as a literal using mainsym 0xe8. */
 572                         if (dec->tables.maincode_lens[0xe8] != 0)
 573                                 may_have_e8_byte = true;
 574                 } else {
 575
 576                         /* Uncompressed block.  */
 577                         const u8 *p;
 578
 579                         p = bitstream_read_bytes(&istream, block_size);
 580                         if (!p)
 581                                 return -1;
 582
 583                         memcpy(&((u8*)uncompressed_data)[window_pos], p, block_size);
 584
 585                         /* Re-align the bitstream if an odd number of bytes was
 586                          * read.  */
 587                         if (block_size & 1)
 588                                 bitstream_read_byte(&istream);
 589
 590                         may_have_e8_byte = true;
 591                 }
 592         }
 593
 594         /* Postprocess the data unless it cannot possibly contain 0xe8 bytes  */
 595         if (may_have_e8_byte)
 596                 lzx_undo_e8_preprocessing(uncompressed_data, uncompressed_size);
 597
 598         return 0;
 599 }
 600
 601 static void
 602 lzx_free_decompressor(void *_dec)
 603 {
 604         struct lzx_decompressor *dec = _dec;
 605
 606         ALIGNED_FREE(dec);
 607 }
 608
 609 static int
 610 lzx_create_decompressor(size_t max_block_size, void **dec_ret)
 611 {
 612         struct lzx_decompressor *dec;
 613         unsigned window_order;
 614
 615         window_order = lzx_get_window_order(max_block_size);
 616         if (window_order == 0)
 617                 return WIMLIB_ERR_INVALID_PARAM;
 618
 619         /* The aligned allocation is needed to ensure that the lzx_tables are
 620          * aligned properly.  */
 621         dec = ALIGNED_MALLOC(sizeof(struct lzx_decompressor),
 622                              DECODE_TABLE_ALIGNMENT);
 623         if (!dec)
 624                 return WIMLIB_ERR_NOMEM;
 625
 626         dec->window_order = window_order;
 627         dec->num_main_syms = lzx_get_num_main_syms(window_order);
 628
 629         *dec_ret = dec;
 630         return 0;
 631 }
 632
 633 const struct decompressor_ops lzx_decompressor_ops = {
 634         .create_decompressor = lzx_create_decompressor,
 635         .decompress          = lzx_decompress,
 636         .free_decompressor   = lzx_free_decompressor,
 637 };