1ebaf3519c8ec8dc169aa46c0737a34f6d06f71b
[wimlib] / src / lzx_decompress.c
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, 2015 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 <string.h>
58
59 #include "wimlib/decompressor_ops.h"
60 #include "wimlib/decompress_common.h"
61 #include "wimlib/error.h"
62 #include "wimlib/lzx_common.h"
63 #include "wimlib/util.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 /* Least-recently used queue for match offsets.  */
95 struct lzx_lru_queue {
96         u32 R[LZX_NUM_RECENT_OFFSETS];
97 };
98
99 static inline void
100 lzx_lru_queue_init(struct lzx_lru_queue *queue)
101 {
102         for (unsigned i = 0; i < LZX_NUM_RECENT_OFFSETS; i++)
103                 queue->R[i] = 1;
104 }
105
106 /* The main LZX decompressor structure.
107  *
108  * Note: we keep track of most of the decompression state outside this
109  * structure.  This structure only exists so that (1) we can store @window_order
110  * and @num_main_syms for multiple calls to lzx_decompress(); and (2) so that we
111  * don't have to allocate the large 'struct lzx_tables' on the stack.  */
112 struct lzx_decompressor {
113         unsigned window_order;
114         unsigned num_main_syms;
115         struct lzx_tables tables;
116 };
117
118 /* Read a Huffman-encoded symbol using the precode.  */
119 static inline unsigned
120 read_huffsym_using_precode(struct input_bitstream *istream,
121                            const u16 precode_decode_table[])
122 {
123         return read_huffsym(istream, precode_decode_table,
124                             LZX_PRECODE_TABLEBITS, LZX_MAX_PRE_CODEWORD_LEN);
125 }
126
127 /* Read a Huffman-encoded symbol using the main code.  */
128 static inline unsigned
129 read_huffsym_using_maincode(struct input_bitstream *istream,
130                             const struct lzx_tables *tables)
131 {
132         return read_huffsym(istream, tables->maincode_decode_table,
133                             LZX_MAINCODE_TABLEBITS, LZX_MAX_MAIN_CODEWORD_LEN);
134 }
135
136 /* Read a Huffman-encoded symbol using the length code.  */
137 static inline unsigned
138 read_huffsym_using_lencode(struct input_bitstream *istream,
139                            const struct lzx_tables *tables)
140 {
141         return read_huffsym(istream, tables->lencode_decode_table,
142                             LZX_LENCODE_TABLEBITS, LZX_MAX_LEN_CODEWORD_LEN);
143 }
144
145 /* Read a Huffman-encoded symbol using the aligned offset code.  */
146 static inline unsigned
147 read_huffsym_using_alignedcode(struct input_bitstream *istream,
148                                const struct lzx_tables *tables)
149 {
150         return read_huffsym(istream, tables->alignedcode_decode_table,
151                             LZX_ALIGNEDCODE_TABLEBITS, LZX_MAX_ALIGNED_CODEWORD_LEN);
152 }
153
154 /*
155  * Read the precode from the compressed input bitstream, then use it to decode
156  * @num_lens codeword length values.
157  *
158  * @istream:
159  *      The input bitstream.
160  *
161  * @lens:
162  *      An array that contains the length values from the previous time the
163  *      codeword lengths for this Huffman code were read, or all 0's if this is
164  *      the first time.  This array must have at least (@num_lens +
165  *      LZX_READ_LENS_MAX_OVERRUN) entries.
166  *
167  * @num_lens:
168  *      Number of length values to decode.
169  *
170  * Returns 0 on success, or -1 if the data was invalid.
171  */
172 static int
173 lzx_read_codeword_lens(struct input_bitstream *istream, u8 *lens, unsigned num_lens)
174 {
175         u16 precode_decode_table[(1 << LZX_PRECODE_TABLEBITS) +
176                                         (LZX_PRECODE_NUM_SYMBOLS * 2)]
177                                         _aligned_attribute(DECODE_TABLE_ALIGNMENT);
178         u8 precode_lens[LZX_PRECODE_NUM_SYMBOLS];
179         u8 *len_ptr = lens;
180         u8 *lens_end = lens + num_lens;
181         int ret;
182
183         /* Read the lengths of the precode codewords.  These are given
184          * explicitly.  */
185         for (int i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++) {
186                 precode_lens[i] = bitstream_read_bits(istream,
187                                                       LZX_PRECODE_ELEMENT_SIZE);
188         }
189
190         /* Make the decoding table for the precode.  */
191         ret = make_huffman_decode_table(precode_decode_table,
192                                         LZX_PRECODE_NUM_SYMBOLS,
193                                         LZX_PRECODE_TABLEBITS,
194                                         precode_lens,
195                                         LZX_MAX_PRE_CODEWORD_LEN);
196         if (ret)
197                 return ret;
198
199         /* Decode the codeword lengths.  */
200         do {
201                 unsigned presym;
202                 u8 len;
203
204                 /* Read the next precode symbol.  */
205                 presym = read_huffsym_using_precode(istream,
206                                                     precode_decode_table);
207                 if (presym < 17) {
208                         /* Difference from old length  */
209                         len = *len_ptr - presym;
210                         if ((s8)len < 0)
211                                 len += 17;
212                         *len_ptr++ = len;
213                 } else {
214                         /* Special RLE values  */
215
216                         unsigned run_len;
217
218                         if (presym == 17) {
219                                 /* Run of 0's  */
220                                 run_len = 4 + bitstream_read_bits(istream, 4);
221                                 len = 0;
222                         } else if (presym == 18) {
223                                 /* Longer run of 0's  */
224                                 run_len = 20 + bitstream_read_bits(istream, 5);
225                                 len = 0;
226                         } else {
227                                 /* 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                                 if (unlikely(presym > 17))
232                                         return -1;
233                                 len = *len_ptr - presym;
234                                 if ((s8)len < 0)
235                                         len += 17;
236                         }
237
238                         do {
239                                 *len_ptr++ = len;
240                         } while (--run_len);
241                         /* Worst case overrun is when presym == 18,
242                          * run_len == 20 + 31, and only 1 length was remaining.
243                          * So LZX_READ_LENS_MAX_OVERRUN == 50.
244                          *
245                          * Overrun while reading the first half of maincode_lens
246                          * can corrupt the previous values in the second half.
247                          * This doesn't really matter because the resulting
248                          * lengths will still be in range, and data that
249                          * generates overruns is invalid anyway.  */
250                 }
251         } while (len_ptr < lens_end);
252         return 0;
253 }
254
255 /*
256  * Read the header of an LZX block and save the block type and size in
257  * *block_type_ret and *block_size_ret, respectively.
258  *
259  * If the block is compressed, also update the Huffman decode @tables with the
260  * new Huffman codes.
261  *
262  * If the block is uncompressed, also update the match offset @queue with the
263  * new match offsets.
264  *
265  * Return 0 on success, or -1 if the data was invalid.
266  */
267 static int
268 lzx_read_block_header(struct input_bitstream *istream,
269                       unsigned num_main_syms,
270                       unsigned window_order,
271                       int *block_type_ret,
272                       u32 *block_size_ret,
273                       struct lzx_tables *tables,
274                       struct lzx_lru_queue *queue)
275 {
276         int block_type;
277         u32 block_size;
278         int ret;
279
280         bitstream_ensure_bits(istream, 4);
281
282         /* The first three bits tell us what kind of block it is, and should be
283          * one of the LZX_BLOCKTYPE_* values.  */
284         block_type = bitstream_pop_bits(istream, 3);
285
286         /* Read the block size.  This mirrors the behavior of
287          * lzx_write_compressed_block() in lzx_compress.c; see that for more
288          * details.  */
289         if (bitstream_pop_bits(istream, 1)) {
290                 block_size = LZX_DEFAULT_BLOCK_SIZE;
291         } else {
292                 u32 tmp;
293                 block_size = 0;
294
295                 tmp = bitstream_read_bits(istream, 8);
296                 block_size |= tmp;
297                 tmp = bitstream_read_bits(istream, 8);
298                 block_size <<= 8;
299                 block_size |= tmp;
300
301                 if (window_order >= 16) {
302                         tmp = bitstream_read_bits(istream, 8);
303                         block_size <<= 8;
304                         block_size |= tmp;
305                 }
306         }
307
308         switch (block_type) {
309
310         case LZX_BLOCKTYPE_ALIGNED:
311
312                 /* Read the aligned offset code and prepare its decode table.
313                  */
314
315                 for (int i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
316                         tables->alignedcode_lens[i] =
317                                 bitstream_read_bits(istream,
318                                                     LZX_ALIGNEDCODE_ELEMENT_SIZE);
319                 }
320
321                 ret = make_huffman_decode_table(tables->alignedcode_decode_table,
322                                                 LZX_ALIGNEDCODE_NUM_SYMBOLS,
323                                                 LZX_ALIGNEDCODE_TABLEBITS,
324                                                 tables->alignedcode_lens,
325                                                 LZX_MAX_ALIGNED_CODEWORD_LEN);
326                 if (ret)
327                         return ret;
328
329                 /* Fall though, since the rest of the header for aligned offset
330                  * blocks is the same as that for verbatim blocks.  */
331
332         case LZX_BLOCKTYPE_VERBATIM:
333
334                 /* Read the main code and prepare its decode table.
335                  *
336                  * Note that the codeword lengths in the main code are encoded
337                  * in two parts: one part for literal symbols, and one part for
338                  * match symbols.  */
339
340                 ret = lzx_read_codeword_lens(istream, tables->maincode_lens,
341                                              LZX_NUM_CHARS);
342                 if (ret)
343                         return ret;
344
345                 ret = lzx_read_codeword_lens(istream,
346                                              tables->maincode_lens + LZX_NUM_CHARS,
347                                              num_main_syms - LZX_NUM_CHARS);
348                 if (ret)
349                         return ret;
350
351                 ret = make_huffman_decode_table(tables->maincode_decode_table,
352                                                 num_main_syms,
353                                                 LZX_MAINCODE_TABLEBITS,
354                                                 tables->maincode_lens,
355                                                 LZX_MAX_MAIN_CODEWORD_LEN);
356                 if (ret)
357                         return ret;
358
359                 /* Read the length code and prepare its decode table.  */
360
361                 ret = lzx_read_codeword_lens(istream, tables->lencode_lens,
362                                              LZX_LENCODE_NUM_SYMBOLS);
363                 if (ret)
364                         return ret;
365
366                 ret = make_huffman_decode_table(tables->lencode_decode_table,
367                                                 LZX_LENCODE_NUM_SYMBOLS,
368                                                 LZX_LENCODE_TABLEBITS,
369                                                 tables->lencode_lens,
370                                                 LZX_MAX_LEN_CODEWORD_LEN);
371                 if (ret)
372                         return ret;
373
374                 break;
375
376         case LZX_BLOCKTYPE_UNCOMPRESSED:
377
378                 /* Before reading the three LRU match offsets from the
379                  * uncompressed block header, the stream must be aligned on a
380                  * 16-bit boundary.  But, unexpectedly, if the stream is
381                  * *already* aligned, the correct thing to do is to throw away
382                  * the next 16 bits.  */
383
384                 bitstream_ensure_bits(istream, 1);
385                 bitstream_align(istream);
386                 queue->R[0] = bitstream_read_u32(istream);
387                 queue->R[1] = bitstream_read_u32(istream);
388                 queue->R[2] = bitstream_read_u32(istream);
389
390                 /* Offsets of 0 are invalid.  */
391                 if (queue->R[0] == 0 || queue->R[1] == 0 || queue->R[2] == 0)
392                         return -1;
393                 break;
394
395         default:
396                 /* Unrecognized block type.  */
397                 return -1;
398         }
399
400         *block_type_ret = block_type;
401         *block_size_ret = block_size;
402         return 0;
403 }
404
405 /*
406  * Decompress a block of LZX-compressed data.
407  *
408  * @block_type:
409  *      The type of the block (LZX_BLOCKTYPE_VERBATIM or LZX_BLOCKTYPE_ALIGNED).
410  * @out_begin
411  *      The beginning of the (uncompressed) output buffer.
412  * @out_next
413  *      Pointer to the location in the (uncompressed) output buffer at which
414  *      this block will start.
415  * @out_block_end
416  *      Pointer to the location in the (uncompressed) output buffer at which
417  *      this block will end.
418  * @tables:
419  *      The Huffman decoding tables for this block.
420  * @queue:
421  *      The least-recently-used queue for match offsets.
422  * @istream:
423  *      The input bitstream, positioned at the start of the block data.
424  *
425  * Returns 0 on success, or -1 if the data was invalid.
426  */
427 static int
428 lzx_decompress_block(int block_type, u8 * const out_begin,
429                      u8 * out_next, u8 * const out_block_end,
430                      const struct lzx_tables *tables,
431                      struct lzx_lru_queue *queue,
432                      struct input_bitstream *istream)
433 {
434         unsigned mainsym;
435         u32 match_len;
436         unsigned offset_slot;
437         u32 match_offset;
438         unsigned num_extra_bits;
439         unsigned ones_if_aligned = 0U - (block_type == LZX_BLOCKTYPE_ALIGNED);
440
441         while (out_next != out_block_end) {
442
443                 mainsym = read_huffsym_using_maincode(istream, tables);
444                 if (mainsym < LZX_NUM_CHARS) {
445                         /* Literal  */
446                         *out_next++ = mainsym;
447                         continue;
448                 }
449
450                 /* Match  */
451
452                 /* Decode the length header and offset slot.  */
453                 mainsym -= LZX_NUM_CHARS;
454                 match_len = mainsym % LZX_NUM_LEN_HEADERS;
455                 offset_slot = mainsym / LZX_NUM_LEN_HEADERS;
456
457                 /* If needed, read a length symbol to decode the full length. */
458                 if (match_len == LZX_NUM_PRIMARY_LENS)
459                         match_len += read_huffsym_using_lencode(istream, tables);
460                 match_len += LZX_MIN_MATCH_LEN;
461
462                 if (offset_slot < LZX_NUM_RECENT_OFFSETS) {
463                         /* Repeat offset  */
464
465                         /* Note: This isn't a real LRU queue, since using the R2
466                          * offset doesn't bump the R1 offset down to R2.  This
467                          * quirk allows all 3 recent offsets to be handled by
468                          * the same code.  (For R0, the swap is a no-op.)  */
469                         match_offset = queue->R[offset_slot];
470                         queue->R[offset_slot] = queue->R[0];
471                         queue->R[0] = match_offset;
472                 } else {
473                         /* Explicit offset  */
474
475                         /* Look up the number of extra bits that need to be read
476                          * to decode offsets with this offset slot.  */
477                         num_extra_bits = lzx_extra_offset_bits[offset_slot];
478
479                         /* Start with the offset slot base value.  */
480                         match_offset = lzx_offset_slot_base[offset_slot];
481
482                         /* In aligned offset blocks, the low-order 3 bits of
483                          * each offset are encoded using the aligned offset
484                          * code.  Otherwise, all the extra bits are literal.  */
485
486                         if ((num_extra_bits & ones_if_aligned) >= LZX_NUM_ALIGNED_OFFSET_BITS) {
487                                 match_offset +=
488                                         bitstream_read_bits(istream,
489                                                             num_extra_bits -
490                                                                 LZX_NUM_ALIGNED_OFFSET_BITS)
491                                                         << LZX_NUM_ALIGNED_OFFSET_BITS;
492                                 match_offset += read_huffsym_using_alignedcode(istream, tables);
493                         } else {
494                                 match_offset += bitstream_read_bits(istream, num_extra_bits);
495                         }
496
497                         /* Adjust the offset.  */
498                         match_offset -= LZX_OFFSET_ADJUSTMENT;
499
500                         /* Update the match offset LRU queue.  */
501                         BUILD_BUG_ON(LZX_NUM_RECENT_OFFSETS != 3);
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 > out_block_end - out_next))
510                         return -1;
511
512                 if (unlikely(match_offset > out_next - out_begin))
513                         return -1;
514
515                 lz_copy(out_next, match_len, match_offset, out_block_end,
516                         LZX_MIN_MATCH_LEN);
517
518                 out_next += match_len;
519         }
520         return 0;
521 }
522
523 static int
524 lzx_decompress(const void *compressed_data, size_t compressed_size,
525                void *uncompressed_data, size_t uncompressed_size,
526                void *_dec)
527 {
528         struct lzx_decompressor *dec = _dec;
529         struct input_bitstream istream;
530         struct lzx_lru_queue queue;
531         u8 * const out_begin = uncompressed_data;
532         u8 *out_next = out_begin;
533         u8 * const out_end = out_begin + uncompressed_size;
534         int block_type;
535         u32 block_size;
536         bool may_have_e8_byte;
537         int ret;
538
539         init_input_bitstream(&istream, compressed_data, compressed_size);
540
541         /* Initialize the recent offsets queue.  */
542         lzx_lru_queue_init(&queue);
543
544         /* Codeword lengths begin as all 0's for delta encoding purposes.  */
545         memset(dec->tables.maincode_lens, 0, dec->num_main_syms);
546         memset(dec->tables.lencode_lens, 0, LZX_LENCODE_NUM_SYMBOLS);
547
548         /* Set this to true if there may be 0xe8 bytes in the uncompressed data.
549          */
550         may_have_e8_byte = false;
551
552         /* The compressed data will consist of one or more blocks.  The
553          * following loop decompresses one block, and it runs until there all
554          * the compressed data has been decompressed, so there are no more
555          * blocks.  */
556
557         while (out_next != out_end) {
558
559                 ret = lzx_read_block_header(&istream, dec->num_main_syms,
560                                             dec->window_order, &block_type,
561                                             &block_size, &dec->tables, &queue);
562                 if (ret)
563                         return ret;
564
565                 if (block_size > out_end - out_next)
566                         return -1;
567
568                 if (block_type != LZX_BLOCKTYPE_UNCOMPRESSED) {
569
570                         /* Compressed block.  */
571
572                         ret = lzx_decompress_block(block_type,
573                                                    out_begin,
574                                                    out_next,
575                                                    out_next + block_size,
576                                                    &dec->tables,
577                                                    &queue,
578                                                    &istream);
579                         if (ret)
580                                 return ret;
581
582                         /* If the first 0xe8 byte was in this block, it must
583                          * have been encoded as a literal using mainsym 0xe8. */
584                         if (dec->tables.maincode_lens[0xe8] != 0)
585                                 may_have_e8_byte = true;
586                 } else {
587
588                         /* Uncompressed block.  */
589                         const u8 *p;
590
591                         p = bitstream_read_bytes(&istream, block_size);
592                         if (!p)
593                                 return -1;
594
595                         memcpy(out_next, p, block_size);
596
597                         /* Re-align the bitstream if an odd number of bytes was
598                          * read.  */
599                         if (block_size & 1)
600                                 bitstream_read_byte(&istream);
601
602                         may_have_e8_byte = true;
603                 }
604
605                 out_next += block_size;
606         }
607
608         /* Postprocess the data unless it cannot possibly contain 0xe8 bytes  */
609         if (may_have_e8_byte)
610                 lzx_undo_e8_preprocessing(uncompressed_data, uncompressed_size);
611
612         return 0;
613 }
614
615 static void
616 lzx_free_decompressor(void *_dec)
617 {
618         struct lzx_decompressor *dec = _dec;
619
620         ALIGNED_FREE(dec);
621 }
622
623 static int
624 lzx_create_decompressor(size_t max_block_size, void **dec_ret)
625 {
626         struct lzx_decompressor *dec;
627         unsigned window_order;
628
629         window_order = lzx_get_window_order(max_block_size);
630         if (window_order == 0)
631                 return WIMLIB_ERR_INVALID_PARAM;
632
633         /* The aligned allocation is needed to ensure that the lzx_tables are
634          * aligned properly.  */
635         dec = ALIGNED_MALLOC(sizeof(struct lzx_decompressor),
636                              DECODE_TABLE_ALIGNMENT);
637         if (!dec)
638                 return WIMLIB_ERR_NOMEM;
639
640         dec->window_order = window_order;
641         dec->num_main_syms = lzx_get_num_main_syms(window_order);
642
643         *dec_ret = dec;
644         return 0;
645 }
646
647 const struct decompressor_ops lzx_decompressor_ops = {
648         .create_decompressor = lzx_create_decompressor,
649         .decompress          = lzx_decompress,
650         .free_decompressor   = lzx_free_decompressor,
651 };