header cleanups
[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 u16
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 u16
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 u16
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 u16
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                                 len = *len_ptr - presym;
232                                 if ((s8)len < 0)
233                                         len += 17;
234                         }
235
236                         do {
237                                 *len_ptr++ = len;
238                         } while (--run_len);
239                         /* Worst case overrun is when presym == 18,
240                          * run_len == 20 + 31, and only 1 length was remaining.
241                          * So LZX_READ_LENS_MAX_OVERRUN == 50.
242                          *
243                          * Overrun while reading the first half of maincode_lens
244                          * can corrupt the previous values in the second half.
245                          * This doesn't really matter because the resulting
246                          * lengths will still be in range, and data that
247                          * generates overruns is invalid anyway.  */
248                 }
249         } while (len_ptr < lens_end);
250         return 0;
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                       unsigned window_order,
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 (window_order >= 16) {
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                 bitstream_ensure_bits(istream, 1);
383                 bitstream_align(istream);
384                 queue->R[0] = bitstream_read_u32(istream);
385                 queue->R[1] = bitstream_read_u32(istream);
386                 queue->R[2] = bitstream_read_u32(istream);
387
388                 /* Offsets of 0 are invalid.  */
389                 if (queue->R[0] == 0 || queue->R[1] == 0 || queue->R[2] == 0)
390                         return -1;
391                 break;
392
393         default:
394                 /* Unrecognized block type.  */
395                 return -1;
396         }
397
398         *block_type_ret = block_type;
399         *block_size_ret = block_size;
400         return 0;
401 }
402
403 /*
404  * Decompress an LZX-compressed block of data.
405  *
406  * @block_type:
407  *      The type of the block (LZX_BLOCKTYPE_VERBATIM or LZX_BLOCKTYPE_ALIGNED).
408  *
409  * @block_size:
410  *      The size of the block, in bytes.
411  *
412  * @window:
413  *      Pointer to the beginning of the decompression window.
414  *
415  * @window_pos:
416  *      The position in the window at which the block starts.
417  *
418  * @tables:
419  *      The Huffman decoding tables for the block.
420  *
421  * @queue:
422  *      The least-recently-used queue for match offsets.
423  *
424  * @istream:
425  *      The input bitstream, positioned at the start of the block data.
426  *
427  * Returns 0 on success, or -1 if the data was invalid.
428  */
429 static int
430 lzx_decompress_block(int block_type, u32 block_size,
431                      u8 *window, u32 window_pos,
432                      const struct lzx_tables *tables,
433                      struct lzx_lru_queue *queue,
434                      struct input_bitstream *istream)
435 {
436         u8 *window_ptr = &window[window_pos];
437         u8 *window_end = window_ptr + block_size;
438         unsigned mainsym;
439         u32 match_len;
440         unsigned offset_slot;
441         u32 match_offset;
442         unsigned num_extra_bits;
443         unsigned ones_if_aligned = 0U - (block_type == LZX_BLOCKTYPE_ALIGNED);
444
445         while (window_ptr != window_end) {
446
447                 mainsym = read_huffsym_using_maincode(istream, tables);
448                 if (mainsym < LZX_NUM_CHARS) {
449                         /* Literal  */
450                         *window_ptr++ = mainsym;
451                         continue;
452                 }
453
454                 /* Match  */
455
456                 /* Decode the length header and offset slot.  */
457                 mainsym -= LZX_NUM_CHARS;
458                 match_len = mainsym % LZX_NUM_LEN_HEADERS;
459                 offset_slot = mainsym / LZX_NUM_LEN_HEADERS;
460
461                 /* If needed, read a length symbol to decode the full length. */
462                 if (match_len == LZX_NUM_PRIMARY_LENS)
463                         match_len += read_huffsym_using_lencode(istream, tables);
464                 match_len += LZX_MIN_MATCH_LEN;
465
466                 if (offset_slot < LZX_NUM_RECENT_OFFSETS) {
467                         /* Repeat offset  */
468
469                         /* Note: This isn't a real LRU queue, since using the R2
470                          * offset doesn't bump the R1 offset down to R2.  This
471                          * quirk allows all 3 recent offsets to be handled by
472                          * the same code.  (For R0, the swap is a no-op.)  */
473                         match_offset = queue->R[offset_slot];
474                         queue->R[offset_slot] = queue->R[0];
475                         queue->R[0] = match_offset;
476                 } else {
477                         /* Explicit offset  */
478
479                         /* Look up the number of extra bits that need to be read
480                          * to decode offsets with this offset slot.  */
481                         num_extra_bits = lzx_extra_offset_bits[offset_slot];
482
483                         /* Start with the offset slot base value.  */
484                         match_offset = lzx_offset_slot_base[offset_slot];
485
486                         /* In aligned offset blocks, the low-order 3 bits of
487                          * each offset are encoded using the aligned offset
488                          * code.  Otherwise, all the extra bits are literal.  */
489
490                         if ((num_extra_bits & ones_if_aligned) >= LZX_NUM_ALIGNED_OFFSET_BITS) {
491                                 match_offset +=
492                                         bitstream_read_bits(istream,
493                                                             num_extra_bits -
494                                                                 LZX_NUM_ALIGNED_OFFSET_BITS)
495                                                         << LZX_NUM_ALIGNED_OFFSET_BITS;
496                                 match_offset += read_huffsym_using_alignedcode(istream, tables);
497                         } else {
498                                 match_offset += bitstream_read_bits(istream, num_extra_bits);
499                         }
500
501                         /* Adjust the offset.  */
502                         match_offset -= LZX_OFFSET_ADJUSTMENT;
503
504                         /* Update the match offset LRU queue.  */
505                         BUILD_BUG_ON(LZX_NUM_RECENT_OFFSETS != 3);
506                         queue->R[2] = queue->R[1];
507                         queue->R[1] = queue->R[0];
508                         queue->R[0] = match_offset;
509                 }
510
511                 /* Validate the match, then copy it to the current position.  */
512
513                 if (unlikely(match_len > window_end - window_ptr))
514                         return -1;
515
516                 if (unlikely(match_offset > window_ptr - window))
517                         return -1;
518
519                 lz_copy(window_ptr, match_len, match_offset, window_end,
520                         LZX_MIN_MATCH_LEN);
521
522                 window_ptr += match_len;
523         }
524         return 0;
525 }
526
527 static int
528 lzx_decompress(const void *compressed_data, size_t compressed_size,
529                void *uncompressed_data, size_t uncompressed_size,
530                void *_dec)
531 {
532         struct lzx_decompressor *dec = _dec;
533         struct input_bitstream istream;
534         struct lzx_lru_queue queue;
535         u32 window_pos;
536         int block_type;
537         u32 block_size;
538         bool may_have_e8_byte;
539         int ret;
540
541         init_input_bitstream(&istream, compressed_data, compressed_size);
542
543         /* Initialize the recent offsets queue.  */
544         lzx_lru_queue_init(&queue);
545
546         /* Codeword lengths begin as all 0's for delta encoding purposes.  */
547         memset(dec->tables.maincode_lens, 0, dec->num_main_syms);
548         memset(dec->tables.lencode_lens, 0, LZX_LENCODE_NUM_SYMBOLS);
549
550         /* Set this to true if there may be 0xe8 bytes in the uncompressed data.
551          */
552         may_have_e8_byte = false;
553
554         /* The compressed data will consist of one or more blocks.  The
555          * following loop decompresses one block, and it runs until there all
556          * the compressed data has been decompressed, so there are no more
557          * blocks.  */
558
559         for (window_pos = 0;
560              window_pos < uncompressed_size;
561              window_pos += block_size)
562         {
563                 ret = lzx_read_block_header(&istream, dec->num_main_syms,
564                                             dec->window_order, &block_type,
565                                             &block_size, &dec->tables, &queue);
566                 if (ret)
567                         return ret;
568
569                 if (block_size > uncompressed_size - window_pos)
570                         return -1;
571
572                 if (block_type != LZX_BLOCKTYPE_UNCOMPRESSED) {
573
574                         /* Compressed block.  */
575
576                         ret = lzx_decompress_block(block_type,
577                                                    block_size,
578                                                    uncompressed_data,
579                                                    window_pos,
580                                                    &dec->tables,
581                                                    &queue,
582                                                    &istream);
583                         if (ret)
584                                 return ret;
585
586                         /* If the first 0xe8 byte was in this block, it must
587                          * have been encoded as a literal using mainsym 0xe8. */
588                         if (dec->tables.maincode_lens[0xe8] != 0)
589                                 may_have_e8_byte = true;
590                 } else {
591
592                         /* Uncompressed block.  */
593                         const u8 *p;
594
595                         p = bitstream_read_bytes(&istream, block_size);
596                         if (!p)
597                                 return -1;
598
599                         memcpy(&((u8*)uncompressed_data)[window_pos], p, block_size);
600
601                         /* Re-align the bitstream if an odd number of bytes was
602                          * read.  */
603                         if (block_size & 1)
604                                 bitstream_read_byte(&istream);
605
606                         may_have_e8_byte = true;
607                 }
608         }
609
610         /* Postprocess the data unless it cannot possibly contain 0xe8 bytes  */
611         if (may_have_e8_byte)
612                 lzx_undo_e8_preprocessing(uncompressed_data, uncompressed_size);
613
614         return 0;
615 }
616
617 static void
618 lzx_free_decompressor(void *_dec)
619 {
620         struct lzx_decompressor *dec = _dec;
621
622         ALIGNED_FREE(dec);
623 }
624
625 static int
626 lzx_create_decompressor(size_t max_block_size, void **dec_ret)
627 {
628         struct lzx_decompressor *dec;
629         unsigned window_order;
630
631         window_order = lzx_get_window_order(max_block_size);
632         if (window_order == 0)
633                 return WIMLIB_ERR_INVALID_PARAM;
634
635         /* The aligned allocation is needed to ensure that the lzx_tables are
636          * aligned properly.  */
637         dec = ALIGNED_MALLOC(sizeof(struct lzx_decompressor),
638                              DECODE_TABLE_ALIGNMENT);
639         if (!dec)
640                 return WIMLIB_ERR_NOMEM;
641
642         dec->window_order = window_order;
643         dec->num_main_syms = lzx_get_num_main_syms(window_order);
644
645         *dec_ret = dec;
646         return 0;
647 }
648
649 const struct decompressor_ops lzx_decompressor_ops = {
650         .create_decompressor = lzx_create_decompressor,
651         .decompress          = lzx_decompress,
652         .free_decompressor   = lzx_free_decompressor,
653 };