4 * LZX compression routines, originally based on code written by Matthew T.
5 * Russotto (liblzxcomp), but heavily modified.
9 * Copyright (C) 2002 Matthew T. Russotto
10 * Copyright (C) 2012 Eric Biggers
12 * This file is part of wimlib, a library for working with WIM files.
14 * wimlib is free software; you can redistribute it and/or modify it under the
15 * terms of the GNU General Public License as published by the Free
16 * Software Foundation; either version 3 of the License, or (at your option)
19 * wimlib is distributed in the hope that it will be useful, but WITHOUT ANY
20 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
21 * A PARTICULAR PURPOSE. See the GNU General Public License for more
24 * You should have received a copy of the GNU General Public License
25 * along with wimlib; if not, see http://www.gnu.org/licenses/.
30 * This file provides lzx_compress(), a function to compress an in-memory buffer
31 * of data using LZX compression, as used in the WIM file format.
33 * Please see the comments in lzx-decompress.c for more information about this
36 * One thing to keep in mind is that there is no sliding window, since the
37 * window is always the entirety of a WIM chunk, which is at most WIM_CHUNK_SIZE
40 * The basic compression algorithm used here should be familiar if you are
41 * familiar with Huffman trees and with other LZ77 and Huffman-based formats
42 * such as DEFLATE. Otherwise it can be quite tricky to understand. Basically
43 * it is the following:
45 * - Preprocess the input data (LZX-specific)
46 * - Go through the input data and determine matches. This part is based on
47 * code from zlib, and a hash table of 3-character strings is used to
48 * accelerate the process of finding matches.
49 * - Build the Huffman trees based on the frequencies of symbols determined
50 * while recording matches.
51 * - Output the block header, including the Huffman trees; then output the
52 * compressed stream of matches and literal characters.
54 * It is possible for a WIM chunk to include multiple LZX blocks, since for some
55 * input data this will produce a better compression ratio (especially since
56 * each block can include new Huffman codes). However, producing multiple LZX
57 * blocks from one input chunk is not yet implemented.
66 /* Structure to contain the Huffman codes for the main, length, and aligned
69 u16 main_codewords[LZX_MAINTREE_NUM_SYMBOLS];
70 u8 main_lens[LZX_MAINTREE_NUM_SYMBOLS];
72 u16 len_codewords[LZX_LENTREE_NUM_SYMBOLS];
73 u8 len_lens[LZX_LENTREE_NUM_SYMBOLS];
75 u16 aligned_codewords[LZX_ALIGNEDTREE_NUM_SYMBOLS];
76 u8 aligned_lens[LZX_ALIGNEDTREE_NUM_SYMBOLS];
79 struct lzx_freq_tables {
80 freq_t main_freq_table[LZX_MAINTREE_NUM_SYMBOLS];
81 freq_t len_freq_table[LZX_LENTREE_NUM_SYMBOLS];
82 freq_t aligned_freq_table[LZX_ALIGNEDTREE_NUM_SYMBOLS];
85 /* Returns the LZX position slot that corresponds to a given formatted offset.
87 * Logically, this returns the smallest i such that
88 * formatted_offset >= lzx_position_base[i].
90 * The actual implementation below takes advantage of the regularity of the
91 * numbers in the lzx_position_base array to calculate the slot directly from
92 * the formatted offset without actually looking at the array.
94 static inline unsigned lzx_get_position_slot(unsigned formatted_offset)
98 * Slots 36-49 (formatted_offset >= 262144) can be found by
99 * (formatted_offset/131072) + 34 == (formatted_offset >> 17) + 34;
100 * however, this check for formatted_offset >= 262144 is commented out
101 * because WIM chunks cannot be that large.
103 if (formatted_offset >= 262144) {
104 return (formatted_offset >> 17) + 34;
108 /* Note: this part here only works if:
110 * 2 <= formatted_offset < 655360
112 * It is < 655360 because the frequency of the position bases
113 * increases starting at the 655360 entry, and it is >= 2
114 * because the below calculation fails if the most significant
115 * bit is lower than the 2's place. */
116 wimlib_assert(formatted_offset >= 2 && formatted_offset < 655360);
117 unsigned mssb_idx = bsr32(formatted_offset);
118 return (mssb_idx << 1) |
119 ((formatted_offset >> (mssb_idx - 1)) & 1);
123 static u32 lzx_record_literal(u8 literal, void *__main_freq_tab)
125 freq_t *main_freq_tab = __main_freq_tab;
126 main_freq_tab[literal]++;
130 /* Constructs a match from an offset and a length, and updates the LRU queue and
131 * the frequency of symbols in the main, length, and aligned offset alphabets.
132 * The return value is a 32-bit number that provides the match in an
133 * intermediate representation documented below. */
134 static u32 lzx_record_match(unsigned match_offset, unsigned match_len,
135 void *__freq_tabs, void *__queue)
137 struct lzx_freq_tables *freq_tabs = __freq_tabs;
138 struct lru_queue *queue = __queue;
139 unsigned formatted_offset;
140 unsigned position_slot;
141 unsigned position_footer = 0;
146 unsigned adjusted_match_len;
148 wimlib_assert(match_len >= LZX_MIN_MATCH && match_len <= LZX_MAX_MATCH);
149 wimlib_assert(match_offset != 0);
151 /* If possible, encode this offset as a repeated offset. */
152 if (match_offset == queue->R0) {
153 formatted_offset = 0;
155 } else if (match_offset == queue->R1) {
156 swap(queue->R0, queue->R1);
157 formatted_offset = 1;
159 } else if (match_offset == queue->R2) {
160 swap(queue->R0, queue->R2);
161 formatted_offset = 2;
164 /* Not a repeated offset. */
166 /* offsets of 0, 1, and 2 are reserved for the repeated offset
167 * codes, so non-repeated offsets must be encoded as 3+. The
168 * minimum offset is 1, so encode the offsets offset by 2. */
169 formatted_offset = match_offset + LZX_MIN_MATCH;
171 queue->R2 = queue->R1;
172 queue->R1 = queue->R0;
173 queue->R0 = match_offset;
175 /* The (now-formatted) offset will actually be encoded as a
176 * small position slot number that maps to a certain hard-coded
177 * offset (position base), followed by a number of extra bits---
178 * the position footer--- that are added to the position base to
179 * get the original formatted offset. */
181 position_slot = lzx_get_position_slot(formatted_offset);
182 position_footer = formatted_offset &
183 ((1 << lzx_get_num_extra_bits(position_slot)) - 1);
186 adjusted_match_len = match_len - LZX_MIN_MATCH;
188 /* Pack the position slot, position footer, and match length into an
189 * intermediate representation.
192 * ---- -----------------------------------------------------------
194 * 31 1 if a match, 0 if a literal.
196 * 30-25 position slot. This can be at most 50, so it will fit in 6
199 * 8-24 position footer. This is the offset of the real formatted
200 * offset from the position base. This can be at most 17 bits
201 * (since lzx_extra_bits[LZX_NUM_POSITION_SLOTS - 1] is 17).
203 * 0-7 length of match, offset by 2. This can be at most
204 * (LZX_MAX_MATCH - 2) == 255, so it will fit in 8 bits. */
206 (position_slot << 25) |
207 (position_footer << 8) |
208 (adjusted_match_len);
210 /* The match length must be at least 2, so let the adjusted match length
211 * be the match length minus 2.
213 * If it is less than 7, the adjusted match length is encoded as a 3-bit
214 * number offset by 2. Otherwise, the 3-bit length header is all 1's
215 * and the actual adjusted length is given as a symbol encoded with the
216 * length tree, offset by 7.
218 if (adjusted_match_len < LZX_NUM_PRIMARY_LENS) {
219 len_header = adjusted_match_len;
221 len_header = LZX_NUM_PRIMARY_LENS;
222 len_footer = adjusted_match_len - LZX_NUM_PRIMARY_LENS;
223 freq_tabs->len_freq_table[len_footer]++;
225 len_pos_header = (position_slot << 3) | len_header;
227 wimlib_assert(len_pos_header < LZX_MAINTREE_NUM_SYMBOLS - LZX_NUM_CHARS);
229 freq_tabs->main_freq_table[len_pos_header + LZX_NUM_CHARS]++;
232 * if (lzx_extra_bits[position_slot] >= 3) */
233 if (position_slot >= 8)
234 freq_tabs->aligned_freq_table[position_footer & 7]++;
240 * Writes a compressed literal match to the output.
242 * @out: The output bitstream.
243 * @block_type: The type of the block (LZX_BLOCKTYPE_ALIGNED or LZX_BLOCKTYPE_VERBATIM)
244 * @match: The match, encoded as a 32-bit number.
245 * @codes: Pointer to a structure that contains the codewords for the
246 * main, length, and aligned offset Huffman codes.
248 static int lzx_write_match(struct output_bitstream *out, int block_type,
249 u32 match, const struct lzx_codes *codes)
251 /* low 8 bits are the match length minus 2 */
252 unsigned match_len_minus_2 = match & 0xff;
253 /* Next 17 bits are the position footer */
254 unsigned position_footer = (match >> 8) & 0x1ffff; /* 17 bits */
255 /* Next 6 bits are the position slot. */
256 unsigned position_slot = (match >> 25) & 0x3f; /* 6 bits */
259 unsigned len_pos_header;
260 unsigned main_symbol;
261 unsigned num_extra_bits;
262 unsigned verbatim_bits;
263 unsigned aligned_bits;
266 /* If the match length is less than MIN_MATCH (= 2) +
267 * NUM_PRIMARY_LENS (= 7), the length header contains
268 * the match length minus MIN_MATCH, and there is no
271 * Otherwise, the length header contains
272 * NUM_PRIMARY_LENS, and the length footer contains
273 * the match length minus NUM_PRIMARY_LENS minus
275 if (match_len_minus_2 < LZX_NUM_PRIMARY_LENS) {
276 len_header = match_len_minus_2;
277 /* No length footer-- mark it with a special
279 len_footer = (unsigned)(-1);
281 len_header = LZX_NUM_PRIMARY_LENS;
282 len_footer = match_len_minus_2 - LZX_NUM_PRIMARY_LENS;
285 /* Combine the position slot with the length header into
286 * a single symbol that will be encoded with the main
288 len_pos_header = (position_slot << 3) | len_header;
290 /* The actual main symbol is offset by LZX_NUM_CHARS because
291 * values under LZX_NUM_CHARS are used to indicate a literal
292 * byte rather than a match. */
293 main_symbol = len_pos_header + LZX_NUM_CHARS;
295 /* Output main symbol. */
296 ret = bitstream_put_bits(out, codes->main_codewords[main_symbol],
297 codes->main_lens[main_symbol]);
301 /* If there is a length footer, output it using the
302 * length Huffman code. */
303 if (len_footer != (unsigned)(-1)) {
304 ret = bitstream_put_bits(out, codes->len_codewords[len_footer],
305 codes->len_lens[len_footer]);
310 wimlib_assert(position_slot < LZX_NUM_POSITION_SLOTS);
312 num_extra_bits = lzx_get_num_extra_bits(position_slot);
314 /* For aligned offset blocks with at least 3 extra bits, output the
315 * verbatim bits literally, then the aligned bits encoded using the
316 * aligned offset tree. Otherwise, only the verbatim bits need to be
318 if ((block_type == LZX_BLOCKTYPE_ALIGNED) && (num_extra_bits >= 3)) {
320 verbatim_bits = position_footer >> 3;
321 ret = bitstream_put_bits(out, verbatim_bits,
326 aligned_bits = (position_footer & 7);
327 ret = bitstream_put_bits(out,
328 codes->aligned_codewords[aligned_bits],
329 codes->aligned_lens[aligned_bits]);
333 /* verbatim bits is the same as the position
334 * footer, in this case. */
335 ret = bitstream_put_bits(out, position_footer, num_extra_bits);
343 * Writes all compressed literals in a block, both matches and literal bytes, to
344 * the output bitstream.
346 * @out: The output bitstream.
347 * @block_type: The type of the block (LZX_BLOCKTYPE_ALIGNED or LZX_BLOCKTYPE_VERBATIM)
348 * @match_tab[]: The array of matches that will be output. It has length
349 * of @num_compressed_literals.
350 * @num_compressed_literals: Number of compressed literals to be output.
351 * @codes: Pointer to a structure that contains the codewords for the
352 * main, length, and aligned offset Huffman codes.
354 static int lzx_write_compressed_literals(struct output_bitstream *ostream,
356 const u32 match_tab[],
357 unsigned num_compressed_literals,
358 const struct lzx_codes *codes)
364 for (i = 0; i < num_compressed_literals; i++) {
365 match = match_tab[i];
367 /* High bit of the match indicates whether the match is an
368 * actual match (1) or a literal uncompressed byte (0) */
369 if (match & 0x80000000) {
371 ret = lzx_write_match(ostream, block_type, match,
377 wimlib_assert(match < LZX_NUM_CHARS);
378 ret = bitstream_put_bits(ostream,
379 codes->main_codewords[match],
380 codes->main_lens[match]);
389 * Writes a compressed Huffman tree to the output, preceded by the pretree for
392 * The Huffman tree is represented in the output as a series of path lengths
393 * from which the canonical Huffman code can be reconstructed. The path lengths
394 * themselves are compressed using a separate Huffman code, the pretree, which
395 * consists of LZX_PRETREE_NUM_SYMBOLS (= 20) symbols that cover all possible code
396 * lengths, plus extra codes for repeated lengths. The path lengths of the
397 * pretree precede the path lengths of the larger code and are uncompressed,
398 * consisting of 20 entries of 4 bits each.
400 * @out: The bitstream for the compressed output.
401 * @lens: The code lengths for the Huffman tree, indexed by symbol.
402 * @num_symbols: The number of symbols in the code.
404 static int lzx_write_compressed_tree(struct output_bitstream *out,
405 const u8 lens[], unsigned num_symbols)
407 /* Frequencies of the length symbols, including the RLE symbols (NOT the
408 * actual lengths themselves). */
409 freq_t pretree_freqs[LZX_PRETREE_NUM_SYMBOLS];
410 u8 pretree_lens[LZX_PRETREE_NUM_SYMBOLS];
411 u16 pretree_codewords[LZX_PRETREE_NUM_SYMBOLS];
412 u8 output_syms[num_symbols * 2];
413 unsigned output_syms_idx;
414 unsigned cur_run_len;
417 unsigned additional_bits;
421 ZERO_ARRAY(pretree_freqs);
423 /* Since the code word lengths use a form of RLE encoding, the goal here
424 * is to find each run of identical lengths when going through them in
425 * symbol order (including runs of length 1). For each run, as many
426 * lengths are encoded using RLE as possible, and the rest are output
429 * output_syms[] will be filled in with the length symbols that will be
430 * output, including RLE codes, not yet encoded using the pre-tree.
432 * cur_run_len keeps track of how many code word lengths are in the
433 * current run of identical lengths.
437 for (i = 1; i <= num_symbols; i++) {
439 if (i != num_symbols && lens[i] == lens[i - 1]) {
440 /* Still in a run--- keep going. */
445 /* Run ended! Check if it is a run of zeroes or a run of
448 /* The symbol that was repeated in the run--- not to be confused
449 * with the length *of* the run (cur_run_len) */
450 len_in_run = lens[i - 1];
452 if (len_in_run == 0) {
453 /* A run of 0's. Encode it in as few length
454 * codes as we can. */
456 /* The magic length 18 indicates a run of 20 + n zeroes,
457 * where n is an uncompressed literal 5-bit integer that
458 * follows the magic length. */
459 while (cur_run_len >= 20) {
461 additional_bits = min(cur_run_len - 20, 0x1f);
463 output_syms[output_syms_idx++] = 18;
464 output_syms[output_syms_idx++] = additional_bits;
465 cur_run_len -= 20 + additional_bits;
468 /* The magic length 17 indicates a run of 4 + n zeroes,
469 * where n is an uncompressed literal 4-bit integer that
470 * follows the magic length. */
471 while (cur_run_len >= 4) {
472 additional_bits = min(cur_run_len - 4, 0xf);
474 output_syms[output_syms_idx++] = 17;
475 output_syms[output_syms_idx++] = additional_bits;
476 cur_run_len -= 4 + additional_bits;
481 /* A run of nonzero lengths. */
483 /* The magic length 19 indicates a run of 4 + n
484 * nonzeroes, where n is a literal bit that follows the
485 * magic length, and where the value of the lengths in
486 * the run is given by an extra length symbol, encoded
487 * with the pretree, that follows the literal bit.
489 * The extra length symbol is encoded as a difference
490 * from the length of the codeword for the first symbol
491 * in the run in the previous tree.
493 while (cur_run_len >= 4) {
494 additional_bits = (cur_run_len > 4);
495 delta = -(char)len_in_run;
499 pretree_freqs[(unsigned char)delta]++;
500 output_syms[output_syms_idx++] = 19;
501 output_syms[output_syms_idx++] = additional_bits;
502 output_syms[output_syms_idx++] = delta;
503 cur_run_len -= 4 + additional_bits;
507 /* Any remaining lengths in the run are outputted without RLE,
508 * as a difference from the length of that codeword in the
510 while (cur_run_len--) {
511 delta = -(char)len_in_run;
515 pretree_freqs[(unsigned char)delta]++;
516 output_syms[output_syms_idx++] = delta;
522 wimlib_assert(output_syms_idx < ARRAY_LEN(output_syms));
524 /* Build the pretree from the frequencies of the length symbols. */
526 make_canonical_huffman_code(LZX_PRETREE_NUM_SYMBOLS,
527 LZX_MAX_CODEWORD_LEN,
528 pretree_freqs, pretree_lens,
531 /* Write the lengths of the pretree codes to the output. */
532 for (i = 0; i < LZX_PRETREE_NUM_SYMBOLS; i++)
533 bitstream_put_bits(out, pretree_lens[i],
534 LZX_PRETREE_ELEMENT_SIZE);
536 /* Write the length symbols, encoded with the pretree, to the output. */
539 while (i < output_syms_idx) {
540 pretree_sym = output_syms[i++];
542 bitstream_put_bits(out, pretree_codewords[pretree_sym],
543 pretree_lens[pretree_sym]);
544 switch (pretree_sym) {
546 bitstream_put_bits(out, output_syms[i++], 4);
549 bitstream_put_bits(out, output_syms[i++], 5);
552 bitstream_put_bits(out, output_syms[i++], 1);
553 bitstream_put_bits(out,
554 pretree_codewords[output_syms[i]],
555 pretree_lens[output_syms[i]]);
565 /* Builds the canonical Huffman code for the main tree, the length tree, and the
566 * aligned offset tree. */
567 static void lzx_make_huffman_codes(const struct lzx_freq_tables *freq_tabs,
568 struct lzx_codes *codes)
570 make_canonical_huffman_code(LZX_MAINTREE_NUM_SYMBOLS,
571 LZX_MAX_CODEWORD_LEN,
572 freq_tabs->main_freq_table,
574 codes->main_codewords);
576 make_canonical_huffman_code(LZX_LENTREE_NUM_SYMBOLS,
577 LZX_MAX_CODEWORD_LEN,
578 freq_tabs->len_freq_table,
580 codes->len_codewords);
582 make_canonical_huffman_code(LZX_ALIGNEDTREE_NUM_SYMBOLS, 8,
583 freq_tabs->aligned_freq_table,
585 codes->aligned_codewords);
588 static void do_call_insn_translation(u32 *call_insn_target, int input_pos,
594 rel_offset = le32_to_cpu(*call_insn_target);
595 if (rel_offset >= -input_pos && rel_offset < file_size) {
596 if (rel_offset < file_size - input_pos) {
597 /* "good translation" */
598 abs_offset = rel_offset + input_pos;
600 /* "compensating translation" */
601 abs_offset = rel_offset - file_size;
603 *call_insn_target = cpu_to_le32(abs_offset);
607 /* This is the reverse of undo_call_insn_preprocessing() in lzx-decompress.c.
608 * See the comment above that function for more information. */
609 static void do_call_insn_preprocessing(u8 uncompressed_data[],
610 int uncompressed_data_len)
612 for (int i = 0; i < uncompressed_data_len - 10; i++) {
613 if (uncompressed_data[i] == 0xe8) {
614 do_call_insn_translation((u32*)&uncompressed_data[i + 1],
616 LZX_WIM_MAGIC_FILESIZE);
623 static const struct lz_params lzx_lz_params = {
625 /* LZX_MIN_MATCH == 2, but 2-character matches are rarely useful; the
626 * minimum match for compression is set to 3 instead. */
629 .max_match = LZX_MAX_MATCH,
630 .good_match = LZX_MAX_MATCH,
631 .nice_match = LZX_MAX_MATCH,
632 .max_chain_len = LZX_MAX_MATCH,
633 .max_lazy_match = LZX_MAX_MATCH,
638 * Performs LZX compression on a block of data.
640 * @__uncompressed_data: Pointer to the data to be compressed.
641 * @uncompressed_len: Length, in bytes, of the data to be compressed.
642 * @compressed_data: Pointer to a location at least (@uncompressed_len - 1)
643 * bytes long into which the compressed data may be
645 * @compressed_len_ret: A pointer to an unsigned int into which the length of
646 * the compressed data may be returned.
648 * Returns zero if compression was successfully performed. In that case
649 * @compressed_data and @compressed_len_ret will contain the compressed data and
650 * its length. A return value of nonzero means that compressing the data did
651 * not reduce its size, and @compressed_data will not contain the full
654 int lzx_compress(const void *__uncompressed_data, unsigned uncompressed_len,
655 void *compressed_data, unsigned *compressed_len_ret)
657 struct output_bitstream ostream;
658 u8 uncompressed_data[uncompressed_len + 8];
659 struct lzx_freq_tables freq_tabs;
660 struct lzx_codes codes;
661 u32 match_tab[uncompressed_len];
662 struct lru_queue queue;
663 unsigned num_matches;
664 unsigned compressed_len;
667 int block_type = LZX_BLOCKTYPE_ALIGNED;
669 if (uncompressed_len < 100)
672 memset(&freq_tabs, 0, sizeof(freq_tabs));
677 /* The input data must be preprocessed. To avoid changing the original
678 * input, copy it to a temporary buffer. */
679 memcpy(uncompressed_data, __uncompressed_data, uncompressed_len);
681 /* Before doing any actual compression, do the call instruction (0xe8
682 * byte) translation on the uncompressed data. */
683 do_call_insn_preprocessing(uncompressed_data, uncompressed_len);
685 /* Determine the sequence of matches and literals that will be output,
686 * and in the process, keep counts of the number of times each symbol
687 * will be output, so that the Huffman trees can be made. */
689 num_matches = lz_analyze_block(uncompressed_data, uncompressed_len,
690 match_tab, lzx_record_match,
691 lzx_record_literal, &freq_tabs,
692 &queue, freq_tabs.main_freq_table,
695 lzx_make_huffman_codes(&freq_tabs, &codes);
697 /* Initialize the output bitstream. */
698 init_output_bitstream(&ostream, compressed_data, uncompressed_len - 1);
700 /* The first three bits tell us what kind of block it is, and are one
701 * of the LZX_BLOCKTYPE_* values. */
702 bitstream_put_bits(&ostream, block_type, 3);
704 /* The next bit indicates whether the block size is the default (32768),
705 * indicated by a 1 bit, or whether the block size is given by the next
706 * 16 bits, indicated by a 0 bit. */
707 if (uncompressed_len == 32768) {
708 bitstream_put_bits(&ostream, 1, 1);
710 bitstream_put_bits(&ostream, 0, 1);
711 bitstream_put_bits(&ostream, uncompressed_len, 16);
714 /* Write out the aligned offset tree. Note that M$ lies and says that
715 * the aligned offset tree comes after the length tree, but that is
716 * wrong; it actually is before the main tree. */
717 if (block_type == LZX_BLOCKTYPE_ALIGNED)
718 for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++)
719 bitstream_put_bits(&ostream, codes.aligned_lens[i],
720 LZX_ALIGNEDTREE_ELEMENT_SIZE);
722 /* Write the pre-tree and lengths for the first LZX_NUM_CHARS symbols in the
724 ret = lzx_write_compressed_tree(&ostream, codes.main_lens,
729 /* Write the pre-tree and symbols for the rest of the main tree. */
730 ret = lzx_write_compressed_tree(&ostream, codes.main_lens +
732 LZX_MAINTREE_NUM_SYMBOLS -
737 /* Write the pre-tree and symbols for the length tree. */
738 ret = lzx_write_compressed_tree(&ostream, codes.len_lens,
739 LZX_LENTREE_NUM_SYMBOLS);
743 /* Write the compressed literals. */
744 ret = lzx_write_compressed_literals(&ostream, block_type,
745 match_tab, num_matches, &codes);
749 ret = flush_output_bitstream(&ostream);
753 compressed_len = ostream.bit_output - (u8*)compressed_data;
755 *compressed_len_ret = compressed_len;
757 #ifdef ENABLE_VERIFY_COMPRESSION
758 /* Verify that we really get the same thing back when decompressing. */
759 u8 buf[uncompressed_len];
760 ret = lzx_decompress(compressed_data, compressed_len, buf,
763 ERROR("lzx_compress(): Failed to decompress data we compressed");
767 for (i = 0; i < uncompressed_len; i++) {
768 if (buf[i] != *((u8*)__uncompressed_data + i)) {
769 ERROR("lzx_compress(): Data we compressed didn't "
770 "decompress to the original data (difference at "
771 "byte %u of %u)", i + 1, uncompressed_len);