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, 2013 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 wimlib_lzx_compress(), a function to compress an in-memory
31 * buffer 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.
65 #include "wimlib/compress.h"
66 #include "wimlib/error.h"
67 #include "wimlib/lzx.h"
68 #include "wimlib/util.h"
74 /* Structure to contain the Huffman codes for the main, length, and aligned
77 u16 main_codewords[LZX_MAINTREE_NUM_SYMBOLS];
78 u8 main_lens[LZX_MAINTREE_NUM_SYMBOLS];
80 u16 len_codewords[LZX_LENTREE_NUM_SYMBOLS];
81 u8 len_lens[LZX_LENTREE_NUM_SYMBOLS];
83 u16 aligned_codewords[LZX_ALIGNEDTREE_NUM_SYMBOLS];
84 u8 aligned_lens[LZX_ALIGNEDTREE_NUM_SYMBOLS];
87 struct lzx_freq_tables {
88 freq_t main_freq_table[LZX_MAINTREE_NUM_SYMBOLS];
89 freq_t len_freq_table[LZX_LENTREE_NUM_SYMBOLS];
90 freq_t aligned_freq_table[LZX_ALIGNEDTREE_NUM_SYMBOLS];
93 /* Returns the LZX position slot that corresponds to a given formatted offset.
95 * Logically, this returns the smallest i such that
96 * formatted_offset >= lzx_position_base[i].
98 * The actual implementation below takes advantage of the regularity of the
99 * numbers in the lzx_position_base array to calculate the slot directly from
100 * the formatted offset without actually looking at the array.
102 static inline unsigned
103 lzx_get_position_slot(unsigned formatted_offset)
107 * Slots 36-49 (formatted_offset >= 262144) can be found by
108 * (formatted_offset/131072) + 34 == (formatted_offset >> 17) + 34;
109 * however, this check for formatted_offset >= 262144 is commented out
110 * because WIM chunks cannot be that large.
112 if (formatted_offset >= 262144) {
113 return (formatted_offset >> 17) + 34;
117 /* Note: this part here only works if:
119 * 2 <= formatted_offset < 655360
121 * It is < 655360 because the frequency of the position bases
122 * increases starting at the 655360 entry, and it is >= 2
123 * because the below calculation fails if the most significant
124 * bit is lower than the 2's place. */
125 wimlib_assert(formatted_offset >= 2 && formatted_offset < 655360);
126 unsigned mssb_idx = bsr32(formatted_offset);
127 return (mssb_idx << 1) |
128 ((formatted_offset >> (mssb_idx - 1)) & 1);
133 lzx_record_literal(u8 literal, void *_main_freq_tab)
135 freq_t *main_freq_tab = _main_freq_tab;
136 main_freq_tab[literal]++;
140 /* Constructs a match from an offset and a length, and updates the LRU queue and
141 * the frequency of symbols in the main, length, and aligned offset alphabets.
142 * The return value is a 32-bit number that provides the match in an
143 * intermediate representation documented below. */
145 lzx_record_match(unsigned match_offset, unsigned match_len,
146 void *_freq_tabs, void *_queue)
148 struct lzx_freq_tables *freq_tabs = _freq_tabs;
149 struct lru_queue *queue = _queue;
150 unsigned position_slot;
151 unsigned position_footer = 0;
156 unsigned adjusted_match_len;
158 wimlib_assert(match_len >= LZX_MIN_MATCH && match_len <= LZX_MAX_MATCH);
159 wimlib_assert(match_offset != 0);
161 /* If possible, encode this offset as a repeated offset. */
162 if (match_offset == queue->R0) {
164 } else if (match_offset == queue->R1) {
165 swap(queue->R0, queue->R1);
167 } else if (match_offset == queue->R2) {
168 swap(queue->R0, queue->R2);
171 /* Not a repeated offset. */
173 /* offsets of 0, 1, and 2 are reserved for the repeated offset
174 * codes, so non-repeated offsets must be encoded as 3+. The
175 * minimum offset is 1, so encode the offsets offset by 2. */
176 unsigned formatted_offset = match_offset + LZX_MIN_MATCH;
178 queue->R2 = queue->R1;
179 queue->R1 = queue->R0;
180 queue->R0 = match_offset;
182 /* The (now-formatted) offset will actually be encoded as a
183 * small position slot number that maps to a certain hard-coded
184 * offset (position base), followed by a number of extra bits---
185 * the position footer--- that are added to the position base to
186 * get the original formatted offset. */
188 position_slot = lzx_get_position_slot(formatted_offset);
189 position_footer = formatted_offset &
190 ((1 << lzx_get_num_extra_bits(position_slot)) - 1);
193 adjusted_match_len = match_len - LZX_MIN_MATCH;
195 /* Pack the position slot, position footer, and match length into an
196 * intermediate representation.
199 * ---- -----------------------------------------------------------
201 * 31 1 if a match, 0 if a literal.
203 * 30-25 position slot. This can be at most 50, so it will fit in 6
206 * 8-24 position footer. This is the offset of the real formatted
207 * offset from the position base. This can be at most 17 bits
208 * (since lzx_extra_bits[LZX_NUM_POSITION_SLOTS - 1] is 17).
210 * 0-7 length of match, offset by 2. This can be at most
211 * (LZX_MAX_MATCH - 2) == 255, so it will fit in 8 bits. */
213 (position_slot << 25) |
214 (position_footer << 8) |
215 (adjusted_match_len);
217 /* The match length must be at least 2, so let the adjusted match length
218 * be the match length minus 2.
220 * If it is less than 7, the adjusted match length is encoded as a 3-bit
221 * number offset by 2. Otherwise, the 3-bit length header is all 1's
222 * and the actual adjusted length is given as a symbol encoded with the
223 * length tree, offset by 7.
225 if (adjusted_match_len < LZX_NUM_PRIMARY_LENS) {
226 len_header = adjusted_match_len;
228 len_header = LZX_NUM_PRIMARY_LENS;
229 len_footer = adjusted_match_len - LZX_NUM_PRIMARY_LENS;
230 freq_tabs->len_freq_table[len_footer]++;
232 len_pos_header = (position_slot << 3) | len_header;
234 wimlib_assert(len_pos_header < LZX_MAINTREE_NUM_SYMBOLS - LZX_NUM_CHARS);
236 freq_tabs->main_freq_table[len_pos_header + LZX_NUM_CHARS]++;
239 * if (lzx_extra_bits[position_slot] >= 3) */
240 if (position_slot >= 8)
241 freq_tabs->aligned_freq_table[position_footer & 7]++;
247 * Writes a compressed literal match to the output.
249 * @out: The output bitstream.
250 * @block_type: The type of the block (LZX_BLOCKTYPE_ALIGNED or LZX_BLOCKTYPE_VERBATIM)
251 * @match: The match, encoded as a 32-bit number.
252 * @codes: Pointer to a structure that contains the codewords for the
253 * main, length, and aligned offset Huffman codes.
256 lzx_write_match(struct output_bitstream *out, int block_type,
257 u32 match, const struct lzx_codes *codes)
259 /* low 8 bits are the match length minus 2 */
260 unsigned match_len_minus_2 = match & 0xff;
261 /* Next 17 bits are the position footer */
262 unsigned position_footer = (match >> 8) & 0x1ffff; /* 17 bits */
263 /* Next 6 bits are the position slot. */
264 unsigned position_slot = (match >> 25) & 0x3f; /* 6 bits */
267 unsigned len_pos_header;
268 unsigned main_symbol;
269 unsigned num_extra_bits;
270 unsigned verbatim_bits;
271 unsigned aligned_bits;
274 /* If the match length is less than MIN_MATCH (= 2) +
275 * NUM_PRIMARY_LENS (= 7), the length header contains
276 * the match length minus MIN_MATCH, and there is no
279 * Otherwise, the length header contains
280 * NUM_PRIMARY_LENS, and the length footer contains
281 * the match length minus NUM_PRIMARY_LENS minus
283 if (match_len_minus_2 < LZX_NUM_PRIMARY_LENS) {
284 len_header = match_len_minus_2;
285 /* No length footer-- mark it with a special
287 len_footer = (unsigned)(-1);
289 len_header = LZX_NUM_PRIMARY_LENS;
290 len_footer = match_len_minus_2 - LZX_NUM_PRIMARY_LENS;
293 /* Combine the position slot with the length header into
294 * a single symbol that will be encoded with the main
296 len_pos_header = (position_slot << 3) | len_header;
298 /* The actual main symbol is offset by LZX_NUM_CHARS because
299 * values under LZX_NUM_CHARS are used to indicate a literal
300 * byte rather than a match. */
301 main_symbol = len_pos_header + LZX_NUM_CHARS;
303 /* Output main symbol. */
304 ret = bitstream_put_bits(out, codes->main_codewords[main_symbol],
305 codes->main_lens[main_symbol]);
309 /* If there is a length footer, output it using the
310 * length Huffman code. */
311 if (len_footer != (unsigned)(-1)) {
312 ret = bitstream_put_bits(out, codes->len_codewords[len_footer],
313 codes->len_lens[len_footer]);
318 wimlib_assert(position_slot < LZX_NUM_POSITION_SLOTS);
320 num_extra_bits = lzx_get_num_extra_bits(position_slot);
322 /* For aligned offset blocks with at least 3 extra bits, output the
323 * verbatim bits literally, then the aligned bits encoded using the
324 * aligned offset tree. Otherwise, only the verbatim bits need to be
326 if ((block_type == LZX_BLOCKTYPE_ALIGNED) && (num_extra_bits >= 3)) {
328 verbatim_bits = position_footer >> 3;
329 ret = bitstream_put_bits(out, verbatim_bits,
334 aligned_bits = (position_footer & 7);
335 ret = bitstream_put_bits(out,
336 codes->aligned_codewords[aligned_bits],
337 codes->aligned_lens[aligned_bits]);
341 /* verbatim bits is the same as the position
342 * footer, in this case. */
343 ret = bitstream_put_bits(out, position_footer, num_extra_bits);
351 * Writes all compressed literals in a block, both matches and literal bytes, to
352 * the output bitstream.
354 * @out: The output bitstream.
355 * @block_type: The type of the block (LZX_BLOCKTYPE_ALIGNED or LZX_BLOCKTYPE_VERBATIM)
356 * @match_tab[]: The array of matches that will be output. It has length
357 * of @num_compressed_literals.
358 * @num_compressed_literals: Number of compressed literals to be output.
359 * @codes: Pointer to a structure that contains the codewords for the
360 * main, length, and aligned offset Huffman codes.
363 lzx_write_compressed_literals(struct output_bitstream *ostream,
365 const u32 match_tab[],
366 unsigned num_compressed_literals,
367 const struct lzx_codes *codes)
373 for (i = 0; i < num_compressed_literals; i++) {
374 match = match_tab[i];
376 /* High bit of the match indicates whether the match is an
377 * actual match (1) or a literal uncompressed byte (0) */
378 if (match & 0x80000000) {
380 ret = lzx_write_match(ostream, block_type, match,
386 wimlib_assert(match < LZX_NUM_CHARS);
387 ret = bitstream_put_bits(ostream,
388 codes->main_codewords[match],
389 codes->main_lens[match]);
398 * Writes a compressed Huffman tree to the output, preceded by the pretree for
401 * The Huffman tree is represented in the output as a series of path lengths
402 * from which the canonical Huffman code can be reconstructed. The path lengths
403 * themselves are compressed using a separate Huffman code, the pretree, which
404 * consists of LZX_PRETREE_NUM_SYMBOLS (= 20) symbols that cover all possible code
405 * lengths, plus extra codes for repeated lengths. The path lengths of the
406 * pretree precede the path lengths of the larger code and are uncompressed,
407 * consisting of 20 entries of 4 bits each.
409 * @out: The bitstream for the compressed output.
410 * @lens: The code lengths for the Huffman tree, indexed by symbol.
411 * @num_symbols: The number of symbols in the code.
414 lzx_write_compressed_tree(struct output_bitstream *out,
415 const u8 lens[], unsigned num_symbols)
417 /* Frequencies of the length symbols, including the RLE symbols (NOT the
418 * actual lengths themselves). */
419 freq_t pretree_freqs[LZX_PRETREE_NUM_SYMBOLS];
420 u8 pretree_lens[LZX_PRETREE_NUM_SYMBOLS];
421 u16 pretree_codewords[LZX_PRETREE_NUM_SYMBOLS];
422 u8 output_syms[num_symbols * 2];
423 unsigned output_syms_idx;
424 unsigned cur_run_len;
427 unsigned additional_bits;
431 ZERO_ARRAY(pretree_freqs);
433 /* Since the code word lengths use a form of RLE encoding, the goal here
434 * is to find each run of identical lengths when going through them in
435 * symbol order (including runs of length 1). For each run, as many
436 * lengths are encoded using RLE as possible, and the rest are output
439 * output_syms[] will be filled in with the length symbols that will be
440 * output, including RLE codes, not yet encoded using the pre-tree.
442 * cur_run_len keeps track of how many code word lengths are in the
443 * current run of identical lengths.
447 for (i = 1; i <= num_symbols; i++) {
449 if (i != num_symbols && lens[i] == lens[i - 1]) {
450 /* Still in a run--- keep going. */
455 /* Run ended! Check if it is a run of zeroes or a run of
458 /* The symbol that was repeated in the run--- not to be confused
459 * with the length *of* the run (cur_run_len) */
460 len_in_run = lens[i - 1];
462 if (len_in_run == 0) {
463 /* A run of 0's. Encode it in as few length
464 * codes as we can. */
466 /* The magic length 18 indicates a run of 20 + n zeroes,
467 * where n is an uncompressed literal 5-bit integer that
468 * follows the magic length. */
469 while (cur_run_len >= 20) {
471 additional_bits = min(cur_run_len - 20, 0x1f);
473 output_syms[output_syms_idx++] = 18;
474 output_syms[output_syms_idx++] = additional_bits;
475 cur_run_len -= 20 + additional_bits;
478 /* The magic length 17 indicates a run of 4 + n zeroes,
479 * where n is an uncompressed literal 4-bit integer that
480 * follows the magic length. */
481 while (cur_run_len >= 4) {
482 additional_bits = min(cur_run_len - 4, 0xf);
484 output_syms[output_syms_idx++] = 17;
485 output_syms[output_syms_idx++] = additional_bits;
486 cur_run_len -= 4 + additional_bits;
491 /* A run of nonzero lengths. */
493 /* The magic length 19 indicates a run of 4 + n
494 * nonzeroes, where n is a literal bit that follows the
495 * magic length, and where the value of the lengths in
496 * the run is given by an extra length symbol, encoded
497 * with the pretree, that follows the literal bit.
499 * The extra length symbol is encoded as a difference
500 * from the length of the codeword for the first symbol
501 * in the run in the previous tree.
503 while (cur_run_len >= 4) {
504 additional_bits = (cur_run_len > 4);
505 delta = -(char)len_in_run;
509 pretree_freqs[(unsigned char)delta]++;
510 output_syms[output_syms_idx++] = 19;
511 output_syms[output_syms_idx++] = additional_bits;
512 output_syms[output_syms_idx++] = delta;
513 cur_run_len -= 4 + additional_bits;
517 /* Any remaining lengths in the run are outputted without RLE,
518 * as a difference from the length of that codeword in the
520 while (cur_run_len--) {
521 delta = -(char)len_in_run;
525 pretree_freqs[(unsigned char)delta]++;
526 output_syms[output_syms_idx++] = delta;
532 wimlib_assert(output_syms_idx < ARRAY_LEN(output_syms));
534 /* Build the pretree from the frequencies of the length symbols. */
536 make_canonical_huffman_code(LZX_PRETREE_NUM_SYMBOLS,
537 LZX_MAX_CODEWORD_LEN,
538 pretree_freqs, pretree_lens,
541 /* Write the lengths of the pretree codes to the output. */
542 for (i = 0; i < LZX_PRETREE_NUM_SYMBOLS; i++)
543 bitstream_put_bits(out, pretree_lens[i],
544 LZX_PRETREE_ELEMENT_SIZE);
546 /* Write the length symbols, encoded with the pretree, to the output. */
549 while (i < output_syms_idx) {
550 pretree_sym = output_syms[i++];
552 bitstream_put_bits(out, pretree_codewords[pretree_sym],
553 pretree_lens[pretree_sym]);
554 switch (pretree_sym) {
556 bitstream_put_bits(out, output_syms[i++], 4);
559 bitstream_put_bits(out, output_syms[i++], 5);
562 bitstream_put_bits(out, output_syms[i++], 1);
563 bitstream_put_bits(out,
564 pretree_codewords[output_syms[i]],
565 pretree_lens[output_syms[i]]);
575 /* Builds the canonical Huffman code for the main tree, the length tree, and the
576 * aligned offset tree. */
578 lzx_make_huffman_codes(const struct lzx_freq_tables *freq_tabs,
579 struct lzx_codes *codes)
581 make_canonical_huffman_code(LZX_MAINTREE_NUM_SYMBOLS,
582 LZX_MAX_CODEWORD_LEN,
583 freq_tabs->main_freq_table,
585 codes->main_codewords);
587 make_canonical_huffman_code(LZX_LENTREE_NUM_SYMBOLS,
588 LZX_MAX_CODEWORD_LEN,
589 freq_tabs->len_freq_table,
591 codes->len_codewords);
593 make_canonical_huffman_code(LZX_ALIGNEDTREE_NUM_SYMBOLS, 8,
594 freq_tabs->aligned_freq_table,
596 codes->aligned_codewords);
600 do_call_insn_translation(u32 *call_insn_target, int input_pos,
606 rel_offset = le32_to_cpu(*call_insn_target);
607 if (rel_offset >= -input_pos && rel_offset < file_size) {
608 if (rel_offset < file_size - input_pos) {
609 /* "good translation" */
610 abs_offset = rel_offset + input_pos;
612 /* "compensating translation" */
613 abs_offset = rel_offset - file_size;
615 *call_insn_target = cpu_to_le32(abs_offset);
619 /* This is the reverse of undo_call_insn_preprocessing() in lzx-decompress.c.
620 * See the comment above that function for more information. */
622 do_call_insn_preprocessing(u8 uncompressed_data[], int uncompressed_data_len)
624 for (int i = 0; i < uncompressed_data_len - 10; i++) {
625 if (uncompressed_data[i] == 0xe8) {
626 do_call_insn_translation((u32*)&uncompressed_data[i + 1],
628 LZX_WIM_MAGIC_FILESIZE);
635 static const struct lz_params lzx_lz_params = {
637 /* LZX_MIN_MATCH == 2, but 2-character matches are rarely useful; the
638 * minimum match for compression is set to 3 instead. */
641 .max_match = LZX_MAX_MATCH,
642 .good_match = LZX_MAX_MATCH,
643 .nice_match = LZX_MAX_MATCH,
644 .max_chain_len = LZX_MAX_MATCH,
645 .max_lazy_match = LZX_MAX_MATCH,
649 /* Documented in wimlib.h */
651 wimlib_lzx_compress(const void *_uncompressed_data, unsigned uncompressed_len,
652 void *compressed_data)
654 struct output_bitstream ostream;
655 u8 uncompressed_data[uncompressed_len + 8];
656 struct lzx_freq_tables freq_tabs;
657 struct lzx_codes codes;
658 u32 match_tab[uncompressed_len];
659 struct lru_queue queue;
660 unsigned num_matches;
661 unsigned compressed_len;
664 int block_type = LZX_BLOCKTYPE_ALIGNED;
666 wimlib_assert(uncompressed_len <= 32768);
668 if (uncompressed_len < 100)
671 memset(&freq_tabs, 0, sizeof(freq_tabs));
676 /* The input data must be preprocessed. To avoid changing the original
677 * input, copy it to a temporary buffer. */
678 memcpy(uncompressed_data, _uncompressed_data, uncompressed_len);
679 memset(uncompressed_data + uncompressed_len, 0, 8);
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 #ifdef ENABLE_VERIFY_COMPRESSION
756 /* Verify that we really get the same thing back when decompressing. */
758 u8 buf[uncompressed_len];
759 ret = wimlib_lzx_decompress(compressed_data, compressed_len,
760 buf, uncompressed_len);
762 ERROR("lzx_compress(): Failed to decompress data we compressed");
766 for (i = 0; i < uncompressed_len; i++) {
767 if (buf[i] != *((u8*)_uncompressed_data + i)) {
768 ERROR("lzx_compress(): Data we compressed didn't "
769 "decompress to the original data (difference at "
770 "byte %u of %u)", i + 1, uncompressed_len);
776 return compressed_len;