4 * A compressor for the LZX compression format, as used in WIM files.
8 * Copyright (C) 2012, 2013, 2014, 2015 Eric Biggers
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
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
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/.
26 * This file contains a compressor for the LZX ("Lempel-Ziv eXtended")
27 * compression format, as used in the WIM (Windows IMaging) file format.
29 * Two different parsing algorithms are implemented: "near-optimal" and "lazy".
30 * "Near-optimal" is significantly slower than "lazy", but results in a better
31 * compression ratio. The "near-optimal" algorithm is used at the default
34 * This file may need some slight modifications to be used outside of the WIM
35 * format. In particular, in other situations the LZX block header might be
36 * slightly different, and sliding window support might be required.
38 * Note: LZX is a compression format derived from DEFLATE, the format used by
39 * zlib and gzip. Both LZX and DEFLATE use LZ77 matching and Huffman coding.
40 * Certain details are quite similar, such as the method for storing Huffman
41 * codes. However, the main differences are:
43 * - LZX preprocesses the data to attempt to make x86 machine code slightly more
44 * compressible before attempting to compress it further.
46 * - LZX uses a "main" alphabet which combines literals and matches, with the
47 * match symbols containing a "length header" (giving all or part of the match
48 * length) and an "offset slot" (giving, roughly speaking, the order of
49 * magnitude of the match offset).
51 * - LZX does not have static Huffman blocks (that is, the kind with preset
52 * Huffman codes); however it does have two types of dynamic Huffman blocks
53 * ("verbatim" and "aligned").
55 * - LZX has a minimum match length of 2 rather than 3. Length 2 matches can be
56 * useful, but generally only if the parser is smart about choosing them.
58 * - In LZX, offset slots 0 through 2 actually represent entries in an LRU queue
59 * of match offsets. This is very useful for certain types of files, such as
60 * binary files that have repeating records.
68 * Start a new LZX block (with new Huffman codes) after this many bytes.
70 * Note: actual block sizes may slightly exceed this value.
72 * TODO: recursive splitting and cost evaluation might be good for an extremely
73 * high compression mode, but otherwise it is almost always far too slow for how
74 * much it helps. Perhaps some sort of heuristic would be useful?
76 #define LZX_DIV_BLOCK_SIZE 32768
79 * LZX_CACHE_PER_POS is the number of lz_match structures to reserve in the
80 * match cache for each byte position. This value should be high enough so that
81 * nearly the time, all matches found in a given block can fit in the match
82 * cache. However, fallback behavior (immediately terminating the block) on
83 * cache overflow is still required.
85 #define LZX_CACHE_PER_POS 7
88 * LZX_CACHE_LENGTH is the number of lz_match structures in the match cache,
89 * excluding the extra "overflow" entries. The per-position multiplier is '1 +
90 * LZX_CACHE_PER_POS' instead of 'LZX_CACHE_PER_POS' because there is an
91 * overhead of one lz_match per position, used to hold the match count at that
94 #define LZX_CACHE_LENGTH (LZX_DIV_BLOCK_SIZE * (1 + LZX_CACHE_PER_POS))
97 * LZX_MAX_MATCHES_PER_POS is an upper bound on the number of matches that can
98 * ever be saved in the match cache for a single position. Since each match we
99 * save for a single position has a distinct length, we can use the number of
100 * possible match lengths in LZX as this bound. This bound is guaranteed to be
101 * valid in all cases, although if 'nice_match_length < LZX_MAX_MATCH_LEN', then
102 * it will never actually be reached.
104 #define LZX_MAX_MATCHES_PER_POS LZX_NUM_LENS
107 * LZX_BIT_COST is a scaling factor that represents the cost to output one bit.
108 * This makes it possible to consider fractional bit costs.
110 * Note: this is only useful as a statistical trick for when the true costs are
111 * unknown. In reality, each token in LZX requires a whole number of bits to
114 #define LZX_BIT_COST 16
117 * Should the compressor take into account the costs of aligned offset symbols?
119 #define LZX_CONSIDER_ALIGNED_COSTS 1
122 * LZX_MAX_FAST_LEVEL is the maximum compression level at which we use the
125 #define LZX_MAX_FAST_LEVEL 34
128 * BT_MATCHFINDER_HASH2_ORDER is the log base 2 of the number of entries in the
129 * hash table for finding length 2 matches. This could be as high as 16, but
130 * using a smaller hash table speeds up compression due to reduced cache
133 #define BT_MATCHFINDER_HASH2_ORDER 12
136 * These are the compressor-side limits on the codeword lengths for each Huffman
137 * code. To make outputting bits slightly faster, some of these limits are
138 * lower than the limits defined by the LZX format. This does not significantly
139 * affect the compression ratio, at least for the block sizes we use.
141 #define MAIN_CODEWORD_LIMIT 12 /* 64-bit: can buffer 4 main symbols */
142 #define LENGTH_CODEWORD_LIMIT 12
143 #define ALIGNED_CODEWORD_LIMIT 7
144 #define PRE_CODEWORD_LIMIT 7
146 #include "wimlib/compress_common.h"
147 #include "wimlib/compressor_ops.h"
148 #include "wimlib/error.h"
149 #include "wimlib/lz_extend.h"
150 #include "wimlib/lzx_common.h"
151 #include "wimlib/unaligned.h"
152 #include "wimlib/util.h"
154 /* Matchfinders with 16-bit positions */
156 #define MF_SUFFIX _16
157 #include "wimlib/bt_matchfinder.h"
158 #include "wimlib/hc_matchfinder.h"
160 /* Matchfinders with 32-bit positions */
164 #define MF_SUFFIX _32
165 #include "wimlib/bt_matchfinder.h"
166 #include "wimlib/hc_matchfinder.h"
168 struct lzx_output_bitstream;
170 /* Codewords for the LZX Huffman codes. */
171 struct lzx_codewords {
172 u32 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
173 u32 len[LZX_LENCODE_NUM_SYMBOLS];
174 u32 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
177 /* Codeword lengths (in bits) for the LZX Huffman codes.
178 * A zero length means the corresponding codeword has zero frequency. */
180 u8 main[LZX_MAINCODE_MAX_NUM_SYMBOLS + 1];
181 u8 len[LZX_LENCODE_NUM_SYMBOLS + 1];
182 u8 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
185 /* Cost model for near-optimal parsing */
188 /* 'match_cost[offset_slot][len - LZX_MIN_MATCH_LEN]' is the cost for a
189 * length 'len' match that has an offset belonging to 'offset_slot'. */
190 u32 match_cost[LZX_MAX_OFFSET_SLOTS][LZX_NUM_LENS];
192 /* Cost for each symbol in the main code */
193 u32 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
195 /* Cost for each symbol in the length code */
196 u32 len[LZX_LENCODE_NUM_SYMBOLS];
198 #if LZX_CONSIDER_ALIGNED_COSTS
199 /* Cost for each symbol in the aligned code */
200 u32 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
204 /* Codewords and lengths for the LZX Huffman codes. */
206 struct lzx_codewords codewords;
207 struct lzx_lens lens;
210 /* Symbol frequency counters for the LZX Huffman codes. */
212 u32 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
213 u32 len[LZX_LENCODE_NUM_SYMBOLS];
214 u32 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
218 * Represents a run of literals followed by a match or end-of-block. This
219 * struct is needed to temporarily store items chosen by the parser, since items
220 * cannot be written until all items for the block have been chosen and the
221 * block's Huffman codes have been computed.
223 struct lzx_sequence {
225 /* The number of literals in the run. This may be 0. The literals are
226 * not stored explicitly in this structure; instead, they are read
227 * directly from the uncompressed data. */
230 /* If the next field doesn't indicate end-of-block, then this is the
231 * match length minus LZX_MIN_MATCH_LEN. */
234 /* If bit 31 is clear, then this field contains the match header in bits
235 * 0-8 and the match offset minus LZX_OFFSET_ADJUSTMENT in bits 9-30.
236 * Otherwise, this sequence's literal run was the last literal run in
237 * the block, so there is no match that follows it. */
238 u32 adjusted_offset_and_match_hdr;
242 * This structure represents a byte position in the input buffer and a node in
243 * the graph of possible match/literal choices.
245 * Logically, each incoming edge to this node is labeled with a literal or a
246 * match that can be taken to reach this position from an earlier position; and
247 * each outgoing edge from this node is labeled with a literal or a match that
248 * can be taken to advance from this position to a later position.
250 struct lzx_optimum_node {
252 /* The cost, in bits, of the lowest-cost path that has been found to
253 * reach this position. This can change as progressively lower cost
254 * paths are found to reach this position. */
258 * The match or literal that was taken to reach this position. This can
259 * change as progressively lower cost paths are found to reach this
262 * This variable is divided into two bitfields.
265 * Low bits are 0, high bits are the literal.
267 * Explicit offset matches:
268 * Low bits are the match length, high bits are the offset plus 2.
270 * Repeat offset matches:
271 * Low bits are the match length, high bits are the queue index.
274 #define OPTIMUM_OFFSET_SHIFT 9
275 #define OPTIMUM_LEN_MASK ((1 << OPTIMUM_OFFSET_SHIFT) - 1)
276 } _aligned_attribute(8);
279 * Least-recently-used queue for match offsets.
281 * This is represented as a 64-bit integer for efficiency. There are three
282 * offsets of 21 bits each. Bit 64 is garbage.
284 struct lzx_lru_queue {
288 #define LZX_QUEUE64_OFFSET_SHIFT 21
289 #define LZX_QUEUE64_OFFSET_MASK (((u64)1 << LZX_QUEUE64_OFFSET_SHIFT) - 1)
291 #define LZX_QUEUE64_R0_SHIFT (0 * LZX_QUEUE64_OFFSET_SHIFT)
292 #define LZX_QUEUE64_R1_SHIFT (1 * LZX_QUEUE64_OFFSET_SHIFT)
293 #define LZX_QUEUE64_R2_SHIFT (2 * LZX_QUEUE64_OFFSET_SHIFT)
295 #define LZX_QUEUE64_R0_MASK (LZX_QUEUE64_OFFSET_MASK << LZX_QUEUE64_R0_SHIFT)
296 #define LZX_QUEUE64_R1_MASK (LZX_QUEUE64_OFFSET_MASK << LZX_QUEUE64_R1_SHIFT)
297 #define LZX_QUEUE64_R2_MASK (LZX_QUEUE64_OFFSET_MASK << LZX_QUEUE64_R2_SHIFT)
300 lzx_lru_queue_init(struct lzx_lru_queue *queue)
302 queue->R = ((u64)1 << LZX_QUEUE64_R0_SHIFT) |
303 ((u64)1 << LZX_QUEUE64_R1_SHIFT) |
304 ((u64)1 << LZX_QUEUE64_R2_SHIFT);
308 lzx_lru_queue_R0(struct lzx_lru_queue queue)
310 return (queue.R >> LZX_QUEUE64_R0_SHIFT) & LZX_QUEUE64_OFFSET_MASK;
314 lzx_lru_queue_R1(struct lzx_lru_queue queue)
316 return (queue.R >> LZX_QUEUE64_R1_SHIFT) & LZX_QUEUE64_OFFSET_MASK;
320 lzx_lru_queue_R2(struct lzx_lru_queue queue)
322 return (queue.R >> LZX_QUEUE64_R2_SHIFT) & LZX_QUEUE64_OFFSET_MASK;
325 /* Push a match offset onto the front (most recently used) end of the queue. */
326 static inline struct lzx_lru_queue
327 lzx_lru_queue_push(struct lzx_lru_queue queue, u32 offset)
329 return (struct lzx_lru_queue) {
330 .R = (queue.R << LZX_QUEUE64_OFFSET_SHIFT) | offset,
334 /* Swap a match offset to the front of the queue. */
335 static inline struct lzx_lru_queue
336 lzx_lru_queue_swap(struct lzx_lru_queue queue, unsigned idx)
342 return (struct lzx_lru_queue) {
343 .R = (lzx_lru_queue_R1(queue) << LZX_QUEUE64_R0_SHIFT) |
344 (lzx_lru_queue_R0(queue) << LZX_QUEUE64_R1_SHIFT) |
345 (queue.R & LZX_QUEUE64_R2_MASK),
348 return (struct lzx_lru_queue) {
349 .R = (lzx_lru_queue_R2(queue) << LZX_QUEUE64_R0_SHIFT) |
350 (queue.R & LZX_QUEUE64_R1_MASK) |
351 (lzx_lru_queue_R0(queue) << LZX_QUEUE64_R2_SHIFT),
355 /* The main LZX compressor structure */
356 struct lzx_compressor {
358 /* The "nice" match length: if a match of this length is found, then
359 * choose it immediately without further consideration. */
360 unsigned nice_match_length;
362 /* The maximum search depth: consider at most this many potential
363 * matches at each position. */
364 unsigned max_search_depth;
366 /* The log base 2 of the LZX window size for LZ match offset encoding
367 * purposes. This will be >= LZX_MIN_WINDOW_ORDER and <=
368 * LZX_MAX_WINDOW_ORDER. */
369 unsigned window_order;
371 /* The number of symbols in the main alphabet. This depends on
372 * @window_order, since @window_order determines the maximum possible
374 unsigned num_main_syms;
376 /* Number of optimization passes per block */
377 unsigned num_optim_passes;
379 /* The preprocessed buffer of data being compressed */
382 /* The number of bytes of data to be compressed, which is the number of
383 * bytes of data in @in_buffer that are actually valid. */
386 /* Pointer to the compress() implementation chosen at allocation time */
387 void (*impl)(struct lzx_compressor *, struct lzx_output_bitstream *);
389 /* If true, the compressor need not preserve the input buffer if it
390 * compresses the data successfully. */
393 /* The Huffman symbol frequency counters for the current block. */
394 struct lzx_freqs freqs;
396 /* The Huffman codes for the current and previous blocks. The one with
397 * index 'codes_index' is for the current block, and the other one is
398 * for the previous block. */
399 struct lzx_codes codes[2];
400 unsigned codes_index;
402 /* The matches and literals that the parser has chosen for the current
403 * block. The required length of this array is limited by the maximum
404 * number of matches that can ever be chosen for a single block, plus
405 * one for the special entry at the end. */
406 struct lzx_sequence chosen_sequences[
407 DIV_ROUND_UP(LZX_DIV_BLOCK_SIZE, LZX_MIN_MATCH_LEN) + 1];
409 /* Tables for mapping adjusted offsets to offset slots */
411 /* offset slots [0, 29] */
412 u8 offset_slot_tab_1[32768];
414 /* offset slots [30, 49] */
415 u8 offset_slot_tab_2[128];
418 /* Data for greedy or lazy parsing */
420 /* Hash chains matchfinder (MUST BE LAST!!!) */
422 struct hc_matchfinder_16 hc_mf_16;
423 struct hc_matchfinder_32 hc_mf_32;
427 /* Data for near-optimal parsing */
430 * The graph nodes for the current block.
432 * We need at least 'LZX_DIV_BLOCK_SIZE +
433 * LZX_MAX_MATCH_LEN - 1' nodes because that is the
434 * maximum block size that may be used. Add 1 because
435 * we need a node to represent end-of-block.
437 * It is possible that nodes past end-of-block are
438 * accessed during match consideration, but this can
439 * only occur if the block was truncated at
440 * LZX_DIV_BLOCK_SIZE. So the same bound still applies.
441 * Note that since nodes past the end of the block will
442 * never actually have an effect on the items that are
443 * chosen for the block, it makes no difference what
444 * their costs are initialized to (if anything).
446 struct lzx_optimum_node optimum_nodes[LZX_DIV_BLOCK_SIZE +
447 LZX_MAX_MATCH_LEN - 1 + 1];
449 /* The cost model for the current block */
450 struct lzx_costs costs;
453 * Cached matches for the current block. This array
454 * contains the matches that were found at each position
455 * in the block. Specifically, for each position, there
456 * is a special 'struct lz_match' whose 'length' field
457 * contains the number of matches that were found at
458 * that position; this is followed by the matches
459 * themselves, if any, sorted by strictly increasing
462 * Note: in rare cases, there will be a very high number
463 * of matches in the block and this array will overflow.
464 * If this happens, we force the end of the current
465 * block. LZX_CACHE_LENGTH is the length at which we
466 * actually check for overflow. The extra slots beyond
467 * this are enough to absorb the worst case overflow,
468 * which occurs if starting at
469 * &match_cache[LZX_CACHE_LENGTH - 1], we write the
470 * match count header, then write
471 * LZX_MAX_MATCHES_PER_POS matches, then skip searching
472 * for matches at 'LZX_MAX_MATCH_LEN - 1' positions and
473 * write the match count header for each.
475 struct lz_match match_cache[LZX_CACHE_LENGTH +
476 LZX_MAX_MATCHES_PER_POS +
477 LZX_MAX_MATCH_LEN - 1];
479 /* Binary trees matchfinder (MUST BE LAST!!!) */
481 struct bt_matchfinder_16 bt_mf_16;
482 struct bt_matchfinder_32 bt_mf_32;
489 * Will a matchfinder using 16-bit positions be sufficient for compressing
490 * buffers of up to the specified size? The limit could be 65536 bytes, but we
491 * also want to optimize out the use of offset_slot_tab_2 in the 16-bit case.
492 * This requires that the limit be no more than the length of offset_slot_tab_1
496 lzx_is_16_bit(size_t max_bufsize)
498 STATIC_ASSERT(ARRAY_LEN(((struct lzx_compressor *)0)->offset_slot_tab_1) == 32768);
499 return max_bufsize <= 32768;
503 * The following macros call either the 16-bit or the 32-bit version of a
504 * matchfinder function based on the value of 'is_16_bit', which will be known
505 * at compilation time.
508 #define CALL_HC_MF(is_16_bit, c, funcname, ...) \
509 ((is_16_bit) ? CONCAT(funcname, _16)(&(c)->hc_mf_16, ##__VA_ARGS__) : \
510 CONCAT(funcname, _32)(&(c)->hc_mf_32, ##__VA_ARGS__));
512 #define CALL_BT_MF(is_16_bit, c, funcname, ...) \
513 ((is_16_bit) ? CONCAT(funcname, _16)(&(c)->bt_mf_16, ##__VA_ARGS__) : \
514 CONCAT(funcname, _32)(&(c)->bt_mf_32, ##__VA_ARGS__));
517 * Structure to keep track of the current state of sending bits to the
518 * compressed output buffer.
520 * The LZX bitstream is encoded as a sequence of 16-bit coding units.
522 struct lzx_output_bitstream {
524 /* Bits that haven't yet been written to the output buffer. */
525 machine_word_t bitbuf;
527 /* Number of bits currently held in @bitbuf. */
530 /* Pointer to the start of the output buffer. */
533 /* Pointer to the position in the output buffer at which the next coding
534 * unit should be written. */
537 /* Pointer just past the end of the output buffer, rounded down to a
538 * 2-byte boundary. */
542 /* Can the specified number of bits always be added to 'bitbuf' after any
543 * pending 16-bit coding units have been flushed? */
544 #define CAN_BUFFER(n) ((n) <= (8 * sizeof(machine_word_t)) - 15)
547 * Initialize the output bitstream.
550 * The output bitstream structure to initialize.
552 * The buffer being written to.
554 * Size of @buffer, in bytes.
557 lzx_init_output(struct lzx_output_bitstream *os, void *buffer, size_t size)
562 os->next = os->start;
563 os->end = os->start + (size & ~1);
566 /* Add some bits to the bitbuffer variable of the output bitstream. The caller
567 * must make sure there is enough room. */
569 lzx_add_bits(struct lzx_output_bitstream *os, u32 bits, unsigned num_bits)
571 os->bitbuf = (os->bitbuf << num_bits) | bits;
572 os->bitcount += num_bits;
575 /* Flush bits from the bitbuffer variable to the output buffer. 'max_num_bits'
576 * specifies the maximum number of bits that may have been added since the last
579 lzx_flush_bits(struct lzx_output_bitstream *os, unsigned max_num_bits)
581 /* Masking the number of bits to shift is only needed to avoid undefined
582 * behavior; we don't actually care about the results of bad shifts. On
583 * x86, the explicit masking generates no extra code. */
584 const u32 shift_mask = 8 * sizeof(os->bitbuf) - 1;
586 if (os->end - os->next < 6)
588 put_unaligned_u16_le(os->bitbuf >> ((os->bitcount - 16) &
589 shift_mask), os->next + 0);
590 if (max_num_bits > 16)
591 put_unaligned_u16_le(os->bitbuf >> ((os->bitcount - 32) &
592 shift_mask), os->next + 2);
593 if (max_num_bits > 32)
594 put_unaligned_u16_le(os->bitbuf >> ((os->bitcount - 48) &
595 shift_mask), os->next + 4);
596 os->next += (os->bitcount >> 4) << 1;
600 /* Add at most 16 bits to the bitbuffer and flush it. */
602 lzx_write_bits(struct lzx_output_bitstream *os, u32 bits, unsigned num_bits)
604 lzx_add_bits(os, bits, num_bits);
605 lzx_flush_bits(os, 16);
609 * Flush the last coding unit to the output buffer if needed. Return the total
610 * number of bytes written to the output buffer, or 0 if an overflow occurred.
613 lzx_flush_output(struct lzx_output_bitstream *os)
615 if (os->end - os->next < 6)
618 if (os->bitcount != 0) {
619 put_unaligned_u16_le(os->bitbuf << (16 - os->bitcount), os->next);
623 return os->next - os->start;
626 /* Build the main, length, and aligned offset Huffman codes used in LZX.
628 * This takes as input the frequency tables for each code and produces as output
629 * a set of tables that map symbols to codewords and codeword lengths. */
631 lzx_make_huffman_codes(struct lzx_compressor *c)
633 const struct lzx_freqs *freqs = &c->freqs;
634 struct lzx_codes *codes = &c->codes[c->codes_index];
636 STATIC_ASSERT(MAIN_CODEWORD_LIMIT >= 9 &&
637 MAIN_CODEWORD_LIMIT <= LZX_MAX_MAIN_CODEWORD_LEN);
638 STATIC_ASSERT(LENGTH_CODEWORD_LIMIT >= 8 &&
639 LENGTH_CODEWORD_LIMIT <= LZX_MAX_LEN_CODEWORD_LEN);
640 STATIC_ASSERT(ALIGNED_CODEWORD_LIMIT >= LZX_NUM_ALIGNED_OFFSET_BITS &&
641 ALIGNED_CODEWORD_LIMIT <= LZX_MAX_ALIGNED_CODEWORD_LEN);
643 make_canonical_huffman_code(c->num_main_syms,
647 codes->codewords.main);
649 make_canonical_huffman_code(LZX_LENCODE_NUM_SYMBOLS,
650 LENGTH_CODEWORD_LIMIT,
653 codes->codewords.len);
655 make_canonical_huffman_code(LZX_ALIGNEDCODE_NUM_SYMBOLS,
656 ALIGNED_CODEWORD_LIMIT,
659 codes->codewords.aligned);
662 /* Reset the symbol frequencies for the LZX Huffman codes. */
664 lzx_reset_symbol_frequencies(struct lzx_compressor *c)
666 memset(&c->freqs, 0, sizeof(c->freqs));
670 lzx_compute_precode_items(const u8 lens[restrict],
671 const u8 prev_lens[restrict],
672 u32 precode_freqs[restrict],
673 unsigned precode_items[restrict])
682 itemptr = precode_items;
685 while (!((len = lens[run_start]) & 0x80)) {
687 /* len = the length being repeated */
689 /* Find the next run of codeword lengths. */
691 run_end = run_start + 1;
693 /* Fast case for a single length. */
694 if (likely(len != lens[run_end])) {
695 delta = prev_lens[run_start] - len;
698 precode_freqs[delta]++;
704 /* Extend the run. */
707 } while (len == lens[run_end]);
712 /* Symbol 18: RLE 20 to 51 zeroes at a time. */
713 while ((run_end - run_start) >= 20) {
714 extra_bits = min((run_end - run_start) - 20, 0x1f);
716 *itemptr++ = 18 | (extra_bits << 5);
717 run_start += 20 + extra_bits;
720 /* Symbol 17: RLE 4 to 19 zeroes at a time. */
721 if ((run_end - run_start) >= 4) {
722 extra_bits = min((run_end - run_start) - 4, 0xf);
724 *itemptr++ = 17 | (extra_bits << 5);
725 run_start += 4 + extra_bits;
729 /* A run of nonzero lengths. */
731 /* Symbol 19: RLE 4 to 5 of any length at a time. */
732 while ((run_end - run_start) >= 4) {
733 extra_bits = (run_end - run_start) > 4;
734 delta = prev_lens[run_start] - len;
738 precode_freqs[delta]++;
739 *itemptr++ = 19 | (extra_bits << 5) | (delta << 6);
740 run_start += 4 + extra_bits;
744 /* Output any remaining lengths without RLE. */
745 while (run_start != run_end) {
746 delta = prev_lens[run_start] - len;
749 precode_freqs[delta]++;
755 return itemptr - precode_items;
759 * Output a Huffman code in the compressed form used in LZX.
761 * The Huffman code is represented in the output as a logical series of codeword
762 * lengths from which the Huffman code, which must be in canonical form, can be
765 * The codeword lengths are themselves compressed using a separate Huffman code,
766 * the "precode", which contains a symbol for each possible codeword length in
767 * the larger code as well as several special symbols to represent repeated
768 * codeword lengths (a form of run-length encoding). The precode is itself
769 * constructed in canonical form, and its codeword lengths are represented
770 * literally in 20 4-bit fields that immediately precede the compressed codeword
771 * lengths of the larger code.
773 * Furthermore, the codeword lengths of the larger code are actually represented
774 * as deltas from the codeword lengths of the corresponding code in the previous
778 * Bitstream to which to write the compressed Huffman code.
780 * The codeword lengths, indexed by symbol, in the Huffman code.
782 * The codeword lengths, indexed by symbol, in the corresponding Huffman
783 * code in the previous block, or all zeroes if this is the first block.
785 * The number of symbols in the Huffman code.
788 lzx_write_compressed_code(struct lzx_output_bitstream *os,
789 const u8 lens[restrict],
790 const u8 prev_lens[restrict],
793 u32 precode_freqs[LZX_PRECODE_NUM_SYMBOLS];
794 u8 precode_lens[LZX_PRECODE_NUM_SYMBOLS];
795 u32 precode_codewords[LZX_PRECODE_NUM_SYMBOLS];
796 unsigned precode_items[num_lens];
797 unsigned num_precode_items;
798 unsigned precode_item;
799 unsigned precode_sym;
801 u8 saved = lens[num_lens];
802 *(u8 *)(lens + num_lens) = 0x80;
804 for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++)
805 precode_freqs[i] = 0;
807 /* Compute the "items" (RLE / literal tokens and extra bits) with which
808 * the codeword lengths in the larger code will be output. */
809 num_precode_items = lzx_compute_precode_items(lens,
814 /* Build the precode. */
815 STATIC_ASSERT(PRE_CODEWORD_LIMIT >= 5 &&
816 PRE_CODEWORD_LIMIT <= LZX_MAX_PRE_CODEWORD_LEN);
817 make_canonical_huffman_code(LZX_PRECODE_NUM_SYMBOLS,
819 precode_freqs, precode_lens,
822 /* Output the lengths of the codewords in the precode. */
823 for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++)
824 lzx_write_bits(os, precode_lens[i], LZX_PRECODE_ELEMENT_SIZE);
826 /* Output the encoded lengths of the codewords in the larger code. */
827 for (i = 0; i < num_precode_items; i++) {
828 precode_item = precode_items[i];
829 precode_sym = precode_item & 0x1F;
830 lzx_add_bits(os, precode_codewords[precode_sym],
831 precode_lens[precode_sym]);
832 if (precode_sym >= 17) {
833 if (precode_sym == 17) {
834 lzx_add_bits(os, precode_item >> 5, 4);
835 } else if (precode_sym == 18) {
836 lzx_add_bits(os, precode_item >> 5, 5);
838 lzx_add_bits(os, (precode_item >> 5) & 1, 1);
839 precode_sym = precode_item >> 6;
840 lzx_add_bits(os, precode_codewords[precode_sym],
841 precode_lens[precode_sym]);
844 STATIC_ASSERT(CAN_BUFFER(2 * PRE_CODEWORD_LIMIT + 1));
845 lzx_flush_bits(os, 2 * PRE_CODEWORD_LIMIT + 1);
848 *(u8 *)(lens + num_lens) = saved;
852 * Write all matches and literal bytes (which were precomputed) in an LZX
853 * compressed block to the output bitstream in the final compressed
857 * The output bitstream.
859 * The chosen type of the LZX compressed block (LZX_BLOCKTYPE_ALIGNED or
860 * LZX_BLOCKTYPE_VERBATIM).
862 * The uncompressed data of the block.
864 * The matches and literals to output, given as a series of sequences.
866 * The main, length, and aligned offset Huffman codes for the current
867 * LZX compressed block.
870 lzx_write_sequences(struct lzx_output_bitstream *os, int block_type,
871 const u8 *block_data, const struct lzx_sequence sequences[],
872 const struct lzx_codes *codes)
874 const struct lzx_sequence *seq = sequences;
875 u32 ones_if_aligned = 0 - (block_type == LZX_BLOCKTYPE_ALIGNED);
878 /* Output the next sequence. */
880 unsigned litrunlen = seq->litrunlen;
882 unsigned main_symbol;
883 unsigned adjusted_length;
885 unsigned offset_slot;
886 unsigned num_extra_bits;
889 /* Output the literal run of the sequence. */
891 if (litrunlen) { /* Is the literal run nonempty? */
893 /* Verify optimization is enabled on 64-bit */
894 STATIC_ASSERT(sizeof(machine_word_t) < 8 ||
895 CAN_BUFFER(4 * MAIN_CODEWORD_LIMIT));
897 if (CAN_BUFFER(4 * MAIN_CODEWORD_LIMIT)) {
899 /* 64-bit: write 4 literals at a time. */
900 while (litrunlen >= 4) {
901 unsigned lit0 = block_data[0];
902 unsigned lit1 = block_data[1];
903 unsigned lit2 = block_data[2];
904 unsigned lit3 = block_data[3];
905 lzx_add_bits(os, codes->codewords.main[lit0],
906 codes->lens.main[lit0]);
907 lzx_add_bits(os, codes->codewords.main[lit1],
908 codes->lens.main[lit1]);
909 lzx_add_bits(os, codes->codewords.main[lit2],
910 codes->lens.main[lit2]);
911 lzx_add_bits(os, codes->codewords.main[lit3],
912 codes->lens.main[lit3]);
913 lzx_flush_bits(os, 4 * MAIN_CODEWORD_LIMIT);
918 unsigned lit = *block_data++;
919 lzx_add_bits(os, codes->codewords.main[lit],
920 codes->lens.main[lit]);
922 unsigned lit = *block_data++;
923 lzx_add_bits(os, codes->codewords.main[lit],
924 codes->lens.main[lit]);
926 unsigned lit = *block_data++;
927 lzx_add_bits(os, codes->codewords.main[lit],
928 codes->lens.main[lit]);
929 lzx_flush_bits(os, 3 * MAIN_CODEWORD_LIMIT);
931 lzx_flush_bits(os, 2 * MAIN_CODEWORD_LIMIT);
934 lzx_flush_bits(os, 1 * MAIN_CODEWORD_LIMIT);
938 /* 32-bit: write 1 literal at a time. */
940 unsigned lit = *block_data++;
941 lzx_add_bits(os, codes->codewords.main[lit],
942 codes->lens.main[lit]);
943 lzx_flush_bits(os, MAIN_CODEWORD_LIMIT);
944 } while (--litrunlen);
948 /* Was this the last literal run? */
949 if (seq->adjusted_offset_and_match_hdr & 0x80000000)
952 /* Nope; output the match. */
954 match_hdr = seq->adjusted_offset_and_match_hdr & 0x1FF;
955 main_symbol = LZX_NUM_CHARS + match_hdr;
956 adjusted_length = seq->adjusted_length;
958 block_data += adjusted_length + LZX_MIN_MATCH_LEN;
960 offset_slot = match_hdr / LZX_NUM_LEN_HEADERS;
961 adjusted_offset = seq->adjusted_offset_and_match_hdr >> 9;
963 num_extra_bits = lzx_extra_offset_bits[offset_slot];
964 extra_bits = adjusted_offset - lzx_offset_slot_base[offset_slot];
966 #define MAX_MATCH_BITS (MAIN_CODEWORD_LIMIT + LENGTH_CODEWORD_LIMIT + \
967 14 + ALIGNED_CODEWORD_LIMIT)
969 /* Verify optimization is enabled on 64-bit */
970 STATIC_ASSERT(sizeof(machine_word_t) < 8 || CAN_BUFFER(MAX_MATCH_BITS));
972 /* Output the main symbol for the match. */
974 lzx_add_bits(os, codes->codewords.main[main_symbol],
975 codes->lens.main[main_symbol]);
976 if (!CAN_BUFFER(MAX_MATCH_BITS))
977 lzx_flush_bits(os, MAIN_CODEWORD_LIMIT);
979 /* If needed, output the length symbol for the match. */
981 if (adjusted_length >= LZX_NUM_PRIMARY_LENS) {
982 lzx_add_bits(os, codes->codewords.len[adjusted_length -
983 LZX_NUM_PRIMARY_LENS],
984 codes->lens.len[adjusted_length -
985 LZX_NUM_PRIMARY_LENS]);
986 if (!CAN_BUFFER(MAX_MATCH_BITS))
987 lzx_flush_bits(os, LENGTH_CODEWORD_LIMIT);
990 /* Output the extra offset bits for the match. In aligned
991 * offset blocks, the lowest 3 bits of the adjusted offset are
992 * Huffman-encoded using the aligned offset code, provided that
993 * there are at least extra 3 offset bits required. All other
994 * extra offset bits are output verbatim. */
996 if ((adjusted_offset & ones_if_aligned) >= 16) {
998 lzx_add_bits(os, extra_bits >> LZX_NUM_ALIGNED_OFFSET_BITS,
999 num_extra_bits - LZX_NUM_ALIGNED_OFFSET_BITS);
1000 if (!CAN_BUFFER(MAX_MATCH_BITS))
1001 lzx_flush_bits(os, 14);
1003 lzx_add_bits(os, codes->codewords.aligned[adjusted_offset &
1004 LZX_ALIGNED_OFFSET_BITMASK],
1005 codes->lens.aligned[adjusted_offset &
1006 LZX_ALIGNED_OFFSET_BITMASK]);
1007 if (!CAN_BUFFER(MAX_MATCH_BITS))
1008 lzx_flush_bits(os, ALIGNED_CODEWORD_LIMIT);
1010 STATIC_ASSERT(CAN_BUFFER(17));
1012 lzx_add_bits(os, extra_bits, num_extra_bits);
1013 if (!CAN_BUFFER(MAX_MATCH_BITS))
1014 lzx_flush_bits(os, 17);
1017 if (CAN_BUFFER(MAX_MATCH_BITS))
1018 lzx_flush_bits(os, MAX_MATCH_BITS);
1020 /* Advance to the next sequence. */
1026 lzx_write_compressed_block(const u8 *block_begin,
1029 unsigned window_order,
1030 unsigned num_main_syms,
1031 const struct lzx_sequence sequences[],
1032 const struct lzx_codes * codes,
1033 const struct lzx_lens * prev_lens,
1034 struct lzx_output_bitstream * os)
1036 /* The first three bits indicate the type of block and are one of the
1037 * LZX_BLOCKTYPE_* constants. */
1038 lzx_write_bits(os, block_type, 3);
1040 /* Output the block size.
1042 * The original LZX format seemed to always encode the block size in 3
1043 * bytes. However, the implementation in WIMGAPI, as used in WIM files,
1044 * uses the first bit to indicate whether the block is the default size
1045 * (32768) or a different size given explicitly by the next 16 bits.
1047 * By default, this compressor uses a window size of 32768 and therefore
1048 * follows the WIMGAPI behavior. However, this compressor also supports
1049 * window sizes greater than 32768 bytes, which do not appear to be
1050 * supported by WIMGAPI. In such cases, we retain the default size bit
1051 * to mean a size of 32768 bytes but output non-default block size in 24
1052 * bits rather than 16. The compatibility of this behavior is unknown
1053 * because WIMs created with chunk size greater than 32768 can seemingly
1054 * only be opened by wimlib anyway. */
1055 if (block_size == LZX_DEFAULT_BLOCK_SIZE) {
1056 lzx_write_bits(os, 1, 1);
1058 lzx_write_bits(os, 0, 1);
1060 if (window_order >= 16)
1061 lzx_write_bits(os, block_size >> 16, 8);
1063 lzx_write_bits(os, block_size & 0xFFFF, 16);
1066 /* If it's an aligned offset block, output the aligned offset code. */
1067 if (block_type == LZX_BLOCKTYPE_ALIGNED) {
1068 for (int i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
1069 lzx_write_bits(os, codes->lens.aligned[i],
1070 LZX_ALIGNEDCODE_ELEMENT_SIZE);
1074 /* Output the main code (two parts). */
1075 lzx_write_compressed_code(os, codes->lens.main,
1078 lzx_write_compressed_code(os, codes->lens.main + LZX_NUM_CHARS,
1079 prev_lens->main + LZX_NUM_CHARS,
1080 num_main_syms - LZX_NUM_CHARS);
1082 /* Output the length code. */
1083 lzx_write_compressed_code(os, codes->lens.len,
1085 LZX_LENCODE_NUM_SYMBOLS);
1087 /* Output the compressed matches and literals. */
1088 lzx_write_sequences(os, block_type, block_begin, sequences, codes);
1091 /* Given the frequencies of symbols in an LZX-compressed block and the
1092 * corresponding Huffman codes, return LZX_BLOCKTYPE_ALIGNED or
1093 * LZX_BLOCKTYPE_VERBATIM if an aligned offset or verbatim block, respectively,
1094 * will take fewer bits to output. */
1096 lzx_choose_verbatim_or_aligned(const struct lzx_freqs * freqs,
1097 const struct lzx_codes * codes)
1099 u32 aligned_cost = 0;
1100 u32 verbatim_cost = 0;
1102 /* A verbatim block requires 3 bits in each place that an aligned symbol
1103 * would be used in an aligned offset block. */
1104 for (unsigned i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
1105 verbatim_cost += LZX_NUM_ALIGNED_OFFSET_BITS * freqs->aligned[i];
1106 aligned_cost += codes->lens.aligned[i] * freqs->aligned[i];
1109 /* Account for output of the aligned offset code. */
1110 aligned_cost += LZX_ALIGNEDCODE_ELEMENT_SIZE * LZX_ALIGNEDCODE_NUM_SYMBOLS;
1112 if (aligned_cost < verbatim_cost)
1113 return LZX_BLOCKTYPE_ALIGNED;
1115 return LZX_BLOCKTYPE_VERBATIM;
1119 * Return the offset slot for the specified adjusted match offset, using the
1120 * compressor's acceleration tables to speed up the mapping.
1122 static inline unsigned
1123 lzx_comp_get_offset_slot(struct lzx_compressor *c, u32 adjusted_offset,
1126 if (is_16_bit || adjusted_offset < ARRAY_LEN(c->offset_slot_tab_1))
1127 return c->offset_slot_tab_1[adjusted_offset];
1128 return c->offset_slot_tab_2[adjusted_offset >> 14];
1132 * Finish an LZX block:
1134 * - build the Huffman codes
1135 * - decide whether to output the block as VERBATIM or ALIGNED
1136 * - output the block
1137 * - swap the indices of the current and previous Huffman codes
1140 lzx_finish_block(struct lzx_compressor *c, struct lzx_output_bitstream *os,
1141 const u8 *block_begin, u32 block_size, u32 seq_idx)
1145 lzx_make_huffman_codes(c);
1147 block_type = lzx_choose_verbatim_or_aligned(&c->freqs,
1148 &c->codes[c->codes_index]);
1149 lzx_write_compressed_block(block_begin,
1154 &c->chosen_sequences[seq_idx],
1155 &c->codes[c->codes_index],
1156 &c->codes[c->codes_index ^ 1].lens,
1158 c->codes_index ^= 1;
1161 /* Tally the Huffman symbol for a literal and increment the literal run length.
1164 lzx_record_literal(struct lzx_compressor *c, unsigned literal, u32 *litrunlen_p)
1166 c->freqs.main[literal]++;
1170 /* Tally the Huffman symbol for a match, save the match data and the length of
1171 * the preceding literal run in the next lzx_sequence, and update the recent
1174 lzx_record_match(struct lzx_compressor *c, unsigned length, u32 offset_data,
1175 u32 recent_offsets[LZX_NUM_RECENT_OFFSETS], bool is_16_bit,
1176 u32 *litrunlen_p, struct lzx_sequence **next_seq_p)
1178 u32 litrunlen = *litrunlen_p;
1179 struct lzx_sequence *next_seq = *next_seq_p;
1180 unsigned offset_slot;
1183 v = length - LZX_MIN_MATCH_LEN;
1185 /* Save the literal run length and adjusted length. */
1186 next_seq->litrunlen = litrunlen;
1187 next_seq->adjusted_length = v;
1189 /* Compute the length header and tally the length symbol if needed */
1190 if (v >= LZX_NUM_PRIMARY_LENS) {
1191 c->freqs.len[v - LZX_NUM_PRIMARY_LENS]++;
1192 v = LZX_NUM_PRIMARY_LENS;
1195 /* Compute the offset slot */
1196 offset_slot = lzx_comp_get_offset_slot(c, offset_data, is_16_bit);
1198 /* Compute the match header. */
1199 v += offset_slot * LZX_NUM_LEN_HEADERS;
1201 /* Save the adjusted offset and match header. */
1202 next_seq->adjusted_offset_and_match_hdr = (offset_data << 9) | v;
1204 /* Tally the main symbol. */
1205 c->freqs.main[LZX_NUM_CHARS + v]++;
1207 /* Update the recent offsets queue. */
1208 if (offset_data < LZX_NUM_RECENT_OFFSETS) {
1209 /* Repeat offset match */
1210 swap(recent_offsets[0], recent_offsets[offset_data]);
1212 /* Explicit offset match */
1214 /* Tally the aligned offset symbol if needed */
1215 if (offset_data >= 16)
1216 c->freqs.aligned[offset_data & LZX_ALIGNED_OFFSET_BITMASK]++;
1218 recent_offsets[2] = recent_offsets[1];
1219 recent_offsets[1] = recent_offsets[0];
1220 recent_offsets[0] = offset_data - LZX_OFFSET_ADJUSTMENT;
1223 /* Reset the literal run length and advance to the next sequence. */
1224 *next_seq_p = next_seq + 1;
1228 /* Finish the last lzx_sequence. The last lzx_sequence is just a literal run;
1229 * there is no match. This literal run may be empty. */
1231 lzx_finish_sequence(struct lzx_sequence *last_seq, u32 litrunlen)
1233 last_seq->litrunlen = litrunlen;
1235 /* Special value to mark last sequence */
1236 last_seq->adjusted_offset_and_match_hdr = 0x80000000;
1240 * Given the minimum-cost path computed through the item graph for the current
1241 * block, walk the path and count how many of each symbol in each Huffman-coded
1242 * alphabet would be required to output the items (matches and literals) along
1245 * Note that the path will be walked backwards (from the end of the block to the
1246 * beginning of the block), but this doesn't matter because this function only
1247 * computes frequencies.
1250 lzx_tally_item_list(struct lzx_compressor *c, u32 block_size, bool is_16_bit)
1252 u32 node_idx = block_size;
1257 unsigned offset_slot;
1259 /* Tally literals until either a match or the beginning of the
1260 * block is reached. */
1262 u32 item = c->optimum_nodes[node_idx].item;
1264 len = item & OPTIMUM_LEN_MASK;
1265 offset_data = item >> OPTIMUM_OFFSET_SHIFT;
1267 if (len != 0) /* Not a literal? */
1270 /* Tally the main symbol for the literal. */
1271 c->freqs.main[offset_data]++;
1273 if (--node_idx == 0) /* Beginning of block was reached? */
1279 /* Tally a match. */
1281 /* Tally the aligned offset symbol if needed. */
1282 if (offset_data >= 16)
1283 c->freqs.aligned[offset_data & LZX_ALIGNED_OFFSET_BITMASK]++;
1285 /* Tally the length symbol if needed. */
1286 v = len - LZX_MIN_MATCH_LEN;;
1287 if (v >= LZX_NUM_PRIMARY_LENS) {
1288 c->freqs.len[v - LZX_NUM_PRIMARY_LENS]++;
1289 v = LZX_NUM_PRIMARY_LENS;
1292 /* Tally the main symbol. */
1293 offset_slot = lzx_comp_get_offset_slot(c, offset_data, is_16_bit);
1294 v += offset_slot * LZX_NUM_LEN_HEADERS;
1295 c->freqs.main[LZX_NUM_CHARS + v]++;
1297 if (node_idx == 0) /* Beginning of block was reached? */
1303 * Like lzx_tally_item_list(), but this function also generates the list of
1304 * lzx_sequences for the minimum-cost path and writes it to c->chosen_sequences,
1305 * ready to be output to the bitstream after the Huffman codes are computed.
1306 * The lzx_sequences will be written to decreasing memory addresses as the path
1307 * is walked backwards, which means they will end up in the expected
1308 * first-to-last order. The return value is the index in c->chosen_sequences at
1309 * which the lzx_sequences begin.
1312 lzx_record_item_list(struct lzx_compressor *c, u32 block_size, bool is_16_bit)
1314 u32 node_idx = block_size;
1315 u32 seq_idx = ARRAY_LEN(c->chosen_sequences) - 1;
1318 /* Special value to mark last sequence */
1319 c->chosen_sequences[seq_idx].adjusted_offset_and_match_hdr = 0x80000000;
1321 lit_start_node = node_idx;
1326 unsigned offset_slot;
1328 /* Record literals until either a match or the beginning of the
1329 * block is reached. */
1331 u32 item = c->optimum_nodes[node_idx].item;
1333 len = item & OPTIMUM_LEN_MASK;
1334 offset_data = item >> OPTIMUM_OFFSET_SHIFT;
1336 if (len != 0) /* Not a literal? */
1339 /* Tally the main symbol for the literal. */
1340 c->freqs.main[offset_data]++;
1342 if (--node_idx == 0) /* Beginning of block was reached? */
1346 /* Save the literal run length for the next sequence (the
1347 * "previous sequence" when walking backwards). */
1348 c->chosen_sequences[seq_idx--].litrunlen = lit_start_node - node_idx;
1350 lit_start_node = node_idx;
1352 /* Record a match. */
1354 /* Tally the aligned offset symbol if needed. */
1355 if (offset_data >= 16)
1356 c->freqs.aligned[offset_data & LZX_ALIGNED_OFFSET_BITMASK]++;
1358 /* Save the adjusted length. */
1359 v = len - LZX_MIN_MATCH_LEN;
1360 c->chosen_sequences[seq_idx].adjusted_length = v;
1362 /* Tally the length symbol if needed. */
1363 if (v >= LZX_NUM_PRIMARY_LENS) {
1364 c->freqs.len[v - LZX_NUM_PRIMARY_LENS]++;
1365 v = LZX_NUM_PRIMARY_LENS;
1368 /* Tally the main symbol. */
1369 offset_slot = lzx_comp_get_offset_slot(c, offset_data, is_16_bit);
1370 v += offset_slot * LZX_NUM_LEN_HEADERS;
1371 c->freqs.main[LZX_NUM_CHARS + v]++;
1373 /* Save the adjusted offset and match header. */
1374 c->chosen_sequences[seq_idx].adjusted_offset_and_match_hdr =
1375 (offset_data << 9) | v;
1377 if (node_idx == 0) /* Beginning of block was reached? */
1382 /* Save the literal run length for the first sequence. */
1383 c->chosen_sequences[seq_idx].litrunlen = lit_start_node - node_idx;
1385 /* Return the index in c->chosen_sequences at which the lzx_sequences
1391 * Find an inexpensive path through the graph of possible match/literal choices
1392 * for the current block. The nodes of the graph are
1393 * c->optimum_nodes[0...block_size]. They correspond directly to the bytes in
1394 * the current block, plus one extra node for end-of-block. The edges of the
1395 * graph are matches and literals. The goal is to find the minimum cost path
1396 * from 'c->optimum_nodes[0]' to 'c->optimum_nodes[block_size]'.
1398 * The algorithm works forwards, starting at 'c->optimum_nodes[0]' and
1399 * proceeding forwards one node at a time. At each node, a selection of matches
1400 * (len >= 2), as well as the literal byte (len = 1), is considered. An item of
1401 * length 'len' provides a new path to reach the node 'len' bytes later. If
1402 * such a path is the lowest cost found so far to reach that later node, then
1403 * that later node is updated with the new path.
1405 * Note that although this algorithm is based on minimum cost path search, due
1406 * to various simplifying assumptions the result is not guaranteed to be the
1407 * true minimum cost, or "optimal", path over the graph of all valid LZX
1408 * representations of this block.
1410 * Also, note that because of the presence of the recent offsets queue (which is
1411 * a type of adaptive state), the algorithm cannot work backwards and compute
1412 * "cost to end" instead of "cost to beginning". Furthermore, the way the
1413 * algorithm handles this adaptive state in the "minimum cost" parse is actually
1414 * only an approximation. It's possible for the globally optimal, minimum cost
1415 * path to contain a prefix, ending at a position, where that path prefix is
1416 * *not* the minimum cost path to that position. This can happen if such a path
1417 * prefix results in a different adaptive state which results in lower costs
1418 * later. The algorithm does not solve this problem; it only considers the
1419 * lowest cost to reach each individual position.
1421 static inline struct lzx_lru_queue
1422 lzx_find_min_cost_path(struct lzx_compressor * const restrict c,
1423 const u8 * const restrict block_begin,
1424 const u32 block_size,
1425 const struct lzx_lru_queue initial_queue,
1428 struct lzx_optimum_node *cur_node = c->optimum_nodes;
1429 struct lzx_optimum_node * const end_node = &c->optimum_nodes[block_size];
1430 struct lz_match *cache_ptr = c->match_cache;
1431 const u8 *in_next = block_begin;
1432 const u8 * const block_end = block_begin + block_size;
1434 /* Instead of storing the match offset LRU queues in the
1435 * 'lzx_optimum_node' structures, we save memory (and cache lines) by
1436 * storing them in a smaller array. This works because the algorithm
1437 * only requires a limited history of the adaptive state. Once a given
1438 * state is more than LZX_MAX_MATCH_LEN bytes behind the current node,
1439 * it is no longer needed. */
1440 struct lzx_lru_queue queues[512];
1442 STATIC_ASSERT(ARRAY_LEN(queues) >= LZX_MAX_MATCH_LEN + 1);
1443 #define QUEUE(in) (queues[(uintptr_t)(in) % ARRAY_LEN(queues)])
1445 /* Initially, the cost to reach each node is "infinity". */
1446 memset(c->optimum_nodes, 0xFF,
1447 (block_size + 1) * sizeof(c->optimum_nodes[0]));
1449 QUEUE(block_begin) = initial_queue;
1451 /* The following loop runs 'block_size' iterations, one per node. */
1453 unsigned num_matches;
1458 * A selection of matches for the block was already saved in
1459 * memory so that we don't have to run the uncompressed data
1460 * through the matchfinder on every optimization pass. However,
1461 * we still search for repeat offset matches during each
1462 * optimization pass because we cannot predict the state of the
1463 * recent offsets queue. But as a heuristic, we don't bother
1464 * searching for repeat offset matches if the general-purpose
1465 * matchfinder failed to find any matches.
1467 * Note that a match of length n at some offset implies there is
1468 * also a match of length l for LZX_MIN_MATCH_LEN <= l <= n at
1469 * that same offset. In other words, we don't necessarily need
1470 * to use the full length of a match. The key heuristic that
1471 * saves a significicant amount of time is that for each
1472 * distinct length, we only consider the smallest offset for
1473 * which that length is available. This heuristic also applies
1474 * to repeat offsets, which we order specially: R0 < R1 < R2 <
1475 * any explicit offset. Of course, this heuristic may be
1476 * produce suboptimal results because offset slots in LZX are
1477 * subject to entropy encoding, but in practice this is a useful
1481 num_matches = cache_ptr->length;
1485 struct lz_match *end_matches = cache_ptr + num_matches;
1486 unsigned next_len = LZX_MIN_MATCH_LEN;
1487 unsigned max_len = min(block_end - in_next, LZX_MAX_MATCH_LEN);
1490 /* Consider R0 match */
1491 matchptr = in_next - lzx_lru_queue_R0(QUEUE(in_next));
1492 if (load_u16_unaligned(matchptr) != load_u16_unaligned(in_next))
1494 STATIC_ASSERT(LZX_MIN_MATCH_LEN == 2);
1496 u32 cost = cur_node->cost +
1497 c->costs.match_cost[0][
1498 next_len - LZX_MIN_MATCH_LEN];
1499 if (cost <= (cur_node + next_len)->cost) {
1500 (cur_node + next_len)->cost = cost;
1501 (cur_node + next_len)->item =
1502 (0 << OPTIMUM_OFFSET_SHIFT) | next_len;
1504 if (unlikely(++next_len > max_len)) {
1505 cache_ptr = end_matches;
1508 } while (in_next[next_len - 1] == matchptr[next_len - 1]);
1512 /* Consider R1 match */
1513 matchptr = in_next - lzx_lru_queue_R1(QUEUE(in_next));
1514 if (load_u16_unaligned(matchptr) != load_u16_unaligned(in_next))
1516 if (matchptr[next_len - 1] != in_next[next_len - 1])
1518 for (unsigned len = 2; len < next_len - 1; len++)
1519 if (matchptr[len] != in_next[len])
1522 u32 cost = cur_node->cost +
1523 c->costs.match_cost[1][
1524 next_len - LZX_MIN_MATCH_LEN];
1525 if (cost <= (cur_node + next_len)->cost) {
1526 (cur_node + next_len)->cost = cost;
1527 (cur_node + next_len)->item =
1528 (1 << OPTIMUM_OFFSET_SHIFT) | next_len;
1530 if (unlikely(++next_len > max_len)) {
1531 cache_ptr = end_matches;
1534 } while (in_next[next_len - 1] == matchptr[next_len - 1]);
1538 /* Consider R2 match */
1539 matchptr = in_next - lzx_lru_queue_R2(QUEUE(in_next));
1540 if (load_u16_unaligned(matchptr) != load_u16_unaligned(in_next))
1542 if (matchptr[next_len - 1] != in_next[next_len - 1])
1544 for (unsigned len = 2; len < next_len - 1; len++)
1545 if (matchptr[len] != in_next[len])
1548 u32 cost = cur_node->cost +
1549 c->costs.match_cost[2][
1550 next_len - LZX_MIN_MATCH_LEN];
1551 if (cost <= (cur_node + next_len)->cost) {
1552 (cur_node + next_len)->cost = cost;
1553 (cur_node + next_len)->item =
1554 (2 << OPTIMUM_OFFSET_SHIFT) | next_len;
1556 if (unlikely(++next_len > max_len)) {
1557 cache_ptr = end_matches;
1560 } while (in_next[next_len - 1] == matchptr[next_len - 1]);
1564 while (next_len > cache_ptr->length)
1565 if (++cache_ptr == end_matches)
1568 /* Consider explicit offset matches */
1570 u32 offset = cache_ptr->offset;
1571 u32 offset_data = offset + LZX_OFFSET_ADJUSTMENT;
1572 unsigned offset_slot = lzx_comp_get_offset_slot(c, offset_data,
1574 u32 base_cost = cur_node->cost;
1576 #if LZX_CONSIDER_ALIGNED_COSTS
1577 if (offset_data >= 16)
1578 base_cost += c->costs.aligned[offset_data &
1579 LZX_ALIGNED_OFFSET_BITMASK];
1583 u32 cost = base_cost +
1584 c->costs.match_cost[offset_slot][
1585 next_len - LZX_MIN_MATCH_LEN];
1586 if (cost < (cur_node + next_len)->cost) {
1587 (cur_node + next_len)->cost = cost;
1588 (cur_node + next_len)->item =
1589 (offset_data << OPTIMUM_OFFSET_SHIFT) | next_len;
1591 } while (++next_len <= cache_ptr->length);
1592 } while (++cache_ptr != end_matches);
1597 /* Consider coding a literal.
1599 * To avoid an extra branch, actually checking the preferability
1600 * of coding the literal is integrated into the queue update
1602 literal = *in_next++;
1603 cost = cur_node->cost + c->costs.main[literal];
1605 /* Advance to the next position. */
1608 /* The lowest-cost path to the current position is now known.
1609 * Finalize the recent offsets queue that results from taking
1610 * this lowest-cost path. */
1612 if (cost <= cur_node->cost) {
1613 /* Literal: queue remains unchanged. */
1614 cur_node->cost = cost;
1615 cur_node->item = (u32)literal << OPTIMUM_OFFSET_SHIFT;
1616 QUEUE(in_next) = QUEUE(in_next - 1);
1618 /* Match: queue update is needed. */
1619 unsigned len = cur_node->item & OPTIMUM_LEN_MASK;
1620 u32 offset_data = cur_node->item >> OPTIMUM_OFFSET_SHIFT;
1621 if (offset_data >= LZX_NUM_RECENT_OFFSETS) {
1622 /* Explicit offset match: insert offset at front */
1624 lzx_lru_queue_push(QUEUE(in_next - len),
1625 offset_data - LZX_OFFSET_ADJUSTMENT);
1627 /* Repeat offset match: swap offset to front */
1629 lzx_lru_queue_swap(QUEUE(in_next - len),
1633 } while (cur_node != end_node);
1635 /* Return the match offset queue at the end of the minimum cost path. */
1636 return QUEUE(block_end);
1639 /* Given the costs for the main and length codewords, compute 'match_costs'. */
1641 lzx_compute_match_costs(struct lzx_compressor *c)
1643 unsigned num_offset_slots = (c->num_main_syms - LZX_NUM_CHARS) /
1644 LZX_NUM_LEN_HEADERS;
1645 struct lzx_costs *costs = &c->costs;
1647 for (unsigned offset_slot = 0; offset_slot < num_offset_slots; offset_slot++) {
1649 u32 extra_cost = (u32)lzx_extra_offset_bits[offset_slot] * LZX_BIT_COST;
1650 unsigned main_symbol = LZX_NUM_CHARS + (offset_slot *
1651 LZX_NUM_LEN_HEADERS);
1654 #if LZX_CONSIDER_ALIGNED_COSTS
1655 if (offset_slot >= 8)
1656 extra_cost -= LZX_NUM_ALIGNED_OFFSET_BITS * LZX_BIT_COST;
1659 for (i = 0; i < LZX_NUM_PRIMARY_LENS; i++)
1660 costs->match_cost[offset_slot][i] =
1661 costs->main[main_symbol++] + extra_cost;
1663 extra_cost += costs->main[main_symbol];
1665 for (; i < LZX_NUM_LENS; i++)
1666 costs->match_cost[offset_slot][i] =
1667 costs->len[i - LZX_NUM_PRIMARY_LENS] + extra_cost;
1671 /* Set default LZX Huffman symbol costs to bootstrap the iterative optimization
1674 lzx_set_default_costs(struct lzx_compressor *c, const u8 *block, u32 block_size)
1677 bool have_byte[256];
1678 unsigned num_used_bytes;
1680 /* The costs below are hard coded to use a scaling factor of 16. */
1681 STATIC_ASSERT(LZX_BIT_COST == 16);
1686 * - Use smaller initial costs for literal symbols when the input buffer
1687 * contains fewer distinct bytes.
1689 * - Assume that match symbols are more costly than literal symbols.
1691 * - Assume that length symbols for shorter lengths are less costly than
1692 * length symbols for longer lengths.
1695 for (i = 0; i < 256; i++)
1696 have_byte[i] = false;
1698 for (i = 0; i < block_size; i++)
1699 have_byte[block[i]] = true;
1702 for (i = 0; i < 256; i++)
1703 num_used_bytes += have_byte[i];
1705 for (i = 0; i < 256; i++)
1706 c->costs.main[i] = 140 - (256 - num_used_bytes) / 4;
1708 for (; i < c->num_main_syms; i++)
1709 c->costs.main[i] = 170;
1711 for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++)
1712 c->costs.len[i] = 103 + (i / 4);
1714 #if LZX_CONSIDER_ALIGNED_COSTS
1715 for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
1716 c->costs.aligned[i] = LZX_NUM_ALIGNED_OFFSET_BITS * LZX_BIT_COST;
1719 lzx_compute_match_costs(c);
1722 /* Update the current cost model to reflect the computed Huffman codes. */
1724 lzx_update_costs(struct lzx_compressor *c)
1727 const struct lzx_lens *lens = &c->codes[c->codes_index].lens;
1729 for (i = 0; i < c->num_main_syms; i++) {
1730 c->costs.main[i] = (lens->main[i] ? lens->main[i] :
1731 MAIN_CODEWORD_LIMIT) * LZX_BIT_COST;
1734 for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++) {
1735 c->costs.len[i] = (lens->len[i] ? lens->len[i] :
1736 LENGTH_CODEWORD_LIMIT) * LZX_BIT_COST;
1739 #if LZX_CONSIDER_ALIGNED_COSTS
1740 for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
1741 c->costs.aligned[i] = (lens->aligned[i] ? lens->aligned[i] :
1742 ALIGNED_CODEWORD_LIMIT) * LZX_BIT_COST;
1746 lzx_compute_match_costs(c);
1749 static inline struct lzx_lru_queue
1750 lzx_optimize_and_write_block(struct lzx_compressor * const restrict c,
1751 struct lzx_output_bitstream * const restrict os,
1752 const u8 * const restrict block_begin,
1753 const u32 block_size,
1754 const struct lzx_lru_queue initial_queue,
1757 unsigned num_passes_remaining = c->num_optim_passes;
1758 struct lzx_lru_queue new_queue;
1761 /* The first optimization pass uses a default cost model. Each
1762 * additional optimization pass uses a cost model derived from the
1763 * Huffman code computed in the previous pass. */
1765 lzx_set_default_costs(c, block_begin, block_size);
1766 lzx_reset_symbol_frequencies(c);
1768 new_queue = lzx_find_min_cost_path(c, block_begin, block_size,
1769 initial_queue, is_16_bit);
1770 if (num_passes_remaining > 1) {
1771 lzx_tally_item_list(c, block_size, is_16_bit);
1772 lzx_make_huffman_codes(c);
1773 lzx_update_costs(c);
1774 lzx_reset_symbol_frequencies(c);
1776 } while (--num_passes_remaining);
1778 seq_idx = lzx_record_item_list(c, block_size, is_16_bit);
1779 lzx_finish_block(c, os, block_begin, block_size, seq_idx);
1784 * This is the "near-optimal" LZX compressor.
1786 * For each block, it performs a relatively thorough graph search to find an
1787 * inexpensive (in terms of compressed size) way to output that block.
1789 * Note: there are actually many things this algorithm leaves on the table in
1790 * terms of compression ratio. So although it may be "near-optimal", it is
1791 * certainly not "optimal". The goal is not to produce the optimal compression
1792 * ratio, which for LZX is probably impossible within any practical amount of
1793 * time, but rather to produce a compression ratio significantly better than a
1794 * simpler "greedy" or "lazy" parse while still being relatively fast.
1797 lzx_compress_near_optimal(struct lzx_compressor *c,
1798 struct lzx_output_bitstream *os,
1801 const u8 * const in_begin = c->in_buffer;
1802 const u8 * in_next = in_begin;
1803 const u8 * const in_end = in_begin + c->in_nbytes;
1804 u32 max_len = LZX_MAX_MATCH_LEN;
1805 u32 nice_len = min(c->nice_match_length, max_len);
1806 u32 next_hashes[2] = {};
1807 struct lzx_lru_queue queue;
1809 CALL_BT_MF(is_16_bit, c, bt_matchfinder_init);
1810 lzx_lru_queue_init(&queue);
1813 /* Starting a new block */
1814 const u8 * const in_block_begin = in_next;
1815 const u8 * const in_block_end =
1816 in_next + min(LZX_DIV_BLOCK_SIZE, in_end - in_next);
1818 /* Run the block through the matchfinder and cache the matches. */
1819 struct lz_match *cache_ptr = c->match_cache;
1821 struct lz_match *lz_matchptr;
1824 /* If approaching the end of the input buffer, adjust
1825 * 'max_len' and 'nice_len' accordingly. */
1826 if (unlikely(max_len > in_end - in_next)) {
1827 max_len = in_end - in_next;
1828 nice_len = min(max_len, nice_len);
1829 if (unlikely(max_len <
1830 BT_MATCHFINDER_REQUIRED_NBYTES))
1833 cache_ptr->length = 0;
1839 /* Check for matches. */
1840 lz_matchptr = CALL_BT_MF(is_16_bit, c,
1841 bt_matchfinder_get_matches,
1846 c->max_search_depth,
1851 cache_ptr->length = lz_matchptr - (cache_ptr + 1);
1852 cache_ptr = lz_matchptr;
1855 * If there was a very long match found, then don't
1856 * cache any matches for the bytes covered by that
1857 * match. This avoids degenerate behavior when
1858 * compressing highly redundant data, where the number
1859 * of matches can be very large.
1861 * This heuristic doesn't actually hurt the compression
1862 * ratio very much. If there's a long match, then the
1863 * data must be highly compressible, so it doesn't
1864 * matter as much what we do.
1866 if (best_len >= nice_len) {
1869 if (unlikely(max_len > in_end - in_next)) {
1870 max_len = in_end - in_next;
1871 nice_len = min(max_len, nice_len);
1872 if (unlikely(max_len <
1873 BT_MATCHFINDER_REQUIRED_NBYTES))
1876 cache_ptr->length = 0;
1881 CALL_BT_MF(is_16_bit, c,
1882 bt_matchfinder_skip_position,
1887 c->max_search_depth,
1890 cache_ptr->length = 0;
1892 } while (--best_len);
1894 } while (in_next < in_block_end &&
1895 likely(cache_ptr < &c->match_cache[LZX_CACHE_LENGTH]));
1897 /* We've finished running the block through the matchfinder.
1898 * Now choose a match/literal sequence and write the block. */
1900 queue = lzx_optimize_and_write_block(c, os, in_block_begin,
1901 in_next - in_block_begin,
1903 } while (in_next != in_end);
1907 lzx_compress_near_optimal_16(struct lzx_compressor *c,
1908 struct lzx_output_bitstream *os)
1910 lzx_compress_near_optimal(c, os, true);
1914 lzx_compress_near_optimal_32(struct lzx_compressor *c,
1915 struct lzx_output_bitstream *os)
1917 lzx_compress_near_optimal(c, os, false);
1921 * Given a pointer to the current byte sequence and the current list of recent
1922 * match offsets, find the longest repeat offset match.
1924 * If no match of at least 2 bytes is found, then return 0.
1926 * If a match of at least 2 bytes is found, then return its length and set
1927 * *rep_max_idx_ret to the index of its offset in @queue.
1930 lzx_find_longest_repeat_offset_match(const u8 * const in_next,
1931 const u32 bytes_remaining,
1932 const u32 recent_offsets[LZX_NUM_RECENT_OFFSETS],
1933 unsigned *rep_max_idx_ret)
1935 STATIC_ASSERT(LZX_NUM_RECENT_OFFSETS == 3);
1937 const unsigned max_len = min(bytes_remaining, LZX_MAX_MATCH_LEN);
1938 const u16 next_2_bytes = load_u16_unaligned(in_next);
1940 unsigned rep_max_len;
1941 unsigned rep_max_idx;
1944 matchptr = in_next - recent_offsets[0];
1945 if (load_u16_unaligned(matchptr) == next_2_bytes)
1946 rep_max_len = lz_extend(in_next, matchptr, 2, max_len);
1951 matchptr = in_next - recent_offsets[1];
1952 if (load_u16_unaligned(matchptr) == next_2_bytes) {
1953 rep_len = lz_extend(in_next, matchptr, 2, max_len);
1954 if (rep_len > rep_max_len) {
1955 rep_max_len = rep_len;
1960 matchptr = in_next - recent_offsets[2];
1961 if (load_u16_unaligned(matchptr) == next_2_bytes) {
1962 rep_len = lz_extend(in_next, matchptr, 2, max_len);
1963 if (rep_len > rep_max_len) {
1964 rep_max_len = rep_len;
1969 *rep_max_idx_ret = rep_max_idx;
1973 /* Fast heuristic scoring for lazy parsing: how "good" is this match? */
1974 static inline unsigned
1975 lzx_explicit_offset_match_score(unsigned len, u32 adjusted_offset)
1977 unsigned score = len;
1979 if (adjusted_offset < 4096)
1982 if (adjusted_offset < 256)
1988 static inline unsigned
1989 lzx_repeat_offset_match_score(unsigned rep_len, unsigned rep_idx)
1994 /* This is the "lazy" LZX compressor. */
1996 lzx_compress_lazy(struct lzx_compressor *c, struct lzx_output_bitstream *os,
1999 const u8 * const in_begin = c->in_buffer;
2000 const u8 * in_next = in_begin;
2001 const u8 * const in_end = in_begin + c->in_nbytes;
2002 unsigned max_len = LZX_MAX_MATCH_LEN;
2003 unsigned nice_len = min(c->nice_match_length, max_len);
2004 STATIC_ASSERT(LZX_NUM_RECENT_OFFSETS == 3);
2005 u32 recent_offsets[3] = {1, 1, 1};
2006 u32 next_hashes[2] = {};
2008 CALL_HC_MF(is_16_bit, c, hc_matchfinder_init);
2011 /* Starting a new block */
2013 const u8 * const in_block_begin = in_next;
2014 const u8 * const in_block_end =
2015 in_next + min(LZX_DIV_BLOCK_SIZE, in_end - in_next);
2016 struct lzx_sequence *next_seq = c->chosen_sequences;
2019 u32 cur_offset_data;
2023 u32 next_offset_data;
2024 unsigned next_score;
2025 unsigned rep_max_len;
2026 unsigned rep_max_idx;
2031 lzx_reset_symbol_frequencies(c);
2034 if (unlikely(max_len > in_end - in_next)) {
2035 max_len = in_end - in_next;
2036 nice_len = min(max_len, nice_len);
2039 /* Find the longest match at the current position. */
2041 cur_len = CALL_HC_MF(is_16_bit, c,
2042 hc_matchfinder_longest_match,
2048 c->max_search_depth,
2053 cur_offset >= 8192 - LZX_OFFSET_ADJUSTMENT &&
2054 cur_offset != recent_offsets[0] &&
2055 cur_offset != recent_offsets[1] &&
2056 cur_offset != recent_offsets[2]))
2058 /* There was no match found, or the only match found
2059 * was a distant length 3 match. Output a literal. */
2060 lzx_record_literal(c, *in_next++, &litrunlen);
2064 if (cur_offset == recent_offsets[0]) {
2066 cur_offset_data = 0;
2067 skip_len = cur_len - 1;
2068 goto choose_cur_match;
2071 cur_offset_data = cur_offset + LZX_OFFSET_ADJUSTMENT;
2072 cur_score = lzx_explicit_offset_match_score(cur_len, cur_offset_data);
2074 /* Consider a repeat offset match */
2075 rep_max_len = lzx_find_longest_repeat_offset_match(in_next,
2081 if (rep_max_len >= 3 &&
2082 (rep_score = lzx_repeat_offset_match_score(rep_max_len,
2083 rep_max_idx)) >= cur_score)
2085 cur_len = rep_max_len;
2086 cur_offset_data = rep_max_idx;
2087 skip_len = rep_max_len - 1;
2088 goto choose_cur_match;
2093 /* We have a match at the current position. */
2095 /* If we have a very long match, choose it immediately. */
2096 if (cur_len >= nice_len) {
2097 skip_len = cur_len - 1;
2098 goto choose_cur_match;
2101 /* See if there's a better match at the next position. */
2103 if (unlikely(max_len > in_end - in_next)) {
2104 max_len = in_end - in_next;
2105 nice_len = min(max_len, nice_len);
2108 next_len = CALL_HC_MF(is_16_bit, c,
2109 hc_matchfinder_longest_match,
2115 c->max_search_depth / 2,
2119 if (next_len <= cur_len - 2) {
2121 skip_len = cur_len - 2;
2122 goto choose_cur_match;
2125 next_offset_data = next_offset + LZX_OFFSET_ADJUSTMENT;
2126 next_score = lzx_explicit_offset_match_score(next_len, next_offset_data);
2128 rep_max_len = lzx_find_longest_repeat_offset_match(in_next,
2134 if (rep_max_len >= 3 &&
2135 (rep_score = lzx_repeat_offset_match_score(rep_max_len,
2136 rep_max_idx)) >= next_score)
2139 if (rep_score > cur_score) {
2140 /* The next match is better, and it's a
2141 * repeat offset match. */
2142 lzx_record_literal(c, *(in_next - 2),
2144 cur_len = rep_max_len;
2145 cur_offset_data = rep_max_idx;
2146 skip_len = cur_len - 1;
2147 goto choose_cur_match;
2150 if (next_score > cur_score) {
2151 /* The next match is better, and it's an
2152 * explicit offset match. */
2153 lzx_record_literal(c, *(in_next - 2),
2156 cur_offset_data = next_offset_data;
2157 cur_score = next_score;
2158 goto have_cur_match;
2162 /* The original match was better. */
2163 skip_len = cur_len - 2;
2166 lzx_record_match(c, cur_len, cur_offset_data,
2167 recent_offsets, is_16_bit,
2168 &litrunlen, &next_seq);
2169 in_next = CALL_HC_MF(is_16_bit, c,
2170 hc_matchfinder_skip_positions,
2176 } while (in_next < in_block_end);
2178 lzx_finish_sequence(next_seq, litrunlen);
2180 lzx_finish_block(c, os, in_block_begin, in_next - in_block_begin, 0);
2182 } while (in_next != in_end);
2186 lzx_compress_lazy_16(struct lzx_compressor *c, struct lzx_output_bitstream *os)
2188 lzx_compress_lazy(c, os, true);
2192 lzx_compress_lazy_32(struct lzx_compressor *c, struct lzx_output_bitstream *os)
2194 lzx_compress_lazy(c, os, false);
2197 /* Generate the acceleration tables for offset slots. */
2199 lzx_init_offset_slot_tabs(struct lzx_compressor *c)
2201 u32 adjusted_offset = 0;
2205 for (; adjusted_offset < ARRAY_LEN(c->offset_slot_tab_1);
2208 if (adjusted_offset >= lzx_offset_slot_base[slot + 1])
2210 c->offset_slot_tab_1[adjusted_offset] = slot;
2213 /* slots [30, 49] */
2214 for (; adjusted_offset < LZX_MAX_WINDOW_SIZE;
2215 adjusted_offset += (u32)1 << 14)
2217 if (adjusted_offset >= lzx_offset_slot_base[slot + 1])
2219 c->offset_slot_tab_2[adjusted_offset >> 14] = slot;
2224 lzx_get_compressor_size(size_t max_bufsize, unsigned compression_level)
2226 if (compression_level <= LZX_MAX_FAST_LEVEL) {
2227 if (lzx_is_16_bit(max_bufsize))
2228 return offsetof(struct lzx_compressor, hc_mf_16) +
2229 hc_matchfinder_size_16(max_bufsize);
2231 return offsetof(struct lzx_compressor, hc_mf_32) +
2232 hc_matchfinder_size_32(max_bufsize);
2234 if (lzx_is_16_bit(max_bufsize))
2235 return offsetof(struct lzx_compressor, bt_mf_16) +
2236 bt_matchfinder_size_16(max_bufsize);
2238 return offsetof(struct lzx_compressor, bt_mf_32) +
2239 bt_matchfinder_size_32(max_bufsize);
2244 lzx_get_needed_memory(size_t max_bufsize, unsigned compression_level,
2249 if (max_bufsize > LZX_MAX_WINDOW_SIZE)
2252 size += lzx_get_compressor_size(max_bufsize, compression_level);
2254 size += max_bufsize; /* in_buffer */
2259 lzx_create_compressor(size_t max_bufsize, unsigned compression_level,
2260 bool destructive, void **c_ret)
2262 unsigned window_order;
2263 struct lzx_compressor *c;
2265 window_order = lzx_get_window_order(max_bufsize);
2266 if (window_order == 0)
2267 return WIMLIB_ERR_INVALID_PARAM;
2269 c = MALLOC(lzx_get_compressor_size(max_bufsize, compression_level));
2273 c->destructive = destructive;
2275 c->num_main_syms = lzx_get_num_main_syms(window_order);
2276 c->window_order = window_order;
2278 if (!c->destructive) {
2279 c->in_buffer = MALLOC(max_bufsize);
2284 if (compression_level <= LZX_MAX_FAST_LEVEL) {
2286 /* Fast compression: Use lazy parsing. */
2288 if (lzx_is_16_bit(max_bufsize))
2289 c->impl = lzx_compress_lazy_16;
2291 c->impl = lzx_compress_lazy_32;
2292 c->max_search_depth = (60 * compression_level) / 20;
2293 c->nice_match_length = (80 * compression_level) / 20;
2295 /* lzx_compress_lazy() needs max_search_depth >= 2 because it
2296 * halves the max_search_depth when attempting a lazy match, and
2297 * max_search_depth cannot be 0. */
2298 if (c->max_search_depth < 2)
2299 c->max_search_depth = 2;
2302 /* Normal / high compression: Use near-optimal parsing. */
2304 if (lzx_is_16_bit(max_bufsize))
2305 c->impl = lzx_compress_near_optimal_16;
2307 c->impl = lzx_compress_near_optimal_32;
2309 /* Scale nice_match_length and max_search_depth with the
2310 * compression level. */
2311 c->max_search_depth = (24 * compression_level) / 50;
2312 c->nice_match_length = (48 * compression_level) / 50;
2314 /* Set a number of optimization passes appropriate for the
2315 * compression level. */
2317 c->num_optim_passes = 1;
2319 if (compression_level >= 45)
2320 c->num_optim_passes++;
2322 /* Use more optimization passes for higher compression levels.
2323 * But the more passes there are, the less they help --- so
2324 * don't add them linearly. */
2325 if (compression_level >= 70) {
2326 c->num_optim_passes++;
2327 if (compression_level >= 100)
2328 c->num_optim_passes++;
2329 if (compression_level >= 150)
2330 c->num_optim_passes++;
2331 if (compression_level >= 200)
2332 c->num_optim_passes++;
2333 if (compression_level >= 300)
2334 c->num_optim_passes++;
2338 /* max_search_depth == 0 is invalid. */
2339 if (c->max_search_depth < 1)
2340 c->max_search_depth = 1;
2342 if (c->nice_match_length > LZX_MAX_MATCH_LEN)
2343 c->nice_match_length = LZX_MAX_MATCH_LEN;
2345 lzx_init_offset_slot_tabs(c);
2352 return WIMLIB_ERR_NOMEM;
2356 lzx_compress(const void *restrict in, size_t in_nbytes,
2357 void *restrict out, size_t out_nbytes_avail, void *restrict _c)
2359 struct lzx_compressor *c = _c;
2360 struct lzx_output_bitstream os;
2363 /* Don't bother trying to compress very small inputs. */
2364 if (in_nbytes < 100)
2367 /* Copy the input data into the internal buffer and preprocess it. */
2369 c->in_buffer = (void *)in;
2371 memcpy(c->in_buffer, in, in_nbytes);
2372 c->in_nbytes = in_nbytes;
2373 lzx_preprocess(c->in_buffer, in_nbytes);
2375 /* Initially, the previous Huffman codeword lengths are all zeroes. */
2377 memset(&c->codes[1].lens, 0, sizeof(struct lzx_lens));
2379 /* Initialize the output bitstream. */
2380 lzx_init_output(&os, out, out_nbytes_avail);
2382 /* Call the compression level-specific compress() function. */
2385 /* Flush the output bitstream and return the compressed size or 0. */
2386 result = lzx_flush_output(&os);
2387 if (!result && c->destructive)
2388 lzx_postprocess(c->in_buffer, c->in_nbytes);
2393 lzx_free_compressor(void *_c)
2395 struct lzx_compressor *c = _c;
2397 if (!c->destructive)
2402 const struct compressor_ops lzx_compressor_ops = {
2403 .get_needed_memory = lzx_get_needed_memory,
2404 .create_compressor = lzx_create_compressor,
2405 .compress = lzx_compress,
2406 .free_compressor = lzx_free_compressor,