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 /* Pop a match offset off the front (most recently used) end of the queue. */
336 lzx_lru_queue_pop(struct lzx_lru_queue *queue_p)
338 u32 offset = queue_p->R & LZX_QUEUE64_OFFSET_MASK;
339 queue_p->R >>= LZX_QUEUE64_OFFSET_SHIFT;
343 /* Swap a match offset to the front of the queue. */
344 static inline struct lzx_lru_queue
345 lzx_lru_queue_swap(struct lzx_lru_queue queue, unsigned idx)
351 return (struct lzx_lru_queue) {
352 .R = (lzx_lru_queue_R1(queue) << LZX_QUEUE64_R0_SHIFT) |
353 (lzx_lru_queue_R0(queue) << LZX_QUEUE64_R1_SHIFT) |
354 (queue.R & LZX_QUEUE64_R2_MASK),
357 return (struct lzx_lru_queue) {
358 .R = (lzx_lru_queue_R2(queue) << LZX_QUEUE64_R0_SHIFT) |
359 (queue.R & LZX_QUEUE64_R1_MASK) |
360 (lzx_lru_queue_R0(queue) << LZX_QUEUE64_R2_SHIFT),
364 /* The main LZX compressor structure */
365 struct lzx_compressor {
367 /* The "nice" match length: if a match of this length is found, then
368 * choose it immediately without further consideration. */
369 unsigned nice_match_length;
371 /* The maximum search depth: consider at most this many potential
372 * matches at each position. */
373 unsigned max_search_depth;
375 /* The log base 2 of the LZX window size for LZ match offset encoding
376 * purposes. This will be >= LZX_MIN_WINDOW_ORDER and <=
377 * LZX_MAX_WINDOW_ORDER. */
378 unsigned window_order;
380 /* The number of symbols in the main alphabet. This depends on
381 * @window_order, since @window_order determines the maximum possible
383 unsigned num_main_syms;
385 /* Number of optimization passes per block */
386 unsigned num_optim_passes;
388 /* The preprocessed buffer of data being compressed */
391 /* The number of bytes of data to be compressed, which is the number of
392 * bytes of data in @in_buffer that are actually valid. */
395 /* Pointer to the compress() implementation chosen at allocation time */
396 void (*impl)(struct lzx_compressor *, struct lzx_output_bitstream *);
398 /* If true, the compressor need not preserve the input buffer if it
399 * compresses the data successfully. */
402 /* The Huffman symbol frequency counters for the current block. */
403 struct lzx_freqs freqs;
405 /* The Huffman codes for the current and previous blocks. The one with
406 * index 'codes_index' is for the current block, and the other one is
407 * for the previous block. */
408 struct lzx_codes codes[2];
409 unsigned codes_index;
411 /* The matches and literals that the parser has chosen for the current
412 * block. The required length of this array is limited by the maximum
413 * number of matches that can ever be chosen for a single block. */
414 struct lzx_sequence chosen_sequences[DIV_ROUND_UP(LZX_DIV_BLOCK_SIZE, LZX_MIN_MATCH_LEN)];
416 /* Tables for mapping adjusted offsets to offset slots */
418 /* offset slots [0, 29] */
419 u8 offset_slot_tab_1[32768];
421 /* offset slots [30, 49] */
422 u8 offset_slot_tab_2[128];
425 /* Data for greedy or lazy parsing */
427 /* Hash chains matchfinder (MUST BE LAST!!!) */
429 struct hc_matchfinder_16 hc_mf_16;
430 struct hc_matchfinder_32 hc_mf_32;
434 /* Data for near-optimal parsing */
437 * The graph nodes for the current block.
439 * We need at least 'LZX_DIV_BLOCK_SIZE +
440 * LZX_MAX_MATCH_LEN - 1' nodes because that is the
441 * maximum block size that may be used. Add 1 because
442 * we need a node to represent end-of-block.
444 * It is possible that nodes past end-of-block are
445 * accessed during match consideration, but this can
446 * only occur if the block was truncated at
447 * LZX_DIV_BLOCK_SIZE. So the same bound still applies.
448 * Note that since nodes past the end of the block will
449 * never actually have an effect on the items that are
450 * chosen for the block, it makes no difference what
451 * their costs are initialized to (if anything).
453 struct lzx_optimum_node optimum_nodes[LZX_DIV_BLOCK_SIZE +
454 LZX_MAX_MATCH_LEN - 1 + 1];
456 /* The cost model for the current block */
457 struct lzx_costs costs;
460 * Cached matches for the current block. This array
461 * contains the matches that were found at each position
462 * in the block. Specifically, for each position, there
463 * is a special 'struct lz_match' whose 'length' field
464 * contains the number of matches that were found at
465 * that position; this is followed by the matches
466 * themselves, if any, sorted by strictly increasing
469 * Note: in rare cases, there will be a very high number
470 * of matches in the block and this array will overflow.
471 * If this happens, we force the end of the current
472 * block. LZX_CACHE_LENGTH is the length at which we
473 * actually check for overflow. The extra slots beyond
474 * this are enough to absorb the worst case overflow,
475 * which occurs if starting at
476 * &match_cache[LZX_CACHE_LENGTH - 1], we write the
477 * match count header, then write
478 * LZX_MAX_MATCHES_PER_POS matches, then skip searching
479 * for matches at 'LZX_MAX_MATCH_LEN - 1' positions and
480 * write the match count header for each.
482 struct lz_match match_cache[LZX_CACHE_LENGTH +
483 LZX_MAX_MATCHES_PER_POS +
484 LZX_MAX_MATCH_LEN - 1];
486 /* Binary trees matchfinder (MUST BE LAST!!!) */
488 struct bt_matchfinder_16 bt_mf_16;
489 struct bt_matchfinder_32 bt_mf_32;
496 * Will a matchfinder using 16-bit positions be sufficient for compressing
497 * buffers of up to the specified size? The limit could be 65536 bytes, but we
498 * also want to optimize out the use of offset_slot_tab_2 in the 16-bit case.
499 * This requires that the limit be no more than the length of offset_slot_tab_1
503 lzx_is_16_bit(size_t max_bufsize)
505 STATIC_ASSERT(ARRAY_LEN(((struct lzx_compressor *)0)->offset_slot_tab_1) == 32768);
506 return max_bufsize <= 32768;
510 * The following macros call either the 16-bit or the 32-bit version of a
511 * matchfinder function based on the value of 'is_16_bit', which will be known
512 * at compilation time.
515 #define CALL_HC_MF(is_16_bit, c, funcname, ...) \
516 ((is_16_bit) ? CONCAT(funcname, _16)(&(c)->hc_mf_16, ##__VA_ARGS__) : \
517 CONCAT(funcname, _32)(&(c)->hc_mf_32, ##__VA_ARGS__));
519 #define CALL_BT_MF(is_16_bit, c, funcname, ...) \
520 ((is_16_bit) ? CONCAT(funcname, _16)(&(c)->bt_mf_16, ##__VA_ARGS__) : \
521 CONCAT(funcname, _32)(&(c)->bt_mf_32, ##__VA_ARGS__));
524 * Structure to keep track of the current state of sending bits to the
525 * compressed output buffer.
527 * The LZX bitstream is encoded as a sequence of 16-bit coding units.
529 struct lzx_output_bitstream {
531 /* Bits that haven't yet been written to the output buffer. */
532 machine_word_t bitbuf;
534 /* Number of bits currently held in @bitbuf. */
537 /* Pointer to the start of the output buffer. */
540 /* Pointer to the position in the output buffer at which the next coding
541 * unit should be written. */
544 /* Pointer just past the end of the output buffer, rounded down to a
545 * 2-byte boundary. */
549 /* Can the specified number of bits always be added to 'bitbuf' after any
550 * pending 16-bit coding units have been flushed? */
551 #define CAN_BUFFER(n) ((n) <= (8 * sizeof(machine_word_t)) - 16)
554 * Initialize the output bitstream.
557 * The output bitstream structure to initialize.
559 * The buffer being written to.
561 * Size of @buffer, in bytes.
564 lzx_init_output(struct lzx_output_bitstream *os, void *buffer, size_t size)
569 os->next = os->start;
570 os->end = os->start + (size & ~1);
573 /* Add some bits to the bitbuffer variable of the output bitstream. The caller
574 * must make sure there is enough room. */
576 lzx_add_bits(struct lzx_output_bitstream *os, u32 bits, unsigned num_bits)
578 os->bitbuf = (os->bitbuf << num_bits) | bits;
579 os->bitcount += num_bits;
582 /* Flush bits from the bitbuffer variable to the output buffer. 'max_num_bits'
583 * specifies the maximum number of bits that may have been added since the last
586 lzx_flush_bits(struct lzx_output_bitstream *os, unsigned max_num_bits)
588 if (os->end - os->next < 6)
590 put_unaligned_u16_le(os->bitbuf >> (os->bitcount - 16), os->next + 0);
591 if (max_num_bits > 16)
592 put_unaligned_u16_le(os->bitbuf >> (os->bitcount - 32), os->next + 2);
593 if (max_num_bits > 32)
594 put_unaligned_u16_le(os->bitbuf >> (os->bitcount - 48), os->next + 4);
595 os->next += (os->bitcount >> 4) << 1;
599 /* Add at most 16 bits to the bitbuffer and flush it. */
601 lzx_write_bits(struct lzx_output_bitstream *os, u32 bits, unsigned num_bits)
603 lzx_add_bits(os, bits, num_bits);
604 lzx_flush_bits(os, 16);
608 * Flush the last coding unit to the output buffer if needed. Return the total
609 * number of bytes written to the output buffer, or 0 if an overflow occurred.
612 lzx_flush_output(struct lzx_output_bitstream *os)
614 if (os->end - os->next < 6)
617 if (os->bitcount != 0) {
618 put_unaligned_u16_le(os->bitbuf << (16 - os->bitcount), os->next);
622 return os->next - os->start;
625 /* Build the main, length, and aligned offset Huffman codes used in LZX.
627 * This takes as input the frequency tables for each code and produces as output
628 * a set of tables that map symbols to codewords and codeword lengths. */
630 lzx_make_huffman_codes(struct lzx_compressor *c)
632 const struct lzx_freqs *freqs = &c->freqs;
633 struct lzx_codes *codes = &c->codes[c->codes_index];
635 STATIC_ASSERT(MAIN_CODEWORD_LIMIT >= 9 &&
636 MAIN_CODEWORD_LIMIT <= LZX_MAX_MAIN_CODEWORD_LEN);
637 STATIC_ASSERT(LENGTH_CODEWORD_LIMIT >= 9 &&
638 LENGTH_CODEWORD_LIMIT <= LZX_MAX_LEN_CODEWORD_LEN);
639 STATIC_ASSERT(ALIGNED_CODEWORD_LIMIT >= LZX_NUM_ALIGNED_OFFSET_BITS &&
640 ALIGNED_CODEWORD_LIMIT <= LZX_MAX_ALIGNED_CODEWORD_LEN);
642 make_canonical_huffman_code(c->num_main_syms,
646 codes->codewords.main);
648 make_canonical_huffman_code(LZX_LENCODE_NUM_SYMBOLS,
649 LENGTH_CODEWORD_LIMIT,
652 codes->codewords.len);
654 make_canonical_huffman_code(LZX_ALIGNEDCODE_NUM_SYMBOLS,
655 ALIGNED_CODEWORD_LIMIT,
658 codes->codewords.aligned);
661 /* Reset the symbol frequencies for the LZX Huffman codes. */
663 lzx_reset_symbol_frequencies(struct lzx_compressor *c)
665 memset(&c->freqs, 0, sizeof(c->freqs));
669 lzx_compute_precode_items(const u8 lens[restrict],
670 const u8 prev_lens[restrict],
671 u32 precode_freqs[restrict],
672 unsigned precode_items[restrict])
681 itemptr = precode_items;
684 while (!((len = lens[run_start]) & 0x80)) {
686 /* len = the length being repeated */
688 /* Find the next run of codeword lengths. */
690 run_end = run_start + 1;
692 /* Fast case for a single length. */
693 if (likely(len != lens[run_end])) {
694 delta = prev_lens[run_start] - len;
697 precode_freqs[delta]++;
703 /* Extend the run. */
706 } while (len == lens[run_end]);
711 /* Symbol 18: RLE 20 to 51 zeroes at a time. */
712 while ((run_end - run_start) >= 20) {
713 extra_bits = min((run_end - run_start) - 20, 0x1f);
715 *itemptr++ = 18 | (extra_bits << 5);
716 run_start += 20 + extra_bits;
719 /* Symbol 17: RLE 4 to 19 zeroes at a time. */
720 if ((run_end - run_start) >= 4) {
721 extra_bits = min((run_end - run_start) - 4, 0xf);
723 *itemptr++ = 17 | (extra_bits << 5);
724 run_start += 4 + extra_bits;
728 /* A run of nonzero lengths. */
730 /* Symbol 19: RLE 4 to 5 of any length at a time. */
731 while ((run_end - run_start) >= 4) {
732 extra_bits = (run_end - run_start) > 4;
733 delta = prev_lens[run_start] - len;
737 precode_freqs[delta]++;
738 *itemptr++ = 19 | (extra_bits << 5) | (delta << 6);
739 run_start += 4 + extra_bits;
743 /* Output any remaining lengths without RLE. */
744 while (run_start != run_end) {
745 delta = prev_lens[run_start] - len;
748 precode_freqs[delta]++;
754 return itemptr - precode_items;
758 * Output a Huffman code in the compressed form used in LZX.
760 * The Huffman code is represented in the output as a logical series of codeword
761 * lengths from which the Huffman code, which must be in canonical form, can be
764 * The codeword lengths are themselves compressed using a separate Huffman code,
765 * the "precode", which contains a symbol for each possible codeword length in
766 * the larger code as well as several special symbols to represent repeated
767 * codeword lengths (a form of run-length encoding). The precode is itself
768 * constructed in canonical form, and its codeword lengths are represented
769 * literally in 20 4-bit fields that immediately precede the compressed codeword
770 * lengths of the larger code.
772 * Furthermore, the codeword lengths of the larger code are actually represented
773 * as deltas from the codeword lengths of the corresponding code in the previous
777 * Bitstream to which to write the compressed Huffman code.
779 * The codeword lengths, indexed by symbol, in the Huffman code.
781 * The codeword lengths, indexed by symbol, in the corresponding Huffman
782 * code in the previous block, or all zeroes if this is the first block.
784 * The number of symbols in the Huffman code.
787 lzx_write_compressed_code(struct lzx_output_bitstream *os,
788 const u8 lens[restrict],
789 const u8 prev_lens[restrict],
792 u32 precode_freqs[LZX_PRECODE_NUM_SYMBOLS];
793 u8 precode_lens[LZX_PRECODE_NUM_SYMBOLS];
794 u32 precode_codewords[LZX_PRECODE_NUM_SYMBOLS];
795 unsigned precode_items[num_lens];
796 unsigned num_precode_items;
797 unsigned precode_item;
798 unsigned precode_sym;
800 u8 saved = lens[num_lens];
801 *(u8 *)(lens + num_lens) = 0x80;
803 for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++)
804 precode_freqs[i] = 0;
806 /* Compute the "items" (RLE / literal tokens and extra bits) with which
807 * the codeword lengths in the larger code will be output. */
808 num_precode_items = lzx_compute_precode_items(lens,
813 /* Build the precode. */
814 STATIC_ASSERT(PRE_CODEWORD_LIMIT >= 5 &&
815 PRE_CODEWORD_LIMIT <= LZX_MAX_PRE_CODEWORD_LEN);
816 make_canonical_huffman_code(LZX_PRECODE_NUM_SYMBOLS,
818 precode_freqs, precode_lens,
821 /* Output the lengths of the codewords in the precode. */
822 for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++)
823 lzx_write_bits(os, precode_lens[i], LZX_PRECODE_ELEMENT_SIZE);
825 /* Output the encoded lengths of the codewords in the larger code. */
826 for (i = 0; i < num_precode_items; i++) {
827 precode_item = precode_items[i];
828 precode_sym = precode_item & 0x1F;
829 lzx_add_bits(os, precode_codewords[precode_sym],
830 precode_lens[precode_sym]);
831 if (precode_sym >= 17) {
832 if (precode_sym == 17) {
833 lzx_add_bits(os, precode_item >> 5, 4);
834 } else if (precode_sym == 18) {
835 lzx_add_bits(os, precode_item >> 5, 5);
837 lzx_add_bits(os, (precode_item >> 5) & 1, 1);
838 precode_sym = precode_item >> 6;
839 lzx_add_bits(os, precode_codewords[precode_sym],
840 precode_lens[precode_sym]);
843 STATIC_ASSERT(CAN_BUFFER(2 * PRE_CODEWORD_LIMIT + 1));
844 lzx_flush_bits(os, 2 * PRE_CODEWORD_LIMIT + 1);
847 *(u8 *)(lens + num_lens) = saved;
851 * Write all matches and literal bytes (which were precomputed) in an LZX
852 * compressed block to the output bitstream in the final compressed
856 * The output bitstream.
858 * The chosen type of the LZX compressed block (LZX_BLOCKTYPE_ALIGNED or
859 * LZX_BLOCKTYPE_VERBATIM).
861 * The uncompressed data of the block.
863 * The matches and literals to output, given as a series of sequences.
865 * The main, length, and aligned offset Huffman codes for the current
866 * LZX compressed block.
869 lzx_write_sequences(struct lzx_output_bitstream *os, int block_type,
870 const u8 *block_data, const struct lzx_sequence sequences[],
871 const struct lzx_codes *codes)
873 const struct lzx_sequence *seq = sequences;
874 u32 ones_if_aligned = 0 - (block_type == LZX_BLOCKTYPE_ALIGNED);
877 /* Output the next sequence. */
879 unsigned litrunlen = seq->litrunlen;
881 unsigned main_symbol;
882 unsigned adjusted_length;
884 unsigned offset_slot;
885 unsigned num_extra_bits;
888 /* Output the literal run of the sequence. */
890 if (litrunlen) { /* Is the literal run nonempty? */
892 /* Verify optimization is enabled on 64-bit */
893 STATIC_ASSERT(sizeof(machine_word_t) < 8 ||
894 CAN_BUFFER(4 * MAIN_CODEWORD_LIMIT));
896 if (CAN_BUFFER(4 * MAIN_CODEWORD_LIMIT)) {
898 /* 64-bit: write 4 literals at a time. */
899 while (litrunlen >= 4) {
900 unsigned lit0 = block_data[0];
901 unsigned lit1 = block_data[1];
902 unsigned lit2 = block_data[2];
903 unsigned lit3 = block_data[3];
904 lzx_add_bits(os, codes->codewords.main[lit0], codes->lens.main[lit0]);
905 lzx_add_bits(os, codes->codewords.main[lit1], codes->lens.main[lit1]);
906 lzx_add_bits(os, codes->codewords.main[lit2], codes->lens.main[lit2]);
907 lzx_add_bits(os, codes->codewords.main[lit3], codes->lens.main[lit3]);
908 lzx_flush_bits(os, 4 * MAIN_CODEWORD_LIMIT);
913 unsigned lit = *block_data++;
914 lzx_add_bits(os, codes->codewords.main[lit], codes->lens.main[lit]);
916 unsigned lit = *block_data++;
917 lzx_add_bits(os, codes->codewords.main[lit], codes->lens.main[lit]);
919 unsigned lit = *block_data++;
920 lzx_add_bits(os, codes->codewords.main[lit], codes->lens.main[lit]);
921 lzx_flush_bits(os, 3 * MAIN_CODEWORD_LIMIT);
923 lzx_flush_bits(os, 2 * MAIN_CODEWORD_LIMIT);
926 lzx_flush_bits(os, 1 * MAIN_CODEWORD_LIMIT);
930 /* 32-bit: write 1 literal at a time. */
932 unsigned lit = *block_data++;
933 lzx_add_bits(os, codes->codewords.main[lit], codes->lens.main[lit]);
934 lzx_flush_bits(os, MAIN_CODEWORD_LIMIT);
935 } while (--litrunlen);
939 /* Was this the last literal run? */
940 if (seq->adjusted_offset_and_match_hdr & 0x80000000)
943 /* Nope; output the match. */
945 match_hdr = seq->adjusted_offset_and_match_hdr & 0x1FF;
946 main_symbol = LZX_NUM_CHARS + match_hdr;
947 adjusted_length = seq->adjusted_length;
949 block_data += adjusted_length + LZX_MIN_MATCH_LEN;
951 offset_slot = match_hdr / LZX_NUM_LEN_HEADERS;
952 adjusted_offset = seq->adjusted_offset_and_match_hdr >> 9;
954 num_extra_bits = lzx_extra_offset_bits[offset_slot];
955 extra_bits = adjusted_offset - lzx_offset_slot_base[offset_slot];
957 #define MAX_MATCH_BITS (MAIN_CODEWORD_LIMIT + LENGTH_CODEWORD_LIMIT + \
958 14 + ALIGNED_CODEWORD_LIMIT)
960 /* Verify optimization is enabled on 64-bit */
961 STATIC_ASSERT(sizeof(machine_word_t) < 8 || CAN_BUFFER(MAX_MATCH_BITS));
963 /* Output the main symbol for the match. */
965 lzx_add_bits(os, codes->codewords.main[main_symbol],
966 codes->lens.main[main_symbol]);
967 if (!CAN_BUFFER(MAX_MATCH_BITS))
968 lzx_flush_bits(os, MAIN_CODEWORD_LIMIT);
970 /* If needed, output the length symbol for the match. */
972 if (adjusted_length >= LZX_NUM_PRIMARY_LENS) {
973 lzx_add_bits(os, codes->codewords.len[adjusted_length - LZX_NUM_PRIMARY_LENS],
974 codes->lens.len[adjusted_length - LZX_NUM_PRIMARY_LENS]);
975 if (!CAN_BUFFER(MAX_MATCH_BITS))
976 lzx_flush_bits(os, LENGTH_CODEWORD_LIMIT);
979 /* Output the extra offset bits for the match. In aligned
980 * offset blocks, the lowest 3 bits of the adjusted offset are
981 * Huffman-encoded using the aligned offset code, provided that
982 * there are at least extra 3 offset bits required. All other
983 * extra offset bits are output verbatim. */
985 if ((adjusted_offset & ones_if_aligned) >= 16) {
987 lzx_add_bits(os, extra_bits >> LZX_NUM_ALIGNED_OFFSET_BITS,
988 num_extra_bits - LZX_NUM_ALIGNED_OFFSET_BITS);
989 if (!CAN_BUFFER(MAX_MATCH_BITS))
990 lzx_flush_bits(os, 14);
992 lzx_add_bits(os, codes->codewords.aligned[adjusted_offset & LZX_ALIGNED_OFFSET_BITMASK],
993 codes->lens.aligned[adjusted_offset & LZX_ALIGNED_OFFSET_BITMASK]);
994 if (!CAN_BUFFER(MAX_MATCH_BITS))
995 lzx_flush_bits(os, ALIGNED_CODEWORD_LIMIT);
997 lzx_add_bits(os, extra_bits, num_extra_bits);
998 if (!CAN_BUFFER(MAX_MATCH_BITS))
999 lzx_flush_bits(os, 17);
1002 if (CAN_BUFFER(MAX_MATCH_BITS))
1003 lzx_flush_bits(os, MAX_MATCH_BITS);
1005 /* Advance to the next sequence. */
1011 lzx_write_compressed_block(const u8 *block_begin,
1014 unsigned window_order,
1015 unsigned num_main_syms,
1016 const struct lzx_sequence sequences[],
1017 const struct lzx_codes * codes,
1018 const struct lzx_lens * prev_lens,
1019 struct lzx_output_bitstream * os)
1021 /* The first three bits indicate the type of block and are one of the
1022 * LZX_BLOCKTYPE_* constants. */
1023 lzx_write_bits(os, block_type, 3);
1025 /* Output the block size.
1027 * The original LZX format seemed to always encode the block size in 3
1028 * bytes. However, the implementation in WIMGAPI, as used in WIM files,
1029 * uses the first bit to indicate whether the block is the default size
1030 * (32768) or a different size given explicitly by the next 16 bits.
1032 * By default, this compressor uses a window size of 32768 and therefore
1033 * follows the WIMGAPI behavior. However, this compressor also supports
1034 * window sizes greater than 32768 bytes, which do not appear to be
1035 * supported by WIMGAPI. In such cases, we retain the default size bit
1036 * to mean a size of 32768 bytes but output non-default block size in 24
1037 * bits rather than 16. The compatibility of this behavior is unknown
1038 * because WIMs created with chunk size greater than 32768 can seemingly
1039 * only be opened by wimlib anyway. */
1040 if (block_size == LZX_DEFAULT_BLOCK_SIZE) {
1041 lzx_write_bits(os, 1, 1);
1043 lzx_write_bits(os, 0, 1);
1045 if (window_order >= 16)
1046 lzx_write_bits(os, block_size >> 16, 8);
1048 lzx_write_bits(os, block_size & 0xFFFF, 16);
1051 /* If it's an aligned offset block, output the aligned offset code. */
1052 if (block_type == LZX_BLOCKTYPE_ALIGNED) {
1053 for (int i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
1054 lzx_write_bits(os, codes->lens.aligned[i],
1055 LZX_ALIGNEDCODE_ELEMENT_SIZE);
1059 /* Output the main code (two parts). */
1060 lzx_write_compressed_code(os, codes->lens.main,
1063 lzx_write_compressed_code(os, codes->lens.main + LZX_NUM_CHARS,
1064 prev_lens->main + LZX_NUM_CHARS,
1065 num_main_syms - LZX_NUM_CHARS);
1067 /* Output the length code. */
1068 lzx_write_compressed_code(os, codes->lens.len,
1070 LZX_LENCODE_NUM_SYMBOLS);
1072 /* Output the compressed matches and literals. */
1073 lzx_write_sequences(os, block_type, block_begin, sequences, codes);
1076 /* Given the frequencies of symbols in an LZX-compressed block and the
1077 * corresponding Huffman codes, return LZX_BLOCKTYPE_ALIGNED or
1078 * LZX_BLOCKTYPE_VERBATIM if an aligned offset or verbatim block, respectively,
1079 * will take fewer bits to output. */
1081 lzx_choose_verbatim_or_aligned(const struct lzx_freqs * freqs,
1082 const struct lzx_codes * codes)
1084 u32 aligned_cost = 0;
1085 u32 verbatim_cost = 0;
1087 /* A verbatim block requires 3 bits in each place that an aligned symbol
1088 * would be used in an aligned offset block. */
1089 for (unsigned i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
1090 verbatim_cost += LZX_NUM_ALIGNED_OFFSET_BITS * freqs->aligned[i];
1091 aligned_cost += codes->lens.aligned[i] * freqs->aligned[i];
1094 /* Account for output of the aligned offset code. */
1095 aligned_cost += LZX_ALIGNEDCODE_ELEMENT_SIZE * LZX_ALIGNEDCODE_NUM_SYMBOLS;
1097 if (aligned_cost < verbatim_cost)
1098 return LZX_BLOCKTYPE_ALIGNED;
1100 return LZX_BLOCKTYPE_VERBATIM;
1104 * Return the offset slot for the specified adjusted match offset, using the
1105 * compressor's acceleration tables to speed up the mapping.
1107 static inline unsigned
1108 lzx_comp_get_offset_slot(struct lzx_compressor *c, u32 adjusted_offset,
1111 if (is_16_bit || adjusted_offset < ARRAY_LEN(c->offset_slot_tab_1))
1112 return c->offset_slot_tab_1[adjusted_offset];
1113 return c->offset_slot_tab_2[adjusted_offset >> 14];
1117 * Finish an LZX block:
1119 * - build the Huffman codes
1120 * - decide whether to output the block as VERBATIM or ALIGNED
1121 * - output the block
1122 * - swap the indices of the current and previous Huffman codes
1125 lzx_finish_block(struct lzx_compressor *c, struct lzx_output_bitstream *os,
1126 const u8 *block_begin, u32 block_size, u32 seq_idx)
1130 lzx_make_huffman_codes(c);
1132 block_type = lzx_choose_verbatim_or_aligned(&c->freqs,
1133 &c->codes[c->codes_index]);
1134 lzx_write_compressed_block(block_begin,
1139 &c->chosen_sequences[seq_idx],
1140 &c->codes[c->codes_index],
1141 &c->codes[c->codes_index ^ 1].lens,
1143 c->codes_index ^= 1;
1146 /* Tally the Huffman symbol for a literal and increment the literal run length.
1149 lzx_record_literal(struct lzx_compressor *c, unsigned literal, u32 *litrunlen_p)
1151 c->freqs.main[literal]++;
1155 /* Tally the Huffman symbol for a match, save the match data and the length of
1156 * the preceding literal run in the next lzx_sequence, and update the recent
1159 lzx_record_match(struct lzx_compressor *c, unsigned length, u32 offset_data,
1160 u32 recent_offsets[LZX_NUM_RECENT_OFFSETS], bool is_16_bit,
1161 u32 *litrunlen_p, struct lzx_sequence **next_seq_p)
1163 u32 litrunlen = *litrunlen_p;
1164 struct lzx_sequence *next_seq = *next_seq_p;
1165 unsigned offset_slot;
1168 v = length - LZX_MIN_MATCH_LEN;
1170 /* Save the literal run length and adjusted length. */
1171 next_seq->litrunlen = litrunlen;
1172 next_seq->adjusted_length = v;
1174 /* Compute the length header and tally the length symbol if needed */
1175 if (v >= LZX_NUM_PRIMARY_LENS) {
1176 c->freqs.len[v - LZX_NUM_PRIMARY_LENS]++;
1177 v = LZX_NUM_PRIMARY_LENS;
1180 /* Compute the offset slot */
1181 offset_slot = lzx_comp_get_offset_slot(c, offset_data, is_16_bit);
1183 /* Compute the match header. */
1184 v += offset_slot * LZX_NUM_LEN_HEADERS;
1186 /* Save the adjusted offset and match header. */
1187 next_seq->adjusted_offset_and_match_hdr = (offset_data << 9) | v;
1189 /* Tally the main symbol. */
1190 c->freqs.main[LZX_NUM_CHARS + v]++;
1192 /* Update the recent offsets queue. */
1193 if (offset_data < LZX_NUM_RECENT_OFFSETS) {
1194 /* Repeat offset match */
1195 swap(recent_offsets[0], recent_offsets[offset_data]);
1197 /* Explicit offset match */
1199 /* Tally the aligned offset symbol if needed */
1200 if (offset_data >= 16)
1201 c->freqs.aligned[offset_data & LZX_ALIGNED_OFFSET_BITMASK]++;
1203 recent_offsets[2] = recent_offsets[1];
1204 recent_offsets[1] = recent_offsets[0];
1205 recent_offsets[0] = offset_data - LZX_OFFSET_ADJUSTMENT;
1208 /* Reset the literal run length and advance to the next sequence. */
1209 *next_seq_p = next_seq + 1;
1213 /* Finish the last lzx_sequence. The last lzx_sequence is just a literal run;
1214 * there is no match. This literal run may be empty. */
1216 lzx_finish_sequence(struct lzx_sequence *last_seq, u32 litrunlen)
1218 last_seq->litrunlen = litrunlen;
1220 /* Special value to mark last sequence */
1221 last_seq->adjusted_offset_and_match_hdr = 0x80000000;
1225 * Given the minimum-cost path computed through the item graph for the current
1226 * block, walk the path and count how many of each symbol in each Huffman-coded
1227 * alphabet would be required to output the items (matches and literals) along
1230 * Note that the path will be walked backwards (from the end of the block to the
1231 * beginning of the block), but this doesn't matter because this function only
1232 * computes frequencies.
1235 lzx_tally_item_list(struct lzx_compressor *c, u32 block_size, bool is_16_bit)
1237 u32 node_idx = block_size;
1242 unsigned offset_slot;
1244 /* Tally literals until either a match or the beginning of the
1245 * block is reached. */
1247 u32 item = c->optimum_nodes[node_idx].item;
1249 len = item & OPTIMUM_LEN_MASK;
1250 offset_data = item >> OPTIMUM_OFFSET_SHIFT;
1252 if (len != 0) /* Not a literal? */
1255 /* Tally the main symbol for the literal. */
1256 c->freqs.main[offset_data]++;
1258 if (--node_idx == 0) /* Beginning of block was reached? */
1264 /* Tally a match. */
1266 /* Tally the aligned offset symbol if needed. */
1267 if (offset_data >= 16)
1268 c->freqs.aligned[offset_data & LZX_ALIGNED_OFFSET_BITMASK]++;
1270 /* Tally the length symbol if needed. */
1271 v = len - LZX_MIN_MATCH_LEN;;
1272 if (v >= LZX_NUM_PRIMARY_LENS) {
1273 c->freqs.len[v - LZX_NUM_PRIMARY_LENS]++;
1274 v = LZX_NUM_PRIMARY_LENS;
1277 /* Tally the main symbol. */
1278 offset_slot = lzx_comp_get_offset_slot(c, offset_data, is_16_bit);
1279 v += offset_slot * LZX_NUM_LEN_HEADERS;
1280 c->freqs.main[LZX_NUM_CHARS + v]++;
1282 if (node_idx == 0) /* Beginning of block was reached? */
1288 * Like lzx_tally_item_list(), but this function also generates the list of
1289 * lzx_sequences for the minimum-cost path and writes it to c->chosen_sequences,
1290 * ready to be output to the bitstream after the Huffman codes are computed.
1291 * The lzx_sequences will be written to decreasing memory addresses as the path
1292 * is walked backwards, which means they will end up in the expected
1293 * first-to-last order. The return value is the index in c->chosen_sequences at
1294 * which the lzx_sequences begin.
1297 lzx_record_item_list(struct lzx_compressor *c, u32 block_size, bool is_16_bit)
1299 u32 node_idx = block_size;
1300 u32 seq_idx = ARRAY_LEN(c->chosen_sequences) - 1;
1303 /* Special value to mark last sequence */
1304 c->chosen_sequences[seq_idx].adjusted_offset_and_match_hdr = 0x80000000;
1306 lit_start_node = node_idx;
1311 unsigned offset_slot;
1313 /* Record literals until either a match or the beginning of the
1314 * block is reached. */
1316 u32 item = c->optimum_nodes[node_idx].item;
1318 len = item & OPTIMUM_LEN_MASK;
1319 offset_data = item >> OPTIMUM_OFFSET_SHIFT;
1321 if (len != 0) /* Not a literal? */
1324 /* Tally the main symbol for the literal. */
1325 c->freqs.main[offset_data]++;
1327 if (--node_idx == 0) /* Beginning of block was reached? */
1331 /* Save the literal run length for the next sequence (the
1332 * "previous sequence" when walking backwards). */
1333 c->chosen_sequences[seq_idx--].litrunlen = lit_start_node - node_idx;
1335 lit_start_node = node_idx;
1337 /* Record a match. */
1339 /* Tally the aligned offset symbol if needed. */
1340 if (offset_data >= 16)
1341 c->freqs.aligned[offset_data & LZX_ALIGNED_OFFSET_BITMASK]++;
1343 /* Save the adjusted length. */
1344 v = len - LZX_MIN_MATCH_LEN;
1345 c->chosen_sequences[seq_idx].adjusted_length = v;
1347 /* Tally the length symbol if needed. */
1348 if (v >= LZX_NUM_PRIMARY_LENS) {
1349 c->freqs.len[v - LZX_NUM_PRIMARY_LENS]++;
1350 v = LZX_NUM_PRIMARY_LENS;
1353 /* Tally the main symbol. */
1354 offset_slot = lzx_comp_get_offset_slot(c, offset_data, is_16_bit);
1355 v += offset_slot * LZX_NUM_LEN_HEADERS;
1356 c->freqs.main[LZX_NUM_CHARS + v]++;
1358 /* Save the adjusted offset and match header. */
1359 c->chosen_sequences[seq_idx].adjusted_offset_and_match_hdr =
1360 (offset_data << 9) | v;
1362 if (node_idx == 0) /* Beginning of block was reached? */
1367 /* Save the literal run length for the first sequence. */
1368 c->chosen_sequences[seq_idx].litrunlen = lit_start_node - node_idx;
1370 /* Return the index in c->chosen_sequences at which the lzx_sequences
1376 * Find an inexpensive path through the graph of possible match/literal choices
1377 * for the current block. The nodes of the graph are
1378 * c->optimum_nodes[0...block_size]. They correspond directly to the bytes in
1379 * the current block, plus one extra node for end-of-block. The edges of the
1380 * graph are matches and literals. The goal is to find the minimum cost path
1381 * from 'c->optimum_nodes[0]' to 'c->optimum_nodes[block_size]'.
1383 * The algorithm works forwards, starting at 'c->optimum_nodes[0]' and
1384 * proceeding forwards one node at a time. At each node, a selection of matches
1385 * (len >= 2), as well as the literal byte (len = 1), is considered. An item of
1386 * length 'len' provides a new path to reach the node 'len' bytes later. If
1387 * such a path is the lowest cost found so far to reach that later node, then
1388 * that later node is updated with the new path.
1390 * Note that although this algorithm is based on minimum cost path search, due
1391 * to various simplifying assumptions the result is not guaranteed to be the
1392 * true minimum cost, or "optimal", path over the graph of all valid LZX
1393 * representations of this block.
1395 * Also, note that because of the presence of the recent offsets queue (which is
1396 * a type of adaptive state), the algorithm cannot work backwards and compute
1397 * "cost to end" instead of "cost to beginning". Furthermore, the way the
1398 * algorithm handles this adaptive state in the "minimum cost" parse is actually
1399 * only an approximation. It's possible for the globally optimal, minimum cost
1400 * path to contain a prefix, ending at a position, where that path prefix is
1401 * *not* the minimum cost path to that position. This can happen if such a path
1402 * prefix results in a different adaptive state which results in lower costs
1403 * later. The algorithm does not solve this problem; it only considers the
1404 * lowest cost to reach each individual position.
1406 static inline struct lzx_lru_queue
1407 lzx_find_min_cost_path(struct lzx_compressor * const restrict c,
1408 const u8 * const restrict block_begin,
1409 const u32 block_size,
1410 const struct lzx_lru_queue initial_queue,
1413 struct lzx_optimum_node *cur_node = c->optimum_nodes;
1414 struct lzx_optimum_node * const end_node = &c->optimum_nodes[block_size];
1415 struct lz_match *cache_ptr = c->match_cache;
1416 const u8 *in_next = block_begin;
1417 const u8 * const block_end = block_begin + block_size;
1419 /* Instead of storing the match offset LRU queues in the
1420 * 'lzx_optimum_node' structures, we save memory (and cache lines) by
1421 * storing them in a smaller array. This works because the algorithm
1422 * only requires a limited history of the adaptive state. Once a given
1423 * state is more than LZX_MAX_MATCH_LEN bytes behind the current node,
1424 * it is no longer needed. */
1425 struct lzx_lru_queue queues[512];
1427 STATIC_ASSERT(ARRAY_LEN(queues) >= LZX_MAX_MATCH_LEN + 1);
1428 #define QUEUE(in) (queues[(uintptr_t)(in) % ARRAY_LEN(queues)])
1430 /* Initially, the cost to reach each node is "infinity". */
1431 memset(c->optimum_nodes, 0xFF,
1432 (block_size + 1) * sizeof(c->optimum_nodes[0]));
1434 QUEUE(block_begin) = initial_queue;
1436 /* The following loop runs 'block_size' iterations, one per node. */
1438 unsigned num_matches;
1443 * A selection of matches for the block was already saved in
1444 * memory so that we don't have to run the uncompressed data
1445 * through the matchfinder on every optimization pass. However,
1446 * we still search for repeat offset matches during each
1447 * optimization pass because we cannot predict the state of the
1448 * recent offsets queue. But as a heuristic, we don't bother
1449 * searching for repeat offset matches if the general-purpose
1450 * matchfinder failed to find any matches.
1452 * Note that a match of length n at some offset implies there is
1453 * also a match of length l for LZX_MIN_MATCH_LEN <= l <= n at
1454 * that same offset. In other words, we don't necessarily need
1455 * to use the full length of a match. The key heuristic that
1456 * saves a significicant amount of time is that for each
1457 * distinct length, we only consider the smallest offset for
1458 * which that length is available. This heuristic also applies
1459 * to repeat offsets, which we order specially: R0 < R1 < R2 <
1460 * any explicit offset. Of course, this heuristic may be
1461 * produce suboptimal results because offset slots in LZX are
1462 * subject to entropy encoding, but in practice this is a useful
1466 num_matches = cache_ptr->length;
1470 struct lz_match *end_matches = cache_ptr + num_matches;
1471 unsigned next_len = LZX_MIN_MATCH_LEN;
1472 unsigned max_len = min(block_end - in_next, LZX_MAX_MATCH_LEN);
1475 /* Consider R0 match */
1476 matchptr = in_next - lzx_lru_queue_R0(QUEUE(in_next));
1477 if (load_u16_unaligned(matchptr) != load_u16_unaligned(in_next))
1479 STATIC_ASSERT(LZX_MIN_MATCH_LEN == 2);
1481 u32 cost = cur_node->cost +
1482 c->costs.match_cost[0][
1483 next_len - LZX_MIN_MATCH_LEN];
1484 if (cost <= (cur_node + next_len)->cost) {
1485 (cur_node + next_len)->cost = cost;
1486 (cur_node + next_len)->item =
1487 (0 << OPTIMUM_OFFSET_SHIFT) | next_len;
1489 if (unlikely(++next_len > max_len)) {
1490 cache_ptr = end_matches;
1493 } while (in_next[next_len - 1] == matchptr[next_len - 1]);
1497 /* Consider R1 match */
1498 matchptr = in_next - lzx_lru_queue_R1(QUEUE(in_next));
1499 if (load_u16_unaligned(matchptr) != load_u16_unaligned(in_next))
1501 if (matchptr[next_len - 1] != in_next[next_len - 1])
1503 for (unsigned len = 2; len < next_len - 1; len++)
1504 if (matchptr[len] != in_next[len])
1507 u32 cost = cur_node->cost +
1508 c->costs.match_cost[1][
1509 next_len - LZX_MIN_MATCH_LEN];
1510 if (cost <= (cur_node + next_len)->cost) {
1511 (cur_node + next_len)->cost = cost;
1512 (cur_node + next_len)->item =
1513 (1 << OPTIMUM_OFFSET_SHIFT) | next_len;
1515 if (unlikely(++next_len > max_len)) {
1516 cache_ptr = end_matches;
1519 } while (in_next[next_len - 1] == matchptr[next_len - 1]);
1523 /* Consider R2 match */
1524 matchptr = in_next - lzx_lru_queue_R2(QUEUE(in_next));
1525 if (load_u16_unaligned(matchptr) != load_u16_unaligned(in_next))
1527 if (matchptr[next_len - 1] != in_next[next_len - 1])
1529 for (unsigned len = 2; len < next_len - 1; len++)
1530 if (matchptr[len] != in_next[len])
1533 u32 cost = cur_node->cost +
1534 c->costs.match_cost[2][
1535 next_len - LZX_MIN_MATCH_LEN];
1536 if (cost <= (cur_node + next_len)->cost) {
1537 (cur_node + next_len)->cost = cost;
1538 (cur_node + next_len)->item =
1539 (2 << OPTIMUM_OFFSET_SHIFT) | next_len;
1541 if (unlikely(++next_len > max_len)) {
1542 cache_ptr = end_matches;
1545 } while (in_next[next_len - 1] == matchptr[next_len - 1]);
1549 while (next_len > cache_ptr->length)
1550 if (++cache_ptr == end_matches)
1553 /* Consider explicit offset matches */
1555 u32 offset = cache_ptr->offset;
1556 u32 offset_data = offset + LZX_OFFSET_ADJUSTMENT;
1557 unsigned offset_slot = lzx_comp_get_offset_slot(c, offset_data,
1559 u32 base_cost = cur_node->cost;
1561 #if LZX_CONSIDER_ALIGNED_COSTS
1562 if (offset_data >= 16)
1563 base_cost += c->costs.aligned[offset_data &
1564 LZX_ALIGNED_OFFSET_BITMASK];
1568 u32 cost = base_cost +
1569 c->costs.match_cost[offset_slot][
1570 next_len - LZX_MIN_MATCH_LEN];
1571 if (cost < (cur_node + next_len)->cost) {
1572 (cur_node + next_len)->cost = cost;
1573 (cur_node + next_len)->item =
1574 (offset_data << OPTIMUM_OFFSET_SHIFT) | next_len;
1576 } while (++next_len <= cache_ptr->length);
1577 } while (++cache_ptr != end_matches);
1582 /* Consider coding a literal.
1584 * To avoid an extra branch, actually checking the preferability
1585 * of coding the literal is integrated into the queue update
1587 literal = *in_next++;
1588 cost = cur_node->cost + c->costs.main[literal];
1590 /* Advance to the next position. */
1593 /* The lowest-cost path to the current position is now known.
1594 * Finalize the recent offsets queue that results from taking
1595 * this lowest-cost path. */
1597 if (cost <= cur_node->cost) {
1598 /* Literal: queue remains unchanged. */
1599 cur_node->cost = cost;
1600 cur_node->item = (u32)literal << OPTIMUM_OFFSET_SHIFT;
1601 QUEUE(in_next) = QUEUE(in_next - 1);
1603 /* Match: queue update is needed. */
1604 unsigned len = cur_node->item & OPTIMUM_LEN_MASK;
1605 u32 offset_data = cur_node->item >> OPTIMUM_OFFSET_SHIFT;
1606 if (offset_data >= LZX_NUM_RECENT_OFFSETS) {
1607 /* Explicit offset match: insert offset at front */
1609 lzx_lru_queue_push(QUEUE(in_next - len),
1610 offset_data - LZX_OFFSET_ADJUSTMENT);
1612 /* Repeat offset match: swap offset to front */
1614 lzx_lru_queue_swap(QUEUE(in_next - len),
1618 } while (cur_node != end_node);
1620 /* Return the match offset queue at the end of the minimum cost path. */
1621 return QUEUE(block_end);
1624 /* Given the costs for the main and length codewords, compute 'match_costs'. */
1626 lzx_compute_match_costs(struct lzx_compressor *c)
1628 unsigned num_offset_slots = (c->num_main_syms - LZX_NUM_CHARS) / LZX_NUM_LEN_HEADERS;
1629 struct lzx_costs *costs = &c->costs;
1631 for (unsigned offset_slot = 0; offset_slot < num_offset_slots; offset_slot++) {
1633 u32 extra_cost = (u32)lzx_extra_offset_bits[offset_slot] * LZX_BIT_COST;
1634 unsigned main_symbol = LZX_NUM_CHARS + (offset_slot * LZX_NUM_LEN_HEADERS);
1637 #if LZX_CONSIDER_ALIGNED_COSTS
1638 if (offset_slot >= 8)
1639 extra_cost -= LZX_NUM_ALIGNED_OFFSET_BITS * LZX_BIT_COST;
1642 for (i = 0; i < LZX_NUM_PRIMARY_LENS; i++)
1643 costs->match_cost[offset_slot][i] =
1644 costs->main[main_symbol++] + extra_cost;
1646 extra_cost += costs->main[main_symbol];
1648 for (; i < LZX_NUM_LENS; i++)
1649 costs->match_cost[offset_slot][i] =
1650 costs->len[i - LZX_NUM_PRIMARY_LENS] + extra_cost;
1654 /* Set default LZX Huffman symbol costs to bootstrap the iterative optimization
1657 lzx_set_default_costs(struct lzx_compressor *c, const u8 *block, u32 block_size)
1660 bool have_byte[256];
1661 unsigned num_used_bytes;
1663 /* The costs below are hard coded to use a scaling factor of 16. */
1664 STATIC_ASSERT(LZX_BIT_COST == 16);
1669 * - Use smaller initial costs for literal symbols when the input buffer
1670 * contains fewer distinct bytes.
1672 * - Assume that match symbols are more costly than literal symbols.
1674 * - Assume that length symbols for shorter lengths are less costly than
1675 * length symbols for longer lengths.
1678 for (i = 0; i < 256; i++)
1679 have_byte[i] = false;
1681 for (i = 0; i < block_size; i++)
1682 have_byte[block[i]] = true;
1685 for (i = 0; i < 256; i++)
1686 num_used_bytes += have_byte[i];
1688 for (i = 0; i < 256; i++)
1689 c->costs.main[i] = 140 - (256 - num_used_bytes) / 4;
1691 for (; i < c->num_main_syms; i++)
1692 c->costs.main[i] = 170;
1694 for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++)
1695 c->costs.len[i] = 103 + (i / 4);
1697 #if LZX_CONSIDER_ALIGNED_COSTS
1698 for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
1699 c->costs.aligned[i] = LZX_NUM_ALIGNED_OFFSET_BITS * LZX_BIT_COST;
1702 lzx_compute_match_costs(c);
1705 /* Update the current cost model to reflect the computed Huffman codes. */
1707 lzx_update_costs(struct lzx_compressor *c)
1710 const struct lzx_lens *lens = &c->codes[c->codes_index].lens;
1712 for (i = 0; i < c->num_main_syms; i++) {
1713 c->costs.main[i] = (lens->main[i] ? lens->main[i] :
1714 MAIN_CODEWORD_LIMIT) * LZX_BIT_COST;
1717 for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++) {
1718 c->costs.len[i] = (lens->len[i] ? lens->len[i] :
1719 LENGTH_CODEWORD_LIMIT) * LZX_BIT_COST;
1722 #if LZX_CONSIDER_ALIGNED_COSTS
1723 for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
1724 c->costs.aligned[i] = (lens->aligned[i] ? lens->aligned[i] :
1725 ALIGNED_CODEWORD_LIMIT) * LZX_BIT_COST;
1729 lzx_compute_match_costs(c);
1732 static inline struct lzx_lru_queue
1733 lzx_optimize_and_write_block(struct lzx_compressor * const restrict c,
1734 struct lzx_output_bitstream * const restrict os,
1735 const u8 * const restrict block_begin,
1736 const u32 block_size,
1737 const struct lzx_lru_queue initial_queue,
1740 unsigned num_passes_remaining = c->num_optim_passes;
1741 struct lzx_lru_queue new_queue;
1744 /* The first optimization pass uses a default cost model. Each
1745 * additional optimization pass uses a cost model derived from the
1746 * Huffman code computed in the previous pass. */
1748 lzx_set_default_costs(c, block_begin, block_size);
1749 lzx_reset_symbol_frequencies(c);
1751 new_queue = lzx_find_min_cost_path(c, block_begin, block_size,
1752 initial_queue, is_16_bit);
1753 if (num_passes_remaining > 1) {
1754 lzx_tally_item_list(c, block_size, is_16_bit);
1755 lzx_make_huffman_codes(c);
1756 lzx_update_costs(c);
1757 lzx_reset_symbol_frequencies(c);
1759 } while (--num_passes_remaining);
1761 seq_idx = lzx_record_item_list(c, block_size, is_16_bit);
1762 lzx_finish_block(c, os, block_begin, block_size, seq_idx);
1767 * This is the "near-optimal" LZX compressor.
1769 * For each block, it performs a relatively thorough graph search to find an
1770 * inexpensive (in terms of compressed size) way to output that block.
1772 * Note: there are actually many things this algorithm leaves on the table in
1773 * terms of compression ratio. So although it may be "near-optimal", it is
1774 * certainly not "optimal". The goal is not to produce the optimal compression
1775 * ratio, which for LZX is probably impossible within any practical amount of
1776 * time, but rather to produce a compression ratio significantly better than a
1777 * simpler "greedy" or "lazy" parse while still being relatively fast.
1780 lzx_compress_near_optimal(struct lzx_compressor *c,
1781 struct lzx_output_bitstream *os,
1784 const u8 * const in_begin = c->in_buffer;
1785 const u8 * in_next = in_begin;
1786 const u8 * const in_end = in_begin + c->in_nbytes;
1787 u32 max_len = LZX_MAX_MATCH_LEN;
1788 u32 nice_len = min(c->nice_match_length, max_len);
1789 u32 next_hashes[2] = {};
1790 struct lzx_lru_queue queue;
1792 CALL_BT_MF(is_16_bit, c, bt_matchfinder_init);
1793 lzx_lru_queue_init(&queue);
1796 /* Starting a new block */
1797 const u8 * const in_block_begin = in_next;
1798 const u8 * const in_block_end =
1799 in_next + min(LZX_DIV_BLOCK_SIZE, in_end - in_next);
1801 /* Run the block through the matchfinder and cache the matches. */
1802 struct lz_match *cache_ptr = c->match_cache;
1804 struct lz_match *lz_matchptr;
1807 /* If approaching the end of the input buffer, adjust
1808 * 'max_len' and 'nice_len' accordingly. */
1809 if (unlikely(max_len > in_end - in_next)) {
1810 max_len = in_end - in_next;
1811 nice_len = min(max_len, nice_len);
1812 if (unlikely(max_len < 5)) {
1814 cache_ptr->length = 0;
1820 /* Check for matches. */
1821 lz_matchptr = CALL_BT_MF(is_16_bit, c, bt_matchfinder_get_matches,
1826 c->max_search_depth,
1831 cache_ptr->length = lz_matchptr - (cache_ptr + 1);
1832 cache_ptr = lz_matchptr;
1835 * If there was a very long match found, then don't
1836 * cache any matches for the bytes covered by that
1837 * match. This avoids degenerate behavior when
1838 * compressing highly redundant data, where the number
1839 * of matches can be very large.
1841 * This heuristic doesn't actually hurt the compression
1842 * ratio very much. If there's a long match, then the
1843 * data must be highly compressible, so it doesn't
1844 * matter as much what we do.
1846 if (best_len >= nice_len) {
1849 if (unlikely(max_len > in_end - in_next)) {
1850 max_len = in_end - in_next;
1851 nice_len = min(max_len, nice_len);
1852 if (unlikely(max_len < 5)) {
1854 cache_ptr->length = 0;
1859 CALL_BT_MF(is_16_bit, c, bt_matchfinder_skip_position,
1864 c->max_search_depth,
1867 cache_ptr->length = 0;
1869 } while (--best_len);
1871 } while (in_next < in_block_end &&
1872 likely(cache_ptr < &c->match_cache[LZX_CACHE_LENGTH]));
1874 /* We've finished running the block through the matchfinder.
1875 * Now choose a match/literal sequence and write the block. */
1877 queue = lzx_optimize_and_write_block(c, os, in_block_begin,
1878 in_next - in_block_begin,
1880 } while (in_next != in_end);
1884 lzx_compress_near_optimal_16(struct lzx_compressor *c,
1885 struct lzx_output_bitstream *os)
1887 lzx_compress_near_optimal(c, os, true);
1891 lzx_compress_near_optimal_32(struct lzx_compressor *c,
1892 struct lzx_output_bitstream *os)
1894 lzx_compress_near_optimal(c, os, false);
1898 * Given a pointer to the current byte sequence and the current list of recent
1899 * match offsets, find the longest repeat offset match.
1901 * If no match of at least 2 bytes is found, then return 0.
1903 * If a match of at least 2 bytes is found, then return its length and set
1904 * *rep_max_idx_ret to the index of its offset in @queue.
1907 lzx_find_longest_repeat_offset_match(const u8 * const in_next,
1908 const u32 bytes_remaining,
1909 const u32 recent_offsets[LZX_NUM_RECENT_OFFSETS],
1910 unsigned *rep_max_idx_ret)
1912 STATIC_ASSERT(LZX_NUM_RECENT_OFFSETS == 3);
1914 const unsigned max_len = min(bytes_remaining, LZX_MAX_MATCH_LEN);
1915 const u16 next_2_bytes = load_u16_unaligned(in_next);
1917 unsigned rep_max_len;
1918 unsigned rep_max_idx;
1921 matchptr = in_next - recent_offsets[0];
1922 if (load_u16_unaligned(matchptr) == next_2_bytes)
1923 rep_max_len = lz_extend(in_next, matchptr, 2, max_len);
1928 matchptr = in_next - recent_offsets[1];
1929 if (load_u16_unaligned(matchptr) == next_2_bytes) {
1930 rep_len = lz_extend(in_next, matchptr, 2, max_len);
1931 if (rep_len > rep_max_len) {
1932 rep_max_len = rep_len;
1937 matchptr = in_next - recent_offsets[2];
1938 if (load_u16_unaligned(matchptr) == next_2_bytes) {
1939 rep_len = lz_extend(in_next, matchptr, 2, max_len);
1940 if (rep_len > rep_max_len) {
1941 rep_max_len = rep_len;
1946 *rep_max_idx_ret = rep_max_idx;
1950 /* Fast heuristic scoring for lazy parsing: how "good" is this match? */
1951 static inline unsigned
1952 lzx_explicit_offset_match_score(unsigned len, u32 adjusted_offset)
1954 unsigned score = len;
1956 if (adjusted_offset < 4096)
1959 if (adjusted_offset < 256)
1965 static inline unsigned
1966 lzx_repeat_offset_match_score(unsigned rep_len, unsigned rep_idx)
1971 /* This is the "lazy" LZX compressor. */
1973 lzx_compress_lazy(struct lzx_compressor *c, struct lzx_output_bitstream *os,
1976 const u8 * const in_begin = c->in_buffer;
1977 const u8 * in_next = in_begin;
1978 const u8 * const in_end = in_begin + c->in_nbytes;
1979 unsigned max_len = LZX_MAX_MATCH_LEN;
1980 unsigned nice_len = min(c->nice_match_length, max_len);
1981 STATIC_ASSERT(LZX_NUM_RECENT_OFFSETS == 3);
1982 u32 recent_offsets[3] = {1, 1, 1};
1983 u32 next_hashes[2] = {};
1985 CALL_HC_MF(is_16_bit, c, hc_matchfinder_init);
1988 /* Starting a new block */
1990 const u8 * const in_block_begin = in_next;
1991 const u8 * const in_block_end =
1992 in_next + min(LZX_DIV_BLOCK_SIZE, in_end - in_next);
1993 struct lzx_sequence *next_seq = c->chosen_sequences;
1996 u32 cur_offset_data;
2000 u32 next_offset_data;
2001 unsigned next_score;
2002 unsigned rep_max_len;
2003 unsigned rep_max_idx;
2008 lzx_reset_symbol_frequencies(c);
2011 if (unlikely(max_len > in_end - in_next)) {
2012 max_len = in_end - in_next;
2013 nice_len = min(max_len, nice_len);
2016 /* Find the longest match at the current position. */
2018 cur_len = CALL_HC_MF(is_16_bit, c, hc_matchfinder_longest_match,
2024 c->max_search_depth,
2029 cur_offset >= 8192 - LZX_OFFSET_ADJUSTMENT &&
2030 cur_offset != recent_offsets[0] &&
2031 cur_offset != recent_offsets[1] &&
2032 cur_offset != recent_offsets[2]))
2034 /* There was no match found, or the only match found
2035 * was a distant length 3 match. Output a literal. */
2036 lzx_record_literal(c, *in_next++, &litrunlen);
2040 if (cur_offset == recent_offsets[0]) {
2042 cur_offset_data = 0;
2043 skip_len = cur_len - 1;
2044 goto choose_cur_match;
2047 cur_offset_data = cur_offset + LZX_OFFSET_ADJUSTMENT;
2048 cur_score = lzx_explicit_offset_match_score(cur_len, cur_offset_data);
2050 /* Consider a repeat offset match */
2051 rep_max_len = lzx_find_longest_repeat_offset_match(in_next,
2057 if (rep_max_len >= 3 &&
2058 (rep_score = lzx_repeat_offset_match_score(rep_max_len,
2059 rep_max_idx)) >= cur_score)
2061 cur_len = rep_max_len;
2062 cur_offset_data = rep_max_idx;
2063 skip_len = rep_max_len - 1;
2064 goto choose_cur_match;
2069 /* We have a match at the current position. */
2071 /* If we have a very long match, choose it immediately. */
2072 if (cur_len >= nice_len) {
2073 skip_len = cur_len - 1;
2074 goto choose_cur_match;
2077 /* See if there's a better match at the next position. */
2079 if (unlikely(max_len > in_end - in_next)) {
2080 max_len = in_end - in_next;
2081 nice_len = min(max_len, nice_len);
2084 next_len = CALL_HC_MF(is_16_bit, c, hc_matchfinder_longest_match,
2090 c->max_search_depth / 2,
2094 if (next_len <= cur_len - 2) {
2096 skip_len = cur_len - 2;
2097 goto choose_cur_match;
2100 next_offset_data = next_offset + LZX_OFFSET_ADJUSTMENT;
2101 next_score = lzx_explicit_offset_match_score(next_len, next_offset_data);
2103 rep_max_len = lzx_find_longest_repeat_offset_match(in_next,
2109 if (rep_max_len >= 3 &&
2110 (rep_score = lzx_repeat_offset_match_score(rep_max_len,
2111 rep_max_idx)) >= next_score)
2114 if (rep_score > cur_score) {
2115 /* The next match is better, and it's a
2116 * repeat offset match. */
2117 lzx_record_literal(c, *(in_next - 2),
2119 cur_len = rep_max_len;
2120 cur_offset_data = rep_max_idx;
2121 skip_len = cur_len - 1;
2122 goto choose_cur_match;
2125 if (next_score > cur_score) {
2126 /* The next match is better, and it's an
2127 * explicit offset match. */
2128 lzx_record_literal(c, *(in_next - 2),
2131 cur_offset_data = next_offset_data;
2132 cur_score = next_score;
2133 goto have_cur_match;
2137 /* The original match was better. */
2138 skip_len = cur_len - 2;
2141 lzx_record_match(c, cur_len, cur_offset_data,
2142 recent_offsets, is_16_bit,
2143 &litrunlen, &next_seq);
2144 in_next = CALL_HC_MF(is_16_bit, c, hc_matchfinder_skip_positions,
2150 } while (in_next < in_block_end);
2152 lzx_finish_sequence(next_seq, litrunlen);
2154 lzx_finish_block(c, os, in_block_begin, in_next - in_block_begin, 0);
2156 } while (in_next != in_end);
2160 lzx_compress_lazy_16(struct lzx_compressor *c, struct lzx_output_bitstream *os)
2162 lzx_compress_lazy(c, os, true);
2166 lzx_compress_lazy_32(struct lzx_compressor *c, struct lzx_output_bitstream *os)
2168 lzx_compress_lazy(c, os, false);
2171 /* Generate the acceleration tables for offset slots. */
2173 lzx_init_offset_slot_tabs(struct lzx_compressor *c)
2175 u32 adjusted_offset = 0;
2179 for (; adjusted_offset < ARRAY_LEN(c->offset_slot_tab_1);
2182 if (adjusted_offset >= lzx_offset_slot_base[slot + 1])
2184 c->offset_slot_tab_1[adjusted_offset] = slot;
2187 /* slots [30, 49] */
2188 for (; adjusted_offset < LZX_MAX_WINDOW_SIZE;
2189 adjusted_offset += (u32)1 << 14)
2191 if (adjusted_offset >= lzx_offset_slot_base[slot + 1])
2193 c->offset_slot_tab_2[adjusted_offset >> 14] = slot;
2198 lzx_get_compressor_size(size_t max_bufsize, unsigned compression_level)
2200 if (compression_level <= LZX_MAX_FAST_LEVEL) {
2201 if (lzx_is_16_bit(max_bufsize))
2202 return offsetof(struct lzx_compressor, hc_mf_16) +
2203 hc_matchfinder_size_16(max_bufsize);
2205 return offsetof(struct lzx_compressor, hc_mf_32) +
2206 hc_matchfinder_size_32(max_bufsize);
2208 if (lzx_is_16_bit(max_bufsize))
2209 return offsetof(struct lzx_compressor, bt_mf_16) +
2210 bt_matchfinder_size_16(max_bufsize);
2212 return offsetof(struct lzx_compressor, bt_mf_32) +
2213 bt_matchfinder_size_32(max_bufsize);
2218 lzx_get_needed_memory(size_t max_bufsize, unsigned compression_level,
2223 if (max_bufsize > LZX_MAX_WINDOW_SIZE)
2226 size += lzx_get_compressor_size(max_bufsize, compression_level);
2228 size += max_bufsize; /* in_buffer */
2233 lzx_create_compressor(size_t max_bufsize, unsigned compression_level,
2234 bool destructive, void **c_ret)
2236 unsigned window_order;
2237 struct lzx_compressor *c;
2239 window_order = lzx_get_window_order(max_bufsize);
2240 if (window_order == 0)
2241 return WIMLIB_ERR_INVALID_PARAM;
2243 c = MALLOC(lzx_get_compressor_size(max_bufsize, compression_level));
2247 c->destructive = destructive;
2249 c->num_main_syms = lzx_get_num_main_syms(window_order);
2250 c->window_order = window_order;
2252 if (!c->destructive) {
2253 c->in_buffer = MALLOC(max_bufsize);
2258 if (compression_level <= LZX_MAX_FAST_LEVEL) {
2260 /* Fast compression: Use lazy parsing. */
2262 if (lzx_is_16_bit(max_bufsize))
2263 c->impl = lzx_compress_lazy_16;
2265 c->impl = lzx_compress_lazy_32;
2266 c->max_search_depth = (60 * compression_level) / 20;
2267 c->nice_match_length = (80 * compression_level) / 20;
2269 /* lzx_compress_lazy() needs max_search_depth >= 2 because it
2270 * halves the max_search_depth when attempting a lazy match, and
2271 * max_search_depth cannot be 0. */
2272 if (c->max_search_depth < 2)
2273 c->max_search_depth = 2;
2276 /* Normal / high compression: Use near-optimal parsing. */
2278 if (lzx_is_16_bit(max_bufsize))
2279 c->impl = lzx_compress_near_optimal_16;
2281 c->impl = lzx_compress_near_optimal_32;
2283 /* Scale nice_match_length and max_search_depth with the
2284 * compression level. */
2285 c->max_search_depth = (24 * compression_level) / 50;
2286 c->nice_match_length = (48 * compression_level) / 50;
2288 /* Set a number of optimization passes appropriate for the
2289 * compression level. */
2291 c->num_optim_passes = 1;
2293 if (compression_level >= 45)
2294 c->num_optim_passes++;
2296 /* Use more optimization passes for higher compression levels.
2297 * But the more passes there are, the less they help --- so
2298 * don't add them linearly. */
2299 if (compression_level >= 70) {
2300 c->num_optim_passes++;
2301 if (compression_level >= 100)
2302 c->num_optim_passes++;
2303 if (compression_level >= 150)
2304 c->num_optim_passes++;
2305 if (compression_level >= 200)
2306 c->num_optim_passes++;
2307 if (compression_level >= 300)
2308 c->num_optim_passes++;
2312 /* max_search_depth == 0 is invalid. */
2313 if (c->max_search_depth < 1)
2314 c->max_search_depth = 1;
2316 if (c->nice_match_length > LZX_MAX_MATCH_LEN)
2317 c->nice_match_length = LZX_MAX_MATCH_LEN;
2319 lzx_init_offset_slot_tabs(c);
2326 return WIMLIB_ERR_NOMEM;
2330 lzx_compress(const void *restrict in, size_t in_nbytes,
2331 void *restrict out, size_t out_nbytes_avail, void *restrict _c)
2333 struct lzx_compressor *c = _c;
2334 struct lzx_output_bitstream os;
2337 /* Don't bother trying to compress very small inputs. */
2338 if (in_nbytes < 100)
2341 /* Copy the input data into the internal buffer and preprocess it. */
2343 c->in_buffer = (void *)in;
2345 memcpy(c->in_buffer, in, in_nbytes);
2346 c->in_nbytes = in_nbytes;
2347 lzx_preprocess(c->in_buffer, in_nbytes);
2349 /* Initially, the previous Huffman codeword lengths are all zeroes. */
2351 memset(&c->codes[1].lens, 0, sizeof(struct lzx_lens));
2353 /* Initialize the output bitstream. */
2354 lzx_init_output(&os, out, out_nbytes_avail);
2356 /* Call the compression level-specific compress() function. */
2359 /* Flush the output bitstream and return the compressed size or 0. */
2360 result = lzx_flush_output(&os);
2361 if (!result && c->destructive)
2362 lzx_postprocess(c->in_buffer, c->in_nbytes);
2367 lzx_free_compressor(void *_c)
2369 struct lzx_compressor *c = _c;
2371 if (!c->destructive)
2376 const struct compressor_ops lzx_compressor_ops = {
2377 .get_needed_memory = lzx_get_needed_memory,
2378 .create_compressor = lzx_create_compressor,
2379 .compress = lzx_compress,
2380 .free_compressor = lzx_free_compressor,