/* * lzx-compress.c * * A compressor that produces output compatible with the LZX compression format. */ /* * Copyright (C) 2012, 2013, 2014 Eric Biggers * * This file is part of wimlib, a library for working with WIM files. * * wimlib is free software; you can redistribute it and/or modify it under the * terms of the GNU General Public License as published by the Free * Software Foundation; either version 3 of the License, or (at your option) * any later version. * * wimlib is distributed in the hope that it will be useful, but WITHOUT ANY * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR * A PARTICULAR PURPOSE. See the GNU General Public License for more * details. * * You should have received a copy of the GNU General Public License * along with wimlib; if not, see http://www.gnu.org/licenses/. */ /* * This file contains a compressor for the LZX ("Lempel-Ziv eXtended"?) * compression format, as used in the WIM (Windows IMaging) file format. This * code may need some slight modifications to be used outside of the WIM format. * In particular, in other situations the LZX block header might be slightly * different, and a sliding window rather than a fixed-size window might be * required. * * ---------------------------------------------------------------------------- * * Format Overview * * The primary reference for LZX is the specification released by Microsoft. * However, the comments in lzx-decompress.c provide more information about LZX * and note some errors in the Microsoft specification. * * LZX shares many similarities with DEFLATE, the format used by zlib and gzip. * Both LZX and DEFLATE use LZ77 matching and Huffman coding. Certain details * are quite similar, such as the method for storing Huffman codes. However, * the main differences are: * * - LZX preprocesses the data to attempt to make x86 machine code slightly more * compressible before attempting to compress it further. * * - LZX uses a "main" alphabet which combines literals and matches, with the * match symbols containing a "length header" (giving all or part of the match * length) and a "position slot" (giving, roughly speaking, the order of * magnitude of the match offset). * * - LZX does not have static Huffman blocks (that is, the kind with preset * Huffman codes); however it does have two types of dynamic Huffman blocks * ("verbatim" and "aligned"). * * - LZX has a minimum match length of 2 rather than 3. * * - In LZX, match offsets 0 through 2 actually represent entries in an LRU * queue of match offsets. This is very useful for certain types of files, * such as binary files that have repeating records. * * ---------------------------------------------------------------------------- * * Algorithmic Overview * * At a high level, any implementation of LZX compression must operate as * follows: * * 1. Preprocess the input data to translate the targets of 32-bit x86 call * instructions to absolute offsets. (Actually, this is required for WIM, * but might not be in other places LZX is used.) * * 2. Find a sequence of LZ77-style matches and literal bytes that expands to * the preprocessed data. * * 3. Divide the match/literal sequence into one or more LZX blocks, each of * which may be "uncompressed", "verbatim", or "aligned". * * 4. Output each LZX block. * * Step (1) is fairly straightforward. It requires looking for 0xe8 bytes in * the input data and performing a translation on the 4 bytes following each * one. * * Step (4) is complicated, but it is mostly determined by the LZX format. The * only real choice we have is what algorithm to use to build the length-limited * canonical Huffman codes. See lzx_write_all_blocks() for details. * * That leaves steps (2) and (3) as where all the hard stuff happens. Focusing * on step (2), we need to do LZ77-style parsing on the input data, or "window", * to divide it into a sequence of matches and literals. Each position in the * window might have multiple matches associated with it, and we need to choose * which one, if any, to actually use. Therefore, the problem can really be * divided into two areas of concern: (a) finding matches at a given position, * which we shall call "match-finding", and (b) choosing whether to use a * match or a literal at a given position, and if using a match, which one (if * there is more than one available). We shall call this "match-choosing". We * first consider match-finding, then match-choosing. * * ---------------------------------------------------------------------------- * * Match-finding * * Given a position in the window, we want to find LZ77-style "matches" with * that position at previous positions in the window. With LZX, the minimum * match length is 2 and the maximum match length is 257. The only restriction * on offsets is that LZX does not allow the last 2 bytes of the window to match * the beginning of the window. * * There are a number of algorithms that can be used for this, including hash * chains, binary trees, and suffix arrays. Binary trees generally work well * for LZX compression since it uses medium-size windows (2^15 to 2^21 bytes). * However, when compressing in a fast mode where many positions are skipped * (not searched for matches), hash chains are faster. * * Since the match-finders are not specific to LZX, I will not explain them in * detail here. Instead, see lz_hash_chains.c and lz_binary_trees.c. * * ---------------------------------------------------------------------------- * * Match-choosing * * Usually, choosing the longest match is best because it encodes the most data * in that one item. However, sometimes the longest match is not optimal * because (a) choosing a long match now might prevent using an even longer * match later, or (b) more generally, what we actually care about is the number * of bits it will ultimately take to output each match or literal, which is * actually dependent on the entropy encoding using by the underlying * compression format. Consequently, a longer match usually, but not always, * takes fewer bits to encode than multiple shorter matches or literals that * cover the same data. * * This problem of choosing the truly best match/literal sequence is probably * impossible to solve efficiently when combined with entropy encoding. If we * knew how many bits it takes to output each match/literal, then we could * choose the optimal sequence using shortest-path search a la Dijkstra's * algorithm. However, with entropy encoding, the chosen match/literal sequence * affects its own encoding. Therefore, we can't know how many bits it will * take to actually output any one match or literal until we have actually * chosen the full sequence of matches and literals. * * Notwithstanding the entropy encoding problem, we also aren't guaranteed to * choose the optimal match/literal sequence unless the match-finder (see * section "Match-finder") provides the match-chooser with all possible matches * at each position. However, this is not computationally efficient. For * example, there might be many matches of the same length, and usually (but not * always) the best choice is the one with the smallest offset. So in practice, * it's fine to only consider the smallest offset for a given match length at a * given position. (Actually, for LZX, it's also worth considering repeat * offsets.) * * In addition, as mentioned earlier, in LZX we have the choice of using * multiple blocks, each of which resets the Huffman codes. This expands the * search space even further. Therefore, to simplify the problem, we currently * we don't attempt to actually choose the LZX blocks based on the data. * Instead, we just divide the data into fixed-size blocks of LZX_DIV_BLOCK_SIZE * bytes each, and always use verbatim or aligned blocks (never uncompressed). * A previous version of this code recursively split the input data into * equal-sized blocks, up to a maximum depth, and chose the lowest-cost block * divisions. However, this made compression much slower and did not actually * help very much. It remains an open question whether a sufficiently fast and * useful block-splitting algorithm is possible for LZX. Essentially the same * problem also applies to DEFLATE. The Microsoft LZX compressor seemingly does * do block splitting, although I don't know how fast or useful it is, * specifically. * * Now, back to the entropy encoding problem. The "solution" is to use an * iterative approach to compute a good, but not necessarily optimal, * match/literal sequence. Start with a fixed assignment of symbol costs and * choose an "optimal" match/literal sequence based on those costs, using * shortest-path seach a la Dijkstra's algorithm. Then, for each iteration of * the optimization, update the costs based on the entropy encoding of the * current match/literal sequence, then choose a new match/literal sequence * based on the updated costs. Usually, the actual cost to output the current * match/literal sequence will decrease in each iteration until it converges on * a fixed point. This result may not be the truly optimal match/literal * sequence, but it usually is much better than one chosen by doing a "greedy" * parse where we always chooe the longest match. * * An alternative to both greedy parsing and iterative, near-optimal parsing is * "lazy" parsing. Briefly, "lazy" parsing considers just the longest match at * each position, but it waits to choose that match until it has also examined * the next position. This is actually a useful approach; it's used by zlib, * for example. Therefore, for fast compression we combine lazy parsing with * the hash chain max-finder. For normal/high compression we combine * near-optimal parsing with the binary tree match-finder. */ #ifdef HAVE_CONFIG_H # include "config.h" #endif #include "wimlib/compressor_ops.h" #include "wimlib/compress_common.h" #include "wimlib/error.h" #include "wimlib/lz_mf.h" #include "wimlib/lzx.h" #include "wimlib/util.h" #include #define LZX_OPTIM_ARRAY_LENGTH 4096 #define LZX_DIV_BLOCK_SIZE 32768 #define LZX_CACHE_PER_POS 8 #define LZX_MAX_MATCHES_PER_POS (LZX_MAX_MATCH_LEN - LZX_MIN_MATCH_LEN + 1) #define LZX_CACHE_LEN (LZX_DIV_BLOCK_SIZE * (LZX_CACHE_PER_POS + 1)) /* Codewords for the LZX main, length, and aligned offset Huffman codes */ struct lzx_codewords { u32 main[LZX_MAINCODE_MAX_NUM_SYMBOLS]; u32 len[LZX_LENCODE_NUM_SYMBOLS]; u32 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS]; }; /* Codeword lengths (in bits) for the LZX main, length, and aligned offset * Huffman codes. * * A 0 length means the codeword has zero frequency. */ struct lzx_lens { u8 main[LZX_MAINCODE_MAX_NUM_SYMBOLS]; u8 len[LZX_LENCODE_NUM_SYMBOLS]; u8 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS]; }; /* Costs for the LZX main, length, and aligned offset Huffman symbols. * * If a codeword has zero frequency, it must still be assigned some nonzero cost * --- generally a high cost, since even if it gets used in the next iteration, * it probably will not be used very many times. */ struct lzx_costs { u8 main[LZX_MAINCODE_MAX_NUM_SYMBOLS]; u8 len[LZX_LENCODE_NUM_SYMBOLS]; u8 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS]; }; /* The LZX main, length, and aligned offset Huffman codes */ struct lzx_codes { struct lzx_codewords codewords; struct lzx_lens lens; }; /* Tables for tallying symbol frequencies in the three LZX alphabets */ struct lzx_freqs { u32 main[LZX_MAINCODE_MAX_NUM_SYMBOLS]; u32 len[LZX_LENCODE_NUM_SYMBOLS]; u32 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS]; }; /* LZX intermediate match/literal format */ struct lzx_item { /* Bit Description * * 31 1 if a match, 0 if a literal. * * 30-25 position slot. This can be at most 50, so it will fit in 6 * bits. * * 8-24 position footer. This is the offset of the real formatted * offset from the position base. This can be at most 17 bits * (since lzx_extra_bits[LZX_MAX_POSITION_SLOTS - 1] is 17). * * 0-7 length of match, minus 2. This can be at most * (LZX_MAX_MATCH_LEN - 2) == 255, so it will fit in 8 bits. */ u32 data; }; /* Specification for an LZX block. */ struct lzx_block_spec { /* One of the LZX_BLOCKTYPE_* constants indicating which type of this * block. */ int block_type; /* 0-based position in the window at which this block starts. */ u32 window_pos; /* The number of bytes of uncompressed data this block represents. */ u32 block_size; /* The match/literal sequence for this block. */ struct lzx_item *chosen_items; /* The length of the @chosen_items sequence. */ u32 num_chosen_items; /* Huffman codes for this block. */ struct lzx_codes codes; }; struct lzx_compressor; struct lzx_compressor_params { struct lz_match (*choose_item_func)(struct lzx_compressor *); enum lz_mf_algo mf_algo; u32 num_optim_passes; u32 min_match_length; u32 nice_match_length; u32 max_search_depth; }; /* State of the LZX compressor. */ struct lzx_compressor { /* The buffer of data to be compressed. * * 0xe8 byte preprocessing is done directly on the data here before * further compression. * * Note that this compressor does *not* use a real sliding window!!!! * It's not needed in the WIM format, since every chunk is compressed * independently. This is by design, to allow random access to the * chunks. */ u8 *cur_window; /* Number of bytes of data to be compressed, which is the number of * bytes of data in @cur_window that are actually valid. */ u32 cur_window_size; /* Allocated size of @cur_window. */ u32 max_window_size; /* Compression parameters. */ struct lzx_compressor_params params; unsigned (*get_matches_func)(struct lzx_compressor *, const struct lz_match **); void (*skip_bytes_func)(struct lzx_compressor *, unsigned n); /* Number of symbols in the main alphabet (depends on the * @max_window_size since it determines the maximum allowed offset). */ unsigned num_main_syms; /* The current match offset LRU queue. */ struct lzx_lru_queue queue; /* Space for the sequences of matches/literals that were chosen for each * block. */ struct lzx_item *chosen_items; /* Information about the LZX blocks the preprocessed input was divided * into. */ struct lzx_block_spec *block_specs; /* Number of LZX blocks the input was divided into; a.k.a. the number of * elements of @block_specs that are valid. */ unsigned num_blocks; /* This is simply filled in with zeroes and used to avoid special-casing * the output of the first compressed Huffman code, which conceptually * has a delta taken from a code with all symbols having zero-length * codewords. */ struct lzx_codes zero_codes; /* The current cost model. */ struct lzx_costs costs; /* Lempel-Ziv match-finder. */ struct lz_mf *mf; /* Position in window of next match to return. */ u32 match_window_pos; /* The end-of-block position. We can't allow any matches to span this * position. */ u32 match_window_end; /* When doing more than one match-choosing pass over the data, matches * found by the match-finder are cached in the following array to * achieve a slight speedup when the same matches are needed on * subsequent passes. This is suboptimal because different matches may * be preferred with different cost models, but seems to be a worthwhile * speedup. */ struct lz_match *cached_matches; struct lz_match *cache_ptr; struct lz_match *cache_limit; /* Match-chooser state, used when doing near-optimal parsing. * * When matches have been chosen, optimum_cur_idx is set to the position * in the window of the next match/literal to return and optimum_end_idx * is set to the position in the window at the end of the last * match/literal to return. */ struct lzx_mc_pos_data *optimum; unsigned optimum_cur_idx; unsigned optimum_end_idx; /* Previous match, used when doing lazy parsing. */ struct lz_match prev_match; }; /* * Match chooser position data: * * An array of these structures is used during the match-choosing algorithm. * They correspond to consecutive positions in the window and are used to keep * track of the cost to reach each position, and the match/literal choices that * need to be chosen to reach that position. */ struct lzx_mc_pos_data { /* The approximate minimum cost, in bits, to reach this position in the * window which has been found so far. */ u32 cost; #define MC_INFINITE_COST ((u32)~0UL) /* The union here is just for clarity, since the fields are used in two * slightly different ways. Initially, the @prev structure is filled in * first, and links go from later in the window to earlier in the * window. Later, @next structure is filled in and links go from * earlier in the window to later in the window. */ union { struct { /* Position of the start of the match or literal that * was taken to get to this position in the approximate * minimum-cost parse. */ u32 link; /* Offset (as in an LZ (length, offset) pair) of the * match or literal that was taken to get to this * position in the approximate minimum-cost parse. */ u32 match_offset; } prev; struct { /* Position at which the match or literal starting at * this position ends in the minimum-cost parse. */ u32 link; /* Offset (as in an LZ (length, offset) pair) of the * match or literal starting at this position in the * approximate minimum-cost parse. */ u32 match_offset; } next; }; /* Adaptive state that exists after an approximate minimum-cost path to * reach this position is taken. * * Note: we update this whenever we update the pending minimum-cost * path. This is in contrast to LZMA, which also has an optimal parser * that maintains a repeat offset queue per position, but will only * compute the queue once that position is actually reached in the * parse, meaning that matches are being considered *starting* at that * position. However, the two methods seem to have approximately the * same performance if appropriate optimizations are used. Intuitively * the LZMA method seems faster, but it actually suffers from 1-2 extra * hard-to-predict branches at each position. Probably it works better * for LZMA than LZX because LZMA has a larger adaptive state than LZX, * and the LZMA encoder considers more possibilities. */ struct lzx_lru_queue queue; }; /* Returns the LZX position slot that corresponds to a given match offset, * taking into account the recent offset queue and updating it if the offset is * found in it. */ static unsigned lzx_get_position_slot(u32 offset, struct lzx_lru_queue *queue) { unsigned position_slot; /* See if the offset was recently used. */ for (int i = 0; i < LZX_NUM_RECENT_OFFSETS; i++) { if (offset == queue->R[i]) { /* Found it. */ /* Bring the repeat offset to the front of the * queue. Note: this is, in fact, not a real * LRU queue because repeat matches are simply * swapped to the front. */ swap(queue->R[0], queue->R[i]); /* The resulting position slot is simply the first index * at which the offset was found in the queue. */ return i; } } /* The offset was not recently used; look up its real position slot. */ position_slot = lzx_get_position_slot_raw(offset + LZX_OFFSET_OFFSET); /* Bring the new offset to the front of the queue. */ for (int i = LZX_NUM_RECENT_OFFSETS - 1; i > 0; i--) queue->R[i] = queue->R[i - 1]; queue->R[0] = offset; return position_slot; } /* Build the main, length, and aligned offset Huffman codes used in LZX. * * This takes as input the frequency tables for each code and produces as output * a set of tables that map symbols to codewords and codeword lengths. */ static void lzx_make_huffman_codes(const struct lzx_freqs *freqs, struct lzx_codes *codes, unsigned num_main_syms) { make_canonical_huffman_code(num_main_syms, LZX_MAX_MAIN_CODEWORD_LEN, freqs->main, codes->lens.main, codes->codewords.main); make_canonical_huffman_code(LZX_LENCODE_NUM_SYMBOLS, LZX_MAX_LEN_CODEWORD_LEN, freqs->len, codes->lens.len, codes->codewords.len); make_canonical_huffman_code(LZX_ALIGNEDCODE_NUM_SYMBOLS, LZX_MAX_ALIGNED_CODEWORD_LEN, freqs->aligned, codes->lens.aligned, codes->codewords.aligned); } /* * Output a precomputed LZX match. * * @out: * The bitstream to which to write the match. * @block_type: * The type of the LZX block (LZX_BLOCKTYPE_ALIGNED or * LZX_BLOCKTYPE_VERBATIM) * @match: * The match data. * @codes: * Pointer to a structure that contains the codewords for the main, length, * and aligned offset Huffman codes for the current LZX compressed block. */ static void lzx_write_match(struct output_bitstream *out, int block_type, struct lzx_item match, const struct lzx_codes *codes) { /* low 8 bits are the match length minus 2 */ unsigned match_len_minus_2 = match.data & 0xff; /* Next 17 bits are the position footer */ unsigned position_footer = (match.data >> 8) & 0x1ffff; /* 17 bits */ /* Next 6 bits are the position slot. */ unsigned position_slot = (match.data >> 25) & 0x3f; /* 6 bits */ unsigned len_header; unsigned len_footer; unsigned main_symbol; unsigned num_extra_bits; unsigned verbatim_bits; unsigned aligned_bits; /* If the match length is less than MIN_MATCH_LEN (= 2) + * NUM_PRIMARY_LENS (= 7), the length header contains * the match length minus MIN_MATCH_LEN, and there is no * length footer. * * Otherwise, the length header contains * NUM_PRIMARY_LENS, and the length footer contains * the match length minus NUM_PRIMARY_LENS minus * MIN_MATCH_LEN. */ if (match_len_minus_2 < LZX_NUM_PRIMARY_LENS) { len_header = match_len_minus_2; } else { len_header = LZX_NUM_PRIMARY_LENS; len_footer = match_len_minus_2 - LZX_NUM_PRIMARY_LENS; } /* Combine the position slot with the length header into a single symbol * that will be encoded with the main code. * * The actual main symbol is offset by LZX_NUM_CHARS because values * under LZX_NUM_CHARS are used to indicate a literal byte rather than a * match. */ main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS; /* Output main symbol. */ bitstream_put_bits(out, codes->codewords.main[main_symbol], codes->lens.main[main_symbol]); /* If there is a length footer, output it using the * length Huffman code. */ if (len_header == LZX_NUM_PRIMARY_LENS) bitstream_put_bits(out, codes->codewords.len[len_footer], codes->lens.len[len_footer]); num_extra_bits = lzx_get_num_extra_bits(position_slot); /* For aligned offset blocks with at least 3 extra bits, output the * verbatim bits literally, then the aligned bits encoded using the * aligned offset code. Otherwise, only the verbatim bits need to be * output. */ if ((block_type == LZX_BLOCKTYPE_ALIGNED) && (num_extra_bits >= 3)) { verbatim_bits = position_footer >> 3; bitstream_put_bits(out, verbatim_bits, num_extra_bits - 3); aligned_bits = (position_footer & 7); bitstream_put_bits(out, codes->codewords.aligned[aligned_bits], codes->lens.aligned[aligned_bits]); } else { /* verbatim bits is the same as the position * footer, in this case. */ bitstream_put_bits(out, position_footer, num_extra_bits); } } /* Output an LZX literal (encoded with the main Huffman code). */ static void lzx_write_literal(struct output_bitstream *out, u8 literal, const struct lzx_codes *codes) { bitstream_put_bits(out, codes->codewords.main[literal], codes->lens.main[literal]); } static unsigned lzx_build_precode(const u8 lens[restrict], const u8 prev_lens[restrict], const unsigned num_syms, u32 precode_freqs[restrict LZX_PRECODE_NUM_SYMBOLS], u8 output_syms[restrict num_syms], u8 precode_lens[restrict LZX_PRECODE_NUM_SYMBOLS], u32 precode_codewords[restrict LZX_PRECODE_NUM_SYMBOLS], unsigned *num_additional_bits_ret) { memset(precode_freqs, 0, LZX_PRECODE_NUM_SYMBOLS * sizeof(precode_freqs[0])); /* Since the code word lengths use a form of RLE encoding, the goal here * is to find each run of identical lengths when going through them in * symbol order (including runs of length 1). For each run, as many * lengths are encoded using RLE as possible, and the rest are output * literally. * * output_syms[] will be filled in with the length symbols that will be * output, including RLE codes, not yet encoded using the precode. * * cur_run_len keeps track of how many code word lengths are in the * current run of identical lengths. */ unsigned output_syms_idx = 0; unsigned cur_run_len = 1; unsigned num_additional_bits = 0; for (unsigned i = 1; i <= num_syms; i++) { if (i != num_syms && lens[i] == lens[i - 1]) { /* Still in a run--- keep going. */ cur_run_len++; continue; } /* Run ended! Check if it is a run of zeroes or a run of * nonzeroes. */ /* The symbol that was repeated in the run--- not to be confused * with the length *of* the run (cur_run_len) */ unsigned len_in_run = lens[i - 1]; if (len_in_run == 0) { /* A run of 0's. Encode it in as few length * codes as we can. */ /* The magic length 18 indicates a run of 20 + n zeroes, * where n is an uncompressed literal 5-bit integer that * follows the magic length. */ while (cur_run_len >= 20) { unsigned additional_bits; additional_bits = min(cur_run_len - 20, 0x1f); num_additional_bits += 5; precode_freqs[18]++; output_syms[output_syms_idx++] = 18; output_syms[output_syms_idx++] = additional_bits; cur_run_len -= 20 + additional_bits; } /* The magic length 17 indicates a run of 4 + n zeroes, * where n is an uncompressed literal 4-bit integer that * follows the magic length. */ while (cur_run_len >= 4) { unsigned additional_bits; additional_bits = min(cur_run_len - 4, 0xf); num_additional_bits += 4; precode_freqs[17]++; output_syms[output_syms_idx++] = 17; output_syms[output_syms_idx++] = additional_bits; cur_run_len -= 4 + additional_bits; } } else { /* A run of nonzero lengths. */ /* The magic length 19 indicates a run of 4 + n * nonzeroes, where n is a literal bit that follows the * magic length, and where the value of the lengths in * the run is given by an extra length symbol, encoded * with the precode, that follows the literal bit. * * The extra length symbol is encoded as a difference * from the length of the codeword for the first symbol * in the run in the previous code. * */ while (cur_run_len >= 4) { unsigned additional_bits; signed char delta; additional_bits = (cur_run_len > 4); num_additional_bits += 1; delta = (signed char)prev_lens[i - cur_run_len] - (signed char)len_in_run; if (delta < 0) delta += 17; precode_freqs[19]++; precode_freqs[(unsigned char)delta]++; output_syms[output_syms_idx++] = 19; output_syms[output_syms_idx++] = additional_bits; output_syms[output_syms_idx++] = delta; cur_run_len -= 4 + additional_bits; } } /* Any remaining lengths in the run are outputted without RLE, * as a difference from the length of that codeword in the * previous code. */ while (cur_run_len > 0) { signed char delta; delta = (signed char)prev_lens[i - cur_run_len] - (signed char)len_in_run; if (delta < 0) delta += 17; precode_freqs[(unsigned char)delta]++; output_syms[output_syms_idx++] = delta; cur_run_len--; } cur_run_len = 1; } /* Build the precode from the frequencies of the length symbols. */ make_canonical_huffman_code(LZX_PRECODE_NUM_SYMBOLS, LZX_MAX_PRE_CODEWORD_LEN, precode_freqs, precode_lens, precode_codewords); *num_additional_bits_ret = num_additional_bits; return output_syms_idx; } /* * Output a Huffman code in the compressed form used in LZX. * * The Huffman code is represented in the output as a logical series of codeword * lengths from which the Huffman code, which must be in canonical form, can be * reconstructed. * * The codeword lengths are themselves compressed using a separate Huffman code, * the "precode", which contains a symbol for each possible codeword length in * the larger code as well as several special symbols to represent repeated * codeword lengths (a form of run-length encoding). The precode is itself * constructed in canonical form, and its codeword lengths are represented * literally in 20 4-bit fields that immediately precede the compressed codeword * lengths of the larger code. * * Furthermore, the codeword lengths of the larger code are actually represented * as deltas from the codeword lengths of the corresponding code in the previous * block. * * @out: * Bitstream to which to write the compressed Huffman code. * @lens: * The codeword lengths, indexed by symbol, in the Huffman code. * @prev_lens: * The codeword lengths, indexed by symbol, in the corresponding Huffman * code in the previous block, or all zeroes if this is the first block. * @num_syms: * The number of symbols in the Huffman code. */ static void lzx_write_compressed_code(struct output_bitstream *out, const u8 lens[restrict], const u8 prev_lens[restrict], unsigned num_syms) { u32 precode_freqs[LZX_PRECODE_NUM_SYMBOLS]; u8 output_syms[num_syms]; u8 precode_lens[LZX_PRECODE_NUM_SYMBOLS]; u32 precode_codewords[LZX_PRECODE_NUM_SYMBOLS]; unsigned i; unsigned num_output_syms; u8 precode_sym; unsigned dummy; num_output_syms = lzx_build_precode(lens, prev_lens, num_syms, precode_freqs, output_syms, precode_lens, precode_codewords, &dummy); /* Write the lengths of the precode codes to the output. */ for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++) bitstream_put_bits(out, precode_lens[i], LZX_PRECODE_ELEMENT_SIZE); /* Write the length symbols, encoded with the precode, to the output. */ for (i = 0; i < num_output_syms; ) { precode_sym = output_syms[i++]; bitstream_put_bits(out, precode_codewords[precode_sym], precode_lens[precode_sym]); switch (precode_sym) { case 17: bitstream_put_bits(out, output_syms[i++], 4); break; case 18: bitstream_put_bits(out, output_syms[i++], 5); break; case 19: bitstream_put_bits(out, output_syms[i++], 1); bitstream_put_bits(out, precode_codewords[output_syms[i]], precode_lens[output_syms[i]]); i++; break; default: break; } } } /* * Write all matches and literal bytes (which were precomputed) in an LZX * compressed block to the output bitstream in the final compressed * representation. * * @ostream * The output bitstream. * @block_type * The chosen type of the LZX compressed block (LZX_BLOCKTYPE_ALIGNED or * LZX_BLOCKTYPE_VERBATIM). * @items * The array of matches/literals to output. * @num_items * Number of matches/literals to output (length of @items). * @codes * The main, length, and aligned offset Huffman codes for the current * LZX compressed block. */ static void lzx_write_items(struct output_bitstream *ostream, int block_type, const struct lzx_item items[], u32 num_items, const struct lzx_codes *codes) { for (u32 i = 0; i < num_items; i++) { /* The high bit of the 32-bit intermediate representation * indicates whether the item is an actual LZ-style match (1) or * a literal byte (0). */ if (items[i].data & 0x80000000) lzx_write_match(ostream, block_type, items[i], codes); else lzx_write_literal(ostream, items[i].data, codes); } } /* Write an LZX aligned offset or verbatim block to the output. */ static void lzx_write_compressed_block(int block_type, unsigned block_size, unsigned max_window_size, unsigned num_main_syms, struct lzx_item * chosen_items, unsigned num_chosen_items, const struct lzx_codes * codes, const struct lzx_codes * prev_codes, struct output_bitstream * ostream) { unsigned i; LZX_ASSERT(block_type == LZX_BLOCKTYPE_ALIGNED || block_type == LZX_BLOCKTYPE_VERBATIM); /* The first three bits indicate the type of block and are one of the * LZX_BLOCKTYPE_* constants. */ bitstream_put_bits(ostream, block_type, 3); /* Output the block size. * * The original LZX format seemed to always encode the block size in 3 * bytes. However, the implementation in WIMGAPI, as used in WIM files, * uses the first bit to indicate whether the block is the default size * (32768) or a different size given explicitly by the next 16 bits. * * By default, this compressor uses a window size of 32768 and therefore * follows the WIMGAPI behavior. However, this compressor also supports * window sizes greater than 32768 bytes, which do not appear to be * supported by WIMGAPI. In such cases, we retain the default size bit * to mean a size of 32768 bytes but output non-default block size in 24 * bits rather than 16. The compatibility of this behavior is unknown * because WIMs created with chunk size greater than 32768 can seemingly * only be opened by wimlib anyway. */ if (block_size == LZX_DEFAULT_BLOCK_SIZE) { bitstream_put_bits(ostream, 1, 1); } else { bitstream_put_bits(ostream, 0, 1); if (max_window_size >= 65536) bitstream_put_bits(ostream, block_size >> 16, 8); bitstream_put_bits(ostream, block_size, 16); } /* Write out lengths of the main code. Note that the LZX specification * incorrectly states that the aligned offset code comes after the * length code, but in fact it is the very first code to be written * (before the main code). */ if (block_type == LZX_BLOCKTYPE_ALIGNED) for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) bitstream_put_bits(ostream, codes->lens.aligned[i], LZX_ALIGNEDCODE_ELEMENT_SIZE); /* Write the precode and lengths for the first LZX_NUM_CHARS symbols in * the main code, which are the codewords for literal bytes. */ lzx_write_compressed_code(ostream, codes->lens.main, prev_codes->lens.main, LZX_NUM_CHARS); /* Write the precode and lengths for the rest of the main code, which * are the codewords for match headers. */ lzx_write_compressed_code(ostream, codes->lens.main + LZX_NUM_CHARS, prev_codes->lens.main + LZX_NUM_CHARS, num_main_syms - LZX_NUM_CHARS); /* Write the precode and lengths for the length code. */ lzx_write_compressed_code(ostream, codes->lens.len, prev_codes->lens.len, LZX_LENCODE_NUM_SYMBOLS); /* Write the actual matches and literals. */ lzx_write_items(ostream, block_type, chosen_items, num_chosen_items, codes); } /* Write out the LZX blocks that were computed. */ static void lzx_write_all_blocks(struct lzx_compressor *c, struct output_bitstream *ostream) { const struct lzx_codes *prev_codes = &c->zero_codes; for (unsigned i = 0; i < c->num_blocks; i++) { const struct lzx_block_spec *spec = &c->block_specs[i]; LZX_DEBUG("Writing block %u/%u (type=%d, size=%u, num_chosen_items=%u)...", i + 1, c->num_blocks, spec->block_type, spec->block_size, spec->num_chosen_items); lzx_write_compressed_block(spec->block_type, spec->block_size, c->max_window_size, c->num_main_syms, spec->chosen_items, spec->num_chosen_items, &spec->codes, prev_codes, ostream); prev_codes = &spec->codes; } } /* Constructs an LZX match from a literal byte and updates the main code symbol * frequencies. */ static inline u32 lzx_tally_literal(u8 lit, struct lzx_freqs *freqs) { freqs->main[lit]++; return (u32)lit; } /* Constructs an LZX match from an offset and a length, and updates the LRU * queue and the frequency of symbols in the main, length, and aligned offset * alphabets. The return value is a 32-bit number that provides the match in an * intermediate representation documented below. */ static inline u32 lzx_tally_match(unsigned match_len, u32 match_offset, struct lzx_freqs *freqs, struct lzx_lru_queue *queue) { unsigned position_slot; unsigned position_footer; u32 len_header; unsigned main_symbol; unsigned len_footer; unsigned adjusted_match_len; LZX_ASSERT(match_len >= LZX_MIN_MATCH_LEN && match_len <= LZX_MAX_MATCH_LEN); /* The match offset shall be encoded as a position slot (itself encoded * as part of the main symbol) and a position footer. */ position_slot = lzx_get_position_slot(match_offset, queue); position_footer = (match_offset + LZX_OFFSET_OFFSET) & ((1U << lzx_get_num_extra_bits(position_slot)) - 1); /* The match length shall be encoded as a length header (itself encoded * as part of the main symbol) and an optional length footer. */ adjusted_match_len = match_len - LZX_MIN_MATCH_LEN; if (adjusted_match_len < LZX_NUM_PRIMARY_LENS) { /* No length footer needed. */ len_header = adjusted_match_len; } else { /* Length footer needed. It will be encoded using the length * code. */ len_header = LZX_NUM_PRIMARY_LENS; len_footer = adjusted_match_len - LZX_NUM_PRIMARY_LENS; freqs->len[len_footer]++; } /* Account for the main symbol. */ main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS; freqs->main[main_symbol]++; /* In an aligned offset block, 3 bits of the position footer are output * as an aligned offset symbol. Account for this, although we may * ultimately decide to output the block as verbatim. */ /* The following check is equivalent to: * * if (lzx_extra_bits[position_slot] >= 3) * * Note that this correctly excludes position slots that correspond to * recent offsets. */ if (position_slot >= 8) freqs->aligned[position_footer & 7]++; /* Pack the position slot, position footer, and match length into an * intermediate representation. See `struct lzx_item' for details. */ LZX_ASSERT(LZX_MAX_POSITION_SLOTS <= 64); LZX_ASSERT(lzx_get_num_extra_bits(LZX_MAX_POSITION_SLOTS - 1) <= 17); LZX_ASSERT(LZX_MAX_MATCH_LEN - LZX_MIN_MATCH_LEN + 1 <= 256); LZX_ASSERT(position_slot <= (1U << (31 - 25)) - 1); LZX_ASSERT(position_footer <= (1U << (25 - 8)) - 1); LZX_ASSERT(adjusted_match_len <= (1U << (8 - 0)) - 1); return 0x80000000 | (position_slot << 25) | (position_footer << 8) | (adjusted_match_len); } /* Returns the cost, in bits, to output a literal byte using the specified cost * model. */ static u32 lzx_literal_cost(u8 c, const struct lzx_costs * costs) { return costs->main[c]; } /* Returns the cost, in bits, to output a repeat offset match of the specified * length and position slot (repeat index) using the specified cost model. */ static u32 lzx_repmatch_cost(u32 len, unsigned position_slot, const struct lzx_costs *costs) { unsigned len_header, main_symbol; u32 cost = 0; len_header = min(len - LZX_MIN_MATCH_LEN, LZX_NUM_PRIMARY_LENS); main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS; /* Account for main symbol. */ cost += costs->main[main_symbol]; /* Account for extra length information. */ if (len_header == LZX_NUM_PRIMARY_LENS) cost += costs->len[len - LZX_MIN_MATCH_LEN - LZX_NUM_PRIMARY_LENS]; return cost; } /* Set the cost model @c->costs from the Huffman codeword lengths specified in * @lens. * * The cost model and codeword lengths are almost the same thing, but the * Huffman codewords with length 0 correspond to symbols with zero frequency * that still need to be assigned actual costs. The specific values assigned * are arbitrary, but they should be fairly high (near the maximum codeword * length) to take into account the fact that uses of these symbols are expected * to be rare. */ static void lzx_set_costs(struct lzx_compressor *c, const struct lzx_lens * lens, unsigned nostat) { unsigned i; /* Main code */ for (i = 0; i < c->num_main_syms; i++) c->costs.main[i] = lens->main[i] ? lens->main[i] : nostat; /* Length code */ for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++) c->costs.len[i] = lens->len[i] ? lens->len[i] : nostat; /* Aligned offset code */ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) c->costs.aligned[i] = lens->aligned[i] ? lens->aligned[i] : nostat / 2; } /* Don't allow matches to span the end of an LZX block. */ static inline u32 maybe_truncate_matches(struct lz_match matches[], u32 num_matches, struct lzx_compressor *c) { if (c->match_window_end < c->cur_window_size && num_matches != 0) { u32 limit = c->match_window_end - c->match_window_pos; if (limit >= LZX_MIN_MATCH_LEN) { u32 i = num_matches - 1; do { if (matches[i].len >= limit) { matches[i].len = limit; /* Truncation might produce multiple * matches with length 'limit'. Keep at * most 1. */ num_matches = i + 1; } } while (i--); } else { num_matches = 0; } } return num_matches; } static unsigned lzx_get_matches_fillcache_singleblock(struct lzx_compressor *c, const struct lz_match **matches_ret) { struct lz_match *cache_ptr; struct lz_match *matches; unsigned num_matches; cache_ptr = c->cache_ptr; matches = cache_ptr + 1; if (likely(cache_ptr <= c->cache_limit)) { num_matches = lz_mf_get_matches(c->mf, matches); cache_ptr->len = num_matches; c->cache_ptr = matches + num_matches; } else { num_matches = 0; } c->match_window_pos++; *matches_ret = matches; return num_matches; } static unsigned lzx_get_matches_fillcache_multiblock(struct lzx_compressor *c, const struct lz_match **matches_ret) { struct lz_match *cache_ptr; struct lz_match *matches; unsigned num_matches; cache_ptr = c->cache_ptr; matches = cache_ptr + 1; if (likely(cache_ptr <= c->cache_limit)) { num_matches = lz_mf_get_matches(c->mf, matches); num_matches = maybe_truncate_matches(matches, num_matches, c); cache_ptr->len = num_matches; c->cache_ptr = matches + num_matches; } else { num_matches = 0; } c->match_window_pos++; *matches_ret = matches; return num_matches; } static unsigned lzx_get_matches_usecache(struct lzx_compressor *c, const struct lz_match **matches_ret) { struct lz_match *cache_ptr; struct lz_match *matches; unsigned num_matches; cache_ptr = c->cache_ptr; matches = cache_ptr + 1; if (cache_ptr <= c->cache_limit) { num_matches = cache_ptr->len; c->cache_ptr = matches + num_matches; } else { num_matches = 0; } c->match_window_pos++; *matches_ret = matches; return num_matches; } static unsigned lzx_get_matches_usecache_nocheck(struct lzx_compressor *c, const struct lz_match **matches_ret) { struct lz_match *cache_ptr; struct lz_match *matches; unsigned num_matches; cache_ptr = c->cache_ptr; matches = cache_ptr + 1; num_matches = cache_ptr->len; c->cache_ptr = matches + num_matches; c->match_window_pos++; *matches_ret = matches; return num_matches; } static unsigned lzx_get_matches_nocache_singleblock(struct lzx_compressor *c, const struct lz_match **matches_ret) { struct lz_match *matches; unsigned num_matches; matches = c->cache_ptr; num_matches = lz_mf_get_matches(c->mf, matches); c->match_window_pos++; *matches_ret = matches; return num_matches; } static unsigned lzx_get_matches_nocache_multiblock(struct lzx_compressor *c, const struct lz_match **matches_ret) { struct lz_match *matches; unsigned num_matches; matches = c->cache_ptr; num_matches = lz_mf_get_matches(c->mf, matches); num_matches = maybe_truncate_matches(matches, num_matches, c); c->match_window_pos++; *matches_ret = matches; return num_matches; } /* * Find matches at the next position in the window. * * Returns the number of matches found and sets *matches_ret to point to the * matches array. The matches will be sorted by strictly increasing length and * offset. */ static inline unsigned lzx_get_matches(struct lzx_compressor *c, const struct lz_match **matches_ret) { return (*c->get_matches_func)(c, matches_ret); } static void lzx_skip_bytes_fillcache(struct lzx_compressor *c, unsigned n) { struct lz_match *cache_ptr; cache_ptr = c->cache_ptr; c->match_window_pos += n; lz_mf_skip_positions(c->mf, n); if (cache_ptr <= c->cache_limit) { do { cache_ptr->len = 0; cache_ptr += 1; } while (--n && cache_ptr <= c->cache_limit); } c->cache_ptr = cache_ptr; } static void lzx_skip_bytes_usecache(struct lzx_compressor *c, unsigned n) { struct lz_match *cache_ptr; cache_ptr = c->cache_ptr; c->match_window_pos += n; if (cache_ptr <= c->cache_limit) { do { cache_ptr += 1 + cache_ptr->len; } while (--n && cache_ptr <= c->cache_limit); } c->cache_ptr = cache_ptr; } static void lzx_skip_bytes_usecache_nocheck(struct lzx_compressor *c, unsigned n) { struct lz_match *cache_ptr; cache_ptr = c->cache_ptr; c->match_window_pos += n; do { cache_ptr += 1 + cache_ptr->len; } while (--n); c->cache_ptr = cache_ptr; } static void lzx_skip_bytes_nocache(struct lzx_compressor *c, unsigned n) { c->match_window_pos += n; lz_mf_skip_positions(c->mf, n); } /* * Skip the specified number of positions in the window (don't search for * matches at them). */ static inline void lzx_skip_bytes(struct lzx_compressor *c, unsigned n) { return (*c->skip_bytes_func)(c, n); } /* * Reverse the linked list of near-optimal matches so that they can be returned * in forwards order. * * Returns the first match in the list. */ static struct lz_match lzx_match_chooser_reverse_list(struct lzx_compressor *c, unsigned cur_pos) { unsigned prev_link, saved_prev_link; unsigned prev_match_offset, saved_prev_match_offset; c->optimum_end_idx = cur_pos; saved_prev_link = c->optimum[cur_pos].prev.link; saved_prev_match_offset = c->optimum[cur_pos].prev.match_offset; do { prev_link = saved_prev_link; prev_match_offset = saved_prev_match_offset; saved_prev_link = c->optimum[prev_link].prev.link; saved_prev_match_offset = c->optimum[prev_link].prev.match_offset; c->optimum[prev_link].next.link = cur_pos; c->optimum[prev_link].next.match_offset = prev_match_offset; cur_pos = prev_link; } while (cur_pos != 0); c->optimum_cur_idx = c->optimum[0].next.link; return (struct lz_match) { .len = c->optimum_cur_idx, .offset = c->optimum[0].next.match_offset, }; } /* * lzx_choose_near_optimal_match() - * * Choose an approximately optimal match or literal to use at the next position * in the string, or "window", being LZ-encoded. * * This is based on algorithms used in 7-Zip, including the DEFLATE encoder * and the LZMA encoder, written by Igor Pavlov. * * Unlike a greedy parser that always takes the longest match, or even a "lazy" * parser with one match/literal look-ahead like zlib, the algorithm used here * may look ahead many matches/literals to determine the approximately optimal * match/literal to code next. The motivation is that the compression ratio is * improved if the compressor can do things like use a shorter-than-possible * match in order to allow a longer match later, and also take into account the * estimated real cost of coding each match/literal based on the underlying * entropy encoding. * * Still, this is not a true optimal parser for several reasons: * * - Real compression formats use entropy encoding of the literal/match * sequence, so the real cost of coding each match or literal is unknown until * the parse is fully determined. It can be approximated based on iterative * parses, but the end result is not guaranteed to be globally optimal. * * - Very long matches are chosen immediately. This is because locations with * long matches are likely to have many possible alternatives that would cause * slow optimal parsing, but also such locations are already highly * compressible so it is not too harmful to just grab the longest match. * * - Not all possible matches at each location are considered because the * underlying match-finder limits the number and type of matches produced at * each position. For example, for a given match length it's usually not * worth it to only consider matches other than the lowest-offset match, * except in the case of a repeat offset. * * - Although we take into account the adaptive state (in LZX, the recent offset * queue), coding decisions made with respect to the adaptive state will be * locally optimal but will not necessarily be globally optimal. This is * because the algorithm only keeps the least-costly path to get to a given * location and does not take into account that a slightly more costly path * could result in a different adaptive state that ultimately results in a * lower global cost. * * - The array space used by this function is bounded, so in degenerate cases it * is forced to start returning matches/literals before the algorithm has * really finished. * * Each call to this function does one of two things: * * 1. Build a sequence of near-optimal matches/literals, up to some point, that * will be returned by subsequent calls to this function, then return the * first one. * * OR * * 2. Return the next match/literal previously computed by a call to this * function. * * The return value is a (length, offset) pair specifying the match or literal * chosen. For literals, the length is 0 or 1 and the offset is meaningless. */ static struct lz_match lzx_choose_near_optimal_item(struct lzx_compressor *c) { unsigned num_matches; const struct lz_match *matches; struct lz_match match; u32 longest_len; u32 longest_rep_len; unsigned longest_rep_slot; unsigned cur_pos; unsigned end_pos; struct lzx_mc_pos_data *optimum = c->optimum; if (c->optimum_cur_idx != c->optimum_end_idx) { /* Case 2: Return the next match/literal already found. */ match.len = optimum[c->optimum_cur_idx].next.link - c->optimum_cur_idx; match.offset = optimum[c->optimum_cur_idx].next.match_offset; c->optimum_cur_idx = optimum[c->optimum_cur_idx].next.link; return match; } /* Case 1: Compute a new list of matches/literals to return. */ c->optimum_cur_idx = 0; c->optimum_end_idx = 0; /* Search for matches at repeat offsets. As a heuristic, we only keep * the one with the longest match length. */ longest_rep_len = LZX_MIN_MATCH_LEN - 1; if (c->match_window_pos >= 1) { unsigned limit = min(LZX_MAX_MATCH_LEN, c->match_window_end - c->match_window_pos); for (int i = 0; i < LZX_NUM_RECENT_OFFSETS; i++) { u32 offset = c->queue.R[i]; const u8 *strptr = &c->cur_window[c->match_window_pos]; const u8 *matchptr = strptr - offset; unsigned len = 0; while (len < limit && strptr[len] == matchptr[len]) len++; if (len > longest_rep_len) { longest_rep_len = len; longest_rep_slot = i; } } } /* If there's a long match with a repeat offset, choose it immediately. */ if (longest_rep_len >= c->params.nice_match_length) { lzx_skip_bytes(c, longest_rep_len); return (struct lz_match) { .len = longest_rep_len, .offset = c->queue.R[longest_rep_slot], }; } /* Find other matches. */ num_matches = lzx_get_matches(c, &matches); /* If there's a long match, choose it immediately. */ if (num_matches) { longest_len = matches[num_matches - 1].len; if (longest_len >= c->params.nice_match_length) { lzx_skip_bytes(c, longest_len - 1); return matches[num_matches - 1]; } } else { longest_len = 1; } /* Calculate the cost to reach the next position by coding a literal. */ optimum[1].queue = c->queue; optimum[1].cost = lzx_literal_cost(c->cur_window[c->match_window_pos - 1], &c->costs); optimum[1].prev.link = 0; /* Calculate the cost to reach any position up to and including that * reached by the longest match. * * Note: We consider only the lowest-offset match that reaches each * position. * * Note: Some of the cost calculation stays the same for each offset, * regardless of how many lengths it gets used for. Therefore, to * improve performance, we hand-code the cost calculation instead of * calling lzx_match_cost() to do a from-scratch cost evaluation at each * length. */ for (unsigned i = 0, len = 2; i < num_matches; i++) { u32 offset; struct lzx_lru_queue queue; u32 position_cost; unsigned position_slot; unsigned num_extra_bits; offset = matches[i].offset; queue = c->queue; position_cost = 0; position_slot = lzx_get_position_slot(offset, &queue); num_extra_bits = lzx_get_num_extra_bits(position_slot); if (num_extra_bits >= 3) { position_cost += num_extra_bits - 3; position_cost += c->costs.aligned[(offset + LZX_OFFSET_OFFSET) & 7]; } else { position_cost += num_extra_bits; } do { unsigned len_header; unsigned main_symbol; u32 cost; cost = position_cost; len_header = min(len - LZX_MIN_MATCH_LEN, LZX_NUM_PRIMARY_LENS); main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS; cost += c->costs.main[main_symbol]; if (len_header == LZX_NUM_PRIMARY_LENS) cost += c->costs.len[len - LZX_MIN_MATCH_LEN - LZX_NUM_PRIMARY_LENS]; optimum[len].queue = queue; optimum[len].prev.link = 0; optimum[len].prev.match_offset = offset; optimum[len].cost = cost; } while (++len <= matches[i].len); } end_pos = longest_len; if (longest_rep_len >= LZX_MIN_MATCH_LEN) { u32 cost; while (end_pos < longest_rep_len) optimum[++end_pos].cost = MC_INFINITE_COST; cost = lzx_repmatch_cost(longest_rep_len, longest_rep_slot, &c->costs); if (cost <= optimum[longest_rep_len].cost) { optimum[longest_rep_len].queue = c->queue; swap(optimum[longest_rep_len].queue.R[0], optimum[longest_rep_len].queue.R[longest_rep_slot]); optimum[longest_rep_len].prev.link = 0; optimum[longest_rep_len].prev.match_offset = optimum[longest_rep_len].queue.R[0]; optimum[longest_rep_len].cost = cost; } } /* Step forward, calculating the estimated minimum cost to reach each * position. The algorithm may find multiple paths to reach each * position; only the lowest-cost path is saved. * * The progress of the parse is tracked in the @optimum array, which for * each position contains the minimum cost to reach that position, the * index of the start of the match/literal taken to reach that position * through the minimum-cost path, the offset of the match taken (not * relevant for literals), and the adaptive state that will exist at * that position after the minimum-cost path is taken. The @cur_pos * variable stores the position at which the algorithm is currently * considering coding choices, and the @end_pos variable stores the * greatest position at which the costs of coding choices have been * saved. * * The loop terminates when any one of the following conditions occurs: * * 1. A match with length greater than or equal to @nice_match_length is * found. When this occurs, the algorithm chooses this match * unconditionally, and consequently the near-optimal match/literal * sequence up to and including that match is fully determined and it * can begin returning the match/literal list. * * 2. @cur_pos reaches a position not overlapped by a preceding match. * In such cases, the near-optimal match/literal sequence up to * @cur_pos is fully determined and it can begin returning the * match/literal list. * * 3. Failing either of the above in a degenerate case, the loop * terminates when space in the @optimum array is exhausted. * This terminates the algorithm and forces it to start returning * matches/literals even though they may not be globally optimal. * * Upon loop termination, a nonempty list of matches/literals will have * been produced and stored in the @optimum array. These * matches/literals are linked in reverse order, so the last thing this * function does is reverse this list and return the first * match/literal, leaving the rest to be returned immediately by * subsequent calls to this function. */ cur_pos = 0; for (;;) { u32 cost; /* Advance to next position. */ cur_pos++; /* Check termination conditions (2) and (3) noted above. */ if (cur_pos == end_pos || cur_pos == LZX_OPTIM_ARRAY_LENGTH) return lzx_match_chooser_reverse_list(c, cur_pos); /* Search for matches at repeat offsets. Again, as a heuristic * we only keep the longest one. */ longest_rep_len = LZX_MIN_MATCH_LEN - 1; unsigned limit = min(LZX_MAX_MATCH_LEN, c->match_window_end - c->match_window_pos); for (int i = 0; i < LZX_NUM_RECENT_OFFSETS; i++) { u32 offset = optimum[cur_pos].queue.R[i]; const u8 *strptr = &c->cur_window[c->match_window_pos]; const u8 *matchptr = strptr - offset; unsigned len = 0; while (len < limit && strptr[len] == matchptr[len]) len++; if (len > longest_rep_len) { longest_rep_len = len; longest_rep_slot = i; } } /* If we found a long match at a repeat offset, choose it * immediately. */ if (longest_rep_len >= c->params.nice_match_length) { /* Build the list of matches to return and get * the first one. */ match = lzx_match_chooser_reverse_list(c, cur_pos); /* Append the long match to the end of the list. */ optimum[cur_pos].next.match_offset = optimum[cur_pos].queue.R[longest_rep_slot]; optimum[cur_pos].next.link = cur_pos + longest_rep_len; c->optimum_end_idx = cur_pos + longest_rep_len; /* Skip over the remaining bytes of the long match. */ lzx_skip_bytes(c, longest_rep_len); /* Return first match in the list. */ return match; } /* Find other matches. */ num_matches = lzx_get_matches(c, &matches); /* If there's a long match, choose it immediately. */ if (num_matches) { longest_len = matches[num_matches - 1].len; if (longest_len >= c->params.nice_match_length) { /* Build the list of matches to return and get * the first one. */ match = lzx_match_chooser_reverse_list(c, cur_pos); /* Append the long match to the end of the list. */ optimum[cur_pos].next.match_offset = matches[num_matches - 1].offset; optimum[cur_pos].next.link = cur_pos + longest_len; c->optimum_end_idx = cur_pos + longest_len; /* Skip over the remaining bytes of the long match. */ lzx_skip_bytes(c, longest_len - 1); /* Return first match in the list. */ return match; } } else { longest_len = 1; } /* If we are reaching any positions for the first time, we need * to initialize their costs to infinity. */ while (end_pos < cur_pos + longest_len) optimum[++end_pos].cost = MC_INFINITE_COST; /* Consider coding a literal. */ cost = optimum[cur_pos].cost + lzx_literal_cost(c->cur_window[c->match_window_pos - 1], &c->costs); if (cost < optimum[cur_pos + 1].cost) { optimum[cur_pos + 1].queue = optimum[cur_pos].queue; optimum[cur_pos + 1].cost = cost; optimum[cur_pos + 1].prev.link = cur_pos; } /* Consider coding a match. * * The hard-coded cost calculation is done for the same reason * stated in the comment for the similar loop earlier. * Actually, it is *this* one that has the biggest effect on * performance; overall LZX compression is > 10% faster with * this code compared to calling lzx_match_cost() with each * length. */ for (unsigned i = 0, len = 2; i < num_matches; i++) { u32 offset; u32 position_cost; unsigned position_slot; unsigned num_extra_bits; offset = matches[i].offset; position_cost = optimum[cur_pos].cost; /* Yet another optimization: instead of calling * lzx_get_position_slot(), hand-inline the search of * the repeat offset queue. Then we can omit the * extra_bits calculation for repeat offset matches, and * also only compute the updated queue if we actually do * find a new lowest cost path. */ for (position_slot = 0; position_slot < LZX_NUM_RECENT_OFFSETS; position_slot++) if (offset == optimum[cur_pos].queue.R[position_slot]) goto have_position_cost; position_slot = lzx_get_position_slot_raw(offset + LZX_OFFSET_OFFSET); num_extra_bits = lzx_get_num_extra_bits(position_slot); if (num_extra_bits >= 3) { position_cost += num_extra_bits - 3; position_cost += c->costs.aligned[ (offset + LZX_OFFSET_OFFSET) & 7]; } else { position_cost += num_extra_bits; } have_position_cost: do { unsigned len_header; unsigned main_symbol; u32 cost; cost = position_cost; len_header = min(len - LZX_MIN_MATCH_LEN, LZX_NUM_PRIMARY_LENS); main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS; cost += c->costs.main[main_symbol]; if (len_header == LZX_NUM_PRIMARY_LENS) { cost += c->costs.len[len - LZX_MIN_MATCH_LEN - LZX_NUM_PRIMARY_LENS]; } if (cost < optimum[cur_pos + len].cost) { if (position_slot < LZX_NUM_RECENT_OFFSETS) { optimum[cur_pos + len].queue = optimum[cur_pos].queue; swap(optimum[cur_pos + len].queue.R[0], optimum[cur_pos + len].queue.R[position_slot]); } else { optimum[cur_pos + len].queue.R[0] = offset; optimum[cur_pos + len].queue.R[1] = optimum[cur_pos].queue.R[0]; optimum[cur_pos + len].queue.R[2] = optimum[cur_pos].queue.R[1]; } optimum[cur_pos + len].prev.link = cur_pos; optimum[cur_pos + len].prev.match_offset = offset; optimum[cur_pos + len].cost = cost; } } while (++len <= matches[i].len); } /* Consider coding a repeat offset match. * * As a heuristic, we only consider the longest length of the * longest repeat offset match. This does not, however, * necessarily mean that we will never consider any other repeat * offsets, because above we detect repeat offset matches that * were found by the regular match-finder. Therefore, this * special handling of the longest repeat-offset match is only * helpful for coding a repeat offset match that was *not* found * by the match-finder, e.g. due to being obscured by a less * distant match that is at least as long. * * Note: an alternative, used in LZMA, is to consider every * length of every repeat offset match. This is a more thorough * search, and it makes it unnecessary to detect repeat offset * matches that were found by the regular match-finder. But by * my tests, for LZX the LZMA method slows down the compressor * by ~10% and doesn't actually help the compression ratio too * much. * * Also tested a compromise approach: consider every 3rd length * of the longest repeat offset match. Still didn't seem quite * worth it, though. */ if (longest_rep_len >= LZX_MIN_MATCH_LEN) { while (end_pos < cur_pos + longest_rep_len) optimum[++end_pos].cost = MC_INFINITE_COST; cost = optimum[cur_pos].cost + lzx_repmatch_cost(longest_rep_len, longest_rep_slot, &c->costs); if (cost <= optimum[cur_pos + longest_rep_len].cost) { optimum[cur_pos + longest_rep_len].queue = optimum[cur_pos].queue; swap(optimum[cur_pos + longest_rep_len].queue.R[0], optimum[cur_pos + longest_rep_len].queue.R[longest_rep_slot]); optimum[cur_pos + longest_rep_len].prev.link = cur_pos; optimum[cur_pos + longest_rep_len].prev.match_offset = optimum[cur_pos + longest_rep_len].queue.R[0]; optimum[cur_pos + longest_rep_len].cost = cost; } } } } static struct lz_match lzx_choose_lazy_item(struct lzx_compressor *c) { const struct lz_match *matches; struct lz_match cur_match; struct lz_match next_match; u32 num_matches; if (c->prev_match.len) { cur_match = c->prev_match; c->prev_match.len = 0; } else { num_matches = lzx_get_matches(c, &matches); if (num_matches == 0 || (matches[num_matches - 1].len <= 3 && (matches[num_matches - 1].len <= 2 || matches[num_matches - 1].offset > 4096))) { return (struct lz_match) { }; } cur_match = matches[num_matches - 1]; } if (cur_match.len >= c->params.nice_match_length) { lzx_skip_bytes(c, cur_match.len - 1); return cur_match; } num_matches = lzx_get_matches(c, &matches); if (num_matches == 0 || (matches[num_matches - 1].len <= 3 && (matches[num_matches - 1].len <= 2 || matches[num_matches - 1].offset > 4096))) { lzx_skip_bytes(c, cur_match.len - 2); return cur_match; } next_match = matches[num_matches - 1]; if (next_match.len <= cur_match.len) { lzx_skip_bytes(c, cur_match.len - 2); return cur_match; } else { c->prev_match = next_match; return (struct lz_match) { }; } } /* * Return the next match or literal to use, delegating to the currently selected * match-choosing algorithm. * * If the length of the returned 'struct lz_match' is less than * LZX_MIN_MATCH_LEN, then it is really a literal. */ static inline struct lz_match lzx_choose_item(struct lzx_compressor *c) { return (*c->params.choose_item_func)(c); } /* Set default symbol costs for the LZX Huffman codes. */ static void lzx_set_default_costs(struct lzx_costs * costs, unsigned num_main_syms) { unsigned i; /* Main code (part 1): Literal symbols */ for (i = 0; i < LZX_NUM_CHARS; i++) costs->main[i] = 8; /* Main code (part 2): Match header symbols */ for (; i < num_main_syms; i++) costs->main[i] = 10; /* Length code */ for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++) costs->len[i] = 8; /* Aligned offset code */ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) costs->aligned[i] = 3; } /* Given the frequencies of symbols in an LZX-compressed block and the * corresponding Huffman codes, return LZX_BLOCKTYPE_ALIGNED or * LZX_BLOCKTYPE_VERBATIM if an aligned offset or verbatim block, respectively, * will take fewer bits to output. */ static int lzx_choose_verbatim_or_aligned(const struct lzx_freqs * freqs, const struct lzx_codes * codes) { unsigned aligned_cost = 0; unsigned verbatim_cost = 0; /* Verbatim blocks have a constant 3 bits per position footer. Aligned * offset blocks have an aligned offset symbol per position footer, plus * an extra 24 bits per block to output the lengths necessary to * reconstruct the aligned offset code itself. */ for (unsigned i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) { verbatim_cost += 3 * freqs->aligned[i]; aligned_cost += codes->lens.aligned[i] * freqs->aligned[i]; } aligned_cost += LZX_ALIGNEDCODE_ELEMENT_SIZE * LZX_ALIGNEDCODE_NUM_SYMBOLS; if (aligned_cost < verbatim_cost) return LZX_BLOCKTYPE_ALIGNED; else return LZX_BLOCKTYPE_VERBATIM; } /* Find a sequence of matches/literals with which to output the specified LZX * block, then set the block's type to that which has the minimum cost to output * (either verbatim or aligned). */ static void lzx_choose_items_for_block(struct lzx_compressor *c, struct lzx_block_spec *spec) { const struct lzx_lru_queue orig_queue = c->queue; u32 num_passes_remaining = c->params.num_optim_passes; struct lzx_freqs freqs; const u8 *window_ptr; const u8 *window_end; struct lzx_item *next_chosen_item; struct lz_match lz_match; struct lzx_item lzx_item; LZX_ASSERT(num_passes >= 1); LZX_ASSERT(lz_mf_get_position(c->mf) == spec->window_pos); c->match_window_end = spec->window_pos + spec->block_size; if (c->params.num_optim_passes > 1) { if (spec->block_size == c->cur_window_size) c->get_matches_func = lzx_get_matches_fillcache_singleblock; else c->get_matches_func = lzx_get_matches_fillcache_multiblock; c->skip_bytes_func = lzx_skip_bytes_fillcache; } else { if (spec->block_size == c->cur_window_size) c->get_matches_func = lzx_get_matches_nocache_singleblock; else c->get_matches_func = lzx_get_matches_nocache_multiblock; c->skip_bytes_func = lzx_skip_bytes_nocache; } /* The first optimal parsing pass is done using the cost model already * set in c->costs. Each later pass is done using a cost model * computed from the previous pass. * * To improve performance we only generate the array containing the * matches and literals in intermediate form on the final pass. */ while (--num_passes_remaining) { c->match_window_pos = spec->window_pos; c->cache_ptr = c->cached_matches; memset(&freqs, 0, sizeof(freqs)); window_ptr = &c->cur_window[spec->window_pos]; window_end = window_ptr + spec->block_size; while (window_ptr != window_end) { lz_match = lzx_choose_item(c); LZX_ASSERT(!(lz_match.len == LZX_MIN_MATCH_LEN && lz_match.offset == c->max_window_size - LZX_MIN_MATCH_LEN)); if (lz_match.len >= LZX_MIN_MATCH_LEN) { lzx_tally_match(lz_match.len, lz_match.offset, &freqs, &c->queue); window_ptr += lz_match.len; } else { lzx_tally_literal(*window_ptr, &freqs); window_ptr += 1; } } lzx_make_huffman_codes(&freqs, &spec->codes, c->num_main_syms); lzx_set_costs(c, &spec->codes.lens, 15); c->queue = orig_queue; if (c->cache_ptr <= c->cache_limit) { c->get_matches_func = lzx_get_matches_usecache_nocheck; c->skip_bytes_func = lzx_skip_bytes_usecache_nocheck; } else { c->get_matches_func = lzx_get_matches_usecache; c->skip_bytes_func = lzx_skip_bytes_usecache; } } c->match_window_pos = spec->window_pos; c->cache_ptr = c->cached_matches; memset(&freqs, 0, sizeof(freqs)); window_ptr = &c->cur_window[spec->window_pos]; window_end = window_ptr + spec->block_size; spec->chosen_items = &c->chosen_items[spec->window_pos]; next_chosen_item = spec->chosen_items; unsigned unseen_cost = 9; while (window_ptr != window_end) { lz_match = lzx_choose_item(c); LZX_ASSERT(!(lz_match.len == LZX_MIN_MATCH_LEN && lz_match.offset == c->max_window_size - LZX_MIN_MATCH_LEN)); if (lz_match.len >= LZX_MIN_MATCH_LEN) { lzx_item.data = lzx_tally_match(lz_match.len, lz_match.offset, &freqs, &c->queue); window_ptr += lz_match.len; } else { lzx_item.data = lzx_tally_literal(*window_ptr, &freqs); window_ptr += 1; } *next_chosen_item++ = lzx_item; /* When doing one-pass "near-optimal" parsing, update the cost * model occassionally. */ if (unlikely((next_chosen_item - spec->chosen_items) % 2048 == 0) && c->params.choose_item_func == lzx_choose_near_optimal_item && c->params.num_optim_passes == 1) { lzx_make_huffman_codes(&freqs, &spec->codes, c->num_main_syms); lzx_set_costs(c, &spec->codes.lens, unseen_cost); if (unseen_cost < 15) unseen_cost++; } } spec->num_chosen_items = next_chosen_item - spec->chosen_items; lzx_make_huffman_codes(&freqs, &spec->codes, c->num_main_syms); spec->block_type = lzx_choose_verbatim_or_aligned(&freqs, &spec->codes); } /* Prepare the input window into one or more LZX blocks ready to be output. */ static void lzx_prepare_blocks(struct lzx_compressor *c) { /* Set up a default cost model. */ if (c->params.choose_item_func == lzx_choose_near_optimal_item) lzx_set_default_costs(&c->costs, c->num_main_syms); /* Set up the block specifications. * TODO: The compression ratio could be slightly improved by performing * data-dependent block splitting instead of using fixed-size blocks. * Doing so well is a computationally hard problem, however. */ c->num_blocks = DIV_ROUND_UP(c->cur_window_size, LZX_DIV_BLOCK_SIZE); for (unsigned i = 0; i < c->num_blocks; i++) { u32 pos = LZX_DIV_BLOCK_SIZE * i; c->block_specs[i].window_pos = pos; c->block_specs[i].block_size = min(c->cur_window_size - pos, LZX_DIV_BLOCK_SIZE); } /* Load the window into the match-finder. */ lz_mf_load_window(c->mf, c->cur_window, c->cur_window_size); /* Determine sequence of matches/literals to output for each block. */ lzx_lru_queue_init(&c->queue); c->optimum_cur_idx = 0; c->optimum_end_idx = 0; c->prev_match.len = 0; for (unsigned i = 0; i < c->num_blocks; i++) lzx_choose_items_for_block(c, &c->block_specs[i]); } static void lzx_build_params(unsigned int compression_level, u32 max_window_size, struct lzx_compressor_params *lzx_params) { if (compression_level < 25) { lzx_params->choose_item_func = lzx_choose_lazy_item; lzx_params->num_optim_passes = 1; if (max_window_size <= 262144) lzx_params->mf_algo = LZ_MF_HASH_CHAINS; else lzx_params->mf_algo = LZ_MF_BINARY_TREES; lzx_params->min_match_length = 3; lzx_params->nice_match_length = 25 + compression_level * 2; lzx_params->max_search_depth = 25 + compression_level; } else { lzx_params->choose_item_func = lzx_choose_near_optimal_item; lzx_params->num_optim_passes = compression_level / 20; if (max_window_size <= 32768 && lzx_params->num_optim_passes == 1) lzx_params->mf_algo = LZ_MF_HASH_CHAINS; else lzx_params->mf_algo = LZ_MF_BINARY_TREES; lzx_params->min_match_length = (compression_level >= 45) ? 2 : 3; lzx_params->nice_match_length = min(((u64)compression_level * 32) / 50, LZX_MAX_MATCH_LEN); lzx_params->max_search_depth = min(((u64)compression_level * 50) / 50, LZX_MAX_MATCH_LEN); } } static void lzx_build_mf_params(const struct lzx_compressor_params *lzx_params, u32 max_window_size, struct lz_mf_params *mf_params) { memset(mf_params, 0, sizeof(*mf_params)); mf_params->algorithm = lzx_params->mf_algo; mf_params->max_window_size = max_window_size; mf_params->min_match_len = lzx_params->min_match_length; mf_params->max_match_len = LZX_MAX_MATCH_LEN; mf_params->max_search_depth = lzx_params->max_search_depth; mf_params->nice_match_len = lzx_params->nice_match_length; } static void lzx_free_compressor(void *_c); static u64 lzx_get_needed_memory(size_t max_window_size, unsigned int compression_level) { struct lzx_compressor_params params; u64 size = 0; if (!lzx_window_size_valid(max_window_size)) return 0; lzx_build_params(compression_level, max_window_size, ¶ms); size += sizeof(struct lzx_compressor); size += max_window_size; size += DIV_ROUND_UP(max_window_size, LZX_DIV_BLOCK_SIZE) * sizeof(struct lzx_block_spec); size += max_window_size * sizeof(struct lzx_item); size += lz_mf_get_needed_memory(params.mf_algo, max_window_size); if (params.choose_item_func == lzx_choose_near_optimal_item) { size += (LZX_OPTIM_ARRAY_LENGTH + params.nice_match_length) * sizeof(struct lzx_mc_pos_data); } if (params.num_optim_passes > 1) size += LZX_CACHE_LEN * sizeof(struct lz_match); else size += LZX_MAX_MATCHES_PER_POS * sizeof(struct lz_match); return size; } static int lzx_create_compressor(size_t max_window_size, unsigned int compression_level, void **c_ret) { struct lzx_compressor *c; struct lzx_compressor_params params; struct lz_mf_params mf_params; if (!lzx_window_size_valid(max_window_size)) return WIMLIB_ERR_INVALID_PARAM; lzx_build_params(compression_level, max_window_size, ¶ms); lzx_build_mf_params(¶ms, max_window_size, &mf_params); if (!lz_mf_params_valid(&mf_params)) return WIMLIB_ERR_INVALID_PARAM; c = CALLOC(1, sizeof(struct lzx_compressor)); if (!c) goto oom; c->params = params; c->num_main_syms = lzx_get_num_main_syms(max_window_size); c->max_window_size = max_window_size; c->cur_window = ALIGNED_MALLOC(max_window_size, 16); if (!c->cur_window) goto oom; c->block_specs = MALLOC(DIV_ROUND_UP(max_window_size, LZX_DIV_BLOCK_SIZE) * sizeof(struct lzx_block_spec)); if (!c->block_specs) goto oom; c->chosen_items = MALLOC(max_window_size * sizeof(struct lzx_item)); if (!c->chosen_items) goto oom; c->mf = lz_mf_alloc(&mf_params); if (!c->mf) goto oom; if (params.choose_item_func == lzx_choose_near_optimal_item) { c->optimum = MALLOC((LZX_OPTIM_ARRAY_LENGTH + params.nice_match_length) * sizeof(struct lzx_mc_pos_data)); if (!c->optimum) goto oom; } if (params.num_optim_passes > 1) { c->cached_matches = MALLOC(LZX_CACHE_LEN * sizeof(struct lz_match)); if (!c->cached_matches) goto oom; c->cache_limit = c->cached_matches + LZX_CACHE_LEN - (LZX_MAX_MATCHES_PER_POS + 1); } else { c->cached_matches = MALLOC(LZX_MAX_MATCHES_PER_POS * sizeof(struct lz_match)); if (!c->cached_matches) goto oom; } *c_ret = c; return 0; oom: lzx_free_compressor(c); return WIMLIB_ERR_NOMEM; } static size_t lzx_compress(const void *uncompressed_data, size_t uncompressed_size, void *compressed_data, size_t compressed_size_avail, void *_c) { struct lzx_compressor *c = _c; struct output_bitstream ostream; size_t compressed_size; if (uncompressed_size < 100) { LZX_DEBUG("Too small to bother compressing."); return 0; } LZX_DEBUG("Attempting to compress %zu bytes...", uncompressed_size); /* The input data must be preprocessed. To avoid changing the original * input, copy it to a temporary buffer. */ memcpy(c->cur_window, uncompressed_data, uncompressed_size); c->cur_window_size = uncompressed_size; /* Before doing any actual compression, do the call instruction (0xe8 * byte) translation on the uncompressed data. */ lzx_do_e8_preprocessing(c->cur_window, c->cur_window_size); /* Prepare the compressed data. */ lzx_prepare_blocks(c); /* Generate the compressed data. */ init_output_bitstream(&ostream, compressed_data, compressed_size_avail); lzx_write_all_blocks(c, &ostream); compressed_size = flush_output_bitstream(&ostream); if (compressed_size == (u32)~0UL) { LZX_DEBUG("Data did not compress to %zu bytes or less!", compressed_size_avail); return 0; } LZX_DEBUG("Done: compressed %zu => %zu bytes.", uncompressed_size, compressed_size); return compressed_size; } static void lzx_free_compressor(void *_c) { struct lzx_compressor *c = _c; if (c) { ALIGNED_FREE(c->cur_window); FREE(c->block_specs); FREE(c->chosen_items); lz_mf_free(c->mf); FREE(c->optimum); FREE(c->cached_matches); FREE(c); } } const struct compressor_ops lzx_compressor_ops = { .get_needed_memory = lzx_get_needed_memory, .create_compressor = lzx_create_compressor, .compress = lzx_compress, .free_compressor = lzx_free_compressor, };