/* * lzx-compress.c * * LZX compression routines */ /* * Copyright (C) 2012, 2013 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 compression format, as used in * the WIM file format. * * Format * ====== * * First, the primary reference for the LZX compression format is the * specification released by Microsoft. * * Second, the comments in lzx-decompress.c provide some more information about * the LZX compression format, including errors in the Microsoft specification. * * Do note that LZX shares many similarities with DEFLATE, the algorithm used by * zlib and gzip. Both LZX and DEFLATE use LZ77 matching and Huffman coding, * and certain other details are quite similar, such as the method for storing * Huffman codes. However, some of the main differences are: * * - LZX preprocesses the data before attempting to compress it. * - 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 footer" (giving, roughly speaking, the order of * magnitude of the match offset). * - LZX does not have static Huffman blocks; however it does have two types of * dynamic Huffman blocks ("aligned offset" and "verbatim"). * - LZX has a minimum match length of 2 rather than 3. * - In LZX, match offsets 0 through 2 actually represent entries in a LRU queue * of match offsets. * * Algorithms * ========== * * There are actually two distinct overall algorithms implemented here. We * shall refer to them as the "slow" algorithm and the "fast" algorithm. The * "slow" algorithm spends more time compressing to achieve a higher compression * ratio compared to the "fast" algorithm. More details are presented below. * * Slow algorithm * -------------- * * The "slow" algorithm to generate LZX-compressed data is roughly as follows: * * 1. Preprocess the input data to translate the targets of x86 call instructions * to absolute offsets. * * 2. Determine the best known sequence of LZ77 matches ((offset, length) pairs) * and literal bytes to divide the input into. Raw match-finding is done * using a very clever binary tree search based on the "Bt3" algorithm from * 7-Zip. Parsing, or match-choosing, is solved essentially as a * minimum-cost path problem, but using a heuristic forward search based on * the Deflate encoder from 7-Zip rather than a more intuitive backward * search, the latter of which would naively require that all matches be * found. This heuristic search, as well as other heuristics such as limits * on the matches considered, considerably speed up this part of the * algorithm, which is the main bottleneck. Finally, after matches and * literals are chosen, the needed Huffman codes needed to output them are * built. * * 3. Up to a certain number of iterations, use the resulting Huffman codes to * refine a cost model and go back to Step #2 to determine an improved * sequence of matches and literals. * * 4. Up to a certain depth, try splitting the current block to see if the * compression ratio can be improved. This may be the case if parts of the * input differ greatly from each other and could benefit from different * Huffman codes. * * 5. Output the resulting block(s) using the match/literal sequences and the * Huffman codes that were computed for each block. * * Fast algorithm * -------------- * * The fast algorithm (and the only one available in wimlib v1.5.1 and earlier) * spends much less time on the main bottlenecks of the compression process --- * that is the match finding, match choosing, and block splitting. Matches are * found and chosen with hash chains using a greedy parse with one position of * look-ahead. No block splitting is done; only compressing the full input into * an aligned offset block is considered. * * API * === * * The old API (retained for backward compatibility) consists of just one function: * * wimlib_lzx_compress() * * The new compressor has more potential parameters and needs more memory, so * the new API ties up memory allocations and compression parameters into a * context: * * wimlib_lzx_alloc_context() * wimlib_lzx_compress2() * wimlib_lzx_free_context() * * Both wimlib_lzx_compress() and wimlib_lzx_compress2() are designed to * compress an in-memory buffer of up to 32768 bytes. There is no sliding * window. This is suitable for the WIM format, which uses fixed-size chunks * that are seemingly always 32768 bytes. If needed, the compressor potentially * could be extended to support a larger and/or sliding window. * * Both wimlib_lzx_compress() and wimlib_lzx_compress2() return 0 if the data * could not be compressed to less than the size of the uncompressed data. * Again, this is suitable for the WIM format, which stores such data chunks * uncompressed. * * The functions in this API are exported from the library, although this is * only in case other programs happen to have uses for it other than WIM * reading/writing as already handled through the rest of the library. * * Acknowledgments * =============== * * Acknowledgments to several other open-source projects that made it possible * to implement this code: * * - 7-Zip (author: Igor Pavlov), for the binary tree match-finding * algorithm, the heuristic near-optimal forward match-choosing * algorithm, and the block splitting algorithm. * * - zlib (author: Jean-loup Gailly and Mark Adler), for the hash table * match-finding algorithm. * * - lzx-compress (author: Matthew T. Russotto), on which some parts of this * code were originally based. */ #ifdef HAVE_CONFIG_H # include "config.h" #endif #include "wimlib.h" #include "wimlib/compress.h" #include "wimlib/error.h" #include "wimlib/lzx.h" #include "wimlib/util.h" #ifdef ENABLE_LZX_DEBUG # include #endif #include /* Experimental parameters not exposed through the API */ #define LZX_PARAM_OPTIM_ARRAY_SIZE 1024 #define LZX_PARAM_ACCOUNT_FOR_LRU 1 #define LZX_PARAM_DONT_SKIP_MATCHES 0 #define LZX_PARAM_USE_EMPIRICAL_DEFAULT_COSTS 1 /* Currently, this constant can't simply be changed because the code currently * uses a static number of position slots. */ #define LZX_MAX_WINDOW_SIZE 32768 /* This may be WIM-specific */ #define LZX_DEFAULT_BLOCK_SIZE 32768 #define LZX_LZ_HASH_BITS 15 #define LZX_LZ_HASH_SIZE (1 << LZX_LZ_HASH_BITS) #define LZX_LZ_HASH_MASK (LZX_LZ_HASH_SIZE - 1) #define LZX_LZ_HASH_SHIFT 5 /* Codewords for the LZX main, length, and aligned offset Huffman codes */ struct lzx_codewords { u16 main[LZX_MAINTREE_NUM_SYMBOLS]; u16 len[LZX_LENTREE_NUM_SYMBOLS]; u16 aligned[LZX_ALIGNEDTREE_NUM_SYMBOLS]; }; /* Lengths for the LZX main, length, and aligned offset Huffman codes */ struct lzx_lens { u8 main[LZX_MAINTREE_NUM_SYMBOLS]; u8 len[LZX_LENTREE_NUM_SYMBOLS]; u8 aligned[LZX_ALIGNEDTREE_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 { freq_t main[LZX_MAINTREE_NUM_SYMBOLS]; freq_t len[LZX_LENTREE_NUM_SYMBOLS]; freq_t aligned[LZX_ALIGNEDTREE_NUM_SYMBOLS]; }; /* LZX intermediate match/literal format */ struct lzx_match { /* 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_NUM_POSITION_SLOTS - 1] is 17). * * 0-7 length of match, minus 2. This can be at most * (LZX_MAX_MATCH - 2) == 255, so it will fit in 8 bits. */ u32 data; }; /* Raw LZ match/literal format: just a length and offset. * * The length is the number of bytes of the match, and the offset is the number * of bytes back in the input the match is from the matched text. * * If @len < LZX_MIN_MATCH, then it's really just a literal byte. */ struct raw_match { u16 len; u16 offset; }; /* Specification for a LZX block */ struct lzx_block_spec { /* Set to 1 if this block has been split (in two --- we only considser * binary splits). In such cases the rest of the fields are * unimportant, since the relevant information is rather in the * structures for the sub-blocks. */ u8 is_split : 1; /* One of the LZX_BLOCKTYPE_* constants indicating which type of this * block. */ u8 block_type : 2; /* 0-based position in the window at which this block starts. */ u16 window_pos; /* The number of bytes of uncompressed data this block represents. */ u16 block_size; /* The position in the 'chosen_matches' array in the `struct * lzx_compressor' at which the match/literal specifications for * this block begin. */ unsigned chosen_matches_start_pos; /* The number of match/literal specifications for this block. */ u16 num_chosen_matches; /* Huffman codes for this block. */ struct lzx_codes codes; }; /* * 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_optimal { /* The approximate minimum cost, in bits, to reach this position in the * window which has been found so far. */ u32 cost; /* 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. */ u16 link; /* Offset, relative to its starting position, of the * match or literal that was taken to get to this * position in the approximate minimum-cost parse. */ u16 match_offset; } prev; struct { /* Position at which the match or literal starting at * this position ends in the minimum-cost parse. */ u16 link; /* Offset, relative to its starting position, of the * match or literal starting at this position in the * approximate minimum-cost parse. */ u16 match_offset; } next; }; #if LZX_PARAM_ACCOUNT_FOR_LRU struct lzx_lru_queue queue; #endif }; /* State of the LZX compressor */ struct lzx_compressor { /* The parameters that were used to create the compressor. */ struct wimlib_lzx_params params; /* 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 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. * * We reserve a few extra bytes to potentially allow reading off the end * of the array in the match-finding code for optimization purposes. */ u8 window[LZX_MAX_WINDOW_SIZE + 12]; /* Number of bytes of data to be compressed, which is the number of * bytes of data in @window that are actually valid. */ unsigned window_size; /* The current match offset LRU queue. */ struct lzx_lru_queue queue; /* Space for sequence of matches/literals that were chosen. * * Each LZX_MAX_WINDOW_SIZE-sized portion of this array is used for a * different block splitting level. */ struct lzx_match *chosen_matches; /* Structures used during block splitting. * * This can be thought of as a binary tree. block_specs[(1) - 1] * represents to the top-level block (root node), and block_specs[(i*2) * - 1] and block_specs[(i*2+1) - 1] represent the sub-blocks (child * nodes) resulting from a binary split of the block represented by * block_spec[(i) - 1]. */ struct lzx_block_spec *block_specs; /* 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; /* Slow algorithm only: The current cost model. */ struct lzx_lens costs; /* Slow algorithm only: Table that maps the hash codes for 3 character * sequences to the most recent position that sequence (or a sequence * sharing the same hash code) appeared in the window. */ u16 *hash_tab; /* Slow algorithm only: Table that maps 2-character sequences to the * most recent position that sequence appeared in the window. */ u16 *digram_tab; /* Slow algorithm only: Table that contains the logical child pointers * in the binary trees in the match-finding code. * * child_tab[i*2] and child_tab[i*2+1] are the left and right pointers, * respectively, from the binary tree root corresponding to window * position i. */ u16 *child_tab; /* Slow algorithm only: Matches that were already found and are saved in * memory for subsequent queries (e.g. when block splitting). */ struct raw_match *cached_matches; /* Slow algorithm only: Next position in 'cached_matches' to either * return or fill in. */ unsigned cached_matches_pos; /* Slow algorithm only: %true if reading from 'cached_matches'; %false * if writing to 'cached_matches'. */ bool matches_already_found; /* Slow algorithm only: Position in window of next match to return. */ unsigned match_window_pos; /* Slow algorithm only: No matches returned shall reach past this * position. */ unsigned match_window_end; /* Slow algorithm only: Temporary space used for match-choosing * algorithm. * * The size of this array must be at least LZX_MAX_MATCH but otherwise * is arbitrary. More space simply allows the match-choosing algorithm * to find better matches (depending on the input, as always). */ struct lzx_optimal *optimum; /* Slow algorithm only: Variables used by the match-choosing algorithm. * * 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. */ u32 optimum_cur_idx; u32 optimum_end_idx; }; /* Returns the LZX position slot that corresponds to a given formatted offset. * * Logically, this returns the smallest i such that * formatted_offset >= lzx_position_base[i]. * * The actual implementation below takes advantage of the regularity of the * numbers in the lzx_position_base array to calculate the slot directly from * the formatted offset without actually looking at the array. */ static unsigned lzx_get_position_slot(unsigned formatted_offset) { #if 0 /* * Slots 36-49 (formatted_offset >= 262144) can be found by * (formatted_offset/131072) + 34 == (formatted_offset >> 17) + 34; * however, this check for formatted_offset >= 262144 is commented out * because WIM chunks cannot be that large. */ if (formatted_offset >= 262144) { return (formatted_offset >> 17) + 34; } else #endif { /* Note: this part here only works if: * * 2 <= formatted_offset < 655360 * * It is < 655360 because the frequency of the position bases * increases starting at the 655360 entry, and it is >= 2 * because the below calculation fails if the most significant * bit is lower than the 2's place. */ LZX_ASSERT(2 <= formatted_offset && formatted_offset < 655360); unsigned mssb_idx = bsr32(formatted_offset); return (mssb_idx << 1) | ((formatted_offset >> (mssb_idx - 1)) & 1); } } /* Compute the hash code for the next 3-character sequence in the window. */ static unsigned lzx_lz_compute_hash(const u8 *window) { unsigned hash; hash = window[0]; hash <<= LZX_LZ_HASH_SHIFT; hash ^= window[1]; hash <<= LZX_LZ_HASH_SHIFT; hash ^= window[2]; return hash & LZX_LZ_HASH_MASK; } /* 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 lengths. */ static void lzx_make_huffman_codes(const struct lzx_freqs *freqs, struct lzx_codes *codes) { make_canonical_huffman_code(LZX_MAINTREE_NUM_SYMBOLS, LZX_MAX_CODEWORD_LEN, freqs->main, codes->lens.main, codes->codewords.main); make_canonical_huffman_code(LZX_LENTREE_NUM_SYMBOLS, LZX_MAX_CODEWORD_LEN, freqs->len, codes->lens.len, codes->codewords.len); make_canonical_huffman_code(LZX_ALIGNEDTREE_NUM_SYMBOLS, 8, freqs->aligned, codes->lens.aligned, codes->codewords.aligned); } /* * Output a LZX match. * * @out: The bitstream to write the match to. * @block_type: The type of the LZX block (LZX_BLOCKTYPE_ALIGNED or LZX_BLOCKTYPE_VERBATIM) * @match: The match. * @codes: Pointer to a structure that contains the codewords for the * main, length, and aligned offset Huffman codes. */ static void lzx_write_match(struct output_bitstream *out, int block_type, struct lzx_match 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 len_pos_header; unsigned main_symbol; unsigned num_extra_bits; unsigned verbatim_bits; unsigned aligned_bits; /* If the match length is less than MIN_MATCH (= 2) + * NUM_PRIMARY_LENS (= 7), the length header contains * the match length minus MIN_MATCH, 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. */ if (match_len_minus_2 < LZX_NUM_PRIMARY_LENS) { len_header = match_len_minus_2; /* No length footer-- mark it with a special * value. */ len_footer = (unsigned)(-1); } 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 * tree. */ len_pos_header = (position_slot << 3) | len_header; /* 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 = len_pos_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_footer != (unsigned)(-1)) { 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 tree. 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); } } static unsigned lzx_build_precode(const u8 lens[restrict], const u8 prev_lens[restrict], unsigned num_syms, freq_t precode_freqs[restrict LZX_PRETREE_NUM_SYMBOLS], u8 output_syms[restrict num_syms], u8 precode_lens[restrict LZX_PRETREE_NUM_SYMBOLS], u16 precode_codewords[restrict LZX_PRETREE_NUM_SYMBOLS], unsigned * num_additional_bits_ret) { unsigned output_syms_idx; unsigned cur_run_len; unsigned i; unsigned len_in_run; unsigned additional_bits; signed char delta; unsigned num_additional_bits = 0; memset(precode_freqs, 0, LZX_PRETREE_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 pre-tree. * * cur_run_len keeps track of how many code word lengths are in the * current run of identical lengths. */ output_syms_idx = 0; cur_run_len = 1; for (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) */ 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) { 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) { 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 tree. * */ while (cur_run_len >= 4) { 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 tree. */ while (cur_run_len > 0) { 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_PRETREE_NUM_SYMBOLS, LZX_MAX_CODEWORD_LEN, precode_freqs, precode_lens, precode_codewords); if (num_additional_bits_ret) *num_additional_bits_ret = num_additional_bits; return output_syms_idx; } /* * Writes a compressed Huffman code to the output, preceded by the precode for * it. * * The Huffman code is represented in the output as a series of path lengths * from which the canonical Huffman code can be reconstructed. The path lengths * themselves are compressed using a separate Huffman code, the precode, which * consists of LZX_PRETREE_NUM_SYMBOLS (= 20) symbols that cover all possible * code lengths, plus extra codes for repeated lengths. The path lengths of the * precode precede the path lengths of the larger code and are uncompressed, * consisting of 20 entries of 4 bits each. * * @out: Bitstream to write the code to. * @lens: The code lengths for the Huffman code, indexed by symbol. * @prev_lens: Code lengths for this Huffman code, indexed by symbol, * in the *previous block*, or all zeroes if this is the * first block. * @num_syms: The number of symbols in the code. */ static void lzx_write_compressed_code(struct output_bitstream *out, const u8 lens[restrict], const u8 prev_lens[restrict], unsigned num_syms) { freq_t precode_freqs[LZX_PRETREE_NUM_SYMBOLS]; u8 output_syms[num_syms]; u8 precode_lens[LZX_PRETREE_NUM_SYMBOLS]; u16 precode_codewords[LZX_PRETREE_NUM_SYMBOLS]; unsigned i; unsigned num_output_syms; u8 precode_sym; num_output_syms = lzx_build_precode(lens, prev_lens, num_syms, precode_freqs, output_syms, precode_lens, precode_codewords, NULL); /* Write the lengths of the precode codes to the output. */ for (i = 0; i < LZX_PRETREE_NUM_SYMBOLS; i++) bitstream_put_bits(out, precode_lens[i], LZX_PRETREE_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; } } } static unsigned lzx_huffman_code_output_cost(const u8 lens[restrict], const freq_t freqs[restrict], unsigned num_syms) { unsigned cost = 0; for (unsigned i = 0; i < num_syms; i++) cost += (unsigned)lens[i] * (unsigned)freqs[i]; return cost; } /* Return the number of bits required to output the lengths for the specified * Huffman code in compressed format (encoded with a precode). */ static unsigned lzx_code_cost(const u8 lens[], const u8 prev_lens[], unsigned num_syms) { u8 output_syms[num_syms]; freq_t precode_freqs[LZX_PRETREE_NUM_SYMBOLS]; u8 precode_lens[LZX_PRETREE_NUM_SYMBOLS]; u16 precode_codewords[LZX_PRETREE_NUM_SYMBOLS]; unsigned cost = 0; unsigned num_additional_bits; /* Acount for the lengths of the precode itself. */ cost += LZX_PRETREE_NUM_SYMBOLS * LZX_PRETREE_ELEMENT_SIZE; lzx_build_precode(lens, prev_lens, num_syms, precode_freqs, output_syms, precode_lens, precode_codewords, &num_additional_bits); /* Account for all precode symbols output. */ cost += lzx_huffman_code_output_cost(precode_lens, precode_freqs, LZX_PRETREE_NUM_SYMBOLS); /* Account for additional bits. */ cost += num_additional_bits; return cost; } /* * Writes all compressed matches and literal bytes in a LZX block to the the * output bitstream. * * @out: The output bitstream. * @block_type: The type of the block (LZX_BLOCKTYPE_ALIGNED or LZX_BLOCKTYPE_VERBATIM) * @match_tab[]: The array of matches that will be output. It has length * of @num_compressed_literals. * @num_compressed_literals: Number of compressed literals to be output. * @codes: Pointer to a structure that contains the codewords for the * main, length, and aligned offset Huffman codes. */ static void lzx_write_matches_and_literals(struct output_bitstream *ostream, int block_type, const struct lzx_match match_tab[], unsigned match_count, const struct lzx_codes *codes) { for (unsigned i = 0; i < match_count; i++) { struct lzx_match match = match_tab[i]; /* High bit of the match indicates whether the match is an * actual match (1) or a literal uncompressed byte (0) */ if (match.data & 0x80000000) { /* match */ lzx_write_match(ostream, block_type, match, codes); } else { /* literal byte */ bitstream_put_bits(ostream, codes->codewords.main[match.data], codes->lens.main[match.data]); } } } static void lzx_assert_codes_valid(const struct lzx_codes * codes) { #ifdef ENABLE_LZX_DEBUG unsigned i; for (i = 0; i < LZX_MAINTREE_NUM_SYMBOLS; i++) LZX_ASSERT(codes->lens.main[i] <= LZX_MAX_CODEWORD_LEN); for (i = 0; i < LZX_LENTREE_NUM_SYMBOLS; i++) LZX_ASSERT(codes->lens.len[i] <= LZX_MAX_CODEWORD_LEN); for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++) LZX_ASSERT(codes->lens.aligned[i] <= 8); const unsigned tablebits = 10; u16 decode_table[(1 << tablebits) + (2 * max(LZX_MAINTREE_NUM_SYMBOLS, LZX_LENTREE_NUM_SYMBOLS))] _aligned_attribute(DECODE_TABLE_ALIGNMENT); LZX_ASSERT(0 == make_huffman_decode_table(decode_table, LZX_MAINTREE_NUM_SYMBOLS, tablebits, codes->lens.main, LZX_MAX_CODEWORD_LEN)); LZX_ASSERT(0 == make_huffman_decode_table(decode_table, LZX_LENTREE_NUM_SYMBOLS, tablebits, codes->lens.len, LZX_MAX_CODEWORD_LEN)); LZX_ASSERT(0 == make_huffman_decode_table(decode_table, LZX_ALIGNEDTREE_NUM_SYMBOLS, min(tablebits, 6), codes->lens.aligned, 8)); #endif /* ENABLE_LZX_DEBUG */ } /* Write a LZX aligned offset or verbatim block to the output. */ static void lzx_write_compressed_block(int block_type, unsigned block_size, struct lzx_match * chosen_matches, unsigned num_chosen_matches, 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); LZX_ASSERT(block_size <= LZX_MAX_WINDOW_SIZE); LZX_ASSERT(num_chosen_matches <= LZX_MAX_WINDOW_SIZE); lzx_assert_codes_valid(codes); /* The first three bits indicate the type of block and are one of the * LZX_BLOCKTYPE_* constants. */ bitstream_put_bits(ostream, block_type, LZX_BLOCKTYPE_NBITS); /* The next bit indicates whether the block size is the default (32768), * indicated by a 1 bit, or whether the block size is given by the next * 16 bits, indicated by a 0 bit. */ if (block_size == LZX_DEFAULT_BLOCK_SIZE) { bitstream_put_bits(ostream, 1, 1); } else { bitstream_put_bits(ostream, 0, 1); bitstream_put_bits(ostream, block_size, LZX_BLOCKSIZE_NBITS); } /* 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 tree to be written * (before the main code). */ if (block_type == LZX_BLOCKTYPE_ALIGNED) for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++) bitstream_put_bits(ostream, codes->lens.aligned[i], LZX_ALIGNEDTREE_ELEMENT_SIZE); LZX_DEBUG("Writing main code..."); /* Write the pre-tree 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 pre-tree 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, LZX_MAINTREE_NUM_SYMBOLS - LZX_NUM_CHARS); LZX_DEBUG("Writing length code..."); /* Write the pre-tree and lengths for the length code. */ lzx_write_compressed_code(ostream, codes->lens.len, prev_codes->lens.len, LZX_LENTREE_NUM_SYMBOLS); LZX_DEBUG("Writing matches and literals..."); /* Write the actual matches and literals. */ lzx_write_matches_and_literals(ostream, block_type, chosen_matches, num_chosen_matches, codes); LZX_DEBUG("Done writing block."); } /* Write the LZX block of index @block_number, or recurse to its children * recursively if it is a split block. * * Return a pointer to the Huffman codes for the last block written. */ static struct lzx_codes * lzx_write_block_recursive(struct lzx_compressor *ctx, unsigned block_number, struct lzx_codes * prev_codes, struct output_bitstream *ostream) { struct lzx_block_spec *spec = &ctx->block_specs[block_number - 1]; if (spec->is_split) { prev_codes = lzx_write_block_recursive(ctx, block_number * 2 + 0, prev_codes, ostream); prev_codes = lzx_write_block_recursive(ctx, block_number * 2 + 1, prev_codes, ostream); } else { LZX_DEBUG("Writing block #%u (type=%d, size=%u, num_chosen_matches=%u)...", block_number, spec->block_type, spec->block_size, spec->num_chosen_matches); lzx_write_compressed_block(spec->block_type, spec->block_size, &ctx->chosen_matches[spec->chosen_matches_start_pos], spec->num_chosen_matches, &spec->codes, prev_codes, ostream); prev_codes = &spec->codes; } return prev_codes; } /* Write out the LZX blocks that were computed. */ static void lzx_write_all_blocks(struct lzx_compressor *ctx, struct output_bitstream *ostream) { lzx_write_block_recursive(ctx, 1, &ctx->zero_codes, ostream); } static u32 lzx_record_literal(u8 literal, void *_freqs) { struct lzx_freqs *freqs = _freqs; freqs->main[literal]++; return (u32)literal; } /* Constructs a 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 u32 lzx_record_match(unsigned match_offset, unsigned match_len, void *_freqs, void *_queue) { struct lzx_freqs *freqs = _freqs; struct lzx_lru_queue *queue = _queue; unsigned position_slot; unsigned position_footer = 0; u32 len_header; u32 len_pos_header; unsigned len_footer; unsigned adjusted_match_len; LZX_ASSERT(match_len >= LZX_MIN_MATCH && match_len <= LZX_MAX_MATCH); /* If possible, encode this offset as a repeated offset. */ if (match_offset == queue->R0) { position_slot = 0; } else if (match_offset == queue->R1) { swap(queue->R0, queue->R1); position_slot = 1; } else if (match_offset == queue->R2) { swap(queue->R0, queue->R2); position_slot = 2; } else { /* Not a repeated offset. */ /* offsets of 0, 1, and 2 are reserved for the repeated offset * codes, so non-repeated offsets must be encoded as 3+. The * minimum offset is 1, so encode the offsets offset by 2. */ unsigned formatted_offset = match_offset + 2; queue->R2 = queue->R1; queue->R1 = queue->R0; queue->R0 = match_offset; /* The (now-formatted) offset will actually be encoded as a * small position slot number that maps to a certain hard-coded * offset (position base), followed by a number of extra bits--- * the position footer--- that are added to the position base to * get the original formatted offset. */ position_slot = lzx_get_position_slot(formatted_offset); position_footer = formatted_offset & ((1 << lzx_get_num_extra_bits(position_slot)) - 1); } adjusted_match_len = match_len - LZX_MIN_MATCH; /* The match length must be at least 2, so let the adjusted match length * be the match length minus 2. * * If it is less than 7, the adjusted match length is encoded as a 3-bit * number offset by 2. Otherwise, the 3-bit length header is all 1's * and the actual adjusted length is given as a symbol encoded with the * length tree, offset by 7. */ if (adjusted_match_len < LZX_NUM_PRIMARY_LENS) { len_header = adjusted_match_len; } else { len_header = LZX_NUM_PRIMARY_LENS; len_footer = adjusted_match_len - LZX_NUM_PRIMARY_LENS; freqs->len[len_footer]++; } len_pos_header = (position_slot << 3) | len_header; freqs->main[len_pos_header + LZX_NUM_CHARS]++; /* Equivalent to: * if (lzx_extra_bits[position_slot] >= 3) */ if (position_slot >= 8) freqs->aligned[position_footer & 7]++; /* Pack the position slot, position footer, and match length into an * intermediate representation. * * bits 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_NUM_POSITION_SLOTS - 1] is 17). * * 0-7 length of match, offset by 2. This can be at most * (LZX_MAX_MATCH - 2) == 255, so it will fit in 8 bits. */ return 0x80000000 | (position_slot << 25) | (position_footer << 8) | (adjusted_match_len); } /* Set the cost model @ctx->costs from the Huffman codeword lengths specified in * @lens. * * These are basically the same thing, except that Huffman codewords with length * 0 corresponds to symbols with zero frequency. These 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 * ctx, const struct lzx_lens * lens) { unsigned i; memcpy(&ctx->costs, lens, sizeof(struct lzx_lens)); for (i = 0; i < LZX_MAINTREE_NUM_SYMBOLS; i++) if (ctx->costs.main[i] == 0) ctx->costs.main[i] = ctx->params.slow.main_nostat_cost; for (i = 0; i < LZX_LENTREE_NUM_SYMBOLS; i++) if (ctx->costs.len[i] == 0) ctx->costs.len[i] = ctx->params.slow.len_nostat_cost; for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++) if (ctx->costs.aligned[i] == 0) ctx->costs.aligned[i] = ctx->params.slow.aligned_nostat_cost; } static u32 lzx_literal_cost(u8 c, const struct lzx_lens * costs) { return costs->main[c]; } /* Given a (length, offset) pair that could be turned into a valid LZX match as * well as costs for the codewords in the main, length, and aligned Huffman * codes, return the approximate number of bits it will take to represent this * match in the compressed output. */ static unsigned lzx_match_cost(unsigned length, unsigned offset, const struct lzx_lens *costs #if LZX_PARAM_ACCOUNT_FOR_LRU , struct lzx_lru_queue *queue #endif ) { unsigned position_slot, len_header, main_symbol; unsigned cost = 0; /* Calculate position slot and length header, then combine them into the * main symbol. */ #if LZX_PARAM_ACCOUNT_FOR_LRU if (offset == queue->R0) { position_slot = 0; } else if (offset == queue->R1) { swap(queue->R0, queue->R1); position_slot = 1; } else if (offset == queue->R2) { swap(queue->R0, queue->R2); position_slot = 2; } else #endif position_slot = lzx_get_position_slot(offset + 2); len_header = min(length - LZX_MIN_MATCH, 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 position information. */ unsigned num_extra_bits = lzx_get_num_extra_bits(position_slot); if (num_extra_bits >= 3) { cost += num_extra_bits - 3; cost += costs->aligned[(offset + LZX_MIN_MATCH) & 7]; } else { cost += num_extra_bits; } /* Account for extra length information. */ if (length - LZX_MIN_MATCH >= LZX_NUM_PRIMARY_LENS) cost += costs->len[length - LZX_MIN_MATCH - LZX_NUM_PRIMARY_LENS]; return cost; } /* This procedure effectively creates a new binary tree corresponding to the * current string at the same time that it searches the existing tree nodes for * matches. */ static unsigned lzx_lz_get_matches(const u8 window[restrict], const unsigned bytes_remaining, const unsigned strstart, const unsigned max_length, u16 child_tab[restrict], unsigned cur_match, const unsigned prev_len, struct raw_match * const matches) { u16 *new_tree_lt_ptr = &child_tab[strstart * 2]; u16 *new_tree_gt_ptr = &child_tab[strstart * 2 + 1]; u16 longest_lt_match_len = 0; u16 longest_gt_match_len = 0; /* Maximum number of nodes to walk down before stopping */ unsigned depth = max_length; /* Length of longest match found so far */ unsigned longest_match_len = prev_len; /* Maximum length of match to return */ unsigned len_limit = min(bytes_remaining, max_length); /* Number of matches found so far */ unsigned num_matches = 0; for (;;) { /* Stop if too many nodes were traversed or if there is no next * node */ if (depth-- == 0 || cur_match == 0) { *new_tree_gt_ptr = 0; *new_tree_lt_ptr = 0; return num_matches; } /* Load the pointers to the children of the binary tree node * corresponding to the current match */ u16 * const cur_match_ptrs = &child_tab[cur_match * 2]; /* Set up pointers to the current match and to the current * string */ const u8 * const matchptr = &window[cur_match]; const u8 * const strptr = &window[strstart]; u16 len = min(longest_lt_match_len, longest_gt_match_len); if (matchptr[len] == strptr[len]) { while (++len != len_limit) if (matchptr[len] != strptr[len]) break; if (len > longest_match_len) { longest_match_len = len; matches[num_matches].len = len; matches[num_matches].offset = strstart - cur_match; num_matches++; if (len == len_limit) { /* Length limit was reached. Link left pointer * in the new tree with left subtree of current * match tree, and link the right pointer in the * new tree with the right subtree of the * current match tree. This in effect deletes * the node for the currrent match, which is * desirable because the current match is the * same as the current string up until the * length limit, so in subsequent queries it * will never be preferable to the current * position. */ *new_tree_lt_ptr = cur_match_ptrs[0]; *new_tree_gt_ptr = cur_match_ptrs[1]; return num_matches; } } } if (matchptr[len] < strptr[len]) { /* Case 1: The current match is lexicographically less * than the current string. * * Since we are searching the binary tree structures, we * need to walk down to the *right* subtree of the * current match's node to get to a match that is * lexicographically *greater* than the current match * but still lexicographically *lesser* than the current * string. * * At the same time, we link the entire binary tree * corresponding to the current match into the * appropriate place in the new binary tree being built * for the current string. */ *new_tree_lt_ptr = cur_match; new_tree_lt_ptr = &cur_match_ptrs[1]; cur_match = *new_tree_lt_ptr; longest_lt_match_len = len; } else { /* Case 2: The current match is lexicographically * greater than the current string. * * This is analogous to Case 1 above, but everything * happens in the other direction. */ *new_tree_gt_ptr = cur_match; new_tree_gt_ptr = &cur_match_ptrs[0]; cur_match = *new_tree_gt_ptr; longest_gt_match_len = len; } } } /* Equivalent to lzx_lz_get_matches(), but only updates the tree and doesn't * return matches. See that function for details (including comments). */ static void lzx_lz_skip_matches(const u8 window[restrict], const unsigned bytes_remaining, const unsigned strstart, const unsigned max_length, u16 child_tab[restrict], unsigned cur_match, const unsigned prev_len) { u16 *new_tree_lt_ptr = &child_tab[strstart * 2]; u16 *new_tree_gt_ptr = &child_tab[strstart * 2 + 1]; u16 longest_lt_match_len = 0; u16 longest_gt_match_len = 0; unsigned depth = max_length; unsigned longest_match_len = prev_len; unsigned len_limit = min(bytes_remaining, max_length); for (;;) { if (depth-- == 0 || cur_match == 0) { *new_tree_gt_ptr = 0; *new_tree_lt_ptr = 0; return; } u16 * const cur_match_ptrs = &child_tab[cur_match * 2]; const u8 * const matchptr = &window[cur_match]; const u8 * const strptr = &window[strstart]; u16 len = min(longest_lt_match_len, longest_gt_match_len); if (matchptr[len] == strptr[len]) { while (++len != len_limit) if (matchptr[len] != strptr[len]) break; if (len > longest_match_len) { longest_match_len = len; if (len == len_limit) { *new_tree_lt_ptr = cur_match_ptrs[0]; *new_tree_gt_ptr = cur_match_ptrs[1]; return; } } } if (matchptr[len] < strptr[len]) { *new_tree_lt_ptr = cur_match; new_tree_lt_ptr = &cur_match_ptrs[1]; cur_match = *new_tree_lt_ptr; longest_lt_match_len = len; } else { *new_tree_gt_ptr = cur_match; new_tree_gt_ptr = &cur_match_ptrs[0]; cur_match = *new_tree_gt_ptr; longest_gt_match_len = len; } } } static unsigned lzx_lz_get_matches_caching(struct lzx_compressor *ctx, struct raw_match **matches_ret); /* Tell the match-finder to skip the specified number of bytes (@n) in the * input. */ static void lzx_lz_skip_bytes(struct lzx_compressor *ctx, unsigned n) { #if LZX_PARAM_DONT_SKIP_MATCHES /* Option 1: Still cache the matches from the positions skipped. They * will then be available in later passes. */ struct raw_match *matches; while (n--) lzx_lz_get_matches_caching(ctx, &matches); #else /* Option 2: Simply mark the positions skipped as having no matches * available. */ LZX_ASSERT(n <= ctx->match_window_end - ctx->match_window_pos); if (ctx->matches_already_found) { while (n--) { LZX_ASSERT(ctx->cached_matches[ctx->cached_matches_pos].offset == ctx->match_window_pos); ctx->cached_matches_pos += ctx->cached_matches[ctx->cached_matches_pos].len + 1; ctx->match_window_pos++; } } else { while (n--) { if (ctx->params.slow.use_len2_matches && ctx->match_window_end - ctx->match_window_pos >= 2) { unsigned c1 = ctx->window[ctx->match_window_pos]; unsigned c2 = ctx->window[ctx->match_window_pos + 1]; unsigned digram = c1 | (c2 << 8); ctx->digram_tab[digram] = ctx->match_window_pos; } if (ctx->match_window_end - ctx->match_window_pos >= 3) { unsigned hash; unsigned cur_match; hash = lzx_lz_compute_hash(&ctx->window[ctx->match_window_pos]); cur_match = ctx->hash_tab[hash]; ctx->hash_tab[hash] = ctx->match_window_pos; lzx_lz_skip_matches(ctx->window, ctx->match_window_end - ctx->match_window_pos, ctx->match_window_pos, ctx->params.slow.num_fast_bytes, ctx->child_tab, cur_match, 1); } ctx->cached_matches[ctx->cached_matches_pos].len = 0; ctx->cached_matches[ctx->cached_matches_pos].offset = ctx->match_window_pos; ctx->cached_matches_pos++; ctx->match_window_pos++; } } #endif /* !LZX_PARAM_DONT_SKIP_MATCHES */ } /* Retrieve a list of matches available at the next position in the input. * * The return value is the number of matches found, and a pointer to them is * written to @matches_ret. The matches will be sorted in order by length. * * This is essentially a wrapper around lzx_lz_get_matches() that caches its * output the first time and also performs the needed hashing. */ static unsigned lzx_lz_get_matches_caching(struct lzx_compressor *ctx, struct raw_match **matches_ret) { unsigned num_matches; struct raw_match *matches; LZX_ASSERT(ctx->match_window_end >= ctx->match_window_pos); matches = &ctx->cached_matches[ctx->cached_matches_pos + 1]; if (ctx->matches_already_found) { num_matches = ctx->cached_matches[ctx->cached_matches_pos].len; LZX_ASSERT(ctx->cached_matches[ctx->cached_matches_pos].offset == ctx->match_window_pos); for (int i = (int)num_matches - 1; i >= 0; i--) { if (ctx->match_window_pos + matches[i].len > ctx->match_window_end) matches[i].len = ctx->match_window_end - ctx->match_window_pos; else break; } } else { unsigned prev_len = 1; struct raw_match * matches_ret = &ctx->cached_matches[ctx->cached_matches_pos + 1]; num_matches = 0; if (ctx->params.slow.use_len2_matches && ctx->match_window_end - ctx->match_window_pos >= 3) { unsigned c1 = ctx->window[ctx->match_window_pos]; unsigned c2 = ctx->window[ctx->match_window_pos + 1]; unsigned digram = c1 | (c2 << 8); unsigned cur_match; cur_match = ctx->digram_tab[digram]; ctx->digram_tab[digram] = ctx->match_window_pos; if (cur_match != 0 && ctx->window[cur_match + 2] != ctx->window[ctx->match_window_pos + 2]) { matches_ret->len = 2; matches_ret->offset = ctx->match_window_pos - cur_match; matches_ret++; num_matches++; prev_len = 2; } } if (ctx->match_window_end - ctx->match_window_pos >= 3) { unsigned hash; unsigned cur_match; hash = lzx_lz_compute_hash(&ctx->window[ctx->match_window_pos]); cur_match = ctx->hash_tab[hash]; ctx->hash_tab[hash] = ctx->match_window_pos; num_matches += lzx_lz_get_matches(ctx->window, ctx->match_window_end - ctx->match_window_pos, ctx->match_window_pos, ctx->params.slow.num_fast_bytes, ctx->child_tab, cur_match, prev_len, matches_ret); } ctx->cached_matches[ctx->cached_matches_pos].len = num_matches; ctx->cached_matches[ctx->cached_matches_pos].offset = ctx->match_window_pos; if (num_matches) { struct raw_match *longest_match_ptr = &ctx->cached_matches[ctx->cached_matches_pos + 1 + num_matches - 1]; u16 len = longest_match_ptr->len; /* If the longest match returned by the match-finder * reached the number of fast bytes, extend it as much * as possible. */ if (len == ctx->params.slow.num_fast_bytes) { const unsigned maxlen = min(ctx->match_window_end - ctx->match_window_pos, LZX_MAX_MATCH); const u8 * const matchptr = &ctx->window[ctx->match_window_pos - longest_match_ptr->offset]; const u8 * const strptr = &ctx->window[ctx->match_window_pos]; while (len < maxlen && matchptr[len] == strptr[len]) len++; } longest_match_ptr->len = len; } } ctx->cached_matches_pos += num_matches + 1; *matches_ret = matches; #if 0 printf("\n"); for (unsigned i = 0; i < num_matches; i++) { printf("Len %u Offset %u\n", matches[i].len, matches[i].offset); } #endif for (unsigned i = 0; i < num_matches; i++) { LZX_ASSERT(matches[i].len <= LZX_MAX_MATCH); if (matches[i].len >= LZX_MIN_MATCH) { LZX_ASSERT(matches[i].offset <= ctx->match_window_pos); LZX_ASSERT(matches[i].len <= ctx->match_window_end - ctx->match_window_pos); LZX_ASSERT(!memcmp(&ctx->window[ctx->match_window_pos], &ctx->window[ctx->match_window_pos - matches[i].offset], matches[i].len)); } } ctx->match_window_pos++; return num_matches; } /* * 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 raw_match lzx_lz_reverse_near_optimal_match_list(struct lzx_compressor *ctx, unsigned cur_pos) { unsigned prev_link, saved_prev_link; unsigned prev_match_offset, saved_prev_match_offset; ctx->optimum_end_idx = cur_pos; saved_prev_link = ctx->optimum[cur_pos].prev.link; saved_prev_match_offset = ctx->optimum[cur_pos].prev.match_offset; do { prev_link = saved_prev_link; prev_match_offset = saved_prev_match_offset; saved_prev_link = ctx->optimum[prev_link].prev.link; saved_prev_match_offset = ctx->optimum[prev_link].prev.match_offset; ctx->optimum[prev_link].next.link = cur_pos; ctx->optimum[prev_link].next.match_offset = prev_match_offset; cur_pos = prev_link; } while (cur_pos != 0); ctx->optimum_cur_idx = ctx->optimum[0].next.link; return (struct raw_match) { .len = ctx->optimum_cur_idx, .offset = ctx->optimum[0].next.match_offset, }; } /* * lzx_lz_get_near_optimal_match() - * * Choose the "best" match or literal to use at the next position in the input. * * Unlike a "greedy" parser that always takes the longest match, or even a * parser with one match/literal look-ahead like zlib, the algorithm used here * may look ahead many matches/literals to determine the best match/literal to * output 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 Huffman code cost * model rather than simply assuming that longer is better. It is not a true * "optimal" parser, however, since some shortcuts can be taken; for example, if * a match is very long, the parser just chooses it immediately before too much * time is wasting considering many different alternatives that are unlikely to * be better. * * This algorithm is based on that used in 7-Zip's deflate encoder. * * Each call to this function does one of two things: * * 1. Build a near-optimal sequence of 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; * * This function relies on the following state in the compressor context: * * ctx->window (read-only: preprocessed data being compressed) * ctx->cost (read-only: cost model to use) * ctx->optimum (internal state; leave uninitialized) * ctx->optimum_cur_idx (must set to 0 before first call) * ctx->optimum_end_idx (must set to 0 before first call) * ctx->hash_tab (must set to 0 before first call) * ctx->cached_matches (internal state; leave uninitialized) * ctx->cached_matches_pos (initialize to 0 before first call; save and * restore value if restarting parse from a * certain position) * ctx->match_window_pos (must initialize to position of next match to * return; subsequent calls return subsequent * matches) * ctx->match_window_end (must initialize to limit of match-finding region; * subsequent calls use the same limit) * * The return value is a (length, offset) pair specifying the match or literal * chosen. */ static struct raw_match lzx_lz_get_near_optimal_match(struct lzx_compressor * ctx) { #if 0 /* Testing: literals only */ ctx->match_window_pos++; return (struct raw_match) { .len = 0 }; #elif 0 /* Testing: greedy parsing */ struct raw_match *matches; unsigned num_matches; struct raw_match match = {.len = 0}; num_matches = lzx_lz_get_matches_caching(ctx, &matches); if (num_matches) { match = matches[num_matches - 1]; lzx_lz_skip_bytes(ctx, match.len - 1); } return match; #else unsigned num_possible_matches; struct raw_match *possible_matches; struct raw_match match; unsigned longest_match_len; unsigned len, match_idx; if (ctx->optimum_cur_idx != ctx->optimum_end_idx) { /* Case 2: Return the next match/literal already found. */ match.len = ctx->optimum[ctx->optimum_cur_idx].next.link - ctx->optimum_cur_idx; match.offset = ctx->optimum[ctx->optimum_cur_idx].next.match_offset; ctx->optimum_cur_idx = ctx->optimum[ctx->optimum_cur_idx].next.link; return match; } /* Case 1: Compute a new list of matches/literals to return. */ ctx->optimum_cur_idx = 0; ctx->optimum_end_idx = 0; /* Get matches at this position. */ num_possible_matches = lzx_lz_get_matches_caching(ctx, &possible_matches); /* If no matches found, return literal. */ if (num_possible_matches == 0) return (struct raw_match){ .len = 0 }; /* The matches that were found are sorted by length. Get the length of * the longest one. */ longest_match_len = possible_matches[num_possible_matches - 1].len; /* Greedy heuristic: if the longest match that was found is greater * than LZX_PARAM_NUM_FAST_BYTES, return it immediately; don't both * doing more work. */ if (longest_match_len > ctx->params.slow.num_fast_bytes) { lzx_lz_skip_bytes(ctx, longest_match_len - 1); return possible_matches[num_possible_matches - 1]; } /* Calculate the cost to reach the next position by outputting a * literal. */ #if LZX_PARAM_ACCOUNT_FOR_LRU ctx->optimum[0].queue = ctx->queue; ctx->optimum[1].queue = ctx->optimum[0].queue; #endif ctx->optimum[1].cost = lzx_literal_cost(ctx->window[ctx->match_window_pos], &ctx->costs); ctx->optimum[1].prev.link = 0; /* Calculate the cost to reach any position up to and including that * reached by the longest match, using the shortest (i.e. closest) match * that reaches each position. */ match_idx = 0; BUILD_BUG_ON(LZX_MIN_MATCH != 2); for (len = LZX_MIN_MATCH; len <= longest_match_len; len++) { LZX_ASSERT(match_idx < num_possible_matches); #if LZX_PARAM_ACCOUNT_FOR_LRU ctx->optimum[len].queue = ctx->optimum[0].queue; #endif ctx->optimum[len].prev.link = 0; ctx->optimum[len].prev.match_offset = possible_matches[match_idx].offset; ctx->optimum[len].cost = lzx_match_cost(len, possible_matches[match_idx].offset, &ctx->costs #if LZX_PARAM_ACCOUNT_FOR_LRU , &ctx->optimum[len].queue #endif ); if (len == possible_matches[match_idx].len) match_idx++; } unsigned cur_pos = 0; /* len_end: greatest index forward at which costs have been calculated * so far */ unsigned len_end = longest_match_len; for (;;) { /* Advance to next position. */ cur_pos++; if (cur_pos == len_end || cur_pos == LZX_PARAM_OPTIM_ARRAY_SIZE) return lzx_lz_reverse_near_optimal_match_list(ctx, cur_pos); /* retrieve the number of matches available at this position */ num_possible_matches = lzx_lz_get_matches_caching(ctx, &possible_matches); unsigned new_len = 0; if (num_possible_matches != 0) { new_len = possible_matches[num_possible_matches - 1].len; /* Greedy heuristic: if we found a match greater than * LZX_PARAM_NUM_FAST_BYTES, stop immediately. */ if (new_len > ctx->params.slow.num_fast_bytes) { /* Build the list of matches to return and get * the first one. */ match = lzx_lz_reverse_near_optimal_match_list(ctx, cur_pos); /* Append the long match to the end of the list. */ ctx->optimum[cur_pos].next.match_offset = possible_matches[num_possible_matches - 1].offset; ctx->optimum[cur_pos].next.link = cur_pos + new_len; ctx->optimum_end_idx = cur_pos + new_len; /* Skip over the remaining bytes of the long match. */ lzx_lz_skip_bytes(ctx, new_len - 1); /* Return first match in the list */ return match; } } /* Consider proceeding with a literal byte. */ u32 cur_cost = ctx->optimum[cur_pos].cost; u32 cur_plus_literal_cost = cur_cost + lzx_literal_cost(ctx->window[ctx->match_window_pos - 1], &ctx->costs); if (cur_plus_literal_cost < ctx->optimum[cur_pos + 1].cost) { ctx->optimum[cur_pos + 1].cost = cur_plus_literal_cost; ctx->optimum[cur_pos + 1].prev.link = cur_pos; #if LZX_PARAM_ACCOUNT_FOR_LRU ctx->optimum[cur_pos + 1].queue = ctx->optimum[cur_pos].queue; #endif } if (num_possible_matches == 0) continue; /* Consider proceeding with a match. */ while (len_end < cur_pos + new_len) ctx->optimum[++len_end].cost = ~(u32)0; match_idx = 0; for (len = LZX_MIN_MATCH; len <= new_len; len++) { LZX_ASSERT(match_idx < num_possible_matches); #if LZX_PARAM_ACCOUNT_FOR_LRU struct lzx_lru_queue q = ctx->optimum[cur_pos].queue; #endif u32 cost = cur_cost + lzx_match_cost(len, possible_matches[match_idx].offset, &ctx->costs #if LZX_PARAM_ACCOUNT_FOR_LRU , &q #endif ); if (cost < ctx->optimum[cur_pos + len].cost) { ctx->optimum[cur_pos + len].cost = cost; ctx->optimum[cur_pos + len].prev.link = cur_pos; ctx->optimum[cur_pos + len].prev.match_offset = possible_matches[match_idx].offset; #if LZX_PARAM_ACCOUNT_FOR_LRU ctx->optimum[cur_pos + len].queue = q; #endif } if (len == possible_matches[match_idx].len) match_idx++; } } #endif } /* Account for extra bits in the main symbols. */ static void lzx_update_mainsym_match_costs(int block_type, u8 main_lens[LZX_MAINTREE_NUM_SYMBOLS]) { unsigned i; LZX_ASSERT(block_type == LZX_BLOCKTYPE_ALIGNED || block_type == LZX_BLOCKTYPE_VERBATIM); for (i = LZX_NUM_CHARS; i < LZX_MAINTREE_NUM_SYMBOLS; i++) { unsigned position_slot = (i >> 3) & 0x1f; /* If it's a verbatim block, add the number of extra bits * corresponding to the position slot. * * If it's an aligned block and there would normally be at least * 3 extra bits, count 3 less because they will be output as an * aligned offset symbol instead. */ unsigned num_extra_bits = lzx_get_num_extra_bits(position_slot); if (block_type == LZX_BLOCKTYPE_ALIGNED && num_extra_bits >= 3) num_extra_bits -= 3; main_lens[i] += num_extra_bits; } } /* * Compute the costs, in bits, to output a compressed block as aligned offset * and verbatim. * * @block_size * Number of bytes of uncompressed data this block represents. * @codes * Huffman codes that will be used to output the block. * @prev_codes * Huffman codes for the previous block, or all zeroes if this is the first * block. * @freqs * Frequencies of Huffman symbol that will be output in the block. * @aligned_cost_ret * Cost of aligned block will be returned here. * @verbatim_cost_ret * Cost of verbatim block will be returned here. */ static void lzx_compute_compressed_block_costs(unsigned block_size, const struct lzx_codes *codes, const struct lzx_codes *prev_codes, const struct lzx_freqs *freqs, unsigned * aligned_cost_ret, unsigned * verbatim_cost_ret) { unsigned common_cost = 0; unsigned aligned_cost = 0; unsigned verbatim_cost = 0; u8 updated_main_lens[LZX_MAINTREE_NUM_SYMBOLS]; /* Account for cost of block header. */ common_cost += LZX_BLOCKTYPE_NBITS; if (block_size == LZX_DEFAULT_BLOCK_SIZE) common_cost += 1; else common_cost += LZX_BLOCKSIZE_NBITS; /* Account for cost of outputting aligned offset code. */ aligned_cost += LZX_ALIGNEDTREE_NUM_SYMBOLS * LZX_ALIGNEDTREE_ELEMENT_SIZE; /* Account for cost of outputting main and length codes. */ common_cost += lzx_code_cost(codes->lens.main, prev_codes->lens.main, LZX_NUM_CHARS); common_cost += lzx_code_cost(codes->lens.main + LZX_NUM_CHARS, prev_codes->lens.main + LZX_NUM_CHARS, LZX_MAINTREE_NUM_SYMBOLS - LZX_NUM_CHARS); common_cost += lzx_code_cost(codes->lens.len, prev_codes->lens.len, LZX_LENTREE_NUM_SYMBOLS); /* Account for cost to output main, length, and aligned symbols, taking * into account extra position bits. */ memcpy(updated_main_lens, codes->lens.main, LZX_MAINTREE_NUM_SYMBOLS); lzx_update_mainsym_match_costs(LZX_BLOCKTYPE_VERBATIM, updated_main_lens); verbatim_cost += lzx_huffman_code_output_cost(updated_main_lens, freqs->main, LZX_MAINTREE_NUM_SYMBOLS); memcpy(updated_main_lens, codes->lens.main, LZX_MAINTREE_NUM_SYMBOLS); lzx_update_mainsym_match_costs(LZX_BLOCKTYPE_ALIGNED, updated_main_lens); aligned_cost += lzx_huffman_code_output_cost(updated_main_lens, freqs->main, LZX_MAINTREE_NUM_SYMBOLS); common_cost += lzx_huffman_code_output_cost(codes->lens.len, freqs->len, LZX_LENTREE_NUM_SYMBOLS); aligned_cost += lzx_huffman_code_output_cost(codes->lens.aligned, freqs->aligned, LZX_ALIGNEDTREE_NUM_SYMBOLS); *aligned_cost_ret = aligned_cost + common_cost; *verbatim_cost_ret = verbatim_cost + common_cost; } /* Prepare a (nonsplit) compressed block. */ static unsigned lzx_prepare_compressed_block(struct lzx_compressor *ctx, unsigned block_number, struct lzx_codes *prev_codes) { struct lzx_block_spec *spec = &ctx->block_specs[block_number - 1]; unsigned orig_cached_matches_pos = ctx->cached_matches_pos; struct lzx_lru_queue orig_queue = ctx->queue; struct lzx_freqs freqs; unsigned cost; /* Here's where the real work happens. The following loop runs one or * more times, each time using a cost model based on the Huffman codes * computed from the previous iteration (the first iteration uses a * default model). Each iteration of the loop uses a heuristic * algorithm to divide the block into near-optimal matches/literals from * beginning to end. */ LZX_ASSERT(ctx->params.slow.num_optim_passes >= 1); spec->num_chosen_matches = 0; for (unsigned pass = 0; pass < ctx->params.slow.num_optim_passes; pass++) { LZX_DEBUG("Block %u: Match-choosing pass %u of %u", block_number, pass + 1, ctx->params.slow.num_optim_passes); /* Reset frequency tables. */ memset(&freqs, 0, sizeof(freqs)); /* Reset match offset LRU queue. */ ctx->queue = orig_queue; /* Reset match-finding position. */ ctx->cached_matches_pos = orig_cached_matches_pos; ctx->match_window_pos = spec->window_pos; ctx->match_window_end = spec->window_pos + spec->block_size; /* Set cost model. */ lzx_set_costs(ctx, &spec->codes.lens); unsigned window_pos = spec->window_pos; unsigned end = window_pos + spec->block_size; while (window_pos < end) { struct raw_match match; struct lzx_match lzx_match; match = lzx_lz_get_near_optimal_match(ctx); if (match.len >= LZX_MIN_MATCH) { /* Best to output a match here. */ LZX_ASSERT(match.len <= LZX_MAX_MATCH); LZX_ASSERT(!memcmp(&ctx->window[window_pos], &ctx->window[window_pos - match.offset], match.len)); /* Tally symbol frequencies. */ lzx_match.data = lzx_record_match(match.offset, match.len, &freqs, &ctx->queue); window_pos += match.len; } else { /* Best to output a literal here. */ /* Tally symbol frequencies. */ lzx_match.data = lzx_record_literal(ctx->window[window_pos], &freqs); window_pos += 1; } /* If it's the last pass, save the match/literal in * intermediate form. */ if (pass == ctx->params.slow.num_optim_passes - 1) { ctx->chosen_matches[spec->chosen_matches_start_pos + spec->num_chosen_matches] = lzx_match; spec->num_chosen_matches++; } } LZX_ASSERT(window_pos == end); /* Build Huffman codes using the new frequencies. */ lzx_make_huffman_codes(&freqs, &spec->codes); /* The first time we get here is when the full input has been * processed, so the match-finding is done. */ ctx->matches_already_found = true; } LZX_DEBUG("Block %u: saved %u matches/literals @ %u", block_number, spec->num_chosen_matches, spec->chosen_matches_start_pos); unsigned aligned_cost; unsigned verbatim_cost; lzx_compute_compressed_block_costs(spec->block_size, &spec->codes, prev_codes, &freqs, &aligned_cost, &verbatim_cost); /* Choose whether to make the block aligned offset or verbatim. */ if (aligned_cost < verbatim_cost) { spec->block_type = LZX_BLOCKTYPE_ALIGNED; cost = aligned_cost; LZX_DEBUG("Using aligned block (cost %u vs %u for verbatim)", aligned_cost, verbatim_cost); } else { spec->block_type = LZX_BLOCKTYPE_VERBATIM; cost = verbatim_cost; LZX_DEBUG("Using verbatim block (cost %u vs %u for aligned)", verbatim_cost, aligned_cost); } LZX_DEBUG("Block %u is %u => %u bytes unsplit.", block_number, spec->block_size, cost / 8); return cost; } /* * lzx_prepare_block_recursive() - * * Given a (possibly nonproper) sub-sequence of the preprocessed input, compute * the LZX block(s) that it should be output as. * * This function initially considers the case where the given sub-sequence of * the preprocessed input be output as a single block. This block is calculated * and its cost (number of bits required to output it) is computed. * * Then, if @max_split_level is greater than zero, a split into two evenly sized * subblocks is considered. The block is recursively split in this way, * potentially up to the depth specified by @max_split_level. The cost of the * split block is compared to the cost of the single block, and the lower cost * solution is used. * * For each compressed output block computed, the sequence of matches/literals * and the corresponding Huffman codes for the block are produced and saved. * * The return value is the approximate number of bits the block (or all * subblocks, in the case that the split block had lower cast), will take up * when written to the compressed output. */ static unsigned lzx_prepare_block_recursive(struct lzx_compressor * ctx, unsigned block_number, unsigned max_split_level, struct lzx_codes **prev_codes_p) { struct lzx_block_spec *spec = &ctx->block_specs[block_number - 1]; unsigned cost; unsigned orig_cached_matches_pos; struct lzx_lru_queue orig_queue, nonsplit_queue; struct lzx_codes *prev_codes = *prev_codes_p; LZX_DEBUG("Preparing block %u...", block_number); /* Save positions of chosen and cached matches, and the match offset LRU * queue, so that they can be restored if splitting is attempted. */ orig_cached_matches_pos = ctx->cached_matches_pos; orig_queue = ctx->queue; /* Consider outputting the input subsequence as a single block. */ spec->is_split = 0; cost = lzx_prepare_compressed_block(ctx, block_number, prev_codes); nonsplit_queue = ctx->queue; *prev_codes_p = &spec->codes; /* If the maximum split level is at least one, consider splitting the * block in two. */ if (max_split_level--) { LZX_DEBUG("Calculating split of block %u...", block_number); struct lzx_block_spec *spec1, *spec2; unsigned split_cost; ctx->cached_matches_pos = orig_cached_matches_pos; ctx->queue = orig_queue; /* Prepare and get the cost of the first sub-block. */ spec1 = &ctx->block_specs[block_number * 2 - 1]; spec1->codes.lens = spec->codes.lens; spec1->window_pos = spec->window_pos; spec1->block_size = spec->block_size / 2; spec1->chosen_matches_start_pos = spec->chosen_matches_start_pos + LZX_MAX_WINDOW_SIZE; split_cost = lzx_prepare_block_recursive(ctx, block_number * 2, max_split_level, &prev_codes); /* Prepare and get the cost of the second sub-block. */ spec2 = spec1 + 1; spec2->codes.lens = spec->codes.lens; spec2->window_pos = spec->window_pos + spec1->block_size; spec2->block_size = spec->block_size - spec1->block_size; spec2->chosen_matches_start_pos = spec1->chosen_matches_start_pos + spec1->block_size; split_cost += lzx_prepare_block_recursive(ctx, block_number * 2 + 1, max_split_level, &prev_codes); /* Compare the cost of the whole block with that of the split * block. Choose the lower cost solution. */ if (split_cost < cost) { LZX_DEBUG("Splitting block %u is worth it " "(%u => %u bytes).", block_number, cost / 8, split_cost / 8); spec->is_split = 1; cost = split_cost; *prev_codes_p = prev_codes; } else { LZX_DEBUG("Splitting block %u is NOT worth it " "(%u => %u bytes).", block_number, cost / 8, split_cost / 8); ctx->queue = nonsplit_queue; } } return cost; } /* Empirical averages */ static const u8 lzx_default_mainsym_costs[LZX_MAINTREE_NUM_SYMBOLS] = { 7, 9, 9, 10, 9, 10, 10, 10, 9, 10, 9, 10, 10, 9, 10, 10, 9, 10, 10, 11, 10, 10, 10, 11, 10, 11, 11, 11, 10, 11, 11, 11, 8, 11, 9, 10, 9, 10, 11, 11, 9, 9, 11, 10, 10, 9, 9, 9, 8, 8, 8, 8, 8, 9, 9, 9, 8, 8, 9, 9, 9, 9, 10, 10, 10, 8, 9, 8, 8, 8, 8, 9, 9, 9, 10, 10, 8, 8, 9, 9, 8, 10, 9, 8, 8, 9, 8, 9, 9, 10, 10, 10, 9, 10, 11, 9, 10, 8, 9, 8, 8, 8, 8, 9, 8, 8, 9, 9, 8, 8, 8, 8, 8, 10, 8, 8, 7, 8, 9, 9, 9, 9, 10, 11, 10, 10, 11, 11, 10, 11, 11, 10, 10, 11, 11, 11, 10, 10, 11, 10, 11, 10, 11, 11, 10, 11, 11, 12, 11, 11, 11, 12, 11, 11, 11, 11, 11, 11, 11, 12, 10, 11, 11, 11, 11, 11, 11, 12, 11, 11, 11, 11, 11, 12, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 12, 11, 11, 10, 11, 11, 11, 11, 12, 11, 11, 10, 11, 11, 11, 10, 12, 11, 11, 10, 10, 11, 10, 10, 11, 11, 11, 10, 11, 11, 11, 10, 11, 11, 11, 10, 11, 11, 11, 10, 11, 10, 9, 8, 7, 10, 10, 11, 10, 11, 7, 9, 9, 11, 11, 11, 12, 11, 9, 10, 10, 12, 12, 13, 13, 12, 11, 10, 12, 12, 14, 14, 14, 13, 12, 9, 12, 13, 14, 14, 14, 14, 14, 9, 10, 13, 14, 14, 14, 14, 14, 9, 9, 11, 11, 13, 13, 13, 14, 9, 9, 11, 12, 12, 13, 13, 13, 8, 8, 11, 11, 12, 12, 12, 11, 9, 9, 10, 11, 12, 12, 12, 11, 8, 9, 10, 10, 11, 12, 11, 10, 9, 9, 10, 11, 11, 12, 11, 10, 8, 9, 10, 10, 11, 11, 11, 9, 9, 9, 10, 11, 11, 11, 11, 9, 8, 8, 10, 10, 11, 11, 11, 9, 9, 9, 10, 10, 11, 11, 11, 9, 9, 8, 9, 10, 11, 11, 11, 9, 10, 9, 10, 11, 11, 11, 11, 9, 14, 9, 9, 10, 10, 11, 10, 9, 14, 9, 10, 11, 11, 11, 11, 9, 14, 9, 10, 10, 11, 11, 11, 9, 14, 10, 10, 11, 11, 12, 11, 10, 14, 10, 10, 10, 11, 11, 11, 10, 14, 11, 11, 11, 11, 12, 12, 10, 14, 10, 11, 11, 11, 12, 11, 10, 14, 11, 11, 11, 12, 12, 12, 11, 15, 11, 11, 11, 12, 12, 12, 11, 14, 12, 12, 12, 12, 13, 12, 11, 15, 12, 12, 12, 13, 13, 13, 12, 15, 14, 13, 14, 14, 14, 14, 13, }; /* Empirical averages */ static const u8 lzx_default_lensym_costs[LZX_LENTREE_NUM_SYMBOLS] = { 5, 5, 5, 5, 5, 6, 5, 5, 6, 7, 7, 7, 8, 8, 7, 8, 9, 9, 9, 9, 10, 9, 9, 10, 9, 10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 13, 12, 12, 12, 13, 12, 13, 13, 12, 12, 13, 12, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 14, 13, 14, 13, 14, 13, 14, 13, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 13, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 10, }; /* * Set default symbol costs. */ static void lzx_set_default_costs(struct lzx_lens * lens) { unsigned i; #if LZX_PARAM_USE_EMPIRICAL_DEFAULT_COSTS memcpy(&lens->main, lzx_default_mainsym_costs, LZX_MAINTREE_NUM_SYMBOLS); memcpy(&lens->len, lzx_default_lensym_costs, LZX_LENTREE_NUM_SYMBOLS); #else /* Literal symbols */ for (i = 0; i < LZX_NUM_CHARS; i++) lens->main[i] = 8; /* Match header symbols */ for (; i < LZX_MAINTREE_NUM_SYMBOLS; i++) lens->main[i] = 10; /* Length symbols */ for (i = 0; i < LZX_LENTREE_NUM_SYMBOLS; i++) lens->len[i] = 8; #endif /* Aligned offset symbols */ for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++) lens->aligned[i] = 3; } /* * lzx_prepare_blocks() - * * Calculate the blocks to split the preprocessed data into. * * Input --- the preprocessed data: * * ctx->window[] * ctx->window_size * * Working space: * Match finding: * ctx->hash_tab * ctx->child_tab * ctx->cached_matches * ctx->cached_matches_pos * ctx->matches_already_found * * Block cost modeling: * ctx->costs * ctx->block_specs (also an output) * * Match choosing: * ctx->optimum * ctx->optimum_cur_idx * ctx->optimum_end_idx * ctx->chosen_matches (also an output) * * Output --- the block specifications and the corresponding match/literal data: * * ctx->block_specs[] * ctx->chosen_matches[] * * The return value is the approximate number of bits the compressed data will * take up. */ static unsigned lzx_prepare_blocks(struct lzx_compressor * ctx) { /* This function merely does some initializations, then passes control * to lzx_prepare_block_recursive(). */ /* 1. Initialize match-finding variables. */ /* Zero all entries in the hash table, indicating that no length-3 * character sequences have been discovered in the input yet. */ memset(ctx->hash_tab, 0, LZX_LZ_HASH_SIZE * 2 * sizeof(ctx->hash_tab[0])); if (ctx->params.slow.use_len2_matches) memset(ctx->digram_tab, 0, 256 * 256 * sizeof(ctx->digram_tab[0])); /* Note: ctx->child_tab need not be initialized. */ /* No matches have been found and cached yet. */ ctx->cached_matches_pos = 0; ctx->matches_already_found = false; /* 2. Initialize match-choosing variables. */ ctx->optimum_cur_idx = 0; ctx->optimum_end_idx = 0; /* Note: ctx->optimum need not be initialized. */ ctx->block_specs[0].chosen_matches_start_pos = 0; /* 3. Set block 1 (index 0) to represent the entire input data. */ ctx->block_specs[0].block_size = ctx->window_size; ctx->block_specs[0].window_pos = 0; /* 4. Set up a default Huffman symbol cost model for block 1 (index 0). * The model will be refined later. */ lzx_set_default_costs(&ctx->block_specs[0].codes.lens); /* 5. Initialize the match offset LRU queue. */ ctx->queue = (struct lzx_lru_queue){1, 1, 1}; /* 6. Pass control to recursive procedure. */ struct lzx_codes * prev_codes = &ctx->zero_codes; return lzx_prepare_block_recursive(ctx, 1, ctx->params.slow.num_split_passes, &prev_codes); } /* * This is the fast version of lzx_prepare_blocks(), which "quickly" prepares a * single compressed block containing the entire input. See the description of * the "Fast algorithm" at the beginning of this file for more information. * * Input --- the preprocessed data: * * ctx->window[] * ctx->window_size * * Working space: * ctx->queue * * Output --- the block specifications and the corresponding match/literal data: * * ctx->block_specs[] * ctx->chosen_matches[] */ static void lzx_prepare_block_fast(struct lzx_compressor * ctx) { unsigned num_matches; struct lzx_freqs freqs; struct lzx_block_spec *spec; /* Parameters to hash chain LZ match finder */ static const struct lz_params lzx_lz_params = { /* LZX_MIN_MATCH == 2, but 2-character matches are rarely * useful; the minimum match for compression is set to 3 * instead. */ .min_match = 3, .max_match = LZX_MAX_MATCH, .good_match = LZX_MAX_MATCH, .nice_match = LZX_MAX_MATCH, .max_chain_len = LZX_MAX_MATCH, .max_lazy_match = LZX_MAX_MATCH, .too_far = 4096, }; /* Initialize symbol frequencies and match offset LRU queue. */ memset(&freqs, 0, sizeof(struct lzx_freqs)); ctx->queue = (struct lzx_lru_queue){ 1, 1, 1 }; /* Determine series of matches/literals to output. */ num_matches = lz_analyze_block(ctx->window, ctx->window_size, (u32*)ctx->chosen_matches, lzx_record_match, lzx_record_literal, &freqs, &ctx->queue, &freqs, &lzx_lz_params); /* Set up block specification. */ spec = &ctx->block_specs[0]; spec->is_split = 0; spec->block_type = LZX_BLOCKTYPE_ALIGNED; spec->window_pos = 0; spec->block_size = ctx->window_size; spec->num_chosen_matches = num_matches; spec->chosen_matches_start_pos = 0; lzx_make_huffman_codes(&freqs, &spec->codes); } static void do_call_insn_translation(u32 *call_insn_target, int input_pos, s32 file_size) { s32 abs_offset; s32 rel_offset; rel_offset = le32_to_cpu(*call_insn_target); if (rel_offset >= -input_pos && rel_offset < file_size) { if (rel_offset < file_size - input_pos) { /* "good translation" */ abs_offset = rel_offset + input_pos; } else { /* "compensating translation" */ abs_offset = rel_offset - file_size; } *call_insn_target = cpu_to_le32(abs_offset); } } /* This is the reverse of undo_call_insn_preprocessing() in lzx-decompress.c. * See the comment above that function for more information. */ static void do_call_insn_preprocessing(u8 data[], int size) { for (int i = 0; i < size - 10; i++) { if (data[i] == 0xe8) { do_call_insn_translation((u32*)&data[i + 1], i, LZX_WIM_MAGIC_FILESIZE); i += 4; } } } /* API function documented in wimlib.h */ WIMLIBAPI unsigned wimlib_lzx_compress2(const void * const restrict uncompressed_data, unsigned const uncompressed_len, void * const restrict compressed_data, struct wimlib_lzx_context * const restrict lzx_ctx) { struct lzx_compressor *ctx = (struct lzx_compressor*)lzx_ctx; struct output_bitstream ostream; unsigned compressed_len; if (uncompressed_len < 100) { LZX_DEBUG("Too small to bother compressing."); return 0; } if (uncompressed_len > 32768) { LZX_DEBUG("Only up to 32768 bytes of uncompressed data are supported."); return 0; } wimlib_assert(lzx_ctx != NULL); LZX_DEBUG("Attempting to compress %u bytes...", uncompressed_len); /* The input data must be preprocessed. To avoid changing the original * input, copy it to a temporary buffer. */ memcpy(ctx->window, uncompressed_data, uncompressed_len); ctx->window_size = uncompressed_len; /* This line is unnecessary; it just avoids inconsequential accesses of * uninitialized memory that would show up in memory-checking tools such * as valgrind. */ memset(&ctx->window[ctx->window_size], 0, 12); LZX_DEBUG("Preprocessing data..."); /* Before doing any actual compression, do the call instruction (0xe8 * byte) translation on the uncompressed data. */ do_call_insn_preprocessing(ctx->window, ctx->window_size); LZX_DEBUG("Preparing blocks..."); /* Prepare the compressed data. */ if (ctx->params.algorithm == WIMLIB_LZX_ALGORITHM_FAST) lzx_prepare_block_fast(ctx); else lzx_prepare_blocks(ctx); LZX_DEBUG("Writing compressed blocks..."); /* Generate the compressed data. */ init_output_bitstream(&ostream, compressed_data, ctx->window_size - 1); lzx_write_all_blocks(ctx, &ostream); LZX_DEBUG("Flushing bitstream..."); if (flush_output_bitstream(&ostream)) { /* If the bitstream cannot be flushed, then the output space was * exhausted. */ LZX_DEBUG("Data did not compress to less than original length!"); return 0; } /* Compute the length of the compressed data. */ compressed_len = ostream.bit_output - (u8*)compressed_data; LZX_DEBUG("Done: compressed %u => %u bytes.", uncompressed_len, compressed_len); #if defined(ENABLE_LZX_DEBUG) || defined(ENABLE_VERIFY_COMPRESSION) /* Verify that we really get the same thing back when decompressing. */ { u8 buf[uncompressed_len]; int ret; unsigned i; ret = wimlib_lzx_decompress(compressed_data, compressed_len, buf, uncompressed_len); if (ret) { ERROR("Failed to decompress data we " "compressed using LZX algorithm"); wimlib_assert(0); return 0; } bool bad = false; const u8 * udata = uncompressed_data; for (i = 0; i < uncompressed_len; i++) { if (buf[i] != udata[i]) { bad = true; ERROR("Data we compressed using LZX algorithm " "didn't decompress to original " "(difference at idx %u: c %#02x, u %#02x)", i, buf[i], udata[i]); } } if (bad) { wimlib_assert(0); return 0; } } #endif return compressed_len; } static bool lzx_params_compatible(const struct wimlib_lzx_params *oldparams, const struct wimlib_lzx_params *newparams) { return 0 == memcmp(oldparams, newparams, sizeof(struct wimlib_lzx_params)); } /* API function documented in wimlib.h */ WIMLIBAPI int wimlib_lzx_alloc_context(const struct wimlib_lzx_params *params, struct wimlib_lzx_context **ctx_pp) { LZX_DEBUG("Allocating LZX context..."); struct lzx_compressor *ctx; static const struct wimlib_lzx_params fast_default = { .size_of_this = sizeof(struct wimlib_lzx_params), .algorithm = WIMLIB_LZX_ALGORITHM_FAST, .use_defaults = 0, .fast = { }, }; static const struct wimlib_lzx_params slow_default = { .size_of_this = sizeof(struct wimlib_lzx_params), .algorithm = WIMLIB_LZX_ALGORITHM_SLOW, .use_defaults = 0, .slow = { .use_len2_matches = 1, .num_fast_bytes = 32, .num_optim_passes = 3, .num_split_passes = 3, .main_nostat_cost = 15, .len_nostat_cost = 15, .aligned_nostat_cost = 7, }, }; if (params == NULL) { LZX_DEBUG("Using default algorithm and parameters."); params = &slow_default; } if (params->algorithm != WIMLIB_LZX_ALGORITHM_SLOW && params->algorithm != WIMLIB_LZX_ALGORITHM_FAST) { LZX_DEBUG("Invalid algorithm."); return WIMLIB_ERR_INVALID_PARAM; } if (params->use_defaults) { if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) params = &slow_default; else params = &fast_default; } if (params->size_of_this != sizeof(struct wimlib_lzx_params)) { LZX_DEBUG("Invalid parameter structure size!"); return WIMLIB_ERR_INVALID_PARAM; } if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) { if (params->slow.num_fast_bytes < 3 || params->slow.num_fast_bytes > 257) { LZX_DEBUG("Invalid number of fast bytes!"); return WIMLIB_ERR_INVALID_PARAM; } if (params->slow.num_optim_passes < 1) { LZX_DEBUG("Invalid number of optimization passes!"); return WIMLIB_ERR_INVALID_PARAM; } if (params->slow.main_nostat_cost < 1 || params->slow.main_nostat_cost > 16) { LZX_DEBUG("Invalid main_nostat_cost!"); return WIMLIB_ERR_INVALID_PARAM; } if (params->slow.len_nostat_cost < 1 || params->slow.len_nostat_cost > 16) { LZX_DEBUG("Invalid len_nostat_cost!"); return WIMLIB_ERR_INVALID_PARAM; } if (params->slow.aligned_nostat_cost < 1 || params->slow.aligned_nostat_cost > 8) { LZX_DEBUG("Invalid aligned_nostat_cost!"); return WIMLIB_ERR_INVALID_PARAM; } } if (ctx_pp == NULL) { LZX_DEBUG("Check parameters only."); return 0; } ctx = *(struct lzx_compressor**)ctx_pp; if (ctx && lzx_params_compatible(&ctx->params, params)) return 0; LZX_DEBUG("Allocating memory."); ctx = MALLOC(sizeof(struct lzx_compressor)); if (ctx == NULL) goto err; size_t block_specs_length; if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) block_specs_length = ((1 << (params->slow.num_split_passes + 1)) - 1); else block_specs_length = 1; ctx->block_specs = MALLOC(block_specs_length * sizeof(ctx->block_specs[0])); if (ctx->block_specs == NULL) goto err_free_ctx; if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) { ctx->hash_tab = MALLOC((LZX_LZ_HASH_SIZE + 2 * LZX_MAX_WINDOW_SIZE) * sizeof(ctx->hash_tab[0])); if (ctx->hash_tab == NULL) goto err_free_block_specs; ctx->child_tab = ctx->hash_tab + LZX_LZ_HASH_SIZE; } else { ctx->hash_tab = NULL; ctx->child_tab = NULL; } if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW && params->slow.use_len2_matches) { ctx->digram_tab = MALLOC(256 * 256 * sizeof(ctx->digram_tab[0])); if (ctx->digram_tab == NULL) goto err_free_hash_tab; } else { ctx->digram_tab = NULL; } if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) { ctx->cached_matches = MALLOC(10 * LZX_MAX_WINDOW_SIZE * sizeof(ctx->cached_matches[0])); if (ctx->cached_matches == NULL) goto err_free_digram_tab; } else { ctx->cached_matches = NULL; } if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) { ctx->optimum = MALLOC((LZX_PARAM_OPTIM_ARRAY_SIZE + LZX_MAX_MATCH) * sizeof(ctx->optimum[0])); if (ctx->optimum == NULL) goto err_free_cached_matches; } else { ctx->optimum = NULL; } size_t chosen_matches_length; if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) chosen_matches_length = LZX_MAX_WINDOW_SIZE * (params->slow.num_split_passes + 1); else chosen_matches_length = LZX_MAX_WINDOW_SIZE; ctx->chosen_matches = MALLOC(chosen_matches_length * sizeof(ctx->chosen_matches[0])); if (ctx->chosen_matches == NULL) goto err_free_optimum; memcpy(&ctx->params, params, sizeof(struct wimlib_lzx_params)); memset(&ctx->zero_codes, 0, sizeof(ctx->zero_codes)); LZX_DEBUG("Successfully allocated new LZX context."); wimlib_lzx_free_context(*ctx_pp); *ctx_pp = (struct wimlib_lzx_context*)ctx; return 0; err_free_optimum: FREE(ctx->optimum); err_free_cached_matches: FREE(ctx->cached_matches); err_free_digram_tab: FREE(ctx->digram_tab); err_free_hash_tab: FREE(ctx->hash_tab); err_free_block_specs: FREE(ctx->block_specs); err_free_ctx: FREE(ctx); err: LZX_DEBUG("Ran out of memory."); return WIMLIB_ERR_NOMEM; } /* API function documented in wimlib.h */ WIMLIBAPI void wimlib_lzx_free_context(struct wimlib_lzx_context *_ctx) { struct lzx_compressor *ctx = (struct lzx_compressor*)_ctx; if (ctx) { FREE(ctx->chosen_matches); FREE(ctx->optimum); FREE(ctx->cached_matches); FREE(ctx->digram_tab); FREE(ctx->hash_tab); FREE(ctx->block_specs); FREE(ctx); } } /* API function documented in wimlib.h */ WIMLIBAPI unsigned wimlib_lzx_compress(const void * const restrict uncompressed_data, unsigned const uncompressed_len, void * const restrict compressed_data) { int ret; struct wimlib_lzx_context *ctx; unsigned compressed_len; ret = wimlib_lzx_alloc_context(NULL, &ctx); if (ret) { wimlib_assert(ret != WIMLIB_ERR_INVALID_PARAM); WARNING("Couldn't allocate LZX compression context: %"TS"", wimlib_get_error_string(ret)); return 0; } compressed_len = wimlib_lzx_compress2(uncompressed_data, uncompressed_len, compressed_data, ctx); wimlib_lzx_free_context(ctx); return compressed_len; }