/*
* lzx-compress.c
- *
- * LZX compression routines
*/
/*
- * Copyright (C) 2012, 2013 Eric Biggers
+ * Copyright (C) 2012, 2013, 2014 Eric Biggers
*
* This file is part of wimlib, a library for working with WIM files.
*
/*
- * This file contains a compressor for the LZX compression format, as used in
- * the WIM file format.
+ * 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
- * ======
+ * Format Overview
*
- * First, the primary reference for the LZX compression format is the
- * specification released by Microsoft.
+ * 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.
*
- * Second, the comments in lzx-decompress.c provide some more information about
- * the LZX compression format, including 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:
*
- * 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 to attempt to make x86 machine code slightly more
+ * compressible before attempting to compress it further.
*
- * - 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
+ * length) and a "position slot" (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()
+ * - 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").
*
- * 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 has a minimum match length of 2 rather than 3.
*
- * - lzx-compress (author: Matthew T. Russotto), on which some parts of this
- * code were originally based.
+ * - 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 the beginning of the window.
+ *
+ * Depending on how good a compression ratio we want (see the "Match-choosing"
+ * section), we may want to find: (a) all matches, or (b) just the longest
+ * match, or (c) just some "promising" matches that we are able to find quickly,
+ * or (d) just the longest match that we're able to find quickly. Below we
+ * introduce the match-finding methods that the code currently uses or has
+ * previously used:
+ *
+ * - Hash chains. Maintain a table that maps hash codes, computed from
+ * fixed-length byte sequences, to linked lists containing previous window
+ * positions. To search for matches, compute the hash for the current
+ * position in the window and search the appropriate hash chain. When
+ * advancing to the next position, prepend the current position to the
+ * appropriate hash list. This is a good approach for producing matches with
+ * stategy (d) and is useful for fast compression. Therefore, we provide an
+ * option to use this method for LZX compression. See lz_hash.c for the
+ * implementation.
+ *
+ * - Binary trees. Similar to hash chains, but each hash bucket contains a
+ * binary tree of previous window positions rather than a linked list. This
+ * is a good approach for producing matches with stategy (c) and is useful for
+ * achieving a good compression ratio. Therefore, we provide an option to use
+ * this method; see lz_bt.c for the implementation.
+ *
+ * - Suffix arrays. This code previously used this method to produce matches
+ * with stategy (c), but I've dropped it because it was slower than the binary
+ * trees approach, used more memory, and did not improve the compression ratio
+ * enough to compensate. Download wimlib v1.6.2 if you want the code.
+ * However, the suffix array method was basically as follows. Build the
+ * suffix array for the entire window. The suffix array contains each
+ * possible window position, sorted by the lexicographic order of the strings
+ * that begin at those positions. Find the matches at a given position by
+ * searching the suffix array outwards, in both directions, from the suffix
+ * array slot for that position. This produces the longest matches first, but
+ * "matches" that actually occur at later positions in the window must be
+ * skipped. To do this skipping, use an auxiliary array with dynamically
+ * constructed linked lists. Also, use the inverse suffix array to quickly
+ * find the suffix array slot for a given position without doing a binary
+ * search.
+ *
+ * ----------------------------------------------------------------------------
+ *
+ * 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.
+ *
+ * Anyway, if you've read through this comment, you hopefully should have a
+ * better idea of why things are done in a certain way in this LZX compressor,
+ * as well as in other compressors for LZ77-based formats (including third-party
+ * ones). In my opinion, the phrase "compression algorithm" is often mis-used
+ * in place of "compression format", since there can be many different
+ * algorithms that all generate compressed data in the same format. The
+ * challenge is to design an algorithm that is efficient but still gives a good
+ * compression ratio.
*/
#ifdef HAVE_CONFIG_H
#endif
#include "wimlib.h"
-#include "wimlib/compress.h"
+#include "wimlib/compressor_ops.h"
+#include "wimlib/compress_common.h"
+#include "wimlib/endianness.h"
#include "wimlib/error.h"
+#include "wimlib/lz.h"
+#include "wimlib/lz_hash.h"
+#include "wimlib/lz_bt.h"
#include "wimlib/lzx.h"
#include "wimlib/util.h"
+#include <string.h>
#ifdef ENABLE_LZX_DEBUG
-# include <wimlib/decompress.h>
+# include "wimlib/decompress_common.h"
#endif
-#include <string.h>
-
-/* 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
+#define LZX_OPTIM_ARRAY_SIZE 4096
-/* Currently, this constant can't simply be changed because the code currently
- * uses a static number of position slots (and may make other assumptions as
- * well). */
-#define LZX_MAX_WINDOW_SIZE 32768
+#define LZX_DIV_BLOCK_SIZE 32768
-/* This may be WIM-specific */
-#define LZX_DEFAULT_BLOCK_SIZE 32768
+#define LZX_CACHE_PER_POS 8
-#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
+#define LZX_CACHE_LEN (LZX_DIV_BLOCK_SIZE * (LZX_CACHE_PER_POS + 1))
+#define LZX_CACHE_SIZE (LZX_CACHE_LEN * sizeof(struct raw_match))
+#define LZX_MAX_MATCHES_PER_POS (LZX_MAX_MATCH_LEN - LZX_MIN_MATCH_LEN + 1)
/* 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];
+ u32 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
+ u32 len[LZX_LENCODE_NUM_SYMBOLS];
+ u32 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
};
-/* Lengths for the LZX main, length, and aligned offset Huffman codes */
+/* 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_MAINTREE_NUM_SYMBOLS];
- u8 len[LZX_LENTREE_NUM_SYMBOLS];
- u8 aligned[LZX_ALIGNEDTREE_NUM_SYMBOLS];
+ 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 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 */
/* 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];
+ input_idx_t main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
+ input_idx_t len[LZX_LENCODE_NUM_SYMBOLS];
+ input_idx_t aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
};
/* LZX intermediate match/literal format */
-struct lzx_match {
+struct lzx_item {
/* Bit Description
*
* 31 1 if a match, 0 if a literal.
*
* 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).
+ * (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 - 2) == 255, so it will fit in 8 bits. */
+ * (LZX_MAX_MATCH_LEN - 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 and @offset is
- * meaningless. */
-struct raw_match {
- u16 len;
- u16 offset;
-};
-
-/* Specification for a LZX block */
+/* Specification for an 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;
+ int block_type;
/* 0-based position in the window at which this block starts. */
- u16 window_pos;
+ input_idx_t window_pos;
/* The number of bytes of uncompressed data this block represents. */
- u16 block_size;
+ input_idx_t 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 match/literal sequence for this block. */
+ struct lzx_item *chosen_items;
- /* The number of match/literal specifications for this block. */
- u16 num_chosen_matches;
+ /* The length of the @chosen_items sequence. */
+ input_idx_t num_chosen_items;
/* 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 (as in a LZ (length, offset) pair) 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 (as in a LZ (length, offset) pair) 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 */
+/* State of the LZX compressor. */
struct lzx_compressor {
/* The parameters that were used to create the compressor. */
- struct wimlib_lzx_params params;
+ struct wimlib_lzx_compressor_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!!!!
+ * 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.
*
* 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];
+ * of the array in the match-finding code for optimization purposes
+ * (currently only needed for the hash chain match-finder). */
+ u8 *window;
/* 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;
+ input_idx_t window_size;
+
+ /* Allocated size of the @window. */
+ input_idx_t max_window_size;
+
+ /* 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 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;
+ /* Space for the sequences of matches/literals that were chosen for each
+ * block. */
+ struct lzx_item *chosen_items;
- /* 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].
- */
+ /* 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;
- /* 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;
+ /* The current cost model. */
+ struct lzx_costs costs;
- /* Slow algorithm only: Next position in 'cached_matches' to either
- * return or fill in. */
- unsigned cached_matches_pos;
+ /* Fast algorithm only: Array of hash table links. */
+ input_idx_t *prev_tab;
- /* Slow algorithm only: %true if reading from 'cached_matches'; %false
- * if writing to 'cached_matches'. */
- bool matches_already_found;
+ /* Slow algorithm only: Binary tree match-finder. */
+ struct lz_bt mf;
- /* Slow algorithm only: Position in window of next match to return. */
- unsigned match_window_pos;
+ /* Position in window of next match to return. */
+ input_idx_t match_window_pos;
- /* Slow algorithm only: No matches returned shall reach past this
+ /* The end-of-block position. We can't allow any matches to span this
* position. */
- unsigned match_window_end;
+ input_idx_t 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;
+ /* 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 raw_match *cached_matches;
+ struct raw_match *cache_ptr;
+ bool matches_cached;
+ struct raw_match *cache_limit;
- /* Slow algorithm only: Variables used by the match-choosing algorithm.
- *
+ /* Match-chooser state.
* 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;
+ struct lzx_mc_pos_data *optimum;
+ unsigned optimum_cur_idx;
+ unsigned 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].
+/*
+ * Match chooser position data:
*
- * 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.
+ * 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. */
+ input_idx_t 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. */
+ input_idx_t match_offset;
+ } prev;
+ struct {
+ /* Position at which the match or literal starting at
+ * this position ends in the minimum-cost parse. */
+ input_idx_t link;
+
+ /* Offset (as in an LZ (length, offset) pair) of the
+ * match or literal starting at this position in the
+ * approximate minimum-cost parse. */
+ input_idx_t match_offset;
+ } next;
+ };
+
+ /* Adaptive state that exists after an approximate minimum-cost path to
+ * reach this position is taken. */
+ 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(unsigned formatted_offset)
+lzx_get_position_slot(u32 offset, struct lzx_lru_queue *queue)
{
-#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);
+ 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;
+ }
}
-}
-/* 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;
+ /* 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 lengths. */
+ * 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)
+ struct lzx_codes *codes,
+ unsigned num_main_syms)
{
- make_canonical_huffman_code(LZX_MAINTREE_NUM_SYMBOLS,
- LZX_MAX_CODEWORD_LEN,
+ 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_LENTREE_NUM_SYMBOLS,
- LZX_MAX_CODEWORD_LEN,
+ 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_ALIGNEDTREE_NUM_SYMBOLS, 8,
+ make_canonical_huffman_code(LZX_ALIGNEDCODE_NUM_SYMBOLS,
+ LZX_MAX_ALIGNED_CODEWORD_LEN,
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.
+ * 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, as a (length, offset) pair.
+ * @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_match match, const struct lzx_codes *codes)
+ 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;
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) +
+ /* 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, and there is no
+ * 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. */
+ * MIN_MATCH_LEN. */
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;
+ /* 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],
/* If there is a length footer, output it using the
* length Huffman code. */
- if (len_footer != (unsigned)(-1)) {
+ 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 tree. Otherwise, only the verbatim bits need to be
+ * aligned offset code. Otherwise, only the verbatim bits need to be
* output. */
if ((block_type == LZX_BLOCKTYPE_ALIGNED) && (num_extra_bits >= 3)) {
}
}
+/* 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],
- unsigned num_syms,
- freq_t precode_freqs[restrict LZX_PRETREE_NUM_SYMBOLS],
+ const unsigned num_syms,
+ input_idx_t precode_freqs[restrict LZX_PRECODE_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)
+ u8 precode_lens[restrict LZX_PRECODE_NUM_SYMBOLS],
+ u32 precode_codewords[restrict LZX_PRECODE_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]));
+ 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
* 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.
+ * 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.
- */
- output_syms_idx = 0;
- cur_run_len = 1;
- for (i = 1; i <= num_syms; i++) {
+ * 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. */
/* 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];
+ unsigned len_in_run = lens[i - 1];
if (len_in_run == 0) {
/* A run of 0's. Encode it in as few length
* 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;
* 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]++;
*
* 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.
+ * 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] -
/* Any remaining lengths in the run are outputted without RLE,
* as a difference from the length of that codeword in the
- * previous tree. */
+ * 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)
/* Build the precode from the frequencies of the length symbols. */
- make_canonical_huffman_code(LZX_PRETREE_NUM_SYMBOLS,
- LZX_MAX_CODEWORD_LEN,
+ make_canonical_huffman_code(LZX_PRECODE_NUM_SYMBOLS,
+ LZX_MAX_PRE_CODEWORD_LEN,
precode_freqs, precode_lens,
precode_codewords);
- if (num_additional_bits_ret)
- *num_additional_bits_ret = num_additional_bits;
+ *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.
+ * 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 prev_lens[restrict],
unsigned num_syms)
{
- freq_t precode_freqs[LZX_PRETREE_NUM_SYMBOLS];
+ input_idx_t precode_freqs[LZX_PRECODE_NUM_SYMBOLS];
u8 output_syms[num_syms];
- u8 precode_lens[LZX_PRETREE_NUM_SYMBOLS];
- u16 precode_codewords[LZX_PRETREE_NUM_SYMBOLS];
+ 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,
output_syms,
precode_lens,
precode_codewords,
- NULL);
+ &dummy);
/* Write the lengths of the precode codes to the output. */
- for (i = 0; i < LZX_PRETREE_NUM_SYMBOLS; i++)
+ for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++)
bitstream_put_bits(out, precode_lens[i],
- LZX_PRETREE_ELEMENT_SIZE);
+ LZX_PRECODE_ELEMENT_SIZE);
/* Write the length symbols, encoded with the precode, to the output. */
}
/*
- * Writes all compressed matches and literal bytes in a LZX block to the the
- * output bitstream.
+ * 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 type of the block (LZX_BLOCKTYPE_ALIGNED or LZX_BLOCKTYPE_VERBATIM).
+ * The chosen type of the LZX compressed block (LZX_BLOCKTYPE_ALIGNED or
+ * LZX_BLOCKTYPE_VERBATIM).
* @match_tab
- * The array of matches/literals that will be output (length @match_count).
+ * The array of matches/literals to output.
* @match_count
- * Number of matches/literals to be output.
+ * Number of matches/literals to output (length of @match_tab).
* @codes
- * Pointer to a structure that contains the codewords for the main, length,
- * and aligned offset Huffman codes.
+ * The main, length, and aligned offset Huffman codes for the current
+ * LZX compressed block.
*/
static void
lzx_write_matches_and_literals(struct output_bitstream *ostream,
int block_type,
- const struct lzx_match match_tab[],
+ const struct lzx_item 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]);
- }
+ struct lzx_item match = match_tab[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 (match.data & 0x80000000)
+ lzx_write_match(ostream, block_type, match, codes);
+ else
+ lzx_write_literal(ostream, match.data, codes);
}
}
-
static void
-lzx_assert_codes_valid(const struct lzx_codes * codes)
+lzx_assert_codes_valid(const struct lzx_codes * codes, unsigned num_main_syms)
{
#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 < num_main_syms; i++)
+ LZX_ASSERT(codes->lens.main[i] <= LZX_MAX_MAIN_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_LENCODE_NUM_SYMBOLS; i++)
+ LZX_ASSERT(codes->lens.len[i] <= LZX_MAX_LEN_CODEWORD_LEN);
- for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++)
- LZX_ASSERT(codes->lens.aligned[i] <= 8);
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
+ LZX_ASSERT(codes->lens.aligned[i] <= LZX_MAX_ALIGNED_CODEWORD_LEN);
const unsigned tablebits = 10;
u16 decode_table[(1 << tablebits) +
- (2 * max(LZX_MAINTREE_NUM_SYMBOLS, LZX_LENTREE_NUM_SYMBOLS))]
+ (2 * max(num_main_syms, LZX_LENCODE_NUM_SYMBOLS))]
_aligned_attribute(DECODE_TABLE_ALIGNMENT);
LZX_ASSERT(0 == make_huffman_decode_table(decode_table,
- LZX_MAINTREE_NUM_SYMBOLS,
- tablebits,
+ num_main_syms,
+ min(tablebits, LZX_MAINCODE_TABLEBITS),
codes->lens.main,
- LZX_MAX_CODEWORD_LEN));
+ LZX_MAX_MAIN_CODEWORD_LEN));
LZX_ASSERT(0 == make_huffman_decode_table(decode_table,
- LZX_LENTREE_NUM_SYMBOLS,
- tablebits,
+ LZX_LENCODE_NUM_SYMBOLS,
+ min(tablebits, LZX_LENCODE_TABLEBITS),
codes->lens.len,
- LZX_MAX_CODEWORD_LEN));
+ LZX_MAX_LEN_CODEWORD_LEN));
LZX_ASSERT(0 == make_huffman_decode_table(decode_table,
- LZX_ALIGNEDTREE_NUM_SYMBOLS,
- min(tablebits, 6),
+ LZX_ALIGNEDCODE_NUM_SYMBOLS,
+ min(tablebits, LZX_ALIGNEDCODE_TABLEBITS),
codes->lens.aligned,
- 8));
+ LZX_MAX_ALIGNED_CODEWORD_LEN));
#endif /* ENABLE_LZX_DEBUG */
}
-/* Write a LZX aligned offset or verbatim block to the output. */
+/* Write an 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,
+ 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)
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);
+ lzx_assert_codes_valid(codes, num_main_syms);
/* 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);
+ bitstream_put_bits(ostream, block_type, 3);
- /* 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. */
+ /* 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);
- bitstream_put_bits(ostream, block_size, LZX_BLOCKSIZE_NBITS);
+
+ 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 tree to be written
+ * 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_ALIGNEDTREE_NUM_SYMBOLS; i++)
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
bitstream_put_bits(ostream, codes->lens.aligned[i],
- LZX_ALIGNEDTREE_ELEMENT_SIZE);
+ LZX_ALIGNEDCODE_ELEMENT_SIZE);
LZX_DEBUG("Writing main code...");
- /* Write the pre-tree and lengths for the first LZX_NUM_CHARS symbols in
+ /* 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 pre-tree and lengths for the rest of the main code, which
+ /* 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,
- LZX_MAINTREE_NUM_SYMBOLS - LZX_NUM_CHARS);
+ num_main_syms - LZX_NUM_CHARS);
LZX_DEBUG("Writing length code...");
- /* Write the pre-tree and lengths for the length code. */
+ /* Write the precode and lengths for the length code. */
lzx_write_compressed_code(ostream,
codes->lens.len,
prev_codes->lens.len,
- LZX_LENTREE_NUM_SYMBOLS);
+ LZX_LENCODE_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,
+ chosen_items, num_chosen_items,
codes);
LZX_DEBUG("Done writing block.");
}
-/* Write the LZX block of index @block_number, or write its children recursively
- * if it is a split block.
- *
- * @prev_codes is a pointer to the Huffman codes for the most recent block
- * written, or all zeroes if this is the first 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)
+/* Write out the LZX blocks that were computed. */
+static void
+lzx_write_all_blocks(struct lzx_compressor *ctx, 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);
+ const struct lzx_codes *prev_codes = &ctx->zero_codes;
+ for (unsigned i = 0; i < ctx->num_blocks; i++) {
+ const struct lzx_block_spec *spec = &ctx->block_specs[i];
+
+ LZX_DEBUG("Writing block %u/%u (type=%d, size=%u, num_chosen_items=%u)...",
+ i + 1, ctx->num_blocks,
+ spec->block_type, spec->block_size,
+ spec->num_chosen_items);
+
lzx_write_compressed_block(spec->block_type,
spec->block_size,
- &ctx->chosen_matches[spec->chosen_matches_start_pos],
- spec->num_chosen_matches,
+ ctx->max_window_size,
+ ctx->num_main_syms,
+ spec->chosen_items,
+ spec->num_chosen_items,
&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)
+/* 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)
{
- struct lzx_freqs *freqs = _freqs;
-
- freqs->main[literal]++;
-
- return (u32)literal;
+ freqs->main[lit]++;
+ return (u32)lit;
}
-/* 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
+/* 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 u32
-lzx_record_match(unsigned match_offset, unsigned match_len,
- void *_freqs, void *_queue)
+static inline u32
+lzx_tally_match(unsigned match_len, u32 match_offset,
+ struct lzx_freqs *freqs, struct lzx_lru_queue *queue)
{
- struct lzx_freqs *freqs = _freqs;
- struct lzx_lru_queue *queue = _queue;
unsigned position_slot;
- unsigned position_footer = 0;
+ unsigned position_footer;
u32 len_header;
- u32 len_pos_header;
+ unsigned main_symbol;
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;
+ 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 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.
- */
+ /* 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]++;
}
- len_pos_header = (position_slot << 3) | len_header;
- freqs->main[len_pos_header + LZX_NUM_CHARS]++;
+ /* Account for the main symbol. */
+ main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS;
+
+ freqs->main[main_symbol]++;
- /* Equivalent to:
- * if (lzx_extra_bits[position_slot] >= 3) */
+ /* 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.
- *
- * 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. */
+ * 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);
}
-/* Set the cost model @ctx->costs from the Huffman codeword lengths specified in
- * @lens.
- *
- * These are basically the same thing, except that 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.
- */
+struct lzx_record_ctx {
+ struct lzx_freqs freqs;
+ struct lzx_lru_queue queue;
+ struct lzx_item *matches;
+};
+
static void
-lzx_set_costs(struct lzx_compressor * ctx, const struct lzx_lens * lens)
+lzx_record_match(unsigned len, unsigned offset, void *_ctx)
{
- unsigned i;
-
- memcpy(&ctx->costs, lens, sizeof(struct lzx_lens));
+ struct lzx_record_ctx *ctx = _ctx;
- for (i = 0; i < LZX_MAINTREE_NUM_SYMBOLS; i++)
- if (ctx->costs.main[i] == 0)
- ctx->costs.main[i] = ctx->params.alg_params.slow.main_nostat_cost;
+ (ctx->matches++)->data = lzx_tally_match(len, offset, &ctx->freqs, &ctx->queue);
+}
- for (i = 0; i < LZX_LENTREE_NUM_SYMBOLS; i++)
- if (ctx->costs.len[i] == 0)
- ctx->costs.len[i] = ctx->params.alg_params.slow.len_nostat_cost;
+static void
+lzx_record_literal(u8 lit, void *_ctx)
+{
+ struct lzx_record_ctx *ctx = _ctx;
- for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++)
- if (ctx->costs.aligned[i] == 0)
- ctx->costs.aligned[i] = ctx->params.alg_params.slow.aligned_nostat_cost;
+ (ctx->matches++)->data = lzx_tally_literal(lit, &ctx->freqs);
}
+/* 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_lens * costs)
+lzx_literal_cost(u8 c, const struct lzx_costs * 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
- )
+ * match in the compressed output. Take into account the match offset LRU
+ * queue and also updates it. */
+static u32
+lzx_match_cost(unsigned length, u32 offset, const struct lzx_costs *costs,
+ struct lzx_lru_queue *queue)
{
- 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);
+ unsigned position_slot;
+ unsigned len_header, main_symbol;
+ unsigned num_extra_bits;
+ u32 cost = 0;
- len_header = min(length - LZX_MIN_MATCH, LZX_NUM_PRIMARY_LENS);
+ position_slot = lzx_get_position_slot(offset, queue);
+
+ len_header = min(length - 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 position information. */
- unsigned num_extra_bits = lzx_get_num_extra_bits(position_slot);
+ 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];
+ cost += costs->aligned[(offset + LZX_OFFSET_OFFSET) & 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];
+ if (len_header == LZX_NUM_PRIMARY_LENS)
+ cost += costs->len[length - LZX_MIN_MATCH_LEN - 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. This is the same algorithm as that used in GetMatchesSpec1() in
- * 7-Zip, but it is hopefully explained a little more clearly below. */
-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)
+/* Set the cost model @ctx->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 * ctx, const struct lzx_lens * lens)
{
- u16 *new_tree_lt_ptr = &child_tab[strstart * 2];
- u16 *new_tree_gt_ptr = &child_tab[strstart * 2 + 1];
+ unsigned i;
+ unsigned num_main_syms = ctx->num_main_syms;
- u16 longest_lt_match_len = 0;
- u16 longest_gt_match_len = 0;
+ /* Main code */
+ for (i = 0; i < num_main_syms; i++) {
+ ctx->costs.main[i] = lens->main[i];
+ if (ctx->costs.main[i] == 0)
+ ctx->costs.main[i] = ctx->params.alg_params.slow.main_nostat_cost;
+ }
- /* Maximum number of nodes to walk down before stopping */
- unsigned depth = max_length;
+ /* Length code */
+ for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++) {
+ ctx->costs.len[i] = lens->len[i];
+ if (ctx->costs.len[i] == 0)
+ ctx->costs.len[i] = ctx->params.alg_params.slow.len_nostat_cost;
+ }
- /* 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];
-
- /* Determine position at which to start comparing */
- u16 len = min(longest_lt_match_len,
- longest_gt_match_len);
-
- if (matchptr[len] == strptr[len]) {
-
- /* Extend the match as far as possible. */
- while (++len != len_limit)
- if (matchptr[len] != strptr[len])
- break;
-
- /* Record this match if it is the longest found so far.
- */
- 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: Mark the positions skipped as having no matches available,
- * but we still need to update the binary tree in case subsequent
- * positions have matches at the current position. */
- 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.alg_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.alg_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++;
- }
+ /* Aligned offset code */
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
+ ctx->costs.aligned[i] = lens->aligned[i];
+ if (ctx->costs.aligned[i] == 0)
+ ctx->costs.aligned[i] = ctx->params.alg_params.slow.aligned_nostat_cost;
}
-#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.
- */
+ * A pointer to the matches array is written into @matches_ret, and the return
+ * value is the number of matches found. */
static unsigned
-lzx_lz_get_matches_caching(struct lzx_compressor *ctx,
- struct raw_match **matches_ret)
+lzx_get_matches(struct lzx_compressor *ctx,
+ const struct raw_match **matches_ret)
{
- unsigned num_matches;
+ struct raw_match *cache_ptr;
struct raw_match *matches;
+ unsigned num_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);
+ LZX_ASSERT(ctx->match_window_pos < ctx->match_window_end);
- 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;
+ cache_ptr = ctx->cache_ptr;
+ matches = cache_ptr + 1;
+ if (likely(cache_ptr <= ctx->cache_limit)) {
+ if (ctx->matches_cached) {
+ num_matches = cache_ptr->len;
+ } else {
+ num_matches = lz_bt_get_matches(&ctx->mf, matches);
+ cache_ptr->len = num_matches;
}
} else {
- unsigned prev_len = 1;
- struct raw_match * matches_ret = &ctx->cached_matches[ctx->cached_matches_pos + 1];
num_matches = 0;
+ }
- if (ctx->params.alg_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.alg_params.slow.num_fast_bytes,
- ctx->child_tab,
- cur_match,
- prev_len,
- matches_ret);
- }
+ /* Don't allow matches to span the end of an LZX block. */
+ if (ctx->match_window_end < ctx->window_size && num_matches != 0) {
+ unsigned limit = ctx->match_window_end - ctx->match_window_pos;
- ctx->cached_matches[ctx->cached_matches_pos].len = num_matches;
- ctx->cached_matches[ctx->cached_matches_pos].offset = ctx->match_window_pos;
+ if (limit >= LZX_MIN_MATCH_LEN) {
- 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.alg_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;
+ unsigned 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;
}
+ cache_ptr->len = num_matches;
}
- ctx->cached_matches_pos += num_matches + 1;
- *matches_ret = matches;
#if 0
- printf("\n");
+ fprintf(stderr, "Pos %u/%u: %u matches\n",
+ ctx->match_window_pos, ctx->window_size, num_matches);
for (unsigned i = 0; i < num_matches; i++)
- {
- printf("Len %u Offset %u\n", matches[i].len, matches[i].offset);
- }
+ fprintf(stderr, "\tLen %u Offset %u\n", matches[i].len, matches[i].offset);
#endif
+#ifdef ENABLE_LZX_DEBUG
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));
+ LZX_ASSERT(matches[i].len >= LZX_MIN_MATCH_LEN);
+ LZX_ASSERT(matches[i].len <= LZX_MAX_MATCH_LEN);
+ LZX_ASSERT(matches[i].len <= ctx->match_window_end - ctx->match_window_pos);
+ LZX_ASSERT(matches[i].offset > 0);
+ LZX_ASSERT(matches[i].offset <= 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));
+ if (i) {
+ LZX_ASSERT(matches[i].len > matches[i - 1].len);
+ LZX_ASSERT(matches[i].offset > matches[i - 1].offset);
}
}
-
+#endif
ctx->match_window_pos++;
+ ctx->cache_ptr = matches + num_matches;
+ *matches_ret = matches;
return num_matches;
}
+static void
+lzx_skip_bytes(struct lzx_compressor *ctx, unsigned n)
+{
+ struct raw_match *cache_ptr;
+
+ LZX_ASSERT(n <= ctx->match_window_end - ctx->match_window_pos);
+
+ cache_ptr = ctx->cache_ptr;
+ ctx->match_window_pos += n;
+ if (ctx->matches_cached) {
+ while (n-- && cache_ptr <= ctx->cache_limit)
+ cache_ptr += 1 + cache_ptr->len;
+ } else {
+ lz_bt_skip_positions(&ctx->mf, n);
+ while (n-- && cache_ptr <= ctx->cache_limit) {
+ cache_ptr->len = 0;
+ cache_ptr += 1;
+ }
+ }
+ ctx->cache_ptr = cache_ptr;
+}
+
/*
* 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)
+lzx_match_chooser_reverse_list(struct lzx_compressor *ctx, unsigned cur_pos)
{
unsigned prev_link, saved_prev_link;
unsigned prev_match_offset, saved_prev_match_offset;
}
/*
- * lzx_lz_get_near_optimal_match() -
+ * lzx_get_near_optimal_match() -
+ *
+ * Choose an approximately optimal match or literal to use at the next position
+ * in the string, or "window", being LZ-encoded.
*
- * Choose the "best" match or literal to use at the next position in the input.
+ * 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
+ * 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 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.
+ * 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 near-optimal sequence of matches/literals, up to some point, that
+ * 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;
- *
- * 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)
+ * function.
*
* The return value is a (length, offset) pair specifying the match or literal
- * chosen. For literals, length is either 0 or 1 and offset is meaningless.
+ * chosen. For literals, the length is 0 or 1 and the offset is meaningless.
*/
static struct raw_match
-lzx_lz_get_near_optimal_match(struct lzx_compressor * ctx)
+lzx_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;
+ const struct raw_match *matches;
struct raw_match match;
- unsigned longest_match_len;
- unsigned len, match_idx;
+ unsigned longest_len;
+ unsigned longest_rep_len;
+ u32 longest_rep_offset;
+ unsigned cur_pos;
+ unsigned end_pos;
if (ctx->optimum_cur_idx != ctx->optimum_end_idx) {
/* Case 2: Return the next match/literal already found. */
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);
+ /* Search for matches at recent offsets. Only keep the one with the
+ * longest match length. */
+ longest_rep_len = LZX_MIN_MATCH_LEN - 1;
+ if (ctx->match_window_pos >= 1) {
+ unsigned limit = min(LZX_MAX_MATCH_LEN,
+ ctx->match_window_end - ctx->match_window_pos);
+ for (int i = 0; i < LZX_NUM_RECENT_OFFSETS; i++) {
+ u32 offset = ctx->queue.R[i];
+ const u8 *strptr = &ctx->window[ctx->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_offset = offset;
+ }
+ }
+ }
- /* If no matches found, return literal. */
- if (num_possible_matches == 0)
- return (struct raw_match){ .len = 0 };
+ /* If there's a long match with a recent offset, take it. */
+ if (longest_rep_len >= ctx->params.alg_params.slow.nice_match_length) {
+ lzx_skip_bytes(ctx, longest_rep_len);
+ return (struct raw_match) {
+ .len = longest_rep_len,
+ .offset = longest_rep_offset,
+ };
+ }
- /* 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;
+ /* Search other matches. */
+ num_matches = lzx_get_matches(ctx, &matches);
- /* Greedy heuristic: if the longest match that was found is greater
- * than the number of fast bytes, return it immediately; don't both
- * doing more work. */
- if (longest_match_len > ctx->params.alg_params.slow.num_fast_bytes) {
- lzx_lz_skip_bytes(ctx, longest_match_len - 1);
- return possible_matches[num_possible_matches - 1];
+ /* If there's a long match, take it. */
+ if (num_matches) {
+ longest_len = matches[num_matches - 1].len;
+ if (longest_len >= ctx->params.alg_params.slow.nice_match_length) {
+ lzx_skip_bytes(ctx, longest_len - 1);
+ return matches[num_matches - 1];
+ }
+ } else {
+ longest_len = 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],
+ /* Calculate the cost to reach the next position by coding a literal.
+ */
+ ctx->optimum[1].queue = ctx->queue;
+ ctx->optimum[1].cost = lzx_literal_cost(ctx->window[ctx->match_window_pos - 1],
&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);
+ * 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 = ctx->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 += ctx->costs.aligned[(offset + LZX_OFFSET_OFFSET) & 7];
+ } else {
+ position_cost += num_extra_bits;
+ }
- #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++;
- }
+ do {
+ unsigned len_header;
+ unsigned main_symbol;
+ u32 cost;
- unsigned cur_pos = 0;
+ cost = position_cost;
- /* len_end: greatest index forward at which costs have been calculated
- * so far */
- unsigned len_end = longest_match_len;
+ len_header = min(len - LZX_MIN_MATCH_LEN, LZX_NUM_PRIMARY_LENS);
+ main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS;
+ cost += ctx->costs.main[main_symbol];
+ if (len_header == LZX_NUM_PRIMARY_LENS)
+ cost += ctx->costs.len[len - LZX_MIN_MATCH_LEN - LZX_NUM_PRIMARY_LENS];
+ ctx->optimum[len].queue = queue;
+ ctx->optimum[len].prev.link = 0;
+ ctx->optimum[len].prev.match_offset = offset;
+ ctx->optimum[len].cost = cost;
+ } while (++len <= matches[i].len);
+ }
+ end_pos = longest_len;
+
+ if (longest_rep_len >= LZX_MIN_MATCH_LEN) {
+ struct lzx_lru_queue queue;
+ u32 cost;
+
+ while (end_pos < longest_rep_len)
+ ctx->optimum[++end_pos].cost = MC_INFINITE_COST;
+
+ queue = ctx->queue;
+ cost = lzx_match_cost(longest_rep_len, longest_rep_offset,
+ &ctx->costs, &queue);
+ if (cost <= ctx->optimum[longest_rep_len].cost) {
+ ctx->optimum[longest_rep_len].queue = queue;
+ ctx->optimum[longest_rep_len].prev.link = 0;
+ ctx->optimum[longest_rep_len].prev.match_offset = longest_rep_offset;
+ ctx->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 @ctx->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. (Actually, the algorithm guarantees that all positions up to
+ * and including @end_pos are reachable by at least one path.)
+ *
+ * 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 @ctx->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++;
- if (cur_pos == len_end || cur_pos == LZX_PARAM_OPTIM_ARRAY_SIZE)
- return lzx_lz_reverse_near_optimal_match_list(ctx, cur_pos);
+ /* Check termination conditions (2) and (3) noted above. */
+ if (cur_pos == end_pos || cur_pos == LZX_OPTIM_ARRAY_SIZE)
+ return lzx_match_chooser_reverse_list(ctx, cur_pos);
+
+ /* Search for matches at recent offsets. */
+ longest_rep_len = LZX_MIN_MATCH_LEN - 1;
+ unsigned limit = min(LZX_MAX_MATCH_LEN,
+ ctx->match_window_end - ctx->match_window_pos);
+ for (int i = 0; i < LZX_NUM_RECENT_OFFSETS; i++) {
+ u32 offset = ctx->optimum[cur_pos].queue.R[i];
+ const u8 *strptr = &ctx->window[ctx->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_offset = offset;
+ }
+ }
+
+ /* If we found a long match at a recent offset, choose it
+ * immediately. */
+ if (longest_rep_len >= ctx->params.alg_params.slow.nice_match_length) {
+ /* Build the list of matches to return and get
+ * the first one. */
+ match = lzx_match_chooser_reverse_list(ctx, cur_pos);
- /* retrieve the number of matches available at this position */
- num_possible_matches = lzx_lz_get_matches_caching(ctx,
- &possible_matches);
+ /* Append the long match to the end of the list. */
+ ctx->optimum[cur_pos].next.match_offset = longest_rep_offset;
+ ctx->optimum[cur_pos].next.link = cur_pos + longest_rep_len;
+ ctx->optimum_end_idx = cur_pos + longest_rep_len;
- unsigned new_len = 0;
+ /* Skip over the remaining bytes of the long match. */
+ lzx_skip_bytes(ctx, longest_rep_len);
- if (num_possible_matches != 0) {
- new_len = possible_matches[num_possible_matches - 1].len;
+ /* Return first match in the list. */
+ return match;
+ }
- /* Greedy heuristic: if we found a match greater than
- * the number of fast bytes, stop immediately. */
- if (new_len > ctx->params.alg_params.slow.num_fast_bytes) {
+ /* Search other matches. */
+ num_matches = lzx_get_matches(ctx, &matches);
+ /* If there's a long match, take it. */
+ if (num_matches) {
+ longest_len = matches[num_matches - 1].len;
+ if (longest_len >= ctx->params.alg_params.slow.nice_match_length) {
/* Build the list of matches to return and get
* the first one. */
- match = lzx_lz_reverse_near_optimal_match_list(ctx, cur_pos);
+ match = lzx_match_chooser_reverse_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;
+ matches[num_matches - 1].offset;
+ ctx->optimum[cur_pos].next.link = cur_pos + longest_len;
+ ctx->optimum_end_idx = cur_pos + longest_len;
/* Skip over the remaining bytes of the long match. */
- lzx_lz_skip_bytes(ctx, new_len - 1);
+ lzx_skip_bytes(ctx, longest_len - 1);
- /* Return first match in the list */
+ /* Return first match in the list. */
return match;
}
+ } else {
+ longest_len = 1;
}
- /* Consider proceeding with a literal byte. */
- u32 cur_cost = ctx->optimum[cur_pos].cost;
- u32 cur_plus_literal_cost = cur_cost +
+ while (end_pos < cur_pos + longest_len)
+ ctx->optimum[++end_pos].cost = MC_INFINITE_COST;
+
+ /* Consider coding a literal. */
+ cost = ctx->optimum[cur_pos].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
+ if (cost < ctx->optimum[cur_pos + 1].cost) {
ctx->optimum[cur_pos + 1].queue = ctx->optimum[cur_pos].queue;
- #endif
+ ctx->optimum[cur_pos + 1].cost = cost;
+ ctx->optimum[cur_pos + 1].prev.link = cur_pos;
}
- 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
+ /* 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;
+ struct lzx_lru_queue queue;
+ u32 position_cost;
+ unsigned position_slot;
+ unsigned num_extra_bits;
+
+ offset = matches[i].offset;
+ queue = ctx->optimum[cur_pos].queue;
+ position_cost = ctx->optimum[cur_pos].cost;
+
+ 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 += ctx->costs.aligned[
+ (offset + LZX_OFFSET_OFFSET) & 7];
+ } else {
+ position_cost += num_extra_bits;
}
- if (len == possible_matches[match_idx].len)
- match_idx++;
+ 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 += ctx->costs.main[main_symbol];
+ if (len_header == LZX_NUM_PRIMARY_LENS) {
+ cost += ctx->costs.len[len -
+ LZX_MIN_MATCH_LEN -
+ LZX_NUM_PRIMARY_LENS];
+ }
+ if (cost < ctx->optimum[cur_pos + len].cost) {
+ ctx->optimum[cur_pos + len].queue = queue;
+ ctx->optimum[cur_pos + len].prev.link = cur_pos;
+ ctx->optimum[cur_pos + len].prev.match_offset = offset;
+ ctx->optimum[cur_pos + len].cost = cost;
+ }
+ } while (++len <= matches[i].len);
}
- }
-#endif
-}
-
-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;
+ if (longest_rep_len >= LZX_MIN_MATCH_LEN) {
+ struct lzx_lru_queue queue;
+
+ while (end_pos < cur_pos + longest_rep_len)
+ ctx->optimum[++end_pos].cost = MC_INFINITE_COST;
+
+ queue = ctx->optimum[cur_pos].queue;
+
+ cost = ctx->optimum[cur_pos].cost +
+ lzx_match_cost(longest_rep_len, longest_rep_offset,
+ &ctx->costs, &queue);
+ if (cost <= ctx->optimum[cur_pos + longest_rep_len].cost) {
+ ctx->optimum[cur_pos + longest_rep_len].queue =
+ queue;
+ ctx->optimum[cur_pos + longest_rep_len].prev.link =
+ cur_pos;
+ ctx->optimum[cur_pos + longest_rep_len].prev.match_offset =
+ longest_rep_offset;
+ ctx->optimum[cur_pos + longest_rep_len].cost =
+ cost;
+ }
+ }
+ }
}
-/* Account for extra bits in the main symbols. */
+/* Set default symbol costs for the LZX Huffman codes. */
static void
-lzx_update_mainsym_match_costs(int block_type,
- u8 main_lens[LZX_MAINTREE_NUM_SYMBOLS])
+lzx_set_default_costs(struct lzx_costs * costs, unsigned num_main_syms)
{
unsigned i;
- LZX_ASSERT(block_type == LZX_BLOCKTYPE_ALIGNED ||
- block_type == LZX_BLOCKTYPE_VERBATIM);
+ /* Main code (part 1): Literal symbols */
+ for (i = 0; i < LZX_NUM_CHARS; i++)
+ costs->main[i] = 8;
- for (i = LZX_NUM_CHARS; i < LZX_MAINTREE_NUM_SYMBOLS; i++) {
- unsigned position_slot = (i >> 3) & 0x1f;
+ /* Main code (part 2): Match header symbols */
+ for (; i < num_main_syms; i++)
+ costs->main[i] = 10;
- /* 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;
- }
+ /* 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;
}
-/*
- * Compute the costs, in bits, to output a compressed block as aligned offset
- * and verbatim.
- *
- * @block_size
- * Number of bytes of uncompressed data the block represents.
- * @codes
- * Huffman codes that will be used when outputting the block.
- * @prev_codes
- * Huffman codes for the previous block, or all zeroes if this is the first
- * block.
- * @freqs
- * Frequencies of Huffman symbols 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)
+/* 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 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;
+ /* 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
- 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;
+ return LZX_BLOCKTYPE_VERBATIM;
}
-/* Prepare a (nonsplit) compressed block. */
-static unsigned
-lzx_prepare_compressed_block(struct lzx_compressor *ctx, unsigned block_number,
- struct lzx_codes *prev_codes)
+/* Find a near-optimal 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_optimize_block(struct lzx_compressor *ctx, struct lzx_block_spec *spec,
+ unsigned num_passes)
{
- 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;
+ const struct lzx_lru_queue orig_queue = ctx->queue;
+ unsigned num_passes_remaining = num_passes;
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.alg_params.slow.num_optim_passes >= 1);
- spec->num_chosen_matches = 0;
- for (unsigned pass = 0; pass < ctx->params.alg_params.slow.num_optim_passes; pass++)
- {
- LZX_DEBUG("Block %u: Match-choosing pass %u of %u",
- block_number, pass + 1,
- ctx->params.alg_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;
+ const u8 *window_ptr;
+ const u8 *window_end;
+ struct lzx_item *next_chosen_match;
+ struct raw_match raw_match;
+ struct lzx_item lzx_item;
- while (window_pos < end) {
- struct raw_match match;
- struct lzx_match lzx_match;
+ LZX_ASSERT(num_passes >= 1);
+ LZX_ASSERT(lz_bt_get_position(&ctx->mf) == spec->window_pos);
- match = lzx_lz_get_near_optimal_match(ctx);
+ ctx->match_window_end = spec->window_pos + spec->block_size;
+ ctx->matches_cached = false;
- if (match.len >= LZX_MIN_MATCH) {
+ /* The first optimal parsing pass is done using the cost model already
+ * set in ctx->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. */
- /* Best to output a match here. */
+ while (--num_passes_remaining) {
+ ctx->match_window_pos = spec->window_pos;
+ ctx->cache_ptr = ctx->cached_matches;
+ memset(&freqs, 0, sizeof(freqs));
+ window_ptr = &ctx->window[spec->window_pos];
+ window_end = window_ptr + spec->block_size;
- LZX_ASSERT(match.len <= LZX_MAX_MATCH);
- LZX_ASSERT(!memcmp(&ctx->window[window_pos],
- &ctx->window[window_pos - match.offset],
- match.len));
+ while (window_ptr != window_end) {
- /* Tally symbol frequencies. */
- lzx_match.data = lzx_record_match(match.offset,
- match.len,
- &freqs,
- &ctx->queue);
+ raw_match = lzx_get_near_optimal_match(ctx);
- window_pos += match.len;
+ LZX_ASSERT(!(raw_match.len == LZX_MIN_MATCH_LEN &&
+ raw_match.offset == ctx->max_window_size -
+ LZX_MIN_MATCH_LEN));
+ if (raw_match.len >= LZX_MIN_MATCH_LEN) {
+ lzx_tally_match(raw_match.len, raw_match.offset,
+ &freqs, &ctx->queue);
+ window_ptr += raw_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.alg_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_tally_literal(*window_ptr, &freqs);
+ window_ptr += 1;
}
}
- 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 cost), 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;
+ lzx_make_huffman_codes(&freqs, &spec->codes, ctx->num_main_syms);
+ lzx_set_costs(ctx, &spec->codes.lens);
ctx->queue = orig_queue;
+ ctx->matches_cached = true;
+ }
- /* 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;
+ ctx->match_window_pos = spec->window_pos;
+ ctx->cache_ptr = ctx->cached_matches;
+ memset(&freqs, 0, sizeof(freqs));
+ window_ptr = &ctx->window[spec->window_pos];
+ window_end = window_ptr + spec->block_size;
+
+ spec->chosen_items = &ctx->chosen_items[spec->window_pos];
+ next_chosen_match = spec->chosen_items;
+
+ while (window_ptr != window_end) {
+ raw_match = lzx_get_near_optimal_match(ctx);
+
+ LZX_ASSERT(!(raw_match.len == LZX_MIN_MATCH_LEN &&
+ raw_match.offset == ctx->max_window_size -
+ LZX_MIN_MATCH_LEN));
+ if (raw_match.len >= LZX_MIN_MATCH_LEN) {
+ lzx_item.data = lzx_tally_match(raw_match.len,
+ raw_match.offset,
+ &freqs, &ctx->queue);
+ window_ptr += raw_match.len;
} else {
- LZX_DEBUG("Splitting block %u is NOT worth it "
- "(%u => %u bytes).",
- block_number, cost / 8, split_cost / 8);
- ctx->queue = nonsplit_queue;
+ lzx_item.data = lzx_tally_literal(*window_ptr, &freqs);
+ window_ptr += 1;
}
+ *next_chosen_match++ = lzx_item;
}
-
- return cost;
+ spec->num_chosen_items = next_chosen_match - spec->chosen_items;
+ lzx_make_huffman_codes(&freqs, &spec->codes, ctx->num_main_syms);
+ spec->block_type = lzx_choose_verbatim_or_aligned(&freqs, &spec->codes);
}
-/* 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.
- */
+/* Prepare the input window into one or more LZX blocks ready to be output. */
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.alg_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. */
+ /* Set up a default cost model. */
+ lzx_set_default_costs(&ctx->costs, ctx->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. */
+ ctx->num_blocks = DIV_ROUND_UP(ctx->window_size, LZX_DIV_BLOCK_SIZE);
+ for (unsigned i = 0; i < ctx->num_blocks; i++) {
+ unsigned pos = LZX_DIV_BLOCK_SIZE * i;
+ ctx->block_specs[i].window_pos = pos;
+ ctx->block_specs[i].block_size = min(ctx->window_size - pos,
+ LZX_DIV_BLOCK_SIZE);
+ }
- /* No matches have been found and cached yet. */
- ctx->cached_matches_pos = 0;
- ctx->matches_already_found = false;
+ /* Load the window into the match-finder. */
+ lz_bt_load_window(&ctx->mf, ctx->window, ctx->window_size);
- /* 2. Initialize match-choosing variables. */
+ /* Determine sequence of matches/literals to output for each block. */
+ lzx_lru_queue_init(&ctx->queue);
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.alg_params.slow.num_split_passes,
- &prev_codes);
+ for (unsigned i = 0; i < ctx->num_blocks; i++) {
+ lzx_optimize_block(ctx, &ctx->block_specs[i],
+ ctx->params.alg_params.slow.num_optim_passes);
+ }
}
/*
* ctx->window[]
* ctx->window_size
*
- * Working space:
- * ctx->queue
- *
- * Output --- the block specifications and the corresponding match/literal data:
+ * Output --- the block specification and the corresponding match/literal data:
*
* ctx->block_specs[]
- * ctx->chosen_matches[]
+ * ctx->num_blocks
+ * ctx->chosen_items[]
*/
static void
lzx_prepare_block_fast(struct lzx_compressor * ctx)
{
- unsigned num_matches;
- struct lzx_freqs freqs;
+ struct lzx_record_ctx record_ctx;
struct lzx_block_spec *spec;
- /* Parameters to hash chain LZ match finder */
+ /* Parameters to hash chain LZ match finder
+ * (lazy with 1 match lookahead) */
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. */
+ /* Although LZX_MIN_MATCH_LEN == 2, length 2 matches typically
+ * aren't worth choosing when using greedy or lazy parsing. */
.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,
+ .max_match = LZX_MAX_MATCH_LEN,
+ .max_offset = LZX_MAX_WINDOW_SIZE,
+ .good_match = LZX_MAX_MATCH_LEN,
+ .nice_match = LZX_MAX_MATCH_LEN,
+ .max_chain_len = LZX_MAX_MATCH_LEN,
+ .max_lazy_match = LZX_MAX_MATCH_LEN,
.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 };
+ memset(&record_ctx.freqs, 0, sizeof(struct lzx_freqs));
+ lzx_lru_queue_init(&record_ctx.queue);
+ record_ctx.matches = ctx->chosen_items;
/* 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);
-
+ lz_analyze_block(ctx->window,
+ ctx->window_size,
+ lzx_record_match,
+ lzx_record_literal,
+ &record_ctx,
+ &lzx_lz_params,
+ ctx->prev_tab);
/* 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);
+ spec->num_chosen_items = (record_ctx.matches - ctx->chosen_items);
+ spec->chosen_items = ctx->chosen_items;
+ lzx_make_huffman_codes(&record_ctx.freqs, &spec->codes,
+ ctx->num_main_syms);
+ ctx->num_blocks = 1;
}
-static void
-do_call_insn_translation(u32 *call_insn_target, int input_pos,
- s32 file_size)
+static size_t
+lzx_compress(const void *uncompressed_data, size_t uncompressed_size,
+ void *compressed_data, size_t compressed_size_avail, void *_ctx)
{
- 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 lzx_compressor *ctx = _ctx;
struct output_bitstream ostream;
- unsigned compressed_len;
+ size_t compressed_size;
- if (uncompressed_len < 100) {
+ if (uncompressed_size < 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.");
+ if (uncompressed_size > ctx->max_window_size) {
+ LZX_DEBUG("Can't compress %zu bytes using window of %u bytes!",
+ uncompressed_size, ctx->max_window_size);
return 0;
}
- wimlib_assert(lzx_ctx != NULL);
-
- LZX_DEBUG("Attempting to compress %u bytes...", uncompressed_len);
+ 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(ctx->window, uncompressed_data, uncompressed_len);
- ctx->window_size = uncompressed_len;
+ memcpy(ctx->window, uncompressed_data, uncompressed_size);
+ ctx->window_size = uncompressed_size;
/* This line is unnecessary; it just avoids inconsequential accesses of
* uninitialized memory that would show up in memory-checking tools such
/* 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_do_e8_preprocessing(ctx->window, ctx->window_size);
LZX_DEBUG("Preparing blocks...");
LZX_DEBUG("Writing compressed blocks...");
/* Generate the compressed data. */
- init_output_bitstream(&ostream, compressed_data, ctx->window_size - 1);
+ init_output_bitstream(&ostream, compressed_data, compressed_size_avail);
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!");
+ compressed_size = flush_output_bitstream(&ostream);
+ if (compressed_size == ~(input_idx_t)0) {
+ LZX_DEBUG("Data did not compress to %zu bytes or less!",
+ compressed_size_avail);
return 0;
}
- /* Compute the length of the compressed data. */
- compressed_len = ostream.bit_output - (u8*)compressed_data;
+ LZX_DEBUG("Done: compressed %zu => %zu bytes.",
+ uncompressed_size, compressed_size);
- 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. */
+ /* Verify that we really get the same thing back when decompressing.
+ * Although this could be disabled by default in all cases, it only
+ * takes around 2-3% of the running time of the slow algorithm to do the
+ * verification. */
+ if (ctx->params.algorithm == WIMLIB_LZX_ALGORITHM_SLOW
+ #if defined(ENABLE_LZX_DEBUG) || defined(ENABLE_VERIFY_COMPRESSION)
+ || 1
+ #endif
+ )
{
- 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;
- }
+ struct wimlib_decompressor *decompressor;
- bool bad = false;
- const u8 * udata = uncompressed_data;
- for (i = 0; i < uncompressed_len; i++) {
- if (buf[i] != udata[i]) {
- bad = true;
+ if (0 == wimlib_create_decompressor(WIMLIB_COMPRESSION_TYPE_LZX,
+ ctx->max_window_size,
+ NULL,
+ &decompressor))
+ {
+ int ret;
+ ret = wimlib_decompress(compressed_data,
+ compressed_size,
+ ctx->window,
+ uncompressed_size,
+ decompressor);
+ wimlib_free_decompressor(decompressor);
+
+ if (ret) {
+ ERROR("Failed to decompress data we "
+ "compressed using LZX algorithm");
+ wimlib_assert(0);
+ return 0;
+ }
+ if (memcmp(uncompressed_data, ctx->window, uncompressed_size)) {
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]);
+ "didn't decompress to original");
+ wimlib_assert(0);
+ return 0;
}
- }
- if (bad) {
- wimlib_assert(0);
- return 0;
+ } else {
+ WARNING("Failed to create decompressor for "
+ "data verification!");
}
}
-#endif
- return compressed_len;
+ return compressed_size;
}
-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)
+static void
+lzx_free_compressor(void *_ctx)
{
+ struct lzx_compressor *ctx = _ctx;
- LZX_DEBUG("Allocating LZX context...");
-
- struct lzx_compressor *ctx;
+ if (ctx) {
+ FREE(ctx->chosen_items);
+ FREE(ctx->cached_matches);
+ FREE(ctx->optimum);
+ lz_bt_destroy(&ctx->mf);
+ FREE(ctx->block_specs);
+ FREE(ctx->prev_tab);
+ FREE(ctx->window);
+ FREE(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,
- .alg_params = {
- .fast = {
- },
+static const struct wimlib_lzx_compressor_params lzx_fast_default = {
+ .hdr = {
+ .size = sizeof(struct wimlib_lzx_compressor_params),
+ },
+ .algorithm = WIMLIB_LZX_ALGORITHM_FAST,
+ .use_defaults = 0,
+ .alg_params = {
+ .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,
- .alg_params = {
- .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,
- },
+ },
+};
+static const struct wimlib_lzx_compressor_params lzx_slow_default = {
+ .hdr = {
+ .size = sizeof(struct wimlib_lzx_compressor_params),
+ },
+ .algorithm = WIMLIB_LZX_ALGORITHM_SLOW,
+ .use_defaults = 0,
+ .alg_params = {
+ .slow = {
+ .use_len2_matches = 1,
+ .nice_match_length = 32,
+ .num_optim_passes = 2,
+ .max_search_depth = 50,
+ .main_nostat_cost = 15,
+ .len_nostat_cost = 15,
+ .aligned_nostat_cost = 7,
},
- };
+ },
+};
+
+static const struct wimlib_lzx_compressor_params *
+lzx_get_params(const struct wimlib_compressor_params_header *_params)
+{
+ const struct wimlib_lzx_compressor_params *params =
+ (const struct wimlib_lzx_compressor_params*)_params;
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->alg_params.slow.num_fast_bytes < 3 ||
- params->alg_params.slow.num_fast_bytes > 257)
- {
- LZX_DEBUG("Invalid number of fast bytes!");
- return WIMLIB_ERR_INVALID_PARAM;
- }
-
- if (params->alg_params.slow.num_optim_passes < 1)
- {
- LZX_DEBUG("Invalid number of optimization passes!");
- return WIMLIB_ERR_INVALID_PARAM;
- }
-
- if (params->alg_params.slow.main_nostat_cost < 1 ||
- params->alg_params.slow.main_nostat_cost > 16)
- {
- LZX_DEBUG("Invalid main_nostat_cost!");
- return WIMLIB_ERR_INVALID_PARAM;
- }
-
- if (params->alg_params.slow.len_nostat_cost < 1 ||
- params->alg_params.slow.len_nostat_cost > 16)
- {
- LZX_DEBUG("Invalid len_nostat_cost!");
- return WIMLIB_ERR_INVALID_PARAM;
- }
-
- if (params->alg_params.slow.aligned_nostat_cost < 1 ||
- params->alg_params.slow.aligned_nostat_cost > 8)
- {
- LZX_DEBUG("Invalid aligned_nostat_cost!");
- return WIMLIB_ERR_INVALID_PARAM;
+ params = &lzx_slow_default;
+ } else {
+ if (params->use_defaults) {
+ if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW)
+ params = &lzx_slow_default;
+ else
+ params = &lzx_fast_default;
}
}
+ return params;
+}
- if (ctx_pp == NULL) {
- LZX_DEBUG("Check parameters only.");
- return 0;
- }
+static int
+lzx_create_compressor(size_t window_size,
+ const struct wimlib_compressor_params_header *_params,
+ void **ctx_ret)
+{
+ const struct wimlib_lzx_compressor_params *params = lzx_get_params(_params);
+ struct lzx_compressor *ctx;
- ctx = *(struct lzx_compressor**)ctx_pp;
+ LZX_DEBUG("Allocating LZX context...");
- if (ctx && lzx_params_compatible(&ctx->params, params))
- return 0;
+ if (!lzx_window_size_valid(window_size))
+ return WIMLIB_ERR_INVALID_PARAM;
LZX_DEBUG("Allocating memory.");
- ctx = MALLOC(sizeof(struct lzx_compressor));
+ ctx = CALLOC(1, sizeof(struct lzx_compressor));
if (ctx == NULL)
- goto err;
-
- size_t block_specs_length;
+ goto oom;
+
+ ctx->num_main_syms = lzx_get_num_main_syms(window_size);
+ ctx->max_window_size = window_size;
+ ctx->window = MALLOC(window_size + 12);
+ if (ctx->window == NULL)
+ goto oom;
+
+ if (params->algorithm == WIMLIB_LZX_ALGORITHM_FAST) {
+ ctx->prev_tab = MALLOC(window_size * sizeof(ctx->prev_tab[0]));
+ if (ctx->prev_tab == NULL)
+ goto oom;
+ }
- if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW)
- block_specs_length = ((1 << (params->alg_params.slow.num_split_passes + 1)) - 1);
- else
- block_specs_length = 1;
+ size_t block_specs_length = DIV_ROUND_UP(window_size, LZX_DIV_BLOCK_SIZE);
ctx->block_specs = MALLOC(block_specs_length * sizeof(ctx->block_specs[0]));
if (ctx->block_specs == NULL)
- goto err_free_ctx;
+ goto oom;
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->alg_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;
+ unsigned min_match_len = LZX_MIN_MATCH_LEN;
+ if (!params->alg_params.slow.use_len2_matches)
+ min_match_len = max(min_match_len, 3);
+
+ if (!lz_bt_init(&ctx->mf,
+ window_size,
+ min_match_len,
+ LZX_MAX_MATCH_LEN,
+ params->alg_params.slow.nice_match_length,
+ params->alg_params.slow.max_search_depth))
+ goto oom;
}
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;
+ ctx->optimum = MALLOC((LZX_OPTIM_ARRAY_SIZE +
+ min(params->alg_params.slow.nice_match_length,
+ LZX_MAX_MATCH_LEN)) *
+ sizeof(ctx->optimum[0]));
+ if (!ctx->optimum)
+ goto oom;
}
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;
+ ctx->cached_matches = MALLOC(LZX_CACHE_SIZE);
+ if (ctx->cached_matches == NULL)
+ goto oom;
+ ctx->cache_limit = ctx->cached_matches +
+ LZX_CACHE_LEN - (LZX_MAX_MATCHES_PER_POS + 1);
}
- size_t chosen_matches_length;
- if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW)
- chosen_matches_length = LZX_MAX_WINDOW_SIZE *
- (params->alg_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;
+ ctx->chosen_items = MALLOC(window_size * sizeof(ctx->chosen_items[0]));
+ if (ctx->chosen_items == NULL)
+ goto oom;
- memcpy(&ctx->params, params, sizeof(struct wimlib_lzx_params));
+ memcpy(&ctx->params, params, sizeof(struct wimlib_lzx_compressor_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;
+ *ctx_ret = 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.");
+oom:
+ lzx_free_compressor(ctx);
return WIMLIB_ERR_NOMEM;
}
-/* API function documented in wimlib.h */
-WIMLIBAPI void
-wimlib_lzx_free_context(struct wimlib_lzx_context *_ctx)
+static u64
+lzx_get_needed_memory(size_t max_block_size,
+ const struct wimlib_compressor_params_header *_params)
{
- struct lzx_compressor *ctx = (struct lzx_compressor*)_ctx;
+ const struct wimlib_lzx_compressor_params *params = lzx_get_params(_params);
- 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);
+ u64 size = 0;
+
+ size += sizeof(struct lzx_compressor);
+
+ size += max_block_size + 12;
+
+ size += DIV_ROUND_UP(max_block_size, LZX_DIV_BLOCK_SIZE) *
+ sizeof(((struct lzx_compressor*)0)->block_specs[0]);
+
+ if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) {
+ size += max_block_size * sizeof(((struct lzx_compressor*)0)->chosen_items[0]);
+ size += lz_bt_get_needed_memory(max_block_size);
+ size += (LZX_OPTIM_ARRAY_SIZE +
+ min(params->alg_params.slow.nice_match_length,
+ LZX_MAX_MATCH_LEN)) *
+ sizeof(((struct lzx_compressor *)0)->optimum[0]);
+ size += LZX_CACHE_SIZE;
+ } else {
+ size += max_block_size * sizeof(((struct lzx_compressor*)0)->prev_tab[0]);
}
+ return size;
}
-/* 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)
+static bool
+lzx_params_valid(const struct wimlib_compressor_params_header *_params)
{
- 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;
+ const struct wimlib_lzx_compressor_params *params =
+ (const struct wimlib_lzx_compressor_params*)_params;
+
+ if (params->hdr.size != sizeof(struct wimlib_lzx_compressor_params)) {
+ LZX_DEBUG("Invalid parameter structure size!");
+ return false;
+ }
+
+ if (params->algorithm != WIMLIB_LZX_ALGORITHM_SLOW &&
+ params->algorithm != WIMLIB_LZX_ALGORITHM_FAST)
+ {
+ LZX_DEBUG("Invalid algorithm.");
+ return false;
}
- compressed_len = wimlib_lzx_compress2(uncompressed_data,
- uncompressed_len,
- compressed_data,
- ctx);
+ if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW &&
+ !params->use_defaults)
+ {
+ if (params->alg_params.slow.num_optim_passes < 1)
+ {
+ LZX_DEBUG("Invalid number of optimization passes!");
+ return false;
+ }
- wimlib_lzx_free_context(ctx);
+ if (params->alg_params.slow.main_nostat_cost < 1 ||
+ params->alg_params.slow.main_nostat_cost > 16)
+ {
+ LZX_DEBUG("Invalid main_nostat_cost!");
+ return false;
+ }
- return compressed_len;
+ if (params->alg_params.slow.len_nostat_cost < 1 ||
+ params->alg_params.slow.len_nostat_cost > 16)
+ {
+ LZX_DEBUG("Invalid len_nostat_cost!");
+ return false;
+ }
+
+ if (params->alg_params.slow.aligned_nostat_cost < 1 ||
+ params->alg_params.slow.aligned_nostat_cost > 8)
+ {
+ LZX_DEBUG("Invalid aligned_nostat_cost!");
+ return false;
+ }
+ }
+ return true;
}
+
+const struct compressor_ops lzx_compressor_ops = {
+ .params_valid = lzx_params_valid,
+ .get_needed_memory = lzx_get_needed_memory,
+ .create_compressor = lzx_create_compressor,
+ .compress = lzx_compress,
+ .free_compressor = lzx_free_compressor,
+};
git://wimlib.net / wimlib / blobdiff