/*
* lzx-compress.c
- *
- * LZX compression routines, originally based on code written by Matthew T.
- * Russotto (liblzxcomp), but heavily modified.
*/
/*
- * Copyright (C) 2002 Matthew T. Russotto
- * 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 provides wimlib_lzx_compress(), a function to compress an in-memory
- * buffer of data using LZX compression, as used in the WIM file format.
- *
- * Please see the comments in lzx-decompress.c for more information about this
- * compression format.
- *
- * One thing to keep in mind is that there is no sliding window, since the
- * window is always the entirety of a WIM chunk, which is at most WIM_CHUNK_SIZE
- * ( = 32768) bytes.
- *
- * The basic compression algorithm used here should be familiar if you are
- * familiar with Huffman trees and with other LZ77 and Huffman-based formats
- * such as DEFLATE. Otherwise it can be quite tricky to understand. Basically
- * it is the following:
- *
- * - Preprocess the input data (LZX-specific)
- * - Go through the input data and determine matches. This part is based on
- * code from zlib, and a hash table of 3-character strings is used to
- * accelerate the process of finding matches.
- * - Build the Huffman trees based on the frequencies of symbols determined
- * while recording matches.
- * - Output the block header, including the Huffman trees; then output the
- * compressed stream of matches and literal characters.
- *
- * It is possible for a WIM chunk to include multiple LZX blocks, since for some
- * input data this will produce a better compression ratio (especially since
- * each block can include new Huffman codes). However, producing multiple LZX
- * blocks from one input chunk is not yet implemented.
+ * This file contains a compressor for the LZX ("Lempel-Ziv eXtended"?)
+ * compression format, as used in the WIM (Windows IMaging) file format. This
+ * code may need some slight modifications to be used outside of the WIM format.
+ * In particular, in other situations the LZX block header might be slightly
+ * different, and a sliding window rather than a fixed-size window might be
+ * required.
+ *
+ * ----------------------------------------------------------------------------
+ *
+ * Format Overview
+ *
+ * The primary reference for LZX is the specification released by Microsoft.
+ * However, the comments in lzx-decompress.c provide more information about LZX
+ * and note some errors in the Microsoft specification.
+ *
+ * LZX shares many similarities with DEFLATE, the format used by zlib and gzip.
+ * Both LZX and DEFLATE use LZ77 matching and Huffman coding. Certain details
+ * are quite similar, such as the method for storing Huffman codes. However,
+ * the main differences are:
+ *
+ * - LZX preprocesses the data to attempt to make x86 machine code slightly more
+ * compressible before attempting to compress it further.
+ *
+ * - LZX uses a "main" alphabet which combines literals and matches, with the
+ * match symbols containing a "length header" (giving all or part of the match
+ * length) and a "position slot" (giving, roughly speaking, the order of
+ * magnitude of the match offset).
+ *
+ * - LZX does not have static Huffman blocks (that is, the kind with preset
+ * Huffman codes); however it does have two types of dynamic Huffman blocks
+ * ("verbatim" and "aligned").
+ *
+ * - LZX has a minimum match length of 2 rather than 3.
+ *
+ * - In LZX, match offsets 0 through 2 actually represent entries in an LRU
+ * queue of match offsets. This is very useful for certain types of files,
+ * such as binary files that have repeating records.
+ *
+ * ----------------------------------------------------------------------------
+ *
+ * Algorithmic Overview
+ *
+ * At a high level, any implementation of LZX compression must operate as
+ * follows:
+ *
+ * 1. Preprocess the input data to translate the targets of 32-bit x86 call
+ * instructions to absolute offsets. (Actually, this is required for WIM,
+ * but might not be in other places LZX is used.)
+ *
+ * 2. Find a sequence of LZ77-style matches and literal bytes that expands to
+ * the preprocessed data.
+ *
+ * 3. Divide the match/literal sequence into one or more LZX blocks, each of
+ * which may be "uncompressed", "verbatim", or "aligned".
+ *
+ * 4. Output each LZX block.
+ *
+ * Step (1) is fairly straightforward. It requires looking for 0xe8 bytes in
+ * the input data and performing a translation on the 4 bytes following each
+ * one.
+ *
+ * Step (4) is complicated, but it is mostly determined by the LZX format. The
+ * only real choice we have is what algorithm to use to build the length-limited
+ * canonical Huffman codes. See lzx_write_all_blocks() for details.
+ *
+ * That leaves steps (2) and (3) as where all the hard stuff happens. Focusing
+ * on step (2), we need to do LZ77-style parsing on the input data, or "window",
+ * to divide it into a sequence of matches and literals. Each position in the
+ * window might have multiple matches associated with it, and we need to choose
+ * which one, if any, to actually use. Therefore, the problem can really be
+ * divided into two areas of concern: (a) finding matches at a given position,
+ * which we shall call "match-finding", and (b) choosing whether to use a
+ * match or a literal at a given position, and if using a match, which one (if
+ * there is more than one available). We shall call this "match-choosing". We
+ * first consider match-finding, then match-choosing.
+ *
+ * ----------------------------------------------------------------------------
+ *
+ * Match-finding
+ *
+ * Given a position in the window, we want to find LZ77-style "matches" with
+ * that position at previous positions in the window. With LZX, the minimum
+ * match length is 2 and the maximum match length is 257. The only restriction
+ * on offsets is that LZX does not allow the last 2 bytes of the window to match
+ * the 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 <stdlib.h>
#include <string.h>
+#ifdef ENABLE_LZX_DEBUG
+# include "wimlib/decompress_common.h"
+#endif
-/* Structure to contain the Huffman codes for the main, length, and aligned
- * offset trees. */
-struct lzx_codes {
- u16 main_codewords[LZX_MAINTREE_NUM_SYMBOLS];
- u8 main_lens[LZX_MAINTREE_NUM_SYMBOLS];
+#define LZX_OPTIM_ARRAY_SIZE 4096
- u16 len_codewords[LZX_LENTREE_NUM_SYMBOLS];
- u8 len_lens[LZX_LENTREE_NUM_SYMBOLS];
+#define LZX_DIV_BLOCK_SIZE 32768
- u16 aligned_codewords[LZX_ALIGNEDTREE_NUM_SYMBOLS];
- u8 aligned_lens[LZX_ALIGNEDTREE_NUM_SYMBOLS];
-};
+#define LZX_CACHE_PER_POS 8
+
+#define LZX_CACHE_LEN (LZX_DIV_BLOCK_SIZE * (LZX_CACHE_PER_POS + 1))
+#define LZX_CACHE_SIZE (LZX_CACHE_LEN * sizeof(struct lz_match))
+#define LZX_MAX_MATCHES_PER_POS (LZX_MAX_MATCH_LEN - LZX_MIN_MATCH_LEN + 1)
-struct lzx_freq_tables {
- freq_t main_freq_table[LZX_MAINTREE_NUM_SYMBOLS];
- freq_t len_freq_table[LZX_LENTREE_NUM_SYMBOLS];
- freq_t aligned_freq_table[LZX_ALIGNEDTREE_NUM_SYMBOLS];
+/* Codewords for the LZX main, length, and aligned offset Huffman codes */
+struct lzx_codewords {
+ u32 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
+ u32 len[LZX_LENCODE_NUM_SYMBOLS];
+ u32 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
};
-/* Returns the LZX position slot that corresponds to a given formatted offset.
+/* Codeword lengths (in bits) for the LZX main, length, and aligned offset
+ * Huffman codes.
*
- * Logically, this returns the smallest i such that
- * formatted_offset >= lzx_position_base[i].
- *
- * The actual implementation below takes advantage of the regularity of the
- * numbers in the lzx_position_base array to calculate the slot directly from
- * the formatted offset without actually looking at the array.
+ * A 0 length means the codeword has zero frequency.
*/
-static inline unsigned
-lzx_get_position_slot(unsigned formatted_offset)
-{
-#if 0
- /*
- * Slots 36-49 (formatted_offset >= 262144) can be found by
- * (formatted_offset/131072) + 34 == (formatted_offset >> 17) + 34;
- * however, this check for formatted_offset >= 262144 is commented out
- * because WIM chunks cannot be that large.
- */
- if (formatted_offset >= 262144) {
- return (formatted_offset >> 17) + 34;
- } else
-#endif
- {
- /* Note: this part here only works if:
- *
- * 2 <= formatted_offset < 655360
- *
- * It is < 655360 because the frequency of the position bases
- * increases starting at the 655360 entry, and it is >= 2
- * because the below calculation fails if the most significant
- * bit is lower than the 2's place. */
- wimlib_assert(formatted_offset >= 2 && formatted_offset < 655360);
- unsigned mssb_idx = bsr32(formatted_offset);
- return (mssb_idx << 1) |
- ((formatted_offset >> (mssb_idx - 1)) & 1);
- }
-}
-
-static u32
-lzx_record_literal(u8 literal, void *_main_freq_tab)
-{
- freq_t *main_freq_tab = _main_freq_tab;
- main_freq_tab[literal]++;
- return literal;
-}
-
-/* Constructs a match from an offset and a length, and updates the LRU queue and
- * the frequency of symbols in the main, length, and aligned offset alphabets.
- * The return value is a 32-bit number that provides the match in an
- * intermediate representation documented below. */
-static u32
-lzx_record_match(unsigned match_offset, unsigned match_len,
- void *_freq_tabs, void *_queue)
-{
- struct lzx_freq_tables *freq_tabs = _freq_tabs;
- struct lru_queue *queue = _queue;
- unsigned position_slot;
- unsigned position_footer = 0;
- u32 match;
- u32 len_header;
- u32 len_pos_header;
- unsigned len_footer;
- unsigned adjusted_match_len;
-
- wimlib_assert(match_len >= LZX_MIN_MATCH && match_len <= LZX_MAX_MATCH);
- wimlib_assert(match_offset != 0);
-
- /* 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 + LZX_MIN_MATCH;
-
- queue->R2 = queue->R1;
- queue->R1 = queue->R0;
- queue->R0 = match_offset;
+struct lzx_lens {
+ u8 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
+ u8 len[LZX_LENCODE_NUM_SYMBOLS];
+ u8 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
+};
- /* 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. */
+/* Costs for the LZX main, length, and aligned offset Huffman symbols.
+ *
+ * If a codeword has zero frequency, it must still be assigned some nonzero cost
+ * --- generally a high cost, since even if it gets used in the next iteration,
+ * it probably will not be used very many times. */
+struct lzx_costs {
+ u8 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
+ u8 len[LZX_LENCODE_NUM_SYMBOLS];
+ u8 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
+};
- position_slot = lzx_get_position_slot(formatted_offset);
- position_footer = formatted_offset &
- ((1 << lzx_get_num_extra_bits(position_slot)) - 1);
- }
+/* The LZX main, length, and aligned offset Huffman codes */
+struct lzx_codes {
+ struct lzx_codewords codewords;
+ struct lzx_lens lens;
+};
- adjusted_match_len = match_len - LZX_MIN_MATCH;
+/* Tables for tallying symbol frequencies in the three LZX alphabets */
+struct lzx_freqs {
+ u32 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
+ u32 len[LZX_LENCODE_NUM_SYMBOLS];
+ u32 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
+};
- /* Pack the position slot, position footer, and match length into an
- * intermediate representation.
- *
- * bits description
- * ---- -----------------------------------------------------------
+/* LZX intermediate match/literal format */
+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, offset by 2. This can be at most
- * (LZX_MAX_MATCH - 2) == 255, so it will fit in 8 bits. */
- match = 0x80000000 |
- (position_slot << 25) |
- (position_footer << 8) |
- (adjusted_match_len);
+ * 0-7 length of match, minus 2. This can be at most
+ * (LZX_MAX_MATCH_LEN - 2) == 255, so it will fit in 8 bits. */
+ u32 data;
+};
+
+/* Specification for an LZX block. */
+struct lzx_block_spec {
+
+ /* One of the LZX_BLOCKTYPE_* constants indicating which type of this
+ * block. */
+ int block_type;
+
+ /* 0-based position in the window at which this block starts. */
+ u32 window_pos;
- /* The match length must be at least 2, so let the adjusted match length
- * be the match length minus 2.
+ /* The number of bytes of uncompressed data this block represents. */
+ u32 block_size;
+
+ /* The match/literal sequence for this block. */
+ struct lzx_item *chosen_items;
+
+ /* The length of the @chosen_items sequence. */
+ u32 num_chosen_items;
+
+ /* Huffman codes for this block. */
+ struct lzx_codes codes;
+};
+
+/* State of the LZX compressor. */
+struct lzx_compressor {
+
+ /* The parameters that were used to create the compressor. */
+ struct wimlib_lzx_compressor_params params;
+
+ /* The buffer of data to be compressed.
*
- * If it is less than 7, the adjusted match length is encoded as a 3-bit
- * number offset by 2. Otherwise, the 3-bit length header is all 1's
- * and the actual adjusted length is given as a symbol encoded with the
- * length tree, offset by 7.
- */
- if (adjusted_match_len < LZX_NUM_PRIMARY_LENS) {
- len_header = adjusted_match_len;
- } else {
- len_header = LZX_NUM_PRIMARY_LENS;
- len_footer = adjusted_match_len - LZX_NUM_PRIMARY_LENS;
- freq_tabs->len_freq_table[len_footer]++;
+ * 0xe8 byte preprocessing is done directly on the data here before
+ * further compression.
+ *
+ * Note that this compressor does *not* use a real sliding window!!!!
+ * It's not needed in the WIM format, since every chunk is compressed
+ * independently. This is by design, to allow random access to the
+ * chunks.
+ *
+ * We reserve a few extra bytes to potentially allow reading off the end
+ * 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. */
+ u32 window_size;
+
+ /* Allocated size of the @window. */
+ u32 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 the sequences of matches/literals that were chosen for each
+ * block. */
+ struct lzx_item *chosen_items;
+
+ /* Information about the LZX blocks the preprocessed input was divided
+ * into. */
+ struct lzx_block_spec *block_specs;
+
+ /* Number of LZX blocks the input was divided into; a.k.a. the number of
+ * elements of @block_specs that are valid. */
+ unsigned num_blocks;
+
+ /* This is simply filled in with zeroes and used to avoid special-casing
+ * the output of the first compressed Huffman code, which conceptually
+ * has a delta taken from a code with all symbols having zero-length
+ * codewords. */
+ struct lzx_codes zero_codes;
+
+ /* The current cost model. */
+ struct lzx_costs costs;
+
+ /* Fast algorithm only: Array of hash table links. */
+ u32 *prev_tab;
+
+ /* Slow algorithm only: Binary tree match-finder. */
+ struct lz_bt mf;
+
+ /* Position in window of next match to return. */
+ u32 match_window_pos;
+
+ /* The end-of-block position. We can't allow any matches to span this
+ * position. */
+ u32 match_window_end;
+
+ /* Matches found by the match-finder are cached in the following array
+ * to achieve a slight speedup when the same matches are needed on
+ * subsequent passes. This is suboptimal because different matches may
+ * be preferred with different cost models, but seems to be a worthwhile
+ * speedup. */
+ struct lz_match *cached_matches;
+ struct lz_match *cache_ptr;
+ bool matches_cached;
+ struct lz_match *cache_limit;
+
+ /* 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. */
+ struct lzx_mc_pos_data *optimum;
+ unsigned optimum_cur_idx;
+ unsigned optimum_end_idx;
+};
+
+/*
+ * Match chooser position data:
+ *
+ * An array of these structures is used during the match-choosing algorithm.
+ * They correspond to consecutive positions in the window and are used to keep
+ * track of the cost to reach each position, and the match/literal choices that
+ * need to be chosen to reach that position.
+ */
+struct lzx_mc_pos_data {
+ /* The approximate minimum cost, in bits, to reach this position in the
+ * window which has been found so far. */
+ u32 cost;
+#define MC_INFINITE_COST ((u32)~0UL)
+
+ /* The union here is just for clarity, since the fields are used in two
+ * slightly different ways. Initially, the @prev structure is filled in
+ * first, and links go from later in the window to earlier in the
+ * window. Later, @next structure is filled in and links go from
+ * earlier in the window to later in the window. */
+ union {
+ struct {
+ /* Position of the start of the match or literal that
+ * was taken to get to this position in the approximate
+ * minimum-cost parse. */
+ u32 link;
+
+ /* Offset (as in an LZ (length, offset) pair) of the
+ * match or literal that was taken to get to this
+ * position in the approximate minimum-cost parse. */
+ u32 match_offset;
+ } prev;
+ struct {
+ /* Position at which the match or literal starting at
+ * this position ends in the minimum-cost parse. */
+ u32 link;
+
+ /* Offset (as in an LZ (length, offset) pair) of the
+ * match or literal starting at this position in the
+ * approximate minimum-cost parse. */
+ u32 match_offset;
+ } next;
+ };
+
+ /* Adaptive state that exists after an approximate minimum-cost path to
+ * reach this position is taken. */
+ struct lzx_lru_queue queue;
+};
+
+/* Returns the LZX position slot that corresponds to a given match offset,
+ * taking into account the recent offset queue and updating it if the offset is
+ * found in it. */
+static unsigned
+lzx_get_position_slot(u32 offset, struct lzx_lru_queue *queue)
+{
+ unsigned position_slot;
+
+ /* See if the offset was recently used. */
+ for (int i = 0; i < LZX_NUM_RECENT_OFFSETS; i++) {
+ if (offset == queue->R[i]) {
+ /* Found it. */
+
+ /* Bring the repeat offset to the front of the
+ * queue. Note: this is, in fact, not a real
+ * LRU queue because repeat matches are simply
+ * swapped to the front. */
+ swap(queue->R[0], queue->R[i]);
+
+ /* The resulting position slot is simply the first index
+ * at which the offset was found in the queue. */
+ return i;
+ }
}
- len_pos_header = (position_slot << 3) | len_header;
- wimlib_assert(len_pos_header < LZX_MAINTREE_NUM_SYMBOLS - LZX_NUM_CHARS);
+ /* The offset was not recently used; look up its real position slot. */
+ position_slot = lzx_get_position_slot_raw(offset + LZX_OFFSET_OFFSET);
- freq_tabs->main_freq_table[len_pos_header + LZX_NUM_CHARS]++;
+ /* 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;
- /* Equivalent to:
- * if (lzx_extra_bits[position_slot] >= 3) */
- if (position_slot >= 8)
- freq_tabs->aligned_freq_table[position_footer & 7]++;
+ return position_slot;
+}
- return match;
+/* Build the main, length, and aligned offset Huffman codes used in LZX.
+ *
+ * This takes as input the frequency tables for each code and produces as output
+ * a set of tables that map symbols to codewords and codeword lengths. */
+static void
+lzx_make_huffman_codes(const struct lzx_freqs *freqs,
+ struct lzx_codes *codes,
+ unsigned num_main_syms)
+{
+ make_canonical_huffman_code(num_main_syms,
+ LZX_MAX_MAIN_CODEWORD_LEN,
+ freqs->main,
+ codes->lens.main,
+ codes->codewords.main);
+
+ make_canonical_huffman_code(LZX_LENCODE_NUM_SYMBOLS,
+ LZX_MAX_LEN_CODEWORD_LEN,
+ freqs->len,
+ codes->lens.len,
+ codes->codewords.len);
+
+ make_canonical_huffman_code(LZX_ALIGNEDCODE_NUM_SYMBOLS,
+ LZX_MAX_ALIGNED_CODEWORD_LEN,
+ freqs->aligned,
+ codes->lens.aligned,
+ codes->codewords.aligned);
}
/*
- * Writes a compressed literal match to the output.
+ * Output a precomputed LZX match.
*
- * @out: The output bitstream.
- * @block_type: The type of the block (LZX_BLOCKTYPE_ALIGNED or LZX_BLOCKTYPE_VERBATIM)
- * @match: The match, encoded as a 32-bit number.
- * @codes: Pointer to a structure that contains the codewords for the
- * main, length, and aligned offset Huffman codes.
+ * @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 int
+static void
lzx_write_match(struct output_bitstream *out, int block_type,
- u32 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 & 0xff;
+ unsigned match_len_minus_2 = match.data & 0xff;
/* Next 17 bits are the position footer */
- unsigned position_footer = (match >> 8) & 0x1ffff; /* 17 bits */
+ unsigned position_footer = (match.data >> 8) & 0x1ffff; /* 17 bits */
/* Next 6 bits are the position slot. */
- unsigned position_slot = (match >> 25) & 0x3f; /* 6 bits */
+ 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;
- int ret;
- /* 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. */
- ret = bitstream_put_bits(out, codes->main_codewords[main_symbol],
- codes->main_lens[main_symbol]);
- if (ret != 0)
- return ret;
+ bitstream_put_bits(out, codes->codewords.main[main_symbol],
+ codes->lens.main[main_symbol]);
/* If there is a length footer, output it using the
* length Huffman code. */
- if (len_footer != (unsigned)(-1)) {
- ret = bitstream_put_bits(out, codes->len_codewords[len_footer],
- codes->len_lens[len_footer]);
- if (ret != 0)
- return ret;
- }
-
- wimlib_assert(position_slot < LZX_NUM_POSITION_SLOTS);
+ 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)) {
verbatim_bits = position_footer >> 3;
- ret = bitstream_put_bits(out, verbatim_bits,
- num_extra_bits - 3);
- if (ret != 0)
- return ret;
+ bitstream_put_bits(out, verbatim_bits,
+ num_extra_bits - 3);
aligned_bits = (position_footer & 7);
- ret = bitstream_put_bits(out,
- codes->aligned_codewords[aligned_bits],
- codes->aligned_lens[aligned_bits]);
- if (ret != 0)
- return ret;
+ bitstream_put_bits(out,
+ codes->codewords.aligned[aligned_bits],
+ codes->lens.aligned[aligned_bits]);
} else {
/* verbatim bits is the same as the position
* footer, in this case. */
- ret = bitstream_put_bits(out, position_footer, num_extra_bits);
- if (ret != 0)
- return ret;
+ bitstream_put_bits(out, position_footer, num_extra_bits);
}
- return 0;
}
-/*
- * Writes all compressed literals in a block, both matches and literal bytes, to
- * the output bitstream.
- *
- * @out: The output bitstream.
- * @block_type: The type of the block (LZX_BLOCKTYPE_ALIGNED or LZX_BLOCKTYPE_VERBATIM)
- * @match_tab[]: The array of matches that will be output. It has length
- * of @num_compressed_literals.
- * @num_compressed_literals: Number of compressed literals to be output.
- * @codes: Pointer to a structure that contains the codewords for the
- * main, length, and aligned offset Huffman codes.
- */
-static int
-lzx_write_compressed_literals(struct output_bitstream *ostream,
- int block_type,
- const u32 match_tab[],
- unsigned num_compressed_literals,
- const struct lzx_codes *codes)
+/* 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)
{
- unsigned i;
- u32 match;
- int ret;
-
- for (i = 0; i < num_compressed_literals; i++) {
- 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 & 0x80000000) {
- /* match */
- ret = lzx_write_match(ostream, block_type, match,
- codes);
- if (ret != 0)
- return ret;
- } else {
- /* literal byte */
- wimlib_assert(match < LZX_NUM_CHARS);
- ret = bitstream_put_bits(ostream,
- codes->main_codewords[match],
- codes->main_lens[match]);
- if (ret != 0)
- return ret;
- }
- }
- return 0;
+ bitstream_put_bits(out,
+ codes->codewords.main[literal],
+ codes->lens.main[literal]);
}
-/*
- * Writes a compressed Huffman tree to the output, preceded by the pretree for
- * it.
- *
- * The Huffman tree 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 pretree, 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
- * pretree precede the path lengths of the larger code and are uncompressed,
- * consisting of 20 entries of 4 bits each.
- *
- * @out: The bitstream for the compressed output.
- * @lens: The code lengths for the Huffman tree, indexed by symbol.
- * @num_symbols: The number of symbols in the code.
- */
-static int
-lzx_write_compressed_tree(struct output_bitstream *out,
- const u8 lens[], unsigned num_symbols)
-{
- /* Frequencies of the length symbols, including the RLE symbols (NOT the
- * actual lengths themselves). */
- freq_t pretree_freqs[LZX_PRETREE_NUM_SYMBOLS];
- u8 pretree_lens[LZX_PRETREE_NUM_SYMBOLS];
- u16 pretree_codewords[LZX_PRETREE_NUM_SYMBOLS];
- u8 output_syms[num_symbols * 2];
- unsigned output_syms_idx;
- unsigned cur_run_len;
- unsigned i;
- unsigned len_in_run;
- unsigned additional_bits;
- char delta;
- u8 pretree_sym;
-
- ZERO_ARRAY(pretree_freqs);
+static unsigned
+lzx_build_precode(const u8 lens[restrict],
+ const u8 prev_lens[restrict],
+ const unsigned num_syms,
+ u32 precode_freqs[restrict LZX_PRECODE_NUM_SYMBOLS],
+ u8 output_syms[restrict num_syms],
+ u8 precode_lens[restrict LZX_PRECODE_NUM_SYMBOLS],
+ u32 precode_codewords[restrict LZX_PRECODE_NUM_SYMBOLS],
+ unsigned *num_additional_bits_ret)
+{
+ memset(precode_freqs, 0,
+ LZX_PRECODE_NUM_SYMBOLS * sizeof(precode_freqs[0]));
/* Since the code word lengths use a form of RLE encoding, the goal here
* is to find each run of identical lengths when going through them in
* 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_symbols; 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_symbols && lens[i] == lens[i - 1]) {
+ if (i != num_syms && lens[i] == lens[i - 1]) {
/* Still in a run--- keep going. */
cur_run_len++;
continue;
/* 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);
- pretree_freqs[18]++;
+ num_additional_bits += 5;
+ precode_freqs[18]++;
output_syms[output_syms_idx++] = 18;
output_syms[output_syms_idx++] = additional_bits;
cur_run_len -= 20 + additional_bits;
* 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);
- pretree_freqs[17]++;
+ num_additional_bits += 4;
+ precode_freqs[17]++;
output_syms[output_syms_idx++] = 17;
output_syms[output_syms_idx++] = additional_bits;
cur_run_len -= 4 + additional_bits;
* nonzeroes, where n is a literal bit that follows the
* magic length, and where the value of the lengths in
* the run is given by an extra length symbol, encoded
- * with the pretree, that follows the literal bit.
+ * with the precode, that follows the literal bit.
*
* The extra length symbol is encoded as a difference
* from the length of the codeword for the first symbol
- * in the run in the previous tree.
+ * in the run in the previous code.
* */
while (cur_run_len >= 4) {
+ unsigned additional_bits;
+ signed char delta;
+
additional_bits = (cur_run_len > 4);
- delta = -(char)len_in_run;
+ num_additional_bits += 1;
+ delta = (signed char)prev_lens[i - cur_run_len] -
+ (signed char)len_in_run;
if (delta < 0)
delta += 17;
- pretree_freqs[19]++;
- pretree_freqs[(unsigned char)delta]++;
+ precode_freqs[19]++;
+ precode_freqs[(unsigned char)delta]++;
output_syms[output_syms_idx++] = 19;
output_syms[output_syms_idx++] = additional_bits;
output_syms[output_syms_idx++] = delta;
/* Any remaining lengths in the run are outputted without RLE,
* as a difference from the length of that codeword in the
- * previous tree. */
- while (cur_run_len--) {
- delta = -(char)len_in_run;
+ * previous code. */
+ while (cur_run_len > 0) {
+ signed char delta;
+
+ delta = (signed char)prev_lens[i - cur_run_len] -
+ (signed char)len_in_run;
if (delta < 0)
delta += 17;
- pretree_freqs[(unsigned char)delta]++;
+ precode_freqs[(unsigned char)delta]++;
output_syms[output_syms_idx++] = delta;
+ cur_run_len--;
}
cur_run_len = 1;
}
- wimlib_assert(output_syms_idx < ARRAY_LEN(output_syms));
-
- /* Build the pretree from the frequencies of the length symbols. */
-
- make_canonical_huffman_code(LZX_PRETREE_NUM_SYMBOLS,
- LZX_MAX_CODEWORD_LEN,
- pretree_freqs, pretree_lens,
- pretree_codewords);
+ /* Build the precode from the frequencies of the length symbols. */
- /* Write the lengths of the pretree codes to the output. */
- for (i = 0; i < LZX_PRETREE_NUM_SYMBOLS; i++)
- bitstream_put_bits(out, pretree_lens[i],
- LZX_PRETREE_ELEMENT_SIZE);
+ make_canonical_huffman_code(LZX_PRECODE_NUM_SYMBOLS,
+ LZX_MAX_PRE_CODEWORD_LEN,
+ precode_freqs, precode_lens,
+ precode_codewords);
- /* Write the length symbols, encoded with the pretree, to the output. */
+ *num_additional_bits_ret = num_additional_bits;
- i = 0;
- while (i < output_syms_idx) {
- pretree_sym = output_syms[i++];
+ return output_syms_idx;
+}
- bitstream_put_bits(out, pretree_codewords[pretree_sym],
- pretree_lens[pretree_sym]);
- switch (pretree_sym) {
+/*
+ * Output a Huffman code in the compressed form used in LZX.
+ *
+ * The Huffman code is represented in the output as a logical series of codeword
+ * lengths from which the Huffman code, which must be in canonical form, can be
+ * reconstructed.
+ *
+ * The codeword lengths are themselves compressed using a separate Huffman code,
+ * the "precode", which contains a symbol for each possible codeword length in
+ * the larger code as well as several special symbols to represent repeated
+ * codeword lengths (a form of run-length encoding). The precode is itself
+ * constructed in canonical form, and its codeword lengths are represented
+ * literally in 20 4-bit fields that immediately precede the compressed codeword
+ * lengths of the larger code.
+ *
+ * Furthermore, the codeword lengths of the larger code are actually represented
+ * as deltas from the codeword lengths of the corresponding code in the previous
+ * block.
+ *
+ * @out:
+ * Bitstream to which to write the compressed Huffman code.
+ * @lens:
+ * The codeword lengths, indexed by symbol, in the Huffman code.
+ * @prev_lens:
+ * The codeword lengths, indexed by symbol, in the corresponding Huffman
+ * code in the previous block, or all zeroes if this is the first block.
+ * @num_syms:
+ * The number of symbols in the Huffman code.
+ */
+static void
+lzx_write_compressed_code(struct output_bitstream *out,
+ const u8 lens[restrict],
+ const u8 prev_lens[restrict],
+ unsigned num_syms)
+{
+ u32 precode_freqs[LZX_PRECODE_NUM_SYMBOLS];
+ u8 output_syms[num_syms];
+ u8 precode_lens[LZX_PRECODE_NUM_SYMBOLS];
+ u32 precode_codewords[LZX_PRECODE_NUM_SYMBOLS];
+ unsigned i;
+ unsigned num_output_syms;
+ u8 precode_sym;
+ unsigned dummy;
+
+ num_output_syms = lzx_build_precode(lens,
+ prev_lens,
+ num_syms,
+ precode_freqs,
+ output_syms,
+ precode_lens,
+ precode_codewords,
+ &dummy);
+
+ /* Write the lengths of the precode codes to the output. */
+ for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++)
+ bitstream_put_bits(out, precode_lens[i],
+ LZX_PRECODE_ELEMENT_SIZE);
+
+ /* Write the length symbols, encoded with the precode, to the output. */
+
+ for (i = 0; i < num_output_syms; ) {
+ precode_sym = output_syms[i++];
+
+ bitstream_put_bits(out, precode_codewords[precode_sym],
+ precode_lens[precode_sym]);
+ switch (precode_sym) {
case 17:
bitstream_put_bits(out, output_syms[i++], 4);
break;
case 19:
bitstream_put_bits(out, output_syms[i++], 1);
bitstream_put_bits(out,
- pretree_codewords[output_syms[i]],
- pretree_lens[output_syms[i]]);
+ precode_codewords[output_syms[i]],
+ precode_lens[output_syms[i]]);
i++;
break;
default:
break;
}
}
- return 0;
}
-/* Builds the canonical Huffman code for the main tree, the length tree, and the
- * aligned offset tree. */
+/*
+ * Write all matches and literal bytes (which were precomputed) in an LZX
+ * compressed block to the output bitstream in the final compressed
+ * representation.
+ *
+ * @ostream
+ * The output bitstream.
+ * @block_type
+ * The chosen type of the LZX compressed block (LZX_BLOCKTYPE_ALIGNED or
+ * LZX_BLOCKTYPE_VERBATIM).
+ * @match_tab
+ * The array of matches/literals to output.
+ * @match_count
+ * Number of matches/literals to output (length of @match_tab).
+ * @codes
+ * The main, length, and aligned offset Huffman codes for the current
+ * LZX compressed block.
+ */
static void
-lzx_make_huffman_codes(const struct lzx_freq_tables *freq_tabs,
- struct lzx_codes *codes)
+lzx_write_matches_and_literals(struct output_bitstream *ostream,
+ int block_type,
+ const struct lzx_item match_tab[],
+ unsigned match_count,
+ const struct lzx_codes *codes)
{
- make_canonical_huffman_code(LZX_MAINTREE_NUM_SYMBOLS,
- LZX_MAX_CODEWORD_LEN,
- freq_tabs->main_freq_table,
- codes->main_lens,
- codes->main_codewords);
+ for (unsigned i = 0; i < match_count; i++) {
+ 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);
+ }
+}
- make_canonical_huffman_code(LZX_LENTREE_NUM_SYMBOLS,
- LZX_MAX_CODEWORD_LEN,
- freq_tabs->len_freq_table,
- codes->len_lens,
- codes->len_codewords);
+static void
+lzx_assert_codes_valid(const struct lzx_codes * codes, unsigned num_main_syms)
+{
+#ifdef ENABLE_LZX_DEBUG
+ unsigned i;
- make_canonical_huffman_code(LZX_ALIGNEDTREE_NUM_SYMBOLS, 8,
- freq_tabs->aligned_freq_table,
- codes->aligned_lens,
- codes->aligned_codewords);
+ for (i = 0; i < num_main_syms; i++)
+ LZX_ASSERT(codes->lens.main[i] <= LZX_MAX_MAIN_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_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(num_main_syms, LZX_LENCODE_NUM_SYMBOLS))]
+ _aligned_attribute(DECODE_TABLE_ALIGNMENT);
+ LZX_ASSERT(0 == make_huffman_decode_table(decode_table,
+ num_main_syms,
+ min(tablebits, LZX_MAINCODE_TABLEBITS),
+ codes->lens.main,
+ LZX_MAX_MAIN_CODEWORD_LEN));
+ LZX_ASSERT(0 == make_huffman_decode_table(decode_table,
+ LZX_LENCODE_NUM_SYMBOLS,
+ min(tablebits, LZX_LENCODE_TABLEBITS),
+ codes->lens.len,
+ LZX_MAX_LEN_CODEWORD_LEN));
+ LZX_ASSERT(0 == make_huffman_decode_table(decode_table,
+ LZX_ALIGNEDCODE_NUM_SYMBOLS,
+ min(tablebits, LZX_ALIGNEDCODE_TABLEBITS),
+ codes->lens.aligned,
+ LZX_MAX_ALIGNED_CODEWORD_LEN));
+#endif /* ENABLE_LZX_DEBUG */
}
+/* Write an LZX aligned offset or verbatim block to the output. */
static void
-do_call_insn_translation(u32 *call_insn_target, int input_pos,
- s32 file_size)
+lzx_write_compressed_block(int block_type,
+ unsigned block_size,
+ unsigned max_window_size,
+ unsigned num_main_syms,
+ struct lzx_item * chosen_items,
+ unsigned num_chosen_items,
+ const struct lzx_codes * codes,
+ const struct lzx_codes * prev_codes,
+ struct output_bitstream * ostream)
{
- s32 abs_offset;
- s32 rel_offset;
+ unsigned i;
+
+ LZX_ASSERT(block_type == LZX_BLOCKTYPE_ALIGNED ||
+ block_type == LZX_BLOCKTYPE_VERBATIM);
+ 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, 3);
+
+ /* Output the block size.
+ *
+ * The original LZX format seemed to always encode the block size in 3
+ * bytes. However, the implementation in WIMGAPI, as used in WIM files,
+ * uses the first bit to indicate whether the block is the default size
+ * (32768) or a different size given explicitly by the next 16 bits.
+ *
+ * By default, this compressor uses a window size of 32768 and therefore
+ * follows the WIMGAPI behavior. However, this compressor also supports
+ * window sizes greater than 32768 bytes, which do not appear to be
+ * supported by WIMGAPI. In such cases, we retain the default size bit
+ * to mean a size of 32768 bytes but output non-default block size in 24
+ * bits rather than 16. The compatibility of this behavior is unknown
+ * because WIMs created with chunk size greater than 32768 can seemingly
+ * only be opened by wimlib anyway. */
+ if (block_size == LZX_DEFAULT_BLOCK_SIZE) {
+ bitstream_put_bits(ostream, 1, 1);
+ } else {
+ bitstream_put_bits(ostream, 0, 1);
+
+ if (max_window_size >= 65536)
+ bitstream_put_bits(ostream, block_size >> 16, 8);
+
+ bitstream_put_bits(ostream, block_size, 16);
+ }
+
+ /* Write out lengths of the main code. Note that the LZX specification
+ * incorrectly states that the aligned offset code comes after the
+ * length code, but in fact it is the very first code to be written
+ * (before the main code). */
+ if (block_type == LZX_BLOCKTYPE_ALIGNED)
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
+ bitstream_put_bits(ostream, codes->lens.aligned[i],
+ LZX_ALIGNEDCODE_ELEMENT_SIZE);
+
+ LZX_DEBUG("Writing main code...");
+
+ /* Write the precode and lengths for the first LZX_NUM_CHARS symbols in
+ * the main code, which are the codewords for literal bytes. */
+ lzx_write_compressed_code(ostream,
+ codes->lens.main,
+ prev_codes->lens.main,
+ LZX_NUM_CHARS);
+
+ /* Write the precode and lengths for the rest of the main code, which
+ * are the codewords for match headers. */
+ lzx_write_compressed_code(ostream,
+ codes->lens.main + LZX_NUM_CHARS,
+ prev_codes->lens.main + LZX_NUM_CHARS,
+ num_main_syms - LZX_NUM_CHARS);
+
+ LZX_DEBUG("Writing length code...");
+
+ /* Write the precode and lengths for the length code. */
+ lzx_write_compressed_code(ostream,
+ codes->lens.len,
+ prev_codes->lens.len,
+ LZX_LENCODE_NUM_SYMBOLS);
+
+ LZX_DEBUG("Writing matches and literals...");
+
+ /* Write the actual matches and literals. */
+ lzx_write_matches_and_literals(ostream, block_type,
+ chosen_items, num_chosen_items,
+ codes);
+
+ LZX_DEBUG("Done writing block.");
+}
+
+/* Write out the LZX blocks that were computed. */
+static void
+lzx_write_all_blocks(struct lzx_compressor *ctx, struct output_bitstream *ostream)
+{
+
+ 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->max_window_size,
+ ctx->num_main_syms,
+ spec->chosen_items,
+ spec->num_chosen_items,
+ &spec->codes,
+ prev_codes,
+ ostream);
+
+ prev_codes = &spec->codes;
+ }
+}
+
+/* Constructs an LZX match from a literal byte and updates the main code symbol
+ * frequencies. */
+static inline u32
+lzx_tally_literal(u8 lit, struct lzx_freqs *freqs)
+{
+ freqs->main[lit]++;
+ return (u32)lit;
+}
+
+/* Constructs an LZX match from an offset and a length, and updates the LRU
+ * queue and the frequency of symbols in the main, length, and aligned offset
+ * alphabets. The return value is a 32-bit number that provides the match in an
+ * intermediate representation documented below. */
+static inline u32
+lzx_tally_match(unsigned match_len, u32 match_offset,
+ struct lzx_freqs *freqs, struct lzx_lru_queue *queue)
+{
+ unsigned position_slot;
+ unsigned position_footer;
+ u32 len_header;
+ unsigned main_symbol;
+ unsigned len_footer;
+ unsigned adjusted_match_len;
+
+ LZX_ASSERT(match_len >= LZX_MIN_MATCH_LEN && match_len <= LZX_MAX_MATCH_LEN);
+
+ /* The match offset shall be encoded as a position slot (itself encoded
+ * as part of the main symbol) and a position footer. */
+ position_slot = lzx_get_position_slot(match_offset, queue);
+ position_footer = (match_offset + LZX_OFFSET_OFFSET) &
+ ((1U << lzx_get_num_extra_bits(position_slot)) - 1);
+
+ /* The match length shall be encoded as a length header (itself encoded
+ * as part of the main symbol) and an optional length footer. */
+ adjusted_match_len = match_len - LZX_MIN_MATCH_LEN;
+ if (adjusted_match_len < LZX_NUM_PRIMARY_LENS) {
+ /* No length footer needed. */
+ len_header = adjusted_match_len;
+ } else {
+ /* Length footer needed. It will be encoded using the length
+ * code. */
+ len_header = LZX_NUM_PRIMARY_LENS;
+ len_footer = adjusted_match_len - LZX_NUM_PRIMARY_LENS;
+ freqs->len[len_footer]++;
+ }
+
+ /* Account for the main symbol. */
+ main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS;
+
+ freqs->main[main_symbol]++;
+
+ /* In an aligned offset block, 3 bits of the position footer are output
+ * as an aligned offset symbol. Account for this, although we may
+ * ultimately decide to output the block as verbatim. */
+
+ /* The following check is equivalent to:
+ *
+ * if (lzx_extra_bits[position_slot] >= 3)
+ *
+ * Note that this correctly excludes position slots that correspond to
+ * recent offsets. */
+ if (position_slot >= 8)
+ freqs->aligned[position_footer & 7]++;
+
+ /* Pack the position slot, position footer, and match length into an
+ * intermediate representation. See `struct lzx_item' for details.
+ */
+ LZX_ASSERT(LZX_MAX_POSITION_SLOTS <= 64);
+ LZX_ASSERT(lzx_get_num_extra_bits(LZX_MAX_POSITION_SLOTS - 1) <= 17);
+ LZX_ASSERT(LZX_MAX_MATCH_LEN - LZX_MIN_MATCH_LEN + 1 <= 256);
+
+ LZX_ASSERT(position_slot <= (1U << (31 - 25)) - 1);
+ LZX_ASSERT(position_footer <= (1U << (25 - 8)) - 1);
+ LZX_ASSERT(adjusted_match_len <= (1U << (8 - 0)) - 1);
+ return 0x80000000 |
+ (position_slot << 25) |
+ (position_footer << 8) |
+ (adjusted_match_len);
+}
+
+struct lzx_record_ctx {
+ struct lzx_freqs freqs;
+ struct lzx_lru_queue queue;
+ struct lzx_item *matches;
+};
+
+static void
+lzx_record_match(unsigned len, unsigned offset, void *_ctx)
+{
+ struct lzx_record_ctx *ctx = _ctx;
+
+ (ctx->matches++)->data = lzx_tally_match(len, offset, &ctx->freqs, &ctx->queue);
+}
+
+static void
+lzx_record_literal(u8 lit, void *_ctx)
+{
+ struct lzx_record_ctx *ctx = _ctx;
+
+ (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_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. 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;
+ unsigned len_header, main_symbol;
+ unsigned num_extra_bits;
+ u32 cost = 0;
+
+ 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. */
+ 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_OFFSET_OFFSET) & 7];
+ } else {
+ cost += num_extra_bits;
+ }
+
+ /* Account for extra length information. */
+ if (len_header == LZX_NUM_PRIMARY_LENS)
+ cost += costs->len[length - LZX_MIN_MATCH_LEN - LZX_NUM_PRIMARY_LENS];
+
+ return cost;
+
+}
- 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;
+/* 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)
+{
+ unsigned i;
+ unsigned num_main_syms = ctx->num_main_syms;
+
+ /* 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;
+ }
+
+ /* 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;
+ }
+
+ /* 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;
+ }
+}
+
+/* Retrieve a list of matches available at the next position in the input.
+ *
+ * A pointer to the matches array is written into @matches_ret, and the return
+ * value is the number of matches found. */
+static unsigned
+lzx_get_matches(struct lzx_compressor *ctx,
+ const struct lz_match **matches_ret)
+{
+ struct lz_match *cache_ptr;
+ struct lz_match *matches;
+ unsigned num_matches;
+
+ LZX_ASSERT(ctx->match_window_pos < ctx->match_window_end);
+
+ 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 {
- /* "compensating translation" */
- abs_offset = rel_offset - file_size;
+ num_matches = lz_bt_get_matches(&ctx->mf, matches);
+ cache_ptr->len = num_matches;
+ }
+ } else {
+ num_matches = 0;
+ }
+
+ /* 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;
+
+ if (limit >= LZX_MIN_MATCH_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;
+ }
+
+#if 0
+ 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++)
+ 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_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);
}
- *call_insn_target = cpu_to_le32(abs_offset);
}
+#endif
+ ctx->match_window_pos++;
+ ctx->cache_ptr = matches + num_matches;
+ *matches_ret = matches;
+ return num_matches;
}
-/* 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 uncompressed_data[], int uncompressed_data_len)
-{
- for (int i = 0; i < uncompressed_data_len - 10; i++) {
- if (uncompressed_data[i] == 0xe8) {
- do_call_insn_translation((u32*)&uncompressed_data[i + 1],
- i,
- LZX_WIM_MAGIC_FILESIZE);
- i += 4;
+lzx_skip_bytes(struct lzx_compressor *ctx, unsigned n)
+{
+ struct lz_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 lz_match
+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;
+
+ ctx->optimum_end_idx = cur_pos;
-static const struct lz_params lzx_lz_params = {
+ saved_prev_link = ctx->optimum[cur_pos].prev.link;
+ saved_prev_match_offset = ctx->optimum[cur_pos].prev.match_offset;
- /* LZX_MIN_MATCH == 2, but 2-character matches are rarely useful; the
- * minimum match for compression is set to 3 instead. */
- .min_match = 3,
+ do {
+ prev_link = saved_prev_link;
+ prev_match_offset = saved_prev_match_offset;
- .max_match = LZX_MAX_MATCH,
- .good_match = LZX_MAX_MATCH,
- .nice_match = LZX_MAX_MATCH,
- .max_chain_len = LZX_MAX_MATCH,
- .max_lazy_match = LZX_MAX_MATCH,
- .too_far = 4096,
-};
+ saved_prev_link = ctx->optimum[prev_link].prev.link;
+ saved_prev_match_offset = ctx->optimum[prev_link].prev.match_offset;
+
+ ctx->optimum[prev_link].next.link = cur_pos;
+ ctx->optimum[prev_link].next.match_offset = prev_match_offset;
+
+ cur_pos = prev_link;
+ } while (cur_pos != 0);
+
+ ctx->optimum_cur_idx = ctx->optimum[0].next.link;
+
+ return (struct lz_match)
+ { .len = ctx->optimum_cur_idx,
+ .offset = ctx->optimum[0].next.match_offset,
+ };
+}
-/* Documented in wimlib.h */
-WIMLIBAPI unsigned
-wimlib_lzx_compress(const void *_uncompressed_data, unsigned uncompressed_len,
- void *compressed_data)
+/*
+ * 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.
+ *
+ * This is based on algorithms used in 7-Zip, including the DEFLATE encoder
+ * and the LZMA encoder, written by Igor Pavlov.
+ *
+ * Unlike a greedy parser that always takes the longest match, or even a "lazy"
+ * parser with one match/literal look-ahead like zlib, the algorithm used here
+ * may look ahead many matches/literals to determine the approximately optimal
+ * match/literal to code next. The motivation is that the compression ratio is
+ * improved if the compressor can do things like use a shorter-than-possible
+ * match in order to allow a longer match later, and also take into account the
+ * estimated real cost of coding each match/literal based on the underlying
+ * entropy encoding.
+ *
+ * Still, this is not a true optimal parser for several reasons:
+ *
+ * - Real compression formats use entropy encoding of the literal/match
+ * sequence, so the real cost of coding each match or literal is unknown until
+ * the parse is fully determined. It can be approximated based on iterative
+ * parses, but the end result is not guaranteed to be globally optimal.
+ *
+ * - Very long matches are chosen immediately. This is because locations with
+ * long matches are likely to have many possible alternatives that would cause
+ * slow optimal parsing, but also such locations are already highly
+ * compressible so it is not too harmful to just grab the longest match.
+ *
+ * - Not all possible matches at each location are considered because the
+ * underlying match-finder limits the number and type of matches produced at
+ * each position. For example, for a given match length it's usually not
+ * worth it to only consider matches other than the lowest-offset match,
+ * except in the case of a repeat offset.
+ *
+ * - Although we take into account the adaptive state (in LZX, the recent offset
+ * queue), coding decisions made with respect to the adaptive state will be
+ * locally optimal but will not necessarily be globally optimal. This is
+ * because the algorithm only keeps the least-costly path to get to a given
+ * location and does not take into account that a slightly more costly path
+ * could result in a different adaptive state that ultimately results in a
+ * lower global cost.
+ *
+ * - The array space used by this function is bounded, so in degenerate cases it
+ * is forced to start returning matches/literals before the algorithm has
+ * really finished.
+ *
+ * Each call to this function does one of two things:
+ *
+ * 1. Build a sequence of near-optimal matches/literals, up to some point, that
+ * will be returned by subsequent calls to this function, then return the
+ * first one.
+ *
+ * OR
+ *
+ * 2. Return the next match/literal previously computed by a call to this
+ * function.
+ *
+ * The return value is a (length, offset) pair specifying the match or literal
+ * chosen. For literals, the length is 0 or 1 and the offset is meaningless.
+ */
+static struct lz_match
+lzx_get_near_optimal_match(struct lzx_compressor *ctx)
{
- struct output_bitstream ostream;
- u8 uncompressed_data[uncompressed_len + 8];
- struct lzx_freq_tables freq_tabs;
- struct lzx_codes codes;
- u32 match_tab[uncompressed_len];
- struct lru_queue queue;
unsigned num_matches;
- unsigned compressed_len;
+ const struct lz_match *matches;
+ struct lz_match match;
+ 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. */
+ match.len = ctx->optimum[ctx->optimum_cur_idx].next.link -
+ ctx->optimum_cur_idx;
+ match.offset = ctx->optimum[ctx->optimum_cur_idx].next.match_offset;
+
+ ctx->optimum_cur_idx = ctx->optimum[ctx->optimum_cur_idx].next.link;
+ return match;
+ }
+
+ /* Case 1: Compute a new list of matches/literals to return. */
+
+ ctx->optimum_cur_idx = 0;
+ ctx->optimum_end_idx = 0;
+
+ /* 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 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 lz_match) {
+ .len = longest_rep_len,
+ .offset = longest_rep_offset,
+ };
+ }
+
+ /* 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) {
+ 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 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.
+ *
+ * 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;
+ }
+
+ 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];
+
+ 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++;
+
+ /* 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);
+
+ /* 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;
+
+ /* Skip over the remaining bytes of the long match. */
+ lzx_skip_bytes(ctx, longest_rep_len);
+
+ /* Return first match in the list. */
+ return match;
+ }
+
+ /* 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_match_chooser_reverse_list(ctx, cur_pos);
+
+ /* Append the long match to the end of the list. */
+ ctx->optimum[cur_pos].next.match_offset =
+ 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_skip_bytes(ctx, longest_len - 1);
+
+ /* Return first match in the list. */
+ return match;
+ }
+ } else {
+ longest_len = 1;
+ }
+
+ 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 (cost < ctx->optimum[cur_pos + 1].cost) {
+ ctx->optimum[cur_pos + 1].queue = ctx->optimum[cur_pos].queue;
+ ctx->optimum[cur_pos + 1].cost = cost;
+ ctx->optimum[cur_pos + 1].prev.link = cur_pos;
+ }
+
+ /* Consider coding a match.
+ *
+ * The hard-coded cost calculation is done for the same reason
+ * stated in the comment for the similar loop earlier.
+ * Actually, it is *this* one that has the biggest effect on
+ * performance; overall LZX compression is > 10% faster with
+ * this code compared to calling lzx_match_cost() with each
+ * length. */
+ for (unsigned i = 0, len = 2; i < num_matches; i++) {
+ u32 offset;
+ 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;
+ }
+
+ 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);
+ }
+
+ 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;
+ }
+ }
+ }
+}
+
+/* Set default symbol costs for the LZX Huffman codes. */
+static void
+lzx_set_default_costs(struct lzx_costs * costs, unsigned num_main_syms)
+{
unsigned i;
- int ret;
- int block_type = LZX_BLOCKTYPE_ALIGNED;
- wimlib_assert(uncompressed_len <= 32768);
+ /* Main code (part 1): Literal symbols */
+ for (i = 0; i < LZX_NUM_CHARS; i++)
+ costs->main[i] = 8;
+
+ /* Main code (part 2): Match header symbols */
+ for (; i < num_main_syms; i++)
+ costs->main[i] = 10;
+
+ /* Length code */
+ for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++)
+ costs->len[i] = 8;
+
+ /* Aligned offset code */
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
+ costs->aligned[i] = 3;
+}
+
+/* Given the frequencies of symbols in an LZX-compressed block and the
+ * corresponding Huffman codes, return LZX_BLOCKTYPE_ALIGNED or
+ * LZX_BLOCKTYPE_VERBATIM if an aligned offset or verbatim block, respectively,
+ * will take fewer bits to output. */
+static int
+lzx_choose_verbatim_or_aligned(const struct lzx_freqs * freqs,
+ const struct lzx_codes * codes)
+{
+ unsigned aligned_cost = 0;
+ unsigned verbatim_cost = 0;
+
+ /* Verbatim blocks have a constant 3 bits per position footer. Aligned
+ * offset blocks have an aligned offset symbol per position footer, plus
+ * an extra 24 bits per block to output the lengths necessary to
+ * reconstruct the aligned offset code itself. */
+ for (unsigned i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
+ verbatim_cost += 3 * freqs->aligned[i];
+ aligned_cost += codes->lens.aligned[i] * freqs->aligned[i];
+ }
+ aligned_cost += LZX_ALIGNEDCODE_ELEMENT_SIZE * LZX_ALIGNEDCODE_NUM_SYMBOLS;
+ if (aligned_cost < verbatim_cost)
+ return LZX_BLOCKTYPE_ALIGNED;
+ else
+ return LZX_BLOCKTYPE_VERBATIM;
+}
+
+/* Find a 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)
+{
+ const struct lzx_lru_queue orig_queue = ctx->queue;
+ unsigned num_passes_remaining = num_passes;
+ struct lzx_freqs freqs;
+ const u8 *window_ptr;
+ const u8 *window_end;
+ struct lzx_item *next_chosen_match;
+ struct lz_match lz_match;
+ struct lzx_item lzx_item;
+
+ LZX_ASSERT(num_passes >= 1);
+ LZX_ASSERT(lz_bt_get_position(&ctx->mf) == spec->window_pos);
+
+ ctx->match_window_end = spec->window_pos + spec->block_size;
+ ctx->matches_cached = false;
+
+ /* 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. */
+
+ 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;
+
+ while (window_ptr != window_end) {
+
+ lz_match = lzx_get_near_optimal_match(ctx);
+
+ LZX_ASSERT(!(lz_match.len == LZX_MIN_MATCH_LEN &&
+ lz_match.offset == ctx->max_window_size -
+ LZX_MIN_MATCH_LEN));
+ if (lz_match.len >= LZX_MIN_MATCH_LEN) {
+ lzx_tally_match(lz_match.len, lz_match.offset,
+ &freqs, &ctx->queue);
+ window_ptr += lz_match.len;
+ } else {
+ lzx_tally_literal(*window_ptr, &freqs);
+ window_ptr += 1;
+ }
+ }
+ 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;
+ }
+
+ 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) {
+ lz_match = lzx_get_near_optimal_match(ctx);
+
+ LZX_ASSERT(!(lz_match.len == LZX_MIN_MATCH_LEN &&
+ lz_match.offset == ctx->max_window_size -
+ LZX_MIN_MATCH_LEN));
+ if (lz_match.len >= LZX_MIN_MATCH_LEN) {
+ lzx_item.data = lzx_tally_match(lz_match.len,
+ lz_match.offset,
+ &freqs, &ctx->queue);
+ window_ptr += lz_match.len;
+ } else {
+ lzx_item.data = lzx_tally_literal(*window_ptr, &freqs);
+ window_ptr += 1;
+ }
+ *next_chosen_match++ = lzx_item;
+ }
+ 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);
+}
+
+/* Prepare the input window into one or more LZX blocks ready to be output. */
+static void
+lzx_prepare_blocks(struct lzx_compressor * ctx)
+{
+ /* 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);
+ }
+
+ /* Load the window into the match-finder. */
+ lz_bt_load_window(&ctx->mf, ctx->window, ctx->window_size);
+
+ /* 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;
+ 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);
+ }
+}
+
+/*
+ * This is the fast version of lzx_prepare_blocks(). This version "quickly"
+ * prepares a single compressed block containing the entire input. See the
+ * description of the "Fast algorithm" at the beginning of this file for more
+ * information.
+ *
+ * Input --- the preprocessed data:
+ *
+ * ctx->window[]
+ * ctx->window_size
+ *
+ * Output --- the block specification and the corresponding match/literal data:
+ *
+ * ctx->block_specs[]
+ * ctx->num_blocks
+ * ctx->chosen_items[]
+ */
+static void
+lzx_prepare_block_fast(struct lzx_compressor * ctx)
+{
+ struct lzx_record_ctx record_ctx;
+ struct lzx_block_spec *spec;
+
+ /* Parameters to hash chain LZ match finder
+ * (lazy with 1 match lookahead) */
+ static const struct lz_params lzx_lz_params = {
+ /* 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_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(&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. */
+ 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->block_type = LZX_BLOCKTYPE_ALIGNED;
+ spec->window_pos = 0;
+ spec->block_size = ctx->window_size;
+ 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;
+}
- if (uncompressed_len < 100)
+static size_t
+lzx_compress(const void *uncompressed_data, size_t uncompressed_size,
+ void *compressed_data, size_t compressed_size_avail, void *_ctx)
+{
+ struct lzx_compressor *ctx = _ctx;
+ struct output_bitstream ostream;
+ size_t compressed_size;
+
+ if (uncompressed_size < 100) {
+ LZX_DEBUG("Too small to bother compressing.");
+ return 0;
+ }
+
+ 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;
+ }
+
+ LZX_DEBUG("Attempting to compress %zu bytes...",
+ uncompressed_size);
- memset(&freq_tabs, 0, sizeof(freq_tabs));
- queue.R0 = 1;
- queue.R1 = 1;
- queue.R2 = 1;
+ /* The input data must be preprocessed. To avoid changing the original
+ * input, copy it to a temporary buffer. */
+ memcpy(ctx->window, uncompressed_data, uncompressed_size);
+ ctx->window_size = uncompressed_size;
- /* The input data must be preprocessed. To avoid changing the original
- * input, copy it to a temporary buffer. */
- memcpy(uncompressed_data, _uncompressed_data, uncompressed_len);
- memset(uncompressed_data + uncompressed_len, 0, 8);
+ /* This line is unnecessary; it just avoids inconsequential accesses of
+ * uninitialized memory that would show up in memory-checking tools such
+ * as valgrind. */
+ memset(&ctx->window[ctx->window_size], 0, 12);
+
+ LZX_DEBUG("Preprocessing data...");
/* Before doing any actual compression, do the call instruction (0xe8
- * byte) translation on the uncompressed data. */
- do_call_insn_preprocessing(uncompressed_data, uncompressed_len);
+ * byte) translation on the uncompressed data. */
+ lzx_do_e8_preprocessing(ctx->window, ctx->window_size);
- /* Determine the sequence of matches and literals that will be output,
- * and in the process, keep counts of the number of times each symbol
- * will be output, so that the Huffman trees can be made. */
+ LZX_DEBUG("Preparing blocks...");
- num_matches = lz_analyze_block(uncompressed_data, uncompressed_len,
- match_tab, lzx_record_match,
- lzx_record_literal, &freq_tabs,
- &queue, freq_tabs.main_freq_table,
- &lzx_lz_params);
+ /* Prepare the compressed data. */
+ if (ctx->params.algorithm == WIMLIB_LZX_ALGORITHM_FAST)
+ lzx_prepare_block_fast(ctx);
+ else
+ lzx_prepare_blocks(ctx);
- lzx_make_huffman_codes(&freq_tabs, &codes);
+ LZX_DEBUG("Writing compressed blocks...");
- /* Initialize the output bitstream. */
- init_output_bitstream(&ostream, compressed_data, uncompressed_len - 1);
+ /* Generate the compressed data. */
+ init_output_bitstream(&ostream, compressed_data, compressed_size_avail);
+ lzx_write_all_blocks(ctx, &ostream);
- /* The first three bits tell us what kind of block it is, and are one
- * of the LZX_BLOCKTYPE_* values. */
- bitstream_put_bits(&ostream, block_type, 3);
+ LZX_DEBUG("Flushing bitstream...");
+ compressed_size = flush_output_bitstream(&ostream);
+ if (compressed_size == (u32)~0UL) {
+ LZX_DEBUG("Data did not compress to %zu bytes or less!",
+ compressed_size_avail);
+ return 0;
+ }
- /* The next bit indicates whether the block size is the default (32768),
- * indicated by a 1 bit, or whether the block size is given by the next
- * 16 bits, indicated by a 0 bit. */
- if (uncompressed_len == 32768) {
- bitstream_put_bits(&ostream, 1, 1);
+ LZX_DEBUG("Done: compressed %zu => %zu bytes.",
+ uncompressed_size, compressed_size);
+
+ /* 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
+ )
+ {
+ struct wimlib_decompressor *decompressor;
+
+ 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");
+ wimlib_assert(0);
+ return 0;
+ }
+ } else {
+ WARNING("Failed to create decompressor for "
+ "data verification!");
+ }
+ }
+ return compressed_size;
+}
+
+static void
+lzx_free_compressor(void *_ctx)
+{
+ struct lzx_compressor *ctx = _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_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_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 = &lzx_slow_default;
} else {
- bitstream_put_bits(&ostream, 0, 1);
- bitstream_put_bits(&ostream, uncompressed_len, 16);
+ if (params->use_defaults) {
+ if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW)
+ params = &lzx_slow_default;
+ else
+ params = &lzx_fast_default;
+ }
}
+ return params;
+}
- /* Write out the aligned offset tree. Note that M$ lies and says that
- * the aligned offset tree comes after the length tree, but that is
- * wrong; it actually is before the main tree. */
- if (block_type == LZX_BLOCKTYPE_ALIGNED)
- for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++)
- bitstream_put_bits(&ostream, codes.aligned_lens[i],
- LZX_ALIGNEDTREE_ELEMENT_SIZE);
-
- /* Write the pre-tree and lengths for the first LZX_NUM_CHARS symbols in the
- * main tree. */
- ret = lzx_write_compressed_tree(&ostream, codes.main_lens,
- LZX_NUM_CHARS);
- if (ret)
- 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;
- /* Write the pre-tree and symbols for the rest of the main tree. */
- ret = lzx_write_compressed_tree(&ostream, codes.main_lens +
- LZX_NUM_CHARS,
- LZX_MAINTREE_NUM_SYMBOLS -
- LZX_NUM_CHARS);
- if (ret)
- return 0;
+ LZX_DEBUG("Allocating LZX context...");
- /* Write the pre-tree and symbols for the length tree. */
- ret = lzx_write_compressed_tree(&ostream, codes.len_lens,
- LZX_LENTREE_NUM_SYMBOLS);
- if (ret)
- return 0;
+ if (!lzx_window_size_valid(window_size))
+ return WIMLIB_ERR_INVALID_PARAM;
- /* Write the compressed literals. */
- ret = lzx_write_compressed_literals(&ostream, block_type,
- match_tab, num_matches, &codes);
- if (ret)
- return 0;
+ ctx = CALLOC(1, sizeof(struct lzx_compressor));
+ if (ctx == NULL)
+ goto oom;
- ret = flush_output_bitstream(&ostream);
- if (ret)
- return 0;
+ 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;
+ }
+
+ 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 oom;
+
+ if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) {
+ 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->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 == NULL)
+ goto oom;
+ }
+
+ if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) {
+ 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);
+ }
+
+ ctx->chosen_items = MALLOC(window_size * sizeof(ctx->chosen_items[0]));
+ if (ctx->chosen_items == NULL)
+ goto oom;
- compressed_len = ostream.bit_output - (u8*)compressed_data;
+ memcpy(&ctx->params, params, sizeof(struct wimlib_lzx_compressor_params));
+ memset(&ctx->zero_codes, 0, sizeof(ctx->zero_codes));
-#ifdef ENABLE_VERIFY_COMPRESSION
- /* Verify that we really get the same thing back when decompressing. */
+ LZX_DEBUG("Successfully allocated new LZX context.");
+
+ *ctx_ret = ctx;
+ return 0;
+
+oom:
+ lzx_free_compressor(ctx);
+ return WIMLIB_ERR_NOMEM;
+}
+
+static u64
+lzx_get_needed_memory(size_t max_block_size,
+ const struct wimlib_compressor_params_header *_params)
+{
+ const struct wimlib_lzx_compressor_params *params = lzx_get_params(_params);
+
+ 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;
+}
+
+static bool
+lzx_params_valid(const struct wimlib_compressor_params_header *_params)
+{
+ 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)
{
- u8 buf[uncompressed_len];
- ret = wimlib_lzx_decompress(compressed_data, compressed_len,
- buf, uncompressed_len);
- if (ret != 0) {
- ERROR("lzx_compress(): Failed to decompress data we compressed");
- abort();
+ LZX_DEBUG("Invalid algorithm.");
+ return false;
+ }
+
+ 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;
}
- for (i = 0; i < uncompressed_len; i++) {
- if (buf[i] != *((u8*)_uncompressed_data + i)) {
- ERROR("lzx_compress(): Data we compressed didn't "
- "decompress to the original data (difference at "
- "byte %u of %u)", i + 1, uncompressed_len);
- abort();
- }
+ 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;
+ }
+
+ 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;
}
}
-#endif
- return compressed_len;
+ 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