/*
* lzx-compress.c
*
- * LZX compression routines, originally based on code written by Matthew T.
- * Russotto (liblzxcomp), but heavily modified.
+ * A compressor that produces output compatible with the LZX compression format.
*/
/*
- * 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 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 beginning of the window.
+ *
+ * There are a number of algorithms that can be used for this, including hash
+ * chains, binary trees, and suffix arrays. Binary trees generally work well
+ * for LZX compression since it uses medium-size windows (2^15 to 2^21 bytes).
+ * However, when compressing in a fast mode where many positions are skipped
+ * (not searched for matches), hash chains are faster.
+ *
+ * Since the match-finders are not specific to LZX, I will not explain them in
+ * detail here. Instead, see lz_hash_chains.c and lz_binary_trees.c.
+ *
+ * ----------------------------------------------------------------------------
+ *
+ * Match-choosing
+ *
+ * Usually, choosing the longest match is best because it encodes the most data
+ * in that one item. However, sometimes the longest match is not optimal
+ * because (a) choosing a long match now might prevent using an even longer
+ * match later, or (b) more generally, what we actually care about is the number
+ * of bits it will ultimately take to output each match or literal, which is
+ * actually dependent on the entropy encoding using by the underlying
+ * compression format. Consequently, a longer match usually, but not always,
+ * takes fewer bits to encode than multiple shorter matches or literals that
+ * cover the same data.
+ *
+ * This problem of choosing the truly best match/literal sequence is probably
+ * impossible to solve efficiently when combined with entropy encoding. If we
+ * knew how many bits it takes to output each match/literal, then we could
+ * choose the optimal sequence using shortest-path search a la Dijkstra's
+ * algorithm. However, with entropy encoding, the chosen match/literal sequence
+ * affects its own encoding. Therefore, we can't know how many bits it will
+ * take to actually output any one match or literal until we have actually
+ * chosen the full sequence of matches and literals.
+ *
+ * Notwithstanding the entropy encoding problem, we also aren't guaranteed to
+ * choose the optimal match/literal sequence unless the match-finder (see
+ * section "Match-finder") provides the match-chooser with all possible matches
+ * at each position. However, this is not computationally efficient. For
+ * example, there might be many matches of the same length, and usually (but not
+ * always) the best choice is the one with the smallest offset. So in practice,
+ * it's fine to only consider the smallest offset for a given match length at a
+ * given position. (Actually, for LZX, it's also worth considering repeat
+ * offsets.)
+ *
+ * In addition, as mentioned earlier, in LZX we have the choice of using
+ * multiple blocks, each of which resets the Huffman codes. This expands the
+ * search space even further. Therefore, to simplify the problem, we currently
+ * we don't attempt to actually choose the LZX blocks based on the data.
+ * Instead, we just divide the data into fixed-size blocks of LZX_DIV_BLOCK_SIZE
+ * bytes each, and always use verbatim or aligned blocks (never uncompressed).
+ * A previous version of this code recursively split the input data into
+ * equal-sized blocks, up to a maximum depth, and chose the lowest-cost block
+ * divisions. However, this made compression much slower and did not actually
+ * help very much. It remains an open question whether a sufficiently fast and
+ * useful block-splitting algorithm is possible for LZX. Essentially the same
+ * problem also applies to DEFLATE. The Microsoft LZX compressor seemingly does
+ * do block splitting, although I don't know how fast or useful it is,
+ * specifically.
+ *
+ * Now, back to the entropy encoding problem. The "solution" is to use an
+ * iterative approach to compute a good, but not necessarily optimal,
+ * match/literal sequence. Start with a fixed assignment of symbol costs and
+ * choose an "optimal" match/literal sequence based on those costs, using
+ * shortest-path seach a la Dijkstra's algorithm. Then, for each iteration of
+ * the optimization, update the costs based on the entropy encoding of the
+ * current match/literal sequence, then choose a new match/literal sequence
+ * based on the updated costs. Usually, the actual cost to output the current
+ * match/literal sequence will decrease in each iteration until it converges on
+ * a fixed point. This result may not be the truly optimal match/literal
+ * sequence, but it usually is much better than one chosen by doing a "greedy"
+ * parse where we always chooe the longest match.
+ *
+ * An alternative to both greedy parsing and iterative, near-optimal parsing is
+ * "lazy" parsing. Briefly, "lazy" parsing considers just the longest match at
+ * each position, but it waits to choose that match until it has also examined
+ * the next position. This is actually a useful approach; it's used by zlib,
+ * for example. Therefore, for fast compression we combine lazy parsing with
+ * the hash chain max-finder. For normal/high compression we combine
+ * near-optimal parsing with the binary tree match-finder.
*/
-#include "lzx.h"
-#include "compress.h"
-#include <stdlib.h>
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include "wimlib/compressor_ops.h"
+#include "wimlib/compress_common.h"
+#include "wimlib/endianness.h"
+#include "wimlib/error.h"
+#include "wimlib/lz_mf.h"
+#include "wimlib/lz_repsearch.h"
+#include "wimlib/lzx.h"
+#include "wimlib/util.h"
#include <string.h>
+#define LZX_OPTIM_ARRAY_LENGTH 4096
+
+#define LZX_DIV_BLOCK_SIZE 32768
+
+#define LZX_CACHE_PER_POS 8
+
+#define LZX_MAX_MATCHES_PER_POS (LZX_MAX_MATCH_LEN - LZX_MIN_MATCH_LEN + 1)
+
+#define LZX_CACHE_LEN (LZX_DIV_BLOCK_SIZE * (LZX_CACHE_PER_POS + 1))
+
+/* Codewords for the LZX main, length, and aligned offset Huffman codes */
+struct lzx_codewords {
+ u32 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
+ u32 len[LZX_LENCODE_NUM_SYMBOLS];
+ u32 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
+};
+
+/* Codeword lengths (in bits) for the LZX main, length, and aligned offset
+ * Huffman codes.
+ *
+ * A 0 length means the codeword has zero frequency.
+ */
+struct lzx_lens {
+ u8 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
+ u8 len[LZX_LENCODE_NUM_SYMBOLS];
+ u8 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
+};
+
+/* Costs for the LZX main, length, and aligned offset Huffman symbols.
+ *
+ * If a codeword has zero frequency, it must still be assigned some nonzero cost
+ * --- generally a high cost, since even if it gets used in the next iteration,
+ * it probably will not be used very many times. */
+struct lzx_costs {
+ u8 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
+ u8 len[LZX_LENCODE_NUM_SYMBOLS];
+ u8 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
+};
-/* Structure to contain the Huffman codes for the main, length, and aligned
- * offset trees. */
+/* The LZX main, length, and aligned offset Huffman codes */
struct lzx_codes {
- u16 main_codewords[LZX_MAINTREE_NUM_SYMBOLS];
- u8 main_lens[LZX_MAINTREE_NUM_SYMBOLS];
+ struct lzx_codewords codewords;
+ struct lzx_lens lens;
+};
+
+/* Tables for tallying symbol frequencies in the three LZX alphabets */
+struct lzx_freqs {
+ u32 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
+ u32 len[LZX_LENCODE_NUM_SYMBOLS];
+ u32 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
+};
+
+/* LZX intermediate match/literal format */
+struct lzx_item {
+ /* Bit Description
+ *
+ * 31 1 if a match, 0 if a literal.
+ *
+ * 30-25 position slot. This can be at most 50, so it will fit in 6
+ * bits.
+ *
+ * 8-24 position footer. This is the offset of the real formatted
+ * offset from the position base. This can be at most 17 bits
+ * (since lzx_extra_bits[LZX_MAX_POSITION_SLOTS - 1] is 17).
+ *
+ * 0-7 length of match, minus 2. This can be at most
+ * (LZX_MAX_MATCH_LEN - 2) == 255, so it will fit in 8 bits. */
+ u32 data;
+};
+
+/* Specification for an LZX block. */
+struct lzx_block_spec {
+
+ /* One of the LZX_BLOCKTYPE_* constants indicating which type of this
+ * block. */
+ int block_type;
- u16 len_codewords[LZX_LENTREE_NUM_SYMBOLS];
- u8 len_lens[LZX_LENTREE_NUM_SYMBOLS];
+ /* 0-based position in the window at which this block starts. */
+ u32 window_pos;
- u16 aligned_codewords[LZX_ALIGNEDTREE_NUM_SYMBOLS];
- u8 aligned_lens[LZX_ALIGNEDTREE_NUM_SYMBOLS];
+ /* The number of bytes of uncompressed data this block represents. */
+ u32 block_size;
+
+ /* The match/literal sequence for this block. */
+ struct lzx_item *chosen_items;
+
+ /* The length of the @chosen_items sequence. */
+ u32 num_chosen_items;
+
+ /* Huffman codes for this block. */
+ struct lzx_codes codes;
};
-struct lzx_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];
+struct lzx_compressor;
+
+struct lzx_compressor_params {
+ struct lz_match (*choose_item_func)(struct lzx_compressor *);
+ enum lz_mf_algo mf_algo;
+ u32 num_optim_passes;
+ u32 min_match_length;
+ u32 nice_match_length;
+ u32 max_search_depth;
+};
+
+/* State of the LZX compressor. */
+struct lzx_compressor {
+
+ /* The buffer of data to be compressed.
+ *
+ * 0xe8 byte preprocessing is done directly on the data here before
+ * further compression.
+ *
+ * Note that this compressor does *not* use a real sliding window!!!!
+ * It's not needed in the WIM format, since every chunk is compressed
+ * independently. This is by design, to allow random access to the
+ * chunks. */
+ u8 *cur_window;
+
+ /* Number of bytes of data to be compressed, which is the number of
+ * bytes of data in @cur_window that are actually valid. */
+ u32 cur_window_size;
+
+ /* Allocated size of @cur_window. */
+ u32 max_window_size;
+
+ /* log2 order of the LZX window size for LZ match offset encoding
+ * purposes. Will be >= LZX_MIN_WINDOW_ORDER and <=
+ * LZX_MAX_WINDOW_ORDER.
+ *
+ * Note: 1 << @window_order is normally equal to @max_window_size, but
+ * it will be greater than @max_window_size in the event that the
+ * compressor was created with a non-power-of-2 block size. (See
+ * lzx_get_window_order().) */
+ unsigned window_order;
+
+ /* Compression parameters. */
+ struct lzx_compressor_params params;
+
+ unsigned (*get_matches_func)(struct lzx_compressor *, const struct lz_match **);
+ void (*skip_bytes_func)(struct lzx_compressor *, unsigned n);
+
+ /* Number of symbols in the main alphabet (depends on the @window_order
+ * since it determines the maximum allowed offset). */
+ unsigned num_main_syms;
+
+ /* The current match offset LRU queue. */
+ struct lzx_lru_queue queue;
+
+ /* Space for the sequences of matches/literals that were chosen for each
+ * block. */
+ struct lzx_item *chosen_items;
+
+ /* Information about the LZX blocks the preprocessed input was divided
+ * into. */
+ struct lzx_block_spec *block_specs;
+
+ /* Number of LZX blocks the input was divided into; a.k.a. the number of
+ * elements of @block_specs that are valid. */
+ unsigned num_blocks;
+
+ /* This is simply filled in with zeroes and used to avoid special-casing
+ * the output of the first compressed Huffman code, which conceptually
+ * has a delta taken from a code with all symbols having zero-length
+ * codewords. */
+ struct lzx_codes zero_codes;
+
+ /* The current cost model. */
+ struct lzx_costs costs;
+
+ /* Lempel-Ziv match-finder. */
+ struct lz_mf *mf;
+
+ /* Position in window of next match to return. */
+ u32 match_window_pos;
+
+ /* The end-of-block position. We can't allow any matches to span this
+ * position. */
+ u32 match_window_end;
+
+ /* When doing more than one match-choosing pass over the data, matches
+ * found by the match-finder are cached in the following array to
+ * achieve a slight speedup when the same matches are needed on
+ * subsequent passes. This is suboptimal because different matches may
+ * be preferred with different cost models, but seems to be a worthwhile
+ * speedup. */
+ struct lz_match *cached_matches;
+ struct lz_match *cache_ptr;
+ struct lz_match *cache_limit;
+
+ /* Match-chooser state, used when doing near-optimal parsing.
+ *
+ * When matches have been chosen, optimum_cur_idx is set to the position
+ * in the window of the next match/literal to return and optimum_end_idx
+ * is set to the position in the window at the end of the last
+ * match/literal to return. */
+ struct lzx_mc_pos_data *optimum;
+ unsigned optimum_cur_idx;
+ unsigned optimum_end_idx;
+
+ /* Previous match, used when doing lazy parsing. */
+ struct lz_match prev_match;
};
-/* Returns the LZX position slot that corresponds to a given formatted offset.
+/*
+ * Match chooser position data:
*
- * Logically, this returns the smallest i such that
- * formatted_offset >= lzx_position_base[i].
+ * An array of these structures is used during the match-choosing algorithm.
+ * They correspond to consecutive positions in the window and are used to keep
+ * track of the cost to reach each position, and the match/literal choices that
+ * need to be chosen to reach that position.
+ */
+struct lzx_mc_pos_data {
+ /* The approximate minimum cost, in bits, to reach this position in the
+ * window which has been found so far. */
+ u32 cost;
+#define MC_INFINITE_COST ((u32)~0UL)
+
+ /* The union here is just for clarity, since the fields are used in two
+ * slightly different ways. Initially, the @prev structure is filled in
+ * first, and links go from later in the window to earlier in the
+ * window. Later, @next structure is filled in and links go from
+ * earlier in the window to later in the window. */
+ union {
+ struct {
+ /* Position of the start of the match or literal that
+ * was taken to get to this position in the approximate
+ * minimum-cost parse. */
+ u32 link;
+
+ /* Offset (as in an LZ (length, offset) pair) of the
+ * match or literal that was taken to get to this
+ * position in the approximate minimum-cost parse. */
+ u32 match_offset;
+ } prev;
+ struct {
+ /* Position at which the match or literal starting at
+ * this position ends in the minimum-cost parse. */
+ u32 link;
+
+ /* Offset (as in an LZ (length, offset) pair) of the
+ * match or literal starting at this position in the
+ * approximate minimum-cost parse. */
+ u32 match_offset;
+ } next;
+ };
+
+ /* Adaptive state that exists after an approximate minimum-cost path to
+ * reach this position is taken.
+ *
+ * Note: we update this whenever we update the pending minimum-cost
+ * path. This is in contrast to LZMA, which also has an optimal parser
+ * that maintains a repeat offset queue per position, but will only
+ * compute the queue once that position is actually reached in the
+ * parse, meaning that matches are being considered *starting* at that
+ * position. However, the two methods seem to have approximately the
+ * same performance if appropriate optimizations are used. Intuitively
+ * the LZMA method seems faster, but it actually suffers from 1-2 extra
+ * hard-to-predict branches at each position. Probably it works better
+ * for LZMA than LZX because LZMA has a larger adaptive state than LZX,
+ * and the LZMA encoder considers more possibilities. */
+ struct lzx_lru_queue queue;
+};
+
+
+/*
+ * Structure to keep track of the current state of sending bits to the
+ * compressed output buffer.
*
- * 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.
+ * The LZX bitstream is encoded as a sequence of 16-bit coding units.
*/
-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);
- }
-}
+struct lzx_output_bitstream {
+
+ /* Bits that haven't yet been written to the output buffer. */
+ u32 bitbuf;
+
+ /* Number of bits currently held in @bitbuf. */
+ u32 bitcount;
+
+ /* Pointer to the start of the output buffer. */
+ le16 *start;
+
+ /* Pointer to the position in the output buffer at which the next coding
+ * unit should be written. */
+ le16 *next;
+
+ /* Pointer past the end of the output buffer. */
+ le16 *end;
+};
-static u32 lzx_record_literal(u8 literal, void *__main_freq_tab)
+/*
+ * Initialize the output bitstream.
+ *
+ * @os
+ * The output bitstream structure to initialize.
+ * @buffer
+ * The buffer being written to.
+ * @size
+ * Size of @buffer, in bytes.
+ */
+static void
+lzx_init_output(struct lzx_output_bitstream *os, void *buffer, u32 size)
{
- freq_t *main_freq_tab = __main_freq_tab;
- main_freq_tab[literal]++;
- return literal;
+ os->bitbuf = 0;
+ os->bitcount = 0;
+ os->start = buffer;
+ os->next = os->start;
+ os->end = os->start + size / sizeof(le16);
}
-/* 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)
+/*
+ * Write some bits to the output bitstream.
+ *
+ * The bits are given by the low-order @num_bits bits of @bits. Higher-order
+ * bits in @bits cannot be set. At most 17 bits can be written at once.
+ *
+ * @max_bits is a compile-time constant that specifies the maximum number of
+ * bits that can ever be written at the call site. Currently, it is used to
+ * optimize away the conditional code for writing a second 16-bit coding unit
+ * when writing fewer than 17 bits.
+ *
+ * If the output buffer space is exhausted, then the bits will be ignored, and
+ * lzx_flush_output() will return 0 when it gets called.
+ */
+static _always_inline_attribute void
+lzx_write_varbits(struct lzx_output_bitstream *os,
+ const u32 bits, const unsigned int num_bits,
+ const unsigned int max_num_bits)
{
- 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;
+ /* This code is optimized for LZX, which never needs to write more than
+ * 17 bits at once. */
+ LZX_ASSERT(num_bits <= 17);
+ LZX_ASSERT(num_bits <= max_num_bits);
+ LZX_ASSERT(os->bitcount <= 15);
+
+ /* Add the bits to the bit buffer variable. @bitcount will be at most
+ * 15, so there will be just enough space for the maximum possible
+ * @num_bits of 17. */
+ os->bitcount += num_bits;
+ os->bitbuf = (os->bitbuf << num_bits) | bits;
+
+ /* Check whether any coding units need to be written. */
+ if (os->bitcount >= 16) {
+
+ os->bitcount -= 16;
+
+ /* Write a coding unit, unless it would overflow the buffer. */
+ if (os->next != os->end)
+ *os->next++ = cpu_to_le16(os->bitbuf >> os->bitcount);
+
+ /* If writing 17 bits, a second coding unit might need to be
+ * written. But because 'max_num_bits' is a compile-time
+ * constant, the compiler will optimize away this code at most
+ * call sites. */
+ if (max_num_bits == 17 && os->bitcount == 16) {
+ if (os->next != os->end)
+ *os->next++ = cpu_to_le16(os->bitbuf);
+ os->bitcount = 0;
+ }
+ }
+}
- 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. */
+/* Use when @num_bits is a compile-time constant. Otherwise use
+ * lzx_write_varbits(). */
+static _always_inline_attribute void
+lzx_write_bits(struct lzx_output_bitstream *os,
+ const u32 bits, const unsigned int num_bits)
+{
+ lzx_write_varbits(os, bits, num_bits, num_bits);
+}
- /* 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;
+/*
+ * Flush the last coding unit to the output buffer if needed. Return the total
+ * number of bytes written to the output buffer, or 0 if an overflow occurred.
+ */
+static u32
+lzx_flush_output(struct lzx_output_bitstream *os)
+{
+ if (os->next == os->end)
+ return 0;
- queue->R2 = queue->R1;
- queue->R1 = queue->R0;
- queue->R0 = match_offset;
+ if (os->bitcount != 0)
+ *os->next++ = cpu_to_le16(os->bitbuf << (16 - os->bitcount));
- /* 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. */
+ return (const u8 *)os->next - (const u8 *)os->start;
+}
- position_slot = lzx_get_position_slot(formatted_offset);
- position_footer = formatted_offset &
- ((1 << lzx_get_num_extra_bits(position_slot)) - 1);
- }
+/* 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;
- adjusted_match_len = match_len - LZX_MIN_MATCH;
+ /* See if the offset was recently used. */
+ for (int i = 0; i < LZX_NUM_RECENT_OFFSETS; i++) {
+ if (offset == queue->R[i]) {
+ /* Found it. */
- /* Pack the position slot, position footer, and match length into an
- * intermediate representation.
- *
- * bits description
- * ---- -----------------------------------------------------------
- *
- * 31 1 if a match, 0 if a literal.
- *
- * 30-25 position slot. This can be at most 50, so it will fit in 6
- * bits.
- *
- * 8-24 position footer. This is the offset of the real formatted
- * offset from the position base. This can be at most 17 bits
- * (since lzx_extra_bits[LZX_NUM_POSITION_SLOTS - 1] is 17).
- *
- * 0-7 length of match, offset by 2. This can be at most
- * (LZX_MAX_MATCH - 2) == 255, so it will fit in 8 bits. */
- match = 0x80000000 |
- (position_slot << 25) |
- (position_footer << 8) |
- (adjusted_match_len);
+ /* 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 match length must be at least 2, so let the adjusted match length
- * be the match length minus 2.
- *
- * If it is less than 7, the adjusted match length is encoded as a 3-bit
- * number offset by 2. Otherwise, the 3-bit length header is all 1's
- * and the actual adjusted length is given as a symbol encoded with the
- * length tree, offset by 7.
- */
- if (adjusted_match_len < LZX_NUM_PRIMARY_LENS) {
- len_header = adjusted_match_len;
- } else {
- len_header = LZX_NUM_PRIMARY_LENS;
- len_footer = adjusted_match_len - LZX_NUM_PRIMARY_LENS;
- freq_tabs->len_freq_table[len_footer]++;
+ /* 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.
+ * @os:
+ * The bitstream to which to write the match.
+ * @ones_if_aligned
+ * A mask of all ones if the block is of type LZX_BLOCKTYPE_ALIGNED,
+ * otherwise 0.
+ * @match:
+ * The match data.
+ * @codes:
+ * Pointer to a structure that contains the codewords for the main, length,
+ * and aligned offset Huffman codes for the current LZX compressed block.
*/
-static int lzx_write_match(struct output_bitstream *out, int block_type,
- u32 match, const struct lzx_codes *codes)
-{
- /* low 8 bits are the match length minus 2 */
- unsigned match_len_minus_2 = match & 0xff;
- /* Next 17 bits are the position footer */
- unsigned position_footer = (match >> 8) & 0x1ffff; /* 17 bits */
- /* Next 6 bits are the position slot. */
- unsigned position_slot = (match >> 25) & 0x3f; /* 6 bits */
+static void
+lzx_write_match(struct lzx_output_bitstream *os, unsigned ones_if_aligned,
+ struct lzx_item match, const struct lzx_codes *codes)
+{
+ unsigned match_len_minus_2 = match.data & 0xff;
+ u32 position_footer = (match.data >> 8) & 0x1ffff;
+ unsigned position_slot = (match.data >> 25) & 0x3f;
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) +
- * NUM_PRIMARY_LENS (= 7), the length header contains
- * the match length minus MIN_MATCH, and there is no
- * length footer.
+
+ /* If the match length is less than MIN_MATCH_LEN (= 2) +
+ * NUM_PRIMARY_LENS (= 7), the length header contains the match length
+ * minus MIN_MATCH_LEN, and there is no length footer.
*
- * Otherwise, the length header contains
- * NUM_PRIMARY_LENS, and the length footer contains
- * the match length minus NUM_PRIMARY_LENS minus
- * MIN_MATCH. */
+ * Otherwise, the length header contains NUM_PRIMARY_LENS, and the
+ * length footer contains the match length minus NUM_PRIMARY_LENS minus
+ * MIN_MATCH_LEN. */
if (match_len_minus_2 < LZX_NUM_PRIMARY_LENS) {
len_header = match_len_minus_2;
- /* 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;
+ lzx_write_varbits(os, codes->codewords.main[main_symbol],
+ codes->lens.main[main_symbol],
+ LZX_MAX_MAIN_CODEWORD_LEN);
/* 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;
+ if (len_header == LZX_NUM_PRIMARY_LENS) {
+ lzx_write_varbits(os, codes->codewords.len[len_footer],
+ codes->lens.len[len_footer],
+ LZX_MAX_LEN_CODEWORD_LEN);
}
- wimlib_assert(position_slot < LZX_NUM_POSITION_SLOTS);
+ /* Output the position footer. */
num_extra_bits = lzx_get_num_extra_bits(position_slot);
- /* For aligned offset blocks with at least 3 extra bits, output the
- * verbatim bits literally, then the aligned bits encoded using the
- * aligned offset tree. Otherwise, only the verbatim bits need to be
- * output. */
- if ((block_type == LZX_BLOCKTYPE_ALIGNED) && (num_extra_bits >= 3)) {
-
- verbatim_bits = position_footer >> 3;
- ret = bitstream_put_bits(out, verbatim_bits,
- num_extra_bits - 3);
- if (ret != 0)
- return ret;
-
- 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;
+ if ((num_extra_bits & ones_if_aligned) >= 3) {
+
+ /* Aligned offset blocks: The low 3 bits of the position footer
+ * are Huffman-encoded using the aligned offset code. The
+ * remaining bits are output literally. */
+
+ lzx_write_varbits(os,
+ position_footer >> 3, num_extra_bits - 3, 14);
+
+ lzx_write_varbits(os,
+ codes->codewords.aligned[position_footer & 7],
+ codes->lens.aligned[position_footer & 7],
+ LZX_MAX_ALIGNED_CODEWORD_LEN);
} 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;
+ /* Verbatim blocks, or fewer than 3 extra bits: All position
+ * footer bits are output literally. */
+ lzx_write_varbits(os, position_footer, num_extra_bits, 17);
}
- return 0;
+}
+
+/* Output an LZX literal (encoded with the main Huffman code). */
+static void
+lzx_write_literal(struct lzx_output_bitstream *os, unsigned literal,
+ const struct lzx_codes *codes)
+{
+ lzx_write_varbits(os, codes->codewords.main[literal],
+ codes->lens.main[literal], LZX_MAX_MAIN_CODEWORD_LEN);
+}
+
+static unsigned
+lzx_compute_precode_items(const u8 lens[restrict],
+ const u8 prev_lens[restrict],
+ const unsigned num_lens,
+ u32 precode_freqs[restrict],
+ unsigned precode_items[restrict])
+{
+ unsigned *itemptr;
+ unsigned run_start;
+ unsigned run_end;
+ unsigned extra_bits;
+ int delta;
+ u8 len;
+
+ itemptr = precode_items;
+ run_start = 0;
+ do {
+ /* Find the next run of codeword lengths. */
+
+ /* len = the length being repeated */
+ len = lens[run_start];
+
+ run_end = run_start + 1;
+
+ /* Fast case for a single length. */
+ if (likely(run_end == num_lens || len != lens[run_end])) {
+ delta = prev_lens[run_start] - len;
+ if (delta < 0)
+ delta += 17;
+ precode_freqs[delta]++;
+ *itemptr++ = delta;
+ run_start++;
+ continue;
+ }
+
+ /* Extend the run. */
+ do {
+ run_end++;
+ } while (run_end != num_lens && len == lens[run_end]);
+
+ if (len == 0) {
+ /* Run of zeroes. */
+
+ /* Symbol 18: RLE 20 to 51 zeroes at a time. */
+ while ((run_end - run_start) >= 20) {
+ extra_bits = min((run_end - run_start) - 20, 0x1f);
+ precode_freqs[18]++;
+ *itemptr++ = 18 | (extra_bits << 5);
+ run_start += 20 + extra_bits;
+ }
+
+ /* Symbol 17: RLE 4 to 19 zeroes at a time. */
+ if ((run_end - run_start) >= 4) {
+ extra_bits = min((run_end - run_start) - 4, 0xf);
+ precode_freqs[17]++;
+ *itemptr++ = 17 | (extra_bits << 5);
+ run_start += 4 + extra_bits;
+ }
+ } else {
+
+ /* A run of nonzero lengths. */
+
+ /* Symbol 19: RLE 4 to 5 of any length at a time. */
+ while ((run_end - run_start) >= 4) {
+ extra_bits = (run_end - run_start) > 4;
+ delta = prev_lens[run_start] - len;
+ if (delta < 0)
+ delta += 17;
+ precode_freqs[19]++;
+ precode_freqs[delta]++;
+ *itemptr++ = 19 | (extra_bits << 5) | (delta << 6);
+ run_start += 4 + extra_bits;
+ }
+ }
+
+ /* Output any remaining lengths without RLE. */
+ while (run_start != run_end) {
+ delta = prev_lens[run_start] - len;
+ if (delta < 0)
+ delta += 17;
+ precode_freqs[delta]++;
+ *itemptr++ = delta;
+ run_start++;
+ }
+ } while (run_start != num_lens);
+
+ return itemptr - precode_items;
}
/*
- * 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.
+ * 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.
+ *
+ * @os:
+ * 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_lens:
+ * The number of symbols in the Huffman code.
*/
-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)
+static void
+lzx_write_compressed_code(struct lzx_output_bitstream *os,
+ const u8 lens[restrict],
+ const u8 prev_lens[restrict],
+ unsigned num_lens)
{
+ u32 precode_freqs[LZX_PRECODE_NUM_SYMBOLS];
+ u8 precode_lens[LZX_PRECODE_NUM_SYMBOLS];
+ u32 precode_codewords[LZX_PRECODE_NUM_SYMBOLS];
+ unsigned precode_items[num_lens];
+ unsigned num_precode_items;
+ unsigned precode_item;
+ unsigned precode_sym;
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;
+
+ for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++)
+ precode_freqs[i] = 0;
+
+ /* Compute the "items" (RLE / literal tokens and extra bits) with which
+ * the codeword lengths in the larger code will be output. */
+ num_precode_items = lzx_compute_precode_items(lens,
+ prev_lens,
+ num_lens,
+ precode_freqs,
+ precode_items);
+
+ /* Build the precode. */
+ make_canonical_huffman_code(LZX_PRECODE_NUM_SYMBOLS,
+ LZX_MAX_PRE_CODEWORD_LEN,
+ precode_freqs, precode_lens,
+ precode_codewords);
+
+ /* Output the lengths of the codewords in the precode. */
+ for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++)
+ lzx_write_bits(os, precode_lens[i], LZX_PRECODE_ELEMENT_SIZE);
+
+ /* Output the encoded lengths of the codewords in the larger code. */
+ for (i = 0; i < num_precode_items; i++) {
+ precode_item = precode_items[i];
+ precode_sym = precode_item & 0x1F;
+ lzx_write_varbits(os, precode_codewords[precode_sym],
+ precode_lens[precode_sym],
+ LZX_MAX_PRE_CODEWORD_LEN);
+ if (precode_sym >= 17) {
+ if (precode_sym == 17) {
+ lzx_write_bits(os, precode_item >> 5, 4);
+ } else if (precode_sym == 18) {
+ lzx_write_bits(os, precode_item >> 5, 5);
+ } else {
+ lzx_write_bits(os, (precode_item >> 5) & 1, 1);
+ precode_sym = precode_item >> 6;
+ lzx_write_varbits(os, precode_codewords[precode_sym],
+ precode_lens[precode_sym],
+ LZX_MAX_PRE_CODEWORD_LEN);
+ }
}
}
- return 0;
}
/*
- * 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.
+ * Write all matches and literal bytes (which were precomputed) in an LZX
+ * compressed block to the output bitstream in the final compressed
+ * representation.
+ *
+ * @os
+ * The output bitstream.
+ * @block_type
+ * The chosen type of the LZX compressed block (LZX_BLOCKTYPE_ALIGNED or
+ * LZX_BLOCKTYPE_VERBATIM).
+ * @items
+ * The array of matches/literals to output.
+ * @num_items
+ * Number of matches/literals to output (length of @items).
+ * @codes
+ * The main, length, and aligned offset Huffman codes for the current
+ * LZX compressed block.
*/
-static 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);
-
- /* Since the code word lengths use a form of RLE encoding, the goal here
- * is to find each run of identical lengths when going through them in
- * symbol order (including runs of length 1). For each run, as many
- * lengths are encoded using RLE as possible, and the rest are output
- * literally.
+static void
+lzx_write_items(struct lzx_output_bitstream *os, int block_type,
+ const struct lzx_item items[], u32 num_items,
+ const struct lzx_codes *codes)
+{
+ unsigned ones_if_aligned = 0U - (block_type == LZX_BLOCKTYPE_ALIGNED);
+
+ for (u32 i = 0; i < num_items; i++) {
+ /* The high bit of the 32-bit intermediate representation
+ * indicates whether the item is an actual LZ-style match (1) or
+ * a literal byte (0). */
+ if (items[i].data & 0x80000000)
+ lzx_write_match(os, ones_if_aligned, items[i], codes);
+ else
+ lzx_write_literal(os, items[i].data, codes);
+ }
+}
+
+/* Write an LZX aligned offset or verbatim block to the output. */
+static void
+lzx_write_compressed_block(int block_type,
+ u32 block_size,
+ unsigned window_order,
+ unsigned num_main_syms,
+ struct lzx_item * chosen_items,
+ u32 num_chosen_items,
+ const struct lzx_codes * codes,
+ const struct lzx_codes * prev_codes,
+ struct lzx_output_bitstream * os)
+{
+ LZX_ASSERT(block_type == LZX_BLOCKTYPE_ALIGNED ||
+ block_type == LZX_BLOCKTYPE_VERBATIM);
+
+ /* The first three bits indicate the type of block and are one of the
+ * LZX_BLOCKTYPE_* constants. */
+ lzx_write_bits(os, block_type, 3);
+
+ /* Output the block size.
*
- * output_syms[] will be filled in with the length symbols that will be
- * output, including RLE codes, not yet encoded using the pre-tree.
+ * 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.
*
- * cur_run_len keeps track of how many code word lengths are in the
- * current run of identical lengths.
+ * 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) {
+ lzx_write_bits(os, 1, 1);
+ } else {
+ lzx_write_bits(os, 0, 1);
+
+ if (window_order >= 16)
+ lzx_write_bits(os, block_size >> 16, 8);
+
+ lzx_write_bits(os, block_size & 0xFFFF, 16);
+ }
+
+ /* Output the aligned offset code. */
+ if (block_type == LZX_BLOCKTYPE_ALIGNED) {
+ for (int i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
+ lzx_write_bits(os, codes->lens.aligned[i],
+ LZX_ALIGNEDCODE_ELEMENT_SIZE);
+ }
+ }
+
+ /* Output the main code (two parts). */
+ lzx_write_compressed_code(os, codes->lens.main,
+ prev_codes->lens.main,
+ LZX_NUM_CHARS);
+ lzx_write_compressed_code(os, codes->lens.main + LZX_NUM_CHARS,
+ prev_codes->lens.main + LZX_NUM_CHARS,
+ num_main_syms - LZX_NUM_CHARS);
+
+ /* Output the length code. */
+ lzx_write_compressed_code(os, codes->lens.len,
+ prev_codes->lens.len,
+ LZX_LENCODE_NUM_SYMBOLS);
+
+ /* Output the compressed matches and literals. */
+ lzx_write_items(os, block_type, chosen_items, num_chosen_items, codes);
+}
+
+/* Write out the LZX blocks that were computed. */
+static void
+lzx_write_all_blocks(struct lzx_compressor *c, struct lzx_output_bitstream *os)
+{
+
+ const struct lzx_codes *prev_codes = &c->zero_codes;
+ for (unsigned i = 0; i < c->num_blocks; i++) {
+ const struct lzx_block_spec *spec = &c->block_specs[i];
+
+ lzx_write_compressed_block(spec->block_type,
+ spec->block_size,
+ c->window_order,
+ c->num_main_syms,
+ spec->chosen_items,
+ spec->num_chosen_items,
+ &spec->codes,
+ prev_codes,
+ os);
+
+ 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;
+ u32 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) &
+ (((u32)1 << 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.
*/
- output_syms_idx = 0;
- cur_run_len = 1;
- for (i = 1; i <= num_symbols; i++) {
+ 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);
+}
- if (i != num_symbols && lens[i] == lens[i - 1]) {
- /* Still in a run--- keep going. */
- cur_run_len++;
- continue;
+/* Returns the cost, in bits, to output a literal byte using the specified cost
+ * model. */
+static u32
+lzx_literal_cost(u8 c, const struct lzx_costs * costs)
+{
+ return costs->main[c];
+}
+
+/* Returns the cost, in bits, to output a repeat offset match of the specified
+ * length and position slot (repeat index) using the specified cost model. */
+static u32
+lzx_repmatch_cost(u32 len, unsigned position_slot, const struct lzx_costs *costs)
+{
+ unsigned len_header, main_symbol;
+ u32 cost = 0;
+
+ len_header = min(len - LZX_MIN_MATCH_LEN, LZX_NUM_PRIMARY_LENS);
+ main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS;
+
+ /* Account for main symbol. */
+ cost += costs->main[main_symbol];
+
+ /* Account for extra length information. */
+ if (len_header == LZX_NUM_PRIMARY_LENS)
+ cost += costs->len[len - LZX_MIN_MATCH_LEN - LZX_NUM_PRIMARY_LENS];
+
+ return cost;
+}
+
+/* Set the cost model @c->costs from the Huffman codeword lengths specified in
+ * @lens.
+ *
+ * The cost model and codeword lengths are almost the same thing, but the
+ * Huffman codewords with length 0 correspond to symbols with zero frequency
+ * that still need to be assigned actual costs. The specific values assigned
+ * are arbitrary, but they should be fairly high (near the maximum codeword
+ * length) to take into account the fact that uses of these symbols are expected
+ * to be rare. */
+static void
+lzx_set_costs(struct lzx_compressor *c, const struct lzx_lens * lens,
+ unsigned nostat)
+{
+ unsigned i;
+
+ /* Main code */
+ for (i = 0; i < c->num_main_syms; i++)
+ c->costs.main[i] = lens->main[i] ? lens->main[i] : nostat;
+
+ /* Length code */
+ for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++)
+ c->costs.len[i] = lens->len[i] ? lens->len[i] : nostat;
+
+ /* Aligned offset code */
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
+ c->costs.aligned[i] = lens->aligned[i] ? lens->aligned[i] : nostat / 2;
+}
+
+/* Don't allow matches to span the end of an LZX block. */
+static inline u32
+maybe_truncate_matches(struct lz_match matches[], u32 num_matches,
+ struct lzx_compressor *c)
+{
+ if (c->match_window_end < c->cur_window_size && num_matches != 0) {
+ u32 limit = c->match_window_end - c->match_window_pos;
+
+ if (limit >= LZX_MIN_MATCH_LEN) {
+
+ u32 i = num_matches - 1;
+ do {
+ if (matches[i].len >= limit) {
+ matches[i].len = limit;
+
+ /* Truncation might produce multiple
+ * matches with length 'limit'. Keep at
+ * most 1. */
+ num_matches = i + 1;
+ }
+ } while (i--);
+ } else {
+ num_matches = 0;
}
+ }
+ return num_matches;
+}
- /* Run ended! Check if it is a run of zeroes or a run of
- * nonzeroes. */
+static unsigned
+lzx_get_matches_fillcache_singleblock(struct lzx_compressor *c,
+ const struct lz_match **matches_ret)
+{
+ struct lz_match *cache_ptr;
+ struct lz_match *matches;
+ unsigned num_matches;
- /* 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];
+ cache_ptr = c->cache_ptr;
+ matches = cache_ptr + 1;
+ if (likely(cache_ptr <= c->cache_limit)) {
+ num_matches = lz_mf_get_matches(c->mf, matches);
+ cache_ptr->len = num_matches;
+ c->cache_ptr = matches + num_matches;
+ } else {
+ num_matches = 0;
+ }
+ c->match_window_pos++;
+ *matches_ret = matches;
+ return num_matches;
+}
- if (len_in_run == 0) {
- /* A run of 0's. Encode it in as few length
- * codes as we can. */
+static unsigned
+lzx_get_matches_fillcache_multiblock(struct lzx_compressor *c,
+ const struct lz_match **matches_ret)
+{
+ struct lz_match *cache_ptr;
+ struct lz_match *matches;
+ unsigned num_matches;
- /* The magic length 18 indicates a run of 20 + n zeroes,
- * where n is an uncompressed literal 5-bit integer that
- * follows the magic length. */
- while (cur_run_len >= 20) {
+ cache_ptr = c->cache_ptr;
+ matches = cache_ptr + 1;
+ if (likely(cache_ptr <= c->cache_limit)) {
+ num_matches = lz_mf_get_matches(c->mf, matches);
+ num_matches = maybe_truncate_matches(matches, num_matches, c);
+ cache_ptr->len = num_matches;
+ c->cache_ptr = matches + num_matches;
+ } else {
+ num_matches = 0;
+ }
+ c->match_window_pos++;
+ *matches_ret = matches;
+ return num_matches;
+}
- additional_bits = min(cur_run_len - 20, 0x1f);
- pretree_freqs[18]++;
- output_syms[output_syms_idx++] = 18;
- output_syms[output_syms_idx++] = additional_bits;
- cur_run_len -= 20 + additional_bits;
- }
+static unsigned
+lzx_get_matches_usecache(struct lzx_compressor *c,
+ const struct lz_match **matches_ret)
+{
+ struct lz_match *cache_ptr;
+ struct lz_match *matches;
+ unsigned num_matches;
- /* The magic length 17 indicates a run of 4 + n zeroes,
- * where n is an uncompressed literal 4-bit integer that
- * follows the magic length. */
- while (cur_run_len >= 4) {
- additional_bits = min(cur_run_len - 4, 0xf);
- pretree_freqs[17]++;
- output_syms[output_syms_idx++] = 17;
- output_syms[output_syms_idx++] = additional_bits;
- cur_run_len -= 4 + additional_bits;
- }
+ cache_ptr = c->cache_ptr;
+ matches = cache_ptr + 1;
+ if (cache_ptr <= c->cache_limit) {
+ num_matches = cache_ptr->len;
+ c->cache_ptr = matches + num_matches;
+ } else {
+ num_matches = 0;
+ }
+ c->match_window_pos++;
+ *matches_ret = matches;
+ return num_matches;
+}
+
+static unsigned
+lzx_get_matches_usecache_nocheck(struct lzx_compressor *c,
+ const struct lz_match **matches_ret)
+{
+ struct lz_match *cache_ptr;
+ struct lz_match *matches;
+ unsigned num_matches;
+
+ cache_ptr = c->cache_ptr;
+ matches = cache_ptr + 1;
+ num_matches = cache_ptr->len;
+ c->cache_ptr = matches + num_matches;
+ c->match_window_pos++;
+ *matches_ret = matches;
+ return num_matches;
+}
+
+static unsigned
+lzx_get_matches_nocache_singleblock(struct lzx_compressor *c,
+ const struct lz_match **matches_ret)
+{
+ struct lz_match *matches;
+ unsigned num_matches;
+
+ matches = c->cache_ptr;
+ num_matches = lz_mf_get_matches(c->mf, matches);
+ c->match_window_pos++;
+ *matches_ret = matches;
+ return num_matches;
+}
+
+static unsigned
+lzx_get_matches_nocache_multiblock(struct lzx_compressor *c,
+ const struct lz_match **matches_ret)
+{
+ struct lz_match *matches;
+ unsigned num_matches;
+
+ matches = c->cache_ptr;
+ num_matches = lz_mf_get_matches(c->mf, matches);
+ num_matches = maybe_truncate_matches(matches, num_matches, c);
+ c->match_window_pos++;
+ *matches_ret = matches;
+ return num_matches;
+}
+
+/*
+ * Find matches at the next position in the window.
+ *
+ * Returns the number of matches found and sets *matches_ret to point to the
+ * matches array. The matches will be sorted by strictly increasing length and
+ * offset.
+ */
+static inline unsigned
+lzx_get_matches(struct lzx_compressor *c,
+ const struct lz_match **matches_ret)
+{
+ return (*c->get_matches_func)(c, matches_ret);
+}
+
+static void
+lzx_skip_bytes_fillcache(struct lzx_compressor *c, unsigned n)
+{
+ struct lz_match *cache_ptr;
+
+ cache_ptr = c->cache_ptr;
+ c->match_window_pos += n;
+ lz_mf_skip_positions(c->mf, n);
+ if (cache_ptr <= c->cache_limit) {
+ do {
+ cache_ptr->len = 0;
+ cache_ptr += 1;
+ } while (--n && cache_ptr <= c->cache_limit);
+ }
+ c->cache_ptr = cache_ptr;
+}
+
+static void
+lzx_skip_bytes_usecache(struct lzx_compressor *c, unsigned n)
+{
+ struct lz_match *cache_ptr;
+
+ cache_ptr = c->cache_ptr;
+ c->match_window_pos += n;
+ if (cache_ptr <= c->cache_limit) {
+ do {
+ cache_ptr += 1 + cache_ptr->len;
+ } while (--n && cache_ptr <= c->cache_limit);
+ }
+ c->cache_ptr = cache_ptr;
+}
+
+static void
+lzx_skip_bytes_usecache_nocheck(struct lzx_compressor *c, unsigned n)
+{
+ struct lz_match *cache_ptr;
+
+ cache_ptr = c->cache_ptr;
+ c->match_window_pos += n;
+ do {
+ cache_ptr += 1 + cache_ptr->len;
+ } while (--n);
+ c->cache_ptr = cache_ptr;
+}
+
+static void
+lzx_skip_bytes_nocache(struct lzx_compressor *c, unsigned n)
+{
+ c->match_window_pos += n;
+ lz_mf_skip_positions(c->mf, n);
+}
+
+/*
+ * Skip the specified number of positions in the window (don't search for
+ * matches at them).
+ */
+static inline void
+lzx_skip_bytes(struct lzx_compressor *c, unsigned n)
+{
+ return (*c->skip_bytes_func)(c, n);
+}
+
+/*
+ * Reverse the linked list of near-optimal matches so that they can be returned
+ * in forwards order.
+ *
+ * Returns the first match in the list.
+ */
+static struct lz_match
+lzx_match_chooser_reverse_list(struct lzx_compressor *c, unsigned cur_pos)
+{
+ unsigned prev_link, saved_prev_link;
+ unsigned prev_match_offset, saved_prev_match_offset;
+
+ c->optimum_end_idx = cur_pos;
+
+ saved_prev_link = c->optimum[cur_pos].prev.link;
+ saved_prev_match_offset = c->optimum[cur_pos].prev.match_offset;
+
+ do {
+ prev_link = saved_prev_link;
+ prev_match_offset = saved_prev_match_offset;
+
+ saved_prev_link = c->optimum[prev_link].prev.link;
+ saved_prev_match_offset = c->optimum[prev_link].prev.match_offset;
+
+ c->optimum[prev_link].next.link = cur_pos;
+ c->optimum[prev_link].next.match_offset = prev_match_offset;
+
+ cur_pos = prev_link;
+ } while (cur_pos != 0);
+
+ c->optimum_cur_idx = c->optimum[0].next.link;
+
+ return (struct lz_match)
+ { .len = c->optimum_cur_idx,
+ .offset = c->optimum[0].next.match_offset,
+ };
+}
+
+/*
+ * Find the longest repeat offset match.
+ *
+ * If no match of at least LZX_MIN_MATCH_LEN bytes is found, then return 0.
+ *
+ * If a match of at least LZX_MIN_MATCH_LEN bytes is found, then return its
+ * length and set *slot_ret to the index of its offset in @queue.
+ */
+static inline u32
+lzx_repsearch(const u8 * const strptr, const u32 bytes_remaining,
+ const struct lzx_lru_queue *queue, unsigned *slot_ret)
+{
+ BUILD_BUG_ON(LZX_MIN_MATCH_LEN != 2);
+ return lz_repsearch(strptr, bytes_remaining, LZX_MAX_MATCH_LEN,
+ queue->R, LZX_NUM_RECENT_OFFSETS, slot_ret);
+}
+
+/*
+ * lzx_choose_near_optimal_item() -
+ *
+ * Choose an approximately optimal match or literal to use at the next position
+ * in the string, or "window", being LZ-encoded.
+ *
+ * This is based on algorithms used in 7-Zip, including the DEFLATE encoder
+ * and the LZMA encoder, written by Igor Pavlov.
+ *
+ * Unlike a greedy parser that always takes the longest match, or even a "lazy"
+ * parser with one match/literal look-ahead like zlib, the algorithm used here
+ * may look ahead many matches/literals to determine the approximately optimal
+ * match/literal to code next. The motivation is that the compression ratio is
+ * improved if the compressor can do things like use a shorter-than-possible
+ * match in order to allow a longer match later, and also take into account the
+ * estimated real cost of coding each match/literal based on the underlying
+ * entropy encoding.
+ *
+ * Still, this is not a true optimal parser for several reasons:
+ *
+ * - Real compression formats use entropy encoding of the literal/match
+ * sequence, so the real cost of coding each match or literal is unknown until
+ * the parse is fully determined. It can be approximated based on iterative
+ * parses, but the end result is not guaranteed to be globally optimal.
+ *
+ * - Very long matches are chosen immediately. This is because locations with
+ * long matches are likely to have many possible alternatives that would cause
+ * slow optimal parsing, but also such locations are already highly
+ * compressible so it is not too harmful to just grab the longest match.
+ *
+ * - Not all possible matches at each location are considered because the
+ * underlying match-finder limits the number and type of matches produced at
+ * each position. For example, for a given match length it's usually not
+ * worth it to only consider matches other than the lowest-offset match,
+ * except in the case of a repeat offset.
+ *
+ * - Although we take into account the adaptive state (in LZX, the recent offset
+ * queue), coding decisions made with respect to the adaptive state will be
+ * locally optimal but will not necessarily be globally optimal. This is
+ * because the algorithm only keeps the least-costly path to get to a given
+ * location and does not take into account that a slightly more costly path
+ * could result in a different adaptive state that ultimately results in a
+ * lower global cost.
+ *
+ * - The array space used by this function is bounded, so in degenerate cases it
+ * is forced to start returning matches/literals before the algorithm has
+ * really finished.
+ *
+ * Each call to this function does one of two things:
+ *
+ * 1. Build a sequence of near-optimal matches/literals, up to some point, that
+ * will be returned by subsequent calls to this function, then return the
+ * first one.
+ *
+ * OR
+ *
+ * 2. Return the next match/literal previously computed by a call to this
+ * function.
+ *
+ * The return value is a (length, offset) pair specifying the match or literal
+ * chosen. For literals, the length is 0 or 1 and the offset is meaningless.
+ */
+static struct lz_match
+lzx_choose_near_optimal_item(struct lzx_compressor *c)
+{
+ unsigned num_matches;
+ const struct lz_match *matches;
+ struct lz_match match;
+ u32 longest_len;
+ u32 longest_rep_len;
+ unsigned longest_rep_slot;
+ unsigned cur_pos;
+ unsigned end_pos;
+ struct lzx_mc_pos_data *optimum = c->optimum;
+
+ if (c->optimum_cur_idx != c->optimum_end_idx) {
+ /* Case 2: Return the next match/literal already found. */
+ match.len = optimum[c->optimum_cur_idx].next.link -
+ c->optimum_cur_idx;
+ match.offset = optimum[c->optimum_cur_idx].next.match_offset;
+
+ c->optimum_cur_idx = optimum[c->optimum_cur_idx].next.link;
+ return match;
+ }
+
+ /* Case 1: Compute a new list of matches/literals to return. */
+
+ c->optimum_cur_idx = 0;
+ c->optimum_end_idx = 0;
+
+ /* Search for matches at repeat offsets. As a heuristic, we only keep
+ * the one with the longest match length. */
+ if (likely(c->match_window_pos >= 1)) {
+ longest_rep_len = lzx_repsearch(&c->cur_window[c->match_window_pos],
+ c->match_window_end - c->match_window_pos,
+ &c->queue,
+ &longest_rep_slot);
+ } else {
+ longest_rep_len = 0;
+ }
+
+ /* If there's a long match with a repeat offset, choose it immediately. */
+ if (longest_rep_len >= c->params.nice_match_length) {
+ lzx_skip_bytes(c, longest_rep_len);
+ return (struct lz_match) {
+ .len = longest_rep_len,
+ .offset = c->queue.R[longest_rep_slot],
+ };
+ }
+
+ /* Find other matches. */
+ num_matches = lzx_get_matches(c, &matches);
+
+ /* If there's a long match, choose it immediately. */
+ if (num_matches) {
+ longest_len = matches[num_matches - 1].len;
+ if (longest_len >= c->params.nice_match_length) {
+ lzx_skip_bytes(c, longest_len - 1);
+ return matches[num_matches - 1];
+ }
+ } else {
+ longest_len = 1;
+ }
+
+ /* Calculate the cost to reach the next position by coding a literal. */
+ optimum[1].queue = c->queue;
+ optimum[1].cost = lzx_literal_cost(c->cur_window[c->match_window_pos - 1],
+ &c->costs);
+ optimum[1].prev.link = 0;
+ /* Calculate the cost to reach any position up to and including that
+ * reached by the longest match.
+ *
+ * Note: We consider only the lowest-offset match that reaches each
+ * position.
+ *
+ * Note: Some of the cost calculation stays the same for each offset,
+ * regardless of how many lengths it gets used for. Therefore, to
+ * improve performance, we hand-code the cost calculation instead of
+ * calling lzx_match_cost() to do a from-scratch cost evaluation at each
+ * length. */
+ for (unsigned i = 0, len = 2; i < num_matches; i++) {
+ u32 offset;
+ struct lzx_lru_queue queue;
+ u32 position_cost;
+ unsigned position_slot;
+ unsigned num_extra_bits;
+
+ offset = matches[i].offset;
+ queue = c->queue;
+ position_cost = 0;
+
+ position_slot = lzx_get_position_slot(offset, &queue);
+ num_extra_bits = lzx_get_num_extra_bits(position_slot);
+ if (num_extra_bits >= 3) {
+ position_cost += num_extra_bits - 3;
+ position_cost += c->costs.aligned[(offset + LZX_OFFSET_OFFSET) & 7];
} else {
+ position_cost += num_extra_bits;
+ }
- /* A run of nonzero lengths. */
+ do {
+ u32 cost;
+ unsigned len_header;
+ unsigned main_symbol;
- /* The magic length 19 indicates a run of 4 + n
- * nonzeroes, where n is a literal bit that follows the
- * magic length, and where the value of the lengths in
- * the run is given by an extra length symbol, encoded
- * with the pretree, that follows the literal bit.
- *
- * The extra length symbol is encoded as a difference
- * from the length of the codeword for the first symbol
- * in the run in the previous tree.
- * */
- while (cur_run_len >= 4) {
- additional_bits = (cur_run_len > 4);
- delta = -(char)len_in_run;
- if (delta < 0)
- delta += 17;
- pretree_freqs[19]++;
- pretree_freqs[(unsigned char)delta]++;
- output_syms[output_syms_idx++] = 19;
- output_syms[output_syms_idx++] = additional_bits;
- output_syms[output_syms_idx++] = delta;
- cur_run_len -= 4 + additional_bits;
+ cost = position_cost;
+
+ if (len - LZX_MIN_MATCH_LEN < LZX_NUM_PRIMARY_LENS) {
+ len_header = len - LZX_MIN_MATCH_LEN;
+ } else {
+ len_header = LZX_NUM_PRIMARY_LENS;
+ cost += c->costs.len[len - LZX_MIN_MATCH_LEN - LZX_NUM_PRIMARY_LENS];
}
+
+ main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS;
+ cost += c->costs.main[main_symbol];
+
+ optimum[len].queue = queue;
+ optimum[len].prev.link = 0;
+ optimum[len].prev.match_offset = offset;
+ optimum[len].cost = cost;
+ } while (++len <= matches[i].len);
+ }
+ end_pos = longest_len;
+
+ if (longest_rep_len) {
+
+ LZX_ASSERT(longest_rep_len >= LZX_MIN_MATCH_LEN);
+
+ u32 cost;
+
+ while (end_pos < longest_rep_len)
+ optimum[++end_pos].cost = MC_INFINITE_COST;
+
+ cost = lzx_repmatch_cost(longest_rep_len, longest_rep_slot,
+ &c->costs);
+ if (cost <= optimum[longest_rep_len].cost) {
+ optimum[longest_rep_len].queue = c->queue;
+ swap(optimum[longest_rep_len].queue.R[0],
+ optimum[longest_rep_len].queue.R[longest_rep_slot]);
+ optimum[longest_rep_len].prev.link = 0;
+ optimum[longest_rep_len].prev.match_offset =
+ optimum[longest_rep_len].queue.R[0];
+ optimum[longest_rep_len].cost = cost;
}
+ }
- /* 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;
- if (delta < 0)
- delta += 17;
+ /* Step forward, calculating the estimated minimum cost to reach each
+ * position. The algorithm may find multiple paths to reach each
+ * position; only the lowest-cost path is saved.
+ *
+ * The progress of the parse is tracked in the @optimum array, which for
+ * each position contains the minimum cost to reach that position, the
+ * index of the start of the match/literal taken to reach that position
+ * through the minimum-cost path, the offset of the match taken (not
+ * relevant for literals), and the adaptive state that will exist at
+ * that position after the minimum-cost path is taken. The @cur_pos
+ * variable stores the position at which the algorithm is currently
+ * considering coding choices, and the @end_pos variable stores the
+ * greatest position at which the costs of coding choices have been
+ * saved.
+ *
+ * The loop terminates when any one of the following conditions occurs:
+ *
+ * 1. A match with length greater than or equal to @nice_match_length is
+ * found. When this occurs, the algorithm chooses this match
+ * unconditionally, and consequently the near-optimal match/literal
+ * sequence up to and including that match is fully determined and it
+ * can begin returning the match/literal list.
+ *
+ * 2. @cur_pos reaches a position not overlapped by a preceding match.
+ * In such cases, the near-optimal match/literal sequence up to
+ * @cur_pos is fully determined and it can begin returning the
+ * match/literal list.
+ *
+ * 3. Failing either of the above in a degenerate case, the loop
+ * terminates when space in the @optimum array is exhausted.
+ * This terminates the algorithm and forces it to start returning
+ * matches/literals even though they may not be globally optimal.
+ *
+ * Upon loop termination, a nonempty list of matches/literals will have
+ * been produced and stored in the @optimum array. These
+ * matches/literals are linked in reverse order, so the last thing this
+ * function does is reverse this list and return the first
+ * match/literal, leaving the rest to be returned immediately by
+ * subsequent calls to this function.
+ */
+ cur_pos = 0;
+ for (;;) {
+ u32 cost;
+
+ /* Advance to next position. */
+ cur_pos++;
+
+ /* Check termination conditions (2) and (3) noted above. */
+ if (cur_pos == end_pos || cur_pos == LZX_OPTIM_ARRAY_LENGTH)
+ return lzx_match_chooser_reverse_list(c, cur_pos);
+
+ /* Search for matches at repeat offsets. Again, as a heuristic
+ * we only keep the longest one. */
+ longest_rep_len = lzx_repsearch(&c->cur_window[c->match_window_pos],
+ c->match_window_end - c->match_window_pos,
+ &optimum[cur_pos].queue,
+ &longest_rep_slot);
+
+ /* If we found a long match at a repeat offset, choose it
+ * immediately. */
+ if (longest_rep_len >= c->params.nice_match_length) {
+ /* Build the list of matches to return and get
+ * the first one. */
+ match = lzx_match_chooser_reverse_list(c, cur_pos);
+
+ /* Append the long match to the end of the list. */
+ optimum[cur_pos].next.match_offset =
+ optimum[cur_pos].queue.R[longest_rep_slot];
+ optimum[cur_pos].next.link = cur_pos + longest_rep_len;
+ c->optimum_end_idx = cur_pos + longest_rep_len;
+
+ /* Skip over the remaining bytes of the long match. */
+ lzx_skip_bytes(c, longest_rep_len);
+
+ /* Return first match in the list. */
+ return match;
+ }
+
+ /* Find other matches. */
+ num_matches = lzx_get_matches(c, &matches);
+
+ /* If there's a long match, choose it immediately. */
+ if (num_matches) {
+ longest_len = matches[num_matches - 1].len;
+ if (longest_len >= c->params.nice_match_length) {
+ /* Build the list of matches to return and get
+ * the first one. */
+ match = lzx_match_chooser_reverse_list(c, cur_pos);
+
+ /* Append the long match to the end of the list. */
+ optimum[cur_pos].next.match_offset =
+ matches[num_matches - 1].offset;
+ optimum[cur_pos].next.link = cur_pos + longest_len;
+ c->optimum_end_idx = cur_pos + longest_len;
+
+ /* Skip over the remaining bytes of the long match. */
+ lzx_skip_bytes(c, longest_len - 1);
- pretree_freqs[(unsigned char)delta]++;
- output_syms[output_syms_idx++] = delta;
+ /* Return first match in the list. */
+ return match;
+ }
+ } else {
+ longest_len = 1;
+ }
+
+ /* If we are reaching any positions for the first time, we need
+ * to initialize their costs to infinity. */
+ while (end_pos < cur_pos + longest_len)
+ optimum[++end_pos].cost = MC_INFINITE_COST;
+
+ /* Consider coding a literal. */
+ cost = optimum[cur_pos].cost +
+ lzx_literal_cost(c->cur_window[c->match_window_pos - 1],
+ &c->costs);
+ if (cost < optimum[cur_pos + 1].cost) {
+ optimum[cur_pos + 1].queue = optimum[cur_pos].queue;
+ optimum[cur_pos + 1].cost = cost;
+ optimum[cur_pos + 1].prev.link = cur_pos;
+ }
+
+ /* Consider coding a match.
+ *
+ * The hard-coded cost calculation is done for the same reason
+ * stated in the comment for the similar loop earlier.
+ * Actually, it is *this* one that has the biggest effect on
+ * performance; overall LZX compression is > 10% faster with
+ * this code compared to calling lzx_match_cost() with each
+ * length. */
+ for (unsigned i = 0, len = 2; i < num_matches; i++) {
+ u32 offset;
+ u32 position_cost;
+ unsigned position_slot;
+ unsigned num_extra_bits;
+
+ offset = matches[i].offset;
+ position_cost = optimum[cur_pos].cost;
+
+ /* Yet another optimization: instead of calling
+ * lzx_get_position_slot(), hand-inline the search of
+ * the repeat offset queue. Then we can omit the
+ * extra_bits calculation for repeat offset matches, and
+ * also only compute the updated queue if we actually do
+ * find a new lowest cost path. */
+ for (position_slot = 0; position_slot < LZX_NUM_RECENT_OFFSETS; position_slot++)
+ if (offset == optimum[cur_pos].queue.R[position_slot])
+ goto have_position_cost;
+
+ position_slot = lzx_get_position_slot_raw(offset + LZX_OFFSET_OFFSET);
+
+ num_extra_bits = lzx_get_num_extra_bits(position_slot);
+ if (num_extra_bits >= 3) {
+ position_cost += num_extra_bits - 3;
+ position_cost += c->costs.aligned[
+ (offset + LZX_OFFSET_OFFSET) & 7];
+ } else {
+ position_cost += num_extra_bits;
+ }
+
+ have_position_cost:
+
+ do {
+ u32 cost;
+ unsigned len_header;
+ unsigned main_symbol;
+
+ cost = position_cost;
+
+ if (len - LZX_MIN_MATCH_LEN < LZX_NUM_PRIMARY_LENS) {
+ len_header = len - LZX_MIN_MATCH_LEN;
+ } else {
+ len_header = LZX_NUM_PRIMARY_LENS;
+ cost += c->costs.len[len -
+ LZX_MIN_MATCH_LEN -
+ LZX_NUM_PRIMARY_LENS];
+ }
+
+ main_symbol = ((position_slot << 3) | len_header) +
+ LZX_NUM_CHARS;
+ cost += c->costs.main[main_symbol];
+
+ if (cost < optimum[cur_pos + len].cost) {
+ if (position_slot < LZX_NUM_RECENT_OFFSETS) {
+ optimum[cur_pos + len].queue = optimum[cur_pos].queue;
+ swap(optimum[cur_pos + len].queue.R[0],
+ optimum[cur_pos + len].queue.R[position_slot]);
+ } else {
+ optimum[cur_pos + len].queue.R[0] = offset;
+ optimum[cur_pos + len].queue.R[1] = optimum[cur_pos].queue.R[0];
+ optimum[cur_pos + len].queue.R[2] = optimum[cur_pos].queue.R[1];
+ }
+ optimum[cur_pos + len].prev.link = cur_pos;
+ optimum[cur_pos + len].prev.match_offset = offset;
+ optimum[cur_pos + len].cost = cost;
+ }
+ } while (++len <= matches[i].len);
}
- 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);
-
- /* 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);
-
- /* Write the length symbols, encoded with the pretree, to the output. */
-
- i = 0;
- while (i < output_syms_idx) {
- pretree_sym = output_syms[i++];
-
- bitstream_put_bits(out, pretree_codewords[pretree_sym],
- pretree_lens[pretree_sym]);
- switch (pretree_sym) {
- case 17:
- bitstream_put_bits(out, output_syms[i++], 4);
- break;
- case 18:
- bitstream_put_bits(out, output_syms[i++], 5);
- break;
- case 19:
- bitstream_put_bits(out, output_syms[i++], 1);
- bitstream_put_bits(out,
- pretree_codewords[output_syms[i]],
- pretree_lens[output_syms[i]]);
- i++;
- break;
- default:
- break;
+ /* Consider coding a repeat offset match.
+ *
+ * As a heuristic, we only consider the longest length of the
+ * longest repeat offset match. This does not, however,
+ * necessarily mean that we will never consider any other repeat
+ * offsets, because above we detect repeat offset matches that
+ * were found by the regular match-finder. Therefore, this
+ * special handling of the longest repeat-offset match is only
+ * helpful for coding a repeat offset match that was *not* found
+ * by the match-finder, e.g. due to being obscured by a less
+ * distant match that is at least as long.
+ *
+ * Note: an alternative, used in LZMA, is to consider every
+ * length of every repeat offset match. This is a more thorough
+ * search, and it makes it unnecessary to detect repeat offset
+ * matches that were found by the regular match-finder. But by
+ * my tests, for LZX the LZMA method slows down the compressor
+ * by ~10% and doesn't actually help the compression ratio too
+ * much.
+ *
+ * Also tested a compromise approach: consider every 3rd length
+ * of the longest repeat offset match. Still didn't seem quite
+ * worth it, though.
+ */
+ if (longest_rep_len) {
+
+ LZX_ASSERT(longest_rep_len >= LZX_MIN_MATCH_LEN);
+
+ while (end_pos < cur_pos + longest_rep_len)
+ optimum[++end_pos].cost = MC_INFINITE_COST;
+
+ cost = optimum[cur_pos].cost +
+ lzx_repmatch_cost(longest_rep_len, longest_rep_slot,
+ &c->costs);
+ if (cost <= optimum[cur_pos + longest_rep_len].cost) {
+ optimum[cur_pos + longest_rep_len].queue =
+ optimum[cur_pos].queue;
+ swap(optimum[cur_pos + longest_rep_len].queue.R[0],
+ optimum[cur_pos + longest_rep_len].queue.R[longest_rep_slot]);
+ optimum[cur_pos + longest_rep_len].prev.link =
+ cur_pos;
+ optimum[cur_pos + longest_rep_len].prev.match_offset =
+ optimum[cur_pos + longest_rep_len].queue.R[0];
+ optimum[cur_pos + longest_rep_len].cost =
+ cost;
+ }
}
}
- return 0;
}
-/* Builds the canonical Huffman code for the main tree, the length tree, and the
- * aligned offset tree. */
-static void lzx_make_huffman_codes(const struct lzx_freq_tables *freq_tabs,
- struct lzx_codes *codes)
+static struct lz_match
+lzx_choose_lazy_item(struct lzx_compressor *c)
{
- make_canonical_huffman_code(LZX_MAINTREE_NUM_SYMBOLS,
- LZX_MAX_CODEWORD_LEN,
- freq_tabs->main_freq_table,
- codes->main_lens,
- codes->main_codewords);
+ const struct lz_match *matches;
+ struct lz_match cur_match;
+ struct lz_match next_match;
+ u32 num_matches;
+
+ if (c->prev_match.len) {
+ cur_match = c->prev_match;
+ c->prev_match.len = 0;
+ } else {
+ num_matches = lzx_get_matches(c, &matches);
+ if (num_matches == 0 ||
+ (matches[num_matches - 1].len <= 3 &&
+ (matches[num_matches - 1].len <= 2 ||
+ matches[num_matches - 1].offset > 4096)))
+ {
+ return (struct lz_match) { };
+ }
- make_canonical_huffman_code(LZX_LENTREE_NUM_SYMBOLS,
- LZX_MAX_CODEWORD_LEN,
- freq_tabs->len_freq_table,
- codes->len_lens,
- codes->len_codewords);
+ cur_match = matches[num_matches - 1];
+ }
+
+ if (cur_match.len >= c->params.nice_match_length) {
+ lzx_skip_bytes(c, cur_match.len - 1);
+ return cur_match;
+ }
+
+ num_matches = lzx_get_matches(c, &matches);
+ if (num_matches == 0 ||
+ (matches[num_matches - 1].len <= 3 &&
+ (matches[num_matches - 1].len <= 2 ||
+ matches[num_matches - 1].offset > 4096)))
+ {
+ lzx_skip_bytes(c, cur_match.len - 2);
+ return cur_match;
+ }
- make_canonical_huffman_code(LZX_ALIGNEDTREE_NUM_SYMBOLS, 8,
- freq_tabs->aligned_freq_table,
- codes->aligned_lens,
- codes->aligned_codewords);
+ next_match = matches[num_matches - 1];
+
+ if (next_match.len <= cur_match.len) {
+ lzx_skip_bytes(c, cur_match.len - 2);
+ return cur_match;
+ } else {
+ c->prev_match = next_match;
+ return (struct lz_match) { };
+ }
}
-static void do_call_insn_translation(u32 *call_insn_target, int input_pos,
- int32_t file_size)
+/*
+ * Return the next match or literal to use, delegating to the currently selected
+ * match-choosing algorithm.
+ *
+ * If the length of the returned 'struct lz_match' is less than
+ * LZX_MIN_MATCH_LEN, then it is really a literal.
+ */
+static inline struct lz_match
+lzx_choose_item(struct lzx_compressor *c)
{
- int32_t abs_offset;
- int32_t rel_offset;
+ return (*c->params.choose_item_func)(c);
+}
- rel_offset = le32_to_cpu(*call_insn_target);
- if (rel_offset >= -input_pos && rel_offset < file_size) {
- if (rel_offset < file_size - input_pos) {
- /* "good translation" */
- abs_offset = rel_offset + input_pos;
- } else {
- /* "compensating translation" */
- abs_offset = rel_offset - file_size;
- }
- *call_insn_target = cpu_to_le32(abs_offset);
+/* Set default symbol costs for the LZX Huffman codes. */
+static void
+lzx_set_default_costs(struct lzx_costs * costs, unsigned num_main_syms)
+{
+ unsigned i;
+
+ /* Main code (part 1): Literal symbols */
+ for (i = 0; i < LZX_NUM_CHARS; i++)
+ costs->main[i] = 8;
+
+ /* Main code (part 2): Match header symbols */
+ for (; i < num_main_syms; i++)
+ costs->main[i] = 10;
+
+ /* Length code */
+ for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++)
+ costs->len[i] = 8;
+
+ /* Aligned offset code */
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
+ costs->aligned[i] = 3;
+}
+
+/* Given the frequencies of symbols in an LZX-compressed block and the
+ * corresponding Huffman codes, return LZX_BLOCKTYPE_ALIGNED or
+ * LZX_BLOCKTYPE_VERBATIM if an aligned offset or verbatim block, respectively,
+ * will take fewer bits to output. */
+static int
+lzx_choose_verbatim_or_aligned(const struct lzx_freqs * freqs,
+ const struct lzx_codes * codes)
+{
+ unsigned aligned_cost = 0;
+ unsigned verbatim_cost = 0;
+
+ /* Verbatim blocks have a constant 3 bits per position footer. Aligned
+ * offset blocks have an aligned offset symbol per position footer, plus
+ * an extra 24 bits per block to output the lengths necessary to
+ * reconstruct the aligned offset code itself. */
+ for (unsigned i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
+ verbatim_cost += 3 * freqs->aligned[i];
+ aligned_cost += codes->lens.aligned[i] * freqs->aligned[i];
}
+ aligned_cost += LZX_ALIGNEDCODE_ELEMENT_SIZE * LZX_ALIGNEDCODE_NUM_SYMBOLS;
+ if (aligned_cost < verbatim_cost)
+ return LZX_BLOCKTYPE_ALIGNED;
+ else
+ return LZX_BLOCKTYPE_VERBATIM;
}
-/* 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)
+/* Find a sequence of matches/literals with which to output the specified LZX
+ * block, then set the block's type to that which has the minimum cost to output
+ * (either verbatim or aligned). */
+static void
+lzx_choose_items_for_block(struct lzx_compressor *c, struct lzx_block_spec *spec)
{
- 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;
+ const struct lzx_lru_queue orig_queue = c->queue;
+ u32 num_passes_remaining = c->params.num_optim_passes;
+ struct lzx_freqs freqs;
+ const u8 *window_ptr;
+ const u8 *window_end;
+ struct lzx_item *next_chosen_item;
+ struct lz_match lz_match;
+ struct lzx_item lzx_item;
+
+ LZX_ASSERT(num_passes_remaining >= 1);
+ LZX_ASSERT(lz_mf_get_position(c->mf) == spec->window_pos);
+
+ c->match_window_end = spec->window_pos + spec->block_size;
+
+ if (c->params.num_optim_passes > 1) {
+ if (spec->block_size == c->cur_window_size)
+ c->get_matches_func = lzx_get_matches_fillcache_singleblock;
+ else
+ c->get_matches_func = lzx_get_matches_fillcache_multiblock;
+ c->skip_bytes_func = lzx_skip_bytes_fillcache;
+ } else {
+ if (spec->block_size == c->cur_window_size)
+ c->get_matches_func = lzx_get_matches_nocache_singleblock;
+ else
+ c->get_matches_func = lzx_get_matches_nocache_multiblock;
+ c->skip_bytes_func = lzx_skip_bytes_nocache;
+ }
+
+ /* The first optimal parsing pass is done using the cost model already
+ * set in c->costs. Each later pass is done using a cost model
+ * computed from the previous pass.
+ *
+ * To improve performance we only generate the array containing the
+ * matches and literals in intermediate form on the final pass. */
+
+ while (--num_passes_remaining) {
+ c->match_window_pos = spec->window_pos;
+ c->cache_ptr = c->cached_matches;
+ memset(&freqs, 0, sizeof(freqs));
+ window_ptr = &c->cur_window[spec->window_pos];
+ window_end = window_ptr + spec->block_size;
+
+ while (window_ptr != window_end) {
+
+ lz_match = lzx_choose_item(c);
+
+ LZX_ASSERT(!(lz_match.len == LZX_MIN_MATCH_LEN &&
+ lz_match.offset == c->max_window_size -
+ LZX_MIN_MATCH_LEN));
+ if (lz_match.len >= LZX_MIN_MATCH_LEN) {
+ lzx_tally_match(lz_match.len, lz_match.offset,
+ &freqs, &c->queue);
+ window_ptr += lz_match.len;
+ } else {
+ lzx_tally_literal(*window_ptr, &freqs);
+ window_ptr += 1;
+ }
+ }
+ lzx_make_huffman_codes(&freqs, &spec->codes, c->num_main_syms);
+ lzx_set_costs(c, &spec->codes.lens, 15);
+ c->queue = orig_queue;
+ if (c->cache_ptr <= c->cache_limit) {
+ c->get_matches_func = lzx_get_matches_usecache_nocheck;
+ c->skip_bytes_func = lzx_skip_bytes_usecache_nocheck;
+ } else {
+ c->get_matches_func = lzx_get_matches_usecache;
+ c->skip_bytes_func = lzx_skip_bytes_usecache;
}
}
+
+ c->match_window_pos = spec->window_pos;
+ c->cache_ptr = c->cached_matches;
+ memset(&freqs, 0, sizeof(freqs));
+ window_ptr = &c->cur_window[spec->window_pos];
+ window_end = window_ptr + spec->block_size;
+
+ spec->chosen_items = &c->chosen_items[spec->window_pos];
+ next_chosen_item = spec->chosen_items;
+
+ unsigned unseen_cost = 9;
+ while (window_ptr != window_end) {
+
+ lz_match = lzx_choose_item(c);
+
+ LZX_ASSERT(!(lz_match.len == LZX_MIN_MATCH_LEN &&
+ lz_match.offset == c->max_window_size -
+ LZX_MIN_MATCH_LEN));
+ if (lz_match.len >= LZX_MIN_MATCH_LEN) {
+ lzx_item.data = lzx_tally_match(lz_match.len,
+ lz_match.offset,
+ &freqs, &c->queue);
+ window_ptr += lz_match.len;
+ } else {
+ lzx_item.data = lzx_tally_literal(*window_ptr, &freqs);
+ window_ptr += 1;
+ }
+ *next_chosen_item++ = lzx_item;
+
+ /* When doing one-pass "near-optimal" parsing, update the cost
+ * model occassionally. */
+ if (unlikely((next_chosen_item - spec->chosen_items) % 2048 == 0) &&
+ c->params.choose_item_func == lzx_choose_near_optimal_item &&
+ c->params.num_optim_passes == 1)
+ {
+ lzx_make_huffman_codes(&freqs, &spec->codes, c->num_main_syms);
+ lzx_set_costs(c, &spec->codes.lens, unseen_cost);
+ if (unseen_cost < 15)
+ unseen_cost++;
+ }
+ }
+ spec->num_chosen_items = next_chosen_item - spec->chosen_items;
+ lzx_make_huffman_codes(&freqs, &spec->codes, c->num_main_syms);
+ spec->block_type = lzx_choose_verbatim_or_aligned(&freqs, &spec->codes);
}
+/* Prepare the input window into one or more LZX blocks ready to be output. */
+static void
+lzx_prepare_blocks(struct lzx_compressor *c)
+{
+ /* Set up a default cost model. */
+ if (c->params.choose_item_func == lzx_choose_near_optimal_item)
+ lzx_set_default_costs(&c->costs, c->num_main_syms);
+
+ /* Set up the block specifications.
+ * TODO: The compression ratio could be slightly improved by performing
+ * data-dependent block splitting instead of using fixed-size blocks.
+ * Doing so well is a computationally hard problem, however. */
+ c->num_blocks = DIV_ROUND_UP(c->cur_window_size, LZX_DIV_BLOCK_SIZE);
+ for (unsigned i = 0; i < c->num_blocks; i++) {
+ u32 pos = LZX_DIV_BLOCK_SIZE * i;
+ c->block_specs[i].window_pos = pos;
+ c->block_specs[i].block_size = min(c->cur_window_size - pos,
+ LZX_DIV_BLOCK_SIZE);
+ }
-static const struct lz_params lzx_lz_params = {
+ /* Load the window into the match-finder. */
+ lz_mf_load_window(c->mf, c->cur_window, c->cur_window_size);
- /* LZX_MIN_MATCH == 2, but 2-character matches are rarely useful; the
- * minimum match for compression is set to 3 instead. */
- .min_match = 3,
+ /* Determine sequence of matches/literals to output for each block. */
+ lzx_lru_queue_init(&c->queue);
+ c->optimum_cur_idx = 0;
+ c->optimum_end_idx = 0;
+ c->prev_match.len = 0;
+ for (unsigned i = 0; i < c->num_blocks; i++)
+ lzx_choose_items_for_block(c, &c->block_specs[i]);
+}
- .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,
-};
+static void
+lzx_build_params(unsigned int compression_level,
+ u32 max_window_size,
+ struct lzx_compressor_params *lzx_params)
+{
+ if (compression_level < 25) {
+ lzx_params->choose_item_func = lzx_choose_lazy_item;
+ lzx_params->num_optim_passes = 1;
+ if (max_window_size <= 262144)
+ lzx_params->mf_algo = LZ_MF_HASH_CHAINS;
+ else
+ lzx_params->mf_algo = LZ_MF_BINARY_TREES;
+ lzx_params->min_match_length = 3;
+ lzx_params->nice_match_length = 25 + compression_level * 2;
+ lzx_params->max_search_depth = 25 + compression_level;
+ } else {
+ lzx_params->choose_item_func = lzx_choose_near_optimal_item;
+ lzx_params->num_optim_passes = compression_level / 20;
+ if (max_window_size <= 32768 && lzx_params->num_optim_passes == 1)
+ lzx_params->mf_algo = LZ_MF_HASH_CHAINS;
+ else
+ lzx_params->mf_algo = LZ_MF_BINARY_TREES;
+ lzx_params->min_match_length = (compression_level >= 45) ? 2 : 3;
+ lzx_params->nice_match_length = min(((u64)compression_level * 32) / 50,
+ LZX_MAX_MATCH_LEN);
+ lzx_params->max_search_depth = min(((u64)compression_level * 50) / 50,
+ LZX_MAX_MATCH_LEN);
+ }
+}
-/*
- * Performs LZX compression on a block of data.
- *
- * @__uncompressed_data: Pointer to the data to be compressed.
- * @uncompressed_len: Length, in bytes, of the data to be compressed.
- * @compressed_data: Pointer to a location at least (@uncompressed_len - 1)
- * bytes long into which the compressed data may be
- * written.
- * @compressed_len_ret: A pointer to an unsigned int into which the length of
- * the compressed data may be returned.
- *
- * Returns zero if compression was successfully performed. In that case
- * @compressed_data and @compressed_len_ret will contain the compressed data and
- * its length. A return value of nonzero means that compressing the data did
- * not reduce its size, and @compressed_data will not contain the full
- * compressed data.
- */
-int lzx_compress(const void *__uncompressed_data, unsigned uncompressed_len,
- void *compressed_data, unsigned *compressed_len_ret)
+static void
+lzx_build_mf_params(const struct lzx_compressor_params *lzx_params,
+ u32 max_window_size, struct lz_mf_params *mf_params)
{
- 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;
- unsigned i;
- int ret;
- int block_type = LZX_BLOCKTYPE_ALIGNED;
+ memset(mf_params, 0, sizeof(*mf_params));
+
+ mf_params->algorithm = lzx_params->mf_algo;
+ mf_params->max_window_size = max_window_size;
+ mf_params->min_match_len = lzx_params->min_match_length;
+ mf_params->max_match_len = LZX_MAX_MATCH_LEN;
+ mf_params->max_search_depth = lzx_params->max_search_depth;
+ mf_params->nice_match_len = lzx_params->nice_match_length;
+}
+
+static void
+lzx_free_compressor(void *_c);
- if (uncompressed_len < 100)
- return 1;
+static u64
+lzx_get_needed_memory(size_t max_block_size, unsigned int compression_level)
+{
+ struct lzx_compressor_params params;
+ u64 size = 0;
+ unsigned window_order;
+ u32 max_window_size;
- memset(&freq_tabs, 0, sizeof(freq_tabs));
- queue.R0 = 1;
- queue.R1 = 1;
- queue.R2 = 1;
+ window_order = lzx_get_window_order(max_block_size);
+ if (window_order == 0)
+ return 0;
+ max_window_size = max_block_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);
+ lzx_build_params(compression_level, max_window_size, ¶ms);
- /* Before doing any actual compression, do the call instruction (0xe8
- * byte) translation on the uncompressed data. */
- do_call_insn_preprocessing(uncompressed_data, uncompressed_len);
+ size += sizeof(struct lzx_compressor);
- /* 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. */
+ size += max_window_size;
- 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);
+ size += DIV_ROUND_UP(max_window_size, LZX_DIV_BLOCK_SIZE) *
+ sizeof(struct lzx_block_spec);
- lzx_make_huffman_codes(&freq_tabs, &codes);
+ size += max_window_size * sizeof(struct lzx_item);
- /* Initialize the output bitstream. */
- init_output_bitstream(&ostream, compressed_data, uncompressed_len - 1);
+ size += lz_mf_get_needed_memory(params.mf_algo, max_window_size);
+ if (params.choose_item_func == lzx_choose_near_optimal_item) {
+ size += (LZX_OPTIM_ARRAY_LENGTH + params.nice_match_length) *
+ sizeof(struct lzx_mc_pos_data);
+ }
+ if (params.num_optim_passes > 1)
+ size += LZX_CACHE_LEN * sizeof(struct lz_match);
+ else
+ size += LZX_MAX_MATCHES_PER_POS * sizeof(struct lz_match);
+ return size;
+}
- /* 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);
+static int
+lzx_create_compressor(size_t max_block_size, unsigned int compression_level,
+ void **c_ret)
+{
+ struct lzx_compressor *c;
+ struct lzx_compressor_params params;
+ struct lz_mf_params mf_params;
+ unsigned window_order;
+ u32 max_window_size;
+
+ window_order = lzx_get_window_order(max_block_size);
+ if (window_order == 0)
+ return WIMLIB_ERR_INVALID_PARAM;
+ max_window_size = max_block_size;
+
+ lzx_build_params(compression_level, max_window_size, ¶ms);
+ lzx_build_mf_params(¶ms, max_window_size, &mf_params);
+ if (!lz_mf_params_valid(&mf_params))
+ return WIMLIB_ERR_INVALID_PARAM;
+
+ c = CALLOC(1, sizeof(struct lzx_compressor));
+ if (!c)
+ goto oom;
+
+ c->params = params;
+ c->num_main_syms = lzx_get_num_main_syms(window_order);
+ c->max_window_size = max_window_size;
+ c->window_order = window_order;
+
+ c->cur_window = ALIGNED_MALLOC(max_window_size, 16);
+ if (!c->cur_window)
+ goto oom;
+
+ c->block_specs = MALLOC(DIV_ROUND_UP(max_window_size,
+ LZX_DIV_BLOCK_SIZE) *
+ sizeof(struct lzx_block_spec));
+ if (!c->block_specs)
+ goto oom;
+
+ c->chosen_items = MALLOC(max_window_size * sizeof(struct lzx_item));
+ if (!c->chosen_items)
+ goto oom;
+
+ c->mf = lz_mf_alloc(&mf_params);
+ if (!c->mf)
+ goto oom;
+
+ if (params.choose_item_func == lzx_choose_near_optimal_item) {
+ c->optimum = MALLOC((LZX_OPTIM_ARRAY_LENGTH +
+ params.nice_match_length) *
+ sizeof(struct lzx_mc_pos_data));
+ if (!c->optimum)
+ goto oom;
+ }
- /* 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);
+ if (params.num_optim_passes > 1) {
+ c->cached_matches = MALLOC(LZX_CACHE_LEN *
+ sizeof(struct lz_match));
+ if (!c->cached_matches)
+ goto oom;
+ c->cache_limit = c->cached_matches + LZX_CACHE_LEN -
+ (LZX_MAX_MATCHES_PER_POS + 1);
} else {
- bitstream_put_bits(&ostream, 0, 1);
- bitstream_put_bits(&ostream, uncompressed_len, 16);
- }
-
- /* 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 != 0)
- return ret;
-
- /* 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 != 0)
- return ret;
-
- /* 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 != 0)
- return ret;
-
- /* Write the compressed literals. */
- ret = lzx_write_compressed_literals(&ostream, block_type,
- match_tab, num_matches, &codes);
- if (ret != 0)
- return ret;
-
- ret = flush_output_bitstream(&ostream);
- if (ret != 0)
- return ret;
-
- compressed_len = ostream.bit_output - (u8*)compressed_data;
-
- *compressed_len_ret = compressed_len;
-
-#ifdef ENABLE_VERIFY_COMPRESSION
- /* Verify that we really get the same thing back when decompressing. */
- u8 buf[uncompressed_len];
- ret = lzx_decompress(compressed_data, compressed_len, buf,
- uncompressed_len);
- if (ret != 0) {
- ERROR("lzx_compress(): Failed to decompress data we compressed");
- abort();
- }
-
- 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();
- }
+ c->cached_matches = MALLOC(LZX_MAX_MATCHES_PER_POS *
+ sizeof(struct lz_match));
+ if (!c->cached_matches)
+ goto oom;
}
-#endif
+
+ *c_ret = c;
return 0;
+
+oom:
+ lzx_free_compressor(c);
+ return WIMLIB_ERR_NOMEM;
}
+
+static size_t
+lzx_compress(const void *uncompressed_data, size_t uncompressed_size,
+ void *compressed_data, size_t compressed_size_avail, void *_c)
+{
+ struct lzx_compressor *c = _c;
+ struct lzx_output_bitstream os;
+
+ /* Don't bother compressing very small inputs. */
+ if (uncompressed_size < 100)
+ return 0;
+
+ /* The input data must be preprocessed. To avoid changing the original
+ * input, copy it to a temporary buffer. */
+ memcpy(c->cur_window, uncompressed_data, uncompressed_size);
+ c->cur_window_size = uncompressed_size;
+
+ /* Preprocess the data. */
+ lzx_do_e8_preprocessing(c->cur_window, c->cur_window_size);
+
+ /* Prepare the compressed data. */
+ lzx_prepare_blocks(c);
+
+ /* Generate the compressed data and return its size, or 0 if an overflow
+ * occurred. */
+ lzx_init_output(&os, compressed_data, compressed_size_avail);
+ lzx_write_all_blocks(c, &os);
+ return lzx_flush_output(&os);
+}
+
+static void
+lzx_free_compressor(void *_c)
+{
+ struct lzx_compressor *c = _c;
+
+ if (c) {
+ ALIGNED_FREE(c->cur_window);
+ FREE(c->block_specs);
+ FREE(c->chosen_items);
+ lz_mf_free(c->mf);
+ FREE(c->optimum);
+ FREE(c->cached_matches);
+ FREE(c);
+ }
+}
+
+const struct compressor_ops lzx_compressor_ops = {
+ .get_needed_memory = lzx_get_needed_memory,
+ .create_compressor = lzx_create_compressor,
+ .compress = lzx_compress,
+ .free_compressor = lzx_free_compressor,
+};
git://wimlib.net / wimlib / blobdiff