*/
/*
- * Copyright (C) 2012, 2013, 2014 Eric Biggers
+ * Copyright (C) 2012, 2013, 2014, 2015 Eric Biggers
*
* This file is free software; you can redistribute it and/or modify it under
* the terms of the GNU Lesser General Public License as published by the Free
*
* This file 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.
+ * slightly different, and sliding window support might be required.
*
* Note: LZX is a compression format derived from DEFLATE, the format used by
* zlib and gzip. Both LZX and DEFLATE use LZ77 matching and Huffman coding.
# include "config.h"
#endif
-#include "wimlib/compress_common.h"
-#include "wimlib/compressor_ops.h"
-#include "wimlib/endianness.h"
-#include "wimlib/error.h"
-#include "wimlib/lz_mf.h"
-#include "wimlib/lz_repsearch.h"
-#include "wimlib/lzx_common.h"
-#include "wimlib/util.h"
+/*
+ * Start a new LZX block (with new Huffman codes) after this many bytes.
+ *
+ * Note: actual block sizes may slightly exceed this value.
+ *
+ * TODO: recursive splitting and cost evaluation might be good for an extremely
+ * high compression mode, but otherwise it is almost always far too slow for how
+ * much it helps. Perhaps some sort of heuristic would be useful?
+ */
+#define LZX_DIV_BLOCK_SIZE 32768
-#include <string.h>
-#include <limits.h>
+/*
+ * LZX_CACHE_PER_POS is the number of lz_match structures to reserve in the
+ * match cache for each byte position. This value should be high enough so that
+ * nearly the time, all matches found in a given block can fit in the match
+ * cache. However, fallback behavior (immediately terminating the block) on
+ * cache overflow is still required.
+ */
+#define LZX_CACHE_PER_POS 6
+
+/*
+ * LZX_CACHE_LENGTH is the number of lz_match structures in the match cache,
+ * excluding the extra "overflow" entries. The per-position multiplier is '1 +
+ * LZX_CACHE_PER_POS' instead of 'LZX_CACHE_PER_POS' because there is an
+ * overhead of one lz_match per position, used to hold the match count at that
+ * position.
+ */
+#define LZX_CACHE_LENGTH (LZX_DIV_BLOCK_SIZE * (1 + LZX_CACHE_PER_POS))
-#define LZX_OPTIM_ARRAY_LENGTH 4096
+/*
+ * LZX_MAX_MATCHES_PER_POS is an upper bound on the number of matches that can
+ * ever be saved in the match cache for a single position. Since each match we
+ * save for a single position has a distinct length, we can use the number of
+ * possible match lengths in LZX as this bound. This bound is guaranteed to be
+ * valid in all cases, although if 'nice_match_length < LZX_MAX_MATCH_LEN', then
+ * it will never actually be reached.
+ */
+#define LZX_MAX_MATCHES_PER_POS LZX_NUM_LENS
-#define LZX_DIV_BLOCK_SIZE 32768
+/*
+ * LZX_BIT_COST is a scaling factor that represents the cost to output one bit.
+ * THis makes it possible to consider fractional bit costs.
+ *
+ * Note: this is only useful as a statistical trick for when the true costs are
+ * unknown. In reality, each token in LZX requires a whole number of bits to
+ * output.
+ */
+#define LZX_BIT_COST 16
+
+/*
+ * Consideration of aligned offset costs is disabled for now, due to
+ * insufficient benefit gained from the time spent.
+ */
+#define LZX_CONSIDER_ALIGNED_COSTS 0
+
+/*
+ * The maximum compression level at which we use the faster algorithm.
+ */
+#define LZX_MAX_FAST_LEVEL 34
+
+/*
+ * LZX_HASH2_ORDER is the log base 2 of the number of entries in the hash table
+ * for finding length 2 matches. This can be as high as 16 (in which case the
+ * hash function is trivial), but using a smaller hash table actually speeds up
+ * compression due to reduced cache pressure.
+ */
+#define LZX_HASH2_ORDER 12
+#define LZX_HASH2_LENGTH (1UL << LZX_HASH2_ORDER)
-#define LZX_CACHE_PER_POS 8
+#include "wimlib/lzx_common.h"
+
+/*
+ * The maximum allowed window order for the matchfinder.
+ */
+#define MATCHFINDER_MAX_WINDOW_ORDER LZX_MAX_WINDOW_ORDER
-#define LZX_MAX_MATCHES_PER_POS (LZX_MAX_MATCH_LEN - LZX_MIN_MATCH_LEN + 1)
+#include <string.h>
-#define LZX_CACHE_LEN (LZX_DIV_BLOCK_SIZE * (LZX_CACHE_PER_POS + 1))
+#include "wimlib/bt_matchfinder.h"
+#include "wimlib/compress_common.h"
+#include "wimlib/compressor_ops.h"
+#include "wimlib/endianness.h"
+#include "wimlib/error.h"
+#include "wimlib/hc_matchfinder.h"
+#include "wimlib/lz_extend.h"
+#include "wimlib/unaligned.h"
+#include "wimlib/util.h"
-struct lzx_compressor;
+struct lzx_output_bitstream;
/* Codewords for the LZX Huffman codes. */
struct lzx_codewords {
u8 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
};
-/* Estimated cost, in bits, to output each symbol in the LZX Huffman codes. */
+/* Cost model for near-optimal parsing */
struct lzx_costs {
- u8 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
- u8 len[LZX_LENCODE_NUM_SYMBOLS];
- u8 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
+
+ /* 'match_cost[offset_slot][len - LZX_MIN_MATCH_LEN]' is the cost for a
+ * length 'len' match that has an offset belonging to 'offset_slot'. */
+ u32 match_cost[LZX_MAX_OFFSET_SLOTS][LZX_NUM_LENS];
+
+ /* Cost for each symbol in the main code */
+ u32 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
+
+ /* Cost for each symbol in the length code */
+ u32 len[LZX_LENCODE_NUM_SYMBOLS];
+
+#if LZX_CONSIDER_ALIGNED_COSTS
+ /* Cost for each symbol in the aligned code */
+ u32 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
+#endif
};
/* Codewords and lengths for the LZX Huffman codes. */
u64 data;
};
-/* Internal compression parameters */
-struct lzx_compressor_params {
- u32 (*choose_items_for_block)(struct lzx_compressor *, u32, u32);
- u32 num_optim_passes;
- enum lz_mf_algo mf_algo;
- u32 min_match_length;
- u32 nice_match_length;
- u32 max_search_depth;
-};
-
/*
- * Match chooser position data:
+ * This structure represents a byte position in the input buffer and a node in
+ * the graph of possible match/literal choices.
*
- * An array of these structures is used during the near-optimal 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.
+ * Logically, each incoming edge to this node is labeled with a literal or a
+ * match that can be taken to reach this position from an earlier position; and
+ * each outgoing edge from this node is labeled with a literal or a match that
+ * can be taken to advance from this position to a later position.
*/
-struct lzx_mc_pos_data {
+struct lzx_optimum_node {
/* The cost, in bits, of the lowest-cost path that has been found to
* reach this position. This can change as progressively lower cost
* paths are found to reach this position. */
u32 cost;
-#define MC_INFINITE_COST UINT32_MAX
- /* The match or literal that was taken to reach this position. This can
+ /*
+ * The match or literal that was taken to reach this position. This can
* change as progressively lower cost paths are found to reach this
* position.
*
* Repeat offset matches:
* Low bits are the match length, high bits are the queue index.
*/
- u32 mc_item_data;
-#define MC_OFFSET_SHIFT 9
-#define MC_LEN_MASK ((1 << MC_OFFSET_SHIFT) - 1)
+ u32 item;
+#define OPTIMUM_OFFSET_SHIFT 9
+#define OPTIMUM_LEN_MASK ((1 << OPTIMUM_OFFSET_SHIFT) - 1)
+} _aligned_attribute(8);
- /* The state of the LZX recent match offsets queue at this position.
- * This is filled in lazily, only after the minimum-cost path to this
- * position is found.
- *
- * Note: the way we handle this adaptive state in the "minimum-cost"
- * parse is actually only an approximation. It's possible for the
- * globally optimal, minimum cost path to contain a prefix, ending at a
- * position, where that path prefix is *not* the minimum cost path to
- * that position. This can happen if such a path prefix results in a
- * different adaptive state which results in lower costs later. We do
- * not solve this problem; we only consider the lowest cost to reach
- * each position, which seems to be an acceptable approximation. */
- struct lzx_lru_queue queue _aligned_attribute(16);
-
-} _aligned_attribute(16);
-
-/* State of the LZX compressor */
-struct lzx_compressor {
+/*
+ * Least-recently-used queue for match offsets.
+ *
+ * This is represented as a 64-bit integer for efficiency. There are three
+ * offsets of 21 bits each. Bit 64 is garbage.
+ */
+struct lzx_lru_queue {
+ u64 R;
+};
- /* Internal compression parameters */
- struct lzx_compressor_params params;
+#define LZX_QUEUE64_OFFSET_SHIFT 21
+#define LZX_QUEUE64_OFFSET_MASK (((u64)1 << LZX_QUEUE64_OFFSET_SHIFT) - 1)
- /* The preprocessed buffer of data being compressed */
- u8 *cur_window;
+#define LZX_QUEUE64_R0_SHIFT (0 * LZX_QUEUE64_OFFSET_SHIFT)
+#define LZX_QUEUE64_R1_SHIFT (1 * LZX_QUEUE64_OFFSET_SHIFT)
+#define LZX_QUEUE64_R2_SHIFT (2 * LZX_QUEUE64_OFFSET_SHIFT)
- /* 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;
+#define LZX_QUEUE64_R0_MASK (LZX_QUEUE64_OFFSET_MASK << LZX_QUEUE64_R0_SHIFT)
+#define LZX_QUEUE64_R1_MASK (LZX_QUEUE64_OFFSET_MASK << LZX_QUEUE64_R1_SHIFT)
+#define LZX_QUEUE64_R2_MASK (LZX_QUEUE64_OFFSET_MASK << LZX_QUEUE64_R2_SHIFT)
- /* 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,
- * a.k.a. the allocated size of @cur_window, 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().) */
+static inline void
+lzx_lru_queue_init(struct lzx_lru_queue *queue)
+{
+ queue->R = ((u64)1 << LZX_QUEUE64_R0_SHIFT) |
+ ((u64)1 << LZX_QUEUE64_R1_SHIFT) |
+ ((u64)1 << LZX_QUEUE64_R2_SHIFT);
+}
+
+static inline u64
+lzx_lru_queue_R0(struct lzx_lru_queue queue)
+{
+ return (queue.R >> LZX_QUEUE64_R0_SHIFT) & LZX_QUEUE64_OFFSET_MASK;
+}
+
+static inline u64
+lzx_lru_queue_R1(struct lzx_lru_queue queue)
+{
+ return (queue.R >> LZX_QUEUE64_R1_SHIFT) & LZX_QUEUE64_OFFSET_MASK;
+}
+
+static inline u64
+lzx_lru_queue_R2(struct lzx_lru_queue queue)
+{
+ return (queue.R >> LZX_QUEUE64_R2_SHIFT) & LZX_QUEUE64_OFFSET_MASK;
+}
+
+/* Push a match offset onto the front (most recently used) end of the queue. */
+static inline struct lzx_lru_queue
+lzx_lru_queue_push(struct lzx_lru_queue queue, u32 offset)
+{
+ return (struct lzx_lru_queue) {
+ .R = (queue.R << LZX_QUEUE64_OFFSET_SHIFT) | offset,
+ };
+}
+
+/* Pop a match offset off the front (most recently used) end of the queue. */
+static inline u32
+lzx_lru_queue_pop(struct lzx_lru_queue *queue_p)
+{
+ u32 offset = queue_p->R & LZX_QUEUE64_OFFSET_MASK;
+ queue_p->R >>= LZX_QUEUE64_OFFSET_SHIFT;
+ return offset;
+}
+
+/* Swap a match offset to the front of the queue. */
+static inline struct lzx_lru_queue
+lzx_lru_queue_swap(struct lzx_lru_queue queue, unsigned idx)
+{
+ if (idx == 0)
+ return queue;
+
+ if (idx == 1)
+ return (struct lzx_lru_queue) {
+ .R = (lzx_lru_queue_R1(queue) << LZX_QUEUE64_R0_SHIFT) |
+ (lzx_lru_queue_R0(queue) << LZX_QUEUE64_R1_SHIFT) |
+ (queue.R & LZX_QUEUE64_R2_MASK),
+ };
+
+ return (struct lzx_lru_queue) {
+ .R = (lzx_lru_queue_R2(queue) << LZX_QUEUE64_R0_SHIFT) |
+ (queue.R & LZX_QUEUE64_R1_MASK) |
+ (lzx_lru_queue_R0(queue) << LZX_QUEUE64_R2_SHIFT),
+ };
+}
+
+/* The main LZX compressor structure */
+struct lzx_compressor {
+
+ /* The "nice" match length: if a match of this length is found, then
+ * choose it immediately without further consideration. */
+ unsigned nice_match_length;
+
+ /* The maximum search depth: consider at most this many potential
+ * matches at each position. */
+ unsigned max_search_depth;
+
+ /* The log base 2 of the LZX window size for LZ match offset encoding
+ * purposes. This will be >= LZX_MIN_WINDOW_ORDER and <=
+ * LZX_MAX_WINDOW_ORDER. */
unsigned window_order;
- /* Number of symbols in the main alphabet. This depends on
+ /* The number of symbols in the main alphabet. This depends on
* @window_order, since @window_order determines the maximum possible
- * offset. It does not, however, depend on the *actual* size of the
- * current data buffer being processed, which might be less than 1 <<
- * @window_order. */
+ * offset. */
unsigned num_main_syms;
- /* Lempel-Ziv match-finder */
- struct lz_mf *mf;
+ /* Number of optimization passes per block */
+ unsigned num_optim_passes;
- /* Match-finder wrapper functions and data for near-optimal parsing.
- *
- * When doing more than one match-choosing pass over the data, matches
- * found by the match-finder are cached 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 it is a very worthwhile speedup. */
- unsigned (*get_matches_func)(struct lzx_compressor *, const struct lz_match **);
- void (*skip_bytes_func)(struct lzx_compressor *, unsigned n);
- u32 match_window_pos;
- u32 match_window_end;
- struct lz_match *cached_matches;
- struct lz_match *cache_ptr;
- struct lz_match *cache_limit;
-
- /* Position data for near-optimal parsing. */
- struct lzx_mc_pos_data optimum[LZX_OPTIM_ARRAY_LENGTH + LZX_MAX_MATCH_LEN];
-
- /* The cost model currently being used for near-optimal parsing. */
- struct lzx_costs costs;
-
- /* The current match offset LRU queue. */
- struct lzx_lru_queue queue;
+ /* The preprocessed buffer of data being compressed */
+ u8 *in_buffer;
- /* Frequency counters for the current block. */
- struct lzx_freqs freqs;
+ /* The number of bytes of data to be compressed, which is the number of
+ * bytes of data in @in_buffer that are actually valid. */
+ size_t in_nbytes;
- /* The Huffman codes for the current and previous blocks. */
- struct lzx_codes codes[2];
+ /* Pointer to the compress() implementation chosen at allocation time */
+ void (*impl)(struct lzx_compressor *, struct lzx_output_bitstream *);
- /* Which 'struct lzx_codes' is being used for the current block. The
- * other was used for the previous block (if this isn't the first
- * block). */
- unsigned int codes_index;
+ /* The Huffman symbol frequency counters for the current block. */
+ struct lzx_freqs freqs;
- /* Dummy lengths that are always 0. */
- struct lzx_lens zero_lens;
+ /* The Huffman codes for the current and previous blocks. The one with
+ * index 'codes_index' is for the current block, and the other one is
+ * for the previous block. */
+ struct lzx_codes codes[2];
+ unsigned codes_index;
- /* Matches/literals that were chosen for the current block. */
- struct lzx_item chosen_items[LZX_DIV_BLOCK_SIZE];
+ /*
+ * The match/literal sequence the algorithm chose for the current block.
+ *
+ * Notes on how large this array actually needs to be:
+ *
+ * - In lzx_compress_near_optimal(), the maximum block size is
+ * 'LZX_DIV_BLOCK_SIZE + LZX_MAX_MATCH_LEN - 1' bytes. This occurs if
+ * a match of the maximum length is found on the last byte. Although
+ * it is impossible for this particular case to actually result in a
+ * parse of all literals, we reserve this many spaces anyway.
+ *
+ * - The worst case for lzx_compress_lazy() is a block of almost all
+ * literals that ends with a series of matches of increasing scores,
+ * causing a sequence of literals to be chosen before the last match
+ * is finally chosen. The number of items actually chosen in this
+ * scenario is limited by the number of distinct match scores that
+ * exist for matches shorter than 'nice_match_length'. Having
+ * 'LZX_MAX_MATCH_LEN - 1' extra spaces is plenty for now.
+ */
+ struct lzx_item chosen_items[LZX_DIV_BLOCK_SIZE + LZX_MAX_MATCH_LEN - 1];
/* Table mapping match offset => offset slot for small offsets */
#define LZX_NUM_FAST_OFFSETS 32768
u8 offset_slot_fast[LZX_NUM_FAST_OFFSETS];
+
+ union {
+ /* Data for greedy or lazy parsing */
+ struct {
+ /* Hash chains matchfinder (MUST BE LAST!!!) */
+ struct hc_matchfinder hc_mf;
+ };
+
+ /* Data for near-optimal parsing */
+ struct {
+ /*
+ * The graph nodes for the current block.
+ *
+ * We need at least 'LZX_DIV_BLOCK_SIZE +
+ * LZX_MAX_MATCH_LEN - 1' nodes because that is the
+ * maximum block size that may be used. Add 1 because
+ * we need a node to represent end-of-block.
+ *
+ * It is possible that nodes past end-of-block are
+ * accessed during match consideration, but this can
+ * only occur if the block was truncated at
+ * LZX_DIV_BLOCK_SIZE. So the same bound still applies.
+ * Note that since nodes past the end of the block will
+ * never actually have an effect on the items that are
+ * chosen for the block, it makes no difference what
+ * their costs are initialized to (if anything).
+ */
+ struct lzx_optimum_node optimum_nodes[LZX_DIV_BLOCK_SIZE +
+ LZX_MAX_MATCH_LEN - 1 + 1];
+
+ /* The cost model for the current block */
+ struct lzx_costs costs;
+
+ /*
+ * Cached matches for the current block. This array
+ * contains the matches that were found at each position
+ * in the block. Specifically, for each position, there
+ * is a special 'struct lz_match' whose 'length' field
+ * contains the number of matches that were found at
+ * that position; this is followed by the matches
+ * themselves, if any, sorted by strictly increasing
+ * length and strictly increasing offset.
+ *
+ * Note: in rare cases, there will be a very high number
+ * of matches in the block and this array will overflow.
+ * If this happens, we force the end of the current
+ * block. LZX_CACHE_LENGTH is the length at which we
+ * actually check for overflow. The extra slots beyond
+ * this are enough to absorb the worst case overflow,
+ * which occurs if starting at
+ * &match_cache[LZX_CACHE_LENGTH - 1], we write the
+ * match count header, then write
+ * LZX_MAX_MATCHES_PER_POS matches, then skip searching
+ * for matches at 'LZX_MAX_MATCH_LEN - 1' positions and
+ * write the match count header for each.
+ */
+ struct lz_match match_cache[LZX_CACHE_LENGTH +
+ LZX_MAX_MATCHES_PER_POS +
+ LZX_MAX_MATCH_LEN - 1];
+
+ /* Hash table for finding length 2 matches */
+ pos_t hash2_tab[LZX_HASH2_LENGTH]
+ _aligned_attribute(MATCHFINDER_ALIGNMENT);
+
+ /* Binary trees matchfinder (MUST BE LAST!!!) */
+ struct bt_matchfinder bt_mf;
+ };
+ };
};
+/* Compute a hash value for the next 2 bytes of uncompressed data. */
+static inline u32
+lz_hash_2_bytes(const u8 *in_next)
+{
+ u16 next_2_bytes = load_u16_unaligned(in_next);
+ if (LZX_HASH2_ORDER == 16)
+ return next_2_bytes;
+ else
+ return lz_hash(next_2_bytes, LZX_HASH2_ORDER);
+}
+
/*
* Structure to keep track of the current state of sending bits to the
* compressed output buffer.
* Size of @buffer, in bytes.
*/
static void
-lzx_init_output(struct lzx_output_bitstream *os, void *buffer, u32 size)
+lzx_init_output(struct lzx_output_bitstream *os, void *buffer, size_t size)
{
os->bitbuf = 0;
os->bitcount = 0;
*/
static inline void
lzx_write_varbits(struct lzx_output_bitstream *os,
- const u32 bits, const unsigned int num_bits,
- const unsigned int max_num_bits)
+ const u32 bits, const unsigned num_bits,
+ const unsigned max_num_bits)
{
/* This code is optimized for LZX, which never needs to write more than
* 17 bits at once. */
* lzx_write_varbits(). */
static inline void
lzx_write_bits(struct lzx_output_bitstream *os,
- const u32 bits, const unsigned int num_bits)
+ const u32 bits, const unsigned num_bits)
{
lzx_write_varbits(os, bits, num_bits, num_bits);
}
* 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)
+lzx_make_huffman_codes(struct lzx_compressor *c)
{
- make_canonical_huffman_code(num_main_syms,
+ const struct lzx_freqs *freqs = &c->freqs;
+ struct lzx_codes *codes = &c->codes[c->codes_index];
+
+ make_canonical_huffman_code(c->num_main_syms,
LZX_MAX_MAIN_CODEWORD_LEN,
freqs->main,
codes->lens.main,
codes->codewords.aligned);
}
+/* Reset the symbol frequencies for the LZX Huffman codes. */
+static void
+lzx_reset_symbol_frequencies(struct lzx_compressor *c)
+{
+ memset(&c->freqs, 0, sizeof(c->freqs));
+}
+
static unsigned
lzx_compute_precode_items(const u8 lens[restrict],
const u8 prev_lens[restrict],
extra_bits = data >> 23;
- /*if (block_type == LZX_BLOCKTYPE_ALIGNED && num_extra_bits >= 3) {*/
- if ((num_extra_bits & ones_if_aligned) >= 3) {
+ if ((num_extra_bits & ones_if_aligned) >= LZX_NUM_ALIGNED_OFFSET_BITS) {
/* Aligned offset blocks: The low 3 bits of the extra offset
* bits are Huffman-encoded using the aligned offset code. The
* remaining bits are output literally. */
- lzx_write_varbits(os, extra_bits >> 3, num_extra_bits - 3, 14);
+ lzx_write_varbits(os, extra_bits >> LZX_NUM_ALIGNED_OFFSET_BITS,
+ num_extra_bits - LZX_NUM_ALIGNED_OFFSET_BITS,
+ 17 - LZX_NUM_ALIGNED_OFFSET_BITS);
- lzx_write_varbits(os, codes->codewords.aligned[extra_bits & 7],
- codes->lens.aligned[extra_bits & 7],
+ lzx_write_varbits(os,
+ codes->codewords.aligned[extra_bits & LZX_ALIGNED_OFFSET_BITMASK],
+ codes->lens.aligned[extra_bits & LZX_ALIGNED_OFFSET_BITMASK],
LZX_MAX_ALIGNED_CODEWORD_LEN);
} else {
/* Verbatim blocks, or fewer than 3 extra bits: All extra
lzx_write_item(os, items[i], ones_if_aligned, codes);
}
-/* Write an LZX aligned offset or verbatim block to the output bitstream. */
static void
lzx_write_compressed_block(int block_type,
u32 block_size,
unsigned window_order,
unsigned num_main_syms,
- struct lzx_item * chosen_items,
+ const struct lzx_item chosen_items[],
u32 num_chosen_items,
const struct lzx_codes * codes,
const struct lzx_lens * prev_lens,
lzx_write_items(os, block_type, chosen_items, num_chosen_items, codes);
}
-/* Don't allow matches to span the end of an LZX block. */
-static inline unsigned
-maybe_truncate_matches(struct lz_match matches[], unsigned 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) {
-
- unsigned i = num_matches - 1;
- do {
- if (matches[i].len >= limit) {
- matches[i].len = limit;
-
- /* Truncation might produce multiple
- * matches with length 'limit'. Keep at
- * most 1. */
- num_matches = i + 1;
- }
- } while (i--);
- } else {
- num_matches = 0;
- }
- }
- return num_matches;
-}
-
-static unsigned
-lzx_get_matches_fillcache_singleblock(struct lzx_compressor *c,
- const struct lz_match **matches_ret)
-{
- struct lz_match *cache_ptr;
- struct lz_match *matches;
- unsigned num_matches;
-
- cache_ptr = c->cache_ptr;
- matches = cache_ptr + 1;
- if (likely(cache_ptr <= c->cache_limit)) {
- num_matches = lz_mf_get_matches(c->mf, matches);
- cache_ptr->len = num_matches;
- c->cache_ptr = matches + num_matches;
- } else {
- num_matches = 0;
- }
- c->match_window_pos++;
- *matches_ret = matches;
- return num_matches;
-}
-
-static unsigned
-lzx_get_matches_fillcache_multiblock(struct lzx_compressor *c,
- const struct lz_match **matches_ret)
+/* 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)
{
- struct lz_match *cache_ptr;
- struct lz_match *matches;
- unsigned num_matches;
-
- cache_ptr = c->cache_ptr;
- matches = cache_ptr + 1;
- if (likely(cache_ptr <= c->cache_limit)) {
- num_matches = lz_mf_get_matches(c->mf, matches);
- num_matches = maybe_truncate_matches(matches, num_matches, c);
- cache_ptr->len = num_matches;
- c->cache_ptr = matches + num_matches;
- } else {
- num_matches = 0;
- }
- c->match_window_pos++;
- *matches_ret = matches;
- return num_matches;
-}
+ u32 aligned_cost = 0;
+ u32 verbatim_cost = 0;
-static unsigned
-lzx_get_matches_usecache(struct lzx_compressor *c,
- const struct lz_match **matches_ret)
-{
- struct lz_match *cache_ptr;
- struct lz_match *matches;
- unsigned num_matches;
-
- cache_ptr = c->cache_ptr;
- matches = cache_ptr + 1;
- if (cache_ptr <= c->cache_limit) {
- num_matches = cache_ptr->len;
- c->cache_ptr = matches + num_matches;
- } else {
- num_matches = 0;
+ /* A verbatim block requires 3 bits in each place that an aligned symbol
+ * would be used in an aligned offset block. */
+ for (unsigned i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
+ verbatim_cost += LZX_NUM_ALIGNED_OFFSET_BITS * freqs->aligned[i];
+ aligned_cost += codes->lens.aligned[i] * freqs->aligned[i];
}
- 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;
-}
+ /* Account for output of the aligned offset code. */
+ aligned_cost += LZX_ALIGNEDCODE_ELEMENT_SIZE * LZX_ALIGNEDCODE_NUM_SYMBOLS;
-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;
+ if (aligned_cost < verbatim_cost)
+ return LZX_BLOCKTYPE_ALIGNED;
+ else
+ return LZX_BLOCKTYPE_VERBATIM;
}
/*
- * Find matches at the next position in the window.
- *
- * This uses a wrapper function around the underlying match-finder.
+ * Finish an LZX block:
*
- * 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.
+ * - build the Huffman codes
+ * - decide whether to output the block as VERBATIM or ALIGNED
+ * - output the block
+ * - swap the indices of the current and previous Huffman codes
*/
-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)
+lzx_finish_block(struct lzx_compressor *c, struct lzx_output_bitstream *os,
+ u32 block_size, u32 num_chosen_items)
{
- 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;
-}
+ int block_type;
-static void
-lzx_skip_bytes_nocache(struct lzx_compressor *c, unsigned n)
-{
- c->match_window_pos += n;
- lz_mf_skip_positions(c->mf, n);
+ lzx_make_huffman_codes(c);
+
+ block_type = lzx_choose_verbatim_or_aligned(&c->freqs,
+ &c->codes[c->codes_index]);
+ lzx_write_compressed_block(block_type,
+ block_size,
+ c->window_order,
+ c->num_main_syms,
+ c->chosen_items,
+ num_chosen_items,
+ &c->codes[c->codes_index],
+ &c->codes[c->codes_index ^ 1].lens,
+ os);
+ c->codes_index ^= 1;
}
-/*
- * Skip the specified number of positions in the window (don't search for
- * matches at them).
- *
- * This uses a wrapper function around the underlying match-finder.
- */
-static inline void
-lzx_skip_bytes(struct lzx_compressor *c, unsigned n)
+/* Return the offset slot for the specified offset, which must be
+ * less than LZX_NUM_FAST_OFFSETS. */
+static inline unsigned
+lzx_get_offset_slot_fast(struct lzx_compressor *c, u32 offset)
{
- return (*c->skip_bytes_func)(c, n);
+ LZX_ASSERT(offset < LZX_NUM_FAST_OFFSETS);
+ return c->offset_slot_fast[offset];
}
/* Tally, and optionally record, the specified literal byte. */
lzx_declare_literal(struct lzx_compressor *c, unsigned literal,
struct lzx_item **next_chosen_item)
{
- unsigned main_symbol = literal;
+ unsigned main_symbol = lzx_main_symbol_for_literal(literal);
c->freqs.main[main_symbol]++;
struct lzx_item **next_chosen_item)
{
unsigned len_header;
- unsigned main_symbol;
unsigned len_symbol;
+ unsigned main_symbol;
if (len - LZX_MIN_MATCH_LEN < LZX_NUM_PRIMARY_LENS) {
len_header = len - LZX_MIN_MATCH_LEN;
c->freqs.len[len_symbol]++;
}
- main_symbol = LZX_NUM_CHARS + ((rep_index << 3) | len_header);
+ main_symbol = lzx_main_symbol_for_match(rep_index, len_header);
c->freqs.main[main_symbol]++;
struct lzx_item **next_chosen_item)
{
unsigned len_header;
- unsigned main_symbol;
unsigned len_symbol;
+ unsigned main_symbol;
unsigned offset_slot;
unsigned num_extra_bits;
u32 extra_bits;
c->freqs.len[len_symbol]++;
}
- offset_slot = lzx_get_offset_slot_raw(offset + LZX_OFFSET_OFFSET);
+ offset_slot = (offset < LZX_NUM_FAST_OFFSETS) ?
+ lzx_get_offset_slot_fast(c, offset) :
+ lzx_get_offset_slot(offset);
- main_symbol = LZX_NUM_CHARS + ((offset_slot << 3) | len_header);
+ main_symbol = lzx_main_symbol_for_match(offset_slot, len_header);
c->freqs.main[main_symbol]++;
- if (offset_slot >= 8)
- c->freqs.aligned[(offset + LZX_OFFSET_OFFSET) & 7]++;
+ num_extra_bits = lzx_extra_offset_bits[offset_slot];
- if (next_chosen_item) {
+ if (num_extra_bits >= LZX_NUM_ALIGNED_OFFSET_BITS)
+ c->freqs.aligned[(offset + LZX_OFFSET_ADJUSTMENT) &
+ LZX_ALIGNED_OFFSET_BITMASK]++;
- num_extra_bits = lzx_extra_offset_bits[offset_slot];
+ if (next_chosen_item) {
- extra_bits = (offset + LZX_OFFSET_OFFSET) -
+ extra_bits = (offset + LZX_OFFSET_ADJUSTMENT) -
lzx_offset_slot_base[offset_slot];
+ BUILD_BUG_ON(LZX_MAINCODE_MAX_NUM_SYMBOLS > (1 << 10));
+ BUILD_BUG_ON(LZX_LENCODE_NUM_SYMBOLS > (1 << 8));
*(*next_chosen_item)++ = (struct lzx_item) {
.data = (u64)main_symbol |
((u64)len_symbol << 10) |
}
}
+
/* Tally, and optionally record, the specified match or literal. */
static inline void
-lzx_declare_item(struct lzx_compressor *c, u32 mc_item_data,
+lzx_declare_item(struct lzx_compressor *c, u32 item,
struct lzx_item **next_chosen_item)
{
- u32 len = mc_item_data & MC_LEN_MASK;
- u32 offset_data = mc_item_data >> MC_OFFSET_SHIFT;
+ u32 len = item & OPTIMUM_LEN_MASK;
+ u32 offset_data = item >> OPTIMUM_OFFSET_SHIFT;
if (len == 1)
lzx_declare_literal(c, offset_data, next_chosen_item);
next_chosen_item);
else
lzx_declare_explicit_offset_match(c, len,
- offset_data - LZX_OFFSET_OFFSET,
+ offset_data - LZX_OFFSET_ADJUSTMENT,
next_chosen_item);
}
static inline void
lzx_record_item_list(struct lzx_compressor *c,
- struct lzx_mc_pos_data *cur_optimum_ptr,
+ struct lzx_optimum_node *cur_node,
struct lzx_item **next_chosen_item)
{
- struct lzx_mc_pos_data *end_optimum_ptr;
+ struct lzx_optimum_node *end_node;
u32 saved_item;
u32 item;
/* The list is currently in reverse order (last item to first item).
* Reverse it. */
- end_optimum_ptr = cur_optimum_ptr;
- saved_item = cur_optimum_ptr->mc_item_data;
+ end_node = cur_node;
+ saved_item = cur_node->item;
do {
item = saved_item;
- cur_optimum_ptr -= item & MC_LEN_MASK;
- saved_item = cur_optimum_ptr->mc_item_data;
- cur_optimum_ptr->mc_item_data = item;
- } while (cur_optimum_ptr != c->optimum);
+ cur_node -= item & OPTIMUM_LEN_MASK;
+ saved_item = cur_node->item;
+ cur_node->item = item;
+ } while (cur_node != c->optimum_nodes);
/* Walk the list of items from beginning to end, tallying and recording
* each item. */
do {
- lzx_declare_item(c, cur_optimum_ptr->mc_item_data, next_chosen_item);
- cur_optimum_ptr += (cur_optimum_ptr->mc_item_data) & MC_LEN_MASK;
- } while (cur_optimum_ptr != end_optimum_ptr);
+ lzx_declare_item(c, cur_node->item, next_chosen_item);
+ cur_node += (cur_node->item) & OPTIMUM_LEN_MASK;
+ } while (cur_node != end_node);
}
static inline void
-lzx_tally_item_list(struct lzx_compressor *c, struct lzx_mc_pos_data *cur_optimum_ptr)
+lzx_tally_item_list(struct lzx_compressor *c, struct lzx_optimum_node *cur_node)
{
/* Since we're just tallying the items, we don't need to reverse the
* list. Processing the items in reverse order is fine. */
do {
- lzx_declare_item(c, cur_optimum_ptr->mc_item_data, NULL);
- cur_optimum_ptr -= (cur_optimum_ptr->mc_item_data & MC_LEN_MASK);
- } while (cur_optimum_ptr != c->optimum);
-}
-
-/* Tally, and optionally (if next_chosen_item != NULL) record, in order, all
- * items in the current list of items found by the match-chooser. */
-static void
-lzx_declare_item_list(struct lzx_compressor *c, struct lzx_mc_pos_data *cur_optimum_ptr,
- struct lzx_item **next_chosen_item)
-{
- if (next_chosen_item)
- lzx_record_item_list(c, cur_optimum_ptr, next_chosen_item);
- else
- lzx_tally_item_list(c, cur_optimum_ptr);
+ lzx_declare_item(c, cur_node->item, NULL);
+ cur_node -= (cur_node->item & OPTIMUM_LEN_MASK);
+ } while (cur_node != c->optimum_nodes);
}
-/* Set the cost model @c->costs from the Huffman codeword lengths specified in
- * @lens.
+/*
+ * Find an inexpensive path through the graph of possible match/literal choices
+ * for the current block. The nodes of the graph are
+ * c->optimum_nodes[0...block_size]. They correspond directly to the bytes in
+ * the current block, plus one extra node for end-of-block. The edges of the
+ * graph are matches and literals. The goal is to find the minimum cost path
+ * from 'c->optimum_nodes[0]' to 'c->optimum_nodes[block_size]'.
*
- * 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)
+ * The algorithm works forwards, starting at 'c->optimum_nodes[0]' and
+ * proceeding forwards one node at a time. At each node, a selection of matches
+ * (len >= 2), as well as the literal byte (len = 1), is considered. An item of
+ * length 'len' provides a new path to reach the node 'len' bytes later. If
+ * such a path is the lowest cost found so far to reach that later node, then
+ * that later node is updated with the new path.
+ *
+ * Note that although this algorithm is based on minimum cost path search, due
+ * to various simplifying assumptions the result is not guaranteed to be the
+ * true minimum cost, or "optimal", path over the graph of all valid LZX
+ * representations of this block.
+ *
+ * Also, note that because of the presence of the recent offsets queue (which is
+ * a type of adaptive state), the algorithm cannot work backwards and compute
+ * "cost to end" instead of "cost to beginning". Furthermore, the way the
+ * algorithm handles this adaptive state in the "minimum-cost" parse is actually
+ * only an approximation. It's possible for the globally optimal, minimum cost
+ * path to contain a prefix, ending at a position, where that path prefix is
+ * *not* the minimum cost path to that position. This can happen if such a path
+ * prefix results in a different adaptive state which results in lower costs
+ * later. The algorithm does not solve this problem; it only considers the
+ * lowest cost to reach each individual position.
+ */
+static struct lzx_lru_queue
+lzx_find_min_cost_path(struct lzx_compressor * const restrict c,
+ const u8 * const restrict block_begin,
+ const u32 block_size,
+ const struct lzx_lru_queue initial_queue)
{
- unsigned i;
-
- /* Main code */
- for (i = 0; i < c->num_main_syms; i++)
- c->costs.main[i] = lens->main[i] ? lens->main[i] : 15;
+ struct lzx_optimum_node *cur_node = c->optimum_nodes;
+ struct lzx_optimum_node * const end_node = &c->optimum_nodes[block_size];
+ struct lz_match *cache_ptr = c->match_cache;
+ const u8 *in_next = block_begin;
+ const u8 * const block_end = block_begin + block_size;
+
+ /* Instead of storing the match offset LRU queues in the
+ * 'lzx_optimum_node' structures, we save memory (and cache lines) by
+ * storing them in a smaller array. This works because the algorithm
+ * only requires a limited history of the adaptive state. Once a given
+ * state is more than LZX_MAX_MATCH_LEN bytes behind the current node,
+ * it is no longer needed. */
+ struct lzx_lru_queue queues[512];
+
+ BUILD_BUG_ON(ARRAY_LEN(queues) < LZX_MAX_MATCH_LEN + 1);
+#define QUEUE(in) (queues[(uintptr_t)(in) % ARRAY_LEN(queues)])
+
+ /* Initially, the cost to reach each node is "infinity". */
+ memset(c->optimum_nodes, 0xFF,
+ (block_size + 1) * sizeof(c->optimum_nodes[0]));
+
+ QUEUE(block_begin) = initial_queue;
+
+ /* The following loop runs 'block_size' iterations, one per node. */
+ do {
+ unsigned num_matches;
+ unsigned literal;
+ u32 cost;
- /* Length code */
- for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++)
- c->costs.len[i] = lens->len[i] ? lens->len[i] : 15;
+ /*
+ * A selection of matches for the block was already saved in
+ * memory so that we don't have to run the uncompressed data
+ * through the matchfinder on every optimization pass. However,
+ * we still search for repeat offset matches during each
+ * optimization pass because we cannot predict the state of the
+ * recent offsets queue. But as a heuristic, we don't bother
+ * searching for repeat offset matches if the general-purpose
+ * matchfinder failed to find any matches.
+ *
+ * Note that a match of length n at some offset implies there is
+ * also a match of length l for LZX_MIN_MATCH_LEN <= l <= n at
+ * that same offset. In other words, we don't necessarily need
+ * to use the full length of a match. The key heuristic that
+ * saves a significicant amount of time is that for each
+ * distinct length, we only consider the smallest offset for
+ * which that length is available. This heuristic also applies
+ * to repeat offsets, which we order specially: R0 < R1 < R2 <
+ * any explicit offset. Of course, this heuristic may be
+ * produce suboptimal results because offset slots in LZX are
+ * subject to entropy encoding, but in practice this is a useful
+ * heuristic.
+ */
- /* Aligned offset code */
- for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
- c->costs.aligned[i] = lens->aligned[i] ? lens->aligned[i] : 7;
-}
+ num_matches = cache_ptr->length;
+ cache_ptr++;
-/* Set default LZX Huffman symbol costs to bootstrap the iterative optimization
- * algorithm. */
-static void
-lzx_set_default_costs(struct lzx_costs * costs, unsigned num_main_syms)
-{
- unsigned i;
+ if (num_matches) {
+ struct lz_match *end_matches = cache_ptr + num_matches;
+ unsigned next_len = LZX_MIN_MATCH_LEN;
+ unsigned max_len = min(block_end - in_next, LZX_MAX_MATCH_LEN);
+ const u8 *matchptr;
+
+ /* Consider R0 match */
+ matchptr = in_next - lzx_lru_queue_R0(QUEUE(in_next));
+ if (load_u16_unaligned(matchptr) != load_u16_unaligned(in_next))
+ goto R0_done;
+ BUILD_BUG_ON(LZX_MIN_MATCH_LEN != 2);
+ do {
+ u32 cost = cur_node->cost +
+ c->costs.match_cost[0][
+ next_len - LZX_MIN_MATCH_LEN];
+ if (cost <= (cur_node + next_len)->cost) {
+ (cur_node + next_len)->cost = cost;
+ (cur_node + next_len)->item =
+ (0 << OPTIMUM_OFFSET_SHIFT) | next_len;
+ }
+ if (unlikely(++next_len > max_len)) {
+ cache_ptr = end_matches;
+ goto done_matches;
+ }
+ } while (in_next[next_len - 1] == matchptr[next_len - 1]);
+
+ R0_done:
+
+ /* Consider R1 match */
+ matchptr = in_next - lzx_lru_queue_R1(QUEUE(in_next));
+ if (load_u16_unaligned(matchptr) != load_u16_unaligned(in_next))
+ goto R1_done;
+ if (matchptr[next_len - 1] != in_next[next_len - 1])
+ goto R1_done;
+ for (unsigned len = 2; len < next_len - 1; len++)
+ if (matchptr[len] != in_next[len])
+ goto R1_done;
+ do {
+ u32 cost = cur_node->cost +
+ c->costs.match_cost[1][
+ next_len - LZX_MIN_MATCH_LEN];
+ if (cost <= (cur_node + next_len)->cost) {
+ (cur_node + next_len)->cost = cost;
+ (cur_node + next_len)->item =
+ (1 << OPTIMUM_OFFSET_SHIFT) | next_len;
+ }
+ if (unlikely(++next_len > max_len)) {
+ cache_ptr = end_matches;
+ goto done_matches;
+ }
+ } while (in_next[next_len - 1] == matchptr[next_len - 1]);
+
+ R1_done:
+
+ /* Consider R2 match */
+ matchptr = in_next - lzx_lru_queue_R2(QUEUE(in_next));
+ if (load_u16_unaligned(matchptr) != load_u16_unaligned(in_next))
+ goto R2_done;
+ if (matchptr[next_len - 1] != in_next[next_len - 1])
+ goto R2_done;
+ for (unsigned len = 2; len < next_len - 1; len++)
+ if (matchptr[len] != in_next[len])
+ goto R2_done;
+ do {
+ u32 cost = cur_node->cost +
+ c->costs.match_cost[2][
+ next_len - LZX_MIN_MATCH_LEN];
+ if (cost <= (cur_node + next_len)->cost) {
+ (cur_node + next_len)->cost = cost;
+ (cur_node + next_len)->item =
+ (2 << OPTIMUM_OFFSET_SHIFT) | next_len;
+ }
+ if (unlikely(++next_len > max_len)) {
+ cache_ptr = end_matches;
+ goto done_matches;
+ }
+ } while (in_next[next_len - 1] == matchptr[next_len - 1]);
- /* Main code (part 1): Literal symbols */
- for (i = 0; i < LZX_NUM_CHARS; i++)
- costs->main[i] = 8;
+ R2_done:
- /* Main code (part 2): Match header symbols */
- for (; i < num_main_syms; i++)
- costs->main[i] = 10;
+ while (next_len > cache_ptr->length)
+ if (++cache_ptr == end_matches)
+ goto done_matches;
- /* Length code */
- for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++)
- costs->len[i] = 8;
+ /* Consider explicit offset matches */
+ do {
+ u32 offset = cache_ptr->offset;
+ u32 offset_data = offset + LZX_OFFSET_ADJUSTMENT;
+ unsigned offset_slot = (offset < LZX_NUM_FAST_OFFSETS) ?
+ lzx_get_offset_slot_fast(c, offset) :
+ lzx_get_offset_slot(offset);
+ do {
+ u32 cost = cur_node->cost +
+ c->costs.match_cost[offset_slot][
+ next_len - LZX_MIN_MATCH_LEN];
+ #if LZX_CONSIDER_ALIGNED_COSTS
+ if (lzx_extra_offset_bits[offset_slot] >=
+ LZX_NUM_ALIGNED_OFFSET_BITS)
+ cost += c->costs.aligned[offset_data &
+ LZX_ALIGNED_OFFSET_BITMASK];
+ #endif
+ if (cost < (cur_node + next_len)->cost) {
+ (cur_node + next_len)->cost = cost;
+ (cur_node + next_len)->item =
+ (offset_data << OPTIMUM_OFFSET_SHIFT) | next_len;
+ }
+ } while (++next_len <= cache_ptr->length);
+ } while (++cache_ptr != end_matches);
+ }
- /* Aligned offset code */
- for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
- costs->aligned[i] = 3;
-}
+ done_matches:
-/* Return the cost, in bits, to output a literal byte using the specified cost
- * model. */
-static inline u32
-lzx_literal_cost(unsigned literal, const struct lzx_costs * costs)
-{
- return costs->main[literal];
-}
+ /* Consider coding a literal.
-/* Return the cost, in bits, to output a match of the specified length and
- * offset slot using the specified cost model. Does not take into account
- * extra offset bits. */
-static inline u32
-lzx_match_cost_raw(unsigned len, unsigned offset_slot,
- const struct lzx_costs *costs)
-{
- u32 cost;
- unsigned len_header;
- unsigned main_symbol;
+ * To avoid an extra branch, actually checking the preferability
+ * of coding the literal is integrated into the queue update
+ * code below. */
+ literal = *in_next++;
+ cost = cur_node->cost +
+ c->costs.main[lzx_main_symbol_for_literal(literal)];
- if (len - LZX_MIN_MATCH_LEN < LZX_NUM_PRIMARY_LENS) {
- len_header = len - LZX_MIN_MATCH_LEN;
- cost = 0;
- } else {
- len_header = LZX_NUM_PRIMARY_LENS;
+ /* Advance to the next position. */
+ cur_node++;
- /* Account for length symbol. */
- cost = costs->len[len - LZX_MIN_MATCH_LEN - LZX_NUM_PRIMARY_LENS];
- }
+ /* The lowest-cost path to the current position is now known.
+ * Finalize the recent offsets queue that results from taking
+ * this lowest-cost path. */
- /* Account for main symbol. */
- main_symbol = LZX_NUM_CHARS + ((offset_slot << 3) | len_header);
- cost += costs->main[main_symbol];
+ if (cost <= cur_node->cost) {
+ /* Literal: queue remains unchanged. */
+ cur_node->cost = cost;
+ cur_node->item = (literal << OPTIMUM_OFFSET_SHIFT) | 1;
+ QUEUE(in_next) = QUEUE(in_next - 1);
+ } else {
+ /* Match: queue update is needed. */
+ unsigned len = cur_node->item & OPTIMUM_LEN_MASK;
+ u32 offset_data = cur_node->item >> OPTIMUM_OFFSET_SHIFT;
+ if (offset_data >= LZX_NUM_RECENT_OFFSETS) {
+ /* Explicit offset match: insert offset at front */
+ QUEUE(in_next) =
+ lzx_lru_queue_push(QUEUE(in_next - len),
+ offset_data - LZX_OFFSET_ADJUSTMENT);
+ } else {
+ /* Repeat offset match: swap offset to front */
+ QUEUE(in_next) =
+ lzx_lru_queue_swap(QUEUE(in_next - len),
+ offset_data);
+ }
+ }
+ } while (cur_node != end_node);
- return cost;
+ /* Return the match offset queue at the end of the minimum-cost path. */
+ return QUEUE(block_end);
}
-/* Equivalent to lzx_match_cost_raw(), but assumes the length is small enough
- * that it doesn't require a length symbol. */
-static inline u32
-lzx_match_cost_raw_smalllen(unsigned len, unsigned offset_slot,
- const struct lzx_costs *costs)
+/* Given the costs for the main and length codewords, compute 'match_costs'. */
+static void
+lzx_compute_match_costs(struct lzx_compressor *c)
{
- LZX_ASSERT(len < LZX_MIN_MATCH_LEN + LZX_NUM_PRIMARY_LENS);
- return costs->main[LZX_NUM_CHARS +
- ((offset_slot << 3) | (len - LZX_MIN_MATCH_LEN))];
-}
+ unsigned num_offset_slots = lzx_get_num_offset_slots(c->window_order);
+ struct lzx_costs *costs = &c->costs;
-/*
- * Consider coding the match at repeat offset index @rep_idx. Consider each
- * length from the minimum (2) to the full match length (@rep_len).
- */
-static inline void
-lzx_consider_repeat_offset_match(struct lzx_compressor *c,
- struct lzx_mc_pos_data *cur_optimum_ptr,
- unsigned rep_len, unsigned rep_idx)
-{
- u32 base_cost = cur_optimum_ptr->cost;
- u32 cost;
- unsigned len;
+ for (unsigned offset_slot = 0; offset_slot < num_offset_slots; offset_slot++) {
-#if 1 /* Optimized version */
+ u32 extra_cost = (u32)lzx_extra_offset_bits[offset_slot] * LZX_BIT_COST;
+ unsigned main_symbol = lzx_main_symbol_for_match(offset_slot, 0);
+ unsigned i;
- if (rep_len < LZX_MIN_MATCH_LEN + LZX_NUM_PRIMARY_LENS) {
- /* All lengths being considered are small. */
- len = 2;
- do {
- cost = base_cost +
- lzx_match_cost_raw_smalllen(len, rep_idx, &c->costs);
- if (cost < (cur_optimum_ptr + len)->cost) {
- (cur_optimum_ptr + len)->mc_item_data =
- (rep_idx << MC_OFFSET_SHIFT) | len;
- (cur_optimum_ptr + len)->cost = cost;
- }
- } while (++len <= rep_len);
- } else {
- /* Some lengths being considered are small, and some are big.
- * Start with the optimized loop for small lengths, then switch
- * to the optimized loop for big lengths. */
- len = 2;
- do {
- cost = base_cost +
- lzx_match_cost_raw_smalllen(len, rep_idx, &c->costs);
- if (cost < (cur_optimum_ptr + len)->cost) {
- (cur_optimum_ptr + len)->mc_item_data =
- (rep_idx << MC_OFFSET_SHIFT) | len;
- (cur_optimum_ptr + len)->cost = cost;
- }
- } while (++len < LZX_MIN_MATCH_LEN + LZX_NUM_PRIMARY_LENS);
+ #if LZX_CONSIDER_ALIGNED_COSTS
+ if (lzx_extra_offset_bits[offset_slot] >= LZX_NUM_ALIGNED_OFFSET_BITS)
+ extra_cost -= LZX_NUM_ALIGNED_OFFSET_BITS * LZX_BIT_COST;
+ #endif
- /* The main symbol is now fixed. */
- base_cost += c->costs.main[LZX_NUM_CHARS +
- ((rep_idx << 3) | LZX_NUM_PRIMARY_LENS)];
- do {
- cost = base_cost +
- c->costs.len[len - LZX_MIN_MATCH_LEN -
- LZX_NUM_PRIMARY_LENS];
- if (cost < (cur_optimum_ptr + len)->cost) {
- (cur_optimum_ptr + len)->mc_item_data =
- (rep_idx << MC_OFFSET_SHIFT) | len;
- (cur_optimum_ptr + len)->cost = cost;
- }
- } while (++len <= rep_len);
- }
+ for (i = 0; i < LZX_NUM_PRIMARY_LENS; i++)
+ costs->match_cost[offset_slot][i] =
+ costs->main[main_symbol++] + extra_cost;
-#else /* Unoptimized version */
+ extra_cost += costs->main[main_symbol];
- len = 2;
- do {
- cost = base_cost +
- lzx_match_cost_raw(len, rep_idx, &c->costs);
- if (cost < (cur_optimum_ptr + len)->cost) {
- (cur_optimum_ptr + len)->mc_item_data =
- (rep_idx << MC_OFFSET_SHIFT) | len;
- (cur_optimum_ptr + len)->cost = cost;
- }
- } while (++len <= rep_len);
-#endif
+ for (; i < LZX_NUM_LENS; i++)
+ costs->match_cost[offset_slot][i] =
+ costs->len[i - LZX_NUM_PRIMARY_LENS] + extra_cost;
+ }
}
-/*
- * Consider coding each match in @matches as an explicit offset match.
- *
- * @matches must be sorted by strictly increasing length and strictly
- * increasing offset. This is guaranteed by the match-finder.
- *
- * We consider each length from the minimum (2) to the longest
- * (matches[num_matches - 1].len). For each length, we consider only
- * the smallest offset for which that length is available. Although
- * this is not guaranteed to be optimal due to the possibility of a
- * larger offset costing less than a smaller offset to code, this is a
- * very useful heuristic.
- */
-static inline void
-lzx_consider_explicit_offset_matches(struct lzx_compressor *c,
- struct lzx_mc_pos_data *cur_optimum_ptr,
- const struct lz_match matches[],
- unsigned num_matches)
+/* Set default LZX Huffman symbol costs to bootstrap the iterative optimization
+ * algorithm. */
+static void
+lzx_set_default_costs(struct lzx_compressor *c, const u8 *block, u32 block_size)
{
- LZX_ASSERT(num_matches > 0);
+ u32 i;
+ bool have_byte[256];
+ unsigned num_used_bytes;
- unsigned i;
- unsigned len;
- unsigned offset_slot;
- u32 position_cost;
- u32 cost;
- u32 offset_data;
+ /* The costs below are hard coded to use a scaling factor of 16. */
+ BUILD_BUG_ON(LZX_BIT_COST != 16);
+ /*
+ * Heuristics:
+ *
+ * - Use smaller initial costs for literal symbols when the input buffer
+ * contains fewer distinct bytes.
+ *
+ * - Assume that match symbols are more costly than literal symbols.
+ *
+ * - Assume that length symbols for shorter lengths are less costly than
+ * length symbols for longer lengths.
+ */
-#if 1 /* Optimized version */
+ for (i = 0; i < 256; i++)
+ have_byte[i] = false;
- if (matches[num_matches - 1].offset < LZX_NUM_FAST_OFFSETS) {
+ for (i = 0; i < block_size; i++)
+ have_byte[block[i]] = true;
- /*
- * Offset is small; the offset slot can be looked up directly in
- * c->offset_slot_fast.
- *
- * Additional optimizations:
- *
- * - Since the offset is small, it falls in the exponential part
- * of the offset slot bases and the number of extra offset
- * bits can be calculated directly as (offset_slot >> 1) - 1.
- *
- * - Just consider the number of extra offset bits; don't
- * account for the aligned offset code. Usually this has
- * almost no effect on the compression ratio.
- *
- * - Start out in a loop optimized for small lengths. When the
- * length becomes high enough that a length symbol will be
- * needed, jump into a loop optimized for big lengths.
- */
+ num_used_bytes = 0;
+ for (i = 0; i < 256; i++)
+ num_used_bytes += have_byte[i];
- LZX_ASSERT(offset_slot <= 37); /* for extra bits formula */
+ for (i = 0; i < 256; i++)
+ c->costs.main[i] = 140 - (256 - num_used_bytes) / 4;
- len = 2;
- i = 0;
- do {
- offset_slot = c->offset_slot_fast[matches[i].offset];
- position_cost = cur_optimum_ptr->cost +
- ((offset_slot >> 1) - 1);
- offset_data = matches[i].offset + LZX_OFFSET_OFFSET;
- do {
- if (len >= LZX_MIN_MATCH_LEN + LZX_NUM_PRIMARY_LENS)
- goto biglen;
- cost = position_cost +
- lzx_match_cost_raw_smalllen(len, offset_slot,
- &c->costs);
- if (cost < (cur_optimum_ptr + len)->cost) {
- (cur_optimum_ptr + len)->cost = cost;
- (cur_optimum_ptr + len)->mc_item_data =
- (offset_data << MC_OFFSET_SHIFT) | len;
- }
- } while (++len <= matches[i].len);
- } while (++i != num_matches);
+ for (; i < c->num_main_syms; i++)
+ c->costs.main[i] = 170;
- return;
+ for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++)
+ c->costs.len[i] = 103 + (i / 4);
- do {
- offset_slot = c->offset_slot_fast[matches[i].offset];
- biglen:
- position_cost = cur_optimum_ptr->cost +
- ((offset_slot >> 1) - 1) +
- c->costs.main[LZX_NUM_CHARS +
- ((offset_slot << 3) |
- LZX_NUM_PRIMARY_LENS)];
- offset_data = matches[i].offset + LZX_OFFSET_OFFSET;
- do {
- cost = position_cost +
- c->costs.len[len - LZX_MIN_MATCH_LEN -
- LZX_NUM_PRIMARY_LENS];
- if (cost < (cur_optimum_ptr + len)->cost) {
- (cur_optimum_ptr + len)->cost = cost;
- (cur_optimum_ptr + len)->mc_item_data =
- (offset_data << MC_OFFSET_SHIFT) | len;
- }
- } while (++len <= matches[i].len);
- } while (++i != num_matches);
- } else {
- len = 2;
- i = 0;
- do {
- offset_data = matches[i].offset + LZX_OFFSET_OFFSET;
- offset_slot = lzx_get_offset_slot_raw(offset_data);
- position_cost = cur_optimum_ptr->cost +
- lzx_extra_offset_bits[offset_slot];
- do {
- cost = position_cost +
- lzx_match_cost_raw(len, offset_slot, &c->costs);
- if (cost < (cur_optimum_ptr + len)->cost) {
- (cur_optimum_ptr + len)->cost = cost;
- (cur_optimum_ptr + len)->mc_item_data =
- (offset_data << MC_OFFSET_SHIFT) | len;
- }
- } while (++len <= matches[i].len);
- } while (++i != num_matches);
- }
+#if LZX_CONSIDER_ALIGNED_COSTS
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
+ c->costs.aligned[i] = LZX_NUM_ALIGNED_OFFSET_BITS * LZX_BIT_COST;
+#endif
-#else /* Unoptimized version */
+ lzx_compute_match_costs(c);
+}
- unsigned num_extra_bits;
+/* Update the current cost model to reflect the computed Huffman codes. */
+static void
+lzx_update_costs(struct lzx_compressor *c)
+{
+ unsigned i;
+ const struct lzx_lens *lens = &c->codes[c->codes_index].lens;
- len = 2;
- i = 0;
- do {
- offset_data = matches[i].offset + LZX_OFFSET_OFFSET;
- position_cost = cur_optimum_ptr->cost;
- offset_slot = lzx_get_offset_slot_raw(offset_data);
- num_extra_bits = lzx_extra_offset_bits[offset_slot];
- if (num_extra_bits >= 3) {
- position_cost += num_extra_bits - 3;
- position_cost += c->costs.aligned[offset_data & 7];
- } else {
- position_cost += num_extra_bits;
- }
- do {
- cost = position_cost +
- lzx_match_cost_raw(len, offset_slot, &c->costs);
- if (cost < (cur_optimum_ptr + len)->cost) {
- (cur_optimum_ptr + len)->cost = cost;
- (cur_optimum_ptr + len)->mc_item_data =
- (offset_data << MC_OFFSET_SHIFT) | len;
- }
- } while (++len <= matches[i].len);
- } while (++i != num_matches);
+ for (i = 0; i < c->num_main_syms; i++)
+ c->costs.main[i] = (lens->main[i] ? lens->main[i] : 15) * LZX_BIT_COST;
+
+ for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++)
+ c->costs.len[i] = (lens->len[i] ? lens->len[i] : 15) * LZX_BIT_COST;
+
+#if LZX_CONSIDER_ALIGNED_COSTS
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
+ c->costs.aligned[i] = (lens->aligned[i] ? lens->aligned[i] : 7) * LZX_BIT_COST;
#endif
+
+ lzx_compute_match_costs(c);
}
-/*
- * Search for repeat offset matches with the current position.
- */
-static inline unsigned
-lzx_repsearch(const u8 * const strptr, const u32 bytes_remaining,
- const struct lzx_lru_queue *queue, unsigned *rep_max_idx_ret)
+static struct lzx_lru_queue
+lzx_optimize_and_write_block(struct lzx_compressor *c,
+ struct lzx_output_bitstream *os,
+ const u8 *block_begin, const u32 block_size,
+ const struct lzx_lru_queue initial_queue)
{
- BUILD_BUG_ON(LZX_NUM_RECENT_OFFSETS != 3);
- return lz_repsearch3(strptr, min(bytes_remaining, LZX_MAX_MATCH_LEN),
- queue->R, rep_max_idx_ret);
+ unsigned num_passes_remaining = c->num_optim_passes;
+ struct lzx_item *next_chosen_item;
+ struct lzx_lru_queue new_queue;
+
+ /* The first optimization pass uses a default cost model. Each
+ * additional optimization pass uses a cost model derived from the
+ * Huffman code computed in the previous pass. */
+
+ lzx_set_default_costs(c, block_begin, block_size);
+ lzx_reset_symbol_frequencies(c);
+ do {
+ new_queue = lzx_find_min_cost_path(c, block_begin, block_size,
+ initial_queue);
+ if (num_passes_remaining > 1) {
+ lzx_tally_item_list(c, c->optimum_nodes + block_size);
+ lzx_make_huffman_codes(c);
+ lzx_update_costs(c);
+ lzx_reset_symbol_frequencies(c);
+ }
+ } while (--num_passes_remaining);
+
+ next_chosen_item = c->chosen_items;
+ lzx_record_item_list(c, c->optimum_nodes + block_size, &next_chosen_item);
+ lzx_finish_block(c, os, block_size, next_chosen_item - c->chosen_items);
+ return new_queue;
}
/*
- * The main near-optimal parsing routine.
+ * This is the "near-optimal" LZX compressor.
*
- * Briefly, the algorithm does an approximate minimum-cost path search to find a
- * "near-optimal" sequence of matches and literals to output, based on the
- * current cost model. The algorithm steps forward, position by position (byte
- * by byte), and updates the minimum cost path to reach each later position that
- * can be reached using a match or literal from the current position. This is
- * essentially Dijkstra's algorithm in disguise: the graph nodes are positions,
- * the graph edges are possible matches/literals to code, and the cost of each
- * edge is the estimated number of bits that will be required to output the
- * corresponding match or literal. But one difference is that we actually
- * compute the lowest-cost path in pieces, where each piece is terminated when
- * there are no choices to be made.
+ * For each block, it performs a relatively thorough graph search to find an
+ * inexpensive (in terms of compressed size) way to output that block.
*
- * This function will run this algorithm on the portion of the window from
- * &c->cur_window[c->match_window_pos] to &c->cur_window[c->match_window_end].
- *
- * On entry, c->queue must be the current state of the match offset LRU queue,
- * and c->costs must be the current cost model to use for Huffman symbols.
- *
- * On exit, c->queue will be the state that the LRU queue would be in if the
- * chosen items were to be coded.
- *
- * If next_chosen_item != NULL, then all items chosen will be recorded (saved in
- * the chosen_items array). Otherwise, all items chosen will only be tallied
- * (symbol frequencies tallied in c->freqs).
+ * Note: there are actually many things this algorithm leaves on the table in
+ * terms of compression ratio. So although it may be "near-optimal", it is
+ * certainly not "optimal". The goal is not to produce the optimal compression
+ * ratio, which for LZX is probably impossible within any practical amount of
+ * time, but rather to produce a compression ratio significantly better than a
+ * simpler "greedy" or "lazy" parse while still being relatively fast.
*/
static void
-lzx_optim_pass(struct lzx_compressor *c, struct lzx_item **next_chosen_item)
+lzx_compress_near_optimal(struct lzx_compressor *c,
+ struct lzx_output_bitstream *os)
{
- const u8 *block_end;
- struct lzx_lru_queue *begin_queue;
- const u8 *window_ptr;
- struct lzx_mc_pos_data *cur_optimum_ptr;
- struct lzx_mc_pos_data *end_optimum_ptr;
- const struct lz_match *matches;
- unsigned num_matches;
- unsigned longest_len;
- unsigned rep_max_len;
- unsigned rep_max_idx;
- unsigned literal;
- unsigned len;
- u32 cost;
- u32 offset_data;
-
- block_end = &c->cur_window[c->match_window_end];
- begin_queue = &c->queue;
-begin:
- /* Start building a new list of items, which will correspond to the next
- * piece of the overall minimum-cost path.
- *
- * *begin_queue is the current state of the match offset LRU queue. */
-
- window_ptr = &c->cur_window[c->match_window_pos];
-
- if (window_ptr == block_end) {
- c->queue = *begin_queue;
- return;
- }
-
- cur_optimum_ptr = c->optimum;
- cur_optimum_ptr->cost = 0;
- cur_optimum_ptr->queue = *begin_queue;
-
- end_optimum_ptr = cur_optimum_ptr;
+ const u8 * const in_begin = c->in_buffer;
+ const u8 * in_next = in_begin;
+ const u8 * const in_end = in_begin + c->in_nbytes;
+ unsigned max_len = LZX_MAX_MATCH_LEN;
+ unsigned nice_len = min(c->nice_match_length, max_len);
+ u32 next_hash;
+ struct lzx_lru_queue queue;
- /* The following loop runs once for each per byte in the window, except
- * in a couple shortcut cases. */
- for (;;) {
+ bt_matchfinder_init(&c->bt_mf);
+ matchfinder_init(c->hash2_tab, LZX_HASH2_LENGTH);
+ next_hash = bt_matchfinder_hash_3_bytes(in_next);
+ lzx_lru_queue_init(&queue);
- /* Find explicit offset matches with the current position. */
- num_matches = lzx_get_matches(c, &matches);
+ do {
+ /* Starting a new block */
+ const u8 * const in_block_begin = in_next;
+ const u8 * const in_block_end =
+ in_next + min(LZX_DIV_BLOCK_SIZE, in_end - in_next);
- if (num_matches) {
- /*
- * Find the longest repeat offset match with the current
- * position.
- *
- * Heuristics:
- *
- * - Only search for repeat offset matches if the
- * match-finder already found at least one match.
- *
- * - Only consider the longest repeat offset match. It
- * seems to be rare for the optimal parse to include a
- * repeat offset match that doesn't have the longest
- * length (allowing for the possibility that not all
- * of that length is actually used).
- */
- rep_max_len = lzx_repsearch(window_ptr,
- block_end - window_ptr,
- &cur_optimum_ptr->queue,
- &rep_max_idx);
-
- if (rep_max_len) {
- /* If there's a very long repeat offset match,
- * choose it immediately. */
- if (rep_max_len >= c->params.nice_match_length) {
-
- swap(cur_optimum_ptr->queue.R[0],
- cur_optimum_ptr->queue.R[rep_max_idx]);
- begin_queue = &cur_optimum_ptr->queue;
-
- cur_optimum_ptr += rep_max_len;
- cur_optimum_ptr->mc_item_data =
- (rep_max_idx << MC_OFFSET_SHIFT) |
- rep_max_len;
-
- lzx_skip_bytes(c, rep_max_len - 1);
- break;
+ /* Run the block through the matchfinder and cache the matches. */
+ struct lz_match *cache_ptr = c->match_cache;
+ do {
+ struct lz_match *lz_matchptr;
+ u32 hash2;
+ pos_t cur_match;
+ unsigned best_len;
+
+ /* If approaching the end of the input buffer, adjust
+ * 'max_len' and 'nice_len' accordingly. */
+ if (unlikely(max_len > in_end - in_next)) {
+ max_len = in_end - in_next;
+ nice_len = min(max_len, nice_len);
+
+ /* This extra check is needed to ensure that
+ * reading the next 3 bytes when looking for a
+ * length 2 match is valid. In addition, we
+ * cannot allow ourselves to find a length 2
+ * match of the very last two bytes with the
+ * very first two bytes, since such a match has
+ * an offset too large to be represented. */
+ if (unlikely(max_len <
+ max(LZ_HASH_REQUIRED_NBYTES, 3)))
+ {
+ in_next++;
+ cache_ptr->length = 0;
+ cache_ptr++;
+ continue;
}
-
- /* If reaching any positions for the first time,
- * initialize their costs to "infinity". */
- while (end_optimum_ptr < cur_optimum_ptr + rep_max_len)
- (++end_optimum_ptr)->cost = MC_INFINITE_COST;
-
- /* Consider coding a repeat offset match. */
- lzx_consider_repeat_offset_match(c,
- cur_optimum_ptr,
- rep_max_len,
- rep_max_idx);
}
- longest_len = matches[num_matches - 1].len;
-
- /* If there's a very long explicit offset match, choose
- * it immediately. */
- if (longest_len >= c->params.nice_match_length) {
-
- cur_optimum_ptr->queue.R[2] =
- cur_optimum_ptr->queue.R[1];
- cur_optimum_ptr->queue.R[1] =
- cur_optimum_ptr->queue.R[0];
- cur_optimum_ptr->queue.R[0] =
- matches[num_matches - 1].offset;
- begin_queue = &cur_optimum_ptr->queue;
-
- offset_data = matches[num_matches - 1].offset +
- LZX_OFFSET_OFFSET;
- cur_optimum_ptr += longest_len;
- cur_optimum_ptr->mc_item_data =
- (offset_data << MC_OFFSET_SHIFT) |
- longest_len;
-
- lzx_skip_bytes(c, longest_len - 1);
- break;
+ lz_matchptr = cache_ptr + 1;
+
+ /* Check for a length 2 match. */
+ hash2 = lz_hash_2_bytes(in_next);
+ cur_match = c->hash2_tab[hash2];
+ c->hash2_tab[hash2] = in_next - in_begin;
+ if (matchfinder_node_valid(cur_match) &&
+ (LZX_HASH2_ORDER == 16 ||
+ load_u16_unaligned(&in_begin[cur_match]) ==
+ load_u16_unaligned(in_next)) &&
+ in_begin[cur_match + 2] != in_next[2])
+ {
+ lz_matchptr->length = 2;
+ lz_matchptr->offset = in_next - &in_begin[cur_match];
+ lz_matchptr++;
}
- /* If reaching any positions for the first time,
- * initialize their costs to "infinity". */
- while (end_optimum_ptr < cur_optimum_ptr + longest_len)
- (++end_optimum_ptr)->cost = MC_INFINITE_COST;
+ /* Check for matches of length >= 3. */
+ lz_matchptr = bt_matchfinder_get_matches(&c->bt_mf,
+ in_begin,
+ in_next,
+ 3,
+ max_len,
+ nice_len,
+ c->max_search_depth,
+ &next_hash,
+ &best_len,
+ lz_matchptr);
+ in_next++;
+ cache_ptr->length = lz_matchptr - (cache_ptr + 1);
+ cache_ptr = lz_matchptr;
- /* Consider coding an explicit offset match. */
- lzx_consider_explicit_offset_matches(c, cur_optimum_ptr,
- matches, num_matches);
- } else {
- /* No matches found. The only choice at this position
- * is to code a literal. */
-
- if (end_optimum_ptr == cur_optimum_ptr) {
- #if 1
- /* Optimization for single literals. */
- if (likely(cur_optimum_ptr == c->optimum)) {
- lzx_declare_literal(c, *window_ptr++,
- next_chosen_item);
- if (window_ptr == block_end) {
- c->queue = cur_optimum_ptr->queue;
- return;
+ /*
+ * If there was a very long match found, then don't
+ * cache any matches for the bytes covered by that
+ * match. This avoids degenerate behavior when
+ * compressing highly redundant data, where the number
+ * of matches can be very large.
+ *
+ * This heuristic doesn't actually hurt the compression
+ * ratio very much. If there's a long match, then the
+ * data must be highly compressible, so it doesn't
+ * matter as much what we do.
+ */
+ if (best_len >= nice_len) {
+ --best_len;
+ do {
+ if (unlikely(max_len > in_end - in_next)) {
+ max_len = in_end - in_next;
+ nice_len = min(max_len, nice_len);
+ if (unlikely(max_len <
+ max(LZ_HASH_REQUIRED_NBYTES, 3)))
+ {
+ in_next++;
+ cache_ptr->length = 0;
+ cache_ptr++;
+ continue;
+ }
}
- continue;
- }
- #endif
- (++end_optimum_ptr)->cost = MC_INFINITE_COST;
+ c->hash2_tab[lz_hash_2_bytes(in_next)] =
+ in_next - in_begin;
+ bt_matchfinder_skip_position(&c->bt_mf,
+ in_begin,
+ in_next,
+ in_end,
+ nice_len,
+ c->max_search_depth,
+ &next_hash);
+ in_next++;
+ cache_ptr->length = 0;
+ cache_ptr++;
+ } while (--best_len);
}
- }
+ } while (in_next < in_block_end &&
+ likely(cache_ptr < &c->match_cache[LZX_CACHE_LENGTH]));
- /* Consider coding a literal.
+ /* We've finished running the block through the matchfinder.
+ * Now choose a match/literal sequence and write the block. */
- * To avoid an extra unpredictable brench, actually checking the
- * preferability of coding a literal is integrated into the
- * queue update code below. */
- literal = *window_ptr++;
- cost = cur_optimum_ptr->cost + lzx_literal_cost(literal, &c->costs);
+ queue = lzx_optimize_and_write_block(c, os, in_block_begin,
+ in_next - in_block_begin,
+ queue);
+ } while (in_next != in_end);
+}
- /* Advance to the next position. */
- cur_optimum_ptr++;
+/*
+ * Given a pointer to the current byte sequence and the current list of recent
+ * match offsets, find the longest repeat offset match.
+ *
+ * If no match of at least 2 bytes is found, then return 0.
+ *
+ * If a match of at least 2 bytes is found, then return its length and set
+ * *rep_max_idx_ret to the index of its offset in @queue.
+*/
+static unsigned
+lzx_find_longest_repeat_offset_match(const u8 * const in_next,
+ const u32 bytes_remaining,
+ struct lzx_lru_queue queue,
+ unsigned *rep_max_idx_ret)
+{
+ BUILD_BUG_ON(LZX_NUM_RECENT_OFFSETS != 3);
+ LZX_ASSERT(bytes_remaining >= 2);
- /* The lowest-cost path to the current position is now known.
- * Finalize the recent offsets queue that results from taking
- * this lowest-cost path. */
+ const unsigned max_len = min(bytes_remaining, LZX_MAX_MATCH_LEN);
+ const u16 next_2_bytes = load_u16_unaligned(in_next);
+ const u8 *matchptr;
+ unsigned rep_max_len;
+ unsigned rep_max_idx;
+ unsigned rep_len;
- if (cost < cur_optimum_ptr->cost) {
- /* Literal: queue remains unchanged. */
- cur_optimum_ptr->cost = cost;
- cur_optimum_ptr->mc_item_data = (literal << MC_OFFSET_SHIFT) | 1;
- cur_optimum_ptr->queue = (cur_optimum_ptr - 1)->queue;
- } else {
- /* Match: queue update is needed. */
- len = cur_optimum_ptr->mc_item_data & MC_LEN_MASK;
- offset_data = cur_optimum_ptr->mc_item_data >> MC_OFFSET_SHIFT;
- if (offset_data >= LZX_NUM_RECENT_OFFSETS) {
- /* Explicit offset match: offset is inserted at front */
- cur_optimum_ptr->queue.R[0] = offset_data - LZX_OFFSET_OFFSET;
- cur_optimum_ptr->queue.R[1] = (cur_optimum_ptr - len)->queue.R[0];
- cur_optimum_ptr->queue.R[2] = (cur_optimum_ptr - len)->queue.R[1];
- } else {
- /* Repeat offset match: offset is swapped to front */
- cur_optimum_ptr->queue = (cur_optimum_ptr - len)->queue;
- swap(cur_optimum_ptr->queue.R[0],
- cur_optimum_ptr->queue.R[offset_data]);
- }
+ matchptr = in_next - lzx_lru_queue_pop(&queue);
+ if (load_u16_unaligned(matchptr) == next_2_bytes)
+ rep_max_len = lz_extend(in_next, matchptr, 2, max_len);
+ else
+ rep_max_len = 0;
+ rep_max_idx = 0;
+
+ matchptr = in_next - lzx_lru_queue_pop(&queue);
+ if (load_u16_unaligned(matchptr) == next_2_bytes) {
+ rep_len = lz_extend(in_next, matchptr, 2, max_len);
+ if (rep_len > rep_max_len) {
+ rep_max_len = rep_len;
+ rep_max_idx = 1;
}
+ }
- /*
- * This loop will terminate when either of the following
- * conditions is true:
- *
- * (1) cur_optimum_ptr == end_optimum_ptr
- *
- * There are no paths that extend beyond the current
- * position. In this case, any path to a later position
- * must pass through the current position, so we can go
- * ahead and choose the list of items that led to this
- * position.
- *
- * (2) cur_optimum_ptr == &c->optimum[LZX_OPTIM_ARRAY_LENGTH]
- *
- * This bounds the number of times the algorithm can step
- * forward before it is guaranteed to start choosing items.
- * This limits the memory usage. But
- * LZX_OPTIM_ARRAY_LENGTH is high enough that on most
- * inputs this limit is never reached.
- *
- * Note: no check for end-of-block is needed because
- * end-of-block will trigger condition (1).
- */
- if (cur_optimum_ptr == end_optimum_ptr ||
- cur_optimum_ptr == &c->optimum[LZX_OPTIM_ARRAY_LENGTH])
- {
- begin_queue = &cur_optimum_ptr->queue;
- break;
+ matchptr = in_next - lzx_lru_queue_pop(&queue);
+ if (load_u16_unaligned(matchptr) == next_2_bytes) {
+ rep_len = lz_extend(in_next, matchptr, 2, max_len);
+ if (rep_len > rep_max_len) {
+ rep_max_len = rep_len;
+ rep_max_idx = 2;
}
}
- /* Choose the current list of items that constitute the minimum-cost
- * path to the current position. */
- lzx_declare_item_list(c, cur_optimum_ptr, next_chosen_item);
- goto begin;
+ *rep_max_idx_ret = rep_max_idx;
+ return rep_max_len;
}
/* Fast heuristic scoring for lazy parsing: how "good" is this match? */
{
unsigned score = len;
- if (adjusted_offset < 2048)
+ if (adjusted_offset < 4096)
score++;
- if (adjusted_offset < 1024)
+ if (adjusted_offset < 256)
score++;
return score;
}
static inline unsigned
-lzx_repeat_offset_match_score(unsigned len, unsigned slot)
+lzx_repeat_offset_match_score(unsigned rep_len, unsigned rep_idx)
{
- return len + 3;
+ return rep_len + 3;
}
-/* Lazy parsing */
-static u32
-lzx_choose_lazy_items_for_block(struct lzx_compressor *c,
- u32 block_start_pos, u32 block_size)
+/* This is the "lazy" LZX compressor. */
+static void
+lzx_compress_lazy(struct lzx_compressor *c, struct lzx_output_bitstream *os)
{
- const u8 *window_ptr;
- const u8 *block_end;
- struct lz_mf *mf;
- struct lz_match *matches;
- unsigned num_matches;
- unsigned cur_len;
- u32 cur_offset_data;
- unsigned cur_score;
- unsigned rep_max_len;
- unsigned rep_max_idx;
- unsigned rep_score;
- unsigned prev_len;
- unsigned prev_score;
- u32 prev_offset_data;
- unsigned skip_len;
- struct lzx_item *next_chosen_item;
-
- window_ptr = &c->cur_window[block_start_pos];
- block_end = window_ptr + block_size;
- matches = c->cached_matches;
- mf = c->mf;
- next_chosen_item = c->chosen_items;
-
- prev_len = 0;
- prev_offset_data = 0;
- prev_score = 0;
-
- while (window_ptr != block_end) {
+ const u8 * const in_begin = c->in_buffer;
+ const u8 * in_next = in_begin;
+ const u8 * const in_end = in_begin + c->in_nbytes;
+ unsigned max_len = LZX_MAX_MATCH_LEN;
+ unsigned nice_len = min(c->nice_match_length, max_len);
+ struct lzx_lru_queue queue;
- /* Find explicit offset matches with the current position. */
- num_matches = lz_mf_get_matches(mf, matches);
- window_ptr++;
+ hc_matchfinder_init(&c->hc_mf);
+ lzx_lru_queue_init(&queue);
- if (num_matches == 0 ||
- (matches[num_matches - 1].len == 3 &&
- matches[num_matches - 1].offset >= 8192 - LZX_OFFSET_OFFSET &&
- matches[num_matches - 1].offset != c->queue.R[0] &&
- matches[num_matches - 1].offset != c->queue.R[1] &&
- matches[num_matches - 1].offset != c->queue.R[2]))
- {
- /* No match found, or the only match found was a distant
- * length 3 match. Output the previous match if there
- * is one; otherwise output a literal. */
+ do {
+ /* Starting a new block */
+
+ const u8 * const in_block_begin = in_next;
+ const u8 * const in_block_end =
+ in_next + min(LZX_DIV_BLOCK_SIZE, in_end - in_next);
+ struct lzx_item *next_chosen_item = c->chosen_items;
+ unsigned cur_len;
+ u32 cur_offset;
+ u32 cur_offset_data;
+ unsigned cur_score;
+ unsigned next_len;
+ u32 next_offset;
+ u32 next_offset_data;
+ unsigned next_score;
+ unsigned rep_max_len;
+ unsigned rep_max_idx;
+ unsigned rep_score;
+ unsigned skip_len;
+
+ lzx_reset_symbol_frequencies(c);
- no_match_found:
+ do {
+ if (unlikely(max_len > in_end - in_next)) {
+ max_len = in_end - in_next;
+ nice_len = min(max_len, nice_len);
+ }
- if (prev_len) {
- skip_len = prev_len - 2;
- goto output_prev_match;
- } else {
- lzx_declare_literal(c, *(window_ptr - 1),
+ /* Find the longest match at the current position. */
+
+ cur_len = hc_matchfinder_longest_match(&c->hc_mf,
+ in_begin,
+ in_next,
+ 2,
+ max_len,
+ nice_len,
+ c->max_search_depth,
+ &cur_offset);
+ if (cur_len < 3 ||
+ (cur_len == 3 &&
+ cur_offset >= 8192 - LZX_OFFSET_ADJUSTMENT &&
+ cur_offset != lzx_lru_queue_R0(queue) &&
+ cur_offset != lzx_lru_queue_R1(queue) &&
+ cur_offset != lzx_lru_queue_R2(queue)))
+ {
+ /* There was no match found, or the only match found
+ * was a distant length 3 match. Output a literal. */
+ lzx_declare_literal(c, *in_next++,
&next_chosen_item);
continue;
}
- }
-
- /* Find the longest repeat offset match with the current
- * position. */
- if (likely(block_end - (window_ptr - 1) >= 2)) {
- rep_max_len = lzx_repsearch((window_ptr - 1),
- block_end - (window_ptr - 1),
- &c->queue, &rep_max_idx);
- } else {
- rep_max_len = 0;
- }
- cur_len = matches[num_matches - 1].len;
- cur_offset_data = matches[num_matches - 1].offset + LZX_OFFSET_OFFSET;
- cur_score = lzx_explicit_offset_match_score(cur_len, cur_offset_data);
-
- /* Select the better of the explicit and repeat offset matches. */
- if (rep_max_len >= 3 &&
- (rep_score = lzx_repeat_offset_match_score(rep_max_len,
- rep_max_idx)) >= cur_score)
- {
- cur_len = rep_max_len;
- cur_offset_data = rep_max_idx;
- cur_score = rep_score;
- }
-
- if (unlikely(cur_len > block_end - (window_ptr - 1))) {
- /* Nearing end of block. */
- cur_len = block_end - (window_ptr - 1);
- if (cur_len < 3)
- goto no_match_found;
- }
-
- if (prev_len == 0 || cur_score > prev_score) {
- /* No previous match, or the current match is better
- * than the previous match.
- *
- * If there's a previous match, then output a literal in
- * its place.
- *
- * In both cases, if the current match is very long,
- * then output it immediately. Otherwise, attempt a
- * lazy match by waiting to see if there's a better
- * match at the next position. */
-
- if (prev_len)
- lzx_declare_literal(c, *(window_ptr - 2), &next_chosen_item);
-
- prev_len = cur_len;
- prev_offset_data = cur_offset_data;
- prev_score = cur_score;
-
- if (prev_len >= c->params.nice_match_length) {
- skip_len = prev_len - 1;
- goto output_prev_match;
+ if (cur_offset == lzx_lru_queue_R0(queue)) {
+ in_next++;
+ cur_offset_data = 0;
+ skip_len = cur_len - 1;
+ goto choose_cur_match;
}
- continue;
- }
-
- /* Current match is not better than the previous match, so
- * output the previous match. */
-
- skip_len = prev_len - 2;
-
- output_prev_match:
- if (prev_offset_data < LZX_NUM_RECENT_OFFSETS) {
- lzx_declare_repeat_offset_match(c, prev_len,
- prev_offset_data,
- &next_chosen_item);
- swap(c->queue.R[0], c->queue.R[prev_offset_data]);
- } else {
- lzx_declare_explicit_offset_match(c, prev_len,
- prev_offset_data - LZX_OFFSET_OFFSET,
- &next_chosen_item);
- c->queue.R[2] = c->queue.R[1];
- c->queue.R[1] = c->queue.R[0];
- c->queue.R[0] = prev_offset_data - LZX_OFFSET_OFFSET;
- }
- lz_mf_skip_positions(mf, skip_len);
- window_ptr += skip_len;
- prev_len = 0;
- }
-
- return next_chosen_item - c->chosen_items;
-}
-
-/* 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)
-{
- u32 aligned_cost = 0;
- u32 verbatim_cost = 0;
-
- /* A verbatim block requires 3 bits in each place that an aligned symbol
- * would be used in an aligned offset block. */
- 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];
- }
-
- /* Account for output of the aligned offset code. */
- aligned_cost += LZX_ALIGNEDCODE_ELEMENT_SIZE * LZX_ALIGNEDCODE_NUM_SYMBOLS;
-
- if (aligned_cost < verbatim_cost)
- return LZX_BLOCKTYPE_ALIGNED;
- else
- return LZX_BLOCKTYPE_VERBATIM;
-}
-/* Near-optimal parsing */
-static u32
-lzx_choose_near_optimal_items_for_block(struct lzx_compressor *c,
- u32 block_start_pos, u32 block_size)
-{
- u32 num_passes_remaining = c->params.num_optim_passes;
- struct lzx_lru_queue orig_queue;
- struct lzx_item *next_chosen_item;
- struct lzx_item **next_chosen_item_ptr;
-
- /* Choose appropriate match-finder wrapper functions. */
- if (num_passes_remaining > 1) {
- if (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 (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;
- }
+ cur_offset_data = cur_offset + LZX_OFFSET_ADJUSTMENT;
+ cur_score = lzx_explicit_offset_match_score(cur_len, cur_offset_data);
+
+ /* Consider a repeat offset match */
+ rep_max_len = lzx_find_longest_repeat_offset_match(in_next,
+ in_end - in_next,
+ queue,
+ &rep_max_idx);
+ in_next++;
+
+ if (rep_max_len >= 3 &&
+ (rep_score = lzx_repeat_offset_match_score(rep_max_len,
+ rep_max_idx)) >= cur_score)
+ {
+ cur_len = rep_max_len;
+ cur_offset_data = rep_max_idx;
+ skip_len = rep_max_len - 1;
+ goto choose_cur_match;
+ }
- /* No matches will extend beyond the end of the block. */
- c->match_window_end = block_start_pos + block_size;
+ have_cur_match:
- /* The first optimization pass will use a default cost model. Each
- * additional optimization pass will use 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. For
- * earlier passes, tallying symbol frequencies is sufficient. */
- lzx_set_default_costs(&c->costs, c->num_main_syms);
+ /* We have a match at the current position. */
- next_chosen_item_ptr = NULL;
- orig_queue = c->queue;
- do {
- /* Reset the match-finder wrapper. */
- c->match_window_pos = block_start_pos;
- c->cache_ptr = c->cached_matches;
-
- if (num_passes_remaining == 1) {
- /* Last pass: actually generate the items. */
- next_chosen_item = c->chosen_items;
- next_chosen_item_ptr = &next_chosen_item;
- }
-
- /* Choose the items. */
- lzx_optim_pass(c, next_chosen_item_ptr);
+ /* If we have a very long match, choose it immediately. */
+ if (cur_len >= nice_len) {
+ skip_len = cur_len - 1;
+ goto choose_cur_match;
+ }
- if (num_passes_remaining > 1) {
- /* This isn't the last pass. */
+ /* See if there's a better match at the next position. */
- /* Make the Huffman codes from the symbol frequencies. */
- lzx_make_huffman_codes(&c->freqs, &c->codes[c->codes_index],
- c->num_main_syms);
+ if (unlikely(max_len > in_end - in_next)) {
+ max_len = in_end - in_next;
+ nice_len = min(max_len, nice_len);
+ }
- /* Update symbol costs. */
- lzx_set_costs(c, &c->codes[c->codes_index].lens);
+ next_len = hc_matchfinder_longest_match(&c->hc_mf,
+ in_begin,
+ in_next,
+ cur_len - 2,
+ max_len,
+ nice_len,
+ c->max_search_depth / 2,
+ &next_offset);
+
+ if (next_len <= cur_len - 2) {
+ in_next++;
+ skip_len = cur_len - 2;
+ goto choose_cur_match;
+ }
- /* Reset symbol frequencies. */
- memset(&c->freqs, 0, sizeof(c->freqs));
+ next_offset_data = next_offset + LZX_OFFSET_ADJUSTMENT;
+ next_score = lzx_explicit_offset_match_score(next_len, next_offset_data);
+
+ rep_max_len = lzx_find_longest_repeat_offset_match(in_next,
+ in_end - in_next,
+ queue,
+ &rep_max_idx);
+ in_next++;
+
+ if (rep_max_len >= 3 &&
+ (rep_score = lzx_repeat_offset_match_score(rep_max_len,
+ rep_max_idx)) >= next_score)
+ {
+
+ if (rep_score > cur_score) {
+ /* The next match is better, and it's a
+ * repeat offset match. */
+ lzx_declare_literal(c, *(in_next - 2),
+ &next_chosen_item);
+ cur_len = rep_max_len;
+ cur_offset_data = rep_max_idx;
+ skip_len = cur_len - 1;
+ goto choose_cur_match;
+ }
+ } else {
+ if (next_score > cur_score) {
+ /* The next match is better, and it's an
+ * explicit offset match. */
+ lzx_declare_literal(c, *(in_next - 2),
+ &next_chosen_item);
+ cur_len = next_len;
+ cur_offset_data = next_offset_data;
+ cur_score = next_score;
+ goto have_cur_match;
+ }
+ }
- /* Reset the match offset LRU queue to what it was at
- * the beginning of the block. */
- c->queue = orig_queue;
+ /* The original match was better. */
+ skip_len = cur_len - 2;
- /* Choose appopriate match-finder wrapper functions. */
- 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;
+ choose_cur_match:
+ if (cur_offset_data < LZX_NUM_RECENT_OFFSETS) {
+ lzx_declare_repeat_offset_match(c, cur_len,
+ cur_offset_data,
+ &next_chosen_item);
+ queue = lzx_lru_queue_swap(queue, cur_offset_data);
} else {
- c->get_matches_func = lzx_get_matches_usecache;
- c->skip_bytes_func = lzx_skip_bytes_usecache;
+ lzx_declare_explicit_offset_match(c, cur_len,
+ cur_offset_data - LZX_OFFSET_ADJUSTMENT,
+ &next_chosen_item);
+ queue = lzx_lru_queue_push(queue, cur_offset_data - LZX_OFFSET_ADJUSTMENT);
}
- }
- } while (--num_passes_remaining);
- /* Return the number of items chosen. */
- return next_chosen_item - c->chosen_items;
+ hc_matchfinder_skip_positions(&c->hc_mf,
+ in_begin,
+ in_next,
+ in_end,
+ skip_len);
+ in_next += skip_len;
+ } while (in_next < in_block_end);
+
+ lzx_finish_block(c, os, in_next - in_block_begin,
+ next_chosen_item - c->chosen_items);
+ } while (in_next != in_end);
}
-/*
- * Choose the matches/literals with which to output the block of data beginning
- * at '&c->cur_window[block_start_pos]' and extending for 'block_size' bytes.
- *
- * The frequences of the Huffman symbols in the block will be tallied in
- * 'c->freqs'.
- *
- * 'c->queue' must specify the state of the queue at the beginning of this block.
- * This function will update it to the state of the queue at the end of this
- * block.
- *
- * Returns the number of matches/literals that were chosen and written to
- * 'c->chosen_items' in the 'struct lzx_item' intermediate representation.
- */
-static u32
-lzx_choose_items_for_block(struct lzx_compressor *c,
- u32 block_start_pos, u32 block_size)
-{
- return (*c->params.choose_items_for_block)(c, block_start_pos, block_size);
-}
-
-/* Initialize c->offset_slot_fast. */
static void
lzx_init_offset_slot_fast(struct lzx_compressor *c)
{
for (u32 offset = 0; offset < LZX_NUM_FAST_OFFSETS; offset++) {
- while (offset + LZX_OFFSET_OFFSET >= lzx_offset_slot_base[slot + 1])
+ while (offset + LZX_OFFSET_ADJUSTMENT >= lzx_offset_slot_base[slot + 1])
slot++;
c->offset_slot_fast[offset] = slot;
}
}
-/* Set internal compression parameters for the specified compression level and
- * maximum window size. */
-static void
-lzx_build_params(unsigned int compression_level, u32 max_window_size,
- struct lzx_compressor_params *lzx_params)
+static size_t
+lzx_get_compressor_size(size_t max_bufsize, unsigned compression_level)
{
- if (compression_level < 25) {
-
- /* Fast compression: Use lazy parsing. */
-
- lzx_params->choose_items_for_block = lzx_choose_lazy_items_for_block;
- lzx_params->num_optim_passes = 1;
-
- /* When lazy parsing, the hash chain match-finding algorithm is
- * fastest unless the window is too large.
- *
- * TODO: something like hash arrays would actually be better
- * than binary trees on large windows. */
- if (max_window_size <= 262144)
- lzx_params->mf_algo = LZ_MF_HASH_CHAINS;
- else
- lzx_params->mf_algo = LZ_MF_BINARY_TREES;
-
- /* When lazy parsing, don't bother with length 2 matches. */
- lzx_params->min_match_length = 3;
-
- /* Scale nice_match_length and max_search_depth with the
- * compression level. */
- lzx_params->nice_match_length = 25 + compression_level * 2;
- lzx_params->max_search_depth = 25 + compression_level;
+ if (compression_level <= LZX_MAX_FAST_LEVEL) {
+ return offsetof(struct lzx_compressor, hc_mf) +
+ hc_matchfinder_size(max_bufsize);
} else {
-
- /* Normal / high compression: Use near-optimal parsing. */
-
- lzx_params->choose_items_for_block = lzx_choose_near_optimal_items_for_block;
-
- /* Set a number of optimization passes appropriate for the
- * compression level. */
-
- lzx_params->num_optim_passes = 1;
-
- if (compression_level >= 40)
- lzx_params->num_optim_passes++;
-
- /* Use more optimization passes for higher compression levels.
- * But the more passes there are, the less they help --- so
- * don't add them linearly. */
- if (compression_level >= 70) {
- lzx_params->num_optim_passes++;
- if (compression_level >= 100)
- lzx_params->num_optim_passes++;
- if (compression_level >= 150)
- lzx_params->num_optim_passes++;
- if (compression_level >= 200)
- lzx_params->num_optim_passes++;
- if (compression_level >= 300)
- lzx_params->num_optim_passes++;
- }
-
- /* When doing near-optimal parsing, the hash chain match-finding
- * algorithm is good if the window size is small and we're only
- * doing one optimization pass. Otherwise, the binary tree
- * algorithm is the way to go. */
- 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;
-
- /* When doing near-optimal parsing, allow length 2 matches if
- * the compression level is sufficiently high. */
- if (compression_level >= 45)
- lzx_params->min_match_length = 2;
- else
- lzx_params->min_match_length = 3;
-
- /* Scale nice_match_length and max_search_depth with the
- * compression level. */
- 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);
+ return offsetof(struct lzx_compressor, bt_mf) +
+ bt_matchfinder_size(max_bufsize);
}
}
-/* Given the internal compression parameters and maximum window size, build the
- * Lempel-Ziv match-finder parameters. */
-static void
-lzx_build_mf_params(const struct lzx_compressor_params *lzx_params,
- u32 max_window_size, struct lz_mf_params *mf_params)
-{
- memset(mf_params, 0, sizeof(*mf_params));
-
- mf_params->algorithm = lzx_params->mf_algo;
- mf_params->max_window_size = max_window_size;
- mf_params->min_match_len = lzx_params->min_match_length;
- mf_params->max_match_len = LZX_MAX_MATCH_LEN;
- mf_params->max_search_depth = lzx_params->max_search_depth;
- mf_params->nice_match_len = lzx_params->nice_match_length;
-}
-
-static void
-lzx_free_compressor(void *_c);
-
static u64
-lzx_get_needed_memory(size_t max_block_size, unsigned int compression_level)
+lzx_get_needed_memory(size_t max_bufsize, unsigned compression_level)
{
- struct lzx_compressor_params params;
u64 size = 0;
- unsigned window_order;
- u32 max_window_size;
- window_order = lzx_get_window_order(max_block_size);
- if (window_order == 0)
+ if (max_bufsize > LZX_MAX_WINDOW_SIZE)
return 0;
- max_window_size = max_block_size;
-
- lzx_build_params(compression_level, max_window_size, ¶ms);
-
- size += sizeof(struct lzx_compressor);
-
- /* cur_window */
- size += max_window_size;
-
- /* mf */
- size += lz_mf_get_needed_memory(params.mf_algo, max_window_size);
- /* cached_matches */
- 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);
+ size += lzx_get_compressor_size(max_bufsize, compression_level);
+ size += max_bufsize; /* in_buffer */
return size;
}
static int
-lzx_create_compressor(size_t max_block_size, unsigned int compression_level,
+lzx_create_compressor(size_t max_bufsize, unsigned 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;
+ struct lzx_compressor *c;
- window_order = lzx_get_window_order(max_block_size);
+ window_order = lzx_get_window_order(max_bufsize);
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));
+ c = ALIGNED_MALLOC(lzx_get_compressor_size(max_bufsize,
+ compression_level),
+ MATCHFINDER_ALIGNMENT);
if (!c)
- goto oom;
+ goto oom0;
- c->params = params;
c->num_main_syms = lzx_get_num_main_syms(window_order);
c->window_order = window_order;
- /* The window is allocated as 16-byte aligned to speed up memcpy() and
- * enable lzx_e8_filter() optimization on x86_64. */
- c->cur_window = ALIGNED_MALLOC(max_window_size, 16);
- if (!c->cur_window)
- goto oom;
-
- c->mf = lz_mf_alloc(&mf_params);
- if (!c->mf)
- goto oom;
-
- if (params.num_optim_passes > 1) {
- c->cached_matches = MALLOC(LZX_CACHE_LEN *
- sizeof(struct lz_match));
- if (!c->cached_matches)
- goto oom;
- c->cache_limit = c->cached_matches + LZX_CACHE_LEN -
- (LZX_MAX_MATCHES_PER_POS + 1);
+ c->in_buffer = MALLOC(max_bufsize);
+ if (!c->in_buffer)
+ goto oom1;
+
+ if (compression_level <= LZX_MAX_FAST_LEVEL) {
+
+ /* Fast compression: Use lazy parsing. */
+
+ c->impl = lzx_compress_lazy;
+ c->max_search_depth = (36 * compression_level) / 20;
+ c->nice_match_length = min((72 * compression_level) / 20,
+ LZX_MAX_MATCH_LEN);
+
} else {
- c->cached_matches = MALLOC(LZX_MAX_MATCHES_PER_POS *
- sizeof(struct lz_match));
- if (!c->cached_matches)
- goto oom;
+
+ /* Normal / high compression: Use near-optimal parsing. */
+
+ c->impl = lzx_compress_near_optimal;
+
+ /* Scale nice_match_length and max_search_depth with the
+ * compression level. */
+ c->max_search_depth = (24 * compression_level) / 50;
+ c->nice_match_length = min((32 * compression_level) / 50,
+ LZX_MAX_MATCH_LEN);
+
+ /* Set a number of optimization passes appropriate for the
+ * compression level. */
+
+ c->num_optim_passes = 1;
+
+ if (compression_level >= 45)
+ c->num_optim_passes++;
+
+ /* Use more optimization passes for higher compression levels.
+ * But the more passes there are, the less they help --- so
+ * don't add them linearly. */
+ if (compression_level >= 70) {
+ c->num_optim_passes++;
+ if (compression_level >= 100)
+ c->num_optim_passes++;
+ if (compression_level >= 150)
+ c->num_optim_passes++;
+ if (compression_level >= 200)
+ c->num_optim_passes++;
+ if (compression_level >= 300)
+ c->num_optim_passes++;
+ }
}
lzx_init_offset_slot_fast(c);
-
*c_ret = c;
return 0;
-oom:
- lzx_free_compressor(c);
+oom1:
+ ALIGNED_FREE(c);
+oom0:
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)
+lzx_compress(const void *in, size_t in_nbytes,
+ void *out, size_t out_nbytes_avail, void *_c)
{
struct lzx_compressor *c = _c;
struct lzx_output_bitstream os;
- u32 num_chosen_items;
- const struct lzx_lens *prev_lens;
- u32 block_start_pos;
- u32 block_size;
- int block_type;
- /* Don't bother compressing very small inputs. */
- if (uncompressed_size < 100)
+ /* Don't bother trying to compress very small inputs. */
+ if (in_nbytes < 100)
return 0;
- /* The input data must be preprocessed. To avoid changing the original
- * input data, 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);
-
- /* Load the window into the match-finder. */
- lz_mf_load_window(c->mf, c->cur_window, c->cur_window_size);
-
- /* Initialize the match offset LRU queue. */
- lzx_lru_queue_init(&c->queue);
-
- /* Initialize the output bitstream. */
- lzx_init_output(&os, compressed_data, compressed_size_avail);
+ /* Copy the input data into the internal buffer and preprocess it. */
+ memcpy(c->in_buffer, in, in_nbytes);
+ c->in_nbytes = in_nbytes;
+ lzx_do_e8_preprocessing(c->in_buffer, in_nbytes);
- /* Compress the data block by block.
- *
- * 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. */
- block_start_pos = 0;
+ /* Initially, the previous Huffman codeword lengths are all zeroes. */
c->codes_index = 0;
- prev_lens = &c->zero_lens;
- do {
- /* Compute the block size. */
- block_size = min(LZX_DIV_BLOCK_SIZE,
- uncompressed_size - block_start_pos);
-
- /* Reset symbol frequencies. */
- memset(&c->freqs, 0, sizeof(c->freqs));
+ memset(&c->codes[1].lens, 0, sizeof(struct lzx_lens));
- /* Prepare the matches/literals for the block. */
- num_chosen_items = lzx_choose_items_for_block(c,
- block_start_pos,
- block_size);
-
- /* Make the Huffman codes from the symbol frequencies. */
- lzx_make_huffman_codes(&c->freqs, &c->codes[c->codes_index],
- c->num_main_syms);
-
- /* Choose the best block type.
- *
- * Note: we currently don't consider uncompressed blocks. */
- block_type = lzx_choose_verbatim_or_aligned(&c->freqs,
- &c->codes[c->codes_index]);
-
- /* Write the compressed block to the output buffer. */
- lzx_write_compressed_block(block_type,
- block_size,
- c->window_order,
- c->num_main_syms,
- c->chosen_items,
- num_chosen_items,
- &c->codes[c->codes_index],
- prev_lens,
- &os);
-
- /* The current codeword lengths become the previous lengths. */
- prev_lens = &c->codes[c->codes_index].lens;
- c->codes_index ^= 1;
-
- block_start_pos += block_size;
+ /* Initialize the output bitstream. */
+ lzx_init_output(&os, out, out_nbytes_avail);
- } while (block_start_pos != uncompressed_size);
+ /* Call the compression level-specific compress() function. */
+ (*c->impl)(c, &os);
+ /* Flush the output bitstream and return the compressed size or 0. */
return lzx_flush_output(&os);
}
{
struct lzx_compressor *c = _c;
- if (c) {
- ALIGNED_FREE(c->cur_window);
- lz_mf_free(c->mf);
- FREE(c->cached_matches);
- FREE(c);
- }
+ FREE(c->in_buffer);
+ ALIGNED_FREE(c);
}
const struct compressor_ops lzx_compressor_ops = {
git://wimlib.net / wimlib / blobdiff