*/
/*
- * 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
+/*
+ * 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
+
+/*
+ * 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 7
+
+/*
+ * 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))
+
+/*
+ * 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
+
+/*
+ * 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
+
+/*
+ * Should the compressor take into account the costs of aligned offset symbols?
+ */
+#define LZX_CONSIDER_ALIGNED_COSTS 1
+
+/*
+ * LZX_MAX_FAST_LEVEL is the maximum compression level at which we use the
+ * faster algorithm.
+ */
+#define LZX_MAX_FAST_LEVEL 34
+
+/*
+ * BT_MATCHFINDER_HASH2_ORDER is the log base 2 of the number of entries in the
+ * hash table for finding length 2 matches. This could be as high as 16, but
+ * using a smaller hash table speeds up compression due to reduced cache
+ * pressure.
+ */
+#define BT_MATCHFINDER_HASH2_ORDER 12
+
+/*
+ * These are the compressor-side limits on the codeword lengths for each Huffman
+ * code. To make outputting bits slightly faster, some of these limits are
+ * lower than the limits defined by the LZX format. This does not significantly
+ * affect the compression ratio, at least for the block sizes we use.
+ */
+#define MAIN_CODEWORD_LIMIT 12 /* 64-bit: can buffer 4 main symbols */
+#define LENGTH_CODEWORD_LIMIT 12
+#define ALIGNED_CODEWORD_LIMIT 7
+#define PRE_CODEWORD_LIMIT 7
+
#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/lz_extend.h"
#include "wimlib/lzx_common.h"
+#include "wimlib/unaligned.h"
#include "wimlib/util.h"
-#include <string.h>
-#include <limits.h>
-
-#define LZX_OPTIM_ARRAY_LENGTH 4096
+/* Matchfinders with 16-bit positions */
+#define mf_pos_t u16
+#define MF_SUFFIX _16
+#include "wimlib/bt_matchfinder.h"
+#include "wimlib/hc_matchfinder.h"
-#define LZX_DIV_BLOCK_SIZE 32768
-
-#define LZX_CACHE_PER_POS 8
-
-#define LZX_MAX_MATCHES_PER_POS (LZX_MAX_MATCH_LEN - LZX_MIN_MATCH_LEN + 1)
-
-#define LZX_CACHE_LEN (LZX_DIV_BLOCK_SIZE * (LZX_CACHE_PER_POS + 1))
+/* Matchfinders with 32-bit positions */
+#undef mf_pos_t
+#undef MF_SUFFIX
+#define mf_pos_t u32
+#define MF_SUFFIX _32
+#include "wimlib/bt_matchfinder.h"
+#include "wimlib/hc_matchfinder.h"
-struct lzx_compressor;
+struct lzx_output_bitstream;
/* Codewords for the LZX Huffman codes. */
struct lzx_codewords {
/* Codeword lengths (in bits) for the LZX Huffman codes.
* A zero length means the corresponding codeword has zero frequency. */
struct lzx_lens {
- u8 main[LZX_MAINCODE_MAX_NUM_SYMBOLS];
- u8 len[LZX_LENCODE_NUM_SYMBOLS];
+ u8 main[LZX_MAINCODE_MAX_NUM_SYMBOLS + 1];
+ u8 len[LZX_LENCODE_NUM_SYMBOLS + 1];
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. */
u32 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
};
-/* Intermediate LZX match/literal format */
-struct lzx_item {
-
- /* Bits 0 - 9: Main symbol
- * Bits 10 - 17: Length symbol
- * Bits 18 - 22: Number of extra offset bits
- * Bits 23+ : Extra offset bits */
- 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;
+/*
+ * Represents a run of literals followed by a match or end-of-block. This
+ * struct is needed to temporarily store items chosen by the parser, since items
+ * cannot be written until all items for the block have been chosen and the
+ * block's Huffman codes have been computed.
+ */
+struct lzx_sequence {
+
+ /* The number of literals in the run. This may be 0. The literals are
+ * not stored explicitly in this structure; instead, they are read
+ * directly from the uncompressed data. */
+ u16 litrunlen;
+
+ /* If the next field doesn't indicate end-of-block, then this is the
+ * match length minus LZX_MIN_MATCH_LEN. */
+ u16 adjusted_length;
+
+ /* If bit 31 is clear, then this field contains the match header in bits
+ * 0-8, and either the match offset plus LZX_OFFSET_ADJUSTMENT or a
+ * recent offset code in bits 9-30. Otherwise (if bit 31 is set), this
+ * sequence's literal run was the last literal run in the block, so
+ * there is no match that follows it. */
+ u32 adjusted_offset_and_match_hdr;
};
/*
- * 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.
*
* This variable is divided into two bitfields.
*
* Literals:
- * Low bits are 1, high bits are the literal.
+ * Low bits are 0, high bits are the literal.
*
* Explicit offset matches:
* Low bits are the match length, high bits are the offset plus 2.
* 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,
+ };
+}
+
+/* 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;
+
+ /* 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;
- /* Frequency counters for the current block. */
+ /* Pointer to the compress() implementation chosen at allocation time */
+ void (*impl)(struct lzx_compressor *, struct lzx_output_bitstream *);
+
+ /* If true, the compressor need not preserve the input buffer if it
+ * compresses the data successfully. */
+ bool destructive;
+
+ /* The Huffman symbol frequency counters for the current block. */
struct lzx_freqs freqs;
- /* The Huffman codes for the current and previous blocks. */
+ /* 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;
+
+ /* The matches and literals that the parser has chosen for the current
+ * block. The required length of this array is limited by the maximum
+ * number of matches that can ever be chosen for a single block, plus
+ * one for the special entry at the end. */
+ struct lzx_sequence chosen_sequences[
+ DIV_ROUND_UP(LZX_DIV_BLOCK_SIZE, LZX_MIN_MATCH_LEN) + 1];
+
+ /* Tables for mapping adjusted offsets to offset slots */
+
+ /* offset slots [0, 29] */
+ u8 offset_slot_tab_1[32768];
+
+ /* offset slots [30, 49] */
+ u8 offset_slot_tab_2[128];
+
+ union {
+ /* Data for greedy or lazy parsing */
+ struct {
+ /* Hash chains matchfinder (MUST BE LAST!!!) */
+ union {
+ struct hc_matchfinder_16 hc_mf_16;
+ struct hc_matchfinder_32 hc_mf_32;
+ };
+ };
- /* 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;
-
- /* Dummy lengths that are always 0. */
- struct lzx_lens zero_lens;
+ /* 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];
- /* Matches/literals that were chosen for the current block. */
- struct lzx_item chosen_items[LZX_DIV_BLOCK_SIZE];
+ /* The cost model for the current block */
+ struct lzx_costs costs;
- /* Table mapping match offset => offset slot for small offsets */
-#define LZX_NUM_FAST_OFFSETS 32768
- u8 offset_slot_fast[LZX_NUM_FAST_OFFSETS];
+ /*
+ * 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.
+ *
+ * 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];
+
+ /* Binary trees matchfinder (MUST BE LAST!!!) */
+ union {
+ struct bt_matchfinder_16 bt_mf_16;
+ struct bt_matchfinder_32 bt_mf_32;
+ };
+ };
+ };
};
+/*
+ * Will a matchfinder using 16-bit positions be sufficient for compressing
+ * buffers of up to the specified size? The limit could be 65536 bytes, but we
+ * also want to optimize out the use of offset_slot_tab_2 in the 16-bit case.
+ * This requires that the limit be no more than the length of offset_slot_tab_1
+ * (currently 32768).
+ */
+static inline bool
+lzx_is_16_bit(size_t max_bufsize)
+{
+ STATIC_ASSERT(ARRAY_LEN(((struct lzx_compressor *)0)->offset_slot_tab_1) == 32768);
+ return max_bufsize <= 32768;
+}
+
+/*
+ * The following macros call either the 16-bit or the 32-bit version of a
+ * matchfinder function based on the value of 'is_16_bit', which will be known
+ * at compilation time.
+ */
+
+#define CALL_HC_MF(is_16_bit, c, funcname, ...) \
+ ((is_16_bit) ? CONCAT(funcname, _16)(&(c)->hc_mf_16, ##__VA_ARGS__) : \
+ CONCAT(funcname, _32)(&(c)->hc_mf_32, ##__VA_ARGS__));
+
+#define CALL_BT_MF(is_16_bit, c, funcname, ...) \
+ ((is_16_bit) ? CONCAT(funcname, _16)(&(c)->bt_mf_16, ##__VA_ARGS__) : \
+ CONCAT(funcname, _32)(&(c)->bt_mf_32, ##__VA_ARGS__));
+
/*
* Structure to keep track of the current state of sending bits to the
* compressed output buffer.
struct lzx_output_bitstream {
/* Bits that haven't yet been written to the output buffer. */
- u32 bitbuf;
+ machine_word_t bitbuf;
/* Number of bits currently held in @bitbuf. */
u32 bitcount;
/* Pointer to the start of the output buffer. */
- le16 *start;
+ u8 *start;
/* Pointer to the position in the output buffer at which the next coding
* unit should be written. */
- le16 *next;
+ u8 *next;
- /* Pointer past the end of the output buffer. */
- le16 *end;
+ /* Pointer just past the end of the output buffer, rounded down to a
+ * 2-byte boundary. */
+ u8 *end;
};
+/* Can the specified number of bits always be added to 'bitbuf' after any
+ * pending 16-bit coding units have been flushed? */
+#define CAN_BUFFER(n) ((n) <= (8 * sizeof(machine_word_t)) - 15)
+
/*
* Initialize the output bitstream.
*
* 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;
os->start = buffer;
os->next = os->start;
- os->end = os->start + size / sizeof(le16);
+ os->end = os->start + (size & ~1);
}
-/*
- * Write some bits to the output bitstream.
- *
- * The bits are given by the low-order @num_bits bits of @bits. Higher-order
- * bits in @bits cannot be set. At most 17 bits can be written at once.
- *
- * @max_num_bits is a compile-time constant that specifies the maximum number of
- * bits that can ever be written at the call site. Currently, it is used to
- * optimize away the conditional code for writing a second 16-bit coding unit
- * when writing fewer than 17 bits.
- *
- * If the output buffer space is exhausted, then the bits will be ignored, and
- * lzx_flush_output() will return 0 when it gets called.
- */
+/* Add some bits to the bitbuffer variable of the output bitstream. The caller
+ * must make sure there is enough room. */
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)
+lzx_add_bits(struct lzx_output_bitstream *os, u32 bits, unsigned num_bits)
{
- /* This code is optimized for LZX, which never needs to write more than
- * 17 bits at once. */
- LZX_ASSERT(num_bits <= 17);
- LZX_ASSERT(num_bits <= max_num_bits);
- LZX_ASSERT(os->bitcount <= 15);
-
- /* Add the bits to the bit buffer variable. @bitcount will be at most
- * 15, so there will be just enough space for the maximum possible
- * @num_bits of 17. */
- os->bitcount += num_bits;
os->bitbuf = (os->bitbuf << num_bits) | bits;
+ os->bitcount += num_bits;
+}
- /* Check whether any coding units need to be written. */
- if (os->bitcount >= 16) {
-
- os->bitcount -= 16;
-
- /* Write a coding unit, unless it would overflow the buffer. */
- if (os->next != os->end)
- put_unaligned_u16_le(os->bitbuf >> os->bitcount, os->next++);
+/* Flush bits from the bitbuffer variable to the output buffer. 'max_num_bits'
+ * specifies the maximum number of bits that may have been added since the last
+ * flush. */
+static inline void
+lzx_flush_bits(struct lzx_output_bitstream *os, unsigned max_num_bits)
+{
+ /* Masking the number of bits to shift is only needed to avoid undefined
+ * behavior; we don't actually care about the results of bad shifts. On
+ * x86, the explicit masking generates no extra code. */
+ const u32 shift_mask = 8 * sizeof(os->bitbuf) - 1;
- /* If writing 17 bits, a second coding unit might need to be
- * written. But because 'max_num_bits' is a compile-time
- * constant, the compiler will optimize away this code at most
- * call sites. */
- if (max_num_bits == 17 && os->bitcount == 16) {
- if (os->next != os->end)
- put_unaligned_u16_le(os->bitbuf, os->next++);
- os->bitcount = 0;
- }
- }
+ if (os->end - os->next < 6)
+ return;
+ put_unaligned_u16_le(os->bitbuf >> ((os->bitcount - 16) &
+ shift_mask), os->next + 0);
+ if (max_num_bits > 16)
+ put_unaligned_u16_le(os->bitbuf >> ((os->bitcount - 32) &
+ shift_mask), os->next + 2);
+ if (max_num_bits > 32)
+ put_unaligned_u16_le(os->bitbuf >> ((os->bitcount - 48) &
+ shift_mask), os->next + 4);
+ os->next += (os->bitcount >> 4) << 1;
+ os->bitcount &= 15;
}
-/* Use when @num_bits is a compile-time constant. Otherwise use
- * lzx_write_varbits(). */
+/* Add at most 16 bits to the bitbuffer and flush it. */
static inline void
-lzx_write_bits(struct lzx_output_bitstream *os,
- const u32 bits, const unsigned int num_bits)
+lzx_write_bits(struct lzx_output_bitstream *os, u32 bits, unsigned num_bits)
{
- lzx_write_varbits(os, bits, num_bits, num_bits);
+ lzx_add_bits(os, bits, num_bits);
+ lzx_flush_bits(os, 16);
}
/*
static u32
lzx_flush_output(struct lzx_output_bitstream *os)
{
- if (os->next == os->end)
+ if (os->end - os->next < 6)
return 0;
- if (os->bitcount != 0)
- put_unaligned_u16_le(os->bitbuf << (16 - os->bitcount), os->next++);
+ if (os->bitcount != 0) {
+ put_unaligned_u16_le(os->bitbuf << (16 - os->bitcount), os->next);
+ os->next += 2;
+ }
- return (const u8 *)os->next - (const u8 *)os->start;
+ return os->next - os->start;
}
/* Build the main, length, and aligned offset Huffman codes used in LZX.
* This takes as input the frequency tables for each code and produces as output
* a set of tables that map symbols to codewords and codeword lengths. */
static void
-lzx_make_huffman_codes(const struct lzx_freqs *freqs, struct lzx_codes *codes,
- unsigned num_main_syms)
+lzx_make_huffman_codes(struct lzx_compressor *c)
{
- make_canonical_huffman_code(num_main_syms,
- LZX_MAX_MAIN_CODEWORD_LEN,
+ const struct lzx_freqs *freqs = &c->freqs;
+ struct lzx_codes *codes = &c->codes[c->codes_index];
+
+ STATIC_ASSERT(MAIN_CODEWORD_LIMIT >= 9 &&
+ MAIN_CODEWORD_LIMIT <= LZX_MAX_MAIN_CODEWORD_LEN);
+ STATIC_ASSERT(LENGTH_CODEWORD_LIMIT >= 8 &&
+ LENGTH_CODEWORD_LIMIT <= LZX_MAX_LEN_CODEWORD_LEN);
+ STATIC_ASSERT(ALIGNED_CODEWORD_LIMIT >= LZX_NUM_ALIGNED_OFFSET_BITS &&
+ ALIGNED_CODEWORD_LIMIT <= LZX_MAX_ALIGNED_CODEWORD_LEN);
+
+ make_canonical_huffman_code(c->num_main_syms,
+ MAIN_CODEWORD_LIMIT,
freqs->main,
codes->lens.main,
codes->codewords.main);
make_canonical_huffman_code(LZX_LENCODE_NUM_SYMBOLS,
- LZX_MAX_LEN_CODEWORD_LEN,
+ LENGTH_CODEWORD_LIMIT,
freqs->len,
codes->lens.len,
codes->codewords.len);
make_canonical_huffman_code(LZX_ALIGNEDCODE_NUM_SYMBOLS,
- LZX_MAX_ALIGNED_CODEWORD_LEN,
+ ALIGNED_CODEWORD_LIMIT,
freqs->aligned,
codes->lens.aligned,
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],
- const unsigned num_lens,
u32 precode_freqs[restrict],
unsigned precode_items[restrict])
{
itemptr = precode_items;
run_start = 0;
- do {
- /* Find the next run of codeword lengths. */
+
+ while (!((len = lens[run_start]) & 0x80)) {
/* len = the length being repeated */
- len = lens[run_start];
+
+ /* Find the next run of codeword lengths. */
run_end = run_start + 1;
/* Fast case for a single length. */
- if (likely(run_end == num_lens || len != lens[run_end])) {
+ if (likely(len != lens[run_end])) {
delta = prev_lens[run_start] - len;
if (delta < 0)
delta += 17;
/* Extend the run. */
do {
run_end++;
- } while (run_end != num_lens && len == lens[run_end]);
+ } while (len == lens[run_end]);
if (len == 0) {
/* Run of zeroes. */
*itemptr++ = delta;
run_start++;
}
- } while (run_start != num_lens);
+ }
return itemptr - precode_items;
}
unsigned precode_item;
unsigned precode_sym;
unsigned i;
+ u8 saved = lens[num_lens];
+ *(u8 *)(lens + num_lens) = 0x80;
for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++)
precode_freqs[i] = 0;
* the codeword lengths in the larger code will be output. */
num_precode_items = lzx_compute_precode_items(lens,
prev_lens,
- num_lens,
precode_freqs,
precode_items);
/* Build the precode. */
+ STATIC_ASSERT(PRE_CODEWORD_LIMIT >= 5 &&
+ PRE_CODEWORD_LIMIT <= LZX_MAX_PRE_CODEWORD_LEN);
make_canonical_huffman_code(LZX_PRECODE_NUM_SYMBOLS,
- LZX_MAX_PRE_CODEWORD_LEN,
+ PRE_CODEWORD_LIMIT,
precode_freqs, precode_lens,
precode_codewords);
for (i = 0; i < num_precode_items; i++) {
precode_item = precode_items[i];
precode_sym = precode_item & 0x1F;
- lzx_write_varbits(os, precode_codewords[precode_sym],
- precode_lens[precode_sym],
- LZX_MAX_PRE_CODEWORD_LEN);
+ lzx_add_bits(os, precode_codewords[precode_sym],
+ precode_lens[precode_sym]);
if (precode_sym >= 17) {
if (precode_sym == 17) {
- lzx_write_bits(os, precode_item >> 5, 4);
+ lzx_add_bits(os, precode_item >> 5, 4);
} else if (precode_sym == 18) {
- lzx_write_bits(os, precode_item >> 5, 5);
+ lzx_add_bits(os, precode_item >> 5, 5);
} else {
- lzx_write_bits(os, (precode_item >> 5) & 1, 1);
+ lzx_add_bits(os, (precode_item >> 5) & 1, 1);
precode_sym = precode_item >> 6;
- lzx_write_varbits(os, precode_codewords[precode_sym],
- precode_lens[precode_sym],
- LZX_MAX_PRE_CODEWORD_LEN);
+ lzx_add_bits(os, precode_codewords[precode_sym],
+ precode_lens[precode_sym]);
}
}
+ STATIC_ASSERT(CAN_BUFFER(2 * PRE_CODEWORD_LIMIT + 1));
+ lzx_flush_bits(os, 2 * PRE_CODEWORD_LIMIT + 1);
}
-}
-
-/* Output a match or literal. */
-static inline void
-lzx_write_item(struct lzx_output_bitstream *os, struct lzx_item item,
- unsigned ones_if_aligned, const struct lzx_codes *codes)
-{
- u64 data = item.data;
- unsigned main_symbol;
- unsigned len_symbol;
- unsigned num_extra_bits;
- u32 extra_bits;
-
- main_symbol = data & 0x3FF;
-
- lzx_write_varbits(os, codes->codewords.main[main_symbol],
- codes->lens.main[main_symbol],
- LZX_MAX_MAIN_CODEWORD_LEN);
-
- if (main_symbol < LZX_NUM_CHARS) /* Literal? */
- return;
-
- len_symbol = (data >> 10) & 0xFF;
-
- if (len_symbol != LZX_LENCODE_NUM_SYMBOLS) {
- lzx_write_varbits(os, codes->codewords.len[len_symbol],
- codes->lens.len[len_symbol],
- LZX_MAX_LEN_CODEWORD_LEN);
- }
-
- num_extra_bits = (data >> 18) & 0x1F;
- if (num_extra_bits == 0) /* Small offset or repeat offset match? */
- return;
-
- extra_bits = data >> 23;
-
- /*if (block_type == LZX_BLOCKTYPE_ALIGNED && num_extra_bits >= 3) {*/
- if ((num_extra_bits & ones_if_aligned) >= 3) {
- /* 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, codes->codewords.aligned[extra_bits & 7],
- codes->lens.aligned[extra_bits & 7],
- LZX_MAX_ALIGNED_CODEWORD_LEN);
- } else {
- /* Verbatim blocks, or fewer than 3 extra bits: All extra
- * offset bits are output literally. */
- lzx_write_varbits(os, extra_bits, num_extra_bits, 17);
- }
+ *(u8 *)(lens + num_lens) = saved;
}
/*
* @block_type
* The chosen type of the LZX compressed block (LZX_BLOCKTYPE_ALIGNED or
* LZX_BLOCKTYPE_VERBATIM).
- * @items
- * The array of matches/literals to output.
- * @num_items
- * Number of matches/literals to output (length of @items).
+ * @block_data
+ * The uncompressed data of the block.
+ * @sequences
+ * The matches and literals to output, given as a series of sequences.
* @codes
* The main, length, and aligned offset Huffman codes for the current
* LZX compressed block.
*/
static void
-lzx_write_items(struct lzx_output_bitstream *os, int block_type,
- const struct lzx_item items[], u32 num_items,
- const struct lzx_codes *codes)
+lzx_write_sequences(struct lzx_output_bitstream *os, int block_type,
+ const u8 *block_data, const struct lzx_sequence sequences[],
+ const struct lzx_codes *codes)
{
- unsigned ones_if_aligned = 0U - (block_type == LZX_BLOCKTYPE_ALIGNED);
+ const struct lzx_sequence *seq = sequences;
+ u32 ones_if_aligned = 0 - (block_type == LZX_BLOCKTYPE_ALIGNED);
+
+ for (;;) {
+ /* Output the next sequence. */
+
+ unsigned litrunlen = seq->litrunlen;
+ unsigned match_hdr;
+ unsigned main_symbol;
+ unsigned adjusted_length;
+ u32 adjusted_offset;
+ unsigned offset_slot;
+ unsigned num_extra_bits;
+ u32 extra_bits;
+
+ /* Output the literal run of the sequence. */
+
+ if (litrunlen) { /* Is the literal run nonempty? */
+
+ /* Verify optimization is enabled on 64-bit */
+ STATIC_ASSERT(sizeof(machine_word_t) < 8 ||
+ CAN_BUFFER(4 * MAIN_CODEWORD_LIMIT));
+
+ if (CAN_BUFFER(4 * MAIN_CODEWORD_LIMIT)) {
+
+ /* 64-bit: write 4 literals at a time. */
+ while (litrunlen >= 4) {
+ unsigned lit0 = block_data[0];
+ unsigned lit1 = block_data[1];
+ unsigned lit2 = block_data[2];
+ unsigned lit3 = block_data[3];
+ lzx_add_bits(os, codes->codewords.main[lit0],
+ codes->lens.main[lit0]);
+ lzx_add_bits(os, codes->codewords.main[lit1],
+ codes->lens.main[lit1]);
+ lzx_add_bits(os, codes->codewords.main[lit2],
+ codes->lens.main[lit2]);
+ lzx_add_bits(os, codes->codewords.main[lit3],
+ codes->lens.main[lit3]);
+ lzx_flush_bits(os, 4 * MAIN_CODEWORD_LIMIT);
+ block_data += 4;
+ litrunlen -= 4;
+ }
+ if (litrunlen--) {
+ unsigned lit = *block_data++;
+ lzx_add_bits(os, codes->codewords.main[lit],
+ codes->lens.main[lit]);
+ if (litrunlen--) {
+ unsigned lit = *block_data++;
+ lzx_add_bits(os, codes->codewords.main[lit],
+ codes->lens.main[lit]);
+ if (litrunlen--) {
+ unsigned lit = *block_data++;
+ lzx_add_bits(os, codes->codewords.main[lit],
+ codes->lens.main[lit]);
+ lzx_flush_bits(os, 3 * MAIN_CODEWORD_LIMIT);
+ } else {
+ lzx_flush_bits(os, 2 * MAIN_CODEWORD_LIMIT);
+ }
+ } else {
+ lzx_flush_bits(os, 1 * MAIN_CODEWORD_LIMIT);
+ }
+ }
+ } else {
+ /* 32-bit: write 1 literal at a time. */
+ do {
+ unsigned lit = *block_data++;
+ lzx_add_bits(os, codes->codewords.main[lit],
+ codes->lens.main[lit]);
+ lzx_flush_bits(os, MAIN_CODEWORD_LIMIT);
+ } while (--litrunlen);
+ }
+ }
+
+ /* Was this the last literal run? */
+ if (seq->adjusted_offset_and_match_hdr & 0x80000000)
+ return;
+
+ /* Nope; output the match. */
+
+ match_hdr = seq->adjusted_offset_and_match_hdr & 0x1FF;
+ main_symbol = LZX_NUM_CHARS + match_hdr;
+ adjusted_length = seq->adjusted_length;
+
+ block_data += adjusted_length + LZX_MIN_MATCH_LEN;
+
+ offset_slot = match_hdr / LZX_NUM_LEN_HEADERS;
+ adjusted_offset = seq->adjusted_offset_and_match_hdr >> 9;
+
+ num_extra_bits = lzx_extra_offset_bits[offset_slot];
+ extra_bits = adjusted_offset - lzx_offset_slot_base[offset_slot];
+
+ #define MAX_MATCH_BITS (MAIN_CODEWORD_LIMIT + LENGTH_CODEWORD_LIMIT + \
+ 14 + ALIGNED_CODEWORD_LIMIT)
+
+ /* Verify optimization is enabled on 64-bit */
+ STATIC_ASSERT(sizeof(machine_word_t) < 8 || CAN_BUFFER(MAX_MATCH_BITS));
+
+ /* Output the main symbol for the match. */
+
+ lzx_add_bits(os, codes->codewords.main[main_symbol],
+ codes->lens.main[main_symbol]);
+ if (!CAN_BUFFER(MAX_MATCH_BITS))
+ lzx_flush_bits(os, MAIN_CODEWORD_LIMIT);
+
+ /* If needed, output the length symbol for the match. */
- for (u32 i = 0; i < num_items; i++)
- lzx_write_item(os, items[i], ones_if_aligned, codes);
+ if (adjusted_length >= LZX_NUM_PRIMARY_LENS) {
+ lzx_add_bits(os, codes->codewords.len[adjusted_length -
+ LZX_NUM_PRIMARY_LENS],
+ codes->lens.len[adjusted_length -
+ LZX_NUM_PRIMARY_LENS]);
+ if (!CAN_BUFFER(MAX_MATCH_BITS))
+ lzx_flush_bits(os, LENGTH_CODEWORD_LIMIT);
+ }
+
+ /* Output the extra offset bits for the match. In aligned
+ * offset blocks, the lowest 3 bits of the adjusted offset are
+ * Huffman-encoded using the aligned offset code, provided that
+ * there are at least extra 3 offset bits required. All other
+ * extra offset bits are output verbatim. */
+
+ if ((adjusted_offset & ones_if_aligned) >= 16) {
+
+ lzx_add_bits(os, extra_bits >> LZX_NUM_ALIGNED_OFFSET_BITS,
+ num_extra_bits - LZX_NUM_ALIGNED_OFFSET_BITS);
+ if (!CAN_BUFFER(MAX_MATCH_BITS))
+ lzx_flush_bits(os, 14);
+
+ lzx_add_bits(os, codes->codewords.aligned[adjusted_offset &
+ LZX_ALIGNED_OFFSET_BITMASK],
+ codes->lens.aligned[adjusted_offset &
+ LZX_ALIGNED_OFFSET_BITMASK]);
+ if (!CAN_BUFFER(MAX_MATCH_BITS))
+ lzx_flush_bits(os, ALIGNED_CODEWORD_LIMIT);
+ } else {
+ STATIC_ASSERT(CAN_BUFFER(17));
+
+ lzx_add_bits(os, extra_bits, num_extra_bits);
+ if (!CAN_BUFFER(MAX_MATCH_BITS))
+ lzx_flush_bits(os, 17);
+ }
+
+ if (CAN_BUFFER(MAX_MATCH_BITS))
+ lzx_flush_bits(os, MAX_MATCH_BITS);
+
+ /* Advance to the next sequence. */
+ seq++;
+ }
}
-/* Write an LZX aligned offset or verbatim block to the output bitstream. */
static void
-lzx_write_compressed_block(int block_type,
+lzx_write_compressed_block(const u8 *block_begin,
+ int block_type,
u32 block_size,
unsigned window_order,
unsigned num_main_syms,
- struct lzx_item * chosen_items,
- u32 num_chosen_items,
+ const struct lzx_sequence sequences[],
const struct lzx_codes * codes,
const struct lzx_lens * prev_lens,
struct lzx_output_bitstream * os)
{
- LZX_ASSERT(block_type == LZX_BLOCKTYPE_ALIGNED ||
- block_type == LZX_BLOCKTYPE_VERBATIM);
-
/* The first three bits indicate the type of block and are one of the
* LZX_BLOCKTYPE_* constants. */
lzx_write_bits(os, block_type, 3);
LZX_LENCODE_NUM_SYMBOLS);
/* Output the compressed matches and literals. */
- lzx_write_items(os, block_type, chosen_items, num_chosen_items, codes);
+ lzx_write_sequences(os, block_type, block_begin, sequences, 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)
+/* 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)
{
- if (c->match_window_end < c->cur_window_size && num_matches != 0) {
- u32 limit = c->match_window_end - c->match_window_pos;
+ u32 aligned_cost = 0;
+ u32 verbatim_cost = 0;
- if (limit >= LZX_MIN_MATCH_LEN) {
+ /* 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];
+ }
- unsigned i = num_matches - 1;
- do {
- if (matches[i].len >= limit) {
- matches[i].len = limit;
+ /* Account for output of the aligned offset code. */
+ aligned_cost += LZX_ALIGNEDCODE_ELEMENT_SIZE * LZX_ALIGNEDCODE_NUM_SYMBOLS;
- /* 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;
+ if (aligned_cost < verbatim_cost)
+ return LZX_BLOCKTYPE_ALIGNED;
+ else
+ return LZX_BLOCKTYPE_VERBATIM;
}
-static unsigned
-lzx_get_matches_fillcache_singleblock(struct lzx_compressor *c,
- const struct lz_match **matches_ret)
+/*
+ * Return the offset slot for the specified adjusted match offset, using the
+ * compressor's acceleration tables to speed up the mapping.
+ */
+static inline unsigned
+lzx_comp_get_offset_slot(struct lzx_compressor *c, u32 adjusted_offset,
+ bool is_16_bit)
{
- 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;
+ if (is_16_bit || adjusted_offset < ARRAY_LEN(c->offset_slot_tab_1))
+ return c->offset_slot_tab_1[adjusted_offset];
+ return c->offset_slot_tab_2[adjusted_offset >> 14];
}
-static unsigned
-lzx_get_matches_fillcache_multiblock(struct lzx_compressor *c,
- const struct lz_match **matches_ret)
+/*
+ * Finish an LZX block:
+ *
+ * - 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 void
+lzx_finish_block(struct lzx_compressor *c, struct lzx_output_bitstream *os,
+ const u8 *block_begin, u32 block_size, u32 seq_idx)
{
- 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;
-}
+ int block_type;
-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;
- }
- c->match_window_pos++;
- *matches_ret = matches;
- return num_matches;
+ lzx_make_huffman_codes(c);
+
+ block_type = lzx_choose_verbatim_or_aligned(&c->freqs,
+ &c->codes[c->codes_index]);
+ lzx_write_compressed_block(block_begin,
+ block_type,
+ block_size,
+ c->window_order,
+ c->num_main_syms,
+ &c->chosen_sequences[seq_idx],
+ &c->codes[c->codes_index],
+ &c->codes[c->codes_index ^ 1].lens,
+ os);
+ c->codes_index ^= 1;
}
-static unsigned
-lzx_get_matches_usecache_nocheck(struct lzx_compressor *c,
- const struct lz_match **matches_ret)
+/* Tally the Huffman symbol for a literal and increment the literal run length.
+ */
+static inline void
+lzx_record_literal(struct lzx_compressor *c, unsigned literal, u32 *litrunlen_p)
{
- 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;
+ c->freqs.main[literal]++;
+ ++*litrunlen_p;
}
-static unsigned
-lzx_get_matches_nocache_singleblock(struct lzx_compressor *c,
- const struct lz_match **matches_ret)
+/* Tally the Huffman symbol for a match, save the match data and the length of
+ * the preceding literal run in the next lzx_sequence, and update the recent
+ * offsets queue. */
+static inline void
+lzx_record_match(struct lzx_compressor *c, unsigned length, u32 offset_data,
+ u32 recent_offsets[LZX_NUM_RECENT_OFFSETS], bool is_16_bit,
+ u32 *litrunlen_p, struct lzx_sequence **next_seq_p)
{
- 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;
+ u32 litrunlen = *litrunlen_p;
+ struct lzx_sequence *next_seq = *next_seq_p;
+ unsigned offset_slot;
+ unsigned v;
+
+ v = length - LZX_MIN_MATCH_LEN;
+
+ /* Save the literal run length and adjusted length. */
+ next_seq->litrunlen = litrunlen;
+ next_seq->adjusted_length = v;
+
+ /* Compute the length header and tally the length symbol if needed */
+ if (v >= LZX_NUM_PRIMARY_LENS) {
+ c->freqs.len[v - LZX_NUM_PRIMARY_LENS]++;
+ v = LZX_NUM_PRIMARY_LENS;
+ }
+
+ /* Compute the offset slot */
+ offset_slot = lzx_comp_get_offset_slot(c, offset_data, is_16_bit);
+
+ /* Compute the match header. */
+ v += offset_slot * LZX_NUM_LEN_HEADERS;
+
+ /* Save the adjusted offset and match header. */
+ next_seq->adjusted_offset_and_match_hdr = (offset_data << 9) | v;
+
+ /* Tally the main symbol. */
+ c->freqs.main[LZX_NUM_CHARS + v]++;
+
+ /* Update the recent offsets queue. */
+ if (offset_data < LZX_NUM_RECENT_OFFSETS) {
+ /* Repeat offset match */
+ swap(recent_offsets[0], recent_offsets[offset_data]);
+ } else {
+ /* Explicit offset match */
+
+ /* Tally the aligned offset symbol if needed */
+ if (offset_data >= 16)
+ c->freqs.aligned[offset_data & LZX_ALIGNED_OFFSET_BITMASK]++;
+
+ recent_offsets[2] = recent_offsets[1];
+ recent_offsets[1] = recent_offsets[0];
+ recent_offsets[0] = offset_data - LZX_OFFSET_ADJUSTMENT;
+ }
+
+ /* Reset the literal run length and advance to the next sequence. */
+ *next_seq_p = next_seq + 1;
+ *litrunlen_p = 0;
}
-static unsigned
-lzx_get_matches_nocache_multiblock(struct lzx_compressor *c,
- const struct lz_match **matches_ret)
+/* Finish the last lzx_sequence. The last lzx_sequence is just a literal run;
+ * there is no match. This literal run may be empty. */
+static inline void
+lzx_finish_sequence(struct lzx_sequence *last_seq, u32 litrunlen)
{
- 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;
+ last_seq->litrunlen = litrunlen;
+
+ /* Special value to mark last sequence */
+ last_seq->adjusted_offset_and_match_hdr = 0x80000000;
}
/*
- * Find matches at the next position in the window.
- *
- * This uses a wrapper function around the underlying match-finder.
+ * Given the minimum-cost path computed through the item graph for the current
+ * block, walk the path and count how many of each symbol in each Huffman-coded
+ * alphabet would be required to output the items (matches and literals) along
+ * the path.
*
- * 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.
+ * Note that the path will be walked backwards (from the end of the block to the
+ * beginning of the block), but this doesn't matter because this function only
+ * computes frequencies.
*/
-static inline unsigned
-lzx_get_matches(struct lzx_compressor *c, const struct lz_match **matches_ret)
+static inline void
+lzx_tally_item_list(struct lzx_compressor *c, u32 block_size, bool is_16_bit)
{
- return (*c->get_matches_func)(c, matches_ret);
-}
+ u32 node_idx = block_size;
+ for (;;) {
+ u32 len;
+ u32 offset_data;
+ unsigned v;
+ unsigned offset_slot;
-static void
-lzx_skip_bytes_fillcache(struct lzx_compressor *c, unsigned n)
-{
- struct lz_match *cache_ptr;
+ /* Tally literals until either a match or the beginning of the
+ * block is reached. */
+ for (;;) {
+ u32 item = c->optimum_nodes[node_idx].item;
- 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;
-}
+ len = item & OPTIMUM_LEN_MASK;
+ offset_data = item >> OPTIMUM_OFFSET_SHIFT;
-static void
-lzx_skip_bytes_usecache(struct lzx_compressor *c, unsigned n)
-{
- struct lz_match *cache_ptr;
+ if (len != 0) /* Not a literal? */
+ break;
- 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;
-}
+ /* Tally the main symbol for the literal. */
+ c->freqs.main[offset_data]++;
-static void
-lzx_skip_bytes_usecache_nocheck(struct lzx_compressor *c, unsigned n)
-{
- struct lz_match *cache_ptr;
+ if (--node_idx == 0) /* Beginning of block was reached? */
+ return;
+ }
- cache_ptr = c->cache_ptr;
- c->match_window_pos += n;
- do {
- cache_ptr += 1 + cache_ptr->len;
- } while (--n);
- c->cache_ptr = cache_ptr;
-}
+ node_idx -= len;
-static void
-lzx_skip_bytes_nocache(struct lzx_compressor *c, unsigned n)
-{
- c->match_window_pos += n;
- lz_mf_skip_positions(c->mf, n);
+ /* Tally a match. */
+
+ /* Tally the aligned offset symbol if needed. */
+ if (offset_data >= 16)
+ c->freqs.aligned[offset_data & LZX_ALIGNED_OFFSET_BITMASK]++;
+
+ /* Tally the length symbol if needed. */
+ v = len - LZX_MIN_MATCH_LEN;;
+ if (v >= LZX_NUM_PRIMARY_LENS) {
+ c->freqs.len[v - LZX_NUM_PRIMARY_LENS]++;
+ v = LZX_NUM_PRIMARY_LENS;
+ }
+
+ /* Tally the main symbol. */
+ offset_slot = lzx_comp_get_offset_slot(c, offset_data, is_16_bit);
+ v += offset_slot * LZX_NUM_LEN_HEADERS;
+ c->freqs.main[LZX_NUM_CHARS + v]++;
+
+ if (node_idx == 0) /* Beginning of block was reached? */
+ return;
+ }
}
/*
- * 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.
+ * Like lzx_tally_item_list(), but this function also generates the list of
+ * lzx_sequences for the minimum-cost path and writes it to c->chosen_sequences,
+ * ready to be output to the bitstream after the Huffman codes are computed.
+ * The lzx_sequences will be written to decreasing memory addresses as the path
+ * is walked backwards, which means they will end up in the expected
+ * first-to-last order. The return value is the index in c->chosen_sequences at
+ * which the lzx_sequences begin.
*/
-static inline void
-lzx_skip_bytes(struct lzx_compressor *c, unsigned n)
+static inline u32
+lzx_record_item_list(struct lzx_compressor *c, u32 block_size, bool is_16_bit)
{
- return (*c->skip_bytes_func)(c, n);
-}
+ u32 node_idx = block_size;
+ u32 seq_idx = ARRAY_LEN(c->chosen_sequences) - 1;
+ u32 lit_start_node;
-/* Tally, and optionally record, the specified literal byte. */
-static inline void
-lzx_declare_literal(struct lzx_compressor *c, unsigned literal,
- struct lzx_item **next_chosen_item)
-{
- unsigned main_symbol = literal;
+ /* Special value to mark last sequence */
+ c->chosen_sequences[seq_idx].adjusted_offset_and_match_hdr = 0x80000000;
- c->freqs.main[main_symbol]++;
+ lit_start_node = node_idx;
+ for (;;) {
+ u32 len;
+ u32 offset_data;
+ unsigned v;
+ unsigned offset_slot;
- if (next_chosen_item) {
- *(*next_chosen_item)++ = (struct lzx_item) {
- .data = main_symbol,
- };
- }
-}
+ /* Record literals until either a match or the beginning of the
+ * block is reached. */
+ for (;;) {
+ u32 item = c->optimum_nodes[node_idx].item;
-/* Tally, and optionally record, the specified repeat offset match. */
-static inline void
-lzx_declare_repeat_offset_match(struct lzx_compressor *c,
- unsigned len, unsigned rep_index,
- struct lzx_item **next_chosen_item)
-{
- unsigned len_header;
- unsigned main_symbol;
- unsigned len_symbol;
+ len = item & OPTIMUM_LEN_MASK;
+ offset_data = item >> OPTIMUM_OFFSET_SHIFT;
- if (len - LZX_MIN_MATCH_LEN < LZX_NUM_PRIMARY_LENS) {
- len_header = len - LZX_MIN_MATCH_LEN;
- len_symbol = LZX_LENCODE_NUM_SYMBOLS;
- } else {
- len_header = LZX_NUM_PRIMARY_LENS;
- len_symbol = len - LZX_MIN_MATCH_LEN - LZX_NUM_PRIMARY_LENS;
- c->freqs.len[len_symbol]++;
- }
+ if (len != 0) /* Not a literal? */
+ break;
- main_symbol = LZX_NUM_CHARS + ((rep_index << 3) | len_header);
+ /* Tally the main symbol for the literal. */
+ c->freqs.main[offset_data]++;
- c->freqs.main[main_symbol]++;
+ if (--node_idx == 0) /* Beginning of block was reached? */
+ goto out;
+ }
- if (next_chosen_item) {
- *(*next_chosen_item)++ = (struct lzx_item) {
- .data = (u64)main_symbol | ((u64)len_symbol << 10),
- };
+ /* Save the literal run length for the next sequence (the
+ * "previous sequence" when walking backwards). */
+ c->chosen_sequences[seq_idx--].litrunlen = lit_start_node - node_idx;
+ node_idx -= len;
+ lit_start_node = node_idx;
+
+ /* Record a match. */
+
+ /* Tally the aligned offset symbol if needed. */
+ if (offset_data >= 16)
+ c->freqs.aligned[offset_data & LZX_ALIGNED_OFFSET_BITMASK]++;
+
+ /* Save the adjusted length. */
+ v = len - LZX_MIN_MATCH_LEN;
+ c->chosen_sequences[seq_idx].adjusted_length = v;
+
+ /* Tally the length symbol if needed. */
+ if (v >= LZX_NUM_PRIMARY_LENS) {
+ c->freqs.len[v - LZX_NUM_PRIMARY_LENS]++;
+ v = LZX_NUM_PRIMARY_LENS;
+ }
+
+ /* Tally the main symbol. */
+ offset_slot = lzx_comp_get_offset_slot(c, offset_data, is_16_bit);
+ v += offset_slot * LZX_NUM_LEN_HEADERS;
+ c->freqs.main[LZX_NUM_CHARS + v]++;
+
+ /* Save the adjusted offset and match header. */
+ c->chosen_sequences[seq_idx].adjusted_offset_and_match_hdr =
+ (offset_data << 9) | v;
+
+ if (node_idx == 0) /* Beginning of block was reached? */
+ goto out;
}
+
+out:
+ /* Save the literal run length for the first sequence. */
+ c->chosen_sequences[seq_idx].litrunlen = lit_start_node - node_idx;
+
+ /* Return the index in c->chosen_sequences at which the lzx_sequences
+ * begin. */
+ return seq_idx;
}
-/* Tally, and optionally record, the specified explicit offset match. */
-static inline void
-lzx_declare_explicit_offset_match(struct lzx_compressor *c, unsigned len, u32 offset,
- struct lzx_item **next_chosen_item)
+/*
+ * 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 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 inline 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,
+ bool is_16_bit)
{
- unsigned len_header;
- unsigned main_symbol;
- unsigned len_symbol;
- unsigned offset_slot;
- unsigned num_extra_bits;
- u32 extra_bits;
+ 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];
+
+ STATIC_ASSERT(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;
- if (len - LZX_MIN_MATCH_LEN < LZX_NUM_PRIMARY_LENS) {
- len_header = len - LZX_MIN_MATCH_LEN;
- len_symbol = LZX_LENCODE_NUM_SYMBOLS;
- } else {
- len_header = LZX_NUM_PRIMARY_LENS;
- len_symbol = len - LZX_MIN_MATCH_LEN - LZX_NUM_PRIMARY_LENS;
- c->freqs.len[len_symbol]++;
- }
+ /*
+ * 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.
+ */
- offset_slot = lzx_get_offset_slot_raw(offset + LZX_OFFSET_OFFSET);
+ num_matches = cache_ptr->length;
+ cache_ptr++;
- main_symbol = LZX_NUM_CHARS + ((offset_slot << 3) | len_header);
+ 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;
+ STATIC_ASSERT(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]);
- c->freqs.main[main_symbol]++;
+ R2_done:
- if (offset_slot >= 8)
- c->freqs.aligned[(offset + LZX_OFFSET_OFFSET) & 7]++;
+ while (next_len > cache_ptr->length)
+ if (++cache_ptr == end_matches)
+ goto done_matches;
- if (next_chosen_item) {
+ /* Consider explicit offset matches */
+ do {
+ u32 offset = cache_ptr->offset;
+ u32 offset_data = offset + LZX_OFFSET_ADJUSTMENT;
+ unsigned offset_slot = lzx_comp_get_offset_slot(c, offset_data,
+ is_16_bit);
+ u32 base_cost = cur_node->cost;
+
+ #if LZX_CONSIDER_ALIGNED_COSTS
+ if (offset_data >= 16)
+ base_cost += c->costs.aligned[offset_data &
+ LZX_ALIGNED_OFFSET_BITMASK];
+ #endif
- num_extra_bits = lzx_extra_offset_bits[offset_slot];
+ do {
+ u32 cost = base_cost +
+ c->costs.match_cost[offset_slot][
+ next_len - LZX_MIN_MATCH_LEN];
+ 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);
+ }
- extra_bits = (offset + LZX_OFFSET_OFFSET) -
- lzx_offset_slot_base[offset_slot];
+ done_matches:
- *(*next_chosen_item)++ = (struct lzx_item) {
- .data = (u64)main_symbol |
- ((u64)len_symbol << 10) |
- ((u64)num_extra_bits << 18) |
- ((u64)extra_bits << 23),
- };
- }
-}
+ /* Consider coding a literal.
-/* Tally, and optionally record, the specified match or literal. */
-static inline void
-lzx_declare_item(struct lzx_compressor *c, u32 mc_item_data,
- struct lzx_item **next_chosen_item)
-{
- u32 len = mc_item_data & MC_LEN_MASK;
- u32 offset_data = mc_item_data >> MC_OFFSET_SHIFT;
-
- if (len == 1)
- lzx_declare_literal(c, offset_data, next_chosen_item);
- else if (offset_data < LZX_NUM_RECENT_OFFSETS)
- lzx_declare_repeat_offset_match(c, len, offset_data,
- next_chosen_item);
- else
- lzx_declare_explicit_offset_match(c, len,
- offset_data - LZX_OFFSET_OFFSET,
- next_chosen_item);
-}
+ * 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[literal];
-static inline void
-lzx_record_item_list(struct lzx_compressor *c,
- struct lzx_mc_pos_data *cur_optimum_ptr,
- struct lzx_item **next_chosen_item)
-{
- struct lzx_mc_pos_data *end_optimum_ptr;
- u32 saved_item;
- u32 item;
+ /* Advance to the next position. */
+ cur_node++;
- /* 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;
- 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);
-
- /* 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);
-}
+ /* The lowest-cost path to the current position is now known.
+ * Finalize the recent offsets queue that results from taking
+ * this lowest-cost path. */
-static inline void
-lzx_tally_item_list(struct lzx_compressor *c, struct lzx_mc_pos_data *cur_optimum_ptr)
-{
- /* 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);
-}
+ if (cost <= cur_node->cost) {
+ /* Literal: queue remains unchanged. */
+ cur_node->cost = cost;
+ cur_node->item = (u32)literal << OPTIMUM_OFFSET_SHIFT;
+ 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);
-/* 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);
+ /* Return the match offset queue at the end of the minimum cost path. */
+ return QUEUE(block_end);
}
-/* Set the cost model @c->costs from the Huffman codeword lengths specified in
- * @lens.
- *
- * The cost model and codeword lengths are almost the same thing, but the
- * Huffman codewords with length 0 correspond to symbols with zero frequency
- * that still need to be assigned actual costs. The specific values assigned
- * are arbitrary, but they should be fairly high (near the maximum codeword
- * length) to take into account the fact that uses of these symbols are expected
- * to be rare. */
+/* Given the costs for the main and length codewords, compute 'match_costs'. */
static void
-lzx_set_costs(struct lzx_compressor *c, const struct lzx_lens * lens)
+lzx_compute_match_costs(struct lzx_compressor *c)
{
- unsigned i;
+ unsigned num_offset_slots = (c->num_main_syms - LZX_NUM_CHARS) /
+ LZX_NUM_LEN_HEADERS;
+ struct lzx_costs *costs = &c->costs;
- /* Main code */
- for (i = 0; i < c->num_main_syms; i++)
- c->costs.main[i] = lens->main[i] ? lens->main[i] : 15;
+ for (unsigned offset_slot = 0; offset_slot < num_offset_slots; offset_slot++) {
- /* Length code */
- for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++)
- c->costs.len[i] = lens->len[i] ? lens->len[i] : 15;
+ u32 extra_cost = (u32)lzx_extra_offset_bits[offset_slot] * LZX_BIT_COST;
+ unsigned main_symbol = LZX_NUM_CHARS + (offset_slot *
+ LZX_NUM_LEN_HEADERS);
+ unsigned i;
- /* Aligned offset code */
- for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
- c->costs.aligned[i] = lens->aligned[i] ? lens->aligned[i] : 7;
+ #if LZX_CONSIDER_ALIGNED_COSTS
+ if (offset_slot >= 8)
+ extra_cost -= LZX_NUM_ALIGNED_OFFSET_BITS * LZX_BIT_COST;
+ #endif
+
+ for (i = 0; i < LZX_NUM_PRIMARY_LENS; i++)
+ costs->match_cost[offset_slot][i] =
+ costs->main[main_symbol++] + extra_cost;
+
+ extra_cost += costs->main[main_symbol];
+
+ for (; i < LZX_NUM_LENS; i++)
+ costs->match_cost[offset_slot][i] =
+ costs->len[i - LZX_NUM_PRIMARY_LENS] + extra_cost;
+ }
}
/* 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)
+lzx_set_default_costs(struct lzx_compressor *c, const u8 *block, u32 block_size)
{
- unsigned i;
+ u32 i;
+ bool have_byte[256];
+ unsigned num_used_bytes;
- /* Main code (part 1): Literal symbols */
- for (i = 0; i < LZX_NUM_CHARS; i++)
- costs->main[i] = 8;
+ /* The costs below are hard coded to use a scaling factor of 16. */
+ STATIC_ASSERT(LZX_BIT_COST == 16);
- /* Main code (part 2): Match header symbols */
- for (; i < num_main_syms; i++)
- costs->main[i] = 10;
+ /*
+ * 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.
+ */
+
+ for (i = 0; i < 256; i++)
+ have_byte[i] = false;
+
+ for (i = 0; i < block_size; i++)
+ have_byte[block[i]] = true;
+
+ num_used_bytes = 0;
+ for (i = 0; i < 256; i++)
+ num_used_bytes += have_byte[i];
+
+ for (i = 0; i < 256; i++)
+ c->costs.main[i] = 140 - (256 - num_used_bytes) / 4;
+
+ for (; i < c->num_main_syms; i++)
+ c->costs.main[i] = 170;
- /* Length code */
for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++)
- costs->len[i] = 8;
+ c->costs.len[i] = 103 + (i / 4);
- /* Aligned offset code */
+#if LZX_CONSIDER_ALIGNED_COSTS
for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
- costs->aligned[i] = 3;
-}
+ c->costs.aligned[i] = LZX_NUM_ALIGNED_OFFSET_BITS * LZX_BIT_COST;
+#endif
-/* 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];
+ lzx_compute_match_costs(c);
}
-/* 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)
+/* Update the current cost model to reflect the computed Huffman codes. */
+static void
+lzx_update_costs(struct lzx_compressor *c)
{
- u32 cost;
- unsigned len_header;
- unsigned main_symbol;
+ unsigned i;
+ const struct lzx_lens *lens = &c->codes[c->codes_index].lens;
- 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;
+ for (i = 0; i < c->num_main_syms; i++) {
+ c->costs.main[i] = (lens->main[i] ? lens->main[i] :
+ MAIN_CODEWORD_LIMIT) * LZX_BIT_COST;
+ }
- /* Account for length symbol. */
- cost = costs->len[len - LZX_MIN_MATCH_LEN - LZX_NUM_PRIMARY_LENS];
+ for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++) {
+ c->costs.len[i] = (lens->len[i] ? lens->len[i] :
+ LENGTH_CODEWORD_LIMIT) * LZX_BIT_COST;
}
- /* Account for main symbol. */
- main_symbol = LZX_NUM_CHARS + ((offset_slot << 3) | len_header);
- cost += costs->main[main_symbol];
+#if LZX_CONSIDER_ALIGNED_COSTS
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
+ c->costs.aligned[i] = (lens->aligned[i] ? lens->aligned[i] :
+ ALIGNED_CODEWORD_LIMIT) * LZX_BIT_COST;
+ }
+#endif
- return cost;
+ lzx_compute_match_costs(c);
}
-/* 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)
+static inline struct lzx_lru_queue
+lzx_optimize_and_write_block(struct lzx_compressor * const restrict c,
+ struct lzx_output_bitstream * const restrict os,
+ const u8 * const restrict block_begin,
+ const u32 block_size,
+ const struct lzx_lru_queue initial_queue,
+ bool is_16_bit)
{
- 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_passes_remaining = c->num_optim_passes;
+ struct lzx_lru_queue new_queue;
+ u32 seq_idx;
-/*
- * 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;
-
-#if 1 /* Optimized version */
-
- 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);
-
- /* 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);
- }
-
-#else /* Unoptimized version */
+ /* 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. */
- len = 2;
+ lzx_set_default_costs(c, block_begin, block_size);
+ lzx_reset_symbol_frequencies(c);
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;
+ new_queue = lzx_find_min_cost_path(c, block_begin, block_size,
+ initial_queue, is_16_bit);
+ if (num_passes_remaining > 1) {
+ lzx_tally_item_list(c, block_size, is_16_bit);
+ lzx_make_huffman_codes(c);
+ lzx_update_costs(c);
+ lzx_reset_symbol_frequencies(c);
}
- } while (++len <= rep_len);
-#endif
+ } while (--num_passes_remaining);
+
+ seq_idx = lzx_record_item_list(c, block_size, is_16_bit);
+ lzx_finish_block(c, os, block_begin, block_size, seq_idx);
+ return new_queue;
}
/*
- * Consider coding each match in @matches as an explicit offset match.
+ * This is the "near-optimal" LZX compressor.
*
- * @matches must be sorted by strictly increasing length and strictly
- * increasing offset. This is guaranteed by the match-finder.
+ * For each block, it performs a relatively thorough graph search to find an
+ * inexpensive (in terms of compressed size) way to output that block.
*
- * 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.
+ * 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 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)
+lzx_compress_near_optimal(struct lzx_compressor *c,
+ struct lzx_output_bitstream *os,
+ bool is_16_bit)
{
- LZX_ASSERT(num_matches > 0);
-
- unsigned i;
- unsigned len;
- unsigned offset_slot;
- u32 position_cost;
- u32 cost;
- u32 offset_data;
-
-
-#if 1 /* Optimized version */
+ const u8 * const in_begin = c->in_buffer;
+ const u8 * in_next = in_begin;
+ const u8 * const in_end = in_begin + c->in_nbytes;
+ u32 max_len = LZX_MAX_MATCH_LEN;
+ u32 nice_len = min(c->nice_match_length, max_len);
+ u32 next_hashes[2] = {};
+ struct lzx_lru_queue queue;
- if (matches[num_matches - 1].offset < LZX_NUM_FAST_OFFSETS) {
+ CALL_BT_MF(is_16_bit, c, bt_matchfinder_init);
+ lzx_lru_queue_init(&queue);
- /*
- * 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.
- */
-
- LZX_ASSERT(offset_slot <= 37); /* for extra bits formula */
+ 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);
- len = 2;
- i = 0;
+ /* Run the block through the matchfinder and cache the matches. */
+ struct lz_match *cache_ptr = c->match_cache;
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;
+ struct lz_match *lz_matchptr;
+ u32 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);
+ if (unlikely(max_len <
+ BT_MATCHFINDER_REQUIRED_NBYTES))
+ {
+ in_next++;
+ cache_ptr->length = 0;
+ cache_ptr++;
+ continue;
}
- } while (++len <= matches[i].len);
- } while (++i != num_matches);
+ }
- return;
+ /* Check for matches. */
+ lz_matchptr = CALL_BT_MF(is_16_bit, c,
+ bt_matchfinder_get_matches,
+ in_begin,
+ in_next - in_begin,
+ max_len,
+ nice_len,
+ c->max_search_depth,
+ next_hashes,
+ &best_len,
+ cache_ptr + 1);
+ in_next++;
+ cache_ptr->length = lz_matchptr - (cache_ptr + 1);
+ cache_ptr = lz_matchptr;
- 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 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 <
+ BT_MATCHFINDER_REQUIRED_NBYTES))
+ {
+ in_next++;
+ cache_ptr->length = 0;
+ cache_ptr++;
+ continue;
+ }
+ }
+ CALL_BT_MF(is_16_bit, c,
+ bt_matchfinder_skip_position,
+ in_begin,
+ in_next - in_begin,
+ max_len,
+ nice_len,
+ c->max_search_depth,
+ next_hashes);
+ 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]));
-#else /* Unoptimized version */
+ /* We've finished running the block through the matchfinder.
+ * Now choose a match/literal sequence and write the block. */
- unsigned num_extra_bits;
+ queue = lzx_optimize_and_write_block(c, os, in_block_begin,
+ in_next - in_block_begin,
+ queue, is_16_bit);
+ } while (in_next != in_end);
+}
- 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);
-#endif
+static void
+lzx_compress_near_optimal_16(struct lzx_compressor *c,
+ struct lzx_output_bitstream *os)
+{
+ lzx_compress_near_optimal(c, os, true);
}
-/*
- * 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 void
+lzx_compress_near_optimal_32(struct lzx_compressor *c,
+ struct lzx_output_bitstream *os)
{
- 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);
+ lzx_compress_near_optimal(c, os, false);
}
/*
- * The main near-optimal parsing routine.
- *
- * 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.
+ * Given a pointer to the current byte sequence and the current list of recent
+ * match offsets, find the longest repeat offset match.
*
- * 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].
+ * If no match of at least 2 bytes is found, then return 0.
*
- * 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).
- */
-static void
-lzx_optim_pass(struct lzx_compressor *c, struct lzx_item **next_chosen_item)
+ * 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,
+ const u32 recent_offsets[LZX_NUM_RECENT_OFFSETS],
+ unsigned *rep_max_idx_ret)
{
- 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;
+ STATIC_ASSERT(LZX_NUM_RECENT_OFFSETS == 3);
+
+ 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 literal;
- unsigned len;
- u32 cost;
- u32 offset_data;
+ unsigned rep_len;
- 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;
-
- /* The following loop runs once for each per byte in the window, except
- * in a couple shortcut cases. */
- for (;;) {
-
- /* Find explicit offset matches with the current position. */
- num_matches = lzx_get_matches(c, &matches);
-
- 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;
- }
-
- /* 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;
- }
-
- /* 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;
-
- /* 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;
- }
- continue;
- }
- #endif
- (++end_optimum_ptr)->cost = MC_INFINITE_COST;
- }
- }
-
- /* Consider coding a literal.
-
- * 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);
-
- /* Advance to the next position. */
- cur_optimum_ptr++;
-
- /* The lowest-cost path to the current position is now known.
- * Finalize the recent offsets queue that results from taking
- * this lowest-cost path. */
-
- 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 - recent_offsets[0];
+ 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 - recent_offsets[1];
+ 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 - recent_offsets[2];
+ 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 inline void
+lzx_compress_lazy(struct lzx_compressor *c, struct lzx_output_bitstream *os,
+ bool is_16_bit)
{
- 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) {
-
- /* Find explicit offset matches with the current position. */
- num_matches = lz_mf_get_matches(mf, matches);
- window_ptr++;
-
- 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. */
-
- no_match_found:
-
- if (prev_len) {
- skip_len = prev_len - 2;
- goto output_prev_match;
- } else {
- lzx_declare_literal(c, *(window_ptr - 1),
- &next_chosen_item);
+ 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);
+ STATIC_ASSERT(LZX_NUM_RECENT_OFFSETS == 3);
+ u32 recent_offsets[3] = {1, 1, 1};
+ u32 next_hashes[2] = {};
+
+ CALL_HC_MF(is_16_bit, c, hc_matchfinder_init);
+
+ 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_sequence *next_seq = c->chosen_sequences;
+ 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;
+ u32 litrunlen = 0;
+
+ lzx_reset_symbol_frequencies(c);
+
+ do {
+ if (unlikely(max_len > in_end - in_next)) {
+ max_len = in_end - in_next;
+ nice_len = min(max_len, nice_len);
+ }
+
+ /* Find the longest match at the current position. */
+
+ cur_len = CALL_HC_MF(is_16_bit, c,
+ hc_matchfinder_longest_match,
+ in_begin,
+ in_next - in_begin,
+ 2,
+ max_len,
+ nice_len,
+ c->max_search_depth,
+ next_hashes,
+ &cur_offset);
+ if (cur_len < 3 ||
+ (cur_len == 3 &&
+ cur_offset >= 8192 - LZX_OFFSET_ADJUSTMENT &&
+ cur_offset != recent_offsets[0] &&
+ cur_offset != recent_offsets[1] &&
+ cur_offset != recent_offsets[2]))
+ {
+ /* There was no match found, or the only match found
+ * was a distant length 3 match. Output a literal. */
+ lzx_record_literal(c, *in_next++, &litrunlen);
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;
- }
+ if (cur_offset == recent_offsets[0]) {
+ in_next++;
+ cur_offset_data = 0;
+ skip_len = cur_len - 1;
+ goto choose_cur_match;
+ }
- 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;
- }
+ 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,
+ recent_offsets,
+ &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;
+ }
- 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;
- }
+ have_cur_match:
- 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. */
+ /* We have a match at the current position. */
- if (prev_len)
- lzx_declare_literal(c, *(window_ptr - 2), &next_chosen_item);
+ /* If we have a very long match, choose it immediately. */
+ if (cur_len >= nice_len) {
+ skip_len = cur_len - 1;
+ goto choose_cur_match;
+ }
- prev_len = cur_len;
- prev_offset_data = cur_offset_data;
- prev_score = cur_score;
+ /* See if there's a better match at the next position. */
- if (prev_len >= c->params.nice_match_length) {
- skip_len = prev_len - 1;
- goto output_prev_match;
+ if (unlikely(max_len > in_end - in_next)) {
+ max_len = in_end - in_next;
+ nice_len = min(max_len, nice_len);
}
- continue;
- }
- /* Current match is not better than the previous match, so
- * output the previous match. */
+ next_len = CALL_HC_MF(is_16_bit, c,
+ hc_matchfinder_longest_match,
+ in_begin,
+ in_next - in_begin,
+ cur_len - 2,
+ max_len,
+ nice_len,
+ c->max_search_depth / 2,
+ next_hashes,
+ &next_offset);
+
+ if (next_len <= cur_len - 2) {
+ in_next++;
+ skip_len = cur_len - 2;
+ goto choose_cur_match;
+ }
- skip_len = prev_len - 2;
+ 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,
+ recent_offsets,
+ &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_record_literal(c, *(in_next - 2),
+ &litrunlen);
+ 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_record_literal(c, *(in_next - 2),
+ &litrunlen);
+ cur_len = next_len;
+ cur_offset_data = next_offset_data;
+ cur_score = next_score;
+ goto have_cur_match;
+ }
+ }
- 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;
- }
+ /* The original match was better. */
+ skip_len = cur_len - 2;
+
+ choose_cur_match:
+ lzx_record_match(c, cur_len, cur_offset_data,
+ recent_offsets, is_16_bit,
+ &litrunlen, &next_seq);
+ in_next = CALL_HC_MF(is_16_bit, c,
+ hc_matchfinder_skip_positions,
+ in_begin,
+ in_next - in_begin,
+ in_end - in_begin,
+ skip_len,
+ next_hashes);
+ } while (in_next < in_block_end);
- return next_chosen_item - c->chosen_items;
+ lzx_finish_sequence(next_seq, litrunlen);
+
+ lzx_finish_block(c, os, in_block_begin, in_next - in_block_begin, 0);
+
+ } while (in_next != in_end);
}
-/* 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)
+static void
+lzx_compress_lazy_16(struct lzx_compressor *c, struct lzx_output_bitstream *os)
{
- u32 aligned_cost = 0;
- u32 verbatim_cost = 0;
+ lzx_compress_lazy(c, os, true);
+}
- /* 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];
- }
+static void
+lzx_compress_lazy_32(struct lzx_compressor *c, struct lzx_output_bitstream *os)
+{
+ lzx_compress_lazy(c, os, false);
+}
- /* Account for output of the aligned offset code. */
- aligned_cost += LZX_ALIGNEDCODE_ELEMENT_SIZE * LZX_ALIGNEDCODE_NUM_SYMBOLS;
+/* Generate the acceleration tables for offset slots. */
+static void
+lzx_init_offset_slot_tabs(struct lzx_compressor *c)
+{
+ u32 adjusted_offset = 0;
+ unsigned slot = 0;
+
+ /* slots [0, 29] */
+ for (; adjusted_offset < ARRAY_LEN(c->offset_slot_tab_1);
+ adjusted_offset++)
+ {
+ if (adjusted_offset >= lzx_offset_slot_base[slot + 1])
+ slot++;
+ c->offset_slot_tab_1[adjusted_offset] = slot;
+ }
- if (aligned_cost < verbatim_cost)
- return LZX_BLOCKTYPE_ALIGNED;
- else
- return LZX_BLOCKTYPE_VERBATIM;
+ /* slots [30, 49] */
+ for (; adjusted_offset < LZX_MAX_WINDOW_SIZE;
+ adjusted_offset += (u32)1 << 14)
+ {
+ if (adjusted_offset >= lzx_offset_slot_base[slot + 1])
+ slot++;
+ c->offset_slot_tab_2[adjusted_offset >> 14] = slot;
+ }
}
-/* Near-optimal parsing */
-static u32
-lzx_choose_near_optimal_items_for_block(struct lzx_compressor *c,
- u32 block_start_pos, u32 block_size)
+static size_t
+lzx_get_compressor_size(size_t max_bufsize, unsigned compression_level)
{
- 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;
+ if (compression_level <= LZX_MAX_FAST_LEVEL) {
+ if (lzx_is_16_bit(max_bufsize))
+ return offsetof(struct lzx_compressor, hc_mf_16) +
+ hc_matchfinder_size_16(max_bufsize);
else
- c->get_matches_func = lzx_get_matches_fillcache_multiblock;
- c->skip_bytes_func = lzx_skip_bytes_fillcache;
+ return offsetof(struct lzx_compressor, hc_mf_32) +
+ hc_matchfinder_size_32(max_bufsize);
} else {
- if (block_size == c->cur_window_size)
- c->get_matches_func = lzx_get_matches_nocache_singleblock;
+ if (lzx_is_16_bit(max_bufsize))
+ return offsetof(struct lzx_compressor, bt_mf_16) +
+ bt_matchfinder_size_16(max_bufsize);
else
- c->get_matches_func = lzx_get_matches_nocache_multiblock;
- c->skip_bytes_func = lzx_skip_bytes_nocache;
+ return offsetof(struct lzx_compressor, bt_mf_32) +
+ bt_matchfinder_size_32(max_bufsize);
}
+}
- /* No matches will extend beyond the end of the block. */
- c->match_window_end = block_start_pos + block_size;
-
- /* 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);
-
- 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 (num_passes_remaining > 1) {
- /* This isn't the last pass. */
-
- /* Make the Huffman codes from the symbol frequencies. */
- lzx_make_huffman_codes(&c->freqs, &c->codes[c->codes_index],
- c->num_main_syms);
-
- /* Update symbol costs. */
- lzx_set_costs(c, &c->codes[c->codes_index].lens);
-
- /* Reset symbol frequencies. */
- memset(&c->freqs, 0, sizeof(c->freqs));
-
- /* Reset the match offset LRU queue to what it was at
- * the beginning of the block. */
- c->queue = orig_queue;
+static u64
+lzx_get_needed_memory(size_t max_bufsize, unsigned compression_level,
+ bool destructive)
+{
+ u64 size = 0;
- /* 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;
- } else {
- c->get_matches_func = lzx_get_matches_usecache;
- c->skip_bytes_func = lzx_skip_bytes_usecache;
- }
- }
- } while (--num_passes_remaining);
+ if (max_bufsize > LZX_MAX_WINDOW_SIZE)
+ return 0;
- /* Return the number of items chosen. */
- return next_chosen_item - c->chosen_items;
+ size += lzx_get_compressor_size(max_bufsize, compression_level);
+ if (!destructive)
+ size += max_bufsize; /* in_buffer */
+ return size;
}
-/*
- * 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)
+static int
+lzx_create_compressor(size_t max_bufsize, unsigned compression_level,
+ bool destructive, void **c_ret)
{
- return (*c->params.choose_items_for_block)(c, block_start_pos, block_size);
-}
+ unsigned window_order;
+ struct lzx_compressor *c;
-/* Initialize c->offset_slot_fast. */
-static void
-lzx_init_offset_slot_fast(struct lzx_compressor *c)
-{
- u8 slot = 0;
+ window_order = lzx_get_window_order(max_bufsize);
+ if (window_order == 0)
+ return WIMLIB_ERR_INVALID_PARAM;
- for (u32 offset = 0; offset < LZX_NUM_FAST_OFFSETS; offset++) {
+ c = MALLOC(lzx_get_compressor_size(max_bufsize, compression_level));
+ if (!c)
+ goto oom0;
- while (offset + LZX_OFFSET_OFFSET >= lzx_offset_slot_base[slot + 1])
- slot++;
+ c->destructive = destructive;
+
+ c->num_main_syms = lzx_get_num_main_syms(window_order);
+ c->window_order = window_order;
- c->offset_slot_fast[offset] = slot;
+ if (!c->destructive) {
+ c->in_buffer = MALLOC(max_bufsize);
+ if (!c->in_buffer)
+ goto oom1;
}
-}
-/* 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)
-{
- if (compression_level < 25) {
+ if (compression_level <= LZX_MAX_FAST_LEVEL) {
/* 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;
+ if (lzx_is_16_bit(max_bufsize))
+ c->impl = lzx_compress_lazy_16;
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;
+ c->impl = lzx_compress_lazy_32;
+ c->max_search_depth = (60 * compression_level) / 20;
+ c->nice_match_length = (80 * compression_level) / 20;
+
+ /* lzx_compress_lazy() needs max_search_depth >= 2 because it
+ * halves the max_search_depth when attempting a lazy match, and
+ * max_search_depth cannot be 0. */
+ if (c->max_search_depth < 2)
+ c->max_search_depth = 2;
} else {
/* Normal / high compression: Use near-optimal parsing. */
- lzx_params->choose_items_for_block = lzx_choose_near_optimal_items_for_block;
+ if (lzx_is_16_bit(max_bufsize))
+ c->impl = lzx_compress_near_optimal_16;
+ else
+ c->impl = lzx_compress_near_optimal_32;
+
+ /* Scale nice_match_length and max_search_depth with the
+ * compression level. */
+ c->max_search_depth = (24 * compression_level) / 50;
+ c->nice_match_length = (48 * compression_level) / 50;
/* Set a number of optimization passes appropriate for the
* compression level. */
- lzx_params->num_optim_passes = 1;
+ c->num_optim_passes = 1;
- if (compression_level >= 40)
- lzx_params->num_optim_passes++;
+ 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) {
- lzx_params->num_optim_passes++;
+ c->num_optim_passes++;
if (compression_level >= 100)
- lzx_params->num_optim_passes++;
+ c->num_optim_passes++;
if (compression_level >= 150)
- lzx_params->num_optim_passes++;
+ c->num_optim_passes++;
if (compression_level >= 200)
- lzx_params->num_optim_passes++;
+ c->num_optim_passes++;
if (compression_level >= 300)
- lzx_params->num_optim_passes++;
+ c->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);
}
-}
-
-/* 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)
-{
- 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)
- 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);
- return size;
-}
-
-static int
-lzx_create_compressor(size_t max_block_size, unsigned int compression_level,
- void **c_ret)
-{
- struct lzx_compressor *c;
- struct lzx_compressor_params params;
- struct lz_mf_params mf_params;
- unsigned window_order;
- u32 max_window_size;
- window_order = lzx_get_window_order(max_block_size);
- if (window_order == 0)
- return WIMLIB_ERR_INVALID_PARAM;
- max_window_size = max_block_size;
-
- lzx_build_params(compression_level, max_window_size, ¶ms);
- lzx_build_mf_params(¶ms, max_window_size, &mf_params);
- if (!lz_mf_params_valid(&mf_params))
- return WIMLIB_ERR_INVALID_PARAM;
+ /* max_search_depth == 0 is invalid. */
+ if (c->max_search_depth < 1)
+ c->max_search_depth = 1;
- c = CALLOC(1, sizeof(struct lzx_compressor));
- if (!c)
- goto oom;
-
- c->params = params;
- c->num_main_syms = lzx_get_num_main_syms(window_order);
- c->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);
- } else {
- c->cached_matches = MALLOC(LZX_MAX_MATCHES_PER_POS *
- sizeof(struct lz_match));
- if (!c->cached_matches)
- goto oom;
- }
-
- lzx_init_offset_slot_fast(c);
+ if (c->nice_match_length > LZX_MAX_MATCH_LEN)
+ c->nice_match_length = LZX_MAX_MATCH_LEN;
+ lzx_init_offset_slot_tabs(c);
*c_ret = c;
return 0;
-oom:
- lzx_free_compressor(c);
+oom1:
+ 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 *restrict in, size_t in_nbytes,
+ void *restrict out, size_t out_nbytes_avail, void *restrict _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;
+ size_t result;
- /* 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. */
+ if (c->destructive)
+ c->in_buffer = (void *)in;
+ else
+ memcpy(c->in_buffer, in, in_nbytes);
+ c->in_nbytes = in_nbytes;
+ lzx_preprocess(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);
+ /* Initialize the output bitstream. */
+ lzx_init_output(&os, out, out_nbytes_avail);
- /* Make the Huffman codes from the symbol frequencies. */
- lzx_make_huffman_codes(&c->freqs, &c->codes[c->codes_index],
- c->num_main_syms);
+ /* Call the compression level-specific compress() function. */
+ (*c->impl)(c, &os);
- /* 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;
-
- } while (block_start_pos != uncompressed_size);
-
- return lzx_flush_output(&os);
+ /* Flush the output bitstream and return the compressed size or 0. */
+ result = lzx_flush_output(&os);
+ if (!result && c->destructive)
+ lzx_postprocess(c->in_buffer, c->in_nbytes);
+ return result;
}
static void
{
struct lzx_compressor *c = _c;
- if (c) {
- ALIGNED_FREE(c->cur_window);
- lz_mf_free(c->mf);
- FREE(c->cached_matches);
- FREE(c);
- }
+ if (!c->destructive)
+ FREE(c->in_buffer);
+ FREE(c);
}
const struct compressor_ops lzx_compressor_ops = {
git://wimlib.net / wimlib / blobdiff