* - LZX preprocesses the data before attempting to compress it.
* - LZX uses a "main" alphabet which combines literals and matches, with the
* match symbols containing a "length header" (giving all or part of the match
- * length) and a "position footer" (giving, roughly speaking, the order of
+ * length) and a "position slot" (giving, roughly speaking, the order of
* magnitude of the match offset).
* - LZX does not have static Huffman blocks; however it does have two types of
* dynamic Huffman blocks ("aligned offset" and "verbatim").
* - LZX has a minimum match length of 2 rather than 3.
- * - In LZX, match offsets 0 through 2 actually represent entries in a LRU queue
- * of match offsets.
+ * - In LZX, match offsets 0 through 2 actually represent entries in an LRU
+ * queue of match offsets.
*
* Algorithms
* ==========
* 1. Preprocess the input data to translate the targets of x86 call instructions
* to absolute offsets.
*
- * 2. Determine the best known sequence of LZ77 matches ((offset, length) pairs)
- * and literal bytes to divide the input into. Raw match-finding is done
- * using a very clever binary tree search based on the "Bt3" algorithm from
- * 7-Zip. Parsing, or match-choosing, is solved essentially as a
- * minimum-cost path problem, but using a heuristic forward search based on
- * the Deflate encoder from 7-Zip rather than a more intuitive backward
- * search, the latter of which would naively require that all matches be
- * found. This heuristic search, as well as other heuristics such as limits
- * on the matches considered, considerably speed up this part of the
- * algorithm, which is the main bottleneck. Finally, after matches and
- * literals are chosen, the needed Huffman codes needed to output them are
- * built.
- *
- * 3. Up to a certain number of iterations, use the resulting Huffman codes to
- * refine a cost model and go back to Step #2 to determine an improved
- * sequence of matches and literals.
+ * 2. Build the suffix array and inverse suffix array for the input data.
+ *
+ * 3. Build the longest common prefix array corresponding to the suffix array.
+ *
+ * 4. For each suffix rank, find the highest lower suffix rank that has a
+ * lower position, the lowest higher suffix rank that has a lower position,
+ * and the length of the common prefix shared between each. (Position =
+ * index of suffix in original string, rank = index of suffix in suffix
+ * array.) This information is later used to link suffix ranks into a
+ * doubly-linked list for searching the suffix array.
+ *
+ * 5. Set a default cost model for matches/literals.
*
- * 4. Up to a certain depth, try splitting the current block to see if the
- * compression ratio can be improved. This may be the case if parts of the
- * input differ greatly from each other and could benefit from different
- * Huffman codes.
+ * 6. Determine the lowest cost sequence of LZ77 matches ((offset, length) pairs)
+ * and literal bytes to divide the input into. Raw match-finding is done by
+ * searching the suffix array using a linked list to avoid considering any
+ * suffixes that start after the current position. Each run of the
+ * match-finder returns the lowest-cost longest match as well as any shorter
+ * matches that have even lower costs. Each such run also adds the suffix
+ * rank of the current position into the linked list being used to search the
+ * suffix array. Parsing, or match-choosing, is solved as a minimum-cost
+ * path problem using a forward "optimal parsing" algorithm based on the
+ * Deflate encoder from 7-Zip. This algorithm moves forward calculating the
+ * minimum cost to reach each byte until either a very long match is found or
+ * until a position is found at which no matches start or overlap.
*
- * 5. Output the resulting block(s) using the match/literal sequences and the
- * Huffman codes that were computed for each block.
+ * 7. Build the Huffman codes needed to output the matches/literals.
+ *
+ * 8. Up to a certain number of iterations, use the resulting Huffman codes to
+ * refine a cost model and go back to Step #6 to determine an improved
+ * sequence of matches and literals.
+ *
+ * 9. Output the resulting block using the match/literal sequences and the
+ * Huffman codes that were computed for the block.
*
* Fast algorithm
* --------------
* Acknowledgments
* ===============
*
- * Acknowledgments to several other open-source projects that made it possible
- * to implement this code:
+ * Acknowledgments to several open-source projects and research papers that made
+ * it possible to implement this code:
+ *
+ * - divsufsort (author: Yuta Mori), for the suffix array construction code.
*
- * - 7-Zip (author: Igor Pavlov), for the binary tree match-finding
- * algorithm, the heuristic near-optimal forward match-choosing
- * algorithm, and the block splitting algorithm.
+ * - "Linear-Time Longest-Common-Prefix Computation in Suffix Arrays and Its
+ * Applications" (Kasai et al. 2001), for the LCP array computation.
+ *
+ * - "LPF computation revisited" (Crochemore et al. 2009) for the prev and next
+ * array computations.
+ *
+ * - 7-Zip (author: Igor Pavlov) for the algorithm for forward optimal parsing
+ * (match-choosing).
*
* - zlib (author: Jean-loup Gailly and Mark Adler), for the hash table
* match-finding algorithm.
#include "wimlib/error.h"
#include "wimlib/lzx.h"
#include "wimlib/util.h"
+#include <pthread.h>
+#include <math.h>
+#include <string.h>
#ifdef ENABLE_LZX_DEBUG
# include <wimlib/decompress.h>
#endif
-#include <string.h>
+#include "divsufsort/divsufsort.h"
-/* Experimental parameters not exposed through the API */
-#define LZX_PARAM_OPTIM_ARRAY_SIZE 1024
-#define LZX_PARAM_ACCOUNT_FOR_LRU 1
-#define LZX_PARAM_DONT_SKIP_MATCHES 0
-#define LZX_PARAM_USE_EMPIRICAL_DEFAULT_COSTS 1
+typedef freq_t input_idx_t;
+typedef u32 sym_cost_t;
+typedef u32 block_cost_t;
+#define INFINITE_SYM_COST ((sym_cost_t)~0U)
+#define INFINITE_BLOCK_COST ((block_cost_t)~0U)
+
+#define LZX_OPTIM_ARRAY_SIZE 4096
/* Currently, this constant can't simply be changed because the code currently
* uses a static number of position slots (and may make other assumptions as
/* This may be WIM-specific */
#define LZX_DEFAULT_BLOCK_SIZE 32768
-#define LZX_LZ_HASH_BITS 15
-#define LZX_LZ_HASH_SIZE (1 << LZX_LZ_HASH_BITS)
-#define LZX_LZ_HASH_MASK (LZX_LZ_HASH_SIZE - 1)
-#define LZX_LZ_HASH_SHIFT 5
+#define LZX_MAX_CACHE_PER_POS 10
/* Codewords for the LZX main, length, and aligned offset Huffman codes */
struct lzx_codewords {
- u16 main[LZX_MAINTREE_NUM_SYMBOLS];
- u16 len[LZX_LENTREE_NUM_SYMBOLS];
- u16 aligned[LZX_ALIGNEDTREE_NUM_SYMBOLS];
+ u16 main[LZX_MAINCODE_NUM_SYMBOLS];
+ u16 len[LZX_LENCODE_NUM_SYMBOLS];
+ u16 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
};
-/* Lengths for the LZX main, length, and aligned offset Huffman codes */
+/* Codeword lengths (in bits) for the LZX main, length, and aligned offset
+ * Huffman codes.
+ *
+ * A 0 length means the codeword has zero frequency.
+ */
struct lzx_lens {
- u8 main[LZX_MAINTREE_NUM_SYMBOLS];
- u8 len[LZX_LENTREE_NUM_SYMBOLS];
- u8 aligned[LZX_ALIGNEDTREE_NUM_SYMBOLS];
+ u8 main[LZX_MAINCODE_NUM_SYMBOLS];
+ u8 len[LZX_LENCODE_NUM_SYMBOLS];
+ u8 aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
+};
+
+/* Costs for the LZX main, length, and aligned offset Huffman symbols.
+ *
+ * If a codeword has zero frequency, it must still be assigned some nonzero cost
+ * --- generally a high cost, since even if it gets used in the next iteration,
+ * it probably will not be used very times. */
+struct lzx_costs {
+ sym_cost_t main[LZX_MAINCODE_NUM_SYMBOLS];
+ sym_cost_t len[LZX_LENCODE_NUM_SYMBOLS];
+ sym_cost_t aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
};
/* The LZX main, length, and aligned offset Huffman codes */
/* Tables for tallying symbol frequencies in the three LZX alphabets */
struct lzx_freqs {
- freq_t main[LZX_MAINTREE_NUM_SYMBOLS];
- freq_t len[LZX_LENTREE_NUM_SYMBOLS];
- freq_t aligned[LZX_ALIGNEDTREE_NUM_SYMBOLS];
+ freq_t main[LZX_MAINCODE_NUM_SYMBOLS];
+ freq_t len[LZX_LENCODE_NUM_SYMBOLS];
+ freq_t aligned[LZX_ALIGNEDCODE_NUM_SYMBOLS];
};
/* LZX intermediate match/literal format */
* (since lzx_extra_bits[LZX_NUM_POSITION_SLOTS - 1] is 17).
*
* 0-7 length of match, minus 2. This can be at most
- * (LZX_MAX_MATCH - 2) == 255, so it will fit in 8 bits. */
+ * (LZX_MAX_MATCH_LEN - 2) == 255, so it will fit in 8 bits. */
u32 data;
};
/* Raw LZ match/literal format: just a length and offset.
*
* The length is the number of bytes of the match, and the offset is the number
- * of bytes back in the input the match is from the matched text.
+ * of bytes back in the input the match is from the current position.
*
- * If @len < LZX_MIN_MATCH, then it's really just a literal byte and @offset is
+ * If @len < LZX_MIN_MATCH_LEN, then it's really just a literal byte and @offset is
* meaningless. */
struct raw_match {
u16 len;
- u16 offset;
+ input_idx_t offset;
};
-/* Specification for a LZX block */
+/* Specification for an LZX block. */
struct lzx_block_spec {
- /* Set to 1 if this block has been split (in two --- we only considser
- * binary splits). In such cases the rest of the fields are
- * unimportant, since the relevant information is rather in the
- * structures for the sub-blocks. */
- u8 is_split : 1;
-
/* One of the LZX_BLOCKTYPE_* constants indicating which type of this
* block. */
- u8 block_type : 2;
+ int block_type;
/* 0-based position in the window at which this block starts. */
- u16 window_pos;
+ input_idx_t window_pos;
/* The number of bytes of uncompressed data this block represents. */
- u16 block_size;
+ input_idx_t block_size;
/* The position in the 'chosen_matches' array in the `struct
* lzx_compressor' at which the match/literal specifications for
* this block begin. */
- unsigned chosen_matches_start_pos;
+ input_idx_t chosen_matches_start_pos;
/* The number of match/literal specifications for this block. */
- u16 num_chosen_matches;
+ input_idx_t num_chosen_matches;
/* Huffman codes for this block. */
struct lzx_codes codes;
struct lzx_optimal {
/* The approximate minimum cost, in bits, to reach this position in the
* window which has been found so far. */
- u32 cost;
+ block_cost_t cost;
/* The union here is just for clarity, since the fields are used in two
* slightly different ways. Initially, the @prev structure is filled in
/* Position of the start of the match or literal that
* was taken to get to this position in the approximate
* minimum-cost parse. */
- u16 link;
+ input_idx_t link;
- /* Offset (as in a LZ (length, offset) pair) of the
+ /* Offset (as in an LZ (length, offset) pair) of the
* match or literal that was taken to get to this
* position in the approximate minimum-cost parse. */
- u16 match_offset;
+ input_idx_t match_offset;
} prev;
struct {
/* Position at which the match or literal starting at
* this position ends in the minimum-cost parse. */
- u16 link;
+ input_idx_t link;
- /* Offset (as in a LZ (length, offset) pair) of the
+ /* Offset (as in an LZ (length, offset) pair) of the
* match or literal starting at this position in the
* approximate minimum-cost parse. */
- u16 match_offset;
+ input_idx_t match_offset;
} next;
};
-#if LZX_PARAM_ACCOUNT_FOR_LRU
+
+ /* The match offset LRU queue that will exist when the approximate
+ * minimum-cost path to reach this position is taken. */
struct lzx_lru_queue queue;
-#endif
};
-/* State of the LZX compressor */
+/* Suffix array link */
+struct salink {
+ /* Rank of highest ranked suffix that has rank lower than the suffix
+ * corresponding to this structure and either has a lower position
+ * (initially) or has a position lower than the highest position at
+ * which matches have been searched for so far, or -1 if there is no
+ * such suffix. */
+ input_idx_t prev;
+
+ /* Rank of lowest ranked suffix that has rank greater than the suffix
+ * corresponding to this structure and either has a lower position
+ * (intially) or has a position lower than the highest position at which
+ * matches have been searched for so far, or -1 if there is no such
+ * suffix. */
+ input_idx_t next;
+
+ /* Length of longest common prefix between the suffix corresponding to
+ * this structure and the suffix with rank @prev, or 0 if @prev is -1.
+ */
+ input_idx_t lcpprev;
+
+ /* Length of longest common prefix between the suffix corresponding to
+ * this structure and the suffix with rank @next, or 0 if @next is -1.
+ */
+ input_idx_t lcpnext;
+};
+
+/* State of the LZX compressor. */
struct lzx_compressor {
/* The parameters that were used to create the compressor. */
* 0xe8 byte preprocessing is done directly on the data here before
* further compression.
*
- * Note that this compressor does *not* use a sliding window!!!!
- * It's not needed in the WIM format, since every chunk is compressed
+ * Note that this compressor does *not* use a sliding window!!!! It's
+ * not needed in the WIM format, since every chunk is compressed
* independently. This is by design, to allow random access to the
* chunks.
*
/* Number of bytes of data to be compressed, which is the number of
* bytes of data in @window that are actually valid. */
- unsigned window_size;
+ input_idx_t window_size;
/* The current match offset LRU queue. */
struct lzx_lru_queue queue;
- /* Space for sequence of matches/literals that were chosen.
- *
- * Each LZX_MAX_WINDOW_SIZE-sized portion of this array is used for a
- * different block splitting level. */
+ /* Space for the sequences of matches/literals that were chosen for each
+ * block. */
struct lzx_match *chosen_matches;
- /* Structures used during block splitting.
- *
- * This can be thought of as a binary tree. block_specs[(1) - 1]
- * represents to the top-level block (root node), and block_specs[(i*2)
- * - 1] and block_specs[(i*2+1) - 1] represent the sub-blocks (child
- * nodes) resulting from a binary split of the block represented by
- * block_spec[(i) - 1].
- */
+ struct raw_match *cached_matches;
+ unsigned cached_matches_pos;
+ bool matches_cached;
+
+ /* Information about the LZX blocks the preprocessed input was divided
+ * into. */
struct lzx_block_spec *block_specs;
+ /* Number of LZX blocks the input was divided into; a.k.a. the number of
+ * elements of @block_specs that are valid. */
+ unsigned num_blocks;
+
/* This is simply filled in with zeroes and used to avoid special-casing
* the output of the first compressed Huffman code, which conceptually
* has a delta taken from a code with all symbols having zero-length
struct lzx_codes zero_codes;
/* Slow algorithm only: The current cost model. */
- struct lzx_lens costs;
-
- /* Slow algorithm only: Table that maps the hash codes for 3 character
- * sequences to the most recent position that sequence (or a sequence
- * sharing the same hash code) appeared in the window. */
- u16 *hash_tab;
-
- /* Slow algorithm only: Table that maps 2-character sequences to the
- * most recent position that sequence appeared in the window. */
- u16 *digram_tab;
+ struct lzx_costs costs;
- /* Slow algorithm only: Table that contains the logical child pointers
- * in the binary trees in the match-finding code.
+ /* Slow algorithm only: Suffix array for window.
+ * This is a mapping from suffix rank to suffix position.
*
- * child_tab[i*2] and child_tab[i*2+1] are the left and right pointers,
- * respectively, from the binary tree root corresponding to window
- * position i. */
- u16 *child_tab;
-
- /* Slow algorithm only: Matches that were already found and are saved in
- * memory for subsequent queries (e.g. when block splitting). */
- struct raw_match *cached_matches;
+ * Suffix rank means the index of the suffix in the sorted list of
+ * suffixes, whereas suffix position means the index in the string at
+ * which the suffix starts.
+ */
+ input_idx_t *SA;
- /* Slow algorithm only: Next position in 'cached_matches' to either
- * return or fill in. */
- unsigned cached_matches_pos;
+ /* Slow algorithm only: Inverse suffix array for window.
+ * This is a mapping from suffix position to suffix rank.
+ * In other words, if 0 <= r < window_size, then ISA[SA[r]] == r. */
+ input_idx_t *ISA;
- /* Slow algorithm only: %true if reading from 'cached_matches'; %false
- * if writing to 'cached_matches'. */
- bool matches_already_found;
+ /* Slow algorithm only: Longest Common Prefix array. LCP[i] is the
+ * number of initial bytes that the suffixes at positions SA[i - 1] and
+ * SA[i] share. LCP[0] is undefined. */
+ input_idx_t *LCP;
- /* Slow algorithm only: Position in window of next match to return. */
- unsigned match_window_pos;
+ /* Slow algorithm only: Suffix array links.
+ *
+ * During a linear scan of the input string to find matches, this array
+ * used to keep track of which rank suffixes in the suffix array appear
+ * before the current position. Instead of searching in the original
+ * suffix array, scans for matches at a given position traverse a linked
+ * list containing only suffixes that appear before that position. */
+ struct salink *salink;
+
+ /* Slow algorithm only: Position in window of next match to return.
+ * This cannot simply be modified, as the match-finder must still be
+ * synchronized on the same position. To seek forwards or backwards,
+ * use lzx_lz_skip_bytes() or lzx_lz_rewind_matchfinder(), respectively.
+ */
+ input_idx_t match_window_pos;
- /* Slow algorithm only: No matches returned shall reach past this
- * position. */
- unsigned match_window_end;
+ /* Slow algorithm only: The match-finder shall ensure the length of
+ * matches does not exceed this position in the input. */
+ input_idx_t match_window_end;
/* Slow algorithm only: Temporary space used for match-choosing
* algorithm.
*
- * The size of this array must be at least LZX_MAX_MATCH but otherwise
- * is arbitrary. More space simply allows the match-choosing algorithm
- * to find better matches (depending on the input, as always). */
+ * The size of this array must be at least LZX_MAX_MATCH_LEN but
+ * otherwise is arbitrary. More space simply allows the match-choosing
+ * algorithm to potentially find better matches (depending on the input,
+ * as always). */
struct lzx_optimal *optimum;
/* Slow algorithm only: Variables used by the match-choosing algorithm.
* numbers in the lzx_position_base array to calculate the slot directly from
* the formatted offset without actually looking at the array.
*/
-static unsigned
-lzx_get_position_slot(unsigned formatted_offset)
+static _always_inline_attribute unsigned
+lzx_get_position_slot_raw(unsigned formatted_offset)
{
#if 0
/*
* increases starting at the 655360 entry, and it is >= 2
* because the below calculation fails if the most significant
* bit is lower than the 2's place. */
- LZX_ASSERT(2 <= formatted_offset && formatted_offset < 655360);
+ LZX_ASSERT(2 <= formatted_offset && formatted_offset < 655360);
unsigned mssb_idx = bsr32(formatted_offset);
return (mssb_idx << 1) |
((formatted_offset >> (mssb_idx - 1)) & 1);
}
}
-/* Compute the hash code for the next 3-character sequence in the window. */
-static unsigned
-lzx_lz_compute_hash(const u8 *window)
+
+/* Returns the LZX position slot that corresponds to a given match offset,
+ * taking into account the recent offset queue (and optionally updating it). */
+static _always_inline_attribute unsigned
+lzx_get_position_slot(unsigned offset, struct lzx_lru_queue *queue)
{
- unsigned hash;
-
- hash = window[0];
- hash <<= LZX_LZ_HASH_SHIFT;
- hash ^= window[1];
- hash <<= LZX_LZ_HASH_SHIFT;
- hash ^= window[2];
- return hash & LZX_LZ_HASH_MASK;
+ unsigned position_slot;
+
+ /* See if the offset was recently used. */
+ for (unsigned i = 0; i < LZX_NUM_RECENT_OFFSETS; i++) {
+ if (offset == queue->R[i]) {
+ /* Found it. */
+
+ /* Bring the repeat offset to the front of the
+ * queue. Note: this is, in fact, not a real
+ * LRU queue because repeat matches are simply
+ * swapped to the front. */
+ swap(queue->R[0], queue->R[i]);
+ /* For recent offsets, the position slot is simply the
+ * index of the entry in the queue. */
+
+ return i;
+ }
+ }
+
+ /* The offset was not recently used; look up its real position slot. */
+ position_slot = lzx_get_position_slot_raw(offset + LZX_OFFSET_OFFSET);
+
+ /* Bring the new offset to the front of the queue. */
+ for (unsigned i = LZX_NUM_RECENT_OFFSETS - 1; i > 0; i--)
+ queue->R[i] = queue->R[i - 1];
+ queue->R[0] = offset;
+
+ return position_slot;
}
/* Build the main, length, and aligned offset Huffman codes used in LZX.
*
* This takes as input the frequency tables for each code and produces as output
- * a set of tables that map symbols to codewords and lengths. */
+ * a set of tables that map symbols to codewords and codeword lengths. */
static void
lzx_make_huffman_codes(const struct lzx_freqs *freqs,
struct lzx_codes *codes)
{
- make_canonical_huffman_code(LZX_MAINTREE_NUM_SYMBOLS,
- LZX_MAX_CODEWORD_LEN,
+ make_canonical_huffman_code(LZX_MAINCODE_NUM_SYMBOLS,
+ LZX_MAX_MAIN_CODEWORD_LEN,
freqs->main,
codes->lens.main,
codes->codewords.main);
- make_canonical_huffman_code(LZX_LENTREE_NUM_SYMBOLS,
- LZX_MAX_CODEWORD_LEN,
+ make_canonical_huffman_code(LZX_LENCODE_NUM_SYMBOLS,
+ LZX_MAX_LEN_CODEWORD_LEN,
freqs->len,
codes->lens.len,
codes->codewords.len);
- make_canonical_huffman_code(LZX_ALIGNEDTREE_NUM_SYMBOLS, 8,
+ make_canonical_huffman_code(LZX_ALIGNEDCODE_NUM_SYMBOLS,
+ LZX_MAX_ALIGNED_CODEWORD_LEN,
freqs->aligned,
codes->lens.aligned,
codes->codewords.aligned);
}
/*
- * Output a LZX match.
+ * Output an LZX match.
*
* @out: The bitstream to write the match to.
* @block_type: The type of the LZX block (LZX_BLOCKTYPE_ALIGNED or LZX_BLOCKTYPE_VERBATIM)
unsigned position_slot = (match.data >> 25) & 0x3f; /* 6 bits */
unsigned len_header;
unsigned len_footer;
- unsigned len_pos_header;
unsigned main_symbol;
unsigned num_extra_bits;
unsigned verbatim_bits;
unsigned aligned_bits;
- /* If the match length is less than MIN_MATCH (= 2) +
+ /* If the match length is less than MIN_MATCH_LEN (= 2) +
* NUM_PRIMARY_LENS (= 7), the length header contains
- * the match length minus MIN_MATCH, and there is no
+ * the match length minus MIN_MATCH_LEN, and there is no
* length footer.
*
* Otherwise, the length header contains
* NUM_PRIMARY_LENS, and the length footer contains
* the match length minus NUM_PRIMARY_LENS minus
- * MIN_MATCH. */
+ * MIN_MATCH_LEN. */
if (match_len_minus_2 < LZX_NUM_PRIMARY_LENS) {
len_header = match_len_minus_2;
/* No length footer-- mark it with a special
len_footer = match_len_minus_2 - LZX_NUM_PRIMARY_LENS;
}
- /* Combine the position slot with the length header into
- * a single symbol that will be encoded with the main
- * tree. */
- len_pos_header = (position_slot << 3) | len_header;
-
- /* The actual main symbol is offset by LZX_NUM_CHARS because
- * values under LZX_NUM_CHARS are used to indicate a literal
- * byte rather than a match. */
- main_symbol = len_pos_header + LZX_NUM_CHARS;
+ /* Combine the position slot with the length header into a single symbol
+ * that will be encoded with the main tree.
+ *
+ * The actual main symbol is offset by LZX_NUM_CHARS because values
+ * under LZX_NUM_CHARS are used to indicate a literal byte rather than a
+ * match. */
+ main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS;
/* Output main symbol. */
bitstream_put_bits(out, codes->codewords.main[main_symbol],
static unsigned
lzx_build_precode(const u8 lens[restrict],
const u8 prev_lens[restrict],
- unsigned num_syms,
- freq_t precode_freqs[restrict LZX_PRETREE_NUM_SYMBOLS],
+ const unsigned num_syms,
+ freq_t precode_freqs[restrict LZX_PRECODE_NUM_SYMBOLS],
u8 output_syms[restrict num_syms],
- u8 precode_lens[restrict LZX_PRETREE_NUM_SYMBOLS],
- u16 precode_codewords[restrict LZX_PRETREE_NUM_SYMBOLS],
- unsigned * num_additional_bits_ret)
+ u8 precode_lens[restrict LZX_PRECODE_NUM_SYMBOLS],
+ u16 precode_codewords[restrict LZX_PRECODE_NUM_SYMBOLS],
+ unsigned *num_additional_bits_ret)
{
- unsigned output_syms_idx;
- unsigned cur_run_len;
- unsigned i;
- unsigned len_in_run;
- unsigned additional_bits;
- signed char delta;
- unsigned num_additional_bits = 0;
-
memset(precode_freqs, 0,
- LZX_PRETREE_NUM_SYMBOLS * sizeof(precode_freqs[0]));
+ LZX_PRECODE_NUM_SYMBOLS * sizeof(precode_freqs[0]));
/* Since the code word lengths use a form of RLE encoding, the goal here
* is to find each run of identical lengths when going through them in
* output, including RLE codes, not yet encoded using the pre-tree.
*
* cur_run_len keeps track of how many code word lengths are in the
- * current run of identical lengths.
- */
- output_syms_idx = 0;
- cur_run_len = 1;
- for (i = 1; i <= num_syms; i++) {
+ * current run of identical lengths. */
+ unsigned output_syms_idx = 0;
+ unsigned cur_run_len = 1;
+ unsigned num_additional_bits = 0;
+ for (unsigned i = 1; i <= num_syms; i++) {
if (i != num_syms && lens[i] == lens[i - 1]) {
/* Still in a run--- keep going. */
/* The symbol that was repeated in the run--- not to be confused
* with the length *of* the run (cur_run_len) */
- len_in_run = lens[i - 1];
+ unsigned len_in_run = lens[i - 1];
if (len_in_run == 0) {
/* A run of 0's. Encode it in as few length
* where n is an uncompressed literal 5-bit integer that
* follows the magic length. */
while (cur_run_len >= 20) {
+ unsigned additional_bits;
additional_bits = min(cur_run_len - 20, 0x1f);
num_additional_bits += 5;
* where n is an uncompressed literal 4-bit integer that
* follows the magic length. */
while (cur_run_len >= 4) {
+ unsigned additional_bits;
+
additional_bits = min(cur_run_len - 4, 0xf);
num_additional_bits += 4;
precode_freqs[17]++;
* in the run in the previous tree.
* */
while (cur_run_len >= 4) {
+ unsigned additional_bits;
+ signed char delta;
+
additional_bits = (cur_run_len > 4);
num_additional_bits += 1;
delta = (signed char)prev_lens[i - cur_run_len] -
* as a difference from the length of that codeword in the
* previous tree. */
while (cur_run_len > 0) {
+ signed char delta;
+
delta = (signed char)prev_lens[i - cur_run_len] -
(signed char)len_in_run;
if (delta < 0)
/* Build the precode from the frequencies of the length symbols. */
- make_canonical_huffman_code(LZX_PRETREE_NUM_SYMBOLS,
- LZX_MAX_CODEWORD_LEN,
+ make_canonical_huffman_code(LZX_PRECODE_NUM_SYMBOLS,
+ LZX_MAX_PRE_CODEWORD_LEN,
precode_freqs, precode_lens,
precode_codewords);
- if (num_additional_bits_ret)
- *num_additional_bits_ret = num_additional_bits;
+ *num_additional_bits_ret = num_additional_bits;
return output_syms_idx;
}
* The Huffman code is represented in the output as a series of path lengths
* from which the canonical Huffman code can be reconstructed. The path lengths
* themselves are compressed using a separate Huffman code, the precode, which
- * consists of LZX_PRETREE_NUM_SYMBOLS (= 20) symbols that cover all possible
+ * consists of LZX_PRECODE_NUM_SYMBOLS (= 20) symbols that cover all possible
* code lengths, plus extra codes for repeated lengths. The path lengths of the
* precode precede the path lengths of the larger code and are uncompressed,
* consisting of 20 entries of 4 bits each.
const u8 prev_lens[restrict],
unsigned num_syms)
{
- freq_t precode_freqs[LZX_PRETREE_NUM_SYMBOLS];
+ freq_t precode_freqs[LZX_PRECODE_NUM_SYMBOLS];
u8 output_syms[num_syms];
- u8 precode_lens[LZX_PRETREE_NUM_SYMBOLS];
- u16 precode_codewords[LZX_PRETREE_NUM_SYMBOLS];
+ u8 precode_lens[LZX_PRECODE_NUM_SYMBOLS];
+ u16 precode_codewords[LZX_PRECODE_NUM_SYMBOLS];
unsigned i;
unsigned num_output_syms;
u8 precode_sym;
+ unsigned dummy;
num_output_syms = lzx_build_precode(lens,
prev_lens,
output_syms,
precode_lens,
precode_codewords,
- NULL);
+ &dummy);
/* Write the lengths of the precode codes to the output. */
- for (i = 0; i < LZX_PRETREE_NUM_SYMBOLS; i++)
+ for (i = 0; i < LZX_PRECODE_NUM_SYMBOLS; i++)
bitstream_put_bits(out, precode_lens[i],
- LZX_PRETREE_ELEMENT_SIZE);
+ LZX_PRECODE_ELEMENT_SIZE);
/* Write the length symbols, encoded with the precode, to the output. */
}
/*
- * Writes all compressed matches and literal bytes in a LZX block to the the
+ * Writes all compressed matches and literal bytes in an LZX block to the the
* output bitstream.
*
* @ostream
}
}
-
static void
lzx_assert_codes_valid(const struct lzx_codes * codes)
{
#ifdef ENABLE_LZX_DEBUG
unsigned i;
- for (i = 0; i < LZX_MAINTREE_NUM_SYMBOLS; i++)
- LZX_ASSERT(codes->lens.main[i] <= LZX_MAX_CODEWORD_LEN);
+ for (i = 0; i < LZX_MAINCODE_NUM_SYMBOLS; i++)
+ LZX_ASSERT(codes->lens.main[i] <= LZX_MAX_MAIN_CODEWORD_LEN);
- for (i = 0; i < LZX_LENTREE_NUM_SYMBOLS; i++)
- LZX_ASSERT(codes->lens.len[i] <= LZX_MAX_CODEWORD_LEN);
+ for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++)
+ LZX_ASSERT(codes->lens.len[i] <= LZX_MAX_LEN_CODEWORD_LEN);
- for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++)
- LZX_ASSERT(codes->lens.aligned[i] <= 8);
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
+ LZX_ASSERT(codes->lens.aligned[i] <= LZX_MAX_ALIGNED_CODEWORD_LEN);
const unsigned tablebits = 10;
u16 decode_table[(1 << tablebits) +
- (2 * max(LZX_MAINTREE_NUM_SYMBOLS, LZX_LENTREE_NUM_SYMBOLS))]
+ (2 * max(LZX_MAINCODE_NUM_SYMBOLS, LZX_LENCODE_NUM_SYMBOLS))]
_aligned_attribute(DECODE_TABLE_ALIGNMENT);
LZX_ASSERT(0 == make_huffman_decode_table(decode_table,
- LZX_MAINTREE_NUM_SYMBOLS,
- tablebits,
+ LZX_MAINCODE_NUM_SYMBOLS,
+ min(tablebits, LZX_MAINCODE_TABLEBITS),
codes->lens.main,
- LZX_MAX_CODEWORD_LEN));
+ LZX_MAX_MAIN_CODEWORD_LEN));
LZX_ASSERT(0 == make_huffman_decode_table(decode_table,
- LZX_LENTREE_NUM_SYMBOLS,
- tablebits,
+ LZX_LENCODE_NUM_SYMBOLS,
+ min(tablebits, LZX_LENCODE_TABLEBITS),
codes->lens.len,
- LZX_MAX_CODEWORD_LEN));
+ LZX_MAX_LEN_CODEWORD_LEN));
LZX_ASSERT(0 == make_huffman_decode_table(decode_table,
- LZX_ALIGNEDTREE_NUM_SYMBOLS,
- min(tablebits, 6),
+ LZX_ALIGNEDCODE_NUM_SYMBOLS,
+ min(tablebits, LZX_ALIGNEDCODE_TABLEBITS),
codes->lens.aligned,
- 8));
+ LZX_MAX_ALIGNED_CODEWORD_LEN));
#endif /* ENABLE_LZX_DEBUG */
}
-/* Write a LZX aligned offset or verbatim block to the output. */
+/* Write an LZX aligned offset or verbatim block to the output. */
static void
lzx_write_compressed_block(int block_type,
unsigned block_size,
* length code, but in fact it is the very first tree to be written
* (before the main code). */
if (block_type == LZX_BLOCKTYPE_ALIGNED)
- for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++)
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
bitstream_put_bits(ostream, codes->lens.aligned[i],
- LZX_ALIGNEDTREE_ELEMENT_SIZE);
+ LZX_ALIGNEDCODE_ELEMENT_SIZE);
LZX_DEBUG("Writing main code...");
lzx_write_compressed_code(ostream,
codes->lens.main + LZX_NUM_CHARS,
prev_codes->lens.main + LZX_NUM_CHARS,
- LZX_MAINTREE_NUM_SYMBOLS - LZX_NUM_CHARS);
+ LZX_MAINCODE_NUM_SYMBOLS - LZX_NUM_CHARS);
LZX_DEBUG("Writing length code...");
lzx_write_compressed_code(ostream,
codes->lens.len,
prev_codes->lens.len,
- LZX_LENTREE_NUM_SYMBOLS);
+ LZX_LENCODE_NUM_SYMBOLS);
LZX_DEBUG("Writing matches and literals...");
LZX_DEBUG("Done writing block.");
}
-/* Write the LZX block of index @block_number, or write its children recursively
- * if it is a split block.
- *
- * @prev_codes is a pointer to the Huffman codes for the most recent block
- * written, or all zeroes if this is the first block.
- *
- * Return a pointer to the Huffman codes for the last block written. */
-static struct lzx_codes *
-lzx_write_block_recursive(struct lzx_compressor *ctx,
- unsigned block_number,
- struct lzx_codes * prev_codes,
- struct output_bitstream *ostream)
+/* Write out the LZX blocks that were computed. */
+static void
+lzx_write_all_blocks(struct lzx_compressor *ctx, struct output_bitstream *ostream)
{
- struct lzx_block_spec *spec = &ctx->block_specs[block_number - 1];
+ const struct lzx_codes *prev_codes = &ctx->zero_codes;
+ for (unsigned i = 0; i < ctx->num_blocks; i++) {
+ const struct lzx_block_spec *spec = &ctx->block_specs[i];
- if (spec->is_split) {
- prev_codes = lzx_write_block_recursive(ctx, block_number * 2 + 0,
- prev_codes, ostream);
- prev_codes = lzx_write_block_recursive(ctx, block_number * 2 + 1,
- prev_codes, ostream);
- } else {
- LZX_DEBUG("Writing block #%u (type=%d, size=%u, num_chosen_matches=%u)...",
- block_number, spec->block_type, spec->block_size,
+ LZX_DEBUG("Writing block %u/%u (type=%d, size=%u, num_chosen_matches=%u)...",
+ i + 1, ctx->num_blocks,
+ spec->block_type, spec->block_size,
spec->num_chosen_matches);
+
lzx_write_compressed_block(spec->block_type,
spec->block_size,
&ctx->chosen_matches[spec->chosen_matches_start_pos],
ostream);
prev_codes = &spec->codes;
}
- return prev_codes;
-}
-
-/* Write out the LZX blocks that were computed. */
-static void
-lzx_write_all_blocks(struct lzx_compressor *ctx, struct output_bitstream *ostream)
-{
- lzx_write_block_recursive(ctx, 1, &ctx->zero_codes, ostream);
}
+/* Constructs an LZX match from a literal byte and updates the main code symbol
+ * frequencies. */
static u32
lzx_record_literal(u8 literal, void *_freqs)
{
return (u32)literal;
}
-/* Constructs a match from an offset and a length, and updates the LRU queue and
- * the frequency of symbols in the main, length, and aligned offset alphabets.
- * The return value is a 32-bit number that provides the match in an
+/* Constructs an LZX match from an offset and a length, and updates the LRU
+ * queue and the frequency of symbols in the main, length, and aligned offset
+ * alphabets. The return value is a 32-bit number that provides the match in an
* intermediate representation documented below. */
static u32
lzx_record_match(unsigned match_offset, unsigned match_len,
struct lzx_freqs *freqs = _freqs;
struct lzx_lru_queue *queue = _queue;
unsigned position_slot;
- unsigned position_footer = 0;
+ unsigned position_footer;
u32 len_header;
- u32 len_pos_header;
+ unsigned main_symbol;
unsigned len_footer;
unsigned adjusted_match_len;
- LZX_ASSERT(match_len >= LZX_MIN_MATCH && match_len <= LZX_MAX_MATCH);
-
- /* If possible, encode this offset as a repeated offset. */
- if (match_offset == queue->R0) {
- position_slot = 0;
- } else if (match_offset == queue->R1) {
- swap(queue->R0, queue->R1);
- position_slot = 1;
- } else if (match_offset == queue->R2) {
- swap(queue->R0, queue->R2);
- position_slot = 2;
- } else {
- /* Not a repeated offset. */
-
- /* offsets of 0, 1, and 2 are reserved for the repeated offset
- * codes, so non-repeated offsets must be encoded as 3+. The
- * minimum offset is 1, so encode the offsets offset by 2. */
- unsigned formatted_offset = match_offset + 2;
-
- queue->R2 = queue->R1;
- queue->R1 = queue->R0;
- queue->R0 = match_offset;
-
- /* The (now-formatted) offset will actually be encoded as a
- * small position slot number that maps to a certain hard-coded
- * offset (position base), followed by a number of extra bits---
- * the position footer--- that are added to the position base to
- * get the original formatted offset. */
-
- position_slot = lzx_get_position_slot(formatted_offset);
- position_footer = formatted_offset &
- ((1 << lzx_get_num_extra_bits(position_slot)) - 1);
- }
+ LZX_ASSERT(match_len >= LZX_MIN_MATCH_LEN && match_len <= LZX_MAX_MATCH_LEN);
- adjusted_match_len = match_len - LZX_MIN_MATCH;
+ /* The match offset shall be encoded as a position slot (itself encoded
+ * as part of the main symbol) and a position footer. */
+ position_slot = lzx_get_position_slot(match_offset, queue);
+ position_footer = (match_offset + LZX_OFFSET_OFFSET) &
+ ((1U << lzx_get_num_extra_bits(position_slot)) - 1);
-
- /* The match length must be at least 2, so let the adjusted match length
- * be the match length minus 2.
- *
- * If it is less than 7, the adjusted match length is encoded as a 3-bit
- * number offset by 2. Otherwise, the 3-bit length header is all 1's
- * and the actual adjusted length is given as a symbol encoded with the
- * length tree, offset by 7.
- */
+ /* The match length shall be encoded as a length header (itself encoded
+ * as part of the main symbol) and an optional length footer. */
+ adjusted_match_len = match_len - LZX_MIN_MATCH_LEN;
if (adjusted_match_len < LZX_NUM_PRIMARY_LENS) {
+ /* No length footer needed. */
len_header = adjusted_match_len;
} else {
+ /* Length footer needed. It will be encoded using the length
+ * code. */
len_header = LZX_NUM_PRIMARY_LENS;
len_footer = adjusted_match_len - LZX_NUM_PRIMARY_LENS;
freqs->len[len_footer]++;
}
- len_pos_header = (position_slot << 3) | len_header;
- freqs->main[len_pos_header + LZX_NUM_CHARS]++;
+ /* Account for the main symbol. */
+ main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS;
+
+ freqs->main[main_symbol]++;
+
+ /* In an aligned offset block, 3 bits of the position footer are output
+ * as an aligned offset symbol. Account for this, although we may
+ * ultimately decide to output the block as verbatim. */
- /* Equivalent to:
- * if (lzx_extra_bits[position_slot] >= 3) */
+ /* The following check is equivalent to:
+ *
+ * if (lzx_extra_bits[position_slot] >= 3)
+ *
+ * Note that this correctly excludes position slots that correspond to
+ * recent offsets. */
if (position_slot >= 8)
freqs->aligned[position_footer & 7]++;
* (since lzx_extra_bits[LZX_NUM_POSITION_SLOTS - 1] is 17).
*
* 0-7 length of match, offset by 2. This can be at most
- * (LZX_MAX_MATCH - 2) == 255, so it will fit in 8 bits. */
+ * (LZX_MAX_MATCH_LEN - 2) == 255, so it will fit in 8 bits. */
+ BUILD_BUG_ON(LZX_NUM_POSITION_SLOTS > 64);
+ LZX_ASSERT(lzx_get_num_extra_bits(LZX_NUM_POSITION_SLOTS - 1) <= 17);
+ BUILD_BUG_ON(LZX_MAX_MATCH_LEN - LZX_MIN_MATCH_LEN + 1 > 256);
return 0x80000000 |
(position_slot << 25) |
(position_footer << 8) |
(adjusted_match_len);
}
-/* Set the cost model @ctx->costs from the Huffman codeword lengths specified in
- * @lens.
- *
- * These are basically the same thing, except that the Huffman codewords with
- * length 0 correspond to symbols with zero frequency that still need to be
- * assigned actual costs. The specific values assigned are arbitrary, but they
- * should be fairly high (near the maximum codeword length) to take into account
- * the fact that uses of these symbols are expected to be rare.
- */
-static void
-lzx_set_costs(struct lzx_compressor * ctx, const struct lzx_lens * lens)
-{
- unsigned i;
-
- memcpy(&ctx->costs, lens, sizeof(struct lzx_lens));
-
- for (i = 0; i < LZX_MAINTREE_NUM_SYMBOLS; i++)
- if (ctx->costs.main[i] == 0)
- ctx->costs.main[i] = ctx->params.alg_params.slow.main_nostat_cost;
-
- for (i = 0; i < LZX_LENTREE_NUM_SYMBOLS; i++)
- if (ctx->costs.len[i] == 0)
- ctx->costs.len[i] = ctx->params.alg_params.slow.len_nostat_cost;
-
- for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++)
- if (ctx->costs.aligned[i] == 0)
- ctx->costs.aligned[i] = ctx->params.alg_params.slow.aligned_nostat_cost;
-}
-
-static u32
-lzx_literal_cost(u8 c, const struct lzx_lens * costs)
+/* Returns the cost, in bits, to output a literal byte using the specified cost
+ * model. */
+static sym_cost_t
+lzx_literal_cost(u8 c, const struct lzx_costs * costs)
{
return costs->main[c];
}
/* Given a (length, offset) pair that could be turned into a valid LZX match as
* well as costs for the codewords in the main, length, and aligned Huffman
* codes, return the approximate number of bits it will take to represent this
- * match in the compressed output. */
-static unsigned
-lzx_match_cost(unsigned length, unsigned offset, const struct lzx_lens *costs
-
-#if LZX_PARAM_ACCOUNT_FOR_LRU
- , struct lzx_lru_queue *queue
-#endif
- )
+ * match in the compressed output. Take into account the match offset LRU
+ * queue and optionally update it. */
+static sym_cost_t
+lzx_match_cost(unsigned length, unsigned offset, const struct lzx_costs *costs,
+ struct lzx_lru_queue *queue)
{
- unsigned position_slot, len_header, main_symbol;
- unsigned cost = 0;
-
- /* Calculate position slot and length header, then combine them into the
- * main symbol. */
-
-#if LZX_PARAM_ACCOUNT_FOR_LRU
- if (offset == queue->R0) {
- position_slot = 0;
- } else if (offset == queue->R1) {
- swap(queue->R0, queue->R1);
- position_slot = 1;
- } else if (offset == queue->R2) {
- swap(queue->R0, queue->R2);
- position_slot = 2;
- } else
-#endif
- position_slot = lzx_get_position_slot(offset + 2);
+ unsigned position_slot;
+ unsigned len_header, main_symbol;
+ sym_cost_t cost = 0;
- len_header = min(length - LZX_MIN_MATCH, LZX_NUM_PRIMARY_LENS);
- main_symbol = ((position_slot << 3) | len_header) + LZX_NUM_CHARS;
+ position_slot = lzx_get_position_slot(offset, queue);
+
+ len_header = min(length - LZX_MIN_MATCH_LEN, LZX_NUM_PRIMARY_LENS);
+ main_symbol = (position_slot << 3) | len_header | LZX_NUM_CHARS;
/* Account for main symbol. */
cost += costs->main[main_symbol];
unsigned num_extra_bits = lzx_get_num_extra_bits(position_slot);
if (num_extra_bits >= 3) {
cost += num_extra_bits - 3;
- cost += costs->aligned[(offset + LZX_MIN_MATCH) & 7];
+ cost += costs->aligned[(offset + LZX_OFFSET_OFFSET) & 7];
} else {
cost += num_extra_bits;
}
/* Account for extra length information. */
- if (length - LZX_MIN_MATCH >= LZX_NUM_PRIMARY_LENS)
- cost += costs->len[length - LZX_MIN_MATCH - LZX_NUM_PRIMARY_LENS];
+ if (len_header == LZX_NUM_PRIMARY_LENS)
+ cost += costs->len[length - LZX_MIN_MATCH_LEN - LZX_NUM_PRIMARY_LENS];
return cost;
+
}
-/* This procedure effectively creates a new binary tree corresponding to the
- * current string at the same time that it searches the existing tree nodes for
- * matches. This is the same algorithm as that used in GetMatchesSpec1() in
- * 7-Zip, but it is hopefully explained a little more clearly below. */
-static unsigned
-lzx_lz_get_matches(const u8 window[restrict],
- const unsigned bytes_remaining,
- const unsigned strstart,
- const unsigned max_length,
- u16 child_tab[restrict],
- unsigned cur_match,
- const unsigned prev_len,
- struct raw_match * const matches)
+/* Very fast heuristic cost evaluation to use in the inner loop of the
+ * match-finder. */
+static sym_cost_t
+lzx_match_cost_fast(unsigned offset, const struct lzx_lru_queue *queue)
+{
+ for (unsigned i = 0; i < LZX_NUM_RECENT_OFFSETS; i++)
+ if (offset == queue->R[i])
+ return i;
+
+ BUILD_BUG_ON(LZX_MAX_WINDOW_SIZE >= (sym_cost_t)~0U);
+ return offset;
+}
+
+/* Set the cost model @ctx->costs from the Huffman codeword lengths specified in
+ * @lens.
+ *
+ * The cost model and codeword lengths are almost the same thing, but the
+ * Huffman codewords with length 0 correspond to symbols with zero frequency
+ * that still need to be assigned actual costs. The specific values assigned
+ * are arbitrary, but they should be fairly high (near the maximum codeword
+ * length) to take into account the fact that uses of these symbols are expected
+ * to be rare. */
+static void
+lzx_set_costs(struct lzx_compressor * ctx, const struct lzx_lens * lens)
{
- u16 *new_tree_lt_ptr = &child_tab[strstart * 2];
- u16 *new_tree_gt_ptr = &child_tab[strstart * 2 + 1];
+ unsigned i;
- u16 longest_lt_match_len = 0;
- u16 longest_gt_match_len = 0;
+ /* Main code */
+ for (i = 0; i < LZX_MAINCODE_NUM_SYMBOLS; i++) {
+ ctx->costs.main[i] = lens->main[i];
+ if (ctx->costs.main[i] == 0)
+ ctx->costs.main[i] = ctx->params.alg_params.slow.main_nostat_cost;
+ }
- /* Maximum number of nodes to walk down before stopping */
- unsigned depth = max_length;
+ /* Length code */
+ for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++) {
+ ctx->costs.len[i] = lens->len[i];
+ if (ctx->costs.len[i] == 0)
+ ctx->costs.len[i] = ctx->params.alg_params.slow.len_nostat_cost;
+ }
- /* Length of longest match found so far */
- unsigned longest_match_len = prev_len;
+ /* Aligned offset code */
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
+ ctx->costs.aligned[i] = lens->aligned[i];
+ if (ctx->costs.aligned[i] == 0)
+ ctx->costs.aligned[i] = ctx->params.alg_params.slow.aligned_nostat_cost;
+ }
+}
- /* Maximum length of match to return */
- unsigned len_limit = min(bytes_remaining, max_length);
+/* Advance the suffix array match-finder to the next position. */
+static void
+lzx_lz_update_salink(input_idx_t i,
+ const input_idx_t SA[restrict],
+ const input_idx_t ISA[restrict],
+ struct salink link[restrict])
+{
+ /* r = Rank of the suffix at the current position. */
+ const input_idx_t r = ISA[i];
- /* Number of matches found so far */
- unsigned num_matches = 0;
+ /* next = rank of LOWEST ranked suffix that is ranked HIGHER than the
+ * current suffix AND has a LOWER position, or -1 if none exists. */
+ const input_idx_t next = link[r].next;
- for (;;) {
+ /* prev = rank of HIGHEST ranked suffix that is ranked LOWER than the
+ * current suffix AND has a LOWER position, or -1 if none exists. */
+ const input_idx_t prev = link[r].prev;
- /* Stop if too many nodes were traversed or if there is no next
- * node */
- if (depth-- == 0 || cur_match == 0) {
- *new_tree_gt_ptr = 0;
- *new_tree_lt_ptr = 0;
- return num_matches;
- }
+ /* Link the suffix at the current position into the linked list that
+ * contains all suffixes in the suffix array that are appear at or
+ * before the current position, sorted by rank.
+ *
+ * Save the values of all fields we overwrite so that rollback is
+ * possible. */
+ if (next != (input_idx_t)~0U) {
- /* Load the pointers to the children of the binary tree node
- * corresponding to the current match */
- u16 * const cur_match_ptrs = &child_tab[cur_match * 2];
-
- /* Set up pointers to the current match and to the current
- * string */
- const u8 * const matchptr = &window[cur_match];
- const u8 * const strptr = &window[strstart];
-
- /* Determine position at which to start comparing */
- u16 len = min(longest_lt_match_len,
- longest_gt_match_len);
-
- if (matchptr[len] == strptr[len]) {
-
- /* Extend the match as far as possible. */
- while (++len != len_limit)
- if (matchptr[len] != strptr[len])
- break;
-
- /* Record this match if it is the longest found so far.
- */
- if (len > longest_match_len) {
- longest_match_len = len;
- matches[num_matches].len = len;
- matches[num_matches].offset = strstart - cur_match;
- num_matches++;
-
- if (len == len_limit) {
- /* Length limit was reached. Link left pointer
- * in the new tree with left subtree of current
- * match tree, and link the right pointer in the
- * new tree with the right subtree of the
- * current match tree. This in effect deletes
- * the node for the currrent match, which is
- * desirable because the current match is the
- * same as the current string up until the
- * length limit, so in subsequent queries it
- * will never be preferable to the current
- * position. */
- *new_tree_lt_ptr = cur_match_ptrs[0];
- *new_tree_gt_ptr = cur_match_ptrs[1];
- return num_matches;
- }
- }
- }
+ link[next].prev = r;
+ link[next].lcpprev = link[r].lcpnext;
+ }
- if (matchptr[len] < strptr[len]) {
- /* Case 1: The current match is lexicographically less
- * than the current string.
- *
- * Since we are searching the binary tree structures, we
- * need to walk down to the *right* subtree of the
- * current match's node to get to a match that is
- * lexicographically *greater* than the current match
- * but still lexicographically *lesser* than the current
- * string.
- *
- * At the same time, we link the entire binary tree
- * corresponding to the current match into the
- * appropriate place in the new binary tree being built
- * for the current string. */
- *new_tree_lt_ptr = cur_match;
- new_tree_lt_ptr = &cur_match_ptrs[1];
- cur_match = *new_tree_lt_ptr;
- longest_lt_match_len = len;
- } else {
- /* Case 2: The current match is lexicographically
- * greater than the current string.
- *
- * This is analogous to Case 1 above, but everything
- * happens in the other direction.
- */
- *new_tree_gt_ptr = cur_match;
- new_tree_gt_ptr = &cur_match_ptrs[0];
- cur_match = *new_tree_gt_ptr;
- longest_gt_match_len = len;
- }
+ if (prev != (input_idx_t)~0U) {
+
+ link[prev].next = r;
+ link[prev].lcpnext = link[r].lcpprev;
}
}
-/* Equivalent to lzx_lz_get_matches(), but only updates the tree and doesn't
- * return matches. See that function for details (including comments). */
+/* Rewind the suffix array match-finder to the specified position.
+ *
+ * This undoes a series of updates by lzx_lz_update_salink(). */
static void
-lzx_lz_skip_matches(const u8 window[restrict],
- const unsigned bytes_remaining,
- const unsigned strstart,
- const unsigned max_length,
- u16 child_tab[restrict],
- unsigned cur_match,
- const unsigned prev_len)
+lzx_lz_rewind_matchfinder(struct lzx_compressor *ctx,
+ const unsigned orig_pos)
+{
+ LZX_DEBUG("Rewind match-finder %u => %u", ctx->match_window_pos, orig_pos);
+
+ if (ctx->match_window_pos == orig_pos)
+ return;
+
+ LZX_ASSERT(ctx->match_window_pos > orig_pos);
+ LZX_ASSERT(orig_pos == 0);
+ ctx->matches_cached = true;
+ ctx->cached_matches_pos = 0;
+ ctx->match_window_pos = orig_pos;
+}
+
+/*
+ * Use the suffix array match-finder to retrieve a list of LZ matches at the
+ * current position.
+ *
+ * [in] @i Current position in the window.
+ * [in] @SA Suffix array for the window.
+ * [in] @ISA Inverse suffix array for the window.
+ * [inout] @link Suffix array links used internally by the match-finder.
+ * [out] @matches The (length, offset) pairs of the resulting matches will
+ * be written here, sorted in decreasing order by
+ * length. All returned lengths will be unique.
+ * [in] @queue Recently used match offsets, used when evaluating the
+ * cost of matches.
+ * [in] @min_match_len Minimum match length to return.
+ * [in] @max_matches_to_consider Maximum number of matches to consider at
+ * the position.
+ * [in] @max_matches_to_return Maximum number of matches to return.
+ *
+ * The return value is the number of matches found and written to @matches.
+ */
+static unsigned
+lzx_lz_get_matches(const input_idx_t i,
+ const input_idx_t SA[const restrict],
+ const input_idx_t ISA[const restrict],
+ struct salink link[const restrict],
+ struct raw_match matches[const restrict],
+ const struct lzx_lru_queue * const restrict queue,
+ const unsigned min_match_len,
+ const uint32_t max_matches_to_consider,
+ const uint32_t max_matches_to_return)
{
- u16 *new_tree_lt_ptr = &child_tab[strstart * 2];
- u16 *new_tree_gt_ptr = &child_tab[strstart * 2 + 1];
+ /* r = Rank of the suffix at the current position. */
+ const input_idx_t r = ISA[i];
- u16 longest_lt_match_len = 0;
- u16 longest_gt_match_len = 0;
+ /* Prepare for searching the current position. */
+ lzx_lz_update_salink(i, SA, ISA, link);
+
+ /* L = rank of next suffix to the left;
+ * R = rank of next suffix to the right;
+ * lenL = length of match between current position and the suffix with rank L;
+ * lenR = length of match between current position and the suffix with rank R.
+ *
+ * This is left and right relative to the rank of the current suffix.
+ * Since the suffixes in the suffix array are sorted, the longest
+ * matches are immediately to the left and right (using the linked list
+ * to ignore all suffixes that occur later in the window). The match
+ * length decreases the farther left and right we go. We shall keep the
+ * length on both sides in sync in order to choose the lowest-cost match
+ * of each length.
+ */
+ input_idx_t L = link[r].prev;
+ input_idx_t R = link[r].next;
+ input_idx_t lenL = link[r].lcpprev;
+ input_idx_t lenR = link[r].lcpnext;
- unsigned depth = max_length;
+ /* nmatches = number of matches found so far. */
+ unsigned nmatches = 0;
- unsigned longest_match_len = prev_len;
+ /* best_cost = cost of lowest-cost match found so far.
+ *
+ * We keep track of this so that we can ignore shorter matches that do
+ * not have lower costs than a longer matches already found.
+ */
+ sym_cost_t best_cost = INFINITE_SYM_COST;
- unsigned len_limit = min(bytes_remaining, max_length);
+ /* count_remaining = maximum number of possible matches remaining to be
+ * considered. */
+ uint32_t count_remaining = max_matches_to_consider;
- for (;;) {
- if (depth-- == 0 || cur_match == 0) {
- *new_tree_gt_ptr = 0;
- *new_tree_lt_ptr = 0;
- return;
- }
+ /* pending = match currently being considered for a specific length. */
+ struct raw_match pending;
- u16 * const cur_match_ptrs = &child_tab[cur_match * 2];
+ while (lenL >= min_match_len || lenR >= min_match_len)
+ {
+ pending.len = lenL;
+ pending.offset = (input_idx_t)~0U;
+ sym_cost_t pending_cost = INFINITE_SYM_COST;
+ sym_cost_t cost;
- const u8 * const matchptr = &window[cur_match];
- const u8 * const strptr = &window[strstart];
+ /* Extend left. */
+ if (lenL >= min_match_len && lenL >= lenR) {
+ for (;;) {
- u16 len = min(longest_lt_match_len,
- longest_gt_match_len);
+ if (--count_remaining == 0)
+ goto out_save_pending;
- if (matchptr[len] == strptr[len]) {
- while (++len != len_limit)
- if (matchptr[len] != strptr[len])
- break;
+ input_idx_t offset = i - SA[L];
- if (len > longest_match_len) {
- longest_match_len = len;
+ /* Save match if it has smaller cost. */
+ cost = lzx_match_cost_fast(offset, queue);
+ if (cost < pending_cost) {
+ pending.offset = offset;
+ pending_cost = cost;
+ }
- if (len == len_limit) {
- *new_tree_lt_ptr = cur_match_ptrs[0];
- *new_tree_gt_ptr = cur_match_ptrs[1];
- return;
+ if (link[L].lcpprev < lenL) {
+ /* Match length decreased. */
+
+ lenL = link[L].lcpprev;
+
+ /* Save the pending match unless the
+ * right side still may have matches of
+ * this length to be scanned, or if a
+ * previous (longer) match had lower
+ * cost. */
+ if (pending.len > lenR) {
+ if (pending_cost < best_cost) {
+ best_cost = pending_cost;
+ matches[nmatches++] = pending;
+ if (nmatches == max_matches_to_return)
+ return nmatches;
+ }
+ pending.len = lenL;
+ pending.offset = (input_idx_t)~0U;
+ pending_cost = INFINITE_SYM_COST;
+ }
+ if (lenL < min_match_len || lenL < lenR)
+ break;
}
+ L = link[L].prev;
}
}
- if (matchptr[len] < strptr[len]) {
- *new_tree_lt_ptr = cur_match;
- new_tree_lt_ptr = &cur_match_ptrs[1];
- cur_match = *new_tree_lt_ptr;
- longest_lt_match_len = len;
- } else {
- *new_tree_gt_ptr = cur_match;
- new_tree_gt_ptr = &cur_match_ptrs[0];
- cur_match = *new_tree_gt_ptr;
- longest_gt_match_len = len;
+ pending.len = lenR;
+
+ /* Extend right. */
+ if (lenR >= min_match_len && lenR > lenL) {
+ for (;;) {
+
+ if (--count_remaining == 0)
+ goto out_save_pending;
+
+ input_idx_t offset = i - SA[R];
+
+ /* Save match if it has smaller cost. */
+ cost = lzx_match_cost_fast(offset, queue);
+ if (cost < pending_cost) {
+ pending.offset = offset;
+ pending_cost = cost;
+ }
+
+ if (link[R].lcpnext < lenR) {
+ /* Match length decreased. */
+
+ lenR = link[R].lcpnext;
+
+ /* Save the pending match unless a
+ * previous (longer) match had lower
+ * cost. */
+ if (pending_cost < best_cost) {
+ matches[nmatches++] = pending;
+ best_cost = pending_cost;
+ if (nmatches == max_matches_to_return)
+ return nmatches;
+ }
+
+ if (lenR < min_match_len || lenR <= lenL)
+ break;
+
+ pending.len = lenR;
+ pending.offset = (input_idx_t)~0U;
+ pending_cost = INFINITE_SYM_COST;
+ }
+ R = link[R].next;
+ }
}
}
+ goto out;
+
+out_save_pending:
+ if (pending.offset != (input_idx_t)~0U)
+ matches[nmatches++] = pending;
+
+out:
+ return nmatches;
}
-static unsigned
-lzx_lz_get_matches_caching(struct lzx_compressor *ctx,
- struct raw_match **matches_ret);
/* Tell the match-finder to skip the specified number of bytes (@n) in the
* input. */
static void
lzx_lz_skip_bytes(struct lzx_compressor *ctx, unsigned n)
{
-
-#if LZX_PARAM_DONT_SKIP_MATCHES
- /* Option 1: Still cache the matches from the positions skipped. They
- * will then be available in later passes. */
- struct raw_match *matches;
- while (n--)
- lzx_lz_get_matches_caching(ctx, &matches);
-#else
- /* Option 2: Mark the positions skipped as having no matches available,
- * but we still need to update the binary tree in case subsequent
- * positions have matches at the current position. */
LZX_ASSERT(n <= ctx->match_window_end - ctx->match_window_pos);
- if (ctx->matches_already_found) {
+ if (ctx->matches_cached) {
+ ctx->match_window_pos += n;
while (n--) {
- LZX_ASSERT(ctx->cached_matches[ctx->cached_matches_pos].offset ==
- ctx->match_window_pos);
- ctx->cached_matches_pos += ctx->cached_matches[ctx->cached_matches_pos].len + 1;
- ctx->match_window_pos++;
+ ctx->cached_matches_pos +=
+ ctx->cached_matches[ctx->cached_matches_pos].len + 1;
}
} else {
while (n--) {
- if (ctx->params.alg_params.slow.use_len2_matches &&
- ctx->match_window_end - ctx->match_window_pos >= 2) {
- unsigned c1 = ctx->window[ctx->match_window_pos];
- unsigned c2 = ctx->window[ctx->match_window_pos + 1];
- unsigned digram = c1 | (c2 << 8);
- ctx->digram_tab[digram] = ctx->match_window_pos;
- }
- if (ctx->match_window_end - ctx->match_window_pos >= 3) {
- unsigned hash;
- unsigned cur_match;
-
- hash = lzx_lz_compute_hash(&ctx->window[ctx->match_window_pos]);
-
- cur_match = ctx->hash_tab[hash];
- ctx->hash_tab[hash] = ctx->match_window_pos;
-
- lzx_lz_skip_matches(ctx->window,
- ctx->match_window_end - ctx->match_window_pos,
- ctx->match_window_pos,
- ctx->params.alg_params.slow.num_fast_bytes,
- ctx->child_tab,
- cur_match, 1);
- }
- ctx->cached_matches[ctx->cached_matches_pos].len = 0;
- ctx->cached_matches[ctx->cached_matches_pos].offset = ctx->match_window_pos;
- ctx->cached_matches_pos++;
- ctx->match_window_pos++;
+ ctx->cached_matches[ctx->cached_matches_pos++].len = 0;
+ lzx_lz_update_salink(ctx->match_window_pos++, ctx->SA,
+ ctx->ISA, ctx->salink);
}
}
-#endif /* !LZX_PARAM_DONT_SKIP_MATCHES */
}
/* Retrieve a list of matches available at the next position in the input.
*
- * The return value is the number of matches found, and a pointer to them is
- * written to @matches_ret. The matches will be sorted in order by length.
- *
- * This is essentially a wrapper around lzx_lz_get_matches() that caches its
- * output the first time and also performs the needed hashing.
- */
+ * The matches are written to ctx->matches in decreasing order of length, and
+ * the return value is the number of matches found. */
static unsigned
lzx_lz_get_matches_caching(struct lzx_compressor *ctx,
+ const struct lzx_lru_queue *queue,
struct raw_match **matches_ret)
{
unsigned num_matches;
struct raw_match *matches;
- LZX_ASSERT(ctx->match_window_end >= ctx->match_window_pos);
+ LZX_ASSERT(ctx->match_window_pos <= ctx->match_window_end);
matches = &ctx->cached_matches[ctx->cached_matches_pos + 1];
- if (ctx->matches_already_found) {
- num_matches = ctx->cached_matches[ctx->cached_matches_pos].len;
- LZX_ASSERT(ctx->cached_matches[ctx->cached_matches_pos].offset == ctx->match_window_pos);
-
- for (int i = (int)num_matches - 1; i >= 0; i--) {
- if (ctx->match_window_pos + matches[i].len > ctx->match_window_end)
- matches[i].len = ctx->match_window_end - ctx->match_window_pos;
- else
- break;
- }
+ if (ctx->matches_cached) {
+ num_matches = matches[-1].len;
} else {
- unsigned prev_len = 1;
- struct raw_match * matches_ret = &ctx->cached_matches[ctx->cached_matches_pos + 1];
- num_matches = 0;
-
- if (ctx->params.alg_params.slow.use_len2_matches &&
- ctx->match_window_end - ctx->match_window_pos >= 3) {
- unsigned c1 = ctx->window[ctx->match_window_pos];
- unsigned c2 = ctx->window[ctx->match_window_pos + 1];
- unsigned digram = c1 | (c2 << 8);
- unsigned cur_match;
-
- cur_match = ctx->digram_tab[digram];
- ctx->digram_tab[digram] = ctx->match_window_pos;
- if (cur_match != 0 &&
- ctx->window[cur_match + 2] != ctx->window[ctx->match_window_pos + 2])
- {
- matches_ret->len = 2;
- matches_ret->offset = ctx->match_window_pos - cur_match;
- matches_ret++;
- num_matches++;
- prev_len = 2;
- }
- }
- if (ctx->match_window_end - ctx->match_window_pos >= 3) {
- unsigned hash;
- unsigned cur_match;
-
- hash = lzx_lz_compute_hash(&ctx->window[ctx->match_window_pos]);
-
- cur_match = ctx->hash_tab[hash];
- ctx->hash_tab[hash] = ctx->match_window_pos;
- num_matches += lzx_lz_get_matches(ctx->window,
- ctx->match_window_end - ctx->match_window_pos,
- ctx->match_window_pos,
- ctx->params.alg_params.slow.num_fast_bytes,
- ctx->child_tab,
- cur_match,
- prev_len,
- matches_ret);
- }
-
- ctx->cached_matches[ctx->cached_matches_pos].len = num_matches;
- ctx->cached_matches[ctx->cached_matches_pos].offset = ctx->match_window_pos;
-
- if (num_matches) {
- struct raw_match *longest_match_ptr =
- &ctx->cached_matches[ctx->cached_matches_pos + 1 +
- num_matches - 1];
- u16 len = longest_match_ptr->len;
-
- /* If the longest match returned by the match-finder
- * reached the number of fast bytes, extend it as much
- * as possible. */
- if (len == ctx->params.alg_params.slow.num_fast_bytes) {
- const unsigned maxlen =
- min(ctx->match_window_end - ctx->match_window_pos,
- LZX_MAX_MATCH);
-
- const u8 * const matchptr =
- &ctx->window[ctx->match_window_pos - longest_match_ptr->offset];
-
- const u8 * const strptr =
- &ctx->window[ctx->match_window_pos];
-
- while (len < maxlen && matchptr[len] == strptr[len])
- len++;
- }
- longest_match_ptr->len = len;
- }
+ unsigned min_match_len = LZX_MIN_MATCH_LEN;
+ if (min_match_len <= 2 && !ctx->params.alg_params.slow.use_len2_matches)
+ min_match_len = 3;
+ const uint32_t max_search_depth = ctx->params.alg_params.slow.max_search_depth;
+ const uint32_t max_matches_per_pos = ctx->params.alg_params.slow.max_matches_per_pos;
+
+ if (unlikely(max_search_depth == 0 || max_matches_per_pos == 0))
+ num_matches = 0;
+ else
+ num_matches = lzx_lz_get_matches(ctx->match_window_pos,
+ ctx->SA,
+ ctx->ISA,
+ ctx->salink,
+ matches,
+ queue,
+ min_match_len,
+ max_search_depth,
+ max_matches_per_pos);
+ matches[-1].len = num_matches;
}
ctx->cached_matches_pos += num_matches + 1;
*matches_ret = matches;
+ /* Cap the length of returned matches to the number of bytes remaining,
+ * if it is not the whole window. */
+ if (ctx->match_window_end < ctx->window_size) {
+ unsigned maxlen = ctx->match_window_end - ctx->match_window_pos;
+ for (unsigned i = 0; i < num_matches; i++)
+ if (matches[i].len > maxlen)
+ matches[i].len = maxlen;
+ }
#if 0
- printf("\n");
+ fprintf(stderr, "Pos %u/%u: %u matches\n",
+ ctx->match_window_pos, ctx->match_window_end, num_matches);
for (unsigned i = 0; i < num_matches; i++)
- {
- printf("Len %u Offset %u\n", matches[i].len, matches[i].offset);
- }
+ fprintf(stderr, "\tLen %u Offset %u\n", matches[i].len, matches[i].offset);
#endif
+#ifdef ENABLE_LZX_DEBUG
for (unsigned i = 0; i < num_matches; i++) {
- LZX_ASSERT(matches[i].len <= LZX_MAX_MATCH);
- if (matches[i].len >= LZX_MIN_MATCH) {
- LZX_ASSERT(matches[i].offset <= ctx->match_window_pos);
- LZX_ASSERT(matches[i].len <= ctx->match_window_end - ctx->match_window_pos);
- LZX_ASSERT(!memcmp(&ctx->window[ctx->match_window_pos],
- &ctx->window[ctx->match_window_pos - matches[i].offset],
- matches[i].len));
- }
+ LZX_ASSERT(matches[i].len >= LZX_MIN_MATCH_LEN);
+ LZX_ASSERT(matches[i].len <= LZX_MAX_MATCH_LEN);
+ LZX_ASSERT(matches[i].len <= ctx->match_window_end - ctx->match_window_pos);
+ LZX_ASSERT(matches[i].offset > 0);
+ LZX_ASSERT(matches[i].offset <= ctx->match_window_pos);
+ LZX_ASSERT(!memcmp(&ctx->window[ctx->match_window_pos],
+ &ctx->window[ctx->match_window_pos - matches[i].offset],
+ matches[i].len));
}
+#endif
ctx->match_window_pos++;
return num_matches;
};
}
+#if 0
+static struct raw_match
+lzx_lz_get_greedy_match(struct lzx_compressor * ctx)
+{
+ struct raw_match *matches;
+
+ if (!lzx_lz_get_matches_caching(ctx, &ctx->queue, &matches))
+ return (struct raw_match) {.len = 0};
+
+ lzx_lz_skip_bytes(ctx, matches[0].len - 1);
+ return matches[0];
+}
+#endif
+
+#if 0
+static struct raw_match
+lzx_lz_get_lazy_match(struct lzx_compressor * ctx)
+{
+ unsigned num_matches;
+ struct raw_match *matches;
+ struct raw_match prev_match;
+ struct lzx_lru_queue queue;
+
+ if (ctx->optimum_cur_idx != ctx->optimum_end_idx)
+ goto retopt;
+
+ /* Check for matches at first position. */
+ num_matches = lzx_lz_get_matches_caching(ctx, &ctx->queue, &matches);
+
+ /* Return literal if no matches were found. */
+ if (num_matches == 0)
+ return (struct raw_match) { .len = 0 };
+
+ /* Immediately choose match if longer than threshold. */
+ if (matches[0].len > ctx->params.alg_params.slow.num_fast_bytes)
+ goto savecur;
+
+ ctx->optimum_cur_idx = ctx->optimum_end_idx = 0;
+ for (;;) {
+ prev_match = matches[0];
+
+ /* Check for matches at next position. */
+ num_matches = lzx_lz_get_matches_caching(ctx, &ctx->queue, &matches);
+
+ /* Choose previous match if there is not a match at this
+ * position. */
+ if (num_matches == 0)
+ goto saveprev;
+
+ /* Choose previous match the longest match at the next position
+ * is the same place, just one character shifted over. */
+ if (matches[0].offset == prev_match.offset ||
+ matches[0].len < prev_match.len)
+ goto saveprev;
+
+ struct lzx_lru_queue q1 = ctx->queue, q2 = ctx->queue;
+ double lazycost = lzx_literal_cost(ctx->window[ctx->match_window_pos - 2],
+ &ctx->costs) +
+ lzx_match_cost(matches[0].len, matches[0].offset,
+ &ctx->costs, &q1);
+ double greedycost = lzx_match_cost(prev_match.len, prev_match.offset,
+ &ctx->costs, &q2);
+ lazycost *= (double)prev_match.len / (1 + matches[0].len);
+
+ /* Choose previous match if greedy cost was lower. */
+ if (greedycost <= lazycost)
+ goto saveprev;
+
+ /* Choose literal at the previous position. */
+ ctx->optimum[ctx->optimum_end_idx++].next.link = 0;
+
+
+ /* Immediately choose match if longer than threshold. */
+ if (matches[0].len > ctx->params.alg_params.slow.num_fast_bytes)
+ goto savecur;
+ }
+
+savecur:
+ lzx_lz_skip_bytes(ctx, 1);
+ prev_match = matches[0];
+
+saveprev:
+ lzx_lz_skip_bytes(ctx, prev_match.len - 2);
+ ctx->optimum[ctx->optimum_end_idx].next.link = prev_match.len;
+ ctx->optimum[ctx->optimum_end_idx].next.match_offset = prev_match.offset;
+ ctx->optimum_end_idx++;
+retopt:
+ prev_match.len = ctx->optimum[ctx->optimum_cur_idx].next.link;
+ prev_match.offset = ctx->optimum[ctx->optimum_cur_idx].next.match_offset;
+ ctx->optimum_cur_idx++;
+ return prev_match;
+}
+#endif
+
+
/*
* lzx_lz_get_near_optimal_match() -
*
- * Choose the "best" match or literal to use at the next position in the input.
+ * Choose the optimal match or literal to use at the next position in the input.
*
- * Unlike a "greedy" parser that always takes the longest match, or even a
+ * Unlike a greedy parser that always takes the longest match, or even a
* parser with one match/literal look-ahead like zlib, the algorithm used here
- * may look ahead many matches/literals to determine the best match/literal to
+ * may look ahead many matches/literals to determine the optimal match/literal to
* output next. The motivation is that the compression ratio is improved if the
* compressor can do things like use a shorter-than-possible match in order to
* allow a longer match later, and also take into account the Huffman code cost
- * model rather than simply assuming that longer is better. It is not a true
- * "optimal" parser, however, since some shortcuts can be taken; for example, if
- * a match is very long, the parser just chooses it immediately before too much
- * time is wasting considering many different alternatives that are unlikely to
- * be better.
+ * model rather than simply assuming that longer is better.
+ *
+ * Still, this is not truly an optimal parser because very long matches are
+ * taken immediately. This is done to avoid considering many different
+ * alternatives that are unlikely to significantly be better.
*
* This algorithm is based on that used in 7-Zip's DEFLATE encoder.
*
* ctx->optimum (internal state; leave uninitialized)
* ctx->optimum_cur_idx (must set to 0 before first call)
* ctx->optimum_end_idx (must set to 0 before first call)
- * ctx->hash_tab (must set to 0 before first call)
- * ctx->cached_matches (internal state; leave uninitialized)
- * ctx->cached_matches_pos (initialize to 0 before first call; save and
- * restore value if restarting parse from a
- * certain position)
+ * ctx->SA (must be built before first call)
+ * ctx->ISA (must be built before first call)
+ * ctx->salink (must be built before first call)
* ctx->match_window_pos (must initialize to position of next match to
* return; subsequent calls return subsequent
* matches)
* subsequent calls use the same limit)
*
* The return value is a (length, offset) pair specifying the match or literal
- * chosen. For literals, length is either 0 or 1 and offset is meaningless.
+ * chosen. For literals, the length is less than LZX_MIN_MATCH_LEN and the
+ * offset is meaningless.
*/
static struct raw_match
lzx_lz_get_near_optimal_match(struct lzx_compressor * ctx)
{
-#if 0
- /* Testing: literals only */
- ctx->match_window_pos++;
- return (struct raw_match) { .len = 0 };
-#elif 0
- /* Testing: greedy parsing */
- struct raw_match *matches;
- unsigned num_matches;
- struct raw_match match = {.len = 0};
-
- num_matches = lzx_lz_get_matches_caching(ctx, &matches);
- if (num_matches) {
- match = matches[num_matches - 1];
- lzx_lz_skip_bytes(ctx, match.len - 1);
- }
- return match;
-#else
unsigned num_possible_matches;
struct raw_match *possible_matches;
struct raw_match match;
unsigned longest_match_len;
- unsigned len, match_idx;
if (ctx->optimum_cur_idx != ctx->optimum_end_idx) {
/* Case 2: Return the next match/literal already found. */
ctx->optimum_end_idx = 0;
/* Get matches at this position. */
- num_possible_matches = lzx_lz_get_matches_caching(ctx, &possible_matches);
+ num_possible_matches = lzx_lz_get_matches_caching(ctx, &ctx->queue, &possible_matches);
/* If no matches found, return literal. */
if (num_possible_matches == 0)
return (struct raw_match){ .len = 0 };
- /* The matches that were found are sorted by length. Get the length of
- * the longest one. */
- longest_match_len = possible_matches[num_possible_matches - 1].len;
+ /* The matches that were found are sorted in decreasing order by length.
+ * Get the length of the longest one. */
+ longest_match_len = possible_matches[0].len;
/* Greedy heuristic: if the longest match that was found is greater
* than the number of fast bytes, return it immediately; don't both
* doing more work. */
if (longest_match_len > ctx->params.alg_params.slow.num_fast_bytes) {
lzx_lz_skip_bytes(ctx, longest_match_len - 1);
- return possible_matches[num_possible_matches - 1];
+ return possible_matches[0];
}
/* Calculate the cost to reach the next position by outputting a
* literal. */
-#if LZX_PARAM_ACCOUNT_FOR_LRU
ctx->optimum[0].queue = ctx->queue;
ctx->optimum[1].queue = ctx->optimum[0].queue;
-#endif
ctx->optimum[1].cost = lzx_literal_cost(ctx->window[ctx->match_window_pos],
&ctx->costs);
ctx->optimum[1].prev.link = 0;
/* Calculate the cost to reach any position up to and including that
* reached by the longest match, using the shortest (i.e. closest) match
* that reaches each position. */
- match_idx = 0;
- BUILD_BUG_ON(LZX_MIN_MATCH != 2);
- for (len = LZX_MIN_MATCH; len <= longest_match_len; len++) {
+ BUILD_BUG_ON(LZX_MIN_MATCH_LEN != 2);
+ for (unsigned len = LZX_MIN_MATCH_LEN, match_idx = num_possible_matches - 1;
+ len <= longest_match_len; len++) {
LZX_ASSERT(match_idx < num_possible_matches);
- #if LZX_PARAM_ACCOUNT_FOR_LRU
ctx->optimum[len].queue = ctx->optimum[0].queue;
- #endif
ctx->optimum[len].prev.link = 0;
ctx->optimum[len].prev.match_offset = possible_matches[match_idx].offset;
ctx->optimum[len].cost = lzx_match_cost(len,
possible_matches[match_idx].offset,
- &ctx->costs
- #if LZX_PARAM_ACCOUNT_FOR_LRU
- , &ctx->optimum[len].queue
- #endif
- );
+ &ctx->costs,
+ &ctx->optimum[len].queue);
if (len == possible_matches[match_idx].len)
- match_idx++;
+ match_idx--;
}
unsigned cur_pos = 0;
* so far */
unsigned len_end = longest_match_len;
-
for (;;) {
/* Advance to next position. */
cur_pos++;
- if (cur_pos == len_end || cur_pos == LZX_PARAM_OPTIM_ARRAY_SIZE)
+ if (cur_pos == len_end || cur_pos == LZX_OPTIM_ARRAY_SIZE)
return lzx_lz_reverse_near_optimal_match_list(ctx, cur_pos);
/* retrieve the number of matches available at this position */
- num_possible_matches = lzx_lz_get_matches_caching(ctx,
+ num_possible_matches = lzx_lz_get_matches_caching(ctx, &ctx->optimum[cur_pos].queue,
&possible_matches);
unsigned new_len = 0;
if (num_possible_matches != 0) {
- new_len = possible_matches[num_possible_matches - 1].len;
+ new_len = possible_matches[0].len;
/* Greedy heuristic: if we found a match greater than
* the number of fast bytes, stop immediately. */
/* Append the long match to the end of the list. */
ctx->optimum[cur_pos].next.match_offset =
- possible_matches[num_possible_matches - 1].offset;
+ possible_matches[0].offset;
ctx->optimum[cur_pos].next.link = cur_pos + new_len;
ctx->optimum_end_idx = cur_pos + new_len;
}
/* Consider proceeding with a literal byte. */
- u32 cur_cost = ctx->optimum[cur_pos].cost;
- u32 cur_plus_literal_cost = cur_cost +
+ block_cost_t cur_cost = ctx->optimum[cur_pos].cost;
+ block_cost_t cur_plus_literal_cost = cur_cost +
lzx_literal_cost(ctx->window[ctx->match_window_pos - 1],
&ctx->costs);
if (cur_plus_literal_cost < ctx->optimum[cur_pos + 1].cost) {
ctx->optimum[cur_pos + 1].cost = cur_plus_literal_cost;
ctx->optimum[cur_pos + 1].prev.link = cur_pos;
- #if LZX_PARAM_ACCOUNT_FOR_LRU
ctx->optimum[cur_pos + 1].queue = ctx->optimum[cur_pos].queue;
- #endif
}
if (num_possible_matches == 0)
/* Consider proceeding with a match. */
while (len_end < cur_pos + new_len)
- ctx->optimum[++len_end].cost = ~(u32)0;
+ ctx->optimum[++len_end].cost = INFINITE_BLOCK_COST;
- match_idx = 0;
- for (len = LZX_MIN_MATCH; len <= new_len; len++) {
+ for (unsigned len = LZX_MIN_MATCH_LEN, match_idx = num_possible_matches - 1;
+ len <= new_len; len++) {
LZX_ASSERT(match_idx < num_possible_matches);
- #if LZX_PARAM_ACCOUNT_FOR_LRU
struct lzx_lru_queue q = ctx->optimum[cur_pos].queue;
- #endif
- u32 cost = cur_cost + lzx_match_cost(len,
- possible_matches[match_idx].offset,
- &ctx->costs
- #if LZX_PARAM_ACCOUNT_FOR_LRU
- , &q
- #endif
- );
+ block_cost_t cost = cur_cost + lzx_match_cost(len,
+ possible_matches[match_idx].offset,
+ &ctx->costs,
+ &q);
if (cost < ctx->optimum[cur_pos + len].cost) {
ctx->optimum[cur_pos + len].cost = cost;
ctx->optimum[cur_pos + len].prev.link = cur_pos;
ctx->optimum[cur_pos + len].prev.match_offset =
possible_matches[match_idx].offset;
- #if LZX_PARAM_ACCOUNT_FOR_LRU
ctx->optimum[cur_pos + len].queue = q;
- #endif
}
if (len == possible_matches[match_idx].len)
- match_idx++;
+ match_idx--;
}
}
-#endif
}
-static unsigned
-lzx_huffman_code_output_cost(const u8 lens[restrict],
- const freq_t freqs[restrict],
- unsigned num_syms)
+/*
+ * Set default symbol costs.
+ */
+static void
+lzx_set_default_costs(struct lzx_costs * costs)
{
- unsigned cost = 0;
+ unsigned i;
+
+ /* Literal symbols */
+ for (i = 0; i < LZX_NUM_CHARS; i++)
+ costs->main[i] = 8;
- for (unsigned i = 0; i < num_syms; i++)
- cost += (unsigned)lens[i] * (unsigned)freqs[i];
+ /* Match header symbols */
+ for (; i < LZX_MAINCODE_NUM_SYMBOLS; i++)
+ costs->main[i] = 10;
- return cost;
+ /* Length symbols */
+ for (i = 0; i < LZX_LENCODE_NUM_SYMBOLS; i++)
+ costs->len[i] = 8;
+
+ /* Aligned offset symbols */
+ for (i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++)
+ costs->aligned[i] = 3;
}
-/* Return the number of bits required to output the lengths for the specified
- * Huffman code in compressed format (encoded with a precode). */
-static unsigned
-lzx_code_cost(const u8 lens[], const u8 prev_lens[], unsigned num_syms)
+/* Given the frequencies of symbols in a 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)
{
- u8 output_syms[num_syms];
- freq_t precode_freqs[LZX_PRETREE_NUM_SYMBOLS];
- u8 precode_lens[LZX_PRETREE_NUM_SYMBOLS];
- u16 precode_codewords[LZX_PRETREE_NUM_SYMBOLS];
- unsigned cost = 0;
- unsigned num_additional_bits;
+ unsigned aligned_cost = 0;
+ unsigned verbatim_cost = 0;
- /* Acount for the lengths of the precode itself. */
- cost += LZX_PRETREE_NUM_SYMBOLS * LZX_PRETREE_ELEMENT_SIZE;
+ /* Verbatim blocks have a constant 3 bits per position footer. Aligned
+ * offset blocks have an aligned offset symbol per position footer, plus
+ * an extra 24 bits to output the lengths necessary to reconstruct the
+ * aligned offset code itself. */
+ for (unsigned i = 0; i < LZX_ALIGNEDCODE_NUM_SYMBOLS; i++) {
+ verbatim_cost += 3 * freqs->aligned[i];
+ aligned_cost += codes->lens.aligned[i] * freqs->aligned[i];
+ }
+ aligned_cost += LZX_ALIGNEDCODE_ELEMENT_SIZE * LZX_ALIGNEDCODE_NUM_SYMBOLS;
+ if (aligned_cost < verbatim_cost)
+ return LZX_BLOCKTYPE_ALIGNED;
+ else
+ return LZX_BLOCKTYPE_VERBATIM;
+}
- lzx_build_precode(lens, prev_lens, num_syms,
- precode_freqs, output_syms,
- precode_lens, precode_codewords,
- &num_additional_bits);
+/* Find a near-optimal sequence of matches/literals with which to output the
+ * specified LZX block, and set its type to that which has the minimum cost to
+ * output. */
+static void
+lzx_optimize_block(struct lzx_compressor *ctx, struct lzx_block_spec *spec,
+ unsigned num_passes)
+{
+ struct lzx_lru_queue orig_queue = ctx->queue;
+ struct lzx_freqs freqs;
- /* Account for all precode symbols output. */
- cost += lzx_huffman_code_output_cost(precode_lens, precode_freqs,
- LZX_PRETREE_NUM_SYMBOLS);
+ ctx->match_window_end = spec->window_pos + spec->block_size;
+ spec->chosen_matches_start_pos = spec->window_pos;
- /* Account for additional bits. */
- cost += num_additional_bits;
+ LZX_ASSERT(num_passes >= 1);
- return cost;
-}
+ /* The first optimal parsing pass is done using the cost model already
+ * set in ctx->costs. Each later pass is done using a cost model
+ * computed from the previous pass. */
+ for (unsigned pass = 0; pass < num_passes; pass++) {
-/* Account for extra bits in the main symbols. */
-static void
-lzx_update_mainsym_match_costs(int block_type,
- u8 main_lens[LZX_MAINTREE_NUM_SYMBOLS])
-{
- unsigned i;
+ lzx_lz_rewind_matchfinder(ctx, spec->window_pos);
+ ctx->queue = orig_queue;
+ spec->num_chosen_matches = 0;
+ memset(&freqs, 0, sizeof(freqs));
- LZX_ASSERT(block_type == LZX_BLOCKTYPE_ALIGNED ||
- block_type == LZX_BLOCKTYPE_VERBATIM);
+ for (unsigned i = spec->window_pos; i < spec->window_pos + spec->block_size; ) {
+ struct raw_match raw_match;
+ struct lzx_match lzx_match;
- for (i = LZX_NUM_CHARS; i < LZX_MAINTREE_NUM_SYMBOLS; i++) {
- unsigned position_slot = (i >> 3) & 0x1f;
+ raw_match = lzx_lz_get_near_optimal_match(ctx);
+ if (raw_match.len >= LZX_MIN_MATCH_LEN) {
+ lzx_match.data = lzx_record_match(raw_match.offset, raw_match.len,
+ &freqs, &ctx->queue);
+ i += raw_match.len;
+ } else {
+ lzx_match.data = lzx_record_literal(ctx->window[i], &freqs);
+ i += 1;
+ }
+ ctx->chosen_matches[spec->chosen_matches_start_pos +
+ spec->num_chosen_matches++] = lzx_match;
+ }
- /* If it's a verbatim block, add the number of extra bits
- * corresponding to the position slot.
- *
- * If it's an aligned block and there would normally be at least
- * 3 extra bits, count 3 less because they will be output as an
- * aligned offset symbol instead. */
- unsigned num_extra_bits = lzx_get_num_extra_bits(position_slot);
-
- if (block_type == LZX_BLOCKTYPE_ALIGNED && num_extra_bits >= 3)
- num_extra_bits -= 3;
- main_lens[i] += num_extra_bits;
+ lzx_make_huffman_codes(&freqs, &spec->codes);
+ if (pass < num_passes - 1)
+ lzx_set_costs(ctx, &spec->codes.lens);
}
+ spec->block_type = lzx_choose_verbatim_or_aligned(&freqs, &spec->codes);
}
-/*
- * Compute the costs, in bits, to output a compressed block as aligned offset
- * and verbatim.
- *
- * @block_size
- * Number of bytes of uncompressed data the block represents.
- * @codes
- * Huffman codes that will be used when outputting the block.
- * @prev_codes
- * Huffman codes for the previous block, or all zeroes if this is the first
- * block.
- * @freqs
- * Frequencies of Huffman symbols that will be output in the block.
- * @aligned_cost_ret
- * Cost of aligned block will be returned here.
- * @verbatim_cost_ret
- * Cost of verbatim block will be returned here.
- */
static void
-lzx_compute_compressed_block_costs(unsigned block_size,
- const struct lzx_codes *codes,
- const struct lzx_codes *prev_codes,
- const struct lzx_freqs *freqs,
- unsigned * aligned_cost_ret,
- unsigned * verbatim_cost_ret)
+lzx_optimize_blocks(struct lzx_compressor *ctx)
{
- unsigned common_cost = 0;
- unsigned aligned_cost = 0;
- unsigned verbatim_cost = 0;
+ lzx_lru_queue_init(&ctx->queue);
+ ctx->optimum_cur_idx = 0;
+ ctx->optimum_end_idx = 0;
- u8 updated_main_lens[LZX_MAINTREE_NUM_SYMBOLS];
+ const unsigned num_passes = ctx->params.alg_params.slow.num_optim_passes;
- /* Account for cost of block header. */
- common_cost += LZX_BLOCKTYPE_NBITS;
- if (block_size == LZX_DEFAULT_BLOCK_SIZE)
- common_cost += 1;
- else
- common_cost += LZX_BLOCKSIZE_NBITS;
-
- /* Account for cost of outputting aligned offset code. */
- aligned_cost += LZX_ALIGNEDTREE_NUM_SYMBOLS * LZX_ALIGNEDTREE_ELEMENT_SIZE;
-
- /* Account for cost of outputting main and length codes. */
- common_cost += lzx_code_cost(codes->lens.main,
- prev_codes->lens.main,
- LZX_NUM_CHARS);
- common_cost += lzx_code_cost(codes->lens.main + LZX_NUM_CHARS,
- prev_codes->lens.main + LZX_NUM_CHARS,
- LZX_MAINTREE_NUM_SYMBOLS - LZX_NUM_CHARS);
- common_cost += lzx_code_cost(codes->lens.len,
- prev_codes->lens.len,
- LZX_LENTREE_NUM_SYMBOLS);
-
- /* Account for cost to output main, length, and aligned symbols, taking
- * into account extra position bits. */
-
- memcpy(updated_main_lens, codes->lens.main, LZX_MAINTREE_NUM_SYMBOLS);
- lzx_update_mainsym_match_costs(LZX_BLOCKTYPE_VERBATIM, updated_main_lens);
- verbatim_cost += lzx_huffman_code_output_cost(updated_main_lens,
- freqs->main,
- LZX_MAINTREE_NUM_SYMBOLS);
- memcpy(updated_main_lens, codes->lens.main, LZX_MAINTREE_NUM_SYMBOLS);
- lzx_update_mainsym_match_costs(LZX_BLOCKTYPE_ALIGNED, updated_main_lens);
- aligned_cost += lzx_huffman_code_output_cost(updated_main_lens,
- freqs->main,
- LZX_MAINTREE_NUM_SYMBOLS);
-
- common_cost += lzx_huffman_code_output_cost(codes->lens.len,
- freqs->len,
- LZX_LENTREE_NUM_SYMBOLS);
-
- aligned_cost += lzx_huffman_code_output_cost(codes->lens.aligned,
- freqs->aligned,
- LZX_ALIGNEDTREE_NUM_SYMBOLS);
-
- *aligned_cost_ret = aligned_cost + common_cost;
- *verbatim_cost_ret = verbatim_cost + common_cost;
+ for (unsigned i = 0; i < ctx->num_blocks; i++)
+ lzx_optimize_block(ctx, &ctx->block_specs[i], num_passes);
}
-/* Prepare a (nonsplit) compressed block. */
-static unsigned
-lzx_prepare_compressed_block(struct lzx_compressor *ctx, unsigned block_number,
- struct lzx_codes *prev_codes)
-{
- struct lzx_block_spec *spec = &ctx->block_specs[block_number - 1];
- unsigned orig_cached_matches_pos = ctx->cached_matches_pos;
- struct lzx_lru_queue orig_queue = ctx->queue;
- struct lzx_freqs freqs;
- unsigned cost;
-
- /* Here's where the real work happens. The following loop runs one or
- * more times, each time using a cost model based on the Huffman codes
- * computed from the previous iteration (the first iteration uses a
- * default model). Each iteration of the loop uses a heuristic
- * algorithm to divide the block into near-optimal matches/literals from
- * beginning to end. */
- LZX_ASSERT(ctx->params.alg_params.slow.num_optim_passes >= 1);
- spec->num_chosen_matches = 0;
- for (unsigned pass = 0; pass < ctx->params.alg_params.slow.num_optim_passes; pass++)
- {
- LZX_DEBUG("Block %u: Match-choosing pass %u of %u",
- block_number, pass + 1,
- ctx->params.alg_params.slow.num_optim_passes);
-
- /* Reset frequency tables. */
- memset(&freqs, 0, sizeof(freqs));
+static bool entropy_val_tab_inited = false;
+static double entropy_val_tab[LZX_MAX_WINDOW_SIZE];
+static pthread_mutex_t entropy_val_tab_mutex = PTHREAD_MUTEX_INITIALIZER;
- /* Reset match offset LRU queue. */
- ctx->queue = orig_queue;
+static double entropy_val(unsigned count)
+{
+ /*return count * log(count);*/
+ return entropy_val_tab[count];
+}
- /* Reset match-finding position. */
- ctx->cached_matches_pos = orig_cached_matches_pos;
- ctx->match_window_pos = spec->window_pos;
- ctx->match_window_end = spec->window_pos + spec->block_size;
+/* Split a LZX block into several if it is advantageous to do so.
+ *
+ * TODO: This doesn't work very well yet. Should optimal parsing be done
+ * before or after splitting? */
+static void
+lzx_block_split(const u32 matches[restrict],
+ const input_idx_t n,
+ const double epsilon,
+ const unsigned max_num_blocks,
+ const unsigned min_block_len,
+ struct lzx_block_spec block_specs[restrict],
+ unsigned * const restrict num_blocks_ret)
+{
+ const double block_overhead = 1500;
+
+ if (!entropy_val_tab_inited) {
+ pthread_mutex_lock(&entropy_val_tab_mutex);
+ if (!entropy_val_tab_inited) {
+ entropy_val_tab[0] = 0;
+ for (input_idx_t i = 1; i < LZX_MAX_WINDOW_SIZE; i++)
+ entropy_val_tab[i] = i * log2(i);
+ entropy_val_tab_inited = true;
+ }
+ pthread_mutex_unlock(&entropy_val_tab_mutex);
+ }
- /* Set cost model. */
- lzx_set_costs(ctx, &spec->codes.lens);
+ u16 main_syms[n];
+ u8 len_syms[n];
+ u8 aligned_syms[n];
+ input_idx_t orig_input_indices[n + 1];
+
+ LZX_ASSERT(epsilon >= 0);
+ LZX_ASSERT(max_num_blocks >= 1);
+
+ /* For convenience, extract the main, length, and aligned symbols from
+ * the matches. Every position will have a main symbol, but not every
+ * position will have a length and aligned symbol. Special values
+ * larger than the valid symbols are used to indicate the absense of a
+ * symbol. */
+ orig_input_indices[0] = 0;
+ for (input_idx_t i = 0, orig_input_idx = 0; i < n; i++) {
+ u32 match = matches[i];
+ u16 main_sym;
+ u8 len_sym = LZX_LENCODE_NUM_SYMBOLS;
+ u8 aligned_sym = LZX_ALIGNEDCODE_NUM_SYMBOLS;
+ if (match & 0x80000000) {
+ unsigned match_len_minus_2 = match & 0xff;
+ unsigned position_footer = (match >> 8) & 0x1ffff;
+ unsigned position_slot = (match >> 25) & 0x3f;
+ unsigned len_header;
+
+ if (match_len_minus_2 < LZX_NUM_PRIMARY_LENS) {
+ len_header = match_len_minus_2;
+ } else {
+ len_header = LZX_NUM_PRIMARY_LENS;
+ len_sym = match_len_minus_2 - LZX_NUM_PRIMARY_LENS;
+ }
+ main_sym = ((position_slot << 3) | len_header) + LZX_NUM_CHARS;
+ if (position_slot >= 8)
+ aligned_sym = position_footer & 7;
+ orig_input_idx += match_len_minus_2 + 2;
+ } else {
+ main_sym = match;
+ orig_input_idx++;
+ }
+ main_syms[i] = main_sym;
+ len_syms[i] = len_sym;
+ aligned_syms[i] = aligned_sym;
+ orig_input_indices[i + 1] = orig_input_idx;
+ }
- unsigned window_pos = spec->window_pos;
- unsigned end = window_pos + spec->block_size;
+ /* Compute the number of sliding windows that will be used for the
+ * entropy calculations. */
+ int num_windows = 0;
+ unsigned window_len;
+ {
+ double e = min_block_len;
+ do {
+ window_len = e;
+ num_windows++;
+ e *= epsilon + 1;
+ } while (window_len < n);
+ }
- while (window_pos < end) {
- struct raw_match match;
- struct lzx_match lzx_match;
+ /* Compute the length of each sliding window. */
+ unsigned window_lens[num_windows];
+ {
+ double e = min_block_len;
+ unsigned window_idx = 0;
+ do {
+ window_len = e;
+ window_lens[window_idx++] = min(window_len, n);
+ e *= epsilon + 1;
+ } while (window_len < n);
+ }
- match = lzx_lz_get_near_optimal_match(ctx);
+ /* Best estimated compression size, in bits, found so far for the input
+ * matches up to each position. */
+ unsigned shortest_paths[n + 1];
- if (match.len >= LZX_MIN_MATCH) {
+ /* Pointers to follow to get the sequence of blocks that represents the
+ * shortest path (in terms of estimated compressed size) up to each
+ * position in the input matches. */
+ input_idx_t back_ptrs[n + 1];
- /* Best to output a match here. */
+ for (input_idx_t i = 0; i < n + 1; i++) {
+ shortest_paths[i] = ~0U;
+ back_ptrs[i] = 0;
+ }
+ shortest_paths[0] = 0;
- LZX_ASSERT(match.len <= LZX_MAX_MATCH);
- LZX_ASSERT(!memcmp(&ctx->window[window_pos],
- &ctx->window[window_pos - match.offset],
- match.len));
+ {
+ /* Initialize the per-window symbol and entropy counters */
+ input_idx_t mainsym_ctrs[num_windows][LZX_MAINCODE_NUM_SYMBOLS];
+ input_idx_t lensym_ctrs[num_windows][LZX_LENCODE_NUM_SYMBOLS + 1];
+ input_idx_t alignedsym_ctrs[num_windows][LZX_ALIGNEDCODE_NUM_SYMBOLS + 1];
+ ZERO_ARRAY(mainsym_ctrs);
+ ZERO_ARRAY(lensym_ctrs);
+ ZERO_ARRAY(alignedsym_ctrs);
- /* Tally symbol frequencies. */
- lzx_match.data = lzx_record_match(match.offset,
- match.len,
- &freqs,
- &ctx->queue);
+ {
+ int start_win_idx = 0;
+ for (input_idx_t i = 0; i < n; i++) {
+ while (i >= window_lens[start_win_idx])
+ start_win_idx++;
+ for (int j = start_win_idx; j < num_windows; j++) {
+ mainsym_ctrs[j][main_syms[i]]++;
+ lensym_ctrs[j][len_syms[i]]++;
+ alignedsym_ctrs[j][aligned_syms[i]]++;
+ }
+ }
+ }
- window_pos += match.len;
- } else {
- /* Best to output a literal here. */
+ double entropy_ctrs[num_windows];
+ for (int i = 0; i < num_windows; i++) {
+ entropy_ctrs[i] = 0;
+ for (unsigned j = 0; j < LZX_MAINCODE_NUM_SYMBOLS; j++)
+ entropy_ctrs[i] += entropy_val(mainsym_ctrs[i][j]);
+ for (unsigned j = 0; j < LZX_LENCODE_NUM_SYMBOLS; j++)
+ entropy_ctrs[i] += entropy_val(lensym_ctrs[i][j]);
+ for (unsigned j = 0; j < LZX_ALIGNEDCODE_NUM_SYMBOLS; j++)
+ entropy_ctrs[i] += entropy_val(alignedsym_ctrs[i][j]);
+ }
- /* Tally symbol frequencies. */
- lzx_match.data = lzx_record_literal(ctx->window[window_pos],
- &freqs);
+ /* Slide the windows along the input and compute the shortest
+ * path to each position in the matches. */
+ int end_window_idx = (int)num_windows - 1;
+ for (input_idx_t i = 0; i < n; i++) {
+ for (int j = 0; j <= end_window_idx; j++) {
+ if (shortest_paths[i] == ~0U)
+ continue;
+ unsigned num_mainsyms = window_lens[j];
+ unsigned num_lensyms = window_lens[j] -
+ lensym_ctrs[j][LZX_LENCODE_NUM_SYMBOLS];
+ unsigned num_alignedsyms = window_lens[j] -
+ alignedsym_ctrs[j][LZX_ALIGNEDCODE_NUM_SYMBOLS];
+ unsigned entropy = entropy_val(num_mainsyms) +
+ entropy_val(num_lensyms) +
+ entropy_val(num_alignedsyms) -
+ entropy_ctrs[j];
+ unsigned est_csize = entropy + block_overhead;
+
+ unsigned end_idx = i + window_lens[j];
+ if (est_csize + shortest_paths[i] < shortest_paths[end_idx]) {
+ shortest_paths[end_idx] = est_csize + shortest_paths[i];
+ back_ptrs[end_idx] = i;
+ }
+ }
+ /* Remove left symbol from windows */
+ for (int j = 0; j <= end_window_idx; j++) {
+ input_idx_t orig_maincnt = mainsym_ctrs[j][main_syms[i]]--;
+ entropy_ctrs[j] -= entropy_val(orig_maincnt);
+ entropy_ctrs[j] += entropy_val(orig_maincnt - 1);
+
+ input_idx_t orig_lencnt =
+ lensym_ctrs[j][len_syms[i]]--;
+ if (len_syms[i] != LZX_LENCODE_NUM_SYMBOLS) {
+ entropy_ctrs[j] -= entropy_val(orig_lencnt);
+ entropy_ctrs[j] += entropy_val(orig_lencnt - 1);
+ }
- window_pos += 1;
+ input_idx_t orig_alignedcnt =
+ alignedsym_ctrs[j][aligned_syms[i]]--;
+ if (aligned_syms[i] != LZX_ALIGNEDCODE_NUM_SYMBOLS) {
+ entropy_ctrs[j] -= entropy_val(orig_alignedcnt);
+ entropy_ctrs[j] += entropy_val(orig_alignedcnt - 1);
+ }
}
- /* If it's the last pass, save the match/literal in
- * intermediate form. */
- if (pass == ctx->params.alg_params.slow.num_optim_passes - 1) {
- ctx->chosen_matches[spec->chosen_matches_start_pos +
- spec->num_chosen_matches] = lzx_match;
+ /* Calculate index of longest window remaining */
+ while (end_window_idx >= 0 && window_lens[end_window_idx] >= n - i)
+ end_window_idx--;
+
+ /* Append right symbol to windows */
+ for (int j = 0; j <= end_window_idx; j++) {
+ input_idx_t orig_maincnt = mainsym_ctrs[j][
+ main_syms[i + window_lens[j]]]++;
+ entropy_ctrs[j] -= entropy_val(orig_maincnt);
+ entropy_ctrs[j] += entropy_val(orig_maincnt + 1);
+
+ input_idx_t orig_lencnt =
+ lensym_ctrs[j][len_syms[i + window_lens[j]]]++;
+ if (len_syms[i + window_lens[j]] != LZX_LENCODE_NUM_SYMBOLS) {
+ entropy_ctrs[j] -= entropy_val(orig_lencnt);
+ entropy_ctrs[j] += entropy_val(orig_lencnt + 1);
+ }
- spec->num_chosen_matches++;
+ input_idx_t orig_alignedcnt =
+ alignedsym_ctrs[j][aligned_syms[i + window_lens[j]]]++;
+ if (aligned_syms[i + window_lens[j]] != LZX_ALIGNEDCODE_NUM_SYMBOLS) {
+ entropy_ctrs[j] -= entropy_val(orig_alignedcnt);
+ entropy_ctrs[j] += entropy_val(orig_alignedcnt + 1);
+ }
}
}
- LZX_ASSERT(window_pos == end);
+ }
- /* Build Huffman codes using the new frequencies. */
- lzx_make_huffman_codes(&freqs, &spec->codes);
+#if 0
+ /* If no cost was computed for the first block (due to it being shorter
+ * than all the windows), merge it with the second block. */
+ for (input_idx_t i = n; i != 0; i = back_ptrs[i])
+ if (back_ptrs[i] != 0 && shortest_paths[back_ptrs[i]] == ~0U)
+ back_ptrs[i] = 0;
+#endif
+
+ /* Calculate number of blocks */
+ input_idx_t num_blocks = 0;
+ for (input_idx_t i = n; i != 0; i = back_ptrs[i])
+ num_blocks++;
- /* The first time we get here is when the full input has been
- * processed, so the match-finding is done. */
- ctx->matches_already_found = true;
+ while (num_blocks > max_num_blocks) {
+ LZX_DEBUG("Joining blocks to bring total under max_num_blucks=%u",
+ max_num_blocks);
+ back_ptrs[n] = back_ptrs[back_ptrs[n]];
+ num_blocks--;
}
- LZX_DEBUG("Block %u: saved %u matches/literals @ %u",
- block_number, spec->num_chosen_matches,
- spec->chosen_matches_start_pos);
+ LZX_ASSERT(num_blocks != 0);
- unsigned aligned_cost;
- unsigned verbatim_cost;
+ /* fill in the 'struct lzx_block_spec' for each block */
+ for (input_idx_t i = n, j = num_blocks - 1; i != 0; i = back_ptrs[i], j--) {
- lzx_compute_compressed_block_costs(spec->block_size,
- &spec->codes,
- prev_codes,
- &freqs,
- &aligned_cost,
- &verbatim_cost);
-
- /* Choose whether to make the block aligned offset or verbatim. */
- if (aligned_cost < verbatim_cost) {
- spec->block_type = LZX_BLOCKTYPE_ALIGNED;
- cost = aligned_cost;
- LZX_DEBUG("Using aligned block (cost %u vs %u for verbatim)",
- aligned_cost, verbatim_cost);
- } else {
- spec->block_type = LZX_BLOCKTYPE_VERBATIM;
- cost = verbatim_cost;
- LZX_DEBUG("Using verbatim block (cost %u vs %u for aligned)",
- verbatim_cost, aligned_cost);
- }
+ block_specs[j].chosen_matches_start_pos = back_ptrs[i];
+ block_specs[j].num_chosen_matches = i - back_ptrs[i];
+ block_specs[j].window_pos = orig_input_indices[back_ptrs[i]];
+ block_specs[j].block_size = orig_input_indices[i] -
+ orig_input_indices[back_ptrs[i]];
+ /*block_specs[j].est_csize = (shortest_paths[i] -*/
+ /*shortest_paths[back_ptrs[i]]) / 8;*/
- LZX_DEBUG("Block %u is %u => %u bytes unsplit.",
- block_number, spec->block_size, cost / 8);
+ LZX_DEBUG("block match_indices [%u, %u) est_csize %u bits\n",
+ back_ptrs[i], i,
+ shortest_paths[i] - shortest_paths[back_ptrs[i]]);
- return cost;
+ struct lzx_freqs freqs = {};
+
+ for (input_idx_t k = back_ptrs[i]; k < i; k++) {
+ freqs.main[main_syms[k]]++;
+ if (len_syms[k] != LZX_LENCODE_NUM_SYMBOLS)
+ freqs.len[len_syms[k]]++;
+ if (aligned_syms[k] != LZX_LENCODE_NUM_SYMBOLS)
+ freqs.aligned[aligned_syms[k]]++;
+ }
+ lzx_make_huffman_codes(&freqs, &block_specs[j].codes);
+
+ block_specs[j].block_type = lzx_choose_verbatim_or_aligned(&freqs,
+ &block_specs[j].codes);
+ }
+ *num_blocks_ret = num_blocks;
}
-/*
- * lzx_prepare_block_recursive() -
- *
- * Given a (possibly nonproper) sub-sequence of the preprocessed input, compute
- * the LZX block(s) that it should be output as.
- *
- * This function initially considers the case where the given sub-sequence of
- * the preprocessed input be output as a single block. This block is calculated
- * and its cost (number of bits required to output it) is computed.
- *
- * Then, if @max_split_level is greater than zero, a split into two evenly sized
- * subblocks is considered. The block is recursively split in this way,
- * potentially up to the depth specified by @max_split_level. The cost of the
- * split block is compared to the cost of the single block, and the lower cost
- * solution is used.
- *
- * For each compressed output block computed, the sequence of matches/literals
- * and the corresponding Huffman codes for the block are produced and saved.
- *
- * The return value is the approximate number of bits the block (or all
- * subblocks, in the case that the split block had lower cost), will take up
- * when written to the compressed output.
- */
-static unsigned
-lzx_prepare_block_recursive(struct lzx_compressor * ctx,
- unsigned block_number,
- unsigned max_split_level,
- struct lzx_codes **prev_codes_p)
-{
- struct lzx_block_spec *spec = &ctx->block_specs[block_number - 1];
- unsigned cost;
- unsigned orig_cached_matches_pos;
- struct lzx_lru_queue orig_queue, nonsplit_queue;
- struct lzx_codes *prev_codes = *prev_codes_p;
- LZX_DEBUG("Preparing block %u...", block_number);
+/* Initialize the suffix array match-finder for the specified input. */
+static void
+lzx_lz_init_matchfinder(const u8 T[const restrict],
+ const input_idx_t n,
+ input_idx_t SA[const restrict],
+ input_idx_t ISA[const restrict],
+ input_idx_t LCP[const restrict],
+ struct salink link[const restrict],
+ const unsigned max_match_len)
+{
+ /* Compute SA (Suffix Array). */
- /* Save positions of chosen and cached matches, and the match offset LRU
- * queue, so that they can be restored if splitting is attempted. */
- orig_cached_matches_pos = ctx->cached_matches_pos;
- orig_queue = ctx->queue;
+ {
+ saidx_t sa[n];
+ /* ISA and link are used as temporary space. */
+ BUILD_BUG_ON(LZX_MAX_WINDOW_SIZE * sizeof(ISA[0]) < 256 * sizeof(saidx_t));
+ BUILD_BUG_ON(LZX_MAX_WINDOW_SIZE * 2 * sizeof(link[0]) < 256 * 256 * sizeof(saidx_t));
+ divsufsort(T, sa, n, (saidx_t*)ISA, (saidx_t*)link);
+ for (input_idx_t i = 0; i < n; i++)
+ SA[i] = sa[i];
+ }
- /* Consider outputting the input subsequence as a single block. */
- spec->is_split = 0;
- cost = lzx_prepare_compressed_block(ctx, block_number, prev_codes);
- nonsplit_queue = ctx->queue;
+#ifdef ENABLE_LZX_DEBUG
- *prev_codes_p = &spec->codes;
+ LZX_ASSERT(n > 0);
- /* If the maximum split level is at least one, consider splitting the
- * block in two. */
- if (max_split_level--) {
+ /* Verify suffix array. */
+ {
+ bool found[n];
+ ZERO_ARRAY(found);
+ for (input_idx_t r = 0; r < n; r++) {
+ input_idx_t i = SA[r];
+ LZX_ASSERT(i < n);
+ LZX_ASSERT(!found[i]);
+ found[i] = true;
+ }
+ }
- LZX_DEBUG("Calculating split of block %u...", block_number);
+ for (input_idx_t r = 0; r < n - 1; r++) {
- struct lzx_block_spec *spec1, *spec2;
- unsigned split_cost;
+ input_idx_t i1 = SA[r];
+ input_idx_t i2 = SA[r + 1];
- ctx->cached_matches_pos = orig_cached_matches_pos;
- ctx->queue = orig_queue;
+ input_idx_t n1 = n - i1;
+ input_idx_t n2 = n - i2;
- /* Prepare and get the cost of the first sub-block. */
- spec1 = &ctx->block_specs[block_number * 2 - 1];
- spec1->codes.lens = spec->codes.lens;
- spec1->window_pos = spec->window_pos;
- spec1->block_size = spec->block_size / 2;
- spec1->chosen_matches_start_pos = spec->chosen_matches_start_pos +
- LZX_MAX_WINDOW_SIZE;
- split_cost = lzx_prepare_block_recursive(ctx,
- block_number * 2,
- max_split_level,
- &prev_codes);
-
- /* Prepare and get the cost of the second sub-block. */
- spec2 = spec1 + 1;
- spec2->codes.lens = spec->codes.lens;
- spec2->window_pos = spec->window_pos + spec1->block_size;
- spec2->block_size = spec->block_size - spec1->block_size;
- spec2->chosen_matches_start_pos = spec1->chosen_matches_start_pos +
- spec1->block_size;
- split_cost += lzx_prepare_block_recursive(ctx,
- block_number * 2 + 1,
- max_split_level,
- &prev_codes);
-
- /* Compare the cost of the whole block with that of the split
- * block. Choose the lower cost solution. */
- if (split_cost < cost) {
- LZX_DEBUG("Splitting block %u is worth it "
- "(%u => %u bytes).",
- block_number, cost / 8, split_cost / 8);
- spec->is_split = 1;
- cost = split_cost;
- *prev_codes_p = prev_codes;
- } else {
- LZX_DEBUG("Splitting block %u is NOT worth it "
- "(%u => %u bytes).",
- block_number, cost / 8, split_cost / 8);
- ctx->queue = nonsplit_queue;
- }
+ LZX_ASSERT(memcmp(&T[i1], &T[i2], min(n1, n2)) <= 0);
}
+ LZX_DEBUG("Verified SA (len %u)", n);
+#endif /* ENABLE_LZX_DEBUG */
- return cost;
-}
+ /* Compute ISA (Inverse Suffix Array) */
+ for (input_idx_t r = 0; r < n; r++)
+ ISA[SA[r]] = r;
-/* Empirical averages */
-static const u8 lzx_default_mainsym_costs[LZX_MAINTREE_NUM_SYMBOLS] = {
- 7, 9, 9, 10, 9, 10, 10, 10, 9, 10, 9, 10, 10, 9, 10, 10, 9, 10, 10, 11,
- 10, 10, 10, 11, 10, 11, 11, 11, 10, 11, 11, 11, 8, 11, 9, 10, 9, 10, 11,
- 11, 9, 9, 11, 10, 10, 9, 9, 9, 8, 8, 8, 8, 8, 9, 9, 9, 8, 8, 9, 9, 9, 9,
- 10, 10, 10, 8, 9, 8, 8, 8, 8, 9, 9, 9, 10, 10, 8, 8, 9, 9, 8, 10, 9, 8,
- 8, 9, 8, 9, 9, 10, 10, 10, 9, 10, 11, 9, 10, 8, 9, 8, 8, 8, 8, 9, 8, 8,
- 9, 9, 8, 8, 8, 8, 8, 10, 8, 8, 7, 8, 9, 9, 9, 9, 10, 11, 10, 10, 11, 11,
- 10, 11, 11, 10, 10, 11, 11, 11, 10, 10, 11, 10, 11, 10, 11, 11, 10, 11,
- 11, 12, 11, 11, 11, 12, 11, 11, 11, 11, 11, 11, 11, 12, 10, 11, 11, 11,
- 11, 11, 11, 12, 11, 11, 11, 11, 11, 12, 11, 11, 10, 11, 11, 11, 11, 11,
- 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11,
- 10, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 12, 11, 11, 10, 11,
- 11, 11, 11, 12, 11, 11, 10, 11, 11, 11, 10, 12, 11, 11, 10, 10, 11, 10,
- 10, 11, 11, 11, 10, 11, 11, 11, 10, 11, 11, 11, 10, 11, 11, 11, 10, 11,
- 10, 9, 8, 7, 10, 10, 11, 10, 11, 7, 9, 9, 11, 11, 11, 12, 11, 9, 10, 10,
- 12, 12, 13, 13, 12, 11, 10, 12, 12, 14, 14, 14, 13, 12, 9, 12, 13, 14,
- 14, 14, 14, 14, 9, 10, 13, 14, 14, 14, 14, 14, 9, 9, 11, 11, 13, 13, 13,
- 14, 9, 9, 11, 12, 12, 13, 13, 13, 8, 8, 11, 11, 12, 12, 12, 11, 9, 9,
- 10, 11, 12, 12, 12, 11, 8, 9, 10, 10, 11, 12, 11, 10, 9, 9, 10, 11, 11,
- 12, 11, 10, 8, 9, 10, 10, 11, 11, 11, 9, 9, 9, 10, 11, 11, 11, 11, 9, 8,
- 8, 10, 10, 11, 11, 11, 9, 9, 9, 10, 10, 11, 11, 11, 9, 9, 8, 9, 10, 11,
- 11, 11, 9, 10, 9, 10, 11, 11, 11, 11, 9, 14, 9, 9, 10, 10, 11, 10, 9,
- 14, 9, 10, 11, 11, 11, 11, 9, 14, 9, 10, 10, 11, 11, 11, 9, 14, 10, 10,
- 11, 11, 12, 11, 10, 14, 10, 10, 10, 11, 11, 11, 10, 14, 11, 11, 11, 11,
- 12, 12, 10, 14, 10, 11, 11, 11, 12, 11, 10, 14, 11, 11, 11, 12, 12, 12,
- 11, 15, 11, 11, 11, 12, 12, 12, 11, 14, 12, 12, 12, 12, 13, 12, 11, 15,
- 12, 12, 12, 13, 13, 13, 12, 15, 14, 13, 14, 14, 14, 14, 13,
-};
+ /* Compute LCP (longest common prefix) array.
+ *
+ * Algorithm adapted from Kasai et al. 2001: "Linear-Time
+ * Longest-Common-Prefix Computation in Suffix Arrays and Its
+ * Applications". */
+ {
+ input_idx_t h = 0;
+ for (input_idx_t i = 0; i < n; i++) {
+ input_idx_t r = ISA[i];
+ if (r > 0) {
+ input_idx_t j = SA[r - 1];
+
+ input_idx_t lim = min(n - i, n - j);
+
+ while (h < lim && T[i + h] == T[j + h])
+ h++;
+ LCP[r] = h;
+ if (h > 0)
+ h--;
+ }
+ }
+ }
-/* Empirical averages */
-static const u8 lzx_default_lensym_costs[LZX_LENTREE_NUM_SYMBOLS] = {
- 5, 5, 5, 5, 5, 6, 5, 5, 6, 7, 7, 7, 8, 8, 7, 8, 9, 9, 9, 9, 10, 9, 9,
- 10, 9, 10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 12, 12, 12, 11, 12, 12,
- 12, 12, 12, 12, 13, 12, 12, 12, 13, 12, 13, 13, 12, 12, 13, 12, 13, 13,
- 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 14, 13, 14, 13, 14, 13,
- 14, 13, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
- 14, 13, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
- 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
- 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
- 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
- 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
- 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
- 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
- 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
- 14, 14, 14, 14, 14, 14, 14, 14, 14, 10,
-};
+#ifdef ENABLE_LZX_DEBUG
+ /* Verify LCP array. */
+ for (input_idx_t r = 0; r < n - 1; r++) {
+ LZX_ASSERT(ISA[SA[r]] == r);
+ LZX_ASSERT(ISA[SA[r + 1]] == r + 1);
-/*
- * Set default symbol costs.
- */
-static void
-lzx_set_default_costs(struct lzx_lens * lens)
-{
- unsigned i;
+ input_idx_t i1 = SA[r];
+ input_idx_t i2 = SA[r + 1];
+ input_idx_t lcp = LCP[r + 1];
-#if LZX_PARAM_USE_EMPIRICAL_DEFAULT_COSTS
- memcpy(&lens->main, lzx_default_mainsym_costs, LZX_MAINTREE_NUM_SYMBOLS);
- memcpy(&lens->len, lzx_default_lensym_costs, LZX_LENTREE_NUM_SYMBOLS);
+ input_idx_t n1 = n - i1;
+ input_idx_t n2 = n - i2;
-#else
- /* Literal symbols */
- for (i = 0; i < LZX_NUM_CHARS; i++)
- lens->main[i] = 8;
+ LZX_ASSERT(lcp <= min(n1, n2));
- /* Match header symbols */
- for (; i < LZX_MAINTREE_NUM_SYMBOLS; i++)
- lens->main[i] = 10;
+ LZX_ASSERT(memcmp(&T[i1], &T[i2], lcp) == 0);
+ if (lcp < min(n1, n2))
+ LZX_ASSERT(T[i1 + lcp] != T[i2 + lcp]);
+ }
+#endif /* ENABLE_LZX_DEBUG */
- /* Length symbols */
- for (i = 0; i < LZX_LENTREE_NUM_SYMBOLS; i++)
- lens->len[i] = 8;
-#endif
+ /* Compute salink.next and salink.lcpnext.
+ *
+ * Algorithm adapted from Crochemore et al. 2009:
+ * "LPF computation revisited".
+ *
+ * Note: we cap lcpnext to the maximum match length so that the
+ * match-finder need not worry about it later. */
+ link[n - 1].next = (input_idx_t)~0U;
+ link[n - 1].prev = (input_idx_t)~0U;
+ link[n - 1].lcpnext = 0;
+ link[n - 1].lcpprev = 0;
+ for (input_idx_t r = n - 2; r != (input_idx_t)~0U; r--) {
+ input_idx_t t = r + 1;
+ input_idx_t l = LCP[t];
+ while (t != (input_idx_t)~0 && SA[t] > SA[r]) {
+ l = min(l, link[t].lcpnext);
+ t = link[t].next;
+ }
+ link[r].next = t;
+ link[r].lcpnext = min(l, max_match_len);
+ LZX_ASSERT(t == (input_idx_t)~0 || l <= n - SA[t]);
+ LZX_ASSERT(l <= n - SA[r]);
+ LZX_ASSERT(memcmp(&T[SA[r]], &T[SA[t]], l) == 0);
+ }
- /* Aligned offset symbols */
- for (i = 0; i < LZX_ALIGNEDTREE_NUM_SYMBOLS; i++)
- lens->aligned[i] = 3;
+ /* Compute salink.prev and salink.lcpprev.
+ *
+ * Algorithm adapted from Crochemore et al. 2009:
+ * "LPF computation revisited".
+ *
+ * Note: we cap lcpprev to the maximum match length so that the
+ * match-finder need not worry about it later. */
+ link[0].prev = (input_idx_t)~0;
+ link[0].next = (input_idx_t)~0;
+ link[0].lcpprev = 0;
+ link[0].lcpnext = 0;
+ for (input_idx_t r = 1; r < n; r++) {
+ input_idx_t t = r - 1;
+ input_idx_t l = LCP[r];
+ while (t != (input_idx_t)~0 && SA[t] > SA[r]) {
+ l = min(l, link[t].lcpprev);
+ t = link[t].prev;
+ }
+ link[r].prev = t;
+ link[r].lcpprev = min(l, max_match_len);
+ LZX_ASSERT(t == (input_idx_t)~0 || l <= n - SA[t]);
+ LZX_ASSERT(l <= n - SA[r]);
+ LZX_ASSERT(memcmp(&T[SA[r]], &T[SA[t]], l) == 0);
+ }
}
-/*
- * lzx_prepare_blocks() -
- *
- * Calculate the blocks to split the preprocessed data into.
- *
- * Input --- the preprocessed data:
- *
- * ctx->window[]
- * ctx->window_size
- *
- * Working space:
- * Match finding:
- * ctx->hash_tab
- * ctx->child_tab
- * ctx->cached_matches
- * ctx->cached_matches_pos
- * ctx->matches_already_found
- *
- * Block cost modeling:
- * ctx->costs
- * ctx->block_specs (also an output)
- *
- * Match choosing:
- * ctx->optimum
- * ctx->optimum_cur_idx
- * ctx->optimum_end_idx
- * ctx->chosen_matches (also an output)
- *
- * Output --- the block specifications and the corresponding match/literal data:
- *
- * ctx->block_specs[]
- * ctx->chosen_matches[]
- *
- * The return value is the approximate number of bits the compressed data will
- * take up.
- */
-static unsigned
+/* Prepare the input window into one or more LZX blocks ready to be output. */
+static void
lzx_prepare_blocks(struct lzx_compressor * ctx)
{
- /* This function merely does some initializations, then passes control
- * to lzx_prepare_block_recursive(). */
-
- /* 1. Initialize match-finding variables. */
-
- /* Zero all entries in the hash table, indicating that no length-3
- * character sequences have been discovered in the input yet. */
- memset(ctx->hash_tab, 0, LZX_LZ_HASH_SIZE * 2 * sizeof(ctx->hash_tab[0]));
- if (ctx->params.alg_params.slow.use_len2_matches)
- memset(ctx->digram_tab, 0, 256 * 256 * sizeof(ctx->digram_tab[0]));
- /* Note: ctx->child_tab need not be initialized. */
-
- /* No matches have been found and cached yet. */
+ /* Initialize the match-finder. */
+ lzx_lz_init_matchfinder(ctx->window, ctx->window_size,
+ ctx->SA, ctx->ISA, ctx->LCP, ctx->salink,
+ LZX_MAX_MATCH_LEN);
ctx->cached_matches_pos = 0;
- ctx->matches_already_found = false;
+ ctx->matches_cached = false;
+ ctx->match_window_pos = 0;
- /* 2. Initialize match-choosing variables. */
- ctx->optimum_cur_idx = 0;
- ctx->optimum_end_idx = 0;
- /* Note: ctx->optimum need not be initialized. */
- ctx->block_specs[0].chosen_matches_start_pos = 0;
+ /* Set up a default cost model. */
+ lzx_set_default_costs(&ctx->costs);
- /* 3. Set block 1 (index 0) to represent the entire input data. */
- ctx->block_specs[0].block_size = ctx->window_size;
+ /* Initially assume that the entire input will be one LZX block. */
+ ctx->block_specs[0].block_type = LZX_BLOCKTYPE_ALIGNED;
ctx->block_specs[0].window_pos = 0;
+ ctx->block_specs[0].block_size = ctx->window_size;
+ ctx->num_blocks = 1;
- /* 4. Set up a default Huffman symbol cost model for block 1 (index 0).
- * The model will be refined later. */
- lzx_set_default_costs(&ctx->block_specs[0].codes.lens);
+ /* Perform near-optimal LZ parsing. */
+ lzx_optimize_blocks(ctx);
- /* 5. Initialize the match offset LRU queue. */
- ctx->queue = (struct lzx_lru_queue){1, 1, 1};
+ /* Possibly divide up the LZX block. */
+ const unsigned max_num_blocks = 1U << ctx->params.alg_params.slow.num_split_passes;
+ if (max_num_blocks > 1) {
+ const double epsilon = 0.2;
+ const unsigned min_block_len = 500;
- /* 6. Pass control to recursive procedure. */
- struct lzx_codes * prev_codes = &ctx->zero_codes;
- return lzx_prepare_block_recursive(ctx, 1,
- ctx->params.alg_params.slow.num_split_passes,
- &prev_codes);
+ lzx_block_split((const u32*)ctx->chosen_matches,
+ ctx->block_specs[0].num_chosen_matches,
+ epsilon, max_num_blocks, min_block_len,
+ ctx->block_specs, &ctx->num_blocks);
+ }
}
/*
* Working space:
* ctx->queue
*
- * Output --- the block specifications and the corresponding match/literal data:
+ * Output --- the block specification and the corresponding match/literal data:
*
* ctx->block_specs[]
+ * ctx->num_blocks
* ctx->chosen_matches[]
*/
static void
struct lzx_freqs freqs;
struct lzx_block_spec *spec;
- /* Parameters to hash chain LZ match finder */
+ /* Parameters to hash chain LZ match finder
+ * (lazy with 1 match lookahead) */
static const struct lz_params lzx_lz_params = {
- /* LZX_MIN_MATCH == 2, but 2-character matches are rarely
- * useful; the minimum match for compression is set to 3
- * instead. */
+ /* Although LZX_MIN_MATCH_LEN == 2, length 2 matches typically
+ * aren't worth choosing when using greedy or lazy parsing. */
.min_match = 3,
- .max_match = LZX_MAX_MATCH,
- .good_match = LZX_MAX_MATCH,
- .nice_match = LZX_MAX_MATCH,
- .max_chain_len = LZX_MAX_MATCH,
- .max_lazy_match = LZX_MAX_MATCH,
+ .max_match = LZX_MAX_MATCH_LEN,
+ .good_match = LZX_MAX_MATCH_LEN,
+ .nice_match = LZX_MAX_MATCH_LEN,
+ .max_chain_len = LZX_MAX_MATCH_LEN,
+ .max_lazy_match = LZX_MAX_MATCH_LEN,
.too_far = 4096,
};
/* Initialize symbol frequencies and match offset LRU queue. */
memset(&freqs, 0, sizeof(struct lzx_freqs));
- ctx->queue = (struct lzx_lru_queue){ 1, 1, 1 };
+ lzx_lru_queue_init(&ctx->queue);
/* Determine series of matches/literals to output. */
num_matches = lz_analyze_block(ctx->window,
/* Set up block specification. */
spec = &ctx->block_specs[0];
- spec->is_split = 0;
spec->block_type = LZX_BLOCKTYPE_ALIGNED;
spec->window_pos = 0;
spec->block_size = ctx->window_size;
spec->num_chosen_matches = num_matches;
spec->chosen_matches_start_pos = 0;
lzx_make_huffman_codes(&freqs, &spec->codes);
+ ctx->num_blocks = 1;
}
static void
LZX_DEBUG("Done: compressed %u => %u bytes.",
uncompressed_len, compressed_len);
-#if defined(ENABLE_LZX_DEBUG) || defined(ENABLE_VERIFY_COMPRESSION)
- /* Verify that we really get the same thing back when decompressing. */
+ /* Verify that we really get the same thing back when decompressing.
+ * TODO: Disable this check by default on the slow algorithm. */
+ if (ctx->params.algorithm == WIMLIB_LZX_ALGORITHM_SLOW
+ #if defined(ENABLE_LZX_DEBUG) || defined(ENABLE_VERIFY_COMPRESSION)
+ || 1
+ #endif
+ )
{
u8 buf[uncompressed_len];
int ret;
- unsigned i;
ret = wimlib_lzx_decompress(compressed_data, compressed_len,
buf, uncompressed_len);
return 0;
}
- bool bad = false;
- const u8 * udata = uncompressed_data;
- for (i = 0; i < uncompressed_len; i++) {
- if (buf[i] != udata[i]) {
- bad = true;
- ERROR("Data we compressed using LZX algorithm "
- "didn't decompress to original "
- "(difference at idx %u: c %#02x, u %#02x)",
- i, buf[i], udata[i]);
- }
- }
- if (bad) {
+ if (memcmp(uncompressed_data, buf, uncompressed_len)) {
+ ERROR("Data we compressed using LZX algorithm "
+ "didn't decompress to original");
wimlib_assert(0);
return 0;
}
}
-#endif
return compressed_len;
}
return 0 == memcmp(oldparams, newparams, sizeof(struct wimlib_lzx_params));
}
+static struct wimlib_lzx_params lzx_user_default_params;
+static struct wimlib_lzx_params *lzx_user_default_params_ptr;
+
+static bool
+lzx_params_valid(const struct wimlib_lzx_params *params)
+{
+ /* Validate parameters. */
+ if (params->size_of_this != sizeof(struct wimlib_lzx_params)) {
+ LZX_DEBUG("Invalid parameter structure size!");
+ return false;
+ }
+
+ if (params->algorithm != WIMLIB_LZX_ALGORITHM_SLOW &&
+ params->algorithm != WIMLIB_LZX_ALGORITHM_FAST)
+ {
+ LZX_DEBUG("Invalid algorithm.");
+ return false;
+ }
+
+ if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) {
+ if (params->alg_params.slow.num_optim_passes < 1)
+ {
+ LZX_DEBUG("Invalid number of optimization passes!");
+ return false;
+ }
+
+ if (params->alg_params.slow.main_nostat_cost < 1 ||
+ params->alg_params.slow.main_nostat_cost > 16)
+ {
+ LZX_DEBUG("Invalid main_nostat_cost!");
+ return false;
+ }
+
+ if (params->alg_params.slow.len_nostat_cost < 1 ||
+ params->alg_params.slow.len_nostat_cost > 16)
+ {
+ LZX_DEBUG("Invalid len_nostat_cost!");
+ return false;
+ }
+
+ if (params->alg_params.slow.aligned_nostat_cost < 1 ||
+ params->alg_params.slow.aligned_nostat_cost > 8)
+ {
+ LZX_DEBUG("Invalid aligned_nostat_cost!");
+ return false;
+ }
+
+ if (params->alg_params.slow.num_split_passes > 31) {
+ LZX_DEBUG("Invalid num_split_passes!");
+ return false;
+ }
+ }
+ return true;
+}
+
+WIMLIBAPI int
+wimlib_lzx_set_default_params(const struct wimlib_lzx_params * params)
+{
+ if (params) {
+ if (!lzx_params_valid(params))
+ return WIMLIB_ERR_INVALID_PARAM;
+ lzx_user_default_params = *params;
+ lzx_user_default_params_ptr = &lzx_user_default_params;
+ } else {
+ lzx_user_default_params_ptr = NULL;
+ }
+ return 0;
+}
+
/* API function documented in wimlib.h */
WIMLIBAPI int
wimlib_lzx_alloc_context(const struct wimlib_lzx_params *params,
.slow = {
.use_len2_matches = 1,
.num_fast_bytes = 32,
- .num_optim_passes = 3,
- .num_split_passes = 3,
+ .num_optim_passes = 2,
+ .num_split_passes = 0,
+ .max_search_depth = 50,
+ .max_matches_per_pos = 3,
.main_nostat_cost = 15,
.len_nostat_cost = 15,
.aligned_nostat_cost = 7,
},
};
- if (params == NULL) {
+ if (params) {
+ if (!lzx_params_valid(params))
+ return WIMLIB_ERR_INVALID_PARAM;
+ } else {
LZX_DEBUG("Using default algorithm and parameters.");
- params = &fast_default;
- }
-
- if (params->algorithm != WIMLIB_LZX_ALGORITHM_SLOW &&
- params->algorithm != WIMLIB_LZX_ALGORITHM_FAST)
- {
- LZX_DEBUG("Invalid algorithm.");
- return WIMLIB_ERR_INVALID_PARAM;
+ if (lzx_user_default_params_ptr)
+ params = lzx_user_default_params_ptr;
+ else
+ params = &slow_default;
}
if (params->use_defaults) {
params = &fast_default;
}
- if (params->size_of_this != sizeof(struct wimlib_lzx_params)) {
- LZX_DEBUG("Invalid parameter structure size!");
- return WIMLIB_ERR_INVALID_PARAM;
- }
-
- if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) {
- if (params->alg_params.slow.num_fast_bytes < 3 ||
- params->alg_params.slow.num_fast_bytes > 257)
- {
- LZX_DEBUG("Invalid number of fast bytes!");
- return WIMLIB_ERR_INVALID_PARAM;
- }
-
- if (params->alg_params.slow.num_optim_passes < 1)
- {
- LZX_DEBUG("Invalid number of optimization passes!");
- return WIMLIB_ERR_INVALID_PARAM;
- }
-
- if (params->alg_params.slow.main_nostat_cost < 1 ||
- params->alg_params.slow.main_nostat_cost > 16)
- {
- LZX_DEBUG("Invalid main_nostat_cost!");
- return WIMLIB_ERR_INVALID_PARAM;
- }
-
- if (params->alg_params.slow.len_nostat_cost < 1 ||
- params->alg_params.slow.len_nostat_cost > 16)
- {
- LZX_DEBUG("Invalid len_nostat_cost!");
- return WIMLIB_ERR_INVALID_PARAM;
- }
-
- if (params->alg_params.slow.aligned_nostat_cost < 1 ||
- params->alg_params.slow.aligned_nostat_cost > 8)
- {
- LZX_DEBUG("Invalid aligned_nostat_cost!");
- return WIMLIB_ERR_INVALID_PARAM;
- }
- }
+ if (ctx_pp) {
+ ctx = *(struct lzx_compressor**)ctx_pp;
- if (ctx_pp == NULL) {
+ if (ctx && lzx_params_compatible(&ctx->params, params))
+ return 0;
+ } else {
LZX_DEBUG("Check parameters only.");
return 0;
}
- ctx = *(struct lzx_compressor**)ctx_pp;
-
- if (ctx && lzx_params_compatible(&ctx->params, params))
- return 0;
-
LZX_DEBUG("Allocating memory.");
ctx = MALLOC(sizeof(struct lzx_compressor));
size_t block_specs_length;
if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW)
- block_specs_length = ((1 << (params->alg_params.slow.num_split_passes + 1)) - 1);
+ block_specs_length = 1U << params->alg_params.slow.num_split_passes;
else
- block_specs_length = 1;
+ block_specs_length = 1U;
ctx->block_specs = MALLOC(block_specs_length * sizeof(ctx->block_specs[0]));
if (ctx->block_specs == NULL)
goto err_free_ctx;
if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) {
- ctx->hash_tab = MALLOC((LZX_LZ_HASH_SIZE + 2 * LZX_MAX_WINDOW_SIZE) *
- sizeof(ctx->hash_tab[0]));
- if (ctx->hash_tab == NULL)
+ ctx->SA = MALLOC(3U * LZX_MAX_WINDOW_SIZE * sizeof(ctx->SA[0]));
+ if (ctx->SA == NULL)
goto err_free_block_specs;
- ctx->child_tab = ctx->hash_tab + LZX_LZ_HASH_SIZE;
+ ctx->ISA = ctx->SA + LZX_MAX_WINDOW_SIZE;
+ ctx->LCP = ctx->ISA + LZX_MAX_WINDOW_SIZE;
+ ctx->salink = MALLOC(LZX_MAX_WINDOW_SIZE * sizeof(ctx->salink[0]));
+ if (ctx->salink == NULL)
+ goto err_free_SA;
} else {
- ctx->hash_tab = NULL;
- ctx->child_tab = NULL;
+ ctx->SA = NULL;
+ ctx->ISA = NULL;
+ ctx->LCP = NULL;
+ ctx->salink = NULL;
}
- if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW &&
- params->alg_params.slow.use_len2_matches)
- {
- ctx->digram_tab = MALLOC(256 * 256 * sizeof(ctx->digram_tab[0]));
- if (ctx->digram_tab == NULL)
- goto err_free_hash_tab;
+ if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) {
+ ctx->optimum = MALLOC((LZX_OPTIM_ARRAY_SIZE + LZX_MAX_MATCH_LEN) *
+ sizeof(ctx->optimum[0]));
+ if (ctx->optimum == NULL)
+ goto err_free_salink;
} else {
- ctx->digram_tab = NULL;
+ ctx->optimum = NULL;
}
if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) {
- ctx->cached_matches = MALLOC(10 * LZX_MAX_WINDOW_SIZE *
+ uint32_t cache_per_pos;
+
+ cache_per_pos = params->alg_params.slow.max_matches_per_pos;
+ if (cache_per_pos > LZX_MAX_CACHE_PER_POS)
+ cache_per_pos = LZX_MAX_CACHE_PER_POS;
+
+ ctx->cached_matches = MALLOC(LZX_MAX_WINDOW_SIZE * (cache_per_pos + 1) *
sizeof(ctx->cached_matches[0]));
if (ctx->cached_matches == NULL)
- goto err_free_digram_tab;
+ goto err_free_optimum;
} else {
ctx->cached_matches = NULL;
}
- if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW) {
- ctx->optimum = MALLOC((LZX_PARAM_OPTIM_ARRAY_SIZE + LZX_MAX_MATCH) *
- sizeof(ctx->optimum[0]));
- if (ctx->optimum == NULL)
- goto err_free_cached_matches;
- } else {
- ctx->optimum = NULL;
- }
-
- size_t chosen_matches_length;
- if (params->algorithm == WIMLIB_LZX_ALGORITHM_SLOW)
- chosen_matches_length = LZX_MAX_WINDOW_SIZE *
- (params->alg_params.slow.num_split_passes + 1);
- else
- chosen_matches_length = LZX_MAX_WINDOW_SIZE;
-
- ctx->chosen_matches = MALLOC(chosen_matches_length *
+ ctx->chosen_matches = MALLOC(LZX_MAX_WINDOW_SIZE *
sizeof(ctx->chosen_matches[0]));
if (ctx->chosen_matches == NULL)
- goto err_free_optimum;
+ goto err_free_cached_matches;
memcpy(&ctx->params, params, sizeof(struct wimlib_lzx_params));
memset(&ctx->zero_codes, 0, sizeof(ctx->zero_codes));
*ctx_pp = (struct wimlib_lzx_context*)ctx;
return 0;
-err_free_optimum:
- FREE(ctx->optimum);
err_free_cached_matches:
FREE(ctx->cached_matches);
-err_free_digram_tab:
- FREE(ctx->digram_tab);
-err_free_hash_tab:
- FREE(ctx->hash_tab);
+err_free_optimum:
+ FREE(ctx->optimum);
+err_free_salink:
+ FREE(ctx->salink);
+err_free_SA:
+ FREE(ctx->SA);
err_free_block_specs:
FREE(ctx->block_specs);
err_free_ctx:
struct lzx_compressor *ctx = (struct lzx_compressor*)_ctx;
if (ctx) {
+ FREE(ctx->cached_matches);
FREE(ctx->chosen_matches);
FREE(ctx->optimum);
- FREE(ctx->cached_matches);
- FREE(ctx->digram_tab);
- FREE(ctx->hash_tab);
+ FREE(ctx->SA);
+ FREE(ctx->salink);
FREE(ctx->block_specs);
FREE(ctx);
}
git://wimlib.net / wimlib / blobdiff