#endif
typedef u32 block_cost_t;
-#define INFINITE_BLOCK_COST ((block_cost_t)~0U)
+#define INFINITE_BLOCK_COST (~(block_cost_t)0)
#define LZX_OPTIM_ARRAY_SIZE 4096
struct lzx_codes codes;
};
-/*
- * An array of these structures is used during the match-choosing algorithm.
- * They correspond to consecutive positions in the window and are used to keep
- * track of the cost to reach each position, and the match/literal choices that
- * need to be chosen to reach that position.
- */
-struct lzx_optimal {
- /* The approximate minimum cost, in bits, to reach this position in the
- * window which has been found so far. */
- 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
- * first, and links go from later in the window to earlier in the
- * window. Later, @next structure is filled in and links go from
- * earlier in the window to later in the window. */
- union {
- struct {
- /* Position of the start of the match or literal that
- * was taken to get to this position in the approximate
- * minimum-cost parse. */
- input_idx_t link;
-
- /* Offset (as in an LZ (length, offset) pair) of the
- * match or literal that was taken to get to this
- * position in the approximate minimum-cost parse. */
- input_idx_t match_offset;
- } prev;
- struct {
- /* Position at which the match or literal starting at
- * this position ends in the minimum-cost parse. */
- input_idx_t link;
-
- /* Offset (as in an LZ (length, offset) pair) of the
- * match or literal starting at this position in the
- * approximate minimum-cost parse. */
- input_idx_t match_offset;
- } next;
- };
-
- /* 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;
-};
+/* Include template for the match-choosing algorithm. */
+#define LZ_COMPRESSOR struct lzx_compressor
+#define LZ_FORMAT_STATE struct lzx_lru_queue
+struct lzx_compressor;
+#include "wimlib/lz_optimal.h"
/* State of the LZX compressor. */
struct lzx_compressor {
unsigned cached_matches_pos;
bool matches_cached;
- /* Slow algorithm only: Temporary space used for match-choosing
- * algorithm.
- *
- * 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.
- *
- * When matches have been chosen, optimum_cur_idx is set to the position
- * in the window of the next match/literal to return and optimum_end_idx
- * is set to the position in the window at the end of the last
- * match/literal to return. */
- u32 optimum_cur_idx;
- u32 optimum_end_idx;
+ /* Match chooser. */
+ struct lz_match_chooser mc;
};
/* Returns the LZX position slot that corresponds to a given match offset,
/* 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)
+lzx_lz_skip_bytes(struct lzx_compressor *ctx, input_idx_t n)
{
LZX_ASSERT(n <= ctx->match_window_end - ctx->match_window_pos);
if (ctx->matches_cached) {
*
* The matches are written to ctx->matches in decreasing order of length, and
* the return value is the number of matches found. */
-static unsigned
+static u32
lzx_lz_get_matches_caching(struct lzx_compressor *ctx,
const struct lzx_lru_queue *queue,
struct raw_match **matches_ret)
{
- unsigned num_matches;
+ u32 num_matches;
struct raw_match *matches;
LZX_ASSERT(ctx->match_window_pos <= ctx->match_window_end);
* 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++)
+ for (u32 i = 0; i < num_matches; i++)
if (matches[i].len > maxlen)
matches[i].len = maxlen;
}
#endif
#ifdef ENABLE_LZX_DEBUG
- for (unsigned i = 0; i < num_matches; i++) {
+ for (u32 i = 0; i < num_matches; i++) {
LZX_ASSERT(matches[i].len >= LZX_MIN_MATCH_LEN);
LZX_ASSERT(matches[i].len <= LZX_MAX_MATCH_LEN);
LZX_ASSERT(matches[i].len <= ctx->match_window_end - ctx->match_window_pos);
return num_matches;
}
-/*
- * Reverse the linked list of near-optimal matches so that they can be returned
- * in forwards order.
- *
- * Returns the first match in the list.
- */
-static struct raw_match
-lzx_lz_reverse_near_optimal_match_list(struct lzx_compressor *ctx,
- unsigned cur_pos)
+static u32
+lzx_get_prev_literal_cost(struct lzx_compressor *ctx)
{
- unsigned prev_link, saved_prev_link;
- unsigned prev_match_offset, saved_prev_match_offset;
-
- ctx->optimum_end_idx = cur_pos;
-
- saved_prev_link = ctx->optimum[cur_pos].prev.link;
- saved_prev_match_offset = ctx->optimum[cur_pos].prev.match_offset;
-
- do {
- prev_link = saved_prev_link;
- prev_match_offset = saved_prev_match_offset;
-
- saved_prev_link = ctx->optimum[prev_link].prev.link;
- saved_prev_match_offset = ctx->optimum[prev_link].prev.match_offset;
-
- ctx->optimum[prev_link].next.link = cur_pos;
- ctx->optimum[prev_link].next.match_offset = prev_match_offset;
-
- cur_pos = prev_link;
- } while (cur_pos != 0);
-
- ctx->optimum_cur_idx = ctx->optimum[0].next.link;
+ return lzx_literal_cost(ctx->window[ctx->match_window_pos - 1],
+ &ctx->costs);
+}
- return (struct raw_match)
- { .len = ctx->optimum_cur_idx,
- .offset = ctx->optimum[0].next.match_offset,
- };
+static u32
+lzx_get_match_cost(struct lzx_compressor *ctx,
+ struct lzx_lru_queue *queue,
+ input_idx_t length, input_idx_t offset)
+{
+ return lzx_match_cost(length, offset, &ctx->costs, queue);
}
-/*
- * lzx_lz_get_near_optimal_match() -
- *
- * 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
- * parser with one match/literal look-ahead like zlib, the algorithm used here
- * 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.
- *
- * Still, this is not truly an optimal parser because very long matches are
- * taken immediately, and the raw match-finder takes some shortcuts. This is
- * done to avoid considering many different alternatives that are unlikely to
- * be significantly better.
- *
- * This algorithm is based on that used in 7-Zip's DEFLATE encoder.
- *
- * Each call to this function does one of two things:
- *
- * 1. Build a near-optimal sequence of matches/literals, up to some point, that
- * will be returned by subsequent calls to this function, then return the
- * first one.
- *
- * OR
- *
- * 2. Return the next match/literal previously computed by a call to this
- * function;
- *
- * This function relies on the following state in the compressor context:
- *
- * ctx->window (read-only: preprocessed data being compressed)
- * ctx->cost (read-only: cost model to use)
- * 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)
- *
- * Plus any state used by the raw match-finder.
- *
- * The return value is a (length, offset) pair specifying the match or literal
- * 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)
+lzx_lz_get_near_optimal_match(struct lzx_compressor *ctx)
{
- unsigned num_possible_matches;
- struct raw_match *possible_matches;
- struct raw_match match;
- unsigned longest_match_len;
-
- if (ctx->optimum_cur_idx != ctx->optimum_end_idx) {
- /* Case 2: Return the next match/literal already found. */
- match.len = ctx->optimum[ctx->optimum_cur_idx].next.link -
- ctx->optimum_cur_idx;
- match.offset = ctx->optimum[ctx->optimum_cur_idx].next.match_offset;
-
- ctx->optimum_cur_idx = ctx->optimum[ctx->optimum_cur_idx].next.link;
- return match;
- }
-
- /* Case 1: Compute a new list of matches/literals to return. */
-
- ctx->optimum_cur_idx = 0;
- ctx->optimum_end_idx = 0;
-
- /* Get matches at this position. */
- 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 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[0];
- }
-
- /* Calculate the cost to reach the next position by outputting a
- * literal. */
- ctx->optimum[0].queue = ctx->queue;
- ctx->optimum[1].queue = ctx->optimum[0].queue;
- 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. */
- 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);
-
- ctx->optimum[len].queue = ctx->optimum[0].queue;
- 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,
- &ctx->optimum[len].queue);
- if (len == possible_matches[match_idx].len)
- match_idx--;
- }
-
- unsigned cur_pos = 0;
-
- /* len_end: greatest index forward at which costs have been calculated
- * so far */
- unsigned len_end = longest_match_len;
-
- for (;;) {
- /* Advance to next position. */
- cur_pos++;
-
- 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, &ctx->optimum[cur_pos].queue,
- &possible_matches);
-
- unsigned new_len = 0;
-
- if (num_possible_matches != 0) {
- new_len = possible_matches[0].len;
-
- /* Greedy heuristic: if we found a match greater than
- * the number of fast bytes, stop immediately. */
- if (new_len > ctx->params.alg_params.slow.num_fast_bytes) {
-
- /* Build the list of matches to return and get
- * the first one. */
- match = lzx_lz_reverse_near_optimal_match_list(ctx, cur_pos);
-
- /* Append the long match to the end of the list. */
- ctx->optimum[cur_pos].next.match_offset =
- possible_matches[0].offset;
- ctx->optimum[cur_pos].next.link = cur_pos + new_len;
- ctx->optimum_end_idx = cur_pos + new_len;
-
- /* Skip over the remaining bytes of the long match. */
- lzx_lz_skip_bytes(ctx, new_len - 1);
-
- /* Return first match in the list */
- return match;
- }
- }
-
- /* Consider proceeding with a literal byte. */
- 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;
- ctx->optimum[cur_pos + 1].queue = ctx->optimum[cur_pos].queue;
- }
-
- if (num_possible_matches == 0)
- continue;
-
- /* Consider proceeding with a match. */
-
- while (len_end < cur_pos + new_len)
- ctx->optimum[++len_end].cost = INFINITE_BLOCK_COST;
-
- for (unsigned len = LZX_MIN_MATCH_LEN, match_idx = num_possible_matches - 1;
- len <= new_len; len++) {
- LZX_ASSERT(match_idx < num_possible_matches);
- struct lzx_lru_queue q = ctx->optimum[cur_pos].queue;
- 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;
- ctx->optimum[cur_pos + len].queue = q;
- }
-
- if (len == possible_matches[match_idx].len)
- match_idx--;
- }
- }
+ return lz_get_near_optimal_match(&ctx->mc,
+ lzx_lz_get_matches_caching,
+ lzx_lz_skip_bytes,
+ lzx_get_prev_literal_cost,
+ lzx_get_match_cost,
+ ctx,
+ &ctx->queue);
}
/*
lzx_optimize_blocks(struct lzx_compressor *ctx)
{
lzx_lru_queue_init(&ctx->queue);
- ctx->optimum_cur_idx = 0;
- ctx->optimum_end_idx = 0;
+ lz_match_chooser_begin(&ctx->mc);
const unsigned num_passes = ctx->params.alg_params.slow.num_optim_passes;
if (ctx) {
FREE(ctx->chosen_matches);
FREE(ctx->cached_matches);
- FREE(ctx->optimum);
+ lz_match_chooser_destroy(&ctx->mc);
lz_sarray_destroy(&ctx->lz_sarray);
FREE(ctx->block_specs);
FREE(ctx->prev_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)
+ if (!lz_match_chooser_init(&ctx->mc,
+ LZX_OPTIM_ARRAY_SIZE,
+ params->alg_params.slow.num_fast_bytes,
+ LZX_MAX_MATCH_LEN))
goto oom;
}
git://wimlib.net / wimlib / blobdiff