+++ /dev/null
-/*
- * lz_sarray.c
- *
- * Suffix array match-finder for Lempel-Ziv compression.
- */
-
-/*
- * Copyright (c) 2013, 2014 Eric Biggers. All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- *
- * 1. Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- *
- * 2. Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in the
- * documentation and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS "AS IS" AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
- * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE
- * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
- * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
- * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
- * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
- * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
- * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
- * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- */
-
-#ifdef HAVE_CONFIG_H
-# include "config.h"
-#endif
-
-#include "wimlib/divsufsort.h"
-#include "wimlib/lz_sarray.h"
-#include "wimlib/util.h"
-#include <string.h>
-
-/* If ENABLE_LZ_DEBUG is defined, verify that the suffix array satisfies its
- * definition.
- *
- * @SA The constructed suffix array.
- * @T The original data.
- * @found Temporary 'bool' array of length @n.
- * @n Length of the data (length of @SA, @T, and @found arrays).
- *
- * WARNING: this is for debug use only as it does not necessarily run in linear
- * time!!! */
-static void
-verify_suffix_array(const lz_sarray_pos_t SA[restrict],
- const u8 T[restrict],
- bool found[restrict],
- lz_sarray_pos_t n)
-{
-#ifdef ENABLE_LZ_DEBUG
- /* Ensure the SA contains exactly one of each i in [0, n - 1]. */
- for (lz_sarray_pos_t i = 0; i < n; i++)
- found[i] = false;
- for (lz_sarray_pos_t r = 0; r < n; r++) {
- lz_sarray_pos_t i = SA[r];
- LZ_ASSERT(i < n);
- LZ_ASSERT(!found[i]);
- found[i] = true;
- }
-
- /* Ensure the suffix with rank r is lexicographically lesser than the
- * suffix with rank (r + 1) for all r in [0, n - 2]. */
- for (lz_sarray_pos_t r = 0; r < n - 1; r++) {
-
- lz_sarray_pos_t i1 = SA[r];
- lz_sarray_pos_t i2 = SA[r + 1];
-
- lz_sarray_pos_t n1 = n - i1;
- lz_sarray_pos_t n2 = n - i2;
-
- int res = memcmp(&T[i1], &T[i2], min(n1, n2));
- LZ_ASSERT(res < 0 || (res == 0 && n1 < n2));
- }
-#endif /* ENABLE_LZ_DEBUG */
-}
-
-/* Compute the inverse suffix array @ISA from the suffix array @SA in linear
- * time.
- *
- * Whereas the suffix array is a mapping from suffix rank to suffix position,
- * the inverse suffix array is a mapping from suffix position to suffix rank.
- */
-static void
-compute_inverse_suffix_array(lz_sarray_pos_t ISA[restrict],
- const lz_sarray_pos_t SA[restrict],
- lz_sarray_pos_t n)
-{
- lz_sarray_pos_t r;
-
- for (r = 0; r < n; r++)
- ISA[SA[r]] = r;
-}
-
-
-/* Compute the LCP (Longest Common Prefix) array in linear time.
- *
- * LCP[r] will be the length of the longest common prefix between the suffixes
- * with positions SA[r - 1] and SA[r]. LCP[0] will be undefined.
- *
- * Algorithm adapted from Kasai et al. 2001: "Linear-Time Longest-Common-Prefix
- * Computation in Suffix Arrays and Its Applications". Modified slightly to
- * take into account that with bytes in the real world, there is no unique
- * symbol at the end of the string. */
-static void
-compute_lcp_array(lz_sarray_pos_t LCP[restrict],
- const lz_sarray_pos_t SA[restrict],
- const lz_sarray_pos_t ISA[restrict],
- const u8 T[restrict],
- lz_sarray_pos_t n)
-{
- lz_sarray_pos_t h, i, r, j, lim;
-
- h = 0;
- for (i = 0; i < n; i++) {
- r = ISA[i];
- if (r > 0) {
- j = SA[r - 1];
- lim = min(n - i, n - j);
-
- while (h < lim && T[i + h] == T[j + h])
- h++;
- LCP[r] = h;
- if (h > 0)
- h--;
- }
- }
-}
-
-/* If ENABLE_LZ_DEBUG is defined, verify that the LCP (Longest Common Prefix)
- * array satisfies its definition.
- *
- * WARNING: this is for debug use only as it does not necessarily run in linear
- * time!!! */
-static void
-verify_lcp_array(lz_sarray_pos_t LCP[restrict],
- const lz_sarray_pos_t SA[restrict],
- const u8 T[restrict],
- lz_sarray_pos_t n)
-{
-#ifdef ENABLE_LZ_DEBUG
- for (lz_sarray_pos_t r = 0; r < n - 1; r++) {
- lz_sarray_pos_t i1 = SA[r];
- lz_sarray_pos_t i2 = SA[r + 1];
- lz_sarray_pos_t lcp = LCP[r + 1];
-
- lz_sarray_pos_t n1 = n - i1;
- lz_sarray_pos_t n2 = n - i2;
-
- LZ_ASSERT(lcp <= min(n1, n2));
-
- LZ_ASSERT(memcmp(&T[i1], &T[i2], lcp) == 0);
- if (lcp < min(n1, n2))
- LZ_ASSERT(T[i1 + lcp] != T[i2 + lcp]);
- }
-#endif /* ENABLE_LZ_DEBUG */
-}
-
-/* Initialize the SA link array in linear time.
- *
- * This is similar to computing the LPF (Longest Previous Factor) array, which
- * is addressed in several papers. In particular the algorithms below are based
- * on Crochemore et al. 2009: "LPF computation revisited". However, this
- * match-finder does not actually compute or use the LPF array per se. Rather,
- * this function sets up some information necessary to compute the LPF array,
- * but later lz_sarray_get_matches() actually uses this information to search
- * the suffix array directly and can keep searching beyond the first (longest)
- * match whose length would be placed in the LPF array. This difference from
- * the theoretical work is necessary because in many real compression formats
- * matches take variable numbers of bits to encode, so a decent parser needs to
- * consider more than just the longest match with unspecified offset.
- *
- * Note: We cap the lcpprev and lcpnext values to the maximum match length so
- * that the match-finder need not worry about it later, in the inner loop.
- *
- * Note: the LCP array is one of the inputs to this function, but it is used as
- * temporary space and therefore will be invalidated.
- */
-static void
-init_salink(struct salink link[restrict],
- lz_sarray_pos_t LCP[restrict],
- const lz_sarray_pos_t SA[restrict],
- const u8 T[restrict],
- lz_sarray_pos_t n,
- lz_sarray_len_t min_match_len,
- lz_sarray_len_t max_match_len)
-{
- /* Calculate salink.dist_to_next and salink.lcpnext.
- *
- * Pass 1 calculates, for each suffix rank, the corresponding
- * "next_initial" value which is the smallest larger rank that
- * corresponds to a suffix starting earlier in the string. It also
- * calculates "lcpnext_initial", which is the longest common prefix with
- * that suffix, although to eliminate checks in lz_sarray_get_matches(),
- * "lcpnext_initial" is set to 0 if it's less than the minimum match
- * length or set to the maximum match length if it's greater than the
- * maximum match length.
- *
- * Pass 2 translates each absolute "next_initial", a 4-byte value, into
- * a relative "dist_to_next", a 1-byte value. This is done to save
- * memory. In the case that the exact relative distance cannot be
- * encoded in 1 byte, it is capped to 255. This is valid as long as
- * lz_sarray_get_matches() validates each position before using it.
- * Note that "lcpnext" need not be updated in this case because it will
- * not be used until the actual next rank has been found anyway.
- */
- link[n - 1].next_initial = LZ_SARRAY_POS_MAX;
- link[n - 1].lcpnext_initial = 0;
- for (lz_sarray_pos_t r = n - 2; r != LZ_SARRAY_POS_MAX; r--) {
- lz_sarray_pos_t t = r + 1;
- lz_sarray_pos_t l = LCP[t];
- while (t != LZ_SARRAY_POS_MAX && SA[t] > SA[r]) {
- l = min(l, link[t].lcpnext_initial);
- t = link[t].next_initial;
- }
- link[r].next_initial = t;
-
- if (l < min_match_len)
- l = 0;
- else if (l > max_match_len)
- l = max_match_len;
- link[r].lcpnext_initial = l;
- }
- for (lz_sarray_pos_t r = 0; r < n; r++) {
- lz_sarray_pos_t next;
- lz_sarray_len_t l;
- lz_sarray_delta_t dist_to_next;
-
- next = link[r].next_initial;
- l = link[r].lcpnext_initial;
-
- if (next == LZ_SARRAY_POS_MAX)
- dist_to_next = 0;
- else if (next - r <= LZ_SARRAY_DELTA_MAX)
- dist_to_next = next - r;
- else
- dist_to_next = LZ_SARRAY_DELTA_MAX;
-
- link[r].lcpnext = l;
- link[r].dist_to_next = dist_to_next;
- }
-
- /* Calculate salink.dist_to_prev and salink.lcpprev.
- *
- * This is analgous to dist_to_next and lcpnext as described above, but
- * in the other direction. That is, here we're interested in, for each
- * rank, the largest smaller rank that corresponds to a suffix starting
- * earlier in the string.
- *
- * To save memory we don't have a "prev_initial" field, but rather store
- * those values in the LCP array. */
- LCP[0] = LZ_SARRAY_POS_MAX;
- link[0].lcpprev = 0;
- for (lz_sarray_pos_t r = 1; r < n; r++) {
- lz_sarray_pos_t t = r - 1;
- lz_sarray_pos_t l = LCP[r];
- while (t != LZ_SARRAY_POS_MAX && SA[t] > SA[r]) {
- l = min(l, link[t].lcpprev);
- t = LCP[t];
- }
- LCP[r] = t;
-
- if (l < min_match_len)
- l = 0;
- else if (l > max_match_len)
- l = max_match_len;
-
- link[r].lcpprev = l;
- }
- for (lz_sarray_pos_t r = 0; r < n; r++) {
-
- lz_sarray_pos_t prev = LCP[r];
-
- if (prev == LZ_SARRAY_POS_MAX)
- link[r].dist_to_prev = 0;
- else if (r - prev <= LZ_SARRAY_DELTA_MAX)
- link[r].dist_to_prev = r - prev;
- else
- link[r].dist_to_prev = LZ_SARRAY_DELTA_MAX;
- }
-}
-
-/* If ENABLE_LZ_DEBUG is defined, verify the values computed by init_salink().
- *
- * WARNING: this is for debug use only as it does not necessarily run in linear
- * time!!! */
-static void
-verify_salink(const struct salink link[],
- const lz_sarray_pos_t SA[],
- const u8 T[],
- lz_sarray_pos_t n,
- lz_sarray_len_t min_match_len,
- lz_sarray_len_t max_match_len)
-{
-#ifdef ENABLE_LZ_DEBUG
- for (lz_sarray_pos_t r = 0; r < n; r++) {
- for (lz_sarray_pos_t prev = r; ; ) {
- if (prev == 0) {
- LZ_ASSERT(link[r].dist_to_prev == 0);
- LZ_ASSERT(link[r].lcpprev == 0);
- break;
- }
-
- prev--;
-
- if (SA[prev] < SA[r]) {
- LZ_ASSERT(link[r].dist_to_prev == min(r - prev, LZ_SARRAY_DELTA_MAX));
-
- lz_sarray_pos_t lcpprev;
- for (lcpprev = 0;
- lcpprev < min(n - SA[prev], n - SA[r]) &&
- T[SA[prev] + lcpprev] == T[SA[r] + lcpprev];
- lcpprev++)
- ;
- if (lcpprev < min_match_len)
- lcpprev = 0;
- else if (lcpprev > max_match_len)
- lcpprev = max_match_len;
-
- LZ_ASSERT(lcpprev == link[r].lcpprev);
- break;
- }
- }
-
- for (lz_sarray_pos_t next = r; ; ) {
- if (next == n - 1) {
- LZ_ASSERT(link[r].dist_to_next == 0);
- LZ_ASSERT(link[r].lcpnext == 0);
- break;
- }
-
- next++;
-
- if (SA[next] < SA[r]) {
- LZ_ASSERT(link[r].dist_to_next == min(next - r, LZ_SARRAY_DELTA_MAX));
-
- lz_sarray_pos_t lcpnext;
- for (lcpnext = 0;
- lcpnext < min(n - SA[next], n - SA[r]) &&
- T[SA[next] + lcpnext] == T[SA[r] + lcpnext];
- lcpnext++)
- ;
- if (lcpnext < min_match_len)
- lcpnext = 0;
- else if (lcpnext > max_match_len)
- lcpnext = max_match_len;
-
- LZ_ASSERT(lcpnext == link[r].lcpnext);
- break;
- }
- }
- }
-#endif
-}
-
-/*
- * Initialize the suffix array match-finder.
- *
- * @mf
- * The suffix array match-finder structure to initialize. This structure
- * is expected to be zeroed before this function is called. In the case
- * that this function fails, lz_sarray_destroy() should be called to free
- * any memory that may have been allocated.
- *
- * @max_window_size
- * The maximum window size to support. This must be greater than 0.
- *
- * The amount of needed memory will depend on this value; see
- * lz_sarray_get_needed_memory() for details.
- *
- * @min_match_len
- * The minimum length of each match to be found. Must be greater than 0.
- *
- * @max_match_len
- * The maximum length of each match to be found. Must be greater than or
- * equal to @min_match_len.
- *
- * @max_matches_to_consider
- * The maximum number of matches to consider at each position. This should
- * be greater than @max_matches_to_return because @max_matches_to_consider
- * counts all the returned matches as well as matches of equal length to
- * returned matches that were not returned. This parameter bounds the
- * amount of work the match-finder does at any one position. This could be
- * anywhere from 1 to 100+ depending on the compression ratio and
- * performance desired.
- *
- * @max_matches_to_return
- * Maximum number of matches to return at each position. Because of the
- * suffix array search algorithm, the order in which matches are returned
- * will be from longest to shortest, so cut-offs due to this parameter will
- * only result in shorter matches being discarded. This parameter could be
- * anywhere from 1 to (@max_match_len - @min_match_len + 1) depending on
- * the compression performance desired. However, making it even moderately
- * large (say, greater than 3) may not be very helpful due to the property
- * that the matches are returned from longest to shortest. But the main
- * thing to keep in mind is that if the compressor decides to output a
- * shorter-than-possible match, ideally it would be best to choose the best
- * match of the desired length rather than truncate a longer match to that
- * length.
- *
- * After initialization, the suffix-array match-finder can be used for any
- * number of input strings (windows) of length less than or equal to
- * @max_window_size by successive calls to lz_sarray_load_window().
- *
- * Returns %true on success, or %false if sufficient memory could not be
- * allocated. See the note for @max_window_size above regarding the needed
- * memory size.
- */
-bool
-lz_sarray_init(struct lz_sarray *mf,
- lz_sarray_pos_t max_window_size,
- lz_sarray_len_t min_match_len,
- lz_sarray_len_t max_match_len,
- u32 max_matches_to_consider,
- u32 max_matches_to_return)
-{
- LZ_ASSERT(min_match_len > 0);
- LZ_ASSERT(max_window_size > 0);
- LZ_ASSERT(max_match_len >= min_match_len);
-
- mf->max_window_size = max_window_size;
- mf->min_match_len = min_match_len;
- mf->max_match_len = max_match_len;
- mf->max_matches_to_consider = max_matches_to_consider;
- mf->max_matches_to_return = max_matches_to_return;
-
- /* SA and ISA will share the same storage block. */
- if ((u64)2 * max_window_size * sizeof(mf->SA[0]) !=
- 2 * max_window_size * sizeof(mf->SA[0]))
- return false;
- mf->SA = MALLOC(max_window_size * sizeof(mf->SA[0]) +
- max(DIVSUFSORT_TMP1_SIZE,
- max_window_size * sizeof(mf->SA[0])));
- if (mf->SA == NULL)
- return false;
-
- if ((u64)max_window_size * sizeof(mf->salink[0]) !=
- max_window_size * sizeof(mf->salink[0]))
- return false;
- mf->salink = MALLOC(max(DIVSUFSORT_TMP2_SIZE,
- max_window_size * sizeof(mf->salink[0])));
- if (mf->salink == NULL)
- return false;
-
- return true;
-}
-
-/*
- * Return the number of bytes of memory that lz_sarray_init() would allocate for
- * the specified maximum window size.
- *
- * This should be (14 * @max_window_size) unless the type definitions have been
- * changed.
- */
-u64
-lz_sarray_get_needed_memory(lz_sarray_pos_t max_window_size)
-{
- u64 size = 0;
-
- /* SA and ISA: 8 bytes per position */
- size += (u64)max_window_size * sizeof(((struct lz_sarray*)0)->SA[0]) +
- max(DIVSUFSORT_TMP1_SIZE,
- (u64)max_window_size * sizeof(((struct lz_sarray*)0)->SA[0]));
-
- /* salink: 6 bytes per position */
- size += max(DIVSUFSORT_TMP2_SIZE,
- (u64)max_window_size * sizeof(((struct lz_sarray*)0)->salink[0]));
-
- return size;
-}
-
-/*
- * Prepare the suffix array match-finder to scan the specified window for
- * matches.
- *
- * @mf Suffix array match-finder previously initialized with lz_sarray_init().
- *
- * @T Window, or "block", in which to find matches.
- *
- * @n Size of window in bytes. This must be positive and less than or equal
- * to the @max_window_size passed to lz_sarray_init().
- *
- * This function runs in linear time (relative to @n).
- */
-void
-lz_sarray_load_window(struct lz_sarray *mf, const u8 T[], lz_sarray_pos_t n)
-{
- lz_sarray_pos_t *ISA, *LCP;
-
- LZ_ASSERT(n > 0 && n <= mf->max_window_size);
-
- /* Compute SA (Suffix Array).
- *
- * divsufsort() needs temporary space --- one array with 256 spaces and
- * one array with 65536 spaces. The implementation of divsufsort() has
- * been modified from the original to use the provided temporary space
- * instead of allocating its own.
- *
- * We also check at build-time that divsufsort() uses the same integer
- * size expected by this code. Unfortunately, divsufsort breaks if
- * 'sa_idx_t' is defined to be a 16-bit integer; however, that would
- * limit blocks to only 65536 bytes anyway. */
- BUILD_BUG_ON(sizeof(lz_sarray_pos_t) != sizeof(saidx_t));
-
- divsufsort(T, mf->SA, n, (saidx_t*)&mf->SA[n], (saidx_t*)mf->salink);
-
- BUILD_BUG_ON(sizeof(bool) > sizeof(mf->salink[0]));
- verify_suffix_array(mf->SA, T, (bool*)mf->salink, n);
-
- /* Compute ISA (Inverse Suffix Array) in a preliminary position.
- *
- * This is just a trick to save memory. Since LCP is unneeded after
- * this function, it can be computed in any available space. The
- * storage for the ISA is the best choice because the ISA can be built
- * quickly in salink for now, then re-built in its real location at the
- * end. This is probably worth it because computing the ISA from the SA
- * is very fast, and since this match-finder is memory-hungry we'd like
- * to save as much memory as possible. */
- BUILD_BUG_ON(sizeof(mf->salink[0]) < sizeof(mf->ISA[0]));
- ISA = (lz_sarray_pos_t*)mf->salink;
- compute_inverse_suffix_array(ISA, mf->SA, n);
-
- /* Compute LCP (Longest Common Prefix) array. */
- LCP = mf->SA + n;
- compute_lcp_array(LCP, mf->SA, ISA, T, n);
- verify_lcp_array(LCP, mf->SA, T, n);
-
- /* Initialize suffix array links. */
- init_salink(mf->salink, LCP, mf->SA, T, n,
- mf->min_match_len, mf->max_match_len);
- verify_salink(mf->salink, mf->SA, T, n,
- mf->min_match_len, mf->max_match_len);
-
- /* Compute ISA (Inverse Suffix Array) in its final position. */
- ISA = mf->SA + n;
- compute_inverse_suffix_array(ISA, mf->SA, n);
-
- /* Save new variables and return. */
- mf->ISA = ISA;
- mf->cur_pos = 0;
- mf->window_size = n;
-}
-
-/* Free memory allocated for the suffix array match-finder. */
-void
-lz_sarray_destroy(struct lz_sarray *mf)
-{
- FREE(mf->SA);
- FREE(mf->salink);
-}
git://wimlib.net / wimlib / blobdiff