/*
* lz_sarray.h
*
- * Suffix array match-finder for LZ (Lempel-Ziv) compression.
+ * Suffix array match-finder for Lempel-Ziv compression.
*/
/*
#ifndef _WIMLIB_LZ_SARRAY_H
#define _WIMLIB_LZ_SARRAY_H
-#include "wimlib/compiler.h"
-#include "wimlib/lz.h"
-#include "wimlib/types.h"
+#include "wimlib/compiler.h" /* must define '_always_inline_attribute' */
+#include "wimlib/lz.h" /* must define 'struct raw_match', 'input_idx_t',
+ and LZ_ASSERT(). */
+#include "wimlib/types.h" /* must define 'bool', 'u8', 'u32' */
struct salink;
-/* Suffix array LZ (Lempel-Ziv) match-finder. */
+/* State of the suffix array LZ (Lempel-Ziv) match-finder.
+ *
+ * This is defined here for benefit of the inlined code. It's not intended for
+ * code outside the match-finder itself to read or write members from this
+ * structure. */
struct lz_sarray {
- /* Allocated window size for the match-finder. */
+ /* Allocated window size for the match-finder.
+ *
+ * Note: this match-finder does not store the window itself, as the
+ * suffix array (@SA) and associated arrays (@ISA, @LCP, @salink) are
+ * sufficient to find matches. This number is the maximum length of
+ * those arrays, or also the maximum window (block) size that can be
+ * passed to lz_sarray_load_window(). */
input_idx_t max_window_size;
/* Minimum match length to return. */
/* Maximum number of matches to return at each position. */
u32 max_matches_to_return;
- /* Current position in the window */
+ /* Current position in the window. */
input_idx_t cur_pos;
/* Current window size. */
input_idx_t window_size;
- /* Suffix array for window.
+ /* Suffix array for the current window.
* This is a mapping from suffix rank to suffix position. */
input_idx_t *SA;
- /* Inverse suffix array for window.
+ /* Inverse suffix array for the current window.
* This is a mapping from suffix position to suffix rank.
* If 0 <= r < window_size, then ISA[SA[r]] == r. */
input_idx_t *ISA;
- /* Longest common prefix array corresponding to the suffix array SA.
- * LCP[i] is the length of the longest common prefix between the
- * suffixes with positions SA[i - 1] and SA[i]. LCP[0] is undefined.
- */
- input_idx_t *LCP;
-
/* Suffix array links.
*
* During a linear scan of the input string to find matches, this array
struct salink *salink;
};
-/* Suffix array link */
+/* Suffix array link; one of these exists for each position in the suffix array.
+ */
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. */
+ * which matches have been searched for so far, or ~(input_idx_t)0 if
+ * there is no such suffix.
+ *
+ * Think of this as a pointer to the closest position in the suffix
+ * array to the left that corresponds to a suffix that begins at a
+ * position in the current dictionary (i.e. before the current position
+ * in the window). */
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. */
+ * matches have been searched for so far, or ~(input_idx_t)0 if there is
+ * no such suffix.
+
+ * Think of this as a pointer to the closest position in the suffix
+ * array to the right that corresponds to a suffix that begins at a
+ * position in the current dictionary (i.e. before the current position
+ * in the window). */
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.
- */
+ * this structure and the suffix with rank @prev, or 0 if @prev is
+ * ~(input_idx_t)0. */
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.
- */
+ * this structure and the suffix with rank @next, or 0 if @next is
+ * ~(input_idx_t)0. */
input_idx_t lcpnext;
};
+/*-----------------------------------*/
+/* Functions defined in lz_sarray.c */
+/*-----------------------------------*/
+
extern bool
lz_sarray_init(struct lz_sarray *mf,
- input_idx_t max_window_size,
- input_idx_t min_match_len,
- input_idx_t max_match_len,
- u32 max_matches_to_consider,
- u32 max_matches_to_return);
+ input_idx_t max_window_size,
+ input_idx_t min_match_len,
+ input_idx_t max_match_len,
+ u32 max_matches_to_consider,
+ u32 max_matches_to_return);
extern void
lz_sarray_destroy(struct lz_sarray *mf);
extern void
-lz_sarray_load_window(struct lz_sarray *mf, const u8 window[],
- input_idx_t window_size);
+lz_sarray_load_window(struct lz_sarray *mf, const u8 T[], input_idx_t n);
-static inline input_idx_t
+/*-------------------*/
+/* Inline functions */
+/*-------------------*/
+
+static _always_inline_attribute input_idx_t
lz_sarray_get_pos(const struct lz_sarray *mf)
{
return mf->cur_pos;
const input_idx_t r = ISA[i];
/* next = rank of LOWEST ranked suffix that is ranked HIGHER than the
- * current suffix AND has a LOWER position, or -1 if none exists. */
+ * current suffix AND has a LOWER position, or ~(input_idx_t)0 if none
+ * exists. */
const input_idx_t next = link[r].next;
/* prev = rank of HIGHEST ranked suffix that is ranked LOWER than the
- * current suffix AND has a LOWER position, or -1 if none exists. */
+ * current suffix AND has a LOWER position, or ~(input_idx_t)0 if none
+ * exists. */
const input_idx_t prev = link[r].prev;
/* 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. */
+ * contains all suffixes referenced by the suffix array that appear at
+ * or before the current position, sorted by rank. */
if (next != ~(input_idx_t)0) {
-
link[next].prev = r;
link[next].lcpprev = link[r].lcpnext;
}
if (prev != ~(input_idx_t)0) {
-
link[prev].next = r;
link[prev].lcpnext = link[r].lcpprev;
}
#define LZ_SARRAY_INFINITE_COST (~(lz_sarray_cost_t)0)
/*
- * Use the suffix array match-finder to retrieve a list of LZ matches at the
+ * Use the suffix array match-finder to retrieve a list of matches at the
* current position.
*
* Returns the number of matches written into @matches. The matches are
* returned in decreasing order by length, and each will be of unique length
- * between the minimum and maximum match lengths passed to lz_sarray_init(). Up
- * to @max_matches_to_return (passed to lz_sarray_init()) matches will be
- * returned.
+ * between the minimum and maximum match lengths (inclusively) passed to
+ * lz_sarray_init(). Up to @max_matches_to_return (passed to lz_sarray_init())
+ * matches will be returned.
*
* @eval_match_cost is a function for evaluating the cost of a match when
- * deciding which ones to return. It is only used for comparing matches of the
- * same length. It needs to be fast, and need not be exact; an implementation
- * might simply rank matches by their offset, for example, although
- * implementations may choose to take into account additional information such
- * as repeat offsets.
+ * deciding which ones to return. It needs to be fast, and need not be exact;
+ * an implementation might simply rank matches by their offset, for example,
+ * although implementations may choose to take into account additional
+ * information such as repeat offsets.
*/
static _always_inline_attribute u32
lz_sarray_get_matches(struct lz_sarray *mf,
/* 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.
- */
+ * not have lower costs than longer matches already found. */
lz_sarray_cost_t best_cost = LZ_SARRAY_INFINITE_COST;
/* count_remaining = maximum number of possible matches remaining to be
/*
* lz_sarray.c
*
- * Suffix array match-finder for LZ (Lempel-Ziv) compression.
+ * Suffix array match-finder for Lempel-Ziv compression.
*/
/*
#include "divsufsort/divsufsort.h"
#include <string.h>
-/* Initialize the suffix array match-finder with the specified parameters.
+/* If ENABLE_LZ_DEBUG is defined, verify that the suffix array satisfies its
+ * definition.
*
- * After initialization, it can be used for any number of input strings of
- * length less than or equal to @max_window_size. */
-bool
-lz_sarray_init(struct lz_sarray *mf,
- input_idx_t max_window_size,
- input_idx_t min_match_len,
- input_idx_t max_match_len,
- u32 max_matches_to_consider,
- u32 max_matches_to_return)
-{
- 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;
-
- mf->SA = MALLOC(3U * max_window_size * sizeof(mf->SA[0]));
- if (mf->SA == NULL)
- return false;
-
- mf->salink = MALLOC(max_window_size * sizeof(mf->salink[0]));
- if (mf->salink == NULL)
- return false;
-
- return true;
-}
-
-/* Free memory allocated for the suffix array match-finder. */
-void
-lz_sarray_destroy(struct lz_sarray *mf)
-{
- FREE(mf->SA);
- FREE(mf->salink);
-}
-
-/* Initialize the suffix array match-finder for the specified input. */
-void
-lz_sarray_load_window(struct lz_sarray *mf, const u8 window[],
- input_idx_t window_size)
+ * @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 input_idx_t SA[restrict],
+ const u8 T[restrict],
+ bool found[restrict],
+ input_idx_t n)
{
- /* Load variables */
- const u8 * const restrict T = window;
- const input_idx_t n = window_size;
- const input_idx_t max_match_len = mf->max_match_len;
- input_idx_t * const restrict SA = mf->SA;
- input_idx_t * const restrict ISA = mf->ISA = SA + window_size;
- input_idx_t * const restrict LCP = mf->LCP = ISA + window_size;
- struct salink * const restrict link = mf->salink;
-
- /* Compute SA (Suffix Array). */
- {
- /* ISA and link are used as temporary space. */
- LZ_ASSERT(mf->max_window_size * sizeof(ISA[0]) >= 256 * sizeof(saidx_t));
- LZ_ASSERT(mf->max_window_size * 2 * sizeof(link[0]) >= 256 * 256 * sizeof(saidx_t));
-
- if (sizeof(input_idx_t) == sizeof(saidx_t)) {
- divsufsort(T, SA, n, (saidx_t*)ISA, (saidx_t*)link);
- } else {
- saidx_t sa[n];
- divsufsort(T, sa, n, (saidx_t*)ISA, (saidx_t*)link);
- for (input_idx_t i = 0; i < n; i++)
- SA[i] = sa[i];
- }
- }
-
#ifdef ENABLE_LZ_DEBUG
-
- LZ_ASSERT(n > 0);
-
- /* Verify suffix array. */
- {
- bool found[n];
- ZERO_ARRAY(found);
- for (input_idx_t r = 0; r < n; r++) {
- input_idx_t i = SA[r];
- LZ_ASSERT(i < n);
- LZ_ASSERT(!found[i]);
- found[i] = true;
- }
+ /* Ensure the SA contains exactly one of each i in [0, n - 1]. */
+ for (input_idx_t i = 0; i < n; i++)
+ found[i] = false;
+ for (input_idx_t r = 0; r < n; r++) {
+ input_idx_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 (input_idx_t r = 0; r < n - 1; r++) {
input_idx_t i1 = SA[r];
input_idx_t n1 = n - i1;
input_idx_t n2 = n - i2;
- LZ_ASSERT(memcmp(&T[i1], &T[i2], min(n1, n2)) <= 0);
+ int res = memcmp(&T[i1], &T[i2], min(n1, n2));
+ LZ_ASSERT(res < 0 || (res == 0 && n1 < n2));
}
- LZ_DEBUG("Verified SA (len %u)", n);
-#endif /* ENABLE_LZ_DEBUG */
+#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(input_idx_t ISA[restrict],
+ const input_idx_t SA[restrict],
+ input_idx_t n)
+{
+ input_idx_t i;
- /* Compute ISA (Inverse Suffix Array) */
- for (input_idx_t r = 0; r < n; r++)
- ISA[SA[r]] = r;
+ for (i = 0; i < n; i++)
+ ISA[SA[i]] = i;
+}
- /* 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--;
- }
+
+/* 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(input_idx_t LCP[restrict],
+ const input_idx_t SA[restrict],
+ const input_idx_t ISA[restrict],
+ const u8 T[restrict],
+ input_idx_t n)
+{
+ input_idx_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(input_idx_t LCP[restrict],
+ const input_idx_t SA[restrict],
+ const u8 T[restrict],
+ input_idx_t n)
+{
#ifdef ENABLE_LZ_DEBUG
- /* Verify LCP array. */
for (input_idx_t r = 0; r < n - 1; r++) {
- LZ_ASSERT(ISA[SA[r]] == r);
- LZ_ASSERT(ISA[SA[r + 1]] == r + 1);
-
input_idx_t i1 = SA[r];
input_idx_t i2 = SA[r + 1];
input_idx_t lcp = LCP[r + 1];
LZ_ASSERT(T[i1 + lcp] != T[i2 + lcp]);
}
#endif /* ENABLE_LZ_DEBUG */
+}
- /* 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. */
+/* 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.
+ */
+static void
+init_salink(struct salink link[restrict],
+ const input_idx_t LCP[restrict],
+ const input_idx_t SA[restrict],
+ const u8 T[restrict],
+ input_idx_t n,
+ input_idx_t max_match_len)
+{
+ /* Compute salink.next and salink.lcpnext. */
link[n - 1].next = ~(input_idx_t)0;
- link[n - 1].prev = ~(input_idx_t)0;
link[n - 1].lcpnext = 0;
- link[n - 1].lcpprev = 0;
for (input_idx_t r = n - 2; r != ~(input_idx_t)0; r--) {
input_idx_t t = r + 1;
input_idx_t l = LCP[t];
}
link[r].next = t;
link[r].lcpnext = min(l, max_match_len);
- LZ_ASSERT(t == ~(input_idx_t)0 || l <= n - SA[t]);
- LZ_ASSERT(l <= n - SA[r]);
- if (t == ~(input_idx_t)0)
- LZ_ASSERT(l == 0);
- else
- LZ_ASSERT(memcmp(&T[SA[r]], &T[SA[t]], l) == 0);
}
- /* 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. */
+ /* Compute salink.prev and salink.lcpprev. */
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];
}
link[r].prev = t;
link[r].lcpprev = min(l, max_match_len);
- LZ_ASSERT(t == ~(input_idx_t)0 || l <= n - SA[t]);
- LZ_ASSERT(l <= n - SA[r]);
- if (t == ~(input_idx_t)0)
- LZ_ASSERT(l == 0);
- else
- LZ_ASSERT(memcmp(&T[SA[r]], &T[SA[t]], l) == 0);
}
+}
+/* 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 input_idx_t SA[],
+ const u8 T[],
+ input_idx_t n,
+ input_idx_t max_match_len)
+{
+#ifdef ENABLE_LZ_DEBUG
+ for (input_idx_t r = 0; r < n; r++) {
+ for (input_idx_t prev = r; ; ) {
+ if (prev == 0) {
+ LZ_ASSERT(link[r].prev == ~(input_idx_t)0);
+ LZ_ASSERT(link[r].lcpprev == 0);
+ break;
+ }
+
+ prev--;
+
+ if (SA[prev] < SA[r]) {
+ LZ_ASSERT(link[r].prev == prev);
+ LZ_ASSERT(link[r].lcpprev <= n - SA[prev]);
+ LZ_ASSERT(link[r].lcpprev <= n - SA[r]);
+ LZ_ASSERT(link[r].lcpprev <= max_match_len);
+ LZ_ASSERT(0 == memcmp(&T[SA[prev]],
+ &T[SA[r]],
+ link[r].lcpprev));
+ if (link[r].lcpprev < n - SA[prev] &&
+ link[r].lcpprev < n - SA[r] &&
+ link[r].lcpprev < max_match_len)
+ {
+ LZ_ASSERT(T[SA[prev] + link[r].lcpprev] !=
+ T[SA[r] + link[r].lcpprev]);
+ }
+ break;
+ }
+ }
+
+ for (input_idx_t next = r; ; ) {
+ if (next == n - 1) {
+ LZ_ASSERT(link[r].next == ~(input_idx_t)0);
+ LZ_ASSERT(link[r].lcpnext == 0);
+ break;
+ }
+
+ next++;
+
+ if (SA[next] < SA[r]) {
+ LZ_ASSERT(link[r].next == next);
+ LZ_ASSERT(link[r].lcpnext <= n - SA[next]);
+ LZ_ASSERT(link[r].lcpnext <= n - SA[r]);
+ LZ_ASSERT(link[r].lcpnext <= max_match_len);
+ LZ_ASSERT(0 == memcmp(&T[SA[next]],
+ &T[SA[r]],
+ link[r].lcpnext));
+ if (link[r].lcpnext < n - SA[next] &&
+ link[r].lcpnext < n - SA[r] &&
+ link[r].lcpnext < max_match_len)
+ {
+ LZ_ASSERT(T[SA[next] + link[r].lcpnext] !=
+ T[SA[r] + 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.
+ *
+ * In the current implementation, the memory needed will be
+ * (6 * sizeof(input_idx_t) * @max_window_size) bytes.
+ * For (sizeof(input_idx_t) == 4) that's 24 times the window size.
+ *
+ * Memory is saved by saving neither the original window nor the LCP
+ * (Longest Common Prefix) array; otherwise 29 times the window size would
+ * be required. (In practice the compressor will likely keep the original
+ * window around anyway, although based on this property of the
+ * match-finder it theoretically it could overwrite it with the compressed
+ * data.)
+ *
+ * @min_match_len
+ * The minimum length of each match to be found.
+ *
+ * @max_match_len
+ * The maximum length of each match to be found.
+ *
+ * @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,
+ input_idx_t max_window_size,
+ input_idx_t min_match_len,
+ input_idx_t max_match_len,
+ u32 max_matches_to_consider,
+ u32 max_matches_to_return)
+{
+ 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. */
+ mf->SA = MALLOC(2 * max_window_size * sizeof(mf->SA[0]));
+ if (mf->SA == NULL)
+ return false;
+
+ mf->salink = MALLOC(max_window_size * sizeof(mf->salink[0]));
+ if (mf->salink == NULL)
+ return false;
+
+ return true;
+}
+
+/*
+ * 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[], input_idx_t n)
+{
+ input_idx_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 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. */
+ LZ_ASSERT(mf->max_window_size * sizeof(mf->SA[0])
+ >= 256 * sizeof(saidx_t));
+ LZ_ASSERT(mf->max_window_size * sizeof(mf->salink[0])
+ >= 256 * 256 * sizeof(saidx_t));
+ BUILD_BUG_ON(sizeof(input_idx_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. */
+ ISA = (input_idx_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->max_match_len);
+ verify_salink(mf->salink, mf->SA, T, n, 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 / commitdiff