bt_matchfinder optimizations
authorEric Biggers <ebiggers3@gmail.com>
Sat, 19 Sep 2015 18:56:09 +0000 (13:56 -0500)
committerEric Biggers <ebiggers3@gmail.com>
Sun, 27 Sep 2015 14:41:15 +0000 (09:41 -0500)
include/wimlib/bt_matchfinder.h
src/lzx_compress.c
src/xpress_compress.c

index 459fedd..70e4f14 100644 (file)
@@ -11,8 +11,8 @@
  *
  * This is a Binary Trees (bt) based matchfinder.
  *
- * The data structure is a hash table where each hash bucket contains a binary
- * tree of sequences whose first 3 bytes share the same hash code.  Each
+ * The main data structure is a hash table where each hash bucket contains a
+ * binary tree of sequences whose first 3 bytes share the same hash code.  Each
  * sequence is identified by its starting position in the input buffer.  Each
  * binary tree is always sorted such that each left child represents a sequence
  * lexicographically lesser than its parent and each right child represents a
@@ -51,7 +51,7 @@
 #include "wimlib/lz_extend.h"
 #include "wimlib/lz_hash.h"
 
-#define BT_MATCHFINDER_HASH_ORDER 16
+#define BT_MATCHFINDER_HASH3_ORDER 16
 
 /* TEMPLATED functions and structures have MF_SUFFIX appended to their name.  */
 #undef TEMPLATED
@@ -72,16 +72,22 @@ struct lz_match {
        u32 offset;
 };
 
-static inline u32
-bt_matchfinder_hash_3_bytes(const u8 *in_next)
-{
-       return lz_hash_3_bytes(in_next, BT_MATCHFINDER_HASH_ORDER);
-}
-
 #endif /* _WIMLIB_BT_MATCHFINDER_H */
 
 struct TEMPLATED(bt_matchfinder) {
-       pos_t hash_tab[1UL << BT_MATCHFINDER_HASH_ORDER];
+
+       /* The hash table for finding length 2 matches, if enabled  */
+#ifdef BT_MATCHFINDER_HASH2_ORDER
+       pos_t hash2_tab[1UL << BT_MATCHFINDER_HASH2_ORDER];
+#endif
+
+       /* The hash table which contains the roots of the binary trees for
+        * finding length 3 matches  */
+       pos_t hash3_tab[1UL << BT_MATCHFINDER_HASH3_ORDER];
+
+       /* The child node references for the binary trees.  The left and right
+        * children of the node for the sequence with position 'pos' are
+        * 'child_tab[pos * 2]' and 'child_tab[pos * 2 + 1]', respectively.  */
        pos_t child_tab[];
 };
 
@@ -102,97 +108,74 @@ TEMPLATED(bt_matchfinder_init)(struct TEMPLATED(bt_matchfinder) *mf)
 }
 
 static inline pos_t *
-TEMPLATED(bt_child)(struct TEMPLATED(bt_matchfinder) *mf, pos_t node, int offset)
+TEMPLATED(bt_left_child)(struct TEMPLATED(bt_matchfinder) *mf, u32 node)
 {
-       return &mf->child_tab[(node << 1) + offset];
+       return &mf->child_tab[(node << 1) + 0];
 }
 
 static inline pos_t *
-TEMPLATED(bt_left_child)(struct TEMPLATED(bt_matchfinder) *mf, pos_t node)
+TEMPLATED(bt_right_child)(struct TEMPLATED(bt_matchfinder) *mf, u32 node)
 {
-       return TEMPLATED(bt_child)(mf, node, 0);
+       return &mf->child_tab[(node << 1) + 1];
 }
 
-static inline pos_t *
-TEMPLATED(bt_right_child)(struct TEMPLATED(bt_matchfinder) *mf, pos_t node)
-{
-       return TEMPLATED(bt_child)(mf, node, 1);
-}
-
-/*
- * Retrieve a list of matches with the current position.
- *
- * @mf
- *     The matchfinder structure.
- * @in_begin
- *     Pointer to the beginning of the input buffer.
- * @in_next
- *     Pointer to the next byte in the input buffer to process.  This is the
- *     pointer to the sequence being matched against.
- * @min_len
- *     Only record matches that are at least this long.
- * @max_len
- *     The maximum permissible match length at this position.
- * @nice_len
- *     Stop searching if a match of at least this length is found.
- *     Must be <= @max_len.
- * @max_search_depth
- *     Limit on the number of potential matches to consider.  Must be >= 1.
- * @next_hash
- *     Pointer to the hash code for the current sequence, which was computed
- *     one position in advance so that the binary tree root could be
- *     prefetched.  This is an input/output parameter.
- * @best_len_ret
- *     The length of the longest match found is written here.  (This is
- *     actually redundant with the 'struct lz_match' array, but this is easier
- *     for the compiler to optimize when inlined and the caller immediately
- *     does a check against 'best_len'.)
- * @lz_matchptr
- *     An array in which this function will record the matches.  The recorded
- *     matches will be sorted by strictly increasing length and strictly
- *     increasing offset.  The maximum number of matches that may be found is
- *     'min(nice_len, max_len) - 3 + 1'.
- *
- * The return value is a pointer to the next available slot in the @lz_matchptr
- * array.  (If no matches were found, this will be the same as @lz_matchptr.)
- */
+/* Advance the binary tree matchfinder by one byte, optionally recording
+ * matches.  @record_matches should be a compile-time constant.  */
 static inline struct lz_match *
-TEMPLATED(bt_matchfinder_get_matches)(struct TEMPLATED(bt_matchfinder) * const restrict mf,
-                                     const u8 * const in_begin,
-                                     const u8 * const in_next,
-                                     const unsigned min_len,
-                                     const unsigned max_len,
-                                     const unsigned nice_len,
-                                     const unsigned max_search_depth,
-                                     u32 * restrict next_hash,
-                                     unsigned * restrict best_len_ret,
-                                     struct lz_match * restrict lz_matchptr)
+TEMPLATED(bt_matchfinder_advance_one_byte)(struct TEMPLATED(bt_matchfinder) * const restrict mf,
+                                          const u8 * const restrict in_begin,
+                                          const ptrdiff_t cur_pos,
+                                          const u32 max_len,
+                                          const u32 nice_len,
+                                          const u32 max_search_depth,
+                                          u32 * const restrict next_hash,
+                                          u32 * const restrict best_len_ret,
+                                          struct lz_match * restrict lz_matchptr,
+                                          const bool record_matches)
 {
-       unsigned depth_remaining = max_search_depth;
-       u32 hash;
-       pos_t cur_node;
+       const u8 *in_next = in_begin + cur_pos;
+       u32 depth_remaining = max_search_depth;
+#ifdef BT_MATCHFINDER_HASH2_ORDER
+       u16 seq2;
+       u32 hash2;
+#endif
+       u32 hash3;
+       u32 cur_node;
        const u8 *matchptr;
        pos_t *pending_lt_ptr, *pending_gt_ptr;
-       unsigned best_lt_len, best_gt_len;
-       unsigned len;
-       unsigned best_len = min_len - 1;
+       u32 best_lt_len, best_gt_len;
+       u32 len;
+       u32 best_len = 2;
 
        if (unlikely(max_len < LZ_HASH3_REQUIRED_NBYTES + 1)) {
                *best_len_ret = best_len;
                return lz_matchptr;
        }
 
-       hash = *next_hash;
-       *next_hash = bt_matchfinder_hash_3_bytes(in_next + 1);
-       cur_node = mf->hash_tab[hash];
-       mf->hash_tab[hash] = in_next - in_begin;
-       prefetchw(&mf->hash_tab[*next_hash]);
+       hash3 = *next_hash;
+       *next_hash = lz_hash(load_u24_unaligned(in_next + 1), BT_MATCHFINDER_HASH3_ORDER);
+       prefetchw(&mf->hash3_tab[*next_hash]);
+
+#ifdef BT_MATCHFINDER_HASH2_ORDER
+       seq2 = load_u16_unaligned(in_next);
+       hash2 = lz_hash(seq2, BT_MATCHFINDER_HASH2_ORDER);
+       cur_node = mf->hash2_tab[hash2];
+       mf->hash2_tab[hash2] = cur_pos;
+       if (record_matches &&
+           seq2 == load_u16_unaligned(&in_begin[cur_node]) &&
+           likely(in_next != in_begin))
+       {
+               lz_matchptr->length = 2;
+               lz_matchptr->offset = in_next - &in_begin[cur_node];
+               lz_matchptr++;
+       }
+#endif
 
-       pending_lt_ptr = TEMPLATED(bt_left_child)(mf, in_next - in_begin);
-       pending_gt_ptr = TEMPLATED(bt_right_child)(mf, in_next - in_begin);
-       best_lt_len = 0;
-       best_gt_len = 0;
-       len = 0;
+       cur_node = mf->hash3_tab[hash3];
+       mf->hash3_tab[hash3] = cur_pos;
+
+       pending_lt_ptr = TEMPLATED(bt_left_child)(mf, cur_pos);
+       pending_gt_ptr = TEMPLATED(bt_right_child)(mf, cur_pos);
 
        if (!cur_node) {
                *pending_lt_ptr = 0;
@@ -201,16 +184,23 @@ TEMPLATED(bt_matchfinder_get_matches)(struct TEMPLATED(bt_matchfinder) * const r
                return lz_matchptr;
        }
 
+       best_lt_len = 0;
+       best_gt_len = 0;
+       len = 0;
+
        for (;;) {
                matchptr = &in_begin[cur_node];
 
                if (matchptr[len] == in_next[len]) {
-                       len = lz_extend(in_next, matchptr, len + 1, max_len);
-                       if (len > best_len) {
-                               best_len = len;
-                               lz_matchptr->length = len;
-                               lz_matchptr->offset = in_next - matchptr;
-                               lz_matchptr++;
+                       len = lz_extend(in_next, matchptr, len + 1,
+                                       (record_matches ? max_len : nice_len));
+                       if (!record_matches || len > best_len) {
+                               if (record_matches) {
+                                       best_len = len;
+                                       lz_matchptr->length = len;
+                                       lz_matchptr->offset = in_next - matchptr;
+                                       lz_matchptr++;
+                               }
                                if (len >= nice_len) {
                                        *pending_lt_ptr = *TEMPLATED(bt_left_child)(mf, cur_node);
                                        *pending_gt_ptr = *TEMPLATED(bt_right_child)(mf, cur_node);
@@ -246,16 +236,76 @@ TEMPLATED(bt_matchfinder_get_matches)(struct TEMPLATED(bt_matchfinder) * const r
 }
 
 /*
+ * Retrieve a list of matches with the current position.
+ *
+ * @mf
+ *     The matchfinder structure.
+ * @in_begin
+ *     Pointer to the beginning of the input buffer.
+ * @cur_pos
+ *     The current position in the input buffer (the position of the sequence
+ *     being matched against).
+ * @max_len
+ *     The maximum permissible match length at this position.
+ * @nice_len
+ *     Stop searching if a match of at least this length is found.
+ *     Must be <= @max_len.
+ * @max_search_depth
+ *     Limit on the number of potential matches to consider.  Must be >= 1.
+ * @next_hash
+ *     Pointer to the hash code for the current sequence, which was computed
+ *     one position in advance so that the binary tree root could be
+ *     prefetched.  This is an input/output parameter.
+ * @best_len_ret
+ *     If a match of length >= 3 was found, then the length of the longest such
+ *     match is written here; otherwise 2 is written here.  (Note: this is
+ *     redundant with the 'struct lz_match' array, but this is easier for the
+ *     compiler to optimize when inlined and the caller immediately does a
+ *     check against 'best_len'.)
+ * @lz_matchptr
+ *     An array in which this function will record the matches.  The recorded
+ *     matches will be sorted by strictly increasing length and increasing
+ *     offset.  The maximum number of matches that may be found is
+ *     'min(nice_len, max_len) - 2 + 1', or one less if length 2 matches are
+ *     disabled.
+ *
+ * The return value is a pointer to the next available slot in the @lz_matchptr
+ * array.  (If no matches were found, this will be the same as @lz_matchptr.)
+ */
+static inline struct lz_match *
+TEMPLATED(bt_matchfinder_get_matches)(struct TEMPLATED(bt_matchfinder) *mf,
+                                     const u8 *in_begin,
+                                     ptrdiff_t cur_pos,
+                                     u32 max_len,
+                                     u32 nice_len,
+                                     u32 max_search_depth,
+                                     u32 *next_hash,
+                                     u32 *best_len_ret,
+                                     struct lz_match *lz_matchptr)
+{
+       return TEMPLATED(bt_matchfinder_advance_one_byte)(mf,
+                                                         in_begin,
+                                                         cur_pos,
+                                                         max_len,
+                                                         nice_len,
+                                                         max_search_depth,
+                                                         next_hash,
+                                                         best_len_ret,
+                                                         lz_matchptr,
+                                                         true);
+}
+
+/*
  * Advance the matchfinder, but don't record any matches.
  *
  * @mf
  *     The matchfinder structure.
  * @in_begin
  *     Pointer to the beginning of the input buffer.
- * @in_next
- *     Pointer to the next byte in the input buffer to process.
- * @in_end
- *     Pointer to the end of the input buffer.
+ * @cur_pos
+ *     The current position in the input buffer.
+ * @max_len
+ *     The maximum permissible match length at this position.
  * @nice_len
  *     Stop searching if a match of at least this length is found.
  * @max_search_depth
@@ -270,76 +320,23 @@ TEMPLATED(bt_matchfinder_get_matches)(struct TEMPLATED(bt_matchfinder) * const r
  * actually record any matches.
  */
 static inline void
-TEMPLATED(bt_matchfinder_skip_position)(struct TEMPLATED(bt_matchfinder) * const restrict mf,
-                                       const u8 * const in_begin,
-                                       const u8 * const in_next,
-                                       const u8 * const in_end,
-                                       const unsigned nice_len,
-                                       const unsigned max_search_depth,
-                                       u32 * restrict next_hash)
+TEMPLATED(bt_matchfinder_skip_position)(struct TEMPLATED(bt_matchfinder) *mf,
+                                       const u8 *in_begin,
+                                       ptrdiff_t cur_pos,
+                                       u32 max_len,
+                                       u32 nice_len,
+                                       u32 max_search_depth,
+                                       u32 *next_hash)
 {
-       unsigned depth_remaining = max_search_depth;
-       u32 hash;
-       pos_t cur_node;
-       const u8 *matchptr;
-       pos_t *pending_lt_ptr, *pending_gt_ptr;
-       unsigned best_lt_len, best_gt_len;
-       unsigned len;
-
-       if (unlikely(in_end - in_next < LZ_HASH3_REQUIRED_NBYTES + 1))
-               return;
-
-       hash = *next_hash;
-       *next_hash = bt_matchfinder_hash_3_bytes(in_next + 1);
-       cur_node = mf->hash_tab[hash];
-       mf->hash_tab[hash] = in_next - in_begin;
-       prefetchw(&mf->hash_tab[*next_hash]);
-
-       depth_remaining = max_search_depth;
-       pending_lt_ptr = TEMPLATED(bt_left_child)(mf, in_next - in_begin);
-       pending_gt_ptr = TEMPLATED(bt_right_child)(mf, in_next - in_begin);
-       best_lt_len = 0;
-       best_gt_len = 0;
-       len = 0;
-
-       if (!cur_node) {
-               *pending_lt_ptr = 0;
-               *pending_gt_ptr = 0;
-               return;
-       }
-
-       for (;;) {
-               matchptr = &in_begin[cur_node];
-
-               if (matchptr[len] == in_next[len]) {
-                       len = lz_extend(in_next, matchptr, len + 1, nice_len);
-                       if (len == nice_len) {
-                               *pending_lt_ptr = *TEMPLATED(bt_left_child)(mf, cur_node);
-                               *pending_gt_ptr = *TEMPLATED(bt_right_child)(mf, cur_node);
-                               return;
-                       }
-               }
-
-               if (matchptr[len] < in_next[len]) {
-                       *pending_lt_ptr = cur_node;
-                       pending_lt_ptr = TEMPLATED(bt_right_child)(mf, cur_node);
-                       cur_node = *pending_lt_ptr;
-                       best_lt_len = len;
-                       if (best_gt_len < len)
-                               len = best_gt_len;
-               } else {
-                       *pending_gt_ptr = cur_node;
-                       pending_gt_ptr = TEMPLATED(bt_left_child)(mf, cur_node);
-                       cur_node = *pending_gt_ptr;
-                       best_gt_len = len;
-                       if (best_lt_len < len)
-                               len = best_lt_len;
-               }
-
-               if (!cur_node || !--depth_remaining) {
-                       *pending_lt_ptr = 0;
-                       *pending_gt_ptr = 0;
-                       return;
-               }
-       }
+       u32 best_len;
+       TEMPLATED(bt_matchfinder_advance_one_byte)(mf,
+                                                  in_begin,
+                                                  cur_pos,
+                                                  max_len,
+                                                  nice_len,
+                                                  max_search_depth,
+                                                  next_hash,
+                                                  &best_len,
+                                                  NULL,
+                                                  false);
 }
index ac65c5d..863bb5e 100644 (file)
 #define LZX_MAX_FAST_LEVEL     34
 
 /*
- * LZX_HASH2_ORDER is the log base 2 of the number of entries in the hash table
- * for finding length 2 matches.  This can be as high as 16 (in which case the
- * hash function is trivial), but using a smaller hash table speeds up
- * compression due to reduced cache pressure.
+ * BT_MATCHFINDER_HASH2_ORDER is the log base 2 of the number of entries in the
+ * hash table for finding length 2 matches.  This could be as high as 16, but
+ * using a smaller hash table speeds up compression due to reduced cache
+ * pressure.
  */
-#define LZX_HASH2_ORDER                12
-#define LZX_HASH2_LENGTH       (1UL << LZX_HASH2_ORDER)
+#define BT_MATCHFINDER_HASH2_ORDER     12
 
 /*
  * These are the compressor-side limits on the codeword lengths for each Huffman
@@ -485,9 +484,6 @@ struct lzx_compressor {
                                                    LZX_MAX_MATCHES_PER_POS +
                                                    LZX_MAX_MATCH_LEN - 1];
 
-                       /* Hash table for finding length 2 matches  */
-                       u32 hash2_tab[LZX_HASH2_LENGTH];
-
                        /* Binary trees matchfinder (MUST BE LAST!!!)  */
                        union {
                                struct bt_matchfinder_16 bt_mf_16;
@@ -1787,12 +1783,10 @@ lzx_compress_near_optimal(struct lzx_compressor *c,
        const u8 * const in_end  = in_begin + c->in_nbytes;
        unsigned max_len = LZX_MAX_MATCH_LEN;
        unsigned nice_len = min(c->nice_match_length, max_len);
-       u32 next_hash;
+       u32 next_hash = 0;
        struct lzx_lru_queue queue;
 
        CALL_BT_MF(is_16_bit, c, bt_matchfinder_init);
-       memset(c->hash2_tab, 0, sizeof(c->hash2_tab));
-       next_hash = bt_matchfinder_hash_3_bytes(in_next);
        lzx_lru_queue_init(&queue);
 
        do {
@@ -1805,8 +1799,6 @@ lzx_compress_near_optimal(struct lzx_compressor *c,
                struct lz_match *cache_ptr = c->match_cache;
                do {
                        struct lz_match *lz_matchptr;
-                       u32 hash2;
-                       pos_t cur_match;
                        unsigned best_len;
 
                        /* If approaching the end of the input buffer, adjust
@@ -1828,33 +1820,16 @@ lzx_compress_near_optimal(struct lzx_compressor *c,
                                }
                        }
 
-                       lz_matchptr = cache_ptr + 1;
-
-                       /* Check for a length 2 match.  */
-                       hash2 = lz_hash_2_bytes(in_next, LZX_HASH2_ORDER);
-                       cur_match = c->hash2_tab[hash2];
-                       c->hash2_tab[hash2] = in_next - in_begin;
-                       if (cur_match != 0 &&
-                           (LZX_HASH2_ORDER == 16 ||
-                            load_u16_unaligned(&in_begin[cur_match]) ==
-                            load_u16_unaligned(in_next)))
-                       {
-                               lz_matchptr->length = 2;
-                               lz_matchptr->offset = in_next - &in_begin[cur_match];
-                               lz_matchptr++;
-                       }
-
-                       /* Check for matches of length >= 3.  */
+                       /* Check for matches.  */
                        lz_matchptr = CALL_BT_MF(is_16_bit, c, bt_matchfinder_get_matches,
                                                 in_begin,
-                                                in_next,
-                                                3,
+                                                in_next - in_begin,
                                                 max_len,
                                                 nice_len,
                                                 c->max_search_depth,
                                                 &next_hash,
                                                 &best_len,
-                                                lz_matchptr);
+                                                cache_ptr + 1);
                        in_next++;
                        cache_ptr->length = lz_matchptr - (cache_ptr + 1);
                        cache_ptr = lz_matchptr;
@@ -1884,12 +1859,10 @@ lzx_compress_near_optimal(struct lzx_compressor *c,
                                                        continue;
                                                }
                                        }
-                                       c->hash2_tab[lz_hash_2_bytes(in_next, LZX_HASH2_ORDER)] =
-                                               in_next - in_begin;
                                        CALL_BT_MF(is_16_bit, c, bt_matchfinder_skip_position,
                                                   in_begin,
-                                                  in_next,
-                                                  in_end,
+                                                  in_next - in_begin,
+                                                  max_len,
                                                   nice_len,
                                                   c->max_search_depth,
                                                   &next_hash);
index 7020a88..734bfc0 100644 (file)
@@ -908,10 +908,9 @@ xpress_find_matches(struct xpress_compressor * restrict c,
        const u8 *in_next = in_begin;
        const u8 * const in_end = in_begin + in_nbytes;
        struct lz_match *cache_ptr = c->match_cache;
-       u32 next_hash;
+       u32 next_hash = 0;
 
        bt_matchfinder_init(&c->bt_mf);
-       next_hash = bt_matchfinder_hash_3_bytes(in_next);
 
        do {
                struct lz_match *matches;
@@ -937,8 +936,7 @@ xpress_find_matches(struct xpress_compressor * restrict c,
                cache_ptr =
                        bt_matchfinder_get_matches(&c->bt_mf,
                                                   in_begin,
-                                                  in_next,
-                                                  XPRESS_MIN_MATCH_LEN,
+                                                  in_next - in_begin,
                                                   in_end - in_next,
                                                   min(in_end - in_next, c->nice_match_length),
                                                   c->max_search_depth,
@@ -965,8 +963,8 @@ xpress_find_matches(struct xpress_compressor * restrict c,
                        do {
                                bt_matchfinder_skip_position(&c->bt_mf,
                                                             in_begin,
-                                                            in_next,
-                                                            in_end,
+                                                            in_next - in_begin,
+                                                            in_end - in_next,
                                                             min(in_end - in_next,
                                                                 c->nice_match_length),
                                                             c->max_search_depth,