diffcore-rename: somewhat optimized.

This changes diffcore-rename to reuse statistics information
gathered during similarity estimation, and updates the hashtable
implementation used to keep track of the statistics to be
denser.  This seems to give better performance.

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff.c

@@ -463,6 +463,8 @@ void diff_free_filespec_data(struct diff_filespec *s)
 		munmap(s->data, s->size);
 	s->should_free = s->should_munmap = 0;
 	s->data = NULL;
+	free(s->cnt_data);
+	s->cnt_data = NULL;
 }
 
 static void prep_temp_blob(struct diff_tempfile *temp,

diffcore-break.c

@@ -68,6 +68,7 @@ static int should_break(struct diff_filespec *src,
 
 	if (diffcore_count_changes(src->data, src->size,
 				   dst->data, dst->size,
+				   NULL, NULL,
 				   0,
 				   &src_copied, &literal_added))
 		return 0;

diffcore-delta.c

@@ -24,11 +24,106 @@
  * The length of the sequence is arbitrarily set to 8 for now.
  */
 
+/* Wild guess at the initial hash size */
+#define INITIAL_HASH_SIZE 10
 #define HASHBASE 65537 /* next_prime(2^16) */
 
-static void hash_chars(unsigned char *buf, unsigned long sz, int *count)
+struct spanhash {
+	unsigned long hashval;
+	unsigned long cnt;
+};
+struct spanhash_top {
+	int alloc_log2;
+	int free;
+	struct spanhash data[FLEX_ARRAY];
+};
+
+static struct spanhash *spanhash_find(struct spanhash_top *top, unsigned long hashval)
 {
-	unsigned int accum1, accum2, i;
+	int sz = 1 << top->alloc_log2;
+	int bucket = hashval & (sz - 1);
+	while (1) {
+		struct spanhash *h = &(top->data[bucket++]);
+		if (!h->cnt)
+			return NULL;
+		if (h->hashval == hashval)
+			return h;
+		if (sz <= bucket)
+			bucket = 0;
+	}
+}
+
+static struct spanhash_top *spanhash_rehash(struct spanhash_top *orig)
+{
+	struct spanhash_top *new;
+	int i;
+	int osz = 1 << orig->alloc_log2;
+	int sz = osz << 1;
+
+	new = xmalloc(sizeof(*orig) + sizeof(struct spanhash) * sz);
+	new->alloc_log2 = orig->alloc_log2 + 1;
+	new->free = osz;
+	memset(new->data, 0, sizeof(struct spanhash) * sz);
+	for (i = 0; i < osz; i++) {
+		struct spanhash *o = &(orig->data[i]);
+		int bucket;
+		if (!o->cnt)
+			continue;
+		bucket = o->hashval & (sz - 1);
+		while (1) {
+			struct spanhash *h = &(new->data[bucket++]);
+			if (!h->cnt) {
+				h->hashval = o->hashval;
+				h->cnt = o->cnt;
+				new->free--;
+				break;
+			}
+			if (sz <= bucket)
+				bucket = 0;
+		}
+	}
+	free(orig);
+	return new;
+}
+
+static struct spanhash_top *add_spanhash(struct spanhash_top *top,
+					 unsigned long hashval)
+{
+	int bucket, lim;
+	struct spanhash *h;
+
+	lim = (1 << top->alloc_log2);
+	bucket = hashval & (lim - 1);
+	while (1) {
+		h = &(top->data[bucket++]);
+		if (!h->cnt) {
+			h->hashval = hashval;
+			h->cnt = 1;
+			top->free--;
+			if (top->free < 0)
+				return spanhash_rehash(top);
+			return top;
+		}
+		if (h->hashval == hashval) {
+			h->cnt++;
+			return top;
+		}
+		if (lim <= bucket)
+			bucket = 0;
+	}
+}
+
+static struct spanhash_top *hash_chars(unsigned char *buf, unsigned long sz)
+{
+	int i;
+	unsigned long accum1, accum2, hashval;
+	struct spanhash_top *hash;
+
+	i = INITIAL_HASH_SIZE;
+	hash = xmalloc(sizeof(*hash) + sizeof(struct spanhash) * (1<<i));
+	hash->alloc_log2 = i;
+	hash->free = (1<<i)/2;
+	memset(hash->data, 0, sizeof(struct spanhash) * (1<<i));
 
 	/* an 8-byte shift register made of accum1 and accum2.  New
 	 * bytes come at LSB of accum2, and shifted up to accum1
@@ -40,44 +135,68 @@ static void hash_chars(unsigned char *buf, unsigned long sz, int *count)
 	while (sz) {
 		accum1 = (accum1 << 8) | (accum2 >> 24);
 		accum2 = (accum2 << 8) | *buf++;
-		/* We want something that hashes permuted byte
-		 * sequences nicely; simpler hash like (accum1 ^
-		 * accum2) does not perform as well.
-		 */
-		i = (accum1 + accum2 * 0x61) % HASHBASE;
-		count[i]++;
+		hashval = (accum1 + accum2 * 0x61) % HASHBASE;
+		hash = add_spanhash(hash, hashval);
 		sz--;
 	}
+	return hash;
 }
 
 int diffcore_count_changes(void *src, unsigned long src_size,
 			   void *dst, unsigned long dst_size,
+			   void **src_count_p,
+			   void **dst_count_p,
 			   unsigned long delta_limit,
 			   unsigned long *src_copied,
 			   unsigned long *literal_added)
 {
-	int *src_count, *dst_count, i;
+	int i, ssz;
+	struct spanhash_top *src_count, *dst_count;
 	unsigned long sc, la;
 
 	if (src_size < 8 || dst_size < 8)
 		return -1;
 
-	src_count = xcalloc(HASHBASE * 2, sizeof(int));
-	dst_count = src_count + HASHBASE;
-	hash_chars(src, src_size, src_count);
-	hash_chars(dst, dst_size, dst_count);
-
-	sc = la = 0;
-	for (i = 0; i < HASHBASE; i++) {
-		if (src_count[i] < dst_count[i]) {
-			la += dst_count[i] - src_count[i];
-			sc += src_count[i];
-		}
-		else /* i.e. if (dst_count[i] <= src_count[i]) */
-			sc += dst_count[i];
+	src_count = dst_count = NULL;
+	if (src_count_p)
+		src_count = *src_count_p;
+	if (!src_count) {
+		src_count = hash_chars(src, src_size);
+		if (src_count_p)
+			*src_count_p = src_count;
 	}
+	if (dst_count_p)
+		dst_count = *dst_count_p;
+	if (!dst_count) {
+		dst_count = hash_chars(dst, dst_size);
+		if (dst_count_p)
+			*dst_count_p = dst_count;
+	}
+	sc = la = 0;
+
+	ssz = 1 << src_count->alloc_log2;
+	for (i = 0; i < ssz; i++) {
+		struct spanhash *s = &(src_count->data[i]);
+		struct spanhash *d;
+		unsigned dst_cnt, src_cnt;
+		if (!s->cnt)
+			continue;
+		src_cnt = s->cnt;
+		d = spanhash_find(dst_count, s->hashval);
+		dst_cnt = d ? d->cnt : 0;
+		if (src_cnt < dst_cnt) {
+			la += dst_cnt - src_cnt;
+			sc += src_cnt;
+		}
+		else
+			sc += dst_cnt;
+	}
+
+	if (!src_count_p)
+		free(src_count);
+	if (!dst_count_p)
+		free(dst_count);
 	*src_copied = sc;
 	*literal_added = la;
-	free(src_count);
 	return 0;
 }

diffcore-rename.c

@@ -166,6 +166,7 @@ static int estimate_similarity(struct diff_filespec *src,
 	delta_limit = base_size * (MAX_SCORE-minimum_score) / MAX_SCORE;
 	if (diffcore_count_changes(src->data, src->size,
 				   dst->data, dst->size,
+				   &src->cnt_data, &dst->cnt_data,
 				   delta_limit,
 				   &src_copied, &literal_added))
 		return 0;
@@ -306,6 +307,8 @@ void diffcore_rename(struct diff_options *options)
 			m->score = estimate_similarity(one, two,
 						       minimum_score);
 		}
+		free(two->cnt_data);
+		two->cnt_data = NULL;
 		dst_cnt++;
 	}
 	/* cost matrix sorted by most to least similar pair */

diffcore.h

@@ -26,6 +26,7 @@ struct diff_filespec {
 	unsigned char sha1[20];
 	char *path;
 	void *data;
+	void *cnt_data;
 	unsigned long size;
 	int xfrm_flags;		 /* for use by the xfrm */
 	unsigned short mode;	 /* file mode */
@@ -103,6 +104,8 @@ void diff_debug_queue(const char *, struct diff_queue_struct *);
 
 extern int diffcore_count_changes(void *src, unsigned long src_size,
 				  void *dst, unsigned long dst_size,
+				  void **src_count_p,
+				  void **dst_count_p,
 				  unsigned long delta_limit,
 				  unsigned long *src_copied,
 				  unsigned long *literal_added);