X-Git-Url: https://git.octo.it/?a=blobdiff_plain;f=diffcore-delta.c;h=7338a40c5964ae6ddfb855465249fc1a2fa5a2a3;hb=ae448e3854d8b6e7e37aa88fa3917f5dd97f3210;hp=471b98f05de2899f6aaa4818966aa99df7ec8f7e;hpb=a7e71bb4898223b0be41e44f52f382c884404434;p=git.git

diff --git a/diffcore-delta.c b/diffcore-delta.c
index 471b98f0..7338a40c 100644
--- a/diffcore-delta.c
+++ b/diffcore-delta.c
@@ -25,12 +25,23 @@
  */
 
 /* Wild guess at the initial hash size */
-#define INITIAL_HASH_SIZE 10
-#define HASHBASE 65537 /* next_prime(2^16) */
+#define INITIAL_HASH_SIZE 9
+
+/* We leave more room in smaller hash but do not let it
+ * grow to have unused hole too much.
+ */
+#define INITIAL_FREE(sz_log2) ((1<<(sz_log2))*(sz_log2-3)/(sz_log2))
+
+/* A prime rather carefully chosen between 2^16..2^17, so that
+ * HASHBASE < INITIAL_FREE(17).  We want to keep the maximum hashtable
+ * size under the current 2<<17 maximum, which can hold this many
+ * different values before overflowing to hashtable of size 2<<18.
+ */
+#define HASHBASE 107927
 
 struct spanhash {
-	unsigned long hashval;
-	unsigned long cnt;
+	unsigned int hashval;
+	unsigned int cnt;
 };
 struct spanhash_top {
 	int alloc_log2;
@@ -38,7 +49,8 @@ struct spanhash_top {
 	struct spanhash data[FLEX_ARRAY];
 };
 
-static struct spanhash *spanhash_find(struct spanhash_top *top, unsigned long hashval)
+static struct spanhash *spanhash_find(struct spanhash_top *top,
+				      unsigned int hashval)
 {
 	int sz = 1 << top->alloc_log2;
 	int bucket = hashval & (sz - 1);
@@ -62,7 +74,7 @@ static struct spanhash_top *spanhash_rehash(struct spanhash_top *orig)
 
 	new = xmalloc(sizeof(*orig) + sizeof(struct spanhash) * sz);
 	new->alloc_log2 = orig->alloc_log2 + 1;
-	new->free = osz;
+	new->free = INITIAL_FREE(new->alloc_log2);
 	memset(new->data, 0, sizeof(struct spanhash) * sz);
 	for (i = 0; i < osz; i++) {
 		struct spanhash *o = &(orig->data[i]);
@@ -87,7 +99,7 @@ static struct spanhash_top *spanhash_rehash(struct spanhash_top *orig)
 }
 
 static struct spanhash_top *add_spanhash(struct spanhash_top *top,
-					 unsigned long hashval)
+					 unsigned int hashval, int cnt)
 {
 	int bucket, lim;
 	struct spanhash *h;
@@ -98,14 +110,14 @@ static struct spanhash_top *add_spanhash(struct spanhash_top *top,
 		h = &(top->data[bucket++]);
 		if (!h->cnt) {
 			h->hashval = hashval;
-			h->cnt = 1;
+			h->cnt = cnt;
 			top->free--;
 			if (top->free < 0)
 				return spanhash_rehash(top);
 			return top;
 		}
 		if (h->hashval == hashval) {
-			h->cnt++;
+			h->cnt += cnt;
 			return top;
 		}
 		if (lim <= bucket)
@@ -113,31 +125,33 @@ static struct spanhash_top *add_spanhash(struct spanhash_top *top,
 	}
 }
 
-static struct spanhash_top *hash_chars(unsigned char *buf, unsigned long sz)
+static struct spanhash_top *hash_chars(unsigned char *buf, unsigned int sz)
 {
-	int i;
-	unsigned long accum1, accum2, hashval;
+	int i, n;
+	unsigned int 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;
+	hash->free = INITIAL_FREE(i);
 	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
-	 */
-	for (i = accum1 = accum2 = 0; i < 7; i++, sz--) {
-		accum1 = (accum1 << 8) | (accum2 >> 24);
-		accum2 = (accum2 << 8) | *buf++;
-	}
+	n = 0;
+	accum1 = accum2 = 0;
 	while (sz) {
-		accum1 = (accum1 << 8) | (accum2 >> 24);
-		accum2 = (accum2 << 8) | *buf++;
-		hashval = (accum1 + accum2 * 0x61) % HASHBASE;
-		hash = add_spanhash(hash, hashval);
+		unsigned int c = *buf++;
+		unsigned int old_1 = accum1;
 		sz--;
+		accum1 = (accum1 << 7) ^ (accum2 >> 25);
+		accum2 = (accum2 << 7) ^ (old_1 >> 25);
+		accum1 += c;
+		if (++n < 64 && c != '\n')
+			continue;
+		hashval = (accum1 + accum2 * 0x61) % HASHBASE;
+		hash = add_spanhash(hash, hashval, n);
+		n = 0;
+		accum1 = accum2 = 0;
 	}
 	return hash;
 }
@@ -154,9 +168,6 @@ int diffcore_count_changes(void *src, unsigned long src_size,
 	struct spanhash_top *src_count, *dst_count;
 	unsigned long sc, la;
 
-	if (src_size < 8 || dst_size < 8)
-		return -1;
-
 	src_count = dst_count = NULL;
 	if (src_count_p)
 		src_count = *src_count_p;