lookup_object: remove hashtable_index() and optimize hash_obj()
hashtable_index() appears to be a close duplicate of hash_obj(). Keep only the later and make it usable for all cases. Also remove the modulus as this is an expensive operation. The size argument is always a power of 2 anyway, so a simple mask operation provides the same result. On a 'git rev-list --all --objects' run this decreased the time spent in lookup_object from 27.5% to 24.1%. [jc: with a few comments on "modulus turned into mask" by Peff] Signed-off-by: Nicolas Pitre <nico@fluxnic.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Nicolas Pitre committed
Sep 10, 2013 at 18:17 UTC
9f36c9b7f77f188db47b80ae1118856249beaa15
1 file changed
+10
-12
object.c
+10
-12
@@ -43,16 +43,17 @@ int type_from_string(const char *str)
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die("invalid object type \"%s\"", str);
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}
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-static unsigned int hash_obj(struct object *obj, unsigned int n)
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+static unsigned int hash_obj(const unsigned char *sha1, unsigned int n)
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{
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unsigned int hash;
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- memcpy(&hash, obj->sha1, sizeof(unsigned int));
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- return hash % n;
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+ memcpy(&hash, sha1, sizeof(unsigned int));
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+ /* Assumes power-of-2 hash sizes in grow_object_hash */
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+ return hash & (n - 1);
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}
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static void insert_obj_hash(struct object *obj, struct object **hash, unsigned int size)
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{
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- unsigned int j = hash_obj(obj, size);
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+ unsigned int j = hash_obj(obj->sha1, size);
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while (hash[j]) {
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j++;
@@ -62,13 +63,6 @@ static void insert_obj_hash(struct object *obj, struct object **hash, unsigned i
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hash[j] = obj;
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}
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-static unsigned int hashtable_index(const unsigned char *sha1)
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-{
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- unsigned int i;
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- memcpy(&i, sha1, sizeof(unsigned int));
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- return i % obj_hash_size;
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-}
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-
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struct object *lookup_object(const unsigned char *sha1)
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{
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unsigned int i, first;
@@ -77,7 +71,7 @@ struct object *lookup_object(const unsigned char *sha1)
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if (!obj_hash)
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return NULL;
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- first = i = hashtable_index(sha1);
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+ first = i = hash_obj(sha1, obj_hash_size);
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while ((obj = obj_hash[i]) != NULL) {
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if (!hashcmp(sha1, obj->sha1))
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break;
@@ -101,6 +95,10 @@ struct object *lookup_object(const unsigned char *sha1)
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static void grow_object_hash(void)
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{
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int i;
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+ /*
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+ * Note that this size must always be power-of-2 to match hash_obj
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+ * above.
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+ */
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int new_hash_size = obj_hash_size < 32 ? 32 : 2 * obj_hash_size;
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struct object **new_hash;
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