Merge branch 'jk/lookup-object-prefer-latest'

Optimizes object lookup when the object hashtable starts to become
crowded.

* jk/lookup-object-prefer-latest:
  lookup_object: prioritize recently found objects

object.c

@@ -71,13 +71,13 @@ static unsigned int hashtable_index(const unsigned char *sha1)
 
 struct object *lookup_object(const unsigned char *sha1)
 {
-	unsigned int i;
+	unsigned int i, first;
 	struct object *obj;
 
 	if (!obj_hash)
 		return NULL;
 
-	i = hashtable_index(sha1);
+	first = i = hashtable_index(sha1);
 	while ((obj = obj_hash[i]) != NULL) {
 		if (!hashcmp(sha1, obj->sha1))
 			break;
@@ -85,6 +85,16 @@ struct object *lookup_object(const unsigned char *sha1)
 		if (i == obj_hash_size)
 			i = 0;
 	}
+	if (obj && i != first) {
+		/*
+		 * Move object to where we started to look for it so
+		 * that we do not need to walk the hash table the next
+		 * time we look for it.
+		 */
+		struct object *tmp = obj_hash[i];
+		obj_hash[i] = obj_hash[first];
+		obj_hash[first] = tmp;
+	}
 	return obj;
 }