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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>
This commit is contained in:
Nicolas Pitre 2013-09-10 18:17:12 -04:00 committed by Junio C Hamano
parent e230c568c4
commit 9f36c9b7f7
1 changed files with 10 additions and 12 deletions
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22
object.c
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@ -43,16 +43,17 @@ int type_from_string(const char *str)
die("invalid object type \"%s\"", str);
}
static unsigned int hash_obj(struct object *obj, unsigned int n)
static unsigned int hash_obj(const unsigned char *sha1, unsigned int n)
{
unsigned int hash;
memcpy(&hash, obj->sha1, sizeof(unsigned int));
return hash % n;
memcpy(&hash, sha1, sizeof(unsigned int));
/* Assumes power-of-2 hash sizes in grow_object_hash */
return hash & (n - 1);
}
static void insert_obj_hash(struct object *obj, struct object **hash, unsigned int size)
{
unsigned int j = hash_obj(obj, size);
unsigned int j = hash_obj(obj->sha1, size);
while (hash[j]) {
j++;
@ -62,13 +63,6 @@ static void insert_obj_hash(struct object *obj, struct object **hash, unsigned i
hash[j] = obj;
}
static unsigned int hashtable_index(const unsigned char *sha1)
{
unsigned int i;
memcpy(&i, sha1, sizeof(unsigned int));
return i % obj_hash_size;
}
struct object *lookup_object(const unsigned char *sha1)
{
unsigned int i, first;
@ -77,7 +71,7 @@ struct object *lookup_object(const unsigned char *sha1)
if (!obj_hash)
return NULL;
first = i = hashtable_index(sha1);
first = i = hash_obj(sha1, obj_hash_size);
while ((obj = obj_hash[i]) != NULL) {
if (!hashcmp(sha1, obj->sha1))
break;
@ -101,6 +95,10 @@ struct object *lookup_object(const unsigned char *sha1)
static void grow_object_hash(void)
{
int i;
/*
* Note that this size must always be power-of-2 to match hash_obj
* above.
*/
int new_hash_size = obj_hash_size < 32 ? 32 : 2 * obj_hash_size;
struct object **new_hash;