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 expansive 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%.

Signed-off-by: Nicolas Pitre <n...@fluxnic.net>

I discovered this patch in my git work tree dating from 2 years ago.

diff --git a/object.c b/object.c
index d8a4b1f..e2dae22 100644
--- a/object.c
+++ b/object.c
@@ -43,16 +43,16 @@ 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));
+       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]) {
@@ -62,13 +62,6 @@ 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 +70,7 @@ 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))
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