On Tue, Sep 10, 2013 at 06:17:12PM -0400, Nicolas Pitre wrote:
> hashtable_index() appears to be a close duplicate of hash_obj().
> Keep only the later and make it usable for all cases.
Thanks. This duplication has often bugged me when looking at that
hash table, but I just never actually wrote the patch.
> 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%.
Nice. This is a tiny bit subtle, though, as the power-of-2 growth
happens elsewhere, and we may want to tweak it later (the decorate.c
hash, for example, grows by 3/2).
Maybe it's worth squashing in one or both of the comments below as a
warning to anybody who tries to tweak it.
---
diff --git a/object.c b/object.c
index e2dae22..5f792cb 100644
--- a/object.c
+++ b/object.c
@@ -47,6 +47,7 @@ static unsigned int hash_obj(const unsigned char *sha1,
unsigned int n)
{
unsigned int hash;
memcpy(&hash, sha1, sizeof(unsigned int));
+ /* Assumes power-of-2 hash sizes in grow_object_hash */
return hash & (n - 1);
}
@@ -94,6 +95,10 @@ static void grow_object_hash(void)
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;
--
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