On Mon, Oct 15, 2018 at 4:21 AM brian m. carlson
<sandals@xxxxxxxxxxxxxxxxxxxx> wrote:
> diff --git a/cache.h b/cache.h
> index a13d14ce0a..0b88c3a344 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -1024,16 +1024,12 @@ extern const struct object_id null_oid;
> static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
> {
> /*
> - * This is a temporary optimization hack. By asserting the size here,
> - * we let the compiler know that it's always going to be 20, which lets
> - * it turn this fixed-size memcmp into a few inline instructions.
> - *
> - * This will need to be extended or ripped out when we learn about
> - * hashes of different sizes.
> + * Teach the compiler that there are only two possibilities of hash size
> + * here, so that it can optimize for this case as much as possible.
> */
> - if (the_hash_algo->rawsz != 20)
> - BUG("hash size not yet supported by hashcmp");
> - return memcmp(sha1, sha2, the_hash_algo->rawsz);
> + if (the_hash_algo->rawsz == GIT_MAX_RAWSZ)
It's tangent. But performance is probably another good reason to
detach the_hash_algo from the_repository so we have one less
dereference to do. (the other good reason is these hash operations
should work in "no-repo" commands as well, where the_repository does
not really make sense).
> + return memcmp(sha1, sha2, GIT_MAX_RAWSZ);
> + return memcmp(sha1, sha2, GIT_SHA1_RAWSZ);
> }
>
> static inline int oidcmp(const struct object_id *oid1, const struct object_id *oid2)
> @@ -1043,7 +1039,13 @@ static inline int oidcmp(const struct object_id *oid1, const struct object_id *o
>
> static inline int hasheq(const unsigned char *sha1, const unsigned char *sha2)
> {
> - return !hashcmp(sha1, sha2);
> + /*
> + * We write this here instead of deferring to hashcmp so that the
> + * compiler can properly inline it and avoid calling memcmp.
> + */
> + if (the_hash_algo->rawsz == GIT_MAX_RAWSZ)
> + return !memcmp(sha1, sha2, GIT_MAX_RAWSZ);
> + return !memcmp(sha1, sha2, GIT_SHA1_RAWSZ);
> }
>
> static inline int oideq(const struct object_id *oid1, const struct object_id *oid2)
--
Duy
