From: Duy Nguyen <pclouds@gmail.com>
To: "brian m. carlson" <sandals@crustytoothpaste.net>
Cc: "Git Mailing List" <git@vger.kernel.org>,
"Jeff King" <peff@peff.net>, "Derrick Stolee" <stolee@gmail.com>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: Re: [PATCH v2 04/13] cache: make hashcmp and hasheq work with larger hashes
Date: Tue, 16 Oct 2018 17:44:47 +0200 [thread overview]
Message-ID: <CACsJy8Cyep229CH8OfcVRqxC4soRiiCDhE_FMPhiEzVf-Z9v+Q@mail.gmail.com> (raw)
In-Reply-To: <20181015021900.1030041-5-sandals@crustytoothpaste.net>
On Mon, Oct 15, 2018 at 4:21 AM brian m. carlson
<sandals@crustytoothpaste.net> 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
next prev parent reply other threads:[~2018-10-16 15:45 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-15 2:18 [PATCH v2 00/13] Base SHA-256 implementation brian m. carlson
2018-10-15 2:18 ` [PATCH v2 01/13] sha1-file: rename algorithm to "sha1" brian m. carlson
2018-10-16 15:17 ` Duy Nguyen
2018-10-17 22:53 ` brian m. carlson
2018-10-15 2:18 ` [PATCH v2 02/13] sha1-file: provide functions to look up hash algorithms brian m. carlson
2018-10-17 13:32 ` SZEDER Gábor
2018-10-15 2:18 ` [PATCH v2 03/13] hex: introduce functions to print arbitrary hashes brian m. carlson
2018-10-16 1:54 ` Junio C Hamano
2018-10-17 23:49 ` brian m. carlson
2018-10-15 2:18 ` [PATCH v2 04/13] cache: make hashcmp and hasheq work with larger hashes brian m. carlson
2018-10-16 15:44 ` Duy Nguyen [this message]
2018-10-15 2:18 ` [PATCH v2 05/13] t: add basic tests for our SHA-1 implementation brian m. carlson
2018-10-15 2:18 ` [PATCH v2 06/13] t: make the sha1 test-tool helper generic brian m. carlson
2018-10-15 2:18 ` [PATCH v2 07/13] sha1-file: add a constant for hash block size brian m. carlson
2018-10-15 2:18 ` [PATCH v2 08/13] t/helper: add a test helper to compute hash speed brian m. carlson
2018-10-15 2:18 ` [PATCH v2 09/13] commit-graph: convert to using the_hash_algo brian m. carlson
2018-10-15 15:10 ` Derrick Stolee
2018-10-15 2:18 ` [PATCH v2 10/13] Add a base implementation of SHA-256 support brian m. carlson
2018-10-15 14:59 ` Duy Nguyen
2018-10-15 23:30 ` brian m. carlson
2018-10-16 14:59 ` Duy Nguyen
2018-10-17 16:12 ` SZEDER Gábor
2018-10-17 23:04 ` brian m. carlson
2018-10-15 2:18 ` [PATCH v2 11/13] sha256: add an SHA-256 implementation using libgcrypt brian m. carlson
2018-10-15 2:18 ` [PATCH v2 12/13] hash: add an SHA-256 implementation using OpenSSL brian m. carlson
2018-10-16 15:36 ` Duy Nguyen
2018-10-15 2:19 ` [PATCH v2 13/13] commit-graph: specify OID version for SHA-256 brian m. carlson
2018-10-15 15:11 ` Derrick Stolee
2018-10-16 2:00 ` Junio C Hamano
2018-10-16 22:39 ` brian m. carlson
2018-10-16 15:35 ` Duy Nguyen
2018-10-16 16:01 ` Derrick Stolee
2018-10-16 16:09 ` Duy Nguyen
2018-10-16 22:44 ` brian m. carlson
2018-10-17 14:31 ` Duy Nguyen
2018-10-18 0:06 ` brian m. carlson
2018-10-18 13:03 ` Derrick Stolee
2018-10-19 22:21 ` brian m. carlson
2018-10-17 12:21 ` Derrick Stolee
2018-10-17 22:38 ` brian m. carlson
2018-10-16 2:00 ` [PATCH v2 00/13] Base SHA-256 implementation Junio C Hamano
2018-10-16 4:01 ` Junio C Hamano
2018-10-16 22:45 ` brian m. carlson
2018-10-16 15:39 ` Duy Nguyen
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