From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: Jacob Keller <jacob.e.keller@intel.com>,
git@vger.kernel.org, Stefan Beller <stefanbeller@gmail.com>,
Johannes Sixt <j6t@kdbg.org>,
Jacob Keller <jacob.keller@gmail.com>
Subject: Re: [PATCH v8 7/8] cache: add empty_tree_oid object
Date: Tue, 23 Aug 2016 09:28:17 -0700 [thread overview]
Message-ID: <xmqqbn0jxxem.fsf@gitster.mtv.corp.google.com> (raw)
In-Reply-To: <20160819205806.vxzzgphqf4lgdor7@sigill.intra.peff.net> (Jeff King's message of "Fri, 19 Aug 2016 16:58:06 -0400")
Jeff King <peff@peff.net> writes:
> I suspect we need more than just the "is_empty" query. At least for the
> blob case, we do hashcpy() it into a struct (which should eventually
> become oidcpy). The empty-tree case even more so, as we pass it to
> random functions like lookup_tree().
>
> Our EMPTY_TREE_SHA1_BIN_LITERAL effectively ends up as a singleton
> in-core, too; it's just handled transparently by the compiler, since
> it's a literal. This effectively gives us _two_ singletons. We could do:
>
> const struct object_id empty_blob_oid = {
> "\xe6\x9d\xe2\x9b\xb2\xd1\xd6\x43\x4b\x8b"
> "\x29\xae\x77\x5a\xd8\xc2\xe4\x8c\x53\x91"
> };
> #define EMPTY_BLOB_SHA1_BIN (empty_blob_oid.hash)
>
> It's possible the use of an actual string literal lets the compiler do
> more optimizations, but I'd doubt it matters in practice. Probably it is
> just sticking that literal somewhere in BSS and filling in the pointer
> to it.
Makes sense; thanks.
next prev parent reply other threads:[~2016-08-23 16:28 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-19 0:00 [PATCH v8 0/8] submodule show inline diff Jacob Keller
2016-08-19 0:00 ` [PATCH v8 1/8] diff.c: remove output_prefix_length field Jacob Keller
2016-08-19 0:00 ` [PATCH v8 2/8] graph: add support for --line-prefix on all graph-aware output Jacob Keller
2016-08-19 0:00 ` [PATCH v8 3/8] diff: prepare for additional submodule formats Jacob Keller
2016-08-19 19:49 ` Junio C Hamano
2016-08-19 0:00 ` [PATCH v8 4/8] submodule: allow add_submodule_odb to work even if path is not checked out Jacob Keller
2016-08-19 20:06 ` Junio C Hamano
2016-08-19 20:32 ` Jacob Keller
2016-08-19 21:11 ` Junio C Hamano
2016-08-19 22:00 ` Jacob Keller
2016-08-19 22:26 ` Junio C Hamano
2016-08-19 23:25 ` Jacob Keller
2016-08-19 0:00 ` [PATCH v8 5/8] submodule: convert show_submodule_summary to use struct object_id * Jacob Keller
2016-08-19 20:12 ` Junio C Hamano
2016-08-19 0:00 ` [PATCH v8 6/8] submodule: refactor show_submodule_summary with helper function Jacob Keller
2016-08-19 20:24 ` Junio C Hamano
2016-08-19 20:33 ` Jacob Keller
2016-08-19 0:00 ` [PATCH v8 7/8] cache: add empty_tree_oid object Jacob Keller
2016-08-19 20:31 ` Junio C Hamano
2016-08-19 20:35 ` Jacob Keller
2016-08-19 20:50 ` Junio C Hamano
2016-08-19 21:14 ` Junio C Hamano
2016-08-19 22:02 ` Jacob Keller
2016-08-19 20:58 ` Jeff King
2016-08-23 16:28 ` Junio C Hamano [this message]
2016-08-19 0:00 ` [PATCH v8 8/8] diff: teach diff to display submodule difference with an inline diff Jacob Keller
2016-08-19 21:52 ` Junio C Hamano
2016-08-19 22:03 ` Jacob Keller
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