From: Kaartic Sivaraam <kaartic.sivaraam@gmail.com>
To: "Derrick Stolee" <stolee@gmail.com>, "Jeff King" <peff@peff.net>,
"brian m. carlson" <sandals@crustytoothpaste.net>,
"Jonathan Nieder" <jrnieder@gmail.com>,
"Paul Smith" <paul@mad-scientist.net>,
git@vger.kernel.org, "Duy Nguyen" <pclouds@gmail.com>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: Re: [ANNOUNCE] Git v2.19.0-rc0
Date: Mon, 03 Sep 2018 00:23:41 +0530 [thread overview]
Message-ID: <39ec35843c3164a9da75466b768636cb7871690d.camel@gmail.com> (raw)
In-Reply-To: <f854aba0-6d28-7f2b-aad2-858983c4af36@gmail.com>
On Thu, 2018-08-23 at 06:26 -0400, Derrick Stolee wrote:
>
> Around the time that my proposed approaches were getting vetoed for
> alignment issues, I figured I was out of my depth here. I reached out to
> Daniel Lemire (of EWAH bitmap fame) on Twitter [1]. His blog is full of
> posts of word-based approaches to different problems, so I thought he
> might know something off the top of his head that would be applicable.
> His conclusion (after looking only a short time) was to take a 'hasheq'
> approach [2] like Peff suggested [3]. Since that requires auditing all
> callers of hashcmp to see if hasheq is appropriate, it is not a good
> solution for 2.19 but (in my opinion) should be evaluated as part of the
> 2.20 cycle.
>
That was an interesting blog post, indeed. It had an interesting
comments section. One comment especially caught my eyes was [a]:
"So the way gcc (and maybe clang) handles this is specifically by
recognizing memcmp and checking whether a only a 2-way result is needed
and then essentially replacing it with a memcmp_eq call.
..."
I find this to be an interesting note. It seems GCC does optimize when
we clearly indicate that we use the result of the memcmp as a boolean.
So would that help in anyway? Maybe it would help in writing a `hasheq`
method easily? I'm not sure.
> [1] https://twitter.com/stolee/status/1032312965754748930
>
> [2]
> https://lemire.me/blog/2018/08/22/avoid-lexicographical-comparisons-when-testing-for-string-equality/
>
> [3]
> https://public-inbox.org/git/20180822030344.GA14684@sigill.intra.peff.net/
>
> [4]
> https://public-inbox.org/git/7ea416cf-b043-1274-e161-85a8780b8e1c@gmail.com/
[a]:
https://lemire.me/blog/2018/08/22/avoid-lexicographical-comparisons-when-testing-for-string-equality/#comment-344073
--
Sivaraam
prev parent reply other threads:[~2018-09-02 18:54 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-20 22:13 [ANNOUNCE] Git v2.19.0-rc0 Junio C Hamano
2018-08-20 22:41 ` Stefan Beller
2018-08-20 23:39 ` Jonathan Nieder
2018-08-21 0:27 ` Jonathan Nieder
2018-08-21 0:46 ` Stefan Beller
2018-08-21 20:41 ` Derrick Stolee
2018-08-21 21:29 ` Jeff King
2018-08-22 0:48 ` brian m. carlson
2018-08-22 3:03 ` Jeff King
2018-08-22 3:36 ` Jeff King
2018-08-22 11:11 ` Derrick Stolee
2018-08-22 5:36 ` brian m. carlson
2018-08-22 6:07 ` Jeff King
2018-08-22 7:39 ` Ævar Arnfjörð Bjarmason
2018-08-22 11:14 ` Derrick Stolee
2018-08-22 15:17 ` Jeff King
2018-08-22 16:08 ` Duy Nguyen
2018-08-22 16:14 ` Duy Nguyen
2018-08-22 16:26 ` Jeff King
2018-08-22 16:49 ` Derrick Stolee
2018-08-22 16:58 ` Duy Nguyen
2018-08-22 17:04 ` Derrick Stolee
2018-08-22 16:59 ` Jeff King
2018-08-22 17:02 ` Junio C Hamano
2018-08-22 15:14 ` Jeff King
2018-08-22 14:28 ` Derrick Stolee
2018-08-22 15:24 ` Jeff King
2018-08-22 12:42 ` Paul Smith
2018-08-22 15:23 ` Jeff King
2018-08-23 1:23 ` Jonathan Nieder
2018-08-23 2:16 ` Jeff King
2018-08-23 2:27 ` Jonathan Nieder
2018-08-23 5:02 ` Jeff King
2018-08-23 5:09 ` brian m. carlson
2018-08-23 5:10 ` Jonathan Nieder
2018-08-23 13:20 ` Junio C Hamano
2018-08-23 16:31 ` wide t/perf output, was " Jeff King
2018-08-23 3:47 ` brian m. carlson
2018-08-23 5:04 ` Jeff King
2018-08-23 10:26 ` Derrick Stolee
2018-08-23 13:16 ` Junio C Hamano
2018-08-23 16:14 ` Jeff King
2018-08-23 23:30 ` Jacob Keller
2018-08-23 23:40 ` Jeff King
2018-08-24 0:06 ` Jeff King
2018-08-24 0:16 ` Jeff King
2018-08-24 2:48 ` Jacob Keller
2018-08-24 2:59 ` Jeff King
2018-08-24 6:45 ` Jeff King
2018-08-24 11:04 ` Derrick Stolee
2018-08-27 19:36 ` Junio C Hamano
2018-08-23 18:53 ` Jeff King
2018-08-23 20:59 ` Derrick Stolee
2018-08-24 6:56 ` Jeff King
2018-08-24 7:57 ` Ævar Arnfjörð Bjarmason
2018-08-24 16:45 ` Derrick Stolee
2018-08-25 8:26 ` Jeff King
2018-09-02 18:53 ` Kaartic Sivaraam [this message]
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