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List: git
Subject: Re: [PATCH 3/4] diffcore-pickaxe: further refactor count_match()
From: René Scharfe <rene.scharfe () lsrfire ! ath ! cx>
Date: 2009-02-28 18:15:46
Message-ID: 49A97F52.4080405 () lsrfire ! ath ! cx
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Junio C Hamano schrieb:
> René Scharfe <rene.scharfe@lsrfire.ath.cx> writes:
>
>> I get this (Ubuntu 8.10 x64, Fedora 10 x64 using the same Linux repo,
>> Windows Vista x64 using a different Linux repo with the same HEAD on
>> NTFS and msysgit, numbers are the elapsed time in seconds, best of five
>> runs):
>>
>> Ubuntu Fedora Windows
>> v1.6.2-rc2 8.14 8.16 9.236
>> v1.6.2-rc2+[1-4] 2.43 2.45 2.995
>> v1.6.2-rc2+[1-4]+memmem 1.31 1.25 2.917
>> v1.6.2-rc2+[1-3]+memmem 1.51 1.16 8.455
>>
>> Ubuntu has glibc 2.8, while Fedora 10 has glibc 2.9, with a new and more
>> efficient memmem() implementation. On Windows, we use our own naive
>> memmem() implementation.
>
> Yeah, what does glibc use these days? Some variant of Boyer-Moore?
No, the algorithm is called Two Way, which, unlike Boyer-Moore, only
needs constant space. The implementation seems to originate from this bug:
http://sourceware.org/bugzilla/show_bug.cgi?id=5514
And the algorithm is documented here:
http://www-igm.univ-mlv.fr/~lecroq/string/node26.html
René
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