Re: [PATCH 3/4] diffcore-pickaxe: further refactor count_match()

From: René Scharfe <rene.scharfe@lsrfire.ath.cx>
Date: Feb 28, 2009, 18:15 UTC
Message-ID: <49A97F52.4080405@lsrfire.ath.cx>
In-Reply-To: <7vmyc6foj3.fsf@gitster.siamese.dyndns.org>

Junio C Hamano schrieb:

Show 18 quoted lines

> 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