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Re: [PATCH] backend: compare word-at-a-time in bcTruelen

From: tomas(at)tuxteam(dot)de
To: Dimitri Fontaine <dfontaine(at)hi-media(dot)com>
Cc: Jeremy Kerr <jk(at)ozlabs(dot)org>, Stephen Frost <sfrost(at)snowman(dot)net>,Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>,Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>,Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org,Alvaro Herrera <alvherre(at)commandprompt(dot)com>,Gurjeet Singh <singh(dot)gurjeet(at)gmail(dot)com>
Subject: Re: [PATCH] backend: compare word-at-a-time in bcTruelen
Date: 2009-06-26 15:29:06
Message-ID: 20090626152906.GA948@tomas (view raw or flat)
Thread:
Lists: pgsql-hackers
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On Fri, Jun 26, 2009 at 05:03:11PM +0200, Dimitri Fontaine wrote:
> Le 26 juin 09 à 14:47, Jeremy Kerr a écrit :
>> For the new function to be faster, we need to know that there are more
>> than 6 (on average, depending on alignment) trailing spaces.
>
> It's becoming somewhat tricky, but maybe the test to do for the 
> optimisation to get used is n >= threshold && str[n-6] == 0x20, àla 
> Boyer/Moore?

That's cute. What about comparing the last aligned word which completely
fits in the buffer? Something along the lines of (assuming four-byte
words)

   * (int*) (4 * ((int) &buf[0]) / 4)

(now that's an ugly one, but you know what I mean?)

Regards
- -- tomás
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