linux-kernel - Re: [PATCH] arch: ia64: kernel: palinfo.c: Optimization of the Code

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Date:	Mon, 2 Jun 2014 19:59:39 +0200
From:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
To:	Clemens Ladisch <clemens@...isch.de>
Cc:	Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghua.yu@...el.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	linux-ia64@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arch: ia64: kernel: palinfo.c: Optimization of the Code

Hi

Thought I would be able to do that. But after testing, I could not
measure any difference.

Thought it would make a noticeable difference, but guess gcc resolve
this in the best way.


Best regards
Rickard Strandqvist


2014-06-02 9:24 GMT+02:00 Clemens Ladisch <clemens@...isch.de>:
> Rickard Strandqvist wrote:
>> From what I know, AND is faster then modulo.
>
> Which is why the compiler does this optimization automatically,
> if it can prove that it is correct.
>
>> -             if (i != 0 && (i%64) == 0)
>> +             if (i != 0 && (i&63) == 0)
>
> Did you prove that i cannot be negative?
>
>
> Regards,
> Clemens
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