linux-kernel - Re: [PATCH] memchr (trivial) optimization

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Date:	Thu, 23 Aug 2007 02:13:20 +0200
From:	Ingo Oeser <ioe-lkml@...eria.de>
To:	"lode leroy" <lode_leroy@...mail.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memchr (trivial) optimization

On Wednesday 22 August 2007, lode leroy wrote:
> While profiling something completely unrelated, I noticed
> that on the workloads I used memchr for, I saw a 30%-40% improvement
> in performance, with the following trivial changes...
> (basically, it saves 3 operations for each call)

Yes, but then you could be a bit more explicit to the compiler
on what you are doing here:
 
void *memchr(const void *s, int c, size_t n)
{
	const unsigned char *p = s;

	for (; n != 0; n--, p++) {
               if ((unsigned char)c == *p) {
                       return (void *)p;
	}
	return NULL;
}

Now the compiler should see the loop more clearly.


Best Regards

Ingo Oeser
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