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

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Message-ID: <20070824155713.GL21720@waste.org>
Date:	Fri, 24 Aug 2007 10:57:13 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Jan Engelhardt <jengelh@...putergmbh.de>
Cc:	Ingo Oeser <ioe-lkml@...eria.de>,
	lode leroy <lode_leroy@...mail.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memchr (trivial) optimization

On Fri, Aug 24, 2007 at 02:54:48PM +0200, Jan Engelhardt wrote:
> 
> On Aug 23 2007 19:13, Matt Mackall wrote:
> >
> >And you can do even better with this:
> >
> >void *memchr(const void *s, int c, size_t n)
> >{
> >       const unsigned char *p = s, *e = s + n;
> >       const unsigned char *e = p + n;
> 
> Uhm, you have two "e"s in there.

Yep, that's what I get for editing in email.

> Or do it glibc-style
> 
> void *memchr(const void *s, unsigned char c, size_t n)
> {
> 	...
> 	for (; p + 3 < e; p += 4) {
> 		if (c == p[0])
> 			return (void *)&p[0];
> 		if (c == p[1])
> 			return (void *)&p[1];
> 		if (c == p[2])
> 			return (void *)&p[2];
> 		if (c == p[3])
> 			return (void *)&p[3];
> 	}
> 	... /* check the rest */
> }

Yes, very funny.

-- 
Mathematics is the supreme nostalgia of our time.
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