From: "David M. Lloyd" <dmlloyd@flurg.com>
To: "David M. Lloyd" <dmlloyd@flurg.com>
Cc: Jan Engelhardt <jengelh@computergmbh.de>,
Vegard Nossum <vegard.nossum@gmail.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"Robert P. J. Day" <rpjday@mindspring.com>
Subject: Re: [PATCH] Optimize is_power_of_2().
Date: Fri, 15 Jun 2007 14:57:23 -0500 [thread overview]
Message-ID: <20070615145723.7aa7aaa0@localhost> (raw)
In-Reply-To: <20070615145420.3a824477@localhost>
On Fri, 15 Jun 2007 14:54:20 -0500
"David M. Lloyd" <dmlloyd@flurg.com> wrote:
> On Fri, 15 Jun 2007 21:47:50 +0200 (CEST)
> Jan Engelhardt <jengelh@computergmbh.de> wrote:
>
> > On Jun 15 2007 18:56, Vegard Nossum wrote:
> > > bool is_power_of_2(unsigned long n)
> > > {
> > >- return (n != 0 && ((n & (n - 1)) == 0));
> > >+ return n * !(n & (n - 1));
> > > }
> >
> > There is a third way which uses neither * nor &&, but []:
>
> I assume using something GCC-specific is right out?
>
> bool is_power_of_to(unsigned long n)
> {
> return __builtin_ffsl(n) == 1;
Pretend I typed this instead:
bool is_power_of_2(unsigned long n)
{
return __builtin_popcountl(n) == 1;
}
All I can say is, it's really hot here :P
- DML
prev parent reply other threads:[~2007-06-15 19:57 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-06-15 16:56 [PATCH] Optimize is_power_of_2() Vegard Nossum
2007-06-15 18:21 ` H. Peter Anvin
2007-06-15 18:28 ` Robert P. J. Day
2007-06-15 20:26 ` H. Peter Anvin
2007-06-15 19:47 ` Jan Engelhardt
2007-06-15 19:54 ` David M. Lloyd
2007-06-15 19:57 ` David M. Lloyd [this message]
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