Date: Thu, 23 Apr 2009 16:57:23 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: David Daney <ddaney@caviumnetworks.com>
Cc: rpjday@crashcourse.ca, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Introduce a boolean "single_bit_set" function.
Message-Id: <20090423165723.16c9f566.akpm@linux-foundation.org>
In-Reply-To: <49F0C817.8050407@caviumnetworks.com>
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	<49F0C817.8050407@caviumnetworks.com>
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On Thu, 23 Apr 2009 12:57:11 -0700
David Daney <ddaney@caviumnetworks.com> wrote:

> > +static inline __attribute__((const))
> > +bool single_bit_set(unsigned long n)
> > +{
> > +        return (n != 0 && ((n & (n - 1)) == 0));
> > +}
> > +
> > +
> 
> 
> It would be nice to be able to override this per architecture.
> 
> For example a more efficient implementation on CPUs that have a 
> population count instruction (__builtin_popcountl()) might be:
> 
> static inline __attribute__((const))
> bool singe_bit_set(unsigned long n)
> {
> 	return __builtin_popcountl(n) == 1;
> }

Already done, via hweight_long().
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