linux-kernel - Re: [PATCH] Introduce a boolean "single_bit

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Message-Id: <20090423165723.16c9f566.akpm@linux-foundation.org>
Date:	Thu, 23 Apr 2009 16:57:23 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	rpjday@...shcourse.ca, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Introduce a boolean "single_bit_set" function.

On Thu, 23 Apr 2009 12:57:11 -0700
David Daney <ddaney@...iumnetworks.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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