Re: [PATCH] Introduce a boolean "single_bit_set" function.

Andrew Morton
2009-04-23T23:59:52Z

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().