Re: [PATCH] Optimize is_power_of_2().

["David M. Lloyd" <dmlloyd@flurg.com>]

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