linux-kernel - Re: [PATCH] Add "is_power_of

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Date:	Thu, 1 Feb 2007 13:39:15 +0100 (CET)
From:	Tim Schmielau <tim@...sik3.uni-rostock.de>
To:	David Howells <dhowells@...hat.com>
cc:	"Robert P. J. Day" <rpjday@...dspring.com>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>,
	Paul Mackerras <paulus@...ba.org>, galak@...nel.crashing.org
Subject: Re: [PATCH] Add "is_power_of_2" checking to log2.h. 

On Thu, 1 Feb 2007, David Howells wrote:
> Robert P. J. Day <rpjday@...dspring.com> wrote:
> 
> > +#define is_power_of_4(x)	is_power_of_2(x) && (ffs(x) & 1))
> 
> If this is such a commonly implemented op, it should probably be implemented
> globally too.
> 
> I also wonder if there's some better way of implementing it than this, but I
> can't think of one offhand.

#define is_power_of_2_or_zero(x) ((x & (x-1))==0)
#define is_power_of_4(x) (is_power_of_2_or_zero(x) \
                          && (x & ((typeof(x))0x55555555)))

?

Tim
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