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

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Message-ID: <Pine.LNX.4.63.0702012225210.23656@gockel.physik3.uni-rostock.de>
Date:	Thu, 1 Feb 2007 22:55:49 +0100 (CET)
From:	Tim Schmielau <tim@...sik3.uni-rostock.de>
To:	Valdis.Kletnieks@...edu
cc:	David Howells <dhowells@...hat.com>,
	"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, Valdis.Kletnieks@...edu wrote:

> On Thu, 01 Feb 2007 13:39:15 +0100, Tim Schmielau said:
> > #define is_power_of_4(x) (is_power_of_2_or_zero(x) \
> >                           && (x & ((typeof(x))0x55555555)))
> 
> Those 5's are going to need more magic if x is a 64-bit typeof?

Yeah, I can't count. Make that

#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))0x5555555555555555ull)))

of course.

Thanks,
Tim
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