Date: Wed, 6 Jan 2010 15:09:28 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Roland Dreier <rdreier@cisco.com>
Cc: linux-kernel@vger.kernel.org, Bart Van Assche <bart.vanassche@gmail.com>,
       David Dillow <dave@thedillows.org>
Subject: Re: [PATCH] Add BUILD_BUG_ON_NOT_POWER_OF_2()
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On Wed, 06 Jan 2010 15:02:40 -0800
Roland Dreier <rdreier@cisco.com> wrote:

> Fair enough... here's your suggestion of BUILD_BUG_ON_NOT_POWER_OF_2().
> <linux/kernel.h> does seem to be going the way of a gazillion very
> specific helper macros, so I guess this fits right in.
> 
>  include/linux/kernel.h |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 3fc9f5a..a1b6652 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -734,6 +734,10 @@ struct sysinfo {
>  /* Force a compilation error if condition is constant and true */
>  #define MAYBE_BUILD_BUG_ON(cond) ((void)sizeof(char[1 - 2 * !!(cond)]))
>  
> +/* Force a compilation error if expression is not a power of 2 */
> +#define BUILD_BUG_ON_NOT_POWER_OF_2(n)			\
> +	BUILD_BUG_ON(((n) != 0 && (((n) & ((n) - 1)) == 0)))
> +
>  /* Force a compilation error if condition is true, but also produce a
>     result (of value 0 and type size_t), so the expression can be used
>     e.g. in a structure initializer (or where-ever else comma expressions

ok..  I'll give it a week or so for better ideas to turn up then I'll
send this Linuswards so that ongoing work can use it.

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