Date: Wed, 06 Jan 2010 16:15:04 -0500
From: David Dillow <dave@thedillows.org>
Subject: Re: [PATCH] log2.h: Macro-ize is_power_of_2() for use in BUILD_BUG_ON
In-reply-to: <aday6kbt14a.fsf@roland-alpha.cisco.com>
To: Roland Dreier <rdreier@cisco.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       Bart Van Assche <bart.vanassche@gmail.com>
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On Wed, 2010-01-06 at 12:44 -0800, Roland Dreier wrote:
> > Perhaps we can avoid worrying about that via
> 
>  > #define BUILD_BUG_ON_NOT_POWER_OF_2(n)	\
>  > 	BUILD_BUG_ON((n != 0 && ((n & (n - 1)) == 0)))
> 
> Having something so specific to this particular case makes me feel like
> maybe it's just not worth it.  At least in the case I'm looking at, we
> could just have:
> 
> /*
>  * The code relies on FOO being a power of 2.  If you break this,
>  * you're dumb.
>  */
> #define FOO_SHIFT	6
> #define FOO		(1 << FOO_SHIFT)
> 
> Your thoughts?

I'm fine with that, but now I'll probably be the dumb one to break it
some day in the future.
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