linux-kernel - Re: [PATCH] log2.h: Macro-ize is_power_of_2() for use in BUILD_BUG

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Message-ID: <aday6kbt14a.fsf@roland-alpha.cisco.com>
Date:	Wed, 06 Jan 2010 12:44:05 -0800
From:	Roland Dreier <rdreier@...co.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Bart Van Assche <bart.vanassche@...il.com>,
	David Dillow <dave@...dillows.org>
Subject: Re: [PATCH] log2.h: Macro-ize is_power_of_2() for use in BUILD_BUG_ON


 > 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?

 - R.
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