From: Roland Dreier <rdreier@cisco.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, Bart Van Assche <bart.vanassche@gmail.com>,
       David Dillow <dave@thedillows.org>
Subject: Re: [PATCH] log2.h: Macro-ize is_power_of_2() for use in BUILD_BUG_ON
References: <ada3a2jugqu.fsf@roland-alpha.cisco.com>
	<20100106123306.ac85e557.akpm@linux-foundation.org>
Date: Wed, 06 Jan 2010 12:44:05 -0800
In-Reply-To: <20100106123306.ac85e557.akpm@linux-foundation.org> (Andrew
	Morton's message of "Wed, 6 Jan 2010 12:33:06 -0800")
Message-ID: <aday6kbt14a.fsf@roland-alpha.cisco.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 714
Lines: 25


 > 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.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/