linux-kernel - Re: [PATCH v5 6/9] bug.h: Prevent double evaulation of in BUILD_BUG

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Date:	Sat, 17 Nov 2012 15:38:41 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Daniel Santos <daniel.santos@...ox.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christopher Li <sparse@...isli.org>,
	David Daney <david.daney@...ium.com>,
	David Howells <dhowells@...hat.com>,
	Joe Perches <joe@...ches.com>,
	Josh Triplett <josh@...htriplett.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-sparse@...r.kernel.org,
	Michel Lespinasse <walken@...gle.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Pavel Pisa <pisa@....felk.cvut.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v5 6/9] bug.h: Prevent double evaulation of in
 BUILD_BUG_ON

On Thu, Nov 15, 2012 at 01:11:15PM -0600, Daniel Santos wrote:
> Ah yes. I did notice that at one point, but I think it slipped
> my mind. Also, the kernel has introduced me to the usage of the
> !! construct, of which I'm well versed in its affects in various
> situations and how gcc's optimizer ends up treating its usage, so
> probably another reason I didn't change it immediately. But it's
> basically shorthand for the expression (condition ? 1 : 0), correct?

I don't think so: "!!" is simply a double negation which turns the
whatever wild construct you have into either 0 or 1, depending on what
it evaluates to.

But I don't know what the standard says so you'll have to check :-)

Thanks.

-- 
Regards/Gruss,
Boris.
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