linux-kernel - Re: [RFC][PATCH] A generic boolean (version 6)

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Message-Id: <1154122271.2451.1.camel@entropy>
Date:	Fri, 28 Jul 2006 14:31:11 -0700
From:	Nicholas Miell <nmiell@...cast.net>
To:	Lars Noschinski <cebewee@....de>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, ricknu-0@...dent.ltu.se,
	Arnd Bergmann <arnd.bergmann@...ibm.com>,
	linux-kernel@...r.kernel.org, Andrew Morton <akpm@...l.org>,
	Jeff Garzik <jeff@...zik.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Vadim Lobanov <vlobanov@...akeasy.net>,
	Jan Engelhardt <jengelh@...ux01.gwdg.de>
Subject: Re: [RFC][PATCH] A generic boolean (version 6)

On Fri, 2006-07-28 at 22:24 +0200, Lars Noschinski wrote:
> * Alan Cox <alan@...rguk.ukuu.org.uk> [2006-07-28 22:14]:
> >Ar Iau, 2006-07-27 am 13:13 -0700, ysgrifennodd Nicholas Miell:
> >> The compiler knows that "b = !!b;" is a no-op.
> >
> >b = !!b isn't a no-op.
> 
> For _Bool it should be:
> 
> >Try printf("%d", !!4);
> 
> printf("%d, %d", (_Bool)4, !!(_Bool)4);
> 
> prints "1, 1". From ISO/IEC 9899:1999:
> 
> When any scalar value is converted to _Bool, the result is 0 if the
> value compares equal to 0; otherwise, the result is 1.
> 

We're not talking about scalar values converted to _Bool, we're talking
about the kernel getting a supposed _Bool from userspace which doesn't
actually contain 0 or 1. (i.e. as far as the kernel and/or gcc is
concerned, the scalar conversion has already taken place)

-- 
Nicholas Miell <nmiell@...cast.net>

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