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

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Message-Id: <1154051792.2535.9.camel@entropy>
Date:	Thu, 27 Jul 2006 18:56:32 -0700
From:	Nicholas Miell <nmiell@...cast.net>
To:	ricknu-0@...dent.ltu.se
Cc:	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>,
	Shorty Porty <getshorty_@...mail.com>,
	Peter Williams <pwil3058@...pond.net.au>,
	Michael Buesch <mb@...sch.de>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Stefan Richter <stefanr@...6.in-berlin.de>, larsbj@...lik.net,
	Paul Jackson <pj@....com>
Subject: Re: [RFC][PATCH] A generic boolean (version 6)

On Fri, 2006-07-28 at 03:29 +0200, ricknu-0@...dent.ltu.se wrote:
> Citerar Nicholas Miell <nmiell@...cast.net>:
> 
> > On Thu, 2006-07-27 at 21:55 +0200, ricknu-0@...dent.ltu.se wrote:
> > > Citerar Nicholas Miell <nmiell@...cast.net>:
> > > 
> > > > If _Bool does end up in the user-kernel ABI, be advised that validating
> > > > them will be tricky ("b == true || b == false" or "!!b" won't work), and
> > > 
> > > Why would !!b not work?
> > > I don't think it should end up in the ABI (at least, not yet). Just asking
> > > because I'm curious. :)
> > > 
> > 
> > The compiler knows that "b = !!b;" is a no-op.
> 
> In what gcc version? Using 4.0.2 myself and got that if b equals 12 (using a
> pointer to add the value to the boolean) then !!b equals 1.

gcc version 4.1.1 20060525 (Red Hat 4.1.1-1) compiles:

#include <stdbool.h>
bool validBool(bool b) { return (b == true || b == false); }
bool normalizeBool(bool b) { return !!b; }

to:

validBool:
        movl    $1, %eax
        ret

normalizeBool:
        movzbl  %dil, %eax
        ret

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

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