linux-kernel - Re: Conversion to generic boolean

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Date:	Tue, 29 Aug 2006 23:26:10 +1000
From:	Peter Williams <pwil3058@...pond.net.au>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
CC:	Christoph Hellwig <hch@...radead.org>,
	Nicholas Miell <nmiell@...cast.net>,
	Richard Knutsson <ricknu-0@...dent.ltu.se>,
	James.Bottomley@...elEye.com, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Conversion to generic boolean

Jan Engelhardt wrote:
>>>> That is error-prone. Not "==FALSE" but what happens if x is (for some 
>>>> reason) not 1 and then "if (x==TRUE)".
>>> If you're using _Bool, that isn't possible. (Except at the boundaries
>>> where you have to validate untrusted data -- and the compiler makes that
>>> more difficult, because it "knows" that a _Bool can only be 0 or 1 and
>>> therefore your check to see if it's not 0 or 1 can "safely" be
>>> eliminated.)
>> gcc lets you happily assign any integer value to bool/_Bool, so unless
> 
> But, it coerces the rvalue into 0 or 1, which may be a gain.

Actually, it's not coercion.  It's the result of evaluating the value as 
a boolean expression.

> 
>> you write sparse support for actually checking things there's not the
>> slightest advantage in value range checking.
> 
> 
> Jan Engelhardt


-- 
Peter Williams                                   pwil3058@...pond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce
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