linux-kernel - Re: [PATCH] remove abs64()

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Date:	Wed, 13 Apr 2011 11:48:08 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	linux-kernel@...r.kernel.org, behlendorf1@...l.gov
Subject: Re: [PATCH] remove abs64()

On Wed, 13 Apr 2011 16:27:03 +0200
Oleg Nesterov <oleg@...hat.com> wrote:

> On 04/13, Alexey Dobriyan wrote:
> >
> > +#define abs(x)								\
> > +({									\
> > +	typeof(x) _x = (x);						\
> > +									\
> > +	__builtin_choose_expr(						\
> > +		__builtin_types_compatible_p(typeof(_x), signed char),	\
> > +		(unsigned char)({ _x < 0 ? -_x : _x; }),		\
> > +	__builtin_choose_expr(						\
> > +		__builtin_types_compatible_p(typeof(_x), short),	\
> > +		(unsigned short)({ _x < 0 ? -_x : _x; }),		\
> > +	__builtin_choose_expr(						\
> > +		__builtin_types_compatible_p(typeof(_x), int),		\
> > +		(unsigned int)({ _x < 0 ? -_x : _x; }),			\
> > +	__builtin_choose_expr(						\
> > +		__builtin_types_compatible_p(typeof(_x), long),		\
> > +		(unsigned long)({ _x < 0 ? -_x : _x; }),		\
> > +	__builtin_choose_expr(						\
> > +		__builtin_types_compatible_p(typeof(_x), long long),	\
> > +		(unsigned long long)({ _x < 0 ? -_x : _x; }),		\
> > +	_x)))));							\
> > +})
> 
> Personally I agree.
> 
> But, we have some stupid users which do something like abs(u32_value)
> and expecting that abs() should treat this value as "signed".
> 

um, yes, I'd forgotten that one.  That's a show-stopper.
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