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

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Date:	Wed, 13 Apr 2011 22:20:31 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	linux-kernel@...r.kernel.org, behlendorf1@...l.gov
Subject: Re: [PATCH] remove abs64()

On 04/13, Andrew Morton wrote:
>
> 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.

May be we can demand to fix them?

I agree with Alexey, it is a bit ugly to have abs() and abs64(), and abs()
itself doesn't look very nice.

What if we simply add

	BUILD_BUG_ON( (typeof(_x)-1) > 0 );

into abs()?

After that it would be trivial to find the offenders and fix them,

	- abs(unsigned_int)
	+ abs((int) unsigned_int)

Oleg.

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