On Wed, 23 Sep 2015 16:44:29 +0300 Alexey Dobriyan <adobri...@gmail.com> wrote:
> On Fri, Sep 18, 2015 at 12:36 AM, <a...@linux-foundation.org> wrote:
>
>
> > -#define abs(x) ({ \
> > - long ret; \
> > - if (sizeof(x) == sizeof(long)) { \
> > - long __x = (x); \
> > - ret = (__x < 0) ? -__x : __x; \
> > - } else { \
> > - int __x = (x); \
> > - ret = (__x < 0) ? -__x : __x; \
> > - } \
> > - ret; \
> > - })
> > +#define abs(x) __builtin_choose_expr(sizeof(x) == sizeof(s64), ({ \
> > + s64 __x = (x); \
> > + (__x < 0) ? -__x : __x; \
> > + }), ({ \
> > + long ret; \
> > + if (sizeof(x) == sizeof(long)) { \
> > + long __x = (x); \
> > + ret = (__x < 0) ? -__x : __x; \
> > + } else { \
> > + int __x = (x); \
> > + ret = (__x < 0) ? -__x : __x; \
> > + } \
> > + ret; \
> > + }))
>
> 1. "char" should be banned, because it's signedness is not well defined.
> 2. there is unnecessary expansion to long.
>
> I've sent kabs() before which didn't go in because it didn't work for
> INT_MAX et al
> (don't worry, this abs() doens't as well) but it is nicer that this
> version in other aspects
> (hopefully).
>
> [PATCH v2] Add kabs()
> http://marc.info/?l=linux-kernel&m=133518745522740&w=4
Looks nice. Care to send along a patch which updates the abs() in
linux-next?
> As for INT_MIN, it pretty impossible to make compiler to not generate a branch
> despite generating correct result without a branch.
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