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Re: [PATCH] PR11706, optimize std::pow(T, int)
- From: Richard Guenther <rguenth at tat dot physik dot uni-tuebingen dot de>
- To: Paolo Carlini <pcarlini at suse dot de>
- Cc: libstdc++ at gcc dot gnu dot org,Gabriel Dos Reis <gdr at integrable-solutions dot net>
- Date: Wed, 12 Jan 2005 16:43:05 +0100 (CET)
- Subject: Re: [PATCH] PR11706, optimize std::pow(T, int)
On Wed, 12 Jan 2005, Richard Guenther wrote:
> On Wed, 12 Jan 2005, Paolo Carlini wrote:
>
> > Richard Guenther wrote:
> >
> > Maybe Gaby wants to add something here, but I seem to remember that
> > we really dislike this kind of approach, calling back pow from __pow_helper
> > via a cast, thus giving away the info that the exponent is integer.
>
> We can dispatch directly to __builtin_pow[lf](), too, and the frontends
Like with
inline _Tp
__pow_helper(_Tp __x, int __n)
{
#if __FAST_MATH__
if (__builtin_constant_p(__n))
#else
if (__builtin_constant_p(__n) && __n >= -2 && __n <= -2)
#endif
{
if (__builtin_types_compatible_p(_Tp, float))
return __builtin_powf(__x, __n);
else if (__builtin_types_compatible_p(_Tp, double))
return __builtin_pow(__x, __n);
else if (__builtin_types_compatible_p(_Tp, long double))
return __builtin_powl(__x, __n);
}
return __n < 0
? _Tp(1)/__cmath_power(__x, -__n)
: __cmath_power(__x, __n);
(untested, maybe only __typeof(__x) works), which would even work if
someone cared to call std::__pow_helper with _Tp other than float, double
or long double.
Richard.
--
Richard Guenther <richard dot guenther at uni-tuebingen dot de>
WWW: http://www.tat.physik.uni-tuebingen.de/~rguenth/