[Bug fortran/100855] pow run time gfortran vs ifort

["nadavhalahmi560 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100855

--- Comment #7 from Nadav Halahmi <nadavhalahmi560 at gmail dot com> ---
(In reply to Dominique d'Humieres from comment #6)
> On a MacOS, Corei9, 2.4Ghz, the program runs in ~1s, almost indpendtly of
> the option level.
> 
> This PR remind me an old problem in which the transcendental functions were
> almost slower for REAL(4) then for REAL(8) on some Unix distros (Fedora(?),
> based of "correct rounding").
> 
> What are your timings if you replace
> 
>     real :: sum, n, q
> 
> with
> 
>     real(8) :: sum, n, q
> 
> and
> 
>             sum = sum + (i ** (0.05 + n))
> 
> with
> 
>             sum = sum + (i ** (0.05_8 + n))
> 
> ?

Timings for this change (notice the result was also changed):
gnu:
   150945570.07620683     
Time =  6.303 seconds.
intel:
   150945570.076207     
Time =  2.349 seconds.

So gnu is indeed faster for real(8), but the result was changed.