https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100855
--- Comment #6 from Dominique d'Humieres <dominiq at lps dot ens.fr> --- 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)) ?