>>>>> "Jeremy" == Jeremy Sanders <j...@ast.cam.ac.uk> writes:
Jeremy> You can see the very large speed differences by telling gfortran Jeremy> to always use double precision numbers. Jeremy> This can be replicated with this simple program: Jeremy> Compiled with gfortran -O2: Jeremy> real 0m29.921s Jeremy> user 0m29.912s Jeremy> sys 0m0.000s Jeremy> Compiled with gfortran -O2 -fdefault-real-8: Jeremy> real 0m4.306s Jeremy> user 0m4.304s Jeremy> sys 0m0.000s Jeremy> This is with a newly built gcc 4.4.1 on Fedora 10 (glibc 2.9), x86-64. I tried it on my 1Ghz PIII laptop running Gentoo with gcc 4.1.1 and glibc 2.10.1. I added -march=pentium3 to the gcc cmd line; that probably made little difference. (glibc was also compiled with -march=pentium3 -O2). I got nearly identical user times for the two compiles; user time was always within 0.03 of 23.40 over multiple runs. Incidently, while the real-8 compile output 271828665.96115601, the real4 compile output 67108976. This does, then, seem to be an x86-64 issue. -JimC -- James Cloos <cl...@jhcloos.com> OpenPGP: 1024D/ED7DAEA6
