On Sat, Jan 14, 2012 at 12:03 AM, R. Alan Monroe <amon...@columbus.rr.com>wrote:
> > FORTRAN is still used in some circles because it's
> > still very fast for number crunching.
>
> A bit off topic, but I've seen this bit of folk wisdom repeated online
> for a long time and have always been skeptical. How does a C command
> that gets compiled to a CPU's MUL instruction differ in any way from a
> Fortran command that also gets compiled to that same CPU's same MUL
> instruction? Honest question.
>
> Alan
>
>
Theoretically, the compiler has more information about the fortran code
than the C code, so can make more optimizations. So in C, the compiler can
not be sure about pointer aliasing, and such things... so it has to be a
little safer about the optimizations. In practice, you can provide hints
to the C compiler to get pretty much the same performance. For a modern C
compiler like gcc, you have things like 'pure', 'restrict', openmp hints,
function level optimization optimizations, and various other vectorisation
hints that let you do lots of optimizations that fortran can do.
See this for more info:
http://stackoverflow.com/questions/146159/is-fortran-faster-than-c
Also see here that fortran is still speedy:
http://shootout.alioth.debian.org/u64q/which-programming-languages-are-fastest.php
cheers,
