NBody (one more question)

[Christophe TROESTLER <debian00@tiscali.be>]

Hi,

I'd like to come back to the nbody mini-benchmark with one more
question (I apologize if I bother some people but I think there are
competent people here who can clarify the situation for me).

When I compile the C code with -O0 (with gcc -o nbody.gcc -Wall
--fast-math nbody.c -lm), I get a time of 1.513s which is comparable
to OCaml (1.607s).  But as soon as I turn on -O options (as with gcc
-o nbody.gcc -Wall -O1 --fast-math nbody.c -lm), the running time
drops down to 0.871s (0.58%).  Can somebody tell me what is the
optimization that has such an effect and whether it could be applied
to OCaml ?  (I am not saying or asking it to be done -- it is not up
to me to decide -- I just want to understand -- and I am not versed
enough in assembly to do it myself unfortunately :( ).

Regards,
ChriS