Timings of Column Radiation Model CRM in original Fortran and hand-translated C versions.

To find the best optimization, we stepped through the -Ox options available. We did not try more advanced combinations.
Timing value is the total time for 10 calls to "radctl". We took the average over 4 runs of the model.
Percentage is ((C time - Fortran time)/Fortran time)*100.
"Matching C" means C version compiled with same optimization flags as fastest Fortran version.
"Fastest C" means a slightly faster optimization setting for C was found. If no "Fastest C" bar appears, then matching C was fastest version.
"Flag" in the table is the fastest flag for each compiler.
Flags tried:

pgf90/pgcc:      -O0, -O1, -O2, -fast, -fastsse
IA-32 ifort/icc: -O0, -O2, -O3, -fast
xlf90/xlc:       -O0, -O2, -O3, -O4, -O5
IA-64 ifort/icc: -O0, -O1, -O2, -O3, -fast
HP/Compaq f90/cc:   -O0, -O1, -O2, -O3, -O4, -O5