gnu fortran compiler on 64 bit machines

[Tim Prince]

zuheyr wrote:
> Hello,
> 
> I am using GNU fortran on 32/64 bit Fedora Core 6 Linux machines using
> Pentium IV and AMD
> Athlon processors. I use fortran 77 and fortran 90.
> 
..
> However, most notably there are also big differences between gnu fortran
> compiled codes on 32 and 64 bit machines. 
> The 64 bit code does not at all run on what 32 bit gnu compiled code runs. 
> 
> In the compilations I used the simplest -O flag but there are differences
> even with -g flag.

Besides checking for uninitialized variables, range errors, etc.
consider using similar options if you want the 32 and 64 bit results to
be similar, such as -march=pentium4 -mfpmath=sse  Remember that the 32-
and 64-bit defaults are different.