Re: compile choices changing results

[Neil Ferguson <nferguso at eso dot org>]

Hello -

We need more information:

- what version of which OS are you using?
- what version of GCC?
- what hardware/CPU architecture are you running on?
- is 'cc' actually an alias or symlink for 'gcc', or is it another compiler 
altogether? Even if 'cc' points to a different version of GCC, that can be 
significant.

Semi-educated guess - are you compiling for x86?

Neil.

Julie Stern wrote:
> Hello,
>    I'm running some code which came with a makefile
> containing -O3 -fomit-frame-pointer -funroll-loops
> and the program results were drastically different from
> running with just cc. (yes, right now its an unfair
> comparison, cc vs. gcc -O3 -fomit-frame-pointer -funroll-loops),
> but I didn't expect the results to be different.
>    Can anyone explain what the compiler options actually
> do in this case?  I can read the man pages, but don't
> understand what it exactly does.  Can anyone explain
> why my results would be different  (2nd and 3rd decimal place
> different in numbers that are in scientitific notation and
> are e06 and e37, so the differences are huge)?  Anybody
> have opinions on cc vs. gcc that can help me decide which
> to use?
>
>     Thanks so much for help and advice.
>
> --Julie