This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: Possible Enhancement - Forcing double prec. on Intel FPUs
- To: loesche at math dot tu-dresden dot de
- Subject: Re: Possible Enhancement - Forcing double prec. on Intel FPUs
- From: Craig Burley <burley at gnu dot org>
- Date: Mon, 15 Jun 1998 13:33:07 -0400 (EDT)
- CC: egcs at cygnus dot com
(Thanks for looking into this...it's not easily grappled with!)
>The easiest way to make the Intel FPU behave as it is expected
>to, is to compile the code with -ffloat-store.
>That option ensures that ALL intermediate results are stored in their
>appropriate memory locations and thereby getting rounded properly.
>Using -ffloat-store in turn causes, by stalling the FPU pipeline,
>a large performance decrease.
I believe this is not quite correct. -ffloat-store applies only
to variables, i.e. any *explicit* stores, as seen in the source
code being compiled. It does not apply to computing intermediate
results.
Therefore, I believe it will prevent use of extended precision
in code like
a = b + c;
d = a * e;
but not in code like:
d = (b + c) * e;
Just FYI. See the egcs/gcc docs for more info.
tq vm, (burley)