-msoft-float

David Boddie davidb at mcs.st-and.ac.uk
Tue Jun 5 09:00:45 PDT 2001


On 5 Jun 2001, Nick Burrett wrote:

> David Boddie <davidb at mcs.st-and.ac.uk> writes:
> 
> > On 5 Jun 2001, Nick Burrett wrote:
> > 
> > > It is possible to do this, but it has never been fully tested.  However,
> > > I don't see the advantage of doing this, since code size will be bigger
> > > and the software floating point libraries are much slower than the FPE.
> > 
> > Can the latest version of gcc for RISC OS manage this?
> 
> It used to, but I turned it off. I decided it was pointless since UnixLib,
> the SharedClibrary and various RISC OS modules use FP instructions.

OK, so if an application spends a lot of time outside these then there
may be a gain.

> > Is there a pre-compiled libgcc available from anywhere or will I have to
> > build my own?
> 
> One needs to fix a few files in GCC and it's Makefiles to get this working
> again.  It'd probably take an hour.

Can I do this, or does it require a certain level of experience with gcc?

> > If I can get this up and running then I can compare soft-float performance
> > against the FPE for my application and attempt to optimize it as required.
> 
> The last time I benchmarked it (something like 4 or 5 years ago) soft-FP
> performance was approx. 3-3.5 times slower than the FPE. You would need to
> write a completely new implementation of the FP-library in order to gain
> any significant speed advantage.

That may be more committment than I was hoping for. How big is the
library?

> I can enable support in the CVS tree, if you like. I haven't tested it for
> so long, I'm not sure it will actually work though.

I downloaded the tarball of gccsdk yesterday. Is it possible for me to
carry out the changes here? I don't mind getting hold of a CVS snapshot,
but I'm trying to minimise the amount of unnecessary work anyone else has
to do.

-- 
David Boddie
Solar MHD Theory Group, St Andrews
http://www-solar.mcs.st-and.ac.uk/~davidb/index2.html




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