Re: [BUG] PPC math-emu multiply problem

[La Monte H.P. Yarroll]

Dan Malek wrote:

> On Jul 29, 2004, at 10:06 AM, Kumar Gala wrote:
>
> > On Jul 29, 2004, at 8:14 AM, Greg Weeks wrote:
> >
> > > I'm seeing what appears to be a bug in the ppc kernel trap math
> > > emulator. An extreme case for multiplies isn't working the way gcc
> > > soft-float or hardware floating point is.
>
> I'm not surprised.  I lifted this code from Sparc, glibc, and adapted
> it as best I could for PPC years ago for the 8xx.  I was happy when
> it appeared to work for the general cases. :-)


Thanks for doing the initial work!

> Due to its overhead, I never expected it to be _the_ solution for
> processors that don't have floating point hardware.  Recompiling
> the libraries with soft-float and using that option when compiling
> is the way to go.


Indeed, when using this board for real we generally recommend
exactly the same thing.

> Remember, don't mix soft-float compilation with libraries compiled
> with HW floating point, and trap emulations.  They are not
> compatible and will return erroneous results.


Unfortunately, LSB does not provide a set of test binaries which
use the softfloat ABI, so in order to get an LSB-comformant distribution
on this CPU, we need to use floating point emulation.  Interestingly,
this is the only LSB floating point test which fails.

--
 Anyone who quotes me in their sig is an idiot. -- Rusty Russell's sig


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