Re: [BUG] PPC math-emu multiply problem

[Tom Rini <trini@kernel.crashing.org>]

On Fri, Jul 30, 2004 at 11:23:22AM -0400, Greg Weeks wrote:

> Greg Weeks wrote:
> 
> >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. :-)
> >>
> >>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.
> >
> >
> >OK, this patch fixes my multiply problem with the LSB test. I still 
> >need to test to make sure I didn't break anything else, but it appears 
> >the rounding is only used when converting back to IEEE format. Is 
> >there some reason this is something really dumb to do?
> >
> When I actually built a kernel rather than just my test code the 
> FP_ROUNDMODE is picked up from the linux/math-emu/soft-fp.h. I don't 
> want to change the common definition unless I'm sure this is the correct 
> solution.
> 
> Signed-off-by: Greg Weeks <greg.weeks@timesys.com> under TS0087

Has anyone had a problem with this?  If not, I'll go and pass it
along...

-- 
Tom Rini
http://gate.crashing.org/~trini/