Re: [BUG] PPC math-emu multiply problem

[Greg Weeks <greg.weeks@timesys.com>]

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?

Signed-off-by: Greg Weeks <greg.weeks@timesys.com> under TS0087

--- tanith-linux-2.6.6/arch/ppc/math-emu/soft-fp.h.orig    2004-07-30 
10:31:34.000000000 -0400
+++ tanith-linux-2.6.6/arch/ppc/math-emu/soft-fp.h    2004-07-30 
10:31:57.000000000 -0400
@@ -15,7 +15,7 @@
 # define FP_RND_PINF        2
 # define FP_RND_MINF        3
 #ifndef FP_ROUNDMODE
-# define FP_ROUNDMODE        FP_RND_NEAREST
+# define FP_ROUNDMODE        FP_RND_ZERO
 #endif
 #endif