Re: [Qemu-devel] Floating point unit bugs

[G 3]

On May 8, 2017, at 5:54 PM, Aurelien Jarno wrote:

> On 2017-05-07 17:48, G 3 wrote:
> > I made a diagnostic program for the floating point unit. It will test
> > various PowerPC floating point instructions for compatibility with  
> > the
> > PowerPC G3 processor. It was tested on a PowerPC G3 and G5 system.  
> > The
> > results of the program in qemu-system-ppc were pretty bad. About  
> > every
> > instruction tested is not implemented correctly.
>
> I don't say that qemu-system-ppc is bug free, but this looks  
> suspicious
> that about every instruction is buggy.

I really hope you don't think I'm blaming anyone. I'm only reporting  
the results of the test.

> Have you tried to run your
> program on a real G3 or G5 system?

Yes. I made sure it ran on a real G3 and G5 system without problem  
before testing it on QEMU. I suspect the Motorola designed G4  
processor will not be compatible. I don't have a working G4 system to  
verify this unfortunately.

> [ snip ]
>
> > Here is the full test results after running this program in qemu- 
> > system-ppc
> > with a Mac OS 10.4 guest:
> >
> >
> >
> >
> > fadd test failed
> > expected answer: 0x3ff3333333333334
> >   actual answer: 0x8200400000000024
> > expected fpscr: 0x82064000
> >   actual fpscr: 0x82004000
>
> This looks highly suspicious that the actual answer match the expected
> answer.

You can use this web page to find the decimal value: http:// 
www6.uniovi.es/~antonio/uned/ieee754/IEEE-754hex64.html

0x3ff3333333333334 = 1.2000000000000002
0x8200400000000024 = -4.8529708162167760e-299

The expected answer and actual answer are very far from each other.