Re: [Qemu-devel] [Bug 645662] x87 fpu emulation not accurate enough

[KONRAD Frederic <frederic.konrad@adacore.com>]

I would write some more basic tests. eg: at instruction level and
compare KVM vs TCG mode to find out which trigo instructions are
differents (probably not only one).

BTW I'm not floating point expert at all :).

Fred

On 11/29/2017 10:59 AM, william lin wrote:
> Hi,
> 
> The goal of the project is to fix the bug. Sorry I should have been more
> clear.
> 
> This bug has been around for 7+ years now. Qemu switched to softfloat and
> it did not fix this. I think its most likely caused by Qemu's internal
> representation not being accurate enough or accuracy lost during
> conversion. However this is basically what is given to us in the bug
> report, and I have not been able to make much progress past this point, so
> we are asking for help.
> 
> Will
> 
> 
> 
> On Nov 29, 2017 3:39 AM, "KONRAD Frederic" <frederic.konrad@adacore.com>
> wrote:
> 
> Hi,
> 
> I have the same problem here with some of our math testsuites.
> It's about some precision issue with trigonometric tests.
> 
> I didn't had time to figure out what happen neither what is
> really going wrong. eg: trigonometric function or?
> 
> A quick workaround is to use KVM when possible.
> 
> Fred
> 
> 
> On 11/29/2017 09:34 AM, william lin wrote:
> 
>> Hello,
>>
>> I have been looking into this bug
>> <https://bugs.launchpad.net/qemu/+bug/645662> for a school project, and
>>
>> after reproducing the bug and tracing through the code, I have run into a
>> wall trying to figure out the best way to approach this. If there is anyone
>> who is familiar with qemu's fpu and is willing, any tips or suggestions
>> will be fantastic.
>>
>> Thanks,
>>
>> Will & Wes
>>
>>