Re: [Qemu-devel] [PATCH] target-i386: implement FPREM and FPREM1 using softfloat only

[Stefan Weil]

Am 28.06.2012 01:00, schrieb Catalin Patulea:
> Hey guys,
>
> I've been hacking up the FPREM and FPREM1 i386 instructions (without KVM) to be 
> implemented using SoftFloat only. This was motivated by some correctness issues
> that we noticed with the current implementation which follows the AMD datasheet.I believe 
> the datasheet explains the operation as if intermediate results had "infinite" 
> precision, but in this case intermediate rounding causes a loss of precision at the final 
> output.
>
> My reference was TestFloat [1], specifically the floatx80_rem suite, which 
> tests the FPREM instruction quite thoroughly (FPREM1 is technically untested 
> but very similar). The current code fails about half the suite; with the patch, 
> all tests pass.
>
> There are still lots of dark corners - the code originates from Bochs' copy of 
> SoftFloat and I tried to port the Bochs exception handling logic as much as I 
> could. Many details still elude me though (see comments in the code). TestFloat 
> does test some of the exception logic but not as thoroughly as I would have 
> liked. If anyone can offer some guidance here, I am happy to fix up the patch.
>
> That's about it.. let me know what you think.
>
> Catalin
>
> [1] http://www.jhauser.us/arithmetic/TestFloat.html

Hi Catalin,

could you please check your patch using the latest scripts/checkpatch.pl?
There are several style issues which should be fixed. I suggest to fix them
even in code which was copied from Bochs.

Thanks,
Stefan W.