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Re: [Qemu-devel] [Qemu-ppc] PowerPC Decimal Floating Point
From: |
Tom Musta |
Subject: |
Re: [Qemu-devel] [Qemu-ppc] PowerPC Decimal Floating Point |
Date: |
Fri, 14 Feb 2014 16:22:07 -0600 |
User-agent: |
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 |
On 2/14/2014 3:22 PM, Richard Henderson wrote:
> On 02/11/2014 11:38 PM, Alexander Graf wrote:
>>>> My proposal is to incorporate the libdecnumber component of libdfp
>>>> (http://www.eglibc.org/cgi-bin/viewvc.cgi/libdfp/trunk/) in a manner
>>>> analogous to how
>>>> softfloat is used for binary floating point. So, for example, the helper
>>>> for the dadd
>>>> instruction would look something like the following:
>>>>
>>>> - map FPSCR state to a decContext.
>>>> - convert the contents of the source FPRs to decNumbers
>>>> (decimal64ToNumber).
>>>> - call decNumberAdd
>>>> - convert the resultant decNumber to DPD (decimal64FromNumber)
>>>> - update FPSCR per the decContext.status and result.
>>>>
>>>> Comments?
>> I think that approach makes a lot of sense, but let's ask Richard and Peter
>> as well.
>
> Reasonable, as far as the implementation details go.
>
> I am a teeny bit concerned which version of libdecnumber is considered most
> "upstream". Ordinarily I'd point to the copy in gcc, but that is of course
> GPLv3 + GCC runtime exception. I see the version from eglibc you quote above
> is LGPLv2.1. I also see that the last change is 18 months old. On the other
> hand, there is only one non-autoconf change in the gcc sources in the same
> period.
>
> The original import is from IBM sources. Is there somewhere "upstream" at IBM
> that we ought to be importing from instead?
>
Richard:
I will check with folks inside of IBM here that I have the latest and greatest.
FWIW ... I have about 20 instructions prototyped and running in a test harness
(not QEMU) and comparing results against actual P7/P8 hardware. So far, this
looks pretty good. I haven't yet worked through any details of importing the
library
into QEMU.