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Re: [Qemu-devel] [PATCH 1/5] softfloat: fix float{32, 64}_muladd options
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] [PATCH 1/5] softfloat: fix float{32, 64}_muladd options |
Date: |
Sun, 9 Sep 2012 12:04:45 +0200 |
User-agent: |
Mutt/1.5.20 (2009-06-14) |
On Sun, Sep 09, 2012 at 10:47:52AM +0100, Peter Maydell wrote:
> On 9 September 2012 10:24, Aurelien Jarno <address@hidden> wrote:
> > On Sun, Sep 09, 2012 at 01:40:52AM +0400, Max Filippov wrote:
> >> I've also stumbled upon this bug, have a patch for it in the xtensa tree.
> >> I guess that the interface was designed to allow combining these flags, why
> >> don't just make them independent:
> >
> > My idea was that negating both the product and c is equivalent to
> > negating the result, so there is no need to allow all of them
> > independent.
>
> But at least some of them can reasonably be independent, so
> at that point you might as well make them all independent flags.
>
> In fact my reading of the PPC ISA is that it needs several combinations:
> fmadd : no flags
> fnmadd : negate_result
> fmsub : negate_c
> fnmsub : negate_result | negate_c
>
> ...and it looks like your patch is incorrectly only setting negate_result
> for the fnmsub case. (I can't see anything handling the fnmadd and fmsub
> insns, do we not implement them?)
fnmadd and fmsub are provided as part as floating point instructions
(something else to clean), not as part as altivec instructions.
> (negate_product will be used by x86 and SPARC, among others.)
>
> thanks
> -- PMM
>
--
Aurelien Jarno GPG: 1024D/F1BCDB73
address@hidden http://www.aurel32.net
- Re: [Qemu-devel] [PATCH 4/5] target-ppc: use the softfloat float32_muladd function, (continued)
- [Qemu-devel] [PATCH 3/5] target-ppc: use the softfloat min/max functions, Aurelien Jarno, 2012/09/08
- [Qemu-devel] [PATCH 5/5] target-ppc: get rid of the HANDLE_NAN{1, 2, 3} macros, Aurelien Jarno, 2012/09/08
- [Qemu-devel] [PATCH 2/5] target-ppc: simplify NaN propagation for vector functions, Aurelien Jarno, 2012/09/08
- Re: [Qemu-devel] [PATCH 1/5] softfloat: fix float{32, 64}_muladd options, Max Filippov, 2012/09/08