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Date: Tue, 9 Feb 2016 00:48:31 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Cc: David Edelsohn <dje.gcc@...il.com>
Subject: Re: Re: musl libc for PPC64
* Rich Felker <dalias@...c.org> [2016-02-08 18:29:45 -0500]:
> On Mon, Feb 08, 2016 at 06:24:27PM -0500, David Edelsohn wrote:
> > I'm not sure what you mean. The software emulation assumes the
> > hardware support is not present. It doesn't mirror back the state to
> > the processor in 64 bit mode. But the emulation is fully IEEE128
> > compliant.
>
> if fesetround(FE_DOWNWARD) succeeds but then long double math still
> rounds to nearest, that's not IEEE compliant.
>
> The big obstacle to having fenv with softfloat on fully-softfloat
> archs is the lack of register state for the rounding mode and
> exception flags, so it should be possible to do this right as long as
> the cpu has status/mode registers for single/double, which the
> soft-quad code can then access/set. If this isn't done right already
> we could either try to get it fixed in libgcc or punt and go with
> ld64.
>
it seems to be supported
https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=libgcc/config/rs6000/sfp-machine.h;h=75d5e1a2d522e0a3d3c5b0463fcfe9b054f7c263;hb=HEAD#l107
so we can implement iso c annex f with 128 bit long doubles.
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