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Date: Tue, 9 Feb 2016 02:03:36 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com, David Edelsohn <dje.gcc@...il.com>
Subject: Re: Re: musl libc for PPC64
* Szabolcs Nagy <nsz@...t70.net> [2016-02-09 00:48:31 +0100]:
> * 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.
hm it seems, this is only for the __float128 type
which will be new in gcc-6.
i don't see how to configure gcc with ieee128 long double.
(other than using the debug option -mabi=ieeelongdouble)
so if musl goes with ieee128 long double abi then it will
only work with latest gcc.
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