Date: Mon, 8 Feb 2016 18:52:55 -0500 From: David Edelsohn <dje.gcc@...il.com> To: Rich Felker <dalias@...c.org> Cc: musl@...ts.openwall.com Subject: Re: Re: musl libc for PPC64 On Mon, Feb 8, 2016 at 6:29 PM, Rich Felker <dalias@...c.org> wrote: > On Mon, Feb 08, 2016 at 06:24:27PM -0500, David Edelsohn wrote: >> You *can* use v2 ABI for BE, but there is no software to run. There >> is no software or ecosystem or operating system that runs v2 ABI BE. >> It's not a hardware limitation, but there is no environment for the >> alternate combination. > > Indeed. At this point there's no musl ecosystem for ppc64 at all > though; whatever we add is a fresh start. > >> >> IBM has announced that the next generation of the processor will >> >> support native IEEE128 floating point in hardware. There will be >> >> software emulation for the current processors. Support is included in >> >> the forthcoming GCC 6. >> > >> > OK. Does the existing software emulation properly update the hardware >> > floating point status (exception flags) and use the rounding mode? >> >> 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. Who would be interested in working on this? Thanks, David
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