Date: Thu, 16 Jan 2020 14:33:43 -0500 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: Considering x86-64 fenv.s to C On Fri, Jan 17, 2020 at 05:56:06AM +1100, Damian McGuckin wrote: > On Thu, 16 Jan 2020, Rich Felker wrote: > > >As an aside, rather than implementing x86-specific C versions of > >these, I'd like to end up with a general framework where the arch > >just exposes a header (fenv_arch.h?) defining some primitives, and > >the actual fenv function logic is all shared C. I'm not sure what > >the right generalization is though. It looks like all archs have a > >get/set exception-flags (status word) operation, but the rest > >varies a bit. > > I will try and put together a summary of what things do and we can > go from there. It will need input from somebody with way more > expertise on ARM and RISC-V (and X87) than I. > > >Would you be interested in assessing what kind of abstraction makes > >sense here? > > I think the abstraction might need to be consensus. Some of it is > not even 'fenv' related. For example, some routines only ever return > zero, while for other FPUs, the same routine can return a (-1) if > the exception mask > had an component (bit) which was not a valid exception. That's one point of having the high level logic in C: not having to repeat it in each arch where it's potentially subtly wrong. The C code should check the validity of the mask before attempting to use the arch primitive to set it. Rich
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