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Date: Fri, 17 Jan 2020 05:56:06 +1100 (AEDT)
From: Damian McGuckin <>
Subject: Re: Considering x86-64 fenv.s to C

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.

Regards - Damian

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