On 11.02.2025 23:11, Martin Storsjö wrote:
On Sun, 9 Feb 2025, Jacek Caban wrote:
Additionally, x86 MinGW's fenv.h defines structures like fenv_t and
certain constants that are incompatible with other fenv.h
implementations. Instead of carrying over these quirks, ARM64EC uses
ARM64 variants that align with MSVC and the broader Windows ecosystem.
I believe that it would be good to include this rationale here in the
commit message of patch 1/3 (possibly other bits of this cover letter
in the commit messages of the other patches as well; I haven't looked
that far yet).
Sure, I will include more details in the next version. I'm considering
changing other targets first (see bellow).
It may also be good to include a bit of introduction in the commit
message; each time I look at fenv.h it takes a bit of time to wrap my
head around how it works, as it differs quite significantly from the
corresponding MSVC ones.
If I remember correctly, our fenv.h directly exposes the architecture
specific control words, as they are provided by the FPU. I.e. the
fenv_t data type, and the flags/masks, have entirely different
definitions across architectures.
On the other hand, the MSVC fenv.h uses architecture independent
generalized definitions outwards, that don't exactly match any
specific architecture, and the fesetenv/fegetenv functions translate
between the architecture specific interface and the external public
interface.
The more I look at it, the more I’m tempted to adjust fenv_t handling to
be closer to MSVC. I think it was originally implemented entirely in
mingwex because msvcrt lacked it before msvcr120, so there wasn’t
anything to be compatible with at the time.
I’d like to try making it compatible with UCRT, but that looks like a
significant amount of work, so I'm not yet sure. If you think it's a bad
idea, please let me know. The ARM version is much closer to the native
implementation, but even there, some of the defines have different
values, likely hardware-specific rather than abstract, as you mentioned.
Thanks,
Jacek
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