Re: port-mips/57680: printf("%.1f") shows wrong resultsonR3000mipseb

[Rin Okuyama <rokuyama.rk%gmail.com@localhost>]

On 2023/11/04 19:16, Izumi Tsutsui wrote:
> > >    Unless some MIPS guru has proper idea how this issue should be fixed,
> > >    I'd like to commit workaround fix to disable -DHonor_FLT_ROUNDS in
> > >    src/lib/libc/gdtoa/Makefile.inc in ${MACHINE_CPU}=="mips" case.
> >
> > (1) How about -current or netbsd-10, which have GCC 10.5?
> >
> >       Less likely, but if this is a temporal problem for specific
> >       versions of GCC, we can restrict the workaround to netbsd-9.
>
> I have not tried it, but last time I tried netbsd-10 kernel
> on NWS-3260 it was very unstable and looked lost software interrupts
> many times, so I'm currently testing NWS-3260 on netbsd-9.

Thanks, I understand the situation :(

> I doubt this problem was really compiler issue and
> I wonder if it's okay to assume "FE_TONEAREST" is default
> because FE_TOZERO works.
>
> > (2) Can we exclude ``mipsn{,64}e[bl]''? -current and netbsd-10 have
> >       ${MACHINE_MIPS64} macro for this purpose, but netbsd-9 does not :(
>
> What's your motivation?
>
> Performance? If so, is it visible or measurable?
> Consistency? If so, is there any rationale of Honor_FLT_ROUNDS
> implementation?  Actually we already have an exception (vax).
>
> If you have a working patch to achive your intention in both
> HEAD and release branches, it's fine.  If not, sorry I don't
> have motivation to prepare such complexities.
>
> I'm trying to fix visible issue (and real problems like invalid
> strings stored in /etc/ntp.conf etc.).  If you want possible
> performace or design consistency, it should be measured or
> defined by people who want it, because we are on Tier-II ports
> "keeping it working is the responsibility of the user community."
>   https://wiki.netbsd.org/ports/

I'm worried about consistency.

IMO, it is less surprising that vax is treated differently here;
it does not comply IEEE 754, and no working fenv implementation
at the moment.

This patch is working both for -current/netbsd-10 and netbsd-9:

https://www.netbsd.org/~rin/gdtoa_port-mips_57680.patch

Thanks,
rin