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Date: Sat, 06 Feb 2021 07:45:31 +0100
From: Paul Zimmermann <Paul.Zimmermann@...ia.fr>
To: Rich Felker <dalias@...c.org>
Cc: musl@...ts.openwall.com
Subject: Re: issue with acoshf
Dear Rich,
> Date: Fri, 5 Feb 2021 11:44:02 -0500
> From: Rich Felker <dalias@...c.org>
> Cc: musl@...ts.openwall.com
> User-Agent: Mutt/1.5.21 (2010-09-15)
>
> On Fri, Feb 05, 2021 at 08:18:02AM +0100, Paul Zimmermann wrote:
> > Hi,
> >
> > while updating to my comparison of the accuracy of mathematical functions [1],
> > I have noticed an issue with acoshf in musl-1.2.2:
> >
> > $ cat test_acosh_musl.c
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <math.h>
> >
> > int
> > main (int argc, char *argv[])
> > {
> > float x = -0x1.1e6ae8p+5;
> > float y;
> > y = acoshf (x);
> > printf ("x=%a y=%a\n", x, y);
> > }
> >
> > With gcc I get NaN as expected:
> >
> > $ gcc -fno-builtin test_acosh_musl.c -lm
> > $ ./a.out
> > x=-0x1.1e6ae8p+5 y=-nan
> >
> > With musl-1.2.2 I get -0x1.2f63acp+3:
> >
> > $ gcc -fno-builtin test_acosh_musl.c $FILES
> > $ ./a.out
> > x=-0x1.1e6ae8p+5 y=-0x1.2f63acp+3
> >
> > Please can someone confirm?
>
> I can't reproduce it on i386 but can on sh w/softfloat. I'm guessing
> you're using an arch without its own special definition of sqrtf or
> logf, so it looks like it would have to be a bug in the
> non-arch-specific version of one of those, but I haven't been able to
> reproduce it in isolation just passing the values passed to them
> (-0x1.c9b6fcp-7 to logf or 0x1.40330cp+10 to sqrtf) manually building
> the generic C versions.
>
> Thanks for the report. I'll keep looking.
>
> Rich
my machine is an Intel(R) Core(TM) i5-4590, and I use gcc version 10.2.1,
under Debian bullseye/sid. Szabolcs sent a patch, and I confirmed it solves
the issue. I'm now testing again acosh and sinh for the whole binary32 domain,
and will report here my findings.
Paul
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