[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-Id: <p9u0frfcib4l.fsf@biscotte.loria.fr>
Date: Fri, 04 Jul 2025 11:00:26 +0200
From: Paul Zimmermann <Paul.Zimmermann@...ia.fr>
To: Rich Felker <dalias@...c.org>
Cc: musl@...ts.openwall.com, maxence.ponsardin@...ia.fr
Subject: Re: sqrt does not emit errno=EDOM
thank you Rich for clarifying the Musl position with respect to errno.
Paul
> Date: Thu, 3 Jul 2025 16:05:17 -0400
> From: Rich Felker <dalias@...c.org>
> Cc: musl@...ts.openwall.com, maxence.ponsardin@...ia.fr
>
> On Thu, Jul 03, 2025 at 09:44:12AM +0200, Paul Zimmermann wrote:
> > Hi,
> >
> > it seems musl does not set errno=EDOM for sqrt(x) when x is negative.
> > Here on cfarm27 (Alpine Linux):
> >
> > $ cat /tmp/e.c
> > #include <stdio.h>
> > #include <math.h>
> > #include <errno.h>
> >
> > int
> > main()
> > {
> > errno = 0;
> > float x = -1.0f;
> > float y = sqrtf (x);
> > printf ("y=%a errno=%d\n", y, errno);
> > }
> >
> > $ gcc /tmp/e.c -lm
> > $ ./a.out
> > y=-nan errno=0
> >
> > Is this a known issue?
>
> It's intentional that none of musl's math library sets errno.
> Implementations have the option to do either or both of setting errno
> or raising fenv exception flags as long as this is reflected in the
> value of math_errhandling.
>
> Generally, the modern view seems to be that setting errno is bad
> practice. It makes it so that the math functions can never be treated
> as pure functions by the compiler (note: fenv also breaks purity but
> the application gets to signal whether it wants FENV_ACCESS or not,
> and if not, they're pure).
>
> Note that on soft float archs without fenv, omitting errno is actually
> nonconforming. It was originally my hope that we'd eventually get soft
> fenv working on these, but they seem to be of waning relevance these
> days anyway. I don't see adding errno as an appropriate fix for this.
> Applications generally don't want it, and any such effort to add it
> would be better spent on workout out a way to do soft fenv.
>
> Rich
>
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
