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From: "kretz at kde dot org" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug math/27460] New: hypot(__DBL_DENORM_MIN__, -0.) incorrectly
 raises FE_INEXACT and FE_UNDERFLOW
Date: Tue, 23 Feb 2021 16:07:29 +0000
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X-Bugzilla-Component: math
X-Bugzilla-Version: 2.31
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D27460

            Bug ID: 27460
           Summary: hypot(__DBL_DENORM_MIN__, -0.) incorrectly raises
                    FE_INEXACT and FE_UNDERFLOW
           Product: glibc
           Version: 2.31
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: kretz at kde dot org
  Target Milestone: ---

Testcase (https://godbolt.org/z/b4Ko4Y):

#include <fenv.h>
#include <math.h>

int main()
{
    volatile double a =3D __DBL_DENORM_MIN__;
    volatile double c =3D -0.;
    feclearexcept(FE_ALL_EXCEPT);
    //c =3D hypot(a, c); // this argument order raises no exceptions
    c =3D hypot(c, a);
    return fetestexcept(FE_ALL_EXCEPT);
}

This program raises FE_INEXACT and FE_UNDERFLOW. Since one argument to hypo=
t is
0 the result is exact: the absolute value of the other argument. If you swi=
tch
the argument order the program raises no floating-point exceptions.

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