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From: "bruno at clisp dot org" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug math/30998] New: fesetexceptflag clears too many floating-point
 exception flags on alpha
Date: Tue, 24 Oct 2023 18:19:55 +0000
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X-Bugzilla-Product: glibc
X-Bugzilla-Component: math
X-Bugzilla-Version: 2.36
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X-Bugzilla-Who: bruno at clisp dot org
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D30998

            Bug ID: 30998
           Summary: fesetexceptflag clears too many floating-point
                    exception flags on alpha
           Product: glibc
           Version: 2.36
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: bruno at clisp dot org
  Target Milestone: ---

Created attachment 15196
  --> https://sourceware.org/bugzilla/attachment.cgi?id=3D15196&action=3Ded=
it
test case foo.c

On Linux/alpha, the function fesetexceptflag() clears some exception flags =
that
are outside the EXCEPTS argument. This violates ISO C 23 =C2=A7 7.6.4.5, wh=
ich says:
  "The fesetexceptflag function attempts to set the floating-point status f=
lags
indicated by the argument excepts to the states stored in the object pointe=
d to
by flagp."

How to reproduce:
Compile and run the attached program.
$ gcc -Wall foo.c -lm
$ ./a.out

Expected: It terminates with exit code 0.
Actual:
a.out: foo.c:58: main: Assertion `fetestexcept (FE_DIVBYZERO) =3D=3D FE_DIV=
BYZERO'
failed.
Aborted

When you compare the program's lines 49 and 58, you see that the invocation
  fesetexceptflag (&saved_flags_2, FE_OVERFLOW)
not only modified the FE_OVERFLOW flag bit, but also cleared the FE_DIVBYZE=
RO
flag bit.

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