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From: "bruno at clisp dot org" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug manual/31019] New: The documentation of feenableexcept is
 incomplete
Date: Wed, 01 Nov 2023 01:29:32 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D31019

            Bug ID: 31019
           Summary: The documentation of feenableexcept is incomplete
           Product: glibc
           Version: 2.35
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: manual
          Assignee: unassigned at sourceware dot org
          Reporter: bruno at clisp dot org
                CC: mtk.manpages at gmail dot com
  Target Milestone: ---

Created attachment 15202
  --> https://sourceware.org/bugzilla/attachment.cgi?id=3D15202&action=3Ded=
it
test case foo.c

The attached simple program, that enables floating-point exception traps on
FE_INVALID, when the exception flag for FE_INVALID is already set, show CPU
dependent behaviour.

How to reproduce:
1. Compile it with: ${CC-gcc} -ggdb -Wall foo.c -lm
2. Run it with: ./a.out; echo $?

Results with glibc:
x86_64       0
i386         Floating point exception (core dumped)
arm64        3
armelhf      3
armel        3
hppa         0
ia64         0
loongarch64  0
m68k         0
mips         0
mips64       0
powerpc      Floating point exception
powerpc64    Floating point exception
powerpc64le  Floating point exception
riscv64      3
s390         0
s390x        0
sh4          0
sparc        0
sparc64      0

I think that it is not possible to make i386 and powerpc* behave like the o=
ther
CPU types; see
https://lists.gnu.org/archive/html/bug-gnulib/2023-10/msg00104.html for why.

Nevertheless it is surprising to see platform-dependent behaviour. This was
also the reason for bug#16209.

Since the function feenableexcept is not defined by a standard, the definit=
ive
documentation is the glibc manual. If there is a situation where the results
are undefined or platform-dependent, the documentation should tell so.

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