[Bug math/19677] [ldbl-128ibm] remainderl equality test incorrect for zero low part

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https://sourceware.org/bugzilla/show_bug.cgi?id=19677

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=cc4084017e211cdeafef2d9036a130cbd6f2cadd

commit cc4084017e211cdeafef2d9036a130cbd6f2cadd
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Mar 8 00:27:21 2016 +0000

    Fix ldbl-128ibm remainderl equality test for zero low part (bug 19677).

    The ldbl-128ibm implementation of remainderl has logic resulting in
    incorrect tests for equality of the absolute values of the arguments
    in the case of zero low parts.  If the low parts are both zero but
    with different signs, this can wrongly cause equal arguments to be
    treated as different, resulting in turn in incorrect signs of zero
    result in nondefault rounding modes arising from the subtractions done
    when the arguments are not equal.

    This patch fixes the logic to convert -0 low parts into +0 before the
    comparison (remquo already has separate logic to deal with signs of
    zero results, so doesn't need such a change).  Tests are added for
    remainderl and remquol similar to that for fmodl, and based on a
    refactoring of it, since the bug depends on low parts which should not
    be relied upon in tests not setting the representation explicitly
    (although in fact the bug shows up in test-ldouble with current GCC).
    Tested for powerpc.

        [BZ #19677]
        * sysdeps/ieee754/ldbl-128ibm/e_remainderl.c
        (__ieee754_remainderl): Put zero low parts in canonical form.
        * sysdeps/ieee754/ldbl-128ibm/test-fmodrem-ldbl-128ibm.c: New
        file.  Based on
        sysdeps/ieee754/ldbl-128ibm/test-fmodl-ldbl-128ibm.c.
        * sysdeps/ieee754/ldbl-128ibm/test-fmodl-ldbl-128ibm.c: Replace
        with wrapper round test-fmodrem-ldbl-128ibm.c.
        * sysdeps/ieee754/ldbl-128ibm/test-remainderl-ldbl-128ibm.c: New
        file.
        * sysdeps/ieee754/ldbl-128ibm/test-remquol-ldbl-128ibm.c:
        Likewise.
        * sysdeps/ieee754/ldbl-128ibm/Makefile (tests): Add
        test-remainderl-ldbl-128ibm and test-remquol-ldbl-128ibm.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                                          |   17 ++++
 sysdeps/ieee754/ldbl-128ibm/Makefile               |    3 +-
 sysdeps/ieee754/ldbl-128ibm/e_remainderl.c         |    4 +
 .../ieee754/ldbl-128ibm/test-fmodl-ldbl-128ibm.c   |   62 +--------------
 .../ieee754/ldbl-128ibm/test-fmodrem-ldbl-128ibm.c |   84 ++++++++++++++++++++
 .../ldbl-128ibm/test-remainderl-ldbl-128ibm.c      |   21 +++++
 .../ieee754/ldbl-128ibm/test-remquol-ldbl-128ibm.c |   30 +++++++
 7 files changed, 161 insertions(+), 60 deletions(-)
 create mode 100644 sysdeps/ieee754/ldbl-128ibm/test-fmodrem-ldbl-128ibm.c
 create mode 100644 sysdeps/ieee754/ldbl-128ibm/test-remainderl-ldbl-128ibm.c
 create mode 100644 sysdeps/ieee754/ldbl-128ibm/test-remquol-ldbl-128ibm.c

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