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[Bug math/20940] hypot sNaN handling


https://sourceware.org/bugzilla/show_bug.cgi?id=20940

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=58307649fb51a3a6adc29a8659d3301393f24671

commit 58307649fb51a3a6adc29a8659d3301393f24671
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed Dec 7 01:16:36 2016 +0000

    Fix hypot sNaN handling (bug 20940).

    TS 18661-1 generally defines libm functions taking sNaN arguments to
    return qNaN and raise "invalid", even for the cases where a
    corresponding qNaN argument would not result in a qNaN return.  This
    includes hypot with one argument being an infinity and the other being
    an sNaN.  This patch duly fixes hypot implementatations in glibc
    (generic and powerpc) to ensure qNaN, computed by arithmetic on the
    arguments, is returned in that case.

    Various implementations do their checks for infinities and NaNs inline
    by manipulating the representations of the arguments.  For simplicity,
    this patch just uses issignaling to check for sNaN arguments.  This
    could be inlined like the existing code (with due care about reversed
    quiet NaN conventions, for implementations where that is relevant),
    but given that all these checks are in cases where it's already known
    at least one argument is not finite, which should be the uncommon
    case, that doesn't seem worthwhile unless performance issues are
    observed in practice.

    Tested for x86_64, x86, mips64 and powerpc.

        [BZ #20940]
        * sysdeps/ieee754/dbl-64/e_hypot.c (__ieee754_hypot): Do not
        return Inf for arguments Inf and sNaN.
        * sysdeps/ieee754/flt-32/e_hypotf.c (__ieee754_hypotf): Likewise.
        * sysdeps/ieee754/ldbl-128/e_hypotl.c (__ieee754_hypotl):
        Likewise.
        * sysdeps/ieee754/ldbl-128ibm/e_hypotl.c (__ieee754_hypotl):
        Likewise.
        * sysdeps/ieee754/ldbl-96/e_hypotl.c (__ieee754_hypotl): Likewise.
        * sysdeps/powerpc/fpu/e_hypot.c (TEST_INF_NAN): Do not return Inf
        for arguments Inf and sNaN.  When returning a NaN, compute it by
        arithmetic on the arguments.
        * sysdeps/powerpc/fpu/e_hypotf.c (TEST_INF_NAN): Likewise.
        * math/libm-test.inc (pow_test_data): Add tests of sNaN arguments.

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

Summary of changes:
 ChangeLog                              |   17 ++++++++++
 math/libm-test.inc                     |   52 ++++++++++++++++++++++++++++++++
 sysdeps/ieee754/dbl-64/e_hypot.c       |    2 +
 sysdeps/ieee754/flt-32/e_hypotf.c      |    4 +-
 sysdeps/ieee754/ldbl-128/e_hypotl.c    |    2 +
 sysdeps/ieee754/ldbl-128ibm/e_hypotl.c |    2 +
 sysdeps/ieee754/ldbl-96/e_hypotl.c     |    2 +
 sysdeps/powerpc/fpu/e_hypot.c          |   10 ++++--
 sysdeps/powerpc/fpu/e_hypotf.c         |   10 ++++--
 9 files changed, 91 insertions(+), 10 deletions(-)

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