[Bug math/16315] Bad overflowing pow results for directed rounding

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https://sourceware.org/bugzilla/show_bug.cgi?id=16315

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=edea402804bce917cfd7cd1af76212e6364c23db

commit edea402804bce917cfd7cd1af76212e6364c23db
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Sun Jun 29 11:49:08 2014 +0000

    Fix ldbl-128 powl sign of result in overflow / underflow cases (bug 17097).

    This patch fixes bug 17097, ldbl-128 powl producing overflowing /
    underflowing results with positive sign when the result should have
    been negative.  This was shown up by the tests in non-default rounding
    modes added by my patch for bug 16315, but isn't actually limited to
    non-default rounding modes: rather, when rounding to nearest the
    wrappers produced a result with the correct sign and so always hid the
    bug unless -lieee was used to disable the wrappers.  The problem is
    that in the cases where Y is large enough that the result overflows or
    underflows for X not very close to 1, but not large enough to overflow
    or underflow for all X != +/- 1 (in the latter case Y is always an
    even integer), a positive overflowing / underflowing result is always
    returned, rather than one with the correct sign.  This patch moves the
    relevant part of computation of the sign earlier and returns a result
    of the correct sign.

    Tested for mips64.

        [BZ #17097]
        * sysdeps/ieee754/ldbl-128/e_powl.c (__ieee754_powl): Return
        result with correct sign in case of exponents that produce
        overflow except for X very close to 1.

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

Summary of changes:
 ChangeLog                         |    7 +++++++
 NEWS                              |    2 +-
 sysdeps/ieee754/ldbl-128/e_powl.c |   26 +++++++++++++-------------
 3 files changed, 21 insertions(+), 14 deletions(-)

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