[Bug math/19674] [ldbl-128ibm] powl incorrect overflow handling

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https://sourceware.org/bugzilla/show_bug.cgi?id=19674

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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c091488e5172025eb4e96fcc1141edb89dbc9afd

commit c091488e5172025eb4e96fcc1141edb89dbc9afd
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Fri Feb 19 01:07:40 2016 +0000

    Fix ldbl-128ibm powl overflow handling (bug 19674).

    The ldbl-128ibm implementation of powl has some problems in the case
    of overflow or underflow, which are mainly visible in non-default
    rounding modes.

    * When overflow or underflow is detected early, the correct sign of an
      overflowing or underflowing result is not allowed for.  This is
      mostly hidden in the default rounding mode by the errno-setting
      wrappers recomputing the result (except in non-default
      error-handling modes such as -lieee), but visible in other rounding
      modes where a result that is not zero or infinity causes the
      wrappers not to do the recomputation.

    * The final scaling is done before the sign is incorporated in the
      result, but should be done afterwards for correct overflowing and
      underflowing results in directed rounding modes.

    This patch fixes those problems.  Tested for powerpc.

        [BZ #19674]
        * sysdeps/ieee754/ldbl-128ibm/e_powl.c (__ieee754_powl): Include
        sign in overflowing and underflowing results when overflow or
        underflow is detected early.  Include sign in result before rather
        than after scaling.

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

Summary of changes:
 ChangeLog                            |    6 ++++++
 sysdeps/ieee754/ldbl-128ibm/e_powl.c |   34 +++++++++++++++++-----------------
 2 files changed, 23 insertions(+), 17 deletions(-)

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