[Bug math/20916] pow handling of sNaN arguments

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https://sourceware.org/bugzilla/show_bug.cgi?id=20916

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=a91fd168a0db38563528dab1a13180fda2a5040c

commit a91fd168a0db38563528dab1a13180fda2a5040c
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Dec 6 00:33:19 2016 +0000

    Fix x86_64/x86 powl handling of sNaN arguments (bug 20916).

    The x86_64/x86 powl implementations mishandle sNaN arguments, both by
    returning sNaN in some cases (instead of doing arithmetic on the
    arguments to produce the result when NaN arguments result in NaN
    results) and by treating sNaN the same as qNaN for arguments (1, sNaN)
    and (sNaN, 0), contrary to TS 18661-1 which requires those cases to
    return qNaN instead of 1.

    This patch makes the x86_64/x86 powl implementations follow TS 18661-1
    semantics for sNaN arguments; sNaN tests are also added for pow.
    Given the problems with testing float and double sNaN arguments on
    32-bit x86 (sNaN tests disabled because the compiler may convert
    unnecessarily to a qNaN when passing arguments), no changes are made
    to the powf and pow implementations there.

    Tested for x86_64 and x86.

        [BZ #20916]
        * sysdeps/i386/fpu/e_powl.S (__ieee754_powl): Do not return 1 for
        arguments (sNaN, 0) or (1, sNaN).  Do arithmetic on NaN arguments
        to compute result.
        * sysdeps/x86_64/fpu/e_powl.S (__ieee754_powl): Likewise.
        * math/libm-test.inc (pow_test_data): Add tests of sNaN arguments.

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

Summary of changes:
 ChangeLog                   |    9 +++++++
 math/libm-test.inc          |   54 ++++++++++++++++++++++++++++++++++++++++++-
 sysdeps/i386/fpu/e_powl.S   |   29 +++++++++++++++++++----
 sysdeps/x86_64/fpu/e_powl.S |   27 ++++++++++++++++++---
 4 files changed, 109 insertions(+), 10 deletions(-)

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