[Bug math/18569] [x86/x86_64] expm1l wrong sign of underflowing zero results

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https://sourceware.org/bugzilla/show_bug.cgi?id=18569

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=cb0937b299182e78307795081489ec1f148bdbd7

commit cb0937b299182e78307795081489ec1f148bdbd7
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Sun Jun 21 18:43:10 2015 +0000

    Fix x86_64 / x86 expm1l (-min_subnorm) result sign (bug 18569).

    In the x86 / x86_64 implementations of expm1l, when expm1l's result
    should underflow to 0 (argument minus the least subnormal, in some
    rounding modes), it can be a zero of the wrong sign.  This patch fixes
    this by returning the argument with underflow forced in that case
    (this is a 1ulp error relative to the correctly rounded result of -0,
    which is OK in terms of the documented accuracy goals, whereas a
    result with the wrong sign never is).

    Tested for x86_64 and x86.

        [BZ #18569]
        * sysdeps/i386/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]: Force
        underflow and return argument in case of subnormal argument.
        * sysdeps/x86_64/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]:
        Likewise.
        * math/auto-libm-test-in: Add more tests of expm1.
        * math/auto-libm-test-out: Regenerated.

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

Summary of changes:
 ChangeLog                   |    8 +
 NEWS                        |    2 +-
 math/auto-libm-test-in      |    4 +
 math/auto-libm-test-out     |  316 +++++++++++++++++++++++++++++++++++++++++++
 sysdeps/i386/fpu/e_expl.S   |    6 +
 sysdeps/x86_64/fpu/e_expl.S |    6 +
 6 files changed, 341 insertions(+), 1 deletions(-)

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