[Bug math/16927] acosh (1) wrong sign of zero in FE_DOWNWARD mode

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https://sourceware.org/bugzilla/show_bug.cgi?id=16927

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=913d03c864ea2547e97f8d2d30fc71a008d4d103

commit 913d03c864ea2547e97f8d2d30fc71a008d4d103
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed May 14 12:35:40 2014 +0000

    Fix acosh (1) in round-downward mode (bug 16927).

    According to C99 and C11 Annex F, acosh (1) should be +0 in all
    rounding modes.  However, some implementations in glibc wrongly return
    -0 in round-downward mode (which is what you get if you end up
    computing log1p (-0), via 1 - 1 being -0 in round-downward mode).
    This patch fixes the problem implementations, by correcting the test
    for an exact 1 value in the ldbl-96 implementation to allow for the
    explicit high bit of the mantissa, and by inserting fabs instructions
    in the i386 implementations; tests of acosh are duly converted to
    ALL_RM_TEST.  I believe all the other sysdeps/ieee754 implementations
    are already OK (I haven't checked the ia64 versions, but if buggy then
    that will be obvious from the results of test runs after this patch is
    in).

    Tested x86_64 and x86 and ulps updated accordingly.

        [BZ #16927]
        * sysdeps/i386/fpu/e_acosh.S (__ieee754_acosh): Use fabs on x-1
        value.
        * sysdeps/i386/fpu/e_acoshf.S (__ieee754_acoshf): Likewise.
        * sysdeps/i386/fpu/e_acoshl.S (__ieee754_acoshl): Likewise.
        * sysdeps/ieee754/ldbl-96/e_acoshl.c (__ieee754_acoshl): Correct
        for explicit high bit of mantissa when testing for argument equal
        to 1.
        * math/libm-test.inc (acosh_test): Use ALL_RM_TEST.
        * sysdeps/i386/fpu/libm-test-ulps: Update.
        * sysdeps/x86_64/fpu/libm-test-ulps: Likewise.

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

Summary of changes:
 ChangeLog                          |   12 ++++++++++++
 NEWS                               |    2 +-
 math/libm-test.inc                 |    4 +---
 sysdeps/i386/fpu/e_acosh.S         |    1 +
 sysdeps/i386/fpu/e_acoshf.S        |    1 +
 sysdeps/i386/fpu/e_acoshl.S        |    1 +
 sysdeps/i386/fpu/libm-test-ulps    |   12 ++++++++++++
 sysdeps/ieee754/ldbl-96/e_acoshl.c |    2 +-
 sysdeps/x86_64/fpu/libm-test-ulps  |   15 +++++++++++++++
 9 files changed, 45 insertions(+), 5 deletions(-)

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