[Bug math/16800] __ieee754_logf incorrect for 0 in round-downward mode

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https://sourceware.org/bugzilla/show_bug.cgi?id=16800

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=a84e78c8b3c4de94b488fdc5321f71feeb99358f

commit a84e78c8b3c4de94b488fdc5321f71feeb99358f
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed Apr 2 17:41:02 2014 +0000

    Fix catan, catanh, __ieee754_logf in round-downward mode (bug 16799, bug
16800).

    This patch fixes incorrect results from catan and catanh of certain
    special inputs in round-downward mode (bug 16799), and incorrect
    results of __ieee754_logf (+/-0) in round-downward mode (bug 16800)
    that show up through catan/catanh when tested in all rounding modes,
    but not directly in the testing for logf because the bug gets hidden
    by the wrappers.

    Both bugs involve a zero that should be +0 being -0 instead: one
    computed as (1-x)*(1+x) in the catan/catanh case, and one as (x-x) in
    the logf case.  The fixes ensure positive zero is used.  Testing of
    catan and catanh in all rounding modes is duly enabled.

    I expect there are various other bugs in special cases in __ieee754_*
    functions that are normally hidden by the wrappers but would show up
    for testing with -lieee (or in future with -fno-math-errno if we
    replace -lieee and _LIB_VERSION with compile-time redirection to new
    *_noerrno symbol names).

    Tested x86_64 and x86 and ulps updated accordingly.

        [BZ #16799]
        [BZ #16800]
        * math/s_catan.c (__catan): Avoid passing -0 denominator to atan2
        with 0 numerator.
        * math/s_catanf.c (__catanf): Likewise.
        * math/s_catanh.c (__catanh): Likewise.
        * math/s_catanhf.c (__catanhf): Likewise.
        * math/s_catanhl.c (__catanhl): Likewise.
        * math/s_catanl.c (__catanl): Likewise.
        * sysdeps/ieee754/flt-32/e_logf.c (__ieee754_logf): Always divide
        by positive zero when computing -Inf result.
        * math/libm-test.inc (catan_test): Use ALL_RM_TEST.
        (catanh_test): Likewise.
        * sysdeps/i386/fpu/libm-test-ulps: Update.
        * sysdeps/x86_64/fpu/libm-test-ulps: Likewise.

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

Summary of changes:
 ChangeLog                         |   16 ++++++
 NEWS                              |    2 +-
 math/libm-test.inc                |    8 +--
 math/s_catan.c                    |    6 ++-
 math/s_catanf.c                   |    6 ++-
 math/s_catanh.c                   |    6 ++-
 math/s_catanhf.c                  |    6 ++-
 math/s_catanhl.c                  |    6 ++-
 math/s_catanl.c                   |    6 ++-
 sysdeps/i386/fpu/libm-test-ulps   |   96 +++++++++++++++++++++++++++++++++++++
 sysdeps/ieee754/flt-32/e_logf.c   |    2 +-
 sysdeps/x86_64/fpu/libm-test-ulps |   96 +++++++++++++++++++++++++++++++++++++
 12 files changed, 242 insertions(+), 14 deletions(-)

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