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[Bug math/19349] [ldbl-128ibm] tanhl inaccurate for small arguments


https://sourceware.org/bugzilla/show_bug.cgi?id=19349

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=ca2fcac629b9b7781ccd52685b28741d89ff128f

commit ca2fcac629b9b7781ccd52685b28741d89ff128f
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed Dec 9 21:20:18 2015 +0000

    Fix ldbl-128ibm tanhl inaccuracy for small arguments (bug 19349).

    The ldbl-128ibm implementation of tanhl is inaccurate for small
    arguments, because it returns x*(1+x) (maybe in an attempt to raise
    "inexact") when x itself would be the accurate return value but
    multiplying by 1+x introduces large errors.  This patch fixes it to
    return x in that case (when the mathematical result is x plus a
    negligible remainder on the order of x^3) to avoid those errors.

    Tested for powerpc.

        [BZ #19349]
        * sysdeps/ieee754/ldbl-128ibm/s_tanhl.c (__tanhl): Return argument
        when small.

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

Summary of changes:
 ChangeLog                             |    4 ++++
 sysdeps/ieee754/ldbl-128ibm/s_tanhl.c |    2 +-
 2 files changed, 5 insertions(+), 1 deletions(-)

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