[Bug math/18221] New: tanf spurious underflows

[Bug math/18221] New: tanf spurious underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18221

            Bug ID: 18221
           Summary: tanf spurious underflows
           Product: glibc
           Version: 2.21
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: jsm28 at gcc dot gnu.org

The flt-32 implementation of tanf produces spurious underflow exceptions.  For
example, on x86_64, tanf (0x1p-27f) produces such an exception.

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[Bug math/18221] tanf spurious underflows

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18221

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
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The branch, master has been updated
       via  5a608ccc2d676aa124f6b55a7b20d071e408ca31 (commit)
      from  ff069f024ae8cf15d53429e034d67ddcece0f67a (commit)

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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=5a608ccc2d676aa124f6b55a7b20d071e408ca31

commit 5a608ccc2d676aa124f6b55a7b20d071e408ca31
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Fri May 15 17:47:29 2015 +0000

    Fix tanf spurious underflows (bug 18221).

    The flt-32 implementation of tanf produces spurious underflow
    exceptions for some small arguments, through computing values on the
    order of x^5.  This patch fixes this by adjusting the threshold for
    returning x (or, as applicable, +/- 1/x) to 2**-13 (the next term in
    the power series being x^3/3).

    Tested for x86_64 and x86.

        [BZ #18221]
        * sysdeps/ieee754/flt-32/k_tanf.c (__kernel_tanf): Use 2**-13 not
        2**-28 as threshold for returning x or +/- 1/x.
        * math/auto-libm-test-in: Add more tests of tan.
        * math/auto-libm-test-out: Regenerated.

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

Summary of changes:
 ChangeLog                       |    6 ++++
 NEWS                            |    2 +-
 math/auto-libm-test-in          |    2 +
 math/auto-libm-test-out         |   50 +++++++++++++++++++++++++++++++++++++++
 sysdeps/ieee754/flt-32/k_tanf.c |    2 +-
 5 files changed, 60 insertions(+), 2 deletions(-)

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[Bug math/18221] tanf spurious underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18221

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #2 from Joseph Myers <jsm28 at gcc dot gnu.org> ---
Fixed for 2.22.

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