[Bug math/18196] New: atanf spurious underflows

[Bug math/18196] New: atanf spurious underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18196

            Bug ID: 18196
           Summary: atanf 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 sysdeps/ieee754/flt-32 version of atanf produces spurious underflow
exceptions for some large arguments.  For example, on x86_64, atanf (0x1p31f)
(whose result is very close to pi/2) produces such an exception.

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[Bug math/18196] atanf spurious underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18196

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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[Bug math/18196] atanf spurious underflows

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18196

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=9a71f1fcf53615c00b5f9e5da4bba92bccb0efb4

commit 9a71f1fcf53615c00b5f9e5da4bba92bccb0efb4
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Thu May 14 23:51:09 2015 +0000

    Fix atanf spurious underflows (bug 18196).

    The sysdeps/ieee754/flt-32 version of atanf produces spurious
    underflow exceptions for some large arguments, because of computations
    that compute x^-4.  This patch fixes this by adjusting the threshold
    for large arguments (for which +/- pi/2 can just be returned, the
    correct result being roughly +/- pi/2 - 1/x) from 2^34 to 2^25.

    Tested for x86_64 and x86.

        [BZ #18196]
        * sysdeps/ieee754/flt-32/s_atanf.c (__atanf): Use 2^25 not 2^34 as
        threshold for large arguments.
        * math/auto-libm-test-in: Add another test of atan.
        * math/auto-libm-test-out: Regenerated.

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

Summary of changes:
 ChangeLog                        |    6 ++++++
 NEWS                             |    4 ++--
 math/auto-libm-test-in           |    1 +
 math/auto-libm-test-out          |   25 +++++++++++++++++++++++++
 sysdeps/ieee754/flt-32/s_atanf.c |    2 +-
 5 files changed, 35 insertions(+), 3 deletions(-)

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