[Bug math/16287] New: ldbl-128 erfl spurious underflows

[Bug math/16287] New: ldbl-128 erfl spurious underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16287

            Bug ID: 16287
           Summary: ldbl-128 erfl spurious underflows
           Product: glibc
           Version: 2.19
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: jsm28 at gcc dot gnu.org

This bug report is from inspection of the ldbl-128 s_erfl.c, not from runtime
testing.  erfl is implemented to call __erfcl for arguments with absolute value
at least 1.0.  For large arguments where __erfcl underflows, this will result
in spurious exceptions when the result of erfl is very close to 1 and doesn't
underflow itself.

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[Bug math/16287] ldbl-128 erfl spurious underflows

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16287

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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[Bug math/16287] ldbl-128 erfl spurious underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16287

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 2.20.

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[Bug math/16287] ldbl-128 erfl spurious underflows

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16287

--- 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  e7dd3c8c1db8c6d293abb995e033893b7328ad19 (commit)
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=e7dd3c8c1db8c6d293abb995e033893b7328ad19

commit e7dd3c8c1db8c6d293abb995e033893b7328ad19
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Jun 24 20:56:56 2014 +0000

    Fix ldbl-128 erfl spurious underflows (bug 16287).

    This patch fixes bug 16287, spurious underflows from ldbl-128 erfl
    arising from it calling erfcl for arguments with absolute value at
    least 1.0, although for large positive arguments erfcl correctly
    underflows but erfl shouldn't.  The fix is simply to avoid calling
    erfcl, and just return 1, for arguments above a cut-off large enough
    that erfl correctly rounds to-nearest as 1 but not so large that erfcl
    underflows.

    Tested mips64.  Also tested x86_64 and x86 to confirm the new tests
    (taken from the tests of erfc) don't cause any problems there; no ulps
    updates needed.

        [BZ #16287]
        * sysdeps/ieee754/ldbl-128/s_erfl.c (__erfl): Return 1 without
        calling __erfcl for arguments at least 16.
        * math/auto-libm-test-in: Add more tests of erf.
        * math/auto-libm-test-out: Regenerated.

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

Summary of changes:
 ChangeLog                         |    6 +
 NEWS                              |   24 ++--
 math/auto-libm-test-in            |   10 ++
 math/auto-libm-test-out           |  294 +++++++++++++++++++++++++++++++++++++
 sysdeps/ieee754/ldbl-128/s_erfl.c |    2 +
 5 files changed, 324 insertions(+), 12 deletions(-)

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