[Bug math/18619] New: [ldbl-128] expm1l wrong sign of underflowing zero results

[Bug math/18619] New: [ldbl-128] expm1l wrong sign of underflowing zero results

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18619

            Bug ID: 18619
           Summary: [ldbl-128] expm1l wrong sign of underflowing zero
                    results
           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
  Target Milestone: ---

Similar to bug 18569 for x86 / x86_64, in the ldbl-128 implementation of
expm1l, when expm1l's result should underflow to 0, it can be a zero of the
wrong sign.

Failure: Test: expm1_upward (-0x4p-16496)
Result:
 is:          0.00000000000000000000e+00   0x0.00000000000000000000p+0
 should be:  -0.00000000000000000000e+00  -0x0.00000000000000000000p+0
 difference:  0.00000000000000000000e+00   0x0.00000000000000000000p+0
 ulp       :  0.0000
 max.ulp   :  3.0000

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[Bug math/18619] [ldbl-128] expm1l wrong sign of underflowing zero results

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18619

--- 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=a04bb3306a9f9f17e5c588c903a438f1182ecd1a

commit a04bb3306a9f9f17e5c588c903a438f1182ecd1a
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed Jul 1 22:27:49 2015 +0000

    Fix ldbl-128 expm1l (-min_subnorm) result sign (bug 18619).

    In the ldbl-128 implementation of expm1l, when expm1l's result should
    underflow to 0 (argument minus the least subnormal, in some rounding
    modes), it can be a zero of the wrong sign.  This patch fixes this in
    the same way previously used for the x86 / x86_64 versions.

    Tested for mips64.

        [BZ #18619]
        * sysdeps/ieee754/ldbl-128/s_expm1l.c (__expm1l): Force underflow
        and return argument in case of subnormal argument.

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

Summary of changes:
 ChangeLog                           |    6 ++++++
 NEWS                                |    2 +-
 sysdeps/ieee754/ldbl-128/s_expm1l.c |   15 ++++++++++++---
 3 files changed, 19 insertions(+), 4 deletions(-)

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[Bug math/18619] [ldbl-128] expm1l wrong sign of underflowing zero results

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18619

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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