[Bug math/16539] New: spurious underflow exception from expm1

[Bug math/16539] New: spurious underflow exception from expm1

[zimmerma+gcc at loria dot fr]

https://sourceware.org/bugzilla/show_bug.cgi?id=16539

            Bug ID: 16539
           Summary: spurious underflow exception from expm1
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: zimmerma+gcc at loria dot fr

this example (in extended precision) gives a spurious underflow:

Testing function expm1 for exponent 0 [seed=8344].
 rounding mode MPFR_RNDN:
      wrong underflow flag for x=4.0000000000000028@-4096
      library gives 4.0000000000000028@-4096
      mpfr    gives 4.0000000000000028@-4096
      underflow: mpfr 0, library 16

Note the glibc result is *above* the smallest subnormal 0x1p-16382, thus no
exception should be raised.

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[Bug math/16539] spurious underflow exception from expm1

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16539

Florian Weimer <fweimer at redhat dot com> changed:

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

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[Bug math/16539] spurious underflow exception from expm1

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16539

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/16539] spurious underflow exception from expm1

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16539

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
This is an automated email from the git hooks/post-receive script. It was
generated because a ref change was pushed to the repository containing
the project "GNU C Library master sources".

The branch, master has been updated
       via  4060283decf711ed95a6c4993ffeaba39f8cd40a (commit)
      from  e7dd3c8c1db8c6d293abb995e033893b7328ad19 (commit)

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=4060283decf711ed95a6c4993ffeaba39f8cd40a

commit 4060283decf711ed95a6c4993ffeaba39f8cd40a
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Jun 24 21:00:08 2014 +0000

    Fix x86/x86_64 expm1l spurious underflow exceptions (bug 16539).

    This patch fixes bug 16539, spurious underflow exceptions from x86 /
    x86-64 expm1l.  The problem is that the computation of a base-2
    exponent with extra precision involves spurious underflows for
    arguments that are small but not subnormal, so a check is added to
    just return the argument in those cases.  (If the argument *is*
    subnormal, underflowing is correct and the existing code will always
    underflow, so it suffices to keep using the existing code in that
    case; some expm1 implementations have a bug (bug 16353) with missing
    underflow exceptions, but I don't think there's such a bug in this
    particular version.)

    Tested x86_64 and x86; no ulps updates needed.

    (auto-libm-test-out diffs omitted below.)

        [BZ #16539]
        * sysdeps/i386/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]: Just
        return the argument for normal arguments with exponent below -64.
        * sysdeps/x86_64/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]:
        Likewise.
        * math/auto-libm-test-in: Add another test of expm1.
        * math/auto-libm-test-out: Regenerated.

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

Summary of changes:
 ChangeLog                   |    8 ++++
 NEWS                        |   22 ++++++------
 math/auto-libm-test-in      |    2 +
 math/auto-libm-test-out     |   81 +++++++++++++++++++++++++++++++++++++++++++
 sysdeps/i386/fpu/e_expl.S   |   10 +++++
 sysdeps/x86_64/fpu/e_expl.S |   10 +++++
 6 files changed, 122 insertions(+), 11 deletions(-)

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[Bug math/16539] spurious underflow exception from expm1

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16539

--- Comment #3 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
This is an automated email from the git hooks/post-receive script. It was
generated because a ref change was pushed to the repository containing
the project "GNU C Library master sources".

The branch, master has been updated
       via  ce9c5b3e955746a9187ffde9b16feea4a357c86a (commit)
      from  3a6e988706d1ce2c88c933619d1f312098698ecd (commit)

Those revisions listed above that are new to this repository have
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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=ce9c5b3e955746a9187ffde9b16feea4a357c86a

commit ce9c5b3e955746a9187ffde9b16feea4a357c86a
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Mon Jun 30 17:38:16 2014 +0000

    Fix ldbl-128 expm1l spurious underflow (bug 16539).

    This patch fixes spurious underflows from ldbl-128 expm1l, as reported
    in <https://sourceware.org/ml/libc-alpha/2014-06/msg00835.html> and
    exposed by the tests added for such a bug in the x86 / x86-64
    version.  The bug and fix are essentially the same, so no separate bug
    is filed in Bugzilla.

    Tested for mips64.

        [BZ #16539]
        * sysdeps/ieee754/ldbl-128/s_expm1l.c: Include <float.h>.
        (__expm1l): Return argument unchanged when small but not
        subnormal.

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

Summary of changes:
 ChangeLog                           |    5 +++++
 sysdeps/ieee754/ldbl-128/s_expm1l.c |    5 +++++
 2 files changed, 10 insertions(+), 0 deletions(-)

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