[Bug math/16677] New: nextafter incorrect in directed rounding modes

[Bug math/16677] New: nextafter incorrect in directed rounding modes

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16677

            Bug ID: 16677
           Summary: nextafter incorrect in directed rounding modes
           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

At least some nextafter implementations compute an overflowing result as x + x
to raise the overflow exception.  However, the result must be independent of
the rounding mode (C11 F.10.8.3); the exception is correct, the finite value in
some rounding modes isn't.  E.g., on x86_64 for float:

testing float (without inline functions)
Failure: Test: nextafter_downward (max_value, inf)
Result:
 is:          3.40282346638528859811e+38   0x1.fffffe00000000000000p+127
 should be:   inf   inf
Failure: Test: nextafter_towardzero (max_value, inf)
Result:
 is:          3.40282346638528859811e+38   0x1.fffffe00000000000000p+127
 should be:   inf   inf
Failure: Test: nextafter_towardzero (-max_value, -inf)
Result:
 is:         -3.40282346638528859811e+38  -0x1.fffffe00000000000000p+127
 should be:  -inf  -inf
Failure: Test: nextafter_upward (-max_value, -inf)
Result:
 is:         -3.40282346638528859811e+38  -0x1.fffffe00000000000000p+127
 should be:  -inf  -inf

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[Bug math/16677] nextafter incorrect in directed rounding modes

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16677

--- 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=e9996ef750d845b46bc7d743c730c73f044720af

commit e9996ef750d845b46bc7d743c730c73f044720af
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Sat Mar 8 14:08:38 2014 +0000

    Add libm-test.inc macro for all-rounding-modes testing.

    This patch adds support in libm-test.inc for automatically running
    tests of a function in all rounding modes, in the form of a macro
    ALL_RM_TEST to loop over all rounding modes when running tests of a
    function, and uses it for functions whose results should always be
    independent of the rounding mode.

    Conversion of tests of nextafter to ALL_RM_TEST was deferred because
    trying that conversion showed up bug 16677.  (Finding such a bug of
    course illustrates the point of testing more systematically in all
    rounding modes rather than only reactively when bugs get reported in a
    particular function in a non-default mode.)  Conversion of tests where
    results can depend on the rounding mode will follow once I add
    gen-libm-test.pl support for using different initializers for the
    expected results for different rounding modes (again, some conversions
    may need deferring until bugs are fixed, depending on how
    straightforward they are to XFAIL in a particular context).

    Some existing tests get run five times rather than four, with
    round-to-nearest tests both run in that as default rounding mode and
    also with it explicitly set with fesetround (FE_TONEAREST).  This
    duplication doesn't seem particularly useful, so ALL_RM_TEST only runs
    tests four times.

    Tested x86_64 and x86.

        * math/libm-test.inc (ALL_RM_TEST): New macro.
        (ceil_test): Use ALL_RM_TEST.
        (cimag_test): Likewise.
        (conj_test): Likewise.
        (copysign_test): Likewise.
        (cproj_test): Likewise.
        (creal_test): Likewise.
        (fabs_test): Likewise.
        (floor_test): Likewise.
        (fmax_test): Likewise.
        (fmin_test): Likewise.
        (fmod_test): Likewise.
        (fpclassify_test): Likewise.
        (frexp_test): Likewise.
        (ilogb_test): Likewise.
        (isfinite_test): Likewise.
        (finite_test): Likewise.
        (isgreater_test): Likewise.
        (isgreaterequal_test): Likewise.
        (isinf_test): Likewise.
        (isless_test): Likewise.
        (islessequal_test): Likewise.
        (islessgreater_test): Likewise.
        (isnan_test): Likewise.
        (isnormal_test): Likewise.
        (issignaling_test): Likewise.
        (isunordered_test): Likewise.
        (logb_test): Likewise.
        (logb_downward_test_data): Remove.
        (logb_test_downward): Likewise.
        (lround_test): Use ALL_RM_TEST.
        (llround_test): Likewise.
        (modf_test): Likewise.
        (nexttoward_test): Likewise.
        (remainder_test): Likewise.
        (drem_test): Likewise.
        (remainder_tonearest_test_data): Likewise.
        (remainder_test_tonearest): Likewise.
        (drem_test_tonearest): Likewise.
        (remainder_towardzero_test_data): Likewise.
        (remainder_test_towardzero): Likewise.
        (drem_test_towardzero): Likewise.
        (remainder_downward_test_data): Likewise.
        (remainder_test_downward): Likewise.
        (drem_test_downward): Likewise.
        (remainder_upward_test_data): Likewise.
        (remainder_test_upward): Likewise.
        (drem_test_upward): Likewise.
        (remquo_test): Use ALL_RM_TEST.  Remove comment about x.
        (round_test): Use ALL_RM_TEST.
        (signbit_test): Likewise.
        (trunc_test): Likewise.
        (significand_test): Likewise.
        (main): Don't call removed functions.

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

Summary of changes:
 ChangeLog          |   57 ++++++++
 math/libm-test.inc |  398 ++++++++++------------------------------------------
 2 files changed, 130 insertions(+), 325 deletions(-)

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[Bug math/16677] nextafter incorrect in directed rounding modes

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16677

--- Comment #2 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
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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=600fa36158cd741d897b2d22c735c60247b982e0

commit 600fa36158cd741d897b2d22c735c60247b982e0
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Mar 11 22:24:00 2014 +0000

    Fix nextafter overflow in non-default rounding modes (bug 16677).

    ISO C requires the result of nextafter to be independent of the
    rounding mode, even when underflow or overflow occurs.  This patch
    fixes the bug in various nextafter implementations that, having done
    an overflowing computation to force an overflow exception (correct),
    they then return the result of that computation rather than an
    infinity computed some other way (incorrect, when the overflowing
    result of arithmetic with that sign and rounding mode is finite but
    the correct result is infinite) - generally by falling through to
    existing code to return a value that in fact is correct for this case
    (but was computed by an integer increment and so without generating
    the exceptions required).  Having fixed the bug, the previously
    deferred conversion of nextafter testing in libm-test.inc to
    ALL_RM_TEST is also included.

    Tested x86_64 and x86; also spot-checked results of nextafter tests
    for powerpc32 and mips64 to test the ldbl-128ibm and ldbl-128
    changes.  (The m68k change is untested.)

        [BZ #16677]
        * math/s_nextafter.c (__nextafter): Do not return value from
        overflowing computation.
        * sysdeps/i386/fpu/s_nextafterl.c (__nextafterl): Likewise.
        * sysdeps/ieee754/flt-32/s_nextafterf.c (__nextafterf): Likewise.
        * sysdeps/ieee754/ldbl-128/s_nextafterl.c (__nextafterl):
        Likewise.
        * sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c (__nextafterl):
        Likewise.
        * sysdeps/m68k/m680x0/fpu/s_nextafterl.c (__nextafterl): Likewise.
        * math/libm-test.inc (nextafter_test): Use ALL_RM_TEST.

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

Summary of changes:
 ChangeLog                                  |   14 ++++++++++++++
 NEWS                                       |    2 +-
 math/libm-test.inc                         |    5 +----
 math/s_nextafter.c                         |    6 ++----
 sysdeps/i386/fpu/s_nextafterl.c            |    5 ++++-
 sysdeps/ieee754/flt-32/s_nextafterf.c      |    6 ++----
 sysdeps/ieee754/ldbl-128/s_nextafterl.c    |    5 ++++-
 sysdeps/ieee754/ldbl-128ibm/s_nextafterl.c |   14 ++++++++++----
 sysdeps/m68k/m680x0/fpu/s_nextafterl.c     |    5 ++++-
 9 files changed, 42 insertions(+), 20 deletions(-)

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[Bug math/16677] nextafter incorrect in directed rounding modes

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16677

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

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

--- Comment #3 from Joseph Myers <jsm28 at gcc dot gnu.org> ---
Fixed for 2.20.

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[Bug math/16677] nextafter incorrect in directed rounding modes

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16677

Florian Weimer <fweimer at redhat dot com> changed:

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

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[Bug math/16677] nextafter incorrect in directed rounding modes

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16677

--- Comment #5 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
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The branch, master has been updated
       via  59a63cca1133a8e1e3219970ee95979ac1f810df (commit)
      from  ef6b619f73e49b6d87c7530e6e9f8a59723b492d (commit)

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commit 59a63cca1133a8e1e3219970ee95979ac1f810df
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Fri Oct 2 17:11:13 2015 +0000

    Fix nexttoward overflow in non-default rounding modes (bug 19059).

    ISO C requires overflowing results from nexttoward to be the
    appropriate infinity independent of the rounding mode, but some
    implementations use a rounding-mode-dependent result (this is the same
    issue as was fixed for nextafter in bug 16677).  This patch fixes the
    problem by making the nexttoward implementations discard the result
    from the floating-point computation that forced an overflow exception
    and then return the infinity previously computed with integer
    arithmetic.

    Tested for x86_64, x86, mips64 and powerpc.

        [BZ #19059]
        * math/s_nexttowardf.c (__nexttowardf): Do not return value from
        overflowing computation.
        * sysdeps/i386/fpu/s_nexttoward.c (__nexttoward): Likewise.
        * sysdeps/i386/fpu/s_nexttowardf.c (__nexttowardf): Likewise.
        * sysdeps/ieee754/ldbl-128/s_nexttoward.c (__nexttoward):
        Likewise.
        * sysdeps/ieee754/ldbl-128/s_nexttowardf.c (__nexttowardf):
        Likewise.
        * sysdeps/ieee754/ldbl-128ibm/s_nexttoward.c (__nexttoward):
        Likewise.
        * sysdeps/ieee754/ldbl-128ibm/s_nexttowardf.c (__nexttowardf):
        Likewise.
        * sysdeps/ieee754/ldbl-96/s_nexttoward.c (__nexttoward): Likewise.
        * sysdeps/ieee754/ldbl-96/s_nexttowardf.c (__nexttowardf):
        Likewise.
        * sysdeps/ieee754/ldbl-opt/s_nexttowardfd.c (__nldbl_nexttowardf):
        Likewise.
        * math/libm-test.inc (nexttoward_test_data): Add more tests.

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

Summary of changes:
 ChangeLog                                   |   20 ++++++++++++++++++++
 NEWS                                        |    2 +-
 math/libm-test.inc                          |    4 ++++
 math/s_nexttowardf.c                        |    4 ++--
 sysdeps/i386/fpu/s_nexttoward.c             |    4 ++--
 sysdeps/i386/fpu/s_nexttowardf.c            |    4 ++--
 sysdeps/ieee754/ldbl-128/s_nexttoward.c     |    4 ++--
 sysdeps/ieee754/ldbl-128/s_nexttowardf.c    |    5 ++++-
 sysdeps/ieee754/ldbl-128ibm/s_nexttoward.c  |    4 ++--
 sysdeps/ieee754/ldbl-128ibm/s_nexttowardf.c |    4 ++--
 sysdeps/ieee754/ldbl-96/s_nexttoward.c      |    4 ++--
 sysdeps/ieee754/ldbl-96/s_nexttowardf.c     |    4 ++--
 sysdeps/ieee754/ldbl-opt/s_nexttowardfd.c   |    4 ++--
 13 files changed, 47 insertions(+), 20 deletions(-)

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