[Bug math/17987] New: remquo bad sign of zero remainder in round-downward mode

[Bug math/17987] New: remquo bad sign of zero remainder in round-downward mode

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=17987

            Bug ID: 17987
           Summary: remquo bad sign of zero remainder in round-downward
                    mode
           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

Various remquo implementations produce a zero remainder with the wrong sign (a
zero remainder should always have the sign of the first argument, as specified
in IEEE 754) in round-downward mode, e.g. for double on x86_64:

Failure: Test: remquo_downward (2, 1)
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   :  0.0000

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[Bug math/17987] remquo bad sign of zero remainder in round-downward mode

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=17987

--- 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  ce8fc784e619ada624dc41ed7603211131e66573 (commit)
      from  0d7036bdb189a1ecb4232101ff83c6dd72439545 (commit)

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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=ce8fc784e619ada624dc41ed7603211131e66573

commit ce8fc784e619ada624dc41ed7603211131e66573
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Feb 17 00:41:50 2015 +0000

    Fix sign of remquo zero remainder in round-downward mode (bug 17987).

    Various remquo implementations produce a zero remainder with the wrong
    sign (a zero remainder should always have the sign of the first
    argument, as specified in IEEE 754) in round-downward mode, resulting
    from the sign of 0 - 0.  This patch checks for zero results and fixes
    their sign accordingly.

    Tested for x86_64, x86, mips64 and powerpc.

        [BZ #17987]
        * sysdeps/ieee754/dbl-64/s_remquo.c (__remquo): Ensure sign of
        zero result does not depend on the sign resulting from
        subtraction.
        * sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c (__remquo):
        Likewise.
        * sysdeps/ieee754/flt-32/s_remquof.c (__remquof): Likewise.
        * sysdeps/ieee754/ldbl-128/s_remquol.c (__remquol): Likewise.
        * sysdeps/ieee754/ldbl-128ibm/s_remquol.c (__remquol): Likewise.
        * sysdeps/ieee754/ldbl-96/s_remquol.c (__remquol): Likewise.
        * math/libm-test.inc (remquo_test_data): Add more tests.

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

Summary of changes:
 ChangeLog                                     |   14 ++++++++++++++
 NEWS                                          |    2 +-
 math/libm-test.inc                            |   10 ++++++++++
 sysdeps/ieee754/dbl-64/s_remquo.c             |    3 +++
 sysdeps/ieee754/dbl-64/wordsize-64/s_remquo.c |    3 +++
 sysdeps/ieee754/flt-32/s_remquof.c            |    3 +++
 sysdeps/ieee754/ldbl-128/s_remquol.c          |    3 +++
 sysdeps/ieee754/ldbl-128ibm/s_remquol.c       |    3 +++
 sysdeps/ieee754/ldbl-96/s_remquol.c           |    3 +++
 9 files changed, 43 insertions(+), 1 deletions(-)

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[Bug math/17987] remquo bad sign of zero remainder in round-downward mode

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=17987

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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