[Bug math/18602] New: jn tests inaccuracy in non-default rounding modes

[Bug math/18602] New: jn tests inaccuracy in non-default rounding modes

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18602

            Bug ID: 18602
           Summary: jn tests inaccuracy in non-default rounding modes
           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: ---

Some existing jn tests, if run in non-default rounding modes, produce errors
above those accepted in glibc.  For example, for double on x86_64:

Failure: Test: jn_towardzero (10, 0xap+0)
Result:
 is:          2.07486106633358258211e-01   0x1.a8ee79d2eac9a0000000p-3
 should be:   2.07486106633358841078e-01   0x1.a8ee79d2eacaf0000000p-3
 difference:  5.82867087928207183722e-16   0x1.50000000000000000000p-51
 ulp       :  21.0000
 max.ulp   :  0.0000

This bug report is specifically *only* about those cases, already in the
testsuite.  It is not about the more general inaccuracy of all the Bessel
function implementations, including in round-to-nearest mode.

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[Bug math/18602] jn tests inaccuracy in non-default rounding modes

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18602

--- 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  a8e2112ae3e57fae592d84af2936a61d6239a248 (commit)
      from  037e4b993fe03d33055f92dddf7242abd9f6d1de (commit)

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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=a8e2112ae3e57fae592d84af2936a61d6239a248

commit a8e2112ae3e57fae592d84af2936a61d6239a248
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Thu Jun 25 21:46:02 2015 +0000

    Use round-to-nearest internally in jn, test with ALL_RM_TEST (bug 18602).

    Some existing jn tests, if run in non-default rounding modes, produce
    errors above those accepted in glibc, which causes problems for moving
    tests of jn to use ALL_RM_TEST.  This patch makes jn set rounding
    to-nearest internally, as was done for yn some time ago, then computes
    the appropriate underflowing value for results that underflowed to
    zero in to-nearest, and moves the tests to ALL_RM_TEST.  It does
    nothing about the general inaccuracy of Bessel function
    implementations in glibc, though it should make jn more accurate on
    average in non-default rounding modes through reduced error
    accumulation.  The recomputation of results that underflowed to zero
    should as a side-effect fix some cases of bug 16559, where jn just
    used an exact zero, but that is *not* the goal of this patch and other
    cases of that bug remain unfixed.

    (Most of the changes in the patch are reindentation to add new scopes
    for SET_RESTORE_ROUND*.)

    Tested for x86_64, x86, powerpc and mips64.

        [BZ #16559]
        [BZ #18602]
        * sysdeps/ieee754/dbl-64/e_jn.c (__ieee754_jn): Set
        round-to-nearest internally then recompute results that
        underflowed to zero in the original rounding mode.
        * sysdeps/ieee754/flt-32/e_jnf.c (__ieee754_jnf): Likewise.
        * sysdeps/ieee754/ldbl-128/e_jnl.c (__ieee754_jnl): Likewise.
        * sysdeps/ieee754/ldbl-128ibm/e_jnl.c (__ieee754_jnl): Likewise.
        * sysdeps/ieee754/ldbl-96/e_jnl.c (__ieee754_jnl): Likewise
        * math/libm-test.inc (jn_test): Use ALL_RM_TEST.
        * sysdeps/i386/fpu/libm-test-ulps: Update.
        * sysdeps/x86_64/fpu/libm-test-ulps: Likewise.

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

Summary of changes:
 ChangeLog                           |   15 ++
 NEWS                                |    2 +-
 math/libm-test.inc                  |    4 +-
 sysdeps/i386/fpu/libm-test-ulps     |   24 +++
 sysdeps/ieee754/dbl-64/e_jn.c       |  312 +++++++++++++++--------------
 sysdeps/ieee754/flt-32/e_jnf.c      |   11 +-
 sysdeps/ieee754/ldbl-128/e_jnl.c    |  374 +++++++++++++++++-----------------
 sysdeps/ieee754/ldbl-128ibm/e_jnl.c |  374 +++++++++++++++++-----------------
 sysdeps/ieee754/ldbl-96/e_jnl.c     |  380 ++++++++++++++++++-----------------
 sysdeps/x86_64/fpu/libm-test-ulps   |   24 +++
 10 files changed, 806 insertions(+), 714 deletions(-)

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[Bug math/18602] jn tests inaccuracy in non-default rounding modes

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18602

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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