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[Bug math/20255] [i386] fdim, fdimf return with excess range and precision / double rounding


https://sourceware.org/bugzilla/show_bug.cgi?id=20255

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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=f4015c8a861803c128112ca41fc62817398bd1c0

commit f4015c8a861803c128112ca41fc62817398bd1c0
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Jun 14 16:04:19 2016 +0000

    Use generic fdim on more architectures (bug 6796, bug 20255, bug 20256).

    Some architectures have their own versions of fdim functions, which
    are missing errno setting (bug 6796) and may also return sNaN instead
    of qNaN for sNaN input, in the case of the x86 / x86_64 long double
    versions (bug 20256).

    These versions are not actually doing anything that a compiler
    couldn't generate, just straightforward comparisons / arithmetic (and,
    in the x86 / x86_64 case, testing for NaNs with fxam, which isn't
    actually needed once you use an unordered comparison and let the NaNs
    pass through the same subtraction as non-NaN inputs).  This patch
    removes the x86 / x86_64 / powerpc versions, so that those
    architectures use the generic C versions, which correctly handle
    setting errno and deal properly with sNaN inputs.  This seems better
    than dealing with setting errno in lots of .S versions.

    The i386 versions also return results with excess range and precision,
    which is not appropriate for a function exactly defined by reference
    to IEEE operations.  For errno setting to work correctly on overflow,
    it's necessary to remove excess range with math_narrow_eval, which
    this patch duly does in the float and double versions so that the
    tests can reliably pass on x86.  For float, this avoids any double
    rounding issues as the long double precision is more than twice that
    of float.  For double, double rounding issues will need to be
    addressed separately, so this patch does not fully fix bug 20255.

    Tested for x86_64, x86 and powerpc.

        [BZ #6796]
        [BZ #20255]
        [BZ #20256]
        * math/s_fdim.c: Include <math_private.h>.
        (__fdim): Use math_narrow_eval on result.
        * math/s_fdimf.c: Include <math_private.h>.
        (__fdimf): Use math_narrow_eval on result.
        * sysdeps/i386/fpu/s_fdim.S: Remove file.
        * sysdeps/i386/fpu/s_fdimf.S: Likewise.
        * sysdeps/i386/fpu/s_fdiml.S: Likewise.
        * sysdeps/i386/i686/fpu/s_fdim.S: Likewise.
        * sysdeps/i386/i686/fpu/s_fdimf.S: Likewise.
        * sysdeps/i386/i686/fpu/s_fdiml.S: Likewise.
        * sysdeps/powerpc/fpu/s_fdim.c: Likewise.
        * sysdeps/powerpc/fpu/s_fdimf.c: Likewise.
        * sysdeps/powerpc/powerpc32/fpu/s_fdim.c: Likewise.
        * sysdeps/powerpc/powerpc64/fpu/s_fdim.c: Likewise.
        * sysdeps/x86_64/fpu/s_fdiml.S: Likewise.
        * math/libm-test.inc (fdim_test_data): Expect errno setting on
        overflow.  Add sNaN tests.

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

Summary of changes:
 ChangeLog                              |   21 +++++++++++++
 math/libm-test.inc                     |   35 ++++++++++++++++++++-
 math/s_fdim.c                          |    3 +-
 math/s_fdimf.c                         |    3 +-
 sysdeps/i386/fpu/s_fdim.S              |   51 --------------------------------
 sysdeps/i386/fpu/s_fdimf.S             |   51 --------------------------------
 sysdeps/i386/fpu/s_fdiml.S             |   51 --------------------------------
 sysdeps/i386/i686/fpu/s_fdim.S         |   43 ---------------------------
 sysdeps/i386/i686/fpu/s_fdimf.S        |   43 ---------------------------
 sysdeps/i386/i686/fpu/s_fdiml.S        |   43 ---------------------------
 sysdeps/powerpc/fpu/s_fdim.c           |   30 ------------------
 sysdeps/powerpc/fpu/s_fdimf.c          |   26 ----------------
 sysdeps/powerpc/powerpc32/fpu/s_fdim.c |    5 ---
 sysdeps/powerpc/powerpc64/fpu/s_fdim.c |    5 ---
 sysdeps/x86_64/fpu/s_fdiml.S           |   43 ---------------------------
 15 files changed, 58 insertions(+), 395 deletions(-)
 delete mode 100644 sysdeps/i386/fpu/s_fdim.S
 delete mode 100644 sysdeps/i386/fpu/s_fdimf.S
 delete mode 100644 sysdeps/i386/fpu/s_fdiml.S
 delete mode 100644 sysdeps/i386/i686/fpu/s_fdim.S
 delete mode 100644 sysdeps/i386/i686/fpu/s_fdimf.S
 delete mode 100644 sysdeps/i386/i686/fpu/s_fdiml.S
 delete mode 100644 sysdeps/powerpc/fpu/s_fdim.c
 delete mode 100644 sysdeps/powerpc/fpu/s_fdimf.c
 delete mode 100644 sysdeps/powerpc/powerpc32/fpu/s_fdim.c
 delete mode 100644 sysdeps/powerpc/powerpc64/fpu/s_fdim.c
 delete mode 100644 sysdeps/x86_64/fpu/s_fdiml.S

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