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[Bug math/19848] powl(10,n) for n=-4,-5,-6,-7 is off by more than 1 ULP


https://sourceware.org/bugzilla/show_bug.cgi?id=19848

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c898991d8bcfacc825097ba389ffccc5367c2b2d

commit c898991d8bcfacc825097ba389ffccc5367c2b2d
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Thu Mar 24 01:32:52 2016 +0000

    Fix x86_64 / x86 powl inaccuracy for integer exponents (bug 19848).

    Bug 19848 reports cases where powl on x86 / x86_64 has error
    accumulation, for small integer exponents, larger than permitted by
    glibc's accuracy goals, at least in some rounding modes.  This patch
    further restricts the exponent range for which the
    small-integer-exponent logic is used to limit the possible error
    accumulation.

    Tested for x86_64 and x86 and ulps updated accordingly.

        [BZ #19848]
        * sysdeps/i386/fpu/e_powl.S (p3): Rename to p2 and change value
        from 8 to 4.
        (__ieee754_powl): Compare integer exponent against 4 not 8.
        * sysdeps/x86_64/fpu/e_powl.S (p3): Rename to p2 and change value
        from 8 to 4.
        (__ieee754_powl): Compare integer exponent against 4 not 8.
        * math/auto-libm-test-in: Add more tests of pow.
        * math/auto-libm-test-out: Regenerated.
        * sysdeps/i386/i686/fpu/multiarch/libm-test-ulps: Update.
        * sysdeps/x86_64/fpu/libm-test-ulps: Likewise.

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

Summary of changes:
 ChangeLog                                      |   14 +
 math/auto-libm-test-in                         |   38 +
 math/auto-libm-test-out                        | 2555 ++++++++++++++++++++++++
 sysdeps/i386/fpu/e_powl.S                      |   10 +-
 sysdeps/i386/i686/fpu/multiarch/libm-test-ulps |    8 +-
 sysdeps/x86_64/fpu/e_powl.S                    |   16 +-
 sysdeps/x86_64/fpu/libm-test-ulps              |    8 +-
 7 files changed, 2628 insertions(+), 21 deletions(-)

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