[Bug math/18825] New: pow missing underflows

[Bug math/18825] New: pow missing underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18825

            Bug ID: 18825
           Summary: pow missing underflows
           Product: glibc
           Version: 2.22
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: jsm28 at gcc dot gnu.org
  Target Milestone: ---

pow functions can sometimes miss underflow exceptions.  E.g., for float on
x86_64:

Failure: pow (0x8p-152, 0xd.b5459p-4): Exception "Underflow" not set

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[Bug math/18825] pow missing underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18825

--- Comment #1 from Joseph Myers <jsm28 at gcc dot gnu.org> ---
For double on x86_64:

Failure: pow (0x8p-152, 0x7.1504fp+0): Exception "Underflow" not set

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[Bug math/18825] pow missing underflows

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18825

--- Comment #2 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  6ace39382120dd0668b2168591611f71b04ac8f3 (commit)
      from  5a9af6376d43b58c6545feb86002812a57956654 (commit)

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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6ace39382120dd0668b2168591611f71b04ac8f3

commit 6ace39382120dd0668b2168591611f71b04ac8f3
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Fri Sep 25 22:29:10 2015 +0000

    Fix pow missing underflows (bug 18825).

    Similar to various other bugs in this area, pow functions can fail to
    raise the underflow exception when the result is tiny and inexact but
    one or more low bits of the intermediate result that is scaled down
    (or, in the i386 case, converted from a wider evaluation format) are
    zero.  This patch forces the exception in a similar way to previous
    fixes, thereby concluding the fixes for known bugs with missing
    underflow exceptions currently filed in Bugzilla.

    Tested for x86_64, x86, mips64 and powerpc.

        [BZ #18825]
        * sysdeps/i386/fpu/i386-math-asm.h (FLT_NARROW_EVAL_UFLOW_NONNAN):
        New macro.
        (DBL_NARROW_EVAL_UFLOW_NONNAN): Likewise.
        (LDBL_CHECK_FORCE_UFLOW_NONNAN): Likewise.
        * sysdeps/i386/fpu/e_pow.S: Use DEFINE_DBL_MIN.
        (__ieee754_pow): Use DBL_NARROW_EVAL_UFLOW_NONNAN instead of
        DBL_NARROW_EVAL, reloading the PIC register as needed.
        * sysdeps/i386/fpu/e_powf.S: Use DEFINE_FLT_MIN.
        (__ieee754_powf): Use FLT_NARROW_EVAL_UFLOW_NONNAN instead of
        FLT_NARROW_EVAL.  Use separate return path for case when first
        argument is NaN.
        * sysdeps/i386/fpu/e_powl.S: Include <i386-math-asm.h>.  Use
        DEFINE_LDBL_MIN.
        (__ieee754_powl): Use LDBL_CHECK_FORCE_UFLOW_NONNAN, reloading the
        PIC register.
        * sysdeps/ieee754/dbl-64/e_pow.c (__ieee754_pow): Use
        math_check_force_underflow_nonneg.
        * sysdeps/ieee754/flt-32/e_powf.c (__ieee754_powf): Force
        underflow for subnormal result.
        * sysdeps/ieee754/ldbl-128/e_powl.c (__ieee754_powl): Likewise.
        * sysdeps/ieee754/ldbl-128ibm/e_powl.c (__ieee754_powl): Use
        math_check_force_underflow_nonneg.
        * sysdeps/x86/fpu/powl_helper.c (__powl_helper): Use
        math_check_force_underflow.
        * sysdeps/x86_64/fpu/x86_64-math-asm.h
        (LDBL_CHECK_FORCE_UFLOW_NONNAN): New macro.
        * sysdeps/x86_64/fpu/e_powl.S: Include <x86_64-math-asm.h>.  Use
        DEFINE_LDBL_MIN.
        (__ieee754_powl): Use LDBL_CHECK_FORCE_UFLOW_NONNAN.
        * math/auto-libm-test-in: Add more tests of pow.
        * math/auto-libm-test-out: Regenerated.

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

Summary of changes:
 ChangeLog                            |   35 +
 NEWS                                 |    6 +-
 math/auto-libm-test-in               |  145 ++
 math/auto-libm-test-out              | 3644 ++++++++++++++++++++++++++++++++++
 sysdeps/i386/fpu/e_pow.S             |    8 +-
 sysdeps/i386/fpu/e_powf.S            |   13 +-
 sysdeps/i386/fpu/e_powl.S            |    6 +
 sysdeps/i386/fpu/i386-math-asm.h     |   46 +
 sysdeps/ieee754/dbl-64/e_pow.c       |    2 +
 sysdeps/ieee754/flt-32/e_powf.c      |    7 +-
 sysdeps/ieee754/ldbl-128/e_powl.c    |    6 +-
 sysdeps/ieee754/ldbl-128ibm/e_powl.c |    1 +
 sysdeps/x86/fpu/powl_helper.c        |    1 +
 sysdeps/x86_64/fpu/e_powl.S          |    3 +
 sysdeps/x86_64/fpu/x86_64-math-asm.h |   13 +
 15 files changed, 3926 insertions(+), 10 deletions(-)

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[Bug math/18825] pow missing underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18825

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |2.23

--- Comment #3 from Joseph Myers <jsm28 at gcc dot gnu.org> ---
Fixed for 2.23.

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