[Bug math/18961] New: [i386] exp missing underflows

[Bug math/18961] New: [i386] exp missing underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18961

            Bug ID: 18961
           Summary: [i386] exp 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: ---
              Host: i?86-*-*

On i386, the double version of exp can miss underflow exceptions if the result
is in the subnormal range for double but the last 11 bits of the 64-bit
extended-precision mantissa happen to be zero.  E.g. (examples producing this
may vary depending on x86 implementations):

Failure: exp (-0x2.c469d9p+8): Exception "Underflow" not set
Failure: exp (-0x2.c46d96p+8): Exception "Underflow" not set
Failure: exp_downward (-0x2.c46727p+8): Exception "Underflow" not set
Failure: exp_downward (-0x2.c469dep+8): Exception "Underflow" not set
Failure: exp_downward (-0x2.c46c04p+8): Exception "Underflow" not set
Failure: exp_towardzero (-0x2.c46adep+8): Exception "Underflow" not set
Failure: exp_towardzero (-0x2.c471b3p+8): Exception "Underflow" not set
Failure: exp_upward (-0x2.c46993p+8): Exception "Underflow" not set

Failure: exp_towardzero (-0x2.c49fap+8): Exception "Underflow" not set
Failure: exp_towardzero (-0x2.c4ac1p+8): Exception "Underflow" not set
Failure: exp_towardzero (-0x2.c4d89p+8): Exception "Underflow" not set

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[Bug math/18961] [i386] exp missing underflows

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18961

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=de5e81691c80468ff97c5260b4020aeaecfe418d

commit de5e81691c80468ff97c5260b4020aeaecfe418d
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Mon Sep 14 22:40:05 2015 +0000

    Fix i386 exp missing underflows (bug 18961).

    On i386, the double version of exp can miss underflow exceptions if
    the result is in the subnormal range for double but the last 11 bits
    of the 64-bit extended-precision mantissa happen to be zero.  This
    patch forces the exception in a similar way to previous fixes.

    As with the exp2 fixes, the expf changes may in fact not be needed to
    ensure underflow exceptions, but are included for consistency and to
    fix the exp part of bug 18875 by ensuring that excess range and
    precision is removed from underflowing return values.

    Tested for x86_64 and x86.

        [BZ #18875]
        [BZ #18961]
        * sysdeps/i386/fpu/e_exp.S (dbl_min): New object.
        (MO): New macro.
        (__ieee754_exp): For small results, force underflow exception and
        remove excess range and precision from return value.
        (__exp_finite): Likewise.
        * sysdeps/i386/fpu/e_expf.S (flt_min): New object.
        (MO): New macro.
        (__ieee754_expf): For small results, force underflow exception and
        remove excess range and precision from return value.
        (__expf_finite): Likewise.
        * math/auto-libm-test-in: Add more tests of exp.
        * math/auto-libm-test-out: Regenerated.

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

Summary of changes:
 ChangeLog                 |   15 ++
 NEWS                      |    2 +-
 math/auto-libm-test-in    |   11 +
 math/auto-libm-test-out   |  583 +++++++++++++++++++++++++++++++++++++++++++++
 sysdeps/i386/fpu/e_exp.S  |   53 ++++-
 sysdeps/i386/fpu/e_expf.S |   53 ++++-
 6 files changed, 712 insertions(+), 5 deletions(-)

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[Bug math/18961] [i386] exp missing underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18961

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

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

--- Comment #2 from Joseph Myers <jsm28 at gcc dot gnu.org> ---
Fixed for 2.23.

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