[Bug math/18803] New: [i386] hypot missing underflows

[Bug math/18803] New: [i386] hypot missing underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18803

            Bug ID: 18803
           Summary: [i386] hypot 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-*-*

The i386 version of hypot can sometimes miss underflow exceptions, e.g.:

Failure: hypot (-0x3.75bd8eea2718p-1028, -0x4p-1076): Exception "Underflow" not 
set
Failure: hypot (-0x3.75bd8eea271cp-1028, -0x4p-1076): Exception "Underflow" not 
set

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[Bug math/18803] hypot missing underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18803

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
               Host|i?86-*-*                    |
            Summary|[i386] hypot missing        |hypot missing underflows
                   |underflows                  |

--- Comment #1 from Joseph Myers <jsm28 at gcc dot gnu.org> ---
In fact this is not restricted to i386; on x86_64:

Failure: hypot (0x1.7ac2de1p-1044, 0x4p-1076): Exception "Underflow" not set

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[Bug math/18803] hypot missing underflows

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18803

--- Comment #2 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=f6987f5aa4c2ef7270bcb0a828808bd3db53520b

commit f6987f5aa4c2ef7270bcb0a828808bd3db53520b
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Thu Sep 24 23:43:57 2015 +0000

    Fix hypot missing underflows (bug 18803).

    Similar to various other bugs in this area, hypot 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.

    Note that this issue cannot arise for implementations of hypotf using
    double (or wider) for intermediate evaluation (if hypotf should
    underflow, that means the double square root is being computed of some
    number of the form N*2^-298, for 0 < N < 2^46, which is exactly
    represented as a double, and whatever the rounding mode such a square
    root cannot have a mantissa with all zeroes after the initial 23
    bits).  Thus no changes are made to hypotf implementations in this
    patch, only to hypot and hypotl.

    Tested for x86_64, x86, mips64 and powerpc.

        [BZ #18803]
        * sysdeps/i386/fpu/e_hypot.S: Use DEFINE_DBL_MIN.
        (MO): New macro.
        (__ieee754_hypot) [PIC]: Load PIC register.
        (__ieee754_hypot): Use DBL_NARROW_EVAL_UFLOW_NONNEG instead of
        DBL_NARROW_EVAL.
        * sysdeps/ieee754/dbl-64/e_hypot.c (__ieee754_hypot): Use
        math_check_force_underflow_nonneg in case where result might be
        tiny.
        * sysdeps/ieee754/ldbl-128/e_hypotl.c (__ieee754_hypotl):
        Likewise.
        * sysdeps/ieee754/ldbl-128ibm/e_hypotl.c (__ieee754_hypotl):
        Likewise.
        * sysdeps/ieee754/ldbl-96/e_hypotl.c (__ieee754_hypotl): Likewise.
        * sysdeps/powerpc/fpu/e_hypot.c (__ieee754_hypot): Likewise.
        * math/auto-libm-test-in: Add more tests of hypot.
        * math/auto-libm-test-out: Regenerated.

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

Summary of changes:
 ChangeLog                              |   20 +
 NEWS                                   |    6 +-
 math/auto-libm-test-in                 |    7 +
 math/auto-libm-test-out                | 1342 ++++++++++++++++++++++++++++++++
 sysdeps/i386/fpu/e_hypot.S             |   13 +-
 sysdeps/ieee754/dbl-64/e_hypot.c       |    4 +-
 sysdeps/ieee754/ldbl-128/e_hypotl.c    |    4 +-
 sysdeps/ieee754/ldbl-128ibm/e_hypotl.c |    6 +-
 sysdeps/ieee754/ldbl-96/e_hypotl.c     |    4 +-
 sysdeps/powerpc/fpu/e_hypot.c          |    4 +-
 10 files changed, 1401 insertions(+), 9 deletions(-)

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[Bug math/18803] hypot missing underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18803

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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