[Bug math/18823] New: csqrt spurious underflows

[Bug math/18823] New: csqrt spurious underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18823

            Bug ID: 18823
           Summary: csqrt spurious 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: ---

csqrt functions can produce spurious underflow exceptions.  E.g., for float on
x86_64:

Failure: Real part of: csqrt (0x8p-152 + 0x5.70b56p-128 i): Exception
"Underflow" set

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[Bug math/18823] csqrt spurious underflows

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18823

--- 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=3fb4cfaf1f1e8d58312720c70d224e2050d469fc

commit 3fb4cfaf1f1e8d58312720c70d224e2050d469fc
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Mon Aug 17 23:02:54 2015 +0000

    Fix csqrt spurious underflows (bug 18823).

    The csqrt functions scale up small arguments to avoid underflows when
    calling hypot functions.  However, even when hypot does not underflow,
    a subsequent calculation of 0.5 * hypot can underflow.  This patch
    duly increases the threshold and scale factor to avoid such underflows
    as well.

    Tested for x86_64, x86 and mips64.

        [BZ #18823]
        * math/s_csqrt.c (__csqrt): Increase threshold and scale factor
        for scaling up small arguments.
        * math/s_csqrtf.c (__csqrtf): Likewise.
        * math/s_csqrtl.c (__csqrtl): Likewise.
        * math/auto-libm-test-in: Add more tests of csqrt.
        * math/auto-libm-test-out: Regenerated.

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

Summary of changes:
 ChangeLog               |   10 +
 NEWS                    |    2 +-
 math/auto-libm-test-in  |    9 +
 math/auto-libm-test-out | 1832 +++++++++++++++++++++++++++++++++++++++++++++++
 math/s_csqrt.c          |    6 +-
 math/s_csqrtf.c         |    6 +-
 math/s_csqrtl.c         |    6 +-
 7 files changed, 1861 insertions(+), 10 deletions(-)

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[Bug math/18823] csqrt spurious underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18823

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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