[Bug math/16361] New: x86 / x86_64 expl / exp10l missing underflows

[Bug math/16361] New: x86 / x86_64 expl / exp10l missing underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16361

            Bug ID: 16361
           Summary: x86 / x86_64 expl / exp10l missing underflows
           Product: glibc
           Version: 2.19
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: jsm28 at gcc dot gnu.org

The x86 and x86_64 implementations of expl / exp10l can fail to produce
underflow exceptions when the unscaled result has trailing 0 bits so the
scaling down to subnormal precision is exact.  An example at least with a patch
I'm testing for bug 16356 is exp10l (-4932) in round-to-zero mode (the precise
cases may depend on the x87 processor implementation).

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug math/16361] x86 / x86_64 expl / exp10l missing underflows

[zimmerma+gcc at loria dot fr]

https://sourceware.org/bugzilla/show_bug.cgi?id=16361

Paul Zimmermann <zimmerma+gcc at loria dot fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |zimmerma+gcc at loria dot fr

--- Comment #1 from Paul Zimmermann <zimmerma+gcc at loria dot fr> ---
another example is:

 rounding mode MPFR_RNDU:
      wrong underflow flag for x=-2.c5b2319c4843acc0@3
      library gives 3.fffffffffffffc88@-4096
      mpfr    gives 3.fffffffffffffc88@-4096
      underflow: mpfr 1, library 0

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug math/16361] [i386/x86_64] x86 / x86_64 expl / exp10l missing underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16361

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
               Host|                            |i?86-*-* x86_64-*-*
            Summary|x86 / x86_64 expl / exp10l  |[i386/x86_64] x86 / x86_64
                   |missing underflows          |expl / exp10l missing
                   |                            |underflows

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug math/16361] [i386/x86_64] x86 / x86_64 expl / exp10l missing underflows

[zimmerma+gcc at loria dot fr]

https://sourceware.org/bugzilla/show_bug.cgi?id=16361

--- Comment #2 from Paul Zimmermann <zimmerma+gcc at loria dot fr> ---
[the example in comment 1 was for exp]

here is an example for exp10:

Testing function exp10 for exponent 0 [seed=8344].
 rounding mode MPFR_RNDN:
      wrong underflow flag for x=-1.343793004f503232@3
      library gives 3.ffffffffffffcbf0@-4096
      mpfr    gives 3.ffffffffffffcbf0@-4096
      underflow: mpfr 1, library 0

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug math/16361] [i386/x86_64] x86 / x86_64 expl / exp10l missing underflows

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16361

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug math/16361] [i386/x86_64] x86 / x86_64 expl / exp10l missing underflows

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16361

--- Comment #3 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
This is an automated email from the git hooks/post-receive script. It was
generated because a ref change was pushed to the repository containing
the project "GNU C Library master sources".

The branch, master has been updated
       via  7540cfc5a8c39eca9ba7b631dd30b35f6530f54d (commit)
      from  d6cc0b4feaacf7514167cde0b3935f0c9b2c2d88 (commit)

Those revisions listed above that are new to this repository have
not appeared on any other notification email; so we list those
revisions in full, below.

- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=7540cfc5a8c39eca9ba7b631dd30b35f6530f54d

commit 7540cfc5a8c39eca9ba7b631dd30b35f6530f54d
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Sun Jun 21 17:48:04 2015 +0000

    Fix x86 / x86_64 expl, exp10l missing underflows (bug 16361).

    Similar to various other bugs in this area, the x86 and x86_64
    implementations of expl / exp10l can fail to produce underflow
    exceptions when the unscaled result has trailing 0 bits so the scaling
    down to subnormal precision is exact.  This patch fixes this by
    forcing the exception in the case of tiny results.

    Tested for x86_64 and x86.

        [BZ #16361]
        * sysdeps/i386/fpu/e_expl.S [!USE_AS_EXPM1L] (cmin): New object.
        [!USE_AS_EXPM1L] (IEEE754_EXPL): Force underflow exception for
        tiny results.
        * sysdeps/x86_64/fpu/e_expl.S [!USE_AS_EXPM1L] (cmin): New object.
        [!USE_AS_EXPM1L] (IEEE754_EXPL): Force underflow exception for
        tiny results.
        * math/auto-libm-test-in: Add more tests of exp and exp10.  Do not
        mark underflow exceptions as possibly missing for bug 16361.
        * math/auto-libm-test-out: Regenerated.

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

Summary of changes:
 ChangeLog                   |   13 ++
 NEWS                        |   28 +++---
 math/auto-libm-test-in      |    5 +-
 math/auto-libm-test-out     |  260 ++++++++++++++++++++++++++++++++++++++----
 sysdeps/i386/fpu/e_expl.S   |   16 +++-
 sysdeps/x86_64/fpu/e_expl.S |   15 +++-
 6 files changed, 294 insertions(+), 43 deletions(-)

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug math/16361] [i386/x86_64] x86 / x86_64 expl / exp10l missing underflows

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16361

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Joseph Myers <jsm28 at gcc dot gnu.org> ---
Fixed for 2.22.

-- 
You are receiving this mail because:
You are on the CC list for the bug.