[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).

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[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

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[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

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[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

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[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-

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[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.

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[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
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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
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- 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(-)

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