[Bug math/16447] erfc (0x6.a8p+4) ldbl-128 throws underflow exception

[Bug math/16447] erfc (0x6.a8p+4) ldbl-128 throws underflow exception

[joseph at codesourcery dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=16447

--- Comment #2 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
I would say that the calculation of "unsafe" (which determines whether 
there is a final scaling step) should be adjusted to count a wider range 
of cases as unsafe - any case where the problem multiplication might 
underflow.

Note that since this has been tracked to a problem with expl, any fix 
should add a corresponding expl input showing the problem as an exp test 
in auto-libm-test-in, rather than only testing the problem indirectly 
through erfc.

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[Bug math/16447] erfc (0x6.a8p+4) ldbl-128 throws underflow exception

[stli at linux dot vnet.ibm.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16447

--- Comment #3 from Stefan Liebler <stli at linux dot vnet.ibm.com> ---
I´ve posted a patch for the exp testcase (expl(-11342.8125)).
I´ve also tested a wider unsafe-check:
unsafe = abs(n_i) >= -16363; 
//unsafe = abs(n_i) >= -LDBL_MIN_EXP - 1;
Then the testcase passes on S/390.
LDBL_MIN_EXP expands to -16381 on S/390.

A small test on S/390 shows that 
expl(-11341.99999L) works as expected, but with
expl(-11341.999999L) the result is same as expl(-11342.8125).
In both cases n_i == -16363.

How to handle the unsafe-check?
Which platform uses this implementation of expl?
Can we simply change the unsafe-check in sysdeps/iee754 or is a new
platform-specific implementation required?

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https://sourceware.org/bugzilla/show_bug.cgi?id\x16529

Carlos O'Donell <carlos at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |carlos at redhat dot com

--- Comment #4 from Carlos O'Donell <carlos at redhat dot com> ---
This bug is my mistake. I'll remove the trailing comma which is only valid C99.

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[Bug math/16447] erfc (0x6.a8p+4) ldbl-128 throws underflow exception

[joseph at codesourcery dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=16447

--- Comment #4 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
On Thu, 6 Feb 2014, stli at linux dot vnet.ibm.com wrote:

> unsafe = abs(n_i) >= -16363; 

Well, abs >= (negative value) doesn't seem right.

To work out what's unsafe, you need to consider how small x22 can be in 
cases where ex2_u.d is small.  The answer is roughly that x22, if not 0, 
is at least 1ulp of the input (not exactly, because of the way values from 
a table get subtracted from the input) - so, roughly, you could have 
problems up to n_i around -16382 + 113.  Certainly saying unsafe = abs 
(n_i) >= 15000 should be safe, even allowing for the way x gets adjusted.

> How to handle the unsafe-check?
> Which platform uses this implementation of expl?
> Can we simply change the unsafe-check in sysdeps/iee754 or is a new
> platform-specific implementation required?

The same correction should apply to all platforms using ldbl-128; no 
platform-specific implementation should be needed.

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[Bug math/16447] erfc (0x6.a8p+4) ldbl-128 throws underflow exception

[cvs-commit at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=16447

--- Comment #5 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  7e6424e343b5213ae12bae83c0d018f4fcafd5cd (commit)
      from  83a3406e0f1dd92cd6c7c2a668c5cec2fe1a0cc6 (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=7e6424e343b5213ae12bae83c0d018f4fcafd5cd

commit 7e6424e343b5213ae12bae83c0d018f4fcafd5cd
Author: Andreas Krebbel <krebbel@linux.vnet.ibm.com>
Date:   Tue Feb 11 13:47:47 2014 +0100

    BZ #16447: Fix ldbl-128 expl implementation.

    Extend the range of numbers handled via unsafe mode.
    Add expl testcase and regenerate ULPs for s390.

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

Summary of changes:
 ChangeLog                         |    9 +++++++++
 math/auto-libm-test-in            |    1 +
 math/auto-libm-test-out           |   25 +++++++++++++++++++++++++
 sysdeps/ieee754/ldbl-128/e_expl.c |    2 +-
 sysdeps/s390/fpu/libm-test-ulps   |    3 +++
 5 files changed, 39 insertions(+), 1 deletions(-)

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[Bug math/16447] erfc (0x6.a8p+4) ldbl-128 throws underflow exception

[krebbel1 at de dot ibm.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16447

Andreas Krebbel <krebbel1 at de dot ibm.com> changed:

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

--- Comment #6 from Andreas Krebbel <krebbel1 at de dot ibm.com> ---
Fixed with the commit above.

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[Bug math/16447] erfc (0x6.a8p+4) ldbl-128 throws underflow exception

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16447

Florian Weimer <fweimer at redhat dot com> changed:

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

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