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* [Bug math/16353] New: expm1 missing underflows
@ 2013-12-20 18:09 jsm28 at gcc dot gnu.org
2014-01-29 11:48 ` [Bug math/16353] " zimmerma+gcc at loria dot fr
` (9 more replies)
0 siblings, 10 replies; 11+ messages in thread
From: jsm28 at gcc dot gnu.org @ 2013-12-20 18:09 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=16353
Bug ID: 16353
Summary: expm1 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
At least some expm1 implementations do not raise the underflow exception for
subnormal arguments, when the result is tiny and inexact. For example, on
x86_64, expm1 (0x1p-1074).
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* [Bug math/16353] expm1 missing underflows
2013-12-20 18:09 [Bug math/16353] New: expm1 missing underflows jsm28 at gcc dot gnu.org
@ 2014-01-29 11:48 ` zimmerma+gcc at loria dot fr
2014-01-29 16:38 ` joseph at codesourcery dot com
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9 siblings, 0 replies; 11+ messages in thread
From: zimmerma+gcc at loria dot fr @ 2014-01-29 11:48 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=16353
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> ---
on the other hand in some cases we get a spurious overflow (here for long
double on x86_64 with the current git version):
Testing function expm1 for exponent 0 [seed=8473].
rounding mode MPFR_RNDN:
wrong underflow flag: mpfr gives 0, library 16
x=3.36210314311209350626e-4932
library gives 3.36210314311209350626e-4932
mpfr gives 3.36210314311209350626e-4932
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* [Bug math/16353] expm1 missing underflows
2013-12-20 18:09 [Bug math/16353] New: expm1 missing underflows jsm28 at gcc dot gnu.org
2014-01-29 11:48 ` [Bug math/16353] " zimmerma+gcc at loria dot fr
@ 2014-01-29 16:38 ` joseph at codesourcery dot com
2014-01-29 16:46 ` zimmerma+gcc at loria dot fr
` (7 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: joseph at codesourcery dot com @ 2014-01-29 16:38 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=16353
--- Comment #2 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
Assuming you mean underflow not overflow, this does not seem spurious
(i.e., the return value and exceptions both appear consistent with an
infinite-precision value that is only slightly inaccurate).
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* [Bug math/16353] expm1 missing underflows
2013-12-20 18:09 [Bug math/16353] New: expm1 missing underflows jsm28 at gcc dot gnu.org
2014-01-29 11:48 ` [Bug math/16353] " zimmerma+gcc at loria dot fr
2014-01-29 16:38 ` joseph at codesourcery dot com
@ 2014-01-29 16:46 ` zimmerma+gcc at loria dot fr
2014-02-07 7:54 ` [Bug math/16353] expm1 missing/spurious underflows zimmerma+gcc at loria dot fr
` (6 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: zimmerma+gcc at loria dot fr @ 2014-01-29 16:46 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=16353
--- Comment #3 from Paul Zimmermann <zimmerma+gcc at loria dot fr> ---
(In reply to joseph@codesourcery.com from comment #2)
> Assuming you mean underflow not overflow, this does not seem spurious
> (i.e., the return value and exceptions both appear consistent with an
> infinite-precision value that is only slightly inaccurate).
ok, then I retract Comment 1. (And yes, I meant underflow.)
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* [Bug math/16353] expm1 missing/spurious underflows
2013-12-20 18:09 [Bug math/16353] New: expm1 missing underflows jsm28 at gcc dot gnu.org
` (2 preceding siblings ...)
2014-01-29 16:46 ` zimmerma+gcc at loria dot fr
@ 2014-02-07 7:54 ` zimmerma+gcc at loria dot fr
2014-02-07 14:35 ` [Bug math/16353] expm1 missing underflows zimmerma+gcc at loria dot fr
` (5 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: zimmerma+gcc at loria dot fr @ 2014-02-07 7:54 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=16353
Paul Zimmermann <zimmerma+gcc at loria dot fr> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|expm1 missing underflows |expm1 missing/spurious
| |underflows
--- Comment #4 from Paul Zimmermann <zimmerma+gcc at loria dot fr> ---
this example (in extended precision) gives a spurious underflow:
Testing function expm1 for exponent 0 [seed=8344].
rounding mode MPFR_RNDN:
wrong underflow flag for x=4.0000000000000028@-4096
library gives 4.0000000000000028@-4096
mpfr gives 4.0000000000000028@-4096
underflow: mpfr 0, library 16
Note the glibc result is *above* the smallest subnormal 0x1p-16382, thus no
exception should be raised.
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* [Bug math/16353] expm1 missing underflows
2013-12-20 18:09 [Bug math/16353] New: expm1 missing underflows jsm28 at gcc dot gnu.org
` (3 preceding siblings ...)
2014-02-07 7:54 ` [Bug math/16353] expm1 missing/spurious underflows zimmerma+gcc at loria dot fr
@ 2014-02-07 14:35 ` zimmerma+gcc at loria dot fr
2014-06-13 11:23 ` fweimer at redhat dot com
` (4 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: zimmerma+gcc at loria dot fr @ 2014-02-07 14:35 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=16353
Paul Zimmermann <zimmerma+gcc at loria dot fr> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|expm1 missing/spurious |expm1 missing underflows
|underflows |
--- Comment #6 from Paul Zimmermann <zimmerma+gcc at loria dot fr> ---
(In reply to joseph@codesourcery.com from comment #5)
> Missing and spurious underflows are separate bugs, please restore this bug
> to its original scope and file a separate bug for the spurious underflow.
sorry, done, new bug for spurious underflow is 16539
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* [Bug math/16353] expm1 missing underflows
2013-12-20 18:09 [Bug math/16353] New: expm1 missing underflows jsm28 at gcc dot gnu.org
` (4 preceding siblings ...)
2014-02-07 14:35 ` [Bug math/16353] expm1 missing underflows zimmerma+gcc at loria dot fr
@ 2014-06-13 11:23 ` fweimer at redhat dot com
2014-06-23 20:21 ` cvs-commit at gcc dot gnu.org
` (3 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: fweimer at redhat dot com @ 2014-06-13 11:23 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=16353
Florian Weimer <fweimer at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Flags| |security-
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* [Bug math/16353] expm1 missing underflows
2013-12-20 18:09 [Bug math/16353] New: expm1 missing underflows jsm28 at gcc dot gnu.org
` (5 preceding siblings ...)
2014-06-13 11:23 ` fweimer at redhat dot com
@ 2014-06-23 20:21 ` cvs-commit at gcc dot gnu.org
2014-06-24 21:01 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2014-06-23 20:21 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=16353
--- Comment #7 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 4648909d56c1e9063017bcddd3271dffadef7cb5 (commit)
from 46a3d3c7d60db15ea65470800bcba695f55ce6f6 (commit)
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=4648909d56c1e9063017bcddd3271dffadef7cb5
commit 4648909d56c1e9063017bcddd3271dffadef7cb5
Author: Joseph Myers <joseph@codesourcery.com>
Date: Mon Jun 23 20:20:10 2014 +0000
Fix cosh spurious underflows from expm1 (bug 16354), inaccurate results
near 0 (bug 17061).
This patch fixes bug 16354, spurious underflows from cosh when a tiny
argument is passed to expm1 and expm1 correctly underflows although
the final result of cosh should be 1. As noted in that bug, some
cases are latent because of expm1 implementations not raising
underflow (bug 16353), but all the implementations are fixed
similarly. They already contained checks for tiny arguments, but the
checks were too late to avoid underflow from expm1 (although they
would avoid underflow from subsequent squaring of the result of
expm1); they are moved before the expm1 calls.
The thresholds used for considering arguments tiny are not
particularly consistent in how they relate to the precision of the
floating-point format in question. They are, however, all sufficient
to ensure that the round-to-nearest result of cosh is indeed 1 below
the threshold (although sometimes they are smaller than necessary).
But the previous logic did not return 1, but the previously computed 1
+ expm1(abs(x)) value. And the thresholds in the ldbl-128 and
ldbl-128ibm code (0x1p-71L - I suspect 0x3f8b was intended in the code
instead of 0x3fb8 - and (roughly) 0x1p-55L) are not sufficient for
that value to be 1. So by moving the test for tiny arguments, and
consequently returning 1 directly now the expm1 value hasn't been
computed by that point, this patch also fixes bug 17061, the (large
number of ulps) inaccuracy for small arguments in those
implementations. Tests for that bug are duly added.
Tested x86_64 and x86 and ulps updated accordingly. Also tested for
mips64 and powerpc32 to validate the ldbl-128 and ldbl-128ibm changes.
[BZ #16354]
[BZ #17061]
* sysdeps/ieee754/dbl-64/e_cosh.c (__ieee754_cosh): Check for
small arguments before calling __expm1.
* sysdeps/ieee754/flt-32/e_coshf.c (__ieee754_coshf): Check for
small arguments before calling __expm1f.
* sysdeps/ieee754/ldbl-128/e_coshl.c (__ieee754_coshl): Check for
small arguments before calling __expm1l.
* sysdeps/ieee754/ldbl-128ibm/e_coshl.c (__ieee754_coshl):
Likewise.
* sysdeps/ieee754/ldbl-96/e_coshl.c (__ieee754_coshl): Likewise.
* math/auto-libm-test-in: Add more cosh tests. Do not allow
spurious underflow for some cosh tests.
* math/auto-libm-test-out: Regenerated.
* sysdeps/i386/fpu/libm-test-ulps: Update.
-----------------------------------------------------------------------
Summary of changes:
ChangeLog | 16 +
NEWS | 20 +-
math/auto-libm-test-in | 13 +-
math/auto-libm-test-out | 732 +++++++++++++++++++--------------
sysdeps/i386/fpu/libm-test-ulps | 1 +
sysdeps/ieee754/dbl-64/e_cosh.c | 4 +-
sysdeps/ieee754/flt-32/e_coshf.c | 2 +-
sysdeps/ieee754/ldbl-128/e_coshl.c | 4 +-
sysdeps/ieee754/ldbl-128ibm/e_coshl.c | 2 +-
sysdeps/ieee754/ldbl-96/e_coshl.c | 2 +-
10 files changed, 458 insertions(+), 338 deletions(-)
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* [Bug math/16353] expm1 missing underflows
2013-12-20 18:09 [Bug math/16353] New: expm1 missing underflows jsm28 at gcc dot gnu.org
` (6 preceding siblings ...)
2014-06-23 20:21 ` cvs-commit at gcc dot gnu.org
@ 2014-06-24 21:01 ` cvs-commit at gcc dot gnu.org
2015-06-22 21:07 ` jsm28 at gcc dot gnu.org
2015-06-22 21:07 ` cvs-commit at gcc dot gnu.org
9 siblings, 0 replies; 11+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2014-06-24 21:01 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=16353
--- Comment #8 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 4060283decf711ed95a6c4993ffeaba39f8cd40a (commit)
from e7dd3c8c1db8c6d293abb995e033893b7328ad19 (commit)
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=4060283decf711ed95a6c4993ffeaba39f8cd40a
commit 4060283decf711ed95a6c4993ffeaba39f8cd40a
Author: Joseph Myers <joseph@codesourcery.com>
Date: Tue Jun 24 21:00:08 2014 +0000
Fix x86/x86_64 expm1l spurious underflow exceptions (bug 16539).
This patch fixes bug 16539, spurious underflow exceptions from x86 /
x86-64 expm1l. The problem is that the computation of a base-2
exponent with extra precision involves spurious underflows for
arguments that are small but not subnormal, so a check is added to
just return the argument in those cases. (If the argument *is*
subnormal, underflowing is correct and the existing code will always
underflow, so it suffices to keep using the existing code in that
case; some expm1 implementations have a bug (bug 16353) with missing
underflow exceptions, but I don't think there's such a bug in this
particular version.)
Tested x86_64 and x86; no ulps updates needed.
(auto-libm-test-out diffs omitted below.)
[BZ #16539]
* sysdeps/i386/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]: Just
return the argument for normal arguments with exponent below -64.
* sysdeps/x86_64/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]:
Likewise.
* math/auto-libm-test-in: Add another test of expm1.
* math/auto-libm-test-out: Regenerated.
-----------------------------------------------------------------------
Summary of changes:
ChangeLog | 8 ++++
NEWS | 22 ++++++------
math/auto-libm-test-in | 2 +
math/auto-libm-test-out | 81 +++++++++++++++++++++++++++++++++++++++++++
sysdeps/i386/fpu/e_expl.S | 10 +++++
sysdeps/x86_64/fpu/e_expl.S | 10 +++++
6 files changed, 122 insertions(+), 11 deletions(-)
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* [Bug math/16353] expm1 missing underflows
2013-12-20 18:09 [Bug math/16353] New: expm1 missing underflows jsm28 at gcc dot gnu.org
` (8 preceding siblings ...)
2015-06-22 21:07 ` jsm28 at gcc dot gnu.org
@ 2015-06-22 21:07 ` cvs-commit at gcc dot gnu.org
9 siblings, 0 replies; 11+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2015-06-22 21:07 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=16353
--- Comment #9 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 branch, master has been updated
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=554edb23ffc7a953ca86309cc5f02dbd1a63abe0
commit 554edb23ffc7a953ca86309cc5f02dbd1a63abe0
Author: Joseph Myers <joseph@codesourcery.com>
Date: Mon Jun 22 21:06:19 2015 +0000
Fix expm1 missing underflows (bug 16353).
Similar to various other bugs in this area, some expm1 implementations
do not raise the underflow exception for subnormal arguments, when the
result is tiny and inexact. This patch forces the exception in a
similar way to previous fixes.
(The issue does not apply to the ldbl-* implementations or to those
for x86 / x86_64 long double. The change to
sysdeps/ieee754/dbl-64/wordsize-64/e_cosh.c is one I missed when
previously fixing bug 16354; the bug in that implementation was
previously latent, but the expm1 fixes stopped it being latent and so
required it to be fixed to avoid spurious underflows from cosh.)
Tested for x86_64 and x86.
[BZ #16353]
* sysdeps/i386/fpu/s_expm1.S (dbl_min): New object.
(__expm1): Force underflow exception for arguments with small
absolute value.
* sysdeps/i386/fpu/s_expm1f.S (flt_min): New object.
(__expm1f): Force underflow exception for arguments with small
absolute value.
* sysdeps/ieee754/dbl-64/s_expm1.c: Include <float.h>.
(__expm1): Force underflow exception for arguments with small
absolute value.
* sysdeps/ieee754/flt-32/s_expm1f.c: Include <float.h>.
(__expm1f): Force underflow exception for arguments with small
absolute value.
* sysdeps/ieee754/dbl-64/wordsize-64/e_cosh.c (__ieee754_cosh):
Check for small arguments before calling __expm1.
* math/auto-libm-test-in: Do not mark underflow exceptions as
possibly missing for bug 16353.
* math/auto-libm-test-out: Regenerated.
-----------------------------------------------------------------------
Summary of changes:
ChangeLog | 21 +++
NEWS | 28 ++--
math/auto-libm-test-in | 11 +-
math/auto-libm-test-out | 226 +++++++++++++-------------
sysdeps/i386/fpu/s_expm1.S | 22 +++
sysdeps/i386/fpu/s_expm1f.S | 22 +++
sysdeps/ieee754/dbl-64/s_expm1.c | 6 +
sysdeps/ieee754/dbl-64/wordsize-64/e_cosh.c | 3 +-
sysdeps/ieee754/flt-32/s_expm1f.c | 6 +
9 files changed, 211 insertions(+), 134 deletions(-)
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* [Bug math/16353] expm1 missing underflows
2013-12-20 18:09 [Bug math/16353] New: expm1 missing underflows jsm28 at gcc dot gnu.org
` (7 preceding siblings ...)
2014-06-24 21:01 ` cvs-commit at gcc dot gnu.org
@ 2015-06-22 21:07 ` jsm28 at gcc dot gnu.org
2015-06-22 21:07 ` cvs-commit at gcc dot gnu.org
9 siblings, 0 replies; 11+ messages in thread
From: jsm28 at gcc dot gnu.org @ 2015-06-22 21:07 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=16353
Joseph Myers <jsm28 at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #10 from Joseph Myers <jsm28 at gcc dot gnu.org> ---
Fixed for 2.22.
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