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* [Bug math/13305] New: cacosh(+/-0.5+0.0*i) returns wrong result
@ 2011-10-17 8:39 kreckel at ginac dot de
2011-10-29 20:17 ` [Bug math/13305] " kreckel at ginac dot de
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: kreckel at ginac dot de @ 2011-10-17 8:39 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=13305
Bug #: 13305
Summary: cacosh(+/-0.5+0.0*i) returns wrong result
Product: glibc
Version: 2.14
Status: NEW
Severity: normal
Priority: P2
Component: math
AssignedTo: aj@suse.de
ReportedBy: kreckel@ginac.de
Classification: Unclassified
Created attachment 6007
--> http://sourceware.org/bugzilla/attachment.cgi?id=6007
patch
The current implementation computes cacosh(0.5+0.0*o)=0.0-1.047*i and
cacosh(-0.5+0.0*i)=0.0-2.094*i. But that result has the wrong sign.
Wes Loewer's patch for BZ#2182 was wrongly applied and should be reverted. The
patch tried to fix the choice of branch cut by inverting res, if Re(res)<0.0.
This is okay for picking the right branch cut but it suffers to the problem
that round-off errors might have occurred in the computation of res. A safer
approach is checking the position of the actual argument z. Indeed, the current
implementation is doing just that a few lines above, but I don't see this in
BZ#2182! Removing the extra test fixes the case.
Impact: A different result is computed only when res, as computed so far, has a
negative real part. But a negative real part of res can only happen due to
round-off errors, as mathematically the argument of log is bounded below by
+1.0.
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* [Bug math/13305] cacosh(+/-0.5+0.0*i) returns wrong result
2011-10-17 8:39 [Bug math/13305] New: cacosh(+/-0.5+0.0*i) returns wrong result kreckel at ginac dot de
@ 2011-10-29 20:17 ` kreckel at ginac dot de
2011-11-19 22:19 ` kreckel at ginac dot de
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: kreckel at ginac dot de @ 2011-10-29 20:17 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=13305
--- Comment #1 from Richard B. Kreckel <kreckel at ginac dot de> 2011-10-29 20:16:38 UTC ---
I just see that in order to correctly account for signed zero, the patch has to
be extended. After computing the square root, the condition if (__real__ x <
0.0) should be modified to if (signbit(x)).
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* [Bug math/13305] cacosh(+/-0.5+0.0*i) returns wrong result
2011-10-17 8:39 [Bug math/13305] New: cacosh(+/-0.5+0.0*i) returns wrong result kreckel at ginac dot de
2011-10-29 20:17 ` [Bug math/13305] " kreckel at ginac dot de
@ 2011-11-19 22:19 ` kreckel at ginac dot de
2011-11-19 22:21 ` kreckel at ginac dot de
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: kreckel at ginac dot de @ 2011-11-19 22:19 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=13305
--- Comment #2 from Richard B. Kreckel <kreckel at ginac dot de> 2011-11-19 22:19:10 UTC ---
I attach a cumulative patch. Please apply. Don't hesitate to contact me if
anything is unclear.
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* [Bug math/13305] cacosh(+/-0.5+0.0*i) returns wrong result
2011-10-17 8:39 [Bug math/13305] New: cacosh(+/-0.5+0.0*i) returns wrong result kreckel at ginac dot de
2011-10-29 20:17 ` [Bug math/13305] " kreckel at ginac dot de
2011-11-19 22:19 ` kreckel at ginac dot de
@ 2011-11-19 22:21 ` kreckel at ginac dot de
2011-12-19 9:37 ` aj at suse dot de
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: kreckel at ginac dot de @ 2011-11-19 22:21 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=13305
--- Comment #3 from Richard B. Kreckel <kreckel at ginac dot de> 2011-11-19 22:20:38 UTC ---
Created attachment 6066
--> http://sourceware.org/bugzilla/attachment.cgi?id=6066
cumulative patch
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* [Bug math/13305] cacosh(+/-0.5+0.0*i) returns wrong result
2011-10-17 8:39 [Bug math/13305] New: cacosh(+/-0.5+0.0*i) returns wrong result kreckel at ginac dot de
` (2 preceding siblings ...)
2011-11-19 22:21 ` kreckel at ginac dot de
@ 2011-12-19 9:37 ` aj at suse dot de
2011-12-22 2:03 ` drepper.fsp at gmail dot com
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: aj at suse dot de @ 2011-12-19 9:37 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=13305
Andreas Jaeger <aj at suse dot de> changed:
What |Removed |Added
----------------------------------------------------------------------------
AssignedTo|aj at suse dot de |drepper.fsp at gmail dot
| |com
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* [Bug math/13305] cacosh(+/-0.5+0.0*i) returns wrong result
2011-10-17 8:39 [Bug math/13305] New: cacosh(+/-0.5+0.0*i) returns wrong result kreckel at ginac dot de
` (3 preceding siblings ...)
2011-12-19 9:37 ` aj at suse dot de
@ 2011-12-22 2:03 ` drepper.fsp at gmail dot com
2011-12-23 16:04 ` drepper.fsp at gmail dot com
2014-06-27 11:51 ` fweimer at redhat dot com
6 siblings, 0 replies; 8+ messages in thread
From: drepper.fsp at gmail dot com @ 2011-12-22 2:03 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=13305
Ulrich Drepper <drepper.fsp at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
--- Comment #4 from Ulrich Drepper <drepper.fsp at gmail dot com> 2011-12-22 02:02:43 UTC ---
I've checked in the patch.
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* [Bug math/13305] cacosh(+/-0.5+0.0*i) returns wrong result
2011-10-17 8:39 [Bug math/13305] New: cacosh(+/-0.5+0.0*i) returns wrong result kreckel at ginac dot de
` (4 preceding siblings ...)
2011-12-22 2:03 ` drepper.fsp at gmail dot com
@ 2011-12-23 16:04 ` drepper.fsp at gmail dot com
2014-06-27 11:51 ` fweimer at redhat dot com
6 siblings, 0 replies; 8+ messages in thread
From: drepper.fsp at gmail dot com @ 2011-12-23 16:04 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=13305
Ulrich Drepper <drepper.fsp at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |bert.barbe at oracle dot
| |com
--- Comment #5 from Ulrich Drepper <drepper.fsp at gmail dot com> 2011-12-23 16:02:28 UTC ---
*** Bug 12786 has been marked as a duplicate of this bug. ***
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* [Bug math/13305] cacosh(+/-0.5+0.0*i) returns wrong result
2011-10-17 8:39 [Bug math/13305] New: cacosh(+/-0.5+0.0*i) returns wrong result kreckel at ginac dot de
` (5 preceding siblings ...)
2011-12-23 16:04 ` drepper.fsp at gmail dot com
@ 2014-06-27 11:51 ` fweimer at redhat dot com
6 siblings, 0 replies; 8+ messages in thread
From: fweimer at redhat dot com @ 2014-06-27 11:51 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=13305
Florian Weimer <fweimer at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Flags| |security-
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2011-10-17 8:39 [Bug math/13305] New: cacosh(+/-0.5+0.0*i) returns wrong result kreckel at ginac dot de
2011-10-29 20:17 ` [Bug math/13305] " kreckel at ginac dot de
2011-11-19 22:19 ` kreckel at ginac dot de
2011-11-19 22:21 ` kreckel at ginac dot de
2011-12-19 9:37 ` aj at suse dot de
2011-12-22 2:03 ` drepper.fsp at gmail dot com
2011-12-23 16:04 ` drepper.fsp at gmail dot com
2014-06-27 11:51 ` fweimer at redhat dot com
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