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[Bug libc/14163] New: Software implementation of cosf is not decreasing on range [0,pi/2]
- From: "martin.brain at cs dot ox.ac.uk" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sources dot redhat dot com
- Date: Thu, 24 May 2012 17:46:27 +0000
- Subject: [Bug libc/14163] New: Software implementation of cosf is not decreasing on range [0,pi/2]
- Auto-submitted: auto-generated
http://sourceware.org/bugzilla/show_bug.cgi?id=14163
Bug #: 14163
Summary: Software implementation of cosf is not decreasing on
range [0,pi/2]
Product: glibc
Version: 2.15
Status: NEW
Severity: normal
Priority: P2
Component: libc
AssignedTo: unassigned@sourceware.org
ReportedBy: martin.brain@cs.ox.ac.uk
CC: drepper.fsp@gmail.com
Classification: Unclassified
Created attachment 6421
--> http://sourceware.org/bugzilla/attachment.cgi?id=6421
An example of one of the glitches
While verifying parts of the software trigonometric functions using CBMC I
found that __kernel_cosf ( glibc-2.15/sysdeps/ieee754/flt-32/k_cosf.c ) has
5530 points in the range [0.1,pi/2] where inaccuracies in the last bit mean
that the function is not descreasing. I.E. x < y but cos(x) < cos(y). The
attached code demonstrates this effect on x86_64 (x86 uses the x87 sin and cos
hardware and so is not effected). Interestingly the corresponding code for sin
does not have this issue.
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