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From: "bagnara at cs dot unipr dot it" <sourceware-bugzilla@sourceware.org> To: glibc-bugs@sources.redhat.com Subject: [Bug math/6869] New: sin() and cos() return grossly wrong results when rounding is set to upward Date: Fri, 05 Sep 2008 19:35:00 -0000 [thread overview] Message-ID: <20080905193441.6869.bagnara@cs.unipr.it> (raw) $ cat bug2.cc #include <fenv.h> #include <iostream> #include <cmath> int main() { double theta = 5.27905511969922880410877041867934167385101318359375; std::cout << "theta = " << theta << "\n"; std::cout << "sin(theta) = " << sin(theta) << "\n"; std::cout << "cos(theta) = " << cos(theta) << "\n"; std::cout << "Repeating after setting the rounding direction to UPWARD:" << std::endl; fesetround(FE_UPWARD); std::cout << "theta = " << theta << "\n"; std::cout << "sin(theta) = " << sin(theta) << "\n"; std::cout << "cos(theta) = " << cos(theta) << "\n"; } $ g++ -W -Wall bug2.cc $ a.out theta = 5.27906 sin(theta) = -0.843695 cos(theta) = 0.536822 Repeating after setting the rounding direction to UPWARD: theta = 5.27906 sin(theta) = -0.119458 cos(theta) = 12.1636 $ This happens on a Fedora 7, x86_64 system, with glibc-2.6-4 and GCC 4.3.2. As you see, after setting the rounding direction to UPWARD, the results are grossly wrong, to the point of cos() returning 12.1636. The value computed by second invocation of sin() is also wrong. -- Summary: sin() and cos() return grossly wrong results when rounding is set to upward Product: glibc Version: unspecified Status: NEW Severity: normal Priority: P2 Component: math AssignedTo: aj at suse dot de ReportedBy: bagnara at cs dot unipr dot it CC: glibc-bugs at sources dot redhat dot com GCC host triplet: athlon64-unknown-linux-gnu http://sourceware.org/bugzilla/show_bug.cgi?id=6869 ------- You are receiving this mail because: ------- You are on the CC list for the bug, or are watching someone who is.
next reply other threads:[~2008-09-05 19:35 UTC|newest] Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2008-09-05 19:35 bagnara at cs dot unipr dot it [this message] 2008-09-05 19:37 ` [Bug math/6869] " bagnara at cs dot unipr dot it 2008-09-05 21:20 ` eberlein at us dot ibm dot com 2008-09-24 10:45 ` anders dot lennartsson at foi dot se 2008-09-29 16:44 ` anders dot lennartsson at foi dot se 2010-03-21 22:24 ` vincent+libc at vinc17 dot org
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