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[Bug math/13837] New: Trig functions experience catastrophic precision loss at large argument magnitudes
- From: "bugdal at aerifal dot cx" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sources dot redhat dot com
- Date: Tue, 13 Mar 2012 03:21:52 +0000
- Subject: [Bug math/13837] New: Trig functions experience catastrophic precision loss at large argument magnitudes
- Auto-submitted: auto-generated
http://sourceware.org/bugzilla/show_bug.cgi?id=13837
Bug #: 13837
Summary: Trig functions experience catastrophic precision loss
at large argument magnitudes
Product: glibc
Version: unspecified
Status: NEW
Severity: critical
Priority: P2
Component: math
AssignedTo: unassigned@sourceware.org
ReportedBy: bugdal@aerifal.cx
Classification: Unclassified
On x86, glibc's sin(0x1p1023) returns:
-0.633004553570852834809556952677667140960693359375
The correct value (rounded to double precision, within 1ulp) is:
0.563127779850884024881452205590903759002685546875
Or, rounded to the DBL_DIG digits (15):
0.563127779850884
In case there's any doubt as to the true value, it agrees with Wolfram Alpha's
estimate of sin(2^1023), which is:
0.5631277798508840134529434079444683477103854907361251
Source:
http://www.wolframalpha.com/input/?i=sin%282%5E1023%29
Apparently glibc's trig functions are failing to perform argument reduction in
any sane way...
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