53 lines
1.8 KiB
C++
53 lines
1.8 KiB
C++
// util.cxx - general-purpose utility functions.
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// Copyright (C) 2002 Curtis L. Olson - curt@me.umn.edu
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//
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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License as
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// published by the Free Software Foundation; either version 2 of the
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// License, or (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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//
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// $Id$
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#include <math.h>
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#include "util.hxx"
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// Originally written by Alex Perry.
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double
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fgGetLowPass (double current, double target, double timeratio)
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{
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if ( timeratio < 0.0 ) {
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if ( timeratio < -1.0 ) {
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// time went backwards; kill the filter
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current = target;
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} else {
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// ignore mildly negative time
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}
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} else if ( timeratio < 0.2 ) {
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// Normal mode of operation; fast
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// approximation to exp(-timeratio)
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current = current * (1.0 - timeratio) + target * timeratio;
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} else if ( timeratio > 5.0 ) {
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// Huge time step; assume filter has settled
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current = target;
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} else {
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// Moderate time step; non linear response
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double keep = exp(-timeratio);
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current = current * keep + target * (1.0 - keep);
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}
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return current;
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}
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// end of util.cxx
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