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63 lines
2 KiB
C
63 lines
2 KiB
C
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/*****************************************************************************/
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/*
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* rrctime.c -- Square Root Raised Cosine Function (Time Domain).
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*
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* Copyright (C) 2001, 2002
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* Thomas Sailer (t.sailer@alumni.ethz.ch)
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (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,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU 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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*
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*/
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/*****************************************************************************/
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#define _GNU_SOURCE
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include <math.h>
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#include <float.h>
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#include "raisedcosine.h"
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/* --------------------------------------------------------------------- */
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/*
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* see Huber: Trelliscodierung, S. 15, or ptolemy source code
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*
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* [ (4 alpha t) cos( pi (1+alpha) t) + sin (pi (1 - alpha)t) ] / [ (pi t) (1 - (4 alpha t)^2) ]
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*/
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double root_raised_cosine_time(double time, double alpha)
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{
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float opap, omap, at4, omat4sq;
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if (fabs(alpha) < 1e-8)
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return sinc(time);
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if (fabs(time) < 1e-8)
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return ((4.0 / M_PI) - 1.0) * alpha + 1.0;
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opap = (1.0 + alpha) * M_PI;
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omap = (1.0 - alpha) * M_PI;
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at4 = alpha * time * 4;
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omat4sq = 1 - at4 * at4;
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if (fabs(omat4sq) < 1e-8)
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return ((4.0 * alpha) * cos(opap * time) - at4 * opap * sin(opap * time) + omap * cos(omap * time)) / (1 - 3 * at4 * at4) * (1.0 / M_PI);
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return (4.0 / M_PI) * alpha / omat4sq * (cos(opap * time) + sin(omap * time) / at4);
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}
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