aptdec/filter.c

/*
 *  Atpdec
 *  Copyright (c) 2004 by Thierry Leconte (F4DWV)
 *
 *      $Id$
 *
 *   This library is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Library General Public License as
 *   published by the Free Software Foundation; either version 2 of
 *   the License, or (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU Library General Public License for more details.
 *
 *   You should have received a copy of the GNU Library General Public
 *   License along with this library; if not, write to the Free Software
 *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 */
#include "filter.h"

float fir(float *buff, const float *coeff, const int len)
{
    int i;
    double r;

    r = 0.0;
    for (i = 0; i < len; i++) {
	r += buff[i] * coeff[i];
    }
    return r;
}

void
iqfir(float *buff, const float *Icoeff, const float *Qcoeff, const int len,
      float *Iptr, float *Qptr)
{
    int i;
    float I, Q;

    I = Q = 0.0;
    for (i = 0; i < len; i++) {
	double v;

	v = buff[i];
	I += v * Icoeff[i];
	Q += v * Qcoeff[i];
    } *Iptr = I;
    *Qptr = Q;
}

float
rsfir(float *buff, const float *coeff, const int len, const double offset,
      const double delta)
{
    int i;
    double n;
    double out;

    out = 0.0;
    for (i = 0, n = offset; n < len - 1; n += delta, i++) {
	int k;
	double alpha;

	k = (int) n;
	alpha = n - k;
	out += buff[i] * (coeff[k] * (1.0 - alpha) + coeff[k + 1] * alpha);
    } return out;
}

double iir(double x, iirbuff_t * buff, const iircoeff_t * coeff)
{
    buff->x[4] = buff->x[3];
    buff->x[3] = buff->x[2];
    buff->x[2] = buff->x[1];
    buff->x[1] = buff->x[0];
    buff->x[0] = x / coeff->G;
    buff->y[2] = buff->y[1];
    buff->y[1] = buff->y[0];
    buff->y[0] = buff->x[4]
	+ coeff->x[2] * buff->x[3]
	+ coeff->x[1] * buff->x[2]
	+ coeff->x[0] * buff->x[1]
	+ buff->x[0] + coeff->y[1] * buff->y[2] + coeff->y[0] * buff->y[1];
    return (buff->y[0]);
}