filter_iir.c

/*
* Copyright (c) 2015-2022 Sergey Bakhurin
* Digital Signal Processing Library [http://dsplib.org]
*
* This file is part of libdspl-2.0.
*
* is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser    General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* DSPL 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 General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with Foobar.    If not, see <http://www.gnu.org/licenses/>.
*/
 
#include <stdlib.h>
#include <string.h>
#include "dspl.h"
 
 
#ifdef DOXYGEN_ENGLISH
#endif
#ifdef DOXYGEN_RUSSIAN
#endif
int DSPL_API filter_iir(double* b, double* a, int ord,
                        double* x, int n, double* y)
{
    double *buf = NULL;
    double *an  = NULL;
    double *bn  = NULL;
    double  u;
    int     k;
    int     m;
    int     count;
 
    if(!b || !x || !y)
        return ERROR_PTR;
 
    if(ord < 1 || n < 1)
        return ERROR_SIZE;
 
    if(a && a[0]==0.0)
        return ERROR_FILTER_A0;
 
    count = ord + 1;
    buf = (double*) malloc(count*sizeof(double));
    an =  (double*) malloc(count*sizeof(double));
 
    memset(buf, 0, count*sizeof(double));
 
    if(!a)
    {
        memset(an, 0, count*sizeof(double));
        bn = b;
    }
    else
    {
        bn =  (double*) malloc(count*sizeof(double));
        for(k = 0; k < count; k++)
        {
            an[k] = a[k] / a[0];
            bn[k] = b[k] / a[0];
        }
    }
 
    for(k = 0; k < n; k++)
    {
        for(m = ord; m > 0; m--)
            buf[m] = buf[m-1];
        u = 0.0;
        for(m = ord; m > 0; m--)
            u += buf[m]*an[m];
 
        buf[0] = x[k] - u;
        y[k] = 0.0;
        for(m = 0; m < count; m++)
            y[k] += buf[m] * bn[m];
    }
 
    if(buf)
        free(buf);
    if(an)
        free(an);
    if(bn && (bn != b))
        free(bn);
    return RES_OK;
}