freeswitch/src/mod/applications/mod_avmd/avmd_goertzel.c

/*
 * Contributor(s):
 *
 * Eric des Courtis <eric.des.courtis@benbria.com>
 */


#include <math.h>

#ifndef __AVMD_GOERTZEL_H__
    #include "avmd_goertzel.h"
#endif

#ifndef __AVMD_BUFFER_H__
    #include "avmd_buffer.h"
#endif


extern double avmd_goertzel(circ_buffer_t *b, size_t pos, double f, size_t num)
{
    double s = 0.0;
    double p = 0.0;
    double p2 = 0.0;
    double coeff;
    size_t i;

    coeff = 2.0 * cos(2.0 * M_PI * f);

    for (i = 0; i < num; i++) {
        /* TODO: optimize to avoid GET_SAMPLE when possible */
        s = GET_SAMPLE(b, i + pos) + (coeff * p) - p2;
        p2 = p;
        p = s;
    }

    return (p2 * p2) + (p * p) - (coeff * p2 * p);
}