File content as of revision 1:ac4bef72d6af:

#include "BiQuad4.h"
#include <stdlib.h>
#include <stddef.h>

// This code is used to make a fourth order BiQuad filter

BiQuad4::BiQuad4(double b0, double b1, double b2, double b3, double b4, double a1, double a2, double a3, double a4) {
    set( b0, b1, b2, b3, b4, a1, a2, a3, a4 );
    resetStateOnGainChange = true;
}

void BiQuad4::set(double b0, double b1, double b2, double b3, double b4, double a1, double a2, double a3, double a4) {

    B[0] = b0; B[1] = b1; B[2] = b2; B[3] = b3; B[4] = b4;
    A[0] = a1; A[1] = a2; A[2] = a3; A[3] = a4;
    
    if( resetStateOnGainChange )
        wz[0] = 0; wz[1] = 0;
}

double BiQuad4::step(double x) {

    double y,w;

    /* Direct form II */
    w =      x - A[0]*wz[0] - A[1]*wz[1]- A[2]*wz[2] - A[3]*wz[3];
    y = B[0]*w + B[1]*wz[0] + B[2]*wz[1] + B[3]*wz[2] + B[4]*wz[3];

    /* Shift */
    wz[3] = wz[2];
    wz[2] = wz[1];
    wz[1] = wz[0];
    wz[0] = w;

    return y;

}