IIR filter

iir.c

struct iir_filter
{
	float *w; // w coefficients
	float *a; // a coefficients
	float *b; // b coefficients
	int n;    // filter size
};

float iir_push( struct iir_filter *f, float x )
{
	// Calculate value at the beginning of the delay line
	f->w[0] = x;
	for ( int i = 1; i < f->n; i++ )
		f->w[0] -= f->w[i] * f->a[i];
		
	// Calculate output value
	float y = 0;
	for ( int i = 0; i < f->n; i++ )
		y += f->w[i] * f->b[i];
	
	// Shift delay line
	memmove( &f->w[1], &f->w[0], ( f->n - 1 ) * sizeof( f->w[0] ) );
	
	return y;
}