correlate-pseudo.java

public static double correlate(double[] a, double[] b) {
    if (a.length != b.length) {
        return Double.NaN;
    }
    double <w,x,y,z> = <0,0,0,0>;
    int i = 0;
    for ( ; i + 3 < a.length; i += 4) {
       <w,x,y,z> += a[<i,i+1,i+2,i+3>] * b[<i,i+1,i+2,i+3>];
    }
    double correlation = w + x + y + z;
    for ( ; i < a.length; i++) {
        correlation += a[i] * b[i];
    }
    return correlation;
}