What does the following function perform?

    public static double CleanAngle(double angle) {

        while (angle < 0)
            angle += 2 * System.Math.PI;

        while (angle > 2 * System.Math.PI)
            angle -= 2 * System.Math.PI;

        return angle;
    }

This is how it is used with ATan2. I believe the actually values passed to ATan2 are always positive.

  static void Main(string[] args) {
        int q = 1;
        //'x- and y-coordinates will always be positive values
        //'therefore, do i need to "clean"?
        foreach (Point  oPoint in new Point[] { new Point(8,20), new Point(-8,20), new Point(8,-20), new Point(-8,-20)}) {
            Debug.WriteLine(Math.Atan2(oPoint.Y, oPoint.X), "unclean " + q.ToString());
            Debug.WriteLine(CleanAngle(Math.Atan2(oPoint.Y, oPoint.X)), "cleaned " + q.ToString());                
            q++;
        }

        //'output
        //'unclean 1: 1.19028994968253
        //'cleaned 1: 1.19028994968253
        //'unclean 2: 1.95130270390726
        //'cleaned 2: 1.95130270390726
        //'unclean 3: -1.19028994968253
        //'cleaned 3: 5.09289535749705
        //'unclean 4: -1.95130270390726
        //'cleaned 4: 4.33188260327232

    }