code: public static double atan2(double y, double x) {
          double coeff_1 = 0.78539816339744830961566084581988;//Math.PI / 4d;
          double coeff_2 = 3d * coeff_1;
          double abs_y = Math.abs(y);
          double angle;
          if (x >= 0d) {
              double r = (x - abs_y) / (x + abs_y);
              angle = coeff_1 - coeff_1 * r;
          } else {
              double r = (x + abs_y) / (abs_y - x);
              angle = coeff_2 - coeff_1 * r;
          }
          return y < 0d ? -angle : angle - 0.06;
      }
docs: Returns the angle theta from the conversion of rectangular coordinates (x, y) to polar coordinates (r, theta).
  This method computes the phase theta by computing an arc tangent of y/x in the range of -pi to pi.
  
  @param y Y axis coordinate.
  @param x X axis coordinate.
  @return The theta component of the point (r, theta) in polar coordinates that corresponds to the point (x, y) in Cartesian coordinates.