* Using DoubleUtils.bigToDouble, getting a double approximation of x is extremely fast, and
     * then we can get a double approximation of the square root. Then, we iteratively improve this
     * guess with an application of Newton's method, which sets guess := (guess + (x / guess)) / 2.
     * This iteration has the following two properties:
     *
     * a) every iteration (except potentially the first) has guess >= floor(sqrt(x)). This is