问如何正确舍入平方根函数？

EN

public static double sqrt(double x) {
    long bits = Double.doubleToLongBits(x);

    // NaN and non-zero negatives:
    if (Double.isNaN(x) || x < 0) return Double.NaN;

    // +-0 and 1:
    if (x == 0d || x == 1d) return x;

    // Halving the exponent to come up with a good initial guess:
    long exp = bits << 1;
    exp = (exp - 0x7fe0000000000000L >> 1) + 0x7fe0000000000000L >>> 1 & 0x7ff0000000000000L;
    double guess = Double.longBitsToDouble(bits & 0x800fffffffffffffL | exp);
    double nextUp, nextDown, guessSq, nextUpSq, nextDownSq;

    // Main loop:
    while (true) {
        guessSq = guess * guess;
        if (guessSq == x) return guess;
        nextUp = Math.nextUp(guess);
        nextUpSq = nextUp * nextUp;
        if (nextUpSq == x) return nextUp;
        if (guessSq < x && x < nextUpSq) {
            double z = x / nextUp;
            if (z * nextUp > x) z = Math.nextDown(z);
            return z < nextUp ? nextUp : guess;
        }
        nextDown = Math.nextDown(guess);
        nextDownSq = nextDown * nextDown;
        if (nextDownSq == x) return nextDown;
        if (nextDownSq < x && x < guessSq) {
            double z = x / guess;
            if (z * guess > x) z = Math.nextDown(z);
            return z < guess ? guess : nextDown;
        }

        // Babylonian method:
        guess = 0.5 * (guess + x / guess);
    }
}