/**
     * 求平方根
     * @param value 定义域
     * @return 值域
     */
    final public static int sqrt(int value) {
        int sqrt = 0;
        for (int k = 0x100000; k != 0; k >>= 2) {
            int tmp = sqrt + k;
            sqrt >>= 1;
            if (tmp <= value) {
                value -= tmp;
                sqrt += k;
            }
        }
        return sqrt;
    }