循环展开

第二种方法用了循环展开,速度快了不少

fun cale0(n:Long) :Unit{
        var fxx = 1L
        val start = System.currentTimeMillis();
        System.out.println("cale0 开始 ----- ")
        for (i in 1..n ) {
            fxx *= i
        }
        val end = System.currentTimeMillis();
        val d = end - start;
        System.out.println("cale0 时长 ----- ${d}ms")
        System.out.println("cale0 结束 ------------ $fxx")
    }

    /**
     * n默认是4的倍数 
     */
    fun cale1(n:Long) :Unit{
        var f0 = 1L
        var f1 = 1L
        var f2 = 1L
        var f3 = 1L
        val start = System.currentTimeMillis();
        System.out.println("cale1 开始 -----")
        for (i in 1..n step 4) {
            f0 *= i
            f1 *= i + 1
            f2 *= i + 2
            f3 *= i + 3
        }
        val end = System.currentTimeMillis();
        val d = end - start;
        System.out.println("cale1 时长 ----- ${d}ms")
        val f = f0 * f1 * f2 * f3
        System.out.println("cale1 结束 ------------ $f")

    }