为什么UInt16阵列似乎比int数组更快？

Question

似乎C#在添加两个数组时UInt16[]比在添加两个数组时更快int[].这对我来说没有意义,因为我会假设数组是字对齐的,因此int[]需要较少的CPU工作,不是吗？

我运行下面的测试代码,得到以下结果:

Int    for 1000 took 9896625613 tick (4227 msec)
UInt16 for 1000 took 6297688551 tick (2689 msec)

测试代码执行以下操作:

1. 创建两个名为aand的数组b,一次.
2. 用随机数据填充它们一次.
3. 启动秒表.
4. 添加a和b逐项添加.这样做了1000次.
5. 停止秒表.
6. 报告花了多长时间.

这是为了int[] a, b和为UInt16 a,b.而每次我运行的代码时,为测试UInt16阵列需要30%不到的时间-50%int阵列.你能解释一下吗？

这是代码,如果你想尝试自己:

public static UInt16[] GenerateRandomDataUInt16(int length)
{
    UInt16[] noise = new UInt16[length];
    Random random = new Random((int)DateTime.Now.Ticks);
    for (int i = 0; i < length; ++i)
    {
        noise[i] = (UInt16)random.Next();
    }

    return noise;
}

public static int[] GenerateRandomDataInt(int length)
{
    int[] noise = new int[length];
    Random random = new Random((int)DateTime.Now.Ticks);
    for (int i = 0; i < length; ++i)
    {
        noise[i] = (int)random.Next();
    }

    return noise;
}

public static int[] AddInt(int[] a, int[] b)
{
    int len = a.Length;
    int[] result = new int[len];
    for (int i = 0; i < len; ++i)
    {
        result[i] = (int)(a[i] + b[i]);
    }
    return result;
}

public static UInt16[] AddUInt16(UInt16[] a, UInt16[] b)
{
    int len = a.Length;
    UInt16[] result = new UInt16[len];
    for (int i = 0; i < len; ++i)
    {
        result[i] = (ushort)(a[i] + b[i]);
    }
    return result;
}


public static void Main()
{
    int count = 1000;
    int len = 128 * 6000;

    int[] aInt = GenerateRandomDataInt(len);
    int[] bInt = GenerateRandomDataInt(len);

    Stopwatch s = new Stopwatch();
    s.Start();
    for (int i=0; i<count; ++i) 
    {
        int[] resultInt = AddInt(aInt, bInt);
    }
    s.Stop();
    Console.WriteLine("Int    for " + count 
                + " took " + s.ElapsedTicks + " tick (" 
                + s.ElapsedMilliseconds + " msec)");

    UInt16[] aUInt16 = GenerateRandomDataUInt16(len);
    UInt16[] bUInt16 = GenerateRandomDataUInt16(len);

    s = new Stopwatch();
    s.Start();
    for (int i=0; i<count; ++i) 
    {
        UInt16[] resultUInt16 = AddUInt16(aUInt16, bUInt16);
    }
    s.Stop();
    Console.WriteLine("UInt16 for " + count 
                + " took " + s.ElapsedTicks + " tick (" 
                + s.ElapsedMilliseconds + " msec)");


}

Answer 1

会发生什么是你看到漏洞的抽象.UInt16占用int的一半内存(16对32位).

这意味着int16数组占用的内存区域占用int32所占区域的一半.因此,更多的区域可以适应处理器缓存,因此可以非常快速地访问.

您可以在具有更多缓存的处理器上尝试该代码,并且差异可能更小.

也尝试使用更大的阵列.