c# - 在 C# 中复制数组的任何更快的方法？

Question

我有三个数组需要组合成一个三维数组。以下代码显示了 Performance Explorer 中的缓慢性能。有没有更快的解决方案？

for (int i = 0; i < sortedIndex.Length; i++) {
    if (i < num_in_left)
    {    
        // add instance to the left child
        leftnode[i, 0] = sortedIndex[i];
        leftnode[i, 1] = sortedInstances[i];
        leftnode[i, 2] = sortedLabels[i];
    }
    else
    { 
        // add instance to the right child
        rightnode[i-num_in_left, 0] = sortedIndex[i];
        rightnode[i-num_in_left, 1] = sortedInstances[i];
        rightnode[i-num_in_left, 2] = sortedLabels[i];
    }                    
}

更新:

我实际上正在尝试执行以下操作:

//given three 1d arrays
double[] sortedIndex, sortedInstances, sortedLabels;
// copy them over to a 3d array (forget about the rightnode for now)
double[] leftnode = new double[sortedIndex.Length, 3];
// some magic happens here so that
leftnode = {sortedIndex, sortedInstances, sortedLabels};

Answer 1

使用Buffer.BlockCopy .它的全部目的是快速执行(参见 Buffer ):

This class provides better performance for manipulating primitive types than similar methods in the System.Array class.

诚然，我没有做过任何基准测试，但那是文档。它也适用于多维数组；只需确保您始终指定要复制多少个字节，而不是多少个元素，并且您正在处理原始数组。

此外，我还没有对此进行测试，但是如果您将委托(delegate)绑定(bind)到 System.Buffer.memcpyimpl，您可能能够从系统中挤出更多的性能> 并直接调用它。签名是:

internal static unsafe void memcpyimpl(byte* src, byte* dest, int len)

它确实需要指针，但我相信它已针对可能的最高速度进行了优化，因此我认为没有任何方法可以比这更快，即使您手头有组装。

---

更新:

由于要求(也为了满足我的好奇心)，我测试了这个:

using System;
using System.Diagnostics;
using System.Reflection;

unsafe delegate void MemCpyImpl(byte* src, byte* dest, int len);

static class Temp
{
    //There really should be a generic CreateDelegate<T>() method... -___-
    static MemCpyImpl memcpyimpl = (MemCpyImpl)Delegate.CreateDelegate(
        typeof(MemCpyImpl), typeof(Buffer).GetMethod("memcpyimpl",
            BindingFlags.Static | BindingFlags.NonPublic));
    const int COUNT = 32, SIZE = 32 << 20;

    //Use different buffers to help avoid CPU cache effects
    static byte[]
        aSource = new byte[SIZE], aTarget = new byte[SIZE],
        bSource = new byte[SIZE], bTarget = new byte[SIZE],
        cSource = new byte[SIZE], cTarget = new byte[SIZE];


    static unsafe void TestUnsafe()
    {
        Stopwatch sw = Stopwatch.StartNew();
        fixed (byte* pSrc = aSource)
        fixed (byte* pDest = aTarget)
            for (int i = 0; i < COUNT; i++)
                memcpyimpl(pSrc, pDest, SIZE);
        sw.Stop();
        Console.WriteLine("Buffer.memcpyimpl: {0:N0} ticks", sw.ElapsedTicks);
    }

    static void TestBlockCopy()
    {
        Stopwatch sw = Stopwatch.StartNew();
        sw.Start();
        for (int i = 0; i < COUNT; i++)
            Buffer.BlockCopy(bSource, 0, bTarget, 0, SIZE);
        sw.Stop();
        Console.WriteLine("Buffer.BlockCopy: {0:N0} ticks",
            sw.ElapsedTicks);
    }

    static void TestArrayCopy()
    {
        Stopwatch sw = Stopwatch.StartNew();
        sw.Start();
        for (int i = 0; i < COUNT; i++)
            Array.Copy(cSource, 0, cTarget, 0, SIZE);
        sw.Stop();
        Console.WriteLine("Array.Copy: {0:N0} ticks", sw.ElapsedTicks);
    }

    static void Main(string[] args)
    {
        for (int i = 0; i < 10; i++)
        {
            TestArrayCopy();
            TestBlockCopy();
            TestUnsafe();
            Console.WriteLine();
        }
    }
}

结果:

Buffer.BlockCopy: 469,151 ticks
Array.Copy: 469,972 ticks
Buffer.memcpyimpl: 496,541 ticks

Buffer.BlockCopy: 421,011 ticks
Array.Copy: 430,694 ticks
Buffer.memcpyimpl: 410,933 ticks

Buffer.BlockCopy: 425,112 ticks
Array.Copy: 420,839 ticks
Buffer.memcpyimpl: 411,520 ticks

Buffer.BlockCopy: 424,329 ticks
Array.Copy: 420,288 ticks
Buffer.memcpyimpl: 405,598 ticks

Buffer.BlockCopy: 422,410 ticks
Array.Copy: 427,826 ticks
Buffer.memcpyimpl: 414,394 ticks

现在改变顺序:

Array.Copy: 419,750 ticks
Buffer.memcpyimpl: 408,919 ticks
Buffer.BlockCopy: 419,774 ticks

Array.Copy: 430,529 ticks
Buffer.memcpyimpl: 412,148 ticks
Buffer.BlockCopy: 424,900 ticks

Array.Copy: 424,706 ticks
Buffer.memcpyimpl: 427,861 ticks
Buffer.BlockCopy: 421,929 ticks

Array.Copy: 420,556 ticks
Buffer.memcpyimpl: 421,541 ticks
Buffer.BlockCopy: 436,430 ticks

Array.Copy: 435,297 ticks
Buffer.memcpyimpl: 432,505 ticks
Buffer.BlockCopy: 441,493 ticks

现在再次更改顺序:

Buffer.memcpyimpl: 430,874 ticks
Buffer.BlockCopy: 429,730 ticks
Array.Copy: 432,746 ticks

Buffer.memcpyimpl: 415,943 ticks
Buffer.BlockCopy: 423,809 ticks
Array.Copy: 428,703 ticks

Buffer.memcpyimpl: 421,270 ticks
Buffer.BlockCopy: 428,262 ticks
Array.Copy: 434,940 ticks

Buffer.memcpyimpl: 423,506 ticks
Buffer.BlockCopy: 427,220 ticks
Array.Copy: 431,606 ticks

Buffer.memcpyimpl: 422,900 ticks
Buffer.BlockCopy: 439,280 ticks
Array.Copy: 432,649 ticks

或者，换句话说:他们非常有竞争力；作为一般规则，memcpyimpl 是最快的，但不一定值得担心。