C# method to implement fast copy through pointer

The example in this article describes how C# implements fast copying through pointers. Share it with everyone for your reference. The specific implementation method is as follows:

// fastcopy.cs
// 编译时使用：/unsafe
using System;
class Test
{
  // unsafe 关键字允许在下列
  // 方法中使用指针：
  static unsafe void Copy(byte[] src, int srcIndex, byte[] dst, int dstIndex, int count)
  {
    if (src == null || srcIndex < 0 ||
      dst == null || dstIndex < 0 || count < 0)
    {
      throw new ArgumentException();
    }
    int srcLen = src.Length;
    int dstLen = dst.Length;
    if (srcLen - srcIndex < count || dstLen - dstIndex < count)
    {
      throw new ArgumentException();
    }
    // 以下固定语句固定
    // src 对象和 dst 对象在内存中的位置，以使这两个对象
    // 不会被垃圾回收移动。
    fixed (byte* pSrc = src, pDst = dst)
    {
      byte* ps = pSrc;
      byte* pd = pDst;
      // 以 4 个字节的块为单位循环计数，一次复制
      // 一个整数（4 个字节）：
      for (int n = 0; n < count / 4; n++)
      {
        *((int*)pd) = *((int*)ps);
        pd += 4;
        ps += 4;
      }
      // 移动未以 4 个字节的块移动的所有字节，
      // 从而完成复制：
      for (int n = 0; n < count % 4; n++)
      {
        *pd = *ps;
        pd++;
        ps++;
      }
    }
  }
  static void Main(string[] args)
  {
    byte[] a = new byte[100];
    byte[] b = new byte[100];
    for (int i = 0; i < 100; ++i)
      a[i] = (byte)i;
    Copy(a, 0, b, 0, 100);
    Console.WriteLine("The first 10 elements are:");
    for (int i = 0; i < 10; ++i)
      Console.Write(b[i] + " ");
    Console.WriteLine("\n");
  }
}

I hope this article will be helpful to everyone’s C# programming.

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