解码校验和代码

我需要解码以下代码，即使用代码

I need to decode the following code i.e use of code

public static string CalcChecksum(string instrFile)
    {
      ulong num1 = 0;
      uint num2 = 256;
      Tools.ReplaceChecksum(ref instrFile, "0000000000");
      byte[] bytes = Encoding.GetEncoding(1252).GetBytes(instrFile);
      int index = 0;
      while (index <= instrFile.Length - 1)
      {
        byte num3 = bytes[index];
        byte num4;
        byte num5;
        byte num6;
        if (index + 1 < instrFile.Length)
        {
          num4 = bytes[index + 1];
          if (index + 2 < instrFile.Length)
          {
            num5 = bytes[index + 2];
            num6 = index + 3 >= instrFile.Length ? (byte) 0 : bytes[index + 3];
          }
          else
          {
            num5 = (byte) 0;
            num6 = (byte) 0;
          }
        }
        else
        {
          num4 = (byte) 0;
          num5 = (byte) 0;
          num6 = (byte) 0;
        }
        ulong num7 = (ulong) (num2 * (num2 * (num2 * (uint) num3 + (uint) num4) + (uint) num5) + (uint) num6);
        num1 += num7;
        if (num1 > 4294967296UL)
          num1 -= 4294967296UL;
        index += 4;
      }
      return num1.ToString("0000000000");
    }

我的尝试：



我试过并输出一个与输入字符串对应的输出数字字符串。

What I have tried:

I have tried and get an output numeral string corresponding to input string to function.