public static void Swap(byte[] data)
{
        for (int i = 0; i < data.Length; i += 2)
        {
                byte b = data[i];
                data[i] = data[i + 1];
                data[i + 1] = b;
        }
}

被改写为不安全的代码,以提高其性能：

public static unsafe void SwapX2(Byte[] Source)  
{  
    fixed (Byte* pSource = &Source[0])  
    {  
        Byte* bp = pSource;  
        Byte* bp_stop = bp + Source.Length;  

        while (bp < bp_stop)  
        {
            *(UInt16*)bp = (UInt16)(*bp << 8 | *(bp + 1));  
            bp += 2;  
        }  
    }  
}

假设一个人想用32位字做同样的事情：

public static void SwapX4(byte[] data)
{
    byte temp;
    for (int i = 0; i < data.Length; i += 4)
    {
        temp = data[i];
        data[i] = data[i + 3];
        data[i + 3] = temp;
        temp = data[i + 1];
        data[i + 1] = data[i + 2];
        data[i + 2] = temp;
    }
}

这将如何以类似的方式重写？

解决方法

public static unsafe void SwapX4(Byte[] Source)  
{  
    fixed (Byte* pSource = &Source[0])  
    {  
        Byte* bp = pSource;  
        Byte* bp_stop = bp + Source.Length;  

        while (bp < bp_stop)  
        {
            *(UInt32*)bp = (UInt32)(
                (*bp       << 24) |
                (*(bp + 1) << 16) |
                (*(bp + 2) <<  8) |
                (*(bp + 3)      ));
            bp += 4;  
        }  
    }  
}

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