在
this question,以下代码：
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;
}
}
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;
}
}
}
请注意,这两个功能(我的SwapX4和SwapX2)只会交换一个小端主机上的任何东西;当在一个大端主机上运行时,它们是一种昂贵的操作.
