我目前正在使用 BitConverter 将两个未签名的短裤打包到一个有符号的 int 中。该代码针对不同的值执行数百万次,我认为该代码可以进一步优化。这是我目前正在做的——你可以假设代码是 C#/NET。
// to two unsigned shorts from one signed int:
int xy = 343423;
byte[] bytes = BitConverter.GetBytes(xy);
ushort m_X = BitConverter.ToUInt16(bytes, 0);
ushort m_Y = BitConverter.ToUInt16(bytes, 2);
// convet two unsigned shorts to one signed int
byte[] xBytes = BitConverter.GetBytes(m_X);
byte[] yBytes = BitConverter.GetBytes(m_Y);
byte[] bytes = new byte[] {
xBytes[0],
xBytes[1],
yBytes[0],
yBytes[1],
};
return BitConverter.ToInt32(bytes, 0);
所以我突然想到,如果我移位,我可以避免构造数组的开销。但是对于我的生活,我无法弄清楚正确的换档操作是什么。我的第一次可悲的尝试涉及以下代码:
int xy = 343423;
const int mask = 0x00000000;
byte b1, b2, b3, b4;
b1 = (byte)((xy >> 24));
b2 = (byte)((xy >> 16));
b3 = (byte)((xy >> 8) & mask);
b4 = (byte)(xy & mask);
ushort m_X = (ushort)((xy << b4) | (xy << b3));
ushort m_Y = (ushort)((xy << b2) | (xy << b1));
有人可以帮助我吗?我在想我需要在移位之前屏蔽高字节和低字节。我看到的一些示例包括使用 type.MaxValue 或任意数字(如负十二)进行减法,这非常令人困惑。
** 更新 **
谢谢你的好答案。以下是基准测试的结果:
// 34ms for bit shift with 10M operations
// 959ms for BitConverter with 10M operations
static void Main(string[] args)
{
Stopwatch stopWatch = new Stopwatch();
stopWatch.Start();
for (int i = 0; i < 10000000; i++)
{
ushort x = (ushort)i;
ushort y = (ushort)(i >> 16);
int result = (y << 16) | x;
}
stopWatch.Stop();
Console.WriteLine((int)stopWatch.Elapsed.TotalMilliseconds + "ms");
stopWatch.Start();
for (int i = 0; i < 10000000; i++)
{
byte[] bytes = BitConverter.GetBytes(i);
ushort x = BitConverter.ToUInt16(bytes, 0);
ushort y = BitConverter.ToUInt16(bytes, 2);
byte[] xBytes = BitConverter.GetBytes(x);
byte[] yBytes = BitConverter.GetBytes(y);
bytes = new byte[] {
xBytes[0],
xBytes[1],
yBytes[0],
yBytes[1],
};
int result = BitConverter.ToInt32(bytes, 0);
}
stopWatch.Stop();
Console.WriteLine((int)stopWatch.Elapsed.TotalMilliseconds + "ms");
Console.ReadKey();
}