从第一个字节中删除位，然后重新加入这些位

Question

I have a devious little problem to which I think I've come up with a solution far more difficult than needs to be.

The problem is that I have two bytes. The first two bits of the first byte are to be removed (as the value is little endian, these bits are effectively in the middle of the 16 bit value). Then the least significant two bits of the second byte are to be moved to the most significant bit locations of the first byte, in place of the removed bits.

My solution is as follows:

byte firstByte = (byte)stream.ReadByte(); // 01000100
byte secondByte = (byte)stream.ReadByte(); // 00010010
// the first and second byte equal the decimal 4676 in this little endian example

byte remainderOfFirstByte = (byte)(firstByte & 63); // 01000100 & 00111111 = 00000100

byte transferredBits = (byte)(secondByte  << 6); // 00010010 << 6 = 10000000

byte remainderOfSecondByte = (byte)(secondByte >> 2); // 00010010 >> 2 = 00000100

byte newFirstByte = (byte)(transferredBits | remainderOfFirstByte); // 10000000 | 00000100 = 10000100
int result = BitConverter.ToInt32(new byte[]{newFirstByte, remainderOfSecondByte, 0, 0}, 0); //10000100 00010000 (the result is decimal 1156)

Is there an easier way* to achieve this? *less verbose, perhaps an inbuilt function or trick I'm missing? (with the exception of doing both the & and << on the same line)

Answer 1

You don't have to mask out bits that a shift would throw away anyway. And you don't have to transfer those bits manually. So it becomes this: (not tested)

int result = (secondByte << 6) | (firstByte & 0x3F);