Java以字节和整数的偏移量和长度传输位

Question

I am trying to transfer a certain number of bits in a byte to the beginning of an int but its not working out as planned.

public int transfer(byte b, int offset, int len, int dest, int bitsInUSe){
             byte mask  = (byte) ((byte)  ((1 << len) - 1) << offset);
               dest = dest<< bitsInUSe;
          dest = b & mask;
              return dest ;
}

eg, with offset 2 and len 3 of byte 00111000 should produce the int> 00000000000000000000000000000110

I only need to put the bits at the beginning of the int but I would need to move any bits that have previously been assigned to the left so they are not overridden, hence the bitsInUse variable.

Answer 1

This should do what you want (I have changed some of variable names). Note that you must pass in values such that currBitsUsed >= len , or the shifted curr and b bits will collide.

public int transfer(byte b, int offset, int len, int curr, int currBitsUsed) {
    byte mask = (byte)((1 << len) - 1);
    return (curr << currBitsUsed) | ((byte)((b) >>> offset) & mask);
}

And here is a version that automatically calculates the number of bits to shift curr to avoid a collision.

public int transfer(byte b, int offset, int len, int curr) {
    int currShift = Math.max(32 - Integer.numberOfLeadingZeros(curr), len);
    byte mask = (byte)((1 << len) - 1);
    return (curr << currShift) | ((byte)((b) >>> offset) & mask);
}