Question

I have a Java BigInteger containing two bytes (ex: 1000000100110111). I would like to shift only a single nibble, the right-most nibble in the left byte (in bold below) to the left by one bit:

1000 0001 00110111

Making the result after the shift:

1000 0010 00110111

Any thoughts on the best way to go about doing this?

Thanks,
Chris

Answer 1

If you only want to shift a single bit, you should rather clear the old and set the new:

bigint.clearBit(n-1)
      .setBit(n)

If you want to shift those next to four most left bits, you could bitmap them out, shift them, and then or them back:

bigint.and(0xf0ff).or(bigint.and(0x0f00).shiftLeft(1))

Or for clarity:

unshifted = bigint.and(0xf0ff);
shifted = bigint.and(0x0f00).shiftLeft(1);
result = unshifted.or(shifted);

If you don’t want 1100 1111 to become 1101 1110 (notice the spill), you can apply the bitmap again on the shifted, before the or.