code: private static void checkRange(int fromIndex, int toIndex) {
  		if (fromIndex < 0)
  			throw new IndexOutOfBoundsException("fromIndex < 0: " + fromIndex);
  		if (toIndex < 0)
  			throw new IndexOutOfBoundsException("toIndex < 0: " + toIndex);
  		if (fromIndex > toIndex)
  			throw new IndexOutOfBoundsException("fromIndex: " + fromIndex +
  					" > toIndex: " + toIndex);
  	}
docs: Checks that fromIndex ... toIndex is a valid range of bit indices.