The common bits are those bits which appear third time So these bits should not be there in both ' ones ' and ' twos ' . common_bit_mask contains all these bits as 0 , so that the bits can be removed from ' ones ' and ' twos ' Value of ' common _ bit _ mask ' will be set as 00 , 00 , 01 and 10 after 1 st , 2 nd , 3 rd and 4 th iterations respectively
common_bit_mask = ~ ( ones & twos ) ;