shouldbe += ntohs(computed_sum);
shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16);
shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16);
shouldbe += ntohs(computed_sum);
shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16);
shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16);