code: private static long add(long xs, long ys){
          long sum = xs + ys;
          // See "Hacker's Delight" section 2-12 for explanation of
          // the overflow test.
          if ( (((sum ^ xs) & (sum ^ ys))) >= 0L) { // not overflowed
              return sum;
          }
          return INFLATED;
      }
docs: /*
  returns INFLATED if oveflow