code: public int addAndGetHi(int delta) {
          while (true) {
              long encoded = get();
              int hi = getHi(encoded) + delta;
              long update = encodeHi(encoded, hi);
              if (compareAndSet(encoded, update))
                  return hi;
          }
      }
docs: Atomically adds the given delta to the current hi value, returning the updated hi value.
  
  @param delta the delta to apply
  @return the updated hi value