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