code: public long addAndGet(final long increment)
      {
          long currentValue;
          long newValue;
  
          do
          {
              currentValue = get();
              newValue = currentValue + increment;
          }
          while (!compareAndSet(currentValue, newValue));
  
          return newValue;
      }
docs: Atomically add the supplied value.
  
  @param increment The value to add to the sequence.
  @return The value after the increment.