code: public final double addAndGet(double delta) 
      {
          while(true) 
          {
              double orig = get();
              double newVal = orig + delta;
              if (compareAndSet(orig, newVal))
                  return newVal;
          }
      }
docs: Atomically adds the given value to the current value.
  
  @param delta the value to add
  @return the updated value