code: public boolean containsValue(Object value) {
      EntryImpl<K, V> entry = _mapFirst;
      while (entry != null) {
        if (value.equals(entry._value)) { return true; }
        entry = entry._after;
      }
      return false;
    }
docs: Indicates if this {@link FastMap} maps one or more keys to the
  specified value.
  
  @param value the value whose presence in this map is to be tested.
  @return <code>true</code> if this map maps one or more keys to the
  specified value.
  @throws NullPointerException if the key is <code>null</code>.