code: private boolean incrementAt(int i, int j)
      {
          int offset = j << 2;
          long mask = (0xfL << offset);
          long t = tableAt(i);
          if ((t & mask) != mask)
          {
              tableAt(i, t + (1L << offset));
              return true;
          }
          return false;
      }
docs: Increments the specified counter by 1 if it is not already at the maximum value (15).
  
  @param i the table index (16 counters)
  @param j the counter to increment
  @return if incremented