code: public static void swap(final int[][] array, final long first, final long second)
      {
          final int t = array[segment(first)][displacement(first)];
          array[segment(first)][displacement(first)] = array[segment(second)][displacement(second)];
          array[segment(second)][displacement(second)] = t;
      }
docs: Swaps the element of the given big array of specified indices.
  
  @param array a big array.
  @param first a position in the big array.
  @param second a position in the big array.