CREATE OR replace FUNCTION left_shift( p_val INT8,
                                      p_shift INT8) returns int8
AS
  $$
  DECLARE
  BEGIN
    RETURN trunc(p_val * power(2,p_shift));
  END;
  $$ LANGUAGE 'plpgsql' immutable;

CREATE OR replace FUNCTION morton (p_col INT8,
                                   p_row INT8) returns int8
AS
  $$
  /*  this procedure calculates the Morton number of a cell
at the given row and col[umn]
Written:  D.M. Mark, Jan 1984;
Converted to Vax/VMS: July 1985
Converted to PostgreSQL, Simon Greener, 2010
*/
  DECLARE
    v_row int8 := 0;
    v_col int8 := 0;
    v_key int8;
    v_level int8;
    v_left_bit int8;
    v_right_bit int8;
    v_quadrant int8;
  BEGIN
    v_row := p_row;
    v_col := p_col;
    v_key := 0;
    v_level := 0;
    WHILE ((v_row>0)
    OR
    (
      v_col>0
    )
    )
    LOOP
      /* Split off the row (left_bit) and column (right_bit) bits and
then combine them to form a bit-pair representing the quadrant */
      v_left_bit := v_row % 2;
      v_right_bit := v_col % 2;
      v_quadrant := v_right_bit + 2*v_left_bit;
      v_key := v_key            + left_shift( v_quadrant,( 2 * v_level ) );
      /* row, column, and level are then modified before the loop continues */
      v_row := v_row     / 2;
      v_col := v_col     / 2;
      v_level := v_level + 1;
    END LOOP;
    RETURN (v_key);
  END;
  $$ LANGUAGE 'plpgsql' immutable;