PROCEDURE drtodate(thedate : integer; VAR yr, mo, day : integer);
  (* 1 Jan 1978 corresponds to Digital Research date = 1  *)
  (* BUG - cannot handle negative values for dates > 2067 *)

    VAR
      i, y1        : integer;
      dayspermonth : ARRAY[1..12] OF 1..31;

    BEGIN (* drtodate *)
    FOR i := 1 TO 12 DO dayspermonth[i] := 31;
    dayspermonth[4] := 30; dayspermonth[6] := 30;
    dayspermonth[9] := 30; dayspermonth[11] := 30;
    IF thedate >= 731 THEN BEGIN (* avoid overflows *)
      yr := 1980; thedate := thedate - 731; END
    ELSE BEGIN
      thedate := thedate + 730; yr := 1976; END;
    (* 0..365=y0; 366..730=y1; 731..1095=y2; 1096..1460=y3 *)
    i := thedate DIV 1461; thedate := thedate MOD 1461;
    y1 := (thedate-1) DIV 365; yr := yr + y1 + 4*i;
    IF y1 = 0 THEN (* leap year *) dayspermonth[2] := 29
    ELSE BEGIN
      thedate := thedate - 1; (* 366 -> 365 -> 1 Jan *)
      dayspermonth[2] := 28; END;
    day := thedate - 365*y1 + 1; mo := 1;
    WHILE day > dayspermonth[mo] DO BEGIN
      day := day - dayspermonth[mo];
      mo := succ(mo); END;
    END; (* drtodate *)

  (* 1-----------------1 *)