Pascal : date to longint and back

function date_val(date : datestr) : longint;
var d,m,y,f : longint;
    e : integer;

begin
  IF DATE='  /  /  ' THEN DATE:=FAR_AWAY_DATE;

  val(copy(date,1,2),d,e);
  val(copy(date,4,2),m,e);
  val(copy(date,7,2),y,e);

  if y>century_mark then y:=y+century1 else y:=y+century2;

  f:=(365*y) + d + (31*(m-1));

  if m<3 then begin
    f:=f + trunc((y-1)/4) - trunc(0.75*(trunc((y-1)/100)+1));
  end
  else begin
    f:=f - trunc(0.4*m+2.3) + trunc(y/4) - trunc(0.75*(trunc(y/100)+1));
  end;

  date_val:=f;
end;


{ ------------------------------------------------------------------------- }

(******************************************)
(*** CONVERT numeric DATE TO string date  *)
(******************************************)
Function Date_Str (DateNum: longint) : Str8;

var
   day,mon,year,temp,e : longint;
   Dstr, Mstr, Ystr : String [2];
   TempA, TempB, TempC: longint;
begin

   TempA := DateNum + 68569;
   TempB := 4 * TempA div 146097;
   TempA := TempA - (146097 * TempB + 3) div 4;
   Year  := 4000 * (TempA + 1) div 1461001;
   TempC := Year;
   TempA := TempA - (1461 * TempC div 4) + 31;
   Mon   := 80 * TempA div 2447;
   TempC := Mon;
   Day   := TempA - (2447 * TempC div 80);
   TempA := Mon div 11;
   Mon   := Mon + 2 - (12 * TempA);
   Year  := 100 * (TempB - 49) + Year + TempA;

   Str (Day :2,Dstr);
   Str (Mon :2,Mstr);
   If Year <= 1999
    then Dec (Year,1900)
    else Dec (Year,2000);

   Str (Year:2,Ystr);

   if Dstr [1] = ' ' then Dstr [1] := '0';
   if Mstr [1] = ' ' then Mstr [1] := '0';
   if Ystr [1] = ' ' then Ystr [1] := '0';

   {if Ystr='0' then Ystr:='00';}

   Date_Str := Dstr + '/' + Mstr + '/' + Ystr;
                      { handle blank field }
   if datenum = 0 then Date_Str := '  /  /  ';

end;