[xkor]

procedure AddChecksum(var data; position: Word);
var
  i,k:Word;
  dt: array[0..0] of Byte absolute data;
begin
  k := (position div 4)-1;
  for i := 0 to k do
    PCardinal(@dt[position])^:=PCardinal(@dt[position])^ xor PCardinal(@dt[i*4])^;
end;