execute IBEBLOCK(BARCODE12 varchar(12) not null) returns(EAN13 varchar(13))
    as declare variable SUM1 integer;
declare variable SUM2 integer;
declare variable I integer;
declare variable CHECKDIGIT integer;
begin
  if (IBEC_LENGTH(BARCODE12) <> 12) then
    exception GENERAL_DB_ERROR('Input barcode length must be exactly 12 digits!');

  SUM1 = 0;
  SUM2 = 0;
  I = 2;
  while (I <= 12) do
  begin
    SUM1 = SUM1 + cast(substring(BARCODE12 from I for 1) as integer);
    I = I + 2;
  end

  SUM1 = SUM1 * 3;
  I = 1;
  while (I <= 11) do
  begin
    SUM2 = SUM2 + cast(substring(BARCODE12 from I for 1) as integer);
    I = I + 2;
  end
  SUM2 = SUM1 + SUM2;

  CHECKDIGIT = 10 - (IBEC_MOD(SUM2, 10));
  if (CHECKDIGIT = 10) then
    CHECKDIGIT = 0;
  EAN13 = BARCODE12 || CHECKDIGIT;
  suspend;
end;