CREATE FUNCTION INT_TO_HEX (
    ANUMBER BIGINT,
    ABYTE_PER_NUMBER SMALLINT = 8)
RETURNS CHAR(66)
AS
DECLARE VARIABLE XMOD SMALLINT;
DECLARE VARIABLE XRESULT VARCHAR(64);
DECLARE FUNCTION TO_HEX(ANUM SMALLINT) RETURNS CHAR
AS
BEGIN
  RETURN CASE ANUM
           WHEN 0 THEN '0'
           WHEN 1 THEN '1'
           WHEN 2 THEN '2'
           WHEN 3 THEN '3'
           WHEN 4 THEN '4'
           WHEN 5 THEN '5'
           WHEN 6 THEN '6'
           WHEN 7 THEN '7'
           WHEN 8 THEN '8'
           WHEN 9 THEN '9'
           WHEN 10 THEN 'A'
           WHEN 11 THEN 'B'
           WHEN 12 THEN 'C'
           WHEN 13 THEN 'D'
           WHEN 14 THEN 'E'
           WHEN 15 THEN 'F'
           ELSE NULL
         END;
END
BEGIN
  XMOD = MOD(ANUMBER, 16);
  ANUMBER = ANUMBER / 16;
  XRESULT = TO_HEX(XMOD);
  WHILE (ANUMBER > 0) DO
  BEGIN
    XMOD = MOD(ANUMBER, 16);
    ANUMBER = ANUMBER / 16;
    XRESULT = TO_HEX(XMOD) || XRESULT;
  END
  RETURN '0x' || LPAD(XRESULT, ABYTE_PER_NUMBER * 2, '0');
END

CREATE FUNCTION INT_TO_HEX (
    ANUMBER BIGINT,
    ABYTE_PER_NUMBER SMALLINT = 8)
RETURNS CHAR(66)
AS
DECLARE VARIABLE XMOD SMALLINT;
DECLARE VARIABLE XRESULT VARCHAR(64);
DECLARE FUNCTION TO_HEX(ANUM SMALLINT) RETURNS CHAR
AS
BEGIN
  RETURN CASE ANUM
           WHEN 0 THEN '0'
           WHEN 1 THEN '1'
           WHEN 2 THEN '2'
           WHEN 3 THEN '3'
           WHEN 4 THEN '4'
           WHEN 5 THEN '5'
           WHEN 6 THEN '6'
           WHEN 7 THEN '7'
           WHEN 8 THEN '8'
           WHEN 9 THEN '9'
           WHEN 10 THEN 'A'
           WHEN 11 THEN 'B'
           WHEN 12 THEN 'C'
           WHEN 13 THEN 'D'
           WHEN 14 THEN 'E'
           WHEN 15 THEN 'F'
           ELSE NULL
         END;
ENDBEGIN -- <- вот здесь слепил END от подфункции с BEGIN от тела функции
  XMOD = MOD(ANUMBER, 16);
  ANUMBER = ANUMBER / 16;
  XRESULT = TO_HEX(XMOD);
  WHILE (ANUMBER > 0) DO
  BEGIN
    XMOD = MOD(ANUMBER, 16);
    ANUMBER = ANUMBER / 16;
    XRESULT = TO_HEX(XMOD) || XRESULT;
  END
  RETURN '0x' || LPAD(XRESULT, ABYTE_PER_NUMBER * 2, '0');
END