MySQL Damerau-Levenshtein

CREATE DEFINER=`root`@`localhost` FUNCTION `DAMLEV`(`s1` VARCHAR(255), `s2` VARCHAR(255)) RETURNS int(11)
    DETERMINISTIC
    SQL SECURITY INVOKER
BEGIN
  DECLARE s1_len, s2_len, i, j, c, c_temp, cost INT;
DECLARE s1_char CHAR;
DECLARE cv0, cv1 VARBINARY(256);
SET s1_len = CHAR_LENGTH(s1), s2_len = CHAR_LENGTH(s2), cv1 = 0x00, j = 1, i = 1, c = 0;
IF s1 = s2 THEN
    RETURN 0;
ELSEIF s1_len = 0 THEN
    RETURN s2_len;
ELSEIF s2_len = 0 THEN
    RETURN s1_len;
ELSE
    WHILE j <= s2_len DO
      SET cv1 = CONCAT(cv1, UNHEX(HEX(j)));
SET j = j + 1;
END WHILE;
WHILE i <= s1_len DO
      SET s1_char = SUBSTRING(s1, i, 1);
SET c = i;
SET cv0 = UNHEX(HEX(i));
SET j = 1;
WHILE j <= s2_len DO
          SET c = c + 1;
IF s1_char = SUBSTRING(s2, j, 1) THEN
                SET cost = 0;
ELSE
                SET cost = 1;
END IF;
SET c_temp = CONV (HEX(SUBSTRING(cv1, j, 1)), 16, 10) + cost;
IF c > c_temp THEN
                SET c = c_temp;
END IF;
SET c_temp = CONV (HEX(SUBSTRING(cv1, j+1, 1)), 16, 10) + 1;
IF c > c_temp THEN
                 SET c = c_temp;
END IF;
IF i > 1 AND j > 1 AND (s1_char = SUBSTRING (s2, j - 1, 1)) AND (SUBSTRING (s1, i - 1, 1) = SUBSTRING(s2, j, 1)) THEN
                        SET c_temp = CONV(HEX(SUBSTRING(cv1, j + 1, 1)), 16, 10);
END IF;
IF c > c_temp THEN
                        SET c = c_temp;
END IF;
SET cv0 = CONCAT(cv0, UNHEX(HEX(c)));
SET j = j + 1;
END WHILE;
SET cv1 = cv0;
SET i = i + 1;
END WHILE;
END IF;
RETURN c;

END