MySQL Type 3 GUID generation function

DELIMITER $$
DROP FUNCTION IF EXISTS guidFromNamespace $$
CREATE FUNCTION guidFromNamespace(
    `namespace` BINARY(16),
    `content` VARCHAR(128)
) RETURNS BINARY(16) DETERMINISTIC
RETURN UNHEX(CONCAT(
    SUBSTR(MD5(CONCAT(namespace,content)),1,12),
    '3',
    SUBSTR(MD5(CONCAT(namespace,content)),14,3),
    CASE
        WHEN SUBSTR(MD5(CONCAT(namespace,content)),17,1) IN ('0','4','c') THEN '8'
        WHEN SUBSTR(MD5(CONCAT(namespace,content)),17,1) IN ('1','5','d') THEN '9'
        WHEN SUBSTR(MD5(CONCAT(namespace,content)),17,1) IN ('2','6','e') THEN 'a'
        WHEN SUBSTR(MD5(CONCAT(namespace,content)),17,1) IN ('3','7','f') THEN 'b'
        ELSE SUBSTR(MD5(CONCAT(namespace,content)),17,1)
    END,
    SUBSTR(MD5(CONCAT(namespace,content)),18,15)
)) $$