simple convert integer(system max numeric) <-> string(always 14 chars)

meconv.php

<?php

function meconv($value)
{
    if (ctype_digit(strval($value))) {
        $str = chr(96 + strlen(base_convert($value, 10, 36)));
        $str .= base_convert($value, 10, 36);
        $str .= md5($value);
        return substr($str, 0, 14);
    } elseif(is_string($value)) {
        $len = ord($value{0}) - 96;
        if ($len >= 1 && $len <= 14) {
            return base_convert(substr($value, 1, $len), 36, 10);
        }
    }

    return false;
}

/*
meconv(PHP_INT_MAX); // fzik0zjc588c0a
meconv('fzik0zjc588c0a'); // 2147483647
meconv('9999999999999998'); // k2qgpckvng1qb7 ('9999999999999998' is system max)
*/

meconv.sql

DELIMITER //
DROP FUNCTION IF EXISTS `MECONV`//
CREATE FUNCTION MECONV( _value VARCHAR(20)) RETURNS VARCHAR(20)
LANGUAGE SQL NOT DETERMINISTIC READS SQL DATA
BEGIN
	DECLARE re VARCHAR(20) DEFAULT NULL;
	
	IF (_value REGEXP '^[0-9]+$') = 1 THEN
		SET re = SUBSTR(CONCAT(CHAR(96 + CHAR_LENGTH(CONV(_value, 10, 36))), LOWER(CONV(_value, 10, 36)), MD5(_value)), 1, 14);
	ELSEIF (_value REGEXP '^[a-m][a-z0-9]{13}$') = 1 THEN
		SET re = CONV(UPPER(SUBSTR(_value, 2, (ASCII(SUBSTR(_value, 1, 1)) - 96))), 36, 10);
	END IF;
	
	RETURN re;
END;
//

/*
SELECT meconv(18446744073709551615); // m3w5e11264sgsf (18446744073709551615 is BIGINT max)
SELECT meconv('m3w5e11264sgsf'); // 18446744073709551615
*/