select
bit_count(cast(conv(substr('00d803fc07fc1ff807f8027f203f607b01fe03ff01fc03b8077f07780fb94039', 1, 16), 16, 10) as unsigned) ^ cast(conv(substr('00d803fc07fc1ff807f8027f203f607b00fe03ff01fe03b8077f07780fb94039', 1, 16), 16, 10) as unsigned)) +
bit_count(cast(conv(substr('00d803fc07fc1ff807f8027f203f607b01fe03ff01fc03b8077f07780fb94039', 17, 16), 16, 10) as unsigned) ^ cast(conv(substr('00d803fc07fc1ff807f8027f203f607b00fe03ff01fe03b8077f07780fb94039', 17, 16), 16, 10) as unsigned)) +
bit_count(cast(conv(substr('00d803fc07fc1ff807f8027f203f607b01fe03ff01fc03b8077f07780fb94039', 33, 16), 16, 10) as unsigned) ^ cast(conv(substr('00d803fc07fc1ff807f8027f203f607b00fe03ff01fe03b8077f07780fb94039', 33, 16), 16, 10) as unsigned)) +
bit_count(cast(conv(substr('00d803fc07fc1ff807f8027f203f607b01fe03ff01fc03b8077f07780fb94039', 49, 16), 16, 10) as unsigned) ^ cast(conv(substr('00d803fc07fc1ff807f8027f203f607b00fe03ff01fe03b8077f07780fb94039', 49, 16), 16, 10) as unsigned));

MariaDB [modscripts]> DELIMITER //
MariaDB [modscripts]> CREATE PROCEDURE Distance(IN fp1 CHAR(64), fp2 CHAR(64))
->  BEGIN
->  SELECT bit_count(cast(conv(substr(fp1, 1, 16), 16, 10) as unsigned) ^ cast(conv(substr(fp2, 1, 16), 16, 10) as unsigned)) +
->  bit_count(cast(conv(substr(fp1, 17, 16), 16, 10) as unsigned) ^ cast(conv(substr(fp2, 17, 16), 16, 10) as unsigned)) +
->  bit_count(cast(conv(substr(fp1, 33, 16), 16, 10) as unsigned) ^ cast(conv(substr(fp2, 33, 16), 16, 10) as unsigned)) +
->  bit_count(cast(conv(substr(fp1, 49, 16), 16, 10) as unsigned) ^ cast(conv(substr(fp2, 49, 16), 16, 10) as unsigned));
->  END //
Query OK, 0 rows affected (0.00 sec)

MariaDB [modscripts]> DELIMITER ;
MariaDB [modscripts]> call Distance(00d803fc07fc1ff807f8027f203f607b01fe03ff01fc03b8077f07780fb94039, 00d803fc07fc1ff807f8027f203f607b00fe03ff01fe03b8077f07780fb94039);
ERROR 1054 (42S22): Unknown column '00d803fc07fc1ff807f8027f203f607b01fe03ff01fc03b8077f07780fb94039' in 'field list'