mysql散列算法

DELIMITER //
create function t(in_str VARCHAR(255))
returns int
begin
declare i int;
declare l int;
declare min_int int;
declare max_int int;
declare r int;
set i = 1;
set r = 0;
set min_int = -2147483648;
set max_int = 2147483647;
select CHAR_LENGTH(in_str) into l;
if l < 1
	then return(0);
end if;
while i <= l do
	set r = overflow(31 * r + ASCII(substring(in_str, i, 1)));
	set i=i+1;
end while;
return(r);
end
//

DELIMITER ;