BKDRHash算法Mysql实现

最近有个数据补漏的任务，要在db里进行分库的数据库根据VISITORID落入不同数据库

java实现如下：

public static int BKDRHash(char[] str) {
    // 31 131 1313 13131 131313 etc..
    int seed = 131;
    int hash = 0;
    for (int i = 0; i < str.length; i++) {
      hash = hash * seed + (str[i]);
    }
    return (hash & 0x7FFFFFFF);
  }    
}

mysql实现：

函数addOverFlow防止数据溢出

CREATE FUNCTION `addOverFlow`(`sum` int,`num` int) RETURNS int(11)
    NO SQL
BEGIN
        DECLARE temp INT;
        SET temp = 0;
        IF num >= 0 THEN
            IF sum >= 2147483647 - num THEN
                SET temp = sum - (2147483647 - num);
                SET sum = -2147483648 + temp - 1;
            ELSE
                SET sum = sum + num;
            END IF;
        ELSE 
            IF sum < -2147483648 - num THEN
                SET temp = (-2147483648 - num) - sum;
                SET sum = 2147483647 - temp + 1;
            ELSE
                SET sum = sum + num;
            END IF;
        END IF;
    RETURN sum;
END

BKDRHash函数：

CREATE FUNCTION `BKDRHash`(`IN_VISITORID` VARCHAR(128)) RETURNS int(11)
    NO SQL
BEGIN
    DECLARE seed INT;
    DECLARE iseed INT;
    DECLARE hashcode INT;
    DECLARE temphashcode INT;
    DECLARE temp INT;
    DECLARE i INT;
    DECLARE strlen INT;
    DECLARE result INT;
    DECLARE charOrd INT;
    SET seed = 131;
    SET iseed = 1;
    SET hashcode = 0;
    SET temphashcode = 0;
    SET i = 1;
    -- 字符串长度
    SET strlen = length(IN_VISITORID);
    -- 结果
    SET result = 0;
    -- 单个字符ascii码
    SET charOrd = 0seed;
    -- 从1开始截取字符串字符
    WHILE i <= strlen DO
        -- 获取单个字符ascii码
        SET charOrd = ASCII(SUBSTRING(IN_VISITORID, i, 1));
        SET temphashcode = hashcode;
        SET iseed = 1;
        -- 把乘法变成加法运算
        WHILE iseed <= seed - 1 DO
            SET hashcode = addOverFlow(hashcode, temphashcode);
            SET iseed = iseed + 1;
        END WHILE;
    -- 加上单个字符的ascii码
        SET hashcode = addOverFlow(hashcode, charOrd);
        SET i = i + 1;

    END WHILE;
    SET result = hashcode & 0x7FFFFFFF;
    RETURN result;
END