写一个Murmurhash3的存储过程

下面是一个MurmurHash3算法的MySQL存储过程实现，使用的是32位版本的MurmurHash3：

DELIMITER $$

CREATE FUNCTION murmurhash3_32bit(input VARCHAR(255), seed INT) RETURNS UNSIGNED INT
BEGIN
    DECLARE m, r, h, k, len INT UNSIGNED;
    DECLARE i INT;

    SET m = 0x5bd1e995;
    SET r = 24;
    SET h = seed ^ LENGTH(input);
    SET len = LENGTH(input);
    SET i = 1;

    WHILE len >= 4 DO
        SET k = (ASCII(SUBSTRING(input, i, 1))) | (ASCII(SUBSTRING(input, i + 1, 1)) << 8) | (ASCII(SUBSTRING(input, i + 2, 1)) << 16) | (ASCII(SUBSTRING(input, i + 3, 1)) << 24);
        k = k * m;
        k = k XOR (k >> r);
        k = k * m;
        h = h * m;
        h = h XOR k;
        len = len - 4;
        i = i + 4;
    END WHILE;

    IF len = 3 THEN
        SET h = h XOR (ASCII(SUBSTRING(input, i + 2, 1)) << 16);
    END IF;

    IF len >= 2 THEN
        SET h = h XOR (ASCII(SUBSTRING(input, i + 1, 1)) << 8);
    END IF;

    IF len >= 1 THEN
        SET h = h XOR ASCII(SUBSTRING(input, i, 1));
        SET k = h * m;
        k = k XOR (k >> r);
        k = k * m;
        h = h * m;
        h = h XOR k;
    END IF;

    SET h = h XOR (h >> 13);
    SET h = h * m;
    SET h = h XOR (h >> 15);

    RETURN h;
END$$

DELIMITER ;

这个存储过程接受两个参数，一个是输入字符串，一个是种子值。它使用MurmurHash3算法对输入字符串进行哈希，并返回一个32位无符号整数。具体实现细节可以参考注释。