MySQL Function to Calculate Murmur Hash Murmurhash (MurmurHashV3)

MurmurHashV3.sql

DROP FUNCTION IF EXISTS MurmurHashV3;
DELIMITER //
CREATE FUNCTION `MurmurHashV3`(`keyx` varchar(65535), `seed` int unsigned)
	RETURNS int unsigned
BEGIN
	DECLARE remainder,bytes,c1,c2,i, m1,m2 INT unsigned;
	DECLARE h1,k1,h1b BIGINT unsigned;
	SET remainder = LENGTH(keyx) & 3;
	SET bytes = LENGTH(keyx) - remainder;
    SET h1 = seed;
    SET c1 = 0xcc9e2d51;
    SET c2 = 0x1b873593;
    SET m1 = 0x85ebca6b, m2 = 0xc2b2ae35;
    SET i = 1;

    WHILE i <= bytes DO
       set k1 = ( ascii(mid(keyx,i,1)) & 0xff ) | 
		((ascii(mid(keyx,i+1,1)) & 0xff) << 8) |
		((ascii(mid(keyx,i+2,1)) & 0xff) << 16) |
		((ascii(mid(keyx,i+3,1)) & 0xff) << 24);
      set i = i + 4;

      set k1 = (k1*c1) & 0xffffffff;
      set k1 = ((k1 << 15) | (k1 >> 17))& 0xffffffff;
      set k1 = (k1*c2) & 0xffffffff;

      set h1 = h1 ^ k1;
      set h1 = ((h1 << 13) | (h1 >> 19))& 0xffffffff;
      set h1b = (h1*5) & 0xffffffff;
      set h1 = (h1b+0xe6546b64)& 0xffffffff;
    END WHILE;

    SET k1 = 0;

   IF remainder>=3  THEN SET k1 = k1^((ascii(mid(keyx,i + 2,1)) & 0xff) << 16); END IF;
	IF remainder>=2 THEN SET k1 = k1^((ascii(mid(keyx,i + 1,1)) & 0xff) << 8); END IF;
	IF remainder>=1 THEN SET k1 = k1^(ascii(mid(keyx,i,1)) & 0xff);
      set k1 = (k1*c1) & 0xffffffff;
      set k1 = ((k1 << 15) | (k1 >> 17))& 0xffffffff;
      set k1 = (k1*c2) & 0xffffffff;
      set h1 = h1 ^ k1;
    END IF;

	 set h1 = h1 ^ LENGTH(keyx);
    set h1 = h1 ^ (h1 >> 16);
	 set h1 = (h1*m1) & 0xffffffff;
    
	 set h1 = h1 ^ (h1 >> 13);
    set h1 = (h1*m2) & 0xffffffff;
    set h1 = h1 ^ (h1 >> 16);

    return h1;
END;//
DELIMITER ;

Select MurmurHashV3('test', 0);

note that it pop warning if your database is in UTF-8 as the varchar(65535) exceed the maximun number of bytes of a varchar (as then you have potentially 65535 characters of 3 bytes each)
and it does not work as expected if you feed it with utf-8 encoded string (as the mid methods will cut by characters of potentially 3 bytes while you're expecting in murmur hash to iterate byte by byte)

I've created a corrected version (which we have tested to produce exactly the same 32 bit hashes as python module mmh3)
http://allan-simon.github.io/blog/posts/murmur_hash_v3_in_mysql_utf8_compatible/