ELFHash SQL实现

当前项目中用到了elfhash函数算出HASH值后再进行分表，
当需要在MYSQL里进行查询时比较麻烦，需要先算出HASH值才能确定用户数据被分到哪个表里，
于是把这个函数用SQL写成函数，方便使用。

CREATE DEFINER=`test`@`127.0.0.1` FUNCTION `elfhash`(strkey varchar(256)) RETURNS int(11)
    NO SQL
BEGIN
    #Routine body goes here...

/*
unsigned long ELFHash(const char *key)
{
    unsigned long h = 0;
    unsigned long x = 0;

    while (*key)
    {
        h = (h << 4) + (*key++);
        if ((x = h & 0xF0000000L) != 0)
        {
            h ^= (x >> 24);
            h &= ~x;
        }
    }
    return (h & 0x7FFFFFFF);
}
*/

    DECLARE h  INT UNSIGNED DEFAULT 0;
    DECLARE x  INT UNSIGNED DEFAULT 0;
    DECLARE k  INT UNSIGNED DEFAULT 0;
    DECLARE strLen INT UNSIGNED DEFAULT 0;
    DECLARE pos  INT UNSIGNED DEFAULT 0;

    SET strLen = LENGTH(strkey)+1;
    WHILE (pos<strLen) DO
        set k = ASCII(MID(strkey,pos,1));
        set h = (h << 4) + k;
        SET x = h & 0xF0000000;
        IF (x!= 0) THEN
            set h = h^(x >> 24);
            set h = h&(~x);
        END IF;

        SET pos = pos +1;
    END WHILE;

    SET h = h & 0x7FFFFFFF;
    RETURN h;

END

转载请注明：爱开源 » ELFHash SQL实现

转载请注明：爱开源 » ELFHash SQL实现