PHP实现的QQ空间g_tk加密算法

function getGTK($skey){
    $len = strlen($skey);
    $hash = 5381;
    for($i = 0; $i < $len; $i++){
        $hash += ((($hash << 5) & 0x7fffffff) + utf8_unicode($skey[$i])) & 0x7fffffff;
        $hash&=0x7fffffff;
    }
    return $hash & 0x7fffffff;//计算g_tk
}

function utf8_unicode($c) {
    switch(strlen($c)) {
        case 1:
            return ord($c);
        case 2:
            $n = (ord($c[0]) & 0x3f) << 6;
            $n += ord($c[1]) & 0x3f;
            return $n;
        case 3:
            $n = (ord($c[0]) & 0x1f) << 12;
            $n += (ord($c[1]) & 0x3f) << 6;
            $n += ord($c[2]) & 0x3f;
            return $n;
        case 4:
            $n = (ord($c[0]) & 0x0f) << 18;
            $n += (ord($c[1]) & 0x3f) << 12;
            $n += (ord($c[2]) & 0x3f) << 6;
            $n += ord($c[3]) & 0x3f;
            return $n;
    }
}