There is more fast implementation of array_diff, but with some limitations. If you need compare two arrays of integers or strings you can use such function:

    public static function arrayDiffEmulation($arrayFrom, $arrayAgainst)
    {
        $arrayAgainst = array_flip($arrayAgainst);
        
        foreach ($arrayFrom as $key => $value) {
            if(isset($arrayAgainst[$value])) {
                unset($arrayFrom[$key]);
            }
        }
        
        return $arrayFrom;
    }

It is ~10x faster than array_diff

php > $t = microtime(true);$a = range(0,25000); $b = range(15000,500000); $c = array_diff($a, $b);echo microtime(true) - $t;
4.4335179328918
php > $t = microtime(true);$a = range(0,25000); $b = range(15000,500000); $c = arrayDiffEmulation($a, $b);echo microtime(true) - $t;
0.37219095230103