public static function mem_check($need)
    {
        $mem_limit = parse_bytes(ini_get('memory_limit'));
        $memory    = function_exists('memory_get_usage') ? memory_get_usage() : 16*1024*1024; // safe value: 16MB

        return $mem_limit > 0 && $memory + $need > $mem_limit ? false : true;
    }