Codeigniter dynamic base_url() setup

$config['base_url'] =  ((isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == "on") ?  "https" : "http");

$config['base_url'] .=  "://".$_SERVER['HTTP_HOST'];

$config['base_url'] .=  str_replace(basename($_SERVER['SCRIPT_NAME']),"",$_SERVER['SCRIPT_NAME']);