include unused full function or many includes

I am in the process of creating a PHP authorization framework which aims to be simple yet fast. My problem is being simple I hope to only have one include needed to use it , however when only having one include it may load unnecessary functions. So my question is which is better, including all function resulting in more memory being used or including a file which has the function to include that function resulting in smaller unnecessary functions but will it use more CPU usage?

for example my login function looks like this:

function login ($submit ='login', $user = 'user', $pass = 'pass') {    if ($_POST[$submit]){        $user = $_POST[$user];    $pass = $_POST[$pass];    if ($user && $pass){ //if user and pass is enterered            require("auth_vars.php"); //require MySQL conection settings            mysql_connect($auth_mysql_server, $auth_mysql_user, $auth_mysql_pass); //connect to MySQL        mysql_select_db($auth_mysql_db); // select MySQL database            $pass = md5($pass); // hash password            $query = mysql_query("SELECT * FROM $auth_mysql_table WHERE user='$user'"); // run query            $numrows = mysql_num_rows($query);            if ($numrows == 1){ //check if user exists                $row = mysql_fetch_assoc ($query);                $dbid = $row[$auth_mysql_id_row];                    $dbuser = $row[$auth_mysql_user_row];                    $dbpass = $row[$auth_mysql_pass_row];                    if ($pass == $dbpass){ // if password is equal to the one in the database start session                        //set session information                        $_SESSION['userid'] = $dbid;                        $_SESSION['username'] = $dbuser;                        header("Location:$auth_path_loggedin"); // goto logged in page                    }                    else return (3);            }            else return (2);            mysql_close(); // close MySql connection        }        else return (1);}else {    // If the user clicks the "Log Out" link.    if(isset($_GET['status']) && $_GET['status'] == 'loggedout') {        logout();//logout        return 4;        //else if the user is denied    }else if(isset($_GET['status']) && $_GET['status'] == 'denied') {        logout(); //to keep it clean in case of errors        return 5;    }}}

now in case the login function is not needed would it be better to do this:

function login ($submit ='login', $user = 'user', $pass = 'pass') {    include ("myloginfunction.php");    login_function($submit, $user, $pass);}

or would it use to much unnecessary CPU usage compare to the amount of memory needed to include whole function