Get appropriate cost for password hashing

password_get_appropriate_cost.php

/**
 * Get appropriate cost 
 * 
 * This code will benchmark your server to determine how high of a cost you can
 * afford. You want to set the highest cost that you can without slowing down
 * you server too much.
 * 
 * @param int $time_limit Time limit in milliseconds
 * @param int $algo Algoritm, default PASSWORD_DEFAULT
 * @return int 
 */
function password_get_appropriate_cost(int $time_limit, int $algo = PASSWORD_DEFAULT) : int
{
    //set start cost
    $cost = 3;
    
    do {
        //increase cost
        $cost++;
        
        //check if cost is out of range for bcrypt
        if ($algo === 1 && ($cost < 4 || $cost > 31)) {
            break;
        }
        
        //start time
        $start = microtime(true);
        
        //generate password
        password_hash("test", $algo, ["cost" => $cost]);
        
        //stop time
        $end = microtime(true);
        
    } while (($end - $start) < ($time_limit / 100));
    
    return $cost;
}