我的密码哈希加上数据库中的salt与数据库中的密码不匹配

Question

我用这个简单的登录代码编写了这个。当我输入密码的哈希我输入加上我的数据库中的盐，这是假设匹配数据库中的密码，但它没有。请帮忙。这是我的代码

if(isset($_POST['uname'],$_POST['password'])){

    $uname = sanitize($_POST['uname']);
    $password = sanitize($_POST['password']);

    if(user_exists($uname)==false){
        $errors[] = 'username invalid!';
    }

    if(empty($errors)==true && empty($_POST)==false){
        $salt = get_salt($uname);
        $pass = get_passwd($uname);

        if(hashgen($password,$salt) === $pass){
            $_SESSION['username'] = $uname;
            header('Location:update.php');
        }else{
            echo 'incorrect username password combination!';
        }
    }else{
        echo '<pre>',print_r($errors),'</pre>';
    }
}


//my functions



function user_exists($name){
    $count = DB::getInstance()->getcount("SELECT COUNT(id) FROM admin WHERE username='{$name}'");
    return ($count !=0) ? true :false;
}


function get_passwd($string){
    $query = DB::getInstance()->query("SELECT password FROM admin WHERE name='{$string}'");
    foreach($query->results() as $row){
        return $row->password;
    }
}

function get_salt($string){
    $query = DB::getInstance()->query("SELECT salt FROM admin WHERE name='{$string}'");
    foreach($query->results() as $row){
        return $row->salt;
    }
}

function hashgen($string,$salt){
    return hash('sha256',$string.$salt);
}

function saltgen($length){
    return mcrypt_create_iv($length);
}