def eval_cluster(labels, cluster_id, is_clean):
    """ Evaluate true positives in provided cluster.

    :param labels: (np.ndarray) array of labels
    :param cluster_id: (int) identifier of the cluster to evaluate
    :param is_clean: (array) bitmap where 1 means the point is not attacked
    :return: (int) number of identified backdoored points
    """
    cluster = labels == cluster_id
    identified = 0

    for i in range(len(is_clean)):
        if cluster[i] and is_clean[i] == 0:
            identified += 1

    return identified