def _p_upperbound(b, m):
    """Compute the upper bound of the p-value according to [3].

    Input arguments:
    b : int
        Number of permutations yielding a test statistic at least
        extreme as the observed value.
    m : int
        Number of permutations

    Output arguments:
        The upper bound of the p-value.
    """
    return (b+1) / (m+1)