Equivalent degrees of freedom for Total Deviation
        FIXME: what is the right behavior for alpha outside 0,-1,-2?
        
        NIST SP1065 page 41, Table 7

def edf_totdev(N, m, alpha):
    """ Equivalent degrees of freedom for Total Deviation
        FIXME: what is the right behavior for alpha outside 0,-1,-2?
        
        NIST SP1065 page 41, Table 7
    """
    alpha = int(alpha)
    if alpha in [0, -1, -2]:
        # alpha  0 WFM
        # alpha -1 FFM
        # alpha -2 RWFM
        NIST_SP1065_table7 = [(1.50, 0.0), (1.17, 0.22), (0.93, 0.36)]
        (b, c) = NIST_SP1065_table7[int(abs(alpha))]
        return b*(float(N)/float(m))-c
    else:
        return edf_simple(N, m, alpha)