def METHOD_NAME(self, q, a, b):
    # XXX Use _lazywhere...
    ans = self._get_norms(a, b)
    _na, _nb, _sa, _sb = ans[:4]
    ppf = np.where(
        a > 0,
        _norm_isf(q * _sb + _sa * (1.0 - q)),
        _norm_ppf(q * _nb + _na * (1.0 - q)),
    )
    return ppf