def METHOD_NAME(cov, cutoff=50, hbar=2, padding_factor=2):
    r"""Calculates the total photon number distribution of a pure state
    with zero mean.
    Args:
        cov (array): :math:`2N\times 2N` covariance matrix in xp-ordering
        cutoff (int): Fock cutoff
        tol (float): tolerance for determining if displacement is negligible
        hbar (float): the value of :math:`\hbar` in the commutation
        padding_factor (int): expanded size of the photon distribution to avoid accumulation of errors
    Returns:
        (array): Total photon number distribution
    """
    if is_pure_cov(cov):
        A = Amat(cov, hbar=hbar)
        (n, _) = A.shape
        N = n // 2
        B = A[0:N, 0:N]
        rs = np.arctanh(np.linalg.svd(B, compute_uv=False))
        return _convolve_squeezed_state_distribution(
            rs, cutoff=cutoff, padding_factor=padding_factor
        )[0:cutoff]
    raise ValueError("The Gaussian state is not pure")