def kdot(x, y, K=2):
    """Algorithm 5.10. Dot product algorithm in K-fold working precision,
    K >= 3.
    """
    xx = x.reshape(-1, x.shape[-1])
    yy = y.reshape(y.shape[0], -1)

    xx = numpy.ascontiguousarray(xx)
    yy = numpy.ascontiguousarray(yy)

    r = _accupy.kdot_helper(xx, yy).reshape((-1,) + x.shape[:-1] + y.shape[1:])
    return ksum(r, K - 1)