Parameters
    ----------
    arrays : generator
    num_items : int

    Should be the same as CPython's tupleobject.c

def _combine_hash_arrays(arrays, num_items):
    """
    Parameters
    ----------
    arrays : generator
    num_items : int

    Should be the same as CPython's tupleobject.c
    """
    try:
        first = next(arrays)
    except StopIteration:
        return np.array([], dtype=np.uint64)

    arrays = itertools.chain([first], arrays)

    mult = np.uint64(1000003)
    out = np.zeros_like(first) + np.uint64(0x345678)
    for i, a in enumerate(arrays):
        inverse_i = num_items - i
        out ^= a
        out *= mult
        mult += np.uint64(82520 + inverse_i + inverse_i)
    assert i + 1 == num_items, 'Fed in wrong num_items'
    out += np.uint64(97531)
    return out