def validate_old_rho_data(old_dict, FS):
    """ check if the old hashes match the new ones,
    otherwise we have to throw away all the old data
    """
    if 'hash_vib' not in old_dict or 'hash_rho' not in old_dict:
        old_dict.clear()
    elif old_dict['hash_vib'] != FS.hash_vib or old_dict['hash_rho'
        ] != FS.hash_rho:
        old_dict.clear()
    old_dict['hash_vib'] = FS.hash_vib
    old_dict['hash_rho'] = FS.hash_rho
    return
