def _calculate_block_start(current_position):
    """ converts pointer position into one being multiple of 8

        Parameters
        ----------------
        current_position : int
            position in file

        Returns
        -----------
        position multiple of 8
    """
    remain = current_position % 8
    if not remain == 0:
        return current_position - remain + 8
    else:
        return current_position
