Return the function who has the greatest address that is less than or equal to `addr`.

        :param int addr: The address to query.
        :return:         A Function instance, or None if there is no other function before `addr`.
        :rtype:          Function or None

def floor_func(self, addr):
        """
        Return the function who has the greatest address that is less than or equal to `addr`.

        :param int addr: The address to query.
        :return:         A Function instance, or None if there is no other function before `addr`.
        :rtype:          Function or None
        """

        try:
            prev_addr = self._function_map.floor_addr(addr)
            return self._function_map[prev_addr]

        except KeyError:
            return None