__init__.py 文件源码

def get_sre(net, target_prefix_len):
        """Calculate first and last /target_prefix_len subnets from net

        Returns: first, last, cnt (all integers)
        """

        assert isinstance(net, (ipaddr.IPv4Network, ipaddr.IPv6Network))
        assert target_prefix_len <= 64, "Max target prefix length is 64"
        assert net.prefixlen <= target_prefix_len, \
            ("Prefix length ({}) must be <= of the target prefix "
             "length ({}): {}".format(net.prefixlen, target_prefix_len, net))

        first = UniqueSmallestRoutableEntriesMonitor.get_first(net)

        tot_len = 64 if net.version == 6 else 32

        # first <= 2^63 -1 to avoid overflows
        assert first <= 9223372036854775807, \
            "Only prefixes <= 7fff:ffff:ffff:ffff::/64 can be processed"

        diff_len = target_prefix_len - net.prefixlen

        last = first | ((2**diff_len - 1) << tot_len - target_prefix_len)

        return first, last, 2**diff_len