Source code for pacman.operations.router_compressors.ordered_covering_router_compressor.remove_default_routes

# Copyright (c) 2017-2019 The University of Manchester
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <>.

based on

from .utils import intersect
from pacman.exceptions import MinimisationFailedError

[docs]def remove_default_routes(table, target_length, check_for_aliases=True): """ Remove from the routing table any entries which could be replaced by default routing. :param list(Entry) table: Routing entries to be merged. :param target_length: Target length of the routing table; the minimisation procedure will halt once either this target is reached or no further minimisation is possible. If ``None`` then the table will be made as small as possible. :type target_length: int or None :param bool check_for_aliases: If ``True`` (the default), default-route candidates are checked for aliased entries before suggesting a route may be default routed. This check is required to ensure correctness in the general case but has a runtime complexity of O(N\\ :sup:`2`) in the worst case for N-entry tables. If ``False``, the alias-check is skipped resulting in O(N) runtime. This option should only be used if the supplied table is guaranteed not to contain any aliased entries. :rtype: list(Entry) :raises MinimisationFailedError: If the smallest table that can be produced is larger than ``target_length``. """ # If alias checking is required, see if we can cheaply prove that no # aliases exist in the table to skip this costly check. if check_for_aliases: # Aliases cannot exist when all entries share the same mask and all # keys are unique. if len(set(e.mask for e in table)) == 1 and \ len(table) == len(set(e.key for e in table)): check_for_aliases = False # Generate a new table with default-route entries removed new_table = list() for i, entry in enumerate(table): if not entry.defaultable: # If the entry cannot be removed then add it to the table new_table.append(entry) elif check_for_aliases: key, mask = entry.key, entry.mask # If there is an intersect with a later entry we have to keep it if any(intersect(key, mask, d.key, d.mask) for d in table[i + 1:]): new_table.append(entry) if target_length and len(new_table) > target_length: raise MinimisationFailedError( f"Best compression is {len(new_table)} which is " f"still higher than the target {target_length}") return new_table