# 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
# 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
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# 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 <http://www.gnu.org/licenses/>.

"""
based on
https://github.com/project-rig/rig/blob/master/rig/routing_table/remove_default_routes.py
"""

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: