2 graph.c -- graph algorithms
3 Copyright (C) 2001 Guus Sliepen <guus@sliepen.warande.net>,
4 2001 Ivo Timmermans <itimmermans@bigfoot.com>
6 This program is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2 of the License, or
9 (at your option) any later version.
11 This program is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program; if not, write to the Free Software
18 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
20 $Id: graph.c,v 1.1.2.3 2001/10/29 13:14:57 guus Exp $
23 /* We need to generate two trees from the graph:
25 1. A minimum spanning tree for broadcasts,
26 2. A single-source shortest path tree for unicasts.
28 Actually, the first one alone would suffice but would make unicast packets
29 take longer routes than necessary.
31 For the MST algorithm we can choose from Prim's or Kruskal's. I personally
32 favour Kruskal's, because we make an extra AVL tree of edges sorted on
33 weights (metric). That tree only has to be updated when an edge is added or
34 removed, and during the MST algorithm we just have go linearly through that
35 tree, adding safe edges until #edges = #nodes - 1.
37 For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a
38 simple breadth-first search is presented here.
49 #include "connection.h"
53 /* Implementation of Kruskal's algorithm.
55 Please note that sorting on weight is already done by add_edge().
58 void mst_kruskal(void)
68 syslog(LOG_DEBUG, _("Running Kruskal's algorithm:"));
70 /* Clear visited status on nodes */
72 for(node = node_tree->head; node; node = node->next)
74 n = (node_t *)node->data;
75 n->status.visited = 0;
81 ((edge_t *)edge_weight_tree->head->data)->from->status.visited = 1;
83 /* Clear MST status on connections */
85 for(node = connection_tree->head; node; node = node->next)
87 c = (connection_t *)node->data;
93 while(safe_edges < nodes - 1)
94 for(skipped = 0, node = edge_weight_tree->head; node; node = node->next)
96 // Algorithm should work without this:
97 // if(safe_edges = nodes - 1)
100 e = (edge_t *)node->data;
102 if(e->from->status.visited == e->to->status.visited)
108 e->from->status.visited = 1;
109 e->to->status.visited = 1;
111 e->connection->status.mst = 1;
115 syslog(LOG_DEBUG, _("Adding safe edge %s - %s weight %d"), e->from->name, e->to->name, e->weight);
121 syslog(LOG_DEBUG, _("Done."));
123 if(safe_edges != nodes - 1)
125 syslog(LOG_ERR, _("Implementation of Kruskal's algorithm is screwed: %d nodes, found %d safe edges"), nodes, safe_edges);
129 /* Implementation of a simple breadth-first search algorithm.
135 avl_node_t *node, *from, *next, *to;
140 avl_tree_t *todo_tree;
142 syslog(LOG_DEBUG, _("Running BFS algorithm:"));
144 todo_tree = avl_alloc_tree(NULL, NULL);
146 /* Clear visited status on nodes */
148 for(node = node_tree->head; node; node = node->next)
150 n = (node_t *)node->data;
151 n->status.visited = 0;
155 /* Begin with myself */
157 myself->status.visited = 1;
158 myself->nexthop = myself;
159 myself->via = myself;
160 node = avl_alloc_node();
162 avl_insert_top(todo_tree, node);
165 /* Loop while todo_tree is filled */
167 while(todo_tree->head)
169 for(from = todo_tree->head; from; from = next)
172 n = (node_t *)from->data;
174 for(to = n->edge_tree->head; to; to = to->next)
176 e = (edge_t *)to->data;
183 if(!check->status.visited)
185 check->status.visited = 1;
186 check->nexthop = (n->nexthop == myself) ? n : n->nexthop;
187 check->via = check; /* FIXME: only if !(e->options & INDIRECT), otherwise use n->via */
188 node = avl_alloc_node();
190 avl_insert_before(todo_tree, from, node);
192 syslog(LOG_DEBUG, _("Node %s nexthop %s via %s"), check->name, check->nexthop->name, check->via->name);
196 avl_delete_node(todo_tree, from);
200 syslog(LOG_DEBUG, _("Done."));
202 avl_free_tree(todo_tree);
206 syslog(LOG_ERR, _("Implementation of BFS algorithm is screwed: %d nodes, visited %d"), nodes, visited);