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 1.1.2.2 2001/10/28 22:42:49 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.
48 #include "connection.h"
52 /* Implementation of Kruskal's algorithm.
54 Please note that sorting on weight is already done by add_edge().
57 void mst_kruskal(void)
66 syslog(LOG_DEBUG, _("Running Kruskal's algorithm:"));
68 /* Clear visited status on nodes */
70 for(node = node_tree->head; node; node = node->next)
72 n = (node_t *)node->data;
73 n->status.visited = 0;
77 /* Clear MST status on connections */
79 for(node = connection_tree->head; node; node = node->next)
81 c = (connection_t *)node->data;
87 for(node = edge_weight_tree->head; node; node = node->next)
89 // Algorithm should work without this:
90 // if(safe_edges = nodes - 1)
93 e = (edge_t *)node->data;
95 if(e->from->status.visited && e->to->status.visited)
98 e->from->status.visited = 1;
99 e->to->status.visited = 1;
101 e->connection->status.mst = 1;
105 syslog(LOG_DEBUG, _("Adding safe edge %s - %s weight %d"), e->from->name, e->to->name, e->weight);
108 syslog(LOG_DEBUG, _("Done."));
110 if(safe_edges != nodes - 1)
112 syslog(LOG_ERR, _("Implementation of Kruskal's algorithm is screwed: %d nodes, found %d safe edges"), nodes, safe_edges);
116 /* Implementation of a simple breadth-first search algorithm.
122 avl_node_t *node, *from, *next, *to;
127 avl_tree_t *todo_tree;
129 syslog(LOG_DEBUG, _("Running BFS algorithm:"));
131 todo_tree = avl_alloc_tree(NULL, NULL);
133 /* Clear visited status on nodes */
135 for(node = node_tree->head; node; node = node->next)
137 n = (node_t *)node->data;
138 n->status.visited = 0;
142 /* Begin with myself */
144 myself->status.visited = 1;
145 myself->nexthop = myself;
146 myself->via = myself;
147 node = avl_alloc_node();
149 avl_insert_top(todo_tree, node);
152 /* Loop while todo_tree is filled */
154 while(todo_tree->head)
156 for(from = todo_tree->head; from; from = next)
159 n = (node_t *)from->data;
161 for(to = n->edge_tree->head; to; to = to->next)
163 e = (edge_t *)to->data;
170 if(!check->status.visited)
172 check->status.visited = 1;
173 check->nexthop = (n->nexthop == myself)?n:n->nexthop;
174 check->via = check; /* FIXME: only if !(e->options & INDIRECT), otherwise use n->via */
175 avl_insert_before(todo_tree, todo_tree->head, to);
180 avl_delete_node(todo_tree, from);
184 syslog(LOG_DEBUG, _("Done."));
188 syslog(LOG_ERR, _("Implementation of BFS algorithm is screwed: %d nodes, visited %d"), nodes, visited);