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 1.1.2.5 2001/10/31 12:50:24 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. The implementation here
36 however is not so fast, because I tried to avoid having to make a forest and
39 For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a
40 simple breadth-first search is presented here.
51 #include "connection.h"
55 /* Implementation of Kruskal's algorithm.
57 Please note that sorting on weight is already done by add_edge().
60 void mst_kruskal(void)
62 avl_node_t *node, *next;
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 for(skipped = 0, node = edge_weight_tree->head; node; node = next)
96 e = (edge_t *)node->data;
98 if(e->from->status.visited == e->to->status.visited)
104 e->from->status.visited = 1;
105 e->to->status.visited = 1;
107 e->connection->status.mst = 1;
113 next = edge_weight_tree->head;
119 /* Implementation of a simple breadth-first search algorithm.
123 void sssp_bfs(int prune)
125 avl_node_t *node, *from, *next, *to;
128 avl_tree_t *todo_tree;
130 todo_tree = avl_alloc_tree(NULL, NULL);
132 /* Clear visited status on nodes */
134 for(node = node_tree->head; node; node = node->next)
136 n = (node_t *)node->data;
137 n->status.visited = 0;
140 /* Begin with myself */
142 myself->status.visited = 1;
143 myself->nexthop = myself;
144 myself->via = myself;
145 node = avl_alloc_node();
147 avl_insert_top(todo_tree, node);
149 /* Loop while todo_tree is filled */
151 while(todo_tree->head)
153 for(from = todo_tree->head; from; from = next)
156 n = (node_t *)from->data;
158 for(to = n->edge_tree->head; to; to = to->next)
160 e = (edge_t *)to->data;
167 if(!check->status.visited)
169 check->status.visited = 1;
170 check->nexthop = (n->nexthop == myself) ? check : n->nexthop;
171 check->via = (e->options & OPTION_INDIRECT || n->via != n) ? n->via : check;
172 node = avl_alloc_node();
174 avl_insert_before(todo_tree, from, node);
178 avl_delete_node(todo_tree, from);
182 avl_free_tree(todo_tree);
184 /* Nodes we haven't visited are unreachable, prune them. */
187 for(node = node_tree->head; node; node = next)
190 n = (node_t *)node->data;
192 if(n->status.visited == 0)