along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
- $Id: graph.c,v 1.1.2.1 2001/10/28 10:16:18 guus Exp $
+ $Id: graph.c,v 1.1.2.3 2001/10/29 13:14:57 guus Exp $
*/
/* We need to generate two trees from the graph:
1. A minimum spanning tree for broadcasts,
2. A single-source shortest path tree for unicasts.
-
+
Actually, the first one alone would suffice but would make unicast packets
take longer routes than necessary.
-
+
For the MST algorithm we can choose from Prim's or Kruskal's. I personally
favour Kruskal's, because we make an extra AVL tree of edges sorted on
weights (metric). That tree only has to be updated when an edge is added or
removed, and during the MST algorithm we just have go linearly through that
tree, adding safe edges until #edges = #nodes - 1.
- For the SSSP algorithm Dijkstra's seems to be a nice choice.
+ For the SSSP algorithm Dijkstra's seems to be a nice choice. Currently a
+ simple breadth-first search is presented here.
*/
#include <syslog.h>
#include "config.h"
+#include <string.h>
+
+#include <avl_tree.h>
#include "node.h"
#include "edge.h"
#include "system.h"
/* Implementation of Kruskal's algorithm.
- Running time: O(V)
- Please note that sorting on weight is already done by add_vertex().
+ Running time: O(EN)
+ Please note that sorting on weight is already done by add_edge().
*/
-void kruskal(void)
+void mst_kruskal(void)
{
avl_node_t *node;
edge_t *e;
node_t *n;
connection_t *c;
- int nodes;
+ int nodes = 0;
int safe_edges = 0;
-
+ int skipped;
+
syslog(LOG_DEBUG, _("Running Kruskal's algorithm:"));
- /* Clear MST status on nodes */
+ /* Clear visited status on nodes */
for(node = node_tree->head; node; node = node->next)
{
n = (node_t *)node->data;
- n->status.mst = 0;
- node++;
+ n->status.visited = 0;
+ nodes++;
}
+ /* Starting point */
+
+ ((edge_t *)edge_weight_tree->head->data)->from->status.visited = 1;
+
/* Clear MST status on connections */
for(node = connection_tree->head; node; node = node->next)
{
- c = (edge_t *)node->data;
+ c = (connection_t *)node->data;
c->status.mst = 0;
}
/* Add safe edges */
- for(node = edge_weight_tree->head; node; node = node->next)
+ while(safe_edges < nodes - 1)
+ for(skipped = 0, node = edge_weight_tree->head; node; node = node->next)
{
// Algorithm should work without this:
// if(safe_edges = nodes - 1)
// break;
e = (edge_t *)node->data;
-
- if(e->from->status.mst && e->to->status.mst)
- continue;
- e->from->status.mst = 1;
- e->to->status.mst = 1;
+ if(e->from->status.visited == e->to->status.visited)
+ {
+ skipped = 1;
+ continue;
+ }
+
+ e->from->status.visited = 1;
+ e->to->status.visited = 1;
if(e->connection)
e->connection->status.mst = 1;
- safe_edges++;
+ safe_edges++;
syslog(LOG_DEBUG, _("Adding safe edge %s - %s weight %d"), e->from->name, e->to->name, e->weight);
+
+ if(skipped)
+ break;
}
syslog(LOG_DEBUG, _("Done."));
syslog(LOG_ERR, _("Implementation of Kruskal's algorithm is screwed: %d nodes, found %d safe edges"), nodes, safe_edges);
}
}
+
+/* Implementation of a simple breadth-first search algorithm.
+ Running time: O(E)
+*/
+
+void sssp_bfs(void)
+{
+ avl_node_t *node, *from, *next, *to;
+ edge_t *e;
+ node_t *n, *check;
+ int nodes = 0;
+ int visited = 0;
+ avl_tree_t *todo_tree;
+
+ syslog(LOG_DEBUG, _("Running BFS algorithm:"));
+
+ todo_tree = avl_alloc_tree(NULL, NULL);
+
+ /* Clear visited status on nodes */
+
+ for(node = node_tree->head; node; node = node->next)
+ {
+ n = (node_t *)node->data;
+ n->status.visited = 0;
+ nodes++;
+ }
+
+ /* Begin with myself */
+
+ myself->status.visited = 1;
+ myself->nexthop = myself;
+ myself->via = myself;
+ node = avl_alloc_node();
+ node->data = myself;
+ avl_insert_top(todo_tree, node);
+ visited++;
+
+ /* Loop while todo_tree is filled */
+
+ while(todo_tree->head)
+ {
+ for(from = todo_tree->head; from; from = next)
+ {
+ next = from->next;
+ n = (node_t *)from->data;
+
+ for(to = n->edge_tree->head; to; to = to->next)
+ {
+ e = (edge_t *)to->data;
+
+ if(e->from == n)
+ check = e->to;
+ else
+ check = e->from;
+
+ if(!check->status.visited)
+ {
+ check->status.visited = 1;
+ check->nexthop = (n->nexthop == myself) ? n : n->nexthop;
+ check->via = check; /* FIXME: only if !(e->options & INDIRECT), otherwise use n->via */
+ node = avl_alloc_node();
+ node->data = check;
+ avl_insert_before(todo_tree, from, node);
+ visited++;
+ syslog(LOG_DEBUG, _("Node %s nexthop %s via %s"), check->name, check->nexthop->name, check->via->name);
+ }
+ }
+
+ avl_delete_node(todo_tree, from);
+ }
+ }
+
+ syslog(LOG_DEBUG, _("Done."));
+
+ avl_free_tree(todo_tree);
+
+ if(visited != nodes)
+ {
+ syslog(LOG_ERR, _("Implementation of BFS algorithm is screwed: %d nodes, visited %d"), nodes, visited);
+ }
+}
projects / tinc / blobdiff