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 1.1.2.5 2001/10/31 12:50:24 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.
+ tree, adding safe edges until #edges = #nodes - 1. The implementation here
+ however is not so fast, because I tried to avoid having to make a forest and
+ merge trees.
- 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;
+ avl_node_t *node, *next;
edge_t *e;
node_t *n;
connection_t *c;
- int nodes;
+ int nodes = 0;
int safe_edges = 0;
-
- syslog(LOG_DEBUG, _("Running Kruskal's algorithm:"));
+ int skipped;
- /* 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)
+ for(skipped = 0, node = edge_weight_tree->head; node; node = next)
{
-// Algorithm should work without this:
-// if(safe_edges = nodes - 1)
-// break;
-
+ next = node->next;
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)
+ {
+ next = edge_weight_tree->head;
+ continue;
+ }
}
+}
+
+/* Implementation of a simple breadth-first search algorithm.
+ Running time: O(E)
+*/
+
+void sssp_bfs(int prune)
+{
+ avl_node_t *node, *from, *next, *to;
+ edge_t *e;
+ node_t *n, *check;
+ avl_tree_t *todo_tree;
- syslog(LOG_DEBUG, _("Done."));
+ todo_tree = avl_alloc_tree(NULL, NULL);
- if(safe_edges != nodes - 1)
+ /* Clear visited status on nodes */
+
+ for(node = node_tree->head; node; node = node->next)
{
- syslog(LOG_ERR, _("Implementation of Kruskal's algorithm is screwed: %d nodes, found %d safe edges"), nodes, safe_edges);
+ n = (node_t *)node->data;
+ n->status.visited = 0;
}
+
+ /* 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);
+
+ /* 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) ? check : n->nexthop;
+ check->via = (e->options & OPTION_INDIRECT || n->via != n) ? n->via : check;
+ node = avl_alloc_node();
+ node->data = check;
+ avl_insert_before(todo_tree, from, node);
+ }
+ }
+
+ avl_delete_node(todo_tree, from);
+ }
+ }
+
+ avl_free_tree(todo_tree);
+
+ /* Nodes we haven't visited are unreachable, prune them. */
+
+ if(prune)
+ for(node = node_tree->head; node; node = next)
+ {
+ next = node->next;
+ n = (node_t *)node->data;
+
+ if(n->status.visited == 0)
+ node_del(n);
+ }
}
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