aga,agar: Dijkstra's algorithm

[ccan] / ccan / aga / dijkstra.c

diff --git a/ccan/aga/dijkstra.c b/ccan/aga/dijkstra.c
new file mode 100644 (file)
index 0000000..97b485f
--- /dev/null
+++ b/ccan/aga/dijkstra.c
@@ -0,0 +1,131 @@
+/* Licensed under LGPLv2+ - see LICENSE file for details */
+#include "config.h"
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <assert.h>
+
+#include <ccan/build_assert/build_assert.h>
+#include <ccan/check_type/check_type.h>
+#include <ccan/order/order.h>
+#include <ccan/lpq/lpq.h>
+
+#include <ccan/aga/aga.h>
+#include "private.h"
+
+/*
+ * Dijkstra's algorithm
+ */
+
+/* Node states */
+#define STATE_INFINITE 0
+#define STATE_FINITE   1
+#define STATE_COMPLETE 2
+
+
+static void candidate_path(struct aga_graph *g, struct aga_node *node,
+                          aga_icost_t distance,
+                          struct aga_node *prev, const void *prevedge)
+{
+       if (aga_update_node(g, node)) {
+               /* New node, treat has having infinite distance */
+               node->u.dijkstra.distance = distance;
+               node->u.dijkstra.prev = prev;
+               node->u.dijkstra.prevedge = prevedge;
+               node->u.dijkstra.complete = false;
+
+               lpq_enqueue(&g->state.dijkstra, node);
+       } else if (distance < node->u.dijkstra.distance) {
+               assert(!node->u.dijkstra.complete);
+
+               node->u.dijkstra.distance = distance;
+               node->u.dijkstra.prev = prev;
+               node->u.dijkstra.prevedge = prevedge;
+
+               lpq_reorder(&g->state.dijkstra, node);
+       }
+}
+
+int aga_dijkstra_start(struct aga_graph *g, struct aga_node *source)
+{
+       total_order_by_field(order, long_reverse,
+                            struct aga_node, u.dijkstra.distance);
+       int rc;
+
+       /* Make sure we're actually using the right ordering for
+        * aga_icost_t */
+       BUILD_ASSERT(check_types_match(long, aga_icost_t) == 0);
+
+       rc = aga_start(g);
+       if (rc < 0)
+               return rc;
+
+       lpq_init(&g->state.dijkstra, order.cb, order.ctx);
+
+       candidate_path(g, source, 0, NULL, NULL);
+
+       return 0;
+}
+
+struct aga_node *aga_dijkstra_step(struct aga_graph *g)
+{
+       struct aga_node *n = lpq_dequeue(&g->state.dijkstra);
+       const void *e;
+       struct aga_edge_info ei;
+       int err;
+
+       if (!aga_check_state(g))
+               return NULL;
+
+       if (!n)
+               return NULL;
+
+       aga_for_each_edge_info(e, ei, err, g, n) {
+               if (ei.icost < 0) {
+                       aga_fail(g, AGA_ERR_NEGATIVE_COST);
+                       return NULL;
+               }
+               candidate_path(g, ei.to,
+                              n->u.dijkstra.distance + ei.icost, n, e);
+       }
+       if (err) {
+               aga_fail(g, err);
+               return NULL;
+       }
+
+       n->u.dijkstra.complete = true;
+
+       return n;
+}
+
+bool aga_dijkstra_path(struct aga_graph *g, struct aga_node *node,
+                      aga_icost_t *total_cost,
+                      struct aga_node **prev, const void **prevedge)
+{
+       if (!aga_check_state(g))
+               return false;
+
+       while (aga_node_needs_update(g, node) || !node->u.dijkstra.complete) {
+               if (!aga_dijkstra_step(g))
+                       return false;
+       };
+
+       if (total_cost)
+               *total_cost = node->u.dijkstra.distance;
+       if (prev)
+               *prev = node->u.dijkstra.prev;
+       if (prevedge)
+               *prevedge = node->u.dijkstra.prevedge;
+
+       return true;
+}
+
+void aga_dijkstra_all_paths(struct aga_graph *g)
+{
+       if (!aga_check_state(g))
+               return;
+
+       while (aga_dijkstra_step(g))
+               ;
+}
+