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// A* graph search algorithm
//
// TODO
// - Set: abstraction for the node set data type.
// - Nearest: save the nearest node when the search is failed or not
// yet finished.
// - Sight: when two nodes are in direct sight of each other, skip
// nodes between them (Thera*).
#include "types.h"
#include <assert.h>
#include <stddef.h>
#ifdef __cplusplus
extern "C" {
#endif
#ifndef ASTAR_SET_SIZE
# define ASTAR_SET_SIZE 1024
#endif
enum {
ASTAR_PROGRESS = 0,
ASTAR_SUCCESS,
ASTAR_FAIL,
};
typedef struct {
i64 id;
i64 parent;
i64 exact_source_to_node;
i64 estimated_node_to_destination;
i64 estimated_source_to_destination;
} astar_node_t;
typedef struct {
b8 stop;
b8 skip;
i64 neighbor;
i64 distance;
} astar_link_t;
typedef struct {
i64 size;
astar_node_t values[ASTAR_SET_SIZE];
} astar_set_t;
typedef struct {
i64 status;
i64 source;
i64 destination;
astar_set_t open;
astar_set_t closed;
} astar_state_t;
#ifndef ASTAR_NEIGHBOR
# define ASTAR_NEIGHBOR(x, n) \
(astar_link_t) { \
.stop = 1, \
}
#endif
#ifndef ASTAR_HEURISTIC
# define ASTAR_HEURISTIC(x, y) (-1)
#endif
#ifdef __GNUC__
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wunused-function"
# pragma GCC diagnostic ignored "-Wunknown-pragmas"
# pragma GCC push_options
# pragma GCC optimize("O3")
#endif
static void astar_iteration(astar_state_t *state) {
assert(state != NULL);
if (state == NULL)
return;
if (state->open.size == 0) {
state->status = ASTAR_FAIL;
return;
}
assert(state->open.values != NULL);
assert(state->closed.values != NULL);
// FIXME
// Use abstractions for set element search
//
// Find a node that is closest to the destination
//
astar_node_t nearest_node;
{
i64 index_nearest = 0;
for (i64 i = 1; i < state->open.size; i++)
if (state->open.values[i].estimated_source_to_destination <
state->open.values[index_nearest]
.estimated_source_to_destination)
index_nearest = i;
nearest_node = state->open.values[index_nearest];
if (index_nearest != state->open.size - 1)
state->open.values[index_nearest] =
state->open.values[state->open.size - 1];
--state->open.size;
}
// Enumerate all neighbors
//
for (i64 k = 0;; ++k) {
// Get a link to the next neighbor node
//
(void) nearest_node.id;
(void) k;
astar_link_t link = ASTAR_NEIGHBOR(nearest_node.id, k);
// If there is no more neighbors, break the loop
if (link.stop)
break;
// If there is no link, proceed to the next link
if (link.skip)
continue;
astar_node_t neighbor_node = {
.id = link.neighbor,
.parent = nearest_node.id,
.exact_source_to_node = nearest_node.exact_source_to_node +
link.distance,
.estimated_node_to_destination = -1,
.estimated_source_to_destination = -1,
};
// Calculate distance estimations
//
(void) neighbor_node.id;
(void) state->destination;
neighbor_node.estimated_node_to_destination = ASTAR_HEURISTIC(
neighbor_node.id, state->destination);
neighbor_node.estimated_source_to_destination =
neighbor_node.exact_source_to_node +
neighbor_node.estimated_node_to_destination;
// Check if we reached the destination
//
if (neighbor_node.id == state->destination) {
assert(state->closed.size + 2 <= ASTAR_SET_SIZE);
// FIXME
// Use abstractions for set element inserting
//
// Add the nearest node to the closed set
//
state->closed.values[state->closed.size] = nearest_node;
++state->closed.size;
// Add the neighbor node to the closed set
//
state->closed.values[state->closed.size] = neighbor_node;
++state->closed.size;
// Finish the search
state->status = ASTAR_SUCCESS;
return;
}
// FIXME
// Use abstractions for the set search
//
// Check if a node with a better estimate is already in the
// closed set
//
i64 index_in_closed = -1;
for (i64 i = 0; i < state->closed.size; ++i)
if (state->closed.values[i].id == neighbor_node.id) {
index_in_closed = i;
break;
}
if (index_in_closed != -1 &&
state->closed.values[index_in_closed]
.estimated_source_to_destination <
neighbor_node.estimated_source_to_destination)
// Skip this node
continue;
// Check if this node is in the open set
//
i64 index_in_open = -1;
for (i64 i = 0; i < state->closed.size; ++i)
if (state->open.values[i].id == neighbor_node.id) {
index_in_open = i;
break;
}
if (index_in_open != -1) {
if (state->open.values[index_in_open]
.estimated_source_to_destination <
neighbor_node.estimated_source_to_destination)
// Skip this node
continue;
// FIXME
// Use abstractions for set element erasing
//
// Remove this node from the open set
//
if (index_in_open != state->open.size - 1)
state->open.values[index_in_open] =
state->open.values[state->open.size - 1];
--state->open.size;
}
// FIXME
// Use abstractions to set element adding
//
// Add this node to the open set
//
assert(state->open.size + 1 <= ASTAR_SET_SIZE);
state->open.values[state->open.size] = neighbor_node;
++state->open.size;
}
// FIXME
// Use abstractions to set element adding
//
// Add the nearest node to the closed set
//
assert(state->closed.size + 1 <= ASTAR_SET_SIZE);
state->closed.values[state->closed.size] = nearest_node;
++state->closed.size;
// Continue the search
state->status = ASTAR_PROGRESS;
return;
}
#ifdef __GNUC__
# pragma GCC pop_options
# pragma GCC diagnostic pop
#endif
#ifdef __cplusplus
}
#endif
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