2 * Empire - A multi-player, client/server Internet based war game.
3 * Copyright (C) 1986-2011, Dave Pare, Jeff Bailey, Thomas Ruschak,
4 * Ken Stevens, Steve McClure, Markus Armbruster
6 * Empire 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 3 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, see <http://www.gnu.org/licenses/>.
21 * See files README, COPYING and CREDITS in the root of the source
22 * tree for related information and legal notices. It is expected
23 * that future projects/authors will amend these files as needed.
27 * pathfind.c: Find cheapest paths
29 * Known contributors to this file:
30 * Markus Armbruster, 2011
44 #ifdef PATH_FIND_DEBUG
45 #define DPRINTF(fmt, ...) ((void)printf(fmt , ## __VA_ARGS__))
47 #define DPRINTF(fmt, ...) ((void)0)
50 static char *bufrotate(char *buf, size_t bufsz, size_t i);
53 * Dijkstra's algorithm. Refer to your graph algorithm textbook for
54 * how it works. Implementation is specialized to hex maps.
56 * Define PATH_FIND_STATS for performance statistics on stdout.
60 * Array of sector data, indexed by sector uid
62 * We need to store a few values per sector visited by the path
63 * search. An array is the stupidest data structure that could
66 * Extra benefit: it works really well for distribution in a
67 * continental game, where we visit most sectors. That's our most
68 * demanding use of path search, and its performance has noticable
69 * impact on the update.
71 * Island game distribution is much less demanding. The array may not
72 * be the best choice here, but it's plainly good enough. Same for
73 * path searches outside the update.
78 * visit < pf_visit : unvisited, remaining members invalid
79 * visit == pf_visit : open, dir & cost tentative, heapi used
80 * visit == pf_visit + 1 : closed, dir & cost final, heapi unused
83 signed char dir; /* cheapest direction to source */
84 int heapi; /* index in heap, valid if open */
85 double cost; /* cost from source */
88 static unsigned short pf_visit;
89 static struct pf_map *pf_map;
92 * Binary heap, cost priority queue of all open sectors
94 * Again, we use the stupidest data structure that could possibly
95 * work: an array. And we make it so large it can hold *all* sectors.
96 * In practice, we need much less space, but a tighter upper bound is
97 * not obvious to me right now.
101 int uid; /* sector uid and */
102 coord x, y; /* coordinates, uid == XYOFFSET(x, y) */
103 double cost; /* cost from source */
106 static int pf_nheap; /* #entries in pf_nheap[] */
107 static struct pf_heap *pf_heap;
112 static coord pf_sx, pf_sy;
114 static natid pf_actor;
115 static double (*pf_sct_cost)(natid, int);
118 * Performance statistics
120 #ifdef PATH_FIND_STATS
121 static unsigned pf_nsearch, pf_nsource, pf_nopen, pf_nclose;
122 static unsigned pf_nheap_max, pf_noway;
123 static double pf_sumcost;
124 #define STAT_INC(v) ((void)((v)++))
125 #define STAT_INCBY(v, i) ((void)((v) += i))
126 #define STAT_HIMARK(v, h) ((void)((v) < (h) ? (v) = (h) : (h)))
127 #else /* !PATH_FIND_STATS */
128 #define STAT_INC(v) ((void)0)
129 #define STAT_INCBY(v, i) ((void)0)
130 #define STAT_HIMARK(v, h) ((void)0)
131 #endif /* !PATH_FIND_STATS */
133 #ifndef NDEBUG /* silence "not used" warning */
134 /* Is sector with uid UID open? */
138 return pf_map[uid].visit == pf_visit;
142 /* Is sector with uid UID closed? */
144 pf_is_closed(int uid)
147 * optimization: check > pf_visit instead of == pf_visit + 1
148 * works because pf_map[uid].visit <= pf_visit + 1
150 return pf_map[uid].visit > pf_visit;
153 /* Is sector with uid UID unvisited? */
155 pf_is_unvisited(int uid)
157 return pf_map[uid].visit < pf_visit;
160 #ifdef PATH_FIND_DEBUG
166 for (i = 0; i < pf_nheap; i++) {
167 uid = pf_heap[i].uid;
168 assert(0 <= uid && uid < WORLD_SZ());
169 assert(pf_map[uid].heapi == i);
170 assert(pf_map[uid].visit == pf_visit);
171 assert(pf_map[uid].cost <= pf_heap[i].cost);
173 assert(c >= pf_nheap || pf_heap[i].cost <= pf_heap[c].cost);
175 assert(c >= pf_nheap || pf_heap[i].cost <= pf_heap[c].cost);
178 for (uid = 0; uid < WORLD_SZ(); uid++) {
179 assert(pf_map[uid].visit <= pf_visit + 1);
180 if (pf_map[uid].visit == pf_visit) {
181 i = pf_map[uid].heapi;
182 assert(0 <= i && i < pf_nheap && pf_heap[i].uid == uid);
187 #define pf_check() ((void)0)
190 /* Swap pf_heap's I-th and J-th elements. */
192 pf_heap_swap(int i, int j)
196 assert(0 <= i && i < pf_nheap);
197 assert(0 <= j && j < pf_nheap);
199 pf_heap[i] = pf_heap[j];
201 pf_map[pf_heap[i].uid].heapi = i;
202 pf_map[pf_heap[j].uid].heapi = j;
205 /* Restore heap property after N-th element's cost increased. */
211 assert(0 <= n && n < pf_nheap);
212 for (r = n; (c = 2 * r + 1) < pf_nheap; r = c) {
213 if (c + 1 < pf_nheap && pf_heap[c].cost > pf_heap[c + 1].cost)
215 if (pf_heap[r].cost < pf_heap[c].cost)
221 /* Restore heap property after N-th element's cost decreased. */
227 assert(0 <= n && n < pf_nheap);
228 for (c = n; (p = (c - 1) / 2), c > 0; c = p) {
229 if (pf_heap[p].cost < pf_heap[c].cost)
236 * Open the unvisited sector X,Y.
237 * UID is sector uid, it equals XYOFFSET(X,Y).
238 * Cheapest path from source comes from direction DIR and has cost COST.
241 pf_open(int uid, coord x, coord y, int dir, double cost)
247 STAT_HIMARK(pf_nheap_max, (unsigned)pf_nheap);
248 DPRINTF("pf: open %d,%d %g %c %d\n", x, y, cost, dirch[dir], i);
249 assert(pf_is_unvisited(uid));
250 pf_map[uid].visit = pf_visit;
251 pf_map[uid].dir = dir;
252 pf_map[uid].heapi = i;
253 pf_map[uid].cost = cost;
254 pf_heap[i].uid = uid;
257 pf_heap[i].cost = cost;
264 * Close the sector at the top of the heap.
269 int uid = pf_heap[0].uid;
272 DPRINTF("pf: close %d,%d %d\n", pf_heap[0].x, pf_heap[0].y, pf_nheap);
273 assert(pf_is_open(uid));
275 pf_heap[0] = pf_heap[pf_nheap];
276 pf_map[pf_heap[0].uid].heapi = 0;
279 pf_map[uid].visit = pf_visit + 1;
284 x_in_dir(coord x, int dir)
288 assert(0 <= x && x < WORLD_X);
289 assert(0 <= dir && dir <= DIR_LAST);
290 xx = x + diroff[dir][0];
299 y_in_dir(coord y, int dir)
303 assert(0 <= y && y < WORLD_Y);
304 assert(0 <= dir && dir <= DIR_LAST);
305 yy = y + diroff[dir][1];
316 assert(DIR_FIRST <= dir && dir <= DIR_LAST);
317 return dir >= DIR_FIRST + 3 ? dir - 3 : dir + 3;
321 * Set the current source and cost function.
322 * SX,SY is the source.
323 * The cost to enter the sector with uid u is COST(ACTOR, u).
324 * Negative value means the sector can't be entered.
327 pf_set_source(coord sx, coord sy, natid actor, double (*cost)(natid, int))
329 STAT_INC(pf_nsource);
330 DPRINTF("pf: source %d,%d\n", sx, sy);
333 pf_suid = XYOFFSET(sx, sy);
338 pf_map = calloc(WORLD_SZ(), sizeof(*pf_map));
339 pf_heap = malloc(WORLD_SZ() * sizeof(*pf_heap));
341 } else if ((unsigned short)(pf_visit + 3) < pf_visit) {
342 DPRINTF("pf: visit wrap-around\n");
343 memset(pf_map, 0, WORLD_SZ() * sizeof(*pf_map));
350 pf_open(pf_suid, pf_sx, pf_sy, DIR_STOP, 0.0);
354 * Find cheapest path from current source to DX,DY, return its cost.
357 path_find_to(coord dx, coord dy)
364 STAT_INC(pf_nsearch);
365 DPRINTF("pf: dest %d,%d\n", dx, dy);
366 duid = XYOFFSET(dx, dy);
367 if (pf_is_closed(duid)) {
368 DPRINTF("pf: done old %g\n", pf_map[duid].cost);
369 STAT_INCBY(pf_sumcost, pf_map[duid].cost);
370 return pf_map[duid].cost;
373 while (pf_nheap > 0 && (uid = pf_heap[0].uid) != duid) {
376 cost = pf_heap[0].cost;
379 for (i = 0; i < 6; i++) { /* for all neighbors */
380 nx = x_in_dir(x, DIR_FIRST + i);
381 ny = y_in_dir(y, DIR_FIRST + i);
382 nuid = XYOFFSET(nx, ny);
384 * Cost to enter NX,NY doesn't depend on direction of
385 * entry. This X,Y is at least as expensive as any
386 * previous one. Therefore, cost to go to NX,NY via X,Y
387 * is at least as high as any previously found route.
388 * Skip neighbors that have a route already.
390 if (!pf_is_unvisited(nuid))
392 c1 = pf_sct_cost(pf_actor, nuid);
395 pf_open(nuid, nx, ny, DIR_FIRST + i, cost + c1);
399 DPRINTF("pf: done new %g\n", !pf_nheap ? -1.0 : pf_map[duid].cost);
404 STAT_INCBY(pf_sumcost, pf_map[duid].cost);
405 return pf_map[duid].cost;
409 * Write route from SX,SY to DX,DY to BUF[BUFSIZ], return its length.
410 * If the route is longer than BUFSIZ-1 characters, it's truncated.
411 * You must compute path cost first, with path_find_to().
412 * SX,SY must be on a shortest path from the current source to DX,DY.
415 path_find_route(char *buf, size_t bufsz,
416 coord sx, coord sy, coord dx, coord dy)
422 suid = XYOFFSET(sx, sy);
423 assert(bufsz > 0 && !pf_is_unvisited(suid));
432 DPRINTF("pf: %d,%d %.*s%.*s\n",
434 (int)(bufsz - i), buf + i,
435 len >= bufsz ? (int)i : 0, buf);
436 uid = XYOFFSET(x, y);
437 assert(!pf_is_unvisited(uid));
439 if (d == DIR_STOP || uid == suid)
445 x = x_in_dir(x, rev_dir(d));
446 y = y_in_dir(y, rev_dir(d));
449 assert(x == sx && y == sy);
451 bufrotate(buf, bufsz, i);
453 assert(i + len < bufsz);
454 memmove(buf, buf + i, len + 1);
460 * Rotate BUF[BUFSZ] to put BUF[I] into BUF[0], and zero-terminate.
463 bufrotate(char *buf, size_t bufsz, size_t i)
469 n = MIN(i, sizeof(tmp));
471 memcpy(buf, buf + n, bufsz - n);
472 memcpy(buf + bufsz - n, tmp, n);
479 #ifdef PATH_FIND_STATS
481 path_find_print_stats(void)
483 printf("pathfind %u searches, %u sources, %u opened, %u closed,"
484 " %u heap max, %zu bytes, %u noway, %g avg cost\n",
485 pf_nsearch, pf_nsource, pf_nopen, pf_nclose,
487 (WORLD_SZ() * (sizeof(*pf_map) + sizeof(*pf_heap))),
488 pf_noway, pf_nsearch ? pf_sumcost / pf_nsearch : 0.0);
493 * Empire interface glue
497 cost_land(natid actor, int uid, int mobtype)
500 * Non-negative cost must not depend on ACTOR, see BestLandPath().
502 struct sctstr *sp = (void *)empfile[EF_SECTOR].cache;
504 if (sp[uid].sct_own != actor)
506 return sector_mcost(&sp[uid], mobtype);
510 cost_move(natid actor, int uid)
512 return cost_land(actor, uid, MOB_MOVE);
516 cost_march(natid actor, int uid)
518 return cost_land(actor, uid, MOB_MARCH);
522 cost_rail(natid actor, int uid)
524 return cost_land(actor, uid, MOB_RAIL);
527 static double (*cost_tab[])(natid, int) = {
528 cost_move, cost_march, cost_rail
532 * Start finding paths from SX,SY.
533 * Use mobility costs for ACTOR and MOBTYPE.
536 path_find_from(coord sx, coord sy, natid actor, int mobtype)
538 pf_set_source(sx, sy, actor, cost_tab[mobtype]);
542 * Find cheapest path from SX,SY to DX,DY, return its mobility cost.
543 * Use mobility costs for ACTOR and MOBTYPE.
546 path_find(coord sx, coord sy, coord dx, coord dy, natid actor, int mobtype)
548 pf_set_source(sx, sy, actor, cost_tab[mobtype]);
549 return path_find_to(dx, dy);