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1 | /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *\ |
2 | * This is GNU Go, a Go program. Contact gnugo@gnu.org, or see * | |
3 | * http://www.gnu.org/software/gnugo/ for more information. * | |
4 | * * | |
5 | * Copyright 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, * | |
6 | * 2008 and 2009 by the Free Software Foundation. * | |
7 | * * | |
8 | * This program is free software; you can redistribute it and/or * | |
9 | * modify it under the terms of the GNU General Public License as * | |
10 | * published by the Free Software Foundation - version 3 or * | |
11 | * (at your option) any later version. * | |
12 | * * | |
13 | * This program is distributed in the hope that it will be useful, * | |
14 | * but WITHOUT ANY WARRANTY; without even the implied warranty of * | |
15 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * | |
16 | * GNU General Public License in file COPYING for more details. * | |
17 | * * | |
18 | * You should have received a copy of the GNU General Public * | |
19 | * License along with this program; if not, write to the Free * | |
20 | * Software Foundation, Inc., 51 Franklin Street, Fifth Floor, * | |
21 | * Boston, MA 02111, USA. * | |
22 | \* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */ | |
23 | ||
24 | ||
25 | #include "gnugo.h" | |
26 | #include "liberty.h" | |
27 | ||
28 | ||
29 | static void endgame_analyze_worm_liberties(int pos, int color); | |
30 | static void endgame_find_backfilling_dame(int str, int color); | |
31 | static int endgame_find_liberties(int str, int *essential_liberties, | |
32 | int essential_libs[MAXLIBS], | |
33 | int *inessential_liberties, | |
34 | int inessential_libs[MAXLIBS], | |
35 | int *false_eye_liberties, | |
36 | int false_eye_libs[MAXLIBS]); | |
37 | ||
38 | ||
39 | /* Generate endgame moves. These are typically moves in settled positions, | |
40 | * they aren't worth many points. Currently, we generate such moves using | |
41 | * patterns in endgames.db and this algorithmic move generator. It is only | |
42 | * called when no move of value higher than 6.0 has been found on board. | |
43 | */ | |
44 | void | |
45 | endgame(int color) | |
46 | { | |
47 | int pos; | |
48 | ||
49 | TRACE("\nEndgame move generator tries to look for additional moves...\n"); | |
50 | ||
51 | /* Try to generate some moves using endgame_analyze_worm_liberties(). See | |
52 | * the description of that function to find what moves it generates. | |
53 | */ | |
54 | for (pos = BOARDMIN; pos < BOARDMAX; pos++) { | |
55 | /* We are only interested in alive, but not invincible worms which are | |
56 | * parts of alive dragons. That is, the position must be stable. | |
57 | */ | |
58 | if (IS_STONE(board[pos]) | |
59 | && worm[pos].origin == pos | |
60 | && dragon[pos].status == ALIVE | |
61 | && !worm[pos].invincible | |
62 | && !worm[pos].inessential | |
63 | && worm[pos].attack_codes[0] == 0) { | |
64 | endgame_analyze_worm_liberties(pos, color); | |
65 | endgame_find_backfilling_dame(pos, color); | |
66 | } | |
67 | } | |
68 | } | |
69 | ||
70 | ||
71 | /* This function handles two cases of endgame moves. Consider these two | |
72 | * positions (from endgame:301,302 and endgame:801,802 respectively): | |
73 | * | |
74 | * OOOOOOO XXXXXO.| | |
75 | * O.XXX.O X.O.O*.| | |
76 | * OOX.XXO X.OOOX.| | |
77 | * .O*X.OX XXXXOX.| | |
78 | * .OXX..X X..XOOO| | |
79 | * .OOOXX. XXXXXXX| | |
80 | * | |
81 | * The two marked with `*' moves are worth one point in gote each (for | |
82 | * both colors). The first one is obvious - once black runs short on | |
83 | * liberties, he'll have to defend in his own eyespace, wasting one | |
84 | * point. In the second position, although black sacrifices one point | |
85 | * by playing in white's territory, he forces white to eventually | |
86 | * capture the black string, losing three points. However, white has | |
87 | * to play at `*' sooner or later if black doesn't take that vertex, so | |
88 | * the move is worth 3 - 1 - 1 = 1 point only, not two. | |
89 | * | |
90 | * This function is able to find such moves. The algorithm is based on | |
91 | * finding so called "inessential liberties". These are defined as | |
92 | * liberties, which satisfy five conditions: | |
93 | * | |
94 | * 1) they are not within an eye (not in someone's territory), | |
95 | * 2) all their adjacent worms and dragons are alive, | |
96 | * 3) they have adjacent worms of both colors, | |
97 | * 4) they have no other adjacent worms of the same color as the worm | |
98 | * under consideration, | |
99 | * 5) they are safe to fill with stones of other than the worm's color. | |
100 | * | |
101 | * Such liberties are supposed to never become territory (they can't become | |
102 | * an additional eye for the worm under consideration), the worm cannot | |
103 | * connect to something via such a liberty and they will (or at least can) | |
104 | * eventually be filled by either of the players. | |
105 | * | |
106 | * FIXME: This function can probably be improved to handle more cases. | |
107 | */ | |
108 | static void | |
109 | endgame_analyze_worm_liberties(int pos, int color) | |
110 | { | |
111 | int k; | |
112 | int worm_color = board[pos]; | |
113 | int other = OTHER_COLOR(worm_color); | |
114 | int essential_liberties; | |
115 | int essential_libs[MAXLIBS]; | |
116 | int inessential_liberties; | |
117 | int inessential_libs[MAXLIBS]; | |
118 | int false_eye_liberties; | |
119 | int false_eye_libs[MAXLIBS]; | |
120 | int num_attacks; | |
121 | int num_attacks2; | |
122 | int attacks[MAXLIBS]; | |
123 | int defenses[MAXLIBS]; | |
124 | int apos; | |
125 | int value; | |
126 | ||
127 | if (!endgame_find_liberties(pos, &essential_liberties, essential_libs, | |
128 | &inessential_liberties, inessential_libs, | |
129 | &false_eye_liberties, false_eye_libs)) | |
130 | return; | |
131 | ||
132 | apos = NO_MOVE; | |
133 | num_attacks = 0; | |
134 | ||
135 | /* Now, try to predict the final state of the position. We fill all | |
136 | * inessential liberties by stones of other than the current worm's | |
137 | * color. This is just a guess, we'll have to check the results later. | |
138 | */ | |
139 | for (k = 0; k < inessential_liberties; k++) { | |
140 | if (!safe_move(inessential_libs[k], other) | |
141 | || !trymove(inessential_libs[k], other, "endgame", pos)) | |
142 | break; | |
143 | } | |
144 | ||
145 | /* If we haven't eaten the worm accidentally, look if any attacks on the | |
146 | * worm have appeared. | |
147 | */ | |
148 | if (k == inessential_liberties && board[pos] != EMPTY) { | |
149 | /* Try to look for moves as in position 1. If the worm still has | |
150 | * more than one liberty, try to play on every essential liberty | |
151 | * and see if an attack appears. | |
152 | */ | |
153 | if (countlib(pos) > 1) { | |
154 | for (k = 0; k < essential_liberties; k++) { | |
155 | int lib = essential_libs[k]; | |
156 | ||
157 | if (safe_move(lib, worm_color) && safe_move(lib, other) | |
158 | && trymove(lib, other, "endgame", pos)) { | |
159 | if (attack(pos, NULL) != 0) { | |
160 | int dpos; | |
161 | ||
162 | if (find_defense(pos, &dpos) && is_proper_eye_space(dpos)) { | |
163 | int i; | |
164 | ||
165 | /* If the attack cannot be defended against by playing on | |
166 | * another essential liberty, filling a pure false eye (an | |
167 | * eye which can't become territory) or capturing an opponent | |
168 | * string in atari, keep it for now. | |
169 | */ | |
170 | for (i = 0; i < essential_liberties; i++) { | |
171 | if (i != k && essential_libs[i] != dpos | |
172 | && does_defend(essential_libs[i], pos)) | |
173 | break; | |
174 | } | |
175 | ||
176 | if (i == essential_liberties) { | |
177 | for (i = 0; i < false_eye_liberties; i++) { | |
178 | if (does_defend(false_eye_libs[i], pos)) | |
179 | break; | |
180 | } | |
181 | ||
182 | if (i == false_eye_liberties) { | |
183 | int adj[MAXCHAIN]; | |
184 | int adjs; | |
185 | ||
186 | adjs = chainlinks2(pos, adj, 1); | |
187 | for (i = 0; i < adjs; i++) { | |
188 | int lib2; | |
189 | findlib(adj[i], 1, &lib2); | |
190 | if (lib2 != dpos && !is_proper_eye_space(lib2) | |
191 | && does_defend(lib2, pos)) | |
192 | break; | |
193 | } | |
194 | ||
195 | if (i == adjs) { | |
196 | attacks[num_attacks] = lib; | |
197 | defenses[num_attacks] = dpos; | |
198 | num_attacks++; | |
199 | } | |
200 | } | |
201 | } | |
202 | } | |
203 | } | |
204 | ||
205 | popgo(); | |
206 | } | |
207 | } | |
208 | } | |
209 | else if (essential_liberties > 0) { | |
210 | /* If the only remaining liberty is essential, it is an attack. */ | |
211 | attacks[num_attacks] = essential_libs[0]; | |
212 | defenses[num_attacks] = NO_MOVE; | |
213 | num_attacks++; | |
214 | } | |
215 | ||
216 | /* Try to find moves as in position 2. */ | |
217 | if (attack(pos, &apos) != 0) { | |
218 | if (is_proper_eye_space(apos)) { | |
219 | /* The attack point is in someone's eye (must be an eye which the worm | |
220 | * bounds). This looks promising. If this attack cannot be averted by | |
221 | * playing on an essential liberty, keep it for further analyzis. | |
222 | */ | |
223 | for (k = 0; k < essential_liberties; k++) { | |
224 | if (does_defend(essential_libs[k], pos)) { | |
225 | apos = NO_MOVE; | |
226 | break; | |
227 | } | |
228 | } | |
229 | ||
230 | if (apos != NO_MOVE && worm_color == color && !does_defend(apos, pos)) | |
231 | apos = NO_MOVE; | |
232 | } | |
233 | else | |
234 | apos = NO_MOVE; | |
235 | } | |
236 | } | |
237 | else { | |
238 | /* We were unable to fill all the liberties. Modify | |
239 | * `inessential_liberties' in order to undo the right number of | |
240 | * moves. | |
241 | */ | |
242 | inessential_liberties = k; | |
243 | } | |
244 | ||
245 | /* Undo all the moves made to fill inessential liberties. */ | |
246 | for (k = 0; k < inessential_liberties; k++) | |
247 | popgo(); | |
248 | ASSERT1(stackp == 0, pos); | |
249 | ||
250 | num_attacks2 = 0; | |
251 | for (k = 0; k < num_attacks; k++) { | |
252 | /* These moves must be safe for the other color, otherwise they are | |
253 | * pointless. Note that checks for safety on previous step were not | |
254 | * sufficient since we had additional stones on board then. | |
255 | */ | |
256 | if (safe_move(attacks[k], other)) { | |
257 | if (defenses[k] != NO_MOVE) { | |
258 | int i; | |
259 | ||
260 | /* Consider this position: | |
261 | * | |
262 | * .X...OO The move at `*' satisfies the conditions above. | |
263 | * .X*OO.O However, it is pointless, since black has a miai | |
264 | * X.OX..O move at `a' to force white to play `b'. That is, | |
265 | * XXObOOO no matter if white plays `*' or `a', black takes | |
266 | * .XXaOXO the other point and white has to fill `b'. So, if | |
267 | * ...XXXX there is a point, adjacent to defense point, safe | |
268 | * for "other" color, we discard the attack. | |
269 | * | |
270 | * Also, in some positions, defense point is adjacent to worm | |
271 | * inessential liberty. In such cases we discard the attack too. | |
272 | */ | |
273 | for (i = 0; i < 4; i++) { | |
274 | int pos2 = defenses[k] + delta[i]; | |
275 | ||
276 | if (board[pos2] == EMPTY) { | |
277 | int m; | |
278 | ||
279 | if (!is_proper_eye_space(pos2) && safe_move(pos2, other)) | |
280 | break; | |
281 | ||
282 | for (m = 0; m < inessential_liberties; m++) { | |
283 | if (inessential_libs[m] == pos2) | |
284 | break; | |
285 | } | |
286 | ||
287 | if (m < inessential_liberties) | |
288 | break; | |
289 | } | |
290 | } | |
291 | ||
292 | /* If this is not the case, the attack is kept for the final trial. */ | |
293 | if (i == 4) | |
294 | attacks[num_attacks2++] = attacks[k]; | |
295 | } | |
296 | else { | |
297 | /* This must be the only attack (filling all inessential liberties | |
298 | * gives an atari). | |
299 | */ | |
300 | ASSERT1(num_attacks == 1, pos); | |
301 | attacks[num_attacks2++] = attacks[k]; | |
302 | } | |
303 | } | |
304 | } | |
305 | ||
306 | value = 0; | |
307 | if (apos != NO_MOVE) { | |
308 | /* We use the number of string's liberties minus 2 as the value of | |
309 | * the move. Minus 2 is explained in the comment before the | |
310 | * function. In some rare cases the value may differ, but this | |
311 | * should be a good guess. | |
312 | */ | |
313 | value = accuratelib(apos, other, MAXLIBS, NULL) - 2; | |
314 | } | |
315 | ||
316 | /* If we haven't found anything interesting or have already dropped it, | |
317 | * there is no point trying more moves, so we return now. | |
318 | */ | |
319 | if (value <= 0 && num_attacks2 == 0) | |
320 | return; | |
321 | ||
322 | /* We filled the liberties with stones of "other" color. That could lead to | |
323 | * some strange attacks, since inessential liberties are not always really | |
324 | * inessential (see trevorb:320 and trevorb:940 for examples where this step | |
325 | * is necessary). Now we fill the liberties with stones of the same color as | |
326 | * the current worm. If the results remain unchanged, then we can probably | |
327 | * trust them. | |
328 | */ | |
329 | for (k = 0; k < inessential_liberties; k++) { | |
330 | if (!trymove(inessential_libs[k], worm_color, "endgame", pos)) | |
331 | break; | |
332 | } | |
333 | ||
334 | /* GNU Go currently doesn't allow suicide, but let's assume it does. */ | |
335 | if (k == inessential_liberties && board[pos] != EMPTY) { | |
336 | if (countlib(pos) > 1) { | |
337 | for (k = 0; k < num_attacks2; k++) { | |
338 | if (trymove(attacks[k], other, "endgame", pos)) { | |
339 | if (attack(pos, NULL) != 0) { | |
340 | TRACE(" endgame move with territorial value %d.0 found at %1m\n", | |
341 | 1, attacks[k]); | |
342 | add_expand_territory_move(attacks[k]); | |
343 | /* FIXME: We just guess the value here. Find a way to calculate it | |
344 | * (more) precisely. | |
345 | */ | |
346 | set_minimum_territorial_value(attacks[k], 1.0); | |
347 | } | |
348 | ||
349 | popgo(); | |
350 | } | |
351 | } | |
352 | } | |
353 | else if (essential_liberties > 0 && essential_libs[0] == attacks[0]) { | |
354 | TRACE(" endgame move with territorial value %d.0 found at %1m\n", | |
355 | 1, attacks[k]); | |
356 | add_expand_territory_move(attacks[0]); | |
357 | /* FIXME: We just guess the value here. Find a way to calculate it | |
358 | * (more) precisely. | |
359 | */ | |
360 | set_minimum_territorial_value(attacks[0], 1.0); | |
361 | } | |
362 | ||
363 | if (value > 0 && does_attack(apos, pos)) { | |
364 | TRACE(" endgame move with territorial value %d.0 found at %1m\n", | |
365 | value, apos); | |
366 | add_expand_territory_move(apos); | |
367 | set_minimum_territorial_value(apos, (float) value); | |
368 | } | |
369 | } | |
370 | else { | |
371 | /* Don't undo moves we didn't play. */ | |
372 | inessential_liberties = k; | |
373 | } | |
374 | ||
375 | /* Undo all the moves made at the third step. */ | |
376 | for (k = 0; k < inessential_liberties; k++) | |
377 | popgo(); | |
378 | ASSERT1(stackp == 0, pos); | |
379 | } | |
380 | ||
381 | /* A backfilling dame is a defense move, usually within potential own | |
382 | * territory, which does not have to be played immediately but after | |
383 | * outer liberties of some string have been filled. If those outer | |
384 | * liberties are dame points (here inessential liberties), it is | |
385 | * usually better to play the backfilling moves before filling the | |
386 | * dame points. If nothing else it reduces the risk for making stupid | |
387 | * blunders while filling dame. | |
388 | */ | |
389 | static void | |
390 | endgame_find_backfilling_dame(int str, int color_to_move) | |
391 | { | |
392 | int k; | |
393 | int color = board[str]; | |
394 | int other = OTHER_COLOR(color); | |
395 | int essential_liberties; | |
396 | int essential_libs[MAXLIBS]; | |
397 | int inessential_liberties; | |
398 | int inessential_libs[MAXLIBS]; | |
399 | int false_eye_liberties; | |
400 | int false_eye_libs[MAXLIBS]; | |
401 | int dpos; | |
402 | int loop_again = 1; | |
403 | int potential_moves[BOARDMAX]; | |
404 | int num_potential_moves = 0; | |
405 | int move = NO_MOVE; | |
406 | ||
407 | while (loop_again) { | |
408 | loop_again = 0; | |
409 | if (!endgame_find_liberties(str, &essential_liberties, essential_libs, | |
410 | &inessential_liberties, inessential_libs, | |
411 | &false_eye_liberties, false_eye_libs)) | |
412 | break; | |
413 | for (k = 0; k < inessential_liberties; k++) { | |
414 | if (!safe_move(inessential_libs[k], other) | |
415 | || !trymove(inessential_libs[k], other, "endgame", str)) | |
416 | continue; | |
417 | increase_depth_values(); | |
418 | if (board[str] == EMPTY) | |
419 | break; | |
420 | if (attack_and_defend(str, NULL, NULL, NULL, &dpos)) { | |
421 | if (worm[dpos].color == EMPTY) { | |
422 | potential_moves[num_potential_moves] = dpos; | |
423 | num_potential_moves++; | |
424 | } | |
425 | forced_backfilling_moves[dpos] = 1; | |
426 | if (trymove(dpos, color, "endgame", str)) | |
427 | increase_depth_values(); | |
428 | loop_again = 1; | |
429 | break; | |
430 | } | |
431 | } | |
432 | } | |
433 | ||
434 | while (stackp > 0) { | |
435 | popgo(); | |
436 | decrease_depth_values(); | |
437 | } | |
438 | ||
439 | for (k = num_potential_moves - 1; k >= 0; k--) | |
440 | if (safe_move(potential_moves[k], color)) { | |
441 | move = potential_moves[k]; | |
442 | TRACE(" backfilling dame found at %1m for string %1m\n", move, str); | |
443 | if (color == color_to_move) { | |
444 | add_expand_territory_move(move); | |
445 | set_minimum_territorial_value(move, 0.1); | |
446 | } | |
447 | break; | |
448 | } | |
449 | } | |
450 | ||
451 | /* Find liberties of the string str with various characteristics. See | |
452 | * the comments above endgame_analyze_worm_liberties() for more | |
453 | * information. | |
454 | */ | |
455 | static int | |
456 | endgame_find_liberties(int str, | |
457 | int *essential_liberties, int essential_libs[MAXLIBS], | |
458 | int *inessential_liberties, | |
459 | int inessential_libs[MAXLIBS], | |
460 | int *false_eye_liberties, int false_eye_libs[MAXLIBS]) | |
461 | { | |
462 | int liberties; | |
463 | int libs[MAXLIBS]; | |
464 | int k; | |
465 | ||
466 | ASSERT1(IS_STONE(board[str]), str); | |
467 | ||
468 | *essential_liberties = 0; | |
469 | *inessential_liberties = 0; | |
470 | *false_eye_liberties = 0; | |
471 | ||
472 | /* Find all string liberties. */ | |
473 | liberties = findlib(str, MAXLIBS, libs); | |
474 | ||
475 | /* Loop over the liberties and find inessential and essential ones. The | |
476 | * latter are defined as those, which are not inside an eye space, but | |
477 | * don't otherwise qualify as inessential. If we find a non-alive (dead | |
478 | * or critical) worm or dragon around, we stop looking for liberties and | |
479 | * skip the current worm (position is unstable). | |
480 | */ | |
481 | for (k = 0; k < liberties; k++) { | |
482 | int lib = libs[k]; | |
483 | ||
484 | if (!is_proper_eye_space(lib)) { | |
485 | int i; | |
486 | int essential = 0; | |
487 | int found_other = 0; | |
488 | ||
489 | for (i = 0; i < 4; i++) { | |
490 | int pos = lib + delta[i]; | |
491 | ||
492 | if (!IS_STONE(board[pos]) || !IS_STONE(worm[pos].color)) | |
493 | continue; | |
494 | ||
495 | if (worm[pos].attack_codes[0] != 0 || dragon[pos].status != ALIVE) | |
496 | return 0; | |
497 | ||
498 | if (board[pos] == board[str]) { | |
499 | if (find_origin(pos) != find_origin(str)) | |
500 | essential = 1; | |
501 | } | |
502 | else | |
503 | found_other = 1; | |
504 | } | |
505 | ||
506 | if (i < 4) | |
507 | break; | |
508 | ||
509 | if (found_other) { | |
510 | if (essential) | |
511 | essential_libs[(*essential_liberties)++] = lib; | |
512 | else | |
513 | inessential_libs[(*inessential_liberties)++] = lib; | |
514 | } | |
515 | else if (is_false_eye(half_eye, lib) && !false_eye_territory[lib]) | |
516 | false_eye_libs[(*false_eye_liberties)++] = lib; | |
517 | } | |
518 | } | |
519 | return 1; | |
520 | } | |
521 | ||
522 | /* | |
523 | * Local Variables: | |
524 | * tab-width: 8 | |
525 | * c-basic-offset: 2 | |
526 | * End: | |
527 | */ |