uct/walk.c

   1 #include <assert.h>
   2 #include <math.h>
   3 #include <pthread.h>
   4 #include <signal.h>
   5 #include <stdio.h>
   6 #include <stdlib.h>
   7 #include <string.h>
   8
   9 #define DEBUG
  10
  11 #include "debug.h"
  12 #include "board.h"
  13 #include "move.h"
  14 #include "playout.h"
  15 #include "probdist.h"
  16 #include "random.h"
  17 #include "tactics/util.h"
  18 #include "uct/dynkomi.h"
  19 #include "uct/internal.h"
  20 #include "uct/search.h"
  21 #include "uct/tree.h"
  22 #include "uct/uct.h"
  23 #include "uct/walk.h"
  24
  25 #define DESCENT_DLEN 512
  26
  27
  28 void
  29 uct_progress_text(struct uct *u, struct tree *t, enum stone color, int playouts, bool final)
  30 {
  31         if (!UDEBUGL(0))
  32                 return;
  33
  34         /* Best move */
  35         struct tree_node *best = u->policy->choose(u->policy, t->root, t->board, color, resign);
  36         if (!best) {
  37                 fprintf(stderr, "... No moves left\n");
  38                 return;
  39         }
  40         fprintf(stderr, "[%d] ", playouts);
  41         fprintf(stderr, "best %f ", tree_node_get_value(t, 1, best->u.value));
  42
  43         /* Dynamic komi */
  44         if (t->use_extra_komi)
  45                 fprintf(stderr, "komi %.1f ", t->extra_komi);
  46
  47         /* Best sequence */
  48         fprintf(stderr, "| seq ");
  49         for (int depth = 0; depth < 4; depth++) {
  50                 if (best && best->u.playouts >= 25) {
  51                         fprintf(stderr, "%3s ", coord2sstr(node_coord(best), t->board));
  52                         best = u->policy->choose(u->policy, best, t->board, color, resign);
  53                 } else {
  54                         fprintf(stderr, "    ");
  55                 }
  56         }
  57
  58         /* Best candidates */
  59         fprintf(stderr, "| can ");
  60         int cans = 4;
  61         struct tree_node *can[cans];
  62         memset(can, 0, sizeof(can));
  63         best = t->root->children;
  64         while (best) {
  65                 int c = 0;
  66                 while ((!can[c] || best->u.playouts > can[c]->u.playouts) && ++c < cans);
  67                 for (int d = 0; d < c; d++) can[d] = can[d + 1];
  68                 if (c > 0) can[c - 1] = best;
  69                 best = best->sibling;
  70         }
  71         while (--cans >= 0) {
  72                 if (can[cans]) {
  73                         fprintf(stderr, "%3s(%.3f) ",
  74                                 coord2sstr(node_coord(can[cans]), t->board),
  75                                 tree_node_get_value(t, 1, can[cans]->u.value));
  76                 } else {
  77                         fprintf(stderr, "           ");
  78                 }
  79         }
  80
  81         fprintf(stderr, "\n");
  82 }
  83
  84 void
  85 uct_progress_json(struct uct *u, struct tree *t, enum stone color, int playouts, bool final, bool big)
  86 {
  87         /* Prefix indicating JSON line. */
  88         fprintf(stderr, "{\"%s\": {", final ? "move" : "frame");
  89
  90         /* Plaout count */
  91         fprintf(stderr, "\"playouts\": %d", playouts);
  92
  93         /* Dynamic komi */
  94         if (t->use_extra_komi)
  95                 fprintf(stderr, ", \"extrakomi\": %.1f", t->extra_komi);
  96
  97         struct tree_node *best = u->policy->choose(u->policy, t->root, t->board, color, resign);
  98         if (best) {
  99                 /* Best move */
 100                 fprintf(stderr, ", \"best\": {\"%s\": %f}",
 101                         coord2sstr(best->coord, t->board),
 102                         tree_node_get_value(t, 1, best->u.value));
 103
 104                 /* Best sequence */
 105                 fprintf(stderr, ", \"seq\": [");
 106                 for (int depth = 0; depth < 4; depth++) {
 107                         if (!best || best->u.playouts < 25) break;
 108                         fprintf(stderr, "%s\"%s\"", depth > 0 ? "," : "",
 109                                 coord2sstr(best->coord, t->board));
 110                         best = u->policy->choose(u->policy, best, t->board, color, resign);
 111                 }
 112                 fprintf(stderr, "]");
 113         }
 114
 115         /* Best candidates */
 116         int cans = 4;
 117         struct tree_node *can[cans];
 118         memset(can, 0, sizeof(can));
 119         best = t->root->children;
 120         while (best) {
 121                 int c = 0;
 122                 while ((!can[c] || best->u.playouts > can[c]->u.playouts) && ++c < cans);
 123                 for (int d = 0; d < c; d++) can[d] = can[d + 1];
 124                 if (c > 0) can[c - 1] = best;
 125                 best = best->sibling;
 126         }
 127         fprintf(stderr, ", \"can\": [");
 128         while (--cans >= 0) {
 129                 if (!can[cans]) break;
 130                 fprintf(stderr, "%s{\"%s\":%.3f}",
 131                         cans < 3 ? "," : "",
 132                         coord2sstr(can[cans]->coord, t->board),
 133                         tree_node_get_value(t, 1, can[cans]->u.value));
 134         }
 135         fprintf(stderr, "]");
 136
 137         if (big) {
 138                 /* Average score. */
 139                 if (t->avg_score.playouts > 0)
 140                         fprintf(stderr, ", \"avg\": {\"score\": %.3f}", t->avg_score.value);
 141                 /* Ownership statistics. Value (0..1000) for each possible
 142                  * point describes likelihood of this point becoming black.
 143                  * Normally, white rate is 1000-value; exception are possible
 144                  * seki points, but these should be rare. */
 145                 fprintf(stderr, ", \"boards\": {\"territory\": [");
 146                 int f = 0;
 147                 foreach_point(t->board) {
 148                         if (board_at(t->board, c) == S_OFFBOARD) continue;
 149                         int rate = u->ownermap.map[c][S_BLACK] * 1000 / u->ownermap.playouts;
 150                         fprintf(stderr, "%s%d", f++ > 0 ? "," : "", rate);
 151                 } foreach_point_end;
 152                 fprintf(stderr, "]}");
 153
 154         }
 155
 156         fprintf(stderr, "}}\n");
 157 }
 158
 159 void
 160 uct_progress_status(struct uct *u, struct tree *t, enum stone color, int playouts, bool final)
 161 {
 162         switch (u->reporting) {
 163                 case UR_TEXT:
 164                         uct_progress_text(u, t, color, playouts, final);
 165                         break;
 166                 case UR_JSON:
 167                 case UR_JSON_BIG:
 168                         uct_progress_json(u, t, color, playouts, final,
 169                                           u->reporting == UR_JSON_BIG);
 170                         break;
 171                 default: assert(0);
 172         }
 173 }
 174
 175
 176 static inline void
 177 record_amaf_move(struct playout_amafmap *amaf, coord_t coord)
 178 {
 179         assert(amaf->gamelen < MAX_GAMELEN);
 180         amaf->game[amaf->gamelen++] = coord;
 181 }
 182
 183
 184 struct uct_playout_callback {
 185         struct uct *uct;
 186         struct tree *tree;
 187         struct tree_node *lnode;
 188 };
 189
 190
 191 static coord_t
 192 uct_playout_hook(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color, int mode)
 193 {
 194         /* XXX: This is used in some non-master branches. */
 195         return pass;
 196 }
 197
 198 static coord_t
 199 uct_playout_prepolicy(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color)
 200 {
 201         return uct_playout_hook(playout, setup, b, color, 0);
 202 }
 203
 204 static coord_t
 205 uct_playout_postpolicy(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color)
 206 {
 207         return uct_playout_hook(playout, setup, b, color, 1);
 208 }
 209
 210
 211 static int
 212 uct_leaf_node(struct uct *u, struct board *b, enum stone player_color,
 213               struct playout_amafmap *amaf,
 214               struct uct_descent *descent, int *dlen,
 215               struct tree_node *significant[2],
 216               struct tree *t, struct tree_node *n, enum stone node_color,
 217               char *spaces)
 218 {
 219         enum stone next_color = stone_other(node_color);
 220         int parity = (next_color == player_color ? 1 : -1);
 221
 222         if (UDEBUGL(7))
 223                 fprintf(stderr, "%s*-- UCT playout #%d start [%s] %f\n",
 224                         spaces, n->u.playouts, coord2sstr(node_coord(n), t->board),
 225                         tree_node_get_value(t, parity, n->u.value));
 226
 227         struct uct_playout_callback upc = {
 228                 .uct = u,
 229                 .tree = t,
 230                 /* TODO: Don't necessarily restart the sequence walk when
 231                  * entering playout. */
 232                 .lnode = NULL,
 233         };
 234
 235         struct playout_setup ps = {
 236                 .gamelen = u->gamelen,
 237                 .mercymin = u->mercymin,
 238                 .prepolicy_hook = uct_playout_prepolicy,
 239                 .postpolicy_hook = uct_playout_postpolicy,
 240                 .hook_data = &upc,
 241         };
 242         int result = play_random_game(&ps, b, next_color,
 243                                       u->playout_amaf ? amaf : NULL,
 244                                       &u->ownermap, u->playout);
 245         if (next_color == S_WHITE) {
 246                 /* We need the result from black's perspective. */
 247                 result = - result;
 248         }
 249         if (UDEBUGL(7))
 250                 fprintf(stderr, "%s -- [%d..%d] %s random playout result %d\n",
 251                         spaces, player_color, next_color, coord2sstr(node_coord(n), t->board), result);
 252
 253         return result;
 254 }
 255
 256 static floating_t
 257 scale_value(struct uct *u, struct board *b, int result)
 258 {
 259         floating_t rval = result > 0 ? 1.0 : result < 0 ? 0.0 : 0.5;
 260         if (u->val_scale && result != 0) {
 261                 int vp = u->val_points;
 262                 if (!vp) {
 263                         vp = board_size(b) - 1; vp *= vp; vp *= 2;
 264                 }
 265
 266                 floating_t sval = (floating_t) abs(result) / vp;
 267                 sval = sval > 1 ? 1 : sval;
 268                 if (result < 0) sval = 1 - sval;
 269                 if (u->val_extra)
 270                         rval += u->val_scale * sval;
 271                 else
 272                         rval = (1 - u->val_scale) * rval + u->val_scale * sval;
 273                 // fprintf(stderr, "score %d => sval %f, rval %f\n", result, sval, rval);
 274         }
 275         return rval;
 276 }
 277
 278 static double
 279 local_value(struct uct *u, struct board *b, coord_t coord, enum stone color)
 280 {
 281         /* Tactical evaluation of move @coord by color @color, given
 282          * simulation end position @b. I.e., a move is tactically good
 283          * if the resulting group stays on board until the game end. */
 284         /* We can also take into account surrounding stones, e.g. to
 285          * encourage taking off external liberties during a semeai. */
 286         double val = board_local_value(u->local_tree_neival, b, coord, color);
 287         return (color == S_WHITE) ? 1.f - val : val;
 288 }
 289
 290 static void
 291 record_local_sequence(struct uct *u, struct tree *t, struct board *endb,
 292                       struct uct_descent *descent, int dlen, int di,
 293                       enum stone seq_color)
 294 {
 295 #define LTREE_DEBUG if (UDEBUGL(6))
 296
 297         /* Ignore pass sequences. */
 298         if (is_pass(node_coord(descent[di].node)))
 299                 return;
 300
 301         LTREE_DEBUG board_print(endb, stderr);
 302         LTREE_DEBUG fprintf(stderr, "recording local %s sequence: ",
 303                 stone2str(seq_color));
 304
 305         /* Sequences starting deeper are less relevant in general. */
 306         int pval = LTREE_PLAYOUTS_MULTIPLIER;
 307         if (u->local_tree && u->local_tree_depth_decay > 0)
 308                 pval = ((floating_t) pval) / pow(u->local_tree_depth_decay, di - 1);
 309         if (!pval) {
 310                 LTREE_DEBUG fprintf(stderr, "too deep @%d\n", di);
 311                 return;
 312         }
 313
 314         /* Pick the right local tree root... */
 315         struct tree_node *lnode = seq_color == S_BLACK ? t->ltree_black : t->ltree_white;
 316         lnode->u.playouts++;
 317
 318         /* ...determine the sequence value... */
 319         double sval = 0.5;
 320         if (u->local_tree_eval != LTE_EACH) {
 321                 sval = local_value(u, endb, node_coord(descent[di].node), seq_color);
 322                 LTREE_DEBUG fprintf(stderr, "(goal %s[%s %1.3f][%d]) ",
 323                         coord2sstr(node_coord(descent[di].node), t->board),
 324                         stone2str(seq_color), sval, descent[di].node->d);
 325
 326                 if (u->local_tree_eval == LTE_TOTAL) {
 327                         int di0 = di;
 328                         while (di < dlen && (di == di0 || descent[di].node->d < u->tenuki_d)) {
 329                                 enum stone color = (di - di0) % 2 ? stone_other(seq_color) : seq_color;
 330                                 double rval = local_value(u, endb, node_coord(descent[di].node), color);
 331                                 if ((di - di0) % 2)
 332                                         rval = 1 - rval;
 333                                 sval += rval;
 334                                 di++;
 335                         }
 336                         sval /= (di - di0 + 1);
 337                         di = di0;
 338                 }
 339         }
 340
 341         /* ...and record the sequence. */
 342         int di0 = di;
 343         while (di < dlen && !is_pass(node_coord(descent[di].node))
 344                && (di == di0 || descent[di].node->d < u->tenuki_d)) {
 345                 enum stone color = (di - di0) % 2 ? stone_other(seq_color) : seq_color;
 346                 double rval;
 347                 if (u->local_tree_eval != LTE_EACH)
 348                         rval = sval;
 349                 else
 350                         rval = local_value(u, endb, node_coord(descent[di].node), color);
 351                 LTREE_DEBUG fprintf(stderr, "%s[%s %1.3f][%d] ",
 352                         coord2sstr(node_coord(descent[di].node), t->board),
 353                         stone2str(color), rval, descent[di].node->d);
 354                 lnode = tree_get_node(t, lnode, node_coord(descent[di++].node), true);
 355                 assert(lnode);
 356                 stats_add_result(&lnode->u, rval, pval);
 357         }
 358
 359         /* Add lnode for tenuki (pass) if we descended further. */
 360         if (di < dlen) {
 361                 double rval = u->local_tree_eval != LTE_EACH ? sval : 0.5;
 362                 LTREE_DEBUG fprintf(stderr, "pass ");
 363                 lnode = tree_get_node(t, lnode, pass, true);
 364                 assert(lnode);
 365                 stats_add_result(&lnode->u, rval, pval);
 366         }
 367
 368         LTREE_DEBUG fprintf(stderr, "\n");
 369 }
 370
 371
 372 int
 373 uct_playout(struct uct *u, struct board *b, enum stone player_color, struct tree *t)
 374 {
 375         struct board b2;
 376         board_copy(&b2, b);
 377
 378         struct playout_amafmap amaf;
 379         amaf.gamelen = amaf.game_baselen = 0;
 380
 381         /* Walk the tree until we find a leaf, then expand it and do
 382          * a random playout. */
 383         struct tree_node *n = t->root;
 384         enum stone node_color = stone_other(player_color);
 385         assert(node_color == t->root_color);
 386
 387         /* Make sure the root node is expanded. */
 388         if (tree_leaf_node(n) && !__sync_lock_test_and_set(&n->is_expanded, 1))
 389                 tree_expand_node(t, n, &b2, player_color, u, 1);
 390
 391         /* Tree descent history. */
 392         /* XXX: This is somewhat messy since @n and descent[dlen-1].node are
 393          * redundant. */
 394         struct uct_descent descent[DESCENT_DLEN];
 395         descent[0].node = n; descent[0].lnode = NULL;
 396         int dlen = 1;
 397         /* Total value of the sequence. */
 398         struct move_stats seq_value = { .playouts = 0 };
 399         /* The last "significant" node along the descent (i.e. node
 400          * with higher than configured number of playouts). For black
 401          * and white. */
 402         struct tree_node *significant[2] = { NULL, NULL };
 403         if (n->u.playouts >= u->significant_threshold)
 404                 significant[node_color - 1] = n;
 405
 406         int result;
 407         int pass_limit = (board_size(&b2) - 2) * (board_size(&b2) - 2) / 2;
 408         int passes = is_pass(b->last_move.coord) && b->moves > 0;
 409
 410         /* debug */
 411         static char spaces[] = "\0                                                      ";
 412         /* /debug */
 413         if (UDEBUGL(8))
 414                 fprintf(stderr, "--- UCT walk with color %d\n", player_color);
 415
 416         while (!tree_leaf_node(n) && passes < 2) {
 417                 spaces[dlen - 1] = ' '; spaces[dlen] = 0;
 418
 419
 420                 /*** Choose a node to descend to: */
 421
 422                 /* Parity is chosen already according to the child color, since
 423                  * it is applied to children. */
 424                 node_color = stone_other(node_color);
 425                 int parity = (node_color == player_color ? 1 : -1);
 426
 427                 assert(dlen < DESCENT_DLEN);
 428                 descent[dlen] = descent[dlen - 1];
 429                 if (u->local_tree && (!descent[dlen].lnode || descent[dlen].node->d >= u->tenuki_d)) {
 430                         /* Start new local sequence. */
 431                         /* Remember that node_color already holds color of the
 432                          * to-be-found child. */
 433                         descent[dlen].lnode = node_color == S_BLACK ? t->ltree_black : t->ltree_white;
 434                 }
 435
 436                 if (!u->random_policy_chance || fast_random(u->random_policy_chance))
 437                         u->policy->descend(u->policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 438                 else
 439                         u->random_policy->descend(u->random_policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 440
 441
 442                 /*** Perform the descent: */
 443
 444                 if (descent[dlen].node->u.playouts >= u->significant_threshold) {
 445                         significant[node_color - 1] = descent[dlen].node;
 446                 }
 447
 448                 seq_value.playouts += descent[dlen].value.playouts;
 449                 seq_value.value += descent[dlen].value.value * descent[dlen].value.playouts;
 450                 n = descent[dlen++].node;
 451                 assert(n == t->root || n->parent);
 452                 if (UDEBUGL(7))
 453                         fprintf(stderr, "%s+-- UCT sent us to [%s:%d] %d,%f\n",
 454                                 spaces, coord2sstr(node_coord(n), t->board),
 455                                 node_coord(n), n->u.playouts,
 456                                 tree_node_get_value(t, parity, n->u.value));
 457
 458                 /* Add virtual loss if we need to; this is used to discourage
 459                  * other threads from visiting this node in case of multiple
 460                  * threads doing the tree search. */
 461                 if (u->virtual_loss)
 462                         stats_add_result(&n->u, node_color == S_BLACK ? 0.0 : 1.0, u->virtual_loss);
 463
 464                 assert(node_coord(n) >= -1);
 465                 record_amaf_move(&amaf, node_coord(n));
 466
 467                 struct move m = { node_coord(n), node_color };
 468                 int res = board_play(&b2, &m);
 469
 470                 if (res < 0 || (!is_pass(m.coord) && !group_at(&b2, m.coord)) /* suicide */
 471                     || b2.superko_violation) {
 472                         if (UDEBUGL(4)) {
 473                                 for (struct tree_node *ni = n; ni; ni = ni->parent)
 474                                         fprintf(stderr, "%s<%"PRIhash"> ", coord2sstr(node_coord(ni), t->board), ni->hash);
 475                                 fprintf(stderr, "marking invalid %s node %d,%d res %d group %d spk %d\n",
 476                                         stone2str(node_color), coord_x(node_coord(n),b), coord_y(node_coord(n),b),
 477                                         res, group_at(&b2, m.coord), b2.superko_violation);
 478                         }
 479                         n->hints |= TREE_HINT_INVALID;
 480                         result = 0;
 481                         goto end;
 482                 }
 483
 484                 if (is_pass(node_coord(n)))
 485                         passes++;
 486                 else
 487                         passes = 0;
 488
 489                 enum stone next_color = stone_other(node_color);
 490                 /* We need to make sure only one thread expands the node. If
 491                  * we are unlucky enough for two threads to meet in the same
 492                  * node, the latter one will simply do another simulation from
 493                  * the node itself, no big deal. t->nodes_size may exceed
 494                  * the maximum in multi-threaded case but not by much so it's ok.
 495                  * The size test must be before the test&set not after, to allow
 496                  * expansion of the node later if enough nodes have been freed. */
 497                 if (tree_leaf_node(n)
 498                     && n->u.playouts - u->virtual_loss >= u->expand_p && t->nodes_size < u->max_tree_size
 499                     && !__sync_lock_test_and_set(&n->is_expanded, 1))
 500                         tree_expand_node(t, n, &b2, next_color, u, -parity);
 501         }
 502
 503         amaf.game_baselen = amaf.gamelen;
 504
 505         if (t->use_extra_komi && u->dynkomi->persim) {
 506                 b2.komi += round(u->dynkomi->persim(u->dynkomi, &b2, t, n));
 507         }
 508
 509         if (passes >= 2) {
 510                 /* XXX: No dead groups support. */
 511                 floating_t score = board_official_score(&b2, NULL);
 512                 /* Result from black's perspective (no matter who
 513                  * the player; black's perspective is always
 514                  * what the tree stores. */
 515                 result = - (score * 2);
 516
 517                 if (UDEBUGL(5))
 518                         fprintf(stderr, "[%d..%d] %s p-p scoring playout result %d (W %f)\n",
 519                                 player_color, node_color, coord2sstr(node_coord(n), t->board), result, score);
 520                 if (UDEBUGL(6))
 521                         board_print(&b2, stderr);
 522
 523                 board_ownermap_fill(&u->ownermap, &b2);
 524
 525         } else { // assert(tree_leaf_node(n));
 526                 /* In case of parallel tree search, the assertion might
 527                  * not hold if two threads chew on the same node. */
 528                 result = uct_leaf_node(u, &b2, player_color, &amaf, descent, &dlen, significant, t, n, node_color, spaces);
 529         }
 530
 531         if (u->policy->wants_amaf && u->playout_amaf_cutoff) {
 532                 unsigned int cutoff = amaf.game_baselen;
 533                 cutoff += (amaf.gamelen - amaf.game_baselen) * u->playout_amaf_cutoff / 100;
 534                 amaf.gamelen = cutoff;
 535         }
 536
 537         /* Record the result. */
 538
 539         assert(n == t->root || n->parent);
 540         floating_t rval = scale_value(u, b, result);
 541         u->policy->update(u->policy, t, n, node_color, player_color, &amaf, &b2, rval);
 542
 543         stats_add_result(&t->avg_score, result / 2, 1);
 544         if (t->use_extra_komi) {
 545                 stats_add_result(&u->dynkomi->score, result / 2, 1);
 546                 stats_add_result(&u->dynkomi->value, rval, 1);
 547         }
 548
 549         if (u->local_tree && n->parent && !is_pass(node_coord(n)) && dlen > 0) {
 550                 /* Get the local sequences and record them in ltree. */
 551                 /* We will look for sequence starts in our descent
 552                  * history, then run record_local_sequence() for each
 553                  * found sequence start; record_local_sequence() may
 554                  * pick longer sequences from descent history then,
 555                  * which is expected as it will create new lnodes. */
 556                 enum stone seq_color = player_color;
 557                 /* First move always starts a sequence. */
 558                 record_local_sequence(u, t, &b2, descent, dlen, 1, seq_color);
 559                 seq_color = stone_other(seq_color);
 560                 for (int dseqi = 2; dseqi < dlen; dseqi++, seq_color = stone_other(seq_color)) {
 561                         if (u->local_tree_allseq) {
 562                                 /* We are configured to record all subsequences. */
 563                                 record_local_sequence(u, t, &b2, descent, dlen, dseqi, seq_color);
 564                                 continue;
 565                         }
 566                         if (descent[dseqi].node->d >= u->tenuki_d) {
 567                                 /* Tenuki! Record the fresh sequence. */
 568                                 record_local_sequence(u, t, &b2, descent, dlen, dseqi, seq_color);
 569                                 continue;
 570                         }
 571                         if (descent[dseqi].lnode && !descent[dseqi].lnode) {
 572                                 /* Record result for in-descent picked sequence. */
 573                                 record_local_sequence(u, t, &b2, descent, dlen, dseqi, seq_color);
 574                                 continue;
 575                         }
 576                 }
 577         }
 578
 579 end:
 580         /* We need to undo the virtual loss we added during descend. */
 581         if (u->virtual_loss) {
 582                 floating_t loss = node_color == S_BLACK ? 0.0 : 1.0;
 583                 for (; n->parent; n = n->parent) {
 584                         stats_rm_result(&n->u, loss, u->virtual_loss);
 585                         loss = 1.0 - loss;
 586                 }
 587         }
 588
 589         board_done_noalloc(&b2);
 590         return result;
 591 }
 592
 593 int
 594 uct_playouts(struct uct *u, struct board *b, enum stone color, struct tree *t, struct time_info *ti)
 595 {
 596         int i;
 597         if (ti && ti->dim == TD_GAMES) {
 598                 for (i = 0; t->root->u.playouts <= ti->len.games && !uct_halt; i++)
 599                         uct_playout(u, b, color, t);
 600         } else {
 601                 for (i = 0; !uct_halt; i++)
 602                         uct_playout(u, b, color, t);
 603         }
 604         return i;
 605 }