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 "uct/dynkomi.h"
  18 #include "uct/internal.h"
  19 #include "uct/search.h"
  20 #include "uct/tree.h"
  21 #include "uct/uct.h"
  22 #include "uct/walk.h"
  23
  24 #define DESCENT_DLEN 512
  25
  26 void
  27 uct_progress_status(struct uct *u, struct tree *t, enum stone color, int playouts)
  28 {
  29         if (!UDEBUGL(0))
  30                 return;
  31
  32         /* Best move */
  33         struct tree_node *best = u->policy->choose(u->policy, t->root, t->board, color, resign);
  34         if (!best) {
  35                 fprintf(stderr, "... No moves left\n");
  36                 return;
  37         }
  38         fprintf(stderr, "[%d] ", playouts);
  39         fprintf(stderr, "best %f ", tree_node_get_value(t, 1, best->u.value));
  40
  41         /* Dynamic komi */
  42         if (t->use_extra_komi)
  43                 fprintf(stderr, "komi %.1f ", t->extra_komi);
  44
  45         /* Best sequence */
  46         fprintf(stderr, "| seq ");
  47         for (int depth = 0; depth < 4; depth++) {
  48                 if (best && best->u.playouts >= 25) {
  49                         fprintf(stderr, "%3s ", coord2sstr(best->coord, t->board));
  50                         best = u->policy->choose(u->policy, best, t->board, color, resign);
  51                 } else {
  52                         fprintf(stderr, "    ");
  53                 }
  54         }
  55
  56         /* Best candidates */
  57         fprintf(stderr, "| can ");
  58         int cans = 4;
  59         struct tree_node *can[cans];
  60         memset(can, 0, sizeof(can));
  61         best = t->root->children;
  62         while (best) {
  63                 int c = 0;
  64                 while ((!can[c] || best->u.playouts > can[c]->u.playouts) && ++c < cans);
  65                 for (int d = 0; d < c; d++) can[d] = can[d + 1];
  66                 if (c > 0) can[c - 1] = best;
  67                 best = best->sibling;
  68         }
  69         while (--cans >= 0) {
  70                 if (can[cans]) {
  71                         fprintf(stderr, "%3s(%.3f) ",
  72                                 coord2sstr(can[cans]->coord, t->board),
  73                                 tree_node_get_value(t, 1, can[cans]->u.value));
  74                 } else {
  75                         fprintf(stderr, "           ");
  76                 }
  77         }
  78
  79         fprintf(stderr, "\n");
  80 }
  81
  82
  83 static void
  84 record_amaf_move(struct playout_amafmap *amaf, coord_t coord, enum stone color)
  85 {
  86         if (amaf->map[coord] == S_NONE || amaf->map[coord] == color) {
  87                 amaf->map[coord] = color;
  88         } else { // XXX: Respect amaf->record_nakade
  89                 amaf_op(amaf->map[coord], +);
  90         }
  91         amaf->game[amaf->gamelen].coord = coord;
  92         amaf->game[amaf->gamelen].color = color;
  93         amaf->gamelen++;
  94         assert(amaf->gamelen < sizeof(amaf->game) / sizeof(amaf->game[0]));
  95 }
  96
  97
  98 struct uct_playout_callback {
  99         struct uct *uct;
 100         struct tree *tree;
 101         struct tree_node *lnode;
 102
 103         coord_t *treepool[2];
 104         int treepool_n[2];
 105 };
 106
 107
 108 static coord_t
 109 uct_playout_hook(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color, int mode)
 110 {
 111         struct uct_playout_callback *upc = setup->hook_data;
 112         struct uct *u = upc->uct;
 113
 114         if (UDEBUGL(8))
 115                 fprintf(stderr, "treepool check [%d] %d, %p,%p\n", mode, u->treepool_chance[mode], upc->treepool[0], upc->treepool[1]);
 116
 117         if (u->treepool_chance[mode] > fast_random(100) && upc->treepool[color - 1]) {
 118                 assert(upc->treepool_n[color - 1] > 0);
 119                 if (UDEBUGL(8)) {
 120                         fprintf(stderr, "Treepool: ");
 121                         for (int i = 0; i < upc->treepool_n[color - 1]; i++)
 122                                 fprintf(stderr, "%s ", coord2sstr(upc->treepool[color - 1][i], b));
 123                         fprintf(stderr, "\n");
 124                 }
 125
 126                 coord_t treepool_move = pass;
 127                 if (u->treepool_pickfactor) {
 128                         /* With pickfactor=10, we get uniform distribution. */
 129                         int prob = 1000 * u->treepool_pickfactor / (upc->treepool_n[color - 1] * 10);
 130                         for (int i = 0; i < upc->treepool_n[color - 1]; i++) {
 131                                 treepool_move = upc->treepool[color - 1][i];
 132                                 if (prob > fast_random(1000)) break;
 133                         }
 134                 } else {
 135                         treepool_move = upc->treepool[color - 1][fast_random(upc->treepool_n[color - 1])];
 136                 }
 137                 if (UDEBUGL(7))
 138                         fprintf(stderr, "Treepool pick <%d> %s,%s\n",
 139                                 upc->treepool_n[color - 1],
 140                                 stone2str(color), coord2sstr(treepool_move, b));
 141
 142                 if (board_is_valid_play(b, color, treepool_move))
 143                         return treepool_move;
 144         }
 145         return pass;
 146 }
 147
 148 static coord_t
 149 uct_playout_prepolicy(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color)
 150 {
 151         return uct_playout_hook(playout, setup, b, color, 0);
 152 }
 153
 154 static coord_t
 155 uct_playout_postpolicy(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color)
 156 {
 157         return uct_playout_hook(playout, setup, b, color, 1);
 158 }
 159
 160 double
 161 treepool_node_value(struct uct *u, struct tree *tree, int parity, struct tree_node *node)
 162 {
 163         /* XXX: Playouts get cast to double */
 164         switch (u->treepool_type) {
 165                 case UTT_RAVE_PLAYOUTS:
 166                         return node->amaf.playouts;
 167                 case UTT_RAVE_VALUE:
 168                         return tree_node_get_value(tree, parity, node->amaf.value);
 169                 case UTT_UCT_PLAYOUTS:
 170                         return node->u.playouts;
 171                 case UTT_UCT_VALUE:
 172                         return tree_node_get_value(tree, parity, node->u.value);
 173                 case UTT_EVALUATE:
 174                 {
 175                         struct uct_descent d = { .node = node };
 176                         assert(u->policy->evaluate);
 177                         return u->policy->evaluate(u->policy, tree, &d, parity);
 178                 }
 179                 default: assert(0);
 180         }
 181         return -1;
 182 }
 183
 184 static void
 185 treepool_setup(struct uct_playout_callback *upc, struct board *b, struct tree_node *node, int color)
 186 {
 187         struct uct *u = upc->uct;
 188         int parity = ((node->depth ^ upc->tree->root->depth) & 1) ? -1 : 1;
 189
 190         /* XXX: Naive O(N^2) way. */
 191         for (int i = 0; i < u->treepool_size; i++) {
 192                 /* For each item, find the highest
 193                  * node not in the pool yet. */
 194                 struct tree_node *best = NULL;
 195                 double best_val = -1;
 196
 197                 assert(node->children && is_pass(node->children->coord));
 198                 for (struct tree_node *ni = node->children->sibling; ni; ni = ni->sibling) {
 199                         /* Do we already have it? */
 200                         bool have = false;
 201                         for (int j = 0; j < upc->treepool_n[color]; j++) {
 202                                 if (upc->treepool[color][j] == ni->coord) {
 203                                         have = true;
 204                                         break;
 205                                 }
 206                         }
 207                         if (have)
 208                                 continue;
 209
 210                         double i_val = treepool_node_value(u, upc->tree, parity, ni);
 211                         if (i_val > best_val) {
 212                                 best = ni;
 213                                 best_val = i_val;
 214                         }
 215                 }
 216
 217                 if (!best) break;
 218                 upc->treepool[color][upc->treepool_n[color]++] = best->coord;
 219         }
 220 }
 221
 222
 223 static int
 224 uct_leaf_node(struct uct *u, struct board *b, enum stone player_color,
 225               struct playout_amafmap *amaf,
 226               struct uct_descent *descent, int *dlen,
 227               struct tree_node *significant[2],
 228               struct tree *t, struct tree_node *n, enum stone node_color,
 229               char *spaces)
 230 {
 231         enum stone next_color = stone_other(node_color);
 232         int parity = (next_color == player_color ? 1 : -1);
 233
 234         /* We need to make sure only one thread expands the node. If
 235          * we are unlucky enough for two threads to meet in the same
 236          * node, the latter one will simply do another simulation from
 237          * the node itself, no big deal. t->nodes_size may exceed
 238          * the maximum in multi-threaded case but not by much so it's ok.
 239          * The size test must be before the test&set not after, to allow
 240          * expansion of the node later if enough nodes have been freed. */
 241         if (n->u.playouts >= u->expand_p && t->nodes_size < u->max_tree_size
 242             && !__sync_lock_test_and_set(&n->is_expanded, 1)) {
 243                 tree_expand_node(t, n, b, next_color, u, parity);
 244         }
 245         if (UDEBUGL(7))
 246                 fprintf(stderr, "%s*-- UCT playout #%d start [%s] %f\n",
 247                         spaces, n->u.playouts, coord2sstr(n->coord, t->board),
 248                         tree_node_get_value(t, parity, n->u.value));
 249
 250         struct uct_playout_callback upc = {
 251                 .uct = u,
 252                 .tree = t,
 253                 /* TODO: Don't necessarily restart the sequence walk when
 254                  * entering playout. */
 255                 .lnode = NULL,
 256         };
 257
 258         coord_t pool[2][u->treepool_size];
 259         if (u->treepool_chance[0] + u->treepool_chance[1] > 0) {
 260                 for (int color = 0; color < 2; color++) {
 261                         /* Prepare tree-based pool of moves to try forcing
 262                          * during the playout. */
 263                         /* We consider the children of the last significant
 264                          * node, picking top N choices. */
 265                         struct tree_node *n = significant[color];
 266                         if (!n || !n->children || !n->children->sibling) {
 267                                 /* No significant node, or it's childless or has
 268                                  * only pass as its child. */
 269                                 upc.treepool[color] = NULL;
 270                                 upc.treepool_n[color] = 0;
 271                         } else {
 272                                 upc.treepool[color] = (coord_t *) &pool[color];
 273                                 treepool_setup(&upc, b, n, color);
 274                         }
 275                 }
 276         }
 277
 278         struct playout_setup ps = {
 279                 .gamelen = u->gamelen,
 280                 .mercymin = u->mercymin,
 281                 .prepolicy_hook = uct_playout_prepolicy,
 282                 .postpolicy_hook = uct_playout_postpolicy,
 283                 .hook_data = &upc,
 284         };
 285         int result = play_random_game(&ps, b, next_color,
 286                                       u->playout_amaf ? amaf : NULL,
 287                                       &u->ownermap, u->playout);
 288         if (next_color == S_WHITE) {
 289                 /* We need the result from black's perspective. */
 290                 result = - result;
 291         }
 292         if (UDEBUGL(7))
 293                 fprintf(stderr, "%s -- [%d..%d] %s random playout result %d\n",
 294                         spaces, player_color, next_color, coord2sstr(n->coord, t->board), result);
 295
 296         return result;
 297 }
 298
 299 static floating_t
 300 scale_value(struct uct *u, struct board *b, int result)
 301 {
 302         floating_t rval = result > 0;
 303         if (u->val_scale) {
 304                 int vp = u->val_points;
 305                 if (!vp) {
 306                         vp = board_size(b) - 1; vp *= vp; vp *= 2;
 307                 }
 308
 309                 floating_t sval = (floating_t) abs(result) / vp;
 310                 sval = sval > 1 ? 1 : sval;
 311                 if (result < 0) sval = 1 - sval;
 312                 if (u->val_extra)
 313                         rval += u->val_scale * sval;
 314                 else
 315                         rval = (1 - u->val_scale) * rval + u->val_scale * sval;
 316                 // fprintf(stderr, "score %d => sval %f, rval %f\n", result, sval, rval);
 317         }
 318         return rval;
 319 }
 320
 321 static void
 322 record_local_sequence(struct uct *u, struct tree *t,
 323                       struct uct_descent *descent, int dlen, int di,
 324                       enum stone seq_color, floating_t rval, int pval)
 325 {
 326         /* Ignore pass sequences. */
 327         if (is_pass(descent[di].node->coord))
 328                 return;
 329
 330         /* Transform the rval appropriately, based on the expected
 331          * result at the root of the sequence. */
 332         if (u->local_tree_rootseqval) {
 333                 float expval = descent[di - 1].value.value;
 334                 rval = stats_temper_value(rval, expval, u->local_tree);
 335         }
 336
 337 #define LTREE_DEBUG if (UDEBUGL(6))
 338         LTREE_DEBUG fprintf(stderr, "recording result %f in local %s sequence: ",
 339                 rval, stone2str(seq_color));
 340         int di0 = di;
 341
 342         /* Pick the right local tree root... */
 343         struct tree_node *lnode = seq_color == S_BLACK ? t->ltree_black : t->ltree_white;
 344         lnode->u.playouts++;
 345
 346         /* ...and record the sequence. */
 347         while (di < dlen && (di == di0 || descent[di].node->d < u->tenuki_d)) {
 348                 LTREE_DEBUG fprintf(stderr, "%s[%d] ",
 349                         coord2sstr(descent[di].node->coord, t->board),
 350                         descent[di].node->d);
 351                 lnode = tree_get_node(t, lnode, descent[di++].node->coord, true);
 352                 assert(lnode);
 353                 stats_add_result(&lnode->u, rval, pval);
 354         }
 355
 356         /* Add lnode for tenuki (pass) if we descended further. */
 357         if (di < dlen) {
 358                 LTREE_DEBUG fprintf(stderr, "pass ");
 359                 lnode = tree_get_node(t, lnode, pass, true);
 360                 assert(lnode);
 361                 stats_add_result(&lnode->u, rval, pval);
 362         }
 363
 364         LTREE_DEBUG fprintf(stderr, "\n");
 365 }
 366
 367
 368 int
 369 uct_playout(struct uct *u, struct board *b, enum stone player_color, struct tree *t)
 370 {
 371         struct board b2;
 372         board_copy(&b2, b);
 373
 374         struct playout_amafmap *amaf = NULL;
 375         if (u->policy->wants_amaf) {
 376                 amaf = calloc2(1, sizeof(*amaf));
 377                 amaf->map = calloc2(board_size2(&b2) + 1, sizeof(*amaf->map));
 378                 amaf->map++; // -1 is pass
 379         }
 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         /* Tree descent history. */
 388         /* XXX: This is somewhat messy since @n and descent[dlen-1].node are
 389          * redundant. */
 390         struct uct_descent descent[DESCENT_DLEN];
 391         descent[0].node = n; descent[0].lnode = NULL;
 392         int dlen = 1;
 393         /* Total value of the sequence. */
 394         struct move_stats seq_value = { .playouts = 0 };
 395         /* The last "significant" node along the descent (i.e. node
 396          * with higher than configured number of playouts). For black
 397          * and white. */
 398         struct tree_node *significant[2] = { NULL, NULL };
 399         if (n->u.playouts >= u->significant_threshold)
 400                 significant[node_color - 1] = n;
 401
 402         int result;
 403         int pass_limit = (board_size(&b2) - 2) * (board_size(&b2) - 2) / 2;
 404         int passes = is_pass(b->last_move.coord) && b->moves > 0;
 405
 406         /* debug */
 407         int depth = 0;
 408         static char spaces[] = "\0                                                      ";
 409         /* /debug */
 410         if (UDEBUGL(8))
 411                 fprintf(stderr, "--- UCT walk with color %d\n", player_color);
 412
 413         while (!tree_leaf_node(n) && passes < 2) {
 414                 spaces[depth++] = ' '; spaces[depth] = 0;
 415
 416
 417                 /*** Choose a node to descend to: */
 418
 419                 /* Parity is chosen already according to the child color, since
 420                  * it is applied to children. */
 421                 node_color = stone_other(node_color);
 422                 int parity = (node_color == player_color ? 1 : -1);
 423
 424                 assert(dlen < DESCENT_DLEN);
 425                 descent[dlen] = descent[dlen - 1];
 426                 if (u->local_tree && (!descent[dlen].lnode || descent[dlen].node->d >= u->tenuki_d)) {
 427                         /* Start new local sequence. */
 428                         /* Remember that node_color already holds color of the
 429                          * to-be-found child. */
 430                         descent[dlen].lnode = node_color == S_BLACK ? t->ltree_black : t->ltree_white;
 431                 }
 432
 433                 if (!u->random_policy_chance || fast_random(u->random_policy_chance))
 434                         u->policy->descend(u->policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 435                 else
 436                         u->random_policy->descend(u->random_policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 437
 438
 439                 /*** Perform the descent: */
 440
 441                 if (descent[dlen].node->u.playouts >= u->significant_threshold) {
 442                         significant[node_color - 1] = descent[dlen].node;
 443                 }
 444
 445                 seq_value.playouts += descent[dlen].value.playouts;
 446                 seq_value.value += descent[dlen].value.value * descent[dlen].value.playouts;
 447                 n = descent[dlen++].node;
 448                 assert(n == t->root || n->parent);
 449                 if (UDEBUGL(7))
 450                         fprintf(stderr, "%s+-- UCT sent us to [%s:%d] %d,%f\n",
 451                                 spaces, coord2sstr(n->coord, t->board),
 452                                 n->coord, n->u.playouts,
 453                                 tree_node_get_value(t, parity, n->u.value));
 454
 455                 /* Add virtual loss if we need to; this is used to discourage
 456                  * other threads from visiting this node in case of multiple
 457                  * threads doing the tree search. */
 458                 if (u->virtual_loss)
 459                         stats_add_result(&n->u, node_color == S_BLACK ? 0.0 : 1.0, u->virtual_loss);
 460
 461                 assert(n->coord >= -1);
 462                 if (amaf && !is_pass(n->coord))
 463                         record_amaf_move(amaf, n->coord, node_color);
 464
 465                 struct move m = { n->coord, node_color };
 466                 int res = board_play(&b2, &m);
 467
 468                 if (res < 0 || (!is_pass(m.coord) && !group_at(&b2, m.coord)) /* suicide */
 469                     || b2.superko_violation) {
 470                         if (UDEBUGL(4)) {
 471                                 for (struct tree_node *ni = n; ni; ni = ni->parent)
 472                                         fprintf(stderr, "%s<%"PRIhash"> ", coord2sstr(ni->coord, t->board), ni->hash);
 473                                 fprintf(stderr, "marking invalid %s node %d,%d res %d group %d spk %d\n",
 474                                         stone2str(node_color), coord_x(n->coord,b), coord_y(n->coord,b),
 475                                         res, group_at(&b2, m.coord), b2.superko_violation);
 476                         }
 477                         n->hints |= TREE_HINT_INVALID;
 478                         result = 0;
 479                         goto end;
 480                 }
 481
 482                 if (is_pass(n->coord))
 483                         passes++;
 484                 else
 485                         passes = 0;
 486         }
 487
 488         if (amaf) {
 489                 amaf->game_baselen = amaf->gamelen;
 490                 amaf->record_nakade = u->playout_amaf_nakade;
 491         }
 492
 493         if (t->use_extra_komi && u->dynkomi->persim) {
 494                 b2.komi += round(u->dynkomi->persim(u->dynkomi, &b2, t, n));
 495         }
 496
 497         if (passes >= 2) {
 498                 /* XXX: No dead groups support. */
 499                 floating_t score = board_official_score(&b2, NULL);
 500                 /* Result from black's perspective (no matter who
 501                  * the player; black's perspective is always
 502                  * what the tree stores. */
 503                 result = - (score * 2);
 504
 505                 if (UDEBUGL(5))
 506                         fprintf(stderr, "[%d..%d] %s p-p scoring playout result %d (W %f)\n",
 507                                 player_color, node_color, coord2sstr(n->coord, t->board), result, score);
 508                 if (UDEBUGL(6))
 509                         board_print(&b2, stderr);
 510
 511                 board_ownermap_fill(&u->ownermap, &b2);
 512
 513         } else { // assert(tree_leaf_node(n));
 514                 /* In case of parallel tree search, the assertion might
 515                  * not hold if two threads chew on the same node. */
 516                 result = uct_leaf_node(u, &b2, player_color, amaf, descent, &dlen, significant, t, n, node_color, spaces);
 517         }
 518
 519         if (amaf && u->playout_amaf_cutoff) {
 520                 unsigned int cutoff = amaf->game_baselen;
 521                 cutoff += (amaf->gamelen - amaf->game_baselen) * u->playout_amaf_cutoff / 100;
 522                 /* Now, reconstruct the amaf map. */
 523                 memset(amaf->map, 0, board_size2(&b2) * sizeof(*amaf->map));
 524                 for (unsigned int i = 0; i < cutoff; i++) {
 525                         coord_t coord = amaf->game[i].coord;
 526                         enum stone color = amaf->game[i].color;
 527                         if (amaf->map[coord] == S_NONE || amaf->map[coord] == color) {
 528                                 amaf->map[coord] = color;
 529                         /* Nakade always recorded for in-tree part */
 530                         } else if (amaf->record_nakade || i <= amaf->game_baselen) {
 531                                 amaf_op(amaf->map[n->coord], +);
 532                         }
 533                 }
 534         }
 535
 536         assert(n == t->root || n->parent);
 537         if (result != 0) {
 538                 floating_t rval = scale_value(u, b, result);
 539                 u->policy->update(u->policy, t, n, node_color, player_color, amaf, rval);
 540
 541                 int pval = LTREE_PLAYOUTS_MULTIPLIER;
 542                 if (u->local_tree && u->local_tree_depth_decay > 0)
 543                         pval = ((floating_t) pval) / pow(u->local_tree_depth_decay, depth);
 544
 545                 if (t->use_extra_komi) {
 546                         stats_add_result(&u->dynkomi->score, result / 2, 1);
 547                         stats_add_result(&u->dynkomi->value, rval, 1);
 548                 }
 549
 550                 if (u->local_tree && n->parent && !is_pass(n->coord) && dlen > 0) {
 551                         /* Possibly transform the rval appropriately. */
 552                         if (!u->local_tree_rootseqval) {
 553                                 floating_t expval = seq_value.value / seq_value.playouts;
 554                                 rval = stats_temper_value(rval, expval, u->local_tree);
 555                         }
 556
 557                         /* Get the local sequences and record them in ltree. */
 558                         /* We will look for sequence starts in our descent
 559                          * history, then run record_local_sequence() for each
 560                          * found sequence start; record_local_sequence() may
 561                          * pick longer sequences from descent history then,
 562                          * which is expected as it will create new lnodes. */
 563                         enum stone seq_color = player_color;
 564                         /* First move always starts a sequence. */
 565                         record_local_sequence(u, t, descent, dlen, 1, seq_color, rval, pval);
 566                         seq_color = stone_other(seq_color);
 567                         for (int dseqi = 2; dseqi < dlen; dseqi++, seq_color = stone_other(seq_color)) {
 568                                 if (u->local_tree_allseq) {
 569                                         /* We are configured to record all subsequences. */
 570                                         record_local_sequence(u, t, descent, dlen, dseqi, seq_color, rval, pval);
 571                                         continue;
 572                                 }
 573                                 if (descent[dseqi].node->d >= u->tenuki_d) {
 574                                         /* Tenuki! Record the fresh sequence. */
 575                                         record_local_sequence(u, t, descent, dlen, dseqi, seq_color, rval, pval);
 576                                         continue;
 577                                 }
 578                                 if (descent[dseqi].lnode && !descent[dseqi].lnode) {
 579                                         /* Record result for in-descent picked sequence. */
 580                                         record_local_sequence(u, t, descent, dlen, dseqi, seq_color, rval, pval);
 581                                         continue;
 582                                 }
 583                         }
 584                 }
 585         }
 586
 587 end:
 588         /* We need to undo the virtual loss we added during descend. */
 589         if (u->virtual_loss) {
 590                 floating_t loss = node_color == S_BLACK ? 0.0 : 1.0;
 591                 for (; n->parent; n = n->parent) {
 592                         stats_rm_result(&n->u, loss, u->virtual_loss);
 593                         loss = 1.0 - loss;
 594                 }
 595         }
 596
 597         if (amaf) {
 598                 free(amaf->map - 1);
 599                 free(amaf);
 600         }
 601         board_done_noalloc(&b2);
 602         return result;
 603 }
 604
 605 int
 606 uct_playouts(struct uct *u, struct board *b, enum stone color, struct tree *t, struct time_info *ti)
 607 {
 608         int i;
 609         if (ti && ti->dim == TD_GAMES) {
 610                 for (i = 0; t->root->u.playouts <= ti->len.games; i++)
 611                         uct_playout(u, b, color, t);
 612         } else {
 613                 for (i = 0; !uct_halt; i++)
 614                         uct_playout(u, b, color, t);
 615         }
 616         return i;
 617 }