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 void
  25 uct_progress_status(struct uct *u, struct tree *t, enum stone color, int playouts)
  26 {
  27         if (!UDEBUGL(0))
  28                 return;
  29
  30         /* Best move */
  31         struct tree_node *best = u->policy->choose(u->policy, t->root, t->board, color, resign);
  32         if (!best) {
  33                 fprintf(stderr, "... No moves left\n");
  34                 return;
  35         }
  36         fprintf(stderr, "[%d] ", playouts);
  37         fprintf(stderr, "best %f ", tree_node_get_value(t, 1, best->u.value));
  38
  39         /* Dynamic komi */
  40         if (t->use_extra_komi)
  41                 fprintf(stderr, "komi %.1f ", t->extra_komi);
  42
  43         /* Best sequence */
  44         fprintf(stderr, "| seq ");
  45         for (int depth = 0; depth < 4; depth++) {
  46                 if (best && best->u.playouts >= 25) {
  47                         fprintf(stderr, "%3s ", coord2sstr(best->coord, t->board));
  48                         best = u->policy->choose(u->policy, best, t->board, color, resign);
  49                 } else {
  50                         fprintf(stderr, "    ");
  51                 }
  52         }
  53
  54         /* Best candidates */
  55         fprintf(stderr, "| can ");
  56         int cans = 4;
  57         struct tree_node *can[cans];
  58         memset(can, 0, sizeof(can));
  59         best = t->root->children;
  60         while (best) {
  61                 int c = 0;
  62                 while ((!can[c] || best->u.playouts > can[c]->u.playouts) && ++c < cans);
  63                 for (int d = 0; d < c; d++) can[d] = can[d + 1];
  64                 if (c > 0) can[c - 1] = best;
  65                 best = best->sibling;
  66         }
  67         while (--cans >= 0) {
  68                 if (can[cans]) {
  69                         fprintf(stderr, "%3s(%.3f) ",
  70                                 coord2sstr(can[cans]->coord, t->board),
  71                                 tree_node_get_value(t, 1, can[cans]->u.value));
  72                 } else {
  73                         fprintf(stderr, "           ");
  74                 }
  75         }
  76
  77         fprintf(stderr, "\n");
  78 }
  79
  80
  81 static void
  82 record_amaf_move(struct playout_amafmap *amaf, coord_t coord, enum stone color)
  83 {
  84         if (amaf->map[coord] == S_NONE || amaf->map[coord] == color) {
  85                 amaf->map[coord] = color;
  86         } else { // XXX: Respect amaf->record_nakade
  87                 amaf_op(amaf->map[coord], +);
  88         }
  89         amaf->game[amaf->gamelen].coord = coord;
  90         amaf->game[amaf->gamelen].color = color;
  91         amaf->gamelen++;
  92         assert(amaf->gamelen < sizeof(amaf->game) / sizeof(amaf->game[0]));
  93 }
  94
  95
  96 struct uct_playout_callback {
  97         struct uct *uct;
  98         struct tree *tree;
  99         struct tree_node *lnode;
 100
 101         coord_t *treepool[2];
 102         int treepool_n[2];
 103 };
 104
 105
 106 static coord_t
 107 uct_playout_hook(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color, int mode)
 108 {
 109         struct uct_playout_callback *upc = setup->hook_data;
 110         struct uct *u = upc->uct;
 111
 112         if (UDEBUGL(8))
 113                 fprintf(stderr, "treepool check [%d] %d, %p,%p\n", mode, u->treepool_chance[mode], upc->treepool[0], upc->treepool[1]);
 114
 115         if (u->treepool_chance[mode] > fast_random(100) && upc->treepool[color - 1]) {
 116                 assert(upc->treepool_n[color - 1] > 0);
 117                 if (UDEBUGL(8)) {
 118                         fprintf(stderr, "Treepool: ");
 119                         for (int i = 0; i < upc->treepool_n[color - 1]; i++)
 120                                 fprintf(stderr, "%s ", coord2sstr(upc->treepool[color - 1][i], b));
 121                         fprintf(stderr, "\n");
 122                 }
 123
 124                 coord_t treepool_move = pass;
 125                 if (u->treepool_pickfactor) {
 126                         /* With pickfactor=10, we get uniform distribution. */
 127                         int prob = 1000 * u->treepool_pickfactor / (upc->treepool_n[color - 1] * 10);
 128                         for (int i = 0; i < upc->treepool_n[color - 1]; i++) {
 129                                 treepool_move = upc->treepool[color - 1][i];
 130                                 if (prob > fast_random(1000)) break;
 131                         }
 132                 } else {
 133                         treepool_move = upc->treepool[color - 1][fast_random(upc->treepool_n[color - 1])];
 134                 }
 135                 if (UDEBUGL(7))
 136                         fprintf(stderr, "Treepool pick <%d> %s,%s\n",
 137                                 upc->treepool_n[color - 1],
 138                                 stone2str(color), coord2sstr(treepool_move, b));
 139
 140                 if (board_is_valid_play(b, color, treepool_move))
 141                         return treepool_move;
 142         }
 143         return pass;
 144 }
 145
 146 static coord_t
 147 uct_playout_prepolicy(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color)
 148 {
 149         return uct_playout_hook(playout, setup, b, color, 0);
 150 }
 151
 152 static coord_t
 153 uct_playout_postpolicy(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color)
 154 {
 155         return uct_playout_hook(playout, setup, b, color, 1);
 156 }
 157
 158 double
 159 treepool_node_value(struct uct *u, struct tree *tree, int parity, struct tree_node *node)
 160 {
 161         /* XXX: Playouts get cast to double */
 162         switch (u->treepool_type) {
 163                 case UTT_RAVE_PLAYOUTS:
 164                         return node->amaf.playouts;
 165                 case UTT_RAVE_VALUE:
 166                         return tree_node_get_value(tree, parity, node->amaf.value);
 167                 case UTT_UCT_PLAYOUTS:
 168                         return node->u.playouts;
 169                 case UTT_UCT_VALUE:
 170                         return tree_node_get_value(tree, parity, node->u.value);
 171                 case UTT_EVALUATE:
 172                 {
 173                         struct uct_descent d = { .node = node };
 174                         assert(u->policy->evaluate);
 175                         return u->policy->evaluate(u->policy, tree, &d, parity);
 176                 }
 177                 default: assert(0);
 178         }
 179         return -1;
 180 }
 181
 182 static void
 183 treepool_setup(struct uct_playout_callback *upc, struct board *b, struct tree_node *node, int color)
 184 {
 185         struct uct *u = upc->uct;
 186         int parity = ((node->depth ^ upc->tree->root->depth) & 1) ? -1 : 1;
 187
 188         /* XXX: Naive O(N^2) way. */
 189         for (int i = 0; i < u->treepool_size; i++) {
 190                 /* For each item, find the highest
 191                  * node not in the pool yet. */
 192                 struct tree_node *best = NULL;
 193                 double best_val = -1;
 194
 195                 assert(node->children && is_pass(node->children->coord));
 196                 for (struct tree_node *ni = node->children->sibling; ni; ni = ni->sibling) {
 197                         /* Do we already have it? */
 198                         bool have = false;
 199                         for (int j = 0; j < upc->treepool_n[color]; j++) {
 200                                 if (upc->treepool[color][j] == ni->coord) {
 201                                         have = true;
 202                                         break;
 203                                 }
 204                         }
 205                         if (have)
 206                                 continue;
 207
 208                         double i_val = treepool_node_value(u, upc->tree, parity, ni);
 209                         if (i_val > best_val) {
 210                                 best = ni;
 211                                 best_val = i_val;
 212                         }
 213                 }
 214
 215                 if (!best) break;
 216                 upc->treepool[color][upc->treepool_n[color]++] = best->coord;
 217         }
 218 }
 219
 220
 221 static int
 222 uct_leaf_node(struct uct *u, struct board *b, enum stone player_color,
 223               struct playout_amafmap *amaf, struct uct_descent *descent,
 224               struct tree_node *significant[2],
 225               struct tree *t, struct tree_node *n, enum stone node_color,
 226               char *spaces)
 227 {
 228         enum stone next_color = stone_other(node_color);
 229         int parity = (next_color == player_color ? 1 : -1);
 230
 231         /* We need to make sure only one thread expands the node. If
 232          * we are unlucky enough for two threads to meet in the same
 233          * node, the latter one will simply do another simulation from
 234          * the node itself, no big deal. t->nodes_size may exceed
 235          * the maximum in multi-threaded case but not by much so it's ok.
 236          * The size test must be before the test&set not after, to allow
 237          * expansion of the node later if enough nodes have been freed. */
 238         if (n->u.playouts >= u->expand_p && t->nodes_size < u->max_tree_size
 239             && !__sync_lock_test_and_set(&n->is_expanded, 1)) {
 240                 tree_expand_node(t, n, b, next_color, u, parity);
 241         }
 242         if (UDEBUGL(7))
 243                 fprintf(stderr, "%s*-- UCT playout #%d start [%s] %f\n",
 244                         spaces, n->u.playouts, coord2sstr(n->coord, t->board),
 245                         tree_node_get_value(t, parity, n->u.value));
 246
 247         struct uct_playout_callback upc = {
 248                 .uct = u,
 249                 .tree = t,
 250                 /* TODO: Don't necessarily restart the sequence walk when
 251                  * entering playout. */
 252                 .lnode = NULL,
 253         };
 254
 255         coord_t pool[2][u->treepool_size];
 256         if (u->treepool_chance[0] + u->treepool_chance[1] > 0) {
 257                 for (int color = 0; color < 2; color++) {
 258                         /* Prepare tree-based pool of moves to try forcing
 259                          * during the playout. */
 260                         /* We consider the children of the last significant
 261                          * node, picking top N choices. */
 262                         struct tree_node *n = significant[color];
 263                         if (!n || !n->children || !n->children->sibling) {
 264                                 /* No significant node, or it's childless or has
 265                                  * only pass as its child. */
 266                                 upc.treepool[color] = NULL;
 267                                 upc.treepool_n[color] = 0;
 268                         } else {
 269                                 upc.treepool[color] = (coord_t *) &pool[color];
 270                                 treepool_setup(&upc, b, n, color);
 271                         }
 272                 }
 273         }
 274
 275         struct playout_setup ps = {
 276                 .gamelen = u->gamelen,
 277                 .mercymin = u->mercymin,
 278                 .prepolicy_hook = uct_playout_prepolicy,
 279                 .postpolicy_hook = uct_playout_postpolicy,
 280                 .hook_data = &upc,
 281         };
 282         int result = play_random_game(&ps, b, next_color,
 283                                       u->playout_amaf ? amaf : NULL,
 284                                       &u->ownermap, u->playout);
 285         if (next_color == S_WHITE) {
 286                 /* We need the result from black's perspective. */
 287                 result = - result;
 288         }
 289         if (UDEBUGL(7))
 290                 fprintf(stderr, "%s -- [%d..%d] %s random playout result %d\n",
 291                         spaces, player_color, next_color, coord2sstr(n->coord, t->board), result);
 292
 293         return result;
 294 }
 295
 296 static floating_t
 297 scale_value(struct uct *u, struct board *b, int result)
 298 {
 299         floating_t rval = result > 0;
 300         if (u->val_scale) {
 301                 int vp = u->val_points;
 302                 if (!vp) {
 303                         vp = board_size(b) - 1; vp *= vp; vp *= 2;
 304                 }
 305
 306                 floating_t sval = (floating_t) abs(result) / vp;
 307                 sval = sval > 1 ? 1 : sval;
 308                 if (result < 0) sval = 1 - sval;
 309                 if (u->val_extra)
 310                         rval += u->val_scale * sval;
 311                 else
 312                         rval = (1 - u->val_scale) * rval + u->val_scale * sval;
 313                 // fprintf(stderr, "score %d => sval %f, rval %f\n", result, sval, rval);
 314         }
 315         return rval;
 316 }
 317
 318 static void
 319 record_local_sequence(struct uct *u, struct tree *t,
 320                       struct uct_descent *descent, int dlen, int di,
 321                       enum stone seq_color, floating_t rval, int pval)
 322 {
 323         /* Ignore pass sequences. */
 324         if (is_pass(descent[di].node->coord))
 325                 return;
 326
 327         /* Transform the rval appropriately, based on the expected
 328          * result at the root of the sequence. */
 329         if (u->local_tree_rootseqval) {
 330                 float expval = descent[di - 1].value.value;
 331                 rval = stats_temper_value(rval, expval, u->local_tree);
 332         }
 333
 334 #define LTREE_DEBUG if (UDEBUGL(6))
 335         LTREE_DEBUG fprintf(stderr, "recording result %f in local %s sequence: ",
 336                 rval, stone2str(seq_color));
 337         int di0 = di;
 338
 339         /* Pick the right local tree root... */
 340         struct tree_node *lnode = seq_color == S_BLACK ? t->ltree_black : t->ltree_white;
 341         lnode->u.playouts++;
 342
 343         /* ...and record the sequence. */
 344         while (di < dlen && (di == di0 || descent[di].node->d < u->tenuki_d)) {
 345                 LTREE_DEBUG fprintf(stderr, "%s[%d] ",
 346                         coord2sstr(descent[di].node->coord, t->board),
 347                         descent[di].node->d);
 348                 lnode = tree_get_node(t, lnode, descent[di++].node->coord, true);
 349                 assert(lnode);
 350                 stats_add_result(&lnode->u, rval, pval);
 351         }
 352
 353         /* Add lnode for tenuki (pass) if we descended further. */
 354         if (di < dlen) {
 355                 LTREE_DEBUG fprintf(stderr, "pass ");
 356                 lnode = tree_get_node(t, lnode, pass, true);
 357                 assert(lnode);
 358                 stats_add_result(&lnode->u, rval, pval);
 359         }
 360
 361         LTREE_DEBUG fprintf(stderr, "\n");
 362 }
 363
 364
 365 int
 366 uct_playout(struct uct *u, struct board *b, enum stone player_color, struct tree *t)
 367 {
 368         struct board b2;
 369         board_copy(&b2, b);
 370
 371         struct playout_amafmap *amaf = NULL;
 372         if (u->policy->wants_amaf) {
 373                 amaf = calloc2(1, sizeof(*amaf));
 374                 amaf->map = calloc2(board_size2(&b2) + 1, sizeof(*amaf->map));
 375                 amaf->map++; // -1 is pass
 376         }
 377
 378         /* Walk the tree until we find a leaf, then expand it and do
 379          * a random playout. */
 380         struct tree_node *n = t->root;
 381         enum stone node_color = stone_other(player_color);
 382         assert(node_color == t->root_color);
 383
 384         /* Tree descent history. */
 385         /* XXX: This is somewhat messy since @n and descent[dlen-1].node are
 386          * redundant. */
 387         #define DLEN 512
 388         struct uct_descent descent[DLEN];
 389         descent[0].node = n; descent[0].lnode = NULL;
 390         int dlen = 1;
 391         /* Total value of the sequence. */
 392         struct move_stats seq_value = { .playouts = 0 };
 393         /* The last "significant" node along the descent (i.e. node
 394          * with higher than configured number of playouts). For black
 395          * and white. */
 396         struct tree_node *significant[2] = { NULL, NULL };
 397         if (n->u.playouts >= u->significant_threshold)
 398                 significant[node_color - 1] = n;
 399
 400         int result;
 401         int pass_limit = (board_size(&b2) - 2) * (board_size(&b2) - 2) / 2;
 402         int passes = is_pass(b->last_move.coord) && b->moves > 0;
 403
 404         /* debug */
 405         int depth = 0;
 406         static char spaces[] = "\0                                                      ";
 407         /* /debug */
 408         if (UDEBUGL(8))
 409                 fprintf(stderr, "--- UCT walk with color %d\n", player_color);
 410
 411         while (!tree_leaf_node(n) && passes < 2) {
 412                 spaces[depth++] = ' '; spaces[depth] = 0;
 413
 414
 415                 /*** Choose a node to descend to: */
 416
 417                 /* Parity is chosen already according to the child color, since
 418                  * it is applied to children. */
 419                 node_color = stone_other(node_color);
 420                 int parity = (node_color == player_color ? 1 : -1);
 421
 422                 assert(dlen < DLEN);
 423                 descent[dlen] = descent[dlen - 1];
 424                 if (u->local_tree && (!descent[dlen].lnode || descent[dlen].node->d >= u->tenuki_d)) {
 425                         /* Start new local sequence. */
 426                         /* Remember that node_color already holds color of the
 427                          * to-be-found child. */
 428                         descent[dlen].lnode = node_color == S_BLACK ? t->ltree_black : t->ltree_white;
 429                 }
 430
 431                 if (!u->random_policy_chance || fast_random(u->random_policy_chance))
 432                         u->policy->descend(u->policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 433                 else
 434                         u->random_policy->descend(u->random_policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 435
 436
 437                 /*** Perform the descent: */
 438
 439                 if (descent[dlen].node->u.playouts >= u->significant_threshold) {
 440                         significant[node_color - 1] = descent[dlen].node;
 441                 }
 442
 443                 seq_value.playouts += descent[dlen].value.playouts;
 444                 seq_value.value += descent[dlen].value.value * descent[dlen].value.playouts;
 445                 n = descent[dlen++].node;
 446                 assert(n == t->root || n->parent);
 447                 if (UDEBUGL(7))
 448                         fprintf(stderr, "%s+-- UCT sent us to [%s:%d] %d,%f\n",
 449                                 spaces, coord2sstr(n->coord, t->board),
 450                                 n->coord, n->u.playouts,
 451                                 tree_node_get_value(t, parity, n->u.value));
 452
 453                 /* Add virtual loss if we need to; this is used to discourage
 454                  * other threads from visiting this node in case of multiple
 455                  * threads doing the tree search. */
 456                 if (u->virtual_loss)
 457                         stats_add_result(&n->u, node_color == S_BLACK ? 0.0 : 1.0, u->virtual_loss);
 458
 459                 assert(n->coord >= -1);
 460                 if (amaf && !is_pass(n->coord))
 461                         record_amaf_move(amaf, n->coord, node_color);
 462
 463                 struct move m = { n->coord, node_color };
 464                 int res = board_play(&b2, &m);
 465
 466                 if (res < 0 || (!is_pass(m.coord) && !group_at(&b2, m.coord)) /* suicide */
 467                     || b2.superko_violation) {
 468                         if (UDEBUGL(4)) {
 469                                 for (struct tree_node *ni = n; ni; ni = ni->parent)
 470                                         fprintf(stderr, "%s<%"PRIhash"> ", coord2sstr(ni->coord, t->board), ni->hash);
 471                                 fprintf(stderr, "marking invalid %s node %d,%d res %d group %d spk %d\n",
 472                                         stone2str(node_color), coord_x(n->coord,b), coord_y(n->coord,b),
 473                                         res, group_at(&b2, m.coord), b2.superko_violation);
 474                         }
 475                         n->hints |= TREE_HINT_INVALID;
 476                         result = 0;
 477                         goto end;
 478                 }
 479
 480                 if (is_pass(n->coord))
 481                         passes++;
 482                 else
 483                         passes = 0;
 484         }
 485
 486         if (amaf) {
 487                 amaf->game_baselen = amaf->gamelen;
 488                 amaf->record_nakade = u->playout_amaf_nakade;
 489         }
 490
 491         if (t->use_extra_komi && u->dynkomi->persim) {
 492                 b2.komi += round(u->dynkomi->persim(u->dynkomi, &b2, t, n));
 493         }
 494
 495         if (passes >= 2) {
 496                 /* XXX: No dead groups support. */
 497                 floating_t score = board_official_score(&b2, NULL);
 498                 /* Result from black's perspective (no matter who
 499                  * the player; black's perspective is always
 500                  * what the tree stores. */
 501                 result = - (score * 2);
 502
 503                 if (UDEBUGL(5))
 504                         fprintf(stderr, "[%d..%d] %s p-p scoring playout result %d (W %f)\n",
 505                                 player_color, node_color, coord2sstr(n->coord, t->board), result, score);
 506                 if (UDEBUGL(6))
 507                         board_print(&b2, stderr);
 508
 509                 board_ownermap_fill(&u->ownermap, &b2);
 510
 511         } else { // assert(tree_leaf_node(n));
 512                 /* In case of parallel tree search, the assertion might
 513                  * not hold if two threads chew on the same node. */
 514                 result = uct_leaf_node(u, &b2, player_color, amaf, &descent[dlen - 1], significant, t, n, node_color, spaces);
 515         }
 516
 517         if (amaf && u->playout_amaf_cutoff) {
 518                 unsigned int cutoff = amaf->game_baselen;
 519                 cutoff += (amaf->gamelen - amaf->game_baselen) * u->playout_amaf_cutoff / 100;
 520                 /* Now, reconstruct the amaf map. */
 521                 memset(amaf->map, 0, board_size2(&b2) * sizeof(*amaf->map));
 522                 for (unsigned int i = 0; i < cutoff; i++) {
 523                         coord_t coord = amaf->game[i].coord;
 524                         enum stone color = amaf->game[i].color;
 525                         if (amaf->map[coord] == S_NONE || amaf->map[coord] == color) {
 526                                 amaf->map[coord] = color;
 527                         /* Nakade always recorded for in-tree part */
 528                         } else if (amaf->record_nakade || i <= amaf->game_baselen) {
 529                                 amaf_op(amaf->map[n->coord], +);
 530                         }
 531                 }
 532         }
 533
 534         assert(n == t->root || n->parent);
 535         if (result != 0) {
 536                 floating_t rval = scale_value(u, b, result);
 537                 u->policy->update(u->policy, t, n, node_color, player_color, amaf, rval);
 538
 539                 int pval = LTREE_PLAYOUTS_MULTIPLIER;
 540                 if (u->local_tree_depth_decay > 0)
 541                         pval = ((floating_t) pval) / pow(u->local_tree_depth_decay, depth);
 542
 543                 if (t->use_extra_komi) {
 544                         stats_add_result(&u->dynkomi->score, result / 2, 1);
 545                         stats_add_result(&u->dynkomi->value, rval, 1);
 546                 }
 547
 548                 if (u->local_tree && n->parent && !is_pass(n->coord) && dlen > 0) {
 549                         /* Possibly transform the rval appropriately. */
 550                         if (!u->local_tree_rootseqval) {
 551                                 floating_t expval = seq_value.value / seq_value.playouts;
 552                                 rval = stats_temper_value(rval, expval, u->local_tree);
 553                         }
 554
 555                         /* Get the local sequences and record them in ltree. */
 556                         /* We will look for sequence starts in our descent
 557                          * history, then run record_local_sequence() for each
 558                          * found sequence start; record_local_sequence() may
 559                          * pick longer sequences from descent history then,
 560                          * which is expected as it will create new lnodes. */
 561                         enum stone seq_color = player_color;
 562                         /* First move always starts a sequence. */
 563                         record_local_sequence(u, t, descent, dlen, 1, seq_color, rval, pval);
 564                         seq_color = stone_other(seq_color);
 565                         for (int dseqi = 2; dseqi < dlen; dseqi++, seq_color = stone_other(seq_color)) {
 566                                 if (u->local_tree_allseq) {
 567                                         /* We are configured to record all subsequences. */
 568                                         record_local_sequence(u, t, descent, dlen, dseqi, seq_color, rval, pval);
 569                                         continue;
 570                                 }
 571                                 if (descent[dseqi].node->d >= u->tenuki_d) {
 572                                         /* Tenuki! Record the fresh sequence. */
 573                                         record_local_sequence(u, t, descent, dlen, dseqi, seq_color, rval, pval);
 574                                         continue;
 575                                 }
 576                                 if (descent[dseqi].lnode && !descent[dseqi].lnode) {
 577                                         /* Record result for in-descent picked sequence. */
 578                                         record_local_sequence(u, t, descent, dlen, dseqi, seq_color, rval, pval);
 579                                         continue;
 580                                 }
 581                         }
 582                 }
 583         }
 584
 585 end:
 586         /* We need to undo the virtual loss we added during descend. */
 587         if (u->virtual_loss) {
 588                 floating_t loss = node_color == S_BLACK ? 0.0 : 1.0;
 589                 for (; n->parent; n = n->parent) {
 590                         stats_rm_result(&n->u, loss, u->virtual_loss);
 591                         loss = 1.0 - loss;
 592                 }
 593         }
 594
 595         if (amaf) {
 596                 free(amaf->map - 1);
 597                 free(amaf);
 598         }
 599         board_done_noalloc(&b2);
 600         return result;
 601 }
 602
 603 int
 604 uct_playouts(struct uct *u, struct board *b, enum stone color, struct tree *t, struct time_info *ti)
 605 {
 606         int i;
 607         if (ti && ti->dim == TD_GAMES) {
 608                 for (i = 0; t->root->u.playouts <= ti->len.games; i++)
 609                         uct_playout(u, b, color, t);
 610         } else {
 611                 for (i = 0; !uct_halt; i++)
 612                         uct_playout(u, b, color, t);
 613         }
 614         return i;
 615 }