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