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)
  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, coord_t *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         if (final) {
  98                 /* Final move choice */
  99                 fprintf(stderr, ", \"choice\": {\"%s\"}",
 100                         coord2sstr(*final, t->board));
 101         } else {
 102                 struct tree_node *best = u->policy->choose(u->policy, t->root, t->board, color, resign);
 103                 if (best) {
 104                         /* Best move */
 105                         fprintf(stderr, ", \"best\": {\"%s\": %f}",
 106                                 coord2sstr(best->coord, t->board),
 107                                 tree_node_get_value(t, 1, best->u.value));
 108                 }
 109         }
 110
 111         /* Best candidates */
 112         int cans = 4;
 113         struct tree_node *can[cans];
 114         memset(can, 0, sizeof(can));
 115         struct tree_node *best = t->root->children;
 116         while (best) {
 117                 int c = 0;
 118                 while ((!can[c] || best->u.playouts > can[c]->u.playouts) && ++c < cans);
 119                 for (int d = 0; d < c; d++) can[d] = can[d + 1];
 120                 if (c > 0) can[c - 1] = best;
 121                 best = best->sibling;
 122         }
 123         fprintf(stderr, ", \"can\": [");
 124         while (--cans >= 0) {
 125                 if (!can[cans]) break;
 126                 /* Best sequence */
 127                 fprintf(stderr, "%s[", cans < 3 ? ", " : "");
 128                 best = can[cans];
 129                 for (int depth = 0; depth < 4; depth++) {
 130                         if (!best || best->u.playouts < 25) break;
 131                         fprintf(stderr, "%s{\"%s\":%.3f}", depth > 0 ? "," : "",
 132                                 coord2sstr(best->coord, t->board),
 133                                 tree_node_get_value(t, 1, best->u.value));
 134                         best = u->policy->choose(u->policy, best, t->board, color, resign);
 135                 }
 136                 fprintf(stderr, "]");
 137         }
 138         fprintf(stderr, "]");
 139
 140         if (big) {
 141                 /* Average score. */
 142                 if (t->avg_score.playouts > 0)
 143                         fprintf(stderr, ", \"avg\": {\"score\": %.3f}", t->avg_score.value);
 144                 /* Per-intersection information. */
 145                 fprintf(stderr, ", \"boards\": {");
 146                 /* Position coloring information. */
 147                 fprintf(stderr, "\"colors\": [");
 148                 int f = 0;
 149                 foreach_point(t->board) {
 150                         if (board_at(t->board, c) == S_OFFBOARD) continue;
 151                         fprintf(stderr, "%s%d", f++ > 0 ? "," : "", board_at(t->board, c));
 152                 } foreach_point_end;
 153                 fprintf(stderr, "]");
 154                 /* Ownership statistics. Value (0..1000) for each possible
 155                  * point describes likelihood of this point becoming black.
 156                  * Normally, white rate is 1000-value; exception are possible
 157                  * seki points, but these should be rare. */
 158                 fprintf(stderr, ", \"territory\": [");
 159                 f = 0;
 160                 foreach_point(t->board) {
 161                         if (board_at(t->board, c) == S_OFFBOARD) continue;
 162                         int rate = u->ownermap.map[c][S_BLACK] * 1000 / u->ownermap.playouts;
 163                         fprintf(stderr, "%s%d", f++ > 0 ? "," : "", rate);
 164                 } foreach_point_end;
 165                 fprintf(stderr, "]");
 166                 fprintf(stderr, "}");
 167         }
 168
 169         fprintf(stderr, "}}\n");
 170 }
 171
 172 void
 173 uct_progress_status(struct uct *u, struct tree *t, enum stone color, int playouts, coord_t *final)
 174 {
 175         switch (u->reporting) {
 176                 case UR_TEXT:
 177                         uct_progress_text(u, t, color, playouts);
 178                         break;
 179                 case UR_JSON:
 180                 case UR_JSON_BIG:
 181                         uct_progress_json(u, t, color, playouts, final,
 182                                           u->reporting == UR_JSON_BIG);
 183                         break;
 184                 default: assert(0);
 185         }
 186 }
 187
 188
 189 static inline void
 190 record_amaf_move(struct playout_amafmap *amaf, coord_t coord, bool is_ko_capture)
 191 {
 192         assert(amaf->gamelen < MAX_GAMELEN);
 193         amaf->is_ko_capture[amaf->gamelen] = is_ko_capture;
 194         amaf->game[amaf->gamelen++] = coord;
 195 }
 196
 197
 198 struct uct_playout_callback {
 199         struct uct *uct;
 200         struct tree *tree;
 201         struct tree_node *lnode;
 202 };
 203
 204
 205 static coord_t
 206 uct_playout_hook(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color, int mode)
 207 {
 208         /* XXX: This is used in some non-master branches. */
 209         return pass;
 210 }
 211
 212 static coord_t
 213 uct_playout_prepolicy(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color)
 214 {
 215         return uct_playout_hook(playout, setup, b, color, 0);
 216 }
 217
 218 static coord_t
 219 uct_playout_postpolicy(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color)
 220 {
 221         return uct_playout_hook(playout, setup, b, color, 1);
 222 }
 223
 224
 225 static int
 226 uct_leaf_node(struct uct *u, struct board *b, enum stone player_color,
 227               struct playout_amafmap *amaf,
 228               struct uct_descent *descent, int *dlen,
 229               struct tree_node *significant[2],
 230               struct tree *t, struct tree_node *n, enum stone node_color,
 231               char *spaces)
 232 {
 233         enum stone next_color = stone_other(node_color);
 234         int parity = (next_color == player_color ? 1 : -1);
 235
 236         if (UDEBUGL(7))
 237                 fprintf(stderr, "%s*-- UCT playout #%d start [%s] %f\n",
 238                         spaces, n->u.playouts, coord2sstr(node_coord(n), t->board),
 239                         tree_node_get_value(t, parity, n->u.value));
 240
 241         struct uct_playout_callback upc = {
 242                 .uct = u,
 243                 .tree = t,
 244                 /* TODO: Don't necessarily restart the sequence walk when
 245                  * entering playout. */
 246                 .lnode = NULL,
 247         };
 248
 249         struct playout_setup ps = {
 250                 .gamelen = u->gamelen,
 251                 .mercymin = u->mercymin,
 252                 .prepolicy_hook = uct_playout_prepolicy,
 253                 .postpolicy_hook = uct_playout_postpolicy,
 254                 .hook_data = &upc,
 255         };
 256         int result = play_random_game(&ps, b, next_color,
 257                                       u->playout_amaf ? amaf : NULL,
 258                                       &u->ownermap, u->playout);
 259         if (next_color == S_WHITE) {
 260                 /* We need the result from black's perspective. */
 261                 result = - result;
 262         }
 263         if (UDEBUGL(7))
 264                 fprintf(stderr, "%s -- [%d..%d] %s random playout result %d\n",
 265                         spaces, player_color, next_color, coord2sstr(node_coord(n), t->board), result);
 266
 267         return result;
 268 }
 269
 270 static floating_t
 271 scale_value(struct uct *u, struct board *b, int result)
 272 {
 273         floating_t rval = result > 0 ? 1.0 : result < 0 ? 0.0 : 0.5;
 274         if (u->val_scale && result != 0) {
 275                 int vp = u->val_points;
 276                 if (!vp) {
 277                         vp = board_size(b) - 1; vp *= vp; vp *= 2;
 278                 }
 279
 280                 floating_t sval = (floating_t) abs(result) / vp;
 281                 sval = sval > 1 ? 1 : sval;
 282                 if (result < 0) sval = 1 - sval;
 283                 if (u->val_extra)
 284                         rval += u->val_scale * sval;
 285                 else
 286                         rval = (1 - u->val_scale) * rval + u->val_scale * sval;
 287                 // fprintf(stderr, "score %d => sval %f, rval %f\n", result, sval, rval);
 288         }
 289         return rval;
 290 }
 291
 292 static double
 293 local_value(struct uct *u, struct board *b, coord_t coord, enum stone color)
 294 {
 295         /* Tactical evaluation of move @coord by color @color, given
 296          * simulation end position @b. I.e., a move is tactically good
 297          * if the resulting group stays on board until the game end. */
 298         /* We can also take into account surrounding stones, e.g. to
 299          * encourage taking off external liberties during a semeai. */
 300         double val = board_local_value(u->local_tree_neival, b, coord, color);
 301         return (color == S_WHITE) ? 1.f - val : val;
 302 }
 303
 304 static void
 305 record_local_sequence(struct uct *u, struct tree *t, struct board *endb,
 306                       struct uct_descent *descent, int dlen, int di,
 307                       enum stone seq_color)
 308 {
 309 #define LTREE_DEBUG if (UDEBUGL(6))
 310
 311         /* Ignore pass sequences. */
 312         if (is_pass(node_coord(descent[di].node)))
 313                 return;
 314
 315         LTREE_DEBUG board_print(endb, stderr);
 316         LTREE_DEBUG fprintf(stderr, "recording local %s sequence: ",
 317                 stone2str(seq_color));
 318
 319         /* Sequences starting deeper are less relevant in general. */
 320         int pval = LTREE_PLAYOUTS_MULTIPLIER;
 321         if (u->local_tree && u->local_tree_depth_decay > 0)
 322                 pval = ((floating_t) pval) / pow(u->local_tree_depth_decay, di - 1);
 323         if (!pval) {
 324                 LTREE_DEBUG fprintf(stderr, "too deep @%d\n", di);
 325                 return;
 326         }
 327
 328         /* Pick the right local tree root... */
 329         struct tree_node *lnode = seq_color == S_BLACK ? t->ltree_black : t->ltree_white;
 330         lnode->u.playouts++;
 331
 332         /* ...determine the sequence value... */
 333         double sval = 0.5;
 334         if (u->local_tree_eval != LTE_EACH) {
 335                 sval = local_value(u, endb, node_coord(descent[di].node), seq_color);
 336                 LTREE_DEBUG fprintf(stderr, "(goal %s[%s %1.3f][%d]) ",
 337                         coord2sstr(node_coord(descent[di].node), t->board),
 338                         stone2str(seq_color), sval, descent[di].node->d);
 339
 340                 if (u->local_tree_eval == LTE_TOTAL) {
 341                         int di0 = di;
 342                         while (di < dlen && (di == di0 || descent[di].node->d < u->tenuki_d)) {
 343                                 enum stone color = (di - di0) % 2 ? stone_other(seq_color) : seq_color;
 344                                 double rval = local_value(u, endb, node_coord(descent[di].node), color);
 345                                 if ((di - di0) % 2)
 346                                         rval = 1 - rval;
 347                                 sval += rval;
 348                                 di++;
 349                         }
 350                         sval /= (di - di0 + 1);
 351                         di = di0;
 352                 }
 353         }
 354
 355         /* ...and record the sequence. */
 356         int di0 = di;
 357         while (di < dlen && !is_pass(node_coord(descent[di].node))
 358                && (di == di0 || descent[di].node->d < u->tenuki_d)) {
 359                 enum stone color = (di - di0) % 2 ? stone_other(seq_color) : seq_color;
 360                 double rval;
 361                 if (u->local_tree_eval != LTE_EACH)
 362                         rval = sval;
 363                 else
 364                         rval = local_value(u, endb, node_coord(descent[di].node), color);
 365                 LTREE_DEBUG fprintf(stderr, "%s[%s %1.3f][%d] ",
 366                         coord2sstr(node_coord(descent[di].node), t->board),
 367                         stone2str(color), rval, descent[di].node->d);
 368                 lnode = tree_get_node(t, lnode, node_coord(descent[di++].node), true);
 369                 assert(lnode);
 370                 stats_add_result(&lnode->u, rval, pval);
 371         }
 372
 373         /* Add lnode for tenuki (pass) if we descended further. */
 374         if (di < dlen) {
 375                 double rval = u->local_tree_eval != LTE_EACH ? sval : 0.5;
 376                 LTREE_DEBUG fprintf(stderr, "pass ");
 377                 lnode = tree_get_node(t, lnode, pass, true);
 378                 assert(lnode);
 379                 stats_add_result(&lnode->u, rval, pval);
 380         }
 381
 382         LTREE_DEBUG fprintf(stderr, "\n");
 383 }
 384
 385
 386 int
 387 uct_playout(struct uct *u, struct board *b, enum stone player_color, struct tree *t)
 388 {
 389         struct board b2;
 390         board_copy(&b2, b);
 391
 392         struct playout_amafmap amaf;
 393         amaf.gamelen = amaf.game_baselen = 0;
 394
 395         /* Walk the tree until we find a leaf, then expand it and do
 396          * a random playout. */
 397         struct tree_node *n = t->root;
 398         enum stone node_color = stone_other(player_color);
 399         assert(node_color == t->root_color);
 400
 401         /* Make sure the root node is expanded. */
 402         if (tree_leaf_node(n) && !__sync_lock_test_and_set(&n->is_expanded, 1))
 403                 tree_expand_node(t, n, &b2, player_color, u, 1);
 404
 405         /* Tree descent history. */
 406         /* XXX: This is somewhat messy since @n and descent[dlen-1].node are
 407          * redundant. */
 408         struct uct_descent descent[DESCENT_DLEN];
 409         descent[0].node = n; descent[0].lnode = NULL;
 410         int dlen = 1;
 411         /* Total value of the sequence. */
 412         struct move_stats seq_value = { .playouts = 0 };
 413         /* The last "significant" node along the descent (i.e. node
 414          * with higher than configured number of playouts). For black
 415          * and white. */
 416         struct tree_node *significant[2] = { NULL, NULL };
 417         if (n->u.playouts >= u->significant_threshold)
 418                 significant[node_color - 1] = n;
 419
 420         int result;
 421         int pass_limit = (board_size(&b2) - 2) * (board_size(&b2) - 2) / 2;
 422         int passes = is_pass(b->last_move.coord) && b->moves > 0;
 423
 424         /* debug */
 425         static char spaces[] = "\0                                                      ";
 426         /* /debug */
 427         if (UDEBUGL(8))
 428                 fprintf(stderr, "--- UCT walk with color %d\n", player_color);
 429
 430         while (!tree_leaf_node(n) && passes < 2) {
 431                 spaces[dlen - 1] = ' '; spaces[dlen] = 0;
 432
 433
 434                 /*** Choose a node to descend to: */
 435
 436                 /* Parity is chosen already according to the child color, since
 437                  * it is applied to children. */
 438                 node_color = stone_other(node_color);
 439                 int parity = (node_color == player_color ? 1 : -1);
 440
 441                 assert(dlen < DESCENT_DLEN);
 442                 descent[dlen] = descent[dlen - 1];
 443                 if (u->local_tree && (!descent[dlen].lnode || descent[dlen].node->d >= u->tenuki_d)) {
 444                         /* Start new local sequence. */
 445                         /* Remember that node_color already holds color of the
 446                          * to-be-found child. */
 447                         descent[dlen].lnode = node_color == S_BLACK ? t->ltree_black : t->ltree_white;
 448                 }
 449
 450                 if (!u->random_policy_chance || fast_random(u->random_policy_chance))
 451                         u->policy->descend(u->policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 452                 else
 453                         u->random_policy->descend(u->random_policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 454
 455
 456                 /*** Perform the descent: */
 457
 458                 if (descent[dlen].node->u.playouts >= u->significant_threshold) {
 459                         significant[node_color - 1] = descent[dlen].node;
 460                 }
 461
 462                 seq_value.playouts += descent[dlen].value.playouts;
 463                 seq_value.value += descent[dlen].value.value * descent[dlen].value.playouts;
 464                 n = descent[dlen++].node;
 465                 assert(n == t->root || n->parent);
 466                 if (UDEBUGL(7))
 467                         fprintf(stderr, "%s+-- UCT sent us to [%s:%d] %d,%f\n",
 468                                 spaces, coord2sstr(node_coord(n), t->board),
 469                                 node_coord(n), n->u.playouts,
 470                                 tree_node_get_value(t, parity, n->u.value));
 471
 472                 /* Add virtual loss if we need to; this is used to discourage
 473                  * other threads from visiting this node in case of multiple
 474                  * threads doing the tree search. */
 475                 if (u->virtual_loss)
 476                         stats_add_result(&n->u, node_color == S_BLACK ? 0.0 : 1.0, u->virtual_loss);
 477
 478                 struct move m = { node_coord(n), node_color };
 479                 int res = board_play(&b2, &m);
 480
 481                 if (res < 0 || (!is_pass(m.coord) && !group_at(&b2, m.coord)) /* suicide */
 482                     || b2.superko_violation) {
 483                         if (UDEBUGL(4)) {
 484                                 for (struct tree_node *ni = n; ni; ni = ni->parent)
 485                                         fprintf(stderr, "%s<%"PRIhash"> ", coord2sstr(node_coord(ni), t->board), ni->hash);
 486                                 fprintf(stderr, "marking invalid %s node %d,%d res %d group %d spk %d\n",
 487                                         stone2str(node_color), coord_x(node_coord(n),b), coord_y(node_coord(n),b),
 488                                         res, group_at(&b2, m.coord), b2.superko_violation);
 489                         }
 490                         n->hints |= TREE_HINT_INVALID;
 491                         result = 0;
 492                         goto end;
 493                 }
 494
 495                 assert(node_coord(n) >= -1);
 496                 record_amaf_move(&amaf, node_coord(n), board_playing_ko_threat(&b2));
 497
 498                 if (is_pass(node_coord(n)))
 499                         passes++;
 500                 else
 501                         passes = 0;
 502
 503                 enum stone next_color = stone_other(node_color);
 504                 /* We need to make sure only one thread expands the node. If
 505                  * we are unlucky enough for two threads to meet in the same
 506                  * node, the latter one will simply do another simulation from
 507                  * the node itself, no big deal. t->nodes_size may exceed
 508                  * the maximum in multi-threaded case but not by much so it's ok.
 509                  * The size test must be before the test&set not after, to allow
 510                  * expansion of the node later if enough nodes have been freed. */
 511                 if (tree_leaf_node(n)
 512                     && n->u.playouts - u->virtual_loss >= u->expand_p && t->nodes_size < u->max_tree_size
 513                     && !__sync_lock_test_and_set(&n->is_expanded, 1))
 514                         tree_expand_node(t, n, &b2, next_color, u, -parity);
 515         }
 516
 517         amaf.game_baselen = amaf.gamelen;
 518
 519         if (t->use_extra_komi && u->dynkomi->persim) {
 520                 b2.komi += round(u->dynkomi->persim(u->dynkomi, &b2, t, n));
 521         }
 522
 523         if (passes >= 2) {
 524                 /* XXX: No dead groups support. */
 525                 floating_t score = board_official_score(&b2, NULL);
 526                 /* Result from black's perspective (no matter who
 527                  * the player; black's perspective is always
 528                  * what the tree stores. */
 529                 result = - (score * 2);
 530
 531                 if (UDEBUGL(5))
 532                         fprintf(stderr, "[%d..%d] %s p-p scoring playout result %d (W %f)\n",
 533                                 player_color, node_color, coord2sstr(node_coord(n), t->board), result, score);
 534                 if (UDEBUGL(6))
 535                         board_print(&b2, stderr);
 536
 537                 board_ownermap_fill(&u->ownermap, &b2);
 538
 539         } else { // assert(tree_leaf_node(n));
 540                 /* In case of parallel tree search, the assertion might
 541                  * not hold if two threads chew on the same node. */
 542                 result = uct_leaf_node(u, &b2, player_color, &amaf, descent, &dlen, significant, t, n, node_color, spaces);
 543         }
 544
 545         if (u->policy->wants_amaf && u->playout_amaf_cutoff) {
 546                 unsigned int cutoff = amaf.game_baselen;
 547                 cutoff += (amaf.gamelen - amaf.game_baselen) * u->playout_amaf_cutoff / 100;
 548                 amaf.gamelen = cutoff;
 549         }
 550
 551         /* Record the result. */
 552
 553         assert(n == t->root || n->parent);
 554         floating_t rval = scale_value(u, b, result);
 555         u->policy->update(u->policy, t, n, node_color, player_color, &amaf, &b2, rval);
 556
 557         stats_add_result(&t->avg_score, result / 2, 1);
 558         if (t->use_extra_komi) {
 559                 stats_add_result(&u->dynkomi->score, result / 2, 1);
 560                 stats_add_result(&u->dynkomi->value, rval, 1);
 561         }
 562
 563         if (u->local_tree && n->parent && !is_pass(node_coord(n)) && dlen > 0) {
 564                 /* Get the local sequences and record them in ltree. */
 565                 /* We will look for sequence starts in our descent
 566                  * history, then run record_local_sequence() for each
 567                  * found sequence start; record_local_sequence() may
 568                  * pick longer sequences from descent history then,
 569                  * which is expected as it will create new lnodes. */
 570                 enum stone seq_color = player_color;
 571                 /* First move always starts a sequence. */
 572                 record_local_sequence(u, t, &b2, descent, dlen, 1, seq_color);
 573                 seq_color = stone_other(seq_color);
 574                 for (int dseqi = 2; dseqi < dlen; dseqi++, seq_color = stone_other(seq_color)) {
 575                         if (u->local_tree_allseq) {
 576                                 /* We are configured to record all subsequences. */
 577                                 record_local_sequence(u, t, &b2, descent, dlen, dseqi, seq_color);
 578                                 continue;
 579                         }
 580                         if (descent[dseqi].node->d >= u->tenuki_d) {
 581                                 /* Tenuki! Record the fresh sequence. */
 582                                 record_local_sequence(u, t, &b2, descent, dlen, dseqi, seq_color);
 583                                 continue;
 584                         }
 585                         if (descent[dseqi].lnode && !descent[dseqi].lnode) {
 586                                 /* Record result for in-descent picked sequence. */
 587                                 record_local_sequence(u, t, &b2, descent, dlen, dseqi, seq_color);
 588                                 continue;
 589                         }
 590                 }
 591         }
 592
 593 end:
 594         /* We need to undo the virtual loss we added during descend. */
 595         if (u->virtual_loss) {
 596                 floating_t loss = node_color == S_BLACK ? 0.0 : 1.0;
 597                 for (; n->parent; n = n->parent) {
 598                         stats_rm_result(&n->u, loss, u->virtual_loss);
 599                         loss = 1.0 - loss;
 600                 }
 601         }
 602
 603         board_done_noalloc(&b2);
 604         return result;
 605 }
 606
 607 int
 608 uct_playouts(struct uct *u, struct board *b, enum stone color, struct tree *t, struct time_info *ti)
 609 {
 610         int i;
 611         if (ti && ti->dim == TD_GAMES) {
 612                 for (i = 0; t->root->u.playouts <= ti->len.games && !uct_halt; i++)
 613                         uct_playout(u, b, color, t);
 614         } else {
 615                 for (i = 0; !uct_halt; i++)
 616                         uct_playout(u, b, color, t);
 617         }
 618         return i;
 619 }