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, "xkomi %.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, enum stone node_color, struct tree_node *significant[2], 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                 if (u->val_byavg) {
 276                         if (u->t->avg_score.playouts < 50)
 277                                 return rval;
 278                         result -= u->t->avg_score.value * 2;
 279                 }
 280
 281                 double scale = u->val_scale;
 282                 if (u->val_bytemp) {
 283                         /* xvalue is 0 at 0.5, 1 at 0 or 1 */
 284                         /* No correction for parity necessary. */
 285                         double xvalue = significant[node_color - 1] ? fabs(significant[node_color - 1]->u.value - 0.5) * 2 : 0;
 286                         scale = u->val_bytemp_min + (u->val_scale - u->val_bytemp_min) * xvalue;
 287                 }
 288
 289                 int vp = u->val_points;
 290                 if (!vp) {
 291                         vp = board_size(b) - 1; vp *= vp; vp *= 2;
 292                 }
 293
 294                 floating_t sval = (floating_t) abs(result) / vp;
 295                 sval = sval > 1 ? 1 : sval;
 296                 if (result < 0) sval = 1 - sval;
 297                 if (u->val_extra)
 298                         rval += scale * sval;
 299                 else
 300                         rval = (1 - scale) * rval + scale * sval;
 301                 // fprintf(stderr, "score %d => sval %f, rval %f\n", result, sval, rval);
 302         }
 303         return rval;
 304 }
 305
 306 static double
 307 local_value(struct uct *u, struct board *b, coord_t coord, enum stone color)
 308 {
 309         /* Tactical evaluation of move @coord by color @color, given
 310          * simulation end position @b. I.e., a move is tactically good
 311          * if the resulting group stays on board until the game end. */
 312         /* We can also take into account surrounding stones, e.g. to
 313          * encourage taking off external liberties during a semeai. */
 314         double val = board_local_value(u->local_tree_neival, b, coord, color);
 315         return (color == S_WHITE) ? 1.f - val : val;
 316 }
 317
 318 static void
 319 record_local_sequence(struct uct *u, struct tree *t, struct board *endb,
 320                       struct uct_descent *descent, int dlen, int di,
 321                       enum stone seq_color)
 322 {
 323 #define LTREE_DEBUG if (UDEBUGL(6))
 324
 325         /* Ignore pass sequences. */
 326         if (is_pass(node_coord(descent[di].node)))
 327                 return;
 328
 329         LTREE_DEBUG board_print(endb, stderr);
 330         LTREE_DEBUG fprintf(stderr, "recording local %s sequence: ",
 331                 stone2str(seq_color));
 332
 333         /* Sequences starting deeper are less relevant in general. */
 334         int pval = LTREE_PLAYOUTS_MULTIPLIER;
 335         if (u->local_tree && u->local_tree_depth_decay > 0)
 336                 pval = ((floating_t) pval) / pow(u->local_tree_depth_decay, di - 1);
 337         if (!pval) {
 338                 LTREE_DEBUG fprintf(stderr, "too deep @%d\n", di);
 339                 return;
 340         }
 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         /* ...determine the sequence value... */
 347         double sval = 0.5;
 348         if (u->local_tree_eval != LTE_EACH) {
 349                 sval = local_value(u, endb, node_coord(descent[di].node), seq_color);
 350                 LTREE_DEBUG fprintf(stderr, "(goal %s[%s %1.3f][%d]) ",
 351                         coord2sstr(node_coord(descent[di].node), t->board),
 352                         stone2str(seq_color), sval, descent[di].node->d);
 353
 354                 if (u->local_tree_eval == LTE_TOTAL) {
 355                         int di0 = di;
 356                         while (di < dlen && (di == di0 || descent[di].node->d < u->tenuki_d)) {
 357                                 enum stone color = (di - di0) % 2 ? stone_other(seq_color) : seq_color;
 358                                 double rval = local_value(u, endb, node_coord(descent[di].node), color);
 359                                 if ((di - di0) % 2)
 360                                         rval = 1 - rval;
 361                                 sval += rval;
 362                                 di++;
 363                         }
 364                         sval /= (di - di0 + 1);
 365                         di = di0;
 366                 }
 367         }
 368
 369         /* ...and record the sequence. */
 370         int di0 = di;
 371         while (di < dlen && !is_pass(node_coord(descent[di].node))
 372                && (di == di0 || descent[di].node->d < u->tenuki_d)) {
 373                 enum stone color = (di - di0) % 2 ? stone_other(seq_color) : seq_color;
 374                 double rval;
 375                 if (u->local_tree_eval != LTE_EACH)
 376                         rval = sval;
 377                 else
 378                         rval = local_value(u, endb, node_coord(descent[di].node), color);
 379                 LTREE_DEBUG fprintf(stderr, "%s[%s %1.3f][%d] ",
 380                         coord2sstr(node_coord(descent[di].node), t->board),
 381                         stone2str(color), rval, descent[di].node->d);
 382                 lnode = tree_get_node(t, lnode, node_coord(descent[di++].node), true);
 383                 assert(lnode);
 384                 stats_add_result(&lnode->u, rval, pval);
 385         }
 386
 387         /* Add lnode for tenuki (pass) if we descended further. */
 388         if (di < dlen) {
 389                 double rval = u->local_tree_eval != LTE_EACH ? sval : 0.5;
 390                 LTREE_DEBUG fprintf(stderr, "pass ");
 391                 lnode = tree_get_node(t, lnode, pass, true);
 392                 assert(lnode);
 393                 stats_add_result(&lnode->u, rval, pval);
 394         }
 395
 396         LTREE_DEBUG fprintf(stderr, "\n");
 397 }
 398
 399
 400 int
 401 uct_playout(struct uct *u, struct board *b, enum stone player_color, struct tree *t)
 402 {
 403         struct board b2;
 404         board_copy(&b2, b);
 405
 406         struct playout_amafmap amaf;
 407         amaf.gamelen = amaf.game_baselen = 0;
 408
 409         /* Walk the tree until we find a leaf, then expand it and do
 410          * a random playout. */
 411         struct tree_node *n = t->root;
 412         enum stone node_color = stone_other(player_color);
 413         assert(node_color == t->root_color);
 414
 415         /* Make sure the root node is expanded. */
 416         if (tree_leaf_node(n) && !__sync_lock_test_and_set(&n->is_expanded, 1))
 417                 tree_expand_node(t, n, &b2, player_color, u, 1);
 418
 419         /* Tree descent history. */
 420         /* XXX: This is somewhat messy since @n and descent[dlen-1].node are
 421          * redundant. */
 422         struct uct_descent descent[DESCENT_DLEN];
 423         descent[0].node = n; descent[0].lnode = NULL;
 424         int dlen = 1;
 425         /* Total value of the sequence. */
 426         struct move_stats seq_value = { .playouts = 0 };
 427         /* The last "significant" node along the descent (i.e. node
 428          * with higher than configured number of playouts). For black
 429          * and white. */
 430         struct tree_node *significant[2] = { NULL, NULL };
 431         if (n->u.playouts >= u->significant_threshold)
 432                 significant[node_color - 1] = n;
 433
 434         int result;
 435         int pass_limit = (board_size(&b2) - 2) * (board_size(&b2) - 2) / 2;
 436         int passes = is_pass(b->last_move.coord) && b->moves > 0;
 437
 438         /* debug */
 439         static char spaces[] = "\0                                                      ";
 440         /* /debug */
 441         if (UDEBUGL(8))
 442                 fprintf(stderr, "--- UCT walk with color %d\n", player_color);
 443
 444         while (!tree_leaf_node(n) && passes < 2) {
 445                 spaces[dlen - 1] = ' '; spaces[dlen] = 0;
 446
 447
 448                 /*** Choose a node to descend to: */
 449
 450                 /* Parity is chosen already according to the child color, since
 451                  * it is applied to children. */
 452                 node_color = stone_other(node_color);
 453                 int parity = (node_color == player_color ? 1 : -1);
 454
 455                 assert(dlen < DESCENT_DLEN);
 456                 descent[dlen] = descent[dlen - 1];
 457                 if (u->local_tree && (!descent[dlen].lnode || descent[dlen].node->d >= u->tenuki_d)) {
 458                         /* Start new local sequence. */
 459                         /* Remember that node_color already holds color of the
 460                          * to-be-found child. */
 461                         descent[dlen].lnode = node_color == S_BLACK ? t->ltree_black : t->ltree_white;
 462                 }
 463
 464                 if (!u->random_policy_chance || fast_random(u->random_policy_chance))
 465                         u->policy->descend(u->policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 466                 else
 467                         u->random_policy->descend(u->random_policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 468
 469
 470                 /*** Perform the descent: */
 471
 472                 if (descent[dlen].node->u.playouts >= u->significant_threshold) {
 473                         significant[node_color - 1] = descent[dlen].node;
 474                 }
 475
 476                 seq_value.playouts += descent[dlen].value.playouts;
 477                 seq_value.value += descent[dlen].value.value * descent[dlen].value.playouts;
 478                 n = descent[dlen++].node;
 479                 assert(n == t->root || n->parent);
 480                 if (UDEBUGL(7))
 481                         fprintf(stderr, "%s+-- UCT sent us to [%s:%d] %d,%f\n",
 482                                 spaces, coord2sstr(node_coord(n), t->board),
 483                                 node_coord(n), n->u.playouts,
 484                                 tree_node_get_value(t, parity, n->u.value));
 485
 486                 /* Add virtual loss if we need to; this is used to discourage
 487                  * other threads from visiting this node in case of multiple
 488                  * threads doing the tree search. */
 489                 if (u->virtual_loss)
 490                         stats_add_result(&n->u, node_color == S_BLACK ? 0.0 : 1.0, u->virtual_loss);
 491
 492                 struct move m = { node_coord(n), node_color };
 493                 int res = board_play(&b2, &m);
 494
 495                 if (res < 0 || (!is_pass(m.coord) && !group_at(&b2, m.coord)) /* suicide */
 496                     || b2.superko_violation) {
 497                         if (UDEBUGL(4)) {
 498                                 for (struct tree_node *ni = n; ni; ni = ni->parent)
 499                                         fprintf(stderr, "%s<%"PRIhash"> ", coord2sstr(node_coord(ni), t->board), ni->hash);
 500                                 fprintf(stderr, "marking invalid %s node %d,%d res %d group %d spk %d\n",
 501                                         stone2str(node_color), coord_x(node_coord(n),b), coord_y(node_coord(n),b),
 502                                         res, group_at(&b2, m.coord), b2.superko_violation);
 503                         }
 504                         n->hints |= TREE_HINT_INVALID;
 505                         result = 0;
 506                         goto end;
 507                 }
 508
 509                 assert(node_coord(n) >= -1);
 510                 record_amaf_move(&amaf, node_coord(n), board_playing_ko_threat(&b2));
 511
 512                 if (is_pass(node_coord(n)))
 513                         passes++;
 514                 else
 515                         passes = 0;
 516
 517                 enum stone next_color = stone_other(node_color);
 518                 /* We need to make sure only one thread expands the node. If
 519                  * we are unlucky enough for two threads to meet in the same
 520                  * node, the latter one will simply do another simulation from
 521                  * the node itself, no big deal. t->nodes_size may exceed
 522                  * the maximum in multi-threaded case but not by much so it's ok.
 523                  * The size test must be before the test&set not after, to allow
 524                  * expansion of the node later if enough nodes have been freed. */
 525                 if (tree_leaf_node(n)
 526                     && n->u.playouts - u->virtual_loss >= u->expand_p && t->nodes_size < u->max_tree_size
 527                     && !__sync_lock_test_and_set(&n->is_expanded, 1))
 528                         tree_expand_node(t, n, &b2, next_color, u, -parity);
 529         }
 530
 531         amaf.game_baselen = amaf.gamelen;
 532
 533         if (t->use_extra_komi && u->dynkomi->persim) {
 534                 b2.komi += round(u->dynkomi->persim(u->dynkomi, &b2, t, n));
 535         }
 536
 537         if (passes >= 2) {
 538                 /* XXX: No dead groups support. */
 539                 floating_t score = board_official_score(&b2, NULL);
 540                 /* Result from black's perspective (no matter who
 541                  * the player; black's perspective is always
 542                  * what the tree stores. */
 543                 result = - (score * 2);
 544
 545                 if (UDEBUGL(5))
 546                         fprintf(stderr, "[%d..%d] %s p-p scoring playout result %d (W %f)\n",
 547                                 player_color, node_color, coord2sstr(node_coord(n), t->board), result, score);
 548                 if (UDEBUGL(6))
 549                         board_print(&b2, stderr);
 550
 551                 board_ownermap_fill(&u->ownermap, &b2);
 552
 553         } else { // assert(tree_leaf_node(n));
 554                 /* In case of parallel tree search, the assertion might
 555                  * not hold if two threads chew on the same node. */
 556                 result = uct_leaf_node(u, &b2, player_color, &amaf, descent, &dlen, significant, t, n, node_color, spaces);
 557         }
 558
 559         if (u->policy->wants_amaf && u->playout_amaf_cutoff) {
 560                 unsigned int cutoff = amaf.game_baselen;
 561                 cutoff += (amaf.gamelen - amaf.game_baselen) * u->playout_amaf_cutoff / 100;
 562                 amaf.gamelen = cutoff;
 563         }
 564
 565         /* Record the result. */
 566
 567         assert(n == t->root || n->parent);
 568         floating_t rval = scale_value(u, b, node_color, significant, result);
 569         u->policy->update(u->policy, t, n, node_color, player_color, &amaf, &b2, rval);
 570
 571         stats_add_result(&t->avg_score, result / 2, 1);
 572         if (t->use_extra_komi) {
 573                 stats_add_result(&u->dynkomi->score, result / 2, 1);
 574                 stats_add_result(&u->dynkomi->value, rval, 1);
 575         }
 576
 577         if (u->local_tree && n->parent && !is_pass(node_coord(n)) && dlen > 0) {
 578                 /* Get the local sequences and record them in ltree. */
 579                 /* We will look for sequence starts in our descent
 580                  * history, then run record_local_sequence() for each
 581                  * found sequence start; record_local_sequence() may
 582                  * pick longer sequences from descent history then,
 583                  * which is expected as it will create new lnodes. */
 584                 enum stone seq_color = player_color;
 585                 /* First move always starts a sequence. */
 586                 record_local_sequence(u, t, &b2, descent, dlen, 1, seq_color);
 587                 seq_color = stone_other(seq_color);
 588                 for (int dseqi = 2; dseqi < dlen; dseqi++, seq_color = stone_other(seq_color)) {
 589                         if (u->local_tree_allseq) {
 590                                 /* We are configured to record all subsequences. */
 591                                 record_local_sequence(u, t, &b2, descent, dlen, dseqi, seq_color);
 592                                 continue;
 593                         }
 594                         if (descent[dseqi].node->d >= u->tenuki_d) {
 595                                 /* Tenuki! Record the fresh sequence. */
 596                                 record_local_sequence(u, t, &b2, descent, dlen, dseqi, seq_color);
 597                                 continue;
 598                         }
 599                         if (descent[dseqi].lnode && !descent[dseqi].lnode) {
 600                                 /* Record result for in-descent picked sequence. */
 601                                 record_local_sequence(u, t, &b2, descent, dlen, dseqi, seq_color);
 602                                 continue;
 603                         }
 604                 }
 605         }
 606
 607 end:
 608         /* We need to undo the virtual loss we added during descend. */
 609         if (u->virtual_loss) {
 610                 floating_t loss = node_color == S_BLACK ? 0.0 : 1.0;
 611                 for (; n->parent; n = n->parent) {
 612                         stats_rm_result(&n->u, loss, u->virtual_loss);
 613                         loss = 1.0 - loss;
 614                 }
 615         }
 616
 617         board_done_noalloc(&b2);
 618         return result;
 619 }
 620
 621 int
 622 uct_playouts(struct uct *u, struct board *b, enum stone color, struct tree *t, struct time_info *ti)
 623 {
 624         int i;
 625         if (ti && ti->dim == TD_GAMES) {
 626                 for (i = 0; t->root->u.playouts <= ti->len.games && !uct_halt; i++)
 627                         uct_playout(u, b, color, t);
 628         } else {
 629                 for (i = 0; !uct_halt; i++)
 630                         uct_playout(u, b, color, t);
 631         }
 632         return i;
 633 }