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