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 "playout/elo.h"
  16 #include "probdist.h"
  17 #include "random.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 void
  26 uct_progress_status(struct uct *u, struct tree *t, enum stone color, int playouts)
  27 {
  28         if (!UDEBUGL(0))
  29                 return;
  30
  31         /* Best move */
  32         struct tree_node *best = u->policy->choose(u->policy, t->root, t->board, color, resign);
  33         if (!best) {
  34                 fprintf(stderr, "... No moves left\n");
  35                 return;
  36         }
  37         fprintf(stderr, "[%d] ", playouts);
  38         fprintf(stderr, "best %f ", tree_node_get_value(t, 1, best->u.value));
  39
  40         /* Dynamic komi */
  41         if (t->use_extra_komi)
  42                 fprintf(stderr, "komi %.1f ", t->extra_komi);
  43
  44         /* Best sequence */
  45         fprintf(stderr, "| seq ");
  46         for (int depth = 0; depth < 4; depth++) {
  47                 if (best && best->u.playouts >= 25) {
  48                         fprintf(stderr, "%3s ", coord2sstr(best->coord, t->board));
  49                         best = u->policy->choose(u->policy, best, t->board, color, resign);
  50                 } else {
  51                         fprintf(stderr, "    ");
  52                 }
  53         }
  54
  55         /* Best candidates */
  56         fprintf(stderr, "| can ");
  57         int cans = 4;
  58         struct tree_node *can[cans];
  59         memset(can, 0, sizeof(can));
  60         best = t->root->children;
  61         while (best) {
  62                 int c = 0;
  63                 while ((!can[c] || best->u.playouts > can[c]->u.playouts) && ++c < cans);
  64                 for (int d = 0; d < c; d++) can[d] = can[d + 1];
  65                 if (c > 0) can[c - 1] = best;
  66                 best = best->sibling;
  67         }
  68         while (--cans >= 0) {
  69                 if (can[cans]) {
  70                         fprintf(stderr, "%3s(%.3f) ",
  71                                 coord2sstr(can[cans]->coord, t->board),
  72                                 tree_node_get_value(t, 1, can[cans]->u.value));
  73                 } else {
  74                         fprintf(stderr, "           ");
  75                 }
  76         }
  77
  78         fprintf(stderr, "\n");
  79 }
  80
  81
  82 static void
  83 record_amaf_move(struct playout_amafmap *amaf, coord_t coord, enum stone color)
  84 {
  85         if (amaf->map[coord] == S_NONE || amaf->map[coord] == color) {
  86                 amaf->map[coord] = color;
  87         } else { // XXX: Respect amaf->record_nakade
  88                 amaf_op(amaf->map[coord], +);
  89         }
  90         amaf->game[amaf->gamelen].coord = coord;
  91         amaf->game[amaf->gamelen].color = color;
  92         amaf->gamelen++;
  93         assert(amaf->gamelen < sizeof(amaf->game) / sizeof(amaf->game[0]));
  94 }
  95
  96 static double
  97 ltree_node_gamma(struct tree_node *li, enum stone color)
  98 {
  99         /* TODO: How to do this? */
 100         #define li_value(color, li) (li->u.playouts * (color == S_BLACK ? li->u.value : (1 - li->u.value)))
 101         return 0.5 + li_value(color, li);
 102 }
 103
 104
 105 struct uct_playout_callback {
 106         struct uct *uct;
 107         struct tree *tree;
 108         struct tree_node *lnode;
 109
 110         coord_t *treepool[2];
 111         int treepool_n[2];
 112 };
 113
 114 static void
 115 uct_playout_probdist(void *data, struct board *b, enum stone to_play, struct probdist *pd)
 116 {
 117         /* Create probability distribution according to found local tree
 118          * sequence. */
 119         struct uct_playout_callback *upc = data;
 120         assert(upc && upc->tree && pd && b);
 121         coord_t c = b->last_move.coord;
 122         enum stone color = b->last_move.color;
 123
 124         if (is_pass(c)) {
 125                 /* Break local sequence. */
 126                 upc->lnode = NULL;
 127         } else if (upc->lnode) {
 128                 /* Try to follow local sequence. */
 129                 upc->lnode = tree_get_node(upc->tree, upc->lnode, c, false);
 130         }
 131
 132         if (!upc->lnode || !upc->lnode->children) {
 133                 /* There's no local sequence, start new one! */
 134                 upc->lnode = color == S_BLACK ? upc->tree->ltree_black : upc->tree->ltree_white;
 135                 upc->lnode = tree_get_node(upc->tree, upc->lnode, c, false);
 136         }
 137
 138         if (!upc->lnode || !upc->lnode->children) {
 139                 /* We have no local sequence and we cannot find any starting
 140                  * by node corresponding to last move. */
 141                 if (!upc->uct->local_tree_pseqroot) {
 142                         /* Give up then, we have nothing to contribute. */
 143                         return;
 144                 }
 145                 /* Construct probability distribution from possible first
 146                  * sequence move. Remember that @color is color of the
 147                  * *last* move. */
 148                 upc->lnode = color == S_BLACK ? upc->tree->ltree_white : upc->tree->ltree_black;
 149                 if (!upc->lnode->children) {
 150                         /* We don't even have anything in our tree yet. */
 151                         return;
 152                 }
 153         }
 154
 155         /* The probdist has the right structure only if BOARD_GAMMA is defined. */
 156 #ifndef BOARD_GAMMA
 157         assert(0);
 158 #endif
 159
 160         /* Construct probability distribution from lnode children. */
 161         struct tree_node *li = upc->lnode->children;
 162         assert(li);
 163         if (is_pass(li->coord)) {
 164                 /* Tenuki. */
 165                 /* TODO: Spread tenuki gamma over all moves we don't touch. */
 166                 li = li->sibling;
 167         }
 168         for (; li; li = li->sibling) {
 169                 if (board_at(b, li->coord) != S_NONE)
 170                         continue;
 171                 double gamma = fixp_to_double(pd->items[li->coord]) * ltree_node_gamma(li, to_play);
 172                 probdist_set(pd, li->coord, double_to_fixp(gamma));
 173         }
 174 }
 175
 176
 177 static coord_t
 178 uct_playout_hook(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color, int mode)
 179 {
 180         struct uct_playout_callback *upc = setup->hook_data;
 181
 182         if (upc->uct->treepool_chance[mode] > fast_random(100) && upc->treepool[color - 1]) {
 183                 assert(upc->treepool_n[color - 1] > 0);
 184                 coord_t treepool_move = upc->treepool[color - 1][fast_random(upc->treepool_n[color - 1])];
 185                 if (board_is_valid_play(b, treepool_move, color))
 186                         return treepool_move;
 187         }
 188         return pass;
 189 }
 190
 191 static coord_t
 192 uct_playout_prepolicy(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color)
 193 {
 194         return uct_playout_hook(playout, setup, b, color, 0);
 195 }
 196
 197 static coord_t
 198 uct_playout_postpolicy(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color)
 199 {
 200         return uct_playout_hook(playout, setup, b, color, 1);
 201 }
 202
 203 double
 204 treepool_node_value(struct uct *u, struct tree *tree, int parity, struct tree_node *node)
 205 {
 206         /* XXX: Playouts get cast to double */
 207         switch (u->treepool_type) {
 208                 case UTT_RAVE_PLAYOUTS:
 209                         return node->amaf.playouts;
 210                 case UTT_RAVE_VALUE:
 211                         return tree_node_get_value(tree, parity, node->amaf.value);
 212                 case UTT_UCT_PLAYOUTS:
 213                         return node->u.playouts;
 214                 case UTT_UCT_VALUE:
 215                         return tree_node_get_value(tree, parity, node->u.value);
 216                 case UTT_EVALUATE:
 217                 {
 218                         struct uct_descent d = { .node = node };
 219                         assert(u->policy->evaluate);
 220                         return u->policy->evaluate(u->policy, tree, &d, parity);
 221                 }
 222                 default: assert(0);
 223         }
 224         return -1;
 225 }
 226
 227 static void
 228 treepool_setup(struct uct_playout_callback *upc, struct tree_node *node, int color)
 229 {
 230         struct uct *u = upc->uct;
 231         int parity = ((node->depth ^ upc->tree->root->depth) & 1) ? -1 : 1;
 232
 233         /* XXX: Naive O(N^2) way. */
 234         for (int i = 0; i < u->treepool_size; i++) {
 235                 /* For each item, find the highest
 236                  * node not in the pool yet. */
 237                 struct tree_node *best = NULL;
 238                 double best_val = -1;
 239
 240                 // first comes pass which we skip
 241                 for (struct tree_node *ni = node->children->sibling; ni; ni = ni->sibling) {
 242                         /* Do we already have it? */
 243                         bool have = false;
 244                         for (int j = 0; j < upc->treepool_n[color]; j++)
 245                                 if (upc->treepool[color][j] == ni->coord) {
 246                                         have = true;
 247                                         break;
 248                                 }
 249                         if (have)
 250                                 continue;
 251
 252                         double i_val = treepool_node_value(u, upc->tree, parity, ni);
 253                         if (i_val > best_val) {
 254                                 best = node;
 255                                 best_val = i_val;
 256                         }
 257                 }
 258
 259                 if (!best) break;
 260                 upc->treepool[color][upc->treepool_n[color]++] = best->coord;
 261         }
 262 }
 263
 264
 265 static int
 266 uct_leaf_node(struct uct *u, struct board *b, enum stone player_color,
 267               struct playout_amafmap *amaf, struct uct_descent *descent,
 268               struct tree *t, struct tree_node *n, enum stone node_color,
 269               char *spaces)
 270 {
 271         enum stone next_color = stone_other(node_color);
 272         int parity = (next_color == player_color ? 1 : -1);
 273
 274         /* We need to make sure only one thread expands the node. If
 275          * we are unlucky enough for two threads to meet in the same
 276          * node, the latter one will simply do another simulation from
 277          * the node itself, no big deal. t->nodes_size may exceed
 278          * the maximum in multi-threaded case but not by much so it's ok.
 279          * The size test must be before the test&set not after, to allow
 280          * expansion of the node later if enough nodes have been freed. */
 281         if (n->u.playouts >= u->expand_p && t->nodes_size < u->max_tree_size
 282             && !__sync_lock_test_and_set(&n->is_expanded, 1)) {
 283                 tree_expand_node(t, n, b, next_color, u, parity);
 284         }
 285         if (UDEBUGL(7))
 286                 fprintf(stderr, "%s*-- UCT playout #%d start [%s] %f\n",
 287                         spaces, n->u.playouts, coord2sstr(n->coord, t->board),
 288                         tree_node_get_value(t, parity, n->u.value));
 289
 290         struct uct_playout_callback upc = {
 291                 .uct = u,
 292                 .tree = t,
 293                 /* TODO: Don't necessarily restart the sequence walk when
 294                  * entering playout. */
 295                 .lnode = NULL,
 296         };
 297
 298         if (u->local_tree_playout) {
 299                 /* N.B.: We know this is ELO playout. */
 300                 playout_elo_callback(u->playout, uct_playout_probdist, &upc);
 301         }
 302
 303         coord_t pool[2][u->treepool_size];
 304         if (u->treepool_chance[0] + u->treepool_chance[1] > 0) {
 305                 for (int color = 0; color < 2; color++) {
 306                         /* Prepare tree-based pool of moves to try forcing
 307                          * during the playout. */
 308                         /* We consider the children of the last significant
 309                          * node, picking top N choices. */
 310                         struct tree_node *n = descent->significant[color];
 311                         if (!n || !n->children || !n->children->sibling) {
 312                                 /* No significant node, or it's childless or has
 313                                  * only pass as its child. */
 314                                 upc.treepool[color] = NULL;
 315                                 upc.treepool_n[color] = 0;
 316                         } else {
 317                                 upc.treepool[color] = (coord_t *) &pool[color];
 318                                 treepool_setup(&upc, n, color);
 319                         }
 320                 }
 321         }
 322
 323         struct playout_setup ps = {
 324                 .gamelen = u->gamelen,
 325                 .mercymin = u->mercymin,
 326                 .prepolicy_hook = uct_playout_prepolicy,
 327                 .postpolicy_hook = uct_playout_postpolicy,
 328                 .hook_data = &upc,
 329         };
 330         int result = play_random_game(&ps, b, next_color,
 331                                       u->playout_amaf ? amaf : NULL,
 332                                       &u->ownermap, u->playout);
 333         if (next_color == S_WHITE) {
 334                 /* We need the result from black's perspective. */
 335                 result = - result;
 336         }
 337         if (UDEBUGL(7))
 338                 fprintf(stderr, "%s -- [%d..%d] %s random playout result %d\n",
 339                         spaces, player_color, next_color, coord2sstr(n->coord, t->board), result);
 340
 341         return result;
 342 }
 343
 344 static float
 345 scale_value(struct uct *u, struct board *b, int result)
 346 {
 347         float rval = result > 0;
 348         if (u->val_scale) {
 349                 int vp = u->val_points;
 350                 if (!vp) {
 351                         vp = board_size(b) - 1; vp *= vp; vp *= 2;
 352                 }
 353
 354                 float sval = (float) abs(result) / vp;
 355                 sval = sval > 1 ? 1 : sval;
 356                 if (result < 0) sval = 1 - sval;
 357                 if (u->val_extra)
 358                         rval += u->val_scale * sval;
 359                 else
 360                         rval = (1 - u->val_scale) * rval + u->val_scale * sval;
 361                 // fprintf(stderr, "score %d => sval %f, rval %f\n", result, sval, rval);
 362         }
 363         return rval;
 364 }
 365
 366 static void
 367 record_local_sequence(struct uct *u, struct tree *t,
 368                       struct uct_descent *descent, int dlen, int di,
 369                       enum stone seq_color, float rval)
 370 {
 371         /* Ignore pass sequences. */
 372         if (is_pass(descent[di].node->coord))
 373                 return;
 374
 375 #define LTREE_DEBUG if (UDEBUGL(6))
 376         LTREE_DEBUG fprintf(stderr, "recording result %f in local %s sequence: ",
 377                 rval, stone2str(seq_color));
 378         int di0 = di;
 379
 380         /* Pick the right local tree root... */
 381         struct tree_node *lnode = seq_color == S_BLACK ? t->ltree_black : t->ltree_white;
 382         lnode->u.playouts++;
 383
 384         /* ...and record the sequence. */
 385         while (di < dlen && (di == di0 || descent[di].node->d < u->tenuki_d)) {
 386                 LTREE_DEBUG fprintf(stderr, "%s[%d] ",
 387                         coord2sstr(descent[di].node->coord, t->board),
 388                         descent[di].node->d);
 389                 lnode = tree_get_node(t, lnode, descent[di++].node->coord, true);
 390                 assert(lnode);
 391                 stats_add_result(&lnode->u, rval, 1);
 392         }
 393
 394         /* Add lnode for tenuki (pass) if we descended further. */
 395         if (di < dlen) {
 396                 LTREE_DEBUG fprintf(stderr, "pass ");
 397                 lnode = tree_get_node(t, lnode, pass, true);
 398                 assert(lnode);
 399                 stats_add_result(&lnode->u, rval, 1);
 400         }
 401
 402         LTREE_DEBUG fprintf(stderr, "\n");
 403 }
 404
 405
 406 int
 407 uct_playout(struct uct *u, struct board *b, enum stone player_color, struct tree *t)
 408 {
 409         struct board b2;
 410         board_copy(&b2, b);
 411
 412         struct playout_amafmap *amaf = NULL;
 413         if (u->policy->wants_amaf) {
 414                 amaf = calloc2(1, sizeof(*amaf));
 415                 amaf->map = calloc2(board_size2(&b2) + 1, sizeof(*amaf->map));
 416                 amaf->map++; // -1 is pass
 417         }
 418
 419         /* Walk the tree until we find a leaf, then expand it and do
 420          * a random playout. */
 421         struct tree_node *n = t->root;
 422         enum stone node_color = stone_other(player_color);
 423         assert(node_color == t->root_color);
 424
 425         /* Tree descent history. */
 426         /* XXX: This is somewhat messy since @n and descent[dlen-1].node are
 427          * redundant. */
 428         #define DLEN 512
 429         struct uct_descent descent[DLEN];
 430         descent[0].node = n; descent[0].lnode = NULL;
 431         descent[0].significant[0] = descent[0].significant[1] = NULL;
 432         int dlen = 1;
 433         /* Total value of the sequence. */
 434         struct move_stats seq_value = { .playouts = 0 };
 435
 436         int result;
 437         int pass_limit = (board_size(&b2) - 2) * (board_size(&b2) - 2) / 2;
 438         int passes = is_pass(b->last_move.coord) && b->moves > 0;
 439
 440         /* debug */
 441         int depth = 0;
 442         static char spaces[] = "\0                                                      ";
 443         /* /debug */
 444         if (UDEBUGL(8))
 445                 fprintf(stderr, "--- UCT walk with color %d\n", player_color);
 446
 447         while (!tree_leaf_node(n) && passes < 2) {
 448                 spaces[depth++] = ' '; spaces[depth] = 0;
 449
 450
 451                 /*** Choose a node to descend to: */
 452
 453                 /* Parity is chosen already according to the child color, since
 454                  * it is applied to children. */
 455                 node_color = stone_other(node_color);
 456                 int parity = (node_color == player_color ? 1 : -1);
 457
 458                 assert(dlen < DLEN);
 459                 descent[dlen] = descent[dlen - 1];
 460                 if (u->local_tree && (!descent[dlen].lnode || descent[dlen].node->d >= u->tenuki_d)) {
 461                         /* Start new local sequence. */
 462                         /* Remember that node_color already holds color of the
 463                          * to-be-found child. */
 464                         descent[dlen].lnode = node_color == S_BLACK ? t->ltree_black : t->ltree_white;
 465                 }
 466
 467                 if (!u->random_policy_chance || fast_random(u->random_policy_chance))
 468                         u->policy->descend(u->policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 469                 else
 470                         u->random_policy->descend(u->random_policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 471
 472
 473                 /*** Perform the descent: */
 474
 475                 if (descent[dlen].node->u.playouts >= u->significant_threshold) {
 476                         descent[dlen].significant[node_color - 1] = n;
 477                 }
 478
 479                 seq_value.playouts += descent[dlen].value.playouts;
 480                 seq_value.value += descent[dlen].value.value * descent[dlen].value.playouts;
 481                 n = descent[dlen++].node;
 482                 assert(n == t->root || n->parent);
 483                 if (UDEBUGL(7))
 484                         fprintf(stderr, "%s+-- UCT sent us to [%s:%d] %f\n",
 485                                 spaces, coord2sstr(n->coord, t->board), n->coord,
 486                                 tree_node_get_value(t, parity, n->u.value));
 487
 488                 /* Add virtual loss if we need to; this is used to discourage
 489                  * other threads from visiting this node in case of multiple
 490                  * threads doing the tree search. */
 491                 if (u->virtual_loss)
 492                         stats_add_result(&n->u, tree_parity(t, parity) > 0 ? 0 : 1, 1);
 493
 494                 assert(n->coord >= -1);
 495                 if (amaf && !is_pass(n->coord))
 496                         record_amaf_move(amaf, n->coord, node_color);
 497
 498                 struct move m = { n->coord, node_color };
 499                 int res = board_play(&b2, &m);
 500
 501                 if (res < 0 || (!is_pass(m.coord) && !group_at(&b2, m.coord)) /* suicide */
 502                     || b2.superko_violation) {
 503                         if (UDEBUGL(4)) {
 504                                 for (struct tree_node *ni = n; ni; ni = ni->parent)
 505                                         fprintf(stderr, "%s<%"PRIhash"> ", coord2sstr(ni->coord, t->board), ni->hash);
 506                                 fprintf(stderr, "marking invalid %s node %d,%d res %d group %d spk %d\n",
 507                                         stone2str(node_color), coord_x(n->coord,b), coord_y(n->coord,b),
 508                                         res, group_at(&b2, m.coord), b2.superko_violation);
 509                         }
 510                         n->hints |= TREE_HINT_INVALID;
 511                         result = 0;
 512                         goto end;
 513                 }
 514
 515                 if (is_pass(n->coord))
 516                         passes++;
 517                 else
 518                         passes = 0;
 519         }
 520
 521         if (amaf) {
 522                 amaf->game_baselen = amaf->gamelen;
 523                 amaf->record_nakade = u->playout_amaf_nakade;
 524         }
 525
 526         if (t->use_extra_komi && u->dynkomi->persim) {
 527                 b2.komi += round(u->dynkomi->persim(u->dynkomi, &b2, t, n));
 528         }
 529
 530         if (passes >= 2) {
 531                 /* XXX: No dead groups support. */
 532                 float score = board_official_score(&b2, NULL);
 533                 /* Result from black's perspective (no matter who
 534                  * the player; black's perspective is always
 535                  * what the tree stores. */
 536                 result = - (score * 2);
 537
 538                 if (UDEBUGL(5))
 539                         fprintf(stderr, "[%d..%d] %s p-p scoring playout result %d (W %f)\n",
 540                                 player_color, node_color, coord2sstr(n->coord, t->board), result, score);
 541                 if (UDEBUGL(6))
 542                         board_print(&b2, stderr);
 543
 544                 board_ownermap_fill(&u->ownermap, &b2);
 545
 546         } else { // assert(tree_leaf_node(n));
 547                 /* In case of parallel tree search, the assertion might
 548                  * not hold if two threads chew on the same node. */
 549                 result = uct_leaf_node(u, &b2, player_color, amaf, &descent[dlen - 1], t, n, node_color, spaces);
 550         }
 551
 552         if (amaf && u->playout_amaf_cutoff) {
 553                 unsigned int cutoff = amaf->game_baselen;
 554                 cutoff += (amaf->gamelen - amaf->game_baselen) * u->playout_amaf_cutoff / 100;
 555                 /* Now, reconstruct the amaf map. */
 556                 memset(amaf->map, 0, board_size2(&b2) * sizeof(*amaf->map));
 557                 for (unsigned int i = 0; i < cutoff; i++) {
 558                         coord_t coord = amaf->game[i].coord;
 559                         enum stone color = amaf->game[i].color;
 560                         if (amaf->map[coord] == S_NONE || amaf->map[coord] == color) {
 561                                 amaf->map[coord] = color;
 562                         /* Nakade always recorded for in-tree part */
 563                         } else if (amaf->record_nakade || i <= amaf->game_baselen) {
 564                                 amaf_op(amaf->map[n->coord], +);
 565                         }
 566                 }
 567         }
 568
 569         assert(n == t->root || n->parent);
 570         if (result != 0) {
 571                 float rval = scale_value(u, b, result);
 572                 u->policy->update(u->policy, t, n, node_color, player_color, amaf, rval);
 573
 574                 if (t->use_extra_komi) {
 575                         stats_add_result(&u->dynkomi->score, result / 2, 1);
 576                         stats_add_result(&u->dynkomi->value, rval, 1);
 577                 }
 578
 579                 if (u->local_tree && n->parent && !is_pass(n->coord) && dlen > 0) {
 580                         /* Possibly transform the rval appropriately. */
 581                         float expval = seq_value.value / seq_value.playouts;
 582                         rval = stats_temper_value(rval, expval, u->local_tree);
 583
 584                         /* Get the local sequences and record them in ltree. */
 585                         /* We will look for sequence starts in our descent
 586                          * history, then run record_local_sequence() for each
 587                          * found sequence start; record_local_sequence() may
 588                          * pick longer sequences from descent history then,
 589                          * which is expected as it will create new lnodes. */
 590                         enum stone seq_color = player_color;
 591                         /* First move always starts a sequence. */
 592                         record_local_sequence(u, t, descent, dlen, 1, seq_color, rval);
 593                         seq_color = stone_other(seq_color);
 594                         for (int dseqi = 2; dseqi < dlen; dseqi++, seq_color = stone_other(seq_color)) {
 595                                 if (u->local_tree_allseq) {
 596                                         /* We are configured to record all subsequences. */
 597                                         record_local_sequence(u, t, descent, dlen, dseqi, seq_color, rval);
 598                                         continue;
 599                                 }
 600                                 if (descent[dseqi].node->d >= u->tenuki_d) {
 601                                         /* Tenuki! Record the fresh sequence. */
 602                                         record_local_sequence(u, t, descent, dlen, dseqi, seq_color, rval);
 603                                         continue;
 604                                 }
 605                                 if (descent[dseqi].lnode && !descent[dseqi].lnode) {
 606                                         /* Record result for in-descent picked sequence. */
 607                                         record_local_sequence(u, t, descent, dlen, dseqi, seq_color, rval);
 608                                         continue;
 609                                 }
 610                         }
 611                 }
 612         }
 613
 614 end:
 615         /* We need to undo the virtual loss we added during descend. */
 616         if (u->virtual_loss) {
 617                 int parity = (node_color == player_color ? 1 : -1);
 618                 for (; n->parent; n = n->parent) {
 619                         stats_rm_result(&n->u, tree_parity(t, parity) > 0 ? 0 : 1, 1);
 620                         parity = -parity;
 621                 }
 622         }
 623
 624         if (amaf) {
 625                 free(amaf->map - 1);
 626                 free(amaf);
 627         }
 628         board_done_noalloc(&b2);
 629         return result;
 630 }
 631
 632 int
 633 uct_playouts(struct uct *u, struct board *b, enum stone color, struct tree *t, struct time_info *ti)
 634 {
 635         int i;
 636         if (ti->dim == TD_GAMES) {
 637                 for (i = 0; t->root->u.playouts <= ti->len.games; i++)
 638                         uct_playout(u, b, color, t);
 639         } else {
 640                 for (i = 0; !uct_halt; i++)
 641                         uct_playout(u, b, color, t);
 642         }
 643         return i;
 644 }