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         struct uct *u = upc->uct;
 182
 183         if (UDEBUGL(8))
 184                 fprintf(stderr, "treepool check [%d] %d, %p,%p\n", mode, u->treepool_chance[mode], upc->treepool[0], upc->treepool[1]);
 185         if (u->treepool_chance[mode] > fast_random(100) && upc->treepool[color - 1]) {
 186                 assert(upc->treepool_n[color - 1] > 0);
 187                 coord_t treepool_move = upc->treepool[color - 1][fast_random(upc->treepool_n[color - 1])];
 188                 if (UDEBUGL(8)) {
 189                         fprintf(stderr, "Treepool: ");
 190                         for (int i = 0; i < upc->treepool_n[color - 1]; i++)
 191                                 fprintf(stderr, "%s ", coord2sstr(upc->treepool[color - 1][i], b));
 192                         fprintf(stderr, "\n");
 193                 }
 194                 if (UDEBUGL(7))
 195                         fprintf(stderr, "Treepool pick <%d> %s,%s\n", upc->treepool_n[color - 1], stone2str(color), coord2sstr(treepool_move, b));
 196                 if (board_is_valid_play(b, color, treepool_move))
 197                         return treepool_move;
 198         }
 199         return pass;
 200 }
 201
 202 static coord_t
 203 uct_playout_prepolicy(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color)
 204 {
 205         return uct_playout_hook(playout, setup, b, color, 0);
 206 }
 207
 208 static coord_t
 209 uct_playout_postpolicy(struct playout_policy *playout, struct playout_setup *setup, struct board *b, enum stone color)
 210 {
 211         return uct_playout_hook(playout, setup, b, color, 1);
 212 }
 213
 214 double
 215 treepool_node_value(struct uct *u, struct tree *tree, int parity, struct tree_node *node)
 216 {
 217         /* XXX: Playouts get cast to double */
 218         switch (u->treepool_type) {
 219                 case UTT_RAVE_PLAYOUTS:
 220                         return node->amaf.playouts;
 221                 case UTT_RAVE_VALUE:
 222                         return tree_node_get_value(tree, parity, node->amaf.value);
 223                 case UTT_UCT_PLAYOUTS:
 224                         return node->u.playouts;
 225                 case UTT_UCT_VALUE:
 226                         return tree_node_get_value(tree, parity, node->u.value);
 227                 case UTT_EVALUATE:
 228                 {
 229                         struct uct_descent d = { .node = node };
 230                         assert(u->policy->evaluate);
 231                         return u->policy->evaluate(u->policy, tree, &d, parity);
 232                 }
 233                 default: assert(0);
 234         }
 235         return -1;
 236 }
 237
 238 static void
 239 treepool_setup(struct uct_playout_callback *upc, struct board *b, struct tree_node *node, int color)
 240 {
 241         struct uct *u = upc->uct;
 242         int parity = ((node->depth ^ upc->tree->root->depth) & 1) ? -1 : 1;
 243
 244         /* XXX: Naive O(N^2) way. */
 245         for (int i = 0; i < u->treepool_size; i++) {
 246                 /* For each item, find the highest
 247                  * node not in the pool yet. */
 248                 struct tree_node *best = NULL;
 249                 double best_val = -1;
 250
 251                 assert(node->children && is_pass(node->children->coord));
 252                 for (struct tree_node *ni = node->children->sibling; ni; ni = ni->sibling) {
 253                         /* Do we already have it? */
 254                         bool have = false;
 255                         for (int j = 0; j < upc->treepool_n[color]; j++) {
 256                                 if (upc->treepool[color][j] == ni->coord) {
 257                                         have = true;
 258                                         break;
 259                                 }
 260                         }
 261                         if (have)
 262                                 continue;
 263
 264                         double i_val = treepool_node_value(u, upc->tree, parity, ni);
 265                         if (i_val > best_val) {
 266                                 best = ni;
 267                                 best_val = i_val;
 268                         }
 269                 }
 270
 271                 if (!best) break;
 272                 upc->treepool[color][upc->treepool_n[color]++] = best->coord;
 273         }
 274 }
 275
 276
 277 static int
 278 uct_leaf_node(struct uct *u, struct board *b, enum stone player_color,
 279               struct playout_amafmap *amaf, struct uct_descent *descent,
 280               struct tree *t, struct tree_node *n, enum stone node_color,
 281               char *spaces)
 282 {
 283         enum stone next_color = stone_other(node_color);
 284         int parity = (next_color == player_color ? 1 : -1);
 285
 286         /* We need to make sure only one thread expands the node. If
 287          * we are unlucky enough for two threads to meet in the same
 288          * node, the latter one will simply do another simulation from
 289          * the node itself, no big deal. t->nodes_size may exceed
 290          * the maximum in multi-threaded case but not by much so it's ok.
 291          * The size test must be before the test&set not after, to allow
 292          * expansion of the node later if enough nodes have been freed. */
 293         if (n->u.playouts >= u->expand_p && t->nodes_size < u->max_tree_size
 294             && !__sync_lock_test_and_set(&n->is_expanded, 1)) {
 295                 tree_expand_node(t, n, b, next_color, u, parity);
 296         }
 297         if (UDEBUGL(7))
 298                 fprintf(stderr, "%s*-- UCT playout #%d start [%s] %f\n",
 299                         spaces, n->u.playouts, coord2sstr(n->coord, t->board),
 300                         tree_node_get_value(t, parity, n->u.value));
 301
 302         struct uct_playout_callback upc = {
 303                 .uct = u,
 304                 .tree = t,
 305                 /* TODO: Don't necessarily restart the sequence walk when
 306                  * entering playout. */
 307                 .lnode = NULL,
 308         };
 309
 310         if (u->local_tree_playout) {
 311                 /* N.B.: We know this is ELO playout. */
 312                 playout_elo_callback(u->playout, uct_playout_probdist, &upc);
 313         }
 314
 315         coord_t pool[2][u->treepool_size];
 316         if (u->treepool_chance[0] + u->treepool_chance[1] > 0) {
 317                 for (int color = 0; color < 2; color++) {
 318                         /* Prepare tree-based pool of moves to try forcing
 319                          * during the playout. */
 320                         /* We consider the children of the last significant
 321                          * node, picking top N choices. */
 322                         struct tree_node *n = descent->significant[color];
 323                         if (!n || !n->children || !n->children->sibling) {
 324                                 /* No significant node, or it's childless or has
 325                                  * only pass as its child. */
 326                                 upc.treepool[color] = NULL;
 327                                 upc.treepool_n[color] = 0;
 328                         } else {
 329                                 upc.treepool[color] = (coord_t *) &pool[color];
 330                                 treepool_setup(&upc, b, n, color);
 331                         }
 332                 }
 333         }
 334
 335         struct playout_setup ps = {
 336                 .gamelen = u->gamelen,
 337                 .mercymin = u->mercymin,
 338                 .prepolicy_hook = uct_playout_prepolicy,
 339                 .postpolicy_hook = uct_playout_postpolicy,
 340                 .hook_data = &upc,
 341         };
 342         int result = play_random_game(&ps, b, next_color,
 343                                       u->playout_amaf ? amaf : NULL,
 344                                       &u->ownermap, u->playout);
 345         if (next_color == S_WHITE) {
 346                 /* We need the result from black's perspective. */
 347                 result = - result;
 348         }
 349         if (UDEBUGL(7))
 350                 fprintf(stderr, "%s -- [%d..%d] %s random playout result %d\n",
 351                         spaces, player_color, next_color, coord2sstr(n->coord, t->board), result);
 352
 353         return result;
 354 }
 355
 356 static float
 357 scale_value(struct uct *u, struct board *b, int result)
 358 {
 359         float rval = result > 0;
 360         if (u->val_scale) {
 361                 int vp = u->val_points;
 362                 if (!vp) {
 363                         vp = board_size(b) - 1; vp *= vp; vp *= 2;
 364                 }
 365
 366                 float sval = (float) abs(result) / vp;
 367                 sval = sval > 1 ? 1 : sval;
 368                 if (result < 0) sval = 1 - sval;
 369                 if (u->val_extra)
 370                         rval += u->val_scale * sval;
 371                 else
 372                         rval = (1 - u->val_scale) * rval + u->val_scale * sval;
 373                 // fprintf(stderr, "score %d => sval %f, rval %f\n", result, sval, rval);
 374         }
 375         return rval;
 376 }
 377
 378 static void
 379 record_local_sequence(struct uct *u, struct tree *t,
 380                       struct uct_descent *descent, int dlen, int di,
 381                       enum stone seq_color, float rval)
 382 {
 383         /* Ignore pass sequences. */
 384         if (is_pass(descent[di].node->coord))
 385                 return;
 386
 387 #define LTREE_DEBUG if (UDEBUGL(6))
 388         LTREE_DEBUG fprintf(stderr, "recording result %f in local %s sequence: ",
 389                 rval, stone2str(seq_color));
 390         int di0 = di;
 391
 392         /* Pick the right local tree root... */
 393         struct tree_node *lnode = seq_color == S_BLACK ? t->ltree_black : t->ltree_white;
 394         lnode->u.playouts++;
 395
 396         /* ...and record the sequence. */
 397         while (di < dlen && (di == di0 || descent[di].node->d < u->tenuki_d)) {
 398                 LTREE_DEBUG fprintf(stderr, "%s[%d] ",
 399                         coord2sstr(descent[di].node->coord, t->board),
 400                         descent[di].node->d);
 401                 lnode = tree_get_node(t, lnode, descent[di++].node->coord, true);
 402                 assert(lnode);
 403                 stats_add_result(&lnode->u, rval, 1);
 404         }
 405
 406         /* Add lnode for tenuki (pass) if we descended further. */
 407         if (di < dlen) {
 408                 LTREE_DEBUG fprintf(stderr, "pass ");
 409                 lnode = tree_get_node(t, lnode, pass, true);
 410                 assert(lnode);
 411                 stats_add_result(&lnode->u, rval, 1);
 412         }
 413
 414         LTREE_DEBUG fprintf(stderr, "\n");
 415 }
 416
 417
 418 int
 419 uct_playout(struct uct *u, struct board *b, enum stone player_color, struct tree *t)
 420 {
 421         struct board b2;
 422         board_copy(&b2, b);
 423
 424         struct playout_amafmap *amaf = NULL;
 425         if (u->policy->wants_amaf) {
 426                 amaf = calloc2(1, sizeof(*amaf));
 427                 amaf->map = calloc2(board_size2(&b2) + 1, sizeof(*amaf->map));
 428                 amaf->map++; // -1 is pass
 429         }
 430
 431         /* Walk the tree until we find a leaf, then expand it and do
 432          * a random playout. */
 433         struct tree_node *n = t->root;
 434         enum stone node_color = stone_other(player_color);
 435         assert(node_color == t->root_color);
 436
 437         /* Tree descent history. */
 438         /* XXX: This is somewhat messy since @n and descent[dlen-1].node are
 439          * redundant. */
 440         #define DLEN 512
 441         struct uct_descent descent[DLEN];
 442         descent[0].node = n; descent[0].lnode = NULL;
 443         descent[0].significant[0] = descent[0].significant[1] = NULL;
 444         int dlen = 1;
 445         /* Total value of the sequence. */
 446         struct move_stats seq_value = { .playouts = 0 };
 447
 448         int result;
 449         int pass_limit = (board_size(&b2) - 2) * (board_size(&b2) - 2) / 2;
 450         int passes = is_pass(b->last_move.coord) && b->moves > 0;
 451
 452         /* debug */
 453         int depth = 0;
 454         static char spaces[] = "\0                                                      ";
 455         /* /debug */
 456         if (UDEBUGL(8))
 457                 fprintf(stderr, "--- UCT walk with color %d\n", player_color);
 458
 459         while (!tree_leaf_node(n) && passes < 2) {
 460                 spaces[depth++] = ' '; spaces[depth] = 0;
 461
 462
 463                 /*** Choose a node to descend to: */
 464
 465                 /* Parity is chosen already according to the child color, since
 466                  * it is applied to children. */
 467                 node_color = stone_other(node_color);
 468                 int parity = (node_color == player_color ? 1 : -1);
 469
 470                 assert(dlen < DLEN);
 471                 descent[dlen] = descent[dlen - 1];
 472                 if (u->local_tree && (!descent[dlen].lnode || descent[dlen].node->d >= u->tenuki_d)) {
 473                         /* Start new local sequence. */
 474                         /* Remember that node_color already holds color of the
 475                          * to-be-found child. */
 476                         descent[dlen].lnode = node_color == S_BLACK ? t->ltree_black : t->ltree_white;
 477                 }
 478
 479                 if (!u->random_policy_chance || fast_random(u->random_policy_chance))
 480                         u->policy->descend(u->policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 481                 else
 482                         u->random_policy->descend(u->random_policy, t, &descent[dlen], parity, b2.moves > pass_limit);
 483
 484
 485                 /*** Perform the descent: */
 486
 487                 if (descent[dlen].node->u.playouts >= u->significant_threshold) {
 488                         descent[dlen].significant[node_color - 1] = n;
 489                 }
 490
 491                 seq_value.playouts += descent[dlen].value.playouts;
 492                 seq_value.value += descent[dlen].value.value * descent[dlen].value.playouts;
 493                 n = descent[dlen++].node;
 494                 assert(n == t->root || n->parent);
 495                 if (UDEBUGL(7))
 496                         fprintf(stderr, "%s+-- UCT sent us to [%s:%d] %d,%f\n",
 497                                 spaces, coord2sstr(n->coord, t->board),
 498                                 n->coord, n->u.playouts,
 499                                 tree_node_get_value(t, parity, n->u.value));
 500
 501                 /* Add virtual loss if we need to; this is used to discourage
 502                  * other threads from visiting this node in case of multiple
 503                  * threads doing the tree search. */
 504                 if (u->virtual_loss)
 505                         stats_add_result(&n->u, tree_parity(t, parity) > 0 ? 0 : 1, 1);
 506
 507                 assert(n->coord >= -1);
 508                 if (amaf && !is_pass(n->coord))
 509                         record_amaf_move(amaf, n->coord, node_color);
 510
 511                 struct move m = { n->coord, node_color };
 512                 int res = board_play(&b2, &m);
 513
 514                 if (res < 0 || (!is_pass(m.coord) && !group_at(&b2, m.coord)) /* suicide */
 515                     || b2.superko_violation) {
 516                         if (UDEBUGL(4)) {
 517                                 for (struct tree_node *ni = n; ni; ni = ni->parent)
 518                                         fprintf(stderr, "%s<%"PRIhash"> ", coord2sstr(ni->coord, t->board), ni->hash);
 519                                 fprintf(stderr, "marking invalid %s node %d,%d res %d group %d spk %d\n",
 520                                         stone2str(node_color), coord_x(n->coord,b), coord_y(n->coord,b),
 521                                         res, group_at(&b2, m.coord), b2.superko_violation);
 522                         }
 523                         n->hints |= TREE_HINT_INVALID;
 524                         result = 0;
 525                         goto end;
 526                 }
 527
 528                 if (is_pass(n->coord))
 529                         passes++;
 530                 else
 531                         passes = 0;
 532         }
 533
 534         if (amaf) {
 535                 amaf->game_baselen = amaf->gamelen;
 536                 amaf->record_nakade = u->playout_amaf_nakade;
 537         }
 538
 539         if (t->use_extra_komi && u->dynkomi->persim) {
 540                 b2.komi += round(u->dynkomi->persim(u->dynkomi, &b2, t, n));
 541         }
 542
 543         if (passes >= 2) {
 544                 /* XXX: No dead groups support. */
 545                 float score = board_official_score(&b2, NULL);
 546                 /* Result from black's perspective (no matter who
 547                  * the player; black's perspective is always
 548                  * what the tree stores. */
 549                 result = - (score * 2);
 550
 551                 if (UDEBUGL(5))
 552                         fprintf(stderr, "[%d..%d] %s p-p scoring playout result %d (W %f)\n",
 553                                 player_color, node_color, coord2sstr(n->coord, t->board), result, score);
 554                 if (UDEBUGL(6))
 555                         board_print(&b2, stderr);
 556
 557                 board_ownermap_fill(&u->ownermap, &b2);
 558
 559         } else { // assert(tree_leaf_node(n));
 560                 /* In case of parallel tree search, the assertion might
 561                  * not hold if two threads chew on the same node. */
 562                 result = uct_leaf_node(u, &b2, player_color, amaf, &descent[dlen - 1], t, n, node_color, spaces);
 563         }
 564
 565         if (amaf && u->playout_amaf_cutoff) {
 566                 unsigned int cutoff = amaf->game_baselen;
 567                 cutoff += (amaf->gamelen - amaf->game_baselen) * u->playout_amaf_cutoff / 100;
 568                 /* Now, reconstruct the amaf map. */
 569                 memset(amaf->map, 0, board_size2(&b2) * sizeof(*amaf->map));
 570                 for (unsigned int i = 0; i < cutoff; i++) {
 571                         coord_t coord = amaf->game[i].coord;
 572                         enum stone color = amaf->game[i].color;
 573                         if (amaf->map[coord] == S_NONE || amaf->map[coord] == color) {
 574                                 amaf->map[coord] = color;
 575                         /* Nakade always recorded for in-tree part */
 576                         } else if (amaf->record_nakade || i <= amaf->game_baselen) {
 577                                 amaf_op(amaf->map[n->coord], +);
 578                         }
 579                 }
 580         }
 581
 582         assert(n == t->root || n->parent);
 583         if (result != 0) {
 584                 float rval = scale_value(u, b, result);
 585                 u->policy->update(u->policy, t, n, node_color, player_color, amaf, rval);
 586
 587                 if (t->use_extra_komi) {
 588                         stats_add_result(&u->dynkomi->score, result / 2, 1);
 589                         stats_add_result(&u->dynkomi->value, rval, 1);
 590                 }
 591
 592                 if (u->local_tree && n->parent && !is_pass(n->coord) && dlen > 0) {
 593                         /* Possibly transform the rval appropriately. */
 594                         float expval = seq_value.value / seq_value.playouts;
 595                         rval = stats_temper_value(rval, expval, u->local_tree);
 596
 597                         /* Get the local sequences and record them in ltree. */
 598                         /* We will look for sequence starts in our descent
 599                          * history, then run record_local_sequence() for each
 600                          * found sequence start; record_local_sequence() may
 601                          * pick longer sequences from descent history then,
 602                          * which is expected as it will create new lnodes. */
 603                         enum stone seq_color = player_color;
 604                         /* First move always starts a sequence. */
 605                         record_local_sequence(u, t, descent, dlen, 1, seq_color, rval);
 606                         seq_color = stone_other(seq_color);
 607                         for (int dseqi = 2; dseqi < dlen; dseqi++, seq_color = stone_other(seq_color)) {
 608                                 if (u->local_tree_allseq) {
 609                                         /* We are configured to record all subsequences. */
 610                                         record_local_sequence(u, t, descent, dlen, dseqi, seq_color, rval);
 611                                         continue;
 612                                 }
 613                                 if (descent[dseqi].node->d >= u->tenuki_d) {
 614                                         /* Tenuki! Record the fresh sequence. */
 615                                         record_local_sequence(u, t, descent, dlen, dseqi, seq_color, rval);
 616                                         continue;
 617                                 }
 618                                 if (descent[dseqi].lnode && !descent[dseqi].lnode) {
 619                                         /* Record result for in-descent picked sequence. */
 620                                         record_local_sequence(u, t, descent, dlen, dseqi, seq_color, rval);
 621                                         continue;
 622                                 }
 623                         }
 624                 }
 625         }
 626
 627 end:
 628         /* We need to undo the virtual loss we added during descend. */
 629         if (u->virtual_loss) {
 630                 int parity = (node_color == player_color ? 1 : -1);
 631                 for (; n->parent; n = n->parent) {
 632                         stats_rm_result(&n->u, tree_parity(t, parity) > 0 ? 0 : 1, 1);
 633                         parity = -parity;
 634                 }
 635         }
 636
 637         if (amaf) {
 638                 free(amaf->map - 1);
 639                 free(amaf);
 640         }
 641         board_done_noalloc(&b2);
 642         return result;
 643 }
 644
 645 int
 646 uct_playouts(struct uct *u, struct board *b, enum stone color, struct tree *t, struct time_info *ti)
 647 {
 648         int i;
 649         if (ti && ti->dim == TD_GAMES) {
 650                 for (i = 0; t->root->u.playouts <= ti->len.games; i++)
 651                         uct_playout(u, b, color, t);
 652         } else {
 653                 for (i = 0; !uct_halt; i++)
 654                         uct_playout(u, b, color, t);
 655         }
 656         return i;
 657 }