tactics.c

   1 #include <assert.h>
   2 #include <stdio.h>
   3 #include <stdlib.h>
   4
   5 #define DEBUG
   6 #include "board.h"
   7 #include "debug.h"
   8 #include "tactics.h"
   9
  10
  11 struct selfatari_state {
  12         int groupcts[S_MAX];
  13         group_t groupids[S_MAX][4];
  14
  15         /* This is set if this move puts a group out of _all_
  16          * liberties; we need to watch out for snapback then. */
  17         bool friend_has_no_libs;
  18         /* We may have one liberty, but be looking for one more.
  19          * In that case, @needs_more_lib is id of group
  20          * already providing one, don't consider it again. */
  21         group_t needs_more_lib;
  22         /* ID of the first liberty, providing it again is not
  23          * interesting. */
  24         coord_t needs_more_lib_except;
  25 };
  26
  27 static int
  28 examine_friendly_groups(struct board *b, enum stone color, coord_t to, struct selfatari_state *s)
  29 {
  30         for (int i = 0; i < s->groupcts[color]; i++) {
  31                 /* We can escape by connecting to this group if it's
  32                  * not in atari. */
  33                 group_t g = s->groupids[color][i];
  34
  35                 if (board_group_info(b, g).libs == 1) {
  36                         if (!s->needs_more_lib)
  37                                 s->friend_has_no_libs = true;
  38                         // or we already have a friend with 1 lib
  39                         continue;
  40                 }
  41
  42                 /* Could we self-atari the group here? */
  43                 if (board_group_info(b, g).libs > 2)
  44                         return false;
  45
  46                 /* We need to have another liberty, and
  47                  * it must not be the other liberty of
  48                  * the group. */
  49                 int lib2 = board_group_other_lib(b, g, to);
  50                 /* Maybe we already looked at another
  51                  * group providing one liberty? */
  52                 if (s->needs_more_lib && s->needs_more_lib != g
  53                     && s->needs_more_lib_except != lib2)
  54                         return false;
  55
  56                 /* Can we get the liberty locally? */
  57                 /* Yes if we are route to more liberties... */
  58                 if (s->groupcts[S_NONE] > 1)
  59                         return false;
  60                 /* ...or one liberty, but not lib2. */
  61                 if (s->groupcts[S_NONE] > 0
  62                     && !coord_is_adjecent(lib2, to, b))
  63                         return false;
  64
  65                 /* ...ok, then we can still contribute a liberty
  66                  * later by capturing something. */
  67                 s->needs_more_lib = g;
  68                 s->needs_more_lib_except = lib2;
  69                 s->friend_has_no_libs = false;
  70         }
  71
  72         return -1;
  73 }
  74
  75 static int
  76 examine_enemy_groups(struct board *b, enum stone color, coord_t to, struct selfatari_state *s)
  77 {
  78         /* We may be able to gain a liberty by capturing this group. */
  79         group_t can_capture = 0;
  80
  81         /* Examine enemy groups: */
  82         for (int i = 0; i < s->groupcts[stone_other(color)]; i++) {
  83                 /* We can escape by capturing this group if it's in atari. */
  84                 group_t g = s->groupids[stone_other(color)][i];
  85                 if (board_group_info(b, g).libs > 1)
  86                         continue;
  87
  88                 /* But we need to get to at least two liberties by this;
  89                  * we already have one outside liberty, or the group is
  90                  * more than 1 stone (in that case, capturing is always
  91                  * nice!). */
  92                 if (s->groupcts[S_NONE] > 0 || !group_is_onestone(b, g))
  93                         return false;
  94                 /* ...or, it's a ko stone, */
  95                 if (neighbor_count_at(b, g, color) + neighbor_count_at(b, g, S_OFFBOARD) == 3) {
  96                         /* and we don't have a group to save: then, just taking
  97                          * single stone means snapback! */
  98                         if (!s->friend_has_no_libs)
  99                                 return false;
 100                 }
 101                 /* ...or, we already have one indirect liberty provided
 102                  * by another group. */
 103                 if (s->needs_more_lib || (can_capture && can_capture != g))
 104                         return false;
 105                 can_capture = g;
 106
 107         }
 108
 109         if (DEBUGL(6))
 110                 fprintf(stderr, "no cap group\n");
 111
 112         if (!s->needs_more_lib && !can_capture && !s->groupcts[S_NONE]) {
 113                 /* We have no hope for more fancy tactics - this move is simply
 114                  * a suicide, not even a self-atari. */
 115                 if (DEBUGL(6))
 116                         fprintf(stderr, "suicide\n");
 117                 return true;
 118         }
 119         /* XXX: I wonder if it makes sense to continue if we actually
 120          * just !s->needs_more_lib. */
 121
 122         return -1;
 123 }
 124
 125 static int
 126 setup_nakade_or_snapback(struct board *b, enum stone color, coord_t to, struct selfatari_state *s)
 127 {
 128         /* There is another possibility - we can self-atari if it is
 129          * a nakade: we put an enemy group in atari from the inside. */
 130         /* This branch also allows eyes falsification:
 131          * O O O . .  (This is different from throw-in to false eye
 132          * X X O O .  checked below in that there is no X stone at the
 133          * X . X O .  right of the star point in this diagram.)
 134          * X X X O O
 135          * X O * . . */
 136         /* TODO: Allow to only nakade if the created shape is dead
 137          * (http://senseis.xmp.net/?Nakade). */
 138
 139         /* This branch also covers snapback, which is kind of special
 140          * nakade case. ;-) */
 141         for (int i = 0; i < s->groupcts[stone_other(color)]; i++) {
 142                 group_t g = s->groupids[stone_other(color)][i];
 143                 if (board_group_info(b, g).libs != 2)
 144                         goto next_group;
 145                 /* Simple check not to re-examine the same group. */
 146                 if (i > 0 && s->groupids[stone_other(color)][i] == s->groupids[stone_other(color)][i - 1])
 147                         continue;
 148
 149                 /* We must make sure the other liberty of that group:
 150                  * (i) is an internal liberty
 151                  * (ii) filling it to capture our group will not gain
 152                  * safety */
 153
 154                 /* Let's look at neighbors of the other liberty: */
 155                 int lib2 = board_group_other_lib(b, g, to);
 156                 foreach_neighbor(b, lib2, {
 157                         /* This neighbor of course does not contribute
 158                          * anything to the enemy. */
 159                         if (board_at(b, c) == S_OFFBOARD)
 160                                 continue;
 161
 162                         /* If the other liberty has empty neighbor,
 163                          * it must be the original liberty; otherwise,
 164                          * since the whole group has only 2 liberties,
 165                          * the other liberty may not be internal and
 166                          * we are nakade'ing eyeless group from outside,
 167                          * which is stupid. */
 168                         if (board_at(b, c) == S_NONE) {
 169                                 if (c == to)
 170                                         continue;
 171                                 else
 172                                         goto next_group;
 173                         }
 174
 175                         int g2 = group_at(b, c);
 176                         /* If the neighbor is of our color, it must
 177                          * be also a 2-lib group. If it is more,
 178                          * we CERTAINLY want that liberty to be played
 179                          * first, what if it is an alive group? If it
 180                          * is in atari, we want to extend from it to
 181                          * prevent eye-making capture. However, if it
 182                          * is 2-lib, it is selfatari connecting two
 183                          * nakade'ing groups! */
 184                         /* X X X X  We will not allow play on 'a',
 185                          * X X a X  because 'b' would capture two
 186                          * X O b X  different groups, forming two
 187                          * X X X X  eyes. */
 188                         if (board_at(b, c) == color) {
 189                                 if (board_group_info(b, group_at(b, c)).libs == 2)
 190                                         continue;
 191                                 goto next_group;
 192                         }
 193
 194                         /* The neighbor is enemy color. It's ok if
 195                          * it's still the same group or this is its
 196                          * only liberty. */
 197                         if (g == g2 || board_group_info(b, g2).libs == 1)
 198                                 continue;
 199                         /* Otherwise, it must have the exact same
 200                          * liberties as the original enemy group. */
 201                         if (board_group_info(b, g2).libs == 2
 202                             && (board_group_info(b, g2).lib[0] == to
 203                                 || board_group_info(b, g2).lib[1] == to))
 204                                 continue;
 205
 206                         goto next_group;
 207                 });
 208
 209                 /* Now, we must distinguish between nakade and eye
 210                  * falsification; we must not falsify an eye by more
 211                  * than two stones. */
 212                 if (s->groupcts[color] < 1 ||
 213                     (s->groupcts[color] == 1 && group_is_onestone(b, s->groupids[color][0])))
 214                         return false;
 215
 216                 /* We would create more than 2-stone group; in that
 217                  * case, the liberty of our result must be lib2,
 218                  * indicating this really is a nakade. */
 219                 for (int j = 0; j < s->groupcts[color]; j++) {
 220                         group_t g2 = s->groupids[color][j];
 221                         assert(board_group_info(b, g2).libs <= 2);
 222                         if (board_group_info(b, g2).libs == 2) {
 223                                 if (board_group_info(b, g2).lib[0] != lib2
 224                                     && board_group_info(b, g2).lib[1] != lib2)
 225                                         goto next_group;
 226                         } else {
 227                                 assert(board_group_info(b, g2).lib[0] == to);
 228                         }
 229                 }
 230
 231                 return false;
 232 next_group:
 233                 /* Unless we are dealing with snapback setup, we don't need to look
 234                  * further. */
 235                 if (s->groupcts[color])
 236                         return -1;
 237         }
 238
 239         return -1;
 240 }
 241
 242 static int
 243 check_throwin(struct board *b, enum stone color, coord_t to, struct selfatari_state *s)
 244 {
 245         /* We can be throwing-in to false eye:
 246          * X X X O X X X O X X X X X
 247          * X . * X * O . X * O O . X
 248          * # # # # # # # # # # # # # */
 249         /* We cannot sensibly throw-in into a corner. */
 250         if (neighbor_count_at(b, to, S_OFFBOARD) < 2
 251             && neighbor_count_at(b, to, stone_other(color))
 252                + neighbor_count_at(b, to, S_OFFBOARD) == 3
 253             && board_is_false_eyelike(b, to, stone_other(color))) {
 254                 assert(s->groupcts[color] <= 1);
 255                 /* Single-stone throw-in may be ok... */
 256                 if (s->groupcts[color] == 0) {
 257                         /* O X .  There is one problem - when it's
 258                          * . * X  actually not a throw-in!
 259                          * # # #  */
 260                         foreach_neighbor(b, to, {
 261                                 if (board_at(b, c) == S_NONE) {
 262                                         /* Is the empty neighbor an escape path? */
 263                                         /* (Note that one S_NONE neighbor is already @to.) */
 264                                         if (neighbor_count_at(b, c, stone_other(color))
 265                                             + neighbor_count_at(b, c, S_OFFBOARD) < 2)
 266                                                 return -1;
 267                                 }
 268                         });
 269                         return false;
 270                 }
 271
 272                 /* Multi-stone throwin...? */
 273                 assert(s->groupcts[color] == 1);
 274                 group_t g = s->groupids[color][0];
 275
 276                 assert(board_group_info(b, g).libs <= 2);
 277                 /* Suicide is definitely NOT ok, no matter what else
 278                  * we could test. */
 279                 if (board_group_info(b, g).libs == 1)
 280                         return true;
 281
 282                 /* In that case, we must be connected to at most one stone,
 283                  * or throwin will not destroy any eyes. */
 284                 if (group_is_onestone(b, g))
 285                         return false;
 286         }
 287         return -1;
 288 }
 289
 290 bool
 291 is_bad_selfatari_slow(struct board *b, enum stone color, coord_t to)
 292 {
 293         if (DEBUGL(5))
 294                 fprintf(stderr, "sar check %s %s\n", stone2str(color), coord2sstr(to, b));
 295         /* Assess if we actually gain any liberties by this escape route.
 296          * Note that this is not 100% as we cannot check whether we are
 297          * connecting out or just to ourselves. */
 298
 299         struct selfatari_state s;
 300         memset(&s, 0, sizeof(s));
 301         int d;
 302
 303         foreach_neighbor(b, to, {
 304                 enum stone color = board_at(b, c);
 305                 s.groupids[color][s.groupcts[color]++] = group_at(b, c);
 306         });
 307
 308         /* We have shortage of liberties; that's the point. */
 309         assert(s.groupcts[S_NONE] <= 1);
 310
 311         d = examine_friendly_groups(b, color, to, &s);
 312         if (d >= 0)
 313                 return d;
 314
 315         if (DEBUGL(6))
 316                 fprintf(stderr, "no friendly group\n");
 317
 318         d = examine_enemy_groups(b, color, to, &s);
 319         if (d >= 0)
 320                 return d;
 321
 322         if (DEBUGL(6))
 323                 fprintf(stderr, "no escape\n");
 324
 325         d = setup_nakade_or_snapback(b, color, to, &s);
 326         if (d >= 0)
 327                 return d;
 328
 329         if (DEBUGL(6))
 330                 fprintf(stderr, "no nakade group\n");
 331
 332         d = check_throwin(b, color, to, &s);
 333         if (d >= 0)
 334                 return d;
 335
 336         if (DEBUGL(6))
 337                 fprintf(stderr, "no throw-in group\n");
 338
 339         /* No way to pull out, no way to connect out. This really
 340          * is a bad self-atari! */
 341         return true;
 342 }
 343
 344
 345 /* Is this ladder breaker friendly for the one who catches ladder. */
 346 static bool
 347 ladder_catcher(struct board *b, int x, int y, enum stone laddered)
 348 {
 349         enum stone breaker = board_atxy(b, x, y);
 350         return breaker == stone_other(laddered) || breaker == S_OFFBOARD;
 351 }
 352
 353 bool
 354 is_border_ladder(struct board *b, coord_t coord, enum stone lcolor)
 355 {
 356         int x = coord_x(coord, b), y = coord_y(coord, b);
 357
 358         if (DEBUGL(5))
 359                 fprintf(stderr, "border ladder\n");
 360         /* Direction along border; xd is horiz. border, yd vertical. */
 361         int xd = 0, yd = 0;
 362         if (board_atxy(b, x + 1, y) == S_OFFBOARD || board_atxy(b, x - 1, y) == S_OFFBOARD)
 363                 yd = 1;
 364         else
 365                 xd = 1;
 366         /* Direction from the border; -1 is above/left, 1 is below/right. */
 367         int dd = (board_atxy(b, x + yd, y + xd) == S_OFFBOARD) ? 1 : -1;
 368         if (DEBUGL(6))
 369                 fprintf(stderr, "xd %d yd %d dd %d\n", xd, yd, dd);
 370         /* | ? ?
 371          * | . O #
 372          * | c X #
 373          * | . O #
 374          * | ? ?   */
 375         /* This is normally caught, unless we have friends both above
 376          * and below... */
 377         if (board_atxy(b, x + xd * 2, y + yd * 2) == lcolor
 378             && board_atxy(b, x - xd * 2, y - yd * 2) == lcolor)
 379                 return false;
 380         /* ...or can't block where we need because of shortage
 381          * of liberties. */
 382         int libs1 = board_group_info(b, group_atxy(b, x + xd - yd * dd, y + yd - xd * dd)).libs;
 383         int libs2 = board_group_info(b, group_atxy(b, x - xd - yd * dd, y - yd - xd * dd)).libs;
 384         if (DEBUGL(6))
 385                 fprintf(stderr, "libs1 %d libs2 %d\n", libs1, libs2);
 386         if (libs1 < 2 && libs2 < 2)
 387                 return false;
 388         if (board_atxy(b, x + xd * 2, y + yd * 2) == lcolor && libs1 < 3)
 389                 return false;
 390         if (board_atxy(b, x - xd * 2, y - yd * 2) == lcolor && libs2 < 3)
 391                 return false;
 392         return true;
 393 }
 394
 395 /* This is very trivial and gets a lot of corner cases wrong.
 396  * We need this to be just very fast. One important point is
 397  * that we sometimes might not notice a ladder but if we do,
 398  * it should always work; thus we can use this for strong
 399  * negative hinting safely. */
 400 bool
 401 is_middle_ladder(struct board *b, coord_t coord, enum stone lcolor)
 402 {
 403         int x = coord_x(coord, b), y = coord_y(coord, b);
 404
 405         /* Figure out the ladder direction */
 406         int xd, yd;
 407         xd = board_atxy(b, x + 1, y) == S_NONE ? 1 : board_atxy(b, x - 1, y) == S_NONE ? -1 : 0;
 408         yd = board_atxy(b, x, y + 1) == S_NONE ? 1 : board_atxy(b, x, y - 1) == S_NONE ? -1 : 0;
 409
 410         if (!xd || !yd) {
 411                 if (DEBUGL(5))
 412                         fprintf(stderr, "no ladder, too little space; self-atari?\n");
 413                 return false;
 414         }
 415
 416         /* For given (xd,yd), we have two possibilities where to move
 417          * next. Consider (-1,-1):
 418          * n X .   n c X
 419          * c O X   X O #
 420          * X # #   . X #
 421          */
 422         bool horiz_first = ladder_catcher(b, x, y - yd, lcolor); // left case
 423         bool vert_first = ladder_catcher(b, x - xd, y, lcolor); // right case
 424
 425         /* We don't have to look at the other 'X' in the position - if it
 426          * wouldn't be there, the group wouldn't be in atari. */
 427
 428         /* We do only tight ladders, not loose ladders. Furthermore,
 429          * the ladders need to be simple:
 430          * . X .             . . X
 431          * c O X supported   . c O unsupported
 432          * X # #             X O #
 433          */
 434         assert(!(horiz_first && vert_first));
 435         if (!horiz_first && !vert_first) {
 436                 /* TODO: In case of basic non-simple ladder, play out both variants. */
 437                 if (DEBUGL(5))
 438                         fprintf(stderr, "non-simple ladder\n");
 439                 return false;
 440         }
 441
 442         /* We do that below for further moves, but now initially - check
 443          * that at 'c', we aren't putting any of the catching stones
 444          * in atari. */
 445 #if 1 // this might be broken?
 446 #define check_catcher_danger(b, x_, y_) do { \
 447         if (board_atxy(b, (x_), (y_)) != S_OFFBOARD \
 448             && board_group_info(b, group_atxy(b, (x_), (y_))).libs <= 2) { \
 449                 if (DEBUGL(5)) \
 450                         fprintf(stderr, "ladder failed - atari at the beginning\n"); \
 451                 return false; \
 452         } } while (0)
 453
 454         if (horiz_first) {
 455                 check_catcher_danger(b, x, y - yd);
 456                 check_catcher_danger(b, x - xd, y + yd);
 457         } else {
 458                 check_catcher_danger(b, x - xd, y);
 459                 check_catcher_danger(b, x + xd, y - yd);
 460         }
 461 #undef check_catcher_danger
 462 #endif
 463
 464 #define ladder_check(xd1_, yd1_, xd2_, yd2_, xd3_, yd3_)        \
 465         if (board_atxy(b, x, y) != S_NONE) { \
 466                 /* Did we hit a stone when playing out ladder? */ \
 467                 if (ladder_catcher(b, x, y, lcolor)) \
 468                         return true; /* ladder works */ \
 469                 if (board_group_info(b, group_atxy(b, x, y)).lib[0] > 0) \
 470                         return false; /* friend that's not in atari himself */ \
 471         } else { \
 472                 /* No. So we are at new position. \
 473                  * We need to check indirect ladder breakers. */ \
 474                 /* . 2 x 3 . \
 475                  * . x o O 1 <- only at O we can check for o at 2 \
 476                  * x o o x .    otherwise x at O would be still deadly \
 477                  * o o x . . \
 478                  * We check for o and x at 1, these are vital. \
 479                  * We check only for o at 2; x at 2 would mean we \
 480                  * need to fork (one step earlier). */ \
 481                 coord_t c1 = coord_xy(b, x + (xd1_), y + (yd1_)); \
 482                 enum stone s1 = board_at(b, c1); \
 483                 if (s1 == lcolor) return false; \
 484                 if (s1 == stone_other(lcolor)) { \
 485                         /* One more thing - if the position at 3 is \
 486                          * friendly and safe, we escaped anyway! */ \
 487                         coord_t c3 = coord_xy(b, x + (xd3_), y + (yd3_)); \
 488                         return board_at(b, c3) != lcolor \
 489                                || board_group_info(b, group_at(b, c3)).libs < 2; \
 490                 } \
 491                 enum stone s2 = board_atxy(b, x + (xd2_), y + (yd2_)); \
 492                 if (s2 == lcolor) return false; \
 493                 /* Then, can X actually "play" 1 in the ladder? */ \
 494                 if (neighbor_count_at(b, c1, lcolor) + neighbor_count_at(b, c1, S_OFFBOARD) >= 2) \
 495                         return false; /* It would be self-atari! */ \
 496         }
 497 #define ladder_horiz    do { if (DEBUGL(6)) fprintf(stderr, "%d,%d horiz step (%d,%d)\n", x, y, xd, yd); x += xd; ladder_check(xd, 0, -2 * xd, yd, 0, yd); } while (0)
 498 #define ladder_vert     do { if (DEBUGL(6)) fprintf(stderr, "%d,%d vert step of (%d,%d)\n", x, y, xd, yd); y += yd; ladder_check(0, yd, xd, -2 * yd, xd, 0); } while (0)
 499
 500         if (ladder_catcher(b, x - xd, y, lcolor))
 501                 ladder_horiz;
 502         do {
 503                 ladder_vert;
 504                 ladder_horiz;
 505         } while (1);
 506 }
 507
 508
 509 bool
 510 board_stone_radar(struct board *b, coord_t coord, int distance)
 511 {
 512         int bounds[4] = {
 513                 coord_x(coord, b) - distance,
 514                 coord_y(coord, b) - distance,
 515                 coord_x(coord, b) + distance,
 516                 coord_y(coord, b) + distance
 517         };
 518         for (int i = 0; i < 4; i++)
 519                 if (bounds[i] < 1)
 520                         bounds[i] = 1;
 521                 else if (bounds[i] > board_size(b) - 2)
 522                         bounds[i] = board_size(b) - 2;
 523         for (int x = bounds[0]; x <= bounds[2]; x++)
 524                 for (int y = bounds[1]; y <= bounds[3]; y++)
 525                         if (board_atxy(b, x, y) != S_NONE) {
 526                                 /* fprintf(stderr, "radar %d,%d,%d: %d,%d (%d)\n",
 527                                         coord_x(coord, b), coord_y(coord, b),
 528                                         distance, x, y, board_atxy(b, x, y)); */
 529                                 return true;
 530                         }
 531         return false;
 532 }
 533
 534
 535 void
 536 cfg_distances(struct board *b, coord_t start, int *distances, int maxdist)
 537 {
 538         /* Queue for d+1 spots; no two spots of the same group
 539          * should appear in the queue. */
 540 #define qinc(x) (x = ((x + 1) >= board_size2(b) ? ((x) + 1 - board_size2(b)) : (x) + 1))
 541         coord_t queue[board_size2(b)]; int qstart = 0, qstop = 0;
 542
 543         foreach_point(b) {
 544                 distances[c] = board_at(b, c) == S_OFFBOARD ? maxdist + 1 : -1;
 545         } foreach_point_end;
 546
 547         queue[qstop++] = start;
 548         for (int d = 0; d <= maxdist; d++) {
 549                 /* Process queued moves, while setting the queue
 550                  * for new wave. */
 551                 int qa = qstart, qb = qstop;
 552                 qstart = qstop;
 553                 for (int q = qa; q < qb; qinc(q)) {
 554 #define cfg_one(coord, grp) do {\
 555         distances[coord] = d; \
 556         foreach_neighbor (b, coord, { \
 557                 if (distances[c] < 0 && (!grp || group_at(b, coord) != grp)) { \
 558                         queue[qstop] = c; \
 559                         qinc(qstop); \
 560                 } \
 561         }); \
 562 } while (0)
 563                         coord_t cq = queue[q];
 564                         if (distances[cq] >= 0)
 565                                 continue; /* We already looked here. */
 566                         if (board_at(b, cq) == S_NONE) {
 567                                 cfg_one(cq, 0);
 568                         } else {
 569                                 group_t g = group_at(b, cq);
 570                                 foreach_in_group(b, g) {
 571                                         cfg_one(c, g);
 572                                 } foreach_in_group_end;
 573                         }
 574 #undef cfg_one
 575                 }
 576         }
 577
 578         foreach_point(b) {
 579                 if (distances[c] < 0)
 580                         distances[c] = maxdist + 1;
 581         } foreach_point_end;
 582 }
 583
 584
 585 float
 586 board_effective_handicap(struct board *b, int first_move_value)
 587 {
 588         /* This can happen if the opponent passes during handicap
 589          * placing phase. */
 590         // assert(b->handicap != 1);
 591         return (b->handicap ? b->handicap : 1) * first_move_value + 0.5 - b->komi;
 592 }
 593
 594
 595 bool
 596 pass_is_safe(struct board *b, enum stone color, struct move_queue *mq)
 597 {
 598         float score = board_official_score(b, mq);
 599         if (color == S_BLACK)
 600                 score = -score;
 601         //fprintf(stderr, "%d score %f\n", color, score);
 602         return (score > 0);
 603 }
 604
 605
 606 /* On average 25% of points remain empty at the end of a game */
 607 #define EXPECTED_FINAL_EMPTY_PERCENT 25
 608
 609 /* Returns estimated number of remaining moves for one player until end of game. */
 610 int
 611 board_estimated_moves_left(struct board *b)
 612 {
 613         int total_points = (board_size(b)-2)*(board_size(b)-2);
 614         int moves_left = (b->flen - total_points*EXPECTED_FINAL_EMPTY_PERCENT/100)/2;
 615         return moves_left > MIN_MOVES_LEFT ? moves_left : MIN_MOVES_LEFT;
 616 }