board.h

   1 /* probdist.h must be included before the include goard since we require
   2  * proper including order. */
   3 #include "probdist.h"
   4
   5 #ifndef PACHI_BOARD_H
   6 #define PACHI_BOARD_H
   7
   8 #include <inttypes.h>
   9 #include <stdbool.h>
  10 #include <stdint.h>
  11
  12 #include "util.h"
  13 #include "stone.h"
  14 #include "move.h"
  15
  16 struct fbook;
  17
  18
  19 /* Maximum supported board size. (Without the S_OFFBOARD edges.) */
  20 #define BOARD_MAX_SIZE 19
  21
  22
  23 /* The board implementation has bunch of optional features.
  24  * Turn them on below: */
  25
  26 #define WANT_BOARD_C // capturable groups queue
  27
  28 //#define BOARD_SIZE 9 // constant board size, allows better optimization
  29
  30 //#define BOARD_SPATHASH // incremental patternsp.h hashes
  31 #define BOARD_SPATHASH_MAXD 3 // maximal diameter
  32
  33 #define BOARD_PAT3 // incremental 3x3 pattern codes
  34
  35 //#define BOARD_TRAITS 1 // incremental point traits (see struct btraits)
  36 //#define BOARD_TRAIT_SAFE 1 // include btraits.safe (rather expensive, unused)
  37 //#define BOARD_TRAIT_SAFE 2 // include btraits.safe based on full is_bad_selfatari()
  38
  39
  40 #define BOARD_MAX_MOVES (BOARD_MAX_SIZE * BOARD_MAX_SIZE)
  41 #define BOARD_MAX_GROUPS (BOARD_MAX_SIZE * BOARD_MAX_SIZE / 2)
  42
  43 enum e_sym {
  44                 SYM_FULL,
  45                 SYM_DIAG_UP,
  46                 SYM_DIAG_DOWN,
  47                 SYM_HORIZ,
  48                 SYM_VERT,
  49                 SYM_NONE
  50 };
  51
  52
  53 /* Some engines might normalize their reading and skip symmetrical
  54  * moves. We will tell them how can they do it. */
  55 struct board_symmetry {
  56         /* Playground is in this rectangle. */
  57         int x1, x2, y1, y2;
  58         /* d ==  0: Full rectangle
  59          * d ==  1: Top triangle */
  60         int d;
  61         /* General symmetry type. */
  62         /* Note that the above is redundant to this, but just provided
  63          * for easier usage. */
  64         enum e_sym type;
  65 };
  66
  67
  68 typedef uint64_t hash_t;
  69 #define PRIhash PRIx64
  70
  71 /* XXX: This really belongs in pattern3.h, unfortunately that would mean
  72  * a dependency hell. */
  73 typedef uint32_t hash3_t; // 3x3 pattern hash
  74
  75
  76 /* Note that "group" is only chain of stones that is solidly
  77  * connected for us. */
  78 typedef coord_t group_t;
  79
  80 struct group {
  81         /* We keep track of only up to GROUP_KEEP_LIBS; over that, we
  82          * don't care. */
  83         /* _Combination_ of these two values can make some difference
  84          * in performance - fine-tune. */
  85 #define GROUP_KEEP_LIBS 10
  86         // refill lib[] only when we hit this; this must be at least 2!
  87         // Moggy requires at least 3 - see below for semantic impact.
  88 #define GROUP_REFILL_LIBS 5
  89         coord_t lib[GROUP_KEEP_LIBS];
  90         /* libs is only LOWER BOUND for the number of real liberties!!!
  91          * It denotes only number of items in lib[], thus you can rely
  92          * on it to store real liberties only up to <= GROUP_REFILL_LIBS. */
  93         int libs;
  94 };
  95
  96 struct neighbor_colors {
  97         char colors[S_MAX];
  98 };
  99
 100
 101 /* Point traits bitmap; we update this information incrementally,
 102  * it can be used e.g. for fast pattern features matching. */
 103 struct btraits {
 104         /* Number of neighbors we can capture. 0=this move is
 105          * not capturing, 1..4=this many neighbors we can capture
 106          * (can be multiple neighbors of same group). */
 107         unsigned cap:3;
 108         /* Number of 1-stone neighbors we can capture. */
 109         unsigned cap1:3;
 110 #ifdef BOARD_TRAIT_SAFE
 111         /* Whether it is SAFE to play here. This is essentially just
 112          * cached result of board_safe_to_play(). (Of course the concept
 113          * of "safety" is not perfect here, but it's the cheapest
 114          * reasonable thing we can do.) */
 115         bool safe:1;
 116 #endif
 117         /* Whether we need to re-compute this coordinate; used to
 118          * weed out duplicates. Maintained only for S_BLACK. */
 119         bool dirty:1;
 120 };
 121
 122
 123 /* You should treat this struct as read-only. Always call functions below if
 124  * you want to change it. */
 125
 126 struct board {
 127         int size; /* Including S_OFFBOARD margin - see below. */
 128         int size2; /* size^2 */
 129         int bits2; /* ceiling(log2(size2)) */
 130         int captures[S_MAX];
 131         floating_t komi;
 132         int handicap;
 133         /* The ruleset is currently almost never taken into account;
 134          * the board implementation is basically Chinese rules (handicap
 135          * stones compensation) w/ suicide (or you can look at it as
 136          * New Zealand w/o handi stones compensation), while the engine
 137          * enforces no-suicide, making for real Chinese rules.
 138          * However, we accept suicide moves by the opponent, so we
 139          * should work with rules allowing suicide, just not taking
 140          * full advantage of them. */
 141         enum go_ruleset {
 142                 RULES_CHINESE, /* default value */
 143                 RULES_AGA,
 144                 RULES_NEW_ZEALAND,
 145                 RULES_JAPANESE,
 146                 RULES_STONES_ONLY, /* do not count eyes */
 147                 /* http://home.snafu.de/jasiek/siming.html */
 148                 /* Simplified ING rules - RULES_CHINESE with handicaps
 149                  * counting as points and pass stones. Also should
 150                  * allow suicide, but Pachi will never suicide
 151                  * nevertheless. */
 152                 /* XXX: I couldn't find the point about pass stones
 153                  * in the rule text, but it is Robert Jasiek's
 154                  * interpretation of them... These rules were
 155                  * used e.g. at the EGC2012 13x13 tournament.
 156                  * They are not supported by KGS. */
 157                 RULES_SIMING,
 158         } rules;
 159
 160         char *fbookfile;
 161         struct fbook *fbook;
 162
 163         /* Iterator offsets for foreach_neighbor*() */
 164         int nei8[8], dnei[4];
 165
 166         int moves;
 167         struct move last_move;
 168         struct move last_move2; /* second-to-last move */
 169         struct move last_move3; /* just before last_move2, only set if last_move is pass */
 170         struct move last_move4; /* just before last_move3, only set if last_move & last_move2 are pass */
 171         /* Whether we tried to add a hash twice; board_play*() can
 172          * set this, but it will still carry out the move as well! */
 173         bool superko_violation;
 174
 175         /* The following two structures are goban maps and are indexed by
 176          * coord.pos. The map is surrounded by a one-point margin from
 177          * S_OFFBOARD stones in order to speed up some internal loops.
 178          * Some of the foreach iterators below might include these points;
 179          * you need to handle them yourselves, if you need to. */
 180
 181         /* Stones played on the board */
 182         enum stone *b; /* enum stone */
 183         /* Group id the stones are part of; 0 == no group */
 184         group_t *g;
 185         /* Positions of next stones in the stone group; 0 == last stone */
 186         coord_t *p;
 187         /* Neighboring colors; numbers of neighbors of index color */
 188         struct neighbor_colors *n;
 189         /* Zobrist hash for each position */
 190         hash_t *h;
 191 #ifdef BOARD_SPATHASH
 192         /* For spatial hashes, we use only 24 bits. */
 193         /* [0] is d==1, we don't keep hash for d==0. */
 194         /* We keep hashes for black-to-play ([][0]) and white-to-play
 195          * ([][1], reversed stone colors since we match all patterns as
 196          * black-to-play). */
 197         uint32_t (*spathash)[BOARD_SPATHASH_MAXD][2];
 198 #endif
 199 #ifdef BOARD_PAT3
 200         /* 3x3 pattern code for each position; see pattern3.h for encoding
 201          * specification. The information is only valid for empty points. */
 202         hash3_t *pat3;
 203 #endif
 204 #ifdef BOARD_TRAITS
 205         /* Incrementally matched point traits information, black-to-play
 206          * ([][0]) and white-to-play ([][1]). */
 207         /* The information is only valid for empty points. */
 208         struct btraits (*t)[2];
 209 #endif
 210         /* Cached information on x-y coordinates so that we avoid division. */
 211         uint8_t (*coord)[2];
 212
 213         /* Group information - indexed by gid (which is coord of base group stone) */
 214         struct group *gi;
 215
 216         /* Positions of free positions - queue (not map) */
 217         /* Note that free position here is any valid move; including single-point eyes!
 218          * However, pass is not included. */
 219         coord_t *f; int flen;
 220
 221 #ifdef WANT_BOARD_C
 222         /* Queue of capturable groups */
 223         group_t *c; int clen;
 224 #endif
 225
 226 #ifdef BOARD_TRAITS
 227         /* Queue of positions that need their traits updated */
 228         coord_t *tq; int tqlen;
 229 #endif
 230
 231         /* Symmetry information */
 232         struct board_symmetry symmetry;
 233
 234         /* Last ko played on the board. */
 235         struct move last_ko;
 236         int last_ko_age;
 237
 238         /* Basic ko check */
 239         struct move ko;
 240
 241         /* Engine-specific state; persistent through board development,
 242          * is reset only at clear_board. */
 243         void *es;
 244
 245         /* Playout-specific state; persistent through board development,
 246          * but its lifetime is maintained in play_random_game(); it should
 247          * not be set outside of it. */
 248         void *ps;
 249
 250
 251         /* --- PRIVATE DATA --- */
 252
 253         /* For superko check: */
 254
 255         /* Board "history" - hashes encountered. Size of the hash should be
 256          * >> board_size^2. */
 257 #define history_hash_bits 12
 258 #define history_hash_mask ((1 << history_hash_bits) - 1)
 259 #define history_hash_prev(i) ((i - 1) & history_hash_mask)
 260 #define history_hash_next(i) ((i + 1) & history_hash_mask)
 261         hash_t history_hash[1 << history_hash_bits];
 262         /* Hash of current board position. */
 263         hash_t hash;
 264         /* Hash of current board position quadrants. */
 265         hash_t qhash[4];
 266 };
 267
 268 #ifdef BOARD_SIZE
 269 /* Avoid unused variable warnings */
 270 #define board_size(b_) (((b_) == (b_)) ? BOARD_SIZE + 2 : 0)
 271 #define board_size2(b_) (board_size(b_) * board_size(b_))
 272 #define real_board_size(b_)  (((b_) == (b_)) ? BOARD_SIZE : 0)
 273 #else
 274 #define board_size(b_) ((b_)->size)
 275 #define board_size2(b_) ((b_)->size2)
 276 #define real_board_size(b_) ((b_)->size - 2)
 277 #endif
 278
 279 /* This is a shortcut for taking different action on smaller
 280  * and large boards (e.g. picking different variable defaults).
 281  * This is of course less optimal than fine-tuning dependency
 282  * function of values on board size, but that is difficult and
 283  * possibly not very rewarding if you are interested just in
 284  * 9x9 and 19x19. */
 285 #define board_large(b_) (board_size(b_)-2 >= 15)
 286 #define board_small(b_) (board_size(b_)-2 <= 9)
 287
 288 #if BOARD_SIZE == 19
 289 #  define board_bits2(b_) 9
 290 #elif BOARD_SIZE == 13
 291 #  define board_bits2(b_) 8
 292 #elif BOARD_SIZE == 9
 293 #  define board_bits2(b_) 7
 294 #else
 295 #  define board_bits2(b_) ((b_)->bits2)
 296 #endif
 297
 298 #define board_at(b_, c) ((b_)->b[c])
 299 #define board_atxy(b_, x, y) ((b_)->b[(x) + board_size(b_) * (y)])
 300
 301 #define group_at(b_, c) ((b_)->g[c])
 302 #define group_atxy(b_, x, y) ((b_)->g[(x) + board_size(b_) * (y)])
 303
 304 /* Warning! Neighbor count is not kept up-to-date for S_NONE! */
 305 #define neighbor_count_at(b_, coord, color) ((b_)->n[coord].colors[(enum stone) color])
 306 #define set_neighbor_count_at(b_, coord, color, count) (neighbor_count_at(b_, coord, color) = (count))
 307 #define inc_neighbor_count_at(b_, coord, color) (neighbor_count_at(b_, coord, color)++)
 308 #define dec_neighbor_count_at(b_, coord, color) (neighbor_count_at(b_, coord, color)--)
 309 #define immediate_liberty_count(b_, coord) (4 - neighbor_count_at(b_, coord, S_BLACK) - neighbor_count_at(b_, coord, S_WHITE) - neighbor_count_at(b_, coord, S_OFFBOARD))
 310
 311 #define trait_at(b_, coord, color) (b_)->t[coord][(color) - 1]
 312
 313 #define groupnext_at(b_, c) ((b_)->p[c])
 314 #define groupnext_atxy(b_, x, y) ((b_)->p[(x) + board_size(b_) * (y)])
 315
 316 #define group_base(g_) (g_)
 317 #define group_is_onestone(b_, g_) (groupnext_at(b_, group_base(g_)) == 0)
 318 #define board_group_info(b_, g_) ((b_)->gi[(g_)])
 319 #define board_group_captured(b_, g_) (board_group_info(b_, g_).libs == 0)
 320 /* board_group_other_lib() makes sense only for groups with two liberties. */
 321 #define board_group_other_lib(b_, g_, l_) (board_group_info(b_, g_).lib[board_group_info(b_, g_).lib[0] != (l_) ? 0 : 1])
 322
 323 #define hash_at(b_, coord, color) ((b_)->h[((color) == S_BLACK ? board_size2(b_) : 0) + coord])
 324
 325 struct board *board_init(char *fbookfile);
 326 struct board *board_copy(struct board *board2, struct board *board1);
 327 void board_done_noalloc(struct board *board);
 328 void board_done(struct board *board);
 329 /* size here is without the S_OFFBOARD margin. */
 330 void board_resize(struct board *board, int size);
 331 void board_clear(struct board *board);
 332
 333 typedef char *(*board_cprint)(struct board *b, coord_t c, char *s, char *end);
 334 void board_print(struct board *board, FILE *f);
 335 void board_print_custom(struct board *board, FILE *f, board_cprint cprint);
 336
 337 /* Place given handicap on the board; coordinates are printed to f. */
 338 void board_handicap(struct board *board, int stones, FILE *f);
 339
 340 /* Returns group id, 0 on allowed suicide, pass or resign, -1 on error */
 341 int board_play(struct board *board, struct move *m);
 342 /* Like above, but plays random move; the move coordinate is recorded
 343  * to *coord. This method will never fill your own eye. pass is played
 344  * when no move can be played. You can impose extra restrictions if you
 345  * supply your own permit function; the permit function can also modify
 346  * the move coordinate to redirect the move elsewhere. */
 347 typedef bool (*ppr_permit)(void *data, struct board *b, struct move *m);
 348 void board_play_random(struct board *b, enum stone color, coord_t *coord, ppr_permit permit, void *permit_data);
 349
 350 /*Undo, supported only for pass moves. Returns -1 on error, 0 otherwise. */
 351 int board_undo(struct board *board);
 352
 353 /* Returns true if given move can be played. */
 354 static bool board_is_valid_play(struct board *b, enum stone color, coord_t coord);
 355 static bool board_is_valid_move(struct board *b, struct move *m);
 356 /* Returns true if ko was just taken. */
 357 static bool board_playing_ko_threat(struct board *b);
 358 /* Returns 0 or ID of neighboring group in atari. */
 359 static group_t board_get_atari_neighbor(struct board *b, coord_t coord, enum stone group_color);
 360 /* Returns true if the move is not obvious self-atari. */
 361 static bool board_safe_to_play(struct board *b, coord_t coord, enum stone color);
 362
 363 /* Determine number of stones in a group, up to @max stones. */
 364 static int group_stone_count(struct board *b, group_t group, int max);
 365
 366 /* Adjust symmetry information as if given coordinate has been played. */
 367 void board_symmetry_update(struct board *b, struct board_symmetry *symmetry, coord_t c);
 368 /* Check if coordinates are within symmetry base. (If false, they can
 369  * be derived from the base.) */
 370 static bool board_coord_in_symmetry(struct board *b, coord_t c);
 371
 372 /* Returns true if given coordinate has all neighbors of given color or the edge. */
 373 static bool board_is_eyelike(struct board *board, coord_t coord, enum stone eye_color);
 374 /* Returns true if given coordinate could be a false eye; this check makes
 375  * sense only if you already know the coordinate is_eyelike(). */
 376 bool board_is_false_eyelike(struct board *board, coord_t coord, enum stone eye_color);
 377 /* Returns true if given coordinate is a 1-pt eye (checks against false eyes, or
 378  * at least tries to). */
 379 bool board_is_one_point_eye(struct board *board, coord_t c, enum stone eye_color);
 380 /* Returns color of a 1pt eye owner, S_NONE if not an eye. */
 381 enum stone board_get_one_point_eye(struct board *board, coord_t c);
 382
 383 /* board_official_score() is the scoring method for yielding score suitable
 384  * for external presentation. For fast scoring of entirely filled boards
 385  * (e.g. playouts), use board_fast_score(). */
 386 /* Positive: W wins */
 387 /* Compare number of stones + 1pt eyes. */
 388 floating_t board_fast_score(struct board *board);
 389 /* Tromp-Taylor scoring, assuming given groups are actually dead. */
 390 struct move_queue;
 391 floating_t board_official_score(struct board *board, struct move_queue *mq);
 392
 393 /* Set board rules according to given string. Returns false in case
 394  * of unknown ruleset name. */
 395 bool board_set_rules(struct board *board, char *name);
 396
 397 /** Iterators */
 398
 399 #define foreach_point(board_) \
 400         do { \
 401                 coord_t c = 0; \
 402                 for (; c < board_size(board_) * board_size(board_); c++)
 403 #define foreach_point_and_pass(board_) \
 404         do { \
 405                 coord_t c = pass; \
 406                 for (; c < board_size(board_) * board_size(board_); c++)
 407 #define foreach_point_end \
 408         } while (0)
 409
 410 #define foreach_free_point(board_) \
 411         do { \
 412                 int fmax__ = (board_)->flen; \
 413                 for (int f__ = 0; f__ < fmax__; f__++) { \
 414                         coord_t c = (board_)->f[f__];
 415 #define foreach_free_point_end \
 416                 } \
 417         } while (0)
 418
 419 #define foreach_in_group(board_, group_) \
 420         do { \
 421                 struct board *board__ = board_; \
 422                 coord_t c = group_base(group_); \
 423                 coord_t c2 = c; c2 = groupnext_at(board__, c2); \
 424                 do {
 425 #define foreach_in_group_end \
 426                         c = c2; c2 = groupnext_at(board__, c2); \
 427                 } while (c != 0); \
 428         } while (0)
 429
 430 /* NOT VALID inside of foreach_point() or another foreach_neighbor(), or rather
 431  * on S_OFFBOARD coordinates. */
 432 #define foreach_neighbor(board_, coord_, loop_body) \
 433         do { \
 434                 struct board *board__ = board_; \
 435                 coord_t coord__ = coord_; \
 436                 coord_t c; \
 437                 c = coord__ - board_size(board__); do { loop_body } while (0); \
 438                 c = coord__ - 1; do { loop_body } while (0); \
 439                 c = coord__ + 1; do { loop_body } while (0); \
 440                 c = coord__ + board_size(board__); do { loop_body } while (0); \
 441         } while (0)
 442
 443 #define foreach_8neighbor(board_, coord_) \
 444         do { \
 445                 int fn__i; \
 446                 coord_t c = (coord_); \
 447                 for (fn__i = 0; fn__i < 8; fn__i++) { \
 448                         c += (board_)->nei8[fn__i];
 449 #define foreach_8neighbor_end \
 450                 } \
 451         } while (0)
 452
 453 #define foreach_diag_neighbor(board_, coord_) \
 454         do { \
 455                 int fn__i; \
 456                 coord_t c = (coord_); \
 457                 for (fn__i = 0; fn__i < 4; fn__i++) { \
 458                         c += (board_)->dnei[fn__i];
 459 #define foreach_diag_neighbor_end \
 460                 } \
 461         } while (0)
 462
 463
 464 static inline bool
 465 board_is_eyelike(struct board *board, coord_t coord, enum stone eye_color)
 466 {
 467         return (neighbor_count_at(board, coord, eye_color)
 468                 + neighbor_count_at(board, coord, S_OFFBOARD)) == 4;
 469 }
 470
 471 /* Group suicides allowed */
 472 static inline bool
 473 board_is_valid_play(struct board *board, enum stone color, coord_t coord)
 474 {
 475         if (board_at(board, coord) != S_NONE)
 476                 return false;
 477         if (!board_is_eyelike(board, coord, stone_other(color)))
 478                 return true;
 479         /* Play within {true,false} eye-ish formation */
 480         if (board->ko.coord == coord && board->ko.color == color)
 481                 return false;
 482 #ifdef BOARD_TRAITS
 483         /* XXX: Disallows suicide. */
 484         return trait_at(board, coord, color).cap > 0;
 485 #else
 486         int groups_in_atari = 0;
 487         foreach_neighbor(board, coord, {
 488                 group_t g = group_at(board, c);
 489                 groups_in_atari += (board_group_info(board, g).libs == 1);
 490         });
 491         return !!groups_in_atari;
 492 #endif
 493 }
 494
 495 /* Check group suicides, slower than board_is_valid_play() */
 496 static inline bool
 497 board_is_valid_play_no_suicide(struct board *board, enum stone color, coord_t coord)
 498 {
 499         if (board_at(board, coord) != S_NONE)
 500                 return false;
 501         if (immediate_liberty_count(board, coord) >= 1)
 502                 return true;
 503         if (board_is_eyelike(board, coord, stone_other(color)) &&
 504             board->ko.coord == coord && board->ko.color == color)
 505                         return false;
 506
 507         // Capturing something ?
 508 #ifdef BOARD_TRAITS
 509         /* XXX: Disallows suicide. */
 510         if (trait_at(board, coord, color).cap > 0)
 511                 return true;
 512 #else
 513         foreach_neighbor(board, coord, {
 514                 if (board_at(board, c) == stone_other(color) &&
 515                     board_group_info(board, group_at(board, c)).libs == 1)
 516                         return true;
 517         });
 518 #endif
 519
 520         // Neighbour with 2 libs ?
 521         foreach_neighbor(board, coord, {
 522                 if (board_at(board, c) == color &&
 523                     board_group_info(board, group_at(board, c)).libs > 1)
 524                         return true;
 525         });
 526
 527         return false;  // Suicide
 528 }
 529
 530
 531 static inline bool
 532 board_is_valid_move(struct board *board, struct move *m)
 533 {
 534         return board_is_valid_play(board, m->color, m->coord);
 535 }
 536
 537 static inline bool
 538 board_playing_ko_threat(struct board *b)
 539 {
 540         return !is_pass(b->ko.coord);
 541 }
 542
 543 static inline group_t
 544 board_get_atari_neighbor(struct board *b, coord_t coord, enum stone group_color)
 545 {
 546 #ifdef BOARD_TRAITS
 547         if (!trait_at(b, coord, stone_other(group_color)).cap) return 0;
 548 #endif
 549         foreach_neighbor(b, coord, {
 550                 group_t g = group_at(b, c);
 551                 if (g && board_at(b, c) == group_color && board_group_info(b, g).libs == 1)
 552                         return g;
 553                 /* We return first match. */
 554         });
 555         return 0;
 556 }
 557
 558 static inline bool
 559 board_safe_to_play(struct board *b, coord_t coord, enum stone color)
 560 {
 561         /* number of free neighbors */
 562         int libs = immediate_liberty_count(b, coord);
 563         if (libs > 1)
 564                 return true;
 565
 566 #ifdef BOARD_TRAITS
 567         /* number of capturable enemy groups */
 568         if (trait_at(b, coord, color).cap > 0)
 569                 return true; // XXX: We don't account for snapback.
 570         /* number of non-capturable friendly groups */
 571         int noncap_ours = neighbor_count_at(b, coord, color) - trait_at(b, coord, stone_other(color)).cap;
 572         if (noncap_ours < 1)
 573                 return false;
 574 /*#else see below */
 575 #endif
 576
 577         /* ok, but we need to check if they don't have just two libs. */
 578         coord_t onelib = -1;
 579         foreach_neighbor(b, coord, {
 580 #ifndef BOARD_TRAITS
 581                 if (board_at(b, c) == stone_other(color) && board_group_info(b, group_at(b, c)).libs == 1)
 582                         return true; // can capture; no snapback check
 583 #endif
 584                 if (board_at(b, c) != color) continue;
 585                 group_t g = group_at(b, c);
 586                 if (board_group_info(b, g).libs == 1) continue; // in atari
 587                 if (board_group_info(b, g).libs == 2) { // two liberties
 588                         if (libs > 0) return true; // we already have one real liberty
 589                         /* we might be connecting two 2-lib groups, which is ok;
 590                          * so remember the other liberty and just make sure it's
 591                          * not the same one */
 592                         if (onelib >= 0 && c != onelib) return true;
 593                         onelib = board_group_other_lib(b, g, c);
 594                         continue;
 595                 }
 596                 // many liberties
 597                 return true;
 598         });
 599         // no good support group
 600         return false;
 601 }
 602
 603 static inline int
 604 group_stone_count(struct board *b, group_t group, int max)
 605 {
 606         int n = 0;
 607         foreach_in_group(b, group) {
 608                 n++;
 609                 if (n >= max) return max;
 610         } foreach_in_group_end;
 611         return n;
 612 }
 613
 614 static inline bool
 615 board_coord_in_symmetry(struct board *b, coord_t c)
 616 {
 617         if (coord_y(c, b) < b->symmetry.y1 || coord_y(c, b) > b->symmetry.y2)
 618                 return false;
 619         if (coord_x(c, b) < b->symmetry.x1 || coord_x(c, b) > b->symmetry.x2)
 620                 return false;
 621         if (b->symmetry.d) {
 622                 int x = coord_x(c, b);
 623                 if (b->symmetry.type == SYM_DIAG_DOWN)
 624                         x = board_size(b) - 1 - x;
 625                 if (x > coord_y(c, b))
 626                         return false;
 627         }
 628         return true;
 629
 630 }
 631
 632 #endif