ladder: use undo

[pachi.git] / board.h

/* probdist.h must be included before the include goard since we require
 * proper including order. */
#include "probdist.h"

#ifndef PACHI_BOARD_H
#define PACHI_BOARD_H

#include <inttypes.h>
#include <stdbool.h>
#include <stdint.h>

#include "util.h"
#include "stone.h"
#include "move.h"

struct fbook;


/* Maximum supported board size. (Without the S_OFFBOARD edges.) */
#define BOARD_MAX_SIZE 19


/* The board implementation has bunch of optional features.
 * Turn them on below: */

#define WANT_BOARD_C // capturable groups queue

//#define BOARD_SIZE 9 // constant board size, allows better optimization

//#define BOARD_SPATHASH // incremental patternsp.h hashes
#define BOARD_SPATHASH_MAXD 3 // maximal diameter

#define BOARD_PAT3 // incremental 3x3 pattern codes

//#define BOARD_TRAITS 1 // incremental point traits (see struct btraits)
//#define BOARD_TRAIT_SAFE 1 // include btraits.safe (rather expensive, unused)
//#define BOARD_TRAIT_SAFE 2 // include btraits.safe based on full is_bad_selfatari()

//#define BOARD_UNDO_CHECKS 1  // Guard against invalid quick_play() / quick_undo() uses

#define BOARD_MAX_COORDS  ((BOARD_MAX_SIZE+2) * (BOARD_MAX_SIZE+2) )
#define BOARD_MAX_MOVES (BOARD_MAX_SIZE * BOARD_MAX_SIZE)
#define BOARD_MAX_GROUPS (BOARD_MAX_SIZE * BOARD_MAX_SIZE / 2)

enum e_sym {
                SYM_FULL,
                SYM_DIAG_UP,
                SYM_DIAG_DOWN,
                SYM_HORIZ,
                SYM_VERT,
                SYM_NONE
};


/* Some engines might normalize their reading and skip symmetrical
 * moves. We will tell them how can they do it. */
struct board_symmetry {
        /* Playground is in this rectangle. */
        int x1, x2, y1, y2;
        /* d ==  0: Full rectangle
         * d ==  1: Top triangle */
        int d;
        /* General symmetry type. */
        /* Note that the above is redundant to this, but just provided
         * for easier usage. */
        enum e_sym type;
};


typedef uint64_t hash_t;
#define PRIhash PRIx64

/* XXX: This really belongs in pattern3.h, unfortunately that would mean
 * a dependency hell. */
typedef uint32_t hash3_t; // 3x3 pattern hash


/* Note that "group" is only chain of stones that is solidly
 * connected for us. */
typedef coord_t group_t;

struct group {
        /* We keep track of only up to GROUP_KEEP_LIBS; over that, we
         * don't care. */
        /* _Combination_ of these two values can make some difference
         * in performance - fine-tune. */
#define GROUP_KEEP_LIBS 10
        // refill lib[] only when we hit this; this must be at least 2!
        // Moggy requires at least 3 - see below for semantic impact.
#define GROUP_REFILL_LIBS 5
        coord_t lib[GROUP_KEEP_LIBS];
        /* libs is only LOWER BOUND for the number of real liberties!!!
         * It denotes only number of items in lib[], thus you can rely
         * on it to store real liberties only up to <= GROUP_REFILL_LIBS. */
        int libs;
};

struct neighbor_colors {
        char colors[S_MAX];
};


/* Point traits bitmap; we update this information incrementally,
 * it can be used e.g. for fast pattern features matching. */
struct btraits {
        /* Number of neighbors we can capture. 0=this move is
         * not capturing, 1..4=this many neighbors we can capture
         * (can be multiple neighbors of same group). */
        unsigned cap:3;
        /* Number of 1-stone neighbors we can capture. */
        unsigned cap1:3;
#ifdef BOARD_TRAIT_SAFE
        /* Whether it is SAFE to play here. This is essentially just
         * cached result of board_safe_to_play(). (Of course the concept
         * of "safety" is not perfect here, but it's the cheapest
         * reasonable thing we can do.) */
        bool safe:1;
#endif
        /* Whether we need to re-compute this coordinate; used to
         * weed out duplicates. Maintained only for S_BLACK. */
        bool dirty:1;
};


/* Quick hack to help ensure tactics code stays within quick board limitations.
 * Ideally we'd have two different types for boards and quick_boards. The idea
 * of having casts / duplicate api all over the place isn't so appealing though... */
#ifndef QUICK_BOARD_CODE
#define FB_ONLY(field)  field
#else
#define FB_ONLY(field)  field ## _disabled
// Try to make error messages more helpful ...
#define clen clen_field_not_supported_for_quick_boards
#define flen flen_field_not_supported_for_quick_boards
#endif

/* You should treat this struct as read-only. Always call functions below if
 * you want to change it. */

struct board {
        int size; /* Including S_OFFBOARD margin - see below. */
        int size2; /* size^2 */
        int bits2; /* ceiling(log2(size2)) */
        int captures[S_MAX];
        floating_t komi;
        int handicap;
        /* The ruleset is currently almost never taken into account;
         * the board implementation is basically Chinese rules (handicap
         * stones compensation) w/ suicide (or you can look at it as
         * New Zealand w/o handi stones compensation), while the engine
         * enforces no-suicide, making for real Chinese rules.
         * However, we accept suicide moves by the opponent, so we
         * should work with rules allowing suicide, just not taking
         * full advantage of them. */
        enum go_ruleset {
                RULES_CHINESE, /* default value */
                RULES_AGA,
                RULES_NEW_ZEALAND,
                RULES_JAPANESE,
                RULES_STONES_ONLY, /* do not count eyes */
                /* http://home.snafu.de/jasiek/siming.html */
                /* Simplified ING rules - RULES_CHINESE with handicaps
                 * counting as points and pass stones. Also should
                 * allow suicide, but Pachi will never suicide
                 * nevertheless. */
                /* XXX: I couldn't find the point about pass stones
                 * in the rule text, but it is Robert Jasiek's
                 * interpretation of them... These rules were
                 * used e.g. at the EGC2012 13x13 tournament.
                 * They are not supported by KGS. */
                RULES_SIMING,
        } rules;

        char *fbookfile;
        struct fbook *fbook;

        /* Iterator offsets for foreach_neighbor*() */
        int nei8[8], dnei[4];

        int moves;
        struct move last_move;
        struct move last_move2; /* second-to-last move */
FB_ONLY(struct move last_move3); /* just before last_move2, only set if last_move is pass */
FB_ONLY(struct move last_move4); /* just before last_move3, only set if last_move & last_move2 are pass */
        /* Whether we tried to add a hash twice; board_play*() can
         * set this, but it will still carry out the move as well! */
FB_ONLY(bool superko_violation);

        /* The following two structures are goban maps and are indexed by
         * coord.pos. The map is surrounded by a one-point margin from
         * S_OFFBOARD stones in order to speed up some internal loops.
         * Some of the foreach iterators below might include these points;
         * you need to handle them yourselves, if you need to. */

        /* Stones played on the board */
        enum stone *b; /* enum stone */
        /* Group id the stones are part of; 0 == no group */
        group_t *g;
        /* Positions of next stones in the stone group; 0 == last stone */
        coord_t *p;
        /* Neighboring colors; numbers of neighbors of index color */
        struct neighbor_colors *n;
        /* Zobrist hash for each position */
        hash_t *h;
#ifdef BOARD_SPATHASH
        /* For spatial hashes, we use only 24 bits. */
        /* [0] is d==1, we don't keep hash for d==0. */
        /* We keep hashes for black-to-play ([][0]) and white-to-play
         * ([][1], reversed stone colors since we match all patterns as
         * black-to-play). */
FB_ONLY(uint32_t (*spathash))[BOARD_SPATHASH_MAXD][2];
#endif
#ifdef BOARD_PAT3
        /* 3x3 pattern code for each position; see pattern3.h for encoding
         * specification. The information is only valid for empty points. */
FB_ONLY(hash3_t *pat3);
#endif
#ifdef BOARD_TRAITS
        /* Incrementally matched point traits information, black-to-play
         * ([][0]) and white-to-play ([][1]). */
        /* The information is only valid for empty points. */
FB_ONLY(struct btraits (*t)[2]);
#endif
        /* Cached information on x-y coordinates so that we avoid division. */
        uint8_t (*coord)[2];

        /* Group information - indexed by gid (which is coord of base group stone) */
        struct group *gi;

        /* Positions of free positions - queue (not map) */
        /* Note that free position here is any valid move; including single-point eyes!
         * However, pass is not included. */
FB_ONLY(coord_t *f);  FB_ONLY(int flen);

#ifdef WANT_BOARD_C
        /* Queue of capturable groups */
FB_ONLY(group_t *c);  FB_ONLY(int clen);
#endif

#ifdef BOARD_TRAITS
        /* Queue of positions that need their traits updated */
FB_ONLY(coord_t *tq);  FB_ONLY(int tqlen);
#endif

        /* Symmetry information */
FB_ONLY(struct board_symmetry symmetry);

        /* Last ko played on the board. */
FB_ONLY(struct move last_ko);
FB_ONLY(int last_ko_age);

        /* Basic ko check */
        struct move ko;

#ifdef BOARD_UNDO_CHECKS
        /* Guard against invalid quick_play() / quick_undo() uses */
        int quicked;
#endif
        
        /* Engine-specific state; persistent through board development,
         * is reset only at clear_board. */
        void *es;

        /* Playout-specific state; persistent through board development,
         * but its lifetime is maintained in play_random_game(); it should
         * not be set outside of it. */
        void *ps;


        /* --- PRIVATE DATA --- */

        /* For superko check: */

        /* Board "history" - hashes encountered. Size of the hash should be
         * >> board_size^2. */
#define history_hash_bits 12
#define history_hash_mask ((1 << history_hash_bits) - 1)
#define history_hash_prev(i) ((i - 1) & history_hash_mask)
#define history_hash_next(i) ((i + 1) & history_hash_mask)
FB_ONLY(hash_t history_hash)[1 << history_hash_bits];
        /* Hash of current board position. */
FB_ONLY(hash_t hash);
        /* Hash of current board position quadrants. */
FB_ONLY(hash_t qhash)[4];
};

struct undo_merge {
        group_t      group;
        coord_t      last;  
        struct group info;
};

struct undo_enemy {
        group_t      group;
        struct group info;
        coord_t      stones[BOARD_MAX_MOVES];  // TODO try small array
};

struct board_undo {
        struct move last_move2;
        struct move ko;
        struct move last_ko;
        int         last_ko_age;
        
        coord_t next_at;
        
        coord_t inserted;
        struct undo_merge merged[4];
        int nmerged;
        int nmerged_tmp;

        struct undo_enemy enemies[4];
        int nenemies;
        int captures; /* number of stones captured */
};


#ifdef BOARD_SIZE
/* Avoid unused variable warnings */
#define board_size(b_) (((b_) == (b_)) ? BOARD_SIZE + 2 : 0)
#define board_size2(b_) (board_size(b_) * board_size(b_))
#define real_board_size(b_)  (((b_) == (b_)) ? BOARD_SIZE : 0)
#else
#define board_size(b_) ((b_)->size)
#define board_size2(b_) ((b_)->size2)
#define real_board_size(b_) ((b_)->size - 2)
#endif

/* This is a shortcut for taking different action on smaller
 * and large boards (e.g. picking different variable defaults).
 * This is of course less optimal than fine-tuning dependency
 * function of values on board size, but that is difficult and
 * possibly not very rewarding if you are interested just in
 * 9x9 and 19x19. */
#define board_large(b_) (board_size(b_)-2 >= 15)
#define board_small(b_) (board_size(b_)-2 <= 9)

#if BOARD_SIZE == 19
#  define board_bits2(b_) 9
#elif BOARD_SIZE == 13
#  define board_bits2(b_) 8
#elif BOARD_SIZE == 9
#  define board_bits2(b_) 7
#else
#  define board_bits2(b_) ((b_)->bits2)
#endif

#define board_at(b_, c) ((b_)->b[c])
#define board_atxy(b_, x, y) ((b_)->b[(x) + board_size(b_) * (y)])

#define group_at(b_, c) ((b_)->g[c])
#define group_atxy(b_, x, y) ((b_)->g[(x) + board_size(b_) * (y)])

/* Warning! Neighbor count is not kept up-to-date for S_NONE! */
#define neighbor_count_at(b_, coord, color) ((b_)->n[coord].colors[(enum stone) color])
#define set_neighbor_count_at(b_, coord, color, count) (neighbor_count_at(b_, coord, color) = (count))
#define inc_neighbor_count_at(b_, coord, color) (neighbor_count_at(b_, coord, color)++)
#define dec_neighbor_count_at(b_, coord, color) (neighbor_count_at(b_, coord, color)--)
#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))

#define trait_at(b_, coord, color) (b_)->t[coord][(color) - 1]

#define groupnext_at(b_, c) ((b_)->p[c])
#define groupnext_atxy(b_, x, y) ((b_)->p[(x) + board_size(b_) * (y)])

#define group_base(g_) (g_)
#define group_is_onestone(b_, g_) (groupnext_at(b_, group_base(g_)) == 0)
#define board_group_info(b_, g_) ((b_)->gi[(g_)])
#define board_group_captured(b_, g_) (board_group_info(b_, g_).libs == 0)
/* board_group_other_lib() makes sense only for groups with two liberties. */
#define board_group_other_lib(b_, g_, l_) (board_group_info(b_, g_).lib[board_group_info(b_, g_).lib[0] != (l_) ? 0 : 1])

#define hash_at(b_, coord, color) ((b_)->h[((color) == S_BLACK ? board_size2(b_) : 0) + coord])

struct board *board_init(char *fbookfile);
struct board *board_copy(struct board *board2, struct board *board1);
void board_done_noalloc(struct board *board);
void board_done(struct board *board);
/* size here is without the S_OFFBOARD margin. */
void board_resize(struct board *board, int size);
void board_clear(struct board *board);

typedef char *(*board_cprint)(struct board *b, coord_t c, char *s, char *end, void *data);
void board_print(struct board *board, FILE *f);
void board_print_custom(struct board *board, FILE *f, board_cprint cprint, void *data);

/* Debugging: Compare 2 boards byte by byte. Don't use that for sorting =) */
int board_cmp(struct board *b1, struct board *b2);
/* Same but only care about fields maintained by quick_play() / quick_undo() */
int board_quick_cmp(struct board *b1, struct board *b2);

/* Place given handicap on the board; coordinates are printed to f. */
void board_handicap(struct board *board, int stones, FILE *f);

/* Returns group id, 0 on allowed suicide, pass or resign, -1 on error */
int board_play(struct board *board, struct move *m);
/* Like above, but plays random move; the move coordinate is recorded
 * to *coord. This method will never fill your own eye. pass is played
 * when no move can be played. You can impose extra restrictions if you
 * supply your own permit function; the permit function can also modify
 * the move coordinate to redirect the move elsewhere. */
typedef bool (*ppr_permit)(void *data, struct board *b, struct move *m);
void board_play_random(struct board *b, enum stone color, coord_t *coord, ppr_permit permit, void *permit_data);

/* Undo, supported only for pass moves. Returns -1 on error, 0 otherwise. */
int board_undo(struct board *board);

/* Returns true if given move can be played. */
static bool board_is_valid_play(struct board *b, enum stone color, coord_t coord);
static bool board_is_valid_move(struct board *b, struct move *m);
/* Returns true if ko was just taken. */
static bool board_playing_ko_threat(struct board *b);
/* Returns 0 or ID of neighboring group in atari. */
static group_t board_get_atari_neighbor(struct board *b, coord_t coord, enum stone group_color);
/* Returns true if the move is not obvious self-atari. */
static bool board_safe_to_play(struct board *b, coord_t coord, enum stone color);

/* Determine number of stones in a group, up to @max stones. */
static int group_stone_count(struct board *b, group_t group, int max);

#ifndef QUICK_BOARD_CODE
/* Adjust symmetry information as if given coordinate has been played. */
void board_symmetry_update(struct board *b, struct board_symmetry *symmetry, coord_t c);
/* Check if coordinates are within symmetry base. (If false, they can
 * be derived from the base.) */
static bool board_coord_in_symmetry(struct board *b, coord_t c);
#endif

/* Returns true if given coordinate has all neighbors of given color or the edge. */
static bool board_is_eyelike(struct board *board, coord_t coord, enum stone eye_color);
/* Returns true if given coordinate could be a false eye; this check makes
 * sense only if you already know the coordinate is_eyelike(). */
bool board_is_false_eyelike(struct board *board, coord_t coord, enum stone eye_color);
/* Returns true if given coordinate is a 1-pt eye (checks against false eyes, or
 * at least tries to). */
bool board_is_one_point_eye(struct board *board, coord_t c, enum stone eye_color);
/* Returns color of a 1pt eye owner, S_NONE if not an eye. */
enum stone board_get_one_point_eye(struct board *board, coord_t c);

/* board_official_score() is the scoring method for yielding score suitable
 * for external presentation. For fast scoring of entirely filled boards
 * (e.g. playouts), use board_fast_score(). */
/* Positive: W wins */
/* Compare number of stones + 1pt eyes. */
floating_t board_fast_score(struct board *board);
/* Tromp-Taylor scoring, assuming given groups are actually dead. */
struct move_queue;
floating_t board_official_score(struct board *board, struct move_queue *mq);

/* Set board rules according to given string. Returns false in case
 * of unknown ruleset name. */
bool board_set_rules(struct board *board, char *name);

/* Quick play/undo to try out a move.
 * WARNING  Only core board structures are maintained !
 *          Code in between can't rely on anything else.
 *
 * Currently this means these can't be used:
 *   - incremental patterns (pat3)
 *   - hashes, superko_violation (spathash, hash, qhash, history_hash)
 *   - list of free positions (f / flen)
 *   - list of capturable groups (c / clen)
 *   - traits (btraits, t, tq, tqlen)
 *   - last_move3, last_move4, last_ko_age
 *   - symmetry information
 *
 * #define QUICK_BOARD_CODE at the top of your file to get compile-time
 * error if you try to access a forbidden field.
 *
 * Invalid quick_play()/quick_undo() combinations (missing undo for example)
 * are caught at next board_play() if BOARD_UNDO_CHECKS is defined.
 */
int  board_quick_play(struct board *board, struct move *m, struct board_undo *u);
void board_quick_undo(struct board *b, struct move *m, struct board_undo *u);

/* quick_play() + quick_undo() combo.
 * Body is executed only if move is valid (silently ignored otherwise).
 * Can break out in body, but definitely *NOT* return / jump around !
 * (caught at run time if BOARD_UNDO_CHECKS defined). Can use
 * with_move_return(val) to return value for non-nested with_move()'s
 * though. */
#define with_move(board_, coord_, color_, body_) \
       do { \
               struct board *board__ = (board_);  /* For with_move_return() */          \
               struct move m_ = { .coord = (coord_), .color = (color_) }; \
               struct board_undo u_; \
               if (board_quick_play(board__, &m_, &u_) >= 0) {    \
                       do { body_ } while(0);                     \
                       board_quick_undo(board__, &m_, &u_); \
               }                                           \
       } while (0)

/* Return value from within with_move() statement.
 * Valid for non-nested with_move() *ONLY* */
#define with_move_return(val_)  \
        do {  typeof(val_) val__ = (val_); board_quick_undo(board__, &m_, &u_); return val__;  } while (0)

/* Same as with_move() but assert out in case of invalid move. */
#define with_move_strict(board_, coord_, color_, body_) \
       do { \
               struct board *board__ = (board_);  /* For with_move_return() */          \
               struct move m_ = { .coord = (coord_), .color = (color_) }; \
               struct board_undo u_; \
               assert (board_quick_play(board__, &m_, &u_) >= 0);  \
               do { body_ } while(0);                     \
               board_quick_undo(board__, &m_, &u_); \
       } while (0)


/** Iterators */

#define foreach_point(board_) \
        do { \
                coord_t c = 0; \
                for (; c < board_size(board_) * board_size(board_); c++)
#define foreach_point_and_pass(board_) \
        do { \
                coord_t c = pass; \
                for (; c < board_size(board_) * board_size(board_); c++)
#define foreach_point_end \
        } while (0)

#define foreach_free_point(board_) \
        do { \
                int fmax__ = (board_)->flen; \
                for (int f__ = 0; f__ < fmax__; f__++) { \
                        coord_t c = (board_)->f[f__];
#define foreach_free_point_end \
                } \
        } while (0)

#define foreach_in_group(board_, group_) \
        do { \
                struct board *board__ = board_; \
                coord_t c = group_base(group_); \
                coord_t c2 = c; c2 = groupnext_at(board__, c2); \
                do {
#define foreach_in_group_end \
                        c = c2; c2 = groupnext_at(board__, c2); \
                } while (c != 0); \
        } while (0)

/* NOT VALID inside of foreach_point() or another foreach_neighbor(), or rather
 * on S_OFFBOARD coordinates. */
#define foreach_neighbor(board_, coord_, loop_body) \
        do { \
                struct board *board__ = board_; \
                coord_t coord__ = coord_; \
                coord_t c; \
                c = coord__ - board_size(board__); do { loop_body } while (0); \
                c = coord__ - 1; do { loop_body } while (0); \
                c = coord__ + 1; do { loop_body } while (0); \
                c = coord__ + board_size(board__); do { loop_body } while (0); \
        } while (0)

#define foreach_8neighbor(board_, coord_) \
        do { \
                int fn__i; \
                coord_t c = (coord_); \
                for (fn__i = 0; fn__i < 8; fn__i++) { \
                        c += (board_)->nei8[fn__i];
#define foreach_8neighbor_end \
                } \
        } while (0)

#define foreach_diag_neighbor(board_, coord_) \
        do { \
                int fn__i; \
                coord_t c = (coord_); \
                for (fn__i = 0; fn__i < 4; fn__i++) { \
                        c += (board_)->dnei[fn__i];
#define foreach_diag_neighbor_end \
                } \
        } while (0)


static inline bool
board_is_eyelike(struct board *board, coord_t coord, enum stone eye_color)
{
        return (neighbor_count_at(board, coord, eye_color)
                + neighbor_count_at(board, coord, S_OFFBOARD)) == 4;
}

/* Group suicides allowed */
static inline bool
board_is_valid_play(struct board *board, enum stone color, coord_t coord)
{
        if (board_at(board, coord) != S_NONE)
                return false;
        if (!board_is_eyelike(board, coord, stone_other(color)))
                return true;
        /* Play within {true,false} eye-ish formation */
        if (board->ko.coord == coord && board->ko.color == color)
                return false;
#ifdef BOARD_TRAITS
        /* XXX: Disallows suicide. */
        return trait_at(board, coord, color).cap > 0;
#else
        int groups_in_atari = 0;
        foreach_neighbor(board, coord, {
                group_t g = group_at(board, c);
                groups_in_atari += (board_group_info(board, g).libs == 1);
        });
        return !!groups_in_atari;
#endif
}

/* Check group suicides, slower than board_is_valid_play() */
static inline bool
board_is_valid_play_no_suicide(struct board *board, enum stone color, coord_t coord)
{
        if (board_at(board, coord) != S_NONE)
                return false;
        if (immediate_liberty_count(board, coord) >= 1)
                return true;
        if (board_is_eyelike(board, coord, stone_other(color)) &&
            board->ko.coord == coord && board->ko.color == color)
                        return false;

        // Capturing something ?
#ifdef BOARD_TRAITS
        /* XXX: Disallows suicide. */
        if (trait_at(board, coord, color).cap > 0)
                return true;
#else
        foreach_neighbor(board, coord, {
                if (board_at(board, c) == stone_other(color) &&
                    board_group_info(board, group_at(board, c)).libs == 1)
                        return true;
        });
#endif

        // Neighbour with 2 libs ?
        foreach_neighbor(board, coord, {
                if (board_at(board, c) == color &&
                    board_group_info(board, group_at(board, c)).libs > 1)
                        return true;
        });

        return false;  // Suicide
}


static inline bool
board_is_valid_move(struct board *board, struct move *m)
{
        return board_is_valid_play(board, m->color, m->coord);
}

static inline bool
board_playing_ko_threat(struct board *b)
{
        return !is_pass(b->ko.coord);
}

static inline group_t
board_get_atari_neighbor(struct board *b, coord_t coord, enum stone group_color)
{
#ifdef BOARD_TRAITS
        if (!trait_at(b, coord, stone_other(group_color)).cap) return 0;
#endif
        foreach_neighbor(b, coord, {
                group_t g = group_at(b, c);
                if (g && board_at(b, c) == group_color && board_group_info(b, g).libs == 1)
                        return g;
                /* We return first match. */
        });
        return 0;
}

static inline bool
board_safe_to_play(struct board *b, coord_t coord, enum stone color)
{
        /* number of free neighbors */
        int libs = immediate_liberty_count(b, coord);
        if (libs > 1)
                return true;

#ifdef BOARD_TRAITS
        /* number of capturable enemy groups */
        if (trait_at(b, coord, color).cap > 0)
                return true; // XXX: We don't account for snapback.
        /* number of non-capturable friendly groups */
        int noncap_ours = neighbor_count_at(b, coord, color) - trait_at(b, coord, stone_other(color)).cap;
        if (noncap_ours < 1)
                return false;
/*#else see below */
#endif

        /* ok, but we need to check if they don't have just two libs. */
        coord_t onelib = -1;
        foreach_neighbor(b, coord, {
#ifndef BOARD_TRAITS
                if (board_at(b, c) == stone_other(color) && board_group_info(b, group_at(b, c)).libs == 1)
                        return true; // can capture; no snapback check
#endif
                if (board_at(b, c) != color) continue;
                group_t g = group_at(b, c);
                if (board_group_info(b, g).libs == 1) continue; // in atari
                if (board_group_info(b, g).libs == 2) { // two liberties
                        if (libs > 0) return true; // we already have one real liberty
                        /* we might be connecting two 2-lib groups, which is ok;
                         * so remember the other liberty and just make sure it's
                         * not the same one */
                        if (onelib >= 0 && c != onelib) return true;
                        onelib = board_group_other_lib(b, g, c);
                        continue;
                }
                // many liberties
                return true;
        });
        // no good support group
        return false;
}

static inline int
group_stone_count(struct board *b, group_t group, int max)
{
        int n = 0;
        foreach_in_group(b, group) {
                n++;
                if (n >= max) return max;
        } foreach_in_group_end;
        return n;
}

#ifndef QUICK_BOARD_CODE
static inline bool
board_coord_in_symmetry(struct board *b, coord_t c)
{
        if (coord_y(c, b) < b->symmetry.y1 || coord_y(c, b) > b->symmetry.y2)
                return false;
        if (coord_x(c, b) < b->symmetry.x1 || coord_x(c, b) > b->symmetry.x2)
                return false;
        if (b->symmetry.d) {
                int x = coord_x(c, b);
                if (b->symmetry.type == SYM_DIAG_DOWN)
                        x = board_size(b) - 1 - x;
                if (x > coord_y(c, b))
                        return false;
        }
        return true;

}
#endif


#endif