Board: Never insert group 0 to board.c[]

[pachi.git] / board.c

#include <alloca.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "board.h"
#include "debug.h"
#include "random.h"

int board_group_capture(struct board *board, int group);

bool random_pass = false;


#if 0
#define profiling_noinline __attribute__((noinline))
#else
#define profiling_noinline
#endif

#define gi_granularity 4
#define gi_allocsize(gids) ((1 << gi_granularity) + ((gids) >> gi_granularity) * (1 << gi_granularity))


static void
board_setup(struct board *b)
{
        memset(b, 0, sizeof(*b));

        struct move m = { pass, S_NONE };
        b->last_move = b->ko = m;
}

struct board *
board_init(void)
{
        struct board *b = malloc(sizeof(struct board));
        board_setup(b);
        return b;
}

struct board *
board_copy(struct board *b2, struct board *b1)
{
        memcpy(b2, b1, sizeof(struct board));

        int bsize = board_size2(b2) * sizeof(*b2->b);
        int gsize = board_size2(b2) * sizeof(*b2->g);
        int fsize = board_size2(b2) * sizeof(*b2->f);
        int nsize = board_size2(b2) * sizeof(*b2->n);
        int psize = board_size2(b2) * sizeof(*b2->p);
        int hsize = board_size2(b2) * 2 * sizeof(*b2->h);
        int gisize = board_size2(b2) * sizeof(*b2->gi);
#ifdef WANT_BOARD_C
        int csize = board_size2(b2) * sizeof(*b2->c);
#else
        int csize = 0;
#endif
        void *x = malloc(bsize + gsize + fsize + psize + nsize + hsize + gisize + csize);
        memcpy(x, b1->b, bsize + gsize + fsize + psize + nsize + hsize + gisize + csize);
        b2->b = x; x += bsize;
        b2->g = x; x += gsize;
        b2->f = x; x += fsize;
        b2->p = x; x += psize;
        b2->n = x; x += nsize;
        b2->h = x; x += hsize;
        b2->gi = x; x += gisize;
#ifdef WANT_BOARD_C
        b2->c = x; x += csize;
#endif

        return b2;
}

void
board_done_noalloc(struct board *board)
{
        if (board->b) free(board->b);
}

void
board_done(struct board *board)
{
        board_done_noalloc(board);
        free(board);
}

void
board_resize(struct board *board, int size)
{
#ifdef BOARD_SIZE
        assert(board_size(board) == size + 2);
#else
        board_size(board) = size + 2 /* S_OFFBOARD margin */;
        board_size2(board) = board_size(board) * board_size(board);
#endif
        if (board->b)
                free(board->b);

        int bsize = board_size2(board) * sizeof(*board->b);
        int gsize = board_size2(board) * sizeof(*board->g);
        int fsize = board_size2(board) * sizeof(*board->f);
        int nsize = board_size2(board) * sizeof(*board->n);
        int psize = board_size2(board) * sizeof(*board->p);
        int hsize = board_size2(board) * 2 * sizeof(*board->h);
        int gisize = board_size2(board) * sizeof(*board->gi);
#ifdef WANT_BOARD_C
        int csize = board_size2(board) * sizeof(*board->c);
#else
        int csize = 0;
#endif
        void *x = malloc(bsize + gsize + fsize + psize + nsize + hsize + gisize + csize);
        memset(x, 0, bsize + gsize + fsize + psize + nsize + hsize + gisize + csize);
        board->b = x; x += bsize;
        board->g = x; x += gsize;
        board->f = x; x += fsize;
        board->p = x; x += psize;
        board->n = x; x += nsize;
        board->h = x; x += hsize;
        board->gi = x; x += gisize;
#ifdef WANT_BOARD_C
        board->c = x; x += csize;
#endif
}

void
board_clear(struct board *board)
{
        int size = board_size(board);

        board_done_noalloc(board);
        board_setup(board);
        board_resize(board, size - 2 /* S_OFFBOARD margin */);

        /* Draw the offboard margin */
        int top_row = board_size2(board) - board_size(board);
        int i;
        for (i = 0; i < board_size(board); i++)
                board->b[i] = board->b[top_row + i] = S_OFFBOARD;
        for (i = 0; i <= top_row; i += board_size(board))
                board->b[i] = board->b[board_size(board) - 1 + i] = S_OFFBOARD;

        foreach_point(board) {
                coord_t coord = c;
                if (board_at(board, coord) == S_OFFBOARD)
                        continue;
                foreach_neighbor(board, c, {
                        inc_neighbor_count_at(board, coord, board_at(board, c));
                } );
        } foreach_point_end;

        /* First, pass is always a free position. */
        board->f[board->flen++] = coord_raw(pass);
        /* All positions are free! Except the margin. */
        for (i = board_size(board); i < (board_size(board) - 1) * board_size(board); i++)
                if (i % board_size(board) != 0 && i % board_size(board) != board_size(board) - 1)
                        board->f[board->flen++] = i;

        /* Initialize zobrist hashtable. */
        foreach_point(board) {
                int max = (sizeof(hash_t) << history_hash_bits);
                /* fast_random() is 16-bit only */
                board->h[coord_raw(c) * 2] = ((hash_t) fast_random(max))
                                | ((hash_t) fast_random(max) << 16)
                                | ((hash_t) fast_random(max) << 32)
                                | ((hash_t) fast_random(max) << 48);
                if (!board->h[coord_raw(c) * 2])
                        /* Would be kinda "oops". */
                        board->h[coord_raw(c) * 2] = 1;
                /* And once again for white */
                board->h[coord_raw(c) * 2 + 1] = ((hash_t) fast_random(max))
                                | ((hash_t) fast_random(max) << 16)
                                | ((hash_t) fast_random(max) << 32)
                                | ((hash_t) fast_random(max) << 48);
                if (!board->h[coord_raw(c) * 2 + 1])
                        board->h[coord_raw(c) * 2 + 1] = 1;
        } foreach_point_end;
}


void
board_print(struct board *board, FILE *f)
{
        fprintf(f, "Move: % 3d  Komi: %2.1f  Captures B: %d W: %d\n     ",
                board->moves, board->komi,
                board->captures[S_BLACK], board->captures[S_WHITE]);
        int x, y;
        char asdf[] = "ABCDEFGHJKLMNOPQRSTUVWXYZ";
        for (x = 1; x < board_size(board) - 1; x++)
                fprintf(f, "%c ", asdf[x - 1]);
        fprintf(f, "\n   +-");
        for (x = 1; x < board_size(board) - 1; x++)
                fprintf(f, "--");
        fprintf(f, "+\n");
        for (y = board_size(board) - 2; y >= 1; y--) {
                fprintf(f, "%2d | ", y);
                for (x = 1; x < board_size(board) - 1; x++) {
                        if (coord_x(board->last_move.coord, board) == x && coord_y(board->last_move.coord, board) == y)
                                fprintf(f, "%c)", stone2char(board_atxy(board, x, y)));
                        else
                                fprintf(f, "%c ", stone2char(board_atxy(board, x, y)));
                }
                if (DEBUGL(6)) {
                        fprintf(f, "| ");
                        for (x = 1; x < board_size(board) - 1; x++) {
                                fprintf(f, "%d ", group_atxy(board, x, y));
                        }
                }
                fprintf(f, "|\n");
        }
        fprintf(f, "   +-");
        for (x = 1; x < board_size(board) - 1; x++)
                fprintf(f, "--");
        fprintf(f, "+\n\n");
}


/* Update board hash with given coordinate. */
static void profiling_noinline
board_hash_update(struct board *board, coord_t coord, enum stone color)
{
        board->hash ^= hash_at(board, coord, color);
        if (DEBUGL(8))
                fprintf(stderr, "board_hash_update(%d,%d,%d) ^ %llx -> %llx\n", color, coord_x(coord, board), coord_y(coord, board), hash_at(board, coord, color), board->hash);
}

/* Commit current board hash to history. */
static void profiling_noinline
board_hash_commit(struct board *board)
{
        if (DEBUGL(8))
                fprintf(stderr, "board_hash_commit %llx\n", board->hash);
        if (likely(board->history_hash[board->hash & history_hash_mask]) == 0) {
                board->history_hash[board->hash & history_hash_mask] = board->hash;
        } else {
                hash_t i = board->hash;
                while (board->history_hash[i & history_hash_mask]) {
                        if (board->history_hash[i & history_hash_mask] == board->hash) {
                                if (DEBUGL(5))
                                        fprintf(stderr, "SUPERKO VIOLATION noted at %d,%d\n",
                                                coord_x(board->last_move.coord, board), coord_y(board->last_move.coord, board));
                                board->superko_violation = true;
                                return;
                        }
                        i = history_hash_next(i);
                }
                board->history_hash[i & history_hash_mask] = board->hash;
        }
}


void
board_handicap_stone(struct board *board, int x, int y, FILE *f)
{
        struct move m;
        m.color = S_BLACK;
        coord_xy(m.coord, x, y, board);

        board_play(board, &m);

        char *str = coord2str(m.coord, board);
        if (DEBUGL(1))
                fprintf(stderr, "choosing handicap %s (%d,%d)\n", str, x, y);
        fprintf(f, "%s ", str);
        free(str);
}

void
board_handicap(struct board *board, int stones, FILE *f)
{
        int margin = 3 + (board_size(board) >= 13);
        int min = margin;
        int mid = board_size(board) / 2;
        int max = board_size(board) - 1 - margin;
        const int places[][2] = {
                { min, min }, { max, max }, { max, min }, { min, max },
                { min, mid }, { max, mid },
                { mid, min }, { mid, max },
                { mid, mid },
        };

        board->handicap = stones;

        if (stones == 5 || stones == 7) {
                board_handicap_stone(board, mid, mid, f);
                stones--;
        }

        int i;
        for (i = 0; i < stones; i++)
                board_handicap_stone(board, places[i][0], places[i][1], f);
}


static void __attribute__((noinline))
check_libs_consistency(struct board *board, group_t g)
{
#ifdef DEBUG
        if (!g) return;
        struct group *gi = &board_group_info(board, g);
        for (int i = 0; i < GROUP_KEEP_LIBS; i++)
                if (gi->lib[i] && board_at(board, gi->lib[i]) != S_NONE) {
                        fprintf(stderr, "BOGUS LIBERTY %s of group %d[%s]\n", coord2sstr(gi->lib[i], board), g, coord2sstr(g, board));
                        assert(0);
                }
#endif
}

static void
board_capturable_add(struct board *board, group_t group)
{
#ifdef WANT_BOARD_C
        //fprintf(stderr, "add of group %d (%d)\n", group, board->clen);
        assert(board->clen < board_size2(board));
        board->c[board->clen++] = group;
#endif
}
static void
board_capturable_rm(struct board *board, group_t group)
{
#ifdef WANT_BOARD_C
        //fprintf(stderr, "rm of group %d\n", group);
        for (int i = 0; i < board->clen; i++) {
                if (unlikely(board->c[i] == group)) {
                        board->c[i] = board->c[--board->clen];
                        return;
                }
        }
        fprintf(stderr, "rm of bad group %d\n", group);
        assert(0);
#endif
}

static void
board_group_addlib(struct board *board, group_t group, coord_t coord, bool fresh)
{
        if (DEBUGL(7)) {
                fprintf(stderr, "Group %d[%s]: Adding liberty %s\n",
                        group, coord2sstr(group, board), coord2sstr(coord, board));
        }

        check_libs_consistency(board, group);

        struct group *gi = &board_group_info(board, group);
        if (gi->libs < GROUP_KEEP_LIBS) {
                if (!fresh)
                        for (int i = 0; i < GROUP_KEEP_LIBS; i++) {
#if 0
                                /* Seems extra branch just slows it down */
                                if (!gi->lib[i])
                                        break;
#endif
                                if (unlikely(gi->lib[i] == coord))
                                        return;
                        }
                if (gi->libs == 0)
                        board_capturable_add(board, group);
                else if (gi->libs == 1)
                        board_capturable_rm(board, group);
                gi->lib[gi->libs++] = coord;
        }

        check_libs_consistency(board, group);
}

static void
board_group_rmlib(struct board *board, group_t group, coord_t coord)
{
        if (DEBUGL(7)) {
                fprintf(stderr, "Group %d[%s]: Removing liberty %s\n",
                        group, coord2sstr(group, board), coord2sstr(coord, board));
        }

        struct group *gi = &board_group_info(board, group);
        for (int i = 0; i < GROUP_KEEP_LIBS; i++) {
#if 0
                /* Seems extra branch just slows it down */
                if (!gi->lib[i])
                        break;
#endif
                if (likely(gi->lib[i] != coord))
                        continue;

                int j = i;
                for (i++; i < GROUP_KEEP_LIBS; i++)
                        if (!gi->lib[i])
                                break; /* Unfilled liberties. */
                gi->lib[j] = gi->lib[i - 1];
                gi->lib[--gi->libs] = 0;

                check_libs_consistency(board, group);
                if (gi->libs < GROUP_KEEP_LIBS - 1) {
                        if (gi->libs == 1)
                                board_capturable_add(board, group);
                        else if (gi->libs == 0)
                                board_capturable_rm(board, group);
                        return;
                }
                /* Postpone refilling lib[] until we need to. */
                if (i > GROUP_REFILL_LIBS)
                        return;
                goto find_extra_lib;
        }

        /* This is ok even if gi->libs < GROUP_KEEP_LIBS since we
         * can call this multiple times per coord. */
        check_libs_consistency(board, group);
        return;

        /* Add extra liberty from the board to our liberty list. */
find_extra_lib:;
        bool watermark[board_size2(board)];
        memset(watermark, 0, sizeof(watermark));

        foreach_in_group(board, group) {
                coord_t coord2 = c;
                foreach_neighbor(board, coord2, {
                        if (likely(watermark[coord_raw(c)]))
                                continue;
                        watermark[coord_raw(c)] = true;
                        if (c != coord && board_at(board, c) == S_NONE) {
                                bool next = false;
                                for (int i = 0; i < GROUP_KEEP_LIBS - 1; i++) {
                                        if (gi->lib[i] == c) {
                                                next = true;
                                                break;
                                        }
                                }
                                if (!next) {
                                        gi->lib[gi->libs++] = c;
                                        if (gi->libs >= GROUP_KEEP_LIBS)
                                                return;
                                }
                        }
                } );
        } foreach_in_group_end;
}


/* This is a low-level routine that doesn't maintain consistency
 * of all the board data structures. Use board_group_capture() from
 * your code. */
static void
board_remove_stone(struct board *board, coord_t c)
{
        enum stone color = board_at(board, c);
        board_at(board, c) = S_NONE;
        group_at(board, c) = 0;
        board_hash_update(board, c, color);

        /* Increase liberties of surrounding groups */
        coord_t coord = c;
        foreach_neighbor(board, coord, {
                dec_neighbor_count_at(board, c, color);
                group_t g = group_at(board, c);
                if (g)
                        board_group_addlib(board, g, coord, true);
        });

        if (DEBUGL(6))
                fprintf(stderr, "pushing free move [%d]: %d,%d\n", board->flen, coord_x(c, board), coord_y(c, board));
        board->f[board->flen++] = coord_raw(c);
}


static void profiling_noinline
add_to_group(struct board *board, int gid, coord_t prevstone, coord_t coord)
{
        foreach_neighbor(board, coord, {
                if (board_at(board, c) == S_NONE)
                        board_group_addlib(board, gid, c, false);
        });

        group_at(board, coord) = gid;
        groupnext_at(board, coord) = groupnext_at(board, prevstone);
        groupnext_at(board, prevstone) = coord_raw(coord);

        if (DEBUGL(8))
                fprintf(stderr, "add_to_group: added (%d,%d ->) %d,%d (-> %d,%d) to group %d\n",
                        coord_x(prevstone, board), coord_y(prevstone, board),
                        coord_x(coord, board), coord_y(coord, board),
                        groupnext_at(board, coord) % board_size(board), groupnext_at(board, coord) / board_size(board),
                        gid);
}

static void profiling_noinline
merge_groups(struct board *board, group_t group_to, group_t group_from)
{
        if (DEBUGL(7))
                fprintf(stderr, "board_play_raw: merging groups %d -> %d\n",
                        group_from, group_to);

        coord_t last_in_group;
        foreach_in_group(board, group_from) {
                last_in_group = c;
                group_at(board, c) = group_to;
        } foreach_in_group_end;
        groupnext_at(board, last_in_group) = groupnext_at(board, group_to);
        groupnext_at(board, group_to) = group_from;

        struct group *gi_from = &board_group_info(board, group_from);
        struct group *gi_to = &board_group_info(board, group_to);
        if (gi_to->libs < GROUP_KEEP_LIBS) {
                for (int i = 0; i < gi_from->libs; i++) {
                        for (int j = 0; j < gi_to->libs; j++)
                                if (gi_to->lib[j] == gi_from->lib[i])
                                        goto next_from_lib;
                        if (gi_to->libs == 0)
                                board_capturable_add(board, group_to);
                        else if (gi_to->libs == 1)
                                board_capturable_rm(board, group_to);
                        gi_to->lib[gi_to->libs++] = gi_from->lib[i];
                        if (gi_to->libs >= GROUP_KEEP_LIBS)
                                break;
next_from_lib:;
                }
        }

        if (gi_from->libs == 1)
                board_capturable_rm(board, group_from);
        memset(gi_from, 0, sizeof(struct group));

        if (DEBUGL(7))
                fprintf(stderr, "board_play_raw: merged group: %d\n",
                        group_to);
}

static group_t profiling_noinline
new_group(struct board *board, coord_t coord)
{
        group_t gid = coord_raw(coord);
        struct group *gi = &board_group_info(board, gid);
        foreach_neighbor(board, coord, {
                if (board_at(board, c) == S_NONE)
                        /* board_group_addlib is ridiculously expensive for us */
#if GROUP_KEEP_LIBS < 4
                        if (gi->libs < GROUP_KEEP_LIBS)
#endif
                        gi->lib[gi->libs++] = c;
        });
        if (gi->libs == 1)
                board_capturable_add(board, gid);
        check_libs_consistency(board, gid);

        group_at(board, coord) = gid;
        groupnext_at(board, coord) = 0;

        if (DEBUGL(8))
                fprintf(stderr, "new_group: added %d,%d to group %d\n",
                        coord_x(coord, board), coord_y(coord, board),
                        gid);

        return gid;
}

static inline int
play_one_neighbor(struct board *board,
                coord_t coord, enum stone color, enum stone other_color,
                coord_t c, int gid)
{
        enum stone ncolor = board_at(board, c);
        group_t ngroup = group_at(board, c);

        inc_neighbor_count_at(board, c, color);

        if (!ngroup)
                return gid;

        board_group_rmlib(board, ngroup, coord);
        if (DEBUGL(7))
                fprintf(stderr, "board_play_raw: reducing libs for group %d (%d:%d,%d)\n",
                        ngroup, ncolor, color, other_color);

        if (ncolor == color && ngroup != gid) {
                if (gid <= 0) {
                        gid = ngroup;
                        add_to_group(board, gid, c, coord);
                } else {
                        merge_groups(board, gid, ngroup);
                }
        } else if (ncolor == other_color) {
                if (DEBUGL(8)) {
                        struct group *gi = &board_group_info(board, ngroup);
                        fprintf(stderr, "testing captured group %d[%s]: ", ngroup, coord2sstr(ngroup, board));
                        for (int i = 0; i < GROUP_KEEP_LIBS; i++)
                                fprintf(stderr, "%s ", coord2sstr(gi->lib[i], board));
                        fprintf(stderr, "\n");
                }
                if (unlikely(board_group_captured(board, ngroup)))
                        board_group_capture(board, ngroup);
        }
        return gid;
}

/* We played on a place with at least one liberty. We will become a member of
 * some group for sure. */
static int profiling_noinline
board_play_outside(struct board *board, struct move *m, int f)
{
        coord_t coord = m->coord;
        enum stone color = m->color;
        enum stone other_color = stone_other(color);
        int gid = 0;

        board->f[f] = board->f[--board->flen];
        if (DEBUGL(6))
                fprintf(stderr, "popping free move [%d->%d]: %d\n", board->flen, f, board->f[f]);

        foreach_neighbor(board, coord, {
                        gid = play_one_neighbor(board, coord, color, other_color, c, gid);
        });

        if (unlikely(gid <= 0))
                gid = new_group(board, coord);

        board_at(board, coord) = color;
        board->last_move = *m;
        board->moves++;
        board_hash_update(board, coord, color);
        struct move ko = { pass, S_NONE };
        board->ko = ko;

        return gid;
}

/* We played in an eye-like shape. Either we capture at least one of the eye
 * sides in the process of playing, or return -1. */
static int profiling_noinline
board_play_in_eye(struct board *board, struct move *m, int f)
{
        coord_t coord = m->coord;
        enum stone color = m->color;
        /* Check ko: Capture at a position of ko capture one move ago */
        if (unlikely(color == board->ko.color && coord_eq(coord, board->ko.coord))) {
                if (DEBUGL(5))
                        fprintf(stderr, "board_check: ko at %d,%d color %d\n", coord_x(coord, board), coord_y(coord, board), color);
                return -1;
        } else if (DEBUGL(6)) {
                fprintf(stderr, "board_check: no ko at %d,%d,%d - ko is %d,%d,%d\n",
                        color, coord_x(coord, board), coord_y(coord, board),
                        board->ko.color, coord_x(board->ko.coord, board), coord_y(board->ko.coord, board));
        }

        struct move ko = { pass, S_NONE };

        int captured_groups = 0;

        foreach_neighbor(board, coord, {
                captured_groups += (board_group_info(board, group_at(board, c)).libs == 1);
        });

        if (likely(captured_groups == 0)) {
                if (DEBUGL(5)) {
                        if (DEBUGL(6))
                                board_print(board, stderr);
                        fprintf(stderr, "board_check: one-stone suicide\n");
                }

                return -1;
        }

        board->f[f] = board->f[--board->flen];
        if (DEBUGL(6))
                fprintf(stderr, "popping free move [%d->%d]: %d\n", board->flen, f, board->f[f]);

        foreach_neighbor(board, coord, {
                inc_neighbor_count_at(board, c, color);

                group_t group = group_at(board, c);
                if (!group)
                        continue;

                board_group_rmlib(board, group, coord);
                if (DEBUGL(7))
                        fprintf(stderr, "board_play_raw: reducing libs for group %d\n",
                                group);

                if (board_group_captured(board, group)) {
                        if (board_group_capture(board, group) == 1) {
                                /* If we captured multiple groups at once,
                                 * we can't be fighting ko so we don't need
                                 * to check for that. */
                                ko.color = stone_other(color);
                                ko.coord = c;
                                if (DEBUGL(5))
                                        fprintf(stderr, "guarding ko at %d,%d,%d\n", ko.color, coord_x(ko.coord, board), coord_y(ko.coord, board));
                        }
                }
        });

        board_at(board, coord) = color;

        board->last_move = *m;
        board->moves++;
        board_hash_update(board, coord, color);
        board_hash_commit(board);
        board->ko = ko;

        return new_group(board, coord);
}

static int __attribute__((flatten))
board_play_f(struct board *board, struct move *m, int f)
{
        if (DEBUGL(7)) {
                fprintf(stderr, "board_play(): ---- Playing %d,%d\n", coord_x(m->coord, board), coord_y(m->coord, board));
        }
        if (likely(!board_is_eyelike(board, &m->coord, stone_other(m->color)))) {
                /* NOT playing in an eye. Thus this move has to succeed. (This
                 * is thanks to New Zealand rules. Otherwise, multi-stone
                 * suicide might fail.) */
                int gid = board_play_outside(board, m, f);
                if (unlikely(board_group_captured(board, gid))) {
                        board_group_capture(board, gid);
                }
                board_hash_commit(board);
                return 0;
        } else {
                return board_play_in_eye(board, m, f);
        }
}

int
board_play(struct board *board, struct move *m)
{
        if (unlikely(is_pass(m->coord) || is_resign(m->coord))) {
                board->last_move = *m;
                return 0;
        }

        int f;
        for (f = 0; f < board->flen; f++)
                if (board->f[f] == coord_raw(m->coord))
                        return board_play_f(board, m, f);

        if (DEBUGL(7))
                fprintf(stderr, "board_check: stone exists\n");
        return -1;
}


static inline bool
board_try_random_move(struct board *b, enum stone color, coord_t *coord, int f)
{
        coord_raw(*coord) = b->f[f];
        if (unlikely(is_pass(*coord)))
                return random_pass;
        struct move m = { *coord, color };
        if (DEBUGL(6))
                fprintf(stderr, "trying random move %d: %d,%d\n", f, coord_x(*coord, b), coord_y(*coord, b));
        return (likely(!board_is_one_point_eye(b, coord, color)) /* bad idea to play into one, usually */
                && likely(board_play_f(b, &m, f) >= 0));
}

void
board_play_random(struct board *b, enum stone color, coord_t *coord)
{
        int base = fast_random(b->flen);
        coord_pos(*coord, base, b);
        if (likely(board_try_random_move(b, color, coord, base)))
                return;

        int f;
        for (f = base + 1; f < b->flen; f++)
                if (board_try_random_move(b, color, coord, f))
                        return;
        for (f = 0; f < base; f++)
                if (board_try_random_move(b, color, coord, f))
                        return;

        *coord = pass;
}


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;
}

bool
board_is_one_point_eye(struct board *board, coord_t *coord, enum stone eye_color)
{
        enum stone color_diag_libs[S_MAX] = {0, 0, 0, 0};

        if (likely(neighbor_count_at(board, *coord, eye_color) + neighbor_count_at(board, *coord, S_OFFBOARD) < 4)) {
                return false;
        }

        /* XXX: We attempt false eye detection but we will yield false
         * positives in case of http://senseis.xmp.net/?TwoHeadedDragon :-( */

        foreach_diag_neighbor(board, *coord) {
                color_diag_libs[(enum stone) board_at(board, c)]++;
        } foreach_diag_neighbor_end;
        color_diag_libs[stone_other(eye_color)] += !!color_diag_libs[S_OFFBOARD];
        return likely(color_diag_libs[stone_other(eye_color)] < 2);
}

enum stone
board_get_one_point_eye(struct board *board, coord_t *coord)
{
        if (board_is_one_point_eye(board, coord, S_WHITE))
                return S_WHITE;
        else if (board_is_one_point_eye(board, coord, S_BLACK))
                return S_BLACK;
        else
                return S_NONE;
}


int profiling_noinline
board_group_capture(struct board *board, int group)
{
        int stones = 0;

        foreach_in_group(board, group) {
                board->captures[stone_other(board_at(board, c))]++;
                board_remove_stone(board, c);
                stones++;
        } foreach_in_group_end;

        if (board_group_info(board, group).libs == 1)
                board_capturable_rm(board, group);
        memset(&board_group_info(board, group), 0, sizeof(struct group));

        return stones;
}

bool
board_group_in_atari(struct board *board, group_t group, coord_t *lastlib)
{
        if (board_group_info(board, group).libs != 1)
                return false;
        *lastlib = board_group_info(board, group).lib[0];
        return true;
}

bool
board_group_can_atari(struct board *board, group_t group, coord_t lastlib[2])
{
        if (board_group_info(board, group).libs != 2)
                return false;
        lastlib[0] = board_group_info(board, group).lib[0];
        lastlib[1] = board_group_info(board, group).lib[1];
        return true;
}


static enum stone
board_tromp_taylor_owner(struct board *board, coord_t c)
{
        int x = coord_x(c, board), y = coord_y(c, board);
        enum stone color = S_NONE;
#define TEST_REACH(xx, yy) \
        { \
                enum stone c2 = board_atxy(board, xx, yy); \
                if (c2 != S_NONE) { \
                        if (color != S_NONE && color != c2) \
                                return S_NONE; \
                        color = c2; \
                        break; \
                } \
        }
        for (int i = x; i > 0; i--)
                TEST_REACH(i, y);
        for (int i = x; i < board_size(board) - 1; i++)
                TEST_REACH(i, y);
        for (int i = y; i > 0; i--)
                TEST_REACH(x, i);
        for (int i = y; i < board_size(board) - 1; i++)
                TEST_REACH(x, i);
        return color;
}

/* Tromp-Taylor Counting */
float
board_official_score(struct board *board)
{

        /* A point P, not colored C, is said to reach C, if there is a path of
         * (vertically or horizontally) adjacent points of P's color from P to
         * a point of color C.
         *
         * A player's score is the number of points of her color, plus the
         * number of empty points that reach only her color. */

        int scores[S_MAX];
        memset(scores, 0, sizeof(scores));

        foreach_point(board) {
                enum stone color = board_at(board, c);
                if (color == S_NONE)
                        color = board_tromp_taylor_owner(board, c);
                scores[color]++;
        } foreach_point_end;

        return board->komi + board->handicap + scores[S_WHITE] - scores[S_BLACK];
}

float
board_fast_score(struct board *board)
{
        int scores[S_MAX];
        memset(scores, 0, sizeof(scores));

        foreach_point(board) {
                enum stone color = board_at(board, c);
                if (color == S_NONE)
                        color = board_get_one_point_eye(board, &c);
                scores[color]++;
                // fprintf(stderr, "%d, %d ++%d = %d\n", coord_x(c, board), coord_y(c, board), color, scores[color]);
        } foreach_point_end;

        return board->komi + board->handicap + scores[S_WHITE] - scores[S_BLACK];
}


bool
valid_escape_route(struct board *b, enum stone color, coord_t to)
{
        /* Assess if we actually gain any liberties by this escape route.
         * Note that this is not 100% as we cannot check whether we are
         * connecting out or just to ourselves. */
        /* Also, we prohibit 1-1 here:
         *  X X X X |
         *  O X O O |
         *  O O X O |
         *  .(O)X . |
         *  --------+
         */
        int friends = neighbor_count_at(b, to, color);
        int borders = neighbor_count_at(b, to, S_OFFBOARD);
        int libs = immediate_liberty_count(b, to);
        return (friends > 1 && friends + borders < 4) || (libs > 1);
}


bool
board_stone_radar(struct board *b, coord_t coord, int distance)
{
        int bounds[4] = {
                coord_x(coord, b) - distance,
                coord_y(coord, b) - distance,
                coord_x(coord, b) + distance,
                coord_y(coord, b) + distance
        };
        for (int i = 0; i < 4; i++)
                if (bounds[i] < 1)
                        bounds[i] = 1;
                else if (bounds[i] > board_size(b) - 2)
                        bounds[i] = board_size(b) - 2;
        for (int x = bounds[0]; x <= bounds[2]; x++)
                for (int y = bounds[1]; y <= bounds[3]; y++)
                        if (board_atxy(b, x, y) != S_NONE) {
                                //fprintf(stderr, "radar %d,%d,%d: %d,%d (%d)\n", coord_x(coord, b), coord_y(coord, b), distance, x, y, board_atxy(b, x, y));
                                return true;
                        }
        return false;
}