Spatial, probability pattern dictionary: Cache previously loaded database

[pachi.git] / board.c

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

//#define DEBUG
#include "board.h"
#include "debug.h"
#include "fbook.h"
#include "mq.h"
#include "random.h"

#ifdef BOARD_SPATHASH
#include "patternsp.h"
#endif
#ifdef BOARD_PAT3
#include "pattern3.h"
#endif
#ifdef BOARD_TRAITS
static void board_trait_recompute(struct board *board, coord_t coord);
#include "tactics/selfatari.h"
#endif


#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->last_move2 = b->last_move3 = b->last_move4 = b->last_ko = b->ko = m;
}

struct board *
board_init(char *fbookfile)
{
        struct board *b = malloc2(sizeof(struct board));
        board_setup(b);

        b->fbookfile = fbookfile;

        // Default setup
        b->size = 9 + 2;
        board_clear(b);

        return b;
}

static size_t
board_alloc(struct board *board)
{
        /* We do not allocate the board structure itself but we allocate
         * all the arrays with board contents. */

        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
#ifdef BOARD_SPATHASH
        int ssize = board_size2(board) * sizeof(*board->spathash);
#else
        int ssize = 0;
#endif
#ifdef BOARD_PAT3
        int p3size = board_size2(board) * sizeof(*board->pat3);
#else
        int p3size = 0;
#endif
#ifdef BOARD_TRAITS
        int tsize = board_size2(board) * sizeof(*board->t);
        int tqsize = board_size2(board) * sizeof(*board->t);
#else
        int tsize = 0;
        int tqsize = 0;
#endif
        int cdsize = board_size2(board) * sizeof(*board->coord);

        size_t size = bsize + gsize + fsize + psize + nsize + hsize + gisize + csize + ssize + p3size + tsize + tqsize + cdsize;
        void *x = malloc2(size);

        /* board->b must come first */
        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
#ifdef BOARD_SPATHASH
        board->spathash = x; x += ssize;
#endif
#ifdef BOARD_PAT3
        board->pat3 = x; x += p3size;
#endif
#ifdef BOARD_TRAITS
        board->t = x; x += tsize;
        board->tq = x; x += tqsize;
#endif
        board->coord = x; x += cdsize;

        return size;
}

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

        size_t size = board_alloc(b2);
        memcpy(b2->b, b1->b, size);

        // XXX: Special semantics.
        b2->fbook = NULL;

        return b2;
}

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

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);
#endif
        assert(size <= BOARD_MAX_SIZE);
        board->size = size + 2 /* S_OFFBOARD margin */;
        board->size2 = board_size(board) * board_size(board);

        board->bits2 = 1;
        while ((1 << board->bits2) < board->size2) board->bits2++;

        if (board->b)
                free(board->b);

        size_t asize = board_alloc(board);
        memset(board->b, 0, asize);
}

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

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

        /* Setup neighborhood iterators */
        board->nei8[0] = -size - 1; // (-1,-1)
        board->nei8[1] = 1;
        board->nei8[2] = 1;
        board->nei8[3] = size - 2; // (-1,0)
        board->nei8[4] = 2;
        board->nei8[5] = size - 2; // (-1,1)
        board->nei8[6] = 1;
        board->nei8[7] = 1;
        board->dnei[0] = -size - 1;
        board->dnei[1] = 2;
        board->dnei[2] = size*2 - 2;
        board->dnei[3] = 2;

        /* Setup initial symmetry */
        if (size % 2) {
                board->symmetry.d = 1;
                board->symmetry.x1 = board->symmetry.y1 = board_size(board) / 2;
                board->symmetry.x2 = board->symmetry.y2 = board_size(board) - 1;
                board->symmetry.type = SYM_FULL;
        } else {
                /* TODO: We do not handle board symmetry on boards
                 * with no tengen yet. */
                board->symmetry.d = 0;
                board->symmetry.x1 = board->symmetry.y1 = 1;
                board->symmetry.x2 = board->symmetry.y2 = board_size(board) - 1;
                board->symmetry.type = SYM_NONE;
        }

        /* Set up coordinate cache */
        foreach_point(board) {
                board->coord[c][0] = c % board_size(board);
                board->coord[c][1] = c / board_size(board);
        } foreach_point_end;

        /* 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;

        /* 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. */
        /* We will need these to be stable across Pachi runs for
         * certain kinds of pattern matching, thus we do not use
         * fast_random() for this. */
        hash_t hseed = 0x3121110101112131;
        foreach_point(board) {
                board->h[c * 2] = (hseed *= 16807);
                if (!board->h[c * 2])
                        board->h[c * 2] = 1;
                /* And once again for white */
                board->h[c * 2 + 1] = (hseed *= 16807);
                if (!board->h[c * 2 + 1])
                        board->h[c * 2 + 1] = 1;
        } foreach_point_end;

#ifdef BOARD_SPATHASH
        /* Initialize spatial hashes. */
        foreach_point(board) {
                for (int d = 1; d <= BOARD_SPATHASH_MAXD; d++) {
                        for (int j = ptind[d]; j < ptind[d + 1]; j++) {
                                ptcoords_at(x, y, c, board, j);
                                board->spathash[coord_xy(board, x, y)][d - 1][0] ^=
                                        pthashes[0][j][board_at(board, c)];
                                board->spathash[coord_xy(board, x, y)][d - 1][1] ^=
                                        pthashes[0][j][stone_other(board_at(board, c))];
                        }
                }
        } foreach_point_end;
#endif
#ifdef BOARD_PAT3
        /* Initialize 3x3 pattern codes. */
        foreach_point(board) {
                if (board_at(board, c) == S_NONE)
                        board->pat3[c] = pattern3_hash(board, c);
        } foreach_point_end;
#endif
#ifdef BOARD_TRAITS
        /* Initialize traits. */
        foreach_point(board) {
                trait_at(board, c, S_BLACK).cap = 0;
                trait_at(board, c, S_WHITE).cap = 0;
                trait_at(board, c, S_BLACK).cap1 = 0;
                trait_at(board, c, S_WHITE).cap1 = 0;
#ifdef BOARD_TRAIT_SAFE
                trait_at(board, c, S_BLACK).safe = true;
                trait_at(board, c, S_WHITE).safe = true;
#endif
        } foreach_point_end;
#endif
}

void
board_clear(struct board *board)
{
        int size = board_size(board);
        floating_t komi = board->komi;
        char *fbookfile = board->fbookfile;

        board_done_noalloc(board);

        static struct board bcache[BOARD_MAX_SIZE + 2];
        assert(size > 0 && size <= BOARD_MAX_SIZE + 2);
        if (bcache[size - 1].size == size) {
                board_copy(board, &bcache[size - 1]);
        } else {
                board_init_data(board);
                board_copy(&bcache[size - 1], board);
        }

        board->komi = komi;
        board->fbookfile = fbookfile;

        if (board->fbookfile) {
                board->fbook = fbook_init(board->fbookfile, board);
        }
}

static char *
board_print_top(struct board *board, char *s, char *end, int c)
{
        for (int i = 0; i < c; i++) {
                char asdf[] = "ABCDEFGHJKLMNOPQRSTUVWXYZ";
                s += snprintf(s, end - s, "      ");
                for (int x = 1; x < board_size(board) - 1; x++)
                        s += snprintf(s, end - s, "%c ", asdf[x - 1]);
                s += snprintf(s, end -s, " ");
        }
        s += snprintf(s, end - s, "\n");
        for (int i = 0; i < c; i++) {
                s += snprintf(s, end - s, "    +-");
                for (int x = 1; x < board_size(board) - 1; x++)
                        s += snprintf(s, end - s, "--");
                s += snprintf(s, end - s, "+");
        }
        s += snprintf(s, end - s, "\n");
        return s;
}

static char *
board_print_bottom(struct board *board, char *s, char *end, int c)
{
        for (int i = 0; i < c; i++) {
                s += snprintf(s, end - s, "    +-");
                for (int x = 1; x < board_size(board) - 1; x++)
                        s += snprintf(s, end - s, "--");
                s += snprintf(s, end - s, "+");
        }
        s += snprintf(s, end - s, "\n");
        return s;
}

static char *
board_print_row(struct board *board, int y, char *s, char *end, board_cprint cprint)
{
        s += snprintf(s, end - s, " %2d | ", y);
        for (int 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)
                        s += snprintf(s, end - s, "%c)", stone2char(board_atxy(board, x, y)));
                else
                        s += snprintf(s, end - s, "%c ", stone2char(board_atxy(board, x, y)));
        }
        s += snprintf(s, end - s, "|");
        if (cprint) {
                s += snprintf(s, end - s, " %2d | ", y);
                for (int x = 1; x < board_size(board) - 1; x++) {
                        s = cprint(board, coord_xy(board, x, y), s, end);
                }
                s += snprintf(s, end - s, "|");
        }
        s += snprintf(s, end - s, "\n");
        return s;
}

void
board_print_custom(struct board *board, FILE *f, board_cprint cprint)
{
        char buf[10240];
        char *s = buf;
        char *end = buf + sizeof(buf);
        s += snprintf(s, end - s, "Move: % 3d  Komi: %2.1f  Handicap: %d  Captures B: %d W: %d\n",
                board->moves, board->komi, board->handicap,
                board->captures[S_BLACK], board->captures[S_WHITE]);
        s = board_print_top(board, s, end, 1 + !!cprint);
        for (int y = board_size(board) - 2; y >= 1; y--)
                s = board_print_row(board, y, s, end, cprint);
        board_print_bottom(board, s, end, 1 + !!cprint);
        fprintf(f, "%s\n", buf);
}

static char *
cprint_group(struct board *board, coord_t c, char *s, char *end)
{
        s += snprintf(s, end - s, "%d ", group_base(group_at(board, c)));
        return s;
}

void
board_print(struct board *board, FILE *f)
{
        board_print_custom(board, f, DEBUGL(6) ? cprint_group : NULL);
}


#ifdef BOARD_TRAITS

#if BOARD_TRAIT_SAFE == 1
static bool
board_trait_safe(struct board *board, coord_t coord, enum stone color)
{
        return board_safe_to_play(board, coord, color);
}
#elif BOARD_TRAIT_SAFE == 2
static bool
board_trait_safe(struct board *board, coord_t coord, enum stone color)
{
        return !is_bad_selfatari(board, color, coord);
}
#endif

static void
board_trait_recompute(struct board *board, coord_t coord)
{
        int sfb = -1, sfw = -1;
#ifdef BOARD_TRAIT_SAFE
        sfb = trait_at(board, coord, S_BLACK).safe = board_trait_safe(board, coord, S_BLACK);
        sfw = trait_at(board, coord, S_WHITE).safe = board_trait_safe(board, coord, S_WHITE);
#endif
        if (DEBUGL(8)) {
                fprintf(stderr, "traits[%s:%s lib=%d] (black cap=%d cap1=%d safe=%d) (white cap=%d cap1=%d safe=%d)\n",
                        coord2sstr(coord, board), stone2str(board_at(board, coord)), immediate_liberty_count(board, coord),
                        trait_at(board, coord, S_BLACK).cap, trait_at(board, coord, S_BLACK).cap1, sfb,
                        trait_at(board, coord, S_WHITE).cap, trait_at(board, coord, S_WHITE).cap1, sfw);
        }
}
#endif

/* Recompute traits for dirty points that we have previously touched
 * somehow (libs of their neighbors changed or so). */
static void
board_traits_recompute(struct board *board)
{
#ifdef BOARD_TRAITS
        for (int i = 0; i < board->tqlen; i++) {
                coord_t coord = board->tq[i];
                trait_at(board, coord, S_BLACK).dirty = false;
                if (board_at(board, coord) != S_NONE)
                        continue;
                board_trait_recompute(board, coord);
        }
        board->tqlen = 0;
#endif
}

/* Queue traits of given point for recomputing. */
static void
board_trait_queue(struct board *board, coord_t coord)
{
#ifdef BOARD_TRAITS
        if (trait_at(board, coord, S_BLACK).dirty)
                return;
        board->tq[board->tqlen++] = coord;
        trait_at(board, coord, S_BLACK).dirty = true;
#endif
}


/* 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);
        board->qhash[coord_quadrant(coord, board)] ^= hash_at(board, coord, color);
        if (DEBUGL(8))
                fprintf(stderr, "board_hash_update(%d,%d,%d) ^ %"PRIhash" -> %"PRIhash"\n", color, coord_x(coord, board), coord_y(coord, board), hash_at(board, coord, color), board->hash);

#ifdef BOARD_SPATHASH
        /* Gridcular metric is reflective, so we update all hashes
         * of appropriate ditance in OUR circle. */
        for (int d = 1; d <= BOARD_SPATHASH_MAXD; d++) {
                for (int j = ptind[d]; j < ptind[d + 1]; j++) {
                        ptcoords_at(x, y, coord, board, j);
                        /* We either changed from S_NONE to color
                         * or vice versa; doesn't matter. */
                        board->spathash[coord_xy(board, x, y)][d - 1][0] ^=
                                pthashes[0][j][color] ^ pthashes[0][j][S_NONE];
                        board->spathash[coord_xy(board, x, y)][d - 1][1] ^=
                                pthashes[0][j][stone_other(color)] ^ pthashes[0][j][S_NONE];
                }
        }
#endif

#if defined(BOARD_PAT3)
        /* @color is not what we need in case of capture. */
        static const int ataribits[8] = { -1, 0, -1, 1, 2, -1, 3, -1 };
        enum stone new_color = board_at(board, coord);
        bool in_atari = false;
        if (new_color == S_NONE) {
                board->pat3[coord] = pattern3_hash(board, coord);
        } else {
                in_atari = (board_group_info(board, group_at(board, coord)).libs == 1);
        }
        foreach_8neighbor(board, coord) {
                /* Internally, the loop uses fn__i=[0..7]. We can use
                 * it directly to address bits within the bitmap of the
                 * neighbors since the bitmap order is reverse to the
                 * loop order. */
                if (board_at(board, c) != S_NONE)
                        continue;
                board->pat3[c] &= ~(3 << (fn__i*2));
                board->pat3[c] |= new_color << (fn__i*2);
                if (ataribits[fn__i] >= 0) {
                        board->pat3[c] &= ~(1 << (16 + ataribits[fn__i]));
                        board->pat3[c] |= in_atari << (16 + ataribits[fn__i]);
                }
#if defined(BOARD_TRAITS)
                board_trait_queue(board, c);
#endif
        } foreach_8neighbor_end;
#endif
}

/* Commit current board hash to history. */
static void profiling_noinline
board_hash_commit(struct board *board)
{
        if (DEBUGL(8))
                fprintf(stderr, "board_hash_commit %"PRIhash"\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_symmetry_update(struct board *b, struct board_symmetry *symmetry, coord_t c)
{
        if (likely(symmetry->type == SYM_NONE)) {
                /* Fully degenerated already. We do not support detection
                 * of restoring of symmetry, assuming that this is too rare
                 * a case to handle. */
                return;
        }

        int x = coord_x(c, b), y = coord_y(c, b), t = board_size(b) / 2;
        int dx = board_size(b) - 1 - x; /* for SYM_DOWN */
        if (DEBUGL(6)) {
                fprintf(stderr, "SYMMETRY [%d,%d,%d,%d|%d=%d] update for %d,%d\n",
                        symmetry->x1, symmetry->y1, symmetry->x2, symmetry->y2,
                        symmetry->d, symmetry->type, x, y);
        }

        switch (symmetry->type) {
                case SYM_FULL:
                        if (x == t && y == t) {
                                /* Tengen keeps full symmetry. */
                                return;
                        }
                        /* New symmetry now? */
                        if (x == y) {
                                symmetry->type = SYM_DIAG_UP;
                                symmetry->x1 = symmetry->y1 = 1;
                                symmetry->x2 = symmetry->y2 = board_size(b) - 1;
                                symmetry->d = 1;
                        } else if (dx == y) {
                                symmetry->type = SYM_DIAG_DOWN;
                                symmetry->x1 = symmetry->y1 = 1;
                                symmetry->x2 = symmetry->y2 = board_size(b) - 1;
                                symmetry->d = 1;
                        } else if (x == t) {
                                symmetry->type = SYM_HORIZ;
                                symmetry->y1 = 1;
                                symmetry->y2 = board_size(b) - 1;
                                symmetry->d = 0;
                        } else if (y == t) {
                                symmetry->type = SYM_VERT;
                                symmetry->x1 = 1;
                                symmetry->x2 = board_size(b) - 1;
                                symmetry->d = 0;
                        } else {
break_symmetry:
                                symmetry->type = SYM_NONE;
                                symmetry->x1 = symmetry->y1 = 1;
                                symmetry->x2 = symmetry->y2 = board_size(b) - 1;
                                symmetry->d = 0;
                        }
                        break;
                case SYM_DIAG_UP:
                        if (x == y)
                                return;
                        goto break_symmetry;
                case SYM_DIAG_DOWN:
                        if (dx == y)
                                return;
                        goto break_symmetry;
                case SYM_HORIZ:
                        if (x == t)
                                return;
                        goto break_symmetry;
                case SYM_VERT:
                        if (y == t)
                                return;
                        goto break_symmetry;
                case SYM_NONE:
                        assert(0);
                        break;
        }

        if (DEBUGL(6)) {
                fprintf(stderr, "NEW SYMMETRY [%d,%d,%d,%d|%d=%d]\n",
                        symmetry->x1, symmetry->y1, symmetry->x2, symmetry->y2,
                        symmetry->d, symmetry->type);
        }
        /* Whew. */
}


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

        board_play(board, &m);
        /* Simulate white passing; otherwise, UCT search can get confused since
         * tree depth parity won't match the color to move. */
        board->moves++;

        char *str = coord2str(m.coord, board);
        if (DEBUGL(1))
                fprintf(stderr, "choosing handicap %s (%d,%d)\n", str, x, y);
        if (f) 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 }, { min, max }, { max, min },
                { 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(group_base(g), board));
                        assert(0);
                }
#endif
}

static void
check_pat3_consistency(struct board *board, coord_t coord)
{
#ifdef DEBUG
        foreach_8neighbor(board, coord) {
                if (board_at(board, c) == S_NONE && pattern3_hash(board, c) != board->pat3[c]) {
                        board_print(board, stderr);
                        fprintf(stderr, "%s(%d)->%s(%d) computed %x != stored %x (%d)\n", coord2sstr(coord, board), coord, coord2sstr(c, board), c, pattern3_hash(board, c), board->pat3[c], fn__i);
                        assert(0);
                }
        } foreach_8neighbor_end;
#endif
}

static void
board_capturable_add(struct board *board, group_t group, coord_t lib, bool onestone)
{
        //fprintf(stderr, "group %s cap %s\n", coord2sstr(group, board), coord2sstr(lib, boarD));
#ifdef BOARD_TRAITS
        /* Increase capturable count trait of my last lib. */
        enum stone capturing_color = stone_other(board_at(board, group));
        assert(capturing_color == S_BLACK || capturing_color == S_WHITE);
        foreach_neighbor(board, lib, {
                if (DEBUGL(8) && group_at(board, c) == group)
                        fprintf(stderr, "%s[%d] %s cap bump bc of %s(%d) member %s onestone %d\n", coord2sstr(lib, board), trait_at(board, lib, capturing_color).cap, stone2str(capturing_color), coord2sstr(group, board), board_group_info(board, group).libs, coord2sstr(c, board), onestone);
                trait_at(board, lib, capturing_color).cap += (group_at(board, c) == group);
                trait_at(board, lib, capturing_color).cap1 += (group_at(board, c) == group && onestone);
        });
        board_trait_queue(board, lib);
#endif

#ifdef BOARD_PAT3
        int fn__i = 0;
        foreach_neighbor(board, lib, {
                board->pat3[lib] |= (group_at(board, c) == group) << (16 + 3 - fn__i);
                fn__i++;
        });
#endif

#ifdef WANT_BOARD_C
        /* Update the list of capturable groups. */
        assert(group);
        assert(board->clen < board_size2(board));
        board->c[board->clen++] = group;
#endif
}
static void
board_capturable_rm(struct board *board, group_t group, coord_t lib, bool onestone)
{
        //fprintf(stderr, "group %s nocap %s\n", coord2sstr(group, board), coord2sstr(lib, board));
#ifdef BOARD_TRAITS
        /* Decrease capturable count trait of my previously-last lib. */
        enum stone capturing_color = stone_other(board_at(board, group));
        assert(capturing_color == S_BLACK || capturing_color == S_WHITE);
        foreach_neighbor(board, lib, {
                if (DEBUGL(8) && group_at(board, c) == group)
                        fprintf(stderr, "%s[%d] cap dump bc of %s(%d) member %s onestone %d\n", coord2sstr(lib, board), trait_at(board, lib, capturing_color).cap, coord2sstr(group, board), board_group_info(board, group).libs, coord2sstr(c, board), onestone);
                trait_at(board, lib, capturing_color).cap -= (group_at(board, c) == group);
                trait_at(board, lib, capturing_color).cap1 -= (group_at(board, c) == group && onestone);
        });
        board_trait_queue(board, lib);
#endif

#ifdef BOARD_PAT3
        int fn__i = 0;
        foreach_neighbor(board, lib, {
                board->pat3[lib] &= ~((group_at(board, c) == group) << (16 + 3 - fn__i));
                fn__i++;
        });
#endif

#ifdef WANT_BOARD_C
        /* Update the list of capturable groups. */
        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_base(group));
        assert(0);
#endif
}

static void
board_atariable_add(struct board *board, group_t group, coord_t lib1, coord_t lib2)
{
#ifdef BOARD_TRAITS
        board_trait_queue(board, lib1);
        board_trait_queue(board, lib2);
#endif
}
static void
board_atariable_rm(struct board *board, group_t group, coord_t lib1, coord_t lib2)
{
#ifdef BOARD_TRAITS
        board_trait_queue(board, lib1);
        board_trait_queue(board, lib2);
#endif
}

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

        check_libs_consistency(board, group);

        struct group *gi = &board_group_info(board, group);
        bool onestone = group_is_onestone(board, group);
        if (gi->libs < GROUP_KEEP_LIBS) {
                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, coord, onestone);
                } else if (gi->libs == 1) {
                        board_capturable_rm(board, group, gi->lib[0], onestone);
                        board_atariable_add(board, group, gi->lib[0], coord);
                } else if (gi->libs == 2) {
                        board_atariable_rm(board, group, gi->lib[0], gi->lib[1]);
                }
                gi->lib[gi->libs++] = coord;
        }

        check_libs_consistency(board, group);
}

static void
board_group_find_extra_libs(struct board *board, group_t group, struct group *gi, coord_t avoid)
{
        /* Add extra liberty from the board to our liberty list. */
        unsigned char watermark[board_size2(board) / 8];
        memset(watermark, 0, sizeof(watermark));
#define watermark_get(c)        (watermark[c >> 3] & (1 << (c & 7)))
#define watermark_set(c)        watermark[c >> 3] |= (1 << (c & 7))

        for (int i = 0; i < GROUP_KEEP_LIBS - 1; i++)
                watermark_set(gi->lib[i]);
        watermark_set(avoid);

        foreach_in_group(board, group) {
                coord_t coord2 = c;
                foreach_neighbor(board, coord2, {
                        if (board_at(board, c) + watermark_get(c) != S_NONE)
                                continue;
                        watermark_set(c);
                        gi->lib[gi->libs++] = c;
                        if (unlikely(gi->libs >= GROUP_KEEP_LIBS))
                                return;
                } );
        } foreach_in_group_end;
#undef watermark_get
#undef watermark_set
}

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

        struct group *gi = &board_group_info(board, group);
        bool onestone = group_is_onestone(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;

                coord_t lib = gi->lib[i] = gi->lib[--gi->libs];
                gi->lib[gi->libs] = 0;

                check_libs_consistency(board, group);

                /* Postpone refilling lib[] until we need to. */
                assert(GROUP_REFILL_LIBS > 1);
                if (gi->libs > GROUP_REFILL_LIBS)
                        return;
                if (gi->libs == GROUP_REFILL_LIBS)
                        board_group_find_extra_libs(board, group, gi, coord);

                if (gi->libs == 2) {
                        board_atariable_add(board, group, gi->lib[0], gi->lib[1]);
                } else if (gi->libs == 1) {
                        board_capturable_add(board, group, gi->lib[0], onestone);
                        board_atariable_rm(board, group, gi->lib[0], lib);
                } else if (gi->libs == 0)
                        board_capturable_rm(board, group, lib, onestone);
                return;
        }

        /* 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;
}


/* This is a low-level routine that doesn't maintain consistency
 * of all the board data structures. */
static void
board_remove_stone(struct board *board, group_t group, 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);
#ifdef BOARD_TRAITS
        /* We mark as cannot-capture now. If this is a ko/snapback,
         * we will get incremented later in board_group_addlib(). */
        trait_at(board, c, S_BLACK).cap = trait_at(board, c, S_BLACK).cap1 = 0;
        trait_at(board, c, S_WHITE).cap = trait_at(board, c, S_WHITE).cap1 = 0;
        board_trait_queue(board, c);
#endif

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

#ifdef BOARD_PAT3
        /* board_hash_update() might have seen the freed up point as able
         * to capture another group in atari that only after the loop
         * above gained enough liberties. Reset pat3 again. */
        board->pat3[c] = pattern3_hash(board, c);
#endif

        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++] = c;
}

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

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

        struct group *gi = &board_group_info(board, group);
        assert(gi->libs == 0);
        memset(gi, 0, sizeof(*gi));

        return stones;
}


static void profiling_noinline
add_to_group(struct board *board, group_t group, coord_t prevstone, coord_t coord)
{
#ifdef BOARD_TRAITS
        struct group *gi = &board_group_info(board, group);
        bool onestone = group_is_onestone(board, group);

        if (gi->libs == 1) {
                /* Our group is temporarily in atari; make sure the capturable
                 * counts also correspond to the newly added stone before we
                 * start adding liberties again so bump-dump ops match. */
                enum stone capturing_color = stone_other(board_at(board, group));
                assert(capturing_color == S_BLACK || capturing_color == S_WHITE);

                coord_t lib = board_group_info(board, group).lib[0];
                if (coord_is_adjecent(lib, coord, board)) {
                        if (DEBUGL(8))
                                fprintf(stderr, "add_to_group %s: %s[%d] bump\n", coord2sstr(group, board), coord2sstr(lib, board), trait_at(board, lib, capturing_color).cap);
                        trait_at(board, lib, capturing_color).cap++;
                        /* This is never a 1-stone group, obviously. */
                        board_trait_queue(board, lib);
                }

                if (onestone) {
                        /* We are not 1-stone group anymore, update the cap1
                         * counter specifically. */
                        foreach_neighbor(board, group, {
                                if (board_at(board, c) != S_NONE) continue;
                                trait_at(board, c, capturing_color).cap1--;
                                board_trait_queue(board, c);
                        });
                }
        }
#endif

        group_at(board, coord) = group;
        groupnext_at(board, coord) = groupnext_at(board, prevstone);
        groupnext_at(board, prevstone) = coord;

        foreach_neighbor(board, coord, {
                if (board_at(board, c) == S_NONE)
                        board_group_addlib(board, group, c);
        });

        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),
                        group_base(group));
}

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_base(group_from), group_base(group_to));
        struct group *gi_from = &board_group_info(board, group_from);
        struct group *gi_to = &board_group_info(board, group_to);
        bool onestone_from = group_is_onestone(board, group_from);
        bool onestone_to = group_is_onestone(board, group_to);

        /* We do this early before the group info is rewritten. */
        if (gi_from->libs == 2)
                board_atariable_rm(board, group_from, gi_from->lib[0], gi_from->lib[1]);
        else if (gi_from->libs == 1)
                board_capturable_rm(board, group_from, gi_from->lib[0], onestone_from);

        if (DEBUGL(7))
                fprintf(stderr,"---- (froml %d, tol %d)\n", gi_from->libs, gi_to->libs);

        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, gi_from->lib[i], onestone_to);
                        } else if (gi_to->libs == 1) {
                                board_capturable_rm(board, group_to, gi_to->lib[0], onestone_to);
                                board_atariable_add(board, group_to, gi_to->lib[0], gi_from->lib[i]);
                        } else if (gi_to->libs == 2) {
                                board_atariable_rm(board, group_to, gi_to->lib[0], gi_to->lib[1]);
                        }
                        gi_to->lib[gi_to->libs++] = gi_from->lib[i];
                        if (gi_to->libs >= GROUP_KEEP_LIBS)
                                break;
next_from_lib:;
                }
        }

        if (gi_to->libs == 1) {
                coord_t lib = board_group_info(board, group_to).lib[0];
#ifdef BOARD_TRAITS
                enum stone capturing_color = stone_other(board_at(board, group_to));
                assert(capturing_color == S_BLACK || capturing_color == S_WHITE);

                /* Our group is currently in atari; make sure we properly
                 * count in even the neighbors from the other group in the
                 * capturable counter. */
                foreach_neighbor(board, lib, {
                        if (DEBUGL(8) && group_at(board, c) == group_from)
                                fprintf(stderr, "%s[%d] cap bump\n", coord2sstr(lib, board), trait_at(board, lib, capturing_color).cap);
                        trait_at(board, lib, capturing_color).cap += (group_at(board, c) == group_from);
                        /* This is never a 1-stone group, obviously. */
                });
                board_trait_queue(board, lib);

                if (onestone_to) {
                        /* We are not 1-stone group anymore, update the cap1
                         * counter specifically. */
                        foreach_neighbor(board, group_to, {
                                if (board_at(board, c) != S_NONE) continue;
                                trait_at(board, c, capturing_color).cap1--;
                                board_trait_queue(board, c);
                        });
                }
#endif
#ifdef BOARD_PAT3
                if (gi_from->libs == 1) {
                        /* We removed group_from from capturable groups,
                         * therefore switching the atari flag off.
                         * We need to set it again since group_to is also
                         * capturable. */
                        int fn__i = 0;
                        foreach_neighbor(board, lib, {
                                board->pat3[lib] |= (group_at(board, c) == group_from) << (16 + 3 - fn__i);
                                fn__i++;
                        });
                }
#endif
        }

        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_base(group_to));
        groupnext_at(board, group_base(group_to)) = group_base(group_from);
        memset(gi_from, 0, sizeof(struct group));

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

static group_t profiling_noinline
new_group(struct board *board, coord_t coord)
{
        group_t group = coord;
        struct group *gi = &board_group_info(board, group);
        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;
        });

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

        if (gi->libs == 2)
                board_atariable_add(board, group, gi->lib[0], gi->lib[1]);
        else if (gi->libs == 1)
                board_capturable_add(board, group, gi->lib[0], true);
        check_libs_consistency(board, group);

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

        return group;
}

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

        inc_neighbor_count_at(board, c, color);
        /* We can be S_NONE, in that case we need to update the safety
         * trait since we might be left with only one liberty. */
        board_trait_queue(board, c);

        if (!ngroup)
                return group;

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

        if (ncolor == color && ngroup != group) {
                if (!group) {
                        group = ngroup;
                        add_to_group(board, group, c, coord);
                } else {
                        merge_groups(board, group, ngroup);
                }
        } else if (ncolor == other_color) {
                if (DEBUGL(8)) {
                        struct group *gi = &board_group_info(board, ngroup);
                        fprintf(stderr, "testing captured group %d[%s]: ", group_base(ngroup), coord2sstr(group_base(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 group;
}

/* We played on a place with at least one liberty. We will become a member of
 * some group for sure. */
static group_t 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);
        group_t group = 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]);

#if defined(BOARD_TRAITS) && defined(DEBUG)
        /* Sanity check that cap matches reality. */
        {
                int a = 0, b = 0;
                foreach_neighbor(board, coord, {
                        group_t g = group_at(board, c);
                        a += g && (board_at(board, c) == other_color && board_group_info(board, g).libs == 1);
                        b += g && (board_at(board, c) == other_color && board_group_info(board, g).libs == 1) && group_is_onestone(board, g);
                });
                assert(a == trait_at(board, coord, color).cap);
                assert(b == trait_at(board, coord, color).cap1);
#ifdef BOARD_TRAIT_SAFE
                assert(board_trait_safe(board, coord, color) == trait_at(board, coord, color).safe);
#endif
        }
#endif
        foreach_neighbor(board, coord, {
                group = play_one_neighbor(board, coord, color, other_color, c, group);
        });

        board_at(board, coord) = color;
        if (unlikely(!group))
                group = new_group(board, coord);

        board->last_move2 = board->last_move;
        board->last_move = *m;
        board->moves++;
        board_hash_update(board, coord, color);
        board_symmetry_update(board, &board->symmetry, coord);
        struct move ko = { pass, S_NONE };
        board->ko = ko;

        check_pat3_consistency(board, coord);

        return group;
}

/* 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 == 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, {
                group_t g = group_at(board, c);
                if (DEBUGL(7))
                        fprintf(stderr, "board_check: group %d has %d libs\n",
                                g, board_group_info(board, g).libs);
                captured_groups += (board_group_info(board, g).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;
        }
#ifdef BOARD_TRAITS
        /* We _will_ for sure capture something. */
        assert(trait_at(board, coord, color).cap > 0);
#ifdef BOARD_TRAIT_SAFE
        assert(trait_at(board, coord, color).safe == board_trait_safe(board, coord, color));
#endif
#endif

        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]);

        int ko_caps = 0;
        coord_t cap_at = pass;
        foreach_neighbor(board, coord, {
                inc_neighbor_count_at(board, c, color);
                /* Originally, this could not have changed any trait
                 * since no neighbors were S_NONE, however by now some
                 * of them might be removed from the board. */
                board_trait_queue(board, c);

                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_base(group));

                if (board_group_captured(board, group)) {
                        ko_caps += board_group_capture(board, group);
                        cap_at = c;
                }
        });
        if (ko_caps == 1) {
                ko.color = stone_other(color);
                ko.coord = cap_at; // unique
                board->last_ko = ko;
                board->last_ko_age = board->moves;
                if (DEBUGL(5))
                        fprintf(stderr, "guarding ko at %d,%s\n", ko.color, coord2sstr(ko.coord, board));
        }

        board_at(board, coord) = color;
        group_t group = new_group(board, coord);

        board->last_move2 = board->last_move;
        board->last_move = *m;
        board->moves++;
        board_hash_update(board, coord, color);
        board_hash_commit(board);
        board_traits_recompute(board);
        board_symmetry_update(board, &board->symmetry, coord);
        board->ko = ko;

        check_pat3_consistency(board, coord);

        return !!group;
}

static int __attribute__((flatten))
board_play_f(struct board *board, struct move *m, int f)
{
        if (DEBUGL(7)) {
                fprintf(stderr, "board_play(%s): ---- Playing %d,%d\n", coord2sstr(m->coord, board), 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.) */
                group_t group = board_play_outside(board, m, f);
                if (unlikely(board_group_captured(board, group))) {
                        board_group_capture(board, group);
                }
                board_hash_commit(board);
                board_traits_recompute(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))) {
                struct move nomove = { pass, S_NONE };
                board->ko = nomove;
                board->last_move4 = board->last_move3;
                board->last_move3 = board->last_move2;
                board->last_move2 = board->last_move;
                board->last_move = *m;
                return 0;
        }

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

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

/* Undo, supported only for pass moves. This form of undo is required by KGS
 * to settle disputes on dead groups. (Undo of real moves would be more complex
 * particularly for capturing moves.) */
int board_undo(struct board *board)
{
        if (!is_pass(board->last_move.coord))
                return -1;
        board->last_move = board->last_move2;
        board->last_move2 = board->last_move3;
        board->last_move3 = board->last_move4;
        if (board->last_ko_age == board->moves)
                board->ko = board->last_ko;
        return 0;
}

static inline bool
board_try_random_move(struct board *b, enum stone color, coord_t *coord, int f, ppr_permit permit, void *permit_data)
{
        *coord = b->f[f];
        struct move m = { *coord, color };
        if (DEBUGL(6))
                fprintf(stderr, "trying random move %d: %d,%d %s %d\n", f, coord_x(*coord, b), coord_y(*coord, b), coord2sstr(*coord, b), board_is_valid_move(b, &m));
        if (unlikely(board_is_one_point_eye(b, *coord, color)) /* bad idea to play into one, usually */
                || !board_is_valid_move(b, &m)
                || (permit && !permit(permit_data, b, &m)))
                return false;
        if (m.coord == *coord) {
                return likely(board_play_f(b, &m, f) >= 0);
        } else {
                *coord = m.coord; // permit modified the coordinate
                return likely(board_play(b, &m) >= 0);
        }
}

void
board_play_random(struct board *b, enum stone color, coord_t *coord, ppr_permit permit, void *permit_data)
{
        if (unlikely(b->flen == 0))
                goto pass;

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

pass:
        *coord = pass;
        struct move m = { pass, color };
        board_play(b, &m);
}


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

        /* 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;
        /* For false eye, we need two enemy stones diagonally in the
         * middle of the board, or just one enemy stone at the edge
         * or in the corner. */
        color_diag_libs[stone_other(eye_color)] += !!color_diag_libs[S_OFFBOARD];
        return color_diag_libs[stone_other(eye_color)] >= 2;
}

bool
board_is_one_point_eye(struct board *board, coord_t coord, enum stone eye_color)
{
        return board_is_eyelike(board, coord, eye_color)
                && !board_is_false_eyelike(board, coord, eye_color);
}

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;
}


floating_t
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 && board->rules != RULES_STONES_ONLY)
                        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];
}

/* Owner map: 0: undecided; 1: black; 2: white; 3: dame */

/* One flood-fill iteration; returns true if next iteration
 * is required. */
static bool
board_tromp_taylor_iter(struct board *board, int *ownermap)
{
        bool needs_update = false;
        foreach_free_point(board) {
                /* Ignore occupied and already-dame positions. */
                assert(board_at(board, c) == S_NONE);
                if (board->rules == RULES_STONES_ONLY)
                    ownermap[c] = 3;
                if (ownermap[c] == 3)
                        continue;
                /* Count neighbors. */
                int nei[4] = {0};
                foreach_neighbor(board, c, {
                        nei[ownermap[c]]++;
                });
                /* If we have neighbors of both colors, or dame,
                 * we are dame too. */
                if ((nei[1] && nei[2]) || nei[3]) {
                        ownermap[c] = 3;
                        /* Speed up the propagation. */
                        foreach_neighbor(board, c, {
                                if (board_at(board, c) == S_NONE)
                                        ownermap[c] = 3;
                        });
                        needs_update = true;
                        continue;
                }
                /* If we have neighbors of one color, we are owned
                 * by that color, too. */
                if (!ownermap[c] && (nei[1] || nei[2])) {
                        int newowner = nei[1] ? 1 : 2;
                        ownermap[c] = newowner;
                        /* Speed up the propagation. */
                        foreach_neighbor(board, c, {
                                if (board_at(board, c) == S_NONE && !ownermap[c])
                                        ownermap[c] = newowner;
                        });
                        needs_update = true;
                        continue;
                }
        } foreach_free_point_end;
        return needs_update;
}

/* Tromp-Taylor Counting */
floating_t
board_official_score(struct board *board, struct move_queue *q)
{

        /* 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 ownermap[board_size2(board)];
        int s[4] = {0};
        const int o[4] = {0, 1, 2, 0};
        foreach_point(board) {
                ownermap[c] = o[board_at(board, c)];
                s[board_at(board, c)]++;
        } foreach_point_end;

        if (q) {
                /* Process dead groups. */
                for (unsigned int i = 0; i < q->moves; i++) {
                        foreach_in_group(board, q->move[i]) {
                                enum stone color = board_at(board, c);
                                ownermap[c] = o[stone_other(color)];
                                s[color]--; s[stone_other(color)]++;
                        } foreach_in_group_end;
                }
        }

        /* We need to special-case empty board. */
        if (!s[S_BLACK] && !s[S_WHITE])
                return board->komi + board->handicap;

        while (board_tromp_taylor_iter(board, ownermap))
                /* Flood-fill... */;

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

        foreach_point(board) {
                assert(board_at(board, c) == S_OFFBOARD || ownermap[c] != 0);
                if (ownermap[c] == 3)
                        continue;
                scores[ownermap[c]]++;
        } foreach_point_end;

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