diff options
Diffstat (limited to 'include/actions.c')
| -rw-r--r-- | include/actions.c | 680 |
1 files changed, 340 insertions, 340 deletions
diff --git a/include/actions.c b/include/actions.c index 4f226e1..795c135 100644 --- a/include/actions.c +++ b/include/actions.c @@ -1,18 +1,18 @@ /* - This file is part of ct. + This file is part of ct. - This program is free software: you can redistribute it and/or modify - it under the terms of the GNU General Public License as published by - the Free Software Foundation, either version 3 of the License, or - (at your option) any later version. + This program is free software: you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation, either version 3 of the License, or + (at your option) any later version. - This program is distributed in the hope that it will be useful, but - WITHOUT ANY WARRANTY; without even the implied warranty of - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU - General Public License for more details. + This program is distributed in the hope that it will be useful, but + WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + General Public License for more details. - You should have received a copy of the GNU General Public License - along with ct. If not, see <https://www.gnu.org/licenses/>. + You should have received a copy of the GNU General Public License + along with ct. If not, see <https://www.gnu.org/licenses/>. */ #include "actions.h" @@ -27,13 +27,13 @@ static inline void list_append(action_list_t *list, const enum A_TYPE type, - const int8_t loc, const uint8_t data0, - const uint8_t data1); + const int8_t loc, const uint8_t data0, + const uint8_t data1); static inline void list_prepend(action_list_t *list, const enum A_TYPE type, - const int8_t loc, const uint8_t data0, - const uint8_t data1); + const int8_t loc, const uint8_t data0, + const uint8_t data1); static inline void inline_next_ply(void); @@ -46,336 +46,336 @@ inline_prev_ply(void); // =================================================================== int action_move_to_front(const action_t action, - action_list_t *list) { - action_node_t *n = list->head; + action_list_t *list) { + action_node_t *n = list->head; - // TODO: what if it's not in the list? + // TODO: what if it's not in the list? - while (n) { - if (n->action == action) { - const action_t t = list->head->action; - list->head->action = action; - n->action = t; - return EXIT_SUCCESS; - } - n = n->next; - } + while (n) { + if (n->action == action) { + const action_t t = list->head->action; + list->head->action = action; + n->action = t; + return EXIT_SUCCESS; + } + n = n->next; + } - return EXIT_FAILURE; + return EXIT_FAILURE; } void action_list_free(action_list_t *list) { - if (list) { - action_node_t *n = list->head, *nn; - while (n) { - nn = n->next; - free(n); - n = nn; - } - free(list); - } + if (list) { + action_node_t *n = list->head, *nn; + while (n) { + nn = n->next; + free(n); + n = nn; + } + free(list); + } } // Keep track of move offsets int8_t move_deltas[4]; void action_list_init(void) { - move_deltas[0] = +board_size; - move_deltas[1] = -board_size; - move_deltas[2] = -1; - move_deltas[3] = +1; + move_deltas[0] = +board_size; + move_deltas[1] = -board_size; + move_deltas[2] = -1; + move_deltas[3] = +1; } // We bias place over move by prepending place actions and appending // move actions to the generated list action_list_t *action_list_generate(void) { - action_list_t *list = malloc(sizeof(struct action_list_s)); - - // TODO: trap errno - list->length = 0; - list->head = NULL; + action_list_t *list = malloc(sizeof(struct action_list_s)); - /* - * The check for whether it's a black piece to be played is actually - * black = (ply < 2) ? (ply==1) : (ply & 1), - * but material will always be sufficient in ply < 2 so we might as - * well save on the conditional. - */ + // TODO: trap errno + list->length = 0; + list->head = NULL; - const uint8_t material = (ply & 1) ? black_count : white_count, - flat = material & 0x7F, - cap = ((ply >= 2) && (material & 0x80)), - standing = ((ply >= 2) && flat); + /* + * The check for whether it's a black piece to be played is actually + * black = (ply < 2) ? (ply==1) : (ply & 1), + * but material will always be sufficient in ply < 2 so we might as + * well save on the conditional. + */ - // Step across the board - for (int row = 0; row < board_size; row++) { - for (int col = 0; col < board_size; col++) { - // We'll need these at various points: the location of this - // square and the maximum number of stones we could pick up - const int loc = THE_COORDS(col, row); - const uint8_t count = DANGER_MIN(COUNT_AT(loc), board_size); + const uint8_t material = (ply & 1) ? black_count : white_count, + flat = material & 0x7F, + cap = ((ply >= 2) && (material & 0x80)), + standing = ((ply >= 2) && flat); - // Only try moves after CPS and if the colour is correct - if (count) { - if (ply >= 2 && ((colours[loc] & 1) == current_colour)) { + // Step across the board + for (int row = 0; row < board_size; row++) { + for (int col = 0; col < board_size; col++) { + // We'll need these at various points: the location of this + // square and the maximum number of stones we could pick up + const int loc = THE_COORDS(col, row); + const uint8_t count = DANGER_MIN(COUNT_AT(loc), board_size); - // Pre-compute end-stops and crushes - uint8_t end_stops[4], crushes[4] = {0, 0, 0, 0}; + // Only try moves after CPS and if the colour is correct + if (count) { + if (ply >= 2 && ((colours[loc] & 1) == current_colour)) { - // These are upper bounds, not counting walls and such. - // UP DOWN LEFT RIGHT - end_stops[0] = DANGER_MIN(board_size - row - 1, count); - end_stops[1] = DANGER_MIN(row, count); - end_stops[2] = DANGER_MIN(col, count); - end_stops[3] = DANGER_MIN(board_size - col - 1, count); + // Pre-compute end-stops and crushes + uint8_t end_stops[4], crushes[4] = {0, 0, 0, 0}; - // Now we check for caps and walls - const uint8_t cap_top = STONE_AT(loc) == STONE_CAPSTONE; - for (int d = 0; d < 4; d++){ - const int delta = move_deltas[d]; - const int stop = end_stops[d]; - end_stops[d] = 0; - for (int k = 1; k <= stop; k++) { - const enum STONE_VARIANT stone = STONE_AT(loc+k*delta); - if (stone == STONE_STANDING) { - if (cap_top) { - crushes[d] = 0xFF; - end_stops[d]++; - } - break; - } else if (stone == STONE_CAPSTONE) { - break; - } - end_stops[d]++; - } - } - /* - * For each direction, generate all possible ordered integer - * partitions of 1 ≤ num ≤ count whose number of summands is - * exactly 1 ≤ summands ≤ min(end_stops[dir], num) -- we - * write summands as steps. - * - * We exploit the `gaps' bijection here and elsewhere - * between ordered {integer partitions of n with s summands} - * and {binary strings of length n-1 with s-1 set bits}. - */ - for (enum MOVE_DIRECTION dir=M_UP; dir<=M_RIGHT; dir++) { - for (uint8_t num = 1; num <= count; num++) { - for (uint8_t steps = 1; - steps <= end_stops[dir] && steps <= num; - steps++) { - uint8_t gaps = - ((1<<(board_size - 2)) - 1) >> (board_size-steps-1); - // For 5x5 this givess 0b0000[0XXX] where steps-1 of - // those X's are 1s (starting with LSB) because 4-1=3 - // and 5-1=4 - do { - /* - * We skip the partition if it calls for multiple - * stones at the end with a crush. - */ - const uint8_t last_drop_check = - (num > 1) ? (gaps & (1 << (num - 2))) : 1; - if (crushes[dir] == 0 || last_drop_check) { - // We have to record a crush! - const uint8_t crush = - (steps == end_stops[dir]) && crushes[dir]; - // Store the move + // These are upper bounds, not counting walls and such. + // UP DOWN LEFT RIGHT + end_stops[0] = DANGER_MIN(board_size - row - 1, count); + end_stops[1] = DANGER_MIN(row, count); + end_stops[2] = DANGER_MIN(col, count); + end_stops[3] = DANGER_MIN(board_size - col - 1, count); - list_append(list, A_MOVE, loc, - (crush << 7) | gaps, - (dir<<4) | num); - } - /* - * With thanks to - * https://graphics.stanford.edu/~seander/bithacks.html#NextBitPermutation - * we have the following magic to generate the next - * permutation of steps-many set bits - */ - uint8_t t = (gaps | (gaps - 1)); - gaps = (t + 1) - | (((~t & -~t) - 1) >> (__builtin_ctz(gaps) + 1)); - } while (gaps && (gaps + 1 <= (1 << (num - 1)))); - } - } - } - } - } // end of if (count) { ... } - else if (material) { - // Empty square, generate placements - if (flat) { - list_prepend(list, A_PLACE, loc, STONE_FLAT, 0); - if (standing) - list_prepend(list, A_PLACE, loc, STONE_STANDING,0); - } - if (cap) - list_prepend(list, A_PLACE, loc, STONE_CAPSTONE, 0); - } + // Now we check for caps and walls + const uint8_t cap_top = STONE_AT(loc) == STONE_CAPSTONE; + for (int d = 0; d < 4; d++){ + const int delta = move_deltas[d]; + const int stop = end_stops[d]; + end_stops[d] = 0; + for (int k = 1; k <= stop; k++) { + const enum STONE_VARIANT stone = STONE_AT(loc+k*delta); + if (stone == STONE_STANDING) { + if (cap_top) { + crushes[d] = 0xFF; + end_stops[d]++; } + break; + } else if (stone == STONE_CAPSTONE) { + break; + } + end_stops[d]++; + } + } + /* + * For each direction, generate all possible ordered integer + * partitions of 1 ≤ num ≤ count whose number of summands is + * exactly 1 ≤ summands ≤ min(end_stops[dir], num) -- we + * write summands as steps. + * + * We exploit the `gaps' bijection here and elsewhere + * between ordered {integer partitions of n with s summands} + * and {binary strings of length n-1 with s-1 set bits}. + */ + for (enum MOVE_DIRECTION dir=M_UP; dir<=M_RIGHT; dir++) { + for (uint8_t num = 1; num <= count; num++) { + for (uint8_t steps = 1; + steps <= end_stops[dir] && steps <= num; + steps++) { + uint8_t gaps = + ((1<<(board_size - 2)) - 1) >> (board_size-steps-1); + // For 5x5 this givess 0b0000[0XXX] where steps-1 of + // those X's are 1s (starting with LSB) because 4-1=3 + // and 5-1=4 + do { + /* + * We skip the partition if it calls for multiple + * stones at the end with a crush. + */ + const uint8_t last_drop_check = + (num > 1) ? (gaps & (1 << (num - 2))) : 1; + if (crushes[dir] == 0 || last_drop_check) { + // We have to record a crush! + const uint8_t crush = + (steps == end_stops[dir]) && crushes[dir]; + // Store the move + + list_append(list, A_MOVE, loc, + (crush << 7) | gaps, + (dir<<4) | num); + } + /* + * With thanks to + * https://graphics.stanford.edu/~seander/bithacks.html#NextBitPermutation + * we have the following magic to generate the next + * permutation of steps-many set bits + */ + uint8_t t = (gaps | (gaps - 1)); + gaps = (t + 1) + | (((~t & -~t) - 1) >> (__builtin_ctz(gaps) + 1)); + } while (gaps && (gaps + 1 <= (1 << (num - 1)))); + } + } + } + } + } // end of if (count) { ... } + else if (material) { + // Empty square, generate placements + if (flat) { + list_prepend(list, A_PLACE, loc, STONE_FLAT, 0); + if (standing) + list_prepend(list, A_PLACE, loc, STONE_STANDING,0); } - return list; + if (cap) + list_prepend(list, A_PLACE, loc, STONE_CAPSTONE, 0); + } + } + } + return list; } void action_take(const action_t action) { - const int8_t loc = A_GET_LOC(action); - if (A_GET_TYPE(action) == A_PLACE) { - const uint8_t black = (current_colour == C_BLACK); - switch (A_GET_DATA0(action)) { - case STONE_FLAT: { - if (black) black_count--; - else white_count--; - colours[loc] = current_colour; - celldat[loc] = NUM_INC | STONE_FLAT; - break; - } - case STONE_STANDING: { - if (black) black_count--; - else white_count--; - colours[loc] = current_colour; - celldat[loc] = NUM_INC | STONE_STANDING; - break; - } - default: { - if (black) black_count &= 0x7F; - else white_count &= 0x7F; - colours[loc] = current_colour; - celldat[loc] = NUM_INC | STONE_CAPSTONE; - break; - } - } - } else { - /* - * See the discussion around line 135 for an explanation of the - * encoding. Here we are not interested in whether we crushed, it - * will work out by anyway because we overwrite the top stone - * type. See (*) later for when we do need to know. - */ - const uint8_t gaps = A_GET_DATA0(action) & 0x7F, - num = A_GET_DATA1(action) & 0x0F, // unpack - dir = A_GET_DATA1(action) >> 4; - int8_t delta = move_deltas[dir]; + const int8_t loc = A_GET_LOC(action); + if (A_GET_TYPE(action) == A_PLACE) { + const uint8_t black = (current_colour == C_BLACK); + switch (A_GET_DATA0(action)) { + case STONE_FLAT: { + if (black) black_count--; + else white_count--; + colours[loc] = current_colour; + celldat[loc] = NUM_INC | STONE_FLAT; + break; + } + case STONE_STANDING: { + if (black) black_count--; + else white_count--; + colours[loc] = current_colour; + celldat[loc] = NUM_INC | STONE_STANDING; + break; + } + default: { + if (black) black_count &= 0x7F; + else white_count &= 0x7F; + colours[loc] = current_colour; + celldat[loc] = NUM_INC | STONE_CAPSTONE; + break; + } + } + } else { + /* + * See the discussion around line 135 for an explanation of the + * encoding. Here we are not interested in whether we crushed, it + * will work out by anyway because we overwrite the top stone + * type. See (*) later for when we do need to know. + */ + const uint8_t gaps = A_GET_DATA0(action) & 0x7F, + num = A_GET_DATA1(action) & 0x0F, // unpack + dir = A_GET_DATA1(action) >> 4; + int8_t delta = move_deltas[dir]; - // Use the Kernighan method to count the set bits - int8_t steps = 1; - for (uint8_t _gaps = gaps; _gaps; steps++) _gaps &= _gaps - 1; + // Use the Kernighan method to count the set bits + int8_t steps = 1; + for (uint8_t _gaps = gaps; _gaps; steps++) _gaps &= _gaps - 1; - // Move top stone type to destination - celldat[loc+steps*delta] &= CLR_STONE; // necessary for crushing - celldat[loc+steps*delta] |= STONE_AT(loc); - celldat[loc] &= CLR_STONE; - celldat[loc] |= STONE_FLAT; // should be optimised out + // Move top stone type to destination + celldat[loc+steps*delta] &= CLR_STONE; // necessary for crushing + celldat[loc+steps*delta] |= STONE_AT(loc); + celldat[loc] &= CLR_STONE; + celldat[loc] |= STONE_FLAT; // should be optimised out - uint8_t total = 1, gap_bit = 1 << (num - 2); // it's not important - // what negative - // shifts do here, we - // don't use gap_bit - // if num < 2 - // move stuff starting at destination - for (uint8_t d = 1; d < num; d++, total++, gap_bit >>= 1) { - // We took a step, move everything over so far - if (gaps & gap_bit) { - colours[loc+steps*delta] <<= total; - colours[loc+steps*delta] |= colours[loc] & ((1 << total) - 1); - colours[loc] >>= total; - celldat[loc+steps*delta] += total*NUM_INC; - celldat[loc] -= total*NUM_INC; - // Reset for next step - total = 0; - steps--; - } - } - // Move what remains (steps == 1 here always, so we simplify) - colours[loc+delta] <<= total; - colours[loc+delta] |= colours[loc] & ((1 << total) - 1); - colours[loc] >>= total; - celldat[loc+delta] += total*NUM_INC; - celldat[loc] -= total*NUM_INC; - } - // Next ply - inline_next_ply(); + uint8_t total = 1, gap_bit = 1 << (num - 2); // it's not important + // what negative + // shifts do here, we + // don't use gap_bit + // if num < 2 + // move stuff starting at destination + for (uint8_t d = 1; d < num; d++, total++, gap_bit >>= 1) { + // We took a step, move everything over so far + if (gaps & gap_bit) { + colours[loc+steps*delta] <<= total; + colours[loc+steps*delta] |= colours[loc] & ((1 << total) - 1); + colours[loc] >>= total; + celldat[loc+steps*delta] += total*NUM_INC; + celldat[loc] -= total*NUM_INC; + // Reset for next step + total = 0; + steps--; + } + } + // Move what remains (steps == 1 here always, so we simplify) + colours[loc+delta] <<= total; + colours[loc+delta] |= colours[loc] & ((1 << total) - 1); + colours[loc] >>= total; + celldat[loc+delta] += total*NUM_INC; + celldat[loc] -= total*NUM_INC; + } + // Next ply + inline_next_ply(); } void action_undo(const action_t action) { - // Previous ply - inline_prev_ply(); + // Previous ply + inline_prev_ply(); - const int8_t loc = A_GET_LOC(action); - if (A_GET_TYPE(action) == A_PLACE) { - const uint8_t black = (current_colour == C_BLACK); - celldat[loc] = 0; - if (A_GET_DATA0(action) == STONE_CAPSTONE) { - if (black) black_count |= 0x80; - else white_count |= 0x80; - } else { - if (black) black_count++; - else white_count++; - } - } else { - // See action_take for comments, this is the time reversal, but - // there is one caveat -- undoing a crush! (*) - const uint8_t gaps = A_GET_DATA0(action) & 0x7F, - crush = A_GET_DATA0(action) & 0x80, - num = A_GET_DATA1(action) & 0x0F, - dir = A_GET_DATA1(action) >> 4; - const int8_t delta = move_deltas[dir]; + const int8_t loc = A_GET_LOC(action); + if (A_GET_TYPE(action) == A_PLACE) { + const uint8_t black = (current_colour == C_BLACK); + celldat[loc] = 0; + if (A_GET_DATA0(action) == STONE_CAPSTONE) { + if (black) black_count |= 0x80; + else white_count |= 0x80; + } else { + if (black) black_count++; + else white_count++; + } + } else { + // See action_take for comments, this is the time reversal, but + // there is one caveat -- undoing a crush! (*) + const uint8_t gaps = A_GET_DATA0(action) & 0x7F, + crush = A_GET_DATA0(action) & 0x80, + num = A_GET_DATA1(action) & 0x0F, + dir = A_GET_DATA1(action) >> 4; + const int8_t delta = move_deltas[dir]; - int8_t steps = 1; - uint8_t gap_bit = 1, total = 1; - for (int8_t d = 1; d < num; d++, total++, gap_bit <<= 1) { - if (gaps & gap_bit) { - colours[loc] <<= total; - colours[loc] |= colours[loc+steps*delta] & ((1 << total) - 1); - colours[loc+steps*delta] >>= total; - celldat[loc] += total*NUM_INC; - celldat[loc+steps*delta] -= total*NUM_INC; - total = 0; - steps++; - } - } - colours[loc] <<= total; - colours[loc] |= colours[loc+steps*delta] & ((1 << total) - 1); - colours[loc+steps*delta] >>= total; + int8_t steps = 1; + uint8_t gap_bit = 1, total = 1; + for (int8_t d = 1; d < num; d++, total++, gap_bit <<= 1) { + if (gaps & gap_bit) { + colours[loc] <<= total; + colours[loc] |= colours[loc+steps*delta] & ((1 << total) - 1); + colours[loc+steps*delta] >>= total; + celldat[loc] += total*NUM_INC; + celldat[loc+steps*delta] -= total*NUM_INC; + total = 0; + steps++; + } + } + colours[loc] <<= total; + colours[loc] |= colours[loc+steps*delta] & ((1 << total) - 1); + colours[loc+steps*delta] >>= total; - celldat[loc] += total*NUM_INC; - // celldat[loc] &= CLR_STONE; is not necessary, as STONE_FLAT == 0 - celldat[loc] |= STONE_AT(loc+steps*delta); - celldat[loc+steps*delta] -= total*NUM_INC; - celldat[loc+steps*delta] &= CLR_STONE; - if (crush) { - celldat[loc+steps*delta] |= STONE_STANDING; - } else { - celldat[loc+steps*delta] |= STONE_FLAT; // should be optimised out - } - } + celldat[loc] += total*NUM_INC; + // celldat[loc] &= CLR_STONE; is not necessary, as STONE_FLAT == 0 + celldat[loc] |= STONE_AT(loc+steps*delta); + celldat[loc+steps*delta] -= total*NUM_INC; + celldat[loc+steps*delta] &= CLR_STONE; + if (crush) { + celldat[loc+steps*delta] |= STONE_STANDING; + } else { + celldat[loc+steps*delta] |= STONE_FLAT; // should be optimised out + } + } } void action_to_ptn(const action_t action, char* out_ptn) { - const int8_t loc = A_GET_LOC(action); - if (A_GET_TYPE(action) == A_PLACE) { - generate_place(loc, A_GET_DATA0(action), out_ptn); - } else { - const uint8_t gaps = A_GET_DATA0(action) & 0x7F, - num = A_GET_DATA1(action) & 0x0F, // unpack - dir = A_GET_DATA1(action) >> 4; + const int8_t loc = A_GET_LOC(action); + if (A_GET_TYPE(action) == A_PLACE) { + generate_place(loc, A_GET_DATA0(action), out_ptn); + } else { + const uint8_t gaps = A_GET_DATA0(action) & 0x7F, + num = A_GET_DATA1(action) & 0x0F, // unpack + dir = A_GET_DATA1(action) >> 4; - uint8_t drops[board_size]; // we only ever need board_size-1 in - // drops actually, the last spot is to - // skip a bounds check at (**) - uint8_t mask = 1, steps = 0; - // Translate to a drop sequence - drops[0] = 1; mask = 1; - for (uint8_t d = 1; d < num; d++) { - if (gaps & mask) { - steps++; - drops[steps] = 1; // (**) no bounds check - } else { - drops[steps] += 1; - } - mask <<= 1; - } - generate_move(loc, dir, steps+1, drops, out_ptn); - } + uint8_t drops[board_size]; // we only ever need board_size-1 in + // drops actually, the last spot is to + // skip a bounds check at (**) + uint8_t mask = 1, steps = 0; + // Translate to a drop sequence + drops[0] = 1; mask = 1; + for (uint8_t d = 1; d < num; d++) { + if (gaps & mask) { + steps++; + drops[steps] = 1; // (**) no bounds check + } else { + drops[steps] += 1; + } + mask <<= 1; + } + generate_move(loc, dir, steps+1, drops, out_ptn); + } } // =================================================================== @@ -384,61 +384,61 @@ void action_to_ptn(const action_t action, char* out_ptn) { static inline void list_append(action_list_t *list, const enum A_TYPE type, - const int8_t loc, const uint8_t data0, - const uint8_t data1) { - action_node_t *new = malloc(sizeof(action_node_t)); - // TODO: trap errno + const int8_t loc, const uint8_t data0, + const uint8_t data1) { + action_node_t *new = malloc(sizeof(action_node_t)); + // TODO: trap errno - new->next = NULL; - new->action = A_BUILD(type, loc, data0, data1); + new->next = NULL; + new->action = A_BUILD(type, loc, data0, data1); - if (list->length) { - list->tail->next = new; - list->tail = new; - } else { - list->head = new; - list->tail = new; - } + if (list->length) { + list->tail->next = new; + list->tail = new; + } else { + list->head = new; + list->tail = new; + } - list->length++; + list->length++; } static inline void list_prepend(action_list_t *list, const enum A_TYPE type, - const int8_t loc, const uint8_t data0, - const uint8_t data1) { - action_node_t *new = malloc(sizeof(action_list_t)); - // TODO: trap errno + const int8_t loc, const uint8_t data0, + const uint8_t data1) { + action_node_t *new = malloc(sizeof(action_list_t)); + // TODO: trap errno - new->next = list->head; - list->head = new; - new->action = A_BUILD(type, loc, data0, data1); + new->next = list->head; + list->head = new; + new->action = A_BUILD(type, loc, data0, data1); - if (list->length == 0) { - list->tail = new; - } + if (list->length == 0) { + list->tail = new; + } - list->length++; + list->length++; } static inline void inline_next_ply(void) { - ply++; - if (ply == 2) { - current_colour = C_WHITE; - } else { - if (current_colour == C_BLACK) current_colour = C_WHITE; - else current_colour = C_BLACK; - } + ply++; + if (ply == 2) { + current_colour = C_WHITE; + } else { + if (current_colour == C_BLACK) current_colour = C_WHITE; + else current_colour = C_BLACK; + } } static inline void inline_prev_ply(void) { - if (ply>0) ply--; - if (ply == 1) { - current_colour = C_WHITE; - } else { - if (current_colour == C_BLACK) current_colour = C_WHITE; - else current_colour = C_BLACK; - } + if (ply>0) ply--; + if (ply == 1) { + current_colour = C_WHITE; + } else { + if (current_colour == C_BLACK) current_colour = C_WHITE; + else current_colour = C_BLACK; + } } |