static int DrawMove(BOARD *board, MOVE move)
{
MakeMove(board, &move);
int draw = AssessDraw(board, 0);
Takeback(board, move);
return draw != ERRORVALUE;
}
static int Quiescent(BOARD *board, int alpha, int beta, int root, CONTROL *control, MOVE killers[][2])
{
int nmoves, nlegal = 0;
int val;
MOVE moves[MAXMOVES];
if(!control->ponder && clock() - control->init_time >= control->max_time*CPMS){
control->stop = 1;
}
val = LazyEval(board);
if(val-LAZYBETA >= beta) return beta;
if(val+LAZYALPHA < alpha) return alpha;
val = StaticEval(board);
UpdateTable(&hash_table, board->zobrist_key, val, 0, 0, HASH_EXACT);
if (val >= beta) return beta;
if (val > alpha) alpha = val;
nmoves = CaptureGen(board, moves);
nmoves = FilterWinning(board, moves, nmoves);
// nmoves = SortMoves(board, moves, nmoves, killers[root]);
for(int i = 0; i < nmoves; i++){
control->node_count++;
MakeMove(board, &moves[i]);
if(!LeftInCheck(board)){
nlegal++;
val = -Quiescent(board, -beta, -alpha, root+1, control, killers);
Takeback(board, moves[i]);
if(val >= beta){
return beta;
}
if(val > alpha){
alpha = val;
}
}else Takeback(board, moves[i]);
}
return alpha;
}
/*This works because the replacement scheme ensures shallow PV is not overwritten,
and may fail if the hash table is full.*/
static int RetrievePV(BOARD *board, MOVE *PV, unsigned int depth)
{
unsigned int PVlen = 0;
MOVE mov = GetHashMove(&hash_table, board->zobrist_key);
while(mov && PVlen <= depth && IsLegal(board, &mov)){
PV[PVlen++] = mov;
MakeMove(board, &mov);
mov = GetHashMove(&hash_table, board->zobrist_key);
}
for(int i = PVlen; i > 0; i--){
Takeback(board, PV[i-1]);
}
return PVlen;
}
static int AlphaBeta(BOARD *board, unsigned int depth, int alpha, int beta,
int root, CONTROL *control, char skip_null, MOVE killers[][2])
{
int nmoves, nlegal = 0;
MOVE moves[MAXMOVES];
MOVE best_move = 0;
char str_mov[MVLEN];
int val = ERRORVALUE;
char hash_flag = HASH_ALPHA;
int reduce = 0, LMR = 0;
if(depth){
if(root > 0){
val = GetHashEval(&hash_table, board->zobrist_key, depth, alpha, beta);
if(val != ERRORVALUE) return val;
}
if(depth > 2 && !InCheck(board, 0)){
if(!skip_null && board->piece_material[board->white_to_move] != 0){
MOVE null_mv = NULL_MOVE;
MakeMove(board, &null_mv);
val = -AlphaBeta(board, depth-3, -beta, -beta+1, root+1, control, 1, killers);
Takeback(board, null_mv);
if(val >= beta) return beta;
}
reduce = 1; /*Try Late Move reductions.*/
}
nmoves = MoveGen(board, moves, 1);
int good = SortMoves(board, moves, nmoves, killers[root]);
for(int i = 0; i < nmoves; i++){
MakeMove(board, &moves[i]);
control->node_count++;
if(!LeftInCheck(board)){
if(root == 0){
if(!control->best_move) control->best_move = moves[i]; /* Better than nothing. */
if(depth > 6 && !control->ponder){
MoveToAlgeb(moves[i], str_mov);
printf("info depth %i hashfull %i currmove %s currmovenumber %i\n",
depth, hash_table.full/(hash_table.size/1000), str_mov, i+1);
}
}
nlegal++;
val = AssesDraw(board);
if(val) {
if(best_move){
LMR = (reduce && i > good && !CAPTMASK(moves[i]) && !InCheck(board, 0)) ? 1 : 0;
val = -AlphaBeta(board, depth-LMR-1, -alpha-1, -alpha, root+1, control, 0, killers);
if(val > alpha){
val = -AlphaBeta(board, depth-1, -alpha-1, -alpha, root+1, control, 0, killers);
if(val > alpha && val < beta){
val = -AlphaBeta(board, depth-1, -beta, -alpha, root+1, control, 0, killers);
}
}
}else val = -AlphaBeta(board, depth-1, -beta, -alpha, root+1, control, 0, killers);
}
Takeback(board, moves[i]);
if(!control->ponder && control->stop) return alpha;
if(val >= beta){
UpdateTable(&hash_table, board->zobrist_key, val, moves[i], depth, HASH_BETA);
if(CAPTMASK(moves[i]) == 0
&& killers[root][0] != moves[i]
&& killers[root][1] != moves[i]){
killers[root][1] = killers[root][0];
killers[root][0] = moves[i];
}
return beta;
}
if(val > alpha){
alpha = val;
hash_flag = HASH_EXACT;
best_move = moves[i];
if(root == 0) control->best_move = best_move;
}
if(root == 0 && ((clock() - control->init_time) > control->wish_time*CPMS)){
/* if short of time, don't search anymore after current move */
control->stop = 1;
return alpha;
}
}else Takeback(board, moves[i]);
}
if(nlegal == 0){
if(InCheck(board, 0)){
/*UpdateTable(&hash_table, board->zobrist_key, MATE_VALUE+root, 0, depth, HASH_EXACT, hash_table.entries);*/
return MATE_VALUE;
}else{
/*UpdateTable(&hash_table, board->zobrist_key, DRAW_VALUE, 0, depth, HASH_EXACT, hash_table.entries);*/
return DRAW_VALUE; /*Stalemate*/
}
}else UpdateTable(&hash_table, board->zobrist_key, alpha, best_move, depth, hash_flag);
}else if(InCheck(board, 0)){
alpha = AlphaBeta(board, 1, alpha, beta, root+1, control, 1, killers);
}else{
alpha = Quiescent(board, alpha, beta, root, control, killers);
}
return alpha;
}
static int AlphaBeta (BOARD *board, int depth, int alpha, int beta,
int root, CONTROL *control, char skip_null, MOVE killers[][2])
{
int nmoves, good = 0, nlegal = 0;
MOVE moves[MAXMOVES];
MOVE best_move = 0;
char str_mov[MVLEN];
int val = ERRORVALUE;
char hash_flag = HASH_ALPHA;
int in_check = InCheck(board, 0);
if (root > control->seldepth) control->seldepth = root;
if (depth > 0 || in_check) {
if (root > 0) {
val = GetHashEval(&hash_table, board->zobrist_key, depth, alpha, beta);
if (val != ERRORVALUE) return val;
}
if (depth > 2 && !in_check) {
if (!skip_null && board->piece_material[board->white_to_move] != 0) {
MOVE null_mv = NULL_MOVE;
MakeMove(board, &null_mv);
val = -AlphaBeta(board, depth-3, -beta, -beta+1, root+1, control, 1, killers);
Takeback(board, null_mv);
if (val >= beta) return beta;
}
}
nmoves = MoveGen(board, moves, 1);
good = SortMoves(board, moves, nmoves, killers[root]);
} else {
if (!control->ponder && clock() - control->init_time >= control->max_time*CPMS) {
control->stop = 1;
}
val = LazyEval(board);
if (val-LAZYBETA >= beta) return beta;
if (val+LAZYALPHA < alpha) return alpha;
val = StaticEval(board);
UpdateTable(&hash_table, board->zobrist_key, val, 0, 0, HASH_EXACT);
if (val >= beta) return beta;
if (val > alpha) alpha = val;
nmoves = CaptureGen(board, moves);
nmoves = FilterWinning(board, moves, nmoves);
}
for (int i = 0; i < nmoves; i++) {
MakeMove(board, &moves[i]);
control->node_count++;
if (LeftInCheck(board)) {
Takeback(board, moves[i]);
continue;
}
if (root == 0) {
if (!control->best_move) control->best_move = moves[i]; /* Better than nothing. */
if (depth > 6 && !control->ponder) {
MoveToAlgeb(moves[i], str_mov);
printf("info depth %i seldepth %i hashfull %i currmove %s currmovenumber %i\n",
depth, control->seldepth, hash_table.full/(hash_table.size/1000), str_mov, i+1);
}
}
nlegal++;
val = AssessDraw(board, control->contempt);
if (val == ERRORVALUE) {
int ext = 0; //InCheck(board, 0) ? 1 : 0;
if (best_move) {
int LMR = (depth > 2 && !in_check && i > good &&
!CAPTMASK(moves[i]) && !InCheck(board, 0)) ? 1 : 0;
val = -AlphaBeta(board, depth+ext-LMR-1, -alpha-1, -alpha, root+1, control, 0, killers);
if (val > alpha) {
val = -AlphaBeta(board, depth+ext-1, -alpha-1, -alpha, root+1, control, 0, killers);
if (val > alpha && val < beta) {
val = -AlphaBeta(board, depth+ext-1, -beta, -alpha, root+1, control, 0, killers);
}
}
} else {
val = -AlphaBeta(board, depth+ext-1, -beta, -alpha, root+1, control, 0, killers);
}
}
Takeback(board, moves[i]);
if (!control->ponder && control->stop) return alpha;
if (val >= beta) {
UpdateTable(&hash_table, board->zobrist_key, val, moves[i], depth, HASH_BETA);
if (CAPTMASK(moves[i]) == 0 && killers[root][0] != moves[i] && killers[root][1] != moves[i]) {
killers[root][1] = killers[root][0];
killers[root][0] = moves[i];
}
return beta;
}
if (val > alpha) {
alpha = val;
hash_flag = HASH_EXACT;
best_move = moves[i];
if (root == 0) control->best_move = best_move;
}
if (root == 0 && ((clock() - control->init_time) > control->wish_time*CPMS)) {
/* if short of time, don't search anymore after current move */
control->stop = 1;
return alpha;
}
}
if (nlegal == 0) {
if (in_check) {
/*UpdateTable(&hash_table, board->zobrist_key, MATE_VALUE+root, 0, depth, HASH_EXACT, hash_table.entries);*/
return MATE_VALUE;
} else if (depth > 0) {
/*UpdateTable(&hash_table, board->zobrist_key, DRAW_VALUE, 0, depth, HASH_EXACT, hash_table.entries);*/
return DRAW_VALUE; /*Stalemate*/
}
} else {
UpdateTable(&hash_table, board->zobrist_key, alpha, best_move, depth, hash_flag);
}
return alpha;
}
