Move Board::think()
{
// ===========================================================================
// This is the entry point for search, it is intended to drive iterative deepening
// The search stops if (whatever comes first):
// - there is no legal move (checkmate or stalemate)
// - there is only one legal move (in this case we don't need to search)
// **later** - time is up
// - the search is interrupted by the user, or by winboard
// - the search depth is reached
// ===========================================================================
int score, legalmoves, currentdepth;
Move singlemove;
// ===========================================================================
// Check if the game has ended, or if there is only one legal move,
// because then we don't need to search:
// ===========================================================================
if (isEndOfgame(legalmoves, singlemove)) return NOMOVE;
if (legalmoves == 1)
{
std::cout << "forced move: "; displayMove(singlemove); std::cout << std::endl;
return singlemove;
}
// ===========================================================================
// There is more than legal 1 move, so prepare to search:
// ===========================================================================
lastPVLength = 0;
memset(lastPV, 0 , sizeof(lastPV));
memset(whiteHeuristics, 0, sizeof(whiteHeuristics));
memset(blackHeuristics, 0, sizeof(blackHeuristics));
inodes = 0;
// display console header
displaySearchStats(1, 0, 0);
timer.init();
msStart = timer.getms();
// iterative deepening:
for (currentdepth = 1; currentdepth <= searchDepth; currentdepth++)
{
// clear the buffers:
memset(moveBufLen, 0, sizeof(moveBufLen));
memset(moveBuffer, 0, sizeof(moveBuffer));
memset(triangularLength, 0, sizeof(triangularLength));
memset(triangularArray, 0, sizeof(triangularArray));
followpv = true;
score = alphabetapvs(0, currentdepth, -LARGE_NUMBER, LARGE_NUMBER);
msStop = timer.getms();
displaySearchStats(2, currentdepth, score);
// stop searching if the current depth leads to a forced mate:
if ((score > (CHECKMATESCORE-currentdepth)) || (score < -(CHECKMATESCORE-currentdepth)))
currentdepth = searchDepth;
}
return (lastPV[0]);
}
int Board::alphabeta(int ply, int depth, int alpha, int beta)
{
// Negascout
int i, j, val;
triangularLength[ply] = ply;
if (depth == 0) return board.eval();
moveBufLen[ply+1] = movegen(moveBufLen[ply]);
for (i = moveBufLen[ply]; i < moveBufLen[ply+1]; i++)
{
makeMove(moveBuffer[i]);
{
if (!isOtherKingAttacked())
{
inodes++;
if (!ply) displaySearchStats(3, ply, i);
val = -alphabeta(ply+1, depth-1, -beta, -alpha);
unmakeMove(moveBuffer[i]);
if (val >= beta)
{
return beta;
}
if (val > alpha)
{
alpha = val; // both sides want to maximize from *their* perspective
triangularArray[ply][ply] = moveBuffer[i]; // save this move
for (j = ply + 1; j < triangularLength[ply + 1]; j++)
{
triangularArray[ply][j] = triangularArray[ply+1][j]; // and append the latest best PV from deeper plies
}
triangularLength[ply] = triangularLength[ply + 1];
if (!ply)
{
msStop = timer.getms();
displaySearchStats(2, depth, val);
}
}
}
else unmakeMove(moveBuffer[i]);
}
}
return alpha;
}
int Board::minimax(int ply, int depth)
{
// Negamax
int i, j, val, best;
best = -LARGE_NUMBER;
triangularLength[ply] = ply;
if (depth == 0) return board.eval();
moveBufLen[ply+1] = movegen(moveBufLen[ply]);
for (i = moveBufLen[ply]; i < moveBufLen[ply+1]; i++)
{
makeMove(moveBuffer[i]);
{
if (!isOtherKingAttacked())
{
inodes++;
if (!ply) displaySearchStats(3, ply, i);
val = -minimax(ply+1, depth-1); // note the minus sign
unmakeMove(moveBuffer[i]);
if (val > best) // both sides want to maximize from *their* perspective
{
best = val;
triangularArray[ply][ply] = moveBuffer[i]; // save this move
for (j = ply + 1; j < triangularLength[ply + 1]; j++)
{
triangularArray[ply][j] = triangularArray[ply+1][j]; // and append the latest best PV from deeper plies
}
triangularLength[ply] = triangularLength[ply + 1];
if (!ply)
{
msStop = timer.getms();
displaySearchStats(2, depth, val);
}
}
}
else unmakeMove(moveBuffer[i]);
}
}
return best;
}
int Board::alphabetapvs(int ply, int depth, int alpha, int beta)
{
// PV search
int i, j, movesfound, pvmovesfound, val;
triangularLength[ply] = ply;
if (depth == 0)
{
followpv = false;
return qsearch(ply, alpha, beta);
}
// repetition check:
if (repetitionCount() >= 3) return DRAWSCORE;
movesfound = 0;
pvmovesfound = 0;
moveBufLen[ply+1] = movegen(moveBufLen[ply]);
for (i = moveBufLen[ply]; i < moveBufLen[ply+1]; i++)
{
selectmove(ply, i, depth, followpv);
makeMove(moveBuffer[i]);
{
if (!isOtherKingAttacked())
{
inodes++;
movesfound++;
if (!ply) displaySearchStats(3, ply, i);
if (pvmovesfound)
{
val = -alphabetapvs(ply+1, depth-1, -alpha-1, -alpha);
if ((val > alpha) && (val < beta))
{
// in case of failure, proceed with normal alphabeta
val = -alphabetapvs(ply+1, depth - 1, -beta, -alpha);
}
}
// normal alphabeta
else val = -alphabetapvs(ply+1, depth-1, -beta, -alpha);
unmakeMove(moveBuffer[i]);
if (val >= beta)
{
// update the history heuristic
if (nextMove)
blackHeuristics[moveBuffer[i].getFrom()][moveBuffer[i].getTosq()] += depth*depth;
else
whiteHeuristics[moveBuffer[i].getFrom()][moveBuffer[i].getTosq()] += depth*depth;
return beta;
}
if (val > alpha)
{
alpha = val; // both sides want to maximize from *their* perspective
pvmovesfound++;
triangularArray[ply][ply] = moveBuffer[i]; // save this move
for (j = ply + 1; j < triangularLength[ply+1]; j++)
{
triangularArray[ply][j] = triangularArray[ply+1][j]; // and append the latest best PV from deeper plies
}
triangularLength[ply] = triangularLength[ply+1];
if (!ply)
{
msStop = timer.getms();
displaySearchStats(2, depth, val);
}
}
}
else unmakeMove(moveBuffer[i]);
}
}
// update the history heuristic
if (pvmovesfound)
{
if (nextMove)
blackHeuristics[triangularArray[ply][ply].getFrom()][triangularArray[ply][ply].getTosq()] += depth*depth;
else
whiteHeuristics[triangularArray[ply][ply].getFrom()][triangularArray[ply][ply].getTosq()] += depth*depth;
}
// 50-move rule:
if (fiftyMove >= 100) return DRAWSCORE;
// Checkmate/stalemate detection:
if (!movesfound)
{
if (isOwnKingAttacked()) return (-CHECKMATESCORE+ply-1);
else return (STALEMATESCORE);
}
return alpha;
}
Move Board::think()
{
// ===========================================================================
// This is the entry point for search, it is intended to drive iterative deepening
// The search stops if (whatever comes first):
// - there is no legal move (checkmate or stalemate)
// - there is only one legal move (in this case we don't need to search)
// - time is up
// - the search is interrupted by the user, or by winboard
// - the search depth is reached
// ===========================================================================
int score, legalmoves, currentdepth;
Move singlemove;
lastScore = 0;
// ===========================================================================
// Check if the game has ended, or if there is only one legal move,
// because then we don't need to search:
// ===========================================================================
if (isEndOfgame(legalmoves, singlemove)) return NOMOVE;
if (legalmoves == 1)
{
//LC std::cout << "forced move: "; displayMove(singlemove); std::cout << std::endl;
/*if (XB_MODE && XB_POST)
{
printf("0 0 0 0 ");
displayMove(singlemove);
std::cout << std::endl;
}*/
return singlemove;
}
// ===========================================================================
// There is more than legal 1 move, so prepare to search:
// ===========================================================================
if (XB_MODE) timeControl();
lastPVLength = 0;
memset(lastPV, 0 , sizeof(lastPV));
memset(whiteHeuristics, 0, sizeof(whiteHeuristics));
memset(blackHeuristics, 0, sizeof(blackHeuristics));
inodes = 0;
countdown = UPDATEINTERVAL;
timedout = false;
// display console header
displaySearchStats(1, 0, 0);
timer.init();
msStart = timer.getms();
// iterative deepening:
for (currentdepth = 1; currentdepth <= searchDepth; currentdepth++)
{
// clear the buffers:
memset(moveBufLen, 0, sizeof(moveBufLen));
memset(moveBuffer, 0, sizeof(moveBuffer));
memset(triangularLength, 0, sizeof(triangularLength));
memset(triangularArray, 0, sizeof(triangularArray));
followpv = true;
allownull = true;
score = alphabetapvs(0, currentdepth, -LARGE_NUMBER, LARGE_NUMBER);
lastScore = score;
// now check if time is up
// if not decide if it makes sense to start another iteration:
if (timedout)
{
//LC std::cout << std::endl;
return (lastPV[0]);
}
else
{
if (!XB_NO_TIME_LIMIT)
{
msStop = timer.getms();
if ((msStop - msStart) > (STOPFRAC * maxTime))
{
//if (!XB_MODE) std::cout << " ok" << std::endl;
return (lastPV[0]);
}
}
}
displaySearchStats(2, currentdepth, score);
// stop searching if the current depth leads to a forced mate:
if ((score > (CHECKMATESCORE-currentdepth)) || (score < -(CHECKMATESCORE-currentdepth)))
currentdepth = searchDepth;
}
return (lastPV[0]);
}
int Board::alphabetapvs(int ply, int depth, int alpha, int beta)
{
// PV search
int i, j, movesfound, pvmovesfound, val;
triangularLength[ply] = ply;
if (depth <= 0)
{
followpv = false;
return qsearch(ply, alpha, beta);
}
// repetition check:
if (repetitionCount() >= 3) return DRAWSCORE;
// now try a null move to get an early beta cut-off:
if (!followpv && allownull)
{
if ((nextMove && (board.totalBlackPieces > NULLMOVE_LIMIT)) || (!nextMove && (board.totalWhitePieces > NULLMOVE_LIMIT)))
{
if (!isOwnKingAttacked())
{
allownull = false;
inodes++;
if (--countdown <=0) readClockAndInput();
nextMove = !nextMove;
hashkey ^= KEY.side;
val = -alphabetapvs(ply, depth - NULLMOVE_REDUCTION, -beta, -beta+1);
nextMove = !nextMove;
hashkey ^= KEY.side;
if (timedout) return 0;
allownull = true;
if (val >= beta) return val;
}
}
}
allownull = true;
movesfound = 0;
pvmovesfound = 0;
moveBufLen[ply+1] = movegen(moveBufLen[ply]);
for (i = moveBufLen[ply]; i < moveBufLen[ply+1]; i++)
{
selectmove(ply, i, depth, followpv);
makeMove(moveBuffer[i]);
{
if (!isOtherKingAttacked())
{
inodes++;
if (--countdown <=0) readClockAndInput();
movesfound++;
if (!ply) displaySearchStats(3, ply, i);
if (pvmovesfound)
{
val = -alphabetapvs(ply+1, depth-1, -alpha-1, -alpha);
if ((val > alpha) && (val < beta))
{
// in case of failure, proceed with normal alphabeta
val = -alphabetapvs(ply+1, depth - 1, -beta, -alpha);
}
}
// normal alphabeta
else val = -alphabetapvs(ply+1, depth-1, -beta, -alpha);
unmakeMove(moveBuffer[i]);
if (timedout) return 0;
if (val >= beta)
{
// update the history heuristic
if (nextMove)
blackHeuristics[moveBuffer[i].getFrom()][moveBuffer[i].getTosq()] += depth*depth;
else
whiteHeuristics[moveBuffer[i].getFrom()][moveBuffer[i].getTosq()] += depth*depth;
return beta;
}
if (val > alpha)
{
alpha = val; // both sides want to maximize from *their* perspective
pvmovesfound++;
triangularArray[ply][ply] = moveBuffer[i]; // save this move
for (j = ply + 1; j < triangularLength[ply+1]; j++)
{
triangularArray[ply][j] = triangularArray[ply+1][j]; // and append the latest best PV from deeper plies
}
triangularLength[ply] = triangularLength[ply+1];
if (!ply) displaySearchStats(2, depth, val);
}
}
else unmakeMove(moveBuffer[i]);
}
}
// update the history heuristic
if (pvmovesfound)
{
if (nextMove)
blackHeuristics[triangularArray[ply][ply].getFrom()][triangularArray[ply][ply].getTosq()] += depth*depth;
else
whiteHeuristics[triangularArray[ply][ply].getFrom()][triangularArray[ply][ply].getTosq()] += depth*depth;
}
// 50-move rule:
if (fiftyMove >= 100) return DRAWSCORE;
// Checkmate/stalemate detection:
if (!movesfound)
{
if (isOwnKingAttacked()) return (-CHECKMATESCORE+ply-1);
else return (STALEMATESCORE);
}
return alpha;
}