Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
- Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+ Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
constexpr int SkipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 };
// Razor and futility margins
- constexpr int RazorMargin[] = {0, 590, 604};
+ constexpr int RazorMargin = 600;
Value futility_margin(Depth d, bool improving) {
return Value((175 - 50 * improving) * d / ONE_PLY);
}
// History and stats update bonus, based on depth
int stat_bonus(Depth depth) {
int d = depth / ONE_PLY;
- return d > 17 ? 0 : 32 * d * d + 64 * d - 64;
+ return d > 17 ? 0 : 29 * d * d + 138 * d - 134;
+ }
+
+ // Add a small random component to draw evaluations to keep search dynamic
+ // and to avoid 3fold-blindness.
+ Value value_draw(Depth depth, Thread* thisThread) {
+ return depth < 4 ? VALUE_DRAW
+ : VALUE_DRAW + Value(2 * (thisThread->nodes.load(std::memory_order_relaxed) % 2) - 1);
}
// Skill structure is used to implement strength limit
Time.availableNodes = 0;
TT.clear();
Threads.clear();
+ Tablebases::init(Options["SyzygyPath"]); // Free up mapped files
}
&& !Skill(Options["Skill Level"]).enabled()
&& rootMoves[0].pv[0] != MOVE_NONE)
{
- for (Thread* th : Threads)
+ std::map<Move, int> votes;
+ Value minScore = this->rootMoves[0].score;
+
+ // Find out minimum score and reset votes for moves which can be voted
+ for (Thread* th: Threads)
{
- Depth depthDiff = th->completedDepth - bestThread->completedDepth;
- Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score;
+ minScore = std::min(minScore, th->rootMoves[0].score);
+ votes[th->rootMoves[0].pv[0]] = 0;
+ }
- // Select the thread with the best score, always if it is a mate
- if ( scoreDiff > 0
- && (depthDiff >= 0 || th->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY))
+ // Vote according to score and depth
+ for (Thread* th : Threads)
+ votes[th->rootMoves[0].pv[0]] += int(th->rootMoves[0].score - minScore)
+ + int(th->completedDepth);
+
+ // Select best thread
+ int bestVote = votes[this->rootMoves[0].pv[0]];
+ for (Thread* th : Threads)
+ {
+ if (votes[th->rootMoves[0].pv[0]] > bestVote)
+ {
+ bestVote = votes[th->rootMoves[0].pv[0]];
bestThread = th;
+ }
}
}
std::memset(ss-4, 0, 7 * sizeof(Stack));
for (int i = 4; i > 0; i--)
- (ss-i)->contHistory = this->contHistory[NO_PIECE][0].get(); // Use as sentinel
+ (ss-i)->continuationHistory = &this->continuationHistory[NO_PIECE][0]; // Use as sentinel
bestValue = delta = alpha = -VALUE_INFINITE;
beta = VALUE_INFINITE;
if (rootDepth >= 5 * ONE_PLY)
{
Value previousScore = rootMoves[pvIdx].previousScore;
- delta = Value(18);
+ delta = Value(20);
alpha = std::max(previousScore - delta,-VALUE_INFINITE);
beta = std::min(previousScore + delta, VALUE_INFINITE);
// Start with a small aspiration window and, in the case of a fail
// high/low, re-search with a bigger window until we don't fail
// high/low anymore.
+ int failedHighCnt = 0;
while (true)
{
- bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false);
+ Depth adjustedDepth = std::max(ONE_PLY, rootDepth - failedHighCnt * ONE_PLY);
+ bestValue = ::search<PV>(rootPos, ss, alpha, beta, adjustedDepth, false);
// Bring the best move to the front. It is critical that sorting
// is done with a stable algorithm because all the values but the
if (mainThread)
{
+ failedHighCnt = 0;
failedLow = true;
Threads.stopOnPonderhit = false;
}
}
else if (bestValue >= beta)
+ {
beta = std::min(bestValue + delta, VALUE_INFINITE);
+ if (mainThread)
+ ++failedHighCnt;
+ }
else
break;
&& !rootNode
&& pos.has_game_cycle(ss->ply))
{
- alpha = VALUE_DRAW;
+ alpha = value_draw(depth, pos.this_thread());
if (alpha >= beta)
return alpha;
}
Key posKey;
Move ttMove, move, excludedMove, bestMove;
Depth extension, newDepth;
- Value bestValue, value, ttValue, eval, maxValue;
+ Value bestValue, value, ttValue, eval, maxValue, pureStaticEval;
bool ttHit, inCheck, givesCheck, improving;
bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture, pvExact;
Piece movedPiece;
if ( Threads.stop.load(std::memory_order_relaxed)
|| pos.is_draw(ss->ply)
|| ss->ply >= MAX_PLY)
- return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos) : VALUE_DRAW;
+ return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos)
+ : value_draw(depth, pos.this_thread());
// Step 3. Mate distance pruning. Even if we mate at the next move our score
// would be at best mate_in(ss->ply+1), but if alpha is already bigger because
(ss+1)->ply = ss->ply + 1;
ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
- ss->contHistory = thisThread->contHistory[NO_PIECE][0].get();
+ ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
(ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
Square prevSq = to_sq((ss-1)->currentMove);
TB::ProbeState err;
TB::WDLScore wdl = Tablebases::probe_wdl(pos, &err);
+ // Force check of time on the next occasion
+ if (thisThread == Threads.main())
+ static_cast<MainThread*>(thisThread)->callsCnt = 0;
+
if (err != TB::ProbeState::FAIL)
{
thisThread->tbHits.fetch_add(1, std::memory_order_relaxed);
// Step 6. Static evaluation of the position
if (inCheck)
{
- ss->staticEval = eval = VALUE_NONE;
+ ss->staticEval = eval = pureStaticEval = VALUE_NONE;
improving = false;
goto moves_loop; // Skip early pruning when in check
}
else if (ttHit)
{
// Never assume anything on values stored in TT
- if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
- eval = ss->staticEval = evaluate(pos);
+ ss->staticEval = eval = pureStaticEval = tte->eval();
+ if (eval == VALUE_NONE)
+ ss->staticEval = eval = pureStaticEval = evaluate(pos);
// Can ttValue be used as a better position evaluation?
if ( ttValue != VALUE_NONE
}
else
{
- ss->staticEval = eval =
- (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
- : -(ss-1)->staticEval + 2 * Eval::Tempo;
+ if ((ss-1)->currentMove != MOVE_NULL)
+ {
+ int p = (ss-1)->statScore;
+ int bonus = p > 0 ? (-p - 2500) / 512 :
+ p < 0 ? (-p + 2500) / 512 : 0;
- tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
- ss->staticEval);
+ pureStaticEval = evaluate(pos);
+ ss->staticEval = eval = pureStaticEval + bonus;
+ }
+ else
+ ss->staticEval = eval = pureStaticEval = -(ss-1)->staticEval + 2 * Eval::Tempo;
+
+ tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, pureStaticEval);
}
// Step 7. Razoring (~2 Elo)
- if ( !PvNode
- && depth < 3 * ONE_PLY
- && eval <= alpha - RazorMargin[depth / ONE_PLY])
- {
- Value ralpha = alpha - (depth >= 2 * ONE_PLY) * RazorMargin[depth / ONE_PLY];
- Value v = qsearch<NonPV>(pos, ss, ralpha, ralpha+1);
- if (depth < 2 * ONE_PLY || v <= ralpha)
- return v;
- }
+ if ( depth < 2 * ONE_PLY
+ && eval <= alpha - RazorMargin)
+ return qsearch<NT>(pos, ss, alpha, beta);
improving = ss->staticEval >= (ss-2)->staticEval
|| (ss-2)->staticEval == VALUE_NONE;
// Step 9. Null move search with verification search (~40 Elo)
if ( !PvNode
&& (ss-1)->currentMove != MOVE_NULL
- && (ss-1)->statScore < 22500
+ && (ss-1)->statScore < 23200
&& eval >= beta
- && ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
+ && pureStaticEval >= beta - 36 * depth / ONE_PLY + 225
&& !excludedMove
&& pos.non_pawn_material(us)
&& (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
assert(eval - beta >= 0);
// Null move dynamic reduction based on depth and value
- Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
+ Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min(int(eval - beta) / 200, 3)) * ONE_PLY;
ss->currentMove = MOVE_NULL;
- ss->contHistory = thisThread->contHistory[NO_PIECE][0].get();
+ ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
pos.do_null_move(st);
while ( (move = mp.next_move()) != MOVE_NONE
&& probCutCount < 3)
- if (pos.legal(move))
+ if (move != excludedMove && pos.legal(move))
{
probCutCount++;
ss->currentMove = move;
- ss->contHistory = thisThread->contHistory[pos.moved_piece(move)][to_sq(move)].get();
+ ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)];
assert(depth >= 5 * ONE_PLY);
moves_loop: // When in check, search starts from here
- const PieceToHistory* contHist[] = { (ss-1)->contHistory, (ss-2)->contHistory, nullptr, (ss-4)->contHistory };
+ const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr, (ss-4)->continuationHistory };
Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
skipQuiets = false;
- ttCapture = false;
+ ttCapture = ttMove && pos.capture_or_promotion(ttMove);
pvExact = PvNode && ttHit && tte->bound() == BOUND_EXACT;
// Step 12. Loop through all pseudo-legal moves until no moves remain
// Singular extension search (~60 Elo). If all moves but one fail low on a
// search of (alpha-s, beta-s), and just one fails high on (alpha, beta),
// then that move is singular and should be extended. To verify this we do
- // a reduced search on on all the other moves but the ttMove and if the
+ // a reduced search on all the other moves but the ttMove and if the
// result is lower than ttValue minus a margin then we will extend the ttMove.
if ( depth >= 8 * ONE_PLY
&& move == ttMove
extension = ONE_PLY;
}
else if ( givesCheck // Check extension (~2 Elo)
- && !moveCountPruning
&& pos.see_ge(move))
extension = ONE_PLY;
+ else if ( pos.can_castle(us) // Extension for king moves that change castling rights
+ && type_of(movedPiece) == KING)
+ extension = ONE_PLY;
+
// Calculate new depth for this move
newDepth = depth - ONE_PLY + extension;
int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
// Countermoves based pruning (~20 Elo)
- if ( lmrDepth < 3
+ if ( lmrDepth < 3 + ((ss-1)->statScore > 0)
&& (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
&& (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
continue;
continue;
}
- if (move == ttMove && captureOrPromotion)
- ttCapture = true;
-
// Update the current move (this must be done after singular extension search)
ss->currentMove = move;
- ss->contHistory = thisThread->contHistory[movedPiece][to_sq(move)].get();
+ ss->continuationHistory = &thisThread->continuationHistory[movedPiece][to_sq(move)];
// Step 15. Make the move
pos.do_move(move, st, givesCheck);
{
Depth r = reduction<PvNode>(improving, depth, moveCount);
- if (captureOrPromotion) // (~5 Elo)
- {
- // Increase reduction by comparing opponent's stat score
- if ((ss-1)->statScore >= 0)
- r += ONE_PLY;
+ // Decrease reduction if opponent's move count is high (~10 Elo)
+ if ((ss-1)->moveCount > 15)
+ r -= ONE_PLY;
- r -= r ? ONE_PLY : DEPTH_ZERO;
- }
- else
+ if (!captureOrPromotion)
{
- // Decrease reduction if opponent's move count is high (~5 Elo)
- if ((ss-1)->moveCount > 15)
- r -= ONE_PLY;
-
// Decrease reduction for exact PV nodes (~0 Elo)
if (pvExact)
r -= ONE_PLY;
r += ONE_PLY;
// Decrease/increase reduction for moves with a good/bad history (~30 Elo)
- r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->statScore / 20000) * ONE_PLY);
+ r -= ss->statScore / 20000 * ONE_PLY;
}
- Depth d = std::max(newDepth - r, ONE_PLY);
+ Depth d = std::max(newDepth - std::max(r, DEPTH_ZERO), ONE_PLY);
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
tte->save(posKey, value_to_tt(bestValue, ss->ply),
bestValue >= beta ? BOUND_LOWER :
PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
- depth, bestMove, ss->staticEval);
+ depth, bestMove, pureStaticEval);
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
ss->pv[0] = MOVE_NONE;
}
+ Thread* thisThread = pos.this_thread();
(ss+1)->ply = ss->ply + 1;
ss->currentMove = bestMove = MOVE_NONE;
+ ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
inCheck = pos.checkers();
moveCount = 0;
&& ttHit
&& tte->depth() >= ttDepth
&& ttValue != VALUE_NONE // Only in case of TT access race
- && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
- : (tte->bound() & BOUND_UPPER)))
+ && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
+ : (tte->bound() & BOUND_UPPER)))
return ttValue;
// Evaluate the position statically
ss->staticEval = bestValue = evaluate(pos);
// Can ttValue be used as a better position evaluation?
- if ( ttValue != VALUE_NONE
+ if ( ttValue != VALUE_NONE
&& (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER)))
bestValue = ttValue;
}
futilityBase = bestValue + 128;
}
+ const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr, (ss-4)->continuationHistory };
+
// Initialize a MovePicker object for the current position, and prepare
// to search the moves. Because the depth is <= 0 here, only captures,
// queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
// be generated.
- MovePicker mp(pos, ttMove, depth, &pos.this_thread()->mainHistory,
- &pos.this_thread()->captureHistory,
+ MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
+ &thisThread->captureHistory,
+ contHist,
to_sq((ss-1)->currentMove));
// Loop through the moves until no moves remain or a beta cutoff occurs
}
ss->currentMove = move;
+ ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)];
// Make and search the move
pos.do_move(move, st, givesCheck);
for (int i : {1, 2, 4})
if (is_ok((ss-i)->currentMove))
- (*(ss-i)->contHistory)[pc][to] << bonus;
+ (*(ss-i)->continuationHistory)[pc][to] << bonus;
}
projects / stockfish / blobdiff