/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
- Copyright (C) 2004-2022 The Stockfish developers (see AUTHORS file)
+ Copyright (C) 2004-2023 The Stockfish developers (see AUTHORS file)
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
// Futility margin
Value futility_margin(Depth d, bool improving) {
- return Value(214 * (d - improving));
+ return Value(154 * (d - improving));
}
// Reductions lookup table, initialized at startup
Depth reduction(bool i, Depth d, int mn, Value delta, Value rootDelta) {
int r = Reductions[d] * Reductions[mn];
- return (r + 1358 - int(delta) * 1024 / int(rootDelta)) / 1024 + (!i && r > 904);
+ return (r + 1449 - int(delta) * 1032 / int(rootDelta)) / 1024 + (!i && r > 941);
}
constexpr int futility_move_count(bool improving, Depth depth) {
- return (3 + depth * depth) / (2 - improving);
+ return improving ? (3 + depth * depth)
+ : (3 + depth * depth) / 2;
}
// History and stats update bonus, based on depth
int stat_bonus(Depth d) {
- return std::min((6 * d + 229) * d - 215 , 2000);
+ return std::min(340 * d - 470, 1855);
}
// Add a small random component to draw evaluations to avoid 3-fold blindness
- Value value_draw(Thread* thisThread) {
- return VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
+ Value value_draw(const Thread* thisThread) {
+ return VALUE_DRAW - 1 + Value(thisThread->nodes & 0x2);
}
// Skill structure is used to implement strength limit. If we have an uci_elo then
struct Skill {
Skill(int skill_level, int uci_elo) {
if (uci_elo)
- level = std::clamp(std::pow((uci_elo - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0);
+ {
+ double e = double(uci_elo - 1320) / (3190 - 1320);
+ level = std::clamp((((37.2473 * e - 40.8525) * e + 22.2943) * e - 0.311438), 0.0, 19.0);
+ }
else
level = double(skill_level);
}
Value value_to_tt(Value v, int ply);
Value value_from_tt(Value v, int ply, int r50c);
- void update_pv(Move* pv, Move move, Move* childPv);
+ void update_pv(Move* pv, Move move, const Move* childPv);
void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus);
void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus);
void update_all_stats(const Position& pos, Stack* ss, Move bestMove, Value bestValue, Value beta, Square prevSq,
void Search::init() {
for (int i = 1; i < MAX_MOVES; ++i)
- Reductions[i] = int((21.9 + std::log(Threads.size()) / 2) * std::log(i));
+ Reductions[i] = int((19.47 + std::log(Threads.size()) / 2) * std::log(i));
}
// Send again PV info if we have a new best thread
if (bestThread != this)
- sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
+ sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth) << sync_endl;
sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
int iterIdx = 0;
std::memset(ss-7, 0, 10 * sizeof(Stack));
- for (int i = 7; i > 0; i--)
+ for (int i = 7; i > 0; --i)
+ {
(ss-i)->continuationHistory = &this->continuationHistory[0][0][NO_PIECE][0]; // Use as a sentinel
+ (ss-i)->staticEval = VALUE_NONE;
+ }
for (int i = 0; i <= MAX_PLY + 2; ++i)
(ss+i)->ply = i;
multiPV = std::min(multiPV, rootMoves.size());
- complexityAverage.set(232, 1);
+ complexityAverage.set(153, 1);
- trend = SCORE_ZERO;
- optimism[ us] = Value(25);
- optimism[~us] = -optimism[us];
+ optimism[us] = optimism[~us] = VALUE_ZERO;
int searchAgainCounter = 0;
pvLast = 0;
if (!Threads.increaseDepth)
- searchAgainCounter++;
+ searchAgainCounter++;
// MultiPV loop. We perform a full root search for each PV line
for (pvIdx = 0; pvIdx < multiPV && !Threads.stop; ++pvIdx)
if (rootDepth >= 4)
{
Value prev = rootMoves[pvIdx].averageScore;
- delta = Value(17) + int(prev) * prev / 16384;
+ delta = Value(10) + int(prev) * prev / 16502;
alpha = std::max(prev - delta,-VALUE_INFINITE);
beta = std::min(prev + delta, VALUE_INFINITE);
- // Adjust trend and optimism based on root move's previousScore
- int tr = sigmoid(prev, 0, 0, 147, 113, 1);
- trend = (us == WHITE ? make_score(tr, tr / 2)
- : -make_score(tr, tr / 2));
-
- int opt = sigmoid(prev, 0, 25, 147, 14464, 256);
+ // Adjust optimism based on root move's previousScore
+ int opt = 120 * prev / (std::abs(prev) + 161);
optimism[ us] = Value(opt);
optimism[~us] = -optimism[us];
}
int failedHighCnt = 0;
while (true)
{
- Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter);
+ // Adjust the effective depth searched, but ensuring at least one effective increment for every
+ // four searchAgain steps (see issue #2717).
+ Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - 3 * (searchAgainCounter + 1) / 4);
bestValue = Stockfish::search<Root>(rootPos, ss, alpha, beta, adjustedDepth, false);
// Bring the best move to the front. It is critical that sorting
&& multiPV == 1
&& (bestValue <= alpha || bestValue >= beta)
&& Time.elapsed() > 3000)
- sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
+ sync_cout << UCI::pv(rootPos, rootDepth) << sync_endl;
// In case of failing low/high increase aspiration window and
// re-search, otherwise exit the loop.
else
break;
- delta += delta / 4 + 5;
+ delta += delta / 4 + 2;
assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
}
if ( mainThread
&& (Threads.stop || pvIdx + 1 == multiPV || Time.elapsed() > 3000))
- sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
+ sync_cout << UCI::pv(rootPos, rootDepth) << sync_endl;
}
if (!Threads.stop)
completedDepth = rootDepth;
- if (rootMoves[0].pv[0] != lastBestMove) {
- lastBestMove = rootMoves[0].pv[0];
- lastBestMoveDepth = rootDepth;
+ if (rootMoves[0].pv[0] != lastBestMove)
+ {
+ lastBestMove = rootMoves[0].pv[0];
+ lastBestMoveDepth = rootDepth;
}
// Have we found a "mate in x"?
&& !Threads.stop
&& !mainThread->stopOnPonderhit)
{
- double fallingEval = (142 + 12 * (mainThread->bestPreviousAverageScore - bestValue)
- + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 825.0;
+ double fallingEval = (69 + 13 * (mainThread->bestPreviousAverageScore - bestValue)
+ + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 619.6;
fallingEval = std::clamp(fallingEval, 0.5, 1.5);
// If the bestMove is stable over several iterations, reduce time accordingly
- timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.92 : 0.95;
- double reduction = (1.47 + mainThread->previousTimeReduction) / (2.32 * timeReduction);
- double bestMoveInstability = 1.073 + std::max(1.0, 2.25 - 9.9 / rootDepth)
- * totBestMoveChanges / Threads.size();
+ timeReduction = lastBestMoveDepth + 8 < completedDepth ? 1.57 : 0.65;
+ double reduction = (1.4 + mainThread->previousTimeReduction) / (2.08 * timeReduction);
+ double bestMoveInstability = 1 + 1.8 * totBestMoveChanges / Threads.size();
int complexity = mainThread->complexityAverage.value();
- double complexPosition = std::clamp(1.0 + (complexity - 232) / 1750.0, 0.5, 1.5);
+ double complexPosition = std::min(1.03 + (complexity - 241) / 1552.0, 1.45);
double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability * complexPosition;
else
Threads.stop = true;
}
- else if ( Threads.increaseDepth
- && !mainThread->ponder
- && Time.elapsed() > totalTime * 0.58)
- Threads.increaseDepth = false;
+ else if ( !mainThread->ponder
+ && Time.elapsed() > totalTime * 0.50)
+ Threads.increaseDepth = false;
else
- Threads.increaseDepth = true;
+ Threads.increaseDepth = true;
}
mainThread->iterValue[iterIdx] = bestValue;
constexpr bool PvNode = nodeType != NonPV;
constexpr bool rootNode = nodeType == Root;
- const Depth maxNextDepth = rootNode ? depth : depth + 1;
// Check if we have an upcoming move which draws by repetition, or
// if the opponent had an alternative move earlier to this position.
Move ttMove, move, excludedMove, bestMove;
Depth extension, newDepth;
Value bestValue, value, ttValue, eval, maxValue, probCutBeta;
- bool givesCheck, improving, didLMR, priorCapture;
- bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture;
+ bool givesCheck, improving, priorCapture, singularQuietLMR;
+ bool capture, moveCountPruning, ttCapture;
Piece movedPiece;
- int moveCount, captureCount, quietCount, bestMoveCount, improvement, complexity;
+ int moveCount, captureCount, quietCount, improvement, complexity;
// Step 1. Initialize node
Thread* thisThread = pos.this_thread();
ss->inCheck = pos.checkers();
priorCapture = pos.captured_piece();
Color us = pos.side_to_move();
- moveCount = bestMoveCount = captureCount = quietCount = ss->moveCount = 0;
+ moveCount = captureCount = quietCount = ss->moveCount = 0;
bestValue = -VALUE_INFINITE;
maxValue = VALUE_INFINITE;
(ss+1)->ttPv = false;
(ss+1)->excludedMove = bestMove = MOVE_NONE;
(ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
+ (ss+2)->cutoffCnt = 0;
ss->doubleExtensions = (ss-1)->doubleExtensions;
- ss->depth = depth;
Square prevSq = to_sq((ss-1)->currentMove);
// Initialize statScore to zero for the grandchildren of the current position.
if (!rootNode)
(ss+2)->statScore = 0;
- // Step 4. Transposition table lookup. We don't want the score of a partial
- // search to overwrite a previous full search TT value, so we use a different
- // position key in case of an excluded move.
+ // Step 4. Transposition table lookup.
excludedMove = ss->excludedMove;
- posKey = excludedMove == MOVE_NONE ? pos.key() : pos.key() ^ make_key(excludedMove);
+ posKey = pos.key();
tte = TT.probe(posKey, ss->ttHit);
ttValue = ss->ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]
: ss->ttHit ? tte->move() : MOVE_NONE;
- ttCapture = ttMove && pos.capture_or_promotion(ttMove);
+ ttCapture = ttMove && pos.capture_stage(ttMove);
+
+ // At this point, if excluded, skip straight to step 6, static eval. However,
+ // to save indentation, we list the condition in all code between here and there.
if (!excludedMove)
ss->ttPv = PvNode || (ss->ttHit && tte->is_pv());
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
&& ss->ttHit
- && tte->depth() > depth - (thisThread->id() % 2 == 1)
+ && !excludedMove
+ && tte->depth() > depth - (tte->bound() == BOUND_EXACT)
&& ttValue != VALUE_NONE // Possible in case of TT access race
- && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
- : (tte->bound() & BOUND_UPPER)))
+ && (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER)))
{
- // If ttMove is quiet, update move sorting heuristics on TT hit (~1 Elo)
+ // If ttMove is quiet, update move sorting heuristics on TT hit (~2 Elo)
if (ttMove)
{
if (ttValue >= beta)
{
- // Bonus for a quiet ttMove that fails high (~3 Elo)
+ // Bonus for a quiet ttMove that fails high (~2 Elo)
if (!ttCapture)
update_quiet_stats(pos, ss, ttMove, stat_bonus(depth));
- // Extra penalty for early quiet moves of the previous ply (~0 Elo)
+ // Extra penalty for early quiet moves of the previous ply (~0 Elo on STC, ~2 Elo on LTC)
if ((ss-1)->moveCount <= 2 && !priorCapture)
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + 1));
}
}
// Step 5. Tablebases probe
- if (!rootNode && TB::Cardinality)
+ if (!rootNode && !excludedMove && TB::Cardinality)
{
int piecesCount = pos.count<ALL_PIECES>();
complexity = 0;
goto moves_loop;
}
+ else if (excludedMove)
+ {
+ // Providing the hint that this node's accumulator will be used often brings significant Elo gain (13 elo)
+ Eval::NNUE::hint_common_parent_position(pos);
+ eval = ss->staticEval;
+ complexity = abs(ss->staticEval - pos.psq_eg_stm());
+ }
else if (ss->ttHit)
{
// Never assume anything about values stored in TT
ss->staticEval = eval = tte->eval();
if (eval == VALUE_NONE)
- ss->staticEval = eval = evaluate(pos);
-
- // Randomize draw evaluation
- if (eval == VALUE_DRAW)
- eval = value_draw(thisThread);
+ ss->staticEval = eval = evaluate(pos, &complexity);
+ else // Fall back to (semi)classical complexity for TT hits, the NNUE complexity is lost
+ {
+ complexity = abs(ss->staticEval - pos.psq_eg_stm());
+ if (PvNode)
+ Eval::NNUE::hint_common_parent_position(pos);
+ }
- // ttValue can be used as a better position evaluation (~4 Elo)
+ // ttValue can be used as a better position evaluation (~7 Elo)
if ( ttValue != VALUE_NONE
&& (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER)))
eval = ttValue;
}
else
{
- ss->staticEval = eval = evaluate(pos);
-
+ ss->staticEval = eval = evaluate(pos, &complexity);
// Save static evaluation into transposition table
- if (!excludedMove)
- tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
+ tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
}
- // Use static evaluation difference to improve quiet move ordering (~3 Elo)
+ thisThread->complexityAverage.update(complexity);
+
+ // Use static evaluation difference to improve quiet move ordering (~4 Elo)
if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture)
{
- int bonus = std::clamp(-16 * int((ss-1)->staticEval + ss->staticEval), -2000, 2000);
+ int bonus = std::clamp(-19 * int((ss-1)->staticEval + ss->staticEval), -1920, 1920);
thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus;
}
// margin and the improving flag are used in various pruning heuristics.
improvement = (ss-2)->staticEval != VALUE_NONE ? ss->staticEval - (ss-2)->staticEval
: (ss-4)->staticEval != VALUE_NONE ? ss->staticEval - (ss-4)->staticEval
- : 200;
-
+ : 156;
improving = improvement > 0;
- complexity = abs(ss->staticEval - (us == WHITE ? eg_value(pos.psq_score()) : -eg_value(pos.psq_score())));
- thisThread->complexityAverage.update(complexity);
+ // Step 7. Razoring (~1 Elo).
+ // If eval is really low check with qsearch if it can exceed alpha, if it can't,
+ // return a fail low.
+ if (eval < alpha - 426 - 252 * depth * depth)
+ {
+ value = qsearch<NonPV>(pos, ss, alpha - 1, alpha);
+ if (value < alpha)
+ return value;
+ }
- // Step 7. Futility pruning: child node (~25 Elo).
+ // Step 8. Futility pruning: child node (~40 Elo).
// The depth condition is important for mate finding.
if ( !ss->ttPv
&& depth < 9
- && eval - futility_margin(depth, improving) - (ss-1)->statScore / 256 >= beta
+ && eval - futility_margin(depth, improving) - (ss-1)->statScore / 280 >= beta
&& eval >= beta
- && eval < 15000) // 50% larger than VALUE_KNOWN_WIN, but smaller than TB wins.
+ && eval < 25128) // larger than VALUE_KNOWN_WIN, but smaller than TB wins
return eval;
- // Step 8. Null move search with verification search (~22 Elo)
+ // Step 9. Null move search with verification search (~35 Elo)
if ( !PvNode
&& (ss-1)->currentMove != MOVE_NULL
- && (ss-1)->statScore < 23767
+ && (ss-1)->statScore < 18755
&& eval >= beta
&& eval >= ss->staticEval
- && ss->staticEval >= beta - 20 * depth - improvement / 15 + 204 + complexity / 25
+ && ss->staticEval >= beta - 19 * depth - improvement / 13 + 253 + complexity / 25
&& !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 = std::min(int(eval - beta) / 205, 3) + depth / 3 + 4;
+ // Null move dynamic reduction based on depth, eval and complexity of position
+ Depth R = std::min(int(eval - beta) / 168, 6) + depth / 3 + 4 - (complexity > 825);
ss->currentMove = MOVE_NULL;
ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
}
}
- probCutBeta = beta + 209 - 44 * improving;
+ probCutBeta = beta + 186 - 54 * improving;
- // Step 9. ProbCut (~4 Elo)
- // If we have a good enough capture and a reduced search returns a value
+ // Step 10. ProbCut (~10 Elo)
+ // If we have a good enough capture (or queen promotion) and a reduced search returns a value
// much above beta, we can (almost) safely prune the previous move.
if ( !PvNode
&& depth > 4
assert(probCutBeta < VALUE_INFINITE);
MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory);
- bool ttPv = ss->ttPv;
- ss->ttPv = false;
while ((move = mp.next_move()) != MOVE_NONE)
if (move != excludedMove && pos.legal(move))
{
- assert(pos.capture_or_promotion(move));
- assert(depth >= 5);
-
- captureOrPromotion = true;
+ assert(pos.capture_stage(move));
ss->currentMove = move;
ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
- [captureOrPromotion]
+ [true]
[pos.moved_piece(move)]
[to_sq(move)];
if (value >= probCutBeta)
{
- // if transposition table doesn't have equal or more deep info write probCut data into it
- if ( !(ss->ttHit
- && tte->depth() >= depth - 3
- && ttValue != VALUE_NONE))
- tte->save(posKey, value_to_tt(value, ss->ply), ttPv,
- BOUND_LOWER,
- depth - 3, move, ss->staticEval);
+ // Save ProbCut data into transposition table
+ tte->save(posKey, value_to_tt(value, ss->ply), ss->ttPv, BOUND_LOWER, depth - 3, move, ss->staticEval);
return value;
}
}
- ss->ttPv = ttPv;
+
+ Eval::NNUE::hint_common_parent_position(pos);
}
- // Step 10. If the position is not in TT, decrease depth by 2 or 1 depending on node type (~3 Elo)
- if ( PvNode
- && depth >= 6
+ // Step 11. If the position is not in TT, decrease depth by 3.
+ // Use qsearch if depth is equal or below zero (~9 Elo)
+ if ( PvNode
&& !ttMove)
- depth -= 2;
+ depth -= 3;
+
+ if (depth <= 0)
+ return qsearch<PV>(pos, ss, alpha, beta);
- if ( cutNode
- && depth >= 9
+ if ( cutNode
+ && depth >= 7
&& !ttMove)
- depth--;
+ depth -= 2;
moves_loop: // When in check, search starts here
- // Step 11. A small Probcut idea, when we are in check (~0 Elo)
- probCutBeta = beta + 409;
+ // Step 12. A small Probcut idea, when we are in check (~4 Elo)
+ probCutBeta = beta + 391;
if ( ss->inCheck
&& !PvNode
- && depth >= 4
+ && depth >= 2
&& ttCapture
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 3
&& ttValue >= probCutBeta
&& abs(ttValue) <= VALUE_KNOWN_WIN
- && abs(beta) <= VALUE_KNOWN_WIN
- )
+ && abs(beta) <= VALUE_KNOWN_WIN)
return probCutBeta;
-
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
nullptr , (ss-4)->continuationHistory,
nullptr , (ss-6)->continuationHistory };
ss->killers);
value = bestValue;
- moveCountPruning = false;
+ moveCountPruning = singularQuietLMR = false;
// Indicate PvNodes that will probably fail low if the node was searched
// at a depth equal or greater than the current depth, and the result of this search was a fail low.
&& (tte->bound() & BOUND_UPPER)
&& tte->depth() >= depth;
- // Step 12. Loop through all pseudo-legal moves until no moves remain
+ // Step 13. Loop through all pseudo-legal moves until no moves remain
// or a beta cutoff occurs.
while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE)
{
(ss+1)->pv = nullptr;
extension = 0;
- captureOrPromotion = pos.capture_or_promotion(move);
+ capture = pos.capture_stage(move);
movedPiece = pos.moved_piece(move);
givesCheck = pos.gives_check(move);
Value delta = beta - alpha;
- // Step 13. Pruning at shallow depth (~98 Elo). Depth conditions are important for mate finding.
+ Depth r = reduction(improving, depth, moveCount, delta, thisThread->rootDelta);
+
+ // Step 14. Pruning at shallow depth (~120 Elo). Depth conditions are important for mate finding.
if ( !rootNode
&& pos.non_pawn_material(us)
&& bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
{
- // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold (~7 Elo)
+ // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold (~8 Elo)
moveCountPruning = moveCount >= futility_move_count(improving, depth);
// Reduced depth of the next LMR search
- int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, delta, thisThread->rootDelta), 0);
+ int lmrDepth = std::max(newDepth - r, 0);
- if ( captureOrPromotion
+ if ( capture
|| givesCheck)
{
- // Futility pruning for captures (~0 Elo)
- if ( !pos.empty(to_sq(move))
- && !givesCheck
+ // Futility pruning for captures (~2 Elo)
+ if ( !givesCheck
&& !PvNode
&& lmrDepth < 6
&& !ss->inCheck
- && ss->staticEval + 342 + 238 * lmrDepth + PieceValue[EG][pos.piece_on(to_sq(move))]
- + captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 8 < alpha)
+ && ss->staticEval + 182 + 230 * lmrDepth + PieceValue[EG][pos.piece_on(to_sq(move))]
+ + captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 7 < alpha)
continue;
- // SEE based pruning (~9 Elo)
- if (!pos.see_ge(move, Value(-217) * depth))
+ // SEE based pruning (~11 Elo)
+ if (!pos.see_ge(move, Value(-206) * depth))
continue;
}
else
// Continuation history based pruning (~2 Elo)
if ( lmrDepth < 5
- && history < -3875 * (depth - 1))
+ && history < -4405 * (depth - 1))
continue;
- history += thisThread->mainHistory[us][from_to(move)];
+ history += 2 * thisThread->mainHistory[us][from_to(move)];
- // Futility pruning: parent node (~9 Elo)
+ lmrDepth += history / 7278;
+ lmrDepth = std::max(lmrDepth, -2);
+
+ // Futility pruning: parent node (~13 Elo)
if ( !ss->inCheck
- && lmrDepth < 8
- && ss->staticEval + 138 + 137 * lmrDepth + history / 64 <= alpha)
+ && lmrDepth < 13
+ && ss->staticEval + 103 + 138 * lmrDepth <= alpha)
continue;
- // Prune moves with negative SEE (~3 Elo)
- if (!pos.see_ge(move, Value(-21 * lmrDepth * lmrDepth - 21 * lmrDepth)))
+ lmrDepth = std::max(lmrDepth, 0);
+
+ // Prune moves with negative SEE (~4 Elo)
+ if (!pos.see_ge(move, Value(-24 * lmrDepth * lmrDepth - 15 * lmrDepth)))
continue;
}
}
- // Step 14. Extensions (~66 Elo)
+ // Step 15. Extensions (~100 Elo)
// We take care to not overdo to avoid search getting stuck.
if (ss->ply < thisThread->rootDepth * 2)
{
- // Singular extension search (~58 Elo). If all moves but one fail low on a
+ // Singular extension search (~94 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 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 ( !rootNode
- && depth >= 6 + 2 * (PvNode && tte->is_pv())
+ && depth >= 4 - (thisThread->completedDepth > 21) + 2 * (PvNode && tte->is_pv())
&& move == ttMove
&& !excludedMove // Avoid recursive singular search
/* && ttValue != VALUE_NONE Already implicit in the next condition */
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 3)
{
- Value singularBeta = ttValue - 3 * depth;
+ Value singularBeta = ttValue - (2 + (ss->ttPv && !PvNode)) * depth;
Depth singularDepth = (depth - 1) / 2;
ss->excludedMove = move;
+ // the search with excludedMove will update ss->staticEval
value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
ss->excludedMove = MOVE_NONE;
if (value < singularBeta)
{
extension = 1;
+ singularQuietLMR = !ttCapture;
// Avoid search explosion by limiting the number of double extensions
if ( !PvNode
- && value < singularBeta - 75
- && ss->doubleExtensions <= 6)
+ && value < singularBeta - 25
+ && ss->doubleExtensions <= 10)
+ {
extension = 2;
+ depth += depth < 13;
+ }
}
// Multi-cut pruning
// If the eval of ttMove is greater than beta, we reduce it (negative extension)
else if (ttValue >= beta)
extension = -2;
+
+ // If the eval of ttMove is less than value, we reduce it (negative extension)
+ else if (ttValue <= value)
+ extension = -1;
}
// Check extensions (~1 Elo)
else if ( givesCheck
- && depth > 6
- && abs(ss->staticEval) > 100)
+ && depth > 10
+ && abs(ss->staticEval) > 88)
extension = 1;
- // Quiet ttMove extensions (~0 Elo)
+ // Quiet ttMove extensions (~1 Elo)
else if ( PvNode
&& move == ttMove
&& move == ss->killers[0]
- && (*contHist[0])[movedPiece][to_sq(move)] >= 10000)
+ && (*contHist[0])[movedPiece][to_sq(move)] >= 5705)
extension = 1;
}
// Update the current move (this must be done after singular extension search)
ss->currentMove = move;
ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
- [captureOrPromotion]
+ [capture]
[movedPiece]
[to_sq(move)];
- // Step 15. Make the move
+ // Step 16. Make the move
pos.do_move(move, st, givesCheck);
- bool doDeeperSearch = false;
-
- // Step 16. Late moves reduction / extension (LMR, ~98 Elo)
- // We use various heuristics for the sons of a node after the first son has
- // been searched. In general we would like to reduce them, but there are many
- // cases where we extend a son if it has good chances to be "interesting".
- if ( depth >= 3
- && moveCount > 1 + 2 * rootNode
- && ( !ss->ttPv
- || !captureOrPromotion
- || (cutNode && (ss-1)->moveCount > 1)))
- {
- Depth r = reduction(improving, depth, moveCount, delta, thisThread->rootDelta);
+ // Decrease reduction if position is or has been on the PV
+ // and node is not likely to fail low. (~3 Elo)
+ if ( ss->ttPv
+ && !likelyFailLow)
+ r -= 2;
- // Decrease reduction at some PvNodes (~2 Elo)
- if ( PvNode
- && bestMoveCount <= 3)
- r--;
+ // Decrease reduction if opponent's move count is high (~1 Elo)
+ if ((ss-1)->moveCount > 7)
+ r--;
- // Decrease reduction if position is or has been on the PV
- // and node is not likely to fail low. (~3 Elo)
- if ( ss->ttPv
- && !likelyFailLow)
- r -= 2;
+ // Increase reduction for cut nodes (~3 Elo)
+ if (cutNode)
+ r += 2;
- // Decrease reduction if opponent's move count is high (~1 Elo)
- if ((ss-1)->moveCount > 13)
- r--;
+ // Increase reduction if ttMove is a capture (~3 Elo)
+ if (ttCapture)
+ r++;
- // Increase reduction for cut nodes (~3 Elo)
- if (cutNode && move != ss->killers[0])
- r += 2;
+ // Decrease reduction for PvNodes based on depth
+ if (PvNode)
+ r -= 1 + 12 / (3 + depth);
- // Increase reduction if ttMove is a capture (~3 Elo)
- if (ttCapture)
- r++;
+ // Decrease reduction if ttMove has been singularly extended (~1 Elo)
+ if (singularQuietLMR)
+ r--;
- ss->statScore = thisThread->mainHistory[us][from_to(move)]
- + (*contHist[0])[movedPiece][to_sq(move)]
- + (*contHist[1])[movedPiece][to_sq(move)]
- + (*contHist[3])[movedPiece][to_sq(move)]
- - 4923;
+ // Decrease reduction if we move a threatened piece (~1 Elo)
+ if ( depth > 9
+ && (mp.threatenedPieces & from_sq(move)))
+ r--;
- // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
- r -= ss->statScore / 14721;
+ // Increase reduction if next ply has a lot of fail high
+ if ((ss+1)->cutoffCnt > 3)
+ r++;
- // In general we want to cap the LMR depth search at newDepth. But if reductions
- // are really negative and movecount is low, we allow this move to be searched
- // deeper than the first move (this may lead to hidden double extensions).
- int deeper = r >= -1 ? 0
- : moveCount <= 5 ? 2
- : PvNode && depth > 6 ? 1
- : cutNode && moveCount <= 7 ? 1
- : 0;
+ // Decrease reduction if move is a killer and we have a good history
+ if (move == ss->killers[0]
+ && (*contHist[0])[movedPiece][to_sq(move)] >= 3722)
+ r--;
- Depth d = std::clamp(newDepth - r, 1, newDepth + deeper);
+ ss->statScore = 2 * thisThread->mainHistory[us][from_to(move)]
+ + (*contHist[0])[movedPiece][to_sq(move)]
+ + (*contHist[1])[movedPiece][to_sq(move)]
+ + (*contHist[3])[movedPiece][to_sq(move)]
+ - 4182;
- value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
+ // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
+ r -= ss->statScore / (11791 + 3992 * (depth > 6 && depth < 19));
- // If the son is reduced and fails high it will be re-searched at full depth
- doFullDepthSearch = value > alpha && d < newDepth;
- doDeeperSearch = value > (alpha + 62 + 20 * (newDepth - d));
- didLMR = true;
- }
- else
+ // Step 17. Late moves reduction / extension (LMR, ~117 Elo)
+ // We use various heuristics for the sons of a node after the first son has
+ // been searched. In general we would like to reduce them, but there are many
+ // cases where we extend a son if it has good chances to be "interesting".
+ if ( depth >= 2
+ && moveCount > 1 + (PvNode && ss->ply <= 1)
+ && ( !ss->ttPv
+ || !capture
+ || (cutNode && (ss-1)->moveCount > 1)))
{
- doFullDepthSearch = !PvNode || moveCount > 1;
- didLMR = false;
- }
+ // In general we want to cap the LMR depth search at newDepth, but when
+ // reduction is negative, we allow this move a limited search extension
+ // beyond the first move depth. This may lead to hidden double extensions.
+ Depth d = std::clamp(newDepth - r, 1, newDepth + 1);
- // Step 17. Full depth search when LMR is skipped or fails high
- if (doFullDepthSearch)
- {
- value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth + doDeeperSearch, !cutNode);
+ value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
- // If the move passed LMR update its stats
- if (didLMR)
+ // Do full depth search when reduced LMR search fails high
+ if (value > alpha && d < newDepth)
{
+ // Adjust full depth search based on LMR results - if result
+ // was good enough search deeper, if it was bad enough search shallower
+ const bool doDeeperSearch = value > (alpha + 58 + 12 * (newDepth - d));
+ const bool doEvenDeeperSearch = value > alpha + 588 && ss->doubleExtensions <= 5;
+ const bool doShallowerSearch = value < bestValue + newDepth;
+
+ ss->doubleExtensions = ss->doubleExtensions + doEvenDeeperSearch;
+
+ newDepth += doDeeperSearch - doShallowerSearch + doEvenDeeperSearch;
+
+ if (newDepth > d)
+ value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
+
int bonus = value > alpha ? stat_bonus(newDepth)
: -stat_bonus(newDepth);
- if (captureOrPromotion)
- bonus /= 4;
-
update_continuation_histories(ss, movedPiece, to_sq(move), bonus);
}
}
+ // Step 18. Full depth search when LMR is skipped. If expected reduction is high, reduce its depth by 1.
+ else if (!PvNode || moveCount > 1)
+ {
+ // Increase reduction for cut nodes and not ttMove (~1 Elo)
+ if (!ttMove && cutNode)
+ r += 2;
+
+ value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth - (r > 4), !cutNode);
+ }
+
// For PV nodes only, do a full PV search on the first move or after a fail
// high (in the latter case search only if value < beta), otherwise let the
// parent node fail low with value <= alpha and try another move.
(ss+1)->pv = pv;
(ss+1)->pv[0] = MOVE_NONE;
- value = -search<PV>(pos, ss+1, -beta, -alpha,
- std::min(maxNextDepth, newDepth), false);
+ value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
}
- // Step 18. Undo move
+ // Step 19. Undo move
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
- // Step 19. Check for a new best move
+ // Step 20. Check for a new best move
// Finished searching the move. If a stop occurred, the return value of
// the search cannot be trusted, and we return immediately without
// updating best move, PV and TT.
// PV move or new best move?
if (moveCount == 1 || value > alpha)
{
- rm.score = value;
+ rm.score = rm.uciScore = value;
rm.selDepth = thisThread->selDepth;
+ rm.scoreLowerbound = rm.scoreUpperbound = false;
+
+ if (value >= beta)
+ {
+ rm.scoreLowerbound = true;
+ rm.uciScore = beta;
+ }
+ else if (value <= alpha)
+ {
+ rm.scoreUpperbound = true;
+ rm.uciScore = alpha;
+ }
+
rm.pv.resize(1);
assert((ss+1)->pv);
if (PvNode && value < beta) // Update alpha! Always alpha < beta
{
alpha = value;
- bestMoveCount++;
+
+ // Reduce other moves if we have found at least one score improvement
+ if ( depth > 1
+ && depth < 6
+ && beta < 10534
+ && alpha > -10534)
+ depth -= 1;
+
+ assert(depth > 0);
}
else
{
+ ss->cutoffCnt++;
assert(value >= beta); // Fail high
break;
}
}
}
+
// If the move is worse than some previously searched move, remember it to update its stats later
if (move != bestMove)
{
- if (captureOrPromotion && captureCount < 32)
+ if (capture && captureCount < 32)
capturesSearched[captureCount++] = move;
- else if (!captureOrPromotion && quietCount < 64)
+ else if (!capture && quietCount < 64)
quietsSearched[quietCount++] = move;
}
}
return VALUE_DRAW;
*/
- // Step 20. Check for mate and stalemate
+ // Step 21. Check for mate and stalemate
// All legal moves have been searched and if there are no legal moves, it
// must be a mate or a stalemate. If we are in a singular extension search then
// return a fail low score.
quietsSearched, quietCount, capturesSearched, captureCount, depth);
// Bonus for prior countermove that caused the fail low
- else if ( (depth >= 3 || PvNode)
- && !priorCapture)
+ else if (!priorCapture)
{
- //Assign extra bonus if current node is PvNode or cutNode
- //or fail low was really bad
- bool extraBonus = PvNode
- || cutNode
- || bestValue < alpha - 94 * depth;
-
- update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * (1 + extraBonus));
+ int bonus = (depth > 5) + (PvNode || cutNode) + (bestValue < alpha - 97 * depth) + ((ss-1)->moveCount > 10);
+ update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * bonus);
}
if (PvNode)
// opponent move is probably good and the new position is added to the search tree.
if (bestValue <= alpha)
ss->ttPv = ss->ttPv || ((ss-1)->ttPv && depth > 3);
- // Otherwise, a counter move has been found and if the position is the last leaf
- // in the search tree, remove the position from the search tree.
- else if (depth > 3)
- ss->ttPv = ss->ttPv && (ss+1)->ttPv;
// Write gathered information in transposition table
if (!excludedMove && !(rootNode && thisThread->pvIdx))
// qsearch() is the quiescence search function, which is called by the main search
// function with zero depth, or recursively with further decreasing depth per call.
+ // (~155 elo)
template <NodeType nodeType>
Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
Move ttMove, move, bestMove;
Depth ttDepth;
Value bestValue, value, ttValue, futilityValue, futilityBase;
- bool pvHit, givesCheck, captureOrPromotion;
+ bool pvHit, givesCheck, capture;
int moveCount;
+ // Step 1. Initialize node
if (PvNode)
{
(ss+1)->pv = pv;
ss->inCheck = pos.checkers();
moveCount = 0;
- // Check for an immediate draw or maximum ply reached
+ // Step 2. Check for an immediate draw or maximum ply reached
if ( pos.is_draw(ss->ply)
|| ss->ply >= MAX_PLY)
return (ss->ply >= MAX_PLY && !ss->inCheck) ? evaluate(pos) : VALUE_DRAW;
// TT entry depth that we are going to use. Note that in qsearch we use
// only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
ttDepth = ss->inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
- : DEPTH_QS_NO_CHECKS;
- // Transposition table lookup
+ : DEPTH_QS_NO_CHECKS;
+
+ // Step 3. Transposition table lookup
posKey = pos.key();
tte = TT.probe(posKey, ss->ttHit);
ttValue = ss->ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE;
ttMove = ss->ttHit ? tte->move() : MOVE_NONE;
pvHit = ss->ttHit && tte->is_pv();
+ // At non-PV nodes we check for an early TT cutoff
if ( !PvNode
&& ss->ttHit
&& tte->depth() >= ttDepth
&& ttValue != VALUE_NONE // Only in case of TT access race
- && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
- : (tte->bound() & BOUND_UPPER)))
+ && (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER)))
return ttValue;
- // Evaluate the position statically
+ // Step 4. Static evaluation of the position
if (ss->inCheck)
{
ss->staticEval = VALUE_NONE;
if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
ss->staticEval = bestValue = evaluate(pos);
- // ttValue can be used as a better position evaluation (~7 Elo)
+ // ttValue can be used as a better position evaluation (~13 Elo)
if ( ttValue != VALUE_NONE
&& (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER)))
bestValue = ttValue;
if (PvNode && bestValue > alpha)
alpha = bestValue;
- futilityBase = bestValue + 155;
+ futilityBase = bestValue + 168;
}
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
int quietCheckEvasions = 0;
- // Loop through the moves until no moves remain or a beta cutoff occurs
+ // Step 5. Loop through all pseudo-legal moves until no moves remain
+ // or a beta cutoff occurs.
while ((move = mp.next_move()) != MOVE_NONE)
{
assert(is_ok(move));
continue;
givesCheck = pos.gives_check(move);
- captureOrPromotion = pos.capture_or_promotion(move);
+ capture = pos.capture_stage(move);
moveCount++;
- // Futility pruning and moveCount pruning (~5 Elo)
- if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
- && !givesCheck
+ // Step 6. Pruning.
+ if (bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
+ {
+ // Futility pruning and moveCount pruning (~10 Elo)
+ if ( !givesCheck
&& to_sq(move) != prevSq
&& futilityBase > -VALUE_KNOWN_WIN
&& type_of(move) != PROMOTION)
{
-
if (moveCount > 2)
continue;
}
}
- // Do not search moves with negative SEE values (~5 Elo)
- if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
- && !pos.see_ge(move))
+ // We prune after 2nd quiet check evasion where being 'in check' is implicitly checked through the counter
+ // and being a 'quiet' apart from being a tt move is assumed after an increment because captures are pushed ahead.
+ if (quietCheckEvasions > 1)
+ break;
+
+ // Continuation history based pruning (~3 Elo)
+ if ( !capture
+ && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < 0
+ && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < 0)
continue;
+ // Do not search moves with bad enough SEE values (~5 Elo)
+ if (!pos.see_ge(move, Value(-110)))
+ continue;
+ }
+
// Speculative prefetch as early as possible
prefetch(TT.first_entry(pos.key_after(move)));
+ // Update the current move
ss->currentMove = move;
ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
- [captureOrPromotion]
+ [capture]
[pos.moved_piece(move)]
[to_sq(move)];
- // Continuation history based pruning (~2 Elo)
- if ( !captureOrPromotion
- && bestValue > VALUE_TB_LOSS_IN_MAX_PLY
- && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold
- && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold)
- continue;
-
- // movecount pruning for quiet check evasions
- if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
- && quietCheckEvasions > 1
- && !captureOrPromotion
- && ss->inCheck)
- continue;
+ quietCheckEvasions += !capture && ss->inCheck;
- quietCheckEvasions += !captureOrPromotion && ss->inCheck;
-
- // Make and search the move
+ // Step 7. Make and search the move
pos.do_move(move, st, givesCheck);
value = -qsearch<nodeType>(pos, ss+1, -beta, -alpha, depth - 1);
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
- // Check for a new best move
+ // Step 8. Check for a new best move
if (value > bestValue)
{
bestValue = value;
}
}
+ // Step 9. Check for mate
// All legal moves have been searched. A special case: if we're in check
// and no legal moves were found, it is checkmate.
if (ss->inCheck && bestValue == -VALUE_INFINITE)
// update_pv() adds current move and appends child pv[]
- void update_pv(Move* pv, Move move, Move* childPv) {
+ void update_pv(Move* pv, Move move, const Move* childPv) {
for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
*pv++ = *childPv++;
void update_all_stats(const Position& pos, Stack* ss, Move bestMove, Value bestValue, Value beta, Square prevSq,
Move* quietsSearched, int quietCount, Move* capturesSearched, int captureCount, Depth depth) {
- int bonus1, bonus2;
Color us = pos.side_to_move();
Thread* thisThread = pos.this_thread();
CapturePieceToHistory& captureHistory = thisThread->captureHistory;
Piece moved_piece = pos.moved_piece(bestMove);
PieceType captured = type_of(pos.piece_on(to_sq(bestMove)));
+ int bonus1 = stat_bonus(depth + 1);
- bonus1 = stat_bonus(depth + 1);
- bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus
+ if (!pos.capture_stage(bestMove))
+ {
+ int bonus2 = bestValue > beta + 153 ? bonus1 // larger bonus
: stat_bonus(depth); // smaller bonus
- if (!pos.capture_or_promotion(bestMove))
- {
// Increase stats for the best move in case it was a quiet move
update_quiet_stats(pos, ss, bestMove, bonus2);
/// UCI::pv() formats PV information according to the UCI protocol. UCI requires
/// that all (if any) unsearched PV lines are sent using a previous search score.
-string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
+string UCI::pv(const Position& pos, Depth depth) {
std::stringstream ss;
TimePoint elapsed = Time.elapsed() + 1;
continue;
Depth d = updated ? depth : std::max(1, depth - 1);
- Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
+ Value v = updated ? rootMoves[i].uciScore : rootMoves[i].previousScore;
if (v == -VALUE_INFINITE)
v = VALUE_ZERO;
if (Options["UCI_ShowWDL"])
ss << UCI::wdl(v, pos.game_ply());
- if (!tb && i == pvIdx)
- ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
+ if (i == pvIdx && !tb && updated) // tablebase- and previous-scores are exact
+ ss << (rootMoves[i].scoreLowerbound ? " lowerbound" : (rootMoves[i].scoreUpperbound ? " upperbound" : ""));
ss << " nodes " << nodesSearched
- << " nps " << nodesSearched * 1000 / elapsed;
-
- if (elapsed > 1000) // Earlier makes little sense
- ss << " hashfull " << TT.hashfull();
-
- ss << " tbhits " << tbHits
+ << " nps " << nodesSearched * 1000 / elapsed
+ << " hashfull " << TT.hashfull()
+ << " tbhits " << tbHits
<< " time " << elapsed
<< " pv";
projects / stockfish / blobdiff