/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
- Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
+ Copyright (C) 2004-2022 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(165 * (d - improving));
}
// Reductions lookup table, initialized at startup
int Reductions[MAX_MOVES]; // [depth or moveNumber]
- Depth reduction(bool i, Depth d, int mn, bool rangeReduction) {
+ Depth reduction(bool i, Depth d, int mn, Value delta, Value rootDelta) {
int r = Reductions[d] * Reductions[mn];
- return (r + 534) / 1024 + (!i && r > 904) + rangeReduction;
+ return (r + 1642 - int(delta) * 1024 / int(rootDelta)) / 1024 + (!i && r > 916);
}
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((12 * d + 282) * d - 349 , 1594);
}
// 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);
- }
-
- // Check if the current thread is in a search explosion
- ExplosionState search_explosion(Thread* thisThread) {
-
- uint64_t nodesNow = thisThread->nodes;
- bool explosive = thisThread->doubleExtensionAverage[WHITE].is_greater(2, 100)
- || thisThread->doubleExtensionAverage[BLACK].is_greater(2, 100);
-
- if (explosive)
- thisThread->nodesLastExplosive = nodesNow;
- else
- thisThread->nodesLastNormal = nodesNow;
-
- if ( explosive
- && thisThread->state == EXPLOSION_NONE
- && nodesNow - thisThread->nodesLastNormal > 6000000)
- thisThread->state = MUST_CALM_DOWN;
-
- if ( thisThread->state == MUST_CALM_DOWN
- && nodesNow - thisThread->nodesLastExplosive > 6000000)
- thisThread->state = EXPLOSION_NONE;
-
- return thisThread->state;
+ 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
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, int depth);
+ 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,
Move* quietsSearched, int quietCount, Move* capturesSearched, int captureCount, Depth depth);
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((20.26 + std::log(Threads.size()) / 2) * std::log(i));
}
bestThread = Threads.get_best_thread();
bestPreviousScore = bestThread->rootMoves[0].score;
+ bestPreviousAverageScore = bestThread->rootMoves[0].averageScore;
+
+ for (Thread* th : Threads)
+ th->previousDepth = bestThread->completedDepth;
// Send again PV info if we have a new best thread
if (bestThread != this)
// The latter is needed for statScore and killer initialization.
Stack stack[MAX_PLY+10], *ss = stack+7;
Move pv[MAX_PLY+1];
- Value bestValue, alpha, beta, delta;
+ Value alpha, beta, delta;
Move lastBestMove = MOVE_NONE;
Depth lastBestMoveDepth = 0;
MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
mainThread->iterValue[i] = mainThread->bestPreviousScore;
}
- std::copy(&lowPlyHistory[2][0], &lowPlyHistory.back().back() + 1, &lowPlyHistory[0][0]);
- std::fill(&lowPlyHistory[MAX_LPH - 2][0], &lowPlyHistory.back().back() + 1, 0);
-
size_t multiPV = size_t(Options["MultiPV"]);
Skill skill(Options["Skill Level"], Options["UCI_LimitStrength"] ? int(Options["UCI_Elo"]) : 0);
multiPV = std::min(multiPV, rootMoves.size());
- doubleExtensionAverage[WHITE].set(0, 100); // initialize the running average at 0%
- doubleExtensionAverage[BLACK].set(0, 100); // initialize the running average at 0%
+ complexityAverage.set(155, 1);
- nodesLastExplosive = nodes;
- nodesLastNormal = nodes;
- state = EXPLOSION_NONE;
- trend = SCORE_ZERO;
+ optimism[us] = optimism[~us] = VALUE_ZERO;
int searchAgainCounter = 0;
// Reset aspiration window starting size
if (rootDepth >= 4)
{
- Value prev = rootMoves[pvIdx].previousScore;
- delta = Value(17) + int(prev) * prev / 16384;
+ Value prev = rootMoves[pvIdx].averageScore;
+ delta = Value(10) + int(prev) * prev / 15620;
alpha = std::max(prev - delta,-VALUE_INFINITE);
beta = std::min(prev + delta, VALUE_INFINITE);
- // Adjust trend based on root move's previousScore (dynamic contempt)
- int tr = 113 * prev / (abs(prev) + 147);
-
- trend = (us == WHITE ? make_score(tr, tr / 2)
- : -make_score(tr, tr / 2));
+ // Adjust optimism based on root move's previousScore
+ int opt = 118 * prev / (std::abs(prev) + 169);
+ optimism[ us] = Value(opt);
+ optimism[~us] = -optimism[us];
}
// Start with a small aspiration window and, in the case of a fail
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
else
break;
- delta += delta / 4 + 5;
+ delta += delta / 4 + 2;
assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
}
if (skill.enabled() && skill.time_to_pick(rootDepth))
skill.pick_best(multiPV);
+ // Use part of the gained time from a previous stable move for the current move
+ for (Thread* th : Threads)
+ {
+ totBestMoveChanges += th->bestMoveChanges;
+ th->bestMoveChanges = 0;
+ }
+
// Do we have time for the next iteration? Can we stop searching now?
if ( Limits.use_time_management()
&& !Threads.stop
&& !mainThread->stopOnPonderhit)
{
- double fallingEval = (318 + 6 * (mainThread->bestPreviousScore - bestValue)
- + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 825.0;
+ double fallingEval = (71 + 12 * (mainThread->bestPreviousAverageScore - bestValue)
+ + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 656.7;
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);
+ timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.37 : 0.65;
+ double reduction = (1.4 + mainThread->previousTimeReduction) / (2.15 * timeReduction);
+ double bestMoveInstability = 1 + 1.7 * totBestMoveChanges / Threads.size();
+ int complexity = mainThread->complexityAverage.value();
+ double complexPosition = std::min(1.0 + (complexity - 261) / 1738.7, 1.5);
- // Use part of the gained time from a previous stable move for the current move
- for (Thread* th : Threads)
- {
- totBestMoveChanges += th->bestMoveChanges;
- th->bestMoveChanges = 0;
- }
- double bestMoveInstability = 1.073 + std::max(1.0, 2.25 - 9.9 / rootDepth)
- * totBestMoveChanges / Threads.size();
- double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability;
+ double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability * complexPosition;
// Cap used time in case of a single legal move for a better viewer experience in tournaments
// yielding correct scores and sufficiently fast moves.
}
else if ( Threads.increaseDepth
&& !mainThread->ponder
- && Time.elapsed() > totalTime * 0.58)
+ && Time.elapsed() > totalTime * 0.53)
Threads.increaseDepth = false;
else
Threads.increaseDepth = true;
template <NodeType nodeType>
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
- Thread* thisThread = pos.this_thread();
-
- // Step 0. Limit search explosion
- if ( ss->ply > 10
- && search_explosion(thisThread) == MUST_CALM_DOWN
- && depth > (ss-1)->depth)
- depth = (ss-1)->depth;
-
constexpr bool PvNode = nodeType != NonPV;
constexpr bool rootNode = nodeType == Root;
const Depth maxNextDepth = rootNode ? depth : depth + 1;
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, singularQuietLMR;
+ bool givesCheck, improving, priorCapture, singularQuietLMR;
+ bool capture, moveCountPruning, ttCapture;
Piece movedPiece;
- int moveCount, captureCount, quietCount, bestMoveCount, improvement;
+ 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;
if (alpha >= beta)
return alpha;
}
+ else
+ thisThread->rootDelta = beta - alpha;
assert(0 <= ss->ply && ss->ply < MAX_PLY);
(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);
- // Update the running average statistics for double extensions
- thisThread->doubleExtensionAverage[us].update(ss->depth > (ss-1)->depth);
-
// Initialize statScore to zero for the grandchildren of the current position.
// So statScore is shared between all grandchildren and only the first grandchild
// starts with statScore = 0. Later grandchildren start with the last calculated
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(ttMove);
if (!excludedMove)
ss->ttPv = PvNode || (ss->ttHit && tte->is_pv());
- // Update low ply history for previous move if we are near root and position is or has been in PV
- if ( ss->ttPv
- && depth > 12
- && ss->ply - 1 < MAX_LPH
- && !priorCapture
- && is_ok((ss-1)->currentMove))
- thisThread->lowPlyHistory[ss->ply - 1][from_to((ss-1)->currentMove)] << stat_bonus(depth - 5);
-
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
&& ss->ttHit
- && tte->depth() > depth - (thisThread->id() % 2 == 1)
+ && 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
+ // If ttMove is quiet, update move sorting heuristics on TT hit (~1 Elo)
if (ttMove)
{
if (ttValue >= beta)
{
- // Bonus for a quiet ttMove that fails high
+ // Bonus for a quiet ttMove that fails high (~3 Elo)
if (!ttCapture)
- update_quiet_stats(pos, ss, ttMove, stat_bonus(depth), depth);
+ update_quiet_stats(pos, ss, ttMove, stat_bonus(depth));
- // Extra penalty for early quiet moves of the previous ply
+ // Extra penalty for early quiet moves of the previous ply (~0 Elo)
if ((ss-1)->moveCount <= 2 && !priorCapture)
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + 1));
}
- // Penalty for a quiet ttMove that fails low
+ // Penalty for a quiet ttMove that fails low (~1 Elo)
else if (!ttCapture)
{
int penalty = -stat_bonus(depth);
ss->staticEval = eval = VALUE_NONE;
improving = false;
improvement = 0;
+ complexity = 0;
goto moves_loop;
}
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());
- // Can ttValue be used as a better position evaluation?
+ // ttValue can be used as a better position evaluation (~4 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);
}
- // Use static evaluation difference to improve quiet move ordering
+ thisThread->complexityAverage.update(complexity);
+
+ // Use static evaluation difference to improve quiet move ordering (~3 Elo)
if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture)
{
- int bonus = std::clamp(-depth * 4 * int((ss-1)->staticEval + ss->staticEval), -1000, 1000);
+ int bonus = std::clamp(-19 * int((ss-1)->staticEval + ss->staticEval), -1914, 1914);
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;
-
+ : 168;
improving = improvement > 0;
- // Step 7. Futility pruning: child node (~50 Elo).
+ // Step 7. Razoring.
+ // If eval is really low check with qsearch if it can exceed alpha, if it can't,
+ // return a fail low.
+ if (eval < alpha - 369 - 254 * depth * depth)
+ {
+ value = qsearch<NonPV>(pos, ss, alpha - 1, alpha);
+ if (value < alpha)
+ return value;
+ }
+
+ // Step 8. Futility pruning: child node (~25 Elo).
// The depth condition is important for mate finding.
- if ( !PvNode
- && depth < 9
- && eval - futility_margin(depth, improving) >= beta
- && eval < 15000) // 50% larger than VALUE_KNOWN_WIN, but smaller than TB wins.
+ if ( !ss->ttPv
+ && depth < 8
+ && eval - futility_margin(depth, improving) - (ss-1)->statScore / 303 >= beta
+ && eval >= beta
+ && eval < 28031) // larger than VALUE_KNOWN_WIN, but smaller than TB wins
return eval;
- // Step 8. Null move search with verification search (~40 Elo)
+ // Step 9. Null move search with verification search (~22 Elo)
if ( !PvNode
&& (ss-1)->currentMove != MOVE_NULL
- && (ss-1)->statScore < 23767
+ && (ss-1)->statScore < 17139
&& eval >= beta
&& eval >= ss->staticEval
- && ss->staticEval >= beta - 20 * depth - improvement / 15 + 204
+ && ss->staticEval >= beta - 20 * depth - improvement / 13 + 233 + 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, 7) + depth / 3 + 4 - (complexity > 861);
ss->currentMove = MOVE_NULL;
ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
}
}
- probCutBeta = beta + 209 - 44 * improving;
+ probCutBeta = beta + 191 - 54 * improving;
- // Step 9. ProbCut (~4 Elo)
+ // Step 10. ProbCut (~4 Elo)
// If we have a good enough capture and a reduced search returns a value
// much above beta, we can (almost) safely prune the previous move.
if ( !PvNode
{
assert(probCutBeta < VALUE_INFINITE);
- MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory);
- bool ttPv = ss->ttPv;
- ss->ttPv = false;
+ MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, depth - 3, &captureHistory);
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(move) || promotion_type(move) == QUEEN);
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;
}
- // Step 10. If the position is not in TT, decrease depth by 2 or 1 depending on node type
- 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 (~4 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 >= 9
&& !ttMove)
- depth--;
+ depth -= 2;
moves_loop: // When in check, search starts here
- int rangeReduction = 0;
-
- // Step 11. A small Probcut idea, when we are in check
- probCutBeta = beta + 409;
+ // Step 12. A small Probcut idea, when we are in check (~0 Elo)
+ probCutBeta = beta + 417;
if ( ss->inCheck
&& !PvNode
- && depth >= 4
+ && depth >= 2
&& ttCapture
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 3
Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
- &thisThread->lowPlyHistory,
&captureHistory,
contHist,
countermove,
- ss->killers,
- ss->ply);
+ ss->killers);
value = bestValue;
- singularQuietLMR = 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(move);
movedPiece = pos.moved_piece(move);
givesCheck = pos.gives_check(move);
// Calculate new depth for this move
newDepth = depth - 1;
- // Step 13. Pruning at shallow depth (~200 Elo). Depth conditions are important for mate finding.
+ Value delta = beta - alpha;
+
+ // Step 14. Pruning at shallow depth (~98 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
+ // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold (~7 Elo)
moveCountPruning = moveCount >= futility_move_count(improving, depth);
// Reduced depth of the next LMR search
- int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, rangeReduction > 2), 0);
+ int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, delta, thisThread->rootDelta), 0);
- if ( captureOrPromotion
+ if ( capture
|| givesCheck)
{
- // Capture history based pruning when the move doesn't give check
+ // Futility pruning for captures (~0 Elo)
if ( !givesCheck
- && lmrDepth < 1
- && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0)
+ && !PvNode
+ && lmrDepth < 7
+ && !ss->inCheck
+ && ss->staticEval + 180 + 201 * lmrDepth + PieceValue[EG][pos.piece_on(to_sq(move))]
+ + captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 6 < alpha)
continue;
- // SEE based pruning
- if (!pos.see_ge(move, Value(-218) * depth)) // (~25 Elo)
+ // SEE based pruning (~9 Elo)
+ if (!pos.see_ge(move, Value(-222) * depth))
continue;
}
else
{
- // Continuation history based pruning (~20 Elo)
- if (lmrDepth < 5
- && (*contHist[0])[movedPiece][to_sq(move)]
- + (*contHist[1])[movedPiece][to_sq(move)]
- + (*contHist[3])[movedPiece][to_sq(move)] < -3000 * depth + 3000)
+ int history = (*contHist[0])[movedPiece][to_sq(move)]
+ + (*contHist[1])[movedPiece][to_sq(move)]
+ + (*contHist[3])[movedPiece][to_sq(move)];
+
+ // Continuation history based pruning (~2 Elo)
+ if ( lmrDepth < 5
+ && history < -3875 * (depth - 1))
continue;
- // Futility pruning: parent node (~5 Elo)
+ history += 2 * thisThread->mainHistory[us][from_to(move)];
+
+ // Futility pruning: parent node (~9 Elo)
if ( !ss->inCheck
- && lmrDepth < 8
- && ss->staticEval + 172 + 145 * lmrDepth <= alpha)
+ && lmrDepth < 13
+ && ss->staticEval + 106 + 145 * lmrDepth + history / 52 <= alpha)
continue;
- // Prune moves with negative SEE (~20 Elo)
- if (!pos.see_ge(move, Value(-21 * lmrDepth * lmrDepth - 21 * lmrDepth)))
+ // Prune moves with negative SEE (~3 Elo)
+ if (!pos.see_ge(move, Value(-24 * lmrDepth * lmrDepth - 15 * lmrDepth)))
continue;
}
}
- // Step 14. Extensions (~75 Elo)
-
- // Singular extension search (~70 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 >= 7
- && move == ttMove
- && !excludedMove // Avoid recursive singular search
- /* && ttValue != VALUE_NONE Already implicit in the next condition */
- && abs(ttValue) < VALUE_KNOWN_WIN
- && (tte->bound() & BOUND_LOWER)
- && tte->depth() >= depth - 3)
+ // Step 15. Extensions (~66 Elo)
+ // We take care to not overdo to avoid search getting stuck.
+ if (ss->ply < thisThread->rootDepth * 2)
{
- Value singularBeta = ttValue - 3 * depth;
- Depth singularDepth = (depth - 1) / 2;
+ // Singular extension search (~58 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 >= 4 - (thisThread->previousDepth > 24) + 2 * (PvNode && tte->is_pv())
+ && move == ttMove
+ && !excludedMove // Avoid recursive singular search
+ /* && ttValue != VALUE_NONE Already implicit in the next condition */
+ && abs(ttValue) < VALUE_KNOWN_WIN
+ && (tte->bound() & BOUND_LOWER)
+ && tte->depth() >= depth - 3)
+ {
+ Value singularBeta = ttValue - (3 + (ss->ttPv && !PvNode)) * depth;
+ Depth singularDepth = (depth - 1) / 2;
- ss->excludedMove = move;
- value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
- ss->excludedMove = MOVE_NONE;
+ ss->excludedMove = move;
+ value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
+ ss->excludedMove = MOVE_NONE;
- if (value < singularBeta)
- {
- extension = 1;
- singularQuietLMR = !ttCapture;
+ if (value < singularBeta)
+ {
+ extension = 1;
+ singularQuietLMR = !ttCapture;
+
+ // Avoid search explosion by limiting the number of double extensions
+ if ( !PvNode
+ && value < singularBeta - 25
+ && ss->doubleExtensions <= 9)
+ extension = 2;
+ }
- // Avoid search explosion by limiting the number of double extensions
- if ( !PvNode
- && value < singularBeta - 75
- && ss->doubleExtensions <= 6)
- extension = 2;
+ // Multi-cut pruning
+ // Our ttMove is assumed to fail high, and now we failed high also on a reduced
+ // search without the ttMove. So we assume this expected Cut-node is not singular,
+ // that multiple moves fail high, and we can prune the whole subtree by returning
+ // a soft bound.
+ else if (singularBeta >= beta)
+ return singularBeta;
+
+ // 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 alpha and value, we reduce it (negative extension)
+ else if (ttValue <= alpha && ttValue <= value)
+ extension = -1;
}
- // Multi-cut pruning
- // Our ttMove is assumed to fail high, and now we failed high also on a reduced
- // search without the ttMove. So we assume this expected Cut-node is not singular,
- // that multiple moves fail high, and we can prune the whole subtree by returning
- // a soft bound.
- else if (singularBeta >= beta)
- return singularBeta;
-
- // If the eval of ttMove is greater than beta, we reduce it (negative extension)
- else if (ttValue >= beta)
- extension = -2;
- }
+ // Check extensions (~1 Elo)
+ else if ( givesCheck
+ && depth > 9
+ && abs(ss->staticEval) > 82)
+ extension = 1;
- // Capture extensions for PvNodes and cutNodes
- else if ( (PvNode || cutNode)
- && captureOrPromotion
- && moveCount != 1)
- extension = 1;
-
- // Check extensions
- else if ( givesCheck
- && depth > 6
- && abs(ss->staticEval) > 100)
- extension = 1;
-
- // Quiet ttMove extensions
- else if ( PvNode
- && move == ttMove
- && move == ss->killers[0]
- && (*contHist[0])[movedPiece][to_sq(move)] >= 10000)
- extension = 1;
+ // Quiet ttMove extensions (~0 Elo)
+ else if ( PvNode
+ && move == ttMove
+ && move == ss->killers[0]
+ && (*contHist[0])[movedPiece][to_sq(move)] >= 5177)
+ extension = 1;
+ }
// Add extension to new depth
newDepth += extension;
// 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);
- // Step 16. Late moves reduction / extension (LMR, ~200 Elo)
+ // Step 17. 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
+ if ( depth >= 2
+ && moveCount > 1 + (PvNode && ss->ply <= 1)
&& ( !ss->ttPv
- || !captureOrPromotion
+ || !capture
|| (cutNode && (ss-1)->moveCount > 1)))
{
- Depth r = reduction(improving, depth, moveCount, rangeReduction > 2);
-
- // Decrease reduction if on the PV (~2 Elo)
- if ( PvNode
- && bestMoveCount <= 3)
- r--;
+ 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)
&& !likelyFailLow)
r -= 2;
- // Increase reduction at root and non-PV nodes when the best move does not change frequently
- if ( (rootNode || !PvNode)
- && thisThread->bestMoveChanges <= 2)
- r++;
-
// Decrease reduction if opponent's move count is high (~1 Elo)
- if ((ss-1)->moveCount > 13)
- r--;
-
- // Decrease reduction if ttMove has been singularly extended (~1 Elo)
- if (singularQuietLMR)
+ if ((ss-1)->moveCount > 7)
r--;
// Increase reduction for cut nodes (~3 Elo)
- if (cutNode && move != ss->killers[0])
+ if (cutNode)
r += 2;
// Increase reduction if ttMove is a capture (~3 Elo)
if (ttCapture)
r++;
- ss->statScore = thisThread->mainHistory[us][from_to(move)]
+ // Decrease reduction for PvNodes based on depth
+ if (PvNode)
+ r -= 1 + 11 / (3 + depth);
+
+ // Decrease reduction if ttMove has been singularly extended (~1 Elo)
+ if (singularQuietLMR)
+ r--;
+
+ // Dicrease reduction if we move a threatened piece (~1 Elo)
+ if ( depth > 9
+ && (mp.threatenedPieces & from_sq(move)))
+ r--;
+
+ // Increase reduction if next ply has a lot of fail high
+ if ((ss+1)->cutoffCnt > 3 && !PvNode)
+ r++;
+
+ 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)]
- - 4923;
+ - 4433;
// Decrease/increase reduction for moves with a good/bad history (~30 Elo)
- r -= ss->statScore / 14721;
-
- // 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;
+ r -= ss->statScore / (13628 + 4000 * (depth > 7 && depth < 19));
- Depth d = std::clamp(newDepth - r, 1, newDepth + deeper);
+ // 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);
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
- // Range reductions (~3 Elo)
- if (ss->staticEval - value < 30 && depth > 7)
- rangeReduction++;
-
- // If the son is reduced and fails high it will be re-searched at full depth
- doFullDepthSearch = value > alpha && d < newDepth;
- didLMR = true;
- }
- else
- {
- doFullDepthSearch = !PvNode || moveCount > 1;
- didLMR = false;
- }
-
- // Step 17. Full depth search when LMR is skipped or fails high
- if (doFullDepthSearch)
- {
- value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
-
- // If the move passed LMR update its stats
- if (didLMR && !captureOrPromotion)
+ // Do full depth search when reduced LMR search fails high
+ if (value > alpha && d < newDepth)
{
+ const bool doDeeperSearch = value > (alpha + 64 + 11 * (newDepth - d));
+ value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth + doDeeperSearch, !cutNode);
+
int bonus = value > alpha ? stat_bonus(newDepth)
: -stat_bonus(newDepth);
+ if (capture)
+ bonus /= 6;
+
update_continuation_histories(ss, movedPiece, to_sq(move), bonus);
}
}
+ // Step 18. Full depth search when LMR is skipped
+ else if (!PvNode || moveCount > 1)
+ {
+ value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !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.
std::min(maxNextDepth, 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.
RootMove& rm = *std::find(thisThread->rootMoves.begin(),
thisThread->rootMoves.end(), move);
+ rm.averageScore = rm.averageScore != -VALUE_INFINITE ? (2 * value + rm.averageScore) / 3 : value;
+
// PV move or new best move?
if (moveCount == 1 || value > alpha)
{
rm.pv.push_back(*m);
// We record how often the best move has been changed in each iteration.
- // This information is used for time management and LMR. In MultiPV mode,
+ // This information is used for time management. In MultiPV mode,
// we must take care to only do this for the first PV line.
if ( moveCount > 1
&& !thisThread->pvIdx)
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 < VALUE_KNOWN_WIN
+ && alpha > -VALUE_KNOWN_WIN)
+ depth -= 1;
+
+ assert(depth > 0);
}
else
{
+ ss->cutoffCnt++;
assert(value >= beta); // Fail high
break;
}
}
}
+ else
+ ss->cutoffCnt = 0;
+
// 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)
+ else if ( (depth >= 5 || PvNode)
&& !priorCapture)
- update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * (1 + (PvNode || cutNode)));
+ {
+ //Assign extra bonus if current node is PvNode or cutNode
+ //or fail low was really bad
+ bool extraBonus = PvNode
+ || cutNode
+ || bestValue < alpha - 62 * depth;
+
+ update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * (1 + extraBonus));
+ }
if (PvNode)
bestValue = std::min(bestValue, maxValue);
// 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) {
Key posKey;
Move ttMove, move, bestMove;
Depth ttDepth;
- Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
- bool pvHit, givesCheck, captureOrPromotion;
+ Value bestValue, value, ttValue, futilityValue, futilityBase;
+ bool pvHit, givesCheck, capture;
int moveCount;
if (PvNode)
{
- oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
(ss+1)->pv = pv;
ss->pv[0] = MOVE_NONE;
}
&& 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
if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
ss->staticEval = bestValue = evaluate(pos);
- // Can ttValue be used as a better position evaluation?
+ // ttValue can be used as a better position evaluation (~7 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 + 153;
}
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
// to search the moves. Because the depth is <= 0 here, only captures,
// queen promotions, and other checks (only if depth >= DEPTH_QS_CHECKS)
// will be generated.
+ Square prevSq = to_sq((ss-1)->currentMove);
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
&thisThread->captureHistory,
contHist,
- to_sq((ss-1)->currentMove));
+ prevSq);
+
+ int quietCheckEvasions = 0;
// Loop through the moves until no moves remain or a beta cutoff occurs
while ((move = mp.next_move()) != MOVE_NONE)
continue;
givesCheck = pos.gives_check(move);
- captureOrPromotion = pos.capture_or_promotion(move);
+ capture = pos.capture(move);
moveCount++;
- // Futility pruning and moveCount pruning
+ // Futility pruning and moveCount pruning (~5 Elo)
if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
&& !givesCheck
+ && to_sq(move) != prevSq
&& futilityBase > -VALUE_KNOWN_WIN
&& type_of(move) != PROMOTION)
{
}
}
- // Do not search moves with negative SEE values
+ // Do not search moves with negative SEE values (~5 Elo)
if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
&& !pos.see_ge(move))
continue;
ss->currentMove = move;
ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck]
- [captureOrPromotion]
+ [capture]
[pos.moved_piece(move)]
[to_sq(move)];
- // Continuation history based pruning
- if ( !captureOrPromotion
+ // Continuation history based pruning (~2 Elo)
+ if ( !capture
&& 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)
+ && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < 0
+ && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < 0)
continue;
+ // movecount pruning for quiet check evasions
+ if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
+ && quietCheckEvasions > 1
+ && !capture
+ && ss->inCheck)
+ continue;
+
+ quietCheckEvasions += !capture && ss->inCheck;
+
// Make and search the move
pos.do_move(move, st, givesCheck);
value = -qsearch<nodeType>(pos, ss+1, -beta, -alpha, depth - 1);
// Save gathered info in transposition table
tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit,
- bestValue >= beta ? BOUND_LOWER :
- PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
+ bestValue >= beta ? BOUND_LOWER : BOUND_UPPER,
ttDepth, bestMove, ss->staticEval);
assert(bestValue > -VALUE_INFINITE && 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(bestMove))
+ {
+ int bonus2 = bestValue > beta + 137 ? 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, depth);
+ update_quiet_stats(pos, ss, bestMove, bonus2);
// Decrease stats for all non-best quiet moves
for (int i = 0; i < quietCount; ++i)
// update_quiet_stats() updates move sorting heuristics
- void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus, int depth) {
+ void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus) {
// Update killers
if (ss->killers[0] != move)
thisThread->mainHistory[us][from_to(move)] << bonus;
update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus);
- // Penalty for reversed move in case of moved piece not being a pawn
- if (type_of(pos.moved_piece(move)) != PAWN)
- thisThread->mainHistory[us][from_to(reverse_move(move))] << -bonus;
-
// Update countermove history
if (is_ok((ss-1)->currentMove))
{
Square prevSq = to_sq((ss-1)->currentMove);
thisThread->counterMoves[pos.piece_on(prevSq)][prevSq] = move;
}
-
- // Update low ply history
- if (depth > 11 && ss->ply < MAX_LPH)
- thisThread->lowPlyHistory[ss->ply][from_to(move)] << stat_bonus(depth - 7);
}
// When playing with strength handicap, choose best move among a set of RootMoves
ss << (v >= beta ? " lowerbound" : v <= alpha ? " 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