X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=src%2Fsearch.cpp;h=4a41a8b0b09e275284424c37bed3d8f2edcb69d3;hb=5372f81cc81d5be3040db6f2dbfff108c460baf9;hp=a487ed1305b1ccdc8aabe5b42858ec71799b5895;hpb=939ffe454d28556ee7653af4d3322b8c8ba470be;p=stockfish diff --git a/src/search.cpp b/src/search.cpp index a487ed13..4a41a8b0 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -1,6 +1,6 @@ /* 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 @@ -61,20 +61,17 @@ namespace { // Different node types, used as a template parameter enum NodeType { NonPV, PV, Root }; - constexpr uint64_t TtHitAverageWindow = 4096; - constexpr uint64_t TtHitAverageResolution = 1024; - // Futility margin Value futility_margin(Depth d, bool improving) { - return Value(214 * (d - improving)); + return Value(168 * (d - improving)); } // Reductions lookup table, initialized at startup int Reductions[MAX_MOVES]; // [depth or moveNumber] - Depth reduction(bool i, Depth d, int mn) { + 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); + return (r + 1463 - int(delta) * 1024 / int(rootDelta)) / 1024 + (!i && r > 1010); } constexpr int futility_move_count(bool improving, Depth depth) { @@ -83,7 +80,7 @@ namespace { // History and stats update bonus, based on depth int stat_bonus(Depth d) { - return d > 14 ? 73 : 6 * d * d + 229 * d - 215; + return std::min((9 * d + 270) * d - 311 , 2145); } // Add a small random component to draw evaluations to avoid 3-fold blindness @@ -91,14 +88,22 @@ namespace { return VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1); } - // Skill structure is used to implement strength limit + // Skill structure is used to implement strength limit. If we have an uci_elo then + // we convert it to a suitable fractional skill level using anchoring to CCRL Elo + // (goldfish 1.13 = 2000) and a fit through Ordo derived Elo for match (TC 60+0.6) + // results spanning a wide range of k values. struct Skill { - explicit Skill(int l) : level(l) {} - bool enabled() const { return level < 20; } - bool time_to_pick(Depth depth) const { return depth == 1 + level; } + 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); + else + level = double(skill_level); + } + bool enabled() const { return level < 20.0; } + bool time_to_pick(Depth depth) const { return depth == 1 + int(level); } Move pick_best(size_t multiPV); - int level; + double level; Move best = MOVE_NONE; }; @@ -112,7 +117,7 @@ namespace { Value value_from_tt(Value v, int ply, int r50c); void update_pv(Move* pv, Move move, 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); @@ -152,7 +157,7 @@ namespace { void Search::init() { for (int i = 1; i < MAX_MOVES; ++i) - Reductions[i] = int(21.9 * std::log(i)); + Reductions[i] = int((20.81 + std::log(Threads.size()) / 2) * std::log(i)); } @@ -222,14 +227,19 @@ void MainThread::search() { Time.availableNodes += Limits.inc[us] - Threads.nodes_searched(); Thread* bestThread = this; + Skill skill = Skill(Options["Skill Level"], Options["UCI_LimitStrength"] ? int(Options["UCI_Elo"]) : 0); if ( int(Options["MultiPV"]) == 1 && !Limits.depth - && !(Skill(Options["Skill Level"]).enabled() || int(Options["UCI_LimitStrength"])) + && !skill.enabled() && rootMoves[0].pv[0] != MOVE_NONE) 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) @@ -256,7 +266,7 @@ void Thread::search() { // 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); @@ -286,23 +296,8 @@ void Thread::search() { 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"]); - - // Pick integer skill levels, but non-deterministically round up or down - // such that the average integer skill corresponds to the input floating point one. - // UCI_Elo is converted to a suitable fractional skill level, using anchoring - // to CCRL Elo (goldfish 1.13 = 2000) and a fit through Ordo derived Elo - // for match (TC 60+0.6) results spanning a wide range of k values. - PRNG rng(now()); - double floatLevel = Options["UCI_LimitStrength"] ? - std::clamp(std::pow((Options["UCI_Elo"] - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0) : - double(Options["Skill Level"]); - int intLevel = int(floatLevel) + - ((floatLevel - int(floatLevel)) * 1024 > rng.rand() % 1024 ? 1 : 0); - Skill skill(intLevel); + Skill skill(Options["Skill Level"], Options["UCI_LimitStrength"] ? int(Options["UCI_Elo"]) : 0); // When playing with strength handicap enable MultiPV search that we will // use behind the scenes to retrieve a set of possible moves. @@ -310,9 +305,12 @@ void Thread::search() { multiPV = std::max(multiPV, (size_t)4); multiPV = std::min(multiPV, rootMoves.size()); - ttHitAverage = TtHitAverageWindow * TtHitAverageResolution / 2; - trend = SCORE_ZERO; + complexityAverage.set(202, 1); + + trend = SCORE_ZERO; + optimism[ us] = Value(39); + optimism[~us] = -optimism[us]; int searchAgainCounter = 0; @@ -353,16 +351,19 @@ void Thread::search() { // Reset aspiration window starting size if (rootDepth >= 4) { - Value prev = rootMoves[pvIdx].previousScore; - delta = Value(17); + Value prev = rootMoves[pvIdx].averageScore; + delta = Value(16) + int(prev) * prev / 19178; 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); - + // Adjust trend and optimism based on root move's previousScore + int tr = sigmoid(prev, 3, 8, 90, 125, 1); trend = (us == WHITE ? make_score(tr, tr / 2) : -make_score(tr, tr / 2)); + + int opt = sigmoid(prev, 8, 17, 144, 13966, 183); + optimism[ us] = Value(opt); + optimism[~us] = -optimism[us]; } // Start with a small aspiration window and, in the case of a fail @@ -415,7 +416,7 @@ void Thread::search() { else break; - delta += delta / 4 + 5; + delta += delta / 4 + 2; assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE); } @@ -449,28 +450,30 @@ void Thread::search() { 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 = (69 + 12 * (mainThread->bestPreviousAverageScore - bestValue) + + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 781.4; 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 + 10 < completedDepth ? 1.63 : 0.73; + double reduction = (1.56 + mainThread->previousTimeReduction) / (2.20 * timeReduction); + double bestMoveInstability = 1 + 1.7 * totBestMoveChanges / Threads.size(); + int complexity = mainThread->complexityAverage.value(); + double complexPosition = std::clamp(1.0 + (complexity - 326) / 1618.1, 0.5, 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. @@ -489,7 +492,7 @@ void Thread::search() { } else if ( Threads.increaseDepth && !mainThread->ponder - && Time.elapsed() > totalTime * 0.58) + && Time.elapsed() > totalTime * 0.43) Threads.increaseDepth = false; else Threads.increaseDepth = true; @@ -553,13 +556,13 @@ namespace { Depth extension, newDepth; Value bestValue, value, ttValue, eval, maxValue, probCutBeta; bool givesCheck, improving, didLMR, priorCapture; - bool captureOrPromotion, doFullDepthSearch, moveCountPruning, - ttCapture, singularQuietLMR; + bool capture, doFullDepthSearch, moveCountPruning, ttCapture; Piece movedPiece; - int moveCount, captureCount, quietCount; + int moveCount, captureCount, quietCount, improvement, complexity; // Step 1. Initialize node Thread* thisThread = pos.this_thread(); + thisThread->depth = depth; ss->inCheck = pos.checkers(); priorCapture = pos.captured_piece(); Color us = pos.side_to_move(); @@ -595,13 +598,17 @@ namespace { 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); // Initialize statScore to zero for the grandchildren of the current position. @@ -621,44 +628,33 @@ namespace { 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(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); - - // thisThread->ttHitAverage can be used to approximate the running average of ttHit - thisThread->ttHitAverage = (TtHitAverageWindow - 1) * thisThread->ttHitAverage / TtHitAverageWindow - + TtHitAverageResolution * ss->ttHit; - // At non-PV nodes we check for an early TT cutoff if ( !PvNode && ss->ttHit - && tte->depth() >= depth + && tte->depth() > depth - (thisThread->id() % 2 == 1) && ttValue != VALUE_NONE // Possible in case of TT access race && (ttValue >= beta ? (tte->bound() & BOUND_LOWER) : (tte->bound() & 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 - if (!pos.capture_or_promotion(ttMove)) - update_quiet_stats(pos, ss, ttMove, stat_bonus(depth), depth); + // Bonus for a quiet ttMove that fails high (~3 Elo) + if (!ttCapture) + 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 - else if (!pos.capture_or_promotion(ttMove)) + // Penalty for a quiet ttMove that fails low (~1 Elo) + else if (!ttCapture) { int penalty = -stat_bonus(depth); thisThread->mainHistory[us][from_to(ttMove)] << penalty; @@ -732,6 +728,8 @@ namespace { // Skip early pruning when in check ss->staticEval = eval = VALUE_NONE; improving = false; + improvement = 0; + complexity = 0; goto moves_loop; } else if (ss->ttHit) @@ -745,63 +743,76 @@ namespace { if (eval == VALUE_DRAW) eval = value_draw(thisThread); - // 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 { - // In case of null move search use previous static eval with a different sign - // and addition of two tempos - if ((ss-1)->currentMove != MOVE_NULL) - ss->staticEval = eval = evaluate(pos); - else - ss->staticEval = eval = -(ss-1)->staticEval; + ss->staticEval = eval = evaluate(pos); // Save static evaluation into transposition table - if(!excludedMove) - tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval); + 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 + // 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(-16 * int((ss-1)->staticEval + ss->staticEval), -2000, 2000); thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus; } - // Set up improving flag that is used in various pruning heuristics - // We define position as improving if static evaluation of position is better - // Than the previous static evaluation at our turn - // In case of us being in check at our previous move we look at move prior to it - improving = (ss-2)->staticEval == VALUE_NONE - ? ss->staticEval > (ss-4)->staticEval || (ss-4)->staticEval == VALUE_NONE - : ss->staticEval > (ss-2)->staticEval; + // Set up the improvement variable, which is the difference between the current + // static evaluation and the previous static evaluation at our turn (if we were + // in check at our previous move we look at the move prior to it). The improvement + // 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 + : 175; - // Step 7. Futility pruning: child node (~50 Elo). - // The depth condition is important for mate finding. + 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. + // If eval is really low check with qsearch if it can exceed alpha, if it can't, + // return a fail low. if ( !PvNode - && depth < 9 - && eval - futility_margin(depth, improving) >= beta - && eval < VALUE_KNOWN_WIN) // Do not return unproven wins + && depth <= 7 + && eval < alpha - 348 - 258 * depth * depth) + { + value = qsearch(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 ( !ss->ttPv + && depth < 8 + && eval - futility_margin(depth, improving) - (ss-1)->statScore / 256 >= beta + && eval >= beta + && eval < 26305) // 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 < 14695 && eval >= beta && eval >= ss->staticEval - && ss->staticEval >= beta - 20 * depth - 22 * improving + 168 * ss->ttPv + 159 + && ss->staticEval >= beta - 15 * depth - improvement / 15 + 198 + complexity / 28 && !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) / 147, 5) + depth / 3 + 4 - (complexity > 753); ss->currentMove = MOVE_NULL; ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0]; @@ -837,9 +848,9 @@ namespace { } } - probCutBeta = beta + 209 - 44 * improving; + probCutBeta = beta + 179 - 46 * 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 @@ -856,20 +867,17 @@ namespace { { assert(probCutBeta < VALUE_INFINITE); - MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory); - int probCutCount = 0; + MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, depth - 3, &captureHistory); bool ttPv = ss->ttPv; + bool captureOrPromotion; ss->ttPv = false; - while ( (move = mp.next_move()) != MOVE_NONE - && probCutCount < 2 + 2 * cutNode) + while ((move = mp.next_move()) != MOVE_NONE) if (move != excludedMove && pos.legal(move)) { - assert(pos.capture_or_promotion(move)); - assert(depth >= 5); + assert(pos.capture(move) || promotion_type(move) == QUEEN); captureOrPromotion = true; - probCutCount++; ss->currentMove = move; ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck] @@ -903,21 +911,24 @@ namespace { ss->ttPv = ttPv; } - // Step 10. If the position is not in TT, decrease depth by 2 + // Step 11. If the position is not in TT, decrease depth by 2 or 1 depending on node type (~3 Elo) if ( PvNode - && depth >= 6 + && depth >= 3 && !ttMove) depth -= 2; -moves_loop: // When in check, search starts here + if ( cutNode + && depth >= 8 + && !ttMove) + depth--; - ttCapture = ttMove && pos.capture_or_promotion(ttMove); +moves_loop: // When in check, search starts here - // 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 + 481; if ( ss->inCheck && !PvNode - && depth >= 4 + && depth >= 2 && ttCapture && (tte->bound() & BOUND_LOWER) && tte->depth() >= depth - 3 @@ -935,16 +946,13 @@ moves_loop: // When in check, search starts here 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; - bool doubleExtension = false; + moveCountPruning = 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. @@ -953,7 +961,7 @@ moves_loop: // When in check, search starts here && (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) { @@ -984,119 +992,134 @@ moves_loop: // When in check, search starts here (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), 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 - if ( !givesCheck - && lmrDepth < 1 - && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0) + // Futility pruning for captures (~0 Elo) + if ( !pos.empty(to_sq(move)) + && !givesCheck + && !PvNode + && lmrDepth < 6 + && !ss->inCheck + && ss->staticEval + 281 + 179 * 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(-203) * depth)) continue; } else { - // Continuation history based pruning (~20 Elo) + 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 - && (*contHist[0])[movedPiece][to_sq(move)] < 23 - 23 * depth * depth - && (*contHist[1])[movedPiece][to_sq(move)] < 23 - 23 * depth * depth) + && history < -3875 * (depth - 1)) continue; - // Futility pruning: parent node (~5 Elo) + history += thisThread->mainHistory[us][from_to(move)]; + + // Futility pruning: parent node (~9 Elo) if ( !ss->inCheck - && lmrDepth < 7 - && ss->staticEval + 174 + 157 * lmrDepth <= alpha) + && lmrDepth < 11 + && ss->staticEval + 122 + 138 * lmrDepth + history / 60 <= 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(-25 * lmrDepth * lmrDepth - 20 * 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 - 2 * depth; - Depth singularDepth = (depth - 1) / 2; - - ss->excludedMove = move; - value = search(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode); - ss->excludedMove = MOVE_NONE; - - if (value < singularBeta) + // 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 > 27) + 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) { - extension = 1; - singularQuietLMR = !ttCapture; + Value singularBeta = ttValue - 3 * depth; + Depth singularDepth = (depth - 1) / 2; - // Avoid search explosion by limiting the number of double extensions to at most 3 - if ( !PvNode - && value < singularBeta - 93 - && ss->doubleExtensions < 3) + ss->excludedMove = move; + value = search(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode); + ss->excludedMove = MOVE_NONE; + + if (value < singularBeta) { - extension = 2; - doubleExtension = true; + extension = 1; + + // Avoid search explosion by limiting the number of double extensions + if ( !PvNode + && value < singularBeta - 26 + && ss->doubleExtensions <= 8) + 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 try also if there is another - // move that pushes it over beta, if so also produce a cutoff. - else if (ttValue >= beta) - { - ss->excludedMove = move; - value = search(pos, ss, beta - 1, beta, (depth + 3) / 2, cutNode); - ss->excludedMove = MOVE_NONE; + // Check extensions (~1 Elo) + else if ( givesCheck + && depth > 9 + && abs(ss->staticEval) > 71) + extension = 1; - if (value >= beta) - return beta; - } + // Quiet ttMove extensions (~0 Elo) + else if ( PvNode + && move == ttMove + && move == ss->killers[0] + && (*contHist[0])[movedPiece][to_sq(move)] >= 5491) + extension = 1; } - else if ( givesCheck - && depth > 6 - && abs(ss->staticEval) > Value(100)) - extension = 1; // Add extension to new depth newDepth += extension; @@ -1108,32 +1131,26 @@ moves_loop: // When in check, search starts here // 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) + bool doDeeperSearch = false; + + // 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 - && ( !captureOrPromotion - || (cutNode && (ss-1)->moveCount > 1) - || !ss->ttPv) - && (!PvNode || ss->ply > 1 || thisThread->id() % 4 != 3)) + if ( depth >= 2 + && moveCount > 1 + (PvNode && ss->ply <= 1) + && ( !ss->ttPv + || !capture + || (cutNode && (ss-1)->moveCount > 1))) { - Depth r = reduction(improving, depth, moveCount); - - if (PvNode) - r--; - - // Decrease reduction if the ttHit running average is large (~0 Elo) - if (thisThread->ttHitAverage > 537 * TtHitAverageResolution * TtHitAverageWindow / 1024) - 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) @@ -1141,17 +1158,8 @@ moves_loop: // When in check, search starts here && !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) @@ -1162,24 +1170,44 @@ moves_loop: // When in check, search starts here if (ttCapture) r++; + // Decrease reduction at PvNodes if bestvalue + // is vastly different from static evaluation + if (PvNode && !ss->inCheck && abs(ss->staticEval - bestValue) > 250) + r--; + + // Decrease reduction for PvNodes based on depth + if (PvNode) + r -= 1 + 15 / ( 3 + depth ); + + // Increase reduction if next ply has a lot of fail high else reset count to 0 + if ((ss+1)->cutoffCnt > 3 && !PvNode) + 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; + - 4334; // Decrease/increase reduction for moves with a good/bad history (~30 Elo) - r -= ss->statScore / 14721; + r -= ss->statScore / 15914; + + // 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 <= 4 ? 2 + : PvNode && depth > 4 ? 1 + : cutNode && moveCount <= 8 ? 1 + : 0; - // 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 in specific cases. - Depth d = std::clamp(newDepth - r, 1, newDepth + (r < -1 && (moveCount <= 5 || (depth > 6 && PvNode)) && !doubleExtension)); + Depth d = std::clamp(newDepth - r, 1, newDepth + deeper); value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); // If the son is reduced and fails high it will be re-searched at full depth doFullDepthSearch = value > alpha && d < newDepth; + doDeeperSearch = value > (alpha + 78 + 11 * (newDepth - d)); didLMR = true; } else @@ -1188,17 +1216,20 @@ moves_loop: // When in check, search starts here didLMR = false; } - // Step 17. Full depth search when LMR is skipped or fails high + // Step 18. Full depth search when LMR is skipped or fails high if (doFullDepthSearch) { - value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); + value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth + doDeeperSearch, !cutNode); // If the move passed LMR update its stats - if (didLMR && !captureOrPromotion) + if (didLMR) { int bonus = value > alpha ? stat_bonus(newDepth) : -stat_bonus(newDepth); + if (capture) + bonus /= 6; + update_continuation_histories(ss, movedPiece, to_sq(move), bonus); } } @@ -1215,12 +1246,12 @@ moves_loop: // When in check, search starts here 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. @@ -1232,6 +1263,8 @@ moves_loop: // When in check, search starts here 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) { @@ -1244,9 +1277,11 @@ moves_loop: // When in check, search starts here for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m) 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 - if (moveCount > 1) + // We record how often the best move has been changed in each iteration. + // 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) ++thisThread->bestMoveChanges; } else @@ -1268,22 +1303,37 @@ moves_loop: // When in check, search starts here update_pv(ss->pv, move, (ss+1)->pv); if (PvNode && value < beta) // Update alpha! Always alpha < beta + { alpha = value; + + // Reduce other moves if we have found at least one score improvement + if ( depth > 2 + && depth < 7 + && 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; } } @@ -1296,7 +1346,7 @@ moves_loop: // When in check, search starts here 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. @@ -1314,9 +1364,17 @@ moves_loop: // When in check, search starts here quietsSearched, quietCount, capturesSearched, captureCount, depth); // Bonus for prior countermove that caused the fail low - else if ( (depth >= 3 || PvNode) + else if ( (depth >= 4 || PvNode) && !priorCapture) - update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth)); + { + //Assign extra bonus if current node is PvNode or cutNode + //or fail low was really bad + bool extraBonus = PvNode + || cutNode + || bestValue < alpha - 70 * depth; + + update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * (1 + extraBonus)); + } if (PvNode) bestValue = std::min(bestValue, maxValue); @@ -1325,10 +1383,6 @@ moves_loop: // When in check, search starts here // 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)) @@ -1363,13 +1417,12 @@ moves_loop: // When in check, search starts here 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; } @@ -1420,14 +1473,13 @@ moves_loop: // When in check, search starts here 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; } else // In case of null move search use previous static eval with a different sign - // and addition of two tempos ss->staticEval = bestValue = (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval; @@ -1446,7 +1498,7 @@ moves_loop: // When in check, search starts here if (PvNode && bestValue > alpha) alpha = bestValue; - futilityBase = bestValue + 155; + futilityBase = bestValue + 118; } const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, @@ -1457,10 +1509,13 @@ moves_loop: // When in check, search starts here // 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) @@ -1472,13 +1527,14 @@ moves_loop: // When in check, search starts here 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) { @@ -1501,7 +1557,7 @@ moves_loop: // When in check, search starts here } } - // 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; @@ -1511,17 +1567,26 @@ moves_loop: // When in check, search starts here 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) 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(pos, ss+1, -beta, -alpha, depth - 1); @@ -1560,8 +1625,7 @@ moves_loop: // When in check, search starts here // 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); @@ -1637,13 +1701,13 @@ moves_loop: // When in check, search starts here PieceType captured = type_of(pos.piece_on(to_sq(bestMove))); bonus1 = stat_bonus(depth + 1); - bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus - : std::min(bonus1, stat_bonus(depth)); // smaller bonus + bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus + : stat_bonus(depth); // smaller bonus - if (!pos.capture_or_promotion(bestMove)) + if (!pos.capture(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) @@ -1690,7 +1754,7 @@ moves_loop: // When in check, search starts here // 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) @@ -1704,20 +1768,12 @@ moves_loop: // When in check, search starts here 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 @@ -1731,8 +1787,8 @@ moves_loop: // When in check, search starts here // RootMoves are already sorted by score in descending order Value topScore = rootMoves[0].score; int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg); - int weakness = 120 - 2 * level; int maxScore = -VALUE_INFINITE; + double weakness = 120 - 2 * level; // Choose best move. For each move score we add two terms, both dependent on // weakness. One is deterministic and bigger for weaker levels, and one is @@ -1740,8 +1796,8 @@ moves_loop: // When in check, search starts here for (size_t i = 0; i < multiPV; ++i) { // This is our magic formula - int push = ( weakness * int(topScore - rootMoves[i].score) - + delta * (rng.rand() % weakness)) / 128; + int push = int(( weakness * int(topScore - rootMoves[i].score) + + delta * (rng.rand() % int(weakness))) / 128); if (rootMoves[i].score + push >= maxScore) {