X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=src%2Fsearch.cpp;h=48694cb2dedebcebaec8dd59491ade87c41d2daf;hb=675f6a038ba98b6b906a4767f009cf6fe91b0c52;hp=d2a641768fe906c76d73442157598f7841656918;hpb=c4d67d77c99b99c9ac387ab622773a320f8d5cc3;p=stockfish diff --git a/src/search.cpp b/src/search.cpp index d2a64176..9b747e78 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 @@ -35,6 +35,8 @@ #include "uci.h" #include "syzygy/tbprobe.h" +namespace Stockfish { + namespace Search { LimitsType Limits; @@ -57,103 +59,66 @@ using namespace Search; namespace { // Different node types, used as a template parameter - enum NodeType { NonPV, PV }; - - constexpr uint64_t TtHitAverageWindow = 4096; - constexpr uint64_t TtHitAverageResolution = 1024; + enum NodeType { NonPV, PV, Root }; // Futility margin Value futility_margin(Depth d, bool improving) { - return Value(234 * (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 + 503) / 1024 + (!i && r > 915); + return (r + 1463 - int(delta) * 1024 / int(rootDelta)) / 1024 + (!i && r > 1010); } 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 d > 14 ? 29 : 8 * d * d + 224 * d - 215; + return std::min((8 * d + 240) * d - 276 , 1907); } - // Add a small random component to draw evaluations to avoid 3fold-blindness - Value value_draw(Thread* thisThread) { - return VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1); + // Add a small random component to draw evaluations to avoid 3-fold blindness + Value value_draw(const Thread* thisThread) { + return VALUE_DRAW - 1 + Value(thisThread->nodes & 0x2); } - // 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; }; - // Breadcrumbs are used to mark nodes as being searched by a given thread - struct Breadcrumb { - std::atomic thread; - std::atomic key; - }; - std::array breadcrumbs; - - // ThreadHolding structure keeps track of which thread left breadcrumbs at the given - // node for potential reductions. A free node will be marked upon entering the moves - // loop by the constructor, and unmarked upon leaving that loop by the destructor. - struct ThreadHolding { - explicit ThreadHolding(Thread* thisThread, Key posKey, int ply) { - location = ply < 8 ? &breadcrumbs[posKey & (breadcrumbs.size() - 1)] : nullptr; - otherThread = false; - owning = false; - if (location) - { - // See if another already marked this location, if not, mark it ourselves - Thread* tmp = (*location).thread.load(std::memory_order_relaxed); - if (tmp == nullptr) - { - (*location).thread.store(thisThread, std::memory_order_relaxed); - (*location).key.store(posKey, std::memory_order_relaxed); - owning = true; - } - else if ( tmp != thisThread - && (*location).key.load(std::memory_order_relaxed) == posKey) - otherThread = true; - } - } - - ~ThreadHolding() { - if (owning) // Free the marked location - (*location).thread.store(nullptr, std::memory_order_relaxed); - } - - bool marked() { return otherThread; } - - private: - Breadcrumb* location; - bool otherThread, owning; - }; - - template + template Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode); - template + template Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = 0); 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); @@ -163,7 +128,7 @@ namespace { uint64_t perft(Position& pos, Depth depth) { StateInfo st; - ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize); + ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize); uint64_t cnt, nodes = 0; const bool leaf = (depth == 2); @@ -193,7 +158,7 @@ namespace { void Search::init() { for (int i = 1; i < MAX_MOVES; ++i) - Reductions[i] = int((21.3 + 2 * std::log(Threads.size())) * std::log(i + 0.25 * std::log(i))); + Reductions[i] = int((20.81 + std::log(Threads.size()) / 2) * std::log(i)); } @@ -263,14 +228,19 @@ 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) @@ -294,10 +264,10 @@ void Thread::search() { // To allow access to (ss-7) up to (ss+2), the stack must be oversized. // The former is needed to allow update_continuation_histories(ss-1, ...), // which accesses its argument at ss-6, also near the root. - // The latter is needed for statScores and killer initialization. + // 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); @@ -309,6 +279,9 @@ void Thread::search() { for (int i = 7; i > 0; i--) (ss-i)->continuationHistory = &this->continuationHistory[0][0][NO_PIECE][0]; // Use as a sentinel + for (int i = 0; i <= MAX_PLY + 2; ++i) + (ss+i)->ply = i; + ss->pv = pv; bestValue = delta = alpha = -VALUE_INFINITE; @@ -324,23 +297,8 @@ 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. @@ -348,21 +306,12 @@ void Thread::search() { multiPV = std::max(multiPV, (size_t)4); multiPV = std::min(multiPV, rootMoves.size()); - ttHitAverage = TtHitAverageWindow * TtHitAverageResolution / 2; - - int ct = int(Options["Contempt"]) * PawnValueEg / 100; // From centipawns - // In analysis mode, adjust contempt in accordance with user preference - if (Limits.infinite || Options["UCI_AnalyseMode"]) - ct = Options["Analysis Contempt"] == "Off" ? 0 - : Options["Analysis Contempt"] == "Both" ? ct - : Options["Analysis Contempt"] == "White" && us == BLACK ? -ct - : Options["Analysis Contempt"] == "Black" && us == WHITE ? -ct - : ct; + complexityAverage.set(174, 1); - // Evaluation score is from the white point of view - contempt = (us == WHITE ? make_score(ct, ct / 2) - : -make_score(ct, ct / 2)); + trend = SCORE_ZERO; + optimism[ us] = Value(39); + optimism[~us] = -optimism[us]; int searchAgainCounter = 0; @@ -403,26 +352,31 @@ 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 contempt based on root move's previousScore (dynamic contempt) - int dct = ct + (113 - ct / 2) * 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)); - contempt = (us == WHITE ? make_score(dct, dct / 2) - : -make_score(dct, dct / 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 // high/low, re-search with a bigger window until we don't fail // high/low anymore. - failedHighCnt = 0; + int failedHighCnt = 0; while (true) { - Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter); - bestValue = ::search(rootPos, ss, alpha, beta, adjustedDepth, false); + // 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(rootPos, ss, alpha, beta, adjustedDepth, false); // Bring the best move to the front. It is critical that sorting // is done with a stable algorithm because all the values but the @@ -465,7 +419,7 @@ void Thread::search() { else break; - delta += delta / 4 + 5; + delta += delta / 4 + 2; assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE); } @@ -499,28 +453,30 @@ 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::min(1.0 + (complexity - 277) / 1819.1, 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 + 2 * 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. @@ -539,7 +495,7 @@ 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; @@ -565,18 +521,18 @@ namespace { // search<>() is the main search function for both PV and non-PV nodes - template + template Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) { - constexpr bool PvNode = NT == PV; - const bool rootNode = PvNode && ss->ply == 0; + 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. - if ( pos.rule50_count() >= 3 + if ( !rootNode + && pos.rule50_count() >= 3 && alpha < VALUE_DRAW - && !rootNode && pos.has_game_cycle(ss->ply)) { alpha = value_draw(pos.this_thread()); @@ -586,7 +542,7 @@ namespace { // Dive into quiescence search when the depth reaches zero if (depth <= 0) - return qsearch(pos, ss, alpha, beta); + return qsearch(pos, ss, alpha, beta); assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE); assert(PvNode || (alpha == beta - 1)); @@ -595,27 +551,27 @@ namespace { Move pv[MAX_PLY+1], capturesSearched[32], quietsSearched[64]; StateInfo st; - ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize); + ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize); TTEntry* tte; Key posKey; Move ttMove, move, excludedMove, bestMove; Depth extension, newDepth; Value bestValue, value, ttValue, eval, maxValue, probCutBeta; - bool formerPv, givesCheck, improving, didLMR, priorCapture; - bool captureOrPromotion, doFullDepthSearch, moveCountPruning, - ttCapture, singularQuietLMR; + bool givesCheck, improving, didLMR, priorCapture; + 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(); - ss->inCheck = pos.checkers(); - priorCapture = pos.captured_piece(); - Color us = pos.side_to_move(); - moveCount = captureCount = quietCount = ss->moveCount = 0; - bestValue = -VALUE_INFINITE; - maxValue = VALUE_INFINITE; + thisThread->depth = depth; + ss->inCheck = pos.checkers(); + priorCapture = pos.captured_piece(); + Color us = pos.side_to_move(); + moveCount = captureCount = quietCount = ss->moveCount = 0; + bestValue = -VALUE_INFINITE; + maxValue = VALUE_INFINITE; // Check for the available remaining time if (thisThread == Threads.main()) @@ -645,14 +601,17 @@ namespace { if (alpha >= beta) return alpha; } + else + thisThread->rootDelta = beta - alpha; assert(0 <= ss->ply && ss->ply < MAX_PLY); - (ss+1)->ply = ss->ply + 1; - (ss+1)->ttPv = false; + (ss+1)->ttPv = false; (ss+1)->excludedMove = bestMove = MOVE_NONE; - (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE; - Square prevSq = to_sq((ss-1)->currentMove); + (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE; + (ss+2)->cutoffCnt = 0; + ss->doubleExtensions = (ss-1)->doubleExtensions; + Square prevSq = to_sq((ss-1)->currentMove); // Initialize statScore to zero for the grandchildren of the current position. // So statScore is shared between all grandchildren and only the first grandchild @@ -671,45 +630,32 @@ 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()); - formerPv = ss->ttPv && !PvNode; - - // 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 - ((int)thisThread->id() & 0x1) - (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 - 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; @@ -783,6 +729,8 @@ 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) @@ -790,67 +738,82 @@ namespace { // Never assume anything about values stored in TT ss->staticEval = eval = tte->eval(); if (eval == VALUE_NONE) - ss->staticEval = eval = evaluate(pos); + 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()); // Randomize draw evaluation 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 + 2 * Tempo; + ss->staticEval = eval = evaluate(pos, &complexity); // Save static evaluation into transposition table - 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 + 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 - 2 * Tempo), -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; - - // Step 7. Futility pruning: child node (~50 Elo) + // 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; + improving = improvement > 0; + + // 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 < 22977 + && (ss-1)->statScore < 14695 && eval >= beta && eval >= ss->staticEval - && ss->staticEval >= beta - 30 * depth - 28 * improving + 84 * ss->ttPv + 168 + && ss->staticEval >= beta - 15 * depth - improvement / 15 + 201 + complexity / 24 && !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 = (1015 + 85 * depth) / 256 + std::min(int(eval - beta) / 191, 3); + // 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 > 650); ss->currentMove = MOVE_NULL; ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0]; @@ -886,9 +849,9 @@ namespace { } } - probCutBeta = beta + 194 - 49 * improving; + probCutBeta = beta + 179 - 46 * improving; - // Step 9. ProbCut (~10 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 @@ -903,35 +866,18 @@ namespace { && ttValue != VALUE_NONE && ttValue < probCutBeta)) { - // if ttMove is a capture and value from transposition table is good enough produce probCut - // cutoff without digging into actual probCut search - if ( ss->ttHit - && tte->depth() >= depth - 3 - && ttValue != VALUE_NONE - && ttValue >= probCutBeta - && ttMove - && pos.capture_or_promotion(ttMove)) - return probCutBeta; - assert(probCutBeta < VALUE_INFINITE); - MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory); - int probCutCount = 0; - bool ttPv = ss->ttPv; - ss->ttPv = false; - while ( (move = mp.next_move()) != MOVE_NONE - && probCutCount < 2 + 2 * cutNode) + 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; - probCutCount++; + 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)]; @@ -948,26 +894,43 @@ namespace { 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 - 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(pos, ss, alpha, beta); + + if ( cutNode + && depth >= 8 + && !ttMove) + depth--; + +moves_loop: // When in check, search starts here + + // Step 12. A small Probcut idea, when we are in check (~0 Elo) + probCutBeta = beta + 481; + if ( ss->inCheck + && !PvNode + && depth >= 2 + && ttCapture + && (tte->bound() & BOUND_LOWER) + && tte->depth() >= depth - 3 + && ttValue >= probCutBeta + && abs(ttValue) <= VALUE_KNOWN_WIN + && abs(beta) <= VALUE_KNOWN_WIN + ) + return probCutBeta; -moves_loop: // When in check, search starts from here const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr , (ss-4)->continuationHistory, @@ -976,21 +939,22 @@ moves_loop: // When in check, search starts from 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; - ttCapture = ttMove && pos.capture_or_promotion(ttMove); + moveCountPruning = false; - // Mark this node as being searched - ThreadHolding th(thisThread, posKey, ss->ply); + // 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. + bool likelyFailLow = PvNode + && ttMove + && (tte->bound() & BOUND_UPPER) + && tte->depth() >= depth; - // Step 11. 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) { @@ -1021,122 +985,138 @@ moves_loop: // When in check, search starts from 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 12. Pruning at shallow depth (~200 Elo) + 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 { - // Countermoves based pruning (~20 Elo) - if ( lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1) - && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold - && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold) + 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) - if ( lmrDepth < 7 - && !ss->inCheck - && ss->staticEval + 254 + 159 * lmrDepth <= alpha - && (*contHist[0])[movedPiece][to_sq(move)] - + (*contHist[1])[movedPiece][to_sq(move)] - + (*contHist[3])[movedPiece][to_sq(move)] - + (*contHist[5])[movedPiece][to_sq(move)] / 2 < 26394) + history += 2 * thisThread->mainHistory[us][from_to(move)]; + + // Futility pruning: parent node (~9 Elo) + if ( !ss->inCheck + && lmrDepth < 11 + && ss->staticEval + 122 + 138 * lmrDepth + history / 60 <= alpha) continue; - // Prune moves with negative SEE (~20 Elo) - if (!pos.see_ge(move, Value(-(30 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth))) + // Prune moves with negative SEE (~3 Elo) + if (!pos.see_ge(move, Value(-25 * lmrDepth * lmrDepth - 20 * lmrDepth))) continue; } } - // Step 13. 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 ( depth >= 7 - && move == ttMove - && !rootNode - && !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 - ((formerPv + 4) * depth) / 2; - Depth singularDepth = (depth - 1 + 3 * formerPv) / 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; - // 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); + value = search(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode); ss->excludedMove = MOVE_NONE; - if (value >= beta) - return beta; + if (value < singularBeta) + { + 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; } - } - // Check extension (~2 Elo) - else if ( givesCheck - && (pos.is_discovery_check_on_king(~us, move) || pos.see_ge(move))) - extension = 1; + // Check extensions (~1 Elo) + else if ( givesCheck + && depth > 9 + && abs(ss->staticEval) > 71) + extension = 1; - // Last captures extension - else if ( PieceValue[EG][pos.captured_piece()] > PawnValueEg - && pos.non_pawn_material() <= 2 * RookValueMg) - extension = 1; + // Quiet ttMove extensions (~0 Elo) + else if ( PvNode + && move == ttMove + && move == ss->killers[0] + && (*contHist[0])[movedPiece][to_sq(move)] >= 5491) + extension = 1; + } // Add extension to new depth newDepth += extension; + ss->doubleExtensions = (ss-1)->doubleExtensions + (extension == 2); // Speculative prefetch as early as possible prefetch(TT.first_entry(pos.key_after(move))); @@ -1144,124 +1124,94 @@ moves_loop: // When in check, search starts from 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 14. Make the move + // Step 16. Make the move pos.do_move(move, st, givesCheck); - // Step 15. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be - // re-searched at full depth. - if ( depth >= 3 - && moveCount > 1 + 2 * rootNode - && ( !captureOrPromotion - || moveCountPruning - || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha - || cutNode - || (!PvNode && !formerPv && thisThread->captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 4506) - || thisThread->ttHitAverage < 432 * TtHitAverageResolution * TtHitAverageWindow / 1024)) + 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 >= 2 + && moveCount > 1 + (PvNode && ss->ply <= 1) + && ( !ss->ttPv + || !capture + || (cutNode && (ss-1)->moveCount > 1))) { - Depth r = reduction(improving, depth, moveCount); + Depth r = reduction(improving, depth, moveCount, delta, thisThread->rootDelta); - // Decrease reduction if the ttHit running average is large - if (thisThread->ttHitAverage > 537 * TtHitAverageResolution * TtHitAverageWindow / 1024) - 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 if other threads are searching this position - if (th.marked()) - 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 (~10 Elo) - if (ss->ttPv) - r -= 2; + // Increase reduction for cut nodes (~3 Elo) + if (cutNode) + r += 2; - // Increase reduction at root and non-PV nodes when the best move does not change frequently - if ((rootNode || !PvNode) && thisThread->rootDepth > 10 && thisThread->bestMoveChanges <= 2) + // Increase reduction if ttMove is a capture (~3 Elo) + if (ttCapture) r++; - // More reductions for late moves if position was not in previous PV - if (moveCountPruning && !formerPv) - r++; + // Decrease reduction for PvNodes based on depth + if (PvNode) + r -= 1 + 15 / (3 + depth); - // Decrease reduction if opponent's move count is high (~5 Elo) - if ((ss-1)->moveCount > 13) - r--; + // Increase reduction if next ply has a lot of fail high else reset count to 0 + if ((ss+1)->cutoffCnt > 3 && !PvNode) + r++; - // Decrease reduction if ttMove has been singularly extended (~3 Elo) - if (singularQuietLMR) - 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)] + - 4334; - if (captureOrPromotion) - { - // Unless giving check, this capture is likely bad - if ( !givesCheck - && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 210 * depth <= alpha) - r++; - } - else - { - // Increase reduction if ttMove is a capture (~5 Elo) - if (ttCapture) - r++; - - // Increase reduction at root if failing high - r += rootNode ? thisThread->failedHighCnt * thisThread->failedHighCnt * moveCount / 512 : 0; - - // Increase reduction for cut nodes (~10 Elo) - if (cutNode) - r += 2; - - // Decrease reduction for moves that escape a capture. Filter out - // castling moves, because they are coded as "king captures rook" and - // hence break make_move(). (~2 Elo) - else if ( type_of(move) == NORMAL - && !pos.see_ge(reverse_move(move))) - r -= 2 + ss->ttPv - (type_of(movedPiece) == PAWN); - - 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)] - - 5287; - - // Decrease/increase reduction by comparing opponent's stat score (~10 Elo) - if (ss->statScore >= -105 && (ss-1)->statScore < -103) - r--; - - else if ((ss-1)->statScore >= -122 && ss->statScore < -129) - r++; - - // Decrease/increase reduction for moves with a good/bad history (~30 Elo) - r -= ss->statScore / 14884; - } + // Decrease/increase reduction for moves with a good/bad history (~30 Elo) + r -= ss->statScore / 15914; - Depth d = std::clamp(newDepth - r, 1, newDepth); + // 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(pos, ss+1, -(alpha+1), -alpha, d, true); - doFullDepthSearch = value > alpha && d != newDepth; - + // 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 { doFullDepthSearch = !PvNode || moveCount > 1; - didLMR = false; } - // Step 16. 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); } } @@ -1278,12 +1228,12 @@ moves_loop: // When in check, search starts from here std::min(maxNextDepth, newDepth), false); } - // Step 17. Undo move + // Step 19. Undo move pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); - // Step 18. 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. @@ -1295,6 +1245,8 @@ moves_loop: // When in check, search starts from 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) { @@ -1307,9 +1259,11 @@ moves_loop: // When in check, search starts from 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 @@ -1331,23 +1285,37 @@ moves_loop: // When in check, search starts from 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 - ss->statScore = 0; 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; } } @@ -1360,7 +1328,7 @@ moves_loop: // When in check, search starts from here return VALUE_DRAW; */ - // Step 19. 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. @@ -1368,8 +1336,9 @@ moves_loop: // When in check, search starts from here assert(moveCount || !ss->inCheck || excludedMove || !MoveList(pos).size()); if (!moveCount) - bestValue = excludedMove ? alpha - : ss->inCheck ? mated_in(ss->ply) : VALUE_DRAW; + bestValue = excludedMove ? alpha : + ss->inCheck ? mated_in(ss->ply) + : VALUE_DRAW; // If there is a move which produces search value greater than alpha we update stats of searched moves else if (bestMove) @@ -1377,9 +1346,17 @@ moves_loop: // When in check, search starts from 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); @@ -1388,10 +1365,6 @@ moves_loop: // When in check, search starts from 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)) @@ -1408,10 +1381,12 @@ moves_loop: // When in check, search starts from here // 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. - template + // (~155 elo) + template Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) { - constexpr bool PvNode = NT == PV; + static_assert(nodeType != Root); + constexpr bool PvNode = nodeType == PV; assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE); assert(PvNode || (alpha == beta - 1)); @@ -1419,25 +1394,23 @@ moves_loop: // When in check, search starts from here Move pv[MAX_PLY+1]; StateInfo st; - ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize); + ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize); TTEntry* tte; 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; } Thread* thisThread = pos.this_thread(); - (ss+1)->ply = ss->ply + 1; bestMove = MOVE_NONE; ss->inCheck = pos.checkers(); moveCount = 0; @@ -1465,8 +1438,7 @@ moves_loop: // When in check, search starts from here && 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 @@ -1483,17 +1455,16 @@ moves_loop: // When in check, search starts from 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 + 2 * Tempo; + : -(ss-1)->staticEval; // Stand pat. Return immediately if static value is at least beta if (bestValue >= beta) @@ -1509,7 +1480,7 @@ moves_loop: // When in check, search starts from here if (PvNode && bestValue > alpha) alpha = bestValue; - futilityBase = bestValue + 155; + futilityBase = bestValue + 118; } const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, @@ -1518,32 +1489,38 @@ moves_loop: // When in check, search starts from here // Initialize a MovePicker object for the current position, and prepare // to search the moves. Because the depth is <= 0 here, only captures, - // queen and checking knight promotions, and other checks(only if depth >= DEPTH_QS_CHECKS) + // 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) { assert(is_ok(move)); + // Check for legality + if (!pos.legal(move)) + continue; + givesCheck = pos.gives_check(move); - captureOrPromotion = pos.capture_or_promotion(move); + capture = pos.capture(move); moveCount++; - // Futility 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 - && !pos.advanced_pawn_push(move)) + && type_of(move) != PROMOTION) { - assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push - // moveCount pruning if (moveCount > 2) continue; @@ -1562,7 +1539,7 @@ moves_loop: // When in check, search starts from 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; @@ -1570,29 +1547,31 @@ moves_loop: // When in check, search starts from here // Speculative prefetch as early as possible prefetch(TT.first_entry(pos.key_after(move))); - // Check for legality just before making the move - if (!pos.legal(move)) - { - moveCount--; - continue; - } - ss->currentMove = move; ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck] - [captureOrPromotion] + [capture] [pos.moved_piece(move)] [to_sq(move)]; - // CounterMove 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); + value = -qsearch(pos, ss+1, -beta, -alpha, depth - 1); pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); @@ -1628,8 +1607,7 @@ moves_loop: // When in check, search starts from 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); @@ -1684,7 +1662,7 @@ moves_loop: // When in check, search starts from here // 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++; @@ -1697,21 +1675,20 @@ moves_loop: // When in check, search starts from here 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 - : stat_bonus(depth); // smaller bonus - - if (!pos.capture_or_promotion(bestMove)) + if (!pos.capture(bestMove)) { + int bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus + : stat_bonus(depth); // smaller bonus + // 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) @@ -1758,7 +1735,7 @@ moves_loop: // When in check, search starts from 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) @@ -1772,20 +1749,12 @@ moves_loop: // When in check, search starts from 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 @@ -1799,8 +1768,8 @@ moves_loop: // When in check, search starts from 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 @@ -1808,8 +1777,8 @@ moves_loop: // When in check, search starts from 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) { @@ -1927,7 +1896,7 @@ string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) { bool RootMove::extract_ponder_from_tt(Position& pos) { StateInfo st; - ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize); + ASSERT_ALIGNED(&st, Eval::NNUE::CacheLineSize); bool ttHit; @@ -1996,3 +1965,5 @@ void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) { m.tbRank = 0; } } + +} // namespace Stockfish