X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=1f6a129039b1d3e4dce57add99b74f63e70aed60;hp=afc4a671251b03c196d1d07a565561158f9524df;hb=ca51d1ee63f376e0eb6efb6f3d5d901e4b2a5bb0;hpb=96362fe3df141eeead4bdb863d2bb2d891886abf diff --git a/src/search.cpp b/src/search.cpp index afc4a671..b4a69092 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -2,7 +2,7 @@ Stockfish, a UCI chess playing engine derived from Glaurung 2.1 Copyright (C) 2004-2008 Tord Romstad (Glaurung author) Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad - Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad + Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad Stockfish is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by @@ -31,8 +31,8 @@ #include "movepick.h" #include "position.h" #include "search.h" -#include "timeman.h" #include "thread.h" +#include "timeman.h" #include "tt.h" #include "uci.h" #include "syzygy/tbprobe.h" @@ -48,7 +48,6 @@ namespace Tablebases { bool RootInTB; bool UseRule50; Depth ProbeDepth; - Value Score; } namespace TB = Tablebases; @@ -62,29 +61,34 @@ namespace { // Different node types, used as a template parameter enum NodeType { NonPV, PV }; - // Sizes and phases of the skip-blocks, used for distributing search depths across the threads - const int SkipSize[] = { 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4 }; - const int SkipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 }; - // Razor and futility margins - const int RazorMargin1 = 590; - const int RazorMargin2 = 604; + constexpr int RazorMargin = 600; Value futility_margin(Depth d, bool improving) { return Value((175 - 50 * improving) * d / ONE_PLY); } - // Futility and reductions lookup tables, initialized at startup - int FutilityMoveCounts[2][16]; // [improving][depth] - int Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber] + // Reductions lookup table, initialized at startup + int Reductions[MAX_MOVES]; // [depth or moveNumber] + + Depth reduction(bool i, Depth d, int mn) { + int r = Reductions[d / ONE_PLY] * Reductions[mn]; + return ((r + 512) / 1024 + (!i && r > 1024)) * ONE_PLY; + } - template Depth reduction(bool i, Depth d, int mn) { - return Reductions[PvNode][i][std::min(d / ONE_PLY, 63)][std::min(mn, 63)] * ONE_PLY; + constexpr int futility_move_count(bool improving, int depth) { + return (5 + depth * depth) * (1 + improving) / 2; } // History and stats update bonus, based on depth int stat_bonus(Depth depth) { int d = depth / ONE_PLY; - return d > 17 ? 0 : d * d + 2 * d - 2; + return d > 17 ? 0 : 29 * d * d + 138 * d - 134; + } + + // Add a small random component to draw evaluations to avoid 3fold-blindness + Value value_draw(Depth depth, Thread* thisThread) { + return depth < 4 * ONE_PLY ? VALUE_DRAW + : VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1); } // Skill structure is used to implement strength limit @@ -98,8 +102,50 @@ namespace { 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 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, and unmarked upon leaving that loop, by the ctor/dtor of this struct. + 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 - Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning); + Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode); template Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO); @@ -108,15 +154,8 @@ namespace { Value value_from_tt(Value v, int ply); 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, Move* quiets, int quietsCnt, int bonus); - void update_capture_stats(const Position& pos, Move move, Move* captures, int captureCnt, int bonus); - - inline bool gives_check(const Position& pos, Move move) { - Color us = pos.side_to_move(); - return type_of(move) == NORMAL && !(pos.blockers_for_king(~us) & pos.pieces(us)) - ? pos.check_squares(type_of(pos.moved_piece(move))) & to_sq(move) - : pos.gives_check(move); - } + void update_quiet_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietCount, int bonus); + void update_capture_stats(const Position& pos, Move move, Move* captures, int captureCount, int bonus); // perft() is our utility to verify move generation. All the leaf nodes up // to the given depth are generated and counted, and the sum is returned. @@ -151,25 +190,8 @@ namespace { void Search::init() { - for (int imp = 0; imp <= 1; ++imp) - for (int d = 1; d < 64; ++d) - for (int mc = 1; mc < 64; ++mc) - { - double r = log(d) * log(mc) / 1.95; - - Reductions[NonPV][imp][d][mc] = int(std::round(r)); - Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0); - - // Increase reduction for non-PV nodes when eval is not improving - if (!imp && Reductions[NonPV][imp][d][mc] >= 2) - Reductions[NonPV][imp][d][mc]++; - } - - for (int d = 0; d < 16; ++d) - { - FutilityMoveCounts[0][d] = int(2.4 + 0.74 * pow(d, 1.78)); - FutilityMoveCounts[1][d] = int(5.0 + 1.00 * pow(d, 2.00)); - } + for (int i = 1; i < MAX_MOVES; ++i) + Reductions[i] = int(22.9 * std::log(i)); } @@ -182,11 +204,12 @@ void Search::clear() { Time.availableNodes = 0; TT.clear(); Threads.clear(); + Tablebases::init(Options["SyzygyPath"]); // Free mapped files } -/// MainThread::search() is called by the main thread when the program receives -/// the UCI 'go' command. It searches from the root position and outputs the "bestmove". +/// MainThread::search() is started when the program receives the UCI 'go' +/// command. It searches from the root position and outputs the "bestmove". void MainThread::search() { @@ -211,8 +234,11 @@ void MainThread::search() { else { for (Thread* th : Threads) + { + th->bestMoveChanges = 0; if (th != this) th->start_searching(); + } Thread::search(); // Let's start searching! } @@ -221,10 +247,9 @@ void MainThread::search() { // Threads.stop. However, if we are pondering or in an infinite search, // the UCI protocol states that we shouldn't print the best move before the // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here - // until the GUI sends one of those commands (which also raises Threads.stop). - Threads.stopOnPonderhit = true; + // until the GUI sends one of those commands. - while (!Threads.stop && (Threads.ponder || Limits.infinite)) + while (!Threads.stop && (ponder || Limits.infinite)) {} // Busy wait for a stop or a ponder reset // Stop the threads if not already stopped (also raise the stop if @@ -241,21 +266,28 @@ void MainThread::search() { if (Limits.npmsec) Time.availableNodes += Limits.inc[us] - Threads.nodes_searched(); - // Check if there are threads with a better score than main thread Thread* bestThread = this; + + // Check if there are threads with a better score than main thread if ( Options["MultiPV"] == 1 && !Limits.depth && !Skill(Options["Skill Level"]).enabled() && rootMoves[0].pv[0] != MOVE_NONE) { + std::map votes; + Value minScore = this->rootMoves[0].score; + + // Find out minimum score and reset votes for moves which can be voted + for (Thread* th: Threads) + minScore = std::min(minScore, th->rootMoves[0].score); + + // Vote according to score and depth, and select the best thread for (Thread* th : Threads) { - Depth depthDiff = th->completedDepth - bestThread->completedDepth; - Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score; + votes[th->rootMoves[0].pv[0]] += + (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth); - // Select the thread with the best score, always if it is a mate - if ( scoreDiff > 0 - && (depthDiff >= 0 || th->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY)) + if (votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]]) bestThread = th; } } @@ -281,26 +313,34 @@ void MainThread::search() { void Thread::search() { - Stack stack[MAX_PLY+7], *ss = stack+4; // To reference from (ss-4) to (ss+2) + // 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. + Stack stack[MAX_PLY+10], *ss = stack+7; + Move pv[MAX_PLY+1]; Value bestValue, alpha, beta, delta; Move lastBestMove = MOVE_NONE; Depth lastBestMoveDepth = DEPTH_ZERO; MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr); - double timeReduction = 1.0; + double timeReduction = 1, totBestMoveChanges = 0; Color us = rootPos.side_to_move(); - std::memset(ss-4, 0, 7 * sizeof(Stack)); - for (int i = 4; i > 0; i--) - (ss-i)->contHistory = this->contHistory[NO_PIECE][0].get(); // Use as sentinel + std::memset(ss-7, 0, 10 * sizeof(Stack)); + for (int i = 7; i > 0; i--) + (ss-i)->continuationHistory = &this->continuationHistory[NO_PIECE][0]; // Use as sentinel + ss->pv = pv; bestValue = delta = alpha = -VALUE_INFINITE; beta = VALUE_INFINITE; - if (mainThread) - mainThread->bestMoveChanges = 0, mainThread->failedLow = false; - - size_t multiPV = Options["MultiPV"]; - Skill skill(Options["Skill Level"]); + multiPV = 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. + PRNG rng(now()); + int intLevel = int(Options["Skill Level"]) + + ((Options["Skill Level"] - int(Options["Skill Level"])) * 1024 > rng.rand() % 1024 ? 1 : 0); + Skill skill(intLevel); // When playing with strength handicap enable MultiPV search that we will // use behind the scenes to retrieve a set of possible moves. @@ -309,60 +349,74 @@ void Thread::search() { multiPV = std::min(multiPV, rootMoves.size()); - int ct = Options["Contempt"] * PawnValueEg / 100; // From centipawns - Eval::Contempt = (us == WHITE ? make_score(ct, ct / 2) - : -make_score(ct, ct / 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; + + // Evaluation score is from the white point of view + contempt = (us == WHITE ? make_score(ct, ct / 2) + : -make_score(ct, ct / 2)); // Iterative deepening loop until requested to stop or the target depth is reached while ( (rootDepth += ONE_PLY) < DEPTH_MAX && !Threads.stop && !(Limits.depth && mainThread && rootDepth / ONE_PLY > Limits.depth)) { - // Distribute search depths across the helper threads - if (idx > 0) - { - int i = (idx - 1) % 20; - if (((rootDepth / ONE_PLY + rootPos.game_ply() + SkipPhase[i]) / SkipSize[i]) % 2) - continue; // Retry with an incremented rootDepth - } - // Age out PV variability metric if (mainThread) - mainThread->bestMoveChanges *= 0.517, mainThread->failedLow = false; + totBestMoveChanges /= 2; // Save the last iteration's scores before first PV line is searched and // all the move scores except the (new) PV are set to -VALUE_INFINITE. for (RootMove& rm : rootMoves) rm.previousScore = rm.score; + size_t pvFirst = 0; + pvLast = 0; + // MultiPV loop. We perform a full root search for each PV line - for (PVIdx = 0; PVIdx < multiPV && !Threads.stop; ++PVIdx) + for (pvIdx = 0; pvIdx < multiPV && !Threads.stop; ++pvIdx) { + if (pvIdx == pvLast) + { + pvFirst = pvLast; + for (pvLast++; pvLast < rootMoves.size(); pvLast++) + if (rootMoves[pvLast].tbRank != rootMoves[pvFirst].tbRank) + break; + } + // Reset UCI info selDepth for each depth and each PV line selDepth = 0; // Reset aspiration window starting size if (rootDepth >= 5 * ONE_PLY) { - delta = Value(18); - alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE); - beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE); + Value previousScore = rootMoves[pvIdx].previousScore; + delta = Value(20); + alpha = std::max(previousScore - delta,-VALUE_INFINITE); + beta = std::min(previousScore + delta, VALUE_INFINITE); - ct = Options["Contempt"] * PawnValueEg / 100; // From centipawns + // Adjust contempt based on root move's previousScore (dynamic contempt) + int dct = ct + 88 * previousScore / (abs(previousScore) + 200); - // Adjust contempt based on current bestValue (dynamic contempt) - ct += int(std::round(48 * atan(float(bestValue) / 128))); - - Eval::Contempt = (us == WHITE ? make_score(ct, ct / 2) - : -make_score(ct, ct / 2)); + contempt = (us == WHITE ? make_score(dct, dct / 2) + : -make_score(dct, dct / 2)); } // Start with a small aspiration window and, in the case of a fail // high/low, re-search with a bigger window until we don't fail // high/low anymore. + int failedHighCnt = 0; while (true) { - bestValue = ::search(rootPos, ss, alpha, beta, rootDepth, false, false); + Depth adjustedDepth = std::max(ONE_PLY, rootDepth - failedHighCnt * ONE_PLY); + bestValue = ::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 @@ -370,7 +424,7 @@ void Thread::search() { // and we want to keep the same order for all the moves except the // new PV that goes to the front. Note that in case of MultiPV // search the already searched PV lines are preserved. - std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end()); + std::stable_sort(rootMoves.begin() + pvIdx, rootMoves.begin() + pvLast); // If search has been stopped, we break immediately. Sorting is // safe because RootMoves is still valid, although it refers to @@ -393,14 +447,15 @@ void Thread::search() { beta = (alpha + beta) / 2; alpha = std::max(bestValue - delta, -VALUE_INFINITE); + failedHighCnt = 0; if (mainThread) - { - mainThread->failedLow = true; - Threads.stopOnPonderhit = false; - } + mainThread->stopOnPonderhit = false; } else if (bestValue >= beta) + { beta = std::min(bestValue + delta, VALUE_INFINITE); + ++failedHighCnt; + } else break; @@ -410,10 +465,10 @@ void Thread::search() { } // Sort the PV lines searched so far and update the GUI - std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1); + std::stable_sort(rootMoves.begin() + pvFirst, rootMoves.begin() + pvIdx + 1); if ( mainThread - && (Threads.stop || PVIdx + 1 == multiPV || Time.elapsed() > 3000)) + && (Threads.stop || pvIdx + 1 == multiPV || Time.elapsed() > 3000)) sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl; } @@ -441,35 +496,35 @@ void Thread::search() { // Do we have time for the next iteration? Can we stop searching now? if ( Limits.use_time_management() && !Threads.stop - && !Threads.stopOnPonderhit) - { - const int F[] = { mainThread->failedLow, - bestValue - mainThread->previousScore }; - - int improvingFactor = std::max(246, std::min(832, 306 + 119 * F[0] - 6 * F[1])); + && !mainThread->stopOnPonderhit) + { + double fallingEval = (314 + 9 * (mainThread->previousScore - bestValue)) / 581.0; + fallingEval = clamp(fallingEval, 0.5, 1.5); - // If the bestMove is stable over several iterations, reduce time accordingly - timeReduction = 1.0; - for (int i : {3, 4, 5}) - if (lastBestMoveDepth * i < completedDepth) - timeReduction *= 1.25; + // If the bestMove is stable over several iterations, reduce time accordingly + timeReduction = lastBestMoveDepth + 10 * ONE_PLY < completedDepth ? 1.95 : 1.0; + double reduction = std::pow(mainThread->previousTimeReduction, 0.528) / timeReduction; - // Use part of the gained time from a previous stable move for the current move - double bestMoveInstability = 1.0 + mainThread->bestMoveChanges; - bestMoveInstability *= std::pow(mainThread->previousTimeReduction, 0.528) / timeReduction; + // 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 + totBestMoveChanges / Threads.size(); - // Stop the search if we have only one legal move, or if available time elapsed - if ( rootMoves.size() == 1 - || Time.elapsed() > Time.optimum() * bestMoveInstability * improvingFactor / 581) - { - // If we are allowed to ponder do not stop the search now but - // keep pondering until the GUI sends "ponderhit" or "stop". - if (Threads.ponder) - Threads.stopOnPonderhit = true; - else - Threads.stop = true; - } + // Stop the search if we have only one legal move, or if available time elapsed + if ( rootMoves.size() == 1 + || Time.elapsed() > Time.optimum() * fallingEval * reduction * bestMoveInstability) + { + // If we are allowed to ponder do not stop the search now but + // keep pondering until the GUI sends "ponderhit" or "stop". + if (mainThread->ponder) + mainThread->stopOnPonderhit = true; + else + Threads.stop = true; } + } } if (!mainThread) @@ -489,15 +544,27 @@ namespace { // search<>() is the main search function for both PV and non-PV nodes template - Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning) { - - // Use quiescence search when needed - if (depth < ONE_PLY) - return qsearch(pos, ss, alpha, beta); + 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; + // 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 + && alpha < VALUE_DRAW + && !rootNode + && pos.has_game_cycle(ss->ply)) + { + alpha = value_draw(depth, pos.this_thread()); + if (alpha >= beta) + return alpha; + } + + // Dive into quiescence search when the depth reaches zero + if (depth < ONE_PLY) + return qsearch(pos, ss, alpha, beta); + assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE); assert(PvNode || (alpha == beta - 1)); assert(DEPTH_ZERO < depth && depth < DEPTH_MAX); @@ -511,15 +578,16 @@ namespace { Move ttMove, move, excludedMove, bestMove; Depth extension, newDepth; Value bestValue, value, ttValue, eval, maxValue; - bool ttHit, inCheck, givesCheck, singularExtensionNode, improving; - bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture, pvExact; + bool ttHit, ttPv, inCheck, givesCheck, improving; + bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture; Piece movedPiece; - int moveCount, captureCount, quietCount; + int moveCount, captureCount, quietCount, singularLMR; // Step 1. Initialize node Thread* thisThread = pos.this_thread(); inCheck = pos.checkers(); - moveCount = captureCount = quietCount = ss->moveCount = 0; + Color us = pos.side_to_move(); + moveCount = captureCount = quietCount = singularLMR = ss->moveCount = 0; bestValue = -VALUE_INFINITE; maxValue = VALUE_INFINITE; @@ -537,7 +605,8 @@ namespace { if ( Threads.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY) - return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos) : VALUE_DRAW; + return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos) + : value_draw(depth, pos.this_thread()); // Step 3. Mate distance pruning. Even if we mate at the next move our score // would be at best mate_in(ss->ply+1), but if alpha is already bigger because @@ -554,8 +623,7 @@ namespace { assert(0 <= ss->ply && ss->ply < MAX_PLY); (ss+1)->ply = ss->ply + 1; - ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE; - ss->contHistory = thisThread->contHistory[NO_PIECE][0].get(); + (ss+1)->excludedMove = bestMove = MOVE_NONE; (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE; Square prevSq = to_sq((ss-1)->currentMove); @@ -564,7 +632,10 @@ namespace { // starts with statScore = 0. Later grandchildren start with the last calculated // statScore of the previous grandchild. This influences the reduction rules in // LMR which are based on the statScore of parent position. - (ss+2)->statScore = 0; + if (rootNode) + (ss + 4)->statScore = 0; + else + (ss + 2)->statScore = 0; // Step 4. Transposition table lookup. We don't want the score of a partial // search to overwrite a previous full search TT value, so we use a different @@ -573,8 +644,9 @@ namespace { posKey = pos.key() ^ Key(excludedMove << 16); // Isn't a very good hash tte = TT.probe(posKey, ttHit); ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE; - ttMove = rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0] + ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0] : ttHit ? tte->move() : MOVE_NONE; + ttPv = PvNode || (ttHit && tte->is_pv()); // At non-PV nodes we check for an early TT cutoff if ( !PvNode @@ -592,15 +664,15 @@ namespace { if (!pos.capture_or_promotion(ttMove)) update_quiet_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth)); - // Extra penalty for a quiet TT move in previous ply when it gets refuted - if ((ss-1)->moveCount == 1 && !pos.captured_piece()) - update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY)); + // Extra penalty for early quiet moves of the previous ply + if ((ss-1)->moveCount <= 2 && !pos.captured_piece()) + update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY)); } // Penalty for a quiet ttMove that fails low else if (!pos.capture_or_promotion(ttMove)) { int penalty = -stat_bonus(depth); - thisThread->mainHistory[pos.side_to_move()][from_to(ttMove)] << penalty; + thisThread->mainHistory[us][from_to(ttMove)] << penalty; update_continuation_histories(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty); } } @@ -620,6 +692,10 @@ namespace { TB::ProbeState err; TB::WDLScore wdl = Tablebases::probe_wdl(pos, &err); + // Force check of time on the next occasion + if (thisThread == Threads.main()) + static_cast(thisThread)->callsCnt = 0; + if (err != TB::ProbeState::FAIL) { thisThread->tbHits.fetch_add(1, std::memory_order_relaxed); @@ -636,9 +712,9 @@ namespace { if ( b == BOUND_EXACT || (b == BOUND_LOWER ? value >= beta : value <= alpha)) { - tte->save(posKey, value_to_tt(value, ss->ply), b, + tte->save(posKey, value_to_tt(value, ss->ply), ttPv, b, std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY), - MOVE_NONE, VALUE_NONE, TT.generation()); + MOVE_NONE, VALUE_NONE); return value; } @@ -654,18 +730,19 @@ namespace { } } - // Step 6. Evaluate the position statically + // Step 6. Static evaluation of the position if (inCheck) { ss->staticEval = eval = VALUE_NONE; improving = false; - goto moves_loop; + goto moves_loop; // Skip early pruning when in check } else if (ttHit) { // Never assume anything on values stored in TT - if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE) - eval = ss->staticEval = evaluate(pos); + ss->staticEval = eval = tte->eval(); + if (eval == VALUE_NONE) + ss->staticEval = eval = evaluate(pos); // Can ttValue be used as a better position evaluation? if ( ttValue != VALUE_NONE @@ -674,63 +751,55 @@ namespace { } else { - ss->staticEval = eval = - (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) - : -(ss-1)->staticEval + 2 * Eval::Tempo; - - tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, - ss->staticEval, TT.generation()); - } - - improving = ss->staticEval >= (ss-2)->staticEval - ||(ss-2)->staticEval == VALUE_NONE; - - if (skipEarlyPruning || !pos.non_pawn_material(pos.side_to_move())) - goto moves_loop; - - // Step 7. Razoring (skipped when in check) - if ( !PvNode - && depth <= 2 * ONE_PLY) - { - if ( depth == ONE_PLY - && eval + RazorMargin1 <= alpha) - return qsearch(pos, ss, alpha, alpha+1); - - else if (eval + RazorMargin2 <= alpha) + if ((ss-1)->currentMove != MOVE_NULL) { - Value ralpha = alpha - RazorMargin2; - - Value v = qsearch(pos, ss, ralpha, ralpha+1); + int bonus = -(ss-1)->statScore / 512; - if (v <= ralpha) - return v; + ss->staticEval = eval = evaluate(pos) + bonus; } + else + ss->staticEval = eval = -(ss-1)->staticEval + 2 * Eval::Tempo; + + tte->save(posKey, VALUE_NONE, ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval); } - // Step 8. Futility pruning: child node (skipped when in check) - if ( !rootNode + // Step 7. Razoring (~2 Elo) + if ( !rootNode // The required rootNode PV handling is not available in qsearch + && depth < 2 * ONE_PLY + && eval <= alpha - RazorMargin) + return qsearch(pos, ss, alpha, beta); + + improving = ss->staticEval >= (ss-2)->staticEval + || (ss-2)->staticEval == VALUE_NONE; + + // Step 8. Futility pruning: child node (~30 Elo) + if ( !PvNode && depth < 7 * ONE_PLY && eval - futility_margin(depth, improving) >= beta && eval < VALUE_KNOWN_WIN) // Do not return unproven wins return eval; - // Step 9. Null move search with verification search + // Step 9. Null move search with verification search (~40 Elo) if ( !PvNode + && (ss-1)->currentMove != MOVE_NULL + && (ss-1)->statScore < 23200 && eval >= beta && ss->staticEval >= beta - 36 * depth / ONE_PLY + 225 - && (ss->ply >= thisThread->nmp_ply || ss->ply % 2 != thisThread->nmp_odd)) + && !excludedMove + && pos.non_pawn_material(us) + && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor)) { assert(eval - beta >= 0); // Null move dynamic reduction based on depth and value - Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY; + Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min(int(eval - beta) / 200, 3)) * ONE_PLY; ss->currentMove = MOVE_NULL; - ss->contHistory = thisThread->contHistory[NO_PIECE][0].get(); + ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0]; pos.do_null_move(st); - Value nullValue = -search(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true); + Value nullValue = -search(pos, ss+1, -beta, -beta+1, depth-R, !cutNode); pos.undo_null_move(); @@ -740,70 +809,67 @@ namespace { if (nullValue >= VALUE_MATE_IN_MAX_PLY) nullValue = beta; - if (abs(beta) < VALUE_KNOWN_WIN && (depth < 12 * ONE_PLY || thisThread->nmp_ply)) + if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 12 * ONE_PLY)) return nullValue; - // Do verification search at high depths. Disable null move pruning - // for side to move for the first part of the remaining search tree. - thisThread->nmp_ply = ss->ply + 3 * (depth-R) / 4; - thisThread->nmp_odd = ss->ply % 2; + assert(!thisThread->nmpMinPly); // Recursive verification is not allowed - Value v = search(pos, ss, beta-1, beta, depth-R, false, true); + // Do verification search at high depths, with null move pruning disabled + // for us, until ply exceeds nmpMinPly. + thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / (4 * ONE_PLY); + thisThread->nmpColor = us; - thisThread->nmp_odd = thisThread->nmp_ply = 0; + Value v = search(pos, ss, beta-1, beta, depth-R, false); + + thisThread->nmpMinPly = 0; if (v >= beta) return nullValue; } } - // Step 10. ProbCut (skipped when in check) + // Step 10. ProbCut (~10 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 && depth >= 5 * ONE_PLY && abs(beta) < VALUE_MATE_IN_MAX_PLY) { - assert(is_ok((ss-1)->currentMove)); - - Value rbeta = std::min(beta + 216 - 48 * improving, VALUE_INFINITE); - MovePicker mp(pos, ttMove, rbeta - ss->staticEval, &thisThread->captureHistory); + Value raisedBeta = std::min(beta + 216 - 48 * improving, VALUE_INFINITE); + MovePicker mp(pos, ttMove, raisedBeta - ss->staticEval, &thisThread->captureHistory); int probCutCount = 0; while ( (move = mp.next_move()) != MOVE_NONE - && probCutCount < 3) - if (pos.legal(move)) + && probCutCount < 2 + 2 * cutNode) + if (move != excludedMove && pos.legal(move)) { probCutCount++; ss->currentMove = move; - ss->contHistory = thisThread->contHistory[pos.moved_piece(move)][to_sq(move)].get(); + ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)]; assert(depth >= 5 * ONE_PLY); pos.do_move(move, st); // Perform a preliminary qsearch to verify that the move holds - value = -qsearch(pos, ss+1, -rbeta, -rbeta+1); + value = -qsearch(pos, ss+1, -raisedBeta, -raisedBeta+1); - // If the qsearch held perform the regular search - if (value >= rbeta) - value = -search(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false); + // If the qsearch held, perform the regular search + if (value >= raisedBeta) + value = -search(pos, ss+1, -raisedBeta, -raisedBeta+1, depth - 4 * ONE_PLY, !cutNode); pos.undo_move(move); - if (value >= rbeta) + if (value >= raisedBeta) return value; } } - // Step 11. Internal iterative deepening (skipped when in check) - if ( depth >= 6 * ONE_PLY - && !ttMove - && (PvNode || ss->staticEval + 256 >= beta)) + // Step 11. Internal iterative deepening (~2 Elo) + if (depth >= 8 * ONE_PLY && !ttMove) { - Depth d = 3 * depth / 4 - 2 * ONE_PLY; - search(pos, ss, alpha, beta, d, cutNode, true); + search(pos, ss, alpha, beta, depth - 7 * ONE_PLY, cutNode); tte = TT.probe(posKey, ttHit); ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE; @@ -812,26 +878,28 @@ namespace { moves_loop: // When in check, search starts from here - const PieceToHistory* contHist[] = { (ss-1)->contHistory, (ss-2)->contHistory, nullptr, (ss-4)->contHistory }; + const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, + nullptr, (ss-4)->continuationHistory, + nullptr, (ss-6)->continuationHistory }; + Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq]; - MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, &thisThread->captureHistory, contHist, countermove, ss->killers); + MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, + &thisThread->captureHistory, + contHist, + countermove, + ss->killers); + value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc + moveCountPruning = false; + ttCapture = ttMove && pos.capture_or_promotion(ttMove); - singularExtensionNode = !rootNode - && depth >= 8 * ONE_PLY - && ttMove != MOVE_NONE - && ttValue != VALUE_NONE - && !excludedMove // Recursive singular search is not allowed - && (tte->bound() & BOUND_LOWER) - && tte->depth() >= depth - 3 * ONE_PLY; - skipQuiets = false; - ttCapture = false; - pvExact = PvNode && ttHit && tte->bound() == BOUND_EXACT; + // Mark this node as being searched. + ThreadHolding th(thisThread, posKey, ss->ply); // Step 12. Loop through all pseudo-legal moves until no moves remain // or a beta cutoff occurs. - while ((move = mp.next_move(skipQuiets)) != MOVE_NONE) + while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE) { assert(is_ok(move)); @@ -840,9 +908,10 @@ moves_loop: // When in check, search starts from here // At root obey the "searchmoves" option and skip moves not listed in Root // Move List. As a consequence any illegal move is also skipped. In MultiPV - // mode we also skip PV moves which have been already searched. - if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx, - thisThread->rootMoves.end(), move)) + // mode we also skip PV moves which have been already searched and those + // of lower "TB rank" if we are in a TB root position. + if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->pvIdx, + thisThread->rootMoves.begin() + thisThread->pvLast, move)) continue; ss->moveCount = ++moveCount; @@ -850,84 +919,126 @@ moves_loop: // When in check, search starts from here if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000) sync_cout << "info depth " << depth / ONE_PLY << " currmove " << UCI::move(move, pos.is_chess960()) - << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl; + << " currmovenumber " << moveCount + thisThread->pvIdx << sync_endl; + + // In MultiPV mode also skip moves which will be searched later as PV moves + if (rootNode && std::count(thisThread->rootMoves.begin() + thisThread->pvIdx + 1, + thisThread->rootMoves.begin() + thisThread->multiPV, move)) + continue; + if (PvNode) (ss+1)->pv = nullptr; extension = DEPTH_ZERO; captureOrPromotion = pos.capture_or_promotion(move); movedPiece = pos.moved_piece(move); - givesCheck = gives_check(pos, move); + givesCheck = pos.gives_check(move); - moveCountPruning = depth < 16 * ONE_PLY - && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY]; + // Step 13. Extensions (~70 Elo) - // Step 13. Extensions - - // Singular extension search. If all moves but one fail low on a search - // of (alpha-s, beta-s), and just one fails high on (alpha, beta), then - // that move is singular and should be extended. To verify this we do a - // reduced search on on all the other moves but the ttMove and if the + // Singular extension search (~60 Elo). If all moves but one fail low on a + // search of (alpha-s, beta-s), and just one fails high on (alpha, beta), + // then that move is singular and should be extended. To verify this we do + // a reduced search on 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 ( singularExtensionNode + if ( depth >= 8 * ONE_PLY && 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 * ONE_PLY && pos.legal(move)) { - Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE); + Value singularBeta = ttValue - 2 * depth / ONE_PLY; + Depth halfDepth = depth / (2 * ONE_PLY) * ONE_PLY; // ONE_PLY invariant ss->excludedMove = move; - value = search(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode, true); + value = search(pos, ss, singularBeta - 1, singularBeta, halfDepth, cutNode); ss->excludedMove = MOVE_NONE; - if (value < rBeta) + if (value < singularBeta) + { extension = ONE_PLY; + singularLMR++; + + if (value < singularBeta - std::min(3 * depth / ONE_PLY, 39)) + singularLMR++; + } + + // 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 ( eval >= beta + && singularBeta >= beta) + return singularBeta; } - else if ( givesCheck // Check extension - && !moveCountPruning - && pos.see_ge(move)) + + // Check extension (~2 Elo) + else if ( givesCheck + && (pos.blockers_for_king(~us) & from_sq(move) || pos.see_ge(move))) + extension = ONE_PLY; + + // Castling extension + else if (type_of(move) == CASTLING) + extension = ONE_PLY; + + // Shuffle extension + else if ( PvNode + && pos.rule50_count() > 18 + && depth < 3 * ONE_PLY + && ++thisThread->shuffleExts < thisThread->nodes.load(std::memory_order_relaxed) / 4) // To avoid too many extensions + extension = ONE_PLY; + + // Passed pawn extension + else if ( move == ss->killers[0] + && pos.advanced_pawn_push(move) + && pos.pawn_passed(us, to_sq(move))) extension = ONE_PLY; // Calculate new depth for this move newDepth = depth - ONE_PLY + extension; - // Step 14. Pruning at shallow depth + // Step 14. Pruning at shallow depth (~170 Elo) if ( !rootNode - && pos.non_pawn_material(pos.side_to_move()) + && pos.non_pawn_material(us) && bestValue > VALUE_MATED_IN_MAX_PLY) { + // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold + moveCountPruning = moveCount >= futility_move_count(improving, depth / ONE_PLY); + if ( !captureOrPromotion && !givesCheck - && (!pos.advanced_pawn_push(move) || pos.non_pawn_material() >= Value(5000))) + && (!pos.advanced_pawn_push(move) || pos.non_pawn_material(~us) > BishopValueMg)) { - // Move count based pruning + // Move count based pruning (~30 Elo) if (moveCountPruning) - { - skipQuiets = true; continue; - } // Reduced depth of the next LMR search - int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY; + int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO); + lmrDepth /= ONE_PLY; - // Countermoves based pruning - if ( lmrDepth < 3 + // Countermoves based pruning (~20 Elo) + if ( lmrDepth < 3 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1) && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold) continue; - // Futility pruning: parent node + // Futility pruning: parent node (~2 Elo) if ( lmrDepth < 7 && !inCheck && ss->staticEval + 256 + 200 * lmrDepth <= alpha) continue; - // Prune moves with negative SEE - if ( lmrDepth < 8 - && !pos.see_ge(move, Value(-35 * lmrDepth * lmrDepth))) + // Prune moves with negative SEE (~10 Elo) + if (!pos.see_ge(move, Value(-29 * lmrDepth * lmrDepth))) continue; } - else if ( depth < 7 * ONE_PLY - && !extension - && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY))) + else if ((!givesCheck || !extension) + && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY))) // (~20 Elo) continue; } @@ -941,12 +1052,9 @@ moves_loop: // When in check, search starts from here continue; } - if (move == ttMove && captureOrPromotion) - ttCapture = true; - // Update the current move (this must be done after singular extension search) ss->currentMove = move; - ss->contHistory = thisThread->contHistory[movedPiece][to_sq(move)].get(); + ss->continuationHistory = &thisThread->continuationHistory[movedPiece][to_sq(move)]; // Step 15. Make the move pos.do_move(move, st, givesCheck); @@ -954,58 +1062,65 @@ moves_loop: // When in check, search starts from here // Step 16. Reduced depth search (LMR). If the move fails high it will be // re-searched at full depth. if ( depth >= 3 * ONE_PLY - && moveCount > 1 - && (!captureOrPromotion || moveCountPruning)) + && moveCount > 1 + 3 * rootNode + && ( !captureOrPromotion + || moveCountPruning + || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha)) { - Depth r = reduction(improving, depth, moveCount); + Depth r = reduction(improving, depth, moveCount); - if (captureOrPromotion) - r -= r ? ONE_PLY : DEPTH_ZERO; - else - { - // Decrease reduction if opponent's move count is high - if ((ss-1)->moveCount > 15) - r -= ONE_PLY; + // Reduction if other threads are searching this position. + if (th.marked()) + r += ONE_PLY; - // Decrease reduction for exact PV nodes - if (pvExact) - r -= ONE_PLY; + // Decrease reduction if position is or has been on the PV + if (ttPv) + r -= 2 * ONE_PLY; - // Increase reduction if ttMove is a capture + // Decrease reduction if opponent's move count is high (~10 Elo) + if ((ss-1)->moveCount > 15) + r -= ONE_PLY; + + // Decrease reduction if move has been singularly extended + r -= singularLMR * ONE_PLY; + + if (!captureOrPromotion) + { + // Increase reduction if ttMove is a capture (~0 Elo) if (ttCapture) r += ONE_PLY; - // Increase reduction for cut nodes + // Increase reduction for cut nodes (~5 Elo) if (cutNode) r += 2 * ONE_PLY; // 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(). + // hence break make_move(). (~5 Elo) else if ( type_of(move) == NORMAL && !pos.see_ge(make_move(to_sq(move), from_sq(move)))) r -= 2 * ONE_PLY; - ss->statScore = thisThread->mainHistory[~pos.side_to_move()][from_to(move)] + 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)] - 4000; - // Decrease/increase reduction by comparing opponent's stat score + // Decrease/increase reduction by comparing opponent's stat score (~10 Elo) if (ss->statScore >= 0 && (ss-1)->statScore < 0) r -= ONE_PLY; else if ((ss-1)->statScore >= 0 && ss->statScore < 0) r += ONE_PLY; - // Decrease/increase reduction for moves with a good/bad history - r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->statScore / 20000) * ONE_PLY); + // Decrease/increase reduction for moves with a good/bad history (~30 Elo) + r -= ss->statScore / 20000 * ONE_PLY; } - Depth d = std::max(newDepth - r, ONE_PLY); + Depth d = clamp(newDepth - r, ONE_PLY, newDepth); - value = -search(pos, ss+1, -(alpha+1), -alpha, d, true, false); + value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); doFullDepthSearch = (value > alpha && d != newDepth); } @@ -1014,7 +1129,7 @@ moves_loop: // When in check, search starts from here // Step 17. Full depth search when LMR is skipped or fails high if (doFullDepthSearch) - value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false); + value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); // For PV nodes only, do a full PV search on the first move or after a fail // high (in the latter case search only if value < beta), otherwise let the @@ -1024,7 +1139,7 @@ moves_loop: // When in check, search starts from here (ss+1)->pv = pv; (ss+1)->pv[0] = MOVE_NONE; - value = -search(pos, ss+1, -beta, -alpha, newDepth, false, false); + value = -search(pos, ss+1, -beta, -alpha, newDepth, false); } // Step 18. Undo move @@ -1059,8 +1174,8 @@ moves_loop: // When in check, search starts from here // We record how often the best move has been changed in each // iteration. This information is used for time management: When // the best move changes frequently, we allocate some more time. - if (moveCount > 1 && thisThread == Threads.main()) - ++static_cast(thisThread)->bestMoveChanges; + if (moveCount > 1) + ++thisThread->bestMoveChanges; } else // All other moves but the PV are set to the lowest value: this @@ -1085,6 +1200,7 @@ moves_loop: // When in check, search starts from here else { assert(value >= beta); // Fail high + ss->statScore = 0; break; } } @@ -1122,28 +1238,30 @@ moves_loop: // When in check, search starts from here { // Quiet best move: update move sorting heuristics if (!pos.capture_or_promotion(bestMove)) - update_quiet_stats(pos, ss, bestMove, quietsSearched, quietCount, stat_bonus(depth)); - else - update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth)); + update_quiet_stats(pos, ss, bestMove, quietsSearched, quietCount, + stat_bonus(depth + (bestValue > beta + PawnValueMg ? ONE_PLY : DEPTH_ZERO))); + + update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth + ONE_PLY)); + + // Extra penalty for a quiet TT or main killer move in previous ply when it gets refuted + if ( ((ss-1)->moveCount == 1 || ((ss-1)->currentMove == (ss-1)->killers[0])) + && !pos.captured_piece()) + update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY)); - // Extra penalty for a quiet TT move in previous ply when it gets refuted - if ((ss-1)->moveCount == 1 && !pos.captured_piece()) - update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY)); } // Bonus for prior countermove that caused the fail low - else if ( depth >= 3 * ONE_PLY - && !pos.captured_piece() - && is_ok((ss-1)->currentMove)) + else if ( (depth >= 3 * ONE_PLY || PvNode) + && !pos.captured_piece()) update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth)); if (PvNode) bestValue = std::min(bestValue, maxValue); if (!excludedMove) - tte->save(posKey, value_to_tt(bestValue, ss->ply), + tte->save(posKey, value_to_tt(bestValue, ss->ply), ttPv, bestValue >= beta ? BOUND_LOWER : PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER, - depth, bestMove, ss->staticEval, TT.generation()); + depth, bestMove, ss->staticEval); assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE); @@ -1151,13 +1269,12 @@ moves_loop: // When in check, search starts from here } - // qsearch() is the quiescence search function, which is called by the main - // search function with depth zero, or recursively with depth less than ONE_PLY. + // 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 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) { constexpr bool PvNode = NT == PV; - const bool inCheck = bool(pos.checkers()); assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE); assert(PvNode || (alpha == beta - 1)); @@ -1171,7 +1288,7 @@ moves_loop: // When in check, search starts from here Move ttMove, move, bestMove; Depth ttDepth; Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha; - bool ttHit, givesCheck, evasionPrunable; + bool ttHit, pvHit, inCheck, givesCheck, evasionPrunable; int moveCount; if (PvNode) @@ -1181,8 +1298,10 @@ moves_loop: // When in check, search starts from here ss->pv[0] = MOVE_NONE; } + Thread* thisThread = pos.this_thread(); (ss+1)->ply = ss->ply + 1; - ss->currentMove = bestMove = MOVE_NONE; + bestMove = MOVE_NONE; + inCheck = pos.checkers(); moveCount = 0; // Check for an immediate draw or maximum ply reached @@ -1202,13 +1321,14 @@ moves_loop: // When in check, search starts from here tte = TT.probe(posKey, ttHit); ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE; ttMove = ttHit ? tte->move() : MOVE_NONE; + pvHit = ttHit && tte->is_pv(); if ( !PvNode && ttHit && tte->depth() >= ttDepth && ttValue != VALUE_NONE // Only in case of TT access race - && (ttValue >= beta ? (tte->bound() & BOUND_LOWER) - : (tte->bound() & BOUND_UPPER))) + && (ttValue >= beta ? (tte->bound() & BOUND_LOWER) + : (tte->bound() & BOUND_UPPER))) return ttValue; // Evaluate the position statically @@ -1226,7 +1346,7 @@ moves_loop: // When in check, search starts from here ss->staticEval = bestValue = evaluate(pos); // Can ttValue be used as a better position evaluation? - if ( ttValue != VALUE_NONE + if ( ttValue != VALUE_NONE && (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))) bestValue = ttValue; } @@ -1239,8 +1359,8 @@ moves_loop: // When in check, search starts from here if (bestValue >= beta) { if (!ttHit) - tte->save(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER, - DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation()); + tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit, BOUND_LOWER, + DEPTH_NONE, MOVE_NONE, ss->staticEval); return bestValue; } @@ -1251,18 +1371,25 @@ moves_loop: // When in check, search starts from here futilityBase = bestValue + 128; } + const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, + nullptr, (ss-4)->continuationHistory, + nullptr, (ss-6)->continuationHistory }; + // Initialize a MovePicker object for the current position, and prepare // to search the moves. Because the depth is <= 0 here, only captures, // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will // be generated. - MovePicker mp(pos, ttMove, depth, &pos.this_thread()->mainHistory, &pos.this_thread()->captureHistory, to_sq((ss-1)->currentMove)); + MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, + &thisThread->captureHistory, + contHist, + to_sq((ss-1)->currentMove)); // Loop through the moves until no moves remain or a beta cutoff occurs while ((move = mp.next_move()) != MOVE_NONE) { assert(is_ok(move)); - givesCheck = gives_check(pos, move); + givesCheck = pos.gives_check(move); moveCount++; @@ -1297,6 +1424,7 @@ moves_loop: // When in check, search starts from here // Don't search moves with negative SEE values if ( (!inCheck || evasionPrunable) + && (!givesCheck || !(pos.blockers_for_king(~pos.side_to_move()) & from_sq(move))) && !pos.see_ge(move)) continue; @@ -1311,6 +1439,7 @@ moves_loop: // When in check, search starts from here } ss->currentMove = move; + ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)]; // Make and search the move pos.do_move(move, st, givesCheck); @@ -1326,21 +1455,15 @@ moves_loop: // When in check, search starts from here if (value > alpha) { + bestMove = move; + if (PvNode) // Update pv even in fail-high case update_pv(ss->pv, move, (ss+1)->pv); if (PvNode && value < beta) // Update alpha here! - { alpha = value; - bestMove = move; - } - else // Fail high - { - tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER, - ttDepth, move, ss->staticEval, TT.generation()); - - return value; - } + else + break; // Fail high } } } @@ -1350,9 +1473,10 @@ moves_loop: // When in check, search starts from here if (inCheck && bestValue == -VALUE_INFINITE) return mated_in(ss->ply); // Plies to mate from the root - tte->save(posKey, value_to_tt(bestValue, ss->ply), - PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER, - ttDepth, bestMove, ss->staticEval, TT.generation()); + tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit, + bestValue >= beta ? BOUND_LOWER : + PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER, + ttDepth, bestMove, ss->staticEval); assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE); @@ -1400,24 +1524,26 @@ moves_loop: // When in check, search starts from here void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus) { - for (int i : {1, 2, 4}) + for (int i : {1, 2, 4, 6}) if (is_ok((ss-i)->currentMove)) - (*(ss-i)->contHistory)[pc][to] << bonus; + (*(ss-i)->continuationHistory)[pc][to] << bonus; } // update_capture_stats() updates move sorting heuristics when a new capture best move is found void update_capture_stats(const Position& pos, Move move, - Move* captures, int captureCnt, int bonus) { + Move* captures, int captureCount, int bonus) { - CapturePieceToHistory& captureHistory = pos.this_thread()->captureHistory; + CapturePieceToHistory& captureHistory = pos.this_thread()->captureHistory; Piece moved_piece = pos.moved_piece(move); PieceType captured = type_of(pos.piece_on(to_sq(move))); - captureHistory[moved_piece][to_sq(move)][captured] << bonus; + + if (pos.capture_or_promotion(move)) + captureHistory[moved_piece][to_sq(move)][captured] << bonus; // Decrease all the other played capture moves - for (int i = 0; i < captureCnt; ++i) + for (int i = 0; i < captureCount; ++i) { moved_piece = pos.moved_piece(captures[i]); captured = type_of(pos.piece_on(to_sq(captures[i]))); @@ -1429,7 +1555,7 @@ moves_loop: // When in check, search starts from here // update_quiet_stats() updates move sorting heuristics when a new quiet best move is found void update_quiet_stats(const Position& pos, Stack* ss, Move move, - Move* quiets, int quietsCnt, int bonus) { + Move* quiets, int quietCount, int bonus) { if (ss->killers[0] != move) { @@ -1449,7 +1575,7 @@ moves_loop: // When in check, search starts from here } // Decrease all the other played quiet moves - for (int i = 0; i < quietsCnt; ++i) + for (int i = 0; i < quietCount; ++i) { thisThread->mainHistory[us][from_to(quiets[i])] << -bonus; update_continuation_histories(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus); @@ -1504,7 +1630,7 @@ void MainThread::check_time() { static TimePoint lastInfoTime = now(); - int elapsed = Time.elapsed(); + TimePoint elapsed = Time.elapsed(); TimePoint tick = Limits.startTime + elapsed; if (tick - lastInfoTime >= 1000) @@ -1514,10 +1640,10 @@ void MainThread::check_time() { } // We should not stop pondering until told so by the GUI - if (Threads.ponder) + if (ponder) return; - if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10) + if ( (Limits.use_time_management() && (elapsed > Time.maximum() - 10 || stopOnPonderhit)) || (Limits.movetime && elapsed >= Limits.movetime) || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes)) Threads.stop = true; @@ -1530,16 +1656,16 @@ void MainThread::check_time() { string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) { std::stringstream ss; - int elapsed = Time.elapsed() + 1; + TimePoint elapsed = Time.elapsed() + 1; const RootMoves& rootMoves = pos.this_thread()->rootMoves; - size_t PVIdx = pos.this_thread()->PVIdx; + size_t pvIdx = pos.this_thread()->pvIdx; size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size()); uint64_t nodesSearched = Threads.nodes_searched(); uint64_t tbHits = Threads.tb_hits() + (TB::RootInTB ? rootMoves.size() : 0); for (size_t i = 0; i < multiPV; ++i) { - bool updated = (i <= PVIdx && rootMoves[i].score != -VALUE_INFINITE); + bool updated = (i <= pvIdx && rootMoves[i].score != -VALUE_INFINITE); if (depth == ONE_PLY && !updated) continue; @@ -1548,7 +1674,7 @@ string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) { Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore; bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY; - v = tb ? TB::Score : v; + v = tb ? rootMoves[i].tbScore : v; if (ss.rdbuf()->in_avail()) // Not at first line ss << "\n"; @@ -1559,7 +1685,7 @@ string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) { << " multipv " << i + 1 << " score " << UCI::value(v); - if (!tb && i == PVIdx) + if (!tb && i == pvIdx) ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : ""); ss << " nodes " << nodesSearched @@ -1592,7 +1718,7 @@ bool RootMove::extract_ponder_from_tt(Position& pos) { assert(pv.size() == 1); - if (!pv[0]) + if (pv[0] == MOVE_NONE) return false; pos.do_move(pv[0], st); @@ -1609,52 +1735,49 @@ bool RootMove::extract_ponder_from_tt(Position& pos) { return pv.size() > 1; } - -void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) { +void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) { RootInTB = false; - UseRule50 = Options["Syzygy50MoveRule"]; - ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY; - Cardinality = Options["SyzygyProbeLimit"]; + UseRule50 = bool(Options["Syzygy50MoveRule"]); + ProbeDepth = int(Options["SyzygyProbeDepth"]) * ONE_PLY; + Cardinality = int(Options["SyzygyProbeLimit"]); + bool dtz_available = true; - // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality + // Tables with fewer pieces than SyzygyProbeLimit are searched with + // ProbeDepth == DEPTH_ZERO if (Cardinality > MaxCardinality) { Cardinality = MaxCardinality; ProbeDepth = DEPTH_ZERO; } - if (Cardinality < popcount(pos.pieces()) || pos.can_castle(ANY_CASTLING)) - return; - - // Don't filter any moves if the user requested analysis on multiple - if (Options["MultiPV"] != 1) - return; + if (Cardinality >= popcount(pos.pieces()) && !pos.can_castle(ANY_CASTLING)) + { + // Rank moves using DTZ tables + RootInTB = root_probe(pos, rootMoves); - // If the current root position is in the tablebases, then RootMoves - // contains only moves that preserve the draw or the win. - RootInTB = root_probe(pos, rootMoves, TB::Score); + if (!RootInTB) + { + // DTZ tables are missing; try to rank moves using WDL tables + dtz_available = false; + RootInTB = root_probe_wdl(pos, rootMoves); + } + } if (RootInTB) - Cardinality = 0; // Do not probe tablebases during the search - - else // If DTZ tables are missing, use WDL tables as a fallback { - // Filter out moves that do not preserve the draw or the win. - RootInTB = root_probe_wdl(pos, rootMoves, TB::Score); + // Sort moves according to TB rank + std::sort(rootMoves.begin(), rootMoves.end(), + [](const RootMove &a, const RootMove &b) { return a.tbRank > b.tbRank; } ); - // Only probe during search if winning - if (RootInTB && TB::Score <= VALUE_DRAW) + // Probe during search only if DTZ is not available and we are winning + if (dtz_available || rootMoves[0].tbScore <= VALUE_DRAW) Cardinality = 0; } - - if (RootInTB && !UseRule50) - TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1 - : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1 - : VALUE_DRAW; - - // Since root_probe() and root_probe_wdl() dirty the root move scores, - // we reset them to -VALUE_INFINITE - for (RootMove& rm : rootMoves) - rm.score = -VALUE_INFINITE; + else + { + // Clean up if root_probe() and root_probe_wdl() have failed + for (auto& m : rootMoves) + m.tbRank = 0; + } }