X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=31b6967c17ff008b97e6c939731a523232d92c17;hp=182d2d7f60493bc0069ec1bdc05ead0153609885;hb=d7022031130ef84b801e087c1804d0cf05bc369b;hpb=c33af32dada1be9f6aed851e8cf87599203e2eb2 diff --git a/src/search.cpp b/src/search.cpp index 182d2d7f..31b6967c 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) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad + Copyright (C) 2015-2018 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; @@ -63,13 +62,24 @@ namespace { 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 }; + constexpr int SkipSize[] = { 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4 }; + constexpr 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 + constexpr int RazorMargin[] = {0, 590, 604}; + Value futility_margin(Depth d, bool improving) { + return Value((175 - 50 * improving) * d / ONE_PLY); + } - // Razoring and futility margin based on depth - // razor_margin[0] is unused as long as depth >= ONE_PLY in search - const int razor_margin[] = { 0, 570, 603, 554 }; - Value futility_margin(Depth d) { return Value(150 * d / ONE_PLY); } + // Margin for pruning capturing moves: almost linear in depth + constexpr int CapturePruneMargin[] = { 0, + 1 * PawnValueEg * 1055 / 1000, + 2 * PawnValueEg * 1042 / 1000, + 3 * PawnValueEg * 963 / 1000, + 4 * PawnValueEg * 1038 / 1000, + 5 * PawnValueEg * 950 / 1000, + 6 * PawnValueEg * 930 / 1000 + }; // Futility and reductions lookup tables, initialized at startup int FutilityMoveCounts[2][16]; // [improving][depth] @@ -82,74 +92,39 @@ namespace { // 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 : 32 * d * d + 64 * d - 64; } // Skill structure is used to implement strength limit struct Skill { - Skill(int l) : level(l) {} + explicit Skill(int l) : level(l) {} bool enabled() const { return level < 20; } bool time_to_pick(Depth depth) const { return depth / ONE_PLY == 1 + level; } - Move best_move(size_t multiPV) { return best ? best : pick_best(multiPV); } Move pick_best(size_t multiPV); int level; Move best = MOVE_NONE; }; - // EasyMoveManager structure is used to detect an 'easy move'. When the PV is stable - // across multiple search iterations, we can quickly return the best move. - struct EasyMoveManager { - - void clear() { - stableCnt = 0; - expectedPosKey = 0; - pv[0] = pv[1] = pv[2] = MOVE_NONE; - } - - Move get(Key key) const { - return expectedPosKey == key ? pv[2] : MOVE_NONE; - } - - void update(Position& pos, const std::vector& newPv) { - - assert(newPv.size() >= 3); - - // Keep track of how many times in a row the 3rd ply remains stable - stableCnt = (newPv[2] == pv[2]) ? stableCnt + 1 : 0; - - if (!std::equal(newPv.begin(), newPv.begin() + 3, pv)) - { - std::copy(newPv.begin(), newPv.begin() + 3, pv); - - StateInfo st[2]; - pos.do_move(newPv[0], st[0]); - pos.do_move(newPv[1], st[1]); - expectedPosKey = pos.key(); - pos.undo_move(newPv[1]); - pos.undo_move(newPv[0]); - } - } - - Key expectedPosKey; - int stableCnt; - Move pv[3]; - }; - - EasyMoveManager EasyMove; - Value DrawValue[COLOR_NB]; - 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 + template Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO); Value value_to_tt(Value v, int ply); 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_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, 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); + } // 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. @@ -180,7 +155,7 @@ namespace { } // namespace -/// Search::init() is called during startup to initialize various lookup tables +/// Search::init() is called at startup to initialize various lookup tables void Search::init() { @@ -194,7 +169,7 @@ void Search::init() { 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) + if (!imp && r > 1.0) Reductions[NonPV][imp][d][mc]++; } @@ -214,12 +189,7 @@ void Search::clear() { Time.availableNodes = 0; TT.clear(); - - for (Thread* th : Threads) - th->clear(); - - Threads.main()->callsCnt = 0; - Threads.main()->previousScore = VALUE_INFINITE; + Threads.clear(); } @@ -239,10 +209,6 @@ void MainThread::search() { Time.init(Limits, us, rootPos.game_ply()); TT.new_search(); - int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns - DrawValue[ us] = VALUE_DRAW - Value(contempt); - DrawValue[~us] = VALUE_DRAW + Value(contempt); - if (rootMoves.empty()) { rootMoves.emplace_back(MOVE_NONE); @@ -285,8 +251,7 @@ void MainThread::search() { // Check if there are threads with a better score than main thread Thread* bestThread = this; - if ( !this->easyMovePlayed - && Options["MultiPV"] == 1 + if ( Options["MultiPV"] == 1 && !Limits.depth && !Skill(Options["Skill Level"]).enabled() && rootMoves[0].pv[0] != MOVE_NONE) @@ -305,7 +270,7 @@ void MainThread::search() { previousScore = bestThread->rootMoves[0].score; - // Send new PV when needed + // Send again PV info if we have a new best thread if (bestThread != this) sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl; @@ -326,23 +291,21 @@ void Thread::search() { Stack stack[MAX_PLY+7], *ss = stack+4; // To reference from (ss-4) to (ss+2) Value bestValue, alpha, beta, delta; - Move easyMove = MOVE_NONE; + Move lastBestMove = MOVE_NONE; + Depth lastBestMoveDepth = DEPTH_ZERO; MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr); + double timeReduction = 1.0; + 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]; // Use as sentinel + (ss-i)->contHistory = this->contHistory[NO_PIECE][0].get(); // Use as sentinel bestValue = delta = alpha = -VALUE_INFINITE; beta = VALUE_INFINITE; if (mainThread) - { - easyMove = EasyMove.get(rootPos.key()); - EasyMove.clear(); - mainThread->easyMovePlayed = mainThread->failedLow = false; - mainThread->bestMoveChanges = 0; - } + mainThread->bestMoveChanges = 0, mainThread->failedLow = false; size_t multiPV = Options["MultiPV"]; Skill skill(Options["Skill Level"]); @@ -354,48 +317,80 @@ void Thread::search() { multiPV = std::min(multiPV, rootMoves.size()); + 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; + + // In evaluate.cpp the evaluation 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 threads - if (idx) + // 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; + 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 *= 0.505, mainThread->failedLow = false; + mainThread->bestMoveChanges *= 0.517, mainThread->failedLow = false; // 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) { + 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) { + Value previousScore = rootMoves[PVIdx].previousScore; delta = Value(18); - alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE); - beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE); + alpha = std::max(previousScore - delta,-VALUE_INFINITE); + beta = std::min(previousScore + delta, VALUE_INFINITE); + + // Adjust contempt based on root move's previousScore (dynamic contempt) + int dct = ct + 88 * previousScore / (abs(previousScore) + 200); + + 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're not failing + // high/low, re-search with a bigger window until we don't fail // high/low anymore. while (true) { - bestValue = ::search(rootPos, ss, alpha, beta, rootDepth, false, false); + bestValue = ::search(rootPos, ss, alpha, beta, rootDepth, 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 @@ -403,11 +398,11 @@ 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 and - // writing PV back to TT is safe because RootMoves is still - // valid, although it refers to the previous iteration. + // If search has been stopped, we break immediately. Sorting is + // safe because RootMoves is still valid, although it refers to + // the previous iteration. if (Threads.stop) break; @@ -443,7 +438,7 @@ 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)) @@ -453,6 +448,11 @@ void Thread::search() { if (!Threads.stop) completedDepth = rootDepth; + if (rootMoves[0].pv[0] != lastBestMove) { + lastBestMove = rootMoves[0].pv[0]; + lastBestMoveDepth = rootDepth; + } + // Have we found a "mate in x"? if ( Limits.mate && bestValue >= VALUE_MATE_IN_MAX_PLY @@ -467,26 +467,28 @@ void Thread::search() { skill.pick_best(multiPV); // Do we have time for the next iteration? Can we stop searching now? - if (Limits.use_time_management()) - { - if (!Threads.stop && !Threads.stopOnPonderhit) + if ( Limits.use_time_management() + && !Threads.stop + && !Threads.stopOnPonderhit) { - // Stop the search if only one legal move is available, or if all - // of the available time has been used, or if we matched an easyMove - // from the previous search and just did a fast verification. const int F[] = { mainThread->failedLow, bestValue - mainThread->previousScore }; - int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1])); - double unstablePvFactor = 1 + mainThread->bestMoveChanges; + int improvingFactor = std::max(246, std::min(832, 306 + 119 * F[0] - 6 * F[1])); - bool doEasyMove = rootMoves[0].pv[0] == easyMove - && mainThread->bestMoveChanges < 0.03 - && Time.elapsed() > Time.optimum() * 5 / 44; + // 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; + // 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; + + // Stop the search if we have only one legal move, or if available time elapsed if ( rootMoves.size() == 1 - || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628 - || (mainThread->easyMovePlayed = doEasyMove, doEasyMove)) + || 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". @@ -496,26 +498,17 @@ void Thread::search() { Threads.stop = true; } } - - if (rootMoves[0].pv.size() >= 3) - EasyMove.update(rootPos, rootMoves[0].pv); - else - EasyMove.clear(); - } } if (!mainThread) return; - // Clear any candidate easy move that wasn't stable for the last search - // iterations; the second condition prevents consecutive fast moves. - if (EasyMove.stableCnt < 6 || mainThread->easyMovePlayed) - EasyMove.clear(); + mainThread->previousTimeReduction = timeReduction; // If skill level is enabled, swap best PV line with the sub-optimal one if (skill.enabled()) - std::swap(rootMoves[0], *std::find(rootMoves.begin(), - rootMoves.end(), skill.best_move(multiPV))); + std::swap(rootMoves[0], *std::find(rootMoves.begin(), rootMoves.end(), + skill.best ? skill.best : skill.pick_best(multiPV))); } @@ -524,9 +517,13 @@ 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) { + Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) { + + // Use quiescence search when needed + if (depth < ONE_PLY) + return qsearch(pos, ss, alpha, beta); - const bool PvNode = NT == PV; + constexpr bool PvNode = NT == PV; const bool rootNode = PvNode && ss->ply == 0; assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE); @@ -535,24 +532,25 @@ namespace { assert(!(PvNode && cutNode)); assert(depth / ONE_PLY * ONE_PLY == depth); - Move pv[MAX_PLY+1], quietsSearched[64]; + Move pv[MAX_PLY+1], capturesSearched[32], quietsSearched[64]; StateInfo st; TTEntry* tte; Key posKey; Move ttMove, move, excludedMove, bestMove; Depth extension, newDepth; - Value bestValue, value, ttValue, eval; - bool ttHit, inCheck, givesCheck, singularExtensionNode, improving; - bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture; + Value bestValue, value, ttValue, eval, maxValue; + bool ttHit, inCheck, givesCheck, improving; + bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture, pvExact; Piece movedPiece; - int moveCount, quietCount; + int moveCount, captureCount, quietCount; // Step 1. Initialize node Thread* thisThread = pos.this_thread(); inCheck = pos.checkers(); - moveCount = quietCount = ss->moveCount = 0; - ss->statScore = 0; + 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()) @@ -565,9 +563,10 @@ namespace { if (!rootNode) { // Step 2. Check for aborted search and immediate draw - 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) - : DrawValue[pos.side_to_move()]; + 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; // 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 @@ -579,21 +578,39 @@ namespace { beta = std::min(mate_in(ss->ply+1), beta); if (alpha >= beta) return alpha; + + // Check if there exists a move which draws by repetition, or an alternative + // earlier move to this position. + if ( pos.rule50_count() >= 3 + && alpha < VALUE_DRAW + && pos.has_game_cycle(ss->ply)) + { + alpha = VALUE_DRAW; + if (alpha >= beta) + return alpha; + } } 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]; + ss->contHistory = thisThread->contHistory[NO_PIECE][0].get(); (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE; 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 + // 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; + // Step 4. Transposition table lookup. We don't want the score of a partial // search to overwrite a previous full search TT value, so we use a different // position key in case of an excluded move. excludedMove = ss->excludedMove; - posKey = pos.key() ^ Key(excludedMove); + 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] @@ -613,7 +630,7 @@ namespace { if (ttValue >= beta) { if (!pos.capture_or_promotion(ttMove)) - update_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth)); + 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()) @@ -623,14 +640,14 @@ namespace { else if (!pos.capture_or_promotion(ttMove)) { int penalty = -stat_bonus(depth); - thisThread->mainHistory.update(pos.side_to_move(), ttMove, penalty); + thisThread->mainHistory[us][from_to(ttMove)] << penalty; update_continuation_histories(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty); } } return ttValue; } - // Step 4a. Tablebase probe + // Step 5. Tablebases probe if (!rootNode && TB::Cardinality) { int piecesCount = pos.count(); @@ -641,7 +658,7 @@ namespace { && !pos.can_castle(ANY_CASTLING)) { TB::ProbeState err; - TB::WDLScore v = Tablebases::probe_wdl(pos, &err); + TB::WDLScore wdl = Tablebases::probe_wdl(pos, &err); if (err != TB::ProbeState::FAIL) { @@ -649,26 +666,41 @@ namespace { int drawScore = TB::UseRule50 ? 1 : 0; - value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply + 1 - : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply - 1 - : VALUE_DRAW + 2 * v * drawScore; + value = wdl < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply + 1 + : wdl > drawScore ? VALUE_MATE - MAX_PLY - ss->ply - 1 + : VALUE_DRAW + 2 * wdl * drawScore; - tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT, - std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY), - MOVE_NONE, VALUE_NONE, TT.generation()); + Bound b = wdl < -drawScore ? BOUND_UPPER + : wdl > drawScore ? BOUND_LOWER : BOUND_EXACT; - return value; + if ( b == BOUND_EXACT + || (b == BOUND_LOWER ? value >= beta : value <= alpha)) + { + tte->save(posKey, value_to_tt(value, ss->ply), b, + std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY), + MOVE_NONE, VALUE_NONE, TT.generation()); + + return value; + } + + if (PvNode) + { + if (b == BOUND_LOWER) + bestValue = value, alpha = std::max(alpha, bestValue); + else + maxValue = value; + } } } } - // Step 5. Evaluate the position statically + // Step 6. Static evaluation of the position if (inCheck) { ss->staticEval = eval = VALUE_NONE; - goto moves_loop; + improving = false; + goto moves_loop; // Skip early pruning when in check } - else if (ttHit) { // Never assume anything on values stored in TT @@ -676,13 +708,13 @@ namespace { eval = ss->staticEval = evaluate(pos); // Can ttValue be used as a better position evaluation? - if ( ttValue != VALUE_NONE + if ( ttValue != VALUE_NONE && (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))) eval = ttValue; } else { - eval = ss->staticEval = + ss->staticEval = eval = (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo; @@ -690,49 +722,49 @@ namespace { ss->staticEval, TT.generation()); } - if (skipEarlyPruning) - goto moves_loop; - - // Step 6. Razoring (skipped when in check) - if ( !PvNode - && depth < 4 * ONE_PLY - && eval + razor_margin[depth / ONE_PLY] <= alpha) + // Step 7. Razoring (~2 Elo) + if ( !PvNode + && depth < 3 * ONE_PLY + && eval <= alpha - RazorMargin[depth / ONE_PLY]) { - if (depth <= ONE_PLY) - return qsearch(pos, ss, alpha, alpha+1); - - Value ralpha = alpha - razor_margin[depth / ONE_PLY]; - Value v = qsearch(pos, ss, ralpha, ralpha+1); - if (v <= ralpha) + Value ralpha = alpha - (depth >= 2 * ONE_PLY) * RazorMargin[depth / ONE_PLY]; + Value v = qsearch(pos, ss, ralpha, ralpha+1); + if (depth < 2 * ONE_PLY || v <= ralpha) return v; } - // Step 7. Futility pruning: child node (skipped when in check) + improving = ss->staticEval >= (ss-2)->staticEval + || (ss-2)->staticEval == VALUE_NONE; + + // Step 8. Futility pruning: child node (~30 Elo) if ( !rootNode && depth < 7 * ONE_PLY - && eval - futility_margin(depth) >= beta - && eval < VALUE_KNOWN_WIN // Do not return unproven wins - && pos.non_pawn_material(pos.side_to_move())) + && eval - futility_margin(depth, improving) >= beta + && eval < VALUE_KNOWN_WIN) // Do not return unproven wins return eval; - // Step 8. Null move search with verification search (is omitted in PV nodes) + // Step 9. Null move search with verification search (~40 Elo) if ( !PvNode + && (ss-1)->currentMove != MOVE_NULL + && (ss-1)->statScore < 22500 && eval >= beta - && (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY) - && pos.non_pawn_material(pos.side_to_move())) + && ss->staticEval >= beta - 36 * depth / ONE_PLY + 225 + && !excludedMove + && pos.non_pawn_material(us) + && (ss->ply > thisThread->nmp_min_ply || us != thisThread->nmp_color)) { - 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; ss->currentMove = MOVE_NULL; - ss->contHistory = &thisThread->contHistory[NO_PIECE][0]; + ss->contHistory = thisThread->contHistory[NO_PIECE][0].get(); pos.do_null_move(st); - Value nullValue = depth-R < ONE_PLY ? -qsearch(pos, ss+1, -beta, -beta+1) - : - 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(); if (nullValue >= beta) @@ -741,81 +773,91 @@ namespace { if (nullValue >= VALUE_MATE_IN_MAX_PLY) nullValue = beta; - if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN) + if (abs(beta) < VALUE_KNOWN_WIN && (depth < 12 * ONE_PLY || thisThread->nmp_min_ply)) return nullValue; - // Do verification search at high depths - Value v = depth-R < ONE_PLY ? qsearch(pos, ss, beta-1, beta) - : search(pos, ss, beta-1, beta, depth-R, false, true); + // 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_min_ply = ss->ply + 3 * (depth-R) / 4 - 1; + thisThread->nmp_color = us; + + Value v = search(pos, ss, beta-1, beta, depth-R, false); + + thisThread->nmp_min_ply = 0; if (v >= beta) return nullValue; } } - // Step 9. 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) { - Value rbeta = std::min(beta + 200, VALUE_INFINITE); - - 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); + int probCutCount = 0; - MovePicker mp(pos, ttMove, rbeta - ss->staticEval); - - while ((move = mp.next_move()) != MOVE_NONE) + while ( (move = mp.next_move()) != MOVE_NONE + && probCutCount < 3) if (pos.legal(move)) { + probCutCount++; + ss->currentMove = move; - ss->contHistory = &thisThread->contHistory[pos.moved_piece(move)][to_sq(move)]; + ss->contHistory = thisThread->contHistory[pos.moved_piece(move)][to_sq(move)].get(); assert(depth >= 5 * ONE_PLY); + pos.do_move(move, st); - value = -search(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false); + + // Perform a preliminary qsearch to verify that the move holds + value = -qsearch(pos, ss+1, -rbeta, -rbeta+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); + pos.undo_move(move); + if (value >= rbeta) return value; } } - // Step 10. 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 * ONE_PLY) - 2) * ONE_PLY; - search(pos, ss, alpha, beta, d, cutNode, true); + Depth d = 3 * depth / 4 - 2 * ONE_PLY; + search(pos, ss, alpha, beta, d, cutNode); tte = TT.probe(posKey, ttHit); + ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE; ttMove = ttHit ? tte->move() : MOVE_NONE; } -moves_loop: // When in check search starts from here +moves_loop: // When in check, search starts from here const PieceToHistory* contHist[] = { (ss-1)->contHistory, (ss-2)->contHistory, nullptr, (ss-4)->contHistory }; Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq]; - MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, 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 - improving = ss->staticEval >= (ss-2)->staticEval - /* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */ - ||(ss-2)->staticEval == VALUE_NONE; - - 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; - // Step 11. Loop through moves - // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs + // 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) { assert(is_ok(move)); @@ -825,9 +867,10 @@ 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. + // 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.end(), move)) + thisThread->rootMoves.begin() + thisThread->PVLast, move)) continue; ss->moveCount = ++moveCount; @@ -836,42 +879,42 @@ moves_loop: // When in check search starts from here sync_cout << "info depth " << depth / ONE_PLY << " currmove " << UCI::move(move, pos.is_chess960()) << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl; - if (PvNode) (ss+1)->pv = nullptr; extension = DEPTH_ZERO; captureOrPromotion = pos.capture_or_promotion(move); movedPiece = pos.moved_piece(move); - - givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates() - ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move) - : pos.gives_check(move); + givesCheck = gives_check(pos, move); moveCountPruning = depth < 16 * ONE_PLY && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY]; - // Step 12. Singular and Gives Check Extensions + // Step 13. Extensions (~70 Elo) - // 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 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 + // 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 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 >= 8 * ONE_PLY && move == ttMove + && !rootNode + && !excludedMove // Recursive singular search is not allowed + && ttValue != VALUE_NONE + && (tte->bound() & BOUND_LOWER) + && tte->depth() >= depth - 3 * ONE_PLY && pos.legal(move)) { Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE); - Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY; ss->excludedMove = move; - value = search(pos, ss, rBeta - 1, rBeta, d, cutNode, true); + value = search(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode); ss->excludedMove = MOVE_NONE; if (value < rBeta) extension = ONE_PLY; } - else if ( givesCheck + else if ( givesCheck // Check extension (~2 Elo) && !moveCountPruning && pos.see_ge(move)) extension = ONE_PLY; @@ -879,16 +922,16 @@ moves_loop: // When in check search starts from here // Calculate new depth for this move newDepth = depth - ONE_PLY + extension; - // Step 13. 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) { if ( !captureOrPromotion && !givesCheck && (!pos.advanced_pawn_push(move) || pos.non_pawn_material() >= Value(5000))) { - // Move count based pruning + // Move count based pruning (~30 Elo) if (moveCountPruning) { skipQuiets = true; @@ -898,26 +941,26 @@ moves_loop: // When in check search starts from here // Reduced depth of the next LMR search int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY; - // Countermoves based pruning + // Countermoves based pruning (~20 Elo) if ( lmrDepth < 3 && (*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 + // Prune moves with negative SEE (~10 Elo) if ( lmrDepth < 8 && !pos.see_ge(move, Value(-35 * lmrDepth * lmrDepth))) continue; } - else if ( depth < 7 * ONE_PLY + else if ( depth < 7 * ONE_PLY // (~20 Elo) && !extension - && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY))) + && !pos.see_ge(move, -Value(CapturePruneMargin[depth / ONE_PLY]))) continue; } @@ -936,12 +979,12 @@ 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->contHistory = &thisThread->contHistory[movedPiece][to_sq(move)]; + ss->contHistory = thisThread->contHistory[movedPiece][to_sq(move)].get(); - // Step 14. Make the move + // Step 15. Make the move pos.do_move(move, st, givesCheck); - // Step 15. Reduced depth search (LMR). If the move fails high it will be + // 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 @@ -949,61 +992,62 @@ moves_loop: // When in check search starts from here { Depth r = reduction(improving, depth, moveCount); - if (captureOrPromotion) + if (captureOrPromotion) // (~5 Elo) r -= r ? ONE_PLY : DEPTH_ZERO; else { - // Decrease reduction if opponent's move count is high + // Decrease reduction if opponent's move count is high (~5 Elo) if ((ss-1)->moveCount > 15) r -= ONE_PLY; - // Increase reduction if ttMove is a capture + // Decrease reduction for exact PV nodes (~0 Elo) + if (pvExact) + r -= ONE_PLY; + + // 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 + // Decrease/increase reduction for moves with a good/bad history (~30 Elo) r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->statScore / 20000) * ONE_PLY); } Depth d = std::max(newDepth - r, ONE_PLY); - 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); } else doFullDepthSearch = !PvNode || moveCount > 1; - // Step 16. Full depth search when LMR is skipped or fails high + // Step 17. Full depth search when LMR is skipped or fails high if (doFullDepthSearch) - value = newDepth < ONE_PLY ? - givesCheck ? -qsearch(pos, ss+1, -(alpha+1), -alpha) - : -qsearch(pos, ss+1, -(alpha+1), -alpha) - : - 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 @@ -1013,18 +1057,15 @@ moves_loop: // When in check search starts from here (ss+1)->pv = pv; (ss+1)->pv[0] = MOVE_NONE; - value = newDepth < ONE_PLY ? - givesCheck ? -qsearch(pos, ss+1, -beta, -alpha) - : -qsearch(pos, ss+1, -beta, -alpha) - : - search(pos, ss+1, -beta, -alpha, newDepth, false, false); + value = -search(pos, ss+1, -beta, -alpha, newDepth, false); } - // Step 17. Undo move + // Step 18. Undo move pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); - // Step 18. Check for a new best move + // Step 19. 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. @@ -1036,7 +1077,7 @@ moves_loop: // When in check search starts from here RootMove& rm = *std::find(thisThread->rootMoves.begin(), thisThread->rootMoves.end(), move); - // PV move or new best move ? + // PV move or new best move? if (moveCount == 1 || value > alpha) { rm.score = value; @@ -1077,13 +1118,20 @@ moves_loop: // When in check search starts from here else { assert(value >= beta); // Fail high + ss->statScore = 0; break; } } } - if (!captureOrPromotion && move != bestMove && quietCount < 64) - quietsSearched[quietCount++] = move; + if (move != bestMove) + { + if (captureOrPromotion && captureCount < 32) + capturesSearched[captureCount++] = move; + + else if (!captureOrPromotion && quietCount < 64) + quietsSearched[quietCount++] = move; + } } // The following condition would detect a stop only after move loop has been @@ -1103,23 +1151,28 @@ moves_loop: // When in check search starts from here if (!moveCount) bestValue = excludedMove ? alpha - : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()]; + : inCheck ? mated_in(ss->ply) : VALUE_DRAW; else if (bestMove) { // Quiet best move: update move sorting heuristics if (!pos.capture_or_promotion(bestMove)) - update_stats(pos, ss, bestMove, quietsSearched, quietCount, stat_bonus(depth)); + update_quiet_stats(pos, ss, bestMove, quietsSearched, quietCount, stat_bonus(depth)); + else + update_capture_stats(pos, bestMove, capturesSearched, captureCount, 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)); } // Bonus for prior countermove that caused the fail low - else if ( depth >= 3 * ONE_PLY + else if ( (depth >= 3 * ONE_PLY || PvNode) && !pos.captured_piece() && is_ok((ss-1)->currentMove)) 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), bestValue >= beta ? BOUND_LOWER : @@ -1134,13 +1187,11 @@ 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. - - template + template Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) { - const bool PvNode = NT == PV; + constexpr bool PvNode = NT == PV; - assert(InCheck == !!pos.checkers()); assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE); assert(PvNode || (alpha == beta - 1)); assert(depth <= DEPTH_ZERO); @@ -1151,9 +1202,9 @@ moves_loop: // When in check search starts from here TTEntry* tte; Key posKey; Move ttMove, move, bestMove; - Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha; - bool ttHit, givesCheck, evasionPrunable; Depth ttDepth; + Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha; + bool ttHit, inCheck, givesCheck, evasionPrunable; int moveCount; if (PvNode) @@ -1163,27 +1214,28 @@ moves_loop: // When in check search starts from here ss->pv[0] = MOVE_NONE; } - ss->currentMove = bestMove = MOVE_NONE; (ss+1)->ply = ss->ply + 1; + ss->currentMove = bestMove = MOVE_NONE; + inCheck = pos.checkers(); moveCount = 0; - // Check for an instant draw or if the maximum ply has been reached - if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY) - return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos) - : DrawValue[pos.side_to_move()]; + // Check for an immediate draw or maximum ply reached + if ( pos.is_draw(ss->ply) + || ss->ply >= MAX_PLY) + return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos) : VALUE_DRAW; assert(0 <= ss->ply && ss->ply < MAX_PLY); // Decide whether or not to include checks: this fixes also the type of // TT entry depth that we are going to use. Note that in qsearch we use // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS. - ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS + ttDepth = inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS; // Transposition table lookup posKey = pos.key(); tte = TT.probe(posKey, ttHit); - ttMove = ttHit ? tte->move() : MOVE_NONE; ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE; + ttMove = ttHit ? tte->move() : MOVE_NONE; if ( !PvNode && ttHit @@ -1194,7 +1246,7 @@ moves_loop: // When in check search starts from here return ttValue; // Evaluate the position statically - if (InCheck) + if (inCheck) { ss->staticEval = VALUE_NONE; bestValue = futilityBase = -VALUE_INFINITE; @@ -1221,7 +1273,7 @@ moves_loop: // When in check search starts from here if (bestValue >= beta) { if (!ttHit) - tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER, + tte->save(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER, DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation()); return bestValue; @@ -1237,21 +1289,21 @@ moves_loop: // When in check search starts from here // 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, to_sq((ss-1)->currentMove)); + MovePicker mp(pos, ttMove, depth, &pos.this_thread()->mainHistory, + &pos.this_thread()->captureHistory, + 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 = type_of(move) == NORMAL && !pos.discovered_check_candidates() - ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move) - : pos.gives_check(move); + givesCheck = gives_check(pos, move); moveCount++; // Futility pruning - if ( !InCheck + if ( !inCheck && !givesCheck && futilityBase > -VALUE_KNOWN_WIN && !pos.advanced_pawn_push(move)) @@ -1274,15 +1326,14 @@ moves_loop: // When in check search starts from here } // Detect non-capture evasions that are candidates to be pruned - evasionPrunable = InCheck + evasionPrunable = inCheck && (depth != DEPTH_ZERO || moveCount > 2) && bestValue > VALUE_MATED_IN_MAX_PLY && !pos.capture(move); // Don't search moves with negative SEE values - if ( (!InCheck || evasionPrunable) - && type_of(move) != PROMOTION - && !pos.see_ge(move)) + if ( (!inCheck || evasionPrunable) + && !pos.see_ge(move)) continue; // Speculative prefetch as early as possible @@ -1299,8 +1350,7 @@ moves_loop: // When in check search starts from here // Make and search the move pos.do_move(move, st, givesCheck); - value = givesCheck ? -qsearch(pos, ss+1, -beta, -alpha, depth - ONE_PLY) - : -qsearch(pos, ss+1, -beta, -alpha, depth - ONE_PLY); + value = -qsearch(pos, ss+1, -beta, -alpha, depth - ONE_PLY); pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); @@ -1333,7 +1383,7 @@ moves_loop: // When in check search starts from here // All legal moves have been searched. A special case: If we're in check // and no legal moves were found, it is checkmate. - if (InCheck && bestValue == -VALUE_INFINITE) + 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), @@ -1388,14 +1438,34 @@ moves_loop: // When in check search starts from here for (int i : {1, 2, 4}) if (is_ok((ss-i)->currentMove)) - (ss-i)->contHistory->update(pc, to, bonus); + (*(ss-i)->contHistory)[pc][to] << bonus; } - // update_stats() updates move sorting heuristics when a new quiet best move is found + // update_capture_stats() updates move sorting heuristics when a new capture best move is found - void update_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) { + + 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; + + // Decrease all the other played capture moves + for (int i = 0; i < captureCnt; ++i) + { + moved_piece = pos.moved_piece(captures[i]); + captured = type_of(pos.piece_on(to_sq(captures[i]))); + captureHistory[moved_piece][to_sq(captures[i])][captured] << -bonus; + } + } + + + // 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) { if (ss->killers[0] != move) { @@ -1403,9 +1473,9 @@ moves_loop: // When in check search starts from here ss->killers[0] = move; } - Color c = pos.side_to_move(); + Color us = pos.side_to_move(); Thread* thisThread = pos.this_thread(); - thisThread->mainHistory.update(c, move, bonus); + thisThread->mainHistory[us][from_to(move)] << bonus; update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus); if (is_ok((ss-1)->currentMove)) @@ -1417,12 +1487,11 @@ moves_loop: // When in check search starts from here // Decrease all the other played quiet moves for (int i = 0; i < quietsCnt; ++i) { - thisThread->mainHistory.update(c, quiets[i], -bonus); + thisThread->mainHistory[us][from_to(quiets[i])] << -bonus; update_continuation_histories(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus); } } - // When playing with strength handicap, choose best move among a set of RootMoves // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen. @@ -1446,7 +1515,7 @@ moves_loop: // When in check search starts from here int push = ( weakness * int(topScore - rootMoves[i].score) + delta * (rng.rand() % weakness)) / 128; - if (rootMoves[i].score + push > maxScore) + if (rootMoves[i].score + push >= maxScore) { maxScore = rootMoves[i].score + push; best = rootMoves[i].pv[0]; @@ -1458,38 +1527,37 @@ moves_loop: // When in check search starts from here } // namespace - // check_time() is used to print debug info and, more importantly, to detect - // when we are out of available time and thus stop the search. +/// MainThread::check_time() is used to print debug info and, more importantly, +/// to detect when we are out of available time and thus stop the search. - void MainThread::check_time() { +void MainThread::check_time() { - if (--callsCnt > 0) - return; + if (--callsCnt > 0) + return; - // At low node count increase the checking rate to about 0.1% of nodes - // otherwise use a default value. - callsCnt = Limits.nodes ? std::min(4096, int(Limits.nodes / 1024)) : 4096; + // When using nodes, ensure checking rate is not lower than 0.1% of nodes + callsCnt = Limits.nodes ? std::min(1024, int(Limits.nodes / 1024)) : 1024; - static TimePoint lastInfoTime = now(); + static TimePoint lastInfoTime = now(); - int elapsed = Time.elapsed(); - TimePoint tick = Limits.startTime + elapsed; + TimePoint elapsed = Time.elapsed(); + TimePoint tick = Limits.startTime + elapsed; - if (tick - lastInfoTime >= 1000) - { - lastInfoTime = tick; - dbg_print(); - } + if (tick - lastInfoTime >= 1000) + { + lastInfoTime = tick; + dbg_print(); + } - // An engine may not stop pondering until told so by the GUI - if (Threads.ponder) - return; + // We should not stop pondering until told so by the GUI + if (Threads.ponder) + return; - if ( (Limits.use_time_management() && elapsed > Time.maximum()) - || (Limits.movetime && elapsed >= Limits.movetime) - || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes)) - Threads.stop = true; - } + if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10) + || (Limits.movetime && elapsed >= Limits.movetime) + || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes)) + Threads.stop = true; +} /// UCI::pv() formats PV information according to the UCI protocol. UCI requires @@ -1498,7 +1566,7 @@ moves_loop: // When in check search starts from here 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 multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size()); @@ -1516,7 +1584,7 @@ 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"; @@ -1577,42 +1645,49 @@ 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; + 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; + else + { + // Assign the same rank to all moves + for (auto& m : rootMoves) + m.TBRank = 0; + } }