X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=e6446768066afa33f95d8b6f2aec9faa62abc90e;hp=639c5bc55bf9a1d6d676d29bf2678ed80241cccf;hb=4ae5a7b45a430aea5f4b21f9455b4db74ed1c44a;hpb=9fff27220917d706988185cbd847e3f355a7fe09 diff --git a/src/search.cpp b/src/search.cpp index 639c5bc5..e6446768 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 @@ -61,22 +61,22 @@ 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 - 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 = 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 @@ -85,11 +85,10 @@ namespace { return d > 17 ? 0 : 29 * d * d + 138 * d - 134; } - // Add a small random component to draw evaluations to keep search dynamic - // and to avoid 3fold-blindness. + // Add a small random component to draw evaluations to avoid 3fold-blindness Value value_draw(Depth depth, Thread* thisThread) { - return depth < 4 ? VALUE_DRAW - : VALUE_DRAW + Value(2 * (thisThread->nodes.load(std::memory_order_relaxed) % 2) - 1); + return depth < 4 * ONE_PLY ? VALUE_DRAW + : VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1); } // Skill structure is used to implement strength limit @@ -103,6 +102,48 @@ 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); @@ -113,15 +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. @@ -156,25 +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 && r > 1.0) - 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)); } @@ -187,11 +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() { @@ -216,8 +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! } @@ -226,10 +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 @@ -246,37 +266,29 @@ 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; + 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); - votes[th->rootMoves[0].pv[0]] = 0; - } - - // Vote according to score and depth - for (Thread* th : Threads) - votes[th->rootMoves[0].pv[0]] += int(th->rootMoves[0].score - minScore) - + int(th->completedDepth); - // Select best thread - int bestVote = votes[this->rootMoves[0].pv[0]]; + // Vote according to score and depth, and select the best thread for (Thread* th : Threads) { - if (votes[th->rootMoves[0].pv[0]] > bestVote) - { - bestVote = votes[th->rootMoves[0].pv[0]]; + votes[th->rootMoves[0].pv[0]] += + (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth); + + if (votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]]) bestThread = th; - } } } @@ -301,27 +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(); - bool failedLow; - std::memset(ss-4, 0, 7 * sizeof(Stack)); - for (int i = 4; i > 0; i--) + 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, 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. @@ -340,7 +359,7 @@ void Thread::search() { : Options["Analysis Contempt"] == "Black" && us == WHITE ? -ct : ct; - // In evaluate.cpp the evaluation is from the white point of view + // Evaluation score is from the white point of view contempt = (us == WHITE ? make_score(ct, ct / 2) : -make_score(ct, ct / 2)); @@ -349,17 +368,9 @@ void Thread::search() { && !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 + SkipPhase[i]) / SkipSize[i]) % 2) - continue; // Retry with an incremented rootDepth - } - // Age out PV variability metric if (mainThread) - mainThread->bestMoveChanges *= 0.517, 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. @@ -387,7 +398,7 @@ void Thread::search() { if (rootDepth >= 5 * ONE_PLY) { Value previousScore = rootMoves[pvIdx].previousScore; - delta = Value(18); + delta = Value(20); alpha = std::max(previousScore - delta,-VALUE_INFINITE); beta = std::min(previousScore + delta, VALUE_INFINITE); @@ -401,9 +412,11 @@ void Thread::search() { // 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); + 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 @@ -434,14 +447,15 @@ void Thread::search() { beta = (alpha + beta) / 2; alpha = std::max(bestValue - delta, -VALUE_INFINITE); + failedHighCnt = 0; if (mainThread) - { - failedLow = true; - Threads.stopOnPonderhit = false; - } + mainThread->stopOnPonderhit = false; } else if (bestValue >= beta) + { beta = std::min(bestValue + delta, VALUE_INFINITE); + ++failedHighCnt; + } else break; @@ -482,35 +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[] = { 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) @@ -563,17 +577,17 @@ namespace { Key posKey; Move ttMove, move, excludedMove, bestMove; Depth extension, newDepth; - Value bestValue, value, ttValue, eval, maxValue, pureStaticEval; - bool ttHit, inCheck, givesCheck, improving; - bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture, pvExact; + Value bestValue, value, ttValue, eval, maxValue; + 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(); Color us = pos.side_to_move(); - moveCount = captureCount = quietCount = ss->moveCount = 0; + moveCount = captureCount = quietCount = singularLMR = ss->moveCount = 0; bestValue = -VALUE_INFINITE; maxValue = VALUE_INFINITE; @@ -591,7 +605,7 @@ 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) + 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 @@ -609,8 +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->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0]; + (ss+1)->excludedMove = bestMove = MOVE_NONE; (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE; Square prevSq = to_sq((ss-1)->currentMove); @@ -619,7 +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 @@ -630,6 +646,7 @@ namespace { ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE; 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 @@ -647,9 +664,9 @@ 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)) @@ -675,6 +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); @@ -691,7 +712,7 @@ 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); @@ -712,16 +733,16 @@ namespace { // Step 6. Static evaluation of the position if (inCheck) { - ss->staticEval = eval = pureStaticEval = VALUE_NONE; + ss->staticEval = eval = VALUE_NONE; improving = false; goto moves_loop; // Skip early pruning when in check } else if (ttHit) { - // Never assume anything on values stored in TT - ss->staticEval = eval = pureStaticEval = tte->eval(); + // Never assume anything about values stored in TT + ss->staticEval = eval = tte->eval(); if (eval == VALUE_NONE) - ss->staticEval = eval = pureStaticEval = evaluate(pos); + ss->staticEval = eval = evaluate(pos); // Can ttValue be used as a better position evaluation? if ( ttValue != VALUE_NONE @@ -732,29 +753,27 @@ namespace { { if ((ss-1)->currentMove != MOVE_NULL) { - int p = (ss-1)->statScore; - int bonus = p > 0 ? (-p - 2500) / 512 : - p < 0 ? (-p + 2500) / 512 : 0; + int bonus = -(ss-1)->statScore / 512; - pureStaticEval = evaluate(pos); - ss->staticEval = eval = pureStaticEval + bonus; + ss->staticEval = eval = evaluate(pos) + bonus; } else - ss->staticEval = eval = pureStaticEval = -(ss-1)->staticEval + 2 * Eval::Tempo; + ss->staticEval = eval = -(ss-1)->staticEval + 2 * Eval::Tempo; - tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, pureStaticEval); + tte->save(posKey, VALUE_NONE, ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval); } // Step 7. Razoring (~2 Elo) - if ( depth < 2 * ONE_PLY - && eval <= alpha - RazorMargin) + 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 ( !rootNode + if ( !PvNode && depth < 7 * ONE_PLY && eval - futility_margin(depth, improving) >= beta && eval < VALUE_KNOWN_WIN) // Do not return unproven wins @@ -765,7 +784,7 @@ namespace { && (ss-1)->currentMove != MOVE_NULL && (ss-1)->statScore < 23200 && eval >= beta - && pureStaticEval >= beta - 36 * depth / ONE_PLY + 225 + && ss->staticEval >= beta - 36 * depth / ONE_PLY + 225 && !excludedMove && pos.non_pawn_material(us) && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor)) @@ -797,7 +816,7 @@ namespace { // 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; + thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / (4 * ONE_PLY); thisThread->nmpColor = us; Value v = search(pos, ss, beta-1, beta, depth-R, false); @@ -816,12 +835,12 @@ namespace { && depth >= 5 * ONE_PLY && abs(beta) < VALUE_MATE_IN_MAX_PLY) { - 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) + && probCutCount < 2 + 2 * cutNode) if (move != excludedMove && pos.legal(move)) { probCutCount++; @@ -834,22 +853,21 @@ namespace { 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); + // 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 (~2 Elo) - if ( depth >= 8 * ONE_PLY - && !ttMove) + if (depth >= 8 * ONE_PLY && !ttMove) { search(pos, ss, alpha, beta, depth - 7 * ONE_PLY, cutNode); @@ -860,7 +878,10 @@ namespace { moves_loop: // When in check, search starts from here - const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr, (ss-4)->continuationHistory }; + 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, @@ -868,15 +889,17 @@ moves_loop: // When in check, search starts from here contHist, countermove, ss->killers); - value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc - skipQuiets = false; + value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc + moveCountPruning = false; ttCapture = ttMove && pos.capture_or_promotion(ttMove); - 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)); @@ -897,16 +920,19 @@ 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; + + // 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); - - moveCountPruning = depth < 16 * ONE_PLY - && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY]; + givesCheck = pos.gives_check(move); // Step 13. Extensions (~70 Elo) @@ -918,22 +944,58 @@ moves_loop: // When in check, search starts from here if ( depth >= 8 * ONE_PLY && move == ttMove && !rootNode - && !excludedMove // Recursive singular search is not allowed - && ttValue != VALUE_NONE + && !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); + 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 (~2 Elo) - && pos.see_ge(move)) + + // Check extension (~2 Elo) + else if ( givesCheck + && (pos.is_discovery_check_on_king(~us, 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 @@ -944,22 +1006,23 @@ moves_loop: // When in check, search starts from here && 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 (~30 Elo) + // Move count based pruning 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 (~20 Elo) - if ( lmrDepth < 3 + ((ss-1)->statScore > 0) + 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; @@ -974,8 +1037,8 @@ moves_loop: // When in check, search starts from here if (!pos.see_ge(move, Value(-29 * lmrDepth * lmrDepth))) continue; } - else if ( !extension // (~20 Elo) - && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY))) + else if ( (!givesCheck || !extension) + && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY))) // (~20 Elo) continue; } @@ -999,21 +1062,30 @@ 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); + + // Reduction if other threads are searching this position. + if (th.marked()) + r += ONE_PLY; + + // Decrease reduction if position is or has been on the PV + if (ttPv) + r -= 2 * ONE_PLY; // 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) { - // 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; @@ -1043,10 +1115,10 @@ moves_loop: // When in check, search starts from here r += ONE_PLY; // Decrease/increase reduction for moves with a good/bad history (~30 Elo) - r -= ss->statScore / 20000 * ONE_PLY; + r -= ss->statScore / 16384 * ONE_PLY; } - Depth d = std::max(newDepth - std::max(r, DEPTH_ZERO), ONE_PLY); + Depth d = clamp(newDepth - r, ONE_PLY, newDepth); value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); @@ -1102,8 +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 @@ -1171,24 +1243,25 @@ moves_loop: // When in check, search starts from here update_capture_stats(pos, bestMove, capturesSearched, captureCount, 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)); + // 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)); + } // Bonus for prior countermove that caused the fail low else if ( (depth >= 3 * ONE_PLY || PvNode) - && !pos.captured_piece() - && is_ok((ss-1)->currentMove)) + && !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, pureStaticEval); + depth, bestMove, ss->staticEval); assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE); @@ -1196,8 +1269,8 @@ 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) { @@ -1215,7 +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, inCheck, givesCheck, evasionPrunable; + bool ttHit, pvHit, inCheck, givesCheck, evasionPrunable; int moveCount; if (PvNode) @@ -1227,8 +1300,7 @@ moves_loop: // When in check, search starts from here Thread* thisThread = pos.this_thread(); (ss+1)->ply = ss->ply + 1; - ss->currentMove = bestMove = MOVE_NONE; - ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0]; + bestMove = MOVE_NONE; inCheck = pos.checkers(); moveCount = 0; @@ -1249,6 +1321,7 @@ 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 @@ -1268,7 +1341,7 @@ moves_loop: // When in check, search starts from here { if (ttHit) { - // Never assume anything on values stored in TT + // Never assume anything about values stored in TT if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE) ss->staticEval = bestValue = evaluate(pos); @@ -1286,7 +1359,7 @@ 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, + tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit, BOUND_LOWER, DEPTH_NONE, MOVE_NONE, ss->staticEval); return bestValue; @@ -1298,7 +1371,9 @@ 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 }; + 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, @@ -1314,7 +1389,7 @@ moves_loop: // When in check, search starts from here { assert(is_ok(move)); - givesCheck = gives_check(pos, move); + givesCheck = pos.gives_check(move); moveCount++; @@ -1349,6 +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; @@ -1379,21 +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); - - return value; - } + else + break; // Fail high } } } @@ -1403,8 +1473,9 @@ 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, + 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); @@ -1453,7 +1524,7 @@ 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)->continuationHistory)[pc][to] << bonus; } @@ -1462,9 +1533,9 @@ moves_loop: // When in check, search starts from here // 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))); @@ -1472,7 +1543,7 @@ moves_loop: // When in check, search starts from here 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]))); @@ -1484,7 +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) { @@ -1504,7 +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); @@ -1569,10 +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; @@ -1647,7 +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); @@ -1705,7 +1776,7 @@ void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) { } else { - // Assign the same rank to all moves + // Clean up if root_probe() and root_probe_wdl() have failed for (auto& m : rootMoves) m.tbRank = 0; }