X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=ff7a2c2309cb91624da7b083be34ff1bf5d8a4cc;hp=c6b59b39b92afa07d0a82331f1d3bc6e367cec82;hb=5a7827d59de5e3dea0d90bdb3e7c57153c0a9f1f;hpb=05f7d59a9a27d9f8bce8bde4e9fed7ecefeb03b9 diff --git a/src/search.cpp b/src/search.cpp index c6b59b39..ff7a2c23 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -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); @@ -116,13 +157,6 @@ namespace { 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); - 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. template @@ -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)); } @@ -187,12 +204,12 @@ void Search::clear() { Time.availableNodes = 0; TT.clear(); Threads.clear(); - Tablebases::init(Options["SyzygyPath"]); // Free up mapped files + 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() { @@ -217,8 +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! } @@ -246,8 +266,9 @@ 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() @@ -260,21 +281,15 @@ void MainThread::search() { for (Thread* th: Threads) minScore = std::min(minScore, th->rootMoves[0].score); - // Vote according to score and depth + // Vote according to score and depth, and select the best thread for (Thread* th : Threads) { - int64_t s = th->rootMoves[0].score - minScore + 1; - votes[th->rootMoves[0].pv[0]] += 200 + s * s * int(th->completedDepth); - } + votes[th->rootMoves[0].pv[0]] += + (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth); - // Select best thread - auto bestVote = votes[this->rootMoves[0].pv[0]]; - for (Thread* th : Threads) - if (votes[th->rootMoves[0].pv[0]] > bestVote) - { - bestVote = votes[th->rootMoves[0].pv[0]]; + if (votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]]) bestThread = th; - } + } } previousScore = bestThread->rootMoves[0].score; @@ -298,33 +313,34 @@ void MainThread::search() { void Thread::search() { - // To allow access to (ss-5) up to (ss+2), the stack must be oversized. + // 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-4, also near the root. + // which accesses its argument at ss-6, also near the root. // The latter is needed for statScores and killer initialization. - Stack stack[MAX_PLY+8], *ss = stack+5; + 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-5, 0, 8 * sizeof(Stack)); - for (int i = 5; 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. @@ -343,7 +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)); @@ -352,17 +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. @@ -439,18 +447,14 @@ void Thread::search() { beta = (alpha + beta) / 2; alpha = std::max(bestValue - delta, -VALUE_INFINITE); + failedHighCnt = 0; if (mainThread) - { - failedHighCnt = 0; - failedLow = true; mainThread->stopOnPonderhit = false; - } } else if (bestValue >= beta) { beta = std::min(bestValue + delta, VALUE_INFINITE); - if (mainThread) - ++failedHighCnt; + ++failedHighCnt; } else break; @@ -494,19 +498,24 @@ void Thread::search() { && !Threads.stop && !mainThread->stopOnPonderhit) { - double fallingEval = (306 + 119 * failedLow + 6 * (mainThread->previousScore - bestValue)) / 581.0; - fallingEval = std::max(0.5, std::min(1.5, fallingEval)); + 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 = 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; + 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 * fallingEval) + || 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". @@ -568,17 +577,17 @@ namespace { Key posKey; Move ttMove, move, excludedMove, bestMove; Depth extension, newDepth; - Value bestValue, value, ttValue, eval, maxValue, pureStaticEval; + Value bestValue, value, ttValue, eval, maxValue; bool ttHit, ttPv, inCheck, givesCheck, improving; - bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture; + 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; @@ -614,8 +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); @@ -624,7 +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 @@ -635,7 +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 = (ttHit && tte->is_pv()) || (PvNode && depth > 4 * ONE_PLY); + ttPv = PvNode || (ttHit && tte->is_pv()); // At non-PV nodes we check for an early TT cutoff if ( !PvNode @@ -653,9 +664,8 @@ namespace { if (!pos.capture_or_promotion(ttMove)) update_quiet_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth)); - // 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()) + // 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 @@ -723,16 +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(); + 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 @@ -745,13 +755,12 @@ namespace { { 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, ttPv, 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) @@ -775,7 +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)) @@ -807,7 +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); @@ -831,7 +840,7 @@ namespace { int probCutCount = 0; while ( (move = mp.next_move()) != MOVE_NONE - && probCutCount < 3) + && probCutCount < 2 + 2 * cutNode) if (move != excludedMove && pos.legal(move)) { probCutCount++; @@ -846,7 +855,7 @@ namespace { // Perform a preliminary qsearch to verify that the move holds value = -qsearch(pos, ss+1, -raisedBeta, -raisedBeta+1); - // If the qsearch held perform the regular search + // If the qsearch held, perform the regular search if (value >= raisedBeta) value = -search(pos, ss+1, -raisedBeta, -raisedBeta+1, depth - 4 * ONE_PLY, !cutNode); @@ -858,8 +867,7 @@ namespace { } // 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); @@ -870,7 +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, @@ -878,14 +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); + // 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)); @@ -906,16 +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) @@ -928,26 +945,35 @@ moves_loop: // When in check, search starts from here && move == ttMove && !rootNode && !excludedMove // Avoid recursive singular search - && ttValue != VALUE_NONE + /* && 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 singularBeta = 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, singularBeta - 1, singularBeta, depth / 2, cutNode); + value = search(pos, ss, singularBeta - 1, singularBeta, halfDepth, cutNode); ss->excludedMove = MOVE_NONE; 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 is multiple moves fail high, and we can prune the whole subtree by returning - // the hard beta bound. - else if (cutNode && singularBeta > beta) - return beta; + // 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; } // Check extension (~2 Elo) @@ -959,6 +985,19 @@ moves_loop: // When in check, search starts from here else if (type_of(move) == CASTLING) extension = ONE_PLY; + // Shuffle extension + else if ( PvNode + && pos.rule50_count() > 18 + && depth < 3 * ONE_PLY + && ++thisThread->shuffleExts < thisThread->nodes.load(std::memory_order_relaxed) / 4) // To avoid too many extensions + extension = ONE_PLY; + + // Passed pawn extension + else if ( move == ss->killers[0] + && pos.advanced_pawn_push(move) + && pos.pawn_passed(us, to_sq(move))) + extension = ONE_PLY; + // Calculate new depth for this move newDepth = depth - ONE_PLY + extension; @@ -967,19 +1006,20 @@ 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.advanced_pawn_push(move) || pos.non_pawn_material(~us) > BishopValueMg)) { // Move count based pruning (~30 Elo) if (moveCountPruning) - { - skipQuiets = true; continue; - } // Reduced depth of the next LMR search - int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY; + int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO); + lmrDepth /= ONE_PLY; // Countermoves based pruning (~20 Elo) if ( lmrDepth < 3 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1) @@ -997,8 +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; } @@ -1022,19 +1062,28 @@ 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 -= ONE_PLY; + 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) { // Increase reduction if ttMove is a capture (~0 Elo) @@ -1066,10 +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); @@ -1125,8 +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 @@ -1212,7 +1261,7 @@ moves_loop: // When in check, search starts from here 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); @@ -1220,8 +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) { @@ -1251,8 +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; @@ -1323,7 +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, @@ -1339,7 +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++; @@ -1374,6 +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; @@ -1473,7 +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; } @@ -1484,7 +1535,7 @@ moves_loop: // When in check, search starts from here void update_capture_stats(const Position& pos, Move move, 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))); @@ -1725,7 +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; }