X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=9ea77b3a4353c9808c2a8ce0139b2b833ba481a6;hp=6cf2f90d409f96dbe4f6a88ce625d71341153493;hb=2c1be0be8ec51005befcd4fc422e88b6e32cef45;hpb=5e91c5dcc8066e9f346a10010ddce70f2d317ef6 diff --git a/src/search.cpp b/src/search.cpp index 6cf2f90d..9ea77b3a 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -1,8 +1,6 @@ /* 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) 2015-2020 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad + Copyright (C) 2004-2020 The Stockfish developers (see AUTHORS file) Stockfish is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by @@ -64,10 +62,9 @@ namespace { constexpr uint64_t TtHitAverageWindow = 4096; constexpr uint64_t TtHitAverageResolution = 1024; - // Razor and futility margins - constexpr int RazorMargin = 527; + // Futility margin Value futility_margin(Depth d, bool improving) { - return Value(227 * (d - improving)); + return Value(234 * (d - improving)); } // Reductions lookup table, initialized at startup @@ -75,7 +72,7 @@ namespace { Depth reduction(bool i, Depth d, int mn) { int r = Reductions[d] * Reductions[mn]; - return (r + 570) / 1024 + (!i && r > 1018); + return (r + 503) / 1024 + (!i && r > 915); } constexpr int futility_move_count(bool improving, Depth depth) { @@ -84,7 +81,7 @@ namespace { // History and stats update bonus, based on depth int stat_bonus(Depth d) { - return d > 15 ? 27 : 17 * d * d + 133 * d - 134; + return d > 14 ? 29 : 8 * d * d + 224 * d - 215; } // Add a small random component to draw evaluations to avoid 3fold-blindness @@ -166,6 +163,8 @@ namespace { uint64_t perft(Position& pos, Depth depth) { StateInfo st; + ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize); + uint64_t cnt, nodes = 0; const bool leaf = (depth == 2); @@ -194,7 +193,7 @@ namespace { void Search::init() { for (int i = 1; i < MAX_MOVES; ++i) - Reductions[i] = int((24.8 + std::log(Threads.size())) * std::log(i)); + Reductions[i] = int((21.3 + 2 * std::log(Threads.size())) * std::log(i + 0.25 * std::log(i))); } @@ -227,6 +226,8 @@ void MainThread::search() { Time.init(Limits, us, rootPos.game_ply()); TT.new_search(); + Eval::NNUE::verify(); + if (rootMoves.empty()) { rootMoves.emplace_back(MOVE_NONE); @@ -335,7 +336,7 @@ void Thread::search() { // for match (TC 60+0.6) results spanning a wide range of k values. PRNG rng(now()); double floatLevel = Options["UCI_LimitStrength"] ? - Utility::clamp(std::pow((Options["UCI_Elo"] - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0) : + std::clamp(std::pow((Options["UCI_Elo"] - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0) : double(Options["Skill Level"]); int intLevel = int(floatLevel) + ((floatLevel - int(floatLevel)) * 1024 > rng.rand() % 1024 ? 1 : 0); @@ -403,12 +404,12 @@ void Thread::search() { if (rootDepth >= 4) { Value prev = rootMoves[pvIdx].previousScore; - delta = Value(19); + delta = Value(17); alpha = std::max(prev - delta,-VALUE_INFINITE); beta = std::min(prev + delta, VALUE_INFINITE); // Adjust contempt based on root move's previousScore (dynamic contempt) - int dct = ct + (110 - ct / 2) * prev / (abs(prev) + 140); + int dct = ct + (113 - ct / 2) * prev / (abs(prev) + 147); contempt = (us == WHITE ? make_score(dct, dct / 2) : -make_score(dct, dct / 2)); @@ -417,7 +418,7 @@ 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; + failedHighCnt = 0; while (true) { Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter); @@ -462,10 +463,7 @@ void Thread::search() { ++failedHighCnt; } else - { - ++rootMoves[pvIdx].bestMoveCount; break; - } delta += delta / 4 + 5; @@ -506,13 +504,13 @@ void Thread::search() { && !Threads.stop && !mainThread->stopOnPonderhit) { - double fallingEval = (296 + 6 * (mainThread->bestPreviousScore - bestValue) - + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 725.0; - fallingEval = Utility::clamp(fallingEval, 0.5, 1.5); + double fallingEval = (318 + 6 * (mainThread->bestPreviousScore - bestValue) + + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 825.0; + fallingEval = std::clamp(fallingEval, 0.5, 1.5); // If the bestMove is stable over several iterations, reduce time accordingly - timeReduction = lastBestMoveDepth + 10 < completedDepth ? 1.92 : 0.95; - double reduction = (1.47 + mainThread->previousTimeReduction) / (2.22 * timeReduction); + timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.92 : 0.95; + double reduction = (1.47 + mainThread->previousTimeReduction) / (2.32 * timeReduction); // Use part of the gained time from a previous stable move for the current move for (Thread* th : Threads) @@ -520,12 +518,16 @@ void Thread::search() { totBestMoveChanges += th->bestMoveChanges; th->bestMoveChanges = 0; } - double bestMoveInstability = 1 + totBestMoveChanges / Threads.size(); + double bestMoveInstability = 1 + 2 * totBestMoveChanges / Threads.size(); + + double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability; - double totalTime = rootMoves.size() == 1 ? 0 : - Time.optimum() * fallingEval * reduction * bestMoveInstability; + // Cap used time in case of a single legal move for a better viewer experience in tournaments + // yielding correct scores and sufficiently fast moves. + if (rootMoves.size() == 1) + totalTime = std::min(500.0, totalTime); - // Stop the search if we have exceeded the totalTime, at least 1ms search + // Stop the search if we have exceeded the totalTime if (Time.elapsed() > totalTime) { // If we are allowed to ponder do not stop the search now but @@ -537,7 +539,7 @@ void Thread::search() { } else if ( Threads.increaseDepth && !mainThread->ponder - && Time.elapsed() > totalTime * 0.56) + && Time.elapsed() > totalTime * 0.58) Threads.increaseDepth = false; else Threads.increaseDepth = true; @@ -568,6 +570,7 @@ namespace { constexpr bool PvNode = NT == PV; const bool rootNode = PvNode && ss->ply == 0; + const Depth maxNextDepth = rootNode ? depth : depth + 1; // Check if we have an upcoming move which draws by repetition, or // if the opponent had an alternative move earlier to this position. @@ -592,12 +595,14 @@ namespace { Move pv[MAX_PLY+1], capturesSearched[32], quietsSearched[64]; StateInfo st; + ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize); + TTEntry* tte; Key posKey; Move ttMove, move, excludedMove, bestMove; Depth extension, newDepth; - Value bestValue, value, ttValue, eval, maxValue, probcutBeta; - bool ttHit, ttPv, formerPv, givesCheck, improving, didLMR, priorCapture; + Value bestValue, value, ttValue, eval, maxValue, probCutBeta; + bool formerPv, givesCheck, improving, didLMR, priorCapture; bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture, singularQuietLMR; Piece movedPiece; @@ -644,6 +649,7 @@ namespace { assert(0 <= ss->ply && ss->ply < MAX_PLY); (ss+1)->ply = ss->ply + 1; + (ss+1)->ttPv = false; (ss+1)->excludedMove = bestMove = MOVE_NONE; (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE; Square prevSq = to_sq((ss-1)->currentMove); @@ -653,9 +659,7 @@ 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. - if (rootNode) - (ss+4)->statScore = 0; - else + if (!rootNode) (ss+2)->statScore = 0; // Step 4. Transposition table lookup. We don't want the score of a partial @@ -663,14 +667,16 @@ namespace { // position key in case of an excluded move. excludedMove = ss->excludedMove; posKey = excludedMove == MOVE_NONE ? pos.key() : pos.key() ^ make_key(excludedMove); - tte = TT.probe(posKey, ttHit); - ttValue = ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE; + tte = TT.probe(posKey, ss->ttHit); + ttValue = ss->ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE; ttMove = rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0] - : ttHit ? tte->move() : MOVE_NONE; - ttPv = PvNode || (ttHit && tte->is_pv()); - formerPv = ttPv && !PvNode; + : ss->ttHit ? tte->move() : MOVE_NONE; + if (!excludedMove) + ss->ttPv = PvNode || (ss->ttHit && tte->is_pv()); + formerPv = ss->ttPv && !PvNode; - if ( ttPv + // Update low ply history for previous move if we are near root and position is or has been in PV + if ( ss->ttPv && depth > 12 && ss->ply - 1 < MAX_LPH && !priorCapture @@ -679,11 +685,11 @@ namespace { // thisThread->ttHitAverage can be used to approximate the running average of ttHit thisThread->ttHitAverage = (TtHitAverageWindow - 1) * thisThread->ttHitAverage / TtHitAverageWindow - + TtHitAverageResolution * ttHit; + + TtHitAverageResolution * ss->ttHit; // At non-PV nodes we check for an early TT cutoff if ( !PvNode - && ttHit + && ss->ttHit && tte->depth() >= depth && ttValue != VALUE_NONE // Possible in case of TT access race && (ttValue >= beta ? (tte->bound() & BOUND_LOWER) @@ -694,6 +700,7 @@ namespace { { if (ttValue >= beta) { + // Bonus for a quiet ttMove that fails high if (!pos.capture_or_promotion(ttMove)) update_quiet_stats(pos, ss, ttMove, stat_bonus(depth), depth); @@ -710,6 +717,8 @@ namespace { } } + // Partial workaround for the graph history interaction problem + // For high rule50 counts don't produce transposition table cutoffs. if (pos.rule50_count() < 90) return ttValue; } @@ -748,7 +757,7 @@ namespace { if ( b == BOUND_EXACT || (b == BOUND_LOWER ? value >= beta : value <= alpha)) { - tte->save(posKey, value_to_tt(value, ss->ply), ttPv, b, + tte->save(posKey, value_to_tt(value, ss->ply), ss->ttPv, b, std::min(MAX_PLY - 1, depth + 6), MOVE_NONE, VALUE_NONE); @@ -776,13 +785,14 @@ namespace { improving = false; goto moves_loop; } - else if (ttHit) + else if (ss->ttHit) { // Never assume anything about values stored in TT ss->staticEval = eval = tte->eval(); if (eval == VALUE_NONE) ss->staticEval = eval = evaluate(pos); + // Randomize draw evaluation if (eval == VALUE_DRAW) eval = value_draw(thisThread); @@ -793,41 +803,46 @@ namespace { } else { + // In case of null move search use previous static eval with a different sign + // and addition of two tempos if ((ss-1)->currentMove != MOVE_NULL) - { - int bonus = -(ss-1)->statScore / 512; - - ss->staticEval = eval = evaluate(pos) + bonus; - } + ss->staticEval = eval = evaluate(pos); else ss->staticEval = eval = -(ss-1)->staticEval + 2 * Tempo; - tte->save(posKey, VALUE_NONE, ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval); + // Save static evaluation into transposition table + tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval); } - // Step 7. Razoring (~1 Elo) - if ( !rootNode // The required rootNode PV handling is not available in qsearch - && depth == 1 - && eval <= alpha - RazorMargin) - return qsearch(pos, ss, alpha, beta); + // Use static evaluation difference to improve quiet move ordering + if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture) + { + int bonus = std::clamp(-depth * 4 * int((ss-1)->staticEval + ss->staticEval - 2 * Tempo), -1000, 1000); + thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus; + } - improving = (ss-2)->staticEval == VALUE_NONE ? (ss->staticEval > (ss-4)->staticEval - || (ss-4)->staticEval == VALUE_NONE) : ss->staticEval > (ss-2)->staticEval; + // Set up improving flag that is used in various pruning heuristics + // We define position as improving if static evaluation of position is better + // Than the previous static evaluation at our turn + // In case of us being in check at our previous move we look at move prior to it + improving = (ss-2)->staticEval == VALUE_NONE + ? ss->staticEval > (ss-4)->staticEval || (ss-4)->staticEval == VALUE_NONE + : ss->staticEval > (ss-2)->staticEval; - // Step 8. Futility pruning: child node (~50 Elo) + // Step 7. Futility pruning: child node (~50 Elo) if ( !PvNode - && depth < 6 + && depth < 9 && eval - futility_margin(depth, improving) >= beta && eval < VALUE_KNOWN_WIN) // Do not return unproven wins return eval; - // Step 9. Null move search with verification search (~40 Elo) + // Step 8. Null move search with verification search (~40 Elo) if ( !PvNode && (ss-1)->currentMove != MOVE_NULL - && (ss-1)->statScore < 23824 + && (ss-1)->statScore < 22977 && eval >= beta && eval >= ss->staticEval - && ss->staticEval >= beta - 33 * depth - 33 * improving + 112 * ttPv + 311 + && ss->staticEval >= beta - 30 * depth - 28 * improving + 84 * ss->ttPv + 168 && !excludedMove && pos.non_pawn_material(us) && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor)) @@ -835,7 +850,7 @@ namespace { assert(eval - beta >= 0); // Null move dynamic reduction based on depth and value - Depth R = (737 + 77 * depth) / 246 + std::min(int(eval - beta) / 192, 3); + Depth R = (1015 + 85 * depth) / 256 + std::min(int(eval - beta) / 191, 3); ss->currentMove = MOVE_NULL; ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0]; @@ -852,7 +867,7 @@ namespace { if (nullValue >= VALUE_TB_WIN_IN_MAX_PLY) nullValue = beta; - if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 13)) + if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 14)) return nullValue; assert(!thisThread->nmpMinPly); // Recursive verification is not allowed @@ -871,30 +886,38 @@ namespace { } } - probcutBeta = beta + 176 - 49 * improving; + probCutBeta = beta + 194 - 49 * improving; - // Step 10. ProbCut (~10 Elo) + // Step 9. 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 > 4 && abs(beta) < VALUE_TB_WIN_IN_MAX_PLY - && !( ttHit + // if value from transposition table is lower than probCutBeta, don't attempt probCut + // there and in further interactions with transposition table cutoff depth is set to depth - 3 + // because probCut search has depth set to depth - 4 but we also do a move before it + // so effective depth is equal to depth - 3 + && !( ss->ttHit && tte->depth() >= depth - 3 && ttValue != VALUE_NONE - && ttValue < probcutBeta)) + && ttValue < probCutBeta)) { - if ( ttHit + // if ttMove is a capture and value from transposition table is good enough produce probCut + // cutoff without digging into actual probCut search + if ( ss->ttHit && tte->depth() >= depth - 3 && ttValue != VALUE_NONE - && ttValue >= probcutBeta + && ttValue >= probCutBeta && ttMove && pos.capture_or_promotion(ttMove)) - return probcutBeta; + return probCutBeta; - assert(probcutBeta < VALUE_INFINITE); - MovePicker mp(pos, ttMove, probcutBeta - ss->staticEval, &captureHistory); + assert(probCutBeta < VALUE_INFINITE); + MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory); int probCutCount = 0; + bool ttPv = ss->ttPv; + ss->ttPv = false; while ( (move = mp.next_move()) != MOVE_NONE && probCutCount < 2 + 2 * cutNode) @@ -915,33 +938,34 @@ namespace { pos.do_move(move, st); // Perform a preliminary qsearch to verify that the move holds - value = -qsearch(pos, ss+1, -probcutBeta, -probcutBeta+1); + value = -qsearch(pos, ss+1, -probCutBeta, -probCutBeta+1); // If the qsearch held, perform the regular search - if (value >= probcutBeta) - value = -search(pos, ss+1, -probcutBeta, -probcutBeta+1, depth - 4, !cutNode); + if (value >= probCutBeta) + value = -search(pos, ss+1, -probCutBeta, -probCutBeta+1, depth - 4, !cutNode); pos.undo_move(move); - if (value >= probcutBeta) + if (value >= probCutBeta) { - tte->save(posKey, value_to_tt(value, ss->ply), ttPv, - BOUND_LOWER, - depth - 3, move, ss->staticEval); + // if transposition table doesn't have equal or more deep info write probCut data into it + if ( !(ss->ttHit + && tte->depth() >= depth - 3 + && ttValue != VALUE_NONE)) + tte->save(posKey, value_to_tt(value, ss->ply), ttPv, + BOUND_LOWER, + depth - 3, move, ss->staticEval); return value; } } + ss->ttPv = ttPv; } - // Step 11. Internal iterative deepening (~1 Elo) - if (depth >= 7 && !ttMove) - { - search(pos, ss, alpha, beta, depth - 7, cutNode); - - tte = TT.probe(posKey, ttHit); - ttValue = ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE; - ttMove = ttHit ? tte->move() : MOVE_NONE; - } + // Step 10. If the position is not in TT, decrease depth by 2 + if ( PvNode + && depth >= 6 + && !ttMove) + depth -= 2; moves_loop: // When in check, search starts from here @@ -966,7 +990,7 @@ moves_loop: // When in check, search starts from here // Mark this node as being searched ThreadHolding th(thisThread, posKey, ss->ply); - // Step 12. Loop through all pseudo-legal moves until no moves remain + // Step 11. Loop through all pseudo-legal moves until no moves remain // or a beta cutoff occurs. while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE) { @@ -983,6 +1007,10 @@ moves_loop: // When in check, search starts from here thisThread->rootMoves.begin() + thisThread->pvLast, move)) continue; + // Check for legality + if (!rootNode && !pos.legal(move)) + continue; + ss->moveCount = ++moveCount; if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000) @@ -1000,7 +1028,7 @@ moves_loop: // When in check, search starts from here // Calculate new depth for this move newDepth = depth - 1; - // Step 13. Pruning at shallow depth (~200 Elo) + // Step 12. Pruning at shallow depth (~200 Elo) if ( !rootNode && pos.non_pawn_material(us) && bestValue > VALUE_TB_LOSS_IN_MAX_PLY) @@ -1011,8 +1039,20 @@ 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), 0); - if ( !captureOrPromotion - && !givesCheck) + if ( captureOrPromotion + || givesCheck) + { + // Capture history based pruning when the move doesn't give check + if ( !givesCheck + && lmrDepth < 1 + && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0) + continue; + + // SEE based pruning + if (!pos.see_ge(move, Value(-218) * depth)) // (~25 Elo) + continue; + } + else { // Countermoves based pruning (~20 Elo) if ( lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1) @@ -1021,59 +1061,36 @@ moves_loop: // When in check, search starts from here continue; // Futility pruning: parent node (~5 Elo) - if ( lmrDepth < 6 + if ( lmrDepth < 7 && !ss->inCheck - && ss->staticEval + 284 + 188 * lmrDepth <= alpha + && ss->staticEval + 254 + 159 * lmrDepth <= alpha && (*contHist[0])[movedPiece][to_sq(move)] + (*contHist[1])[movedPiece][to_sq(move)] + (*contHist[3])[movedPiece][to_sq(move)] - + (*contHist[5])[movedPiece][to_sq(move)] / 2 < 28388) + + (*contHist[5])[movedPiece][to_sq(move)] / 2 < 26394) continue; // Prune moves with negative SEE (~20 Elo) - if (!pos.see_ge(move, Value(-(29 - std::min(lmrDepth, 17)) * lmrDepth * lmrDepth))) - continue; - } - else - { - // Capture history based pruning when the move doesn't give check - if ( !givesCheck - && lmrDepth < 1 - && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0) - continue; - - // Futility pruning for captures - if ( !givesCheck - && lmrDepth < 6 - && !(PvNode && abs(bestValue) < 2) - && PieceValue[MG][type_of(movedPiece)] >= PieceValue[MG][type_of(pos.piece_on(to_sq(move)))] - && !ss->inCheck - && ss->staticEval + 267 + 391 * lmrDepth - + PieceValue[MG][type_of(pos.piece_on(to_sq(move)))] <= alpha) - continue; - - // See based pruning - if (!pos.see_ge(move, Value(-202) * depth)) // (~25 Elo) + if (!pos.see_ge(move, Value(-(30 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth))) continue; } } - // Step 14. Extensions (~75 Elo) + // Step 13. Extensions (~75 Elo) // Singular extension search (~70 Elo). If all moves but one fail low on a // search of (alpha-s, beta-s), and just one fails high on (alpha, beta), // then that move is singular and should be extended. To verify this we do // a reduced search on all the other moves but the ttMove and if the - // result is lower than ttValue minus a margin then we will extend the ttMove. - if ( depth >= 6 + // result is lower than ttValue minus a margin, then we will extend the ttMove. + if ( depth >= 7 && move == ttMove && !rootNode && !excludedMove // Avoid recursive singular search /* && ttValue != VALUE_NONE Already implicit in the next condition */ && abs(ttValue) < VALUE_KNOWN_WIN && (tte->bound() & BOUND_LOWER) - && tte->depth() >= depth - 3 - && pos.legal(move)) + && tte->depth() >= depth - 3) { Value singularBeta = ttValue - ((formerPv + 4) * depth) / 2; Depth singularDepth = (depth - 1 + 3 * formerPv) / 2; @@ -1113,40 +1130,17 @@ moves_loop: // When in check, search starts from here && (pos.is_discovery_check_on_king(~us, move) || pos.see_ge(move))) extension = 1; - // Passed pawn extension - else if ( move == ss->killers[0] - && pos.advanced_pawn_push(move) - && pos.pawn_passed(us, to_sq(move))) - extension = 1; - // Last captures extension else if ( PieceValue[EG][pos.captured_piece()] > PawnValueEg && pos.non_pawn_material() <= 2 * RookValueMg) extension = 1; - // Castling extension - if (type_of(move) == CASTLING) - extension = 1; - - // Late irreversible move extension - if ( move == ttMove - && pos.rule50_count() > 80 - && (captureOrPromotion || type_of(movedPiece) == PAWN)) - extension = 2; - // Add extension to new depth newDepth += extension; // Speculative prefetch as early as possible prefetch(TT.first_entry(pos.key_after(move))); - // Check for legality just before making the move - if (!rootNode && !pos.legal(move)) - { - ss->moveCount = --moveCount; - continue; - } - // Update the current move (this must be done after singular extension search) ss->currentMove = move; ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck] @@ -1154,34 +1148,39 @@ moves_loop: // When in check, search starts from here [movedPiece] [to_sq(move)]; - // Step 15. Make the move + // Step 14. Make the move pos.do_move(move, st, givesCheck); - // Step 16. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be + // Step 15. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be // re-searched at full depth. if ( depth >= 3 && moveCount > 1 + 2 * rootNode - && (!rootNode || thisThread->best_move_count(move) == 0) && ( !captureOrPromotion || moveCountPruning || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha || cutNode - || thisThread->ttHitAverage < 415 * TtHitAverageResolution * TtHitAverageWindow / 1024)) + || (!PvNode && !formerPv && thisThread->captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 4506) + || thisThread->ttHitAverage < 432 * TtHitAverageResolution * TtHitAverageWindow / 1024)) { Depth r = reduction(improving, depth, moveCount); // Decrease reduction if the ttHit running average is large - if (thisThread->ttHitAverage > 473 * TtHitAverageResolution * TtHitAverageWindow / 1024) + if (thisThread->ttHitAverage > 537 * TtHitAverageResolution * TtHitAverageWindow / 1024) r--; - // Reduction if other threads are searching this position + // Increase reduction if other threads are searching this position if (th.marked()) r++; // Decrease reduction if position is or has been on the PV (~10 Elo) - if (ttPv) + if (ss->ttPv) r -= 2; + // Increase reduction at root and non-PV nodes when the best move does not change frequently + if ((rootNode || !PvNode) && thisThread->rootDepth > 10 && thisThread->bestMoveChanges <= 2) + r++; + + // More reductions for late moves if position was not in previous PV if (moveCountPruning && !formerPv) r++; @@ -1191,14 +1190,24 @@ moves_loop: // When in check, search starts from here // Decrease reduction if ttMove has been singularly extended (~3 Elo) if (singularQuietLMR) - r -= 1 + formerPv; + r--; - if (!captureOrPromotion) + if (captureOrPromotion) + { + // Unless giving check, this capture is likely bad + if ( !givesCheck + && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 210 * depth <= alpha) + r++; + } + else { // Increase reduction if ttMove is a capture (~5 Elo) if (ttCapture) r++; + // Increase reduction at root if failing high + r += rootNode ? thisThread->failedHighCnt * thisThread->failedHighCnt * moveCount / 512 : 0; + // Increase reduction for cut nodes (~10 Elo) if (cutNode) r += 2; @@ -1208,37 +1217,26 @@ moves_loop: // When in check, search starts from here // hence break make_move(). (~2 Elo) else if ( type_of(move) == NORMAL && !pos.see_ge(reverse_move(move))) - r -= 2 + ttPv - (type_of(movedPiece) == PAWN); + r -= 2 + ss->ttPv - (type_of(movedPiece) == PAWN); ss->statScore = thisThread->mainHistory[us][from_to(move)] + (*contHist[0])[movedPiece][to_sq(move)] + (*contHist[1])[movedPiece][to_sq(move)] + (*contHist[3])[movedPiece][to_sq(move)] - - 4826; + - 5287; // Decrease/increase reduction by comparing opponent's stat score (~10 Elo) - if (ss->statScore >= -100 && (ss-1)->statScore < -112) + if (ss->statScore >= -105 && (ss-1)->statScore < -103) r--; - else if ((ss-1)->statScore >= -125 && ss->statScore < -138) + else if ((ss-1)->statScore >= -122 && ss->statScore < -129) r++; // Decrease/increase reduction for moves with a good/bad history (~30 Elo) - r -= ss->statScore / 14615; - } - else - { - // Increase reduction for captures/promotions if late move and at low depth - if (depth < 8 && moveCount > 2) - r++; - - // Unless giving check, this capture is likely bad - if ( !givesCheck - && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 211 * depth <= alpha) - r++; + r -= ss->statScore / 14884; } - Depth d = Utility::clamp(newDepth - r, 1, newDepth); + Depth d = std::clamp(newDepth - r, 1, newDepth); value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); @@ -1253,19 +1251,17 @@ moves_loop: // When in check, search starts from here didLMR = false; } - // Step 17. Full depth search when LMR is skipped or fails high + // Step 16. Full depth search when LMR is skipped or fails high if (doFullDepthSearch) { value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); + // If the move passed LMR update its stats if (didLMR && !captureOrPromotion) { int bonus = value > alpha ? stat_bonus(newDepth) : -stat_bonus(newDepth); - if (move == ss->killers[0]) - bonus += bonus / 4; - update_continuation_histories(ss, movedPiece, to_sq(move), bonus); } } @@ -1278,15 +1274,16 @@ moves_loop: // When in check, search starts from here (ss+1)->pv = pv; (ss+1)->pv[0] = MOVE_NONE; - value = -search(pos, ss+1, -beta, -alpha, newDepth, false); + value = -search(pos, ss+1, -beta, -alpha, + std::min(maxNextDepth, newDepth), false); } - // Step 18. Undo move + // Step 17. Undo move pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); - // Step 19. Check for a new best move + // Step 18. 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. @@ -1311,8 +1308,7 @@ moves_loop: // When in check, search starts from here rm.pv.push_back(*m); // We record how often the best move has been changed in each - // iteration. This information is used for time management: when - // the best move changes frequently, we allocate some more time. + // iteration. This information is used for time management and LMR if (moveCount > 1) ++thisThread->bestMoveChanges; } @@ -1345,6 +1341,7 @@ moves_loop: // When in check, search starts from here } } + // If the move is worse than some previously searched move, remember it to update its stats later if (move != bestMove) { if (captureOrPromotion && captureCount < 32) @@ -1363,7 +1360,7 @@ moves_loop: // When in check, search starts from here return VALUE_DRAW; */ - // Step 20. Check for mate and stalemate + // Step 19. Check for mate and stalemate // All legal moves have been searched and if there are no legal moves, it // must be a mate or a stalemate. If we are in a singular extension search then // return a fail low score. @@ -1374,6 +1371,7 @@ moves_loop: // When in check, search starts from here bestValue = excludedMove ? alpha : ss->inCheck ? mated_in(ss->ply) : VALUE_DRAW; + // If there is a move which produces search value greater than alpha we update stats of searched moves else if (bestMove) update_all_stats(pos, ss, bestMove, bestValue, beta, prevSq, quietsSearched, quietCount, capturesSearched, captureCount, depth); @@ -1386,8 +1384,18 @@ moves_loop: // When in check, search starts from here if (PvNode) bestValue = std::min(bestValue, maxValue); + // If no good move is found and the previous position was ttPv, then the previous + // opponent move is probably good and the new position is added to the search tree. + if (bestValue <= alpha) + ss->ttPv = ss->ttPv || ((ss-1)->ttPv && depth > 3); + // Otherwise, a counter move has been found and if the position is the last leaf + // in the search tree, remove the position from the search tree. + else if (depth > 3) + ss->ttPv = ss->ttPv && (ss+1)->ttPv; + + // Write gathered information in transposition table if (!excludedMove && !(rootNode && thisThread->pvIdx)) - tte->save(posKey, value_to_tt(bestValue, ss->ply), ttPv, + tte->save(posKey, value_to_tt(bestValue, ss->ply), ss->ttPv, bestValue >= beta ? BOUND_LOWER : PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER, depth, bestMove, ss->staticEval); @@ -1411,12 +1419,14 @@ moves_loop: // When in check, search starts from here Move pv[MAX_PLY+1]; StateInfo st; + ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize); + TTEntry* tte; Key posKey; Move ttMove, move, bestMove; Depth ttDepth; Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha; - bool ttHit, pvHit, givesCheck, captureOrPromotion; + bool pvHit, givesCheck, captureOrPromotion; int moveCount; if (PvNode) @@ -1446,13 +1456,13 @@ moves_loop: // When in check, search starts from here : DEPTH_QS_NO_CHECKS; // Transposition table lookup posKey = pos.key(); - tte = TT.probe(posKey, ttHit); - ttValue = ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE; - ttMove = ttHit ? tte->move() : MOVE_NONE; - pvHit = ttHit && tte->is_pv(); + tte = TT.probe(posKey, ss->ttHit); + ttValue = ss->ttHit ? value_from_tt(tte->value(), ss->ply, pos.rule50_count()) : VALUE_NONE; + ttMove = ss->ttHit ? tte->move() : MOVE_NONE; + pvHit = ss->ttHit && tte->is_pv(); if ( !PvNode - && ttHit + && ss->ttHit && tte->depth() >= ttDepth && ttValue != VALUE_NONE // Only in case of TT access race && (ttValue >= beta ? (tte->bound() & BOUND_LOWER) @@ -1467,7 +1477,7 @@ moves_loop: // When in check, search starts from here } else { - if (ttHit) + if (ss->ttHit) { // Never assume anything about values stored in TT if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE) @@ -1479,6 +1489,8 @@ moves_loop: // When in check, search starts from here bestValue = ttValue; } else + // In case of null move search use previous static eval with a different sign + // and addition of two tempos ss->staticEval = bestValue = (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Tempo; @@ -1486,7 +1498,8 @@ moves_loop: // When in check, search starts from here // Stand pat. Return immediately if static value is at least beta if (bestValue >= beta) { - if (!ttHit) + // Save gathered info in transposition table + if (!ss->ttHit) tte->save(posKey, value_to_tt(bestValue, ss->ply), false, BOUND_LOWER, DEPTH_NONE, MOVE_NONE, ss->staticEval); @@ -1496,7 +1509,7 @@ moves_loop: // When in check, search starts from here if (PvNode && bestValue > alpha) alpha = bestValue; - futilityBase = bestValue + 141; + futilityBase = bestValue + 155; } const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, @@ -1523,13 +1536,17 @@ moves_loop: // When in check, search starts from here moveCount++; // Futility pruning - if ( !ss->inCheck + if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY && !givesCheck && futilityBase > -VALUE_KNOWN_WIN && !pos.advanced_pawn_push(move)) { assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push + // moveCount pruning + if (moveCount > 2) + continue; + futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))]; if (futilityValue <= alpha) @@ -1546,7 +1563,8 @@ moves_loop: // When in check, search starts from here } // Do not search moves with negative SEE values - if ( !ss->inCheck && !pos.see_ge(move)) + if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY + && !pos.see_ge(move)) continue; // Speculative prefetch as early as possible @@ -1565,6 +1583,13 @@ moves_loop: // When in check, search starts from here [pos.moved_piece(move)] [to_sq(move)]; + // CounterMove based pruning + if ( !captureOrPromotion + && bestValue > VALUE_TB_LOSS_IN_MAX_PLY + && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold + && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold) + continue; + // Make and search the move pos.do_move(move, st, givesCheck); value = -qsearch(pos, ss+1, -beta, -alpha, depth - 1); @@ -1595,8 +1620,13 @@ 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 (ss->inCheck && bestValue == -VALUE_INFINITE) + { + assert(!MoveList(pos).size()); + return mated_in(ss->ply); // Plies to mate from the root + } + // Save gathered info in transposition table tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit, bestValue >= beta ? BOUND_LOWER : PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER, @@ -1680,9 +1710,10 @@ moves_loop: // When in check, search starts from here if (!pos.capture_or_promotion(bestMove)) { + // Increase stats for the best move in case it was a quiet move update_quiet_stats(pos, ss, bestMove, bonus2, depth); - // Decrease all the non-best quiet moves + // Decrease stats for all non-best quiet moves for (int i = 0; i < quietCount; ++i) { thisThread->mainHistory[us][from_to(quietsSearched[i])] << -bonus2; @@ -1690,14 +1721,16 @@ moves_loop: // When in check, search starts from here } } else + // Increase stats for the best move in case it was a capture move captureHistory[moved_piece][to_sq(bestMove)][captured] << bonus1; - // 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])) + // Extra penalty for a quiet early move that was not a TT move or + // main killer move in previous ply when it gets refuted. + if ( ((ss-1)->moveCount == 1 + (ss-1)->ttHit || ((ss-1)->currentMove == (ss-1)->killers[0])) && !pos.captured_piece()) update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -bonus1); - // Decrease all the non-best capture moves + // Decrease stats for all non-best capture moves for (int i = 0; i < captureCount; ++i) { moved_piece = pos.moved_piece(capturesSearched[i]); @@ -1714,6 +1747,7 @@ moves_loop: // When in check, search starts from here for (int i : {1, 2, 4, 6}) { + // Only update first 2 continuation histories if we are in check if (ss->inCheck && i > 2) break; if (is_ok((ss-i)->currentMove)) @@ -1726,6 +1760,7 @@ moves_loop: // When in check, search starts from here void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus, int depth) { + // Update killers if (ss->killers[0] != move) { ss->killers[1] = ss->killers[0]; @@ -1737,17 +1772,20 @@ moves_loop: // When in check, search starts from here thisThread->mainHistory[us][from_to(move)] << bonus; update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus); + // Penalty for reversed move in case of moved piece not being a pawn if (type_of(pos.moved_piece(move)) != PAWN) thisThread->mainHistory[us][from_to(reverse_move(move))] << -bonus; + // Update countermove history if (is_ok((ss-1)->currentMove)) { Square prevSq = to_sq((ss-1)->currentMove); thisThread->counterMoves[pos.piece_on(prevSq)][prevSq] = move; } + // Update low ply history if (depth > 11 && ss->ply < MAX_LPH) - thisThread->lowPlyHistory[ss->ply][from_to(move)] << stat_bonus(depth - 6); + thisThread->lowPlyHistory[ss->ply][from_to(move)] << stat_bonus(depth - 7); } // When playing with strength handicap, choose best move among a set of RootMoves @@ -1836,12 +1874,15 @@ string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) { { bool updated = rootMoves[i].score != -VALUE_INFINITE; - if (depth == 1 && !updated) + if (depth == 1 && !updated && i > 0) continue; - Depth d = updated ? depth : depth - 1; + Depth d = updated ? depth : std::max(1, depth - 1); Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore; + if (v == -VALUE_INFINITE) + v = VALUE_ZERO; + bool tb = TB::RootInTB && abs(v) < VALUE_MATE_IN_MAX_PLY; v = tb ? rootMoves[i].tbScore : v; @@ -1886,6 +1927,8 @@ string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) { bool RootMove::extract_ponder_from_tt(Position& pos) { StateInfo st; + ASSERT_ALIGNED(&st, Eval::NNUE::kCacheLineSize); + bool ttHit; assert(pv.size() == 1); @@ -1939,7 +1982,7 @@ void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) { if (RootInTB) { // Sort moves according to TB rank - std::sort(rootMoves.begin(), rootMoves.end(), + std::stable_sort(rootMoves.begin(), rootMoves.end(), [](const RootMove &a, const RootMove &b) { return a.tbRank > b.tbRank; } ); // Probe during search only if DTZ is not available and we are winning