X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=fef1b518160abf00e7e6e4ac14a7e656d2ed4046;hp=99c2b09f9ef42b4032c95864e7f4e0e497147ec5;hb=d558f8a673b56b32ab6da8050f41b9e02fe1758b;hpb=c0ff241464338f7e5bb815b4f72c2a95d12244a0 diff --git a/src/search.cpp b/src/search.cpp index 99c2b09f..fef1b518 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -59,14 +59,14 @@ using namespace Search; namespace { // Different node types, used as a template parameter - enum NodeType { NonPV, PV }; + enum NodeType { NonPV, PV, Root }; constexpr uint64_t TtHitAverageWindow = 4096; constexpr uint64_t TtHitAverageResolution = 1024; // Futility margin Value futility_margin(Depth d, bool improving) { - return Value(234 * (d - improving)); + return Value(214 * (d - improving)); } // Reductions lookup table, initialized at startup @@ -74,7 +74,7 @@ namespace { Depth reduction(bool i, Depth d, int mn) { int r = Reductions[d] * Reductions[mn]; - return (r + 503) / 1024 + (!i && r > 915); + return (r + 534) / 1024 + (!i && r > 904); } constexpr int futility_move_count(bool improving, Depth depth) { @@ -83,7 +83,7 @@ namespace { // History and stats update bonus, based on depth int stat_bonus(Depth d) { - return d > 14 ? 66 : 6 * d * d + 231 * d - 206; + return d > 14 ? 73 : 6 * d * d + 229 * d - 215; } // Add a small random component to draw evaluations to avoid 3-fold blindness @@ -102,53 +102,10 @@ 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 structure 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 by the constructor, and unmarked upon leaving that loop by the destructor. - 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 + template Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode); - template + template Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = 0); Value value_to_tt(Value v, int ply); @@ -195,7 +152,7 @@ namespace { void Search::init() { for (int i = 1; i < MAX_MOVES; ++i) - Reductions[i] = int((21.3 + 2 * std::log(Threads.size())) * std::log(i + 0.25 * std::log(i))); + Reductions[i] = int(21.9 * std::log(i)); } @@ -296,7 +253,7 @@ void Thread::search() { // 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. + // The latter is needed for statScore and killer initialization. Stack stack[MAX_PLY+10], *ss = stack+7; Move pv[MAX_PLY+1]; Value bestValue, alpha, beta, delta; @@ -311,6 +268,9 @@ void Thread::search() { for (int i = 7; i > 0; i--) (ss-i)->continuationHistory = &this->continuationHistory[0][0][NO_PIECE][0]; // Use as a sentinel + for (int i = 0; i <= MAX_PLY + 2; ++i) + (ss+i)->ply = i; + ss->pv = pv; bestValue = delta = alpha = -VALUE_INFINITE; @@ -352,19 +312,7 @@ void Thread::search() { multiPV = std::min(multiPV, rootMoves.size()); ttHitAverage = TtHitAverageWindow * TtHitAverageResolution / 2; - int ct = int(Options["Contempt"]) * PawnValueEg / 100; // From centipawns - - // In analysis mode, adjust contempt in accordance with user preference - if (Limits.infinite || Options["UCI_AnalyseMode"]) - ct = Options["Analysis Contempt"] == "Off" ? 0 - : Options["Analysis Contempt"] == "Both" ? ct - : Options["Analysis Contempt"] == "White" && us == BLACK ? -ct - : Options["Analysis Contempt"] == "Black" && us == WHITE ? -ct - : ct; - - // Evaluation score is from the white point of view - contempt = (us == WHITE ? make_score(ct, ct / 2) - : -make_score(ct, ct / 2)); + trend = SCORE_ZERO; int searchAgainCounter = 0; @@ -410,21 +358,21 @@ void Thread::search() { 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 + (113 - ct / 2) * prev / (abs(prev) + 147); + // Adjust trend based on root move's previousScore (dynamic contempt) + int tr = 113 * prev / (abs(prev) + 147); - contempt = (us == WHITE ? make_score(dct, dct / 2) - : -make_score(dct, dct / 2)); + trend = (us == WHITE ? make_score(tr, tr / 2) + : -make_score(tr, tr / 2)); } // Start with a small aspiration window and, in the case of a fail // high/low, re-search with a bigger window until we don't fail // high/low anymore. - failedHighCnt = 0; + int failedHighCnt = 0; while (true) { Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter); - bestValue = Stockfish::search(rootPos, ss, alpha, beta, adjustedDepth, false); + bestValue = Stockfish::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 @@ -520,8 +468,8 @@ void Thread::search() { totBestMoveChanges += th->bestMoveChanges; th->bestMoveChanges = 0; } - double bestMoveInstability = 1 + 2 * totBestMoveChanges / Threads.size(); - + double bestMoveInstability = 1.073 + std::max(1.0, 2.25 - 9.9 / rootDepth) + * totBestMoveChanges / Threads.size(); double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability; // Cap used time in case of a single legal move for a better viewer experience in tournaments @@ -567,18 +515,18 @@ namespace { // search<>() is the main search function for both PV and non-PV nodes - template + template Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) { - constexpr bool PvNode = NT == PV; - const bool rootNode = PvNode && ss->ply == 0; + constexpr bool PvNode = nodeType != NonPV; + constexpr bool rootNode = nodeType == Root; 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. - if ( pos.rule50_count() >= 3 + if ( !rootNode + && pos.rule50_count() >= 3 && alpha < VALUE_DRAW - && !rootNode && pos.has_game_cycle(ss->ply)) { alpha = value_draw(pos.this_thread()); @@ -588,7 +536,7 @@ namespace { // Dive into quiescence search when the depth reaches zero if (depth <= 0) - return qsearch(pos, ss, alpha, beta); + return qsearch(pos, ss, alpha, beta); assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE); assert(PvNode || (alpha == beta - 1)); @@ -604,7 +552,7 @@ namespace { Move ttMove, move, excludedMove, bestMove; Depth extension, newDepth; Value bestValue, value, ttValue, eval, maxValue, probCutBeta; - bool formerPv, givesCheck, improving, didLMR, priorCapture; + bool givesCheck, improving, didLMR, priorCapture; bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture, singularQuietLMR; Piece movedPiece; @@ -650,11 +598,11 @@ namespace { assert(0 <= ss->ply && ss->ply < MAX_PLY); - (ss+1)->ply = ss->ply + 1; - (ss+1)->ttPv = false; + (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); + (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE; + ss->doubleExtensions = (ss-1)->doubleExtensions; + Square prevSq = to_sq((ss-1)->currentMove); // Initialize statScore to zero for the grandchildren of the current position. // So statScore is shared between all grandchildren and only the first grandchild @@ -675,7 +623,6 @@ namespace { : ss->ttHit ? tte->move() : MOVE_NONE; if (!excludedMove) ss->ttPv = PvNode || (ss->ttHit && tte->is_pv()); - formerPv = ss->ttPv && !PvNode; // Update low ply history for previous move if we are near root and position is or has been in PV if ( ss->ttPv @@ -810,16 +757,17 @@ namespace { if ((ss-1)->currentMove != MOVE_NULL) ss->staticEval = eval = evaluate(pos); else - ss->staticEval = eval = -(ss-1)->staticEval + 2 * Tempo; + ss->staticEval = eval = -(ss-1)->staticEval; // Save static evaluation into transposition table + if(!excludedMove) tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval); } // 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); + int bonus = std::clamp(-depth * 4 * int((ss-1)->staticEval + ss->staticEval), -1000, 1000); thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus; } @@ -833,7 +781,6 @@ namespace { // Step 7. Futility pruning: child node (~50 Elo) if ( !PvNode - && depth < 9 && eval - futility_margin(depth, improving) >= beta && eval < VALUE_KNOWN_WIN) // Do not return unproven wins return eval; @@ -841,10 +788,10 @@ namespace { // Step 8. Null move search with verification search (~40 Elo) if ( !PvNode && (ss-1)->currentMove != MOVE_NULL - && (ss-1)->statScore < 24185 + && (ss-1)->statScore < 23767 && eval >= beta && eval >= ss->staticEval - && ss->staticEval >= beta - 24 * depth - 34 * improving + 162 * ss->ttPv + 159 + && ss->staticEval >= beta - 20 * depth - 22 * improving + 168 * ss->ttPv + 159 && !excludedMove && pos.non_pawn_material(us) && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor)) @@ -852,7 +799,7 @@ namespace { assert(eval - beta >= 0); // Null move dynamic reduction based on depth and value - Depth R = (1062 + 68 * depth) / 256 + std::min(int(eval - beta) / 190, 3); + Depth R = (1090 + 81 * depth) / 256 + std::min(int(eval - beta) / 205, 3); ss->currentMove = MOVE_NULL; ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0]; @@ -890,7 +837,7 @@ namespace { probCutBeta = beta + 209 - 44 * improving; - // Step 9. ProbCut (~10 Elo) + // Step 9. ProbCut (~4 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 @@ -905,16 +852,6 @@ namespace { && ttValue != VALUE_NONE && ttValue < probCutBeta)) { - // 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 - && ttMove - && pos.capture_or_promotion(ttMove)) - return probCutBeta; - assert(probCutBeta < VALUE_INFINITE); MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory); @@ -975,7 +912,7 @@ moves_loop: // When in check, search starts from here ttCapture = ttMove && pos.capture_or_promotion(ttMove); // Step 11. A small Probcut idea, when we are in check - probCutBeta = beta + 400; + probCutBeta = beta + 409; if ( ss->inCheck && !PvNode && depth >= 4 @@ -1005,9 +942,14 @@ moves_loop: // When in check, search starts from here value = bestValue; singularQuietLMR = moveCountPruning = false; + bool doubleExtension = false; - // Mark this node as being searched - ThreadHolding th(thisThread, posKey, ss->ply); + // Indicate PvNodes that will probably fail low if the node was searched + // at a depth equal or greater than the current depth, and the result of this search was a fail low. + bool likelyFailLow = PvNode + && ttMove + && (tte->bound() & BOUND_UPPER) + && tte->depth() >= depth; // Step 12. Loop through all pseudo-legal moves until no moves remain // or a beta cutoff occurs. @@ -1044,14 +986,6 @@ moves_loop: // When in check, search starts from here movedPiece = pos.moved_piece(move); givesCheck = pos.gives_check(move); - // Indicate PvNodes that will probably fail low if node was searched with non-PV search - // at depth equal or greater to current depth and result of this search was far below alpha - bool likelyFailLow = PvNode - && ttMove - && (tte->bound() & BOUND_UPPER) - && ttValue < alpha + 200 + 100 * depth - && tte->depth() >= depth; - // Calculate new depth for this move newDepth = depth - 1; @@ -1081,15 +1015,14 @@ moves_loop: // When in check, search starts from here } else { - // Countermoves based pruning (~20 Elo) - if ( lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1) + // Continuation history based pruning (~20 Elo) + if ( lmrDepth < 5 && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold) continue; // Futility pruning: parent node (~5 Elo) - if ( lmrDepth < 7 - && !ss->inCheck + if ( !ss->inCheck && ss->staticEval + 174 + 157 * lmrDepth <= alpha && (*contHist[0])[movedPiece][to_sq(move)] + (*contHist[1])[movedPiece][to_sq(move)] @@ -1110,17 +1043,17 @@ moves_loop: // When in check, search starts from here // 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 >= 7 + if ( !rootNode + && 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) { - Value singularBeta = ttValue - ((formerPv + 4) * depth) / 2; - Depth singularDepth = (depth - 1 + 3 * formerPv) / 2; + Value singularBeta = ttValue - 2 * depth; + Depth singularDepth = (depth - 1) / 2; ss->excludedMove = move; value = search(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode); @@ -1130,6 +1063,15 @@ moves_loop: // When in check, search starts from here { extension = 1; singularQuietLMR = !ttCapture; + + // Avoid search explosion by limiting the number of double extensions to at most 3 + if ( !PvNode + && value < singularBeta - 93 + && ss->doubleExtensions < 3) + { + extension = 2; + doubleExtension = true; + } } // Multi-cut pruning @@ -1152,14 +1094,14 @@ moves_loop: // When in check, search starts from here return beta; } } - - // Check extension (~2 Elo) - else if ( givesCheck - && (pos.is_discovered_check_on_king(~us, move) || pos.see_ge(move))) + else if ( givesCheck + && depth > 6 + && abs(ss->staticEval) > Value(100)) extension = 1; // Add extension to new depth newDepth += extension; + ss->doubleExtensions = (ss-1)->doubleExtensions + (extension == 2); // Speculative prefetch as early as possible prefetch(TT.first_entry(pos.key_after(move))); @@ -1181,102 +1123,63 @@ moves_loop: // When in check, search starts from here if ( depth >= 3 && moveCount > 1 + 2 * rootNode && ( !captureOrPromotion - || moveCountPruning - || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha - || cutNode - || (!PvNode && !formerPv && captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 3678) - || thisThread->ttHitAverage < 432 * TtHitAverageResolution * TtHitAverageWindow / 1024) + || (cutNode && (ss-1)->moveCount > 1) + || !ss->ttPv) && (!PvNode || ss->ply > 1 || thisThread->id() % 4 != 3)) { Depth r = reduction(improving, depth, moveCount); - // Decrease reduction if the ttHit running average is large - if (thisThread->ttHitAverage > 537 * TtHitAverageResolution * TtHitAverageWindow / 1024) + if (PvNode) r--; - // Increase reduction if other threads are searching this position - if (th.marked()) - r++; + // Decrease reduction if the ttHit running average is large (~0 Elo) + if (thisThread->ttHitAverage > 537 * TtHitAverageResolution * TtHitAverageWindow / 1024) + r--; // Decrease reduction if position is or has been on the PV - // and node is not likely to fail low. (~10 Elo) + // and node is not likely to fail low. (~3 Elo) if ( ss->ttPv && !likelyFailLow) 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++; - - // Decrease reduction if opponent's move count is high (~5 Elo) + // Decrease reduction if opponent's move count is high (~1 Elo) if ((ss-1)->moveCount > 13) r--; - // Decrease reduction if ttMove has been singularly extended (~3 Elo) + // Decrease reduction if ttMove has been singularly extended (~1 Elo) if (singularQuietLMR) r--; - if (captureOrPromotion) - { - // Increase reduction for non-checking captures likely to be bad - if ( !givesCheck - && ss->staticEval + PieceValue[EG][pos.captured_piece()] + 210 * depth <= alpha) - r++; - } - else + // Increase reduction for cut nodes (~3 Elo) + if (cutNode && move != ss->killers[0]) + r += 2; + + if (!captureOrPromotion) { - // Increase reduction if ttMove is a capture (~5 Elo) + // Increase reduction if ttMove is a capture (~3 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; - - // Decrease reduction for moves that escape a capture. Filter out - // castling moves, because they are coded as "king captures rook" and - // hence break reverse_move() (~2 Elo) - else if ( type_of(move) == NORMAL - && !pos.see_ge(reverse_move(move))) - 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)] - - 4741; - - // Decrease/increase reduction by comparing opponent's stat score (~10 Elo) - if (ss->statScore >= -89 && (ss-1)->statScore < -116) - r--; - - else if ((ss-1)->statScore >= -112 && ss->statScore < -100) - r++; + - 4923; // Decrease/increase reduction for moves with a good/bad history (~30 Elo) - // If we are not in check use statScore, but if we are in check we use - // the sum of main history and first continuation history with an offset. - if (ss->inCheck) - r -= (thisThread->mainHistory[us][from_to(move)] - + (*contHist[0])[movedPiece][to_sq(move)] - 3833) / 16384; - else - r -= ss->statScore / 14790; + if (!ss->inCheck) + r -= ss->statScore / 14721; } // In general we want to cap the LMR depth search at newDepth. But if // reductions are really negative and movecount is low, we allow this move - // to be searched deeper than the first move. - Depth d = std::clamp(newDepth - r, 1, newDepth + (r < -1 && moveCount <= 5)); + // to be searched deeper than the first move, unless ttMove was extended by 2. + Depth d = std::clamp(newDepth - r, 1, newDepth + (r < -1 && moveCount <= 5 && !doubleExtension)); value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); @@ -1374,7 +1277,6 @@ moves_loop: // When in check, search starts from here else { assert(value >= beta); // Fail high - ss->statScore = 0; break; } } @@ -1448,10 +1350,11 @@ moves_loop: // When in check, search starts from here // qsearch() is the quiescence search function, which is called by the main search // function with zero depth, or recursively with further decreasing depth per call. - template + template Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) { - constexpr bool PvNode = NT == PV; + static_assert(nodeType != Root); + constexpr bool PvNode = nodeType == PV; assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE); assert(PvNode || (alpha == beta - 1)); @@ -1477,7 +1380,6 @@ moves_loop: // When in check, search starts from here } Thread* thisThread = pos.this_thread(); - (ss+1)->ply = ss->ply + 1; bestMove = MOVE_NONE; ss->inCheck = pos.checkers(); moveCount = 0; @@ -1533,7 +1435,7 @@ moves_loop: // When in check, search starts from here // and addition of two tempos ss->staticEval = bestValue = (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) - : -(ss-1)->staticEval + 2 * Tempo; + : -(ss-1)->staticEval; // Stand pat. Return immediately if static value is at least beta if (bestValue >= beta) @@ -1558,7 +1460,7 @@ moves_loop: // When in check, search starts from here // Initialize a MovePicker object for the current position, and prepare // to search the moves. Because the depth is <= 0 here, only captures, - // queen and checking knight promotions, and other checks(only if depth >= DEPTH_QS_CHECKS) + // queen promotions, and other checks (only if depth >= DEPTH_QS_CHECKS) // will be generated. MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, &thisThread->captureHistory, @@ -1621,7 +1523,7 @@ moves_loop: // When in check, search starts from here [pos.moved_piece(move)] [to_sq(move)]; - // CounterMove based pruning + // Continuation history based pruning if ( !captureOrPromotion && bestValue > VALUE_TB_LOSS_IN_MAX_PLY && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold @@ -1630,7 +1532,7 @@ moves_loop: // When in check, search starts from here // Make and search the move pos.do_move(move, st, givesCheck); - value = -qsearch(pos, ss+1, -beta, -alpha, depth - 1); + value = -qsearch(pos, ss+1, -beta, -alpha, depth - 1); pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);