X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=src%2Fsearch.cpp;h=fcdb8d67545fd302ed782f743bc41b9cc6d53912;hb=5c75c1c2fbb7bb4f0bf7c44fb855c415b788cbf7;hp=4507460a5b639e40573e6af83e35b6f70eaa6767;hpb=39af98c807d236b6511b6e399caf40102398900c;p=stockfish diff --git a/src/search.cpp b/src/search.cpp index 4507460a..fcdb8d67 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -1,6 +1,6 @@ /* Stockfish, a UCI chess playing engine derived from Glaurung 2.1 - Copyright (C) 2004-2022 The Stockfish developers (see AUTHORS file) + Copyright (C) 2004-2023 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 @@ -63,7 +63,7 @@ namespace { // Futility margin Value futility_margin(Depth d, bool improving) { - return Value(165 * (d - improving)); + return Value(154 * (d - improving)); } // Reductions lookup table, initialized at startup @@ -71,7 +71,7 @@ namespace { Depth reduction(bool i, Depth d, int mn, Value delta, Value rootDelta) { int r = Reductions[d] * Reductions[mn]; - return (r + 1642 - int(delta) * 1024 / int(rootDelta)) / 1024 + (!i && r > 916); + return (r + 1449 - int(delta) * 1032 / int(rootDelta)) / 1024 + (!i && r > 941); } constexpr int futility_move_count(bool improving, Depth depth) { @@ -81,7 +81,7 @@ namespace { // History and stats update bonus, based on depth int stat_bonus(Depth d) { - return std::min((12 * d + 282) * d - 349 , 1480); + return std::min(340 * d - 470, 1855); } // Add a small random component to draw evaluations to avoid 3-fold blindness @@ -96,7 +96,10 @@ namespace { struct Skill { Skill(int skill_level, int uci_elo) { if (uci_elo) - level = std::clamp(std::pow((uci_elo - 1346.6) / 143.4, 1 / 0.806), 0.0, 20.0); + { + double e = double(uci_elo - 1320) / (3190 - 1320); + level = std::clamp((((37.2473 * e - 40.8525) * e + 22.2943) * e - 0.311438), 0.0, 19.0); + } else level = double(skill_level); } @@ -158,7 +161,7 @@ namespace { void Search::init() { for (int i = 1; i < MAX_MOVES; ++i) - Reductions[i] = int((20.26 + std::log(Threads.size()) / 2) * std::log(i)); + Reductions[i] = int((19.47 + std::log(Threads.size()) / 2) * std::log(i)); } @@ -239,9 +242,6 @@ void MainThread::search() { bestPreviousScore = bestThread->rootMoves[0].score; bestPreviousAverageScore = bestThread->rootMoves[0].averageScore; - for (Thread* th : Threads) - th->previousDepth = bestThread->completedDepth; - // Send again PV info if we have a new best thread if (bestThread != this) sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth) << sync_endl; @@ -276,8 +276,11 @@ void Thread::search() { int iterIdx = 0; std::memset(ss-7, 0, 10 * sizeof(Stack)); - for (int i = 7; i > 0; i--) + for (int i = 7; i > 0; --i) + { (ss-i)->continuationHistory = &this->continuationHistory[0][0][NO_PIECE][0]; // Use as a sentinel + (ss-i)->staticEval = VALUE_NONE; + } for (int i = 0; i <= MAX_PLY + 2; ++i) (ss+i)->ply = i; @@ -307,7 +310,7 @@ void Thread::search() { multiPV = std::min(multiPV, rootMoves.size()); - complexityAverage.set(155, 1); + complexityAverage.set(153, 1); optimism[us] = optimism[~us] = VALUE_ZERO; @@ -331,7 +334,7 @@ void Thread::search() { pvLast = 0; if (!Threads.increaseDepth) - searchAgainCounter++; + searchAgainCounter++; // MultiPV loop. We perform a full root search for each PV line for (pvIdx = 0; pvIdx < multiPV && !Threads.stop; ++pvIdx) @@ -351,12 +354,12 @@ void Thread::search() { if (rootDepth >= 4) { Value prev = rootMoves[pvIdx].averageScore; - delta = Value(10) + int(prev) * prev / 15620; + delta = Value(10) + int(prev) * prev / 16502; alpha = std::max(prev - delta,-VALUE_INFINITE); beta = std::min(prev + delta, VALUE_INFINITE); // Adjust optimism based on root move's previousScore - int opt = 118 * prev / (std::abs(prev) + 169); + int opt = 120 * prev / (std::abs(prev) + 161); optimism[ us] = Value(opt); optimism[~us] = -optimism[us]; } @@ -429,9 +432,10 @@ void Thread::search() { if (!Threads.stop) completedDepth = rootDepth; - if (rootMoves[0].pv[0] != lastBestMove) { - lastBestMove = rootMoves[0].pv[0]; - lastBestMoveDepth = rootDepth; + if (rootMoves[0].pv[0] != lastBestMove) + { + lastBestMove = rootMoves[0].pv[0]; + lastBestMoveDepth = rootDepth; } // Have we found a "mate in x"? @@ -459,16 +463,16 @@ void Thread::search() { && !Threads.stop && !mainThread->stopOnPonderhit) { - double fallingEval = (71 + 12 * (mainThread->bestPreviousAverageScore - bestValue) - + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 656.7; + double fallingEval = (69 + 13 * (mainThread->bestPreviousAverageScore - bestValue) + + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 619.6; fallingEval = std::clamp(fallingEval, 0.5, 1.5); // If the bestMove is stable over several iterations, reduce time accordingly - timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.37 : 0.65; - double reduction = (1.4 + mainThread->previousTimeReduction) / (2.15 * timeReduction); - double bestMoveInstability = 1 + 1.7 * totBestMoveChanges / Threads.size(); + timeReduction = lastBestMoveDepth + 8 < completedDepth ? 1.57 : 0.65; + double reduction = (1.4 + mainThread->previousTimeReduction) / (2.08 * timeReduction); + double bestMoveInstability = 1 + 1.8 * totBestMoveChanges / Threads.size(); int complexity = mainThread->complexityAverage.value(); - double complexPosition = std::min(1.0 + (complexity - 261) / 1738.7, 1.5); + double complexPosition = std::min(1.03 + (complexity - 241) / 1552.0, 1.45); double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability * complexPosition; @@ -487,12 +491,11 @@ void Thread::search() { else Threads.stop = true; } - else if ( Threads.increaseDepth - && !mainThread->ponder - && Time.elapsed() > totalTime * 0.53) - Threads.increaseDepth = false; + else if ( !mainThread->ponder + && Time.elapsed() > totalTime * 0.50) + Threads.increaseDepth = false; else - Threads.increaseDepth = true; + Threads.increaseDepth = true; } mainThread->iterValue[iterIdx] = bestValue; @@ -520,7 +523,6 @@ namespace { 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. @@ -614,36 +616,38 @@ namespace { if (!rootNode) (ss+2)->statScore = 0; - // Step 4. Transposition table lookup. We don't want the score of a partial - // search to overwrite a previous full search TT value, so we use a different - // position key in case of an excluded move. + // Step 4. Transposition table lookup. excludedMove = ss->excludedMove; - posKey = excludedMove == MOVE_NONE ? pos.key() : pos.key() ^ make_key(excludedMove); + posKey = pos.key(); 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] : ss->ttHit ? tte->move() : MOVE_NONE; - ttCapture = ttMove && pos.capture(ttMove); + ttCapture = ttMove && pos.capture_stage(ttMove); + + // At this point, if excluded, skip straight to step 6, static eval. However, + // to save indentation, we list the condition in all code between here and there. if (!excludedMove) ss->ttPv = PvNode || (ss->ttHit && tte->is_pv()); // At non-PV nodes we check for an early TT cutoff if ( !PvNode && ss->ttHit + && !excludedMove && tte->depth() > depth - (tte->bound() == BOUND_EXACT) && ttValue != VALUE_NONE // Possible in case of TT access race && (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER))) { - // If ttMove is quiet, update move sorting heuristics on TT hit (~1 Elo) + // If ttMove is quiet, update move sorting heuristics on TT hit (~2 Elo) if (ttMove) { if (ttValue >= beta) { - // Bonus for a quiet ttMove that fails high (~3 Elo) + // Bonus for a quiet ttMove that fails high (~2 Elo) if (!ttCapture) update_quiet_stats(pos, ss, ttMove, stat_bonus(depth)); - // Extra penalty for early quiet moves of the previous ply (~0 Elo) + // Extra penalty for early quiet moves of the previous ply (~0 Elo on STC, ~2 Elo on LTC) if ((ss-1)->moveCount <= 2 && !priorCapture) update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + 1)); } @@ -663,7 +667,7 @@ namespace { } // Step 5. Tablebases probe - if (!rootNode && TB::Cardinality) + if (!rootNode && !excludedMove && TB::Cardinality) { int piecesCount = pos.count(); @@ -726,6 +730,13 @@ namespace { complexity = 0; goto moves_loop; } + else if (excludedMove) + { + // Providing the hint that this node's accumulator will be used often brings significant Elo gain (13 elo) + Eval::NNUE::hint_common_parent_position(pos); + eval = ss->staticEval; + complexity = abs(ss->staticEval - pos.psq_eg_stm()); + } else if (ss->ttHit) { // Never assume anything about values stored in TT @@ -733,9 +744,13 @@ namespace { if (eval == VALUE_NONE) ss->staticEval = eval = evaluate(pos, &complexity); else // Fall back to (semi)classical complexity for TT hits, the NNUE complexity is lost + { complexity = abs(ss->staticEval - pos.psq_eg_stm()); + if (PvNode) + Eval::NNUE::hint_common_parent_position(pos); + } - // ttValue can be used as a better position evaluation (~4 Elo) + // ttValue can be used as a better position evaluation (~7 Elo) if ( ttValue != VALUE_NONE && (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))) eval = ttValue; @@ -743,18 +758,16 @@ namespace { else { ss->staticEval = eval = evaluate(pos, &complexity); - // Save static evaluation into transposition table - if (!excludedMove) - tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval); + tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval); } thisThread->complexityAverage.update(complexity); - // Use static evaluation difference to improve quiet move ordering (~3 Elo) + // Use static evaluation difference to improve quiet move ordering (~4 Elo) if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture) { - int bonus = std::clamp(-19 * int((ss-1)->staticEval + ss->staticEval), -1914, 1914); + int bonus = std::clamp(-19 * int((ss-1)->staticEval + ss->staticEval), -1920, 1920); thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus; } @@ -764,35 +777,35 @@ namespace { // margin and the improving flag are used in various pruning heuristics. improvement = (ss-2)->staticEval != VALUE_NONE ? ss->staticEval - (ss-2)->staticEval : (ss-4)->staticEval != VALUE_NONE ? ss->staticEval - (ss-4)->staticEval - : 168; + : 156; improving = improvement > 0; - // Step 7. Razoring. + // Step 7. Razoring (~1 Elo). // If eval is really low check with qsearch if it can exceed alpha, if it can't, // return a fail low. - if (eval < alpha - 369 - 254 * depth * depth) + if (eval < alpha - 426 - 252 * depth * depth) { value = qsearch(pos, ss, alpha - 1, alpha); if (value < alpha) return value; } - // Step 8. Futility pruning: child node (~25 Elo). + // Step 8. Futility pruning: child node (~40 Elo). // The depth condition is important for mate finding. if ( !ss->ttPv - && depth < 8 - && eval - futility_margin(depth, improving) - (ss-1)->statScore / 303 >= beta + && depth < 9 + && eval - futility_margin(depth, improving) - (ss-1)->statScore / 280 >= beta && eval >= beta - && eval < 28031) // larger than VALUE_KNOWN_WIN, but smaller than TB wins + && eval < 25128) // larger than VALUE_KNOWN_WIN, but smaller than TB wins return eval; - // Step 9. Null move search with verification search (~22 Elo) + // Step 9. Null move search with verification search (~35 Elo) if ( !PvNode && (ss-1)->currentMove != MOVE_NULL - && (ss-1)->statScore < 17139 + && (ss-1)->statScore < 18755 && eval >= beta && eval >= ss->staticEval - && ss->staticEval >= beta - 20 * depth - improvement / 13 + 233 + complexity / 25 + && ss->staticEval >= beta - 19 * depth - improvement / 13 + 253 + complexity / 25 && !excludedMove && pos.non_pawn_material(us) && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor)) @@ -800,7 +813,7 @@ namespace { assert(eval - beta >= 0); // Null move dynamic reduction based on depth, eval and complexity of position - Depth R = std::min(int(eval - beta) / 168, 7) + depth / 3 + 4 - (complexity > 861); + Depth R = std::min(int(eval - beta) / 168, 6) + depth / 3 + 4 - (complexity > 825); ss->currentMove = MOVE_NULL; ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0]; @@ -836,10 +849,10 @@ namespace { } } - probCutBeta = beta + 191 - 54 * improving; + probCutBeta = beta + 186 - 54 * improving; - // Step 10. ProbCut (~4 Elo) - // If we have a good enough capture and a reduced search returns a value + // Step 10. ProbCut (~10 Elo) + // If we have a good enough capture (or queen promotion) and a reduced search returns a value // much above beta, we can (almost) safely prune the previous move. if ( !PvNode && depth > 4 @@ -860,7 +873,7 @@ namespace { while ((move = mp.next_move()) != MOVE_NONE) if (move != excludedMove && pos.legal(move)) { - assert(pos.capture(move) || promotion_type(move) == QUEEN); + assert(pos.capture_stage(move)); ss->currentMove = move; ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck] @@ -886,10 +899,12 @@ namespace { return value; } } + + Eval::NNUE::hint_common_parent_position(pos); } // Step 11. If the position is not in TT, decrease depth by 3. - // Use qsearch if depth is equal or below zero (~4 Elo) + // Use qsearch if depth is equal or below zero (~9 Elo) if ( PvNode && !ttMove) depth -= 3; @@ -898,14 +913,14 @@ namespace { return qsearch(pos, ss, alpha, beta); if ( cutNode - && depth >= 9 + && depth >= 7 && !ttMove) depth -= 2; moves_loop: // When in check, search starts here - // Step 12. A small Probcut idea, when we are in check (~0 Elo) - probCutBeta = beta + 417; + // Step 12. A small Probcut idea, when we are in check (~4 Elo) + probCutBeta = beta + 391; if ( ss->inCheck && !PvNode && depth >= 2 @@ -914,11 +929,9 @@ moves_loop: // When in check, search starts here && tte->depth() >= depth - 3 && ttValue >= probCutBeta && abs(ttValue) <= VALUE_KNOWN_WIN - && abs(beta) <= VALUE_KNOWN_WIN - ) + && abs(beta) <= VALUE_KNOWN_WIN) return probCutBeta; - const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr , (ss-4)->continuationHistory, nullptr , (ss-6)->continuationHistory }; @@ -972,7 +985,7 @@ moves_loop: // When in check, search starts here (ss+1)->pv = nullptr; extension = 0; - capture = pos.capture(move); + capture = pos.capture_stage(move); movedPiece = pos.moved_piece(move); givesCheck = pos.gives_check(move); @@ -981,31 +994,33 @@ moves_loop: // When in check, search starts here Value delta = beta - alpha; - // Step 14. Pruning at shallow depth (~98 Elo). Depth conditions are important for mate finding. + Depth r = reduction(improving, depth, moveCount, delta, thisThread->rootDelta); + + // Step 14. Pruning at shallow depth (~120 Elo). Depth conditions are important for mate finding. if ( !rootNode && pos.non_pawn_material(us) && bestValue > VALUE_TB_LOSS_IN_MAX_PLY) { - // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold (~7 Elo) + // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold (~8 Elo) moveCountPruning = moveCount >= futility_move_count(improving, depth); // Reduced depth of the next LMR search - int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, delta, thisThread->rootDelta), 0); + int lmrDepth = std::max(newDepth - r, 0); if ( capture || givesCheck) { - // Futility pruning for captures (~0 Elo) + // Futility pruning for captures (~2 Elo) if ( !givesCheck && !PvNode - && lmrDepth < 7 + && lmrDepth < 6 && !ss->inCheck - && ss->staticEval + 180 + 201 * lmrDepth + PieceValue[EG][pos.piece_on(to_sq(move))] - + captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 6 < alpha) + && ss->staticEval + 182 + 230 * lmrDepth + PieceValue[EG][pos.piece_on(to_sq(move))] + + captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 7 < alpha) continue; - // SEE based pruning (~9 Elo) - if (!pos.see_ge(move, Value(-222) * depth)) + // SEE based pruning (~11 Elo) + if (!pos.see_ge(move, Value(-206) * depth)) continue; } else @@ -1016,34 +1031,39 @@ moves_loop: // When in check, search starts here // Continuation history based pruning (~2 Elo) if ( lmrDepth < 5 - && history < -3875 * (depth - 1)) + && history < -4405 * (depth - 1)) continue; history += 2 * thisThread->mainHistory[us][from_to(move)]; - // Futility pruning: parent node (~9 Elo) + lmrDepth += history / 7278; + lmrDepth = std::max(lmrDepth, -2); + + // Futility pruning: parent node (~13 Elo) if ( !ss->inCheck && lmrDepth < 13 - && ss->staticEval + 106 + 145 * lmrDepth + history / 52 <= alpha) + && ss->staticEval + 103 + 138 * lmrDepth <= alpha) continue; - // Prune moves with negative SEE (~3 Elo) + lmrDepth = std::max(lmrDepth, 0); + + // Prune moves with negative SEE (~4 Elo) if (!pos.see_ge(move, Value(-24 * lmrDepth * lmrDepth - 15 * lmrDepth))) continue; } } - // Step 15. Extensions (~66 Elo) + // Step 15. Extensions (~100 Elo) // We take care to not overdo to avoid search getting stuck. if (ss->ply < thisThread->rootDepth * 2) { - // Singular extension search (~58 Elo). If all moves but one fail low on a + // Singular extension search (~94 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 ( !rootNode - && depth >= 4 - (thisThread->previousDepth > 24) + 2 * (PvNode && tte->is_pv()) + && depth >= 4 - (thisThread->completedDepth > 21) + 2 * (PvNode && tte->is_pv()) && move == ttMove && !excludedMove // Avoid recursive singular search /* && ttValue != VALUE_NONE Already implicit in the next condition */ @@ -1051,10 +1071,11 @@ moves_loop: // When in check, search starts here && (tte->bound() & BOUND_LOWER) && tte->depth() >= depth - 3) { - Value singularBeta = ttValue - (3 + (ss->ttPv && !PvNode)) * depth; + Value singularBeta = ttValue - (2 + (ss->ttPv && !PvNode)) * depth; Depth singularDepth = (depth - 1) / 2; ss->excludedMove = move; + // the search with excludedMove will update ss->staticEval value = search(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode); ss->excludedMove = MOVE_NONE; @@ -1069,7 +1090,7 @@ moves_loop: // When in check, search starts here && ss->doubleExtensions <= 10) { extension = 2; - depth += depth < 12; + depth += depth < 13; } } @@ -1085,22 +1106,22 @@ moves_loop: // When in check, search starts here else if (ttValue >= beta) extension = -2; - // If the eval of ttMove is less than alpha and value, we reduce it (negative extension) - else if (ttValue <= alpha && ttValue <= value) + // If the eval of ttMove is less than value, we reduce it (negative extension) + else if (ttValue <= value) extension = -1; } // Check extensions (~1 Elo) else if ( givesCheck - && depth > 9 - && abs(ss->staticEval) > 82) + && depth > 10 + && abs(ss->staticEval) > 88) extension = 1; - // Quiet ttMove extensions (~0 Elo) + // Quiet ttMove extensions (~1 Elo) else if ( PvNode && move == ttMove && move == ss->killers[0] - && (*contHist[0])[movedPiece][to_sq(move)] >= 5177) + && (*contHist[0])[movedPiece][to_sq(move)] >= 5705) extension = 1; } @@ -1121,62 +1142,65 @@ moves_loop: // When in check, search starts here // Step 16. Make the move pos.do_move(move, st, givesCheck); - // Step 17. Late moves reduction / extension (LMR, ~98 Elo) - // We use various heuristics for the sons of a node after the first son has - // been searched. In general we would like to reduce them, but there are many - // cases where we extend a son if it has good chances to be "interesting". - if ( depth >= 2 - && moveCount > 1 + (PvNode && ss->ply <= 1) - && ( !ss->ttPv - || !capture - || (cutNode && (ss-1)->moveCount > 1))) - { - Depth r = reduction(improving, depth, moveCount, delta, thisThread->rootDelta); + // Decrease reduction if position is or has been on the PV + // and node is not likely to fail low. (~3 Elo) + if ( ss->ttPv + && !likelyFailLow) + r -= 2; - // Decrease reduction if position is or has been on the PV - // and node is not likely to fail low. (~3 Elo) - if ( ss->ttPv - && !likelyFailLow) - r -= 2; + // Decrease reduction if opponent's move count is high (~1 Elo) + if ((ss-1)->moveCount > 7) + r--; - // Decrease reduction if opponent's move count is high (~1 Elo) - if ((ss-1)->moveCount > 7) - r--; + // Increase reduction for cut nodes (~3 Elo) + if (cutNode) + r += 2; - // Increase reduction for cut nodes (~3 Elo) - if (cutNode) - r += 2; + // Increase reduction if ttMove is a capture (~3 Elo) + if (ttCapture) + r++; - // Increase reduction if ttMove is a capture (~3 Elo) - if (ttCapture) - r++; + // Decrease reduction for PvNodes based on depth + if (PvNode) + r -= 1 + 12 / (3 + depth); - // Decrease reduction for PvNodes based on depth - if (PvNode) - r -= 1 + 11 / (3 + depth); + // Decrease reduction if ttMove has been singularly extended (~1 Elo) + if (singularQuietLMR) + r--; - // Decrease reduction if ttMove has been singularly extended (~1 Elo) - if (singularQuietLMR) - r--; + // Decrease reduction if we move a threatened piece (~1 Elo) + if ( depth > 9 + && (mp.threatenedPieces & from_sq(move))) + r--; - // Decrease reduction if we move a threatened piece (~1 Elo) - if ( depth > 9 - && (mp.threatenedPieces & from_sq(move))) - r--; + // Increase reduction if next ply has a lot of fail high + if ((ss+1)->cutoffCnt > 3) + r++; - // Increase reduction if next ply has a lot of fail high - if ((ss+1)->cutoffCnt > 3) - r++; + // Decrease reduction if move is a killer and we have a good history + if (move == ss->killers[0] + && (*contHist[0])[movedPiece][to_sq(move)] >= 3722) + r--; - ss->statScore = 2 * thisThread->mainHistory[us][from_to(move)] - + (*contHist[0])[movedPiece][to_sq(move)] - + (*contHist[1])[movedPiece][to_sq(move)] - + (*contHist[3])[movedPiece][to_sq(move)] - - 4433; + ss->statScore = 2 * thisThread->mainHistory[us][from_to(move)] + + (*contHist[0])[movedPiece][to_sq(move)] + + (*contHist[1])[movedPiece][to_sq(move)] + + (*contHist[3])[movedPiece][to_sq(move)] + - 4182; - // Decrease/increase reduction for moves with a good/bad history (~30 Elo) - r -= ss->statScore / (13000 + 4152 * (depth > 7 && depth < 19)); + // Decrease/increase reduction for moves with a good/bad history (~30 Elo) + r -= ss->statScore / (11791 + 3992 * (depth > 6 && depth < 19)); + // Step 17. Late moves reduction / extension (LMR, ~117 Elo) + // We use various heuristics for the sons of a node after the first son has + // been searched. In general we would like to reduce them, but there are many + // cases where we extend a son if it has good chances to be "interesting". + if ( depth >= 2 + && moveCount > 1 + (PvNode && ss->ply <= 1) + && ( !ss->ttPv + || !capture + || (cutNode && (ss-1)->moveCount > 1))) + { // In general we want to cap the LMR depth search at newDepth, but when // reduction is negative, we allow this move a limited search extension // beyond the first move depth. This may lead to hidden double extensions. @@ -1189,8 +1213,8 @@ moves_loop: // When in check, search starts here { // Adjust full depth search based on LMR results - if result // was good enough search deeper, if it was bad enough search shallower - const bool doDeeperSearch = value > (alpha + 64 + 11 * (newDepth - d)); - const bool doEvenDeeperSearch = value > alpha + 582 && ss->doubleExtensions <= 5; + const bool doDeeperSearch = value > (alpha + 58 + 12 * (newDepth - d)); + const bool doEvenDeeperSearch = value > alpha + 588 && ss->doubleExtensions <= 5; const bool doShallowerSearch = value < bestValue + newDepth; ss->doubleExtensions = ss->doubleExtensions + doEvenDeeperSearch; @@ -1203,17 +1227,18 @@ moves_loop: // When in check, search starts here int bonus = value > alpha ? stat_bonus(newDepth) : -stat_bonus(newDepth); - if (capture) - bonus /= 6; - update_continuation_histories(ss, movedPiece, to_sq(move), bonus); } } - // Step 18. Full depth search when LMR is skipped + // Step 18. Full depth search when LMR is skipped. If expected reduction is high, reduce its depth by 1. else if (!PvNode || moveCount > 1) { - value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); + // Increase reduction for cut nodes and not ttMove (~1 Elo) + if (!ttMove && cutNode) + r += 2; + + value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth - (r > 4), !cutNode); } // For PV nodes only, do a full PV search on the first move or after a fail @@ -1224,8 +1249,7 @@ moves_loop: // When in check, search starts here (ss+1)->pv = pv; (ss+1)->pv[0] = MOVE_NONE; - value = -search(pos, ss+1, -beta, -alpha, - std::min(maxNextDepth, newDepth), false); + value = -search(pos, ss+1, -beta, -alpha, newDepth, false); } // Step 19. Undo move @@ -1254,14 +1278,17 @@ moves_loop: // When in check, search starts here rm.selDepth = thisThread->selDepth; rm.scoreLowerbound = rm.scoreUpperbound = false; - if (value >= beta) { - rm.scoreLowerbound = true; - rm.uciScore = beta; + if (value >= beta) + { + rm.scoreLowerbound = true; + rm.uciScore = beta; } - else if (value <= alpha) { - rm.scoreUpperbound = true; - rm.uciScore = alpha; + else if (value <= alpha) + { + rm.scoreUpperbound = true; + rm.uciScore = alpha; } + rm.pv.resize(1); assert((ss+1)->pv); @@ -1301,8 +1328,8 @@ moves_loop: // When in check, search starts here // Reduce other moves if we have found at least one score improvement if ( depth > 1 && depth < 6 - && beta < VALUE_KNOWN_WIN - && alpha > -VALUE_KNOWN_WIN) + && beta < 10534 + && alpha > -10534) depth -= 1; assert(depth > 0); @@ -1354,16 +1381,10 @@ moves_loop: // When in check, search starts here quietsSearched, quietCount, capturesSearched, captureCount, depth); // Bonus for prior countermove that caused the fail low - else if ( (depth >= 5 || PvNode) - && !priorCapture) + else if (!priorCapture) { - //Assign extra bonus if current node is PvNode or cutNode - //or fail low was really bad - bool extraBonus = PvNode - || cutNode - || bestValue < alpha - 62 * depth; - - update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * (1 + extraBonus)); + int bonus = (depth > 5) + (PvNode || cutNode) + (bestValue < alpha - 97 * depth) + ((ss-1)->moveCount > 10); + update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * bonus); } if (PvNode) @@ -1412,6 +1433,7 @@ moves_loop: // When in check, search starts here bool pvHit, givesCheck, capture; int moveCount; + // Step 1. Initialize node if (PvNode) { (ss+1)->pv = pv; @@ -1423,7 +1445,7 @@ moves_loop: // When in check, search starts here ss->inCheck = pos.checkers(); moveCount = 0; - // Check for an immediate draw or maximum ply reached + // Step 2. Check for an immediate draw or maximum ply reached if ( pos.is_draw(ss->ply) || ss->ply >= MAX_PLY) return (ss->ply >= MAX_PLY && !ss->inCheck) ? evaluate(pos) : VALUE_DRAW; @@ -1434,14 +1456,16 @@ moves_loop: // When in check, search starts here // TT entry depth that we are going to use. Note that in qsearch we use // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS. ttDepth = ss->inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS - : DEPTH_QS_NO_CHECKS; - // Transposition table lookup + : DEPTH_QS_NO_CHECKS; + + // Step 3. Transposition table lookup posKey = pos.key(); 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(); + // At non-PV nodes we check for an early TT cutoff if ( !PvNode && ss->ttHit && tte->depth() >= ttDepth @@ -1449,7 +1473,7 @@ moves_loop: // When in check, search starts here && (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER))) return ttValue; - // Evaluate the position statically + // Step 4. Static evaluation of the position if (ss->inCheck) { ss->staticEval = VALUE_NONE; @@ -1463,7 +1487,7 @@ moves_loop: // When in check, search starts here if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE) ss->staticEval = bestValue = evaluate(pos); - // ttValue can be used as a better position evaluation (~7 Elo) + // ttValue can be used as a better position evaluation (~13 Elo) if ( ttValue != VALUE_NONE && (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))) bestValue = ttValue; @@ -1488,7 +1512,7 @@ moves_loop: // When in check, search starts here if (PvNode && bestValue > alpha) alpha = bestValue; - futilityBase = bestValue + 153; + futilityBase = bestValue + 168; } const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, @@ -1507,7 +1531,8 @@ moves_loop: // When in check, search starts here int quietCheckEvasions = 0; - // Loop through the moves until no moves remain or a beta cutoff occurs + // Step 5. Loop through all pseudo-legal moves until no moves remain + // or a beta cutoff occurs. while ((move = mp.next_move()) != MOVE_NONE) { assert(is_ok(move)); @@ -1517,13 +1542,15 @@ moves_loop: // When in check, search starts here continue; givesCheck = pos.gives_check(move); - capture = pos.capture(move); + capture = pos.capture_stage(move); moveCount++; - // Futility pruning and moveCount pruning (~5 Elo) - if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY - && !givesCheck + // Step 6. Pruning. + if (bestValue > VALUE_TB_LOSS_IN_MAX_PLY) + { + // Futility pruning and moveCount pruning (~10 Elo) + if ( !givesCheck && to_sq(move) != prevSq && futilityBase > -VALUE_KNOWN_WIN && type_of(move) != PROMOTION) @@ -1546,43 +1573,42 @@ moves_loop: // When in check, search starts here } } - // Do not search moves with negative SEE values (~5 Elo) - if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY - && !pos.see_ge(move)) + // We prune after 2nd quiet check evasion where being 'in check' is implicitly checked through the counter + // and being a 'quiet' apart from being a tt move is assumed after an increment because captures are pushed ahead. + if (quietCheckEvasions > 1) + break; + + // Continuation history based pruning (~3 Elo) + if ( !capture + && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < 0 + && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < 0) continue; + // Do not search moves with bad enough SEE values (~5 Elo) + if (!pos.see_ge(move, Value(-110))) + continue; + } + // Speculative prefetch as early as possible prefetch(TT.first_entry(pos.key_after(move))); + // Update the current move ss->currentMove = move; ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck] [capture] [pos.moved_piece(move)] [to_sq(move)]; - // Continuation history based pruning (~2 Elo) - if ( !capture - && bestValue > VALUE_TB_LOSS_IN_MAX_PLY - && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < 0 - && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < 0) - continue; - - // We prune after 2nd quiet check evasion where being 'in check' is implicitly checked through the counter - // and being a 'quiet' apart from being a tt move is assumed after an increment because captures are pushed ahead. - if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY - && quietCheckEvasions > 1) - break; - quietCheckEvasions += !capture && ss->inCheck; - // Make and search the move + // Step 7. Make and search the move pos.do_move(move, st, givesCheck); value = -qsearch(pos, ss+1, -beta, -alpha, depth - 1); pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); - // Check for a new best move + // Step 8. Check for a new best move if (value > bestValue) { bestValue = value; @@ -1602,6 +1628,7 @@ moves_loop: // When in check, search starts here } } + // Step 9. Check for mate // 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) @@ -1688,9 +1715,9 @@ moves_loop: // When in check, search starts here PieceType captured = type_of(pos.piece_on(to_sq(bestMove))); int bonus1 = stat_bonus(depth + 1); - if (!pos.capture(bestMove)) + if (!pos.capture_stage(bestMove)) { - int bonus2 = bestValue > beta + 137 ? bonus1 // larger bonus + int bonus2 = bestValue > beta + 153 ? bonus1 // larger bonus : stat_bonus(depth); // smaller bonus // Increase stats for the best move in case it was a quiet move