X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=src%2Fsearch.cpp;h=1e82203a7775f7e4232f5b27f469667c6049b7c6;hb=5930c0defbe01576315d7d081447f94a01daf337;hp=f6bc0aa9a8098a7250037749b3c81f231b277307;hpb=d2f79ff0e0efc33797120f59355c2a5571b4ab80;p=stockfish diff --git a/src/search.cpp b/src/search.cpp index f6bc0aa9..1e82203a 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -34,6 +34,7 @@ #include "tt.h" #include "uci.h" #include "syzygy/tbprobe.h" +#include "nnue/evaluate_nnue.h" namespace Stockfish { @@ -63,7 +64,7 @@ namespace { // Futility margin Value futility_margin(Depth d, bool improving) { - return Value(158 * (d - improving)); + return Value(140 * (d - improving)); } // Reductions lookup table, initialized at startup @@ -71,7 +72,7 @@ namespace { Depth reduction(bool i, Depth d, int mn, Value delta, Value rootDelta) { int r = Reductions[d] * Reductions[mn]; - return (r + 1460 - int(delta) * 1024 / int(rootDelta)) / 1024 + (!i && r > 937); + return (r + 1372 - int(delta) * 1073 / int(rootDelta)) / 1024 + (!i && r > 936); } constexpr int futility_move_count(bool improving, Depth depth) { @@ -81,7 +82,7 @@ namespace { // History and stats update bonus, based on depth int stat_bonus(Depth d) { - return std::min(350 * d - 400, 1650); + return std::min(336 * d - 547, 1561); } // Add a small random component to draw evaluations to avoid 3-fold blindness @@ -161,7 +162,7 @@ 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((20.57 + std::log(Threads.size()) / 2) * std::log(i)); } @@ -287,8 +288,7 @@ void Thread::search() { ss->pv = pv; - bestValue = delta = alpha = -VALUE_INFINITE; - beta = VALUE_INFINITE; + bestValue = -VALUE_INFINITE; if (mainThread) { @@ -310,10 +310,6 @@ void Thread::search() { multiPV = std::min(multiPV, rootMoves.size()); - complexityAverage.set(153, 1); - - optimism[us] = optimism[~us] = VALUE_ZERO; - int searchAgainCounter = 0; // Iterative deepening loop until requested to stop or the target depth is reached @@ -334,7 +330,7 @@ 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) @@ -351,18 +347,15 @@ void Thread::search() { selDepth = 0; // Reset aspiration window starting size - if (rootDepth >= 4) - { - Value prev = rootMoves[pvIdx].averageScore; - delta = Value(10) + int(prev) * prev / 15400; - alpha = std::max(prev - delta,-VALUE_INFINITE); - beta = std::min(prev + delta, VALUE_INFINITE); - - // Adjust optimism based on root move's previousScore - int opt = 116 * prev / (std::abs(prev) + 170); - optimism[ us] = Value(opt); - optimism[~us] = -optimism[us]; - } + Value prev = rootMoves[pvIdx].averageScore; + delta = Value(10) + int(prev) * prev / 15799; + alpha = std::max(prev - delta,-VALUE_INFINITE); + beta = std::min(prev + delta, VALUE_INFINITE); + + // Adjust optimism based on root move's previousScore + int opt = 109 * prev / (std::abs(prev) + 141); + optimism[ us] = Value(opt); + optimism[~us] = -optimism[us]; // 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 @@ -416,7 +409,7 @@ void Thread::search() { else break; - delta += delta / 4 + 2; + delta += delta / 3; assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE); } @@ -432,9 +425,10 @@ 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"? @@ -462,18 +456,16 @@ 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(); - int complexity = mainThread->complexityAverage.value(); - double complexPosition = std::min(1.0 + (complexity - 261) / 1738.7, 1.5); + 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(); - double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability * complexPosition; + double totalTime = 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. @@ -491,7 +483,7 @@ void Thread::search() { Threads.stop = true; } else if ( !mainThread->ponder - && Time.elapsed() > totalTime * 0.53) + && Time.elapsed() > totalTime * 0.50) Threads.increaseDepth = false; else Threads.increaseDepth = true; @@ -556,7 +548,7 @@ namespace { bool givesCheck, improving, priorCapture, singularQuietLMR; bool capture, moveCountPruning, ttCapture; Piece movedPiece; - int moveCount, captureCount, quietCount, improvement, complexity; + int moveCount, captureCount, quietCount, improvement; // Step 1. Initialize node Thread* thisThread = pos.this_thread(); @@ -600,39 +592,32 @@ namespace { assert(0 <= ss->ply && ss->ply < MAX_PLY); - (ss+1)->ttPv = false; (ss+1)->excludedMove = bestMove = MOVE_NONE; (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE; (ss+2)->cutoffCnt = 0; 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 - // 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+2)->statScore = 0; + Square prevSq = is_ok((ss-1)->currentMove) ? to_sq((ss-1)->currentMove) : SQ_NONE; + ss->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 + && ttValue != VALUE_NONE // Possible in case of TT access race or if !ttHit && (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER))) { // If ttMove is quiet, update move sorting heuristics on TT hit (~2 Elo) @@ -645,7 +630,7 @@ namespace { update_quiet_stats(pos, ss, ttMove, stat_bonus(depth)); // Extra penalty for early quiet moves of the previous ply (~0 Elo on STC, ~2 Elo on LTC) - if ((ss-1)->moveCount <= 2 && !priorCapture) + if (prevSq != SQ_NONE && (ss-1)->moveCount <= 2 && !priorCapture) update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + 1)); } // Penalty for a quiet ttMove that fails low (~1 Elo) @@ -664,7 +649,7 @@ namespace { } // Step 5. Tablebases probe - if (!rootNode && TB::Cardinality) + if (!rootNode && !excludedMove && TB::Cardinality) { int piecesCount = pos.count(); @@ -724,17 +709,22 @@ namespace { ss->staticEval = eval = VALUE_NONE; improving = false; improvement = 0; - 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; + } 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, &complexity); - else // Fall back to (semi)classical complexity for TT hits, the NNUE complexity is lost - complexity = abs(ss->staticEval - pos.psq_eg_stm()); + ss->staticEval = eval = evaluate(pos); + else if (PvNode) + Eval::NNUE::hint_common_parent_position(pos); // ttValue can be used as a better position evaluation (~7 Elo) if ( ttValue != VALUE_NONE @@ -743,19 +733,15 @@ namespace { } else { - ss->staticEval = eval = evaluate(pos, &complexity); - + ss->staticEval = eval = evaluate(pos); // 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 (~4 Elo) if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture) { - int bonus = std::clamp(-19 * int((ss-1)->staticEval + ss->staticEval), -1940, 1940); + int bonus = std::clamp(-18 * int((ss-1)->staticEval + ss->staticEval), -1817, 1817); thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus; } @@ -765,13 +751,13 @@ 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 - : 172; + : 173; improving = improvement > 0; // 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 - 394 - 255 * depth * depth) + if (eval < alpha - 456 - 252 * depth * depth) { value = qsearch(pos, ss, alpha - 1, alpha); if (value < alpha) @@ -781,27 +767,27 @@ namespace { // 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 / 304 >= beta + && depth < 9 + && eval - futility_margin(depth, improving) - (ss-1)->statScore / 306 >= beta && eval >= beta - && eval < 28580) // larger than VALUE_KNOWN_WIN, but smaller than TB wins + && eval < 24923) // larger than VALUE_KNOWN_WIN, but smaller than TB wins return eval; // Step 9. Null move search with verification search (~35 Elo) if ( !PvNode && (ss-1)->currentMove != MOVE_NULL - && (ss-1)->statScore < 18200 + && (ss-1)->statScore < 17329 && eval >= beta && eval >= ss->staticEval - && ss->staticEval >= beta - 20 * depth - improvement / 14 + 235 + complexity / 24 + && ss->staticEval >= beta - 21 * depth - improvement * 99 / 1300 + 258 && !excludedMove && pos.non_pawn_material(us) - && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor)) + && (ss->ply >= thisThread->nmpMinPly)) { assert(eval - beta >= 0); - // Null move dynamic reduction based on depth, eval and complexity of position - Depth R = std::min(int(eval - beta) / 165, 6) + depth / 3 + 4 - (complexity > 800); + // Null move dynamic reduction based on depth and eval + Depth R = std::min(int(eval - beta) / 173, 6) + depth / 3 + 4; ss->currentMove = MOVE_NULL; ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0]; @@ -824,9 +810,8 @@ namespace { assert(!thisThread->nmpMinPly); // Recursive verification is not allowed // Do verification search at high depths, with null move pruning disabled - // for us, until ply exceeds nmpMinPly. + // until ply exceeds nmpMinPly. thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / 4; - thisThread->nmpColor = us; Value v = search(pos, ss, beta-1, beta, depth-R, false); @@ -837,20 +822,19 @@ namespace { } } - probCutBeta = beta + 180 - 54 * improving; + probCutBeta = beta + 168 - 61 * improving; // Step 10. ProbCut (~10 Elo) - // If we have a good enough capture and a reduced search returns a value + // 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 + && depth > 3 && abs(beta) < VALUE_TB_WIN_IN_MAX_PLY // 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 + && !( tte->depth() >= depth - 3 && ttValue != VALUE_NONE && ttValue < probCutBeta)) { @@ -861,7 +845,7 @@ 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] @@ -887,44 +871,43 @@ namespace { return value; } } + + Eval::NNUE::hint_common_parent_position(pos); } - // Step 11. If the position is not in TT, decrease depth by 3. + // Step 11. If the position is not in TT, decrease depth by 2 (or by 4 if the TT entry for the current position was hit and the stored depth is greater than or equal to the current depth). // Use qsearch if depth is equal or below zero (~9 Elo) if ( PvNode && !ttMove) - depth -= 3; + depth -= 2 + 2 * (ss->ttHit && tte->depth() >= depth); if (depth <= 0) return qsearch(pos, ss, alpha, beta); if ( cutNode - && depth >= 9 + && depth >= 8 && !ttMove) depth -= 2; moves_loop: // When in check, search starts here // Step 12. A small Probcut idea, when we are in check (~4 Elo) - probCutBeta = beta + 402; + probCutBeta = beta + 413; if ( ss->inCheck && !PvNode - && depth >= 2 && ttCapture && (tte->bound() & BOUND_LOWER) - && tte->depth() >= depth - 3 + && tte->depth() >= depth - 4 && 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 }; - Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq]; + Move countermove = prevSq != SQ_NONE ? thisThread->counterMoves[pos.piece_on(prevSq)][prevSq] : MOVE_NONE; MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, &captureHistory, @@ -973,7 +956,7 @@ 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); @@ -982,6 +965,8 @@ moves_loop: // When in check, search starts here Value delta = beta - alpha; + 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) @@ -991,23 +976,22 @@ moves_loop: // When in check, search starts here 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 = newDepth - r; if ( capture || givesCheck) { // Futility pruning for captures (~2 Elo) if ( !givesCheck - && !PvNode && lmrDepth < 7 && !ss->inCheck - && ss->staticEval + 185 + 203 * 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 + 197 + 248 * 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 (~11 Elo) - if (!pos.see_ge(move, Value(-220) * depth)) - continue; + if (!pos.see_ge(move, Value(-205) * depth)) + continue; } else { @@ -1016,25 +1000,25 @@ moves_loop: // When in check, search starts here + (*contHist[3])[movedPiece][to_sq(move)]; // Continuation history based pruning (~2 Elo) - if ( lmrDepth < 5 - && history < -4180 * (depth - 1)) + if ( lmrDepth < 6 + && history < -3832 * depth) continue; history += 2 * thisThread->mainHistory[us][from_to(move)]; - lmrDepth += history / 7208; + lmrDepth += history / 7011; lmrDepth = std::max(lmrDepth, -2); // Futility pruning: parent node (~13 Elo) if ( !ss->inCheck - && lmrDepth < 13 - && ss->staticEval + 103 + 136 * lmrDepth <= alpha) + && lmrDepth < 12 + && ss->staticEval + 112 + 138 * lmrDepth <= alpha) continue; lmrDepth = std::max(lmrDepth, 0); // Prune moves with negative SEE (~4 Elo) - if (!pos.see_ge(move, Value(-25 * lmrDepth * lmrDepth - 16 * lmrDepth))) + if (!pos.see_ge(move, Value(-27 * lmrDepth * lmrDepth - 16 * lmrDepth))) continue; } } @@ -1057,7 +1041,7 @@ 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 - (82 + 65 * (ss->ttPv && !PvNode)) * depth / 64; Depth singularDepth = (depth - 1) / 2; ss->excludedMove = move; @@ -1071,11 +1055,11 @@ moves_loop: // When in check, search starts here // Avoid search explosion by limiting the number of double extensions if ( !PvNode - && value < singularBeta - 25 - && ss->doubleExtensions <= 10) + && value < singularBeta - 21 + && ss->doubleExtensions <= 11) { extension = 2; - depth += depth < 12; + depth += depth < 13; } } @@ -1087,26 +1071,28 @@ moves_loop: // When in check, search starts here else if (singularBeta >= beta) return singularBeta; - // If the eval of ttMove is greater than beta, we reduce it (negative extension) + // If the eval of ttMove is greater than beta, we reduce it (negative extension) (~7 Elo) else if (ttValue >= beta) - extension = -2; + extension = -2 - !PvNode; - // 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) (~1 Elo) + else if (ttValue <= value) + extension = -1; + + // If the eval of ttMove is less than alpha, we reduce it (negative extension) (~1 Elo) + else if (ttValue <= alpha) extension = -1; } // Check extensions (~1 Elo) - else if ( givesCheck - && depth > 9 - && abs(ss->staticEval) > 78) + else if ( givesCheck && depth > 8) extension = 1; // Quiet ttMove extensions (~1 Elo) else if ( PvNode && move == ttMove && move == ss->killers[0] - && (*contHist[0])[movedPiece][to_sq(move)] >= 5600) + && (*contHist[0])[movedPiece][to_sq(move)] >= 5168) extension = 1; } @@ -1127,16 +1113,15 @@ moves_loop: // When in check, search starts here // Step 16. Make the move pos.do_move(move, st, givesCheck); - 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) + // Decrease further on cutNodes. (~1 Elo) if ( ss->ttPv && !likelyFailLow) - r -= 2; + r -= cutNode && tte->depth() >= depth + 3 ? 3 : 2; // Decrease reduction if opponent's move count is high (~1 Elo) - if ((ss-1)->moveCount > 7) + if ((ss-1)->moveCount > 8) r--; // Increase reduction for cut nodes (~3 Elo) @@ -1147,36 +1132,29 @@ moves_loop: // When in check, search starts here if (ttCapture) r++; - // Decrease reduction for PvNodes based on depth + // Decrease reduction for PvNodes based on depth (~2 Elo) if (PvNode) - r -= 1 + 11 / (3 + depth); + r -= 1 + 12 / (3 + depth); // 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--; - - // Increase reduction if next ply has a lot of fail high + // Increase reduction if next ply has a lot of fail high (~5 Elo) 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)] >= 3600) + else if (move == ttMove) 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)] - - 4467; + - 4006; - // Decrease/increase reduction for moves with a good/bad history (~30 Elo) - r -= ss->statScore / (12800 + 4410 * (depth > 7 && depth < 19)); + // Decrease/increase reduction for moves with a good/bad history (~25 Elo) + r -= ss->statScore / (11124 + 4740 * (depth > 5 && depth < 22)); // Step 17. Late moves reduction / extension (LMR, ~117 Elo) // We use various heuristics for the sons of a node after the first son has @@ -1200,8 +1178,8 @@ 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 + 66 + 11 * (newDepth - d)); - const bool doEvenDeeperSearch = value > alpha + 582 && ss->doubleExtensions <= 5; + const bool doDeeperSearch = value > (bestValue + 64 + 11 * (newDepth - d)); + const bool doEvenDeeperSearch = value > alpha + 711 && ss->doubleExtensions <= 6; const bool doShallowerSearch = value < bestValue + newDepth; ss->doubleExtensions = ss->doubleExtensions + doEvenDeeperSearch; @@ -1211,8 +1189,9 @@ moves_loop: // When in check, search starts here if (newDepth > d) value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); - int bonus = value > alpha ? stat_bonus(newDepth) - : -stat_bonus(newDepth); + int bonus = value <= alpha ? -stat_bonus(newDepth) + : value >= beta ? stat_bonus(newDepth) + : 0; update_continuation_histories(ss, movedPiece, to_sq(move), bonus); } @@ -1221,11 +1200,11 @@ moves_loop: // When in check, search starts here // Step 18. Full depth search when LMR is skipped. If expected reduction is high, reduce its depth by 1. else if (!PvNode || moveCount > 1) { - // Increase reduction for cut nodes and not ttMove (~1 Elo) - if (!ttMove && cutNode) - r += 2; + // 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); + value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth - (r > 3), !cutNode); } // For PV nodes only, do a full PV search on the first move or after a fail @@ -1265,14 +1244,17 @@ 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); @@ -1305,24 +1287,23 @@ moves_loop: // When in check, search starts here if (PvNode && !rootNode) // Update pv even in fail-high case update_pv(ss->pv, move, (ss+1)->pv); - if (PvNode && value < beta) // Update alpha! Always alpha < beta + if (value >= beta) { - alpha = value; - - // 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) - depth -= 1; - - assert(depth > 0); + ss->cutoffCnt += 1 + !ttMove; + assert(value >= beta); // Fail high + break; } else { - ss->cutoffCnt++; - assert(value >= beta); // Fail high - break; + // Reduce other moves if we have found at least one score improvement (~1 Elo) + // Reduce more for depth > 3 and depth < 12 (~1 Elo) + if ( depth > 1 + && beta < 14362 + && value > -12393) + depth -= depth > 3 && depth < 12 ? 2 : 1; + + assert(depth > 0); + alpha = value; // Update alpha! Always alpha < beta } } } @@ -1365,11 +1346,9 @@ 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 || bestValue < alpha - 65 * depth) - && !priorCapture) + else if (!priorCapture && prevSq != SQ_NONE) { - // Extra bonuses for PV/Cut nodes or bad fail lows - int bonus = 1 + (PvNode || cutNode) + (bestValue < alpha - 88 * depth); + int bonus = (depth > 5) + (PvNode || cutNode) + (bestValue < alpha - 113 * depth) + ((ss-1)->moveCount > 12); update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * bonus); } @@ -1377,7 +1356,7 @@ moves_loop: // When in check, search starts here 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. + // opponent move is probably good and the new position is added to the search tree. (~7 Elo) if (bestValue <= alpha) ss->ttPv = ss->ttPv || ((ss-1)->ttPv && depth > 3); @@ -1396,7 +1375,7 @@ moves_loop: // When in check, search starts 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. - // (~155 elo) + // (~155 Elo) template Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) { @@ -1419,6 +1398,7 @@ moves_loop: // When in check, search starts here bool pvHit, givesCheck, capture; int moveCount; + // Step 1. Initialize node if (PvNode) { (ss+1)->pv = pv; @@ -1430,7 +1410,7 @@ 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; @@ -1441,22 +1421,23 @@ 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 - && ttValue != VALUE_NONE // Only in case of TT access race + && ttValue != VALUE_NONE // Only in case of TT access race or if !ttHit && (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; @@ -1495,7 +1476,7 @@ moves_loop: // When in check, search starts here if (PvNode && bestValue > alpha) alpha = bestValue; - futilityBase = bestValue + 158; + futilityBase = bestValue + 200; } const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, @@ -1506,7 +1487,7 @@ moves_loop: // When in check, search starts here // to search the moves. Because the depth is <= 0 here, only captures, // queen promotions, and other checks (only if depth >= DEPTH_QS_CHECKS) // will be generated. - Square prevSq = to_sq((ss-1)->currentMove); + Square prevSq = (ss-1)->currentMove != MOVE_NULL ? to_sq((ss-1)->currentMove) : SQ_NONE; MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, &thisThread->captureHistory, contHist, @@ -1514,7 +1495,8 @@ 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)); @@ -1524,13 +1506,15 @@ moves_loop: // When in check, search starts here continue; givesCheck = pos.gives_check(move); - capture = pos.capture(move); + capture = pos.capture_stage(move); moveCount++; + // Step 6. Pruning. + if (bestValue > VALUE_TB_LOSS_IN_MAX_PLY) + { // Futility pruning and moveCount pruning (~10 Elo) - if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY - && !givesCheck + if ( !givesCheck && to_sq(move) != prevSq && futilityBase > -VALUE_KNOWN_WIN && type_of(move) != PROMOTION) @@ -1553,43 +1537,42 @@ moves_loop: // When in check, search starts here } } + // 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 ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY - && !pos.see_ge(move, Value(-108))) + if (!pos.see_ge(move, Value(-95))) 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 (~3 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; @@ -1609,6 +1592,7 @@ 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) @@ -1692,12 +1676,13 @@ moves_loop: // When in check, search starts here Thread* thisThread = pos.this_thread(); CapturePieceToHistory& captureHistory = thisThread->captureHistory; Piece moved_piece = pos.moved_piece(bestMove); - PieceType captured = type_of(pos.piece_on(to_sq(bestMove))); + PieceType captured; + int bonus1 = stat_bonus(depth + 1); - if (!pos.capture(bestMove)) + if (!pos.capture_stage(bestMove)) { - int bonus2 = bestValue > beta + 146 ? bonus1 // larger bonus + int bonus2 = bestValue > beta + 145 ? bonus1 // larger bonus : stat_bonus(depth); // smaller bonus // Increase stats for the best move in case it was a quiet move @@ -1711,12 +1696,16 @@ moves_loop: // When in check, search starts here } } else + { // Increase stats for the best move in case it was a capture move + captured = type_of(pos.piece_on(to_sq(bestMove))); captureHistory[moved_piece][to_sq(bestMove)][captured] << bonus1; + } // 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])) + if ( prevSq != SQ_NONE + && ((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);