X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=src%2Fsearch.cpp;h=77619345c8f397cc9f7d577a20063f460c6973d5;hb=a41390079147aea89cb5222089a45e1958ebec8e;hp=70dc4b2100cba60644fbe7ff58f76ec84b3c67bf;hpb=95a2ac1e073a6f7c3af8aeef2fc4fe8cbd6650cf;p=stockfish diff --git a/src/search.cpp b/src/search.cpp index 70dc4b21..77619345 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) 2004-2021 The Stockfish developers (see AUTHORS file) + Copyright (C) 2004-2022 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 @@ -63,53 +63,30 @@ namespace { // Futility margin Value futility_margin(Depth d, bool improving) { - return Value(214 * (d - improving)); + return Value(165 * (d - improving)); } // Reductions lookup table, initialized at startup int Reductions[MAX_MOVES]; // [depth or moveNumber] - Depth reduction(bool i, Depth d, int mn, bool rangeReduction) { + Depth reduction(bool i, Depth d, int mn, Value delta, Value rootDelta) { int r = Reductions[d] * Reductions[mn]; - return (r + 534) / 1024 + (!i && r > 904) + rangeReduction; + return (r + 1642 - int(delta) * 1024 / int(rootDelta)) / 1024 + (!i && r > 916); } constexpr int futility_move_count(bool improving, Depth depth) { - return (3 + depth * depth) / (2 - improving); + return improving ? (3 + depth * depth) + : (3 + depth * depth) / 2; } // History and stats update bonus, based on depth int stat_bonus(Depth d) { - return std::min((6 * d + 229) * d - 215 , 2000); + return std::min((12 * d + 282) * d - 349 , 1594); } // Add a small random component to draw evaluations to avoid 3-fold blindness - Value value_draw(Thread* thisThread) { - return VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1); - } - - // Check if the current thread is in a search explosion - ExplosionState search_explosion(Thread* thisThread) { - - uint64_t nodesNow = thisThread->nodes; - bool explosive = thisThread->doubleExtensionAverage[WHITE].is_greater(2, 100) - || thisThread->doubleExtensionAverage[BLACK].is_greater(2, 100); - - if (explosive) - thisThread->nodesLastExplosive = nodesNow; - else - thisThread->nodesLastNormal = nodesNow; - - if ( explosive - && thisThread->state == EXPLOSION_NONE - && nodesNow - thisThread->nodesLastNormal > 6000000) - thisThread->state = MUST_CALM_DOWN; - - if ( thisThread->state == MUST_CALM_DOWN - && nodesNow - thisThread->nodesLastExplosive > 6000000) - thisThread->state = EXPLOSION_NONE; - - return thisThread->state; + Value value_draw(const Thread* thisThread) { + return VALUE_DRAW - 1 + Value(thisThread->nodes & 0x2); } // Skill structure is used to implement strength limit. If we have an uci_elo then @@ -139,9 +116,9 @@ namespace { Value value_to_tt(Value v, int ply); Value value_from_tt(Value v, int ply, int r50c); - void update_pv(Move* pv, Move move, Move* childPv); + void update_pv(Move* pv, Move move, const Move* childPv); void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus); - void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus, int depth); + void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus); void update_all_stats(const Position& pos, Stack* ss, Move bestMove, Value bestValue, Value beta, Square prevSq, Move* quietsSearched, int quietCount, Move* capturesSearched, int captureCount, Depth depth); @@ -181,7 +158,7 @@ namespace { void Search::init() { for (int i = 1; i < MAX_MOVES; ++i) - Reductions[i] = int((21.9 + std::log(Threads.size()) / 2) * std::log(i)); + Reductions[i] = int((20.26 + std::log(Threads.size()) / 2) * std::log(i)); } @@ -260,6 +237,10 @@ void MainThread::search() { bestThread = Threads.get_best_thread(); 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) @@ -316,9 +297,6 @@ void Thread::search() { mainThread->iterValue[i] = mainThread->bestPreviousScore; } - std::copy(&lowPlyHistory[2][0], &lowPlyHistory.back().back() + 1, &lowPlyHistory[0][0]); - std::fill(&lowPlyHistory[MAX_LPH - 2][0], &lowPlyHistory.back().back() + 1, 0); - size_t multiPV = size_t(Options["MultiPV"]); Skill skill(Options["Skill Level"], Options["UCI_LimitStrength"] ? int(Options["UCI_Elo"]) : 0); @@ -329,15 +307,9 @@ void Thread::search() { multiPV = std::min(multiPV, rootMoves.size()); - doubleExtensionAverage[WHITE].set(0, 100); // initialize the running average at 0% - doubleExtensionAverage[BLACK].set(0, 100); // initialize the running average at 0% + complexityAverage.set(155, 1); - nodesLastExplosive = nodes; - nodesLastNormal = nodes; - state = EXPLOSION_NONE; - trend = SCORE_ZERO; - optimism[ us] = Value(25); - optimism[~us] = -optimism[us]; + optimism[us] = optimism[~us] = VALUE_ZERO; int searchAgainCounter = 0; @@ -379,16 +351,12 @@ void Thread::search() { if (rootDepth >= 4) { Value prev = rootMoves[pvIdx].averageScore; - delta = Value(17) + int(prev) * prev / 16384; + delta = Value(10) + int(prev) * prev / 15620; alpha = std::max(prev - delta,-VALUE_INFINITE); beta = std::min(prev + delta, VALUE_INFINITE); - // Adjust trend and optimism based on root move's previousScore - int tr = sigmoid(prev, 0, 0, 147, 113, 1); - trend = (us == WHITE ? make_score(tr, tr / 2) - : -make_score(tr, tr / 2)); - - int opt = sigmoid(prev, 0, 25, 147, 14464, 256); + // Adjust optimism based on root move's previousScore + int opt = 118 * prev / (std::abs(prev) + 169); optimism[ us] = Value(opt); optimism[~us] = -optimism[us]; } @@ -399,7 +367,9 @@ void Thread::search() { int failedHighCnt = 0; while (true) { - Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter); + // Adjust the effective depth searched, but ensuring at least one effective increment for every + // four searchAgain steps (see issue #2717). + Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - 3 * (searchAgainCounter + 1) / 4); bestValue = Stockfish::search(rootPos, ss, alpha, beta, adjustedDepth, false); // Bring the best move to the front. It is critical that sorting @@ -443,7 +413,7 @@ void Thread::search() { else break; - delta += delta / 4 + 5; + delta += delta / 4 + 2; assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE); } @@ -477,28 +447,30 @@ void Thread::search() { if (skill.enabled() && skill.time_to_pick(rootDepth)) skill.pick_best(multiPV); + // Use part of the gained time from a previous stable move for the current move + for (Thread* th : Threads) + { + totBestMoveChanges += th->bestMoveChanges; + th->bestMoveChanges = 0; + } + // Do we have time for the next iteration? Can we stop searching now? if ( Limits.use_time_management() && !Threads.stop && !mainThread->stopOnPonderhit) { - double fallingEval = (318 + 6 * (mainThread->bestPreviousScore - bestValue) - + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 825.0; + double fallingEval = (71 + 12 * (mainThread->bestPreviousAverageScore - bestValue) + + 6 * (mainThread->iterValue[iterIdx] - bestValue)) / 656.7; fallingEval = std::clamp(fallingEval, 0.5, 1.5); // If the bestMove is stable over several iterations, reduce time accordingly - timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.92 : 0.95; - double reduction = (1.47 + mainThread->previousTimeReduction) / (2.32 * timeReduction); + 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); - // Use part of the gained time from a previous stable move for the current move - for (Thread* th : Threads) - { - totBestMoveChanges += th->bestMoveChanges; - th->bestMoveChanges = 0; - } - double bestMoveInstability = 1.073 + std::max(1.0, 2.25 - 9.9 / rootDepth) - * totBestMoveChanges / Threads.size(); - double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability; + double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability * complexPosition; // Cap used time in case of a single legal move for a better viewer experience in tournaments // yielding correct scores and sufficiently fast moves. @@ -517,7 +489,7 @@ void Thread::search() { } else if ( Threads.increaseDepth && !mainThread->ponder - && Time.elapsed() > totalTime * 0.58) + && Time.elapsed() > totalTime * 0.53) Threads.increaseDepth = false; else Threads.increaseDepth = true; @@ -546,14 +518,6 @@ namespace { template Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) { - Thread* thisThread = pos.this_thread(); - - // Step 0. Limit search explosion - if ( ss->ply > 10 - && search_explosion(thisThread) == MUST_CALM_DOWN - && depth > (ss-1)->depth) - depth = (ss-1)->depth; - constexpr bool PvNode = nodeType != NonPV; constexpr bool rootNode = nodeType == Root; const Depth maxNextDepth = rootNode ? depth : depth + 1; @@ -588,17 +552,17 @@ namespace { Move ttMove, move, excludedMove, bestMove; Depth extension, newDepth; Value bestValue, value, ttValue, eval, maxValue, probCutBeta; - bool givesCheck, improving, didLMR, priorCapture; - bool captureOrPromotion, doFullDepthSearch, moveCountPruning, - ttCapture, singularQuietLMR; + bool givesCheck, improving, priorCapture, singularQuietLMR; + bool capture, moveCountPruning, ttCapture; Piece movedPiece; - int moveCount, captureCount, quietCount, bestMoveCount, improvement; + int moveCount, captureCount, quietCount, improvement, complexity; // Step 1. Initialize node + Thread* thisThread = pos.this_thread(); ss->inCheck = pos.checkers(); priorCapture = pos.captured_piece(); Color us = pos.side_to_move(); - moveCount = bestMoveCount = captureCount = quietCount = ss->moveCount = 0; + moveCount = captureCount = quietCount = ss->moveCount = 0; bestValue = -VALUE_INFINITE; maxValue = VALUE_INFINITE; @@ -638,13 +602,10 @@ namespace { (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; - ss->depth = depth; Square prevSq = to_sq((ss-1)->currentMove); - // Update the running average statistics for double extensions - thisThread->doubleExtensionAverage[us].update(ss->depth > (ss-1)->depth); - // 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 @@ -662,40 +623,31 @@ namespace { 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_or_promotion(ttMove); + ttCapture = ttMove && pos.capture(ttMove); if (!excludedMove) ss->ttPv = PvNode || (ss->ttHit && tte->is_pv()); - // 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 - && is_ok((ss-1)->currentMove)) - thisThread->lowPlyHistory[ss->ply - 1][from_to((ss-1)->currentMove)] << stat_bonus(depth - 5); - // At non-PV nodes we check for an early TT cutoff if ( !PvNode && ss->ttHit - && tte->depth() > depth - (thisThread->id() % 2 == 1) + && tte->depth() > depth - (tte->bound() == BOUND_EXACT) && ttValue != VALUE_NONE // Possible in case of TT access race - && (ttValue >= beta ? (tte->bound() & BOUND_LOWER) - : (tte->bound() & BOUND_UPPER))) + && (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER))) { - // If ttMove is quiet, update move sorting heuristics on TT hit + // If ttMove is quiet, update move sorting heuristics on TT hit (~1 Elo) if (ttMove) { if (ttValue >= beta) { - // Bonus for a quiet ttMove that fails high + // Bonus for a quiet ttMove that fails high (~3 Elo) if (!ttCapture) - update_quiet_stats(pos, ss, ttMove, stat_bonus(depth), depth); + update_quiet_stats(pos, ss, ttMove, stat_bonus(depth)); - // Extra penalty for early quiet moves of the previous ply + // Extra penalty for early quiet moves of the previous ply (~0 Elo) if ((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 + // Penalty for a quiet ttMove that fails low (~1 Elo) else if (!ttCapture) { int penalty = -stat_bonus(depth); @@ -771,6 +723,7 @@ namespace { ss->staticEval = eval = VALUE_NONE; improving = false; improvement = 0; + complexity = 0; goto moves_loop; } else if (ss->ttHit) @@ -778,30 +731,30 @@ namespace { // 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); + 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()); - // Can ttValue be used as a better position evaluation? + // ttValue can be used as a better position evaluation (~4 Elo) if ( ttValue != VALUE_NONE && (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))) eval = ttValue; } else { - ss->staticEval = eval = evaluate(pos); + 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); } - // Use static evaluation difference to improve quiet move ordering + thisThread->complexityAverage.update(complexity); + + // Use static evaluation difference to improve quiet move ordering (~3 Elo) if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture) { - int bonus = std::clamp(-16 * int((ss-1)->staticEval + ss->staticEval), -2000, 2000); + int bonus = std::clamp(-19 * int((ss-1)->staticEval + ss->staticEval), -1914, 1914); thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus; } @@ -811,33 +764,43 @@ 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 - : 200; - + : 168; improving = improvement > 0; - // Step 7. Futility pruning: child node (~50 Elo). + // Step 7. Razoring. + // 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) + { + value = qsearch(pos, ss, alpha - 1, alpha); + if (value < alpha) + return value; + } + + // Step 8. Futility pruning: child node (~25 Elo). // The depth condition is important for mate finding. if ( !ss->ttPv - && depth < 9 - && eval - futility_margin(depth, improving) >= beta - && eval < 15000) // 50% larger than VALUE_KNOWN_WIN, but smaller than TB wins. + && depth < 8 + && eval - futility_margin(depth, improving) - (ss-1)->statScore / 303 >= beta + && eval >= beta + && eval < 28031) // larger than VALUE_KNOWN_WIN, but smaller than TB wins return eval; - // Step 8. Null move search with verification search (~40 Elo) + // Step 9. Null move search with verification search (~22 Elo) if ( !PvNode && (ss-1)->currentMove != MOVE_NULL - && (ss-1)->statScore < 23767 + && (ss-1)->statScore < 17139 && eval >= beta && eval >= ss->staticEval - && ss->staticEval >= beta - 20 * depth - improvement / 15 + 204 + && ss->staticEval >= beta - 20 * depth - improvement / 13 + 233 + complexity / 25 && !excludedMove && pos.non_pawn_material(us) && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor)) { assert(eval - beta >= 0); - // Null move dynamic reduction based on depth and value - Depth R = std::min(int(eval - beta) / 205, 3) + depth / 3 + 4; + // 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); ss->currentMove = MOVE_NULL; ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0]; @@ -873,9 +836,9 @@ namespace { } } - probCutBeta = beta + 209 - 44 * improving; + probCutBeta = beta + 191 - 54 * improving; - // Step 9. ProbCut (~4 Elo) + // Step 10. 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 @@ -892,21 +855,16 @@ namespace { { assert(probCutBeta < VALUE_INFINITE); - MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory); - bool ttPv = ss->ttPv; - ss->ttPv = false; + MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, depth - 3, &captureHistory); while ((move = mp.next_move()) != MOVE_NONE) if (move != excludedMove && pos.legal(move)) { - assert(pos.capture_or_promotion(move)); - assert(depth >= 5); - - captureOrPromotion = true; + assert(pos.capture(move) || promotion_type(move) == QUEEN); ss->currentMove = move; ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck] - [captureOrPromotion] + [true] [pos.moved_piece(move)] [to_sq(move)]; @@ -923,39 +881,34 @@ namespace { if (value >= probCutBeta) { - // 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); + // Save ProbCut data into transposition table + tte->save(posKey, value_to_tt(value, ss->ply), ss->ttPv, BOUND_LOWER, depth - 3, move, ss->staticEval); return value; } } - ss->ttPv = ttPv; } - // Step 10. If the position is not in TT, decrease depth by 2 or 1 depending on node type - if ( PvNode - && depth >= 6 + // Step 11. If the position is not in TT, decrease depth by 3. + // Use qsearch if depth is equal or below zero (~4 Elo) + if ( PvNode && !ttMove) - depth -= 2; + depth -= 3; + + if (depth <= 0) + return qsearch(pos, ss, alpha, beta); - if ( cutNode - && depth >= 9 + if ( cutNode + && depth >= 9 && !ttMove) - depth--; + depth -= 2; moves_loop: // When in check, search starts here - int rangeReduction = 0; - - // Step 11. A small Probcut idea, when we are in check - probCutBeta = beta + 409; + // Step 12. A small Probcut idea, when we are in check (~0 Elo) + probCutBeta = beta + 417; if ( ss->inCheck && !PvNode - && depth >= 4 + && depth >= 2 && ttCapture && (tte->bound() & BOUND_LOWER) && tte->depth() >= depth - 3 @@ -973,15 +926,13 @@ moves_loop: // When in check, search starts here Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq]; MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, - &thisThread->lowPlyHistory, &captureHistory, contHist, countermove, - ss->killers, - ss->ply); + ss->killers); value = bestValue; - singularQuietLMR = moveCountPruning = false; + moveCountPruning = singularQuietLMR = false; // 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. @@ -990,7 +941,7 @@ moves_loop: // When in check, search starts here && (tte->bound() & BOUND_UPPER) && tte->depth() >= depth; - // Step 12. Loop through all pseudo-legal moves until no moves remain + // Step 13. Loop through all pseudo-legal moves until no moves remain // or a beta cutoff occurs. while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE) { @@ -1021,35 +972,40 @@ moves_loop: // When in check, search starts here (ss+1)->pv = nullptr; extension = 0; - captureOrPromotion = pos.capture_or_promotion(move); + capture = pos.capture(move); movedPiece = pos.moved_piece(move); givesCheck = pos.gives_check(move); // Calculate new depth for this move newDepth = depth - 1; - // Step 13. Pruning at shallow depth (~200 Elo). Depth conditions are important for mate finding. + Value delta = beta - alpha; + + // Step 14. Pruning at shallow depth (~98 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 + // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold (~7 Elo) moveCountPruning = moveCount >= futility_move_count(improving, depth); // Reduced depth of the next LMR search - int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, rangeReduction > 2), 0); + int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, delta, thisThread->rootDelta), 0); - if ( captureOrPromotion + if ( capture || givesCheck) { - // Capture history based pruning when the move doesn't give check + // Futility pruning for captures (~0 Elo) if ( !givesCheck - && lmrDepth < 1 - && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0) + && !PvNode + && lmrDepth < 7 + && !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) continue; - // SEE based pruning - if (!pos.see_ge(move, Value(-218) * depth)) // (~25 Elo) + // SEE based pruning (~9 Elo) + if (!pos.see_ge(move, Value(-222) * depth)) continue; } else @@ -1058,91 +1014,92 @@ moves_loop: // When in check, search starts here + (*contHist[1])[movedPiece][to_sq(move)] + (*contHist[3])[movedPiece][to_sq(move)]; - // Continuation history based pruning (~20 Elo) + // Continuation history based pruning (~2 Elo) if ( lmrDepth < 5 - && history < -3000 * depth + 3000) + && history < -3875 * (depth - 1)) continue; - history += thisThread->mainHistory[us][from_to(move)]; + history += 2 * thisThread->mainHistory[us][from_to(move)]; - // Futility pruning: parent node (~5 Elo) + // Futility pruning: parent node (~9 Elo) if ( !ss->inCheck - && lmrDepth < 8 - && ss->staticEval + 142 + 139 * lmrDepth + history / 64 <= alpha) + && lmrDepth < 13 + && ss->staticEval + 106 + 145 * lmrDepth + history / 52 <= alpha) continue; - // Prune moves with negative SEE (~20 Elo) - if (!pos.see_ge(move, Value(-21 * lmrDepth * lmrDepth - 21 * lmrDepth))) + // Prune moves with negative SEE (~3 Elo) + if (!pos.see_ge(move, Value(-24 * lmrDepth * lmrDepth - 15 * lmrDepth))) continue; } } - // Step 14. 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 ( !rootNode - && depth >= 7 - && move == ttMove - && !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) + // Step 15. Extensions (~66 Elo) + // We take care to not overdo to avoid search getting stuck. + if (ss->ply < thisThread->rootDepth * 2) { - Value singularBeta = ttValue - 3 * depth; - Depth singularDepth = (depth - 1) / 2; + // Singular extension search (~58 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()) + && move == ttMove + && !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 - (3 + (ss->ttPv && !PvNode)) * depth; + Depth singularDepth = (depth - 1) / 2; - ss->excludedMove = move; - value = search(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode); - ss->excludedMove = MOVE_NONE; + ss->excludedMove = move; + value = search(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode); + ss->excludedMove = MOVE_NONE; - if (value < singularBeta) - { - extension = 1; - singularQuietLMR = !ttCapture; + if (value < singularBeta) + { + extension = 1; + singularQuietLMR = !ttCapture; + + // Avoid search explosion by limiting the number of double extensions + if ( !PvNode + && value < singularBeta - 25 + && ss->doubleExtensions <= 9) + extension = 2; + } - // Avoid search explosion by limiting the number of double extensions - if ( !PvNode - && value < singularBeta - 75 - && ss->doubleExtensions <= 6) - extension = 2; + // Multi-cut pruning + // Our ttMove is assumed to fail high, and now we failed high also on a reduced + // search without the ttMove. So we assume this expected Cut-node is not singular, + // that multiple moves fail high, and we can prune the whole subtree by returning + // a soft bound. + else if (singularBeta >= beta) + return singularBeta; + + // If the eval of ttMove is greater than beta, we reduce it (negative extension) + 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) + extension = -1; } - // Multi-cut pruning - // Our ttMove is assumed to fail high, and now we failed high also on a reduced - // search without the ttMove. So we assume this expected Cut-node is not singular, - // that multiple moves fail high, and we can prune the whole subtree by returning - // a soft bound. - else if (singularBeta >= beta) - return singularBeta; - - // If the eval of ttMove is greater than beta, we reduce it (negative extension) - else if (ttValue >= beta) - extension = -2; - } + // Check extensions (~1 Elo) + else if ( givesCheck + && depth > 9 + && abs(ss->staticEval) > 82) + extension = 1; - // Capture extensions for PvNodes and cutNodes - else if ( (PvNode || cutNode) - && captureOrPromotion - && moveCount != 1) - extension = 1; - - // Check extensions - else if ( givesCheck - && depth > 6 - && abs(ss->staticEval) > 100) - extension = 1; - - // Quiet ttMove extensions - else if ( PvNode - && move == ttMove - && move == ss->killers[0] - && (*contHist[0])[movedPiece][to_sq(move)] >= 10000) - extension = 1; + // Quiet ttMove extensions (~0 Elo) + else if ( PvNode + && move == ttMove + && move == ss->killers[0] + && (*contHist[0])[movedPiece][to_sq(move)] >= 5177) + extension = 1; + } // Add extension to new depth newDepth += extension; @@ -1154,30 +1111,24 @@ moves_loop: // When in check, search starts here // Update the current move (this must be done after singular extension search) ss->currentMove = move; ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck] - [captureOrPromotion] + [capture] [movedPiece] [to_sq(move)]; - // Step 15. Make the move + // Step 16. Make the move pos.do_move(move, st, givesCheck); - // Step 16. Late moves reduction / extension (LMR, ~200 Elo) + // 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 >= 3 - && moveCount > 1 + 2 * rootNode + if ( depth >= 2 + && moveCount > 1 + (PvNode && ss->ply <= 1) && ( !ss->ttPv - || !captureOrPromotion + || !capture || (cutNode && (ss-1)->moveCount > 1))) { - Depth r = reduction(improving, depth, moveCount, rangeReduction > 2); - - // Decrease reduction at some PvNodes (~2 Elo) - if ( PvNode - && bestMoveCount <= 3 - && beta - alpha >= thisThread->rootDelta / 4) - r--; + 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) @@ -1185,78 +1136,73 @@ moves_loop: // When in check, search starts here && !likelyFailLow) r -= 2; - // Increase reduction at non-PV nodes when the best move does not change frequently - if ( !PvNode - && thisThread->bestMoveChanges <= 2) - r++; - // 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 (~1 Elo) - if (singularQuietLMR) + if ((ss-1)->moveCount > 7) r--; // Increase reduction for cut nodes (~3 Elo) - if (cutNode && move != ss->killers[0]) + if (cutNode) r += 2; // Increase reduction if ttMove is a capture (~3 Elo) if (ttCapture) r++; - ss->statScore = thisThread->mainHistory[us][from_to(move)] + // 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--; + + // Dicrease 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 && !PvNode) + 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)] - - 4923; + - 4433; // Decrease/increase reduction for moves with a good/bad history (~30 Elo) - 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 (this may lead to hidden double extensions). - int deeper = r >= -1 ? 0 - : moveCount <= 5 ? 2 - : PvNode && depth > 6 ? 1 - : cutNode && moveCount <= 7 ? 1 - : 0; + r -= ss->statScore / (13628 + 4000 * (depth > 7 && depth < 19)); - Depth d = std::clamp(newDepth - r, 1, newDepth + deeper); + // 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. + Depth d = std::clamp(newDepth - r, 1, newDepth + 1); value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); - // Range reductions (~3 Elo) - if (ss->staticEval - value < 30 && depth > 7) - rangeReduction++; - - // If the son is reduced and fails high it will be re-searched at full depth - doFullDepthSearch = value > alpha && d < newDepth; - didLMR = true; - } - else - { - doFullDepthSearch = !PvNode || moveCount > 1; - didLMR = false; - } - - // Step 17. 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) + // Do full depth search when reduced LMR search fails high + if (value > alpha && d < newDepth) { + const bool doDeeperSearch = value > (alpha + 64 + 11 * (newDepth - d)); + value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth + doDeeperSearch, !cutNode); + 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 + else if (!PvNode || moveCount > 1) + { + value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); + } + // For PV nodes only, do a full PV search on the first move or after a fail // high (in the latter case search only if value < beta), otherwise let the // parent node fail low with value <= alpha and try another move. @@ -1269,12 +1215,12 @@ moves_loop: // When in check, search starts here std::min(maxNextDepth, newDepth), false); } - // Step 18. Undo move + // Step 19. Undo move pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); - // Step 19. Check for a new best move + // Step 20. 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. @@ -1301,7 +1247,7 @@ moves_loop: // When in check, search starts 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 and LMR. In MultiPV mode, + // This information is used for time management. In MultiPV mode, // we must take care to only do this for the first PV line. if ( moveCount > 1 && !thisThread->pvIdx) @@ -1328,23 +1274,35 @@ moves_loop: // When in check, search starts here if (PvNode && value < beta) // Update alpha! Always alpha < beta { alpha = value; - bestMoveCount++; + + // 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); } else { + ss->cutoffCnt++; assert(value >= beta); // Fail high break; } } } + else + ss->cutoffCnt = 0; + // If the move is worse than some previously searched move, remember it to update its stats later if (move != bestMove) { - if (captureOrPromotion && captureCount < 32) + if (capture && captureCount < 32) capturesSearched[captureCount++] = move; - else if (!captureOrPromotion && quietCount < 64) + else if (!capture && quietCount < 64) quietsSearched[quietCount++] = move; } } @@ -1357,7 +1315,7 @@ moves_loop: // When in check, search starts here return VALUE_DRAW; */ - // Step 20. Check for mate and stalemate + // Step 21. 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. @@ -1375,9 +1333,17 @@ 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 >= 3 || PvNode) + else if ( (depth >= 5 || PvNode) && !priorCapture) - update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * (1 + (PvNode || cutNode))); + { + //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)); + } if (PvNode) bestValue = std::min(bestValue, maxValue); @@ -1386,10 +1352,6 @@ moves_loop: // When in check, search starts here // 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)) @@ -1406,6 +1368,7 @@ 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) template Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) { @@ -1425,7 +1388,7 @@ moves_loop: // When in check, search starts here Move ttMove, move, bestMove; Depth ttDepth; Value bestValue, value, ttValue, futilityValue, futilityBase; - bool pvHit, givesCheck, captureOrPromotion; + bool pvHit, givesCheck, capture; int moveCount; if (PvNode) @@ -1462,8 +1425,7 @@ moves_loop: // When in check, search starts here && ss->ttHit && tte->depth() >= ttDepth && ttValue != VALUE_NONE // Only in case of TT access race - && (ttValue >= beta ? (tte->bound() & BOUND_LOWER) - : (tte->bound() & BOUND_UPPER))) + && (tte->bound() & (ttValue >= beta ? BOUND_LOWER : BOUND_UPPER))) return ttValue; // Evaluate the position statically @@ -1480,7 +1442,7 @@ moves_loop: // When in check, search starts here if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE) ss->staticEval = bestValue = evaluate(pos); - // Can ttValue be used as a better position evaluation? + // ttValue can be used as a better position evaluation (~7 Elo) if ( ttValue != VALUE_NONE && (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))) bestValue = ttValue; @@ -1505,7 +1467,7 @@ moves_loop: // When in check, search starts here if (PvNode && bestValue > alpha) alpha = bestValue; - futilityBase = bestValue + 155; + futilityBase = bestValue + 153; } const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, @@ -1516,10 +1478,13 @@ 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); MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, &thisThread->captureHistory, contHist, - to_sq((ss-1)->currentMove)); + prevSq); + + int quietCheckEvasions = 0; // Loop through the moves until no moves remain or a beta cutoff occurs while ((move = mp.next_move()) != MOVE_NONE) @@ -1531,13 +1496,14 @@ moves_loop: // When in check, search starts here continue; givesCheck = pos.gives_check(move); - captureOrPromotion = pos.capture_or_promotion(move); + capture = pos.capture(move); moveCount++; - // Futility pruning and moveCount pruning + // Futility pruning and moveCount pruning (~5 Elo) if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY && !givesCheck + && to_sq(move) != prevSq && futilityBase > -VALUE_KNOWN_WIN && type_of(move) != PROMOTION) { @@ -1560,7 +1526,7 @@ moves_loop: // When in check, search starts here } } - // Do not search moves with negative SEE values + // Do not search moves with negative SEE values (~5 Elo) if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY && !pos.see_ge(move)) continue; @@ -1570,17 +1536,26 @@ moves_loop: // When in check, search starts here ss->currentMove = move; ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck] - [captureOrPromotion] + [capture] [pos.moved_piece(move)] [to_sq(move)]; - // Continuation history based pruning - if ( !captureOrPromotion + // Continuation history based pruning (~2 Elo) + if ( !capture && 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) + && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < 0 + && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < 0) continue; + // movecount pruning for quiet check evasions + if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY + && quietCheckEvasions > 1 + && !capture + && ss->inCheck) + continue; + + quietCheckEvasions += !capture && ss->inCheck; + // Make and search the move pos.do_move(move, st, givesCheck); value = -qsearch(pos, ss+1, -beta, -alpha, depth - 1); @@ -1674,7 +1649,7 @@ moves_loop: // When in check, search starts here // update_pv() adds current move and appends child pv[] - void update_pv(Move* pv, Move move, Move* childPv) { + void update_pv(Move* pv, Move move, const Move* childPv) { for (*pv++ = move; childPv && *childPv != MOVE_NONE; ) *pv++ = *childPv++; @@ -1687,21 +1662,20 @@ moves_loop: // When in check, search starts here void update_all_stats(const Position& pos, Stack* ss, Move bestMove, Value bestValue, Value beta, Square prevSq, Move* quietsSearched, int quietCount, Move* capturesSearched, int captureCount, Depth depth) { - int bonus1, bonus2; Color us = pos.side_to_move(); 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))); + int bonus1 = stat_bonus(depth + 1); - bonus1 = stat_bonus(depth + 1); - bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus + if (!pos.capture(bestMove)) + { + int bonus2 = bestValue > beta + 137 ? bonus1 // larger bonus : stat_bonus(depth); // smaller bonus - 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); + update_quiet_stats(pos, ss, bestMove, bonus2); // Decrease stats for all non-best quiet moves for (int i = 0; i < quietCount; ++i) @@ -1748,7 +1722,7 @@ moves_loop: // When in check, search starts here // update_quiet_stats() updates move sorting heuristics - void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus, int depth) { + void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus) { // Update killers if (ss->killers[0] != move) @@ -1768,10 +1742,6 @@ moves_loop: // When in check, search starts here 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 - 7); } // When playing with strength handicap, choose best move among a set of RootMoves @@ -1888,12 +1858,9 @@ string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) { ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : ""); ss << " nodes " << nodesSearched - << " nps " << nodesSearched * 1000 / elapsed; - - if (elapsed > 1000) // Earlier makes little sense - ss << " hashfull " << TT.hashfull(); - - ss << " tbhits " << tbHits + << " nps " << nodesSearched * 1000 / elapsed + << " hashfull " << TT.hashfull() + << " tbhits " << tbHits << " time " << elapsed << " pv";