X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=9a2bd41565911c1bd1179df7d074a20b72ed0846;hp=b8756d381397bd9aeed94a899a1e361695ff3b8d;hb=8a74c089286913f24a641aa37532006088d0f438;hpb=e1f181ee643dcaa92c606b74b3abd23dede136cd diff --git a/src/search.cpp b/src/search.cpp index b8756d38..9a2bd415 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -61,9 +61,6 @@ namespace { // Different node types, used as a template parameter enum NodeType { NonPV, PV, Root }; - constexpr uint64_t TtHitAverageWindow = 4096; - constexpr uint64_t TtHitAverageResolution = 1024; - // Futility margin Value futility_margin(Depth d, bool improving) { return Value(214 * (d - improving)); @@ -72,9 +69,9 @@ namespace { // Reductions lookup table, initialized at startup int Reductions[MAX_MOVES]; // [depth or moveNumber] - Depth reduction(bool i, Depth d, int mn) { + Depth reduction(bool i, Depth d, int mn, bool rangeReduction) { int r = Reductions[d] * Reductions[mn]; - return (r + 534) / 1024 + (!i && r > 904); + return (r + 534) / 1024 + (!i && r > 904) + rangeReduction; } constexpr int futility_move_count(bool improving, Depth depth) { @@ -83,7 +80,7 @@ namespace { // History and stats update bonus, based on depth int stat_bonus(Depth d) { - return d > 14 ? 73 : 6 * d * d + 229 * d - 215; + return std::min((6 * d + 229) * d - 215 , 2000); } // Add a small random component to draw evaluations to avoid 3-fold blindness @@ -91,6 +88,30 @@ namespace { 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; + } + // Skill structure is used to implement strength limit struct Skill { explicit Skill(int l) : level(l) {} @@ -152,7 +173,7 @@ namespace { void Search::init() { for (int i = 1; i < MAX_MOVES; ++i) - Reductions[i] = int(21.3 * std::log(i + 0.25 * std::log(i))); + Reductions[i] = int((21.9 + std::log(Threads.size()) / 2) * std::log(i)); } @@ -310,21 +331,14 @@ void Thread::search() { multiPV = std::max(multiPV, (size_t)4); multiPV = std::min(multiPV, rootMoves.size()); - ttHitAverage = TtHitAverageWindow * TtHitAverageResolution / 2; - - int ct = int(Options["Contempt"]) * PawnValueEg / 100; // From centipawns - // In analysis mode, adjust contempt in accordance with user preference - if (Limits.infinite || Options["UCI_AnalyseMode"]) - ct = Options["Analysis Contempt"] == "Off" ? 0 - : Options["Analysis Contempt"] == "Both" ? ct - : Options["Analysis Contempt"] == "White" && us == BLACK ? -ct - : Options["Analysis Contempt"] == "Black" && us == WHITE ? -ct - : ct; + doubleExtensionAverage[WHITE].set(0, 100); // initialize the running average at 0% + doubleExtensionAverage[BLACK].set(0, 100); // initialize the running average at 0% - // Evaluation score is from the white point of view - contempt = (us == WHITE ? make_score(ct, ct / 2) - : -make_score(ct, ct / 2)); + nodesLastExplosive = nodes; + nodesLastNormal = nodes; + state = EXPLOSION_NONE; + trend = SCORE_ZERO; int searchAgainCounter = 0; @@ -370,11 +384,11 @@ void Thread::search() { alpha = std::max(prev - delta,-VALUE_INFINITE); beta = std::min(prev + delta, VALUE_INFINITE); - // Adjust contempt based on root move's previousScore (dynamic contempt) - int dct = ct + (113 - ct / 2) * prev / (abs(prev) + 147); + // Adjust trend based on root move's previousScore (dynamic contempt) + int tr = 113 * prev / (abs(prev) + 147); - contempt = (us == WHITE ? make_score(dct, dct / 2) - : -make_score(dct, dct / 2)); + trend = (us == WHITE ? make_score(tr, tr / 2) + : -make_score(tr, tr / 2)); } // Start with a small aspiration window and, in the case of a fail @@ -530,6 +544,14 @@ 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; @@ -568,14 +590,13 @@ namespace { bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture, singularQuietLMR; Piece movedPiece; - int moveCount, captureCount, quietCount; + int moveCount, captureCount, quietCount, bestMoveCount, improvement; // Step 1. Initialize node - Thread* thisThread = pos.this_thread(); ss->inCheck = pos.checkers(); priorCapture = pos.captured_piece(); Color us = pos.side_to_move(); - moveCount = captureCount = quietCount = ss->moveCount = 0; + moveCount = bestMoveCount = captureCount = quietCount = ss->moveCount = 0; bestValue = -VALUE_INFINITE; maxValue = VALUE_INFINITE; @@ -614,8 +635,12 @@ namespace { (ss+1)->excludedMove = bestMove = MOVE_NONE; (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE; 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 @@ -633,6 +658,7 @@ 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); if (!excludedMove) ss->ttPv = PvNode || (ss->ttHit && tte->is_pv()); @@ -644,10 +670,6 @@ namespace { && is_ok((ss-1)->currentMove)) thisThread->lowPlyHistory[ss->ply - 1][from_to((ss-1)->currentMove)] << stat_bonus(depth - 5); - // thisThread->ttHitAverage can be used to approximate the running average of ttHit - thisThread->ttHitAverage = (TtHitAverageWindow - 1) * thisThread->ttHitAverage / TtHitAverageWindow - + TtHitAverageResolution * ss->ttHit; - // At non-PV nodes we check for an early TT cutoff if ( !PvNode && ss->ttHit @@ -662,7 +684,7 @@ namespace { if (ttValue >= beta) { // Bonus for a quiet ttMove that fails high - if (!pos.capture_or_promotion(ttMove)) + if (!ttCapture) update_quiet_stats(pos, ss, ttMove, stat_bonus(depth), depth); // Extra penalty for early quiet moves of the previous ply @@ -670,7 +692,7 @@ namespace { update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + 1)); } // Penalty for a quiet ttMove that fails low - else if (!pos.capture_or_promotion(ttMove)) + else if (!ttCapture) { int penalty = -stat_bonus(depth); thisThread->mainHistory[us][from_to(ttMove)] << penalty; @@ -744,6 +766,7 @@ namespace { // Skip early pruning when in check ss->staticEval = eval = VALUE_NONE; improving = false; + improvement = 0; goto moves_loop; } else if (ss->ttHit) @@ -765,13 +788,13 @@ namespace { else { // In case of null move search use previous static eval with a different sign - // and addition of two tempos if ((ss-1)->currentMove != MOVE_NULL) ss->staticEval = eval = evaluate(pos); else ss->staticEval = eval = -(ss-1)->staticEval; // Save static evaluation into transposition table + if(!excludedMove) tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval); } @@ -782,15 +805,18 @@ namespace { thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus; } - // Set up improving flag that is used in various pruning heuristics - // We define position as improving if static evaluation of position is better - // Than the previous static evaluation at our turn - // In case of us being in check at our previous move we look at move prior to it - improving = (ss-2)->staticEval == VALUE_NONE - ? ss->staticEval > (ss-4)->staticEval || (ss-4)->staticEval == VALUE_NONE - : ss->staticEval > (ss-2)->staticEval; + // Set up the improvement variable, which is the difference between the current + // static evaluation and the previous static evaluation at our turn (if we were + // in check at our previous move we look at the move prior to it). The improvement + // 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; - // Step 7. Futility pruning: child node (~50 Elo) + improving = improvement > 0; + + // Step 7. Futility pruning: child node (~50 Elo). + // The depth condition is important for mate finding. if ( !PvNode && depth < 9 && eval - futility_margin(depth, improving) >= beta @@ -803,7 +829,7 @@ namespace { && (ss-1)->statScore < 23767 && eval >= beta && eval >= ss->staticEval - && ss->staticEval >= beta - 20 * depth - 22 * improving + 168 * ss->ttPv + 159 + && ss->staticEval >= beta - 20 * depth - improvement / 15 + 168 * ss->ttPv + 177 && !excludedMove && pos.non_pawn_material(us) && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor)) @@ -811,7 +837,7 @@ namespace { assert(eval - beta >= 0); // Null move dynamic reduction based on depth and value - Depth R = (1090 + 81 * depth) / 256 + std::min(int(eval - beta) / 205, 3); + Depth R = std::min(int(eval - beta) / 205, 3) + depth / 3 + 4; ss->currentMove = MOVE_NULL; ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0]; @@ -913,15 +939,20 @@ namespace { ss->ttPv = ttPv; } - // Step 10. If the position is not in TT, decrease depth by 2 + // Step 10. If the position is not in TT, decrease depth by 2 or 1 depending on node type if ( PvNode && depth >= 6 && !ttMove) depth -= 2; -moves_loop: // When in check, search starts from here + if ( cutNode + && depth >= 9 + && !ttMove) + depth--; - ttCapture = ttMove && pos.capture_or_promotion(ttMove); +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; @@ -954,7 +985,6 @@ moves_loop: // When in check, search starts from here value = bestValue; singularQuietLMR = moveCountPruning = false; - bool doubleExtension = 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. @@ -1001,7 +1031,7 @@ moves_loop: // When in check, search starts from here // Calculate new depth for this move newDepth = depth - 1; - // Step 13. Pruning at shallow depth (~200 Elo) + // Step 13. Pruning at shallow depth (~200 Elo). Depth conditions are important for mate finding. if ( !rootNode && pos.non_pawn_material(us) && bestValue > VALUE_TB_LOSS_IN_MAX_PLY) @@ -1010,7 +1040,7 @@ moves_loop: // When in check, search starts from here moveCountPruning = moveCount >= futility_move_count(improving, depth); // Reduced depth of the next LMR search - int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0); + int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, rangeReduction > 2), 0); if ( captureOrPromotion || givesCheck) @@ -1028,23 +1058,20 @@ moves_loop: // When in check, search starts from here else { // Continuation history based pruning (~20 Elo) - if ( lmrDepth < 5 - && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold - && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold) + if (lmrDepth < 5 + && (*contHist[0])[movedPiece][to_sq(move)] + + (*contHist[1])[movedPiece][to_sq(move)] + + (*contHist[3])[movedPiece][to_sq(move)] < -3000 * depth + 3000) continue; // Futility pruning: parent node (~5 Elo) - if ( lmrDepth < 7 - && !ss->inCheck - && ss->staticEval + 174 + 157 * lmrDepth <= alpha - && (*contHist[0])[movedPiece][to_sq(move)] - + (*contHist[1])[movedPiece][to_sq(move)] - + (*contHist[3])[movedPiece][to_sq(move)] - + (*contHist[5])[movedPiece][to_sq(move)] / 3 < 28255) + if ( !ss->inCheck + && lmrDepth < 8 + && ss->staticEval + 172 + 145 * lmrDepth <= alpha) continue; // Prune moves with negative SEE (~20 Elo) - if (!pos.see_ge(move, Value(-(30 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth))) + if (!pos.see_ge(move, Value(-21 * lmrDepth * lmrDepth - 21 * lmrDepth))) continue; } } @@ -1065,7 +1092,7 @@ moves_loop: // When in check, search starts from here && (tte->bound() & BOUND_LOWER) && tte->depth() >= depth - 3) { - Value singularBeta = ttValue - 2 * depth; + Value singularBeta = ttValue - 3 * depth; Depth singularDepth = (depth - 1) / 2; ss->excludedMove = move; @@ -1077,14 +1104,11 @@ moves_loop: // When in check, search starts from here extension = 1; singularQuietLMR = !ttCapture; - // Avoid search explosion by limiting the number of double extensions to at most 3 + // Avoid search explosion by limiting the number of double extensions if ( !PvNode - && value < singularBeta - 93 - && ss->doubleExtensions < 3) - { + && value < singularBeta - 75 + && ss->doubleExtensions <= 6) extension = 2; - doubleExtension = true; - } } // Multi-cut pruning @@ -1095,21 +1119,28 @@ moves_loop: // When in check, search starts from here else if (singularBeta >= beta) return singularBeta; - // If the eval of ttMove is greater than beta we try also if there is another - // move that pushes it over beta, if so also produce a cutoff. + // If the eval of ttMove is greater than beta, we reduce it (negative extension) else if (ttValue >= beta) - { - ss->excludedMove = move; - value = search(pos, ss, beta - 1, beta, (depth + 3) / 2, cutNode); - ss->excludedMove = MOVE_NONE; - - if (value >= beta) - return beta; - } + extension = -2; } + + // 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) > Value(100)) + && 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; // Add extension to new depth @@ -1140,13 +1171,11 @@ moves_loop: // When in check, search starts from here || !ss->ttPv) && (!PvNode || ss->ply > 1 || thisThread->id() % 4 != 3)) { - Depth r = reduction(improving, depth, moveCount); - - if (PvNode) - r--; + Depth r = reduction(improving, depth, moveCount, rangeReduction > 2); - // Decrease reduction if the ttHit running average is large (~0 Elo) - if (thisThread->ttHitAverage > 537 * TtHitAverageResolution * TtHitAverageWindow / 1024) + // Decrease reduction if on the PV (~2 Elo) + if ( PvNode + && bestMoveCount <= 3) r--; // Decrease reduction if position is or has been on the PV @@ -1157,7 +1186,6 @@ moves_loop: // When in check, search starts from here // Increase reduction at root and non-PV nodes when the best move does not change frequently if ( (rootNode || !PvNode) - && thisThread->rootDepth > 10 && thisThread->bestMoveChanges <= 2) r++; @@ -1170,33 +1198,39 @@ moves_loop: // When in check, search starts from here r--; // Increase reduction for cut nodes (~3 Elo) - if (cutNode) - r += 1 + !captureOrPromotion; + if (cutNode && move != ss->killers[0]) + r += 2; - if (!captureOrPromotion) - { - // Increase reduction if ttMove is a capture (~3 Elo) - if (ttCapture) - r++; - - ss->statScore = thisThread->mainHistory[us][from_to(move)] - + (*contHist[0])[movedPiece][to_sq(move)] - + (*contHist[1])[movedPiece][to_sq(move)] - + (*contHist[3])[movedPiece][to_sq(move)] - - 4923; - - // Decrease/increase reduction for moves with a good/bad history (~30 Elo) - if (!ss->inCheck) - r -= ss->statScore / 14721; - } + // Increase reduction if ttMove is a capture (~3 Elo) + if (ttCapture) + r++; + + ss->statScore = thisThread->mainHistory[us][from_to(move)] + + (*contHist[0])[movedPiece][to_sq(move)] + + (*contHist[1])[movedPiece][to_sq(move)] + + (*contHist[3])[movedPiece][to_sq(move)] + - 4923; + + // 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 <= 3 && r <= -3 ? 2 + : moveCount <= 5 ? 1 + : PvNode && depth > 6 ? 1 + : 0; - // 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, unless ttMove was extended by 2. - Depth d = std::clamp(newDepth - r, 1, newDepth + (r < -1 && moveCount <= 5 && !doubleExtension)); + Depth d = std::clamp(newDepth - r, 1, newDepth + deeper); 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; @@ -1263,9 +1297,11 @@ moves_loop: // When in check, search starts from here for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m) 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 - if (moveCount > 1) + // 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, + // we must take care to only do this for the first PV line. + if ( moveCount > 1 + && !thisThread->pvIdx) ++thisThread->bestMoveChanges; } else @@ -1287,7 +1323,10 @@ moves_loop: // When in check, search starts from here update_pv(ss->pv, move, (ss+1)->pv); if (PvNode && value < beta) // Update alpha! Always alpha < beta + { alpha = value; + bestMoveCount++; + } else { assert(value >= beta); // Fail high @@ -1335,7 +1374,7 @@ moves_loop: // When in check, search starts from here // Bonus for prior countermove that caused the fail low else if ( (depth >= 3 || PvNode) && !priorCapture) - update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth)); + update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * (1 + (PvNode || cutNode))); if (PvNode) bestValue = std::min(bestValue, maxValue); @@ -1446,7 +1485,6 @@ moves_loop: // When in check, search starts from here } else // In case of null move search use previous static eval with a different sign - // and addition of two tempos ss->staticEval = bestValue = (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval; @@ -1486,6 +1524,10 @@ moves_loop: // When in check, search starts from here { assert(is_ok(move)); + // Check for legality + if (!pos.legal(move)) + continue; + givesCheck = pos.gives_check(move); captureOrPromotion = pos.capture_or_promotion(move); @@ -1524,13 +1566,6 @@ moves_loop: // When in check, search starts from here // Speculative prefetch as early as possible prefetch(TT.first_entry(pos.key_after(move))); - // Check for legality just before making the move - if (!pos.legal(move)) - { - moveCount--; - continue; - } - ss->currentMove = move; ss->continuationHistory = &thisThread->continuationHistory[ss->inCheck] [captureOrPromotion] @@ -1659,8 +1694,8 @@ moves_loop: // When in check, search starts from here PieceType captured = type_of(pos.piece_on(to_sq(bestMove))); bonus1 = stat_bonus(depth + 1); - bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus - : std::min(bonus1, stat_bonus(depth)); // smaller bonus + bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus + : stat_bonus(depth); // smaller bonus if (!pos.capture_or_promotion(bestMove)) {