X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=f0783363e79766fc682dabbf42fc4d0d0cda9469;hp=f132e3ecc03307269030299443dcf931233b5108;hb=f2681232e516da164196d7238482729da038ae1e;hpb=16b31bb249ccb9f4f625001f9772799d286e2f04 diff --git a/src/search.cpp b/src/search.cpp index f132e3ec..f0783363 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -31,8 +31,8 @@ #include "movepick.h" #include "position.h" #include "search.h" -#include "timeman.h" #include "thread.h" +#include "timeman.h" #include "tt.h" #include "uci.h" #include "syzygy/tbprobe.h" @@ -63,12 +63,24 @@ namespace { enum NodeType { NonPV, PV }; // Sizes and phases of the skip-blocks, used for distributing search depths across the threads - const int SkipSize[] = { 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4 }; - const int SkipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 }; + constexpr int SkipSize[] = { 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4 }; + constexpr int SkipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 }; - // Razoring and futility margins - const int RazorMargin = 590; - Value futility_margin(Depth d) { return Value(150 * d / ONE_PLY); } + // Razor and futility margins + constexpr int RazorMargin[] = {0, 590, 604}; + Value futility_margin(Depth d, bool improving) { + return Value((175 - 50 * improving) * d / ONE_PLY); + } + + // Margin for pruning capturing moves: almost linear in depth + constexpr int CapturePruneMargin[] = { 0, + 1 * PawnValueEg * 1055 / 1000, + 2 * PawnValueEg * 1042 / 1000, + 3 * PawnValueEg * 963 / 1000, + 4 * PawnValueEg * 1038 / 1000, + 5 * PawnValueEg * 950 / 1000, + 6 * PawnValueEg * 930 / 1000 + }; // Futility and reductions lookup tables, initialized at startup int FutilityMoveCounts[2][16]; // [improving][depth] @@ -98,7 +110,7 @@ namespace { template Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning); - template + template Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO); Value value_to_tt(Value v, int ply); @@ -108,6 +120,13 @@ namespace { void update_quiet_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, int bonus); void update_capture_stats(const Position& pos, Move move, Move* captures, int captureCnt, int bonus); + inline bool gives_check(const Position& pos, Move move) { + Color us = pos.side_to_move(); + return type_of(move) == NORMAL && !(pos.blockers_for_king(~us) & pos.pieces(us)) + ? pos.check_squares(type_of(pos.moved_piece(move))) & to_sq(move) + : pos.gives_check(move); + } + // perft() is our utility to verify move generation. All the leaf nodes up // to the given depth are generated and counted, and the sum is returned. template @@ -151,7 +170,7 @@ void Search::init() { Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0); // Increase reduction for non-PV nodes when eval is not improving - if (!imp && Reductions[NonPV][imp][d][mc] >= 2) + if (!imp && r > 1.0) Reductions[NonPV][imp][d][mc]++; } @@ -281,7 +300,7 @@ void Thread::search() { std::memset(ss-4, 0, 7 * sizeof(Stack)); for (int i = 4; i > 0; i--) - (ss-i)->contHistory = &this->contHistory[NO_PIECE][0]; // Use as sentinel + (ss-i)->contHistory = this->contHistory[NO_PIECE][0].get(); // Use as sentinel bestValue = delta = alpha = -VALUE_INFINITE; beta = VALUE_INFINITE; @@ -300,8 +319,8 @@ void Thread::search() { multiPV = std::min(multiPV, rootMoves.size()); int ct = Options["Contempt"] * PawnValueEg / 100; // From centipawns - Eval::Contempt = (us == WHITE ? make_score(ct, ct / 2) - : -make_score(ct, ct / 2)); + contempt = (us == WHITE ? make_score(ct, ct / 2) + : -make_score(ct, ct / 2)); // Iterative deepening loop until requested to stop or the target depth is reached while ( (rootDepth += ONE_PLY) < DEPTH_MAX @@ -318,7 +337,7 @@ void Thread::search() { // Age out PV variability metric if (mainThread) - mainThread->bestMoveChanges *= 0.505, mainThread->failedLow = false; + mainThread->bestMoveChanges *= 0.517, mainThread->failedLow = false; // Save the last iteration's scores before first PV line is searched and // all the move scores except the (new) PV are set to -VALUE_INFINITE. @@ -334,18 +353,18 @@ void Thread::search() { // Reset aspiration window starting size if (rootDepth >= 5 * ONE_PLY) { + Value previousScore = rootMoves[PVIdx].previousScore; delta = Value(18); - alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE); - beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE); + alpha = std::max(previousScore - delta,-VALUE_INFINITE); + beta = std::min(previousScore + delta, VALUE_INFINITE); + + ct = Options["Contempt"] * PawnValueEg / 100; // From centipawns - // Adjust contempt based on current bestValue - ct = Options["Contempt"] * PawnValueEg / 100 // From centipawns - + (bestValue > 500 ? 50: // Dynamic contempt - bestValue < -500 ? -50: - bestValue / 10); + // Adjust contempt based on root move's previousScore (dynamic contempt) + ct += int(std::round(48 * atan(float(previousScore) / 128))); - Eval::Contempt = (us == WHITE ? make_score(ct, ct / 2) - : -make_score(ct, ct / 2)); + contempt = (us == WHITE ? make_score(ct, ct / 2) + : -make_score(ct, ct / 2)); } // Start with a small aspiration window and, in the case of a fail @@ -437,21 +456,21 @@ void Thread::search() { const int F[] = { mainThread->failedLow, bestValue - mainThread->previousScore }; - int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1])); + int improvingFactor = std::max(246, std::min(832, 306 + 119 * F[0] - 6 * F[1])); // If the bestMove is stable over several iterations, reduce time accordingly timeReduction = 1.0; for (int i : {3, 4, 5}) if (lastBestMoveDepth * i < completedDepth) - timeReduction *= 1.3; + timeReduction *= 1.25; // Use part of the gained time from a previous stable move for the current move - double unstablePvFactor = 1.0 + mainThread->bestMoveChanges; - unstablePvFactor *= std::pow(mainThread->previousTimeReduction, 0.51) / timeReduction; + double bestMoveInstability = 1.0 + mainThread->bestMoveChanges; + bestMoveInstability *= std::pow(mainThread->previousTimeReduction, 0.528) / timeReduction; // Stop the search if we have only one legal move, or if available time elapsed if ( rootMoves.size() == 1 - || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 605) + || Time.elapsed() > Time.optimum() * bestMoveInstability * improvingFactor / 581) { // If we are allowed to ponder do not stop the search now but // keep pondering until the GUI sends "ponderhit" or "stop". @@ -482,7 +501,11 @@ namespace { template Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning) { - const bool PvNode = NT == PV; + // Use quiescence search when needed + if (depth < ONE_PLY) + return qsearch(pos, ss, alpha, beta); + + constexpr bool PvNode = NT == PV; const bool rootNode = PvNode && ss->ply == 0; assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE); @@ -507,7 +530,6 @@ namespace { Thread* thisThread = pos.this_thread(); inCheck = pos.checkers(); moveCount = captureCount = quietCount = ss->moveCount = 0; - ss->statScore = 0; bestValue = -VALUE_INFINITE; maxValue = VALUE_INFINITE; @@ -543,10 +565,17 @@ namespace { (ss+1)->ply = ss->ply + 1; ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE; - ss->contHistory = &thisThread->contHistory[NO_PIECE][0]; + ss->contHistory = thisThread->contHistory[NO_PIECE][0].get(); (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE; 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. + (ss+2)->statScore = 0; + // Step 4. Transposition table lookup. We don't want the score of a partial // search to overwrite a previous full search TT value, so we use a different // position key in case of an excluded move. @@ -581,7 +610,7 @@ namespace { else if (!pos.capture_or_promotion(ttMove)) { int penalty = -stat_bonus(depth); - thisThread->mainHistory.update(pos.side_to_move(), ttMove, penalty); + thisThread->mainHistory[pos.side_to_move()][from_to(ttMove)] << penalty; update_continuation_histories(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty); } } @@ -639,6 +668,7 @@ namespace { if (inCheck) { ss->staticEval = eval = VALUE_NONE; + improving = false; goto moves_loop; } else if (ttHit) @@ -662,19 +692,27 @@ namespace { ss->staticEval, TT.generation()); } + improving = ss->staticEval >= (ss-2)->staticEval + ||(ss-2)->staticEval == VALUE_NONE; + if (skipEarlyPruning || !pos.non_pawn_material(pos.side_to_move())) goto moves_loop; // Step 7. Razoring (skipped when in check) - if ( !PvNode - && depth <= ONE_PLY - && eval + RazorMargin <= alpha) - return qsearch(pos, ss, alpha, alpha+1); + if ( !PvNode + && depth < 3 * ONE_PLY + && eval <= alpha - RazorMargin[depth / ONE_PLY]) + { + Value ralpha = alpha - (depth >= 2 * ONE_PLY) * RazorMargin[depth / ONE_PLY]; + Value v = qsearch(pos, ss, ralpha, ralpha+1); + if (depth < 2 * ONE_PLY || v <= ralpha) + return v; + } // Step 8. Futility pruning: child node (skipped when in check) if ( !rootNode && depth < 7 * ONE_PLY - && eval - futility_margin(depth) >= beta + && eval - futility_margin(depth, improving) >= beta && eval < VALUE_KNOWN_WIN) // Do not return unproven wins return eval; @@ -690,11 +728,12 @@ namespace { Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY; ss->currentMove = MOVE_NULL; - ss->contHistory = &thisThread->contHistory[NO_PIECE][0]; + ss->contHistory = thisThread->contHistory[NO_PIECE][0].get(); pos.do_null_move(st); - Value nullValue = depth-R < ONE_PLY ? -qsearch(pos, ss+1, -beta, -beta+1) - : - search(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true); + + Value nullValue = -search(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true); + pos.undo_null_move(); if (nullValue >= beta) @@ -711,8 +750,7 @@ namespace { thisThread->nmp_ply = ss->ply + 3 * (depth-R) / 4; thisThread->nmp_odd = ss->ply % 2; - Value v = depth-R < ONE_PLY ? qsearch(pos, ss, beta-1, beta) - : search(pos, ss, beta-1, beta, depth-R, false, true); + Value v = search(pos, ss, beta-1, beta, depth-R, false, true); thisThread->nmp_odd = thisThread->nmp_ply = 0; @@ -730,20 +768,32 @@ namespace { { assert(is_ok((ss-1)->currentMove)); - Value rbeta = std::min(beta + 200, VALUE_INFINITE); + Value rbeta = std::min(beta + 216 - 48 * improving, VALUE_INFINITE); MovePicker mp(pos, ttMove, rbeta - ss->staticEval, &thisThread->captureHistory); + int probCutCount = 0; - while ((move = mp.next_move()) != MOVE_NONE) + while ( (move = mp.next_move()) != MOVE_NONE + && probCutCount < 3) if (pos.legal(move)) { + probCutCount++; + ss->currentMove = move; - ss->contHistory = &thisThread->contHistory[pos.moved_piece(move)][to_sq(move)]; + ss->contHistory = thisThread->contHistory[pos.moved_piece(move)][to_sq(move)].get(); assert(depth >= 5 * ONE_PLY); pos.do_move(move, st); - value = -search(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false); + + // Perform a preliminary qsearch to verify that the move holds + value = -qsearch(pos, ss+1, -rbeta, -rbeta+1); + + // If the qsearch held perform the regular search + if (value >= rbeta) + value = -search(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false); + pos.undo_move(move); + if (value >= rbeta) return value; } @@ -752,7 +802,7 @@ namespace { // Step 11. Internal iterative deepening (skipped when in check) if ( depth >= 6 * ONE_PLY && !ttMove - && (PvNode || ss->staticEval + 256 >= beta)) + && (PvNode || ss->staticEval + 128 >= beta)) { Depth d = 3 * depth / 4 - 2 * ONE_PLY; search(pos, ss, alpha, beta, d, cutNode, true); @@ -769,9 +819,6 @@ moves_loop: // When in check, search starts from here MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, &thisThread->captureHistory, contHist, countermove, ss->killers); value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc - improving = ss->staticEval >= (ss-2)->staticEval - /* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */ - ||(ss-2)->staticEval == VALUE_NONE; singularExtensionNode = !rootNode && depth >= 8 * ONE_PLY @@ -812,10 +859,7 @@ moves_loop: // When in check, search starts from here extension = DEPTH_ZERO; captureOrPromotion = pos.capture_or_promotion(move); movedPiece = pos.moved_piece(move); - - givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates() - ? pos.check_squares(type_of(movedPiece)) & to_sq(move) - : pos.gives_check(move); + givesCheck = gives_check(pos, move); moveCountPruning = depth < 16 * ONE_PLY && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY]; @@ -885,7 +929,7 @@ moves_loop: // When in check, search starts from here } else if ( depth < 7 * ONE_PLY && !extension - && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY))) + && !pos.see_ge(move, -Value(CapturePruneMargin[depth / ONE_PLY]))) continue; } @@ -904,7 +948,7 @@ moves_loop: // When in check, search starts from here // Update the current move (this must be done after singular extension search) ss->currentMove = move; - ss->contHistory = &thisThread->contHistory[movedPiece][to_sq(move)]; + ss->contHistory = thisThread->contHistory[movedPiece][to_sq(move)].get(); // Step 15. Make the move pos.do_move(move, st, givesCheck); @@ -972,10 +1016,7 @@ moves_loop: // When in check, search starts from here // Step 17. Full depth search when LMR is skipped or fails high if (doFullDepthSearch) - value = newDepth < ONE_PLY ? - givesCheck ? -qsearch(pos, ss+1, -(alpha+1), -alpha) - : -qsearch(pos, ss+1, -(alpha+1), -alpha) - : - search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false); + value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false); // 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 @@ -985,10 +1026,7 @@ moves_loop: // When in check, search starts from here (ss+1)->pv = pv; (ss+1)->pv[0] = MOVE_NONE; - value = newDepth < ONE_PLY ? - givesCheck ? -qsearch(pos, ss+1, -beta, -alpha) - : -qsearch(pos, ss+1, -beta, -alpha) - : - search(pos, ss+1, -beta, -alpha, newDepth, false, false); + value = -search(pos, ss+1, -beta, -alpha, newDepth, false, false); } // Step 18. Undo move @@ -1117,17 +1155,15 @@ moves_loop: // When in check, search starts from here // qsearch() is the quiescence search function, which is called by the main // search function with depth zero, or recursively with depth less than ONE_PLY. - - template + template Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) { - const bool PvNode = NT == PV; + constexpr bool PvNode = NT == PV; assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE); assert(PvNode || (alpha == beta - 1)); assert(depth <= DEPTH_ZERO); assert(depth / ONE_PLY * ONE_PLY == depth); - assert(InCheck == bool(pos.checkers())); Move pv[MAX_PLY+1]; StateInfo st; @@ -1136,7 +1172,7 @@ moves_loop: // When in check, search starts from here Move ttMove, move, bestMove; Depth ttDepth; Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha; - bool ttHit, givesCheck, evasionPrunable; + bool ttHit, inCheck, givesCheck, evasionPrunable; int moveCount; if (PvNode) @@ -1148,19 +1184,20 @@ moves_loop: // When in check, search starts from here (ss+1)->ply = ss->ply + 1; ss->currentMove = bestMove = MOVE_NONE; + inCheck = pos.checkers(); moveCount = 0; // Check for an immediate draw or maximum ply reached if ( pos.is_draw(ss->ply) || ss->ply >= MAX_PLY) - return (ss->ply >= MAX_PLY && !InCheck) ? evaluate(pos) : VALUE_DRAW; + return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos) : VALUE_DRAW; assert(0 <= ss->ply && ss->ply < MAX_PLY); // Decide whether or not to include checks: this fixes also the type of // 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 = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS + ttDepth = inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS; // Transposition table lookup posKey = pos.key(); @@ -1177,7 +1214,7 @@ moves_loop: // When in check, search starts from here return ttValue; // Evaluate the position statically - if (InCheck) + if (inCheck) { ss->staticEval = VALUE_NONE; bestValue = futilityBase = -VALUE_INFINITE; @@ -1227,14 +1264,12 @@ moves_loop: // When in check, search starts from here { assert(is_ok(move)); - givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates() - ? pos.check_squares(type_of(pos.moved_piece(move))) & to_sq(move) - : pos.gives_check(move); + givesCheck = gives_check(pos, move); moveCount++; // Futility pruning - if ( !InCheck + if ( !inCheck && !givesCheck && futilityBase > -VALUE_KNOWN_WIN && !pos.advanced_pawn_push(move)) @@ -1257,13 +1292,13 @@ moves_loop: // When in check, search starts from here } // Detect non-capture evasions that are candidates to be pruned - evasionPrunable = InCheck + evasionPrunable = inCheck && (depth != DEPTH_ZERO || moveCount > 2) && bestValue > VALUE_MATED_IN_MAX_PLY && !pos.capture(move); // Don't search moves with negative SEE values - if ( (!InCheck || evasionPrunable) + if ( (!inCheck || evasionPrunable) && !pos.see_ge(move)) continue; @@ -1281,8 +1316,7 @@ moves_loop: // When in check, search starts from here // Make and search the move pos.do_move(move, st, givesCheck); - value = givesCheck ? -qsearch(pos, ss+1, -beta, -alpha, depth - ONE_PLY) - : -qsearch(pos, ss+1, -beta, -alpha, depth - ONE_PLY); + value = -qsearch(pos, ss+1, -beta, -alpha, depth - ONE_PLY); pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); @@ -1315,7 +1349,7 @@ moves_loop: // When in check, search starts from here // All legal moves have been searched. A special case: If we're in check // and no legal moves were found, it is checkmate. - if (InCheck && bestValue == -VALUE_INFINITE) + if (inCheck && bestValue == -VALUE_INFINITE) return mated_in(ss->ply); // Plies to mate from the root tte->save(posKey, value_to_tt(bestValue, ss->ply), @@ -1370,7 +1404,7 @@ moves_loop: // When in check, search starts from here for (int i : {1, 2, 4}) if (is_ok((ss-i)->currentMove)) - (ss-i)->contHistory->update(pc, to, bonus); + (*(ss-i)->contHistory)[pc][to] << bonus; } @@ -1382,14 +1416,14 @@ moves_loop: // When in check, search starts from here CapturePieceToHistory& captureHistory = pos.this_thread()->captureHistory; Piece moved_piece = pos.moved_piece(move); PieceType captured = type_of(pos.piece_on(to_sq(move))); - captureHistory.update(moved_piece, to_sq(move), captured, bonus); + captureHistory[moved_piece][to_sq(move)][captured] << bonus; // Decrease all the other played capture moves for (int i = 0; i < captureCnt; ++i) { moved_piece = pos.moved_piece(captures[i]); captured = type_of(pos.piece_on(to_sq(captures[i]))); - captureHistory.update(moved_piece, to_sq(captures[i]), captured, -bonus); + captureHistory[moved_piece][to_sq(captures[i])][captured] << -bonus; } } @@ -1407,7 +1441,7 @@ moves_loop: // When in check, search starts from here Color us = pos.side_to_move(); Thread* thisThread = pos.this_thread(); - thisThread->mainHistory.update(us, move, bonus); + thisThread->mainHistory[us][from_to(move)] << bonus; update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus); if (is_ok((ss-1)->currentMove)) @@ -1419,7 +1453,7 @@ moves_loop: // When in check, search starts from here // Decrease all the other played quiet moves for (int i = 0; i < quietsCnt; ++i) { - thisThread->mainHistory.update(us, quiets[i], -bonus); + thisThread->mainHistory[us][from_to(quiets[i])] << -bonus; update_continuation_histories(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus); } } @@ -1468,11 +1502,11 @@ void MainThread::check_time() { return; // When using nodes, ensure checking rate is not lower than 0.1% of nodes - callsCnt = Limits.nodes ? std::min(4096, int(Limits.nodes / 1024)) : 4096; + callsCnt = Limits.nodes ? std::min(1024, int(Limits.nodes / 1024)) : 1024; static TimePoint lastInfoTime = now(); - int elapsed = Time.elapsed(); + TimePoint elapsed = Time.elapsed(); TimePoint tick = Limits.startTime + elapsed; if (tick - lastInfoTime >= 1000) @@ -1498,7 +1532,7 @@ void MainThread::check_time() { string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) { std::stringstream ss; - int elapsed = Time.elapsed() + 1; + TimePoint elapsed = Time.elapsed() + 1; const RootMoves& rootMoves = pos.this_thread()->rootMoves; size_t PVIdx = pos.this_thread()->PVIdx; size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());