X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=1572333b9c35085734c06646001b707657d7bb88;hp=847fc762e53644abb7959622e211a1c3966b3f03;hb=83fb4547f640c63c2dbbf0d5637bd8d1cf216a60;hpb=ec6aab01366ba1d2de27084d3cc7415a31aa5a24 diff --git a/src/search.cpp b/src/search.cpp index 847fc762..1572333b 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -2,7 +2,7 @@ Stockfish, a UCI chess playing engine derived from Glaurung 2.1 Copyright (C) 2004-2008 Tord Romstad (Glaurung author) Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad - Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad + Copyright (C) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad Stockfish is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by @@ -29,6 +29,7 @@ #include "misc.h" #include "movegen.h" #include "movepick.h" +#include "position.h" #include "search.h" #include "timeman.h" #include "thread.h" @@ -45,7 +46,6 @@ namespace Search { namespace Tablebases { int Cardinality; - uint64_t Hits; bool RootInTB; bool UseRule50; Depth ProbeDepth; @@ -65,14 +65,20 @@ namespace { // Razoring and futility margin based on depth const int razor_margin[4] = { 483, 570, 603, 554 }; - Value futility_margin(Depth d) { return Value(200 * d); } + Value futility_margin(Depth d) { return Value(150 * d / ONE_PLY); } // Futility and reductions lookup tables, initialized at startup - int FutilityMoveCounts[2][16]; // [improving][depth] - Depth Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber] + int FutilityMoveCounts[2][16]; // [improving][depth] + int Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber] template Depth reduction(bool i, Depth d, int mn) { - return Reductions[PvNode][i][std::min(d, 63 * ONE_PLY)][std::min(mn, 63)]; + return Reductions[PvNode][i][std::min(d / ONE_PLY, 63)][std::min(mn, 63)] * ONE_PLY; + } + + // History and stats update bonus, based on depth + Value stat_bonus(Depth depth) { + int d = depth / ONE_PLY ; + return Value(d * d + 2 * d - 2); } // Skill structure is used to implement strength limit @@ -113,8 +119,8 @@ namespace { std::copy(newPv.begin(), newPv.begin() + 3, pv); StateInfo st[2]; - pos.do_move(newPv[0], st[0], pos.gives_check(newPv[0], CheckInfo(pos))); - pos.do_move(newPv[1], st[1], pos.gives_check(newPv[1], CheckInfo(pos))); + pos.do_move(newPv[0], st[0]); + pos.do_move(newPv[1], st[1]); expectedPosKey = pos.key(); pos.undo_move(newPv[1]); pos.undo_move(newPv[0]); @@ -157,18 +163,18 @@ namespace { EasyMoveManager EasyMove; Value DrawValue[COLOR_NB]; - CounterMoveHistoryStats CounterMoveHistory; template - Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode); + Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning); template - Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth); + Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO); Value value_to_tt(Value v, int ply); Value value_from_tt(Value v, int ply); void update_pv(Move* pv, Move move, Move* childPv); - void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt); + void update_cm_stats(Stack* ss, Piece pc, Square s, Value bonus); + void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, Value bonus); void check_time(); } // namespace @@ -183,15 +189,13 @@ void Search::init() { for (int mc = 1; mc < 64; ++mc) { double r = log(d) * log(mc) / 2; - if (r < 0.80) - continue; - Reductions[NonPV][imp][d][mc] = int(std::round(r)) * ONE_PLY; - Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - ONE_PLY, DEPTH_ZERO); + Reductions[NonPV][imp][d][mc] = int(std::round(r)); + 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 * ONE_PLY) - Reductions[NonPV][imp][d][mc] += ONE_PLY; + if (!imp && Reductions[NonPV][imp][d][mc] >= 2) + Reductions[NonPV][imp][d][mc]++; } for (int d = 0; d < 16; ++d) @@ -207,12 +211,13 @@ void Search::init() { void Search::clear() { TT.clear(); - CounterMoveHistory.clear(); for (Thread* th : Threads) { - th->history.clear(); th->counterMoves.clear(); + th->history.clear(); + th->counterMoveHistory.clear(); + th->resetCalls = true; } Threads.main()->previousScore = VALUE_INFINITE; @@ -226,7 +231,6 @@ uint64_t Search::perft(Position& pos, Depth depth) { StateInfo st; uint64_t cnt, nodes = 0; - CheckInfo ci(pos); const bool leaf = (depth == 2 * ONE_PLY); for (const auto& m : MoveList(pos)) @@ -235,7 +239,7 @@ uint64_t Search::perft(Position& pos, Depth depth) { cnt = 1, nodes++; else { - pos.do_move(m, st, pos.gives_check(m, ci)); + pos.do_move(m, st); cnt = leaf ? MoveList(pos).size() : perft(pos, depth - ONE_PLY); nodes += cnt; pos.undo_move(m); @@ -261,19 +265,6 @@ void MainThread::search() { DrawValue[ us] = VALUE_DRAW - Value(contempt); DrawValue[~us] = VALUE_DRAW + Value(contempt); - TB::Hits = 0; - TB::RootInTB = false; - TB::UseRule50 = Options["Syzygy50MoveRule"]; - TB::ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY; - TB::Cardinality = Options["SyzygyProbeLimit"]; - - // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality - if (TB::Cardinality > TB::MaxCardinality) - { - TB::Cardinality = TB::MaxCardinality; - TB::ProbeDepth = DEPTH_ZERO; - } - if (rootMoves.empty()) { rootMoves.push_back(RootMove(MOVE_NONE)); @@ -283,38 +274,6 @@ void MainThread::search() { } else { - if ( TB::Cardinality >= rootPos.count(WHITE) - + rootPos.count(BLACK) - && !rootPos.can_castle(ANY_CASTLING)) - { - // If the current root position is in the tablebases, then RootMoves - // contains only moves that preserve the draw or the win. - TB::RootInTB = Tablebases::root_probe(rootPos, rootMoves, TB::Score); - - if (TB::RootInTB) - TB::Cardinality = 0; // Do not probe tablebases during the search - - else // If DTZ tables are missing, use WDL tables as a fallback - { - // Filter out moves that do not preserve the draw or the win. - TB::RootInTB = Tablebases::root_probe_wdl(rootPos, rootMoves, TB::Score); - - // Only probe during search if winning - if (TB::Score <= VALUE_DRAW) - TB::Cardinality = 0; - } - - if (TB::RootInTB) - { - TB::Hits = rootMoves.size(); - - if (!TB::UseRule50) - TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1 - : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1 - : VALUE_DRAW; - } - } - for (Thread* th : Threads) if (th != this) th->start_searching(); @@ -350,13 +309,18 @@ void MainThread::search() { Thread* bestThread = this; if ( !this->easyMovePlayed && Options["MultiPV"] == 1 + && !Limits.depth && !Skill(Options["Skill Level"]).enabled() && rootMoves[0].pv[0] != MOVE_NONE) { for (Thread* th : Threads) - if ( th->completedDepth > bestThread->completedDepth - && th->rootMoves[0].score > bestThread->rootMoves[0].score) + { + Depth depthDiff = th->completedDepth - bestThread->completedDepth; + Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score; + + if (scoreDiff > 0 && depthDiff >= 0) bestThread = th; + } } previousScore = bestThread->rootMoves[0].score; @@ -380,12 +344,12 @@ void MainThread::search() { void Thread::search() { - Stack stack[MAX_PLY+7], *ss = stack+5; // To allow referencing (ss-5) and (ss+2) + Stack stack[MAX_PLY+7], *ss = stack+4; // To allow referencing (ss-4) and (ss+2) Value bestValue, alpha, beta, delta; Move easyMove = MOVE_NONE; MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr); - std::memset(ss-5, 0, 8 * sizeof(Stack)); + std::memset(ss-4, 0, 7 * sizeof(Stack)); bestValue = delta = alpha = -VALUE_INFINITE; beta = VALUE_INFINITE; @@ -410,15 +374,17 @@ void Thread::search() { multiPV = std::min(multiPV, rootMoves.size()); - // Iterative deepening loop until requested to stop or the target depth is reached. - while (++rootDepth < DEPTH_MAX && !Signals.stop && (!Limits.depth || rootDepth <= Limits.depth)) + // Iterative deepening loop until requested to stop or the target depth is reached + while ( (rootDepth += ONE_PLY) < DEPTH_MAX + && !Signals.stop + && (!Limits.depth || Threads.main()->rootDepth / ONE_PLY <= Limits.depth)) { // Set up the new depths for the helper threads skipping on average every // 2nd ply (using a half-density matrix). if (!mainThread) { const Row& row = HalfDensity[(idx - 1) % HalfDensitySize]; - if (row[(rootDepth + rootPos.game_ply()) % row.size()]) + if (row[(rootDepth / ONE_PLY + rootPos.game_ply()) % row.size()]) continue; } @@ -447,7 +413,7 @@ void Thread::search() { // high/low anymore. while (true) { - bestValue = ::search(rootPos, ss, alpha, beta, rootDepth, false); + bestValue = ::search(rootPos, ss, alpha, beta, rootDepth, false, false); // Bring the best move to the front. It is critical that sorting // is done with a stable algorithm because all the values but the @@ -457,11 +423,6 @@ void Thread::search() { // search the already searched PV lines are preserved. std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end()); - // Write PV back to the transposition table in case the relevant - // entries have been overwritten during the search. - for (size_t i = 0; i <= PVIdx; ++i) - rootMoves[i].insert_pv_in_tt(rootPos); - // If search has been stopped, break immediately. Sorting and // writing PV back to TT is safe because RootMoves is still // valid, although it refers to the previous iteration. @@ -506,13 +467,9 @@ void Thread::search() { std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1); if (!mainThread) - break; - - if (Signals.stop) - sync_cout << "info nodes " << Threads.nodes_searched() - << " time " << Time.elapsed() << sync_endl; + continue; - else if (PVIdx + 1 == multiPV || Time.elapsed() > 3000) + if (Signals.stop || PVIdx + 1 == multiPV || Time.elapsed() > 3000) sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl; } @@ -540,19 +497,19 @@ void Thread::search() { // Stop the search if only one legal move is available, or if all // of the available time has been used, or if we matched an easyMove // from the previous search and just did a fast verification. - const bool F[] = { !mainThread->failedLow, - bestValue >= mainThread->previousScore }; + const int F[] = { mainThread->failedLow, + bestValue - mainThread->previousScore }; - int improvingFactor = 640 - 160*F[0] - 126*F[1] - 124*F[0]*F[1]; + int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1])); double unstablePvFactor = 1 + mainThread->bestMoveChanges; bool doEasyMove = rootMoves[0].pv[0] == easyMove && mainThread->bestMoveChanges < 0.03 - && Time.elapsed() > Time.optimum() * 25 / 204; + && Time.elapsed() > Time.optimum() * 5 / 44; if ( rootMoves.size() == 1 - || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 634 - || (mainThread->easyMovePlayed = doEasyMove)) + || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628 + || (mainThread->easyMovePlayed = doEasyMove, doEasyMove)) { // If we are allowed to ponder do not stop the search now but // keep pondering until the GUI sends "ponderhit" or "stop". @@ -590,7 +547,7 @@ namespace { // search<>() is the main search function for both PV and non-PV nodes template - Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) { + Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning) { const bool PvNode = NT == PV; const bool rootNode = PvNode && (ss-1)->ply == 0; @@ -598,22 +555,26 @@ namespace { assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE); assert(PvNode || (alpha == beta - 1)); assert(DEPTH_ZERO < depth && depth < DEPTH_MAX); + assert(!(PvNode && cutNode)); + assert(depth / ONE_PLY * ONE_PLY == depth); Move pv[MAX_PLY+1], quietsSearched[64]; StateInfo st; TTEntry* tte; Key posKey; Move ttMove, move, excludedMove, bestMove; - Depth extension, newDepth, predictedDepth; - Value bestValue, value, ttValue, eval, nullValue, futilityValue; + Depth extension, newDepth; + Value bestValue, value, ttValue, eval; bool ttHit, inCheck, givesCheck, singularExtensionNode, improving; - bool captureOrPromotion, doFullDepthSearch; + bool captureOrPromotion, doFullDepthSearch, moveCountPruning; + Piece moved_piece; int moveCount, quietCount; // Step 1. Initialize node Thread* thisThread = pos.this_thread(); inCheck = pos.checkers(); moveCount = quietCount = ss->moveCount = 0; + ss->history = VALUE_ZERO; bestValue = -VALUE_INFINITE; ss->ply = (ss-1)->ply + 1; @@ -621,9 +582,13 @@ namespace { if (thisThread->resetCalls.load(std::memory_order_relaxed)) { thisThread->resetCalls = false; - thisThread->callsCnt = 0; + // At low node count increase the checking rate to about 0.1% of nodes + // otherwise use a default value. + thisThread->callsCnt = Limits.nodes ? std::min((int64_t)4096, Limits.nodes / 1024) + : 4096; } - if (++thisThread->callsCnt > 4096) + + if (--thisThread->callsCnt <= 0) { for (Thread* th : Threads) th->resetCalls = true; @@ -638,7 +603,7 @@ namespace { if (!rootNode) { // Step 2. Check for aborted search and immediate draw - if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw() || ss->ply >= MAX_PLY) + if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY) return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos) : DrawValue[pos.side_to_move()]; @@ -658,14 +623,14 @@ namespace { ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE; ss->counterMoves = nullptr; - (ss+1)->skipEarlyPruning = false; (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE; + Square prevSq = to_sq((ss-1)->currentMove); // 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. excludedMove = ss->excludedMove; - posKey = excludedMove ? pos.exclusion_key() : pos.key(); + posKey = pos.key() ^ Key(excludedMove); tte = TT.probe(posKey, ttHit); ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE; ttMove = rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0] @@ -679,30 +644,45 @@ namespace { && (ttValue >= beta ? (tte->bound() & BOUND_LOWER) : (tte->bound() & BOUND_UPPER))) { - ss->currentMove = ttMove; // Can be MOVE_NONE - - // If ttMove is quiet, update killers, history, counter move on TT hit - if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove)) - update_stats(pos, ss, ttMove, depth, nullptr, 0); + // If ttMove is quiet, update move sorting heuristics on TT hit + if (ttMove) + { + if (ttValue >= beta) + { + if (!pos.capture_or_promotion(ttMove)) + update_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth)); + // Extra penalty for a quiet TT move in previous ply when it gets refuted + if ((ss-1)->moveCount == 1 && !pos.captured_piece()) + update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY)); + } + // Penalty for a quiet ttMove that fails low + else if (!pos.capture_or_promotion(ttMove)) + { + Value penalty = -stat_bonus(depth + ONE_PLY); + thisThread->history.update(pos.side_to_move(), ttMove, penalty); + update_cm_stats(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty); + } + } return ttValue; } // Step 4a. Tablebase probe if (!rootNode && TB::Cardinality) { - int piecesCnt = pos.count(WHITE) + pos.count(BLACK); + int piecesCount = pos.count(WHITE) + pos.count(BLACK); - if ( piecesCnt <= TB::Cardinality - && (piecesCnt < TB::Cardinality || depth >= TB::ProbeDepth) + if ( piecesCount <= TB::Cardinality + && (piecesCount < TB::Cardinality || depth >= TB::ProbeDepth) && pos.rule50_count() == 0 && !pos.can_castle(ANY_CASTLING)) { - int found, v = Tablebases::probe_wdl(pos, &found); + TB::ProbeState err; + TB::WDLScore v = Tablebases::probe_wdl(pos, &err); - if (found) + if (err != TB::ProbeState::FAIL) { - TB::Hits++; + thisThread->tbHits++; int drawScore = TB::UseRule50 ? 1 : 0; @@ -747,21 +727,20 @@ namespace { ss->staticEval, TT.generation()); } - if (ss->skipEarlyPruning) + if (skipEarlyPruning) goto moves_loop; // Step 6. Razoring (skipped when in check) if ( !PvNode && depth < 4 * ONE_PLY - && eval + razor_margin[depth] <= alpha - && ttMove == MOVE_NONE) + && ttMove == MOVE_NONE + && eval + razor_margin[depth / ONE_PLY] <= alpha) { - if ( depth <= ONE_PLY - && eval + razor_margin[3 * ONE_PLY] <= alpha) - return qsearch(pos, ss, alpha, beta, DEPTH_ZERO); + if (depth <= ONE_PLY) + return qsearch(pos, ss, alpha, alpha+1); - Value ralpha = alpha - razor_margin[depth]; - Value v = qsearch(pos, ss, ralpha, ralpha+1, DEPTH_ZERO); + Value ralpha = alpha - razor_margin[depth / ONE_PLY]; + Value v = qsearch(pos, ss, ralpha, ralpha+1); if (v <= ralpha) return v; } @@ -772,12 +751,12 @@ namespace { && eval - futility_margin(depth) >= beta && eval < VALUE_KNOWN_WIN // Do not return unproven wins && pos.non_pawn_material(pos.side_to_move())) - return eval - futility_margin(depth); + return eval; // Step 8. Null move search with verification search (is omitted in PV nodes) if ( !PvNode - && depth >= 2 * ONE_PLY && eval >= beta + && (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY) && pos.non_pawn_material(pos.side_to_move())) { ss->currentMove = MOVE_NULL; @@ -786,13 +765,11 @@ namespace { assert(eval - beta >= 0); // Null move dynamic reduction based on depth and value - Depth R = ((823 + 67 * depth) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY; + Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY; pos.do_null_move(st); - (ss+1)->skipEarlyPruning = true; - nullValue = depth-R < ONE_PLY ? -qsearch(pos, ss+1, -beta, -beta+1, DEPTH_ZERO) - : - search(pos, ss+1, -beta, -beta+1, depth-R, !cutNode); - (ss+1)->skipEarlyPruning = false; + Value nullValue = depth-R < ONE_PLY ? -qsearch(pos, ss+1, -beta, -beta+1) + : - search(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true); pos.undo_null_move(); if (nullValue >= beta) @@ -805,10 +782,8 @@ namespace { return nullValue; // Do verification search at high depths - ss->skipEarlyPruning = true; - Value v = depth-R < ONE_PLY ? qsearch(pos, ss, beta-1, beta, DEPTH_ZERO) - : search(pos, ss, beta-1, beta, depth-R, false); - ss->skipEarlyPruning = false; + Value v = depth-R < ONE_PLY ? qsearch(pos, ss, beta-1, beta) + : search(pos, ss, beta-1, beta, depth-R, false, true); if (v >= beta) return nullValue; @@ -816,9 +791,8 @@ namespace { } // Step 9. ProbCut (skipped when in check) - // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type]) - // and a reduced search returns a value much above beta, we can (almost) - // safely prune the previous move. + // 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 && depth >= 5 * ONE_PLY && abs(beta) < VALUE_MATE_IN_MAX_PLY) @@ -830,16 +804,15 @@ namespace { assert((ss-1)->currentMove != MOVE_NONE); assert((ss-1)->currentMove != MOVE_NULL); - MovePicker mp(pos, ttMove, PieceValue[MG][pos.captured_piece_type()]); - CheckInfo ci(pos); + MovePicker mp(pos, ttMove, rbeta - ss->staticEval); while ((move = mp.next_move()) != MOVE_NONE) - if (pos.legal(move, ci.pinned)) + if (pos.legal(move)) { ss->currentMove = move; - ss->counterMoves = &CounterMoveHistory[pos.moved_piece(move)][to_sq(move)]; - pos.do_move(move, st, pos.gives_check(move, ci)); - value = -search(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode); + ss->counterMoves = &thisThread->counterMoveHistory[pos.moved_piece(move)][to_sq(move)]; + pos.do_move(move, st); + value = -search(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode, false); pos.undo_move(move); if (value >= rbeta) return value; @@ -847,14 +820,12 @@ namespace { } // Step 10. Internal iterative deepening (skipped when in check) - if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY) + if ( depth >= 6 * ONE_PLY && !ttMove && (PvNode || ss->staticEval + 256 >= beta)) { - Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4); - ss->skipEarlyPruning = true; - search(pos, ss, alpha, beta, d, true); - ss->skipEarlyPruning = false; + Depth d = (3 * depth / (4 * ONE_PLY) - 2) * ONE_PLY; + search(pos, ss, alpha, beta, d, cutNode, true); tte = TT.probe(posKey, ttHit); ttMove = ttHit ? tte->move() : MOVE_NONE; @@ -862,21 +833,20 @@ namespace { moves_loop: // When in check search starts from here - Square prevSq = to_sq((ss-1)->currentMove); - const CounterMoveStats& cmh = CounterMoveHistory[pos.piece_on(prevSq)][prevSq]; + const CounterMoveStats* cmh = (ss-1)->counterMoves; + const CounterMoveStats* fmh = (ss-2)->counterMoves; + const CounterMoveStats* fmh2 = (ss-4)->counterMoves; MovePicker mp(pos, ttMove, depth, ss); - CheckInfo ci(pos); value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc improving = ss->staticEval >= (ss-2)->staticEval - || ss->staticEval == VALUE_NONE + /* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */ ||(ss-2)->staticEval == VALUE_NONE; singularExtensionNode = !rootNode && depth >= 8 * ONE_PLY && ttMove != MOVE_NONE - /* && ttValue != VALUE_NONE Already implicit in the next condition */ - && abs(ttValue) < VALUE_KNOWN_WIN + && ttValue != VALUE_NONE && !excludedMove // Recursive singular search is not allowed && (tte->bound() & BOUND_LOWER) && tte->depth() >= depth - 3 * ONE_PLY; @@ -909,13 +879,20 @@ moves_loop: // When in check search starts from here extension = DEPTH_ZERO; captureOrPromotion = pos.capture_or_promotion(move); + moved_piece = pos.moved_piece(move); - givesCheck = type_of(move) == NORMAL && !ci.dcCandidates - ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move) - : pos.gives_check(move, ci); + givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates() + ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move) + : pos.gives_check(move); - // Step 12. Extend checks - if (givesCheck && pos.see_sign(move) >= VALUE_ZERO) + moveCountPruning = depth < 16 * ONE_PLY + && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY]; + + // Step 12. Extensions + // Extend checks + if ( givesCheck + && !moveCountPruning + && pos.see_ge(move, VALUE_ZERO)) extension = ONE_PLY; // Singular extension search. If all moves but one fail low on a search of @@ -926,73 +903,73 @@ moves_loop: // When in check search starts from here if ( singularExtensionNode && move == ttMove && !extension - && pos.legal(move, ci.pinned)) + && pos.legal(move)) { - Value rBeta = ttValue - 2 * depth / ONE_PLY; + Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE); + Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY; ss->excludedMove = move; - ss->skipEarlyPruning = true; - value = search(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode); - ss->skipEarlyPruning = false; + value = search(pos, ss, rBeta - 1, rBeta, d, cutNode, true); ss->excludedMove = MOVE_NONE; if (value < rBeta) extension = ONE_PLY; } - // Update the current move (this must be done after singular extension search) + // Calculate new depth for this move newDepth = depth - ONE_PLY + extension; // Step 13. Pruning at shallow depth - if ( !rootNode - && !captureOrPromotion - && !inCheck - && !givesCheck - && !pos.advanced_pawn_push(move) - && bestValue > VALUE_MATED_IN_MAX_PLY) + if ( !rootNode + && bestValue > VALUE_MATED_IN_MAX_PLY) { - // Move count based pruning - if ( depth < 16 * ONE_PLY - && moveCount >= FutilityMoveCounts[improving][depth]) - continue; + if ( !captureOrPromotion + && !givesCheck + && !pos.advanced_pawn_push(move)) + { + // Move count based pruning + if (moveCountPruning) + continue; - // History based pruning - if ( depth <= 4 * ONE_PLY - && move != ss->killers[0] - && thisThread->history[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO - && cmh[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO) - continue; + // Reduced depth of the next LMR search + int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY; - predictedDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO); + // Countermoves based pruning + if ( lmrDepth < 3 + && (!cmh || (*cmh )[moved_piece][to_sq(move)] < VALUE_ZERO) + && (!fmh || (*fmh )[moved_piece][to_sq(move)] < VALUE_ZERO) + && (!fmh2 || (*fmh2)[moved_piece][to_sq(move)] < VALUE_ZERO || (cmh && fmh))) + continue; - // Futility pruning: parent node - if (predictedDepth < 7 * ONE_PLY) - { - futilityValue = ss->staticEval + futility_margin(predictedDepth) + 256; + // Futility pruning: parent node + if ( lmrDepth < 7 + && !inCheck + && ss->staticEval + 256 + 200 * lmrDepth <= alpha) + continue; - if (futilityValue <= alpha) - { - bestValue = std::max(bestValue, futilityValue); + // Prune moves with negative SEE + if ( lmrDepth < 8 + && !pos.see_ge(move, Value(-35 * lmrDepth * lmrDepth))) continue; - } } - - // Prune moves with negative SEE at low depths - if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO) - continue; + else if ( depth < 7 * ONE_PLY + && !extension + && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY))) + continue; } // Speculative prefetch as early as possible prefetch(TT.first_entry(pos.key_after(move))); // Check for legality just before making the move - if (!rootNode && !pos.legal(move, ci.pinned)) + if (!rootNode && !pos.legal(move)) { ss->moveCount = --moveCount; continue; } + // Update the current move (this must be done after singular extension search) ss->currentMove = move; - ss->counterMoves = &CounterMoveHistory[pos.moved_piece(move)][to_sq(move)]; + ss->counterMoves = &thisThread->counterMoveHistory[moved_piece][to_sq(move)]; // Step 14. Make the move pos.do_move(move, st, givesCheck); @@ -1001,36 +978,47 @@ moves_loop: // When in check search starts from here // re-searched at full depth. if ( depth >= 3 * ONE_PLY && moveCount > 1 - && !captureOrPromotion) + && (!captureOrPromotion || moveCountPruning)) { Depth r = reduction(improving, depth, moveCount); - Value hValue = thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)]; - Value cmhValue = cmh[pos.piece_on(to_sq(move))][to_sq(move)]; - - // Increase reduction for cut nodes and moves with a bad history - if ( (!PvNode && cutNode) - || (hValue < VALUE_ZERO && cmhValue <= VALUE_ZERO)) - r += ONE_PLY; - - // Decrease/increase reduction for moves with a good/bad history - int rHist = (hValue + cmhValue) / 14980; - r = std::max(DEPTH_ZERO, r - rHist * ONE_PLY); - - // Decrease reduction for moves that escape a capture. Filter out - // castling moves, because they are coded as "king captures rook" and - // hence break make_move(). Also use see() instead of see_sign(), - // because the destination square is empty. - if ( r - && type_of(move) == NORMAL - && type_of(pos.piece_on(to_sq(move))) != PAWN - && pos.see(make_move(to_sq(move), from_sq(move))) < VALUE_ZERO) - r = std::max(DEPTH_ZERO, r - ONE_PLY); + + if (captureOrPromotion) + r -= r ? ONE_PLY : DEPTH_ZERO; + else + { + // Increase reduction for cut nodes + if (cutNode) + r += 2 * ONE_PLY; + + // Decrease reduction for moves that escape a capture. Filter out + // castling moves, because they are coded as "king captures rook" and + // hence break make_move(). + else if ( type_of(move) == NORMAL + && !pos.see_ge(make_move(to_sq(move), from_sq(move)), VALUE_ZERO)) + r -= 2 * ONE_PLY; + + ss->history = (cmh ? (*cmh )[moved_piece][to_sq(move)] : VALUE_ZERO) + + (fmh ? (*fmh )[moved_piece][to_sq(move)] : VALUE_ZERO) + + (fmh2 ? (*fmh2)[moved_piece][to_sq(move)] : VALUE_ZERO) + + thisThread->history.get(~pos.side_to_move(), move) + - 4000; // Correction factor + + // Decrease/increase reduction by comparing opponent's stat score + if (ss->history > VALUE_ZERO && (ss-1)->history < VALUE_ZERO) + r -= ONE_PLY; + + else if (ss->history < VALUE_ZERO && (ss-1)->history > VALUE_ZERO) + r += ONE_PLY; + + // Decrease/increase reduction for moves with a good/bad history + r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->history / 20000) * ONE_PLY); + } Depth d = std::max(newDepth - r, ONE_PLY); - value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); + value = -search(pos, ss+1, -(alpha+1), -alpha, d, true, false); - doFullDepthSearch = (value > alpha && r != DEPTH_ZERO); + doFullDepthSearch = (value > alpha && d != newDepth); } else doFullDepthSearch = !PvNode || moveCount > 1; @@ -1038,9 +1026,9 @@ moves_loop: // When in check search starts from here // Step 16. Full depth search when LMR is skipped or fails high if (doFullDepthSearch) value = newDepth < ONE_PLY ? - givesCheck ? -qsearch(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO) - : -qsearch(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO) - : - search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); + 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); // 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 @@ -1051,9 +1039,9 @@ moves_loop: // When in check search starts from here (ss+1)->pv[0] = MOVE_NONE; value = newDepth < ONE_PLY ? - givesCheck ? -qsearch(pos, ss+1, -beta, -alpha, DEPTH_ZERO) - : -qsearch(pos, ss+1, -beta, -alpha, DEPTH_ZERO) - : - search(pos, ss+1, -beta, -alpha, newDepth, false); + givesCheck ? -qsearch(pos, ss+1, -beta, -alpha) + : -qsearch(pos, ss+1, -beta, -alpha) + : - search(pos, ss+1, -beta, -alpha, newDepth, false, false); } // Step 17. Undo move @@ -1103,13 +1091,6 @@ moves_loop: // When in check search starts from here if (value > alpha) { - // If there is an easy move for this position, clear it if unstable - if ( PvNode - && thisThread == Threads.main() - && EasyMove.get(pos.key()) - && (move != EasyMove.get(pos.key()) || moveCount > 1)) - EasyMove.clear(); - bestMove = move; if (PvNode && !rootNode) // Update pv even in fail-high case @@ -1141,31 +1122,28 @@ moves_loop: // When in check search starts from here // 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. + + assert(moveCount || !inCheck || excludedMove || !MoveList(pos).size()); + if (!moveCount) bestValue = excludedMove ? alpha : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()]; + else if (bestMove) + { - // Quiet best move: update killers, history and countermoves - else if (bestMove && !pos.capture_or_promotion(bestMove)) - update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount); + // Quiet best move: update move sorting heuristics + if (!pos.capture_or_promotion(bestMove)) + update_stats(pos, ss, bestMove, quietsSearched, quietCount, stat_bonus(depth)); + // Extra penalty for a quiet TT move in previous ply when it gets refuted + if ((ss-1)->moveCount == 1 && !pos.captured_piece()) + update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY)); + } // Bonus for prior countermove that caused the fail low else if ( depth >= 3 * ONE_PLY - && !bestMove - && !inCheck - && !pos.captured_piece_type() + && !pos.captured_piece() && is_ok((ss-1)->currentMove)) - { - Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1); - if ((ss-2)->counterMoves) - (ss-2)->counterMoves->update(pos.piece_on(prevSq), prevSq, bonus); - - if ((ss-3)->counterMoves) - (ss-3)->counterMoves->update(pos.piece_on(prevSq), prevSq, bonus); - - if ((ss-5)->counterMoves) - (ss-5)->counterMoves->update(pos.piece_on(prevSq), prevSq, bonus); - } + update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth)); tte->save(posKey, value_to_tt(bestValue, ss->ply), bestValue >= beta ? BOUND_LOWER : @@ -1179,8 +1157,7 @@ moves_loop: // When in check search starts from here // qsearch() is the quiescence search function, which is called by the main - // search function when the remaining depth is zero (or, to be more precise, - // less than ONE_PLY). + // search function with depth zero, or recursively with depth less than ONE_PLY. template Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) { @@ -1191,6 +1168,7 @@ moves_loop: // When in check search starts from here 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); Move pv[MAX_PLY+1]; StateInfo st; @@ -1212,7 +1190,7 @@ moves_loop: // When in check search starts from here ss->ply = (ss-1)->ply + 1; // Check for an instant draw or if the maximum ply has been reached - if (pos.is_draw() || ss->ply >= MAX_PLY) + if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY) return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos) : DrawValue[pos.side_to_move()]; @@ -1236,10 +1214,7 @@ moves_loop: // When in check search starts from here && ttValue != VALUE_NONE // Only in case of TT access race && (ttValue >= beta ? (tte->bound() & BOUND_LOWER) : (tte->bound() & BOUND_UPPER))) - { - ss->currentMove = ttMove; // Can be MOVE_NONE return ttValue; - } // Evaluate the position statically if (InCheck) @@ -1286,16 +1261,15 @@ moves_loop: // When in check search starts from here // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will // be generated. MovePicker mp(pos, ttMove, depth, to_sq((ss-1)->currentMove)); - CheckInfo ci(pos); // Loop through the moves until no moves remain or a beta cutoff occurs while ((move = mp.next_move()) != MOVE_NONE) { assert(is_ok(move)); - givesCheck = type_of(move) == NORMAL && !ci.dcCandidates - ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move) - : pos.gives_check(move, ci); + givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates() + ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move) + : pos.gives_check(move); // Futility pruning if ( !InCheck @@ -1313,7 +1287,7 @@ moves_loop: // When in check search starts from here continue; } - if (futilityBase <= alpha && pos.see(move) <= VALUE_ZERO) + if (futilityBase <= alpha && !pos.see_ge(move, VALUE_ZERO + 1)) { bestValue = std::max(bestValue, futilityBase); continue; @@ -1328,14 +1302,14 @@ moves_loop: // When in check search starts from here // Don't search moves with negative SEE values if ( (!InCheck || evasionPrunable) && type_of(move) != PROMOTION - && pos.see_sign(move) < VALUE_ZERO) + && !pos.see_ge(move, VALUE_ZERO)) continue; // 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, ci.pinned)) + if (!pos.legal(move)) continue; ss->currentMove = move; @@ -1424,11 +1398,29 @@ moves_loop: // When in check search starts from here } - // update_stats() updates killers, history, countermove and countermove plus - // follow-up move history when a new quiet best move is found. + // update_cm_stats() updates countermove and follow-up move history + + void update_cm_stats(Stack* ss, Piece pc, Square s, Value bonus) { + + CounterMoveStats* cmh = (ss-1)->counterMoves; + CounterMoveStats* fmh1 = (ss-2)->counterMoves; + CounterMoveStats* fmh2 = (ss-4)->counterMoves; + + if (cmh) + cmh->update(pc, s, bonus); + + if (fmh1) + fmh1->update(pc, s, bonus); + + if (fmh2) + fmh2->update(pc, s, bonus); + } + + + // update_stats() updates move sorting heuristics when a new quiet best move is found void update_stats(const Position& pos, Stack* ss, Move move, - Depth depth, Move* quiets, int quietsCnt) { + Move* quiets, int quietsCnt, Value bonus) { if (ss->killers[0] != move) { @@ -1436,54 +1428,22 @@ moves_loop: // When in check search starts from here ss->killers[0] = move; } - Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1); - - Square prevSq = to_sq((ss-1)->currentMove); - CounterMoveStats* cmh = (ss-1)->counterMoves; - CounterMoveStats* fmh = (ss-2)->counterMoves; - CounterMoveStats* fmh2 = (ss-4)->counterMoves; + Color c = pos.side_to_move(); Thread* thisThread = pos.this_thread(); + thisThread->history.update(c, move, bonus); + update_cm_stats(ss, pos.moved_piece(move), to_sq(move), bonus); - thisThread->history.update(pos.moved_piece(move), to_sq(move), bonus); - - if (cmh) + if ((ss-1)->counterMoves) { + Square prevSq = to_sq((ss-1)->currentMove); thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move); - cmh->update(pos.moved_piece(move), to_sq(move), bonus); } - if (fmh) - fmh->update(pos.moved_piece(move), to_sq(move), bonus); - - if (fmh2) - fmh2->update(pos.moved_piece(move), to_sq(move), bonus); - // Decrease all the other played quiet moves for (int i = 0; i < quietsCnt; ++i) { - thisThread->history.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus); - - if (cmh) - cmh->update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus); - - if (fmh) - fmh->update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus); - - if (fmh2) - fmh2->update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus); - } - - // Extra penalty for a quiet TT move in previous ply when it gets refuted - if ((ss-1)->moveCount == 1 && !pos.captured_piece_type()) - { - if ((ss-2)->counterMoves) - (ss-2)->counterMoves->update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY); - - if ((ss-3)->counterMoves) - (ss-3)->counterMoves->update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY); - - if ((ss-5)->counterMoves) - (ss-5)->counterMoves->update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY); + thisThread->history.update(c, quiets[i], -bonus); + update_cm_stats(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus); } } @@ -1544,7 +1504,7 @@ moves_loop: // When in check search starts from here if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10) || (Limits.movetime && elapsed >= Limits.movetime) - || (Limits.nodes && Threads.nodes_searched() >= Limits.nodes)) + || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes)) Signals.stop = true; } @@ -1561,7 +1521,8 @@ string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) { 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()); - uint64_t nodes_searched = Threads.nodes_searched(); + uint64_t nodesSearched = Threads.nodes_searched(); + uint64_t tbHits = Threads.tb_hits() + (TB::RootInTB ? rootMoves.size() : 0); for (size_t i = 0; i < multiPV; ++i) { @@ -1588,13 +1549,13 @@ string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) { if (!tb && i == PVIdx) ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : ""); - ss << " nodes " << nodes_searched - << " nps " << nodes_searched * 1000 / elapsed; + ss << " nodes " << nodesSearched + << " nps " << nodesSearched * 1000 / elapsed; if (elapsed > 1000) // Earlier makes little sense ss << " hashfull " << TT.hashfull(); - ss << " tbhits " << TB::Hits + ss << " tbhits " << tbHits << " time " << elapsed << " pv"; @@ -1606,55 +1567,71 @@ string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) { } -/// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and -/// inserts the PV back into the TT. This makes sure the old PV moves are searched -/// first, even if the old TT entries have been overwritten. - -void RootMove::insert_pv_in_tt(Position& pos) { - - StateInfo state[MAX_PLY], *st = state; - bool ttHit; - - for (Move m : pv) - { - assert(MoveList(pos).contains(m)); - - TTEntry* tte = TT.probe(pos.key(), ttHit); - - if (!ttHit || tte->move() != m) // Don't overwrite correct entries - tte->save(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, - m, VALUE_NONE, TT.generation()); - - pos.do_move(m, *st++, pos.gives_check(m, CheckInfo(pos))); - } - - for (size_t i = pv.size(); i > 0; ) - pos.undo_move(pv[--i]); -} - - /// RootMove::extract_ponder_from_tt() is called in case we have no ponder move /// before exiting the search, for instance, in case we stop the search during a /// fail high at root. We try hard to have a ponder move to return to the GUI, /// otherwise in case of 'ponder on' we have nothing to think on. -bool RootMove::extract_ponder_from_tt(Position& pos) -{ +bool RootMove::extract_ponder_from_tt(Position& pos) { + StateInfo st; bool ttHit; assert(pv.size() == 1); - pos.do_move(pv[0], st, pos.gives_check(pv[0], CheckInfo(pos))); + if (!pv[0]) + return false; + + pos.do_move(pv[0], st); TTEntry* tte = TT.probe(pos.key(), ttHit); - pos.undo_move(pv[0]); if (ttHit) { Move m = tte->move(); // Local copy to be SMP safe if (MoveList(pos).contains(m)) - return pv.push_back(m), true; + pv.push_back(m); + } + + pos.undo_move(pv[0]); + return pv.size() > 1; +} + +void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) { + + RootInTB = false; + UseRule50 = Options["Syzygy50MoveRule"]; + ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY; + Cardinality = Options["SyzygyProbeLimit"]; + + // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality + if (Cardinality > MaxCardinality) + { + Cardinality = MaxCardinality; + ProbeDepth = DEPTH_ZERO; + } + + if (Cardinality < popcount(pos.pieces()) || pos.can_castle(ANY_CASTLING)) + return; + + // If the current root position is in the tablebases, then RootMoves + // contains only moves that preserve the draw or the win. + RootInTB = root_probe(pos, rootMoves, TB::Score); + + if (RootInTB) + Cardinality = 0; // Do not probe tablebases during the search + + else // If DTZ tables are missing, use WDL tables as a fallback + { + // Filter out moves that do not preserve the draw or the win. + RootInTB = root_probe_wdl(pos, rootMoves, TB::Score); + + // Only probe during search if winning + if (RootInTB && TB::Score <= VALUE_DRAW) + Cardinality = 0; } - return false; + if (RootInTB && !UseRule50) + TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1 + : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1 + : VALUE_DRAW; }