X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=f0783363e79766fc682dabbf42fc4d0d0cda9469;hp=c72f0afbc114930d84691f678399b374fee4554f;hb=f2681232e516da164196d7238482729da038ae1e;hpb=1c50d8cbf554733c0db6ab423b413d75cc0c1928 diff --git a/src/search.cpp b/src/search.cpp index c72f0afb..f0783363 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) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad + Copyright (C) 2015-2018 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 @@ -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" @@ -63,13 +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 }; + + // 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); + } - // Razoring and futility margin based on depth - // razor_margin[0] is unused as long as depth >= ONE_PLY in search - const int razor_margin[] = { 0, 570, 603, 554 }; - Value futility_margin(Depth d) { return Value(150 * 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] @@ -99,16 +110,22 @@ 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); Value value_from_tt(Value v, int ply); void update_pv(Move* pv, Move move, Move* childPv); void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus); - void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, int bonus); + 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); - bool pv_is_draw(Position& pos); + + 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. @@ -139,7 +156,7 @@ namespace { } // namespace -/// Search::init() is called during startup to initialize various lookup tables +/// Search::init() is called at startup to initialize various lookup tables void Search::init() { @@ -153,7 +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]++; } @@ -193,11 +210,6 @@ void MainThread::search() { Time.init(Limits, us, rootPos.game_ply()); TT.new_search(); - int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns - - Eval::Contempt = (us == WHITE ? make_score(contempt, contempt / 2) - : -make_score(contempt, contempt / 2)); - if (rootMoves.empty()) { rootMoves.emplace_back(MOVE_NONE); @@ -259,7 +271,7 @@ void MainThread::search() { previousScore = bestThread->rootMoves[0].score; - // Send new PV when needed + // Send again PV info if we have a new best thread if (bestThread != this) sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl; @@ -284,19 +296,17 @@ void Thread::search() { Depth lastBestMoveDepth = DEPTH_ZERO; MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr); double timeReduction = 1.0; + Color us = rootPos.side_to_move(); 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; if (mainThread) - { - mainThread->failedLow = false; - mainThread->bestMoveChanges = 0; - } + mainThread->bestMoveChanges = 0, mainThread->failedLow = false; size_t multiPV = Options["MultiPV"]; Skill skill(Options["Skill Level"]); @@ -308,22 +318,26 @@ void Thread::search() { multiPV = std::min(multiPV, rootMoves.size()); + int ct = Options["Contempt"] * PawnValueEg / 100; // From centipawns + 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 && !Threads.stop && !(Limits.depth && mainThread && rootDepth / ONE_PLY > Limits.depth)) { - // Distribute search depths across the threads - if (idx) + // Distribute search depths across the helper threads + if (idx > 0) { int i = (idx - 1) % 20; - if (((rootDepth / ONE_PLY + rootPos.game_ply() + skipPhase[i]) / skipSize[i]) % 2) - continue; + if (((rootDepth / ONE_PLY + rootPos.game_ply() + SkipPhase[i]) / SkipSize[i]) % 2) + continue; // Retry with an incremented rootDepth } // 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. @@ -339,13 +353,22 @@ 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 root move's previousScore (dynamic contempt) + ct += int(std::round(48 * atan(float(previousScore) / 128))); + + 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 - // high/low, re-search with a bigger window until we're not failing + // high/low, re-search with a bigger window until we don't fail // high/low anymore. while (true) { @@ -359,9 +382,9 @@ void Thread::search() { // search the already searched PV lines are preserved. std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end()); - // If search has been stopped, we break immediately. Sorting and - // writing PV back to TT is safe because RootMoves is still - // valid, although it refers to the previous iteration. + // If search has been stopped, we break immediately. Sorting is + // safe because RootMoves is still valid, although it refers to + // the previous iteration. if (Threads.stop) break; @@ -426,34 +449,28 @@ void Thread::search() { skill.pick_best(multiPV); // Do we have time for the next iteration? Can we stop searching now? - if (Limits.use_time_management()) - { - if (!Threads.stop && !Threads.stopOnPonderhit) + if ( Limits.use_time_management() + && !Threads.stop + && !Threads.stopOnPonderhit) { - // Stop the search if only one legal move is available, or if all - // of the available time has been used const int F[] = { mainThread->failedLow, bestValue - mainThread->previousScore }; - int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1])); - - Color us = rootPos.side_to_move(); - bool thinkHard = bestValue == VALUE_DRAW - && Limits.time[us] - Time.elapsed() > Limits.time[~us] - && ::pv_is_draw(rootPos); - double unstablePvFactor = 1 + mainThread->bestMoveChanges + thinkHard; + 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 for this move, - // the longer the move has been stable, the more. - // Use part of the gained time from a previous stable move for the current move. - timeReduction = 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 && !thinkHard) - timeReduction *= 1.3; - unstablePvFactor *= std::pow(mainThread->previousTimeReduction, 0.51) / timeReduction; + if (lastBestMoveDepth * i < completedDepth) + timeReduction *= 1.25; + // Use part of the gained time from a previous stable move for the current move + 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 / 628) + || 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". @@ -463,7 +480,6 @@ void Thread::search() { Threads.stop = true; } } - } } if (!mainThread) @@ -485,7 +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); @@ -500,7 +520,7 @@ namespace { Key posKey; Move ttMove, move, excludedMove, bestMove; Depth extension, newDepth; - Value bestValue, value, ttValue, eval; + Value bestValue, value, ttValue, eval, maxValue; bool ttHit, inCheck, givesCheck, singularExtensionNode, improving; bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture, pvExact; Piece movedPiece; @@ -510,8 +530,8 @@ namespace { Thread* thisThread = pos.this_thread(); inCheck = pos.checkers(); moveCount = captureCount = quietCount = ss->moveCount = 0; - ss->statScore = 0; bestValue = -VALUE_INFINITE; + maxValue = VALUE_INFINITE; // Check for the available remaining time if (thisThread == Threads.main()) @@ -524,8 +544,10 @@ namespace { if (!rootNode) { // Step 2. Check for aborted search and immediate draw - if (Threads.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY) - return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos) : VALUE_DRAW; + if ( Threads.stop.load(std::memory_order_relaxed) + || pos.is_draw(ss->ply) + || ss->ply >= MAX_PLY) + return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos) : VALUE_DRAW; // Step 3. Mate distance pruning. Even if we mate at the next move our score // would be at best mate_in(ss->ply+1), but if alpha is already bigger because @@ -543,15 +565,22 @@ 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. excludedMove = ss->excludedMove; - posKey = pos.key() ^ Key(excludedMove << 16); // isn't a very good hash + posKey = pos.key() ^ Key(excludedMove << 16); // Isn't a very good hash tte = TT.probe(posKey, ttHit); ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE; ttMove = rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0] @@ -571,7 +600,7 @@ namespace { if (ttValue >= beta) { if (!pos.capture_or_promotion(ttMove)) - update_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth)); + update_quiet_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()) @@ -581,14 +610,14 @@ 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); } } return ttValue; } - // Step 4a. Tablebase probe + // Step 5. Tablebases probe if (!rootNode && TB::Cardinality) { int piecesCount = pos.count(); @@ -599,7 +628,7 @@ namespace { && !pos.can_castle(ANY_CASTLING)) { TB::ProbeState err; - TB::WDLScore v = Tablebases::probe_wdl(pos, &err); + TB::WDLScore wdl = Tablebases::probe_wdl(pos, &err); if (err != TB::ProbeState::FAIL) { @@ -607,26 +636,41 @@ namespace { int drawScore = TB::UseRule50 ? 1 : 0; - value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply + 1 - : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply - 1 - : VALUE_DRAW + 2 * v * drawScore; + value = wdl < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply + 1 + : wdl > drawScore ? VALUE_MATE - MAX_PLY - ss->ply - 1 + : VALUE_DRAW + 2 * wdl * drawScore; + + Bound b = wdl < -drawScore ? BOUND_UPPER + : wdl > drawScore ? BOUND_LOWER : BOUND_EXACT; - tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT, - std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY), - MOVE_NONE, VALUE_NONE, TT.generation()); + if ( b == BOUND_EXACT + || (b == BOUND_LOWER ? value >= beta : value <= alpha)) + { + tte->save(posKey, value_to_tt(value, ss->ply), b, + std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY), + MOVE_NONE, VALUE_NONE, TT.generation()); - return value; + return value; + } + + if (PvNode) + { + if (b == BOUND_LOWER) + bestValue = value, alpha = std::max(alpha, bestValue); + else + maxValue = value; + } } } } - // Step 5. Evaluate the position statically + // Step 6. Evaluate the position statically if (inCheck) { ss->staticEval = eval = VALUE_NONE; + improving = false; goto moves_loop; } - else if (ttHit) { // Never assume anything on values stored in TT @@ -634,13 +678,13 @@ namespace { eval = ss->staticEval = evaluate(pos); // Can ttValue be used as a better position evaluation? - if ( ttValue != VALUE_NONE + if ( ttValue != VALUE_NONE && (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))) eval = ttValue; } else { - eval = ss->staticEval = + ss->staticEval = eval = (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo; @@ -648,48 +692,48 @@ 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 6. Razoring (skipped when in check) - if ( !PvNode - && depth < 4 * ONE_PLY - && eval + razor_margin[depth / ONE_PLY] <= alpha) + // Step 7. Razoring (skipped when in check) + if ( !PvNode + && depth < 3 * ONE_PLY + && eval <= alpha - RazorMargin[depth / ONE_PLY]) { - if (depth <= ONE_PLY) - return qsearch(pos, ss, alpha, alpha+1); - - Value ralpha = alpha - razor_margin[depth / ONE_PLY]; - Value v = qsearch(pos, ss, ralpha, ralpha+1); - if (v <= ralpha) + 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 7. Futility pruning: child node (skipped when in check) + // Step 8. Futility pruning: child node (skipped when in check) if ( !rootNode && depth < 7 * ONE_PLY - && eval - futility_margin(depth) >= beta - && eval < VALUE_KNOWN_WIN) // Do not return unproven wins + && eval - futility_margin(depth, improving) >= beta + && eval < VALUE_KNOWN_WIN) // Do not return unproven wins return eval; - // Step 8. Null move search with verification search (is omitted in PV nodes) + // Step 9. Null move search with verification search if ( !PvNode && eval >= beta && ss->staticEval >= beta - 36 * depth / ONE_PLY + 225 - && (ss->ply >= thisThread->nmp_ply || ss->ply % 2 == thisThread->pair)) + && (ss->ply >= thisThread->nmp_ply || ss->ply % 2 != thisThread->nmp_odd)) { - assert(eval - beta >= 0); // Null move dynamic reduction based on depth and value 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) @@ -698,77 +742,83 @@ namespace { if (nullValue >= VALUE_MATE_IN_MAX_PLY) nullValue = beta; - if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN) + if (abs(beta) < VALUE_KNOWN_WIN && (depth < 12 * ONE_PLY || thisThread->nmp_ply)) return nullValue; - // Do verification search at high depths - R += ONE_PLY; - // disable null move pruning for side to move for the first part of the remaining search tree - int nmp_ply = thisThread->nmp_ply; - int pair = thisThread->pair; + // Do verification search at high depths. Disable null move pruning + // for side to move for the first part of the remaining search tree. thisThread->nmp_ply = ss->ply + 3 * (depth-R) / 4; - thisThread->pair = (ss->ply % 2) == 0; + 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); - thisThread->pair = pair; - thisThread->nmp_ply = nmp_ply; + Value v = search(pos, ss, beta-1, beta, depth-R, false, true); + + thisThread->nmp_odd = thisThread->nmp_ply = 0; if (v >= beta) return nullValue; } } - // Step 9. ProbCut (skipped when in check) + // Step 10. ProbCut (skipped when in check) // 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) { - Value rbeta = std::min(beta + 200, VALUE_INFINITE); - assert(is_ok((ss-1)->currentMove)); + 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; } } - // Step 10. Internal iterative deepening (skipped when in check) + // 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 * ONE_PLY) - 2) * ONE_PLY; + Depth d = 3 * depth / 4 - 2 * ONE_PLY; search(pos, ss, alpha, beta, d, cutNode, true); tte = TT.probe(posKey, ttHit); + ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE; ttMove = ttHit ? tte->move() : MOVE_NONE; } -moves_loop: // When in check search starts from here +moves_loop: // When in check, search starts from here const PieceToHistory* contHist[] = { (ss-1)->contHistory, (ss-2)->contHistory, nullptr, (ss-4)->contHistory }; Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq]; 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 @@ -781,8 +831,8 @@ moves_loop: // When in check search starts from here ttCapture = false; pvExact = PvNode && ttHit && tte->bound() == BOUND_EXACT; - // Step 11. Loop through moves - // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs + // Step 12. Loop through all pseudo-legal moves until no moves remain + // or a beta cutoff occurs. while ((move = mp.next_move(skipQuiets)) != MOVE_NONE) { assert(is_ok(move)); @@ -803,42 +853,37 @@ moves_loop: // When in check search starts from here sync_cout << "info depth " << depth / ONE_PLY << " currmove " << UCI::move(move, pos.is_chess960()) << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl; - if (PvNode) (ss+1)->pv = nullptr; 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]; - // Step 12. Singular and Gives Check Extensions + // Step 13. Extensions - // Singular extension search. 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. + // Singular extension search. 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 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 ( singularExtensionNode && move == ttMove && pos.legal(move)) { Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE); - Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY; ss->excludedMove = move; - value = search(pos, ss, rBeta - 1, rBeta, d, cutNode, true); + value = search(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode, true); ss->excludedMove = MOVE_NONE; if (value < rBeta) extension = ONE_PLY; } - else if ( givesCheck + else if ( givesCheck // Check extension && !moveCountPruning && pos.see_ge(move)) extension = ONE_PLY; @@ -846,7 +891,7 @@ moves_loop: // When in check search starts from here // Calculate new depth for this move newDepth = depth - ONE_PLY + extension; - // Step 13. Pruning at shallow depth + // Step 14. Pruning at shallow depth if ( !rootNode && pos.non_pawn_material(pos.side_to_move()) && bestValue > VALUE_MATED_IN_MAX_PLY) @@ -884,7 +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; } @@ -903,12 +948,12 @@ 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 14. Make the move + // Step 15. Make the move pos.do_move(move, st, givesCheck); - // Step 15. Reduced depth search (LMR). If the move fails high it will be + // Step 16. Reduced depth search (LMR). If the move fails high it will be // re-searched at full depth. if ( depth >= 3 * ONE_PLY && moveCount > 1 @@ -969,12 +1014,9 @@ moves_loop: // When in check search starts from here else doFullDepthSearch = !PvNode || moveCount > 1; - // Step 16. Full depth search when LMR is skipped or fails high + // 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 @@ -984,18 +1026,15 @@ 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 17. Undo move + // Step 18. Undo move pos.undo_move(move); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); - // Step 18. Check for a new best move + // Step 19. 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. @@ -1007,7 +1046,7 @@ moves_loop: // When in check search starts from here RootMove& rm = *std::find(thisThread->rootMoves.begin(), thisThread->rootMoves.end(), move); - // PV move or new best move ? + // PV move or new best move? if (moveCount == 1 || value > alpha) { rm.score = value; @@ -1053,10 +1092,14 @@ moves_loop: // When in check search starts from here } } - if (!captureOrPromotion && move != bestMove && quietCount < 64) - quietsSearched[quietCount++] = move; - else if (captureOrPromotion && move != bestMove && captureCount < 32) - capturesSearched[captureCount++] = move; + if (move != bestMove) + { + if (captureOrPromotion && captureCount < 32) + capturesSearched[captureCount++] = move; + + else if (!captureOrPromotion && quietCount < 64) + quietsSearched[quietCount++] = move; + } } // The following condition would detect a stop only after move loop has been @@ -1081,7 +1124,7 @@ moves_loop: // When in check search starts from here { // Quiet best move: update move sorting heuristics if (!pos.capture_or_promotion(bestMove)) - update_stats(pos, ss, bestMove, quietsSearched, quietCount, stat_bonus(depth)); + update_quiet_stats(pos, ss, bestMove, quietsSearched, quietCount, stat_bonus(depth)); else update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth)); @@ -1095,6 +1138,9 @@ moves_loop: // When in check search starts from here && is_ok((ss-1)->currentMove)) update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth)); + if (PvNode) + bestValue = std::min(bestValue, maxValue); + if (!excludedMove) tte->save(posKey, value_to_tt(bestValue, ss->ply), bestValue >= beta ? BOUND_LOWER : @@ -1109,13 +1155,11 @@ 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(InCheck == bool(pos.checkers())); assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE); assert(PvNode || (alpha == beta - 1)); assert(depth <= DEPTH_ZERO); @@ -1126,9 +1170,9 @@ moves_loop: // When in check search starts from here TTEntry* tte; Key posKey; Move ttMove, move, bestMove; - Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha; - bool ttHit, givesCheck, evasionPrunable; Depth ttDepth; + Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha; + bool ttHit, inCheck, givesCheck, evasionPrunable; int moveCount; if (PvNode) @@ -1138,26 +1182,28 @@ moves_loop: // When in check search starts from here ss->pv[0] = MOVE_NONE; } - ss->currentMove = bestMove = MOVE_NONE; (ss+1)->ply = ss->ply + 1; + ss->currentMove = bestMove = MOVE_NONE; + inCheck = pos.checkers(); moveCount = 0; - // Check for an instant draw or if the maximum ply has been reached - if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY) - return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos) : VALUE_DRAW; + // 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; 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(); tte = TT.probe(posKey, ttHit); - ttMove = ttHit ? tte->move() : MOVE_NONE; ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE; + ttMove = ttHit ? tte->move() : MOVE_NONE; if ( !PvNode && ttHit @@ -1168,7 +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; @@ -1218,14 +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)) @@ -1248,15 +1292,14 @@ 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) - && type_of(move) != PROMOTION - && !pos.see_ge(move)) + if ( (!inCheck || evasionPrunable) + && !pos.see_ge(move)) continue; // Speculative prefetch as early as possible @@ -1273,8 +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); @@ -1307,7 +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), @@ -1362,7 +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; } @@ -1374,22 +1416,22 @@ 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; } } - // update_stats() updates move sorting heuristics when a new quiet best move is found + // update_quiet_stats() updates move sorting heuristics when a new quiet best move is found - void update_stats(const Position& pos, Stack* ss, Move move, - Move* quiets, int quietsCnt, int bonus) { + void update_quiet_stats(const Position& pos, Stack* ss, Move move, + Move* quiets, int quietsCnt, int bonus) { if (ss->killers[0] != move) { @@ -1397,9 +1439,9 @@ moves_loop: // When in check search starts from here ss->killers[0] = move; } - Color c = pos.side_to_move(); + Color us = pos.side_to_move(); Thread* thisThread = pos.this_thread(); - thisThread->mainHistory.update(c, 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)) @@ -1411,30 +1453,11 @@ 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(c, 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); } } - - // Is the PV leading to a draw position? Assumes all pv moves are legal - bool pv_is_draw(Position& pos) { - - StateInfo st[MAX_PLY]; - auto& pv = pos.this_thread()->rootMoves[0].pv; - - for (size_t i = 0; i < pv.size(); ++i) - pos.do_move(pv[i], st[i]); - - bool isDraw = pos.is_draw(pv.size()); - - for (size_t i = pv.size(); i > 0; --i) - pos.undo_move(pv[i-1]); - - return isDraw; - } - - // When playing with strength handicap, choose best move among a set of RootMoves // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen. @@ -1470,38 +1493,37 @@ moves_loop: // When in check search starts from here } // namespace - // check_time() is used to print debug info and, more importantly, to detect - // when we are out of available time and thus stop the search. +/// MainThread::check_time() is used to print debug info and, more importantly, +/// to detect when we are out of available time and thus stop the search. - void MainThread::check_time() { +void MainThread::check_time() { - if (--callsCnt > 0) - return; + if (--callsCnt > 0) + return; - // At low node count increase the checking rate to about 0.1% of nodes - // otherwise use a default value. - callsCnt = Limits.nodes ? std::min(4096, int(Limits.nodes / 1024)) : 4096; + // When using nodes, ensure checking rate is not lower than 0.1% of nodes + callsCnt = Limits.nodes ? std::min(1024, int(Limits.nodes / 1024)) : 1024; - static TimePoint lastInfoTime = now(); + static TimePoint lastInfoTime = now(); - int elapsed = Time.elapsed(); - TimePoint tick = Limits.startTime + elapsed; + TimePoint elapsed = Time.elapsed(); + TimePoint tick = Limits.startTime + elapsed; - if (tick - lastInfoTime >= 1000) - { - lastInfoTime = tick; - dbg_print(); - } + if (tick - lastInfoTime >= 1000) + { + lastInfoTime = tick; + dbg_print(); + } - // An engine may not stop pondering until told so by the GUI - if (Threads.ponder) - return; + // We should not stop pondering until told so by the GUI + if (Threads.ponder) + return; - if ( (Limits.use_time_management() && elapsed > Time.maximum()) - || (Limits.movetime && elapsed >= Limits.movetime) - || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes)) - Threads.stop = true; - } + if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10) + || (Limits.movetime && elapsed >= Limits.movetime) + || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes)) + Threads.stop = true; +} /// UCI::pv() formats PV information according to the UCI protocol. UCI requires @@ -1510,7 +1532,7 @@ moves_loop: // When in check search starts from here 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()); @@ -1589,6 +1611,7 @@ bool RootMove::extract_ponder_from_tt(Position& pos) { return pv.size() > 1; } + void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) { RootInTB = false; @@ -1631,4 +1654,9 @@ void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1 : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1 : VALUE_DRAW; + + // Since root_probe() and root_probe_wdl() dirty the root move scores, + // we reset them to -VALUE_INFINITE + for (RootMove& rm : rootMoves) + rm.score = -VALUE_INFINITE; }