2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
5 Copyright (C) 2015-2017 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
7 Stockfish is free software: you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation, either version 3 of the License, or
10 (at your option) any later version.
12 Stockfish is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
24 #include <cstring> // For std::memset
38 #include "syzygy/tbprobe.h"
46 namespace Tablebases {
55 namespace TB = Tablebases;
59 using namespace Search;
63 // Different node types, used as a template parameter
64 enum NodeType { NonPV, PV };
66 // Razoring and futility margin based on depth
67 const int razor_margin[4] = { 483, 570, 603, 554 };
68 Value futility_margin(Depth d) { return Value(150 * d / ONE_PLY); }
70 // Futility and reductions lookup tables, initialized at startup
71 int FutilityMoveCounts[2][16]; // [improving][depth]
72 int Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
74 template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
75 return Reductions[PvNode][i][std::min(d / ONE_PLY, 63)][std::min(mn, 63)] * ONE_PLY;
78 // History and stats update bonus, based on depth
79 Value stat_bonus(Depth depth) {
80 int d = depth / ONE_PLY ;
81 return Value(d * d + 2 * d - 2);
84 // Skill structure is used to implement strength limit
86 Skill(int l) : level(l) {}
87 bool enabled() const { return level < 20; }
88 bool time_to_pick(Depth depth) const { return depth / ONE_PLY == 1 + level; }
89 Move best_move(size_t multiPV) { return best ? best : pick_best(multiPV); }
90 Move pick_best(size_t multiPV);
93 Move best = MOVE_NONE;
96 // EasyMoveManager structure is used to detect an 'easy move'. When the PV is
97 // stable across multiple search iterations, we can quickly return the best move.
98 struct EasyMoveManager {
103 pv[0] = pv[1] = pv[2] = MOVE_NONE;
106 Move get(Key key) const {
107 return expectedPosKey == key ? pv[2] : MOVE_NONE;
110 void update(Position& pos, const std::vector<Move>& newPv) {
112 assert(newPv.size() >= 3);
114 // Keep track of how many times in a row the 3rd ply remains stable
115 stableCnt = (newPv[2] == pv[2]) ? stableCnt + 1 : 0;
117 if (!std::equal(newPv.begin(), newPv.begin() + 3, pv))
119 std::copy(newPv.begin(), newPv.begin() + 3, pv);
122 pos.do_move(newPv[0], st[0]);
123 pos.do_move(newPv[1], st[1]);
124 expectedPosKey = pos.key();
125 pos.undo_move(newPv[1]);
126 pos.undo_move(newPv[0]);
135 EasyMoveManager EasyMove;
136 Value DrawValue[COLOR_NB];
138 template <NodeType NT>
139 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning);
141 template <NodeType NT, bool InCheck>
142 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO);
144 Value value_to_tt(Value v, int ply);
145 Value value_from_tt(Value v, int ply);
146 void update_pv(Move* pv, Move move, Move* childPv);
147 void update_cm_stats(Stack* ss, Piece pc, Square s, Value bonus);
148 void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, Value bonus);
154 /// Search::init() is called during startup to initialize various lookup tables
156 void Search::init() {
158 for (int imp = 0; imp <= 1; ++imp)
159 for (int d = 1; d < 64; ++d)
160 for (int mc = 1; mc < 64; ++mc)
162 double r = log(d) * log(mc) / 2;
164 Reductions[NonPV][imp][d][mc] = int(std::round(r));
165 Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0);
167 // Increase reduction for non-PV nodes when eval is not improving
168 if (!imp && Reductions[NonPV][imp][d][mc] >= 2)
169 Reductions[NonPV][imp][d][mc]++;
172 for (int d = 0; d < 16; ++d)
174 FutilityMoveCounts[0][d] = int(2.4 + 0.773 * pow(d + 0.00, 1.8));
175 FutilityMoveCounts[1][d] = int(2.9 + 1.045 * pow(d + 0.49, 1.8));
180 /// Search::clear() resets search state to zero, to obtain reproducible results
182 void Search::clear() {
186 for (Thread* th : Threads)
188 th->counterMoves.clear();
190 th->counterMoveHistory.clear();
191 th->resetCalls = true;
194 Threads.main()->previousScore = VALUE_INFINITE;
198 /// Search::perft() is our utility to verify move generation. All the leaf nodes
199 /// up to the given depth are generated and counted, and the sum is returned.
201 uint64_t Search::perft(Position& pos, Depth depth) {
204 uint64_t cnt, nodes = 0;
205 const bool leaf = (depth == 2 * ONE_PLY);
207 for (const auto& m : MoveList<LEGAL>(pos))
209 if (Root && depth <= ONE_PLY)
214 cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
219 sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
224 template uint64_t Search::perft<true>(Position&, Depth);
227 /// MainThread::search() is called by the main thread when the program receives
228 /// the UCI 'go' command. It searches from the root position and outputs the "bestmove".
230 void MainThread::search() {
232 Color us = rootPos.side_to_move();
233 Time.init(Limits, us, rootPos.game_ply());
235 int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
236 DrawValue[ us] = VALUE_DRAW - Value(contempt);
237 DrawValue[~us] = VALUE_DRAW + Value(contempt);
239 if (rootMoves.empty())
241 rootMoves.push_back(RootMove(MOVE_NONE));
242 sync_cout << "info depth 0 score "
243 << UCI::value(rootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
248 for (Thread* th : Threads)
250 th->start_searching();
252 Thread::search(); // Let's start searching!
255 // When playing in 'nodes as time' mode, subtract the searched nodes from
256 // the available ones before exiting.
258 Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
260 // When we reach the maximum depth, we can arrive here without a raise of
261 // Signals.stop. However, if we are pondering or in an infinite search,
262 // the UCI protocol states that we shouldn't print the best move before the
263 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
264 // until the GUI sends one of those commands (which also raises Signals.stop).
265 if (!Signals.stop && (Limits.ponder || Limits.infinite))
267 Signals.stopOnPonderhit = true;
271 // Stop the threads if not already stopped
274 // Wait until all threads have finished
275 for (Thread* th : Threads)
277 th->wait_for_search_finished();
279 // Check if there are threads with a better score than main thread
280 Thread* bestThread = this;
281 if ( !this->easyMovePlayed
282 && Options["MultiPV"] == 1
284 && !Skill(Options["Skill Level"]).enabled()
285 && rootMoves[0].pv[0] != MOVE_NONE)
287 for (Thread* th : Threads)
289 Depth depthDiff = th->completedDepth - bestThread->completedDepth;
290 Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score;
292 if (scoreDiff > 0 && depthDiff >= 0)
297 previousScore = bestThread->rootMoves[0].score;
299 // Send new PV when needed
300 if (bestThread != this)
301 sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
303 sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
305 if (bestThread->rootMoves[0].pv.size() > 1 || bestThread->rootMoves[0].extract_ponder_from_tt(rootPos))
306 std::cout << " ponder " << UCI::move(bestThread->rootMoves[0].pv[1], rootPos.is_chess960());
308 std::cout << sync_endl;
311 // Sizes and phases of the skip-blocks, used for distributing search depths across the threads.
312 static int skipsize[20] = {1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4};
313 static int phase [20] = {0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7};
315 // Thread::search() is the main iterative deepening loop. It calls search()
316 // repeatedly with increasing depth until the allocated thinking time has been
317 // consumed, the user stops the search, or the maximum search depth is reached.
319 void Thread::search() {
321 Stack stack[MAX_PLY+7], *ss = stack+4; // To allow referencing (ss-4) and (ss+2)
322 Value bestValue, alpha, beta, delta;
323 Move easyMove = MOVE_NONE;
324 MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
326 std::memset(ss-4, 0, 7 * sizeof(Stack));
328 bestValue = delta = alpha = -VALUE_INFINITE;
329 beta = VALUE_INFINITE;
330 completedDepth = DEPTH_ZERO;
334 easyMove = EasyMove.get(rootPos.key());
336 mainThread->easyMovePlayed = mainThread->failedLow = false;
337 mainThread->bestMoveChanges = 0;
341 size_t multiPV = Options["MultiPV"];
342 Skill skill(Options["Skill Level"]);
344 // When playing with strength handicap enable MultiPV search that we will
345 // use behind the scenes to retrieve a set of possible moves.
347 multiPV = std::max(multiPV, (size_t)4);
349 multiPV = std::min(multiPV, rootMoves.size());
351 int hIdx = (idx - 1) % 20; // helper index, cycle after 20 threads
353 // Iterative deepening loop until requested to stop or the target depth is reached
354 while ( (rootDepth += ONE_PLY) < DEPTH_MAX
356 && (!Limits.depth || Threads.main()->rootDepth / ONE_PLY <= Limits.depth))
358 // skip half of the plies in blocks depending on game ply and helper index.
359 if (idx && ((rootDepth / ONE_PLY + rootPos.game_ply() + phase[hIdx]) / skipsize[hIdx]) % 2)
362 // Age out PV variability metric
364 mainThread->bestMoveChanges *= 0.505, mainThread->failedLow = false;
366 // Save the last iteration's scores before first PV line is searched and
367 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
368 for (RootMove& rm : rootMoves)
369 rm.previousScore = rm.score;
371 // MultiPV loop. We perform a full root search for each PV line
372 for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
374 // Reset aspiration window starting size
375 if (rootDepth >= 5 * ONE_PLY)
378 alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
379 beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
382 // Start with a small aspiration window and, in the case of a fail
383 // high/low, re-search with a bigger window until we're not failing
387 bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false, false);
389 // Bring the best move to the front. It is critical that sorting
390 // is done with a stable algorithm because all the values but the
391 // first and eventually the new best one are set to -VALUE_INFINITE
392 // and we want to keep the same order for all the moves except the
393 // new PV that goes to the front. Note that in case of MultiPV
394 // search the already searched PV lines are preserved.
395 std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
397 // If search has been stopped, we break immediately. Sorting and
398 // writing PV back to TT is safe because RootMoves is still
399 // valid, although it refers to the previous iteration.
403 // When failing high/low give some update (without cluttering
404 // the UI) before a re-search.
407 && (bestValue <= alpha || bestValue >= beta)
408 && Time.elapsed() > 3000)
409 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
411 // In case of failing low/high increase aspiration window and
412 // re-search, otherwise exit the loop.
413 if (bestValue <= alpha)
415 beta = (alpha + beta) / 2;
416 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
420 mainThread->failedLow = true;
421 Signals.stopOnPonderhit = false;
424 else if (bestValue >= beta)
426 alpha = (alpha + beta) / 2;
427 beta = std::min(bestValue + delta, VALUE_INFINITE);
432 delta += delta / 4 + 5;
434 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
437 // Sort the PV lines searched so far and update the GUI
438 std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
443 if (Signals.stop || PVIdx + 1 == multiPV || Time.elapsed() > 3000)
444 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
448 completedDepth = rootDepth;
453 // If skill level is enabled and time is up, pick a sub-optimal best move
454 if (skill.enabled() && skill.time_to_pick(rootDepth))
455 skill.pick_best(multiPV);
457 // Have we found a "mate in x"?
459 && bestValue >= VALUE_MATE_IN_MAX_PLY
460 && VALUE_MATE - bestValue <= 2 * Limits.mate)
463 // Do we have time for the next iteration? Can we stop searching now?
464 if (Limits.use_time_management())
466 if (!Signals.stop && !Signals.stopOnPonderhit)
468 // Stop the search if only one legal move is available, or if all
469 // of the available time has been used, or if we matched an easyMove
470 // from the previous search and just did a fast verification.
471 const int F[] = { mainThread->failedLow,
472 bestValue - mainThread->previousScore };
474 int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1]));
475 double unstablePvFactor = 1 + mainThread->bestMoveChanges;
477 bool doEasyMove = rootMoves[0].pv[0] == easyMove
478 && mainThread->bestMoveChanges < 0.03
479 && Time.elapsed() > Time.optimum() * 5 / 44;
481 if ( rootMoves.size() == 1
482 || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628
483 || (mainThread->easyMovePlayed = doEasyMove, doEasyMove))
485 // If we are allowed to ponder do not stop the search now but
486 // keep pondering until the GUI sends "ponderhit" or "stop".
488 Signals.stopOnPonderhit = true;
494 if (rootMoves[0].pv.size() >= 3)
495 EasyMove.update(rootPos, rootMoves[0].pv);
504 // Clear any candidate easy move that wasn't stable for the last search
505 // iterations; the second condition prevents consecutive fast moves.
506 if (EasyMove.stableCnt < 6 || mainThread->easyMovePlayed)
509 // If skill level is enabled, swap best PV line with the sub-optimal one
511 std::swap(rootMoves[0], *std::find(rootMoves.begin(),
512 rootMoves.end(), skill.best_move(multiPV)));
518 // search<>() is the main search function for both PV and non-PV nodes
520 template <NodeType NT>
521 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning) {
523 const bool PvNode = NT == PV;
524 const bool rootNode = PvNode && (ss-1)->ply == 0;
526 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
527 assert(PvNode || (alpha == beta - 1));
528 assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
529 assert(!(PvNode && cutNode));
530 assert(depth / ONE_PLY * ONE_PLY == depth);
532 Move pv[MAX_PLY+1], quietsSearched[64];
536 Move ttMove, move, excludedMove, bestMove;
537 Depth extension, newDepth;
538 Value bestValue, value, ttValue, eval;
539 bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
540 bool captureOrPromotion, doFullDepthSearch, moveCountPruning;
542 int moveCount, quietCount;
544 // Step 1. Initialize node
545 Thread* thisThread = pos.this_thread();
546 inCheck = pos.checkers();
547 moveCount = quietCount = ss->moveCount = 0;
548 ss->history = VALUE_ZERO;
549 bestValue = -VALUE_INFINITE;
550 ss->ply = (ss-1)->ply + 1;
552 // Check for the available remaining time
553 if (thisThread->resetCalls.load(std::memory_order_relaxed))
555 thisThread->resetCalls = false;
556 // At low node count increase the checking rate to about 0.1% of nodes
557 // otherwise use a default value.
558 thisThread->callsCnt = Limits.nodes ? std::min((int64_t)4096, Limits.nodes / 1024)
562 if (--thisThread->callsCnt <= 0)
564 for (Thread* th : Threads)
565 th->resetCalls = true;
570 // Used to send selDepth info to GUI
571 if (PvNode && thisThread->maxPly < ss->ply)
572 thisThread->maxPly = ss->ply;
576 // Step 2. Check for aborted search and immediate draw
577 if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
578 return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
579 : DrawValue[pos.side_to_move()];
581 // Step 3. Mate distance pruning. Even if we mate at the next move our score
582 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
583 // a shorter mate was found upward in the tree then there is no need to search
584 // because we will never beat the current alpha. Same logic but with reversed
585 // signs applies also in the opposite condition of being mated instead of giving
586 // mate. In this case return a fail-high score.
587 alpha = std::max(mated_in(ss->ply), alpha);
588 beta = std::min(mate_in(ss->ply+1), beta);
593 assert(0 <= ss->ply && ss->ply < MAX_PLY);
595 ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
596 ss->counterMoves = nullptr;
597 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
598 Square prevSq = to_sq((ss-1)->currentMove);
600 // Step 4. Transposition table lookup. We don't want the score of a partial
601 // search to overwrite a previous full search TT value, so we use a different
602 // position key in case of an excluded move.
603 excludedMove = ss->excludedMove;
604 posKey = pos.key() ^ Key(excludedMove);
605 tte = TT.probe(posKey, ttHit);
606 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
607 ttMove = rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
608 : ttHit ? tte->move() : MOVE_NONE;
610 // At non-PV nodes we check for an early TT cutoff
613 && tte->depth() >= depth
614 && ttValue != VALUE_NONE // Possible in case of TT access race
615 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
616 : (tte->bound() & BOUND_UPPER)))
618 // If ttMove is quiet, update move sorting heuristics on TT hit
623 if (!pos.capture_or_promotion(ttMove))
624 update_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth));
626 // Extra penalty for a quiet TT move in previous ply when it gets refuted
627 if ((ss-1)->moveCount == 1 && !pos.captured_piece())
628 update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
630 // Penalty for a quiet ttMove that fails low
631 else if (!pos.capture_or_promotion(ttMove))
633 Value penalty = -stat_bonus(depth + ONE_PLY);
634 thisThread->history.update(pos.side_to_move(), ttMove, penalty);
635 update_cm_stats(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
641 // Step 4a. Tablebase probe
642 if (!rootNode && TB::Cardinality)
644 int piecesCount = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
646 if ( piecesCount <= TB::Cardinality
647 && (piecesCount < TB::Cardinality || depth >= TB::ProbeDepth)
648 && pos.rule50_count() == 0
649 && !pos.can_castle(ANY_CASTLING))
652 TB::WDLScore v = Tablebases::probe_wdl(pos, &err);
654 if (err != TB::ProbeState::FAIL)
656 thisThread->tbHits++;
658 int drawScore = TB::UseRule50 ? 1 : 0;
660 value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
661 : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply
662 : VALUE_DRAW + 2 * v * drawScore;
664 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
665 std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
666 MOVE_NONE, VALUE_NONE, TT.generation());
673 // Step 5. Evaluate the position statically
676 ss->staticEval = eval = VALUE_NONE;
682 // Never assume anything on values stored in TT
683 if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
684 eval = ss->staticEval = evaluate(pos);
686 // Can ttValue be used as a better position evaluation?
687 if (ttValue != VALUE_NONE)
688 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
693 eval = ss->staticEval =
694 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
695 : -(ss-1)->staticEval + 2 * Eval::Tempo;
697 tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
698 ss->staticEval, TT.generation());
701 if (skipEarlyPruning)
704 // Step 6. Razoring (skipped when in check)
706 && depth < 4 * ONE_PLY
707 && eval + razor_margin[depth / ONE_PLY] <= alpha)
709 if (depth <= ONE_PLY)
710 return qsearch<NonPV, false>(pos, ss, alpha, alpha+1);
712 Value ralpha = alpha - razor_margin[depth / ONE_PLY];
713 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1);
718 // Step 7. Futility pruning: child node (skipped when in check)
720 && depth < 7 * ONE_PLY
721 && eval - futility_margin(depth) >= beta
722 && eval < VALUE_KNOWN_WIN // Do not return unproven wins
723 && pos.non_pawn_material(pos.side_to_move()))
726 // Step 8. Null move search with verification search (is omitted in PV nodes)
729 && (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY)
730 && pos.non_pawn_material(pos.side_to_move()))
732 ss->currentMove = MOVE_NULL;
733 ss->counterMoves = nullptr;
735 assert(eval - beta >= 0);
737 // Null move dynamic reduction based on depth and value
738 Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
740 pos.do_null_move(st);
741 Value nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1)
742 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true);
743 pos.undo_null_move();
745 if (nullValue >= beta)
747 // Do not return unproven mate scores
748 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
751 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
754 // Do verification search at high depths
755 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta)
756 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false, true);
763 // Step 9. ProbCut (skipped when in check)
764 // If we have a good enough capture and a reduced search returns a value
765 // much above beta, we can (almost) safely prune the previous move.
767 && depth >= 5 * ONE_PLY
768 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
770 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
771 Depth rdepth = depth - 4 * ONE_PLY;
773 assert(rdepth >= ONE_PLY);
774 assert((ss-1)->currentMove != MOVE_NONE);
775 assert((ss-1)->currentMove != MOVE_NULL);
777 MovePicker mp(pos, ttMove, rbeta - ss->staticEval);
779 while ((move = mp.next_move()) != MOVE_NONE)
782 ss->currentMove = move;
783 ss->counterMoves = &thisThread->counterMoveHistory[pos.moved_piece(move)][to_sq(move)];
784 pos.do_move(move, st);
785 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode, false);
792 // Step 10. Internal iterative deepening (skipped when in check)
793 if ( depth >= 6 * ONE_PLY
795 && (PvNode || ss->staticEval + 256 >= beta))
797 Depth d = (3 * depth / (4 * ONE_PLY) - 2) * ONE_PLY;
798 search<NT>(pos, ss, alpha, beta, d, cutNode, true);
800 tte = TT.probe(posKey, ttHit);
801 ttMove = ttHit ? tte->move() : MOVE_NONE;
804 moves_loop: // When in check search starts from here
806 const CounterMoveStats* cmh = (ss-1)->counterMoves;
807 const CounterMoveStats* fmh = (ss-2)->counterMoves;
808 const CounterMoveStats* fmh2 = (ss-4)->counterMoves;
810 MovePicker mp(pos, ttMove, depth, ss);
811 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
812 improving = ss->staticEval >= (ss-2)->staticEval
813 /* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */
814 ||(ss-2)->staticEval == VALUE_NONE;
816 singularExtensionNode = !rootNode
817 && depth >= 8 * ONE_PLY
818 && ttMove != MOVE_NONE
819 && ttValue != VALUE_NONE
820 && !excludedMove // Recursive singular search is not allowed
821 && (tte->bound() & BOUND_LOWER)
822 && tte->depth() >= depth - 3 * ONE_PLY;
824 // Step 11. Loop through moves
825 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
826 while ((move = mp.next_move()) != MOVE_NONE)
830 if (move == excludedMove)
833 // At root obey the "searchmoves" option and skip moves not listed in Root
834 // Move List. As a consequence any illegal move is also skipped. In MultiPV
835 // mode we also skip PV moves which have been already searched.
836 if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
837 thisThread->rootMoves.end(), move))
840 ss->moveCount = ++moveCount;
842 if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
843 sync_cout << "info depth " << depth / ONE_PLY
844 << " currmove " << UCI::move(move, pos.is_chess960())
845 << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
848 (ss+1)->pv = nullptr;
850 extension = DEPTH_ZERO;
851 captureOrPromotion = pos.capture_or_promotion(move);
852 moved_piece = pos.moved_piece(move);
854 givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
855 ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
856 : pos.gives_check(move);
858 moveCountPruning = depth < 16 * ONE_PLY
859 && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];
861 // Step 12. Extensions
865 && pos.see_ge(move, VALUE_ZERO))
868 // Singular extension search. If all moves but one fail low on a search of
869 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
870 // is singular and should be extended. To verify this we do a reduced search
871 // on all the other moves but the ttMove and if the result is lower than
872 // ttValue minus a margin then we extend the ttMove.
873 if ( singularExtensionNode
878 Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
879 Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY;
880 ss->excludedMove = move;
881 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, d, cutNode, true);
882 ss->excludedMove = MOVE_NONE;
888 // Calculate new depth for this move
889 newDepth = depth - ONE_PLY + extension;
891 // Step 13. Pruning at shallow depth
893 && bestValue > VALUE_MATED_IN_MAX_PLY)
895 if ( !captureOrPromotion
897 && (!pos.advanced_pawn_push(move) || pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) >= 5000))
899 // Move count based pruning
900 if (moveCountPruning)
903 // Reduced depth of the next LMR search
904 int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
906 // Countermoves based pruning
908 && (!cmh || (*cmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
909 && (!fmh || (*fmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
910 && (!fmh2 || (*fmh2)[moved_piece][to_sq(move)] < VALUE_ZERO || (cmh && fmh)))
913 // Futility pruning: parent node
916 && ss->staticEval + 256 + 200 * lmrDepth <= alpha)
919 // Prune moves with negative SEE
921 && !pos.see_ge(move, Value(-35 * lmrDepth * lmrDepth)))
924 else if ( depth < 7 * ONE_PLY
926 && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY)))
930 // Speculative prefetch as early as possible
931 prefetch(TT.first_entry(pos.key_after(move)));
933 // Check for legality just before making the move
934 if (!rootNode && !pos.legal(move))
936 ss->moveCount = --moveCount;
940 // Update the current move (this must be done after singular extension search)
941 ss->currentMove = move;
942 ss->counterMoves = &thisThread->counterMoveHistory[moved_piece][to_sq(move)];
944 // Step 14. Make the move
945 pos.do_move(move, st, givesCheck);
947 // Step 15. Reduced depth search (LMR). If the move fails high it will be
948 // re-searched at full depth.
949 if ( depth >= 3 * ONE_PLY
951 && (!captureOrPromotion || moveCountPruning))
953 Depth r = reduction<PvNode>(improving, depth, moveCount);
955 if (captureOrPromotion)
956 r -= r ? ONE_PLY : DEPTH_ZERO;
959 // Increase reduction for cut nodes
963 // Decrease reduction for moves that escape a capture. Filter out
964 // castling moves, because they are coded as "king captures rook" and
965 // hence break make_move().
966 else if ( type_of(move) == NORMAL
967 && !pos.see_ge(make_move(to_sq(move), from_sq(move)), VALUE_ZERO))
970 ss->history = (cmh ? (*cmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
971 + (fmh ? (*fmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
972 + (fmh2 ? (*fmh2)[moved_piece][to_sq(move)] : VALUE_ZERO)
973 + thisThread->history.get(~pos.side_to_move(), move)
974 - 4000; // Correction factor
976 // Decrease/increase reduction by comparing opponent's stat score
977 if (ss->history > VALUE_ZERO && (ss-1)->history < VALUE_ZERO)
980 else if (ss->history < VALUE_ZERO && (ss-1)->history > VALUE_ZERO)
983 // Decrease/increase reduction for moves with a good/bad history
984 r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->history / 20000) * ONE_PLY);
987 Depth d = std::max(newDepth - r, ONE_PLY);
989 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true, false);
991 doFullDepthSearch = (value > alpha && d != newDepth);
994 doFullDepthSearch = !PvNode || moveCount > 1;
996 // Step 16. Full depth search when LMR is skipped or fails high
997 if (doFullDepthSearch)
998 value = newDepth < ONE_PLY ?
999 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha)
1000 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha)
1001 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false);
1003 // For PV nodes only, do a full PV search on the first move or after a fail
1004 // high (in the latter case search only if value < beta), otherwise let the
1005 // parent node fail low with value <= alpha and try another move.
1006 if (PvNode && (moveCount == 1 || (value > alpha && (rootNode || value < beta))))
1009 (ss+1)->pv[0] = MOVE_NONE;
1011 value = newDepth < ONE_PLY ?
1012 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha)
1013 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha)
1014 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, false);
1017 // Step 17. Undo move
1018 pos.undo_move(move);
1020 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1022 // Step 18. Check for a new best move
1023 // Finished searching the move. If a stop occurred, the return value of
1024 // the search cannot be trusted, and we return immediately without
1025 // updating best move, PV and TT.
1026 if (Signals.stop.load(std::memory_order_relaxed))
1031 RootMove& rm = *std::find(thisThread->rootMoves.begin(),
1032 thisThread->rootMoves.end(), move);
1034 // PV move or new best move ?
1035 if (moveCount == 1 || value > alpha)
1042 for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
1043 rm.pv.push_back(*m);
1045 // We record how often the best move has been changed in each
1046 // iteration. This information is used for time management: When
1047 // the best move changes frequently, we allocate some more time.
1048 if (moveCount > 1 && thisThread == Threads.main())
1049 ++static_cast<MainThread*>(thisThread)->bestMoveChanges;
1052 // All other moves but the PV are set to the lowest value: this is
1053 // not a problem when sorting because the sort is stable and the
1054 // move position in the list is preserved - just the PV is pushed up.
1055 rm.score = -VALUE_INFINITE;
1058 if (value > bestValue)
1066 if (PvNode && !rootNode) // Update pv even in fail-high case
1067 update_pv(ss->pv, move, (ss+1)->pv);
1069 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1073 assert(value >= beta); // Fail high
1079 if (!captureOrPromotion && move != bestMove && quietCount < 64)
1080 quietsSearched[quietCount++] = move;
1083 // The following condition would detect a stop only after move loop has been
1084 // completed. But in this case bestValue is valid because we have fully
1085 // searched our subtree, and we can anyhow save the result in TT.
1091 // Step 20. Check for mate and stalemate
1092 // All legal moves have been searched and if there are no legal moves, it
1093 // must be a mate or a stalemate. If we are in a singular extension search then
1094 // return a fail low score.
1096 assert(moveCount || !inCheck || excludedMove || !MoveList<LEGAL>(pos).size());
1099 bestValue = excludedMove ? alpha
1100 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1104 // Quiet best move: update move sorting heuristics
1105 if (!pos.capture_or_promotion(bestMove))
1106 update_stats(pos, ss, bestMove, quietsSearched, quietCount, stat_bonus(depth));
1108 // Extra penalty for a quiet TT move in previous ply when it gets refuted
1109 if ((ss-1)->moveCount == 1 && !pos.captured_piece())
1110 update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
1112 // Bonus for prior countermove that caused the fail low
1113 else if ( depth >= 3 * ONE_PLY
1114 && !pos.captured_piece()
1115 && is_ok((ss-1)->currentMove))
1116 update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
1118 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1119 bestValue >= beta ? BOUND_LOWER :
1120 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1121 depth, bestMove, ss->staticEval, TT.generation());
1123 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1129 // qsearch() is the quiescence search function, which is called by the main
1130 // search function with depth zero, or recursively with depth less than ONE_PLY.
1132 template <NodeType NT, bool InCheck>
1133 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1135 const bool PvNode = NT == PV;
1137 assert(InCheck == !!pos.checkers());
1138 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1139 assert(PvNode || (alpha == beta - 1));
1140 assert(depth <= DEPTH_ZERO);
1141 assert(depth / ONE_PLY * ONE_PLY == depth);
1147 Move ttMove, move, bestMove;
1148 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1149 bool ttHit, givesCheck, evasionPrunable;
1154 oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
1156 ss->pv[0] = MOVE_NONE;
1159 ss->currentMove = bestMove = MOVE_NONE;
1160 ss->ply = (ss-1)->ply + 1;
1162 // Check for an instant draw or if the maximum ply has been reached
1163 if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
1164 return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
1165 : DrawValue[pos.side_to_move()];
1167 assert(0 <= ss->ply && ss->ply < MAX_PLY);
1169 // Decide whether or not to include checks: this fixes also the type of
1170 // TT entry depth that we are going to use. Note that in qsearch we use
1171 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1172 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1173 : DEPTH_QS_NO_CHECKS;
1175 // Transposition table lookup
1177 tte = TT.probe(posKey, ttHit);
1178 ttMove = ttHit ? tte->move() : MOVE_NONE;
1179 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
1183 && tte->depth() >= ttDepth
1184 && ttValue != VALUE_NONE // Only in case of TT access race
1185 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1186 : (tte->bound() & BOUND_UPPER)))
1189 // Evaluate the position statically
1192 ss->staticEval = VALUE_NONE;
1193 bestValue = futilityBase = -VALUE_INFINITE;
1199 // Never assume anything on values stored in TT
1200 if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
1201 ss->staticEval = bestValue = evaluate(pos);
1203 // Can ttValue be used as a better position evaluation?
1204 if (ttValue != VALUE_NONE)
1205 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1206 bestValue = ttValue;
1209 ss->staticEval = bestValue =
1210 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
1211 : -(ss-1)->staticEval + 2 * Eval::Tempo;
1213 // Stand pat. Return immediately if static value is at least beta
1214 if (bestValue >= beta)
1217 tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1218 DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
1223 if (PvNode && bestValue > alpha)
1226 futilityBase = bestValue + 128;
1229 // Initialize a MovePicker object for the current position, and prepare
1230 // to search the moves. Because the depth is <= 0 here, only captures,
1231 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1233 MovePicker mp(pos, ttMove, depth, to_sq((ss-1)->currentMove));
1235 // Loop through the moves until no moves remain or a beta cutoff occurs
1236 while ((move = mp.next_move()) != MOVE_NONE)
1238 assert(is_ok(move));
1240 givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
1241 ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
1242 : pos.gives_check(move);
1247 && futilityBase > -VALUE_KNOWN_WIN
1248 && !pos.advanced_pawn_push(move))
1250 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1252 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1254 if (futilityValue <= alpha)
1256 bestValue = std::max(bestValue, futilityValue);
1260 if (futilityBase <= alpha && !pos.see_ge(move, VALUE_ZERO + 1))
1262 bestValue = std::max(bestValue, futilityBase);
1267 // Detect non-capture evasions that are candidates to be pruned
1268 evasionPrunable = InCheck
1269 && bestValue > VALUE_MATED_IN_MAX_PLY
1270 && !pos.capture(move);
1272 // Don't search moves with negative SEE values
1273 if ( (!InCheck || evasionPrunable)
1274 && type_of(move) != PROMOTION
1275 && !pos.see_ge(move, VALUE_ZERO))
1278 // Speculative prefetch as early as possible
1279 prefetch(TT.first_entry(pos.key_after(move)));
1281 // Check for legality just before making the move
1282 if (!pos.legal(move))
1285 ss->currentMove = move;
1287 // Make and search the move
1288 pos.do_move(move, st, givesCheck);
1289 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1290 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1291 pos.undo_move(move);
1293 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1295 // Check for a new best move
1296 if (value > bestValue)
1302 if (PvNode) // Update pv even in fail-high case
1303 update_pv(ss->pv, move, (ss+1)->pv);
1305 if (PvNode && value < beta) // Update alpha here!
1312 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1313 ttDepth, move, ss->staticEval, TT.generation());
1321 // All legal moves have been searched. A special case: If we're in check
1322 // and no legal moves were found, it is checkmate.
1323 if (InCheck && bestValue == -VALUE_INFINITE)
1324 return mated_in(ss->ply); // Plies to mate from the root
1326 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1327 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1328 ttDepth, bestMove, ss->staticEval, TT.generation());
1330 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1336 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1337 // "plies to mate from the current position". Non-mate scores are unchanged.
1338 // The function is called before storing a value in the transposition table.
1340 Value value_to_tt(Value v, int ply) {
1342 assert(v != VALUE_NONE);
1344 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1345 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1349 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1350 // from the transposition table (which refers to the plies to mate/be mated
1351 // from current position) to "plies to mate/be mated from the root".
1353 Value value_from_tt(Value v, int ply) {
1355 return v == VALUE_NONE ? VALUE_NONE
1356 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1357 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1361 // update_pv() adds current move and appends child pv[]
1363 void update_pv(Move* pv, Move move, Move* childPv) {
1365 for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
1371 // update_cm_stats() updates countermove and follow-up move history
1373 void update_cm_stats(Stack* ss, Piece pc, Square s, Value bonus) {
1375 CounterMoveStats* cmh = (ss-1)->counterMoves;
1376 CounterMoveStats* fmh1 = (ss-2)->counterMoves;
1377 CounterMoveStats* fmh2 = (ss-4)->counterMoves;
1380 cmh->update(pc, s, bonus);
1383 fmh1->update(pc, s, bonus);
1386 fmh2->update(pc, s, bonus);
1390 // update_stats() updates move sorting heuristics when a new quiet best move is found
1392 void update_stats(const Position& pos, Stack* ss, Move move,
1393 Move* quiets, int quietsCnt, Value bonus) {
1395 if (ss->killers[0] != move)
1397 ss->killers[1] = ss->killers[0];
1398 ss->killers[0] = move;
1401 Color c = pos.side_to_move();
1402 Thread* thisThread = pos.this_thread();
1403 thisThread->history.update(c, move, bonus);
1404 update_cm_stats(ss, pos.moved_piece(move), to_sq(move), bonus);
1406 if ((ss-1)->counterMoves)
1408 Square prevSq = to_sq((ss-1)->currentMove);
1409 thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move);
1412 // Decrease all the other played quiet moves
1413 for (int i = 0; i < quietsCnt; ++i)
1415 thisThread->history.update(c, quiets[i], -bonus);
1416 update_cm_stats(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1421 // When playing with strength handicap, choose best move among a set of RootMoves
1422 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1424 Move Skill::pick_best(size_t multiPV) {
1426 const RootMoves& rootMoves = Threads.main()->rootMoves;
1427 static PRNG rng(now()); // PRNG sequence should be non-deterministic
1429 // RootMoves are already sorted by score in descending order
1430 Value topScore = rootMoves[0].score;
1431 int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
1432 int weakness = 120 - 2 * level;
1433 int maxScore = -VALUE_INFINITE;
1435 // Choose best move. For each move score we add two terms, both dependent on
1436 // weakness. One is deterministic and bigger for weaker levels, and one is
1437 // random. Then we choose the move with the resulting highest score.
1438 for (size_t i = 0; i < multiPV; ++i)
1440 // This is our magic formula
1441 int push = ( weakness * int(topScore - rootMoves[i].score)
1442 + delta * (rng.rand<unsigned>() % weakness)) / 128;
1444 if (rootMoves[i].score + push > maxScore)
1446 maxScore = rootMoves[i].score + push;
1447 best = rootMoves[i].pv[0];
1455 // check_time() is used to print debug info and, more importantly, to detect
1456 // when we are out of available time and thus stop the search.
1460 static TimePoint lastInfoTime = now();
1462 int elapsed = Time.elapsed();
1463 TimePoint tick = Limits.startTime + elapsed;
1465 if (tick - lastInfoTime >= 1000)
1467 lastInfoTime = tick;
1471 // An engine may not stop pondering until told so by the GUI
1475 if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
1476 || (Limits.movetime && elapsed >= Limits.movetime)
1477 || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
1478 Signals.stop = true;
1484 /// UCI::pv() formats PV information according to the UCI protocol. UCI requires
1485 /// that all (if any) unsearched PV lines are sent using a previous search score.
1487 string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
1489 std::stringstream ss;
1490 int elapsed = Time.elapsed() + 1;
1491 const RootMoves& rootMoves = pos.this_thread()->rootMoves;
1492 size_t PVIdx = pos.this_thread()->PVIdx;
1493 size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
1494 uint64_t nodesSearched = Threads.nodes_searched();
1495 uint64_t tbHits = Threads.tb_hits() + (TB::RootInTB ? rootMoves.size() : 0);
1497 for (size_t i = 0; i < multiPV; ++i)
1499 bool updated = (i <= PVIdx);
1501 if (depth == ONE_PLY && !updated)
1504 Depth d = updated ? depth : depth - ONE_PLY;
1505 Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
1507 bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
1508 v = tb ? TB::Score : v;
1510 if (ss.rdbuf()->in_avail()) // Not at first line
1514 << " depth " << d / ONE_PLY
1515 << " seldepth " << pos.this_thread()->maxPly
1516 << " multipv " << i + 1
1517 << " score " << UCI::value(v);
1519 if (!tb && i == PVIdx)
1520 ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1522 ss << " nodes " << nodesSearched
1523 << " nps " << nodesSearched * 1000 / elapsed;
1525 if (elapsed > 1000) // Earlier makes little sense
1526 ss << " hashfull " << TT.hashfull();
1528 ss << " tbhits " << tbHits
1529 << " time " << elapsed
1532 for (Move m : rootMoves[i].pv)
1533 ss << " " << UCI::move(m, pos.is_chess960());
1540 /// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
1541 /// before exiting the search, for instance, in case we stop the search during a
1542 /// fail high at root. We try hard to have a ponder move to return to the GUI,
1543 /// otherwise in case of 'ponder on' we have nothing to think on.
1545 bool RootMove::extract_ponder_from_tt(Position& pos) {
1550 assert(pv.size() == 1);
1555 pos.do_move(pv[0], st);
1556 TTEntry* tte = TT.probe(pos.key(), ttHit);
1560 Move m = tte->move(); // Local copy to be SMP safe
1561 if (MoveList<LEGAL>(pos).contains(m))
1565 pos.undo_move(pv[0]);
1566 return pv.size() > 1;
1569 void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) {
1572 UseRule50 = Options["Syzygy50MoveRule"];
1573 ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
1574 Cardinality = Options["SyzygyProbeLimit"];
1576 // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
1577 if (Cardinality > MaxCardinality)
1579 Cardinality = MaxCardinality;
1580 ProbeDepth = DEPTH_ZERO;
1583 if (Cardinality < popcount(pos.pieces()) || pos.can_castle(ANY_CASTLING))
1586 // If the current root position is in the tablebases, then RootMoves
1587 // contains only moves that preserve the draw or the win.
1588 RootInTB = root_probe(pos, rootMoves, TB::Score);
1591 Cardinality = 0; // Do not probe tablebases during the search
1593 else // If DTZ tables are missing, use WDL tables as a fallback
1595 // Filter out moves that do not preserve the draw or the win.
1596 RootInTB = root_probe_wdl(pos, rootMoves, TB::Score);
1598 // Only probe during search if winning
1599 if (RootInTB && TB::Score <= VALUE_DRAW)
1603 if (RootInTB && !UseRule50)
1604 TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
1605 : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1