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) 2015-2016 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 // Skill structure is used to implement strength limit
80 Skill(int l) : level(l) {}
81 bool enabled() const { return level < 20; }
82 bool time_to_pick(Depth depth) const { return depth / ONE_PLY == 1 + level; }
83 Move best_move(size_t multiPV) { return best ? best : pick_best(multiPV); }
84 Move pick_best(size_t multiPV);
87 Move best = MOVE_NONE;
90 // EasyMoveManager structure is used to detect an 'easy move'. When the PV is
91 // stable across multiple search iterations, we can quickly return the best move.
92 struct EasyMoveManager {
97 pv[0] = pv[1] = pv[2] = MOVE_NONE;
100 Move get(Key key) const {
101 return expectedPosKey == key ? pv[2] : MOVE_NONE;
104 void update(Position& pos, const std::vector<Move>& newPv) {
106 assert(newPv.size() >= 3);
108 // Keep track of how many times in a row the 3rd ply remains stable
109 stableCnt = (newPv[2] == pv[2]) ? stableCnt + 1 : 0;
111 if (!std::equal(newPv.begin(), newPv.begin() + 3, pv))
113 std::copy(newPv.begin(), newPv.begin() + 3, pv);
116 pos.do_move(newPv[0], st[0]);
117 pos.do_move(newPv[1], st[1]);
118 expectedPosKey = pos.key();
119 pos.undo_move(newPv[1]);
120 pos.undo_move(newPv[0]);
129 // Set of rows with half bits set to 1 and half to 0. It is used to allocate
130 // the search depths across the threads.
131 typedef std::vector<int> Row;
133 const Row HalfDensity[] = {
146 {0, 0, 0, 0, 1, 1, 1, 1},
147 {0, 0, 0, 1, 1, 1, 1, 0},
148 {0, 0, 1, 1, 1, 1, 0 ,0},
149 {0, 1, 1, 1, 1, 0, 0 ,0},
150 {1, 1, 1, 1, 0, 0, 0 ,0},
151 {1, 1, 1, 0, 0, 0, 0 ,1},
152 {1, 1, 0, 0, 0, 0, 1 ,1},
153 {1, 0, 0, 0, 0, 1, 1 ,1},
156 Value bonus(Depth depth) { int d = depth / ONE_PLY ; return Value(d * d + 2 * d - 2); }
157 Value penalty(Depth depth) { int d = depth / ONE_PLY ; return -Value(d * d + 4 * d + 1); }
159 const size_t HalfDensitySize = std::extent<decltype(HalfDensity)>::value;
161 EasyMoveManager EasyMove;
162 Value DrawValue[COLOR_NB];
164 template <NodeType NT>
165 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning);
167 template <NodeType NT, bool InCheck>
168 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO);
170 Value value_to_tt(Value v, int ply);
171 Value value_from_tt(Value v, int ply);
172 void update_pv(Move* pv, Move move, Move* childPv);
173 void update_cm_stats(Stack* ss, Piece pc, Square s, Value bonus);
174 void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, Value bonus);
180 /// Search::init() is called during startup to initialize various lookup tables
182 void Search::init() {
184 for (int imp = 0; imp <= 1; ++imp)
185 for (int d = 1; d < 64; ++d)
186 for (int mc = 1; mc < 64; ++mc)
188 double r = log(d) * log(mc) / 2;
190 Reductions[NonPV][imp][d][mc] = int(std::round(r));
191 Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0);
193 // Increase reduction for non-PV nodes when eval is not improving
194 if (!imp && Reductions[NonPV][imp][d][mc] >= 2)
195 Reductions[NonPV][imp][d][mc]++;
198 for (int d = 0; d < 16; ++d)
200 FutilityMoveCounts[0][d] = int(2.4 + 0.773 * pow(d + 0.00, 1.8));
201 FutilityMoveCounts[1][d] = int(2.9 + 1.045 * pow(d + 0.49, 1.8));
206 /// Search::clear() resets search state to zero, to obtain reproducible results
208 void Search::clear() {
212 for (Thread* th : Threads)
215 th->counterMoves.clear();
217 th->counterMoveHistory.clear();
218 th->resetCalls = true;
221 Threads.main()->previousScore = VALUE_INFINITE;
225 /// Search::perft() is our utility to verify move generation. All the leaf nodes
226 /// up to the given depth are generated and counted, and the sum is returned.
228 uint64_t Search::perft(Position& pos, Depth depth) {
231 uint64_t cnt, nodes = 0;
232 const bool leaf = (depth == 2 * ONE_PLY);
234 for (const auto& m : MoveList<LEGAL>(pos))
236 if (Root && depth <= ONE_PLY)
241 cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
246 sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
251 template uint64_t Search::perft<true>(Position&, Depth);
254 /// MainThread::search() is called by the main thread when the program receives
255 /// the UCI 'go' command. It searches from the root position and outputs the "bestmove".
257 void MainThread::search() {
259 Color us = rootPos.side_to_move();
260 Time.init(Limits, us, rootPos.game_ply());
262 int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
263 DrawValue[ us] = VALUE_DRAW - Value(contempt);
264 DrawValue[~us] = VALUE_DRAW + Value(contempt);
266 if (rootMoves.empty())
268 rootMoves.push_back(RootMove(MOVE_NONE));
269 sync_cout << "info depth 0 score "
270 << UCI::value(rootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
275 for (Thread* th : Threads)
277 th->start_searching();
279 Thread::search(); // Let's start searching!
282 // When playing in 'nodes as time' mode, subtract the searched nodes from
283 // the available ones before exiting.
285 Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
287 // When we reach the maximum depth, we can arrive here without a raise of
288 // Signals.stop. However, if we are pondering or in an infinite search,
289 // the UCI protocol states that we shouldn't print the best move before the
290 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
291 // until the GUI sends one of those commands (which also raises Signals.stop).
292 if (!Signals.stop && (Limits.ponder || Limits.infinite))
294 Signals.stopOnPonderhit = true;
298 // Stop the threads if not already stopped
301 // Wait until all threads have finished
302 for (Thread* th : Threads)
304 th->wait_for_search_finished();
306 // Check if there are threads with a better score than main thread
307 Thread* bestThread = this;
308 if ( !this->easyMovePlayed
309 && Options["MultiPV"] == 1
311 && !Skill(Options["Skill Level"]).enabled()
312 && rootMoves[0].pv[0] != MOVE_NONE)
314 for (Thread* th : Threads)
316 Depth depthDiff = th->completedDepth - bestThread->completedDepth;
317 Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score;
319 if ( (depthDiff > 0 && scoreDiff >= 0)
320 || (scoreDiff > 0 && depthDiff >= 0))
325 previousScore = bestThread->rootMoves[0].score;
327 // Send new PV when needed
328 if (bestThread != this)
329 sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
331 sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
333 if (bestThread->rootMoves[0].pv.size() > 1 || bestThread->rootMoves[0].extract_ponder_from_tt(rootPos))
334 std::cout << " ponder " << UCI::move(bestThread->rootMoves[0].pv[1], rootPos.is_chess960());
336 std::cout << sync_endl;
340 // Thread::search() is the main iterative deepening loop. It calls search()
341 // repeatedly with increasing depth until the allocated thinking time has been
342 // consumed, the user stops the search, or the maximum search depth is reached.
344 void Thread::search() {
346 Stack stack[MAX_PLY+7], *ss = stack+4; // To allow referencing (ss-4) and (ss+2)
347 Value bestValue, alpha, beta, delta;
348 Move easyMove = MOVE_NONE;
349 MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
351 std::memset(ss-4, 0, 7 * sizeof(Stack));
353 bestValue = delta = alpha = -VALUE_INFINITE;
354 beta = VALUE_INFINITE;
355 completedDepth = DEPTH_ZERO;
359 easyMove = EasyMove.get(rootPos.key());
361 mainThread->easyMovePlayed = mainThread->failedLow = false;
362 mainThread->bestMoveChanges = 0;
366 size_t multiPV = Options["MultiPV"];
367 Skill skill(Options["Skill Level"]);
369 // When playing with strength handicap enable MultiPV search that we will
370 // use behind the scenes to retrieve a set of possible moves.
372 multiPV = std::max(multiPV, (size_t)4);
374 multiPV = std::min(multiPV, rootMoves.size());
376 // Iterative deepening loop until requested to stop or the target depth is reached
377 while ( (rootDepth += ONE_PLY) < DEPTH_MAX
379 && (!Limits.depth || Threads.main()->rootDepth / ONE_PLY <= Limits.depth))
381 // Set up the new depths for the helper threads skipping on average every
382 // 2nd ply (using a half-density matrix).
385 const Row& row = HalfDensity[(idx - 1) % HalfDensitySize];
386 if (row[(rootDepth / ONE_PLY + rootPos.game_ply()) % row.size()])
390 // Age out PV variability metric
392 mainThread->bestMoveChanges *= 0.505, mainThread->failedLow = false;
394 // Save the last iteration's scores before first PV line is searched and
395 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
396 for (RootMove& rm : rootMoves)
397 rm.previousScore = rm.score;
399 // MultiPV loop. We perform a full root search for each PV line
400 for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
402 // Reset aspiration window starting size
403 if (rootDepth >= 5 * ONE_PLY)
406 alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
407 beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
410 // Start with a small aspiration window and, in the case of a fail
411 // high/low, re-search with a bigger window until we're not failing
415 bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false, false);
417 // Bring the best move to the front. It is critical that sorting
418 // is done with a stable algorithm because all the values but the
419 // first and eventually the new best one are set to -VALUE_INFINITE
420 // and we want to keep the same order for all the moves except the
421 // new PV that goes to the front. Note that in case of MultiPV
422 // search the already searched PV lines are preserved.
423 std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
425 // If search has been stopped, break immediately. Sorting and
426 // writing PV back to TT is safe because RootMoves is still
427 // valid, although it refers to the previous iteration.
431 // When failing high/low give some update (without cluttering
432 // the UI) before a re-search.
435 && (bestValue <= alpha || bestValue >= beta)
436 && Time.elapsed() > 3000)
437 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
439 // In case of failing low/high increase aspiration window and
440 // re-search, otherwise exit the loop.
441 if (bestValue <= alpha)
443 beta = (alpha + beta) / 2;
444 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
448 mainThread->failedLow = true;
449 Signals.stopOnPonderhit = false;
452 else if (bestValue >= beta)
454 alpha = (alpha + beta) / 2;
455 beta = std::min(bestValue + delta, VALUE_INFINITE);
460 delta += delta / 4 + 5;
462 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
465 // Sort the PV lines searched so far and update the GUI
466 std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
471 if (Signals.stop || PVIdx + 1 == multiPV || Time.elapsed() > 3000)
472 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
476 completedDepth = rootDepth;
481 // If skill level is enabled and time is up, pick a sub-optimal best move
482 if (skill.enabled() && skill.time_to_pick(rootDepth))
483 skill.pick_best(multiPV);
485 // Have we found a "mate in x"?
487 && bestValue >= VALUE_MATE_IN_MAX_PLY
488 && VALUE_MATE - bestValue <= 2 * Limits.mate)
491 // Do we have time for the next iteration? Can we stop searching now?
492 if (Limits.use_time_management())
494 if (!Signals.stop && !Signals.stopOnPonderhit)
496 // Stop the search if only one legal move is available, or if all
497 // of the available time has been used, or if we matched an easyMove
498 // from the previous search and just did a fast verification.
499 const int F[] = { mainThread->failedLow,
500 bestValue - mainThread->previousScore };
502 int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1]));
503 double unstablePvFactor = 1 + mainThread->bestMoveChanges;
505 bool doEasyMove = rootMoves[0].pv[0] == easyMove
506 && mainThread->bestMoveChanges < 0.03
507 && Time.elapsed() > Time.optimum() * 5 / 42;
509 if ( rootMoves.size() == 1
510 || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628
511 || (mainThread->easyMovePlayed = doEasyMove, doEasyMove))
513 // If we are allowed to ponder do not stop the search now but
514 // keep pondering until the GUI sends "ponderhit" or "stop".
516 Signals.stopOnPonderhit = true;
522 if (rootMoves[0].pv.size() >= 3)
523 EasyMove.update(rootPos, rootMoves[0].pv);
532 // Clear any candidate easy move that wasn't stable for the last search
533 // iterations; the second condition prevents consecutive fast moves.
534 if (EasyMove.stableCnt < 6 || mainThread->easyMovePlayed)
537 // If skill level is enabled, swap best PV line with the sub-optimal one
539 std::swap(rootMoves[0], *std::find(rootMoves.begin(),
540 rootMoves.end(), skill.best_move(multiPV)));
546 // search<>() is the main search function for both PV and non-PV nodes
548 template <NodeType NT>
549 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning) {
551 const bool PvNode = NT == PV;
552 const bool rootNode = PvNode && (ss-1)->ply == 0;
554 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
555 assert(PvNode || (alpha == beta - 1));
556 assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
557 assert(!(PvNode && cutNode));
558 assert(depth / ONE_PLY * ONE_PLY == depth);
560 Move pv[MAX_PLY+1], quietsSearched[64];
564 Move ttMove, move, excludedMove, bestMove;
565 Depth extension, newDepth;
566 Value bestValue, value, ttValue, eval, nullValue;
567 bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
568 bool captureOrPromotion, doFullDepthSearch, moveCountPruning;
570 int moveCount, quietCount;
572 // Step 1. Initialize node
573 Thread* thisThread = pos.this_thread();
574 inCheck = pos.checkers();
575 moveCount = quietCount = ss->moveCount = 0;
576 ss->history = VALUE_ZERO;
577 bestValue = -VALUE_INFINITE;
578 ss->ply = (ss-1)->ply + 1;
580 // Check for the available remaining time
581 if (thisThread->resetCalls.load(std::memory_order_relaxed))
583 thisThread->resetCalls = false;
584 // At low node count increase the checking rate to about 0.1% of nodes
585 // otherwise use a default value.
586 thisThread->callsCnt = Limits.nodes ? std::min((int64_t)4096, Limits.nodes / 1024)
590 if (--thisThread->callsCnt <= 0)
592 for (Thread* th : Threads)
593 th->resetCalls = true;
598 // Used to send selDepth info to GUI
599 if (PvNode && thisThread->maxPly < ss->ply)
600 thisThread->maxPly = ss->ply;
604 // Step 2. Check for aborted search and immediate draw
605 if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
606 return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
607 : DrawValue[pos.side_to_move()];
609 // Step 3. Mate distance pruning. Even if we mate at the next move our score
610 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
611 // a shorter mate was found upward in the tree then there is no need to search
612 // because we will never beat the current alpha. Same logic but with reversed
613 // signs applies also in the opposite condition of being mated instead of giving
614 // mate. In this case return a fail-high score.
615 alpha = std::max(mated_in(ss->ply), alpha);
616 beta = std::min(mate_in(ss->ply+1), beta);
621 assert(0 <= ss->ply && ss->ply < MAX_PLY);
623 ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
624 ss->counterMoves = nullptr;
625 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
626 Square prevSq = to_sq((ss-1)->currentMove);
628 // Step 4. Transposition table lookup. We don't want the score of a partial
629 // search to overwrite a previous full search TT value, so we use a different
630 // position key in case of an excluded move.
631 excludedMove = ss->excludedMove;
632 posKey = pos.key() ^ Key(excludedMove);
633 tte = TT.probe(posKey, ttHit);
634 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
635 ttMove = rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
636 : ttHit ? tte->move() : MOVE_NONE;
638 // At non-PV nodes we check for an early TT cutoff
641 && tte->depth() >= depth
642 && ttValue != VALUE_NONE // Possible in case of TT access race
643 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
644 : (tte->bound() & BOUND_UPPER)))
646 // If ttMove is quiet, update killers, history, counter move on TT hit
647 if (ttValue >= beta && ttMove)
649 if (!pos.capture_or_promotion(ttMove))
650 update_stats(pos, ss, ttMove, nullptr, 0, bonus(depth));
652 // Extra penalty for a quiet TT move in previous ply when it gets refuted
653 if ((ss-1)->moveCount == 1 && !pos.captured_piece())
654 update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, penalty(depth));
659 // Step 4a. Tablebase probe
660 if (!rootNode && TB::Cardinality)
662 int piecesCount = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
664 if ( piecesCount <= TB::Cardinality
665 && (piecesCount < TB::Cardinality || depth >= TB::ProbeDepth)
666 && pos.rule50_count() == 0
667 && !pos.can_castle(ANY_CASTLING))
670 TB::WDLScore v = Tablebases::probe_wdl(pos, &err);
672 if (err != TB::ProbeState::FAIL)
674 thisThread->tbHits++;
676 int drawScore = TB::UseRule50 ? 1 : 0;
678 value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
679 : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply
680 : VALUE_DRAW + 2 * v * drawScore;
682 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
683 std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
684 MOVE_NONE, VALUE_NONE, TT.generation());
691 // Step 5. Evaluate the position statically
694 ss->staticEval = eval = VALUE_NONE;
700 // Never assume anything on values stored in TT
701 if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
702 eval = ss->staticEval = evaluate(pos);
704 // Can ttValue be used as a better position evaluation?
705 if (ttValue != VALUE_NONE)
706 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
711 eval = ss->staticEval =
712 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
713 : -(ss-1)->staticEval + 2 * Eval::Tempo;
715 tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
716 ss->staticEval, TT.generation());
719 if (skipEarlyPruning)
722 // Step 6. Razoring (skipped when in check)
724 && depth < 4 * ONE_PLY
725 && ttMove == MOVE_NONE
726 && eval + razor_margin[depth / ONE_PLY] <= alpha)
728 if (depth <= ONE_PLY)
729 return qsearch<NonPV, false>(pos, ss, alpha, alpha+1);
731 Value ralpha = alpha - razor_margin[depth / ONE_PLY];
732 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1);
737 // Step 7. Futility pruning: child node (skipped when in check)
739 && depth < 7 * ONE_PLY
740 && eval - futility_margin(depth) >= beta
741 && eval < VALUE_KNOWN_WIN // Do not return unproven wins
742 && pos.non_pawn_material(pos.side_to_move()))
745 // Step 8. Null move search with verification search (is omitted in PV nodes)
748 && (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY)
749 && pos.non_pawn_material(pos.side_to_move()))
751 ss->currentMove = MOVE_NULL;
752 ss->counterMoves = nullptr;
754 assert(eval - beta >= 0);
756 // Null move dynamic reduction based on depth and value
757 Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
759 pos.do_null_move(st);
760 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1)
761 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true);
762 pos.undo_null_move();
764 if (nullValue >= beta)
766 // Do not return unproven mate scores
767 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
770 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
773 // Do verification search at high depths
774 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta)
775 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false, true);
782 // Step 9. ProbCut (skipped when in check)
783 // If we have a good enough capture and a reduced search returns a value
784 // much above beta, we can (almost) safely prune the previous move.
786 && depth >= 5 * ONE_PLY
787 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
789 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
790 Depth rdepth = depth - 4 * ONE_PLY;
792 assert(rdepth >= ONE_PLY);
793 assert((ss-1)->currentMove != MOVE_NONE);
794 assert((ss-1)->currentMove != MOVE_NULL);
796 MovePicker mp(pos, ttMove, rbeta - ss->staticEval);
798 while ((move = mp.next_move()) != MOVE_NONE)
801 ss->currentMove = move;
802 ss->counterMoves = &thisThread->counterMoveHistory[pos.moved_piece(move)][to_sq(move)];
803 pos.do_move(move, st);
804 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode, false);
811 // Step 10. Internal iterative deepening (skipped when in check)
812 if ( depth >= 6 * ONE_PLY
814 && (PvNode || ss->staticEval + 256 >= beta))
816 Depth d = (3 * depth / (4 * ONE_PLY) - 2) * ONE_PLY;
817 search<NT>(pos, ss, alpha, beta, d, cutNode, true);
819 tte = TT.probe(posKey, ttHit);
820 ttMove = ttHit ? tte->move() : MOVE_NONE;
823 moves_loop: // When in check search starts from here
825 const CounterMoveStats* cmh = (ss-1)->counterMoves;
826 const CounterMoveStats* fmh = (ss-2)->counterMoves;
827 const CounterMoveStats* fmh2 = (ss-4)->counterMoves;
829 MovePicker mp(pos, ttMove, depth, ss);
830 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
831 improving = ss->staticEval >= (ss-2)->staticEval
832 /* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */
833 ||(ss-2)->staticEval == VALUE_NONE;
835 singularExtensionNode = !rootNode
836 && depth >= 8 * ONE_PLY
837 && ttMove != MOVE_NONE
838 && ttValue != VALUE_NONE
839 && !excludedMove // Recursive singular search is not allowed
840 && (tte->bound() & BOUND_LOWER)
841 && tte->depth() >= depth - 3 * ONE_PLY;
843 // Step 11. Loop through moves
844 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
845 while ((move = mp.next_move()) != MOVE_NONE)
849 if (move == excludedMove)
852 // At root obey the "searchmoves" option and skip moves not listed in Root
853 // Move List. As a consequence any illegal move is also skipped. In MultiPV
854 // mode we also skip PV moves which have been already searched.
855 if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
856 thisThread->rootMoves.end(), move))
859 ss->moveCount = ++moveCount;
861 if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
862 sync_cout << "info depth " << depth / ONE_PLY
863 << " currmove " << UCI::move(move, pos.is_chess960())
864 << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
867 (ss+1)->pv = nullptr;
869 extension = DEPTH_ZERO;
870 captureOrPromotion = pos.capture_or_promotion(move);
871 moved_piece = pos.moved_piece(move);
873 givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
874 ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
875 : pos.gives_check(move);
877 moveCountPruning = depth < 16 * ONE_PLY
878 && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];
880 // Step 12. Extend checks
883 && pos.see_ge(move, VALUE_ZERO))
886 // Singular extension search. If all moves but one fail low on a search of
887 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
888 // is singular and should be extended. To verify this we do a reduced search
889 // on all the other moves but the ttMove and if the result is lower than
890 // ttValue minus a margin then we extend the ttMove.
891 if ( singularExtensionNode
896 Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
897 Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY;
898 ss->excludedMove = move;
899 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, d, cutNode, true);
900 ss->excludedMove = MOVE_NONE;
906 // Update the current move (this must be done after singular extension search)
907 newDepth = depth - ONE_PLY + extension;
909 // Step 13. Pruning at shallow depth
911 && bestValue > VALUE_MATED_IN_MAX_PLY)
913 if ( !captureOrPromotion
915 && !pos.advanced_pawn_push(move))
917 // Move count based pruning
918 if (moveCountPruning)
921 // Reduced depth of the next LMR search
922 int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
924 // Countermoves based pruning
926 && (!cmh || (*cmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
927 && (!fmh || (*fmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
928 && (!fmh2 || (*fmh2)[moved_piece][to_sq(move)] < VALUE_ZERO || (cmh && fmh)))
931 // Futility pruning: parent node
934 && ss->staticEval + 256 + 200 * lmrDepth <= alpha)
937 // Prune moves with negative SEE
939 && !pos.see_ge(move, Value(-35 * lmrDepth * lmrDepth)))
942 else if ( depth < 7 * ONE_PLY
944 && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY)))
948 // Speculative prefetch as early as possible
949 prefetch(TT.first_entry(pos.key_after(move)));
951 // Check for legality just before making the move
952 if (!rootNode && !pos.legal(move))
954 ss->moveCount = --moveCount;
958 ss->currentMove = move;
959 ss->counterMoves = &thisThread->counterMoveHistory[moved_piece][to_sq(move)];
961 // Step 14. Make the move
962 pos.do_move(move, st, givesCheck);
964 // Step 15. Reduced depth search (LMR). If the move fails high it will be
965 // re-searched at full depth.
966 if ( depth >= 3 * ONE_PLY
968 && (!captureOrPromotion || moveCountPruning))
970 Depth r = reduction<PvNode>(improving, depth, moveCount);
972 if (captureOrPromotion)
973 r -= r ? ONE_PLY : DEPTH_ZERO;
976 // Increase reduction for cut nodes
980 // Decrease reduction for moves that escape a capture. Filter out
981 // castling moves, because they are coded as "king captures rook" and
982 // hence break make_move().
983 else if ( type_of(move) == NORMAL
984 && !pos.see_ge(make_move(to_sq(move), from_sq(move)), VALUE_ZERO))
987 ss->history = thisThread->history[moved_piece][to_sq(move)]
988 + (cmh ? (*cmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
989 + (fmh ? (*fmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
990 + (fmh2 ? (*fmh2)[moved_piece][to_sq(move)] : VALUE_ZERO)
991 + thisThread->fromTo.get(~pos.side_to_move(), move)
992 - 8000; // Correction factor
994 // Decrease/increase reduction by comparing opponent's stat score
995 if (ss->history > VALUE_ZERO && (ss-1)->history < VALUE_ZERO)
998 else if (ss->history < VALUE_ZERO && (ss-1)->history > VALUE_ZERO)
1001 // Decrease/increase reduction for moves with a good/bad history
1002 r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->history / 20000) * ONE_PLY);
1005 Depth d = std::max(newDepth - r, ONE_PLY);
1007 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true, false);
1009 doFullDepthSearch = (value > alpha && d != newDepth);
1012 doFullDepthSearch = !PvNode || moveCount > 1;
1014 // Step 16. Full depth search when LMR is skipped or fails high
1015 if (doFullDepthSearch)
1016 value = newDepth < ONE_PLY ?
1017 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha)
1018 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha)
1019 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false);
1021 // For PV nodes only, do a full PV search on the first move or after a fail
1022 // high (in the latter case search only if value < beta), otherwise let the
1023 // parent node fail low with value <= alpha and try another move.
1024 if (PvNode && (moveCount == 1 || (value > alpha && (rootNode || value < beta))))
1027 (ss+1)->pv[0] = MOVE_NONE;
1029 value = newDepth < ONE_PLY ?
1030 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha)
1031 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha)
1032 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, false);
1035 // Step 17. Undo move
1036 pos.undo_move(move);
1038 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1040 // Step 18. Check for a new best move
1041 // Finished searching the move. If a stop occurred, the return value of
1042 // the search cannot be trusted, and we return immediately without
1043 // updating best move, PV and TT.
1044 if (Signals.stop.load(std::memory_order_relaxed))
1049 RootMove& rm = *std::find(thisThread->rootMoves.begin(),
1050 thisThread->rootMoves.end(), move);
1052 // PV move or new best move ?
1053 if (moveCount == 1 || value > alpha)
1060 for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
1061 rm.pv.push_back(*m);
1063 // We record how often the best move has been changed in each
1064 // iteration. This information is used for time management: When
1065 // the best move changes frequently, we allocate some more time.
1066 if (moveCount > 1 && thisThread == Threads.main())
1067 ++static_cast<MainThread*>(thisThread)->bestMoveChanges;
1070 // All other moves but the PV are set to the lowest value: this is
1071 // not a problem when sorting because the sort is stable and the
1072 // move position in the list is preserved - just the PV is pushed up.
1073 rm.score = -VALUE_INFINITE;
1076 if (value > bestValue)
1084 if (PvNode && !rootNode) // Update pv even in fail-high case
1085 update_pv(ss->pv, move, (ss+1)->pv);
1087 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1091 assert(value >= beta); // Fail high
1097 if (!captureOrPromotion && move != bestMove && quietCount < 64)
1098 quietsSearched[quietCount++] = move;
1101 // The following condition would detect a stop only after move loop has been
1102 // completed. But in this case bestValue is valid because we have fully
1103 // searched our subtree, and we can anyhow save the result in TT.
1109 // Step 20. Check for mate and stalemate
1110 // All legal moves have been searched and if there are no legal moves, it
1111 // must be a mate or a stalemate. If we are in a singular extension search then
1112 // return a fail low score.
1114 assert(moveCount || !inCheck || excludedMove || !MoveList<LEGAL>(pos).size());
1117 bestValue = excludedMove ? alpha
1118 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1122 // Quiet best move: update killers, history and countermoves
1123 if (!pos.capture_or_promotion(bestMove))
1124 update_stats(pos, ss, bestMove, quietsSearched, quietCount, bonus(depth));
1126 // Extra penalty for a quiet TT move in previous ply when it gets refuted
1127 if ((ss-1)->moveCount == 1 && !pos.captured_piece())
1128 update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, penalty(depth));
1130 // Bonus for prior countermove that caused the fail low
1131 else if ( depth >= 3 * ONE_PLY
1132 && !pos.captured_piece()
1133 && is_ok((ss-1)->currentMove))
1134 update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, bonus(depth));
1136 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1137 bestValue >= beta ? BOUND_LOWER :
1138 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1139 depth, bestMove, ss->staticEval, TT.generation());
1141 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1147 // qsearch() is the quiescence search function, which is called by the main
1148 // search function with depth zero, or recursively with depth less than ONE_PLY.
1150 template <NodeType NT, bool InCheck>
1151 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1153 const bool PvNode = NT == PV;
1155 assert(InCheck == !!pos.checkers());
1156 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1157 assert(PvNode || (alpha == beta - 1));
1158 assert(depth <= DEPTH_ZERO);
1159 assert(depth / ONE_PLY * ONE_PLY == depth);
1165 Move ttMove, move, bestMove;
1166 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1167 bool ttHit, givesCheck, evasionPrunable;
1172 oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
1174 ss->pv[0] = MOVE_NONE;
1177 ss->currentMove = bestMove = MOVE_NONE;
1178 ss->ply = (ss-1)->ply + 1;
1180 // Check for an instant draw or if the maximum ply has been reached
1181 if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
1182 return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
1183 : DrawValue[pos.side_to_move()];
1185 assert(0 <= ss->ply && ss->ply < MAX_PLY);
1187 // Decide whether or not to include checks: this fixes also the type of
1188 // TT entry depth that we are going to use. Note that in qsearch we use
1189 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1190 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1191 : DEPTH_QS_NO_CHECKS;
1193 // Transposition table lookup
1195 tte = TT.probe(posKey, ttHit);
1196 ttMove = ttHit ? tte->move() : MOVE_NONE;
1197 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
1201 && tte->depth() >= ttDepth
1202 && ttValue != VALUE_NONE // Only in case of TT access race
1203 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1204 : (tte->bound() & BOUND_UPPER)))
1207 // Evaluate the position statically
1210 ss->staticEval = VALUE_NONE;
1211 bestValue = futilityBase = -VALUE_INFINITE;
1217 // Never assume anything on values stored in TT
1218 if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
1219 ss->staticEval = bestValue = evaluate(pos);
1221 // Can ttValue be used as a better position evaluation?
1222 if (ttValue != VALUE_NONE)
1223 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1224 bestValue = ttValue;
1227 ss->staticEval = bestValue =
1228 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
1229 : -(ss-1)->staticEval + 2 * Eval::Tempo;
1231 // Stand pat. Return immediately if static value is at least beta
1232 if (bestValue >= beta)
1235 tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1236 DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
1241 if (PvNode && bestValue > alpha)
1244 futilityBase = bestValue + 128;
1247 // Initialize a MovePicker object for the current position, and prepare
1248 // to search the moves. Because the depth is <= 0 here, only captures,
1249 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1251 MovePicker mp(pos, ttMove, depth, to_sq((ss-1)->currentMove));
1253 // Loop through the moves until no moves remain or a beta cutoff occurs
1254 while ((move = mp.next_move()) != MOVE_NONE)
1256 assert(is_ok(move));
1258 givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
1259 ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
1260 : pos.gives_check(move);
1265 && futilityBase > -VALUE_KNOWN_WIN
1266 && !pos.advanced_pawn_push(move))
1268 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1270 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1272 if (futilityValue <= alpha)
1274 bestValue = std::max(bestValue, futilityValue);
1278 if (futilityBase <= alpha && !pos.see_ge(move, VALUE_ZERO + 1))
1280 bestValue = std::max(bestValue, futilityBase);
1285 // Detect non-capture evasions that are candidates to be pruned
1286 evasionPrunable = InCheck
1287 && bestValue > VALUE_MATED_IN_MAX_PLY
1288 && !pos.capture(move);
1290 // Don't search moves with negative SEE values
1291 if ( (!InCheck || evasionPrunable)
1292 && type_of(move) != PROMOTION
1293 && !pos.see_ge(move, VALUE_ZERO))
1296 // Speculative prefetch as early as possible
1297 prefetch(TT.first_entry(pos.key_after(move)));
1299 // Check for legality just before making the move
1300 if (!pos.legal(move))
1303 ss->currentMove = move;
1305 // Make and search the move
1306 pos.do_move(move, st, givesCheck);
1307 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1308 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1309 pos.undo_move(move);
1311 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1313 // Check for a new best move
1314 if (value > bestValue)
1320 if (PvNode) // Update pv even in fail-high case
1321 update_pv(ss->pv, move, (ss+1)->pv);
1323 if (PvNode && value < beta) // Update alpha here!
1330 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1331 ttDepth, move, ss->staticEval, TT.generation());
1339 // All legal moves have been searched. A special case: If we're in check
1340 // and no legal moves were found, it is checkmate.
1341 if (InCheck && bestValue == -VALUE_INFINITE)
1342 return mated_in(ss->ply); // Plies to mate from the root
1344 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1345 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1346 ttDepth, bestMove, ss->staticEval, TT.generation());
1348 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1354 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1355 // "plies to mate from the current position". Non-mate scores are unchanged.
1356 // The function is called before storing a value in the transposition table.
1358 Value value_to_tt(Value v, int ply) {
1360 assert(v != VALUE_NONE);
1362 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1363 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1367 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1368 // from the transposition table (which refers to the plies to mate/be mated
1369 // from current position) to "plies to mate/be mated from the root".
1371 Value value_from_tt(Value v, int ply) {
1373 return v == VALUE_NONE ? VALUE_NONE
1374 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1375 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1379 // update_pv() adds current move and appends child pv[]
1381 void update_pv(Move* pv, Move move, Move* childPv) {
1383 for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
1389 // update_cm_stats() updates countermove and follow-up move history
1391 void update_cm_stats(Stack* ss, Piece pc, Square s, Value bonus) {
1393 CounterMoveStats* cmh = (ss-1)->counterMoves;
1394 CounterMoveStats* fmh1 = (ss-2)->counterMoves;
1395 CounterMoveStats* fmh2 = (ss-4)->counterMoves;
1398 cmh->update(pc, s, bonus);
1401 fmh1->update(pc, s, bonus);
1404 fmh2->update(pc, s, bonus);
1408 // update_stats() updates killers, history, countermove and countermove plus
1409 // follow-up move history when a new quiet best move is found.
1411 void update_stats(const Position& pos, Stack* ss, Move move,
1412 Move* quiets, int quietsCnt, Value bonus) {
1414 if (ss->killers[0] != move)
1416 ss->killers[1] = ss->killers[0];
1417 ss->killers[0] = move;
1420 Color c = pos.side_to_move();
1421 Thread* thisThread = pos.this_thread();
1422 thisThread->fromTo.update(c, move, bonus);
1423 thisThread->history.update(pos.moved_piece(move), to_sq(move), bonus);
1424 update_cm_stats(ss, pos.moved_piece(move), to_sq(move), bonus);
1426 if ((ss-1)->counterMoves)
1428 Square prevSq = to_sq((ss-1)->currentMove);
1429 thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move);
1432 // Decrease all the other played quiet moves
1433 for (int i = 0; i < quietsCnt; ++i)
1435 thisThread->fromTo.update(c, quiets[i], -bonus);
1436 thisThread->history.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1437 update_cm_stats(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1442 // When playing with strength handicap, choose best move among a set of RootMoves
1443 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1445 Move Skill::pick_best(size_t multiPV) {
1447 const RootMoves& rootMoves = Threads.main()->rootMoves;
1448 static PRNG rng(now()); // PRNG sequence should be non-deterministic
1450 // RootMoves are already sorted by score in descending order
1451 Value topScore = rootMoves[0].score;
1452 int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
1453 int weakness = 120 - 2 * level;
1454 int maxScore = -VALUE_INFINITE;
1456 // Choose best move. For each move score we add two terms, both dependent on
1457 // weakness. One is deterministic and bigger for weaker levels, and one is
1458 // random. Then we choose the move with the resulting highest score.
1459 for (size_t i = 0; i < multiPV; ++i)
1461 // This is our magic formula
1462 int push = ( weakness * int(topScore - rootMoves[i].score)
1463 + delta * (rng.rand<unsigned>() % weakness)) / 128;
1465 if (rootMoves[i].score + push > maxScore)
1467 maxScore = rootMoves[i].score + push;
1468 best = rootMoves[i].pv[0];
1476 // check_time() is used to print debug info and, more importantly, to detect
1477 // when we are out of available time and thus stop the search.
1481 static TimePoint lastInfoTime = now();
1483 int elapsed = Time.elapsed();
1484 TimePoint tick = Limits.startTime + elapsed;
1486 if (tick - lastInfoTime >= 1000)
1488 lastInfoTime = tick;
1492 // An engine may not stop pondering until told so by the GUI
1496 if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
1497 || (Limits.movetime && elapsed >= Limits.movetime)
1498 || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
1499 Signals.stop = true;
1505 /// UCI::pv() formats PV information according to the UCI protocol. UCI requires
1506 /// that all (if any) unsearched PV lines are sent using a previous search score.
1508 string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
1510 std::stringstream ss;
1511 int elapsed = Time.elapsed() + 1;
1512 const RootMoves& rootMoves = pos.this_thread()->rootMoves;
1513 size_t PVIdx = pos.this_thread()->PVIdx;
1514 size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
1515 uint64_t nodesSearched = Threads.nodes_searched();
1516 uint64_t tbHits = Threads.tb_hits() + (TB::RootInTB ? rootMoves.size() : 0);
1518 for (size_t i = 0; i < multiPV; ++i)
1520 bool updated = (i <= PVIdx);
1522 if (depth == ONE_PLY && !updated)
1525 Depth d = updated ? depth : depth - ONE_PLY;
1526 Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
1528 bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
1529 v = tb ? TB::Score : v;
1531 if (ss.rdbuf()->in_avail()) // Not at first line
1535 << " depth " << d / ONE_PLY
1536 << " seldepth " << pos.this_thread()->maxPly
1537 << " multipv " << i + 1
1538 << " score " << UCI::value(v);
1540 if (!tb && i == PVIdx)
1541 ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1543 ss << " nodes " << nodesSearched
1544 << " nps " << nodesSearched * 1000 / elapsed;
1546 if (elapsed > 1000) // Earlier makes little sense
1547 ss << " hashfull " << TT.hashfull();
1549 ss << " tbhits " << tbHits
1550 << " time " << elapsed
1553 for (Move m : rootMoves[i].pv)
1554 ss << " " << UCI::move(m, pos.is_chess960());
1561 /// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
1562 /// before exiting the search, for instance, in case we stop the search during a
1563 /// fail high at root. We try hard to have a ponder move to return to the GUI,
1564 /// otherwise in case of 'ponder on' we have nothing to think on.
1566 bool RootMove::extract_ponder_from_tt(Position& pos) {
1571 assert(pv.size() == 1);
1576 pos.do_move(pv[0], st);
1577 TTEntry* tte = TT.probe(pos.key(), ttHit);
1581 Move m = tte->move(); // Local copy to be SMP safe
1582 if (MoveList<LEGAL>(pos).contains(m))
1586 pos.undo_move(pv[0]);
1587 return pv.size() > 1;
1590 void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) {
1593 UseRule50 = Options["Syzygy50MoveRule"];
1594 ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
1595 Cardinality = Options["SyzygyProbeLimit"];
1597 // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
1598 if (Cardinality > MaxCardinality)
1600 Cardinality = MaxCardinality;
1601 ProbeDepth = DEPTH_ZERO;
1604 if (Cardinality < popcount(pos.pieces()) || pos.can_castle(ANY_CASTLING))
1607 // If the current root position is in the tablebases, then RootMoves
1608 // contains only moves that preserve the draw or the win.
1609 RootInTB = root_probe(pos, rootMoves, TB::Score);
1612 Cardinality = 0; // Do not probe tablebases during the search
1614 else // If DTZ tables are missing, use WDL tables as a fallback
1616 // Filter out moves that do not preserve the draw or the win.
1617 RootInTB = root_probe_wdl(pos, rootMoves, TB::Score);
1619 // Only probe during search if winning
1620 if (RootInTB && TB::Score <= VALUE_DRAW)
1624 if (RootInTB && !UseRule50)
1625 TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
1626 : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1