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 const size_t HalfDensitySize = std::extent<decltype(HalfDensity)>::value;
158 Value bonus(Depth depth) { int d = depth / ONE_PLY ; return Value(d * d + 2 * d - 2); }
159 Value penalty(Depth depth) { int d = depth / ONE_PLY ; return -Value(d * d + 4 * d + 1); }
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 (scoreDiff > 0 && depthDiff >= 0)
324 previousScore = bestThread->rootMoves[0].score;
326 // Send new PV when needed
327 if (bestThread != this)
328 sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
330 sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
332 if (bestThread->rootMoves[0].pv.size() > 1 || bestThread->rootMoves[0].extract_ponder_from_tt(rootPos))
333 std::cout << " ponder " << UCI::move(bestThread->rootMoves[0].pv[1], rootPos.is_chess960());
335 std::cout << sync_endl;
339 // Thread::search() is the main iterative deepening loop. It calls search()
340 // repeatedly with increasing depth until the allocated thinking time has been
341 // consumed, the user stops the search, or the maximum search depth is reached.
343 void Thread::search() {
345 Stack stack[MAX_PLY+7], *ss = stack+4; // To allow referencing (ss-4) and (ss+2)
346 Value bestValue, alpha, beta, delta;
347 Move easyMove = MOVE_NONE;
348 MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
350 std::memset(ss-4, 0, 7 * sizeof(Stack));
352 bestValue = delta = alpha = -VALUE_INFINITE;
353 beta = VALUE_INFINITE;
354 completedDepth = DEPTH_ZERO;
358 easyMove = EasyMove.get(rootPos.key());
360 mainThread->easyMovePlayed = mainThread->failedLow = false;
361 mainThread->bestMoveChanges = 0;
365 size_t multiPV = Options["MultiPV"];
366 Skill skill(Options["Skill Level"]);
368 // When playing with strength handicap enable MultiPV search that we will
369 // use behind the scenes to retrieve a set of possible moves.
371 multiPV = std::max(multiPV, (size_t)4);
373 multiPV = std::min(multiPV, rootMoves.size());
375 // Iterative deepening loop until requested to stop or the target depth is reached
376 while ( (rootDepth += ONE_PLY) < DEPTH_MAX
378 && (!Limits.depth || Threads.main()->rootDepth / ONE_PLY <= Limits.depth))
380 // Set up the new depths for the helper threads skipping on average every
381 // 2nd ply (using a half-density matrix).
384 const Row& row = HalfDensity[(idx - 1) % HalfDensitySize];
385 if (row[(rootDepth / ONE_PLY + rootPos.game_ply()) % row.size()])
389 // Age out PV variability metric
391 mainThread->bestMoveChanges *= 0.505, mainThread->failedLow = false;
393 // Save the last iteration's scores before first PV line is searched and
394 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
395 for (RootMove& rm : rootMoves)
396 rm.previousScore = rm.score;
398 // MultiPV loop. We perform a full root search for each PV line
399 for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
401 // Reset aspiration window starting size
402 if (rootDepth >= 5 * ONE_PLY)
405 alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
406 beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
409 // Start with a small aspiration window and, in the case of a fail
410 // high/low, re-search with a bigger window until we're not failing
414 bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false, false);
416 // Bring the best move to the front. It is critical that sorting
417 // is done with a stable algorithm because all the values but the
418 // first and eventually the new best one are set to -VALUE_INFINITE
419 // and we want to keep the same order for all the moves except the
420 // new PV that goes to the front. Note that in case of MultiPV
421 // search the already searched PV lines are preserved.
422 std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
424 // If search has been stopped, break immediately. Sorting and
425 // writing PV back to TT is safe because RootMoves is still
426 // valid, although it refers to the previous iteration.
430 // When failing high/low give some update (without cluttering
431 // the UI) before a re-search.
434 && (bestValue <= alpha || bestValue >= beta)
435 && Time.elapsed() > 3000)
436 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
438 // In case of failing low/high increase aspiration window and
439 // re-search, otherwise exit the loop.
440 if (bestValue <= alpha)
442 beta = (alpha + beta) / 2;
443 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
447 mainThread->failedLow = true;
448 Signals.stopOnPonderhit = false;
451 else if (bestValue >= beta)
453 alpha = (alpha + beta) / 2;
454 beta = std::min(bestValue + delta, VALUE_INFINITE);
459 delta += delta / 4 + 5;
461 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
464 // Sort the PV lines searched so far and update the GUI
465 std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
470 if (Signals.stop || PVIdx + 1 == multiPV || Time.elapsed() > 3000)
471 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
475 completedDepth = rootDepth;
480 // If skill level is enabled and time is up, pick a sub-optimal best move
481 if (skill.enabled() && skill.time_to_pick(rootDepth))
482 skill.pick_best(multiPV);
484 // Have we found a "mate in x"?
486 && bestValue >= VALUE_MATE_IN_MAX_PLY
487 && VALUE_MATE - bestValue <= 2 * Limits.mate)
490 // Do we have time for the next iteration? Can we stop searching now?
491 if (Limits.use_time_management())
493 if (!Signals.stop && !Signals.stopOnPonderhit)
495 // Stop the search if only one legal move is available, or if all
496 // of the available time has been used, or if we matched an easyMove
497 // from the previous search and just did a fast verification.
498 const int F[] = { mainThread->failedLow,
499 bestValue - mainThread->previousScore };
501 int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1]));
502 double unstablePvFactor = 1 + mainThread->bestMoveChanges;
504 bool doEasyMove = rootMoves[0].pv[0] == easyMove
505 && mainThread->bestMoveChanges < 0.03
506 && Time.elapsed() > Time.optimum() * 5 / 42;
508 if ( rootMoves.size() == 1
509 || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628
510 || (mainThread->easyMovePlayed = doEasyMove, doEasyMove))
512 // If we are allowed to ponder do not stop the search now but
513 // keep pondering until the GUI sends "ponderhit" or "stop".
515 Signals.stopOnPonderhit = true;
521 if (rootMoves[0].pv.size() >= 3)
522 EasyMove.update(rootPos, rootMoves[0].pv);
531 // Clear any candidate easy move that wasn't stable for the last search
532 // iterations; the second condition prevents consecutive fast moves.
533 if (EasyMove.stableCnt < 6 || mainThread->easyMovePlayed)
536 // If skill level is enabled, swap best PV line with the sub-optimal one
538 std::swap(rootMoves[0], *std::find(rootMoves.begin(),
539 rootMoves.end(), skill.best_move(multiPV)));
545 // search<>() is the main search function for both PV and non-PV nodes
547 template <NodeType NT>
548 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning) {
550 const bool PvNode = NT == PV;
551 const bool rootNode = PvNode && (ss-1)->ply == 0;
553 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
554 assert(PvNode || (alpha == beta - 1));
555 assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
556 assert(!(PvNode && cutNode));
557 assert(depth / ONE_PLY * ONE_PLY == depth);
559 Move pv[MAX_PLY+1], quietsSearched[64];
563 Move ttMove, move, excludedMove, bestMove;
564 Depth extension, newDepth;
565 Value bestValue, value, ttValue, eval, nullValue;
566 bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
567 bool captureOrPromotion, doFullDepthSearch, moveCountPruning;
569 int moveCount, quietCount;
571 // Step 1. Initialize node
572 Thread* thisThread = pos.this_thread();
573 inCheck = pos.checkers();
574 moveCount = quietCount = ss->moveCount = 0;
575 ss->history = VALUE_ZERO;
576 bestValue = -VALUE_INFINITE;
577 ss->ply = (ss-1)->ply + 1;
579 // Check for the available remaining time
580 if (thisThread->resetCalls.load(std::memory_order_relaxed))
582 thisThread->resetCalls = false;
583 // At low node count increase the checking rate to about 0.1% of nodes
584 // otherwise use a default value.
585 thisThread->callsCnt = Limits.nodes ? std::min((int64_t)4096, Limits.nodes / 1024)
589 if (--thisThread->callsCnt <= 0)
591 for (Thread* th : Threads)
592 th->resetCalls = true;
597 // Used to send selDepth info to GUI
598 if (PvNode && thisThread->maxPly < ss->ply)
599 thisThread->maxPly = ss->ply;
603 // Step 2. Check for aborted search and immediate draw
604 if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
605 return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
606 : DrawValue[pos.side_to_move()];
608 // Step 3. Mate distance pruning. Even if we mate at the next move our score
609 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
610 // a shorter mate was found upward in the tree then there is no need to search
611 // because we will never beat the current alpha. Same logic but with reversed
612 // signs applies also in the opposite condition of being mated instead of giving
613 // mate. In this case return a fail-high score.
614 alpha = std::max(mated_in(ss->ply), alpha);
615 beta = std::min(mate_in(ss->ply+1), beta);
620 assert(0 <= ss->ply && ss->ply < MAX_PLY);
622 ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
623 ss->counterMoves = nullptr;
624 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
625 Square prevSq = to_sq((ss-1)->currentMove);
627 // Step 4. Transposition table lookup. We don't want the score of a partial
628 // search to overwrite a previous full search TT value, so we use a different
629 // position key in case of an excluded move.
630 excludedMove = ss->excludedMove;
631 posKey = pos.key() ^ Key(excludedMove);
632 tte = TT.probe(posKey, ttHit);
633 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
634 ttMove = rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
635 : ttHit ? tte->move() : MOVE_NONE;
637 // At non-PV nodes we check for an early TT cutoff
640 && tte->depth() >= depth
641 && ttValue != VALUE_NONE // Possible in case of TT access race
642 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
643 : (tte->bound() & BOUND_UPPER)))
645 // If ttMove is quiet, update killers, history, counter move on TT hit
646 if (ttValue >= beta && ttMove)
648 if (!pos.capture_or_promotion(ttMove))
649 update_stats(pos, ss, ttMove, nullptr, 0, bonus(depth));
651 // Extra penalty for a quiet TT move in previous ply when it gets refuted
652 if ((ss-1)->moveCount == 1 && !pos.captured_piece())
653 update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, penalty(depth));
658 // Step 4a. Tablebase probe
659 if (!rootNode && TB::Cardinality)
661 int piecesCount = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
663 if ( piecesCount <= TB::Cardinality
664 && (piecesCount < TB::Cardinality || depth >= TB::ProbeDepth)
665 && pos.rule50_count() == 0
666 && !pos.can_castle(ANY_CASTLING))
669 TB::WDLScore v = Tablebases::probe_wdl(pos, &err);
671 if (err != TB::ProbeState::FAIL)
673 thisThread->tbHits++;
675 int drawScore = TB::UseRule50 ? 1 : 0;
677 value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
678 : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply
679 : VALUE_DRAW + 2 * v * drawScore;
681 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
682 std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
683 MOVE_NONE, VALUE_NONE, TT.generation());
690 // Step 5. Evaluate the position statically
693 ss->staticEval = eval = VALUE_NONE;
699 // Never assume anything on values stored in TT
700 if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
701 eval = ss->staticEval = evaluate(pos);
703 // Can ttValue be used as a better position evaluation?
704 if (ttValue != VALUE_NONE)
705 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
710 eval = ss->staticEval =
711 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
712 : -(ss-1)->staticEval + 2 * Eval::Tempo;
714 tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
715 ss->staticEval, TT.generation());
718 if (skipEarlyPruning)
721 // Step 6. Razoring (skipped when in check)
723 && depth < 4 * ONE_PLY
724 && ttMove == MOVE_NONE
725 && eval + razor_margin[depth / ONE_PLY] <= alpha)
727 if (depth <= ONE_PLY)
728 return qsearch<NonPV, false>(pos, ss, alpha, alpha+1);
730 Value ralpha = alpha - razor_margin[depth / ONE_PLY];
731 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1);
736 // Step 7. Futility pruning: child node (skipped when in check)
738 && depth < 7 * ONE_PLY
739 && eval - futility_margin(depth) >= beta
740 && eval < VALUE_KNOWN_WIN // Do not return unproven wins
741 && pos.non_pawn_material(pos.side_to_move()))
744 // Step 8. Null move search with verification search (is omitted in PV nodes)
747 && (ss->staticEval >= beta - 35 * (depth / ONE_PLY - 6) || depth >= 13 * ONE_PLY)
748 && pos.non_pawn_material(pos.side_to_move()))
750 ss->currentMove = MOVE_NULL;
751 ss->counterMoves = nullptr;
753 assert(eval - beta >= 0);
755 // Null move dynamic reduction based on depth and value
756 Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
758 pos.do_null_move(st);
759 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1)
760 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true);
761 pos.undo_null_move();
763 if (nullValue >= beta)
765 // Do not return unproven mate scores
766 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
769 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
772 // Do verification search at high depths
773 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta)
774 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false, true);
781 // Step 9. ProbCut (skipped when in check)
782 // If we have a good enough capture and a reduced search returns a value
783 // much above beta, we can (almost) safely prune the previous move.
785 && depth >= 5 * ONE_PLY
786 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
788 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
789 Depth rdepth = depth - 4 * ONE_PLY;
791 assert(rdepth >= ONE_PLY);
792 assert((ss-1)->currentMove != MOVE_NONE);
793 assert((ss-1)->currentMove != MOVE_NULL);
795 MovePicker mp(pos, ttMove, rbeta - ss->staticEval);
797 while ((move = mp.next_move()) != MOVE_NONE)
800 ss->currentMove = move;
801 ss->counterMoves = &thisThread->counterMoveHistory[pos.moved_piece(move)][to_sq(move)];
802 pos.do_move(move, st);
803 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode, false);
810 // Step 10. Internal iterative deepening (skipped when in check)
811 if ( depth >= 6 * ONE_PLY
813 && (PvNode || ss->staticEval + 256 >= beta))
815 Depth d = (3 * depth / (4 * ONE_PLY) - 2) * ONE_PLY;
816 search<NT>(pos, ss, alpha, beta, d, cutNode, true);
818 tte = TT.probe(posKey, ttHit);
819 ttMove = ttHit ? tte->move() : MOVE_NONE;
822 moves_loop: // When in check search starts from here
824 const CounterMoveStats* cmh = (ss-1)->counterMoves;
825 const CounterMoveStats* fmh = (ss-2)->counterMoves;
826 const CounterMoveStats* fmh2 = (ss-4)->counterMoves;
828 MovePicker mp(pos, ttMove, depth, ss);
829 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
830 improving = ss->staticEval >= (ss-2)->staticEval
831 /* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */
832 ||(ss-2)->staticEval == VALUE_NONE;
834 singularExtensionNode = !rootNode
835 && depth >= 8 * ONE_PLY
836 && ttMove != MOVE_NONE
837 && ttValue != VALUE_NONE
838 && !excludedMove // Recursive singular search is not allowed
839 && (tte->bound() & BOUND_LOWER)
840 && tte->depth() >= depth - 3 * ONE_PLY;
842 // Step 11. Loop through moves
843 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
844 while ((move = mp.next_move()) != MOVE_NONE)
848 if (move == excludedMove)
851 // At root obey the "searchmoves" option and skip moves not listed in Root
852 // Move List. As a consequence any illegal move is also skipped. In MultiPV
853 // mode we also skip PV moves which have been already searched.
854 if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
855 thisThread->rootMoves.end(), move))
858 ss->moveCount = ++moveCount;
860 if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
861 sync_cout << "info depth " << depth / ONE_PLY
862 << " currmove " << UCI::move(move, pos.is_chess960())
863 << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
866 (ss+1)->pv = nullptr;
868 extension = DEPTH_ZERO;
869 captureOrPromotion = pos.capture_or_promotion(move);
870 moved_piece = pos.moved_piece(move);
872 givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
873 ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
874 : pos.gives_check(move);
876 moveCountPruning = depth < 16 * ONE_PLY
877 && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];
879 // Step 12. Extend checks
882 && pos.see_ge(move, VALUE_ZERO))
885 // Singular extension search. If all moves but one fail low on a search of
886 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
887 // is singular and should be extended. To verify this we do a reduced search
888 // on all the other moves but the ttMove and if the result is lower than
889 // ttValue minus a margin then we extend the ttMove.
890 if ( singularExtensionNode
895 Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
896 Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY;
897 ss->excludedMove = move;
898 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, d, cutNode, true);
899 ss->excludedMove = MOVE_NONE;
905 // Update the current move (this must be done after singular extension search)
906 newDepth = depth - ONE_PLY + extension;
908 // Step 13. Pruning at shallow depth
910 && bestValue > VALUE_MATED_IN_MAX_PLY)
912 if ( !captureOrPromotion
914 && !pos.advanced_pawn_push(move))
916 // Move count based pruning
917 if (moveCountPruning)
920 // Reduced depth of the next LMR search
921 int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
923 // Countermoves based pruning
925 && (!cmh || (*cmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
926 && (!fmh || (*fmh )[moved_piece][to_sq(move)] < VALUE_ZERO)
927 && (!fmh2 || (*fmh2)[moved_piece][to_sq(move)] < VALUE_ZERO || (cmh && fmh)))
930 // Futility pruning: parent node
933 && ss->staticEval + 256 + 200 * lmrDepth <= alpha)
936 // Prune moves with negative SEE
938 && !pos.see_ge(move, Value(-35 * lmrDepth * lmrDepth)))
941 else if ( depth < 7 * ONE_PLY
943 && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY)))
947 // Speculative prefetch as early as possible
948 prefetch(TT.first_entry(pos.key_after(move)));
950 // Check for legality just before making the move
951 if (!rootNode && !pos.legal(move))
953 ss->moveCount = --moveCount;
957 ss->currentMove = move;
958 ss->counterMoves = &thisThread->counterMoveHistory[moved_piece][to_sq(move)];
960 // Step 14. Make the move
961 pos.do_move(move, st, givesCheck);
963 // Step 15. Reduced depth search (LMR). If the move fails high it will be
964 // re-searched at full depth.
965 if ( depth >= 3 * ONE_PLY
967 && (!captureOrPromotion || moveCountPruning))
969 Depth r = reduction<PvNode>(improving, depth, moveCount);
971 if (captureOrPromotion)
972 r -= r ? ONE_PLY : DEPTH_ZERO;
975 // Increase reduction for cut nodes
979 // Decrease reduction for moves that escape a capture. Filter out
980 // castling moves, because they are coded as "king captures rook" and
981 // hence break make_move().
982 else if ( type_of(move) == NORMAL
983 && !pos.see_ge(make_move(to_sq(move), from_sq(move)), VALUE_ZERO))
986 ss->history = thisThread->history[moved_piece][to_sq(move)]
987 + (cmh ? (*cmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
988 + (fmh ? (*fmh )[moved_piece][to_sq(move)] : VALUE_ZERO)
989 + (fmh2 ? (*fmh2)[moved_piece][to_sq(move)] : VALUE_ZERO)
990 + thisThread->fromTo.get(~pos.side_to_move(), move)
991 - 8000; // Correction factor
993 // Decrease/increase reduction by comparing opponent's stat score
994 if (ss->history > VALUE_ZERO && (ss-1)->history < VALUE_ZERO)
997 else if (ss->history < VALUE_ZERO && (ss-1)->history > VALUE_ZERO)
1000 // Decrease/increase reduction for moves with a good/bad history
1001 r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->history / 20000) * ONE_PLY);
1004 Depth d = std::max(newDepth - r, ONE_PLY);
1006 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true, false);
1008 doFullDepthSearch = (value > alpha && d != newDepth);
1011 doFullDepthSearch = !PvNode || moveCount > 1;
1013 // Step 16. Full depth search when LMR is skipped or fails high
1014 if (doFullDepthSearch)
1015 value = newDepth < ONE_PLY ?
1016 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha)
1017 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha)
1018 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false);
1020 // For PV nodes only, do a full PV search on the first move or after a fail
1021 // high (in the latter case search only if value < beta), otherwise let the
1022 // parent node fail low with value <= alpha and try another move.
1023 if (PvNode && (moveCount == 1 || (value > alpha && (rootNode || value < beta))))
1026 (ss+1)->pv[0] = MOVE_NONE;
1028 value = newDepth < ONE_PLY ?
1029 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha)
1030 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha)
1031 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, false);
1034 // Step 17. Undo move
1035 pos.undo_move(move);
1037 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1039 // Step 18. Check for a new best move
1040 // Finished searching the move. If a stop occurred, the return value of
1041 // the search cannot be trusted, and we return immediately without
1042 // updating best move, PV and TT.
1043 if (Signals.stop.load(std::memory_order_relaxed))
1048 RootMove& rm = *std::find(thisThread->rootMoves.begin(),
1049 thisThread->rootMoves.end(), move);
1051 // PV move or new best move ?
1052 if (moveCount == 1 || value > alpha)
1059 for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
1060 rm.pv.push_back(*m);
1062 // We record how often the best move has been changed in each
1063 // iteration. This information is used for time management: When
1064 // the best move changes frequently, we allocate some more time.
1065 if (moveCount > 1 && thisThread == Threads.main())
1066 ++static_cast<MainThread*>(thisThread)->bestMoveChanges;
1069 // All other moves but the PV are set to the lowest value: this is
1070 // not a problem when sorting because the sort is stable and the
1071 // move position in the list is preserved - just the PV is pushed up.
1072 rm.score = -VALUE_INFINITE;
1075 if (value > bestValue)
1083 if (PvNode && !rootNode) // Update pv even in fail-high case
1084 update_pv(ss->pv, move, (ss+1)->pv);
1086 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1090 assert(value >= beta); // Fail high
1096 if (!captureOrPromotion && move != bestMove && quietCount < 64)
1097 quietsSearched[quietCount++] = move;
1100 // The following condition would detect a stop only after move loop has been
1101 // completed. But in this case bestValue is valid because we have fully
1102 // searched our subtree, and we can anyhow save the result in TT.
1108 // Step 20. Check for mate and stalemate
1109 // All legal moves have been searched and if there are no legal moves, it
1110 // must be a mate or a stalemate. If we are in a singular extension search then
1111 // return a fail low score.
1113 assert(moveCount || !inCheck || excludedMove || !MoveList<LEGAL>(pos).size());
1116 bestValue = excludedMove ? alpha
1117 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1121 // Quiet best move: update killers, history and countermoves
1122 if (!pos.capture_or_promotion(bestMove))
1123 update_stats(pos, ss, bestMove, quietsSearched, quietCount, bonus(depth));
1125 // Extra penalty for a quiet TT move in previous ply when it gets refuted
1126 if ((ss-1)->moveCount == 1 && !pos.captured_piece())
1127 update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, penalty(depth));
1129 // Bonus for prior countermove that caused the fail low
1130 else if ( depth >= 3 * ONE_PLY
1131 && !pos.captured_piece()
1132 && is_ok((ss-1)->currentMove))
1133 update_cm_stats(ss-1, pos.piece_on(prevSq), prevSq, bonus(depth));
1135 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1136 bestValue >= beta ? BOUND_LOWER :
1137 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1138 depth, bestMove, ss->staticEval, TT.generation());
1140 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1146 // qsearch() is the quiescence search function, which is called by the main
1147 // search function with depth zero, or recursively with depth less than ONE_PLY.
1149 template <NodeType NT, bool InCheck>
1150 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1152 const bool PvNode = NT == PV;
1154 assert(InCheck == !!pos.checkers());
1155 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1156 assert(PvNode || (alpha == beta - 1));
1157 assert(depth <= DEPTH_ZERO);
1158 assert(depth / ONE_PLY * ONE_PLY == depth);
1164 Move ttMove, move, bestMove;
1165 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1166 bool ttHit, givesCheck, evasionPrunable;
1171 oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
1173 ss->pv[0] = MOVE_NONE;
1176 ss->currentMove = bestMove = MOVE_NONE;
1177 ss->ply = (ss-1)->ply + 1;
1179 // Check for an instant draw or if the maximum ply has been reached
1180 if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
1181 return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
1182 : DrawValue[pos.side_to_move()];
1184 assert(0 <= ss->ply && ss->ply < MAX_PLY);
1186 // Decide whether or not to include checks: this fixes also the type of
1187 // TT entry depth that we are going to use. Note that in qsearch we use
1188 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1189 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1190 : DEPTH_QS_NO_CHECKS;
1192 // Transposition table lookup
1194 tte = TT.probe(posKey, ttHit);
1195 ttMove = ttHit ? tte->move() : MOVE_NONE;
1196 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
1200 && tte->depth() >= ttDepth
1201 && ttValue != VALUE_NONE // Only in case of TT access race
1202 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1203 : (tte->bound() & BOUND_UPPER)))
1206 // Evaluate the position statically
1209 ss->staticEval = VALUE_NONE;
1210 bestValue = futilityBase = -VALUE_INFINITE;
1216 // Never assume anything on values stored in TT
1217 if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
1218 ss->staticEval = bestValue = evaluate(pos);
1220 // Can ttValue be used as a better position evaluation?
1221 if (ttValue != VALUE_NONE)
1222 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1223 bestValue = ttValue;
1226 ss->staticEval = bestValue =
1227 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
1228 : -(ss-1)->staticEval + 2 * Eval::Tempo;
1230 // Stand pat. Return immediately if static value is at least beta
1231 if (bestValue >= beta)
1234 tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1235 DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
1240 if (PvNode && bestValue > alpha)
1243 futilityBase = bestValue + 128;
1246 // Initialize a MovePicker object for the current position, and prepare
1247 // to search the moves. Because the depth is <= 0 here, only captures,
1248 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1250 MovePicker mp(pos, ttMove, depth, to_sq((ss-1)->currentMove));
1252 // Loop through the moves until no moves remain or a beta cutoff occurs
1253 while ((move = mp.next_move()) != MOVE_NONE)
1255 assert(is_ok(move));
1257 givesCheck = type_of(move) == NORMAL && !pos.discovered_check_candidates()
1258 ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
1259 : pos.gives_check(move);
1264 && futilityBase > -VALUE_KNOWN_WIN
1265 && !pos.advanced_pawn_push(move))
1267 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1269 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1271 if (futilityValue <= alpha)
1273 bestValue = std::max(bestValue, futilityValue);
1277 if (futilityBase <= alpha && !pos.see_ge(move, VALUE_ZERO + 1))
1279 bestValue = std::max(bestValue, futilityBase);
1284 // Detect non-capture evasions that are candidates to be pruned
1285 evasionPrunable = InCheck
1286 && bestValue > VALUE_MATED_IN_MAX_PLY
1287 && !pos.capture(move);
1289 // Don't search moves with negative SEE values
1290 if ( (!InCheck || evasionPrunable)
1291 && type_of(move) != PROMOTION
1292 && !pos.see_ge(move, VALUE_ZERO))
1295 // Speculative prefetch as early as possible
1296 prefetch(TT.first_entry(pos.key_after(move)));
1298 // Check for legality just before making the move
1299 if (!pos.legal(move))
1302 ss->currentMove = move;
1304 // Make and search the move
1305 pos.do_move(move, st, givesCheck);
1306 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1307 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1308 pos.undo_move(move);
1310 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1312 // Check for a new best move
1313 if (value > bestValue)
1319 if (PvNode) // Update pv even in fail-high case
1320 update_pv(ss->pv, move, (ss+1)->pv);
1322 if (PvNode && value < beta) // Update alpha here!
1329 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1330 ttDepth, move, ss->staticEval, TT.generation());
1338 // All legal moves have been searched. A special case: If we're in check
1339 // and no legal moves were found, it is checkmate.
1340 if (InCheck && bestValue == -VALUE_INFINITE)
1341 return mated_in(ss->ply); // Plies to mate from the root
1343 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1344 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1345 ttDepth, bestMove, ss->staticEval, TT.generation());
1347 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1353 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1354 // "plies to mate from the current position". Non-mate scores are unchanged.
1355 // The function is called before storing a value in the transposition table.
1357 Value value_to_tt(Value v, int ply) {
1359 assert(v != VALUE_NONE);
1361 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1362 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1366 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1367 // from the transposition table (which refers to the plies to mate/be mated
1368 // from current position) to "plies to mate/be mated from the root".
1370 Value value_from_tt(Value v, int ply) {
1372 return v == VALUE_NONE ? VALUE_NONE
1373 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1374 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1378 // update_pv() adds current move and appends child pv[]
1380 void update_pv(Move* pv, Move move, Move* childPv) {
1382 for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
1388 // update_cm_stats() updates countermove and follow-up move history
1390 void update_cm_stats(Stack* ss, Piece pc, Square s, Value bonus) {
1392 CounterMoveStats* cmh = (ss-1)->counterMoves;
1393 CounterMoveStats* fmh1 = (ss-2)->counterMoves;
1394 CounterMoveStats* fmh2 = (ss-4)->counterMoves;
1397 cmh->update(pc, s, bonus);
1400 fmh1->update(pc, s, bonus);
1403 fmh2->update(pc, s, bonus);
1407 // update_stats() updates killers, history, countermove and countermove plus
1408 // follow-up move history when a new quiet best move is found.
1410 void update_stats(const Position& pos, Stack* ss, Move move,
1411 Move* quiets, int quietsCnt, Value bonus) {
1413 if (ss->killers[0] != move)
1415 ss->killers[1] = ss->killers[0];
1416 ss->killers[0] = move;
1419 Color c = pos.side_to_move();
1420 Thread* thisThread = pos.this_thread();
1421 thisThread->fromTo.update(c, move, bonus);
1422 thisThread->history.update(pos.moved_piece(move), to_sq(move), bonus);
1423 update_cm_stats(ss, pos.moved_piece(move), to_sq(move), bonus);
1425 if ((ss-1)->counterMoves)
1427 Square prevSq = to_sq((ss-1)->currentMove);
1428 thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move);
1431 // Decrease all the other played quiet moves
1432 for (int i = 0; i < quietsCnt; ++i)
1434 thisThread->fromTo.update(c, quiets[i], -bonus);
1435 thisThread->history.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1436 update_cm_stats(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1441 // When playing with strength handicap, choose best move among a set of RootMoves
1442 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1444 Move Skill::pick_best(size_t multiPV) {
1446 const RootMoves& rootMoves = Threads.main()->rootMoves;
1447 static PRNG rng(now()); // PRNG sequence should be non-deterministic
1449 // RootMoves are already sorted by score in descending order
1450 Value topScore = rootMoves[0].score;
1451 int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
1452 int weakness = 120 - 2 * level;
1453 int maxScore = -VALUE_INFINITE;
1455 // Choose best move. For each move score we add two terms, both dependent on
1456 // weakness. One is deterministic and bigger for weaker levels, and one is
1457 // random. Then we choose the move with the resulting highest score.
1458 for (size_t i = 0; i < multiPV; ++i)
1460 // This is our magic formula
1461 int push = ( weakness * int(topScore - rootMoves[i].score)
1462 + delta * (rng.rand<unsigned>() % weakness)) / 128;
1464 if (rootMoves[i].score + push > maxScore)
1466 maxScore = rootMoves[i].score + push;
1467 best = rootMoves[i].pv[0];
1475 // check_time() is used to print debug info and, more importantly, to detect
1476 // when we are out of available time and thus stop the search.
1480 static TimePoint lastInfoTime = now();
1482 int elapsed = Time.elapsed();
1483 TimePoint tick = Limits.startTime + elapsed;
1485 if (tick - lastInfoTime >= 1000)
1487 lastInfoTime = tick;
1491 // An engine may not stop pondering until told so by the GUI
1495 if ( (Limits.use_time_management() && elapsed > Time.maximum() - 10)
1496 || (Limits.movetime && elapsed >= Limits.movetime)
1497 || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
1498 Signals.stop = true;
1504 /// UCI::pv() formats PV information according to the UCI protocol. UCI requires
1505 /// that all (if any) unsearched PV lines are sent using a previous search score.
1507 string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
1509 std::stringstream ss;
1510 int elapsed = Time.elapsed() + 1;
1511 const RootMoves& rootMoves = pos.this_thread()->rootMoves;
1512 size_t PVIdx = pos.this_thread()->PVIdx;
1513 size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
1514 uint64_t nodesSearched = Threads.nodes_searched();
1515 uint64_t tbHits = Threads.tb_hits() + (TB::RootInTB ? rootMoves.size() : 0);
1517 for (size_t i = 0; i < multiPV; ++i)
1519 bool updated = (i <= PVIdx);
1521 if (depth == ONE_PLY && !updated)
1524 Depth d = updated ? depth : depth - ONE_PLY;
1525 Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
1527 bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
1528 v = tb ? TB::Score : v;
1530 if (ss.rdbuf()->in_avail()) // Not at first line
1534 << " depth " << d / ONE_PLY
1535 << " seldepth " << pos.this_thread()->maxPly
1536 << " multipv " << i + 1
1537 << " score " << UCI::value(v);
1539 if (!tb && i == PVIdx)
1540 ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1542 ss << " nodes " << nodesSearched
1543 << " nps " << nodesSearched * 1000 / elapsed;
1545 if (elapsed > 1000) // Earlier makes little sense
1546 ss << " hashfull " << TT.hashfull();
1548 ss << " tbhits " << tbHits
1549 << " time " << elapsed
1552 for (Move m : rootMoves[i].pv)
1553 ss << " " << UCI::move(m, pos.is_chess960());
1560 /// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
1561 /// before exiting the search, for instance, in case we stop the search during a
1562 /// fail high at root. We try hard to have a ponder move to return to the GUI,
1563 /// otherwise in case of 'ponder on' we have nothing to think on.
1565 bool RootMove::extract_ponder_from_tt(Position& pos) {
1570 assert(pv.size() == 1);
1575 pos.do_move(pv[0], st);
1576 TTEntry* tte = TT.probe(pos.key(), ttHit);
1580 Move m = tte->move(); // Local copy to be SMP safe
1581 if (MoveList<LEGAL>(pos).contains(m))
1585 pos.undo_move(pv[0]);
1586 return pv.size() > 1;
1589 void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) {
1592 UseRule50 = Options["Syzygy50MoveRule"];
1593 ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
1594 Cardinality = Options["SyzygyProbeLimit"];
1596 // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
1597 if (Cardinality > MaxCardinality)
1599 Cardinality = MaxCardinality;
1600 ProbeDepth = DEPTH_ZERO;
1603 if (Cardinality < popcount(pos.pieces()) || pos.can_castle(ANY_CASTLING))
1606 // If the current root position is in the tablebases, then RootMoves
1607 // contains only moves that preserve the draw or the win.
1608 RootInTB = root_probe(pos, rootMoves, TB::Score);
1611 Cardinality = 0; // Do not probe tablebases during the search
1613 else // If DTZ tables are missing, use WDL tables as a fallback
1615 // Filter out moves that do not preserve the draw or the win.
1616 RootInTB = root_probe_wdl(pos, rootMoves, TB::Score);
1618 // Only probe during search if winning
1619 if (RootInTB && TB::Score <= VALUE_DRAW)
1623 if (RootInTB && !UseRule50)
1624 TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
1625 : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1