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
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
23 #include <cstring> // For std::memset
36 #include "syzygy/tbprobe.h"
42 StateStackPtr SetupStates;
45 namespace Tablebases {
55 namespace TB = Tablebases;
59 using namespace Search;
63 // Different node types, used as template parameter
64 enum NodeType { Root, PV, NonPV };
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(200 * d); }
70 // Futility and reductions lookup tables, initialized at startup
71 int FutilityMoveCounts[2][16]; // [improving][depth]
72 Depth 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, 63 * ONE_PLY)][std::min(mn, 63)];
78 // Skill struct is used to implement strength limiting
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 struct is used to detect a so called 'easy move'; when PV is
91 // stable across multiple search iterations we can fast 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 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], pos.gives_check(newPv[0], CheckInfo(pos)));
117 pos.do_move(newPv[1], st[1], pos.gives_check(newPv[1], CheckInfo(pos)));
118 expectedPosKey = pos.key();
119 pos.undo_move(newPv[1]);
120 pos.undo_move(newPv[0]);
129 EasyMoveManager EasyMove;
130 double BestMoveChanges;
131 Value DrawValue[COLOR_NB];
132 CounterMovesHistoryStats CounterMovesHistory;
134 template <NodeType NT>
135 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
137 template <NodeType NT, bool InCheck>
138 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
140 Value value_to_tt(Value v, int ply);
141 Value value_from_tt(Value v, int ply);
142 void update_pv(Move* pv, Move move, Move* childPv);
143 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
149 /// Search::init() is called during startup to initialize various lookup tables
151 void Search::init() {
153 const double K[][2] = {{ 0.799, 2.281 }, { 0.484, 3.023 }};
155 for (int pv = 0; pv <= 1; ++pv)
156 for (int imp = 0; imp <= 1; ++imp)
157 for (int d = 1; d < 64; ++d)
158 for (int mc = 1; mc < 64; ++mc)
160 double r = K[pv][0] + log(d) * log(mc) / K[pv][1];
163 Reductions[pv][imp][d][mc] = int(r) * ONE_PLY;
165 // Increase reduction when eval is not improving
166 if (!pv && !imp && Reductions[pv][imp][d][mc] >= 2 * ONE_PLY)
167 Reductions[pv][imp][d][mc] += ONE_PLY;
170 for (int d = 0; d < 16; ++d)
172 FutilityMoveCounts[0][d] = int(2.4 + 0.773 * pow(d + 0.00, 1.8));
173 FutilityMoveCounts[1][d] = int(2.9 + 1.045 * pow(d + 0.49, 1.8));
178 /// Search::clear() resets to zero search state, to obtain reproducible results
180 void Search::clear() {
183 CounterMovesHistory.clear();
185 for (Thread* th : Threads)
188 th->counterMoves.clear();
193 /// Search::perft() is our utility to verify move generation. All the leaf nodes
194 /// up to the given depth are generated and counted and the sum returned.
196 uint64_t Search::perft(Position& pos, Depth depth) {
199 uint64_t cnt, nodes = 0;
201 const bool leaf = (depth == 2 * ONE_PLY);
203 for (const auto& m : MoveList<LEGAL>(pos))
205 if (Root && depth <= ONE_PLY)
209 pos.do_move(m, st, pos.gives_check(m, ci));
210 cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
215 sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
220 template uint64_t Search::perft<true>(Position&, Depth);
223 /// MainThread::search() is called by the main thread when the program receives
224 /// the UCI 'go' command. It searches from root position and at the end prints
225 /// the "bestmove" to output.
227 void MainThread::search() {
229 Color us = rootPos.side_to_move();
230 Time.init(Limits, us, rootPos.game_ply());
232 int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
233 DrawValue[ us] = VALUE_DRAW - Value(contempt);
234 DrawValue[~us] = VALUE_DRAW + Value(contempt);
237 TB::RootInTB = false;
238 TB::UseRule50 = Options["Syzygy50MoveRule"];
239 TB::ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
240 TB::Cardinality = Options["SyzygyProbeLimit"];
242 // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
243 if (TB::Cardinality > TB::MaxCardinality)
245 TB::Cardinality = TB::MaxCardinality;
246 TB::ProbeDepth = DEPTH_ZERO;
249 if (rootMoves.empty())
251 rootMoves.push_back(RootMove(MOVE_NONE));
252 sync_cout << "info depth 0 score "
253 << UCI::value(rootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
258 if (TB::Cardinality >= rootPos.count<ALL_PIECES>(WHITE)
259 + rootPos.count<ALL_PIECES>(BLACK))
261 // If the current root position is in the tablebases then RootMoves
262 // contains only moves that preserve the draw or win.
263 TB::RootInTB = Tablebases::root_probe(rootPos, rootMoves, TB::Score);
266 TB::Cardinality = 0; // Do not probe tablebases during the search
268 else // If DTZ tables are missing, use WDL tables as a fallback
270 // Filter out moves that do not preserve a draw or win
271 TB::RootInTB = Tablebases::root_probe_wdl(rootPos, rootMoves, TB::Score);
273 // Only probe during search if winning
274 if (TB::Score <= VALUE_DRAW)
280 TB::Hits = rootMoves.size();
283 TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
284 : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1
289 for (Thread* th : Threads)
292 th->rootDepth = DEPTH_ZERO;
295 th->rootPos = Position(rootPos, th);
296 th->rootMoves = rootMoves;
297 th->start_searching();
301 Thread::search(); // Let's start searching!
304 // When playing in 'nodes as time' mode, subtract the searched nodes from
305 // the available ones before to exit.
307 Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
309 // When we reach the maximum depth, we can arrive here without a raise of
310 // Signals.stop. However, if we are pondering or in an infinite search,
311 // the UCI protocol states that we shouldn't print the best move before the
312 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
313 // until the GUI sends one of those commands (which also raises Signals.stop).
314 if (!Signals.stop && (Limits.ponder || Limits.infinite))
316 Signals.stopOnPonderhit = true;
320 // Stop the threads if not already stopped
323 // Wait until all threads have finished
324 for (Thread* th : Threads)
326 th->wait_for_search_finished();
328 // Check if there are threads with a better score than main thread.
329 Thread* bestThread = this;
330 for (Thread* th : Threads)
331 if ( th->completedDepth > bestThread->completedDepth
332 && th->rootMoves[0].score > bestThread->rootMoves[0].score)
335 // Send new PV when needed.
336 // FIXME: Breaks multiPV, and skill levels
337 if (bestThread != this)
338 sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
340 sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
342 if (bestThread->rootMoves[0].pv.size() > 1 || bestThread->rootMoves[0].extract_ponder_from_tt(rootPos))
343 std::cout << " ponder " << UCI::move(bestThread->rootMoves[0].pv[1], rootPos.is_chess960());
345 std::cout << sync_endl;
349 // Thread::search() is the main iterative deepening loop. It calls search()
350 // repeatedly with increasing depth until the allocated thinking time has been
351 // consumed, user stops the search, or the maximum search depth is reached.
353 void Thread::search() {
355 Stack stack[MAX_PLY+4], *ss = stack+2; // To allow referencing (ss-2) and (ss+2)
356 Value bestValue, alpha, beta, delta;
357 Move easyMove = MOVE_NONE;
358 bool isMainThread = (this == Threads.main());
360 std::memset(ss-2, 0, 5 * sizeof(Stack));
362 bestValue = delta = alpha = -VALUE_INFINITE;
363 beta = VALUE_INFINITE;
364 completedDepth = DEPTH_ZERO;
368 easyMove = EasyMove.get(rootPos.key());
374 size_t multiPV = Options["MultiPV"];
375 Skill skill(Options["Skill Level"]);
377 // When playing with strength handicap enable MultiPV search that we will
378 // use behind the scenes to retrieve a set of possible moves.
380 multiPV = std::max(multiPV, (size_t)4);
382 multiPV = std::min(multiPV, rootMoves.size());
384 // Iterative deepening loop until requested to stop or target depth reached
385 while (++rootDepth < DEPTH_MAX && !Signals.stop && (!Limits.depth || rootDepth <= Limits.depth))
387 // Set up the new depth for the helper threads
389 rootDepth = std::min(DEPTH_MAX - ONE_PLY, Threads.main()->rootDepth + Depth(int(2.2 * log(1 + this->idx))));
391 // Age out PV variability metric
393 BestMoveChanges *= 0.5;
395 // Save the last iteration's scores before first PV line is searched and
396 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
397 for (RootMove& rm : rootMoves)
398 rm.previousScore = rm.score;
400 // MultiPV loop. We perform a full root search for each PV line
401 for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
403 // Reset aspiration window starting size
404 if (rootDepth >= 5 * ONE_PLY)
407 alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
408 beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
411 // Start with a small aspiration window and, in the case of a fail
412 // high/low, re-search with a bigger window until we're not failing
416 bestValue = ::search<Root>(rootPos, ss, alpha, beta, rootDepth, false);
418 // Bring the best move to the front. It is critical that sorting
419 // is done with a stable algorithm because all the values but the
420 // first and eventually the new best one are set to -VALUE_INFINITE
421 // and we want to keep the same order for all the moves except the
422 // new PV that goes to the front. Note that in case of MultiPV
423 // search the already searched PV lines are preserved.
424 std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
426 // Write PV back to transposition table in case the relevant
427 // entries have been overwritten during the search.
428 for (size_t i = 0; i <= PVIdx; ++i)
429 rootMoves[i].insert_pv_in_tt(rootPos);
431 // If search has been stopped break immediately. Sorting and
432 // writing PV back to TT is safe because RootMoves is still
433 // valid, although it refers to previous iteration.
437 // When failing high/low give some update (without cluttering
438 // the UI) before a re-search.
441 && (bestValue <= alpha || bestValue >= beta)
442 && Time.elapsed() > 3000)
443 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
445 // In case of failing low/high increase aspiration window and
446 // re-search, otherwise exit the loop.
447 if (bestValue <= alpha)
449 beta = (alpha + beta) / 2;
450 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
454 Signals.failedLowAtRoot = true;
455 Signals.stopOnPonderhit = false;
458 else if (bestValue >= beta)
460 alpha = (alpha + beta) / 2;
461 beta = std::min(bestValue + delta, VALUE_INFINITE);
466 delta += delta / 4 + 5;
468 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
471 // Sort the PV lines searched so far and update the GUI
472 std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
478 sync_cout << "info nodes " << Threads.nodes_searched()
479 << " time " << Time.elapsed() << sync_endl;
481 else if (PVIdx + 1 == multiPV || Time.elapsed() > 3000)
482 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
486 completedDepth = rootDepth;
491 // If skill level is enabled and time is up, pick a sub-optimal best move
492 if (skill.enabled() && skill.time_to_pick(rootDepth))
493 skill.pick_best(multiPV);
495 // Have we found a "mate in x"?
497 && bestValue >= VALUE_MATE_IN_MAX_PLY
498 && VALUE_MATE - bestValue <= 2 * Limits.mate)
501 // Do we have time for the next iteration? Can we stop searching now?
502 if (Limits.use_time_management())
504 if (!Signals.stop && !Signals.stopOnPonderhit)
506 // Take some extra time if the best move has changed
507 if (rootDepth > 4 * ONE_PLY && multiPV == 1)
508 Time.pv_instability(BestMoveChanges);
510 // Stop the search if only one legal move is available or all
511 // of the available time has been used or we matched an easyMove
512 // from the previous search and just did a fast verification.
513 if ( rootMoves.size() == 1
514 || Time.elapsed() > Time.available()
515 || ( rootMoves[0].pv[0] == easyMove
516 && BestMoveChanges < 0.03
517 && Time.elapsed() > Time.available() / 10))
519 // If we are allowed to ponder do not stop the search now but
520 // keep pondering until the GUI sends "ponderhit" or "stop".
522 Signals.stopOnPonderhit = true;
528 if (rootMoves[0].pv.size() >= 3)
529 EasyMove.update(rootPos, rootMoves[0].pv);
538 // Clear any candidate easy move that wasn't stable for the last search
539 // iterations; the second condition prevents consecutive fast moves.
540 if (EasyMove.stableCnt < 6 || Time.elapsed() < Time.available())
543 // If skill level is enabled, swap best PV line with the sub-optimal one
545 std::swap(rootMoves[0], *std::find(rootMoves.begin(),
546 rootMoves.end(), skill.best_move(multiPV)));
552 // search<>() is the main search function for both PV and non-PV nodes
554 template <NodeType NT>
555 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
557 const bool RootNode = NT == Root;
558 const bool PvNode = NT == PV || NT == Root;
560 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
561 assert(PvNode || (alpha == beta - 1));
562 assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
564 Move pv[MAX_PLY+1], quietsSearched[64];
568 Move ttMove, move, excludedMove, bestMove;
569 Depth extension, newDepth, predictedDepth;
570 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
571 bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
572 bool captureOrPromotion, doFullDepthSearch;
573 int moveCount, quietCount;
575 // Step 1. Initialize node
576 Thread* thisThread = pos.this_thread();
577 inCheck = pos.checkers();
578 moveCount = quietCount = ss->moveCount = 0;
579 bestValue = -VALUE_INFINITE;
580 ss->ply = (ss-1)->ply + 1;
582 // Check for available remaining time
583 if (thisThread->resetCalls.load(std::memory_order_relaxed))
585 thisThread->resetCalls = false;
586 thisThread->callsCnt = 0;
588 if (++thisThread->callsCnt > 4096)
590 for (Thread* th : Threads)
591 th->resetCalls = true;
596 // Used to send selDepth info to GUI
597 if (PvNode && thisThread->maxPly < ss->ply)
598 thisThread->maxPly = ss->ply;
602 // Step 2. Check for aborted search and immediate draw
603 if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw() || ss->ply >= MAX_PLY)
604 return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
605 : DrawValue[pos.side_to_move()];
607 // Step 3. Mate distance pruning. Even if we mate at the next move our score
608 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
609 // a shorter mate was found upward in the tree then there is no need to search
610 // because we will never beat the current alpha. Same logic but with reversed
611 // signs applies also in the opposite condition of being mated instead of giving
612 // mate. In this case return a fail-high score.
613 alpha = std::max(mated_in(ss->ply), alpha);
614 beta = std::min(mate_in(ss->ply+1), beta);
619 assert(0 <= ss->ply && ss->ply < MAX_PLY);
621 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
622 (ss+1)->skipEarlyPruning = false; (ss+1)->reduction = DEPTH_ZERO;
623 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
625 // Step 4. Transposition table lookup. We don't want the score of a partial
626 // search to overwrite a previous full search TT value, so we use a different
627 // position key in case of an excluded move.
628 excludedMove = ss->excludedMove;
629 posKey = excludedMove ? pos.exclusion_key() : pos.key();
630 tte = TT.probe(posKey, ttHit);
631 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
632 ss->ttMove = ttMove = RootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
633 : ttHit ? tte->move() : MOVE_NONE;
635 // At non-PV nodes we check for an early TT cutoff
638 && tte->depth() >= depth
639 && ttValue != VALUE_NONE // Possible in case of TT access race
640 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
641 : (tte->bound() & BOUND_UPPER)))
643 ss->currentMove = ttMove; // Can be MOVE_NONE
645 // If ttMove is quiet, update killers, history, counter move on TT hit
646 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove))
647 update_stats(pos, ss, ttMove, depth, nullptr, 0);
652 // Step 4a. Tablebase probe
653 if (!RootNode && TB::Cardinality)
655 int piecesCnt = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
657 if ( piecesCnt <= TB::Cardinality
658 && (piecesCnt < TB::Cardinality || depth >= TB::ProbeDepth)
659 && pos.rule50_count() == 0)
661 int found, v = Tablebases::probe_wdl(pos, &found);
667 int drawScore = TB::UseRule50 ? 1 : 0;
669 value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
670 : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply
671 : VALUE_DRAW + 2 * v * drawScore;
673 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
674 std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
675 MOVE_NONE, VALUE_NONE, TT.generation());
682 // Step 5. Evaluate the position statically
685 ss->staticEval = eval = VALUE_NONE;
691 // Never assume anything on values stored in TT
692 if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
693 eval = ss->staticEval = evaluate(pos);
695 // Can ttValue be used as a better position evaluation?
696 if (ttValue != VALUE_NONE)
697 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
702 eval = ss->staticEval =
703 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
704 : -(ss-1)->staticEval + 2 * Eval::Tempo;
706 tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
707 ss->staticEval, TT.generation());
710 if (ss->skipEarlyPruning)
713 // Step 6. Razoring (skipped when in check)
715 && depth < 4 * ONE_PLY
716 && eval + razor_margin[depth] <= alpha
717 && ttMove == MOVE_NONE)
719 if ( depth <= ONE_PLY
720 && eval + razor_margin[3 * ONE_PLY] <= alpha)
721 return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
723 Value ralpha = alpha - razor_margin[depth];
724 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
729 // Step 7. Futility pruning: child node (skipped when in check)
731 && depth < 7 * ONE_PLY
732 && eval - futility_margin(depth) >= beta
733 && eval < VALUE_KNOWN_WIN // Do not return unproven wins
734 && pos.non_pawn_material(pos.side_to_move()))
735 return eval - futility_margin(depth);
737 // Step 8. Null move search with verification search (is omitted in PV nodes)
739 && depth >= 2 * ONE_PLY
741 && pos.non_pawn_material(pos.side_to_move()))
743 ss->currentMove = MOVE_NULL;
745 assert(eval - beta >= 0);
747 // Null move dynamic reduction based on depth and value
748 Depth R = ((823 + 67 * depth) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
750 pos.do_null_move(st);
751 (ss+1)->skipEarlyPruning = true;
752 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
753 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
754 (ss+1)->skipEarlyPruning = false;
755 pos.undo_null_move();
757 if (nullValue >= beta)
759 // Do not return unproven mate scores
760 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
763 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
766 // Do verification search at high depths
767 ss->skipEarlyPruning = true;
768 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
769 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
770 ss->skipEarlyPruning = false;
777 // Step 9. ProbCut (skipped when in check)
778 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
779 // and a reduced search returns a value much above beta, we can (almost)
780 // safely prune the previous move.
782 && depth >= 5 * ONE_PLY
783 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
785 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
786 Depth rdepth = depth - 4 * ONE_PLY;
788 assert(rdepth >= ONE_PLY);
789 assert((ss-1)->currentMove != MOVE_NONE);
790 assert((ss-1)->currentMove != MOVE_NULL);
792 MovePicker mp(pos, ttMove, thisThread->history, PieceValue[MG][pos.captured_piece_type()]);
795 while ((move = mp.next_move()) != MOVE_NONE)
796 if (pos.legal(move, ci.pinned))
798 ss->currentMove = move;
799 pos.do_move(move, st, pos.gives_check(move, ci));
800 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
807 // Step 10. Internal iterative deepening (skipped when in check)
808 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
810 && (PvNode || ss->staticEval + 256 >= beta))
812 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
813 ss->skipEarlyPruning = true;
814 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
815 ss->skipEarlyPruning = false;
817 tte = TT.probe(posKey, ttHit);
818 ttMove = ttHit ? tte->move() : MOVE_NONE;
821 moves_loop: // When in check search starts from here
823 Square prevSq = to_sq((ss-1)->currentMove);
824 Move cm = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
825 const CounterMovesStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq];
827 MovePicker mp(pos, ttMove, depth, thisThread->history, cmh, cm, ss);
829 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
830 improving = ss->staticEval >= (ss-2)->staticEval
831 || ss->staticEval == VALUE_NONE
832 ||(ss-2)->staticEval == VALUE_NONE;
834 singularExtensionNode = !RootNode
835 && depth >= 8 * ONE_PLY
836 && ttMove != MOVE_NONE
837 /* && ttValue != VALUE_NONE Already implicit in the next condition */
838 && abs(ttValue) < VALUE_KNOWN_WIN
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())
863 Signals.firstRootMove = (moveCount == 1);
865 if (Time.elapsed() > 3000)
866 sync_cout << "info depth " << depth / ONE_PLY
867 << " currmove " << UCI::move(move, pos.is_chess960())
868 << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
872 (ss+1)->pv = nullptr;
874 extension = DEPTH_ZERO;
875 captureOrPromotion = pos.capture_or_promotion(move);
877 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
878 ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
879 : pos.gives_check(move, ci);
881 // Step 12. Extend checks
882 if (givesCheck && pos.see_sign(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
893 && pos.legal(move, ci.pinned))
895 Value rBeta = ttValue - 2 * depth / ONE_PLY;
896 ss->excludedMove = move;
897 ss->skipEarlyPruning = true;
898 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
899 ss->skipEarlyPruning = false;
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 && !captureOrPromotion
914 && !pos.advanced_pawn_push(move)
915 && bestValue > VALUE_MATED_IN_MAX_PLY)
917 // Move count based pruning
918 if ( depth < 16 * ONE_PLY
919 && moveCount >= FutilityMoveCounts[improving][depth])
922 // History based pruning
923 if ( depth <= 4 * ONE_PLY
924 && move != ss->killers[0]
925 && thisThread->history[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO
926 && cmh[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO)
929 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
931 // Futility pruning: parent node
932 if (predictedDepth < 7 * ONE_PLY)
934 futilityValue = ss->staticEval + futility_margin(predictedDepth) + 256;
936 if (futilityValue <= alpha)
938 bestValue = std::max(bestValue, futilityValue);
943 // Prune moves with negative SEE at low depths
944 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
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, ci.pinned))
954 ss->moveCount = --moveCount;
958 ss->currentMove = 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
968 && move != ss->killers[0]
969 && move != ss->killers[1])
971 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
973 // Increase reduction for cut nodes and moves with a bad history
974 if ( (!PvNode && cutNode)
975 || ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)] < VALUE_ZERO
976 && cmh[pos.piece_on(to_sq(move))][to_sq(move)] <= VALUE_ZERO))
977 ss->reduction += ONE_PLY;
979 // Decrease reduction for moves with a good history
980 if ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO
981 && cmh[pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO)
982 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
984 // Decrease reduction for moves that escape a capture
986 && type_of(move) == NORMAL
987 && type_of(pos.piece_on(to_sq(move))) != PAWN
988 && pos.see(make_move(to_sq(move), from_sq(move))) < VALUE_ZERO)
989 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
991 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
993 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
995 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
996 ss->reduction = DEPTH_ZERO;
999 doFullDepthSearch = !PvNode || moveCount > 1;
1001 // Step 16. Full depth search, when LMR is skipped or fails high
1002 if (doFullDepthSearch)
1003 value = newDepth < ONE_PLY ?
1004 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1005 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1006 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
1008 // For PV nodes only, do a full PV search on the first move or after a fail
1009 // high (in the latter case search only if value < beta), otherwise let the
1010 // parent node fail low with value <= alpha and to try another move.
1011 if (PvNode && (moveCount == 1 || (value > alpha && (RootNode || value < beta))))
1014 (ss+1)->pv[0] = MOVE_NONE;
1016 value = newDepth < ONE_PLY ?
1017 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1018 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1019 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
1022 // Step 17. Undo move
1023 pos.undo_move(move);
1025 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1027 // Step 18. Check for new best move
1028 // Finished searching the move. If a stop occurred, the return value of
1029 // the search cannot be trusted, and we return immediately without
1030 // updating best move, PV and TT.
1031 if (Signals.stop.load(std::memory_order_relaxed))
1036 RootMove& rm = *std::find(thisThread->rootMoves.begin(),
1037 thisThread->rootMoves.end(), move);
1039 // PV move or new best move ?
1040 if (moveCount == 1 || value > alpha)
1047 for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
1048 rm.pv.push_back(*m);
1050 // We record how often the best move has been changed in each
1051 // iteration. This information is used for time management: When
1052 // the best move changes frequently, we allocate some more time.
1053 if (moveCount > 1 && thisThread == Threads.main())
1057 // All other moves but the PV are set to the lowest value: this is
1058 // not a problem when sorting because the sort is stable and the
1059 // move position in the list is preserved - just the PV is pushed up.
1060 rm.score = -VALUE_INFINITE;
1063 if (value > bestValue)
1069 // If there is an easy move for this position, clear it if unstable
1071 && thisThread == Threads.main()
1072 && EasyMove.get(pos.key())
1073 && (move != EasyMove.get(pos.key()) || moveCount > 1))
1078 if (PvNode && !RootNode) // Update pv even in fail-high case
1079 update_pv(ss->pv, move, (ss+1)->pv);
1081 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1085 assert(value >= beta); // Fail high
1091 if (!captureOrPromotion && move != bestMove && quietCount < 64)
1092 quietsSearched[quietCount++] = move;
1095 // Following condition would detect a stop only after move loop has been
1096 // completed. But in this case bestValue is valid because we have fully
1097 // searched our subtree, and we can anyhow save the result in TT.
1103 // Step 20. Check for mate and stalemate
1104 // All legal moves have been searched and if there are no legal moves, it
1105 // must be mate or stalemate. If we are in a singular extension search then
1106 // return a fail low score.
1108 bestValue = excludedMove ? alpha
1109 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1111 // Quiet best move: update killers, history and countermoves
1112 else if (bestMove && !pos.capture_or_promotion(bestMove))
1113 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount);
1115 // Bonus for prior countermove that caused the fail low
1116 else if ( depth >= 3 * ONE_PLY
1119 && !pos.captured_piece_type()
1120 && is_ok((ss - 1)->currentMove)
1121 && is_ok((ss - 2)->currentMove))
1123 Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
1124 Square prevPrevSq = to_sq((ss - 2)->currentMove);
1125 CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
1126 prevCmh.update(pos.piece_on(prevSq), prevSq, bonus);
1129 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1130 bestValue >= beta ? BOUND_LOWER :
1131 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1132 depth, bestMove, ss->staticEval, TT.generation());
1134 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1140 // qsearch() is the quiescence search function, which is called by the main
1141 // search function when the remaining depth is zero (or, to be more precise,
1142 // less than ONE_PLY).
1144 template <NodeType NT, bool InCheck>
1145 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1147 const bool PvNode = NT == PV;
1149 assert(NT == PV || NT == NonPV);
1150 assert(InCheck == !!pos.checkers());
1151 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1152 assert(PvNode || (alpha == beta - 1));
1153 assert(depth <= DEPTH_ZERO);
1159 Move ttMove, move, bestMove;
1160 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1161 bool ttHit, givesCheck, evasionPrunable;
1166 oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
1168 ss->pv[0] = MOVE_NONE;
1171 ss->currentMove = bestMove = MOVE_NONE;
1172 ss->ply = (ss-1)->ply + 1;
1174 // Check for an instant draw or if the maximum ply has been reached
1175 if (pos.is_draw() || ss->ply >= MAX_PLY)
1176 return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
1177 : DrawValue[pos.side_to_move()];
1179 assert(0 <= ss->ply && ss->ply < MAX_PLY);
1181 // Decide whether or not to include checks: this fixes also the type of
1182 // TT entry depth that we are going to use. Note that in qsearch we use
1183 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1184 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1185 : DEPTH_QS_NO_CHECKS;
1187 // Transposition table lookup
1189 tte = TT.probe(posKey, ttHit);
1190 ttMove = ttHit ? tte->move() : MOVE_NONE;
1191 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
1195 && tte->depth() >= ttDepth
1196 && ttValue != VALUE_NONE // Only in case of TT access race
1197 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1198 : (tte->bound() & BOUND_UPPER)))
1200 ss->currentMove = ttMove; // Can be MOVE_NONE
1204 // Evaluate the position statically
1207 ss->staticEval = VALUE_NONE;
1208 bestValue = futilityBase = -VALUE_INFINITE;
1214 // Never assume anything on values stored in TT
1215 if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
1216 ss->staticEval = bestValue = evaluate(pos);
1218 // Can ttValue be used as a better position evaluation?
1219 if (ttValue != VALUE_NONE)
1220 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1221 bestValue = ttValue;
1224 ss->staticEval = bestValue =
1225 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
1226 : -(ss-1)->staticEval + 2 * Eval::Tempo;
1228 // Stand pat. Return immediately if static value is at least beta
1229 if (bestValue >= beta)
1232 tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1233 DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
1238 if (PvNode && bestValue > alpha)
1241 futilityBase = bestValue + 128;
1244 // Initialize a MovePicker object for the current position, and prepare
1245 // to search the moves. Because the depth is <= 0 here, only captures,
1246 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1248 MovePicker mp(pos, ttMove, depth, pos.this_thread()->history, to_sq((ss-1)->currentMove));
1251 // Loop through the moves until no moves remain or a beta cutoff occurs
1252 while ((move = mp.next_move()) != MOVE_NONE)
1254 assert(is_ok(move));
1256 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1257 ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1258 : pos.gives_check(move, ci);
1263 && futilityBase > -VALUE_KNOWN_WIN
1264 && !pos.advanced_pawn_push(move))
1266 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1268 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1270 if (futilityValue <= alpha)
1272 bestValue = std::max(bestValue, futilityValue);
1276 if (futilityBase <= alpha && pos.see(move) <= VALUE_ZERO)
1278 bestValue = std::max(bestValue, futilityBase);
1283 // Detect non-capture evasions that are candidates to be pruned
1284 evasionPrunable = InCheck
1285 && bestValue > VALUE_MATED_IN_MAX_PLY
1286 && !pos.capture(move);
1288 // Don't search moves with negative SEE values
1289 if ( (!InCheck || evasionPrunable)
1290 && type_of(move) != PROMOTION
1291 && pos.see_sign(move) < VALUE_ZERO)
1294 // Speculative prefetch as early as possible
1295 prefetch(TT.first_entry(pos.key_after(move)));
1297 // Check for legality just before making the move
1298 if (!pos.legal(move, ci.pinned))
1301 ss->currentMove = move;
1303 // Make and search the move
1304 pos.do_move(move, st, givesCheck);
1305 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1306 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1307 pos.undo_move(move);
1309 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1311 // Check for new best move
1312 if (value > bestValue)
1318 if (PvNode) // Update pv even in fail-high case
1319 update_pv(ss->pv, move, (ss+1)->pv);
1321 if (PvNode && value < beta) // Update alpha here!
1328 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1329 ttDepth, move, ss->staticEval, TT.generation());
1337 // All legal moves have been searched. A special case: If we're in check
1338 // and no legal moves were found, it is checkmate.
1339 if (InCheck && bestValue == -VALUE_INFINITE)
1340 return mated_in(ss->ply); // Plies to mate from the root
1342 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1343 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1344 ttDepth, bestMove, ss->staticEval, TT.generation());
1346 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1352 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1353 // "plies to mate from the current position". Non-mate scores are unchanged.
1354 // The function is called before storing a value in the transposition table.
1356 Value value_to_tt(Value v, int ply) {
1358 assert(v != VALUE_NONE);
1360 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1361 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1365 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1366 // from the transposition table (which refers to the plies to mate/be mated
1367 // from current position) to "plies to mate/be mated from the root".
1369 Value value_from_tt(Value v, int ply) {
1371 return v == VALUE_NONE ? VALUE_NONE
1372 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1373 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1377 // update_pv() adds current move and appends child pv[]
1379 void update_pv(Move* pv, Move move, Move* childPv) {
1381 for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
1387 // update_stats() updates killers, history, countermove and countermove
1388 // history when a new quiet best move is found.
1390 void update_stats(const Position& pos, Stack* ss, Move move,
1391 Depth depth, Move* quiets, int quietsCnt) {
1393 if (ss->killers[0] != move)
1395 ss->killers[1] = ss->killers[0];
1396 ss->killers[0] = move;
1399 Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
1401 Square prevSq = to_sq((ss-1)->currentMove);
1402 CounterMovesStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq];
1403 Thread* thisThread = pos.this_thread();
1405 thisThread->history.update(pos.moved_piece(move), to_sq(move), bonus);
1407 if (is_ok((ss-1)->currentMove))
1409 thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move);
1410 cmh.update(pos.moved_piece(move), to_sq(move), bonus);
1413 // Decrease all the other played quiet moves
1414 for (int i = 0; i < quietsCnt; ++i)
1416 thisThread->history.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1418 if (is_ok((ss-1)->currentMove))
1419 cmh.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1422 // Extra penalty for a quiet TT move in previous ply when it gets refuted
1423 if ( (ss-1)->moveCount == 1
1424 && !pos.captured_piece_type()
1425 && is_ok((ss-2)->currentMove))
1427 Square prevPrevSq = to_sq((ss-2)->currentMove);
1428 CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
1429 prevCmh.update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY);
1434 // When playing with strength handicap, choose best move among a set of RootMoves
1435 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1437 Move Skill::pick_best(size_t multiPV) {
1439 const Search::RootMoveVector& rootMoves = Threads.main()->rootMoves;
1440 static PRNG rng(now()); // PRNG sequence should be non-deterministic
1442 // RootMoves are already sorted by score in descending order
1443 Value topScore = rootMoves[0].score;
1444 int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
1445 int weakness = 120 - 2 * level;
1446 int maxScore = -VALUE_INFINITE;
1448 // Choose best move. For each move score we add two terms, both dependent on
1449 // weakness. One deterministic and bigger for weaker levels, and one random,
1450 // then we choose the move with the resulting highest score.
1451 for (size_t i = 0; i < multiPV; ++i)
1453 // This is our magic formula
1454 int push = ( weakness * int(topScore - rootMoves[i].score)
1455 + delta * (rng.rand<unsigned>() % weakness)) / 128;
1457 if (rootMoves[i].score + push > maxScore)
1459 maxScore = rootMoves[i].score + push;
1460 best = rootMoves[i].pv[0];
1468 // check_time() is used to print debug info and, more importantly, to detect
1469 // when we are out of available time and thus stop the search.
1473 static TimePoint lastInfoTime = now();
1475 int elapsed = Time.elapsed();
1476 TimePoint tick = Limits.startTime + elapsed;
1478 if (tick - lastInfoTime >= 1000)
1480 lastInfoTime = tick;
1484 // An engine may not stop pondering until told so by the GUI
1488 if (Limits.use_time_management())
1490 bool stillAtFirstMove = Signals.firstRootMove.load(std::memory_order_relaxed)
1491 && !Signals.failedLowAtRoot.load(std::memory_order_relaxed)
1492 && elapsed > Time.available() * 3 / 4;
1494 if (stillAtFirstMove || elapsed > Time.maximum() - 10)
1495 Signals.stop = true;
1497 else if (Limits.movetime && elapsed >= Limits.movetime)
1498 Signals.stop = true;
1500 else if (Limits.nodes && Threads.nodes_searched() >= Limits.nodes)
1501 Signals.stop = true;
1507 /// UCI::pv() formats PV information according to the UCI protocol. UCI requires
1508 /// that all (if any) unsearched PV lines are sent using a previous search score.
1510 string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
1512 std::stringstream ss;
1513 int elapsed = Time.elapsed() + 1;
1514 const Search::RootMoveVector& rootMoves = pos.this_thread()->rootMoves;
1515 size_t PVIdx = pos.this_thread()->PVIdx;
1516 size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
1517 uint64_t nodes_searched = Threads.nodes_searched();
1519 for (size_t i = 0; i < multiPV; ++i)
1521 bool updated = (i <= PVIdx);
1523 if (depth == ONE_PLY && !updated)
1526 Depth d = updated ? depth : depth - ONE_PLY;
1527 Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
1529 bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
1530 v = tb ? TB::Score : v;
1532 if (ss.rdbuf()->in_avail()) // Not at first line
1536 << " depth " << d / ONE_PLY
1537 << " seldepth " << pos.this_thread()->maxPly
1538 << " multipv " << i + 1
1539 << " score " << UCI::value(v);
1541 if (!tb && i == PVIdx)
1542 ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1544 ss << " nodes " << nodes_searched
1545 << " nps " << nodes_searched * 1000 / elapsed;
1547 if (elapsed > 1000) // Earlier makes little sense
1548 ss << " hashfull " << TT.hashfull();
1550 ss << " tbhits " << TB::Hits
1551 << " time " << elapsed
1554 for (Move m : rootMoves[i].pv)
1555 ss << " " << UCI::move(m, pos.is_chess960());
1562 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1563 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1564 /// first, even if the old TT entries have been overwritten.
1566 void RootMove::insert_pv_in_tt(Position& pos) {
1568 StateInfo state[MAX_PLY], *st = state;
1573 assert(MoveList<LEGAL>(pos).contains(m));
1575 TTEntry* tte = TT.probe(pos.key(), ttHit);
1577 if (!ttHit || tte->move() != m) // Don't overwrite correct entries
1578 tte->save(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE,
1579 m, VALUE_NONE, TT.generation());
1581 pos.do_move(m, *st++, pos.gives_check(m, CheckInfo(pos)));
1584 for (size_t i = pv.size(); i > 0; )
1585 pos.undo_move(pv[--i]);
1589 /// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
1590 /// before exiting the search, for instance in case we stop the search during a
1591 /// fail high at root. We try hard to have a ponder move to return to the GUI,
1592 /// otherwise in case of 'ponder on' we have nothing to think on.
1594 bool RootMove::extract_ponder_from_tt(Position& pos)
1599 assert(pv.size() == 1);
1601 pos.do_move(pv[0], st, pos.gives_check(pv[0], CheckInfo(pos)));
1602 TTEntry* tte = TT.probe(pos.key(), ttHit);
1603 pos.undo_move(pv[0]);
1607 Move m = tte->move(); // Local copy to be SMP safe
1608 if (MoveList<LEGAL>(pos).contains(m))
1609 return pv.push_back(m), true;