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 if (Options["MultiPV"] == 1 && !Skill(Options["Skill Level"]).enabled())
331 for (Thread* th : Threads)
332 if ( th->completedDepth > bestThread->completedDepth
333 && th->rootMoves[0].score > bestThread->rootMoves[0].score)
336 // Send new PV when needed.
337 // FIXME: Breaks multiPV, and skill levels
338 if (bestThread != this)
339 sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
341 sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
343 if (bestThread->rootMoves[0].pv.size() > 1 || bestThread->rootMoves[0].extract_ponder_from_tt(rootPos))
344 std::cout << " ponder " << UCI::move(bestThread->rootMoves[0].pv[1], rootPos.is_chess960());
346 std::cout << sync_endl;
350 // Thread::search() is the main iterative deepening loop. It calls search()
351 // repeatedly with increasing depth until the allocated thinking time has been
352 // consumed, user stops the search, or the maximum search depth is reached.
354 void Thread::search() {
356 Stack stack[MAX_PLY+4], *ss = stack+2; // To allow referencing (ss-2) and (ss+2)
357 Value bestValue, alpha, beta, delta;
358 Move easyMove = MOVE_NONE;
359 bool isMainThread = (this == Threads.main());
361 std::memset(ss-2, 0, 5 * sizeof(Stack));
363 bestValue = delta = alpha = -VALUE_INFINITE;
364 beta = VALUE_INFINITE;
365 completedDepth = DEPTH_ZERO;
369 easyMove = EasyMove.get(rootPos.key());
375 size_t multiPV = Options["MultiPV"];
376 Skill skill(Options["Skill Level"]);
378 // When playing with strength handicap enable MultiPV search that we will
379 // use behind the scenes to retrieve a set of possible moves.
381 multiPV = std::max(multiPV, (size_t)4);
383 multiPV = std::min(multiPV, rootMoves.size());
385 // Iterative deepening loop until requested to stop or target depth reached
386 while (++rootDepth < DEPTH_MAX && !Signals.stop && (!Limits.depth || rootDepth <= Limits.depth))
388 // Set up the new depth for the helper threads
390 rootDepth = std::min(DEPTH_MAX - ONE_PLY, Threads.main()->rootDepth + Depth(int(2.2 * log(1 + this->idx))));
392 // Age out PV variability metric
394 BestMoveChanges *= 0.5;
396 // Save the last iteration's scores before first PV line is searched and
397 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
398 for (RootMove& rm : rootMoves)
399 rm.previousScore = rm.score;
401 // MultiPV loop. We perform a full root search for each PV line
402 for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
404 // Reset aspiration window starting size
405 if (rootDepth >= 5 * ONE_PLY)
408 alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
409 beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
412 // Start with a small aspiration window and, in the case of a fail
413 // high/low, re-search with a bigger window until we're not failing
417 bestValue = ::search<Root>(rootPos, ss, alpha, beta, rootDepth, false);
419 // Bring the best move to the front. It is critical that sorting
420 // is done with a stable algorithm because all the values but the
421 // first and eventually the new best one are set to -VALUE_INFINITE
422 // and we want to keep the same order for all the moves except the
423 // new PV that goes to the front. Note that in case of MultiPV
424 // search the already searched PV lines are preserved.
425 std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
427 // Write PV back to transposition table in case the relevant
428 // entries have been overwritten during the search.
429 for (size_t i = 0; i <= PVIdx; ++i)
430 rootMoves[i].insert_pv_in_tt(rootPos);
432 // If search has been stopped break immediately. Sorting and
433 // writing PV back to TT is safe because RootMoves is still
434 // valid, although it refers to previous iteration.
438 // When failing high/low give some update (without cluttering
439 // the UI) before a re-search.
442 && (bestValue <= alpha || bestValue >= beta)
443 && Time.elapsed() > 3000)
444 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
446 // In case of failing low/high increase aspiration window and
447 // re-search, otherwise exit the loop.
448 if (bestValue <= alpha)
450 beta = (alpha + beta) / 2;
451 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
455 Signals.failedLowAtRoot = true;
456 Signals.stopOnPonderhit = false;
459 else if (bestValue >= beta)
461 alpha = (alpha + beta) / 2;
462 beta = std::min(bestValue + delta, VALUE_INFINITE);
467 delta += delta / 4 + 5;
469 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
472 // Sort the PV lines searched so far and update the GUI
473 std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
479 sync_cout << "info nodes " << Threads.nodes_searched()
480 << " time " << Time.elapsed() << sync_endl;
482 else if (PVIdx + 1 == multiPV || Time.elapsed() > 3000)
483 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
487 completedDepth = rootDepth;
492 // If skill level is enabled and time is up, pick a sub-optimal best move
493 if (skill.enabled() && skill.time_to_pick(rootDepth))
494 skill.pick_best(multiPV);
496 // Have we found a "mate in x"?
498 && bestValue >= VALUE_MATE_IN_MAX_PLY
499 && VALUE_MATE - bestValue <= 2 * Limits.mate)
502 // Do we have time for the next iteration? Can we stop searching now?
503 if (Limits.use_time_management())
505 if (!Signals.stop && !Signals.stopOnPonderhit)
507 // Take some extra time if the best move has changed
508 if (rootDepth > 4 * ONE_PLY && multiPV == 1)
509 Time.pv_instability(BestMoveChanges);
511 // Stop the search if only one legal move is available or all
512 // of the available time has been used or we matched an easyMove
513 // from the previous search and just did a fast verification.
514 if ( rootMoves.size() == 1
515 || Time.elapsed() > Time.available()
516 || ( rootMoves[0].pv[0] == easyMove
517 && BestMoveChanges < 0.03
518 && Time.elapsed() > Time.available() / 10))
520 // If we are allowed to ponder do not stop the search now but
521 // keep pondering until the GUI sends "ponderhit" or "stop".
523 Signals.stopOnPonderhit = true;
529 if (rootMoves[0].pv.size() >= 3)
530 EasyMove.update(rootPos, rootMoves[0].pv);
539 // Clear any candidate easy move that wasn't stable for the last search
540 // iterations; the second condition prevents consecutive fast moves.
541 if (EasyMove.stableCnt < 6 || Time.elapsed() < Time.available())
544 // If skill level is enabled, swap best PV line with the sub-optimal one
546 std::swap(rootMoves[0], *std::find(rootMoves.begin(),
547 rootMoves.end(), skill.best_move(multiPV)));
553 // search<>() is the main search function for both PV and non-PV nodes
555 template <NodeType NT>
556 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
558 const bool RootNode = NT == Root;
559 const bool PvNode = NT == PV || NT == Root;
561 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
562 assert(PvNode || (alpha == beta - 1));
563 assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
565 Move pv[MAX_PLY+1], quietsSearched[64];
569 Move ttMove, move, excludedMove, bestMove;
570 Depth extension, newDepth, predictedDepth;
571 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
572 bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
573 bool captureOrPromotion, doFullDepthSearch;
574 int moveCount, quietCount;
576 // Step 1. Initialize node
577 Thread* thisThread = pos.this_thread();
578 inCheck = pos.checkers();
579 moveCount = quietCount = ss->moveCount = 0;
580 bestValue = -VALUE_INFINITE;
581 ss->ply = (ss-1)->ply + 1;
583 // Check for available remaining time
584 if (thisThread->resetCalls.load(std::memory_order_relaxed))
586 thisThread->resetCalls = false;
587 thisThread->callsCnt = 0;
589 if (++thisThread->callsCnt > 4096)
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 >= 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->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
623 (ss+1)->skipEarlyPruning = false; (ss+1)->reduction = DEPTH_ZERO;
624 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
626 // Step 4. Transposition table lookup. We don't want the score of a partial
627 // search to overwrite a previous full search TT value, so we use a different
628 // position key in case of an excluded move.
629 excludedMove = ss->excludedMove;
630 posKey = excludedMove ? pos.exclusion_key() : pos.key();
631 tte = TT.probe(posKey, ttHit);
632 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
633 ss->ttMove = ttMove = RootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
634 : ttHit ? tte->move() : MOVE_NONE;
636 // At non-PV nodes we check for an early TT cutoff
639 && tte->depth() >= depth
640 && ttValue != VALUE_NONE // Possible in case of TT access race
641 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
642 : (tte->bound() & BOUND_UPPER)))
644 ss->currentMove = ttMove; // Can be MOVE_NONE
646 // If ttMove is quiet, update killers, history, counter move on TT hit
647 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove))
648 update_stats(pos, ss, ttMove, depth, nullptr, 0);
653 // Step 4a. Tablebase probe
654 if (!RootNode && TB::Cardinality)
656 int piecesCnt = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
658 if ( piecesCnt <= TB::Cardinality
659 && (piecesCnt < TB::Cardinality || depth >= TB::ProbeDepth)
660 && pos.rule50_count() == 0)
662 int found, v = Tablebases::probe_wdl(pos, &found);
668 int drawScore = TB::UseRule50 ? 1 : 0;
670 value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
671 : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply
672 : VALUE_DRAW + 2 * v * drawScore;
674 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
675 std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
676 MOVE_NONE, VALUE_NONE, TT.generation());
683 // Step 5. Evaluate the position statically
686 ss->staticEval = eval = VALUE_NONE;
692 // Never assume anything on values stored in TT
693 if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
694 eval = ss->staticEval = evaluate(pos);
696 // Can ttValue be used as a better position evaluation?
697 if (ttValue != VALUE_NONE)
698 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
703 eval = ss->staticEval =
704 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
705 : -(ss-1)->staticEval + 2 * Eval::Tempo;
707 tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
708 ss->staticEval, TT.generation());
711 if (ss->skipEarlyPruning)
714 // Step 6. Razoring (skipped when in check)
716 && depth < 4 * ONE_PLY
717 && eval + razor_margin[depth] <= alpha
718 && ttMove == MOVE_NONE)
720 if ( depth <= ONE_PLY
721 && eval + razor_margin[3 * ONE_PLY] <= alpha)
722 return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
724 Value ralpha = alpha - razor_margin[depth];
725 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
730 // Step 7. Futility pruning: child node (skipped when in check)
732 && depth < 7 * ONE_PLY
733 && eval - futility_margin(depth) >= beta
734 && eval < VALUE_KNOWN_WIN // Do not return unproven wins
735 && pos.non_pawn_material(pos.side_to_move()))
736 return eval - futility_margin(depth);
738 // Step 8. Null move search with verification search (is omitted in PV nodes)
740 && depth >= 2 * ONE_PLY
742 && pos.non_pawn_material(pos.side_to_move()))
744 ss->currentMove = MOVE_NULL;
746 assert(eval - beta >= 0);
748 // Null move dynamic reduction based on depth and value
749 Depth R = ((823 + 67 * depth) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
751 pos.do_null_move(st);
752 (ss+1)->skipEarlyPruning = true;
753 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
754 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
755 (ss+1)->skipEarlyPruning = false;
756 pos.undo_null_move();
758 if (nullValue >= beta)
760 // Do not return unproven mate scores
761 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
764 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
767 // Do verification search at high depths
768 ss->skipEarlyPruning = true;
769 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
770 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
771 ss->skipEarlyPruning = false;
778 // Step 9. ProbCut (skipped when in check)
779 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
780 // and a reduced search returns a value much above beta, we can (almost)
781 // safely prune the previous move.
783 && depth >= 5 * ONE_PLY
784 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
786 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
787 Depth rdepth = depth - 4 * ONE_PLY;
789 assert(rdepth >= ONE_PLY);
790 assert((ss-1)->currentMove != MOVE_NONE);
791 assert((ss-1)->currentMove != MOVE_NULL);
793 MovePicker mp(pos, ttMove, thisThread->history, PieceValue[MG][pos.captured_piece_type()]);
796 while ((move = mp.next_move()) != MOVE_NONE)
797 if (pos.legal(move, ci.pinned))
799 ss->currentMove = move;
800 pos.do_move(move, st, pos.gives_check(move, ci));
801 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
808 // Step 10. Internal iterative deepening (skipped when in check)
809 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
811 && (PvNode || ss->staticEval + 256 >= beta))
813 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
814 ss->skipEarlyPruning = true;
815 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
816 ss->skipEarlyPruning = false;
818 tte = TT.probe(posKey, ttHit);
819 ttMove = ttHit ? tte->move() : MOVE_NONE;
822 moves_loop: // When in check search starts from here
824 Square prevSq = to_sq((ss-1)->currentMove);
825 Move cm = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
826 const CounterMovesStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq];
828 MovePicker mp(pos, ttMove, depth, thisThread->history, cmh, cm, ss);
830 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
831 improving = ss->staticEval >= (ss-2)->staticEval
832 || ss->staticEval == VALUE_NONE
833 ||(ss-2)->staticEval == VALUE_NONE;
835 singularExtensionNode = !RootNode
836 && depth >= 8 * ONE_PLY
837 && ttMove != MOVE_NONE
838 /* && ttValue != VALUE_NONE Already implicit in the next condition */
839 && abs(ttValue) < VALUE_KNOWN_WIN
840 && !excludedMove // Recursive singular search is not allowed
841 && (tte->bound() & BOUND_LOWER)
842 && tte->depth() >= depth - 3 * ONE_PLY;
844 // Step 11. Loop through moves
845 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
846 while ((move = mp.next_move()) != MOVE_NONE)
850 if (move == excludedMove)
853 // At root obey the "searchmoves" option and skip moves not listed in Root
854 // Move List. As a consequence any illegal move is also skipped. In MultiPV
855 // mode we also skip PV moves which have been already searched.
856 if (RootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
857 thisThread->rootMoves.end(), move))
860 ss->moveCount = ++moveCount;
862 if (RootNode && thisThread == Threads.main())
864 Signals.firstRootMove = (moveCount == 1);
866 if (Time.elapsed() > 3000)
867 sync_cout << "info depth " << depth / ONE_PLY
868 << " currmove " << UCI::move(move, pos.is_chess960())
869 << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
873 (ss+1)->pv = nullptr;
875 extension = DEPTH_ZERO;
876 captureOrPromotion = pos.capture_or_promotion(move);
878 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
879 ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
880 : pos.gives_check(move, ci);
882 // Step 12. Extend checks
883 if (givesCheck && pos.see_sign(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
894 && pos.legal(move, ci.pinned))
896 Value rBeta = ttValue - 2 * depth / ONE_PLY;
897 ss->excludedMove = move;
898 ss->skipEarlyPruning = true;
899 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
900 ss->skipEarlyPruning = false;
901 ss->excludedMove = MOVE_NONE;
907 // Update the current move (this must be done after singular extension search)
908 newDepth = depth - ONE_PLY + extension;
910 // Step 13. Pruning at shallow depth
912 && !captureOrPromotion
915 && !pos.advanced_pawn_push(move)
916 && bestValue > VALUE_MATED_IN_MAX_PLY)
918 // Move count based pruning
919 if ( depth < 16 * ONE_PLY
920 && moveCount >= FutilityMoveCounts[improving][depth])
923 // History based pruning
924 if ( depth <= 4 * ONE_PLY
925 && move != ss->killers[0]
926 && thisThread->history[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO
927 && cmh[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO)
930 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
932 // Futility pruning: parent node
933 if (predictedDepth < 7 * ONE_PLY)
935 futilityValue = ss->staticEval + futility_margin(predictedDepth) + 256;
937 if (futilityValue <= alpha)
939 bestValue = std::max(bestValue, futilityValue);
944 // Prune moves with negative SEE at low depths
945 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
949 // Speculative prefetch as early as possible
950 prefetch(TT.first_entry(pos.key_after(move)));
952 // Check for legality just before making the move
953 if (!RootNode && !pos.legal(move, ci.pinned))
955 ss->moveCount = --moveCount;
959 ss->currentMove = 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
969 && move != ss->killers[0]
970 && move != ss->killers[1])
972 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
974 // Increase reduction for cut nodes and moves with a bad history
975 if ( (!PvNode && cutNode)
976 || ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)] < VALUE_ZERO
977 && cmh[pos.piece_on(to_sq(move))][to_sq(move)] <= VALUE_ZERO))
978 ss->reduction += ONE_PLY;
980 // Decrease reduction for moves with a good history
981 if ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO
982 && cmh[pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO)
983 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
985 // Decrease reduction for moves that escape a capture
987 && type_of(move) == NORMAL
988 && type_of(pos.piece_on(to_sq(move))) != PAWN
989 && pos.see(make_move(to_sq(move), from_sq(move))) < VALUE_ZERO)
990 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
992 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
994 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
996 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
997 ss->reduction = DEPTH_ZERO;
1000 doFullDepthSearch = !PvNode || moveCount > 1;
1002 // Step 16. Full depth search, when LMR is skipped or fails high
1003 if (doFullDepthSearch)
1004 value = newDepth < ONE_PLY ?
1005 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1006 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1007 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
1009 // For PV nodes only, do a full PV search on the first move or after a fail
1010 // high (in the latter case search only if value < beta), otherwise let the
1011 // parent node fail low with value <= alpha and to try another move.
1012 if (PvNode && (moveCount == 1 || (value > alpha && (RootNode || value < beta))))
1015 (ss+1)->pv[0] = MOVE_NONE;
1017 value = newDepth < ONE_PLY ?
1018 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1019 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1020 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
1023 // Step 17. Undo move
1024 pos.undo_move(move);
1026 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1028 // Step 18. Check for new best move
1029 // Finished searching the move. If a stop occurred, the return value of
1030 // the search cannot be trusted, and we return immediately without
1031 // updating best move, PV and TT.
1032 if (Signals.stop.load(std::memory_order_relaxed))
1037 RootMove& rm = *std::find(thisThread->rootMoves.begin(),
1038 thisThread->rootMoves.end(), move);
1040 // PV move or new best move ?
1041 if (moveCount == 1 || value > alpha)
1048 for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
1049 rm.pv.push_back(*m);
1051 // We record how often the best move has been changed in each
1052 // iteration. This information is used for time management: When
1053 // the best move changes frequently, we allocate some more time.
1054 if (moveCount > 1 && thisThread == Threads.main())
1058 // All other moves but the PV are set to the lowest value: this is
1059 // not a problem when sorting because the sort is stable and the
1060 // move position in the list is preserved - just the PV is pushed up.
1061 rm.score = -VALUE_INFINITE;
1064 if (value > bestValue)
1070 // If there is an easy move for this position, clear it if unstable
1072 && thisThread == Threads.main()
1073 && EasyMove.get(pos.key())
1074 && (move != EasyMove.get(pos.key()) || moveCount > 1))
1079 if (PvNode && !RootNode) // Update pv even in fail-high case
1080 update_pv(ss->pv, move, (ss+1)->pv);
1082 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1086 assert(value >= beta); // Fail high
1092 if (!captureOrPromotion && move != bestMove && quietCount < 64)
1093 quietsSearched[quietCount++] = move;
1096 // Following condition would detect a stop only after move loop has been
1097 // completed. But in this case bestValue is valid because we have fully
1098 // searched our subtree, and we can anyhow save the result in TT.
1104 // Step 20. Check for mate and stalemate
1105 // All legal moves have been searched and if there are no legal moves, it
1106 // must be mate or stalemate. If we are in a singular extension search then
1107 // return a fail low score.
1109 bestValue = excludedMove ? alpha
1110 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1112 // Quiet best move: update killers, history and countermoves
1113 else if (bestMove && !pos.capture_or_promotion(bestMove))
1114 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount);
1116 // Bonus for prior countermove that caused the fail low
1117 else if ( depth >= 3 * ONE_PLY
1120 && !pos.captured_piece_type()
1121 && is_ok((ss - 1)->currentMove)
1122 && is_ok((ss - 2)->currentMove))
1124 Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
1125 Square prevPrevSq = to_sq((ss - 2)->currentMove);
1126 CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
1127 prevCmh.update(pos.piece_on(prevSq), prevSq, bonus);
1130 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1131 bestValue >= beta ? BOUND_LOWER :
1132 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1133 depth, bestMove, ss->staticEval, TT.generation());
1135 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1141 // qsearch() is the quiescence search function, which is called by the main
1142 // search function when the remaining depth is zero (or, to be more precise,
1143 // less than ONE_PLY).
1145 template <NodeType NT, bool InCheck>
1146 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1148 const bool PvNode = NT == PV;
1150 assert(NT == PV || NT == NonPV);
1151 assert(InCheck == !!pos.checkers());
1152 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1153 assert(PvNode || (alpha == beta - 1));
1154 assert(depth <= DEPTH_ZERO);
1160 Move ttMove, move, bestMove;
1161 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1162 bool ttHit, givesCheck, evasionPrunable;
1167 oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
1169 ss->pv[0] = MOVE_NONE;
1172 ss->currentMove = bestMove = MOVE_NONE;
1173 ss->ply = (ss-1)->ply + 1;
1175 // Check for an instant draw or if the maximum ply has been reached
1176 if (pos.is_draw() || ss->ply >= MAX_PLY)
1177 return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
1178 : DrawValue[pos.side_to_move()];
1180 assert(0 <= ss->ply && ss->ply < MAX_PLY);
1182 // Decide whether or not to include checks: this fixes also the type of
1183 // TT entry depth that we are going to use. Note that in qsearch we use
1184 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1185 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1186 : DEPTH_QS_NO_CHECKS;
1188 // Transposition table lookup
1190 tte = TT.probe(posKey, ttHit);
1191 ttMove = ttHit ? tte->move() : MOVE_NONE;
1192 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
1196 && tte->depth() >= ttDepth
1197 && ttValue != VALUE_NONE // Only in case of TT access race
1198 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1199 : (tte->bound() & BOUND_UPPER)))
1201 ss->currentMove = ttMove; // Can be MOVE_NONE
1205 // Evaluate the position statically
1208 ss->staticEval = VALUE_NONE;
1209 bestValue = futilityBase = -VALUE_INFINITE;
1215 // Never assume anything on values stored in TT
1216 if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
1217 ss->staticEval = bestValue = evaluate(pos);
1219 // Can ttValue be used as a better position evaluation?
1220 if (ttValue != VALUE_NONE)
1221 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1222 bestValue = ttValue;
1225 ss->staticEval = bestValue =
1226 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
1227 : -(ss-1)->staticEval + 2 * Eval::Tempo;
1229 // Stand pat. Return immediately if static value is at least beta
1230 if (bestValue >= beta)
1233 tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1234 DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
1239 if (PvNode && bestValue > alpha)
1242 futilityBase = bestValue + 128;
1245 // Initialize a MovePicker object for the current position, and prepare
1246 // to search the moves. Because the depth is <= 0 here, only captures,
1247 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1249 MovePicker mp(pos, ttMove, depth, pos.this_thread()->history, 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 && !ci.dcCandidates
1258 ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1259 : pos.gives_check(move, ci);
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(move) <= VALUE_ZERO)
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_sign(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, ci.pinned))
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 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_stats() updates killers, history, countermove and countermove
1389 // history when a new quiet best move is found.
1391 void update_stats(const Position& pos, Stack* ss, Move move,
1392 Depth depth, Move* quiets, int quietsCnt) {
1394 if (ss->killers[0] != move)
1396 ss->killers[1] = ss->killers[0];
1397 ss->killers[0] = move;
1400 Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
1402 Square prevSq = to_sq((ss-1)->currentMove);
1403 CounterMovesStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq];
1404 Thread* thisThread = pos.this_thread();
1406 thisThread->history.update(pos.moved_piece(move), to_sq(move), bonus);
1408 if (is_ok((ss-1)->currentMove))
1410 thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move);
1411 cmh.update(pos.moved_piece(move), to_sq(move), bonus);
1414 // Decrease all the other played quiet moves
1415 for (int i = 0; i < quietsCnt; ++i)
1417 thisThread->history.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1419 if (is_ok((ss-1)->currentMove))
1420 cmh.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1423 // Extra penalty for a quiet TT move in previous ply when it gets refuted
1424 if ( (ss-1)->moveCount == 1
1425 && !pos.captured_piece_type()
1426 && is_ok((ss-2)->currentMove))
1428 Square prevPrevSq = to_sq((ss-2)->currentMove);
1429 CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
1430 prevCmh.update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY);
1435 // When playing with strength handicap, choose best move among a set of RootMoves
1436 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1438 Move Skill::pick_best(size_t multiPV) {
1440 const Search::RootMoveVector& rootMoves = Threads.main()->rootMoves;
1441 static PRNG rng(now()); // PRNG sequence should be non-deterministic
1443 // RootMoves are already sorted by score in descending order
1444 Value topScore = rootMoves[0].score;
1445 int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
1446 int weakness = 120 - 2 * level;
1447 int maxScore = -VALUE_INFINITE;
1449 // Choose best move. For each move score we add two terms, both dependent on
1450 // weakness. One deterministic and bigger for weaker levels, and one random,
1451 // then we choose the move with the resulting highest score.
1452 for (size_t i = 0; i < multiPV; ++i)
1454 // This is our magic formula
1455 int push = ( weakness * int(topScore - rootMoves[i].score)
1456 + delta * (rng.rand<unsigned>() % weakness)) / 128;
1458 if (rootMoves[i].score + push > maxScore)
1460 maxScore = rootMoves[i].score + push;
1461 best = rootMoves[i].pv[0];
1469 // check_time() is used to print debug info and, more importantly, to detect
1470 // when we are out of available time and thus stop the search.
1474 static TimePoint lastInfoTime = now();
1476 int elapsed = Time.elapsed();
1477 TimePoint tick = Limits.startTime + elapsed;
1479 if (tick - lastInfoTime >= 1000)
1481 lastInfoTime = tick;
1485 // An engine may not stop pondering until told so by the GUI
1489 if (Limits.use_time_management())
1491 bool stillAtFirstMove = Signals.firstRootMove.load(std::memory_order_relaxed)
1492 && !Signals.failedLowAtRoot.load(std::memory_order_relaxed)
1493 && elapsed > Time.available() * 3 / 4;
1495 if (stillAtFirstMove || elapsed > Time.maximum() - 10)
1496 Signals.stop = true;
1498 else if (Limits.movetime && elapsed >= Limits.movetime)
1499 Signals.stop = true;
1501 else if (Limits.nodes && Threads.nodes_searched() >= Limits.nodes)
1502 Signals.stop = true;
1508 /// UCI::pv() formats PV information according to the UCI protocol. UCI requires
1509 /// that all (if any) unsearched PV lines are sent using a previous search score.
1511 string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
1513 std::stringstream ss;
1514 int elapsed = Time.elapsed() + 1;
1515 const Search::RootMoveVector& rootMoves = pos.this_thread()->rootMoves;
1516 size_t PVIdx = pos.this_thread()->PVIdx;
1517 size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
1518 uint64_t nodes_searched = Threads.nodes_searched();
1520 for (size_t i = 0; i < multiPV; ++i)
1522 bool updated = (i <= PVIdx);
1524 if (depth == ONE_PLY && !updated)
1527 Depth d = updated ? depth : depth - ONE_PLY;
1528 Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
1530 bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
1531 v = tb ? TB::Score : v;
1533 if (ss.rdbuf()->in_avail()) // Not at first line
1537 << " depth " << d / ONE_PLY
1538 << " seldepth " << pos.this_thread()->maxPly
1539 << " multipv " << i + 1
1540 << " score " << UCI::value(v);
1542 if (!tb && i == PVIdx)
1543 ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1545 ss << " nodes " << nodes_searched
1546 << " nps " << nodes_searched * 1000 / elapsed;
1548 if (elapsed > 1000) // Earlier makes little sense
1549 ss << " hashfull " << TT.hashfull();
1551 ss << " tbhits " << TB::Hits
1552 << " time " << elapsed
1555 for (Move m : rootMoves[i].pv)
1556 ss << " " << UCI::move(m, pos.is_chess960());
1563 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1564 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1565 /// first, even if the old TT entries have been overwritten.
1567 void RootMove::insert_pv_in_tt(Position& pos) {
1569 StateInfo state[MAX_PLY], *st = state;
1574 assert(MoveList<LEGAL>(pos).contains(m));
1576 TTEntry* tte = TT.probe(pos.key(), ttHit);
1578 if (!ttHit || tte->move() != m) // Don't overwrite correct entries
1579 tte->save(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE,
1580 m, VALUE_NONE, TT.generation());
1582 pos.do_move(m, *st++, pos.gives_check(m, CheckInfo(pos)));
1585 for (size_t i = pv.size(); i > 0; )
1586 pos.undo_move(pv[--i]);
1590 /// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
1591 /// before exiting the search, for instance in case we stop the search during a
1592 /// fail high at root. We try hard to have a ponder move to return to the GUI,
1593 /// otherwise in case of 'ponder on' we have nothing to think on.
1595 bool RootMove::extract_ponder_from_tt(Position& pos)
1600 assert(pv.size() == 1);
1602 pos.do_move(pv[0], st, pos.gives_check(pv[0], CheckInfo(pos)));
1603 TTEntry* tte = TT.probe(pos.key(), ttHit);
1604 pos.undo_move(pv[0]);
1608 Move m = tte->move(); // Local copy to be SMP safe
1609 if (MoveList<LEGAL>(pos).contains(m))
1610 return pv.push_back(m), true;