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"
40 volatile SignalsType Signals;
42 RootMoveVector RootMoves;
44 StateStackPtr SetupStates;
47 namespace Tablebases {
57 namespace TB = Tablebases;
61 using namespace Search;
65 // Different node types, used as template parameter
66 enum NodeType { Root, PV, NonPV };
68 // Razoring and futility margin based on depth
69 Value razor_margin(Depth d) { return Value(512 + 32 * d); }
70 Value futility_margin(Depth d) { return Value(200 * d); }
72 // Futility and reductions lookup tables, initialized at startup
73 int FutilityMoveCounts[2][16]; // [improving][depth]
74 Depth Reductions[2][2][64][64]; // [pv][improving][depth][moveNumber]
76 template <bool PvNode> Depth reduction(bool i, Depth d, int mn) {
77 return Reductions[PvNode][i][std::min(d, 63 * ONE_PLY)][std::min(mn, 63)];
80 // Skill struct is used to implement strength limiting
82 Skill(int l) : level(l) {}
83 bool enabled() const { return level < 20; }
84 bool time_to_pick(Depth depth) const { return depth / ONE_PLY == 1 + level; }
85 Move best_move(size_t multiPV) { return best ? best : pick_best(multiPV); }
86 Move pick_best(size_t multiPV);
89 Move best = MOVE_NONE;
92 // EasyMoveManager struct is used to detect a so called 'easy move'; when PV is
93 // stable across multiple search iterations we can fast return the best move.
94 struct EasyMoveManager {
99 pv[0] = pv[1] = pv[2] = MOVE_NONE;
102 Move get(Key key) const {
103 return expectedPosKey == key ? pv[2] : MOVE_NONE;
106 void update(Position& pos, const std::vector<Move>& newPv) {
108 assert(newPv.size() >= 3);
110 // Keep track of how many times in a row 3rd ply remains stable
111 stableCnt = (newPv[2] == pv[2]) ? stableCnt + 1 : 0;
113 if (!std::equal(newPv.begin(), newPv.begin() + 3, pv))
115 std::copy(newPv.begin(), newPv.begin() + 3, pv);
118 pos.do_move(newPv[0], st[0], pos.gives_check(newPv[0], CheckInfo(pos)));
119 pos.do_move(newPv[1], st[1], pos.gives_check(newPv[1], CheckInfo(pos)));
120 expectedPosKey = pos.key();
121 pos.undo_move(newPv[1]);
122 pos.undo_move(newPv[0]);
132 EasyMoveManager EasyMove;
133 double BestMoveChanges;
134 Value DrawValue[COLOR_NB];
135 HistoryStats History;
136 CounterMovesHistoryStats CounterMovesHistory;
137 MovesStats Countermoves;
139 template <NodeType NT, bool SpNode>
140 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
142 template <NodeType NT, bool InCheck>
143 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
145 void id_loop(Position& pos);
146 Value value_to_tt(Value v, int ply);
147 Value value_from_tt(Value v, int ply);
148 void update_pv(Move* pv, Move move, Move* childPv);
149 void update_stats(const Position& pos, Stack* ss, Move move, Depth depth, Move* quiets, int quietsCnt);
154 /// Search::init() is called during startup to initialize various lookup tables
156 void Search::init() {
158 const double K[][2] = {{ 0.83, 2.25 }, { 0.50, 3.00 }};
160 for (int pv = 0; pv <= 1; ++pv)
161 for (int imp = 0; imp <= 1; ++imp)
162 for (int d = 1; d < 64; ++d)
163 for (int mc = 1; mc < 64; ++mc)
165 double r = K[pv][0] + log(d) * log(mc) / K[pv][1];
168 Reductions[pv][imp][d][mc] = int(r) * ONE_PLY;
170 // Increase reduction when eval is not improving
171 if (!pv && !imp && Reductions[pv][imp][d][mc] >= 2 * ONE_PLY)
172 Reductions[pv][imp][d][mc] += ONE_PLY;
175 for (int d = 0; d < 16; ++d)
177 FutilityMoveCounts[0][d] = int(2.4 + 0.773 * pow(d + 0.00, 1.8));
178 FutilityMoveCounts[1][d] = int(2.9 + 1.045 * pow(d + 0.49, 1.8));
183 /// Search::reset() clears all search memory, to obtain reproducible search results
185 void Search::reset () {
189 CounterMovesHistory.clear();
190 Countermoves.clear();
194 /// Search::perft() is our utility to verify move generation. All the leaf nodes
195 /// up to the given depth are generated and counted and the sum returned.
197 uint64_t Search::perft(Position& pos, Depth depth) {
200 uint64_t cnt, nodes = 0;
202 const bool leaf = (depth == 2 * ONE_PLY);
204 for (const auto& m : MoveList<LEGAL>(pos))
206 if (Root && depth <= ONE_PLY)
210 pos.do_move(m, st, pos.gives_check(m, ci));
211 cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
216 sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
221 template uint64_t Search::perft<true>(Position& pos, Depth depth);
224 /// Search::think() is the external interface to Stockfish's search, and is
225 /// called by the main thread when the program receives the UCI 'go' command. It
226 /// searches from RootPos and at the end prints the "bestmove" to output.
228 void Search::think() {
230 Color us = RootPos.side_to_move();
231 Time.init(Limits, us, RootPos.game_ply(), now());
233 int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
234 DrawValue[ us] = VALUE_DRAW - Value(contempt);
235 DrawValue[~us] = VALUE_DRAW + Value(contempt);
238 TB::RootInTB = false;
239 TB::UseRule50 = Options["Syzygy50MoveRule"];
240 TB::ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
241 TB::Cardinality = Options["SyzygyProbeLimit"];
243 // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
244 if (TB::Cardinality > TB::MaxCardinality)
246 TB::Cardinality = TB::MaxCardinality;
247 TB::ProbeDepth = DEPTH_ZERO;
250 if (RootMoves.empty())
252 RootMoves.push_back(RootMove(MOVE_NONE));
253 sync_cout << "info depth 0 score "
254 << UCI::value(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
259 if (TB::Cardinality >= RootPos.count<ALL_PIECES>(WHITE)
260 + RootPos.count<ALL_PIECES>(BLACK))
262 // If the current root position is in the tablebases then RootMoves
263 // contains only moves that preserve the draw or win.
264 TB::RootInTB = Tablebases::root_probe(RootPos, RootMoves, TB::Score);
267 TB::Cardinality = 0; // Do not probe tablebases during the search
269 else // If DTZ tables are missing, use WDL tables as a fallback
271 // Filter out moves that do not preserve a draw or win
272 TB::RootInTB = Tablebases::root_probe_wdl(RootPos, RootMoves, TB::Score);
274 // Only probe during search if winning
275 if (TB::Score <= VALUE_DRAW)
281 TB::Hits = RootMoves.size();
284 TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
285 : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1
290 for (Thread* th : Threads)
293 th->notify_one(); // Wake up all the threads
296 Threads.timer->run = true;
297 Threads.timer->notify_one(); // Start the recurring timer
299 id_loop(RootPos); // Let's start searching !
301 Threads.timer->run = false;
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] - RootPos.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;
317 RootPos.this_thread()->wait_for(Signals.stop);
320 sync_cout << "bestmove " << UCI::move(RootMoves[0].pv[0], RootPos.is_chess960());
322 if (RootMoves[0].pv.size() > 1 || RootMoves[0].extract_ponder_from_tt(RootPos))
323 std::cout << " ponder " << UCI::move(RootMoves[0].pv[1], RootPos.is_chess960());
325 std::cout << sync_endl;
331 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
332 // with increasing depth until the allocated thinking time has been consumed,
333 // user stops the search, or the maximum search depth is reached.
335 void id_loop(Position& pos) {
337 Stack stack[MAX_PLY+4], *ss = stack+2; // To allow referencing (ss-2) and (ss+2)
339 Value bestValue, alpha, beta, delta;
341 Move easyMove = EasyMove.get(pos.key());
344 std::memset(ss-2, 0, 5 * sizeof(Stack));
348 bestValue = delta = alpha = -VALUE_INFINITE;
349 beta = VALUE_INFINITE;
353 size_t multiPV = Options["MultiPV"];
354 Skill skill(Options["Skill Level"]);
356 // When playing with strength handicap enable MultiPV search that we will
357 // use behind the scenes to retrieve a set of possible moves.
359 multiPV = std::max(multiPV, (size_t)4);
361 multiPV = std::min(multiPV, RootMoves.size());
363 // Iterative deepening loop until requested to stop or target depth reached
364 while (++depth < DEPTH_MAX && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
366 // Age out PV variability metric
367 BestMoveChanges *= 0.5;
369 // Save the last iteration's scores before first PV line is searched and
370 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
371 for (RootMove& rm : RootMoves)
372 rm.previousScore = rm.score;
374 // MultiPV loop. We perform a full root search for each PV line
375 for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
377 // Reset aspiration window starting size
378 if (depth >= 5 * ONE_PLY)
381 alpha = std::max(RootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
382 beta = std::min(RootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
385 // Start with a small aspiration window and, in the case of a fail
386 // high/low, re-search with a bigger window until we're not failing
390 bestValue = search<Root, false>(pos, ss, alpha, beta, depth, false);
392 // Bring the best move to the front. It is critical that sorting
393 // is done with a stable algorithm because all the values but the
394 // first and eventually the new best one are set to -VALUE_INFINITE
395 // and we want to keep the same order for all the moves except the
396 // new PV that goes to the front. Note that in case of MultiPV
397 // search the already searched PV lines are preserved.
398 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
400 // Write PV back to transposition table in case the relevant
401 // entries have been overwritten during the search.
402 for (size_t i = 0; i <= PVIdx; ++i)
403 RootMoves[i].insert_pv_in_tt(pos);
405 // If search has been stopped break immediately. Sorting and
406 // writing PV back to TT is safe because RootMoves is still
407 // valid, although it refers to previous iteration.
411 // When failing high/low give some update (without cluttering
412 // the UI) before a re-search.
414 && (bestValue <= alpha || bestValue >= beta)
415 && Time.elapsed() > 3000)
416 sync_cout << UCI::pv(pos, depth, alpha, beta) << sync_endl;
418 // In case of failing low/high increase aspiration window and
419 // re-search, otherwise exit the loop.
420 if (bestValue <= alpha)
422 beta = (alpha + beta) / 2;
423 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
425 Signals.failedLowAtRoot = true;
426 Signals.stopOnPonderhit = false;
428 else if (bestValue >= beta)
430 alpha = (alpha + beta) / 2;
431 beta = std::min(bestValue + delta, VALUE_INFINITE);
438 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
441 // Sort the PV lines searched so far and update the GUI
442 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
445 sync_cout << "info nodes " << RootPos.nodes_searched()
446 << " time " << Time.elapsed() << sync_endl;
448 else if (PVIdx + 1 == multiPV || Time.elapsed() > 3000)
449 sync_cout << UCI::pv(pos, depth, alpha, beta) << sync_endl;
452 // If skill level is enabled and time is up, pick a sub-optimal best move
453 if (skill.enabled() && skill.time_to_pick(depth))
454 skill.pick_best(multiPV);
456 // Have we found a "mate in x"?
458 && bestValue >= VALUE_MATE_IN_MAX_PLY
459 && VALUE_MATE - bestValue <= 2 * Limits.mate)
462 // Do we have time for the next iteration? Can we stop searching now?
463 if (Limits.use_time_management())
465 if (!Signals.stop && !Signals.stopOnPonderhit)
467 // Take some extra time if the best move has changed
468 if (depth > 4 * ONE_PLY && multiPV == 1)
469 Time.pv_instability(BestMoveChanges);
471 // Stop the search if only one legal move is available or all
472 // of the available time has been used or we matched an easyMove
473 // from the previous search and just did a fast verification.
474 if ( RootMoves.size() == 1
475 || Time.elapsed() > Time.available()
476 || ( RootMoves[0].pv[0] == easyMove
477 && BestMoveChanges < 0.03
478 && Time.elapsed() > Time.available() / 10))
480 // If we are allowed to ponder do not stop the search now but
481 // keep pondering until the GUI sends "ponderhit" or "stop".
483 Signals.stopOnPonderhit = true;
489 if (RootMoves[0].pv.size() >= 3)
490 EasyMove.update(pos, RootMoves[0].pv);
496 // Clear any candidate easy move that wasn't stable for the last search
497 // iterations; the second condition prevents consecutive fast moves.
498 if (EasyMove.stableCnt < 6 || Time.elapsed() < Time.available())
501 // If skill level is enabled, swap best PV line with the sub-optimal one
503 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
504 RootMoves.end(), skill.best_move(multiPV)));
508 // search<>() is the main search function for both PV and non-PV nodes and for
509 // normal and SplitPoint nodes. When called just after a split point the search
510 // is simpler because we have already probed the hash table, done a null move
511 // search, and searched the first move before splitting, so we don't have to
512 // repeat all this work again. We also don't need to store anything to the hash
513 // table here: This is taken care of after we return from the split point.
515 template <NodeType NT, bool SpNode>
516 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
518 const bool RootNode = NT == Root;
519 const bool PvNode = NT == PV || NT == Root;
521 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
522 assert(PvNode || (alpha == beta - 1));
523 assert(depth > DEPTH_ZERO);
525 Move pv[MAX_PLY+1], quietsSearched[64];
528 SplitPoint* splitPoint;
530 Move ttMove, move, excludedMove, bestMove;
531 Depth extension, newDepth, predictedDepth;
532 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
533 bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
534 bool captureOrPromotion, dangerous, doFullDepthSearch;
535 int moveCount, quietCount;
537 // Step 1. Initialize node
538 Thread* thisThread = pos.this_thread();
539 inCheck = pos.checkers();
543 splitPoint = ss->splitPoint;
544 bestMove = splitPoint->bestMove;
545 bestValue = splitPoint->bestValue;
548 ttMove = excludedMove = MOVE_NONE;
549 ttValue = VALUE_NONE;
551 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
556 moveCount = quietCount = 0;
557 bestValue = -VALUE_INFINITE;
558 ss->ply = (ss-1)->ply + 1;
560 // Used to send selDepth info to GUI
561 if (PvNode && thisThread->maxPly < ss->ply)
562 thisThread->maxPly = ss->ply;
566 // Step 2. Check for aborted search and immediate draw
567 if (Signals.stop || pos.is_draw() || ss->ply >= MAX_PLY)
568 return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
570 // Step 3. Mate distance pruning. Even if we mate at the next move our score
571 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
572 // a shorter mate was found upward in the tree then there is no need to search
573 // because we will never beat the current alpha. Same logic but with reversed
574 // signs applies also in the opposite condition of being mated instead of giving
575 // mate. In this case return a fail-high score.
576 alpha = std::max(mated_in(ss->ply), alpha);
577 beta = std::min(mate_in(ss->ply+1), beta);
582 assert(0 <= ss->ply && ss->ply < MAX_PLY);
584 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
585 (ss+1)->skipEarlyPruning = false; (ss+1)->reduction = DEPTH_ZERO;
586 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
588 // Step 4. Transposition table lookup
589 // We don't want the score of a partial search to overwrite a previous full search
590 // TT value, so we use a different position key in case of an excluded move.
591 excludedMove = ss->excludedMove;
592 posKey = excludedMove ? pos.exclusion_key() : pos.key();
593 tte = TT.probe(posKey, ttHit);
594 ss->ttMove = ttMove = RootNode ? RootMoves[PVIdx].pv[0] : ttHit ? tte->move() : MOVE_NONE;
595 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
597 // At non-PV nodes we check for a fail high/low. We don't prune at PV nodes
600 && tte->depth() >= depth
601 && ttValue != VALUE_NONE // Only in case of TT access race
602 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
603 : (tte->bound() & BOUND_UPPER)))
605 ss->currentMove = ttMove; // Can be MOVE_NONE
607 // If ttMove is quiet, update killers, history, counter move on TT hit
608 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove))
609 update_stats(pos, ss, ttMove, depth, nullptr, 0);
614 // Step 4a. Tablebase probe
615 if (!RootNode && TB::Cardinality)
617 int piecesCnt = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
619 if ( piecesCnt <= TB::Cardinality
620 && (piecesCnt < TB::Cardinality || depth >= TB::ProbeDepth)
621 && pos.rule50_count() == 0)
623 int found, v = Tablebases::probe_wdl(pos, &found);
629 int drawScore = TB::UseRule50 ? 1 : 0;
631 value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
632 : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply
633 : VALUE_DRAW + 2 * v * drawScore;
635 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
636 std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
637 MOVE_NONE, VALUE_NONE, TT.generation());
644 // Step 5. Evaluate the position statically
647 ss->staticEval = eval = VALUE_NONE;
653 // Never assume anything on values stored in TT
654 if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
655 eval = ss->staticEval = evaluate(pos);
657 // Can ttValue be used as a better position evaluation?
658 if (ttValue != VALUE_NONE)
659 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
664 eval = ss->staticEval =
665 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo;
667 tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
670 if (ss->skipEarlyPruning)
673 // Step 6. Razoring (skipped when in check)
675 && depth < 4 * ONE_PLY
676 && eval + razor_margin(depth) <= alpha
677 && ttMove == MOVE_NONE
678 && !pos.pawn_on_7th(pos.side_to_move()))
680 if ( depth <= ONE_PLY
681 && eval + razor_margin(3 * ONE_PLY) <= alpha)
682 return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
684 Value ralpha = alpha - razor_margin(depth);
685 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
690 // Step 7. Futility pruning: child node (skipped when in check)
692 && depth < 7 * ONE_PLY
693 && eval - futility_margin(depth) >= beta
694 && eval < VALUE_KNOWN_WIN // Do not return unproven wins
695 && pos.non_pawn_material(pos.side_to_move()))
696 return eval - futility_margin(depth);
698 // Step 8. Null move search with verification search (is omitted in PV nodes)
700 && depth >= 2 * ONE_PLY
702 && pos.non_pawn_material(pos.side_to_move()))
704 ss->currentMove = MOVE_NULL;
706 assert(eval - beta >= 0);
708 // Null move dynamic reduction based on depth and value
709 Depth R = ((823 + 67 * depth) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
711 pos.do_null_move(st);
712 (ss+1)->skipEarlyPruning = true;
713 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
714 : - search<NonPV, false>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
715 (ss+1)->skipEarlyPruning = false;
716 pos.undo_null_move();
718 if (nullValue >= beta)
720 // Do not return unproven mate scores
721 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
724 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
727 // Do verification search at high depths
728 ss->skipEarlyPruning = true;
729 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
730 : search<NonPV, false>(pos, ss, beta-1, beta, depth-R, false);
731 ss->skipEarlyPruning = false;
738 // Step 9. ProbCut (skipped when in check)
739 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
740 // and a reduced search returns a value much above beta, we can (almost) safely
741 // prune the previous move.
743 && depth >= 5 * ONE_PLY
744 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
746 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
747 Depth rdepth = depth - 4 * ONE_PLY;
749 assert(rdepth >= ONE_PLY);
750 assert((ss-1)->currentMove != MOVE_NONE);
751 assert((ss-1)->currentMove != MOVE_NULL);
753 MovePicker mp(pos, ttMove, History, CounterMovesHistory, pos.captured_piece_type());
756 while ((move = mp.next_move<false>()) != MOVE_NONE)
757 if (pos.legal(move, ci.pinned))
759 ss->currentMove = move;
760 pos.do_move(move, st, pos.gives_check(move, ci));
761 value = -search<NonPV, false>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
768 // Step 10. Internal iterative deepening (skipped when in check)
769 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
771 && (PvNode || ss->staticEval + 256 >= beta))
773 Depth d = 2 * (depth - 2 * ONE_PLY) - (PvNode ? DEPTH_ZERO : depth / 2);
774 ss->skipEarlyPruning = true;
775 search<PvNode ? PV : NonPV, false>(pos, ss, alpha, beta, d / 2, true);
776 ss->skipEarlyPruning = false;
778 tte = TT.probe(posKey, ttHit);
779 ttMove = ttHit ? tte->move() : MOVE_NONE;
782 moves_loop: // When in check and at SpNode search starts from here
784 Square prevMoveSq = to_sq((ss-1)->currentMove);
785 Move countermove = Countermoves[pos.piece_on(prevMoveSq)][prevMoveSq];
787 MovePicker mp(pos, ttMove, depth, History, CounterMovesHistory, countermove, ss);
789 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
790 improving = ss->staticEval >= (ss-2)->staticEval
791 || ss->staticEval == VALUE_NONE
792 ||(ss-2)->staticEval == VALUE_NONE;
794 singularExtensionNode = !RootNode
796 && depth >= 8 * ONE_PLY
797 && ttMove != MOVE_NONE
798 /* && ttValue != VALUE_NONE Already implicit in the next condition */
799 && abs(ttValue) < VALUE_KNOWN_WIN
800 && !excludedMove // Recursive singular search is not allowed
801 && (tte->bound() & BOUND_LOWER)
802 && tte->depth() >= depth - 3 * ONE_PLY;
804 // Step 11. Loop through moves
805 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
806 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
810 if (move == excludedMove)
813 // At root obey the "searchmoves" option and skip moves not listed in Root
814 // Move List. As a consequence any illegal move is also skipped. In MultiPV
815 // mode we also skip PV moves which have been already searched.
816 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
821 // Shared counter cannot be decremented later if the move turns out to be illegal
822 if (!pos.legal(move, ci.pinned))
825 moveCount = ++splitPoint->moveCount;
826 splitPoint->spinlock.release();
833 Signals.firstRootMove = (moveCount == 1);
835 if (thisThread == Threads.main() && Time.elapsed() > 3000)
836 sync_cout << "info depth " << depth / ONE_PLY
837 << " currmove " << UCI::move(move, pos.is_chess960())
838 << " currmovenumber " << moveCount + PVIdx << sync_endl;
842 (ss+1)->pv = nullptr;
844 extension = DEPTH_ZERO;
845 captureOrPromotion = pos.capture_or_promotion(move);
847 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
848 ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
849 : pos.gives_check(move, ci);
851 dangerous = givesCheck
852 || type_of(move) != NORMAL
853 || pos.advanced_pawn_push(move);
855 // Step 12. Extend checks
856 if (givesCheck && pos.see_sign(move) >= VALUE_ZERO)
859 // Singular extension search. If all moves but one fail low on a search of
860 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
861 // is singular and should be extended. To verify this we do a reduced search
862 // on all the other moves but the ttMove and if the result is lower than
863 // ttValue minus a margin then we extend the ttMove.
864 if ( singularExtensionNode
867 && pos.legal(move, ci.pinned))
869 Value rBeta = ttValue - 2 * depth / ONE_PLY;
870 ss->excludedMove = move;
871 ss->skipEarlyPruning = true;
872 value = search<NonPV, false>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
873 ss->skipEarlyPruning = false;
874 ss->excludedMove = MOVE_NONE;
880 // Update the current move (this must be done after singular extension search)
881 newDepth = depth - ONE_PLY + extension;
883 // Step 13. Pruning at shallow depth
885 && !captureOrPromotion
888 && bestValue > VALUE_MATED_IN_MAX_PLY)
890 // Move count based pruning
891 if ( depth < 16 * ONE_PLY
892 && moveCount >= FutilityMoveCounts[improving][depth])
895 splitPoint->spinlock.acquire();
900 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
902 // Futility pruning: parent node
903 if (predictedDepth < 7 * ONE_PLY)
905 futilityValue = ss->staticEval + futility_margin(predictedDepth) + 256;
907 if (futilityValue <= alpha)
909 bestValue = std::max(bestValue, futilityValue);
913 splitPoint->spinlock.acquire();
914 if (bestValue > splitPoint->bestValue)
915 splitPoint->bestValue = bestValue;
921 // Prune moves with negative SEE at low depths
922 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
925 splitPoint->spinlock.acquire();
931 // Speculative prefetch as early as possible
932 prefetch(TT.first_entry(pos.key_after(move)));
934 // Check for legality just before making the move
935 if (!RootNode && !SpNode && !pos.legal(move, ci.pinned))
941 ss->currentMove = move;
943 // Step 14. Make the move
944 pos.do_move(move, st, givesCheck);
946 // Step 15. Reduced depth search (LMR). If the move fails high it will be
947 // re-searched at full depth.
948 if ( depth >= 3 * ONE_PLY
950 && !captureOrPromotion
951 && move != ss->killers[0]
952 && move != ss->killers[1])
954 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
956 if ( (!PvNode && cutNode)
957 || ( History[pos.piece_on(to_sq(move))][to_sq(move)] < VALUE_ZERO
958 && CounterMovesHistory[pos.piece_on(prevMoveSq)][prevMoveSq]
959 [pos.piece_on(to_sq(move))][to_sq(move)] <= VALUE_ZERO))
960 ss->reduction += ONE_PLY;
962 if (move == countermove)
963 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
965 // Decrease reduction for moves that escape a capture
967 && type_of(move) == NORMAL
968 && type_of(pos.piece_on(to_sq(move))) != PAWN
969 && pos.see(make_move(to_sq(move), from_sq(move))) < VALUE_ZERO)
970 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
972 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
974 alpha = splitPoint->alpha;
976 value = -search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, d, true);
978 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
979 ss->reduction = DEPTH_ZERO;
982 doFullDepthSearch = !PvNode || moveCount > 1;
984 // Step 16. Full depth search, when LMR is skipped or fails high
985 if (doFullDepthSearch)
988 alpha = splitPoint->alpha;
990 value = newDepth < ONE_PLY ?
991 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
992 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
993 : - search<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
996 // For PV nodes only, do a full PV search on the first move or after a fail
997 // high (in the latter case search only if value < beta), otherwise let the
998 // parent node fail low with value <= alpha and to try another move.
999 if (PvNode && (moveCount == 1 || (value > alpha && (RootNode || value < beta))))
1002 (ss+1)->pv[0] = MOVE_NONE;
1004 value = newDepth < ONE_PLY ?
1005 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1006 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1007 : - search<PV, false>(pos, ss+1, -beta, -alpha, newDepth, false);
1010 // Step 17. Undo move
1011 pos.undo_move(move);
1013 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1015 // Step 18. Check for new best move
1018 splitPoint->spinlock.acquire();
1019 bestValue = splitPoint->bestValue;
1020 alpha = splitPoint->alpha;
1023 // Finished searching the move. If a stop or a cutoff occurred, the return
1024 // value of the search cannot be trusted, and we return immediately without
1025 // updating best move, PV and TT.
1026 if (Signals.stop || thisThread->cutoff_occurred())
1031 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
1033 // PV move or new best move ?
1034 if (moveCount == 1 || value > alpha)
1041 for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
1042 rm.pv.push_back(*m);
1044 // We record how often the best move has been changed in each
1045 // iteration. This information is used for time management: When
1046 // the best move changes frequently, we allocate some more time.
1051 // All other moves but the PV are set to the lowest value: this is
1052 // not a problem when sorting because the sort is stable and the
1053 // move position in the list is preserved - just the PV is pushed up.
1054 rm.score = -VALUE_INFINITE;
1057 if (value > bestValue)
1059 bestValue = SpNode ? splitPoint->bestValue = value : value;
1063 // If there is an easy move for this position, clear it if unstable
1065 && EasyMove.get(pos.key())
1066 && (move != EasyMove.get(pos.key()) || moveCount > 1))
1069 bestMove = SpNode ? splitPoint->bestMove = move : move;
1071 if (PvNode && !RootNode) // Update pv even in fail-high case
1072 update_pv(SpNode ? splitPoint->ss->pv : ss->pv, move, (ss+1)->pv);
1074 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1075 alpha = SpNode ? splitPoint->alpha = value : value;
1078 assert(value >= beta); // Fail high
1081 splitPoint->cutoff = true;
1088 if (!SpNode && !captureOrPromotion && move != bestMove && quietCount < 64)
1089 quietsSearched[quietCount++] = move;
1091 // Step 19. Check for splitting the search
1093 && Threads.size() >= 2
1094 && depth >= Threads.minimumSplitDepth
1095 && ( !thisThread->activeSplitPoint
1096 || !thisThread->activeSplitPoint->allSlavesSearching
1097 || ( Threads.size() > MAX_SLAVES_PER_SPLITPOINT
1098 && thisThread->activeSplitPoint->slavesMask.count() == MAX_SLAVES_PER_SPLITPOINT))
1099 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1101 assert(bestValue > -VALUE_INFINITE && bestValue < beta);
1103 thisThread->split(pos, ss, alpha, beta, &bestValue, &bestMove,
1104 depth, moveCount, &mp, NT, cutNode);
1106 if (Signals.stop || thisThread->cutoff_occurred())
1109 if (bestValue >= beta)
1117 // Following condition would detect a stop or a cutoff set only after move
1118 // loop has been completed. But in this case bestValue is valid because we
1119 // have fully searched our subtree, and we can anyhow save the result in TT.
1121 if (Signals.stop || thisThread->cutoff_occurred())
1125 // Step 20. Check for mate and stalemate
1126 // All legal moves have been searched and if there are no legal moves, it
1127 // must be mate or stalemate. If we are in a singular extension search then
1128 // return a fail low score.
1130 bestValue = excludedMove ? alpha
1131 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1133 // Quiet best move: update killers, history and countermoves
1134 else if (bestMove && !pos.capture_or_promotion(bestMove))
1135 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount);
1137 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1138 bestValue >= beta ? BOUND_LOWER :
1139 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1140 depth, bestMove, ss->staticEval, TT.generation());
1142 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1148 // qsearch() is the quiescence search function, which is called by the main
1149 // search function when the remaining depth is zero (or, to be more precise,
1150 // less than ONE_PLY).
1152 template <NodeType NT, bool InCheck>
1153 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1155 const bool PvNode = NT == PV;
1157 assert(NT == PV || NT == NonPV);
1158 assert(InCheck == !!pos.checkers());
1159 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1160 assert(PvNode || (alpha == beta - 1));
1161 assert(depth <= DEPTH_ZERO);
1167 Move ttMove, move, bestMove;
1168 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1169 bool ttHit, givesCheck, evasionPrunable;
1174 oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
1176 ss->pv[0] = MOVE_NONE;
1179 ss->currentMove = bestMove = MOVE_NONE;
1180 ss->ply = (ss-1)->ply + 1;
1182 // Check for an instant draw or if the maximum ply has been reached
1183 if (pos.is_draw() || ss->ply >= MAX_PLY)
1184 return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos) : DrawValue[pos.side_to_move()];
1186 assert(0 <= ss->ply && ss->ply < MAX_PLY);
1188 // Decide whether or not to include checks: this fixes also the type of
1189 // TT entry depth that we are going to use. Note that in qsearch we use
1190 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1191 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1192 : DEPTH_QS_NO_CHECKS;
1194 // Transposition table lookup
1196 tte = TT.probe(posKey, ttHit);
1197 ttMove = ttHit ? tte->move() : MOVE_NONE;
1198 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
1202 && tte->depth() >= ttDepth
1203 && ttValue != VALUE_NONE // Only in case of TT access race
1204 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1205 : (tte->bound() & BOUND_UPPER)))
1207 ss->currentMove = ttMove; // Can be MOVE_NONE
1211 // Evaluate the position statically
1214 ss->staticEval = VALUE_NONE;
1215 bestValue = futilityBase = -VALUE_INFINITE;
1221 // Never assume anything on values stored in TT
1222 if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
1223 ss->staticEval = bestValue = evaluate(pos);
1225 // Can ttValue be used as a better position evaluation?
1226 if (ttValue != VALUE_NONE)
1227 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1228 bestValue = ttValue;
1231 ss->staticEval = bestValue =
1232 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss-1)->staticEval + 2 * Eval::Tempo;
1234 // Stand pat. Return immediately if static value is at least beta
1235 if (bestValue >= beta)
1238 tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1239 DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
1244 if (PvNode && bestValue > alpha)
1247 futilityBase = bestValue + 128;
1250 // Initialize a MovePicker object for the current position, and prepare
1251 // to search the moves. Because the depth is <= 0 here, only captures,
1252 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1254 MovePicker mp(pos, ttMove, depth, History, CounterMovesHistory, to_sq((ss-1)->currentMove));
1257 // Loop through the moves until no moves remain or a beta cutoff occurs
1258 while ((move = mp.next_move<false>()) != MOVE_NONE)
1260 assert(is_ok(move));
1262 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1263 ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1264 : pos.gives_check(move, ci);
1269 && futilityBase > -VALUE_KNOWN_WIN
1270 && !pos.advanced_pawn_push(move))
1272 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1274 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1276 if (futilityValue <= alpha)
1278 bestValue = std::max(bestValue, futilityValue);
1282 if (futilityBase <= alpha && pos.see(move) <= VALUE_ZERO)
1284 bestValue = std::max(bestValue, futilityBase);
1289 // Detect non-capture evasions that are candidates to be pruned
1290 evasionPrunable = InCheck
1291 && bestValue > VALUE_MATED_IN_MAX_PLY
1292 && !pos.capture(move);
1294 // Don't search moves with negative SEE values
1295 if ( (!InCheck || evasionPrunable)
1296 && type_of(move) != PROMOTION
1297 && pos.see_sign(move) < VALUE_ZERO)
1300 // Speculative prefetch as early as possible
1301 prefetch(TT.first_entry(pos.key_after(move)));
1303 // Check for legality just before making the move
1304 if (!pos.legal(move, ci.pinned))
1307 ss->currentMove = move;
1309 // Make and search the move
1310 pos.do_move(move, st, givesCheck);
1311 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1312 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1313 pos.undo_move(move);
1315 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1317 // Check for new best move
1318 if (value > bestValue)
1324 if (PvNode) // Update pv even in fail-high case
1325 update_pv(ss->pv, move, (ss+1)->pv);
1327 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1334 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1335 ttDepth, move, ss->staticEval, TT.generation());
1343 // All legal moves have been searched. A special case: If we're in check
1344 // and no legal moves were found, it is checkmate.
1345 if (InCheck && bestValue == -VALUE_INFINITE)
1346 return mated_in(ss->ply); // Plies to mate from the root
1348 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1349 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1350 ttDepth, bestMove, ss->staticEval, TT.generation());
1352 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1358 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1359 // "plies to mate from the current position". Non-mate scores are unchanged.
1360 // The function is called before storing a value in the transposition table.
1362 Value value_to_tt(Value v, int ply) {
1364 assert(v != VALUE_NONE);
1366 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1367 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1371 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1372 // from the transposition table (which refers to the plies to mate/be mated
1373 // from current position) to "plies to mate/be mated from the root".
1375 Value value_from_tt(Value v, int ply) {
1377 return v == VALUE_NONE ? VALUE_NONE
1378 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1379 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1383 // update_pv() adds current move and appends child pv[]
1385 void update_pv(Move* pv, Move move, Move* childPv) {
1387 for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
1393 // update_stats() updates killers, history, countermove history and
1394 // countermoves stats for a quiet best move.
1396 void update_stats(const Position& pos, Stack* ss, Move move,
1397 Depth depth, Move* quiets, int quietsCnt) {
1399 if (ss->killers[0] != move)
1401 ss->killers[1] = ss->killers[0];
1402 ss->killers[0] = move;
1405 Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY));
1407 Square prevSq = to_sq((ss-1)->currentMove);
1408 HistoryStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq];
1410 History.update(pos.moved_piece(move), to_sq(move), bonus);
1412 if (is_ok((ss-1)->currentMove))
1414 Countermoves.update(pos.piece_on(prevSq), prevSq, move);
1415 cmh.update(pos.moved_piece(move), to_sq(move), bonus);
1418 // Decrease all the other played quiet moves
1419 for (int i = 0; i < quietsCnt; ++i)
1421 History.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1423 if (is_ok((ss-1)->currentMove))
1424 cmh.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1427 // Extra penalty for TT move in previous ply when it gets refuted
1428 if (is_ok((ss-2)->currentMove) && (ss-1)->currentMove == (ss-1)->ttMove)
1430 Square prevPrevSq = to_sq((ss-2)->currentMove);
1431 HistoryStats& ttMoveCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
1432 ttMoveCmh.update(pos.piece_on(prevSq), prevSq, -bonus - 2 * depth / ONE_PLY - 1);
1437 // When playing with strength handicap, choose best move among a set of RootMoves
1438 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1440 Move Skill::pick_best(size_t multiPV) {
1442 // PRNG sequence should be non-deterministic, so we seed it with the time at init
1443 static PRNG rng(now());
1445 // RootMoves are already sorted by score in descending order
1446 int variance = std::min(RootMoves[0].score - RootMoves[multiPV - 1].score, PawnValueMg);
1447 int weakness = 120 - 2 * level;
1448 int maxScore = -VALUE_INFINITE;
1450 // Choose best move. For each move score we add two terms both dependent on
1451 // weakness. One deterministic and bigger for weaker levels, and one random,
1452 // then we choose the move with the resulting highest score.
1453 for (size_t i = 0; i < multiPV; ++i)
1455 // This is our magic formula
1456 int push = ( weakness * int(RootMoves[0].score - RootMoves[i].score)
1457 + variance * (rng.rand<unsigned>() % weakness)) / 128;
1459 if (RootMoves[i].score + push > maxScore)
1461 maxScore = RootMoves[i].score + push;
1462 best = RootMoves[i].pv[0];
1471 /// UCI::pv() formats PV information according to the UCI protocol. UCI requires
1472 /// that all (if any) unsearched PV lines are sent using a previous search score.
1474 string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
1476 std::stringstream ss;
1477 int elapsed = Time.elapsed() + 1;
1478 size_t multiPV = std::min((size_t)Options["MultiPV"], RootMoves.size());
1481 for (Thread* th : Threads)
1482 if (th->maxPly > selDepth)
1483 selDepth = th->maxPly;
1485 for (size_t i = 0; i < multiPV; ++i)
1487 bool updated = (i <= PVIdx);
1489 if (depth == ONE_PLY && !updated)
1492 Depth d = updated ? depth : depth - ONE_PLY;
1493 Value v = updated ? RootMoves[i].score : RootMoves[i].previousScore;
1495 bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
1496 v = tb ? TB::Score : v;
1498 if (ss.rdbuf()->in_avail()) // Not at first line
1502 << " depth " << d / ONE_PLY
1503 << " seldepth " << selDepth
1504 << " multipv " << i + 1
1505 << " score " << UCI::value(v);
1507 if (!tb && i == PVIdx)
1508 ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1510 ss << " nodes " << pos.nodes_searched()
1511 << " nps " << pos.nodes_searched() * 1000 / elapsed;
1513 if (elapsed > 1000) // Earlier makes little sense
1514 ss << " hashfull " << TT.hashfull();
1516 ss << " tbhits " << TB::Hits
1517 << " time " << elapsed
1520 for (Move m : RootMoves[i].pv)
1521 ss << " " << UCI::move(m, pos.is_chess960());
1528 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1529 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1530 /// first, even if the old TT entries have been overwritten.
1532 void RootMove::insert_pv_in_tt(Position& pos) {
1534 StateInfo state[MAX_PLY], *st = state;
1539 assert(MoveList<LEGAL>(pos).contains(m));
1541 TTEntry* tte = TT.probe(pos.key(), ttHit);
1543 if (!ttHit || tte->move() != m) // Don't overwrite correct entries
1544 tte->save(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, m, VALUE_NONE, TT.generation());
1546 pos.do_move(m, *st++, pos.gives_check(m, CheckInfo(pos)));
1549 for (size_t i = pv.size(); i > 0; )
1550 pos.undo_move(pv[--i]);
1554 /// RootMove::extract_ponder_from_tt() is called in case we have no ponder move before
1555 /// exiting the search, for instance in case we stop the search during a fail high at
1556 /// root. We try hard to have a ponder move to return to the GUI, otherwise in case of
1557 /// 'ponder on' we have nothing to think on.
1559 bool RootMove::extract_ponder_from_tt(Position& pos)
1564 assert(pv.size() == 1);
1566 pos.do_move(pv[0], st, pos.gives_check(pv[0], CheckInfo(pos)));
1567 TTEntry* tte = TT.probe(pos.key(), ttHit);
1568 pos.undo_move(pv[0]);
1572 Move m = tte->move(); // Local copy to be SMP safe
1573 if (MoveList<LEGAL>(pos).contains(m))
1574 return pv.push_back(m), true;
1581 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1583 void Thread::idle_loop() {
1585 // Pointer 'this_sp' is not null only if we are called from split(), and not
1586 // at the thread creation. This means we are the split point's master.
1587 SplitPoint* this_sp = activeSplitPoint;
1589 assert(!this_sp || (this_sp->master == this && searching));
1591 while (!exit && !(this_sp && this_sp->slavesMask.none()))
1593 // If this thread has been assigned work, launch a search
1598 assert(activeSplitPoint);
1599 SplitPoint* sp = activeSplitPoint;
1603 Stack stack[MAX_PLY+4], *ss = stack+2; // To allow referencing (ss-2) and (ss+2)
1604 Position pos(*sp->pos, this);
1606 std::memcpy(ss-2, sp->ss-2, 5 * sizeof(Stack));
1607 ss->splitPoint = sp;
1609 sp->spinlock.acquire();
1611 assert(activePosition == nullptr);
1613 activePosition = &pos;
1615 if (sp->nodeType == NonPV)
1616 search<NonPV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1618 else if (sp->nodeType == PV)
1619 search<PV, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1621 else if (sp->nodeType == Root)
1622 search<Root, true>(pos, ss, sp->alpha, sp->beta, sp->depth, sp->cutNode);
1630 activePosition = nullptr;
1631 sp->slavesMask.reset(idx);
1632 sp->allSlavesSearching = false;
1633 sp->nodes += pos.nodes_searched();
1635 // After releasing the lock we can't access any SplitPoint related data
1636 // in a safe way because it could have been released under our feet by
1638 sp->spinlock.release();
1640 // Try to late join to another split point if none of its slaves has
1641 // already finished.
1642 SplitPoint* bestSp = NULL;
1643 int minLevel = INT_MAX;
1645 for (Thread* th : Threads)
1647 const size_t size = th->splitPointsSize; // Local copy
1648 sp = size ? &th->splitPoints[size - 1] : nullptr;
1651 && sp->allSlavesSearching
1652 && sp->slavesMask.count() < MAX_SLAVES_PER_SPLITPOINT
1656 assert(!(this_sp && this_sp->slavesMask.none()));
1657 assert(Threads.size() > 2);
1659 // Prefer to join to SP with few parents to reduce the probability
1660 // that a cut-off occurs above us, and hence we waste our work.
1662 for (SplitPoint* p = th->activeSplitPoint; p; p = p->parentSplitPoint)
1665 if (level < minLevel)
1677 // Recheck the conditions under lock protection
1678 sp->spinlock.acquire();
1680 if ( sp->allSlavesSearching
1681 && sp->slavesMask.count() < MAX_SLAVES_PER_SPLITPOINT)
1687 sp->slavesMask.set(idx);
1688 activeSplitPoint = sp;
1695 sp->spinlock.release();
1699 // If search is finished then sleep, otherwise just yield
1700 if (!Threads.main()->thinking)
1704 std::unique_lock<Mutex> lk(mutex);
1705 while (!exit && !Threads.main()->thinking)
1706 sleepCondition.wait(lk);
1709 std::this_thread::yield(); // Wait for a new job or for our slaves to finish
1714 /// check_time() is called by the timer thread when the timer triggers. It is
1715 /// used to print debug info and, more importantly, to detect when we are out of
1716 /// available time and thus stop the search.
1720 static TimePoint lastInfoTime = now();
1721 int elapsed = Time.elapsed();
1723 if (now() - lastInfoTime >= 1000)
1725 lastInfoTime = now();
1729 // An engine may not stop pondering until told so by the GUI
1733 if (Limits.use_time_management())
1735 bool stillAtFirstMove = Signals.firstRootMove
1736 && !Signals.failedLowAtRoot
1737 && elapsed > Time.available() * 75 / 100;
1739 if ( stillAtFirstMove
1740 || elapsed > Time.maximum() - 2 * TimerThread::Resolution)
1741 Signals.stop = true;
1743 else if (Limits.movetime && elapsed >= Limits.movetime)
1744 Signals.stop = true;
1746 else if (Limits.nodes)
1748 int64_t nodes = RootPos.nodes_searched();
1750 // Loop across all split points and sum accumulated SplitPoint nodes plus
1751 // all the currently active positions nodes.
1753 for (Thread* th : Threads)
1754 for (size_t i = 0; i < th->splitPointsSize; ++i)
1756 SplitPoint& sp = th->splitPoints[i];
1758 sp.spinlock.acquire();
1762 for (size_t idx = 0; idx < Threads.size(); ++idx)
1763 if (sp.slavesMask.test(idx) && Threads[idx]->activePosition)
1764 nodes += Threads[idx]->activePosition->nodes_searched();
1766 sp.spinlock.release();
1769 if (nodes >= Limits.nodes)
1770 Signals.stop = true;