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);
148 /// Search::init() is called during startup to initialize various lookup tables
150 void Search::init() {
152 const double K[][2] = {{ 0.799, 2.281 }, { 0.484, 3.023 }};
154 for (int pv = 0; pv <= 1; ++pv)
155 for (int imp = 0; imp <= 1; ++imp)
156 for (int d = 1; d < 64; ++d)
157 for (int mc = 1; mc < 64; ++mc)
159 double r = K[pv][0] + log(d) * log(mc) / K[pv][1];
162 Reductions[pv][imp][d][mc] = int(r) * ONE_PLY;
164 // Increase reduction when eval is not improving
165 if (!pv && !imp && Reductions[pv][imp][d][mc] >= 2 * ONE_PLY)
166 Reductions[pv][imp][d][mc] += ONE_PLY;
169 for (int d = 0; d < 16; ++d)
171 FutilityMoveCounts[0][d] = int(2.4 + 0.773 * pow(d + 0.00, 1.8));
172 FutilityMoveCounts[1][d] = int(2.9 + 1.045 * pow(d + 0.49, 1.8));
177 /// Search::clear() resets to zero search state, to obtain reproducible results
179 void Search::clear() {
182 CounterMovesHistory.clear();
184 for (Thread* th : Threads)
187 th->counterMoves.clear();
192 /// Search::perft() is our utility to verify move generation. All the leaf nodes
193 /// up to the given depth are generated and counted and the sum returned.
195 uint64_t Search::perft(Position& pos, Depth depth) {
198 uint64_t cnt, nodes = 0;
200 const bool leaf = (depth == 2 * ONE_PLY);
202 for (const auto& m : MoveList<LEGAL>(pos))
204 if (Root && depth <= ONE_PLY)
208 pos.do_move(m, st, pos.gives_check(m, ci));
209 cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
214 sync_cout << UCI::move(m, pos.is_chess960()) << ": " << cnt << sync_endl;
219 template uint64_t Search::perft<true>(Position&, Depth);
222 /// MainThread::think() is called by the main thread when the program receives
223 /// the UCI 'go' command. It searches from root position and at the end prints
224 /// the "bestmove" to output.
226 void MainThread::think() {
228 Color us = rootPos.side_to_move();
229 Time.init(Limits, us, rootPos.game_ply());
231 int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
232 DrawValue[ us] = VALUE_DRAW - Value(contempt);
233 DrawValue[~us] = VALUE_DRAW + Value(contempt);
236 TB::RootInTB = false;
237 TB::UseRule50 = Options["Syzygy50MoveRule"];
238 TB::ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
239 TB::Cardinality = Options["SyzygyProbeLimit"];
241 // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
242 if (TB::Cardinality > TB::MaxCardinality)
244 TB::Cardinality = TB::MaxCardinality;
245 TB::ProbeDepth = DEPTH_ZERO;
248 if (rootMoves.empty())
250 rootMoves.push_back(RootMove(MOVE_NONE));
251 sync_cout << "info depth 0 score "
252 << UCI::value(rootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
257 if (TB::Cardinality >= rootPos.count<ALL_PIECES>(WHITE)
258 + rootPos.count<ALL_PIECES>(BLACK))
260 // If the current root position is in the tablebases then RootMoves
261 // contains only moves that preserve the draw or win.
262 TB::RootInTB = Tablebases::root_probe(rootPos, rootMoves, TB::Score);
265 TB::Cardinality = 0; // Do not probe tablebases during the search
267 else // If DTZ tables are missing, use WDL tables as a fallback
269 // Filter out moves that do not preserve a draw or win
270 TB::RootInTB = Tablebases::root_probe_wdl(rootPos, rootMoves, TB::Score);
272 // Only probe during search if winning
273 if (TB::Score <= VALUE_DRAW)
279 TB::Hits = rootMoves.size();
282 TB::Score = TB::Score > VALUE_DRAW ? VALUE_MATE - MAX_PLY - 1
283 : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1
288 for (Thread* th : Threads)
291 th->rootDepth = DEPTH_ZERO;
292 th->searching = true;
295 th->rootPos = Position(rootPos, th);
296 th->rootMoves = rootMoves;
297 th->notify_one(); // Wake up the thread and start searching
301 Threads.timer->run = true;
302 Threads.timer->notify_one(); // Start the recurring timer
304 search(true); // Let's start searching!
306 // Stop the threads and the timer
308 Threads.timer->run = false;
310 // Wait until all threads have finished
311 for (Thread* th : Threads)
313 th->wait_while(th->searching);
316 // When playing in 'nodes as time' mode, subtract the searched nodes from
317 // the available ones before to exit.
319 Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
321 // When we reach the maximum depth, we can arrive here without a raise of
322 // Signals.stop. However, if we are pondering or in an infinite search,
323 // the UCI protocol states that we shouldn't print the best move before the
324 // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
325 // until the GUI sends one of those commands (which also raises Signals.stop).
326 if (!Signals.stop && (Limits.ponder || Limits.infinite))
328 Signals.stopOnPonderhit = true;
332 // Check if there are threads with a better score than main thread.
333 Thread* bestThread = this;
334 for (Thread* th : Threads)
335 if ( th->completedDepth > bestThread->completedDepth
336 && th->rootMoves[0].score > bestThread->rootMoves[0].score)
339 // Send new PV when needed.
340 // FIXME: Breaks multiPV, and skill levels
341 if (bestThread != this)
342 sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
344 sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
346 if (bestThread->rootMoves[0].pv.size() > 1 || bestThread->rootMoves[0].extract_ponder_from_tt(rootPos))
347 std::cout << " ponder " << UCI::move(bestThread->rootMoves[0].pv[1], rootPos.is_chess960());
349 std::cout << sync_endl;
353 // Thread::search() is the main iterative deepening loop. It calls search()
354 // repeatedly with increasing depth until the allocated thinking time has been
355 // consumed, user stops the search, or the maximum search depth is reached.
357 void Thread::search(bool isMainThread) {
359 Stack stack[MAX_PLY+4], *ss = stack+2; // To allow referencing (ss-2) and (ss+2)
360 Value bestValue, alpha, beta, delta;
361 Move easyMove = MOVE_NONE;
363 std::memset(ss-2, 0, 5 * sizeof(Stack));
365 bestValue = delta = alpha = -VALUE_INFINITE;
366 beta = VALUE_INFINITE;
367 completedDepth = DEPTH_ZERO;
371 easyMove = EasyMove.get(rootPos.key());
377 size_t multiPV = Options["MultiPV"];
378 Skill skill(Options["Skill Level"]);
380 // When playing with strength handicap enable MultiPV search that we will
381 // use behind the scenes to retrieve a set of possible moves.
383 multiPV = std::max(multiPV, (size_t)4);
385 multiPV = std::min(multiPV, rootMoves.size());
387 // Iterative deepening loop until requested to stop or target depth reached
388 while (++rootDepth < DEPTH_MAX && !Signals.stop && (!Limits.depth || rootDepth <= Limits.depth))
390 // Set up the new depth for the helper threads
392 rootDepth = Threads.main()->rootDepth + Depth(int(2.2 * log(1 + this->idx)));
394 // Age out PV variability metric
396 BestMoveChanges *= 0.5;
398 // Save the last iteration's scores before first PV line is searched and
399 // all the move scores except the (new) PV are set to -VALUE_INFINITE.
400 for (RootMove& rm : rootMoves)
401 rm.previousScore = rm.score;
403 // MultiPV loop. We perform a full root search for each PV line
404 for (PVIdx = 0; PVIdx < multiPV && !Signals.stop; ++PVIdx)
406 // Reset aspiration window starting size
407 if (rootDepth >= 5 * ONE_PLY)
410 alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
411 beta = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
414 // Start with a small aspiration window and, in the case of a fail
415 // high/low, re-search with a bigger window until we're not failing
419 bestValue = ::search<Root>(rootPos, ss, alpha, beta, rootDepth, false);
421 // Bring the best move to the front. It is critical that sorting
422 // is done with a stable algorithm because all the values but the
423 // first and eventually the new best one are set to -VALUE_INFINITE
424 // and we want to keep the same order for all the moves except the
425 // new PV that goes to the front. Note that in case of MultiPV
426 // search the already searched PV lines are preserved.
427 std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
429 // Write PV back to transposition table in case the relevant
430 // entries have been overwritten during the search.
431 for (size_t i = 0; i <= PVIdx; ++i)
432 rootMoves[i].insert_pv_in_tt(rootPos);
434 // If search has been stopped break immediately. Sorting and
435 // writing PV back to TT is safe because RootMoves is still
436 // valid, although it refers to previous iteration.
440 // When failing high/low give some update (without cluttering
441 // the UI) before a re-search.
444 && (bestValue <= alpha || bestValue >= beta)
445 && Time.elapsed() > 3000)
446 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
448 // In case of failing low/high increase aspiration window and
449 // re-search, otherwise exit the loop.
450 if (bestValue <= alpha)
452 beta = (alpha + beta) / 2;
453 alpha = std::max(bestValue - delta, -VALUE_INFINITE);
457 Signals.failedLowAtRoot = true;
458 Signals.stopOnPonderhit = false;
461 else if (bestValue >= beta)
463 alpha = (alpha + beta) / 2;
464 beta = std::min(bestValue + delta, VALUE_INFINITE);
469 delta += delta / 4 + 5;
471 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
474 // Sort the PV lines searched so far and update the GUI
475 std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
481 sync_cout << "info nodes " << Threads.nodes_searched()
482 << " time " << Time.elapsed() << sync_endl;
484 else if (PVIdx + 1 == multiPV || Time.elapsed() > 3000)
485 sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
489 completedDepth = rootDepth;
494 // If skill level is enabled and time is up, pick a sub-optimal best move
495 if (skill.enabled() && skill.time_to_pick(rootDepth))
496 skill.pick_best(multiPV);
498 // Have we found a "mate in x"?
500 && bestValue >= VALUE_MATE_IN_MAX_PLY
501 && VALUE_MATE - bestValue <= 2 * Limits.mate)
504 // Do we have time for the next iteration? Can we stop searching now?
505 if (Limits.use_time_management())
507 if (!Signals.stop && !Signals.stopOnPonderhit)
509 // Take some extra time if the best move has changed
510 if (rootDepth > 4 * ONE_PLY && multiPV == 1)
511 Time.pv_instability(BestMoveChanges);
513 // Stop the search if only one legal move is available or all
514 // of the available time has been used or we matched an easyMove
515 // from the previous search and just did a fast verification.
516 if ( rootMoves.size() == 1
517 || Time.elapsed() > Time.available()
518 || ( rootMoves[0].pv[0] == easyMove
519 && BestMoveChanges < 0.03
520 && Time.elapsed() > Time.available() / 10))
522 // If we are allowed to ponder do not stop the search now but
523 // keep pondering until the GUI sends "ponderhit" or "stop".
525 Signals.stopOnPonderhit = true;
531 if (rootMoves[0].pv.size() >= 3)
532 EasyMove.update(rootPos, rootMoves[0].pv);
539 notify_one(); // Wake up main thread if is sleeping waiting for us
544 // Clear any candidate easy move that wasn't stable for the last search
545 // iterations; the second condition prevents consecutive fast moves.
546 if (EasyMove.stableCnt < 6 || Time.elapsed() < Time.available())
549 // If skill level is enabled, swap best PV line with the sub-optimal one
551 std::swap(rootMoves[0], *std::find(rootMoves.begin(),
552 rootMoves.end(), skill.best_move(multiPV)));
558 // search<>() is the main search function for both PV and non-PV nodes
560 template <NodeType NT>
561 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
563 const bool RootNode = NT == Root;
564 const bool PvNode = NT == PV || NT == Root;
566 assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
567 assert(PvNode || (alpha == beta - 1));
568 assert(depth > DEPTH_ZERO);
570 Move pv[MAX_PLY+1], quietsSearched[64];
574 Move ttMove, move, excludedMove, bestMove;
575 Depth extension, newDepth, predictedDepth;
576 Value bestValue, value, ttValue, eval, nullValue, futilityValue;
577 bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
578 bool captureOrPromotion, doFullDepthSearch;
579 int moveCount, quietCount;
581 // Step 1. Initialize node
582 Thread* thisThread = pos.this_thread();
583 inCheck = pos.checkers();
584 moveCount = quietCount = ss->moveCount = 0;
585 bestValue = -VALUE_INFINITE;
586 ss->ply = (ss-1)->ply + 1;
588 // Used to send selDepth info to GUI
589 if (PvNode && thisThread->maxPly < ss->ply)
590 thisThread->maxPly = ss->ply;
594 // Step 2. Check for aborted search and immediate draw
595 if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw() || ss->ply >= MAX_PLY)
596 return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos)
597 : DrawValue[pos.side_to_move()];
599 // Step 3. Mate distance pruning. Even if we mate at the next move our score
600 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
601 // a shorter mate was found upward in the tree then there is no need to search
602 // because we will never beat the current alpha. Same logic but with reversed
603 // signs applies also in the opposite condition of being mated instead of giving
604 // mate. In this case return a fail-high score.
605 alpha = std::max(mated_in(ss->ply), alpha);
606 beta = std::min(mate_in(ss->ply+1), beta);
611 assert(0 <= ss->ply && ss->ply < MAX_PLY);
613 ss->currentMove = ss->ttMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
614 (ss+1)->skipEarlyPruning = false; (ss+1)->reduction = DEPTH_ZERO;
615 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
617 // Step 4. Transposition table lookup. We don't want the score of a partial
618 // search to overwrite a previous full search TT value, so we use a different
619 // position key in case of an excluded move.
620 excludedMove = ss->excludedMove;
621 posKey = excludedMove ? pos.exclusion_key() : pos.key();
622 tte = TT.probe(posKey, ttHit);
623 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
624 ss->ttMove = ttMove = RootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
625 : ttHit ? tte->move() : MOVE_NONE;
627 // At non-PV nodes we check for an early TT cutoff
630 && tte->depth() >= depth
631 && ttValue != VALUE_NONE // Possible in case of TT access race
632 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
633 : (tte->bound() & BOUND_UPPER)))
635 ss->currentMove = ttMove; // Can be MOVE_NONE
637 // If ttMove is quiet, update killers, history, counter move on TT hit
638 if (ttValue >= beta && ttMove && !pos.capture_or_promotion(ttMove))
639 update_stats(pos, ss, ttMove, depth, nullptr, 0);
644 // Step 4a. Tablebase probe
645 if (!RootNode && TB::Cardinality)
647 int piecesCnt = pos.count<ALL_PIECES>(WHITE) + pos.count<ALL_PIECES>(BLACK);
649 if ( piecesCnt <= TB::Cardinality
650 && (piecesCnt < TB::Cardinality || depth >= TB::ProbeDepth)
651 && pos.rule50_count() == 0)
653 int found, v = Tablebases::probe_wdl(pos, &found);
659 int drawScore = TB::UseRule50 ? 1 : 0;
661 value = v < -drawScore ? -VALUE_MATE + MAX_PLY + ss->ply
662 : v > drawScore ? VALUE_MATE - MAX_PLY - ss->ply
663 : VALUE_DRAW + 2 * v * drawScore;
665 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_EXACT,
666 std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
667 MOVE_NONE, VALUE_NONE, TT.generation());
674 // Step 5. Evaluate the position statically
677 ss->staticEval = eval = VALUE_NONE;
683 // Never assume anything on values stored in TT
684 if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
685 eval = ss->staticEval = evaluate(pos);
687 // Can ttValue be used as a better position evaluation?
688 if (ttValue != VALUE_NONE)
689 if (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER))
694 eval = ss->staticEval =
695 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
696 : -(ss-1)->staticEval + 2 * Eval::Tempo;
698 tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
699 ss->staticEval, TT.generation());
702 if (ss->skipEarlyPruning)
705 // Step 6. Razoring (skipped when in check)
707 && depth < 4 * ONE_PLY
708 && eval + razor_margin[depth] <= alpha
709 && ttMove == MOVE_NONE)
711 if ( depth <= ONE_PLY
712 && eval + razor_margin[3 * ONE_PLY] <= alpha)
713 return qsearch<NonPV, false>(pos, ss, alpha, beta, DEPTH_ZERO);
715 Value ralpha = alpha - razor_margin[depth];
716 Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1, DEPTH_ZERO);
721 // Step 7. Futility pruning: child node (skipped when in check)
723 && depth < 7 * ONE_PLY
724 && eval - futility_margin(depth) >= beta
725 && eval < VALUE_KNOWN_WIN // Do not return unproven wins
726 && pos.non_pawn_material(pos.side_to_move()))
727 return eval - futility_margin(depth);
729 // Step 8. Null move search with verification search (is omitted in PV nodes)
731 && depth >= 2 * ONE_PLY
733 && pos.non_pawn_material(pos.side_to_move()))
735 ss->currentMove = MOVE_NULL;
737 assert(eval - beta >= 0);
739 // Null move dynamic reduction based on depth and value
740 Depth R = ((823 + 67 * depth) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
742 pos.do_null_move(st);
743 (ss+1)->skipEarlyPruning = true;
744 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1, DEPTH_ZERO)
745 : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
746 (ss+1)->skipEarlyPruning = false;
747 pos.undo_null_move();
749 if (nullValue >= beta)
751 // Do not return unproven mate scores
752 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
755 if (depth < 12 * ONE_PLY && abs(beta) < VALUE_KNOWN_WIN)
758 // Do verification search at high depths
759 ss->skipEarlyPruning = true;
760 Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta, DEPTH_ZERO)
761 : search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
762 ss->skipEarlyPruning = false;
769 // Step 9. ProbCut (skipped when in check)
770 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
771 // and a reduced search returns a value much above beta, we can (almost)
772 // safely prune the previous move.
774 && depth >= 5 * ONE_PLY
775 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
777 Value rbeta = std::min(beta + 200, VALUE_INFINITE);
778 Depth rdepth = depth - 4 * ONE_PLY;
780 assert(rdepth >= ONE_PLY);
781 assert((ss-1)->currentMove != MOVE_NONE);
782 assert((ss-1)->currentMove != MOVE_NULL);
784 MovePicker mp(pos, ttMove, thisThread->history, PieceValue[MG][pos.captured_piece_type()]);
787 while ((move = mp.next_move()) != MOVE_NONE)
788 if (pos.legal(move, ci.pinned))
790 ss->currentMove = move;
791 pos.do_move(move, st, pos.gives_check(move, ci));
792 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth, !cutNode);
799 // Step 10. Internal iterative deepening (skipped when in check)
800 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
802 && (PvNode || ss->staticEval + 256 >= beta))
804 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
805 ss->skipEarlyPruning = true;
806 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d, true);
807 ss->skipEarlyPruning = false;
809 tte = TT.probe(posKey, ttHit);
810 ttMove = ttHit ? tte->move() : MOVE_NONE;
813 moves_loop: // When in check search starts from here
815 Square prevSq = to_sq((ss-1)->currentMove);
816 Move cm = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
817 const CounterMovesStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq];
819 MovePicker mp(pos, ttMove, depth, thisThread->history, cmh, cm, ss);
821 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
822 improving = ss->staticEval >= (ss-2)->staticEval
823 || ss->staticEval == VALUE_NONE
824 ||(ss-2)->staticEval == VALUE_NONE;
826 singularExtensionNode = !RootNode
827 && depth >= 8 * ONE_PLY
828 && ttMove != MOVE_NONE
829 /* && ttValue != VALUE_NONE Already implicit in the next condition */
830 && abs(ttValue) < VALUE_KNOWN_WIN
831 && !excludedMove // Recursive singular search is not allowed
832 && (tte->bound() & BOUND_LOWER)
833 && tte->depth() >= depth - 3 * ONE_PLY;
835 // Step 11. Loop through moves
836 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
837 while ((move = mp.next_move()) != MOVE_NONE)
841 if (move == excludedMove)
844 // At root obey the "searchmoves" option and skip moves not listed in Root
845 // Move List. As a consequence any illegal move is also skipped. In MultiPV
846 // mode we also skip PV moves which have been already searched.
847 if (RootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
848 thisThread->rootMoves.end(), move))
851 ss->moveCount = ++moveCount;
853 if (RootNode && thisThread == Threads.main())
855 Signals.firstRootMove = (moveCount == 1);
857 if (Time.elapsed() > 3000)
858 sync_cout << "info depth " << depth / ONE_PLY
859 << " currmove " << UCI::move(move, pos.is_chess960())
860 << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
864 (ss+1)->pv = nullptr;
866 extension = DEPTH_ZERO;
867 captureOrPromotion = pos.capture_or_promotion(move);
869 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
870 ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
871 : pos.gives_check(move, ci);
873 // Step 12. Extend checks
874 if (givesCheck && pos.see_sign(move) >= VALUE_ZERO)
877 // Singular extension search. If all moves but one fail low on a search of
878 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
879 // is singular and should be extended. To verify this we do a reduced search
880 // on all the other moves but the ttMove and if the result is lower than
881 // ttValue minus a margin then we extend the ttMove.
882 if ( singularExtensionNode
885 && pos.legal(move, ci.pinned))
887 Value rBeta = ttValue - 2 * depth / ONE_PLY;
888 ss->excludedMove = move;
889 ss->skipEarlyPruning = true;
890 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
891 ss->skipEarlyPruning = false;
892 ss->excludedMove = MOVE_NONE;
898 // Update the current move (this must be done after singular extension search)
899 newDepth = depth - ONE_PLY + extension;
901 // Step 13. Pruning at shallow depth
903 && !captureOrPromotion
906 && !pos.advanced_pawn_push(move)
907 && bestValue > VALUE_MATED_IN_MAX_PLY)
909 // Move count based pruning
910 if ( depth < 16 * ONE_PLY
911 && moveCount >= FutilityMoveCounts[improving][depth])
914 // History based pruning
915 if ( depth <= 3 * ONE_PLY
916 && thisThread->history[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO
917 && cmh[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO)
920 predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
922 // Futility pruning: parent node
923 if (predictedDepth < 7 * ONE_PLY)
925 futilityValue = ss->staticEval + futility_margin(predictedDepth) + 256;
927 if (futilityValue <= alpha)
929 bestValue = std::max(bestValue, futilityValue);
934 // Prune moves with negative SEE at low depths
935 if (predictedDepth < 4 * ONE_PLY && pos.see_sign(move) < VALUE_ZERO)
939 // Speculative prefetch as early as possible
940 prefetch(TT.first_entry(pos.key_after(move)));
942 // Check for legality just before making the move
943 if (!RootNode && !pos.legal(move, ci.pinned))
945 ss->moveCount = --moveCount;
949 ss->currentMove = move;
951 // Step 14. Make the move
952 pos.do_move(move, st, givesCheck);
954 // Step 15. Reduced depth search (LMR). If the move fails high it will be
955 // re-searched at full depth.
956 if ( depth >= 3 * ONE_PLY
958 && !captureOrPromotion
959 && move != ss->killers[0]
960 && move != ss->killers[1])
962 ss->reduction = reduction<PvNode>(improving, depth, moveCount);
964 // Increase reduction for cut nodes and moves with a bad history
965 if ( (!PvNode && cutNode)
966 || ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)] < VALUE_ZERO
967 && cmh[pos.piece_on(to_sq(move))][to_sq(move)] <= VALUE_ZERO))
968 ss->reduction += ONE_PLY;
970 // Decrease reduction for moves with a good history
971 if ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO
972 && cmh[pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO)
973 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
975 // Decrease reduction for moves that escape a capture
977 && type_of(move) == NORMAL
978 && type_of(pos.piece_on(to_sq(move))) != PAWN
979 && pos.see(make_move(to_sq(move), from_sq(move))) < VALUE_ZERO)
980 ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY);
982 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
984 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
986 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
987 ss->reduction = DEPTH_ZERO;
990 doFullDepthSearch = !PvNode || moveCount > 1;
992 // Step 16. Full depth search, when LMR is skipped or fails high
993 if (doFullDepthSearch)
994 value = newDepth < ONE_PLY ?
995 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
996 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
997 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
999 // For PV nodes only, do a full PV search on the first move or after a fail
1000 // high (in the latter case search only if value < beta), otherwise let the
1001 // parent node fail low with value <= alpha and to try another move.
1002 if (PvNode && (moveCount == 1 || (value > alpha && (RootNode || value < beta))))
1005 (ss+1)->pv[0] = MOVE_NONE;
1007 value = newDepth < ONE_PLY ?
1008 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1009 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1010 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
1013 // Step 17. Undo move
1014 pos.undo_move(move);
1016 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1018 // Step 18. Check for new best move
1019 // Finished searching the move. If a stop occurred, the return value of
1020 // the search cannot be trusted, and we return immediately without
1021 // updating best move, PV and TT.
1022 if (Signals.stop.load(std::memory_order_relaxed))
1027 RootMove& rm = *std::find(thisThread->rootMoves.begin(),
1028 thisThread->rootMoves.end(), move);
1030 // PV move or new best move ?
1031 if (moveCount == 1 || value > alpha)
1038 for (Move* m = (ss+1)->pv; *m != MOVE_NONE; ++m)
1039 rm.pv.push_back(*m);
1041 // We record how often the best move has been changed in each
1042 // iteration. This information is used for time management: When
1043 // the best move changes frequently, we allocate some more time.
1044 if (moveCount > 1 && thisThread == Threads.main())
1048 // All other moves but the PV are set to the lowest value: this is
1049 // not a problem when sorting because the sort is stable and the
1050 // move position in the list is preserved - just the PV is pushed up.
1051 rm.score = -VALUE_INFINITE;
1054 if (value > bestValue)
1060 // If there is an easy move for this position, clear it if unstable
1062 && thisThread == Threads.main()
1063 && EasyMove.get(pos.key())
1064 && (move != EasyMove.get(pos.key()) || moveCount > 1))
1069 if (PvNode && !RootNode) // Update pv even in fail-high case
1070 update_pv(ss->pv, move, (ss+1)->pv);
1072 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1076 assert(value >= beta); // Fail high
1082 if (!captureOrPromotion && move != bestMove && quietCount < 64)
1083 quietsSearched[quietCount++] = move;
1086 // Following condition would detect a stop only after move loop has been
1087 // completed. But in this case bestValue is valid because we have fully
1088 // searched our subtree, and we can anyhow save the result in TT.
1094 // Step 20. Check for mate and stalemate
1095 // All legal moves have been searched and if there are no legal moves, it
1096 // must be mate or stalemate. If we are in a singular extension search then
1097 // return a fail low score.
1099 bestValue = excludedMove ? alpha
1100 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1102 // Quiet best move: update killers, history and countermoves
1103 else if (bestMove && !pos.capture_or_promotion(bestMove))
1104 update_stats(pos, ss, bestMove, depth, quietsSearched, quietCount);
1106 // Bonus for prior countermove that caused the fail low
1107 else if ( depth >= 3 * ONE_PLY
1110 && !pos.captured_piece_type()
1111 && is_ok((ss - 1)->currentMove)
1112 && is_ok((ss - 2)->currentMove))
1114 Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
1115 Square prevPrevSq = to_sq((ss - 2)->currentMove);
1116 CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
1117 prevCmh.update(pos.piece_on(prevSq), prevSq, bonus);
1120 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1121 bestValue >= beta ? BOUND_LOWER :
1122 PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
1123 depth, bestMove, ss->staticEval, TT.generation());
1125 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1131 // qsearch() is the quiescence search function, which is called by the main
1132 // search function when the remaining depth is zero (or, to be more precise,
1133 // less than ONE_PLY).
1135 template <NodeType NT, bool InCheck>
1136 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1138 const bool PvNode = NT == PV;
1140 assert(NT == PV || NT == NonPV);
1141 assert(InCheck == !!pos.checkers());
1142 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1143 assert(PvNode || (alpha == beta - 1));
1144 assert(depth <= DEPTH_ZERO);
1150 Move ttMove, move, bestMove;
1151 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1152 bool ttHit, givesCheck, evasionPrunable;
1157 oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
1159 ss->pv[0] = MOVE_NONE;
1162 ss->currentMove = bestMove = MOVE_NONE;
1163 ss->ply = (ss-1)->ply + 1;
1165 // Check for an instant draw or if the maximum ply has been reached
1166 if (pos.is_draw() || ss->ply >= MAX_PLY)
1167 return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos)
1168 : DrawValue[pos.side_to_move()];
1170 assert(0 <= ss->ply && ss->ply < MAX_PLY);
1172 // Decide whether or not to include checks: this fixes also the type of
1173 // TT entry depth that we are going to use. Note that in qsearch we use
1174 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1175 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1176 : DEPTH_QS_NO_CHECKS;
1178 // Transposition table lookup
1180 tte = TT.probe(posKey, ttHit);
1181 ttMove = ttHit ? tte->move() : MOVE_NONE;
1182 ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
1186 && tte->depth() >= ttDepth
1187 && ttValue != VALUE_NONE // Only in case of TT access race
1188 && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
1189 : (tte->bound() & BOUND_UPPER)))
1191 ss->currentMove = ttMove; // Can be MOVE_NONE
1195 // Evaluate the position statically
1198 ss->staticEval = VALUE_NONE;
1199 bestValue = futilityBase = -VALUE_INFINITE;
1205 // Never assume anything on values stored in TT
1206 if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
1207 ss->staticEval = bestValue = evaluate(pos);
1209 // Can ttValue be used as a better position evaluation?
1210 if (ttValue != VALUE_NONE)
1211 if (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER))
1212 bestValue = ttValue;
1215 ss->staticEval = bestValue =
1216 (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
1217 : -(ss-1)->staticEval + 2 * Eval::Tempo;
1219 // Stand pat. Return immediately if static value is at least beta
1220 if (bestValue >= beta)
1223 tte->save(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1224 DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
1229 if (PvNode && bestValue > alpha)
1232 futilityBase = bestValue + 128;
1235 // Initialize a MovePicker object for the current position, and prepare
1236 // to search the moves. Because the depth is <= 0 here, only captures,
1237 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1239 MovePicker mp(pos, ttMove, depth, pos.this_thread()->history, to_sq((ss-1)->currentMove));
1242 // Loop through the moves until no moves remain or a beta cutoff occurs
1243 while ((move = mp.next_move()) != MOVE_NONE)
1245 assert(is_ok(move));
1247 givesCheck = type_of(move) == NORMAL && !ci.dcCandidates
1248 ? ci.checkSquares[type_of(pos.piece_on(from_sq(move)))] & to_sq(move)
1249 : pos.gives_check(move, ci);
1254 && futilityBase > -VALUE_KNOWN_WIN
1255 && !pos.advanced_pawn_push(move))
1257 assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
1259 futilityValue = futilityBase + PieceValue[EG][pos.piece_on(to_sq(move))];
1261 if (futilityValue <= alpha)
1263 bestValue = std::max(bestValue, futilityValue);
1267 if (futilityBase <= alpha && pos.see(move) <= VALUE_ZERO)
1269 bestValue = std::max(bestValue, futilityBase);
1274 // Detect non-capture evasions that are candidates to be pruned
1275 evasionPrunable = InCheck
1276 && bestValue > VALUE_MATED_IN_MAX_PLY
1277 && !pos.capture(move);
1279 // Don't search moves with negative SEE values
1280 if ( (!InCheck || evasionPrunable)
1281 && type_of(move) != PROMOTION
1282 && pos.see_sign(move) < VALUE_ZERO)
1285 // Speculative prefetch as early as possible
1286 prefetch(TT.first_entry(pos.key_after(move)));
1288 // Check for legality just before making the move
1289 if (!pos.legal(move, ci.pinned))
1292 ss->currentMove = move;
1294 // Make and search the move
1295 pos.do_move(move, st, givesCheck);
1296 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1297 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1298 pos.undo_move(move);
1300 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1302 // Check for new best move
1303 if (value > bestValue)
1309 if (PvNode) // Update pv even in fail-high case
1310 update_pv(ss->pv, move, (ss+1)->pv);
1312 if (PvNode && value < beta) // Update alpha here!
1319 tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1320 ttDepth, move, ss->staticEval, TT.generation());
1328 // All legal moves have been searched. A special case: If we're in check
1329 // and no legal moves were found, it is checkmate.
1330 if (InCheck && bestValue == -VALUE_INFINITE)
1331 return mated_in(ss->ply); // Plies to mate from the root
1333 tte->save(posKey, value_to_tt(bestValue, ss->ply),
1334 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1335 ttDepth, bestMove, ss->staticEval, TT.generation());
1337 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1343 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1344 // "plies to mate from the current position". Non-mate scores are unchanged.
1345 // The function is called before storing a value in the transposition table.
1347 Value value_to_tt(Value v, int ply) {
1349 assert(v != VALUE_NONE);
1351 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1352 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1356 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1357 // from the transposition table (which refers to the plies to mate/be mated
1358 // from current position) to "plies to mate/be mated from the root".
1360 Value value_from_tt(Value v, int ply) {
1362 return v == VALUE_NONE ? VALUE_NONE
1363 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1364 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1368 // update_pv() adds current move and appends child pv[]
1370 void update_pv(Move* pv, Move move, Move* childPv) {
1372 for (*pv++ = move; childPv && *childPv != MOVE_NONE; )
1378 // update_stats() updates killers, history, countermove and countermove
1379 // history when a new quiet best move is found.
1381 void update_stats(const Position& pos, Stack* ss, Move move,
1382 Depth depth, Move* quiets, int quietsCnt) {
1384 if (ss->killers[0] != move)
1386 ss->killers[1] = ss->killers[0];
1387 ss->killers[0] = move;
1390 Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1);
1392 Square prevSq = to_sq((ss-1)->currentMove);
1393 CounterMovesStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq];
1394 Thread* thisThread = pos.this_thread();
1396 thisThread->history.update(pos.moved_piece(move), to_sq(move), bonus);
1398 if (is_ok((ss-1)->currentMove))
1400 thisThread->counterMoves.update(pos.piece_on(prevSq), prevSq, move);
1401 cmh.update(pos.moved_piece(move), to_sq(move), bonus);
1404 // Decrease all the other played quiet moves
1405 for (int i = 0; i < quietsCnt; ++i)
1407 thisThread->history.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1409 if (is_ok((ss-1)->currentMove))
1410 cmh.update(pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
1413 // Extra penalty for a quiet TT move in previous ply when it gets refuted
1414 if ( (ss-1)->moveCount == 1
1415 && !pos.captured_piece_type()
1416 && is_ok((ss-2)->currentMove))
1418 Square prevPrevSq = to_sq((ss-2)->currentMove);
1419 CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq];
1420 prevCmh.update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY);
1425 // When playing with strength handicap, choose best move among a set of RootMoves
1426 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1428 Move Skill::pick_best(size_t multiPV) {
1430 const Search::RootMoveVector& rootMoves = Threads.main()->rootMoves;
1431 static PRNG rng(now()); // PRNG sequence should be non-deterministic
1433 // RootMoves are already sorted by score in descending order
1434 Value topScore = rootMoves[0].score;
1435 int delta = std::min(topScore - rootMoves[multiPV - 1].score, PawnValueMg);
1436 int weakness = 120 - 2 * level;
1437 int maxScore = -VALUE_INFINITE;
1439 // Choose best move. For each move score we add two terms, both dependent on
1440 // weakness. One deterministic and bigger for weaker levels, and one random,
1441 // then we choose the move with the resulting highest score.
1442 for (size_t i = 0; i < multiPV; ++i)
1444 // This is our magic formula
1445 int push = ( weakness * int(topScore - rootMoves[i].score)
1446 + delta * (rng.rand<unsigned>() % weakness)) / 128;
1448 if (rootMoves[i].score + push > maxScore)
1450 maxScore = rootMoves[i].score + push;
1451 best = rootMoves[i].pv[0];
1461 /// UCI::pv() formats PV information according to the UCI protocol. UCI requires
1462 /// that all (if any) unsearched PV lines are sent using a previous search score.
1464 string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
1466 std::stringstream ss;
1467 int elapsed = Time.elapsed() + 1;
1468 const Search::RootMoveVector& rootMoves = pos.this_thread()->rootMoves;
1469 size_t PVIdx = pos.this_thread()->PVIdx;
1470 size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
1471 uint64_t nodes_searched = Threads.nodes_searched();
1473 for (size_t i = 0; i < multiPV; ++i)
1475 bool updated = (i <= PVIdx);
1477 if (depth == ONE_PLY && !updated)
1480 Depth d = updated ? depth : depth - ONE_PLY;
1481 Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
1483 bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
1484 v = tb ? TB::Score : v;
1486 if (ss.rdbuf()->in_avail()) // Not at first line
1490 << " depth " << d / ONE_PLY
1491 << " seldepth " << pos.this_thread()->maxPly
1492 << " multipv " << i + 1
1493 << " score " << UCI::value(v);
1495 if (!tb && i == PVIdx)
1496 ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1498 ss << " nodes " << nodes_searched
1499 << " nps " << nodes_searched * 1000 / elapsed;
1501 if (elapsed > 1000) // Earlier makes little sense
1502 ss << " hashfull " << TT.hashfull();
1504 ss << " tbhits " << TB::Hits
1505 << " time " << elapsed
1508 for (Move m : rootMoves[i].pv)
1509 ss << " " << UCI::move(m, pos.is_chess960());
1516 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1517 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1518 /// first, even if the old TT entries have been overwritten.
1520 void RootMove::insert_pv_in_tt(Position& pos) {
1522 StateInfo state[MAX_PLY], *st = state;
1527 assert(MoveList<LEGAL>(pos).contains(m));
1529 TTEntry* tte = TT.probe(pos.key(), ttHit);
1531 if (!ttHit || tte->move() != m) // Don't overwrite correct entries
1532 tte->save(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE,
1533 m, VALUE_NONE, TT.generation());
1535 pos.do_move(m, *st++, pos.gives_check(m, CheckInfo(pos)));
1538 for (size_t i = pv.size(); i > 0; )
1539 pos.undo_move(pv[--i]);
1543 /// RootMove::extract_ponder_from_tt() is called in case we have no ponder move
1544 /// before exiting the search, for instance in case we stop the search during a
1545 /// fail high at root. We try hard to have a ponder move to return to the GUI,
1546 /// otherwise in case of 'ponder on' we have nothing to think on.
1548 bool RootMove::extract_ponder_from_tt(Position& pos)
1553 assert(pv.size() == 1);
1555 pos.do_move(pv[0], st, pos.gives_check(pv[0], CheckInfo(pos)));
1556 TTEntry* tte = TT.probe(pos.key(), ttHit);
1557 pos.undo_move(pv[0]);
1561 Move m = tte->move(); // Local copy to be SMP safe
1562 if (MoveList<LEGAL>(pos).contains(m))
1563 return pv.push_back(m), true;
1570 /// TimerThread::check_time() is called by when the timer triggers. It is used
1571 /// to print debug info and, more importantly, to detect when we are out of
1572 /// available time and thus stop the search.
1574 void TimerThread::check_time() {
1576 static TimePoint lastInfoTime = now();
1577 int elapsed = Time.elapsed();
1579 if (now() - lastInfoTime >= 1000)
1581 lastInfoTime = now();
1585 // An engine may not stop pondering until told so by the GUI
1589 if (Limits.use_time_management())
1591 bool stillAtFirstMove = Signals.firstRootMove
1592 && !Signals.failedLowAtRoot
1593 && elapsed > Time.available() * 3 / 4;
1595 if ( stillAtFirstMove
1596 || elapsed > Time.maximum() - 2 * TimerThread::Resolution)
1597 Signals.stop = true;
1599 else if (Limits.movetime && elapsed >= Limits.movetime)
1600 Signals.stop = true;
1602 else if (Limits.nodes && Threads.nodes_searched() >= Limits.nodes)
1603 Signals.stop = true;