2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2013 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/>.
36 #include "ucioption.h"
40 volatile SignalsType Signals;
42 std::vector<RootMove> RootMoves;
45 Time::point SearchTime;
46 StateStackPtr SetupStates;
51 using namespace Search;
55 // Set to true to force running with one thread. Used for debugging
56 const bool FakeSplit = false;
58 // This is the minimum interval in msec between two check_time() calls
59 const int TimerResolution = 5;
61 // Different node types, used as template parameter
62 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
64 // Dynamic razoring margin based on depth
65 inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
67 // Futility lookup tables (initialized at startup) and their access functions
68 Value FutilityMargins[16][64]; // [depth][moveNumber]
69 int FutilityMoveCounts[32]; // [depth]
71 inline Value futility_margin(Depth d, int mn) {
73 return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
77 // Reduction lookup tables (initialized at startup) and their access function
78 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
80 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
82 return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
88 Value DrawValue[COLOR_NB];
92 template <NodeType NT>
93 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
95 template <NodeType NT, bool InCheck>
96 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
98 void id_loop(Position& pos);
99 Value value_to_tt(Value v, int ply);
100 Value value_from_tt(Value v, int ply);
101 bool check_is_dangerous(const Position& pos, Move move, Value futilityBase, Value beta);
102 bool allows(const Position& pos, Move first, Move second);
103 bool refutes(const Position& pos, Move first, Move second);
104 string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
107 Skill(int l) : level(l), best(MOVE_NONE) {}
109 if (enabled()) // Swap best PV line with the sub-optimal one
110 std::swap(RootMoves[0], *std::find(RootMoves.begin(),
111 RootMoves.end(), best ? best : pick_move()));
114 bool enabled() const { return level < 20; }
115 bool time_to_pick(int depth) const { return depth == 1 + level; }
125 /// Search::init() is called during startup to initialize various lookup tables
127 void Search::init() {
129 int d; // depth (ONE_PLY == 2)
130 int hd; // half depth (ONE_PLY == 1)
133 // Init reductions array
134 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
136 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
137 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
138 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
139 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
142 // Init futility margins array
143 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
144 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
146 // Init futility move count array
147 for (d = 0; d < 32; d++)
148 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(double(d), 2.0));
152 /// Search::perft() is our utility to verify move generation. All the leaf nodes
153 /// up to the given depth are generated and counted and the sum returned.
155 size_t Search::perft(Position& pos, Depth depth) {
157 // At the last ply just return the number of legal moves (leaf nodes)
158 if (depth == ONE_PLY)
159 return MoveList<LEGAL>(pos).size();
165 for (MoveList<LEGAL> ml(pos); !ml.end(); ++ml)
167 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
168 cnt += perft(pos, depth - ONE_PLY);
169 pos.undo_move(ml.move());
176 /// Search::think() is the external interface to Stockfish's search, and is
177 /// called by the main thread when the program receives the UCI 'go' command. It
178 /// searches from RootPos and at the end prints the "bestmove" to output.
180 void Search::think() {
182 static PolyglotBook book; // Defined static to initialize the PRNG only once
184 RootColor = RootPos.side_to_move();
185 TimeMgr.init(Limits, RootPos.game_ply(), RootColor);
187 if (RootMoves.empty())
189 RootMoves.push_back(MOVE_NONE);
190 sync_cout << "info depth 0 score "
191 << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)
197 if (Options["OwnBook"] && !Limits.infinite && !Limits.mate)
199 Move bookMove = book.probe(RootPos, Options["Book File"], Options["Best Book Move"]);
201 if (bookMove && std::count(RootMoves.begin(), RootMoves.end(), bookMove))
203 std::swap(RootMoves[0], *std::find(RootMoves.begin(), RootMoves.end(), bookMove));
208 if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
210 int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns
211 cf = cf * Material::game_phase(RootPos) / PHASE_MIDGAME; // Scale down with phase
212 DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
213 DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
216 DrawValue[WHITE] = DrawValue[BLACK] = VALUE_DRAW;
218 if (Options["Use Search Log"])
220 Log log(Options["Search Log Filename"]);
221 log << "\nSearching: " << RootPos.fen()
222 << "\ninfinite: " << Limits.infinite
223 << " ponder: " << Limits.ponder
224 << " time: " << Limits.time[RootColor]
225 << " increment: " << Limits.inc[RootColor]
226 << " moves to go: " << Limits.movestogo
230 // Reset the threads, still sleeping: will be wake up at split time
231 for (size_t i = 0; i < Threads.size(); i++)
232 Threads[i]->maxPly = 0;
234 Threads.sleepWhileIdle = Options["Use Sleeping Threads"];
236 // Set best timer interval to avoid lagging under time pressure. Timer is
237 // used to check for remaining available thinking time.
238 Threads.timer->msec =
239 Limits.use_time_management() ? std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)) :
240 Limits.nodes ? 2 * TimerResolution
243 Threads.timer->notify_one(); // Wake up the recurring timer
245 id_loop(RootPos); // Let's start searching !
247 Threads.timer->msec = 0; // Stop the timer
248 Threads.sleepWhileIdle = true; // Send idle threads to sleep
250 if (Options["Use Search Log"])
252 Time::point elapsed = Time::now() - SearchTime + 1;
254 Log log(Options["Search Log Filename"]);
255 log << "Nodes: " << RootPos.nodes_searched()
256 << "\nNodes/second: " << RootPos.nodes_searched() * 1000 / elapsed
257 << "\nBest move: " << move_to_san(RootPos, RootMoves[0].pv[0]);
260 RootPos.do_move(RootMoves[0].pv[0], st);
261 log << "\nPonder move: " << move_to_san(RootPos, RootMoves[0].pv[1]) << std::endl;
262 RootPos.undo_move(RootMoves[0].pv[0]);
267 // When search is stopped this info is not printed
268 sync_cout << "info nodes " << RootPos.nodes_searched()
269 << " time " << Time::now() - SearchTime + 1 << sync_endl;
271 // When we reach max depth we arrive here even without Signals.stop is raised,
272 // but if we are pondering or in infinite search, according to UCI protocol,
273 // we shouldn't print the best move before the GUI sends a "stop" or "ponderhit"
274 // command. We simply wait here until GUI sends one of those commands (that
275 // raise Signals.stop).
276 if (!Signals.stop && (Limits.ponder || Limits.infinite))
278 Signals.stopOnPonderhit = true;
279 RootPos.this_thread()->wait_for(Signals.stop);
282 // Best move could be MOVE_NONE when searching on a stalemate position
283 sync_cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], RootPos.is_chess960())
284 << " ponder " << move_to_uci(RootMoves[0].pv[1], RootPos.is_chess960())
291 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
292 // with increasing depth until the allocated thinking time has been consumed,
293 // user stops the search, or the maximum search depth is reached.
295 void id_loop(Position& pos) {
297 Stack ss[MAX_PLY_PLUS_2];
298 int depth, prevBestMoveChanges;
299 Value bestValue, alpha, beta, delta;
301 memset(ss, 0, 4 * sizeof(Stack));
302 depth = BestMoveChanges = 0;
303 bestValue = delta = -VALUE_INFINITE;
304 ss->currentMove = MOVE_NULL; // Hack to skip update gains
309 PVSize = Options["MultiPV"];
310 Skill skill(Options["Skill Level"]);
312 // Do we have to play with skill handicap? In this case enable MultiPV search
313 // that we will use behind the scenes to retrieve a set of possible moves.
314 if (skill.enabled() && PVSize < 4)
317 PVSize = std::min(PVSize, RootMoves.size());
319 // Iterative deepening loop until requested to stop or target depth reached
320 while (++depth <= MAX_PLY && !Signals.stop && (!Limits.depth || depth <= Limits.depth))
322 // Save last iteration's scores before first PV line is searched and all
323 // the move scores but the (new) PV are set to -VALUE_INFINITE.
324 for (size_t i = 0; i < RootMoves.size(); i++)
325 RootMoves[i].prevScore = RootMoves[i].score;
327 prevBestMoveChanges = BestMoveChanges; // Only sensible when PVSize == 1
330 // MultiPV loop. We perform a full root search for each PV line
331 for (PVIdx = 0; PVIdx < PVSize; PVIdx++)
333 // Set aspiration window default width
334 if (depth >= 5 && abs(RootMoves[PVIdx].prevScore) < VALUE_KNOWN_WIN)
337 alpha = RootMoves[PVIdx].prevScore - delta;
338 beta = RootMoves[PVIdx].prevScore + delta;
342 alpha = -VALUE_INFINITE;
343 beta = VALUE_INFINITE;
346 // Start with a small aspiration window and, in case of fail high/low,
347 // research with bigger window until not failing high/low anymore.
350 // Search starts from ss+1 to allow referencing (ss-1). This is
351 // needed by update gains and ss copy when splitting at Root.
352 bestValue = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
354 // Bring to front the best move. It is critical that sorting is
355 // done with a stable algorithm because all the values but the first
356 // and eventually the new best one are set to -VALUE_INFINITE and
357 // we want to keep the same order for all the moves but the new
358 // PV that goes to the front. Note that in case of MultiPV search
359 // the already searched PV lines are preserved.
360 std::stable_sort(RootMoves.begin() + PVIdx, RootMoves.end());
362 // Write PV back to transposition table in case the relevant
363 // entries have been overwritten during the search.
364 for (size_t i = 0; i <= PVIdx; i++)
365 RootMoves[i].insert_pv_in_tt(pos);
367 // If search has been stopped return immediately. Sorting and
368 // writing PV back to TT is safe becuase RootMoves is still
369 // valid, although refers to previous iteration.
373 // In case of failing high/low increase aspiration window and
374 // research, otherwise exit the loop.
375 if (bestValue > alpha && bestValue < beta)
378 // Give some update (without cluttering the UI) before to research
379 if (Time::now() - SearchTime > 3000)
380 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
382 if (abs(bestValue) >= VALUE_KNOWN_WIN)
384 alpha = -VALUE_INFINITE;
385 beta = VALUE_INFINITE;
387 else if (bestValue >= beta)
394 Signals.failedLowAtRoot = true;
395 Signals.stopOnPonderhit = false;
401 assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
404 // Sort the PV lines searched so far and update the GUI
405 std::stable_sort(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
407 if (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
408 sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
411 // Do we need to pick now the sub-optimal best move ?
412 if (skill.enabled() && skill.time_to_pick(depth))
415 if (Options["Use Search Log"])
417 Log log(Options["Search Log Filename"]);
418 log << pretty_pv(pos, depth, bestValue, Time::now() - SearchTime, &RootMoves[0].pv[0])
422 // Do we have found a "mate in x"?
424 && bestValue >= VALUE_MATE_IN_MAX_PLY
425 && VALUE_MATE - bestValue <= 2 * Limits.mate)
428 // Do we have time for the next iteration? Can we stop searching now?
429 if (Limits.use_time_management() && !Signals.stopOnPonderhit)
431 bool stop = false; // Local variable, not the volatile Signals.stop
433 // Take in account some extra time if the best move has changed
434 if (depth > 4 && depth < 50 && PVSize == 1)
435 TimeMgr.pv_instability(BestMoveChanges, prevBestMoveChanges);
437 // Stop search if most of available time is already consumed. We
438 // probably don't have enough time to search the first move at the
439 // next iteration anyway.
440 if (Time::now() - SearchTime > (TimeMgr.available_time() * 62) / 100)
443 // Stop search early if one move seems to be much better than others
447 && bestValue > VALUE_MATED_IN_MAX_PLY
448 && ( RootMoves.size() == 1
449 || Time::now() - SearchTime > (TimeMgr.available_time() * 20) / 100))
451 Value rBeta = bestValue - 2 * PawnValueMg;
452 (ss+1)->excludedMove = RootMoves[0].pv[0];
453 (ss+1)->skipNullMove = true;
454 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth - 3) * ONE_PLY);
455 (ss+1)->skipNullMove = false;
456 (ss+1)->excludedMove = MOVE_NONE;
464 // If we are allowed to ponder do not stop the search now but
465 // keep pondering until GUI sends "ponderhit" or "stop".
467 Signals.stopOnPonderhit = true;
476 // search<>() is the main search function for both PV and non-PV nodes and for
477 // normal and SplitPoint nodes. When called just after a split point the search
478 // is simpler because we have already probed the hash table, done a null move
479 // search, and searched the first move before splitting, we don't have to repeat
480 // all this work again. We also don't need to store anything to the hash table
481 // here: This is taken care of after we return from the split point.
483 template <NodeType NT>
484 Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
486 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
487 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
488 const bool RootNode = (NT == Root || NT == SplitPointRoot);
490 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
491 assert(PvNode || (alpha == beta - 1));
492 assert(depth > DEPTH_ZERO);
494 Move movesSearched[64];
497 SplitPoint* splitPoint;
499 Move ttMove, move, excludedMove, bestMove, threatMove;
501 Value bestValue, value, ttValue;
502 Value eval, nullValue, futilityValue;
503 bool inCheck, givesCheck, pvMove, singularExtensionNode;
504 bool captureOrPromotion, dangerous, doFullDepthSearch;
505 int moveCount, playedMoveCount;
507 // Step 1. Initialize node
508 Thread* thisThread = pos.this_thread();
509 moveCount = playedMoveCount = 0;
510 inCheck = pos.checkers();
514 splitPoint = ss->splitPoint;
515 bestMove = splitPoint->bestMove;
516 threatMove = splitPoint->threatMove;
517 bestValue = splitPoint->bestValue;
519 ttMove = excludedMove = MOVE_NONE;
520 ttValue = VALUE_NONE;
522 assert(splitPoint->bestValue > -VALUE_INFINITE && splitPoint->moveCount > 0);
524 goto split_point_start;
527 bestValue = -VALUE_INFINITE;
528 ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
529 ss->ply = (ss-1)->ply + 1;
530 ss->futilityMoveCount = 0;
531 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
532 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
534 // Used to send selDepth info to GUI
535 if (PvNode && thisThread->maxPly < ss->ply)
536 thisThread->maxPly = ss->ply;
540 // Step 2. Check for aborted search and immediate draw
541 if (Signals.stop || pos.is_draw() || ss->ply > MAX_PLY)
542 return DrawValue[pos.side_to_move()];
544 // Step 3. Mate distance pruning. Even if we mate at the next move our score
545 // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
546 // a shorter mate was found upward in the tree then there is no need to search
547 // further, we will never beat current alpha. Same logic but with reversed signs
548 // applies also in the opposite condition of being mated instead of giving mate,
549 // in this case return a fail-high score.
550 alpha = std::max(mated_in(ss->ply), alpha);
551 beta = std::min(mate_in(ss->ply+1), beta);
556 // Step 4. Transposition table lookup
557 // We don't want the score of a partial search to overwrite a previous full search
558 // TT value, so we use a different position key in case of an excluded move.
559 excludedMove = ss->excludedMove;
560 posKey = excludedMove ? pos.exclusion_key() : pos.key();
561 tte = TT.probe(posKey);
562 ttMove = RootNode ? RootMoves[PVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
563 ttValue = tte ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
565 // At PV nodes we check for exact scores, while at non-PV nodes we check for
566 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
567 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
568 // we should also update RootMoveList to avoid bogus output.
571 && tte->depth() >= depth
572 && ttValue != VALUE_NONE // Only in case of TT access race
573 && ( PvNode ? tte->type() == BOUND_EXACT
574 : ttValue >= beta ? (tte->type() & BOUND_LOWER)
575 : (tte->type() & BOUND_UPPER)))
578 ss->currentMove = ttMove; // Can be MOVE_NONE
582 && !pos.is_capture_or_promotion(ttMove)
583 && ttMove != ss->killers[0])
585 ss->killers[1] = ss->killers[0];
586 ss->killers[0] = ttMove;
591 // Step 5. Evaluate the position statically and update parent's gain statistics
593 ss->staticEval = ss->evalMargin = eval = VALUE_NONE;
597 // Never assume anything on values stored in TT
598 if ( (ss->staticEval = eval = tte->eval_value()) == VALUE_NONE
599 ||(ss->evalMargin = tte->eval_margin()) == VALUE_NONE)
600 eval = ss->staticEval = evaluate(pos, ss->evalMargin);
602 // Can ttValue be used as a better position evaluation?
603 if (ttValue != VALUE_NONE)
604 if ( ((tte->type() & BOUND_LOWER) && ttValue > eval)
605 || ((tte->type() & BOUND_UPPER) && ttValue < eval))
610 eval = ss->staticEval = evaluate(pos, ss->evalMargin);
611 TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
612 ss->staticEval, ss->evalMargin);
615 // Update gain for the parent non-capture move given the static position
616 // evaluation before and after the move.
617 if ( (move = (ss-1)->currentMove) != MOVE_NULL
618 && (ss-1)->staticEval != VALUE_NONE
619 && ss->staticEval != VALUE_NONE
620 && !pos.captured_piece_type()
621 && type_of(move) == NORMAL)
623 Square to = to_sq(move);
624 Gain.update(pos.piece_on(to), to, -(ss-1)->staticEval - ss->staticEval);
627 // Step 6. Razoring (is omitted in PV nodes)
629 && depth < 4 * ONE_PLY
631 && eval + razor_margin(depth) < beta
632 && ttMove == MOVE_NONE
633 && abs(beta) < VALUE_MATE_IN_MAX_PLY
634 && !pos.pawn_on_7th(pos.side_to_move()))
636 Value rbeta = beta - razor_margin(depth);
637 Value v = qsearch<NonPV, false>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
639 // Logically we should return (v + razor_margin(depth)), but
640 // surprisingly this did slightly weaker in tests.
644 // Step 7. Static null move pruning (is omitted in PV nodes)
645 // We're betting that the opponent doesn't have a move that will reduce
646 // the score by more than futility_margin(depth) if we do a null move.
649 && depth < 4 * ONE_PLY
651 && eval - futility_margin(depth, (ss-1)->futilityMoveCount) >= beta
652 && abs(beta) < VALUE_MATE_IN_MAX_PLY
653 && abs(eval) < VALUE_KNOWN_WIN
654 && pos.non_pawn_material(pos.side_to_move()))
655 return eval - futility_margin(depth, (ss-1)->futilityMoveCount);
657 // Step 8. Null move search with verification search (is omitted in PV nodes)
663 && abs(beta) < VALUE_MATE_IN_MAX_PLY
664 && pos.non_pawn_material(pos.side_to_move()))
666 ss->currentMove = MOVE_NULL;
668 // Null move dynamic reduction based on depth
669 Depth R = 3 * ONE_PLY + depth / 4;
671 // Null move dynamic reduction based on value
672 if (eval - PawnValueMg > beta)
675 pos.do_null_move(st);
676 (ss+1)->skipNullMove = true;
677 nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
678 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R);
679 (ss+1)->skipNullMove = false;
680 pos.undo_null_move();
682 if (nullValue >= beta)
684 // Do not return unproven mate scores
685 if (nullValue >= VALUE_MATE_IN_MAX_PLY)
688 if (depth < 12 * ONE_PLY)
691 // Do verification search at high depths
692 ss->skipNullMove = true;
693 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R);
694 ss->skipNullMove = false;
701 // The null move failed low, which means that we may be faced with
702 // some kind of threat. If the previous move was reduced, check if
703 // the move that refuted the null move was somehow connected to the
704 // move which was reduced. If a connection is found, return a fail
705 // low score (which will cause the reduced move to fail high in the
706 // parent node, which will trigger a re-search with full depth).
707 threatMove = (ss+1)->currentMove;
709 if ( depth < 5 * ONE_PLY
711 && threatMove != MOVE_NONE
712 && allows(pos, (ss-1)->currentMove, threatMove))
717 // Step 9. ProbCut (is omitted in PV nodes)
718 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
719 // and a reduced search returns a value much above beta, we can (almost) safely
720 // prune the previous move.
722 && depth >= 5 * ONE_PLY
725 && excludedMove == MOVE_NONE
726 && abs(beta) < VALUE_MATE_IN_MAX_PLY)
728 Value rbeta = beta + 200;
729 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
731 assert(rdepth >= ONE_PLY);
732 assert((ss-1)->currentMove != MOVE_NONE);
733 assert((ss-1)->currentMove != MOVE_NULL);
735 MovePicker mp(pos, ttMove, Hist, pos.captured_piece_type());
738 while ((move = mp.next_move<false>()) != MOVE_NONE)
739 if (pos.pl_move_is_legal(move, ci.pinned))
741 ss->currentMove = move;
742 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
743 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
750 // Step 10. Internal iterative deepening
751 if ( depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)
752 && ttMove == MOVE_NONE
753 && (PvNode || (!inCheck && ss->staticEval + Value(256) >= beta)))
755 Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
757 ss->skipNullMove = true;
758 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
759 ss->skipNullMove = false;
761 tte = TT.probe(posKey);
762 ttMove = tte ? tte->move() : MOVE_NONE;
765 split_point_start: // At split points actual search starts from here
767 MovePicker mp(pos, ttMove, depth, Hist, ss, PvNode ? -VALUE_INFINITE : beta);
769 value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
770 singularExtensionNode = !RootNode
772 && depth >= (PvNode ? 6 * ONE_PLY : 8 * ONE_PLY)
773 && ttMove != MOVE_NONE
774 && !excludedMove // Recursive singular search is not allowed
775 && (tte->type() & BOUND_LOWER)
776 && tte->depth() >= depth - 3 * ONE_PLY;
778 // Step 11. Loop through moves
779 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
780 while ((move = mp.next_move<SpNode>()) != MOVE_NONE)
784 if (move == excludedMove)
787 // At root obey the "searchmoves" option and skip moves not listed in Root
788 // Move List, as a consequence any illegal move is also skipped. In MultiPV
789 // mode we also skip PV moves which have been already searched.
790 if (RootNode && !std::count(RootMoves.begin() + PVIdx, RootMoves.end(), move))
795 // Shared counter cannot be decremented later if move turns out to be illegal
796 if (!pos.pl_move_is_legal(move, ci.pinned))
799 moveCount = ++splitPoint->moveCount;
800 splitPoint->mutex.unlock();
807 Signals.firstRootMove = (moveCount == 1);
809 if (thisThread == Threads.main_thread() && Time::now() - SearchTime > 3000)
810 sync_cout << "info depth " << depth / ONE_PLY
811 << " currmove " << move_to_uci(move, pos.is_chess960())
812 << " currmovenumber " << moveCount + PVIdx << sync_endl;
816 captureOrPromotion = pos.is_capture_or_promotion(move);
817 givesCheck = pos.move_gives_check(move, ci);
818 dangerous = givesCheck
819 || pos.is_passed_pawn_push(move)
820 || type_of(move) == CASTLE
821 || ( captureOrPromotion // Entering a pawn endgame?
822 && type_of(pos.piece_on(to_sq(move))) != PAWN
823 && type_of(move) == NORMAL
824 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
825 - PieceValue[MG][pos.piece_on(to_sq(move))] == VALUE_ZERO));
827 // Step 12. Extend checks and, in PV nodes, also dangerous moves
828 if (PvNode && dangerous)
831 else if (givesCheck && pos.see_sign(move) >= 0)
834 // Singular extension search. If all moves but one fail low on a search of
835 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
836 // is singular and should be extended. To verify this we do a reduced search
837 // on all the other moves but the ttMove, if result is lower than ttValue minus
838 // a margin then we extend ttMove.
839 if ( singularExtensionNode
842 && pos.pl_move_is_legal(move, ci.pinned)
843 && abs(ttValue) < VALUE_KNOWN_WIN)
845 assert(ttValue != VALUE_NONE);
847 Value rBeta = ttValue - int(depth);
848 ss->excludedMove = move;
849 ss->skipNullMove = true;
850 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
851 ss->skipNullMove = false;
852 ss->excludedMove = MOVE_NONE;
858 // Update current move (this must be done after singular extension search)
859 newDepth = depth - ONE_PLY + ext;
861 // Step 13. Futility pruning (is omitted in PV nodes)
863 && !captureOrPromotion
866 /* && move != ttMove Already implicit in the next condition */
867 && bestValue > VALUE_MATED_IN_MAX_PLY)
869 // Move count based pruning
870 if ( depth < 16 * ONE_PLY
871 && moveCount >= FutilityMoveCounts[depth]
872 && (!threatMove || !refutes(pos, move, threatMove)))
875 splitPoint->mutex.lock();
880 // Value based pruning
881 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
882 // but fixing this made program slightly weaker.
883 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
884 futilityValue = ss->staticEval + ss->evalMargin + futility_margin(predictedDepth, moveCount)
885 + Gain[pos.piece_moved(move)][to_sq(move)];
887 if (futilityValue < beta)
889 bestValue = std::max(bestValue, futilityValue);
893 splitPoint->mutex.lock();
894 if (bestValue > splitPoint->bestValue)
895 splitPoint->bestValue = bestValue;
900 // Prune moves with negative SEE at low depths
901 if ( predictedDepth < 4 * ONE_PLY
902 && pos.see_sign(move) < 0)
905 splitPoint->mutex.lock();
910 // We have not pruned the move that will be searched, but remember how
911 // far in the move list we are to be more aggressive in the child node.
912 ss->futilityMoveCount = moveCount;
915 ss->futilityMoveCount = 0;
917 // Check for legality only before to do the move
918 if (!RootNode && !SpNode && !pos.pl_move_is_legal(move, ci.pinned))
924 pvMove = PvNode && moveCount == 1;
925 ss->currentMove = move;
926 if (!SpNode && !captureOrPromotion && playedMoveCount < 64)
927 movesSearched[playedMoveCount++] = move;
929 // Step 14. Make the move
930 pos.do_move(move, st, ci, givesCheck);
932 // Step 15. Reduced depth search (LMR). If the move fails high will be
933 // re-searched at full depth.
934 if ( depth > 3 * ONE_PLY
936 && !captureOrPromotion
939 && move != ss->killers[0]
940 && move != ss->killers[1])
942 ss->reduction = reduction<PvNode>(depth, moveCount);
943 Depth d = std::max(newDepth - ss->reduction, ONE_PLY);
945 alpha = splitPoint->alpha;
947 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
949 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
950 ss->reduction = DEPTH_ZERO;
953 doFullDepthSearch = !pvMove;
955 // Step 16. Full depth search, when LMR is skipped or fails high
956 if (doFullDepthSearch)
959 alpha = splitPoint->alpha;
961 value = newDepth < ONE_PLY ?
962 givesCheck ? -qsearch<NonPV, true>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
963 : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
964 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
967 // Only for PV nodes do a full PV search on the first move or after a fail
968 // high, in the latter case search only if value < beta, otherwise let the
969 // parent node to fail low with value <= alpha and to try another move.
970 if (PvNode && (pvMove || (value > alpha && (RootNode || value < beta))))
971 value = newDepth < ONE_PLY ?
972 givesCheck ? -qsearch<PV, true>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
973 : -qsearch<PV, false>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
974 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
975 // Step 17. Undo move
978 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
980 // Step 18. Check for new best move
983 splitPoint->mutex.lock();
984 bestValue = splitPoint->bestValue;
985 alpha = splitPoint->alpha;
988 // Finished searching the move. If Signals.stop is true, the search
989 // was aborted because the user interrupted the search or because we
990 // ran out of time. In this case, the return value of the search cannot
991 // be trusted, and we don't update the best move and/or PV.
992 if (Signals.stop || thisThread->cutoff_occurred())
993 return value; // To avoid returning VALUE_INFINITE
997 RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
999 // PV move or new best move ?
1000 if (pvMove || value > alpha)
1003 rm.extract_pv_from_tt(pos);
1005 // We record how often the best move has been changed in each
1006 // iteration. This information is used for time management: When
1007 // the best move changes frequently, we allocate some more time.
1012 // All other moves but the PV are set to the lowest value, this
1013 // is not a problem when sorting becuase sort is stable and move
1014 // position in the list is preserved, just the PV is pushed up.
1015 rm.score = -VALUE_INFINITE;
1018 if (value > bestValue)
1020 bestValue = SpNode ? splitPoint->bestValue = value : value;
1024 bestMove = SpNode ? splitPoint->bestMove = move : move;
1026 if (PvNode && value < beta) // Update alpha! Always alpha < beta
1027 alpha = SpNode ? splitPoint->alpha = value : value;
1030 assert(value >= beta); // Fail high
1033 splitPoint->cutoff = true;
1040 // Step 19. Check for splitting the search
1042 && depth >= Threads.minimumSplitDepth
1043 && Threads.available_slave(thisThread)
1044 && thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
1046 assert(bestValue < beta);
1048 thisThread->split<FakeSplit>(pos, ss, alpha, beta, &bestValue, &bestMove,
1049 depth, threatMove, moveCount, &mp, NT);
1050 if (bestValue >= beta)
1058 // Step 20. Check for mate and stalemate
1059 // All legal moves have been searched and if there are no legal moves, it
1060 // must be mate or stalemate. Note that we can have a false positive in
1061 // case of Signals.stop or thread.cutoff_occurred() are set, but this is
1062 // harmless because return value is discarded anyhow in the parent nodes.
1063 // If we are in a singular extension search then return a fail low score.
1064 // A split node has at least one move, the one tried before to be splitted.
1066 return excludedMove ? alpha
1067 : inCheck ? mated_in(ss->ply) : DrawValue[pos.side_to_move()];
1069 // If we have pruned all the moves without searching return a fail-low score
1070 if (bestValue == -VALUE_INFINITE)
1072 assert(!playedMoveCount);
1077 if (bestValue >= beta) // Failed high
1079 TT.store(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER, depth,
1080 bestMove, ss->staticEval, ss->evalMargin);
1082 if (!pos.is_capture_or_promotion(bestMove) && !inCheck)
1084 if (bestMove != ss->killers[0])
1086 ss->killers[1] = ss->killers[0];
1087 ss->killers[0] = bestMove;
1090 // Increase history value of the cut-off move
1091 Value bonus = Value(int(depth) * int(depth));
1092 Hist.update(pos.piece_moved(bestMove), to_sq(bestMove), bonus);
1094 // Decrease history of all the other played non-capture moves
1095 for (int i = 0; i < playedMoveCount - 1; i++)
1097 Move m = movesSearched[i];
1098 Hist.update(pos.piece_moved(m), to_sq(m), -bonus);
1102 else // Failed low or PV search
1103 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1104 PvNode && bestMove != MOVE_NONE ? BOUND_EXACT : BOUND_UPPER,
1105 depth, bestMove, ss->staticEval, ss->evalMargin);
1107 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1113 // qsearch() is the quiescence search function, which is called by the main
1114 // search function when the remaining depth is zero (or, to be more precise,
1115 // less than ONE_PLY).
1117 template <NodeType NT, bool InCheck>
1118 Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
1120 const bool PvNode = (NT == PV);
1122 assert(NT == PV || NT == NonPV);
1123 assert(InCheck == !!pos.checkers());
1124 assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
1125 assert(PvNode || (alpha == beta - 1));
1126 assert(depth <= DEPTH_ZERO);
1131 Move ttMove, move, bestMove;
1132 Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
1133 bool givesCheck, enoughMaterial, evasionPrunable;
1136 // To flag BOUND_EXACT a node with eval above alpha and no available moves
1140 ss->currentMove = bestMove = MOVE_NONE;
1141 ss->ply = (ss-1)->ply + 1;
1143 // Check for an instant draw or maximum ply reached
1144 if (pos.is_draw() || ss->ply > MAX_PLY)
1145 return DrawValue[pos.side_to_move()];
1147 // Decide whether or not to include checks, this fixes also the type of
1148 // TT entry depth that we are going to use. Note that in qsearch we use
1149 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1150 ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
1151 : DEPTH_QS_NO_CHECKS;
1153 // Transposition table lookup. At PV nodes, we don't use the TT for
1154 // pruning, but only for move ordering.
1156 tte = TT.probe(posKey);
1157 ttMove = tte ? tte->move() : MOVE_NONE;
1158 ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;
1161 && tte->depth() >= ttDepth
1162 && ttValue != VALUE_NONE // Only in case of TT access race
1163 && ( PvNode ? tte->type() == BOUND_EXACT
1164 : ttValue >= beta ? (tte->type() & BOUND_LOWER)
1165 : (tte->type() & BOUND_UPPER)))
1167 ss->currentMove = ttMove; // Can be MOVE_NONE
1171 // Evaluate the position statically
1174 ss->staticEval = ss->evalMargin = VALUE_NONE;
1175 bestValue = futilityBase = -VALUE_INFINITE;
1176 enoughMaterial = false;
1182 // Never assume anything on values stored in TT
1183 if ( (ss->staticEval = bestValue = tte->eval_value()) == VALUE_NONE
1184 ||(ss->evalMargin = tte->eval_margin()) == VALUE_NONE)
1185 ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
1188 ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
1190 // Stand pat. Return immediately if static value is at least beta
1191 if (bestValue >= beta)
1194 TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER,
1195 DEPTH_NONE, MOVE_NONE, ss->staticEval, ss->evalMargin);
1200 if (PvNode && bestValue > alpha)
1203 futilityBase = ss->staticEval + ss->evalMargin + Value(128);
1204 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMg;
1207 // Initialize a MovePicker object for the current position, and prepare
1208 // to search the moves. Because the depth is <= 0 here, only captures,
1209 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1211 MovePicker mp(pos, ttMove, depth, Hist, to_sq((ss-1)->currentMove));
1214 // Loop through the moves until no moves remain or a beta cutoff occurs
1215 while ((move = mp.next_move<false>()) != MOVE_NONE)
1217 assert(is_ok(move));
1219 givesCheck = pos.move_gives_check(move, ci);
1227 && type_of(move) != PROMOTION
1228 && !pos.is_passed_pawn_push(move))
1230 futilityValue = futilityBase
1231 + PieceValue[EG][pos.piece_on(to_sq(move))]
1232 + (type_of(move) == ENPASSANT ? PawnValueEg : VALUE_ZERO);
1234 if (futilityValue < beta)
1236 bestValue = std::max(bestValue, futilityValue);
1240 // Prune moves with negative or equal SEE and also moves with positive
1241 // SEE where capturing piece loses a tempo and SEE < beta - futilityBase.
1242 if ( futilityBase < beta
1243 && depth < DEPTH_ZERO
1244 && pos.see(move, beta - futilityBase) <= 0)
1246 bestValue = std::max(bestValue, futilityBase);
1251 // Detect non-capture evasions that are candidate to be pruned
1252 evasionPrunable = !PvNode
1254 && bestValue > VALUE_MATED_IN_MAX_PLY
1255 && !pos.is_capture(move)
1256 && !pos.can_castle(pos.side_to_move());
1258 // Don't search moves with negative SEE values
1260 && (!InCheck || evasionPrunable)
1262 && type_of(move) != PROMOTION
1263 && pos.see_sign(move) < 0)
1266 // Don't search useless checks
1271 && !pos.is_capture_or_promotion(move)
1272 && ss->staticEval + PawnValueMg / 4 < beta
1273 && !check_is_dangerous(pos, move, futilityBase, beta))
1276 // Check for legality only before to do the move
1277 if (!pos.pl_move_is_legal(move, ci.pinned))
1280 ss->currentMove = move;
1282 // Make and search the move
1283 pos.do_move(move, st, ci, givesCheck);
1284 value = givesCheck ? -qsearch<NT, true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
1285 : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
1286 pos.undo_move(move);
1288 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1290 // Check for new best move
1291 if (value > bestValue)
1297 if (PvNode && value < beta) // Update alpha here! Always alpha < beta
1304 TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
1305 ttDepth, move, ss->staticEval, ss->evalMargin);
1313 // All legal moves have been searched. A special case: If we're in check
1314 // and no legal moves were found, it is checkmate.
1315 if (InCheck && bestValue == -VALUE_INFINITE)
1316 return mated_in(ss->ply); // Plies to mate from the root
1318 TT.store(posKey, value_to_tt(bestValue, ss->ply),
1319 PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
1320 ttDepth, bestMove, ss->staticEval, ss->evalMargin);
1322 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1328 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1329 // "plies to mate from the current position". Non-mate scores are unchanged.
1330 // The function is called before storing a value to the transposition table.
1332 Value value_to_tt(Value v, int ply) {
1334 assert(v != VALUE_NONE);
1336 return v >= VALUE_MATE_IN_MAX_PLY ? v + ply
1337 : v <= VALUE_MATED_IN_MAX_PLY ? v - ply : v;
1341 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score
1342 // from the transposition table (where refers to the plies to mate/be mated
1343 // from current position) to "plies to mate/be mated from the root".
1345 Value value_from_tt(Value v, int ply) {
1347 return v == VALUE_NONE ? VALUE_NONE
1348 : v >= VALUE_MATE_IN_MAX_PLY ? v - ply
1349 : v <= VALUE_MATED_IN_MAX_PLY ? v + ply : v;
1353 // check_is_dangerous() tests if a checking move can be pruned in qsearch()
1355 bool check_is_dangerous(const Position& pos, Move move, Value futilityBase, Value beta)
1357 Piece pc = pos.piece_moved(move);
1358 Square from = from_sq(move);
1359 Square to = to_sq(move);
1360 Color them = ~pos.side_to_move();
1361 Square ksq = pos.king_square(them);
1362 Bitboard enemies = pos.pieces(them);
1363 Bitboard kingAtt = pos.attacks_from<KING>(ksq);
1364 Bitboard occ = pos.pieces() ^ from ^ ksq;
1365 Bitboard oldAtt = pos.attacks_from(pc, from, occ);
1366 Bitboard newAtt = pos.attacks_from(pc, to, occ);
1368 // Checks which give opponent's king at most one escape square are dangerous
1369 if (!more_than_one(kingAtt & ~(enemies | newAtt | to)))
1372 // Queen contact check is very dangerous
1373 if (type_of(pc) == QUEEN && (kingAtt & to))
1376 // Creating new double threats with checks is dangerous
1377 Bitboard b = (enemies ^ ksq) & newAtt & ~oldAtt;
1380 // Note that here we generate illegal "double move"!
1381 if (futilityBase + PieceValue[EG][pos.piece_on(pop_lsb(&b))] >= beta)
1389 // allows() tests whether the 'first' move at previous ply somehow makes the
1390 // 'second' move possible, for instance if the moving piece is the same in
1391 // both moves. Normally the second move is the threat (the best move returned
1392 // from a null search that fails low).
1394 bool allows(const Position& pos, Move first, Move second) {
1396 assert(is_ok(first));
1397 assert(is_ok(second));
1398 assert(color_of(pos.piece_on(from_sq(second))) == ~pos.side_to_move());
1399 assert(color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());
1401 Square m1from = from_sq(first);
1402 Square m2from = from_sq(second);
1403 Square m1to = to_sq(first);
1404 Square m2to = to_sq(second);
1406 // The piece is the same or second's destination was vacated by the first move
1407 if (m1to == m2from || m2to == m1from)
1410 // Second one moves through the square vacated by first one
1411 if (between_bb(m2from, m2to) & m1from)
1414 // Second's destination is defended by the first move's piece
1415 Bitboard m1att = pos.attacks_from(pos.piece_on(m1to), m1to, pos.pieces() ^ m2from);
1419 // Second move gives a discovered check through the first's checking piece
1420 if (m1att & pos.king_square(pos.side_to_move()))
1422 assert(between_bb(m1to, pos.king_square(pos.side_to_move())) & m2from);
1430 // refutes() tests whether a 'first' move is able to defend against a 'second'
1431 // opponent's move. In this case will not be pruned. Normally the second move
1432 // is the threat (the best move returned from a null search that fails low).
1434 bool refutes(const Position& pos, Move first, Move second) {
1436 assert(is_ok(first));
1437 assert(is_ok(second));
1439 Square m1from = from_sq(first);
1440 Square m2from = from_sq(second);
1441 Square m1to = to_sq(first);
1442 Square m2to = to_sq(second);
1444 // Don't prune moves of the threatened piece
1448 // If the threatened piece has value less than or equal to the value of the
1449 // threat piece, don't prune moves which defend it.
1450 if ( pos.is_capture(second)
1451 && ( PieceValue[MG][pos.piece_on(m2from)] >= PieceValue[MG][pos.piece_on(m2to)]
1452 || type_of(pos.piece_on(m2from)) == KING))
1454 // Update occupancy as if the piece and the threat are moving
1455 Bitboard occ = pos.pieces() ^ m1from ^ m1to ^ m2from;
1456 Piece piece = pos.piece_on(m1from);
1458 // The moved piece attacks the square 'tto' ?
1459 if (pos.attacks_from(piece, m1to, occ) & m2to)
1462 // Scan for possible X-ray attackers behind the moved piece
1463 Bitboard xray = (attacks_bb< ROOK>(m2to, occ) & pos.pieces(color_of(piece), QUEEN, ROOK))
1464 | (attacks_bb<BISHOP>(m2to, occ) & pos.pieces(color_of(piece), QUEEN, BISHOP));
1466 // Verify attackers are triggered by our move and not already existing
1467 if (xray && (xray ^ (xray & pos.attacks_from<QUEEN>(m2to))))
1471 // Don't prune safe moves which block the threat path
1472 if ((between_bb(m2from, m2to) & m1to) && pos.see_sign(first) >= 0)
1479 // When playing with strength handicap choose best move among the MultiPV set
1480 // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
1482 Move Skill::pick_move() {
1486 // PRNG sequence should be not deterministic
1487 for (int i = Time::now() % 50; i > 0; i--)
1488 rk.rand<unsigned>();
1490 // RootMoves are already sorted by score in descending order
1491 int variance = std::min(RootMoves[0].score - RootMoves[PVSize - 1].score, PawnValueMg);
1492 int weakness = 120 - 2 * level;
1493 int max_s = -VALUE_INFINITE;
1496 // Choose best move. For each move score we add two terms both dependent on
1497 // weakness, one deterministic and bigger for weaker moves, and one random,
1498 // then we choose the move with the resulting highest score.
1499 for (size_t i = 0; i < PVSize; i++)
1501 int s = RootMoves[i].score;
1503 // Don't allow crazy blunders even at very low skills
1504 if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)
1507 // This is our magic formula
1508 s += ( weakness * int(RootMoves[0].score - s)
1509 + variance * (rk.rand<unsigned>() % weakness)) / 128;
1514 best = RootMoves[i].pv[0];
1521 // uci_pv() formats PV information according to UCI protocol. UCI requires
1522 // to send all the PV lines also if are still to be searched and so refer to
1523 // the previous search score.
1525 string uci_pv(const Position& pos, int depth, Value alpha, Value beta) {
1527 std::stringstream s;
1528 Time::point elaspsed = Time::now() - SearchTime + 1;
1529 size_t uciPVSize = std::min((size_t)Options["MultiPV"], RootMoves.size());
1532 for (size_t i = 0; i < Threads.size(); i++)
1533 if (Threads[i]->maxPly > selDepth)
1534 selDepth = Threads[i]->maxPly;
1536 for (size_t i = 0; i < uciPVSize; i++)
1538 bool updated = (i <= PVIdx);
1540 if (depth == 1 && !updated)
1543 int d = updated ? depth : depth - 1;
1544 Value v = updated ? RootMoves[i].score : RootMoves[i].prevScore;
1546 if (s.rdbuf()->in_avail()) // Not at first line
1549 s << "info depth " << d
1550 << " seldepth " << selDepth
1551 << " score " << (i == PVIdx ? score_to_uci(v, alpha, beta) : score_to_uci(v))
1552 << " nodes " << pos.nodes_searched()
1553 << " nps " << pos.nodes_searched() * 1000 / elaspsed
1554 << " time " << elaspsed
1555 << " multipv " << i + 1
1558 for (size_t j = 0; RootMoves[i].pv[j] != MOVE_NONE; j++)
1559 s << " " << move_to_uci(RootMoves[i].pv[j], pos.is_chess960());
1568 /// RootMove::extract_pv_from_tt() builds a PV by adding moves from the TT table.
1569 /// We consider also failing high nodes and not only BOUND_EXACT nodes so to
1570 /// allow to always have a ponder move even when we fail high at root, and a
1571 /// long PV to print that is important for position analysis.
1573 void RootMove::extract_pv_from_tt(Position& pos) {
1575 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1585 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1587 pos.do_move(pv[ply++], *st++);
1588 tte = TT.probe(pos.key());
1591 && pos.is_pseudo_legal(m = tte->move()) // Local copy, TT could change
1592 && pos.pl_move_is_legal(m, pos.pinned_pieces())
1594 && (!pos.is_draw() || ply < 2));
1596 pv.push_back(MOVE_NONE); // Must be zero-terminating
1598 while (ply) pos.undo_move(pv[--ply]);
1602 /// RootMove::insert_pv_in_tt() is called at the end of a search iteration, and
1603 /// inserts the PV back into the TT. This makes sure the old PV moves are searched
1604 /// first, even if the old TT entries have been overwritten.
1606 void RootMove::insert_pv_in_tt(Position& pos) {
1608 StateInfo state[MAX_PLY_PLUS_2], *st = state;
1613 tte = TT.probe(pos.key());
1615 if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
1616 TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], VALUE_NONE, VALUE_NONE);
1618 assert(MoveList<LEGAL>(pos).contains(pv[ply]));
1620 pos.do_move(pv[ply++], *st++);
1622 } while (pv[ply] != MOVE_NONE);
1624 while (ply) pos.undo_move(pv[--ply]);
1628 /// Thread::idle_loop() is where the thread is parked when it has no work to do
1630 void Thread::idle_loop() {
1632 // Pointer 'this_sp' is not null only if we are called from split(), and not
1633 // at the thread creation. So it means we are the split point's master.
1634 SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
1636 assert(!this_sp || (this_sp->masterThread == this && searching));
1640 // If we are not searching, wait for a condition to be signaled instead of
1641 // wasting CPU time polling for work.
1642 while ((!searching && Threads.sleepWhileIdle) || exit)
1650 // Grab the lock to avoid races with Thread::notify_one()
1653 // If we are master and all slaves have finished then exit idle_loop
1654 if (this_sp && !this_sp->slavesMask)
1660 // Do sleep after retesting sleep conditions under lock protection, in
1661 // particular we need to avoid a deadlock in case a master thread has,
1662 // in the meanwhile, allocated us and sent the notify_one() call before
1663 // we had the chance to grab the lock.
1664 if (!searching && !exit)
1665 sleepCondition.wait(mutex);
1670 // If this thread has been assigned work, launch a search
1675 Threads.mutex.lock();
1678 SplitPoint* sp = activeSplitPoint;
1680 Threads.mutex.unlock();
1682 Stack ss[MAX_PLY_PLUS_2];
1683 Position pos(*sp->pos, this);
1685 memcpy(ss, sp->ss - 1, 4 * sizeof(Stack));
1686 (ss+1)->splitPoint = sp;
1690 assert(activePosition == NULL);
1692 activePosition = &pos;
1694 switch (sp->nodeType) {
1696 search<SplitPointRoot>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1699 search<SplitPointPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1702 search<SplitPointNonPV>(pos, ss+1, sp->alpha, sp->beta, sp->depth);
1711 activePosition = NULL;
1712 sp->slavesMask &= ~(1ULL << idx);
1713 sp->nodes += pos.nodes_searched();
1715 // Wake up master thread so to allow it to return from the idle loop
1716 // in case we are the last slave of the split point.
1717 if ( Threads.sleepWhileIdle
1718 && this != sp->masterThread
1721 assert(!sp->masterThread->searching);
1722 sp->masterThread->notify_one();
1725 // After releasing the lock we cannot access anymore any SplitPoint
1726 // related data in a safe way becuase it could have been released under
1727 // our feet by the sp master. Also accessing other Thread objects is
1728 // unsafe because if we are exiting there is a chance are already freed.
1732 // If this thread is the master of a split point and all slaves have finished
1733 // their work at this split point, return from the idle loop.
1734 if (this_sp && !this_sp->slavesMask)
1736 this_sp->mutex.lock();
1737 bool finished = !this_sp->slavesMask; // Retest under lock protection
1738 this_sp->mutex.unlock();
1746 /// check_time() is called by the timer thread when the timer triggers. It is
1747 /// used to print debug info and, more important, to detect when we are out of
1748 /// available time and so stop the search.
1752 static Time::point lastInfoTime = Time::now();
1753 int64_t nodes = 0; // Workaround silly 'uninitialized' gcc warning
1755 if (Time::now() - lastInfoTime >= 1000)
1757 lastInfoTime = Time::now();
1766 Threads.mutex.lock();
1768 nodes = RootPos.nodes_searched();
1770 // Loop across all split points and sum accumulated SplitPoint nodes plus
1771 // all the currently active positions nodes.
1772 for (size_t i = 0; i < Threads.size(); i++)
1773 for (int j = 0; j < Threads[i]->splitPointsSize; j++)
1775 SplitPoint& sp = Threads[i]->splitPoints[j];
1780 Bitboard sm = sp.slavesMask;
1783 Position* pos = Threads[pop_lsb(&sm)]->activePosition;
1785 nodes += pos->nodes_searched();
1791 Threads.mutex.unlock();
1794 Time::point elapsed = Time::now() - SearchTime;
1795 bool stillAtFirstMove = Signals.firstRootMove
1796 && !Signals.failedLowAtRoot
1797 && elapsed > TimeMgr.available_time();
1799 bool noMoreTime = elapsed > TimeMgr.maximum_time() - 2 * TimerResolution
1800 || stillAtFirstMove;
1802 if ( (Limits.use_time_management() && noMoreTime)
1803 || (Limits.movetime && elapsed >= Limits.movetime)
1804 || (Limits.nodes && nodes >= Limits.nodes))
1805 Signals.stop = true;