2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 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/>.
40 #include "ucioption.h"
48 // Set to true to force running with one thread. Used for debugging
49 const bool FakeSplit = false;
51 // Different node types, used as template parameter
52 enum NodeType { Root, PV, NonPV, SplitPointPV, SplitPointNonPV };
54 // RootMove struct is used for moves at the root of the tree. For each root
55 // move, we store a pv_score, a node count, and a PV (really a refutation
56 // in the case of moves which fail low). Value pv_score is normally set at
57 // -VALUE_INFINITE for all non-pv moves.
60 // RootMove::operator<() is the comparison function used when
61 // sorting the moves. A move m1 is considered to be better
62 // than a move m2 if it has an higher pv_score
63 bool operator<(const RootMove& m) const { return pv_score < m.pv_score; }
65 void extract_pv_from_tt(Position& pos);
66 void insert_pv_in_tt(Position& pos);
73 // RootMoveList struct is mainly a std::vector of RootMove objects
74 struct RootMoveList : public std::vector<RootMove> {
76 void init(Position& pos, Move searchMoves[]);
77 RootMove* find(const Move& m, int startIndex = 0);
85 // Lookup table to check if a Piece is a slider and its access function
86 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
87 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
91 // Maximum depth for razoring
92 const Depth RazorDepth = 4 * ONE_PLY;
94 // Dynamic razoring margin based on depth
95 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
97 // Maximum depth for use of dynamic threat detection when null move fails low
98 const Depth ThreatDepth = 5 * ONE_PLY;
100 // Step 9. Internal iterative deepening
102 // Minimum depth for use of internal iterative deepening
103 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
105 // At Non-PV nodes we do an internal iterative deepening search
106 // when the static evaluation is bigger then beta - IIDMargin.
107 const Value IIDMargin = Value(0x100);
109 // Step 11. Decide the new search depth
111 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
112 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
113 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
114 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
115 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
117 // Minimum depth for use of singular extension
118 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
120 // Step 12. Futility pruning
122 // Futility margin for quiescence search
123 const Value FutilityMarginQS = Value(0x80);
125 // Futility lookup tables (initialized at startup) and their access functions
126 Value FutilityMargins[16][64]; // [depth][moveNumber]
127 int FutilityMoveCounts[32]; // [depth]
129 inline Value futility_margin(Depth d, int mn) {
131 return d < 7 * ONE_PLY ? FutilityMargins[Max(d, 1)][Min(mn, 63)]
132 : 2 * VALUE_INFINITE;
135 inline int futility_move_count(Depth d) {
137 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
140 // Step 14. Reduced search
142 // Reduction lookup tables (initialized at startup) and their access function
143 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
145 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
147 return (Depth) Reductions[PvNode][Min(d / ONE_PLY, 63)][Min(mn, 63)];
150 // Easy move margin. An easy move candidate must be at least this much
151 // better than the second best move.
152 const Value EasyMoveMargin = Value(0x200);
155 /// Namespace variables
161 int MultiPV, UCIMultiPV, MultiPVIteration;
163 // Time management variables
164 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
169 std::ofstream LogFile;
171 // Skill level adjustment
173 bool SkillLevelEnabled;
175 // Node counters, used only by thread[0] but try to keep in different cache
176 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
177 bool SendSearchedNodes;
179 int NodesBetweenPolls = 30000;
187 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
189 template <NodeType NT>
190 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
192 template <NodeType NT>
193 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
195 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
196 bool connected_moves(const Position& pos, Move m1, Move m2);
197 Value value_to_tt(Value v, int ply);
198 Value value_from_tt(Value v, int ply);
199 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
200 bool connected_threat(const Position& pos, Move m, Move threat);
201 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
202 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
203 void update_gains(const Position& pos, Move move, Value before, Value after);
204 void do_skill_level(Move* best, Move* ponder);
206 int current_search_time(int set = 0);
207 string score_to_uci(Value v, Value alpha = -VALUE_INFINITE, Value beta = VALUE_INFINITE);
208 string speed_to_uci(int64_t nodes);
209 string pv_to_uci(const Move pv[], int pvNum, bool chess960);
210 string pretty_pv(Position& pos, int depth, Value score, int time, Move pv[]);
211 string depth_to_uci(Depth depth);
212 void poll(const Position& pos);
213 void wait_for_stop_or_ponderhit();
215 // MovePickerExt template class extends MovePicker and allows to choose at compile
216 // time the proper moves source according to the type of node. In the default case
217 // we simply create and use a standard MovePicker object.
218 template<NodeType> struct MovePickerExt : public MovePicker {
220 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
221 : MovePicker(p, ttm, d, h, ss, b) {}
224 // In case of a SpNode we use split point's shared MovePicker object as moves source
225 template<> struct MovePickerExt<SplitPointNonPV> : public MovePicker {
227 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
228 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
230 Move get_next_move() { return mp->get_next_move(); }
234 template<> struct MovePickerExt<SplitPointPV> : public MovePickerExt<SplitPointNonPV> {
236 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
237 : MovePickerExt<SplitPointNonPV>(p, ttm, d, h, ss, b) {}
240 // Overload operator<<() to make it easier to print moves in a coordinate
241 // notation compatible with UCI protocol.
242 std::ostream& operator<<(std::ostream& os, Move m) {
244 bool chess960 = (os.iword(0) != 0); // See set960()
245 return os << move_to_uci(m, chess960);
248 // When formatting a move for std::cout we must know if we are in Chess960
249 // or not. To keep using the handy operator<<() on the move the trick is to
250 // embed this flag in the stream itself. Function-like named enum set960 is
251 // used as a custom manipulator and the stream internal general-purpose array,
252 // accessed through ios_base::iword(), is used to pass the flag to the move's
253 // operator<<() that will read it to properly format castling moves.
256 std::ostream& operator<< (std::ostream& os, const set960& f) {
258 os.iword(0) = int(f);
262 // extension() decides whether a move should be searched with normal depth,
263 // or with extended depth. Certain classes of moves (checking moves, in
264 // particular) are searched with bigger depth than ordinary moves and in
265 // any case are marked as 'dangerous'. Note that also if a move is not
266 // extended, as example because the corresponding UCI option is set to zero,
267 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
268 template <bool PvNode>
269 FORCE_INLINE Depth extension(const Position& pos, Move m, bool captureOrPromotion,
270 bool moveIsCheck, bool* dangerous) {
271 assert(m != MOVE_NONE);
273 Depth result = DEPTH_ZERO;
274 *dangerous = moveIsCheck;
276 if (moveIsCheck && pos.see_sign(m) >= 0)
277 result += CheckExtension[PvNode];
279 if (piece_type(pos.piece_on(move_from(m))) == PAWN)
281 Color c = pos.side_to_move();
282 if (relative_rank(c, move_to(m)) == RANK_7)
284 result += PawnPushTo7thExtension[PvNode];
287 if (pos.pawn_is_passed(c, move_to(m)))
289 result += PassedPawnExtension[PvNode];
294 if ( captureOrPromotion
295 && piece_type(pos.piece_on(move_to(m))) != PAWN
296 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
297 - piece_value_midgame(pos.piece_on(move_to(m))) == VALUE_ZERO)
298 && !move_is_special(m))
300 result += PawnEndgameExtension[PvNode];
304 return Min(result, ONE_PLY);
310 /// init_search() is called during startup to initialize various lookup tables
314 int d; // depth (ONE_PLY == 2)
315 int hd; // half depth (ONE_PLY == 1)
318 // Init reductions array
319 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
321 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
322 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
323 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
324 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
327 // Init futility margins array
328 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
329 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
331 // Init futility move count array
332 for (d = 0; d < 32; d++)
333 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
337 /// perft() is our utility to verify move generation. All the leaf nodes up to
338 /// the given depth are generated and counted and the sum returned.
340 int64_t perft(Position& pos, Depth depth) {
345 // Generate all legal moves
346 MoveList<MV_LEGAL> ml(pos);
348 // If we are at the last ply we don't need to do and undo
349 // the moves, just to count them.
350 if (depth <= ONE_PLY)
353 // Loop through all legal moves
355 for ( ; !ml.end(); ++ml)
357 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
358 sum += perft(pos, depth - ONE_PLY);
359 pos.undo_move(ml.move());
365 /// think() is the external interface to Stockfish's search, and is called when
366 /// the program receives the UCI 'go' command. It initializes various global
367 /// variables, and calls id_loop(). It returns false when a "quit" command is
368 /// received during the search.
370 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
374 // Initialize global search-related variables
375 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
377 current_search_time(get_system_time());
379 TimeMgr.init(Limits, pos.startpos_ply_counter());
381 // Set output steram in normal or chess960 mode
382 cout << set960(pos.is_chess960());
384 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
386 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
387 else if (Limits.time && Limits.time < 1000)
388 NodesBetweenPolls = 1000;
389 else if (Limits.time && Limits.time < 5000)
390 NodesBetweenPolls = 5000;
392 NodesBetweenPolls = 30000;
394 // Look for a book move
395 if (Options["OwnBook"].value<bool>())
397 if (Options["Book File"].value<string>() != book.name())
398 book.open(Options["Book File"].value<string>());
400 Move bookMove = book.get_move(pos, Options["Best Book Move"].value<bool>());
401 if (bookMove != MOVE_NONE)
404 wait_for_stop_or_ponderhit();
406 cout << "bestmove " << bookMove << endl;
412 UCIMultiPV = Options["MultiPV"].value<int>();
413 SkillLevel = Options["Skill Level"].value<int>();
415 read_evaluation_uci_options(pos.side_to_move());
416 Threads.read_uci_options();
418 // If needed allocate pawn and material hash tables and adjust TT size
419 Threads.init_hash_tables();
420 TT.set_size(Options["Hash"].value<int>());
422 if (Options["Clear Hash"].value<bool>())
424 Options["Clear Hash"].set_value("false");
428 // Do we have to play with skill handicap? In this case enable MultiPV that
429 // we will use behind the scenes to retrieve a set of possible moves.
430 SkillLevelEnabled = (SkillLevel < 20);
431 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
433 // Wake up needed threads and reset maxPly counter
434 for (int i = 0; i < Threads.size(); i++)
436 Threads[i].wake_up();
437 Threads[i].maxPly = 0;
440 // Write to log file and keep it open to be accessed during the search
441 if (Options["Use Search Log"].value<bool>())
443 string name = Options["Search Log Filename"].value<string>();
444 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
446 if (LogFile.is_open())
447 LogFile << "\nSearching: " << pos.to_fen()
448 << "\ninfinite: " << Limits.infinite
449 << " ponder: " << Limits.ponder
450 << " time: " << Limits.time
451 << " increment: " << Limits.increment
452 << " moves to go: " << Limits.movesToGo
456 // We're ready to start thinking. Call the iterative deepening loop function
457 Move ponderMove = MOVE_NONE;
458 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
460 // Write final search statistics and close log file
461 if (LogFile.is_open())
463 int t = current_search_time();
465 LogFile << "Nodes: " << pos.nodes_searched()
466 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
467 << "\nBest move: " << move_to_san(pos, bestMove);
470 pos.do_move(bestMove, st);
471 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
472 pos.undo_move(bestMove); // Return from think() with unchanged position
476 // This makes all the threads to go to sleep
479 // If we are pondering or in infinite search, we shouldn't print the
480 // best move before we are told to do so.
481 if (!StopRequest && (Limits.ponder || Limits.infinite))
482 wait_for_stop_or_ponderhit();
484 // Could be MOVE_NONE when searching on a stalemate position
485 cout << "bestmove " << bestMove;
487 // UCI protol is not clear on allowing sending an empty ponder move, instead
488 // it is clear that ponder move is optional. So skip it if empty.
489 if (ponderMove != MOVE_NONE)
490 cout << " ponder " << ponderMove;
500 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
501 // with increasing depth until the allocated thinking time has been consumed,
502 // user stops the search, or the maximum search depth is reached.
504 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
506 SearchStack ss[PLY_MAX_PLUS_2];
507 Value bestValues[PLY_MAX_PLUS_2];
508 int bestMoveChanges[PLY_MAX_PLUS_2];
509 int depth, aspirationDelta;
510 Value value, alpha, beta;
511 Move bestMove, easyMove, skillBest, skillPonder;
513 // Initialize stuff before a new search
514 memset(ss, 0, 4 * sizeof(SearchStack));
517 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
518 depth = aspirationDelta = 0;
519 value = alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
520 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
522 // Moves to search are verified and copied
523 Rml.init(pos, searchMoves);
525 // Handle special case of searching on a mate/stalemate position
528 cout << "info" << depth_to_uci(DEPTH_ZERO)
529 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW, alpha, beta) << endl;
534 // Iterative deepening loop until requested to stop or target depth reached
535 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
537 // Remember best moves and values from previous iteration
538 RootMoveList prevRml = Rml;
540 Rml.bestMoveChanges = 0;
542 // MultiPV iteration loop
543 for (MultiPVIteration = 0; MultiPVIteration < Min(MultiPV, (int)Rml.size()); MultiPVIteration++)
545 // Calculate dynamic aspiration window based on previous iterations
546 if (depth >= 5 && abs(prevRml[MultiPVIteration].pv_score) < VALUE_KNOWN_WIN)
548 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
549 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
551 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
552 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
554 alpha = Max(prevRml[MultiPVIteration].pv_score - aspirationDelta, -VALUE_INFINITE);
555 beta = Min(prevRml[MultiPVIteration].pv_score + aspirationDelta, VALUE_INFINITE);
559 alpha = -VALUE_INFINITE;
560 beta = VALUE_INFINITE;
563 // Start with a small aspiration window and, in case of fail high/low,
564 // research with bigger window until not failing high/low anymore.
566 // Search starting from ss+1 to allow calling update_gains()
567 value = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
569 // It is critical that sorting is done with a stable algorithm
570 // because all the values but the first are usually set to
571 // -VALUE_INFINITE and we want to keep the same order for all
572 // the moves but the new PV that goes to head.
573 sort<RootMove>(Rml.begin() + MultiPVIteration, Rml.end());
575 // In case we have found an exact score reorder the PV moves
576 // before leaving the fail high/low loop, otherwise leave the
577 // last PV move in its position so to be searched again.
578 if (value > alpha && value < beta)
579 sort<RootMove>(Rml.begin(), Rml.begin() + MultiPVIteration);
581 // Write PV back to transposition table in case the relevant entries
582 // have been overwritten during the search.
583 for (int i = 0; i <= MultiPVIteration; i++)
584 Rml[i].insert_pv_in_tt(pos);
586 // Value cannot be trusted. Break out immediately!
590 // Send full PV info to GUI if we are going to leave the loop or
591 // if we have a fail high/low and we are deep in the search.
592 if ((value > alpha && value < beta) || current_search_time() > 2000)
593 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
595 bool updated = (i <= MultiPVIteration);
597 if (depth == 1 && !updated)
600 const RootMoveList& rml = (updated ? Rml : prevRml);
603 << depth_to_uci((updated ? depth : depth - 1) * ONE_PLY)
604 << (i == MultiPVIteration ? score_to_uci(rml[i].pv_score, alpha, beta)
605 : score_to_uci(rml[i].pv_score))
606 << speed_to_uci(pos.nodes_searched())
607 << pv_to_uci(&rml[i].pv[0], i + 1, pos.is_chess960())
611 // In case of failing high/low increase aspiration window and research,
612 // otherwise exit the fail high/low loop.
615 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
616 aspirationDelta += aspirationDelta / 2;
618 else if (value <= alpha)
620 AspirationFailLow = true;
621 StopOnPonderhit = false;
623 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
624 aspirationDelta += aspirationDelta / 2;
629 } while (abs(value) < VALUE_KNOWN_WIN);
632 // Collect info about search result
633 bestMove = Rml[0].pv[0];
634 *ponderMove = Rml[0].pv[1];
635 bestValues[depth] = value;
636 bestMoveChanges[depth] = Rml.bestMoveChanges;
638 // Do we need to pick now the best and the ponder moves ?
639 if (SkillLevelEnabled && depth == 1 + SkillLevel)
640 do_skill_level(&skillBest, &skillPonder);
642 if (LogFile.is_open())
643 LogFile << pretty_pv(pos, depth, value, current_search_time(), &Rml[0].pv[0]) << endl;
645 // Init easyMove after first iteration or drop if differs from the best move
646 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
648 else if (bestMove != easyMove)
649 easyMove = MOVE_NONE;
651 // Check for some early stop condition
652 if (!StopRequest && Limits.useTimeManagement())
654 // Stop search early if one move seems to be much better than the
655 // others or if there is only a single legal move. Also in the latter
656 // case we search up to some depth anyway to get a proper score.
658 && easyMove == bestMove
660 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
661 && current_search_time() > TimeMgr.available_time() / 16)
662 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
663 && current_search_time() > TimeMgr.available_time() / 32)))
666 // Take in account some extra time if the best move has changed
667 if (depth > 4 && depth < 50)
668 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
670 // Stop search if most of available time is already consumed. We probably don't
671 // have enough time to search the first move at the next iteration anyway.
672 if (current_search_time() > (TimeMgr.available_time() * 62) / 100)
675 // If we are allowed to ponder do not stop the search now but keep pondering
676 if (StopRequest && Limits.ponder)
679 StopOnPonderhit = true;
684 // When using skills overwrite best and ponder moves with the sub-optimal ones
685 if (SkillLevelEnabled)
687 if (skillBest == MOVE_NONE) // Still unassigned ?
688 do_skill_level(&skillBest, &skillPonder);
690 bestMove = skillBest;
691 *ponderMove = skillPonder;
698 // search<>() is the main search function for both PV and non-PV nodes and for
699 // normal and SplitPoint nodes. When called just after a split point the search
700 // is simpler because we have already probed the hash table, done a null move
701 // search, and searched the first move before splitting, we don't have to repeat
702 // all this work again. We also don't need to store anything to the hash table
703 // here: This is taken care of after we return from the split point.
705 template <NodeType NT>
706 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
708 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV);
709 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV);
710 const bool RootNode = (NT == Root);
712 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
713 assert(beta > alpha && beta <= VALUE_INFINITE);
714 assert(PvNode || alpha == beta - 1);
715 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
717 Move movesSearched[MAX_MOVES];
722 Move ttMove, move, excludedMove, threatMove;
725 Value bestValue, value, oldAlpha;
726 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
727 bool isPvMove, inCheck, singularExtensionNode, givesCheck, captureOrPromotion, dangerous;
728 int moveCount = 0, playedMoveCount = 0;
729 Thread& thread = Threads[pos.thread()];
730 SplitPoint* sp = NULL;
732 refinedValue = bestValue = value = -VALUE_INFINITE;
734 inCheck = pos.in_check();
735 ss->ply = (ss-1)->ply + 1;
737 // Used to send selDepth info to GUI
738 if (PvNode && thread.maxPly < ss->ply)
739 thread.maxPly = ss->ply;
741 // Step 1. Initialize node and poll. Polling can abort search
744 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
745 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
746 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
752 ttMove = excludedMove = MOVE_NONE;
753 threatMove = sp->threatMove;
754 goto split_point_start;
757 if (pos.thread() == 0 && ++NodesSincePoll > NodesBetweenPolls)
763 // Step 2. Check for aborted search and immediate draw
765 || pos.is_draw<false>()
766 || ss->ply > PLY_MAX) && !RootNode)
769 // Step 3. Mate distance pruning
772 alpha = Max(value_mated_in(ss->ply), alpha);
773 beta = Min(value_mate_in(ss->ply+1), beta);
778 // Step 4. Transposition table lookup
779 // We don't want the score of a partial search to overwrite a previous full search
780 // TT value, so we use a different position key in case of an excluded move.
781 excludedMove = ss->excludedMove;
782 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
783 tte = TT.probe(posKey);
784 ttMove = tte ? tte->move() : MOVE_NONE;
786 // At PV nodes we check for exact scores, while at non-PV nodes we check for
787 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
788 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
789 // we should also update RootMoveList to avoid bogus output.
790 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
791 : ok_to_use_TT(tte, depth, beta, ss->ply)))
794 ss->bestMove = ttMove; // Can be MOVE_NONE
795 return value_from_tt(tte->value(), ss->ply);
798 // Step 5. Evaluate the position statically and update parent's gain statistics
800 ss->eval = ss->evalMargin = VALUE_NONE;
803 assert(tte->static_value() != VALUE_NONE);
805 ss->eval = tte->static_value();
806 ss->evalMargin = tte->static_value_margin();
807 refinedValue = refine_eval(tte, ss->eval, ss->ply);
811 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
812 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
815 // Save gain for the parent non-capture move
816 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
818 // Step 6. Razoring (is omitted in PV nodes)
820 && depth < RazorDepth
822 && refinedValue + razor_margin(depth) < beta
823 && ttMove == MOVE_NONE
824 && abs(beta) < VALUE_MATE_IN_PLY_MAX
825 && !pos.has_pawn_on_7th(pos.side_to_move()))
827 Value rbeta = beta - razor_margin(depth);
828 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
830 // Logically we should return (v + razor_margin(depth)), but
831 // surprisingly this did slightly weaker in tests.
835 // Step 7. Static null move pruning (is omitted in PV nodes)
836 // We're betting that the opponent doesn't have a move that will reduce
837 // the score by more than futility_margin(depth) if we do a null move.
840 && depth < RazorDepth
842 && refinedValue - futility_margin(depth, 0) >= beta
843 && abs(beta) < VALUE_MATE_IN_PLY_MAX
844 && pos.non_pawn_material(pos.side_to_move()))
845 return refinedValue - futility_margin(depth, 0);
847 // Step 8. Null move search with verification search (is omitted in PV nodes)
852 && refinedValue >= beta
853 && abs(beta) < VALUE_MATE_IN_PLY_MAX
854 && pos.non_pawn_material(pos.side_to_move()))
856 ss->currentMove = MOVE_NULL;
858 // Null move dynamic reduction based on depth
859 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
861 // Null move dynamic reduction based on value
862 if (refinedValue - PawnValueMidgame > beta)
865 pos.do_null_move(st);
866 (ss+1)->skipNullMove = true;
867 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
868 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
869 (ss+1)->skipNullMove = false;
870 pos.undo_null_move();
872 if (nullValue >= beta)
874 // Do not return unproven mate scores
875 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
878 if (depth < 6 * ONE_PLY)
881 // Do verification search at high depths
882 ss->skipNullMove = true;
883 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
884 ss->skipNullMove = false;
891 // The null move failed low, which means that we may be faced with
892 // some kind of threat. If the previous move was reduced, check if
893 // the move that refuted the null move was somehow connected to the
894 // move which was reduced. If a connection is found, return a fail
895 // low score (which will cause the reduced move to fail high in the
896 // parent node, which will trigger a re-search with full depth).
897 threatMove = (ss+1)->bestMove;
899 if ( depth < ThreatDepth
901 && threatMove != MOVE_NONE
902 && connected_moves(pos, (ss-1)->currentMove, threatMove))
907 // Step 9. ProbCut (is omitted in PV nodes)
908 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
909 // and a reduced search returns a value much above beta, we can (almost) safely
910 // prune the previous move.
912 && depth >= RazorDepth + ONE_PLY
915 && excludedMove == MOVE_NONE
916 && abs(beta) < VALUE_MATE_IN_PLY_MAX)
918 Value rbeta = beta + 200;
919 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
921 assert(rdepth >= ONE_PLY);
923 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
926 while ((move = mp.get_next_move()) != MOVE_NONE)
927 if (pos.pl_move_is_legal(move, ci.pinned))
929 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
930 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
937 // Step 10. Internal iterative deepening
938 if ( depth >= IIDDepth[PvNode]
939 && ttMove == MOVE_NONE
940 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
942 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
944 ss->skipNullMove = true;
945 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
946 ss->skipNullMove = false;
948 tte = TT.probe(posKey);
949 ttMove = tte ? tte->move() : MOVE_NONE;
952 split_point_start: // At split points actual search starts from here
954 // Initialize a MovePicker object for the current position
955 MovePickerExt<NT> mp(pos, RootNode ? Rml[MultiPVIteration].pv[0] : ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
957 ss->bestMove = MOVE_NONE;
958 futilityBase = ss->eval + ss->evalMargin;
959 singularExtensionNode = !RootNode
961 && depth >= SingularExtensionDepth[PvNode]
962 && ttMove != MOVE_NONE
963 && !excludedMove // Do not allow recursive singular extension search
964 && (tte->type() & VALUE_TYPE_LOWER)
965 && tte->depth() >= depth - 3 * ONE_PLY;
968 lock_grab(&(sp->lock));
969 bestValue = sp->bestValue;
972 // Step 11. Loop through moves
973 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
974 while ( bestValue < beta
975 && (move = mp.get_next_move()) != MOVE_NONE
976 && !thread.cutoff_occurred())
978 assert(move_is_ok(move));
980 if (move == excludedMove)
983 // At root obey the "searchmoves" option and skip moves not listed in Root Move List.
984 // Also in MultiPV mode we skip moves which already have got an exact score
985 // in previous MultiPV Iteration.
986 if (RootNode && !Rml.find(move, MultiPVIteration))
989 // At PV and SpNode nodes we want all moves to be legal since the beginning
990 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
995 moveCount = ++sp->moveCount;
996 lock_release(&(sp->lock));
1003 // This is used by time management
1004 FirstRootMove = (moveCount == 1);
1006 // Save the current node count before the move is searched
1007 nodes = pos.nodes_searched();
1009 // If it's time to send nodes info, do it here where we have the
1010 // correct accumulated node counts searched by each thread.
1011 if (SendSearchedNodes)
1013 SendSearchedNodes = false;
1014 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1017 // For long searches send current move info to GUI
1018 if (current_search_time() > 2000)
1019 cout << "info" << depth_to_uci(depth)
1020 << " currmove " << move << " currmovenumber " << moveCount + MultiPVIteration << endl;
1023 // At Root and at first iteration do a PV search on all the moves to score root moves
1024 isPvMove = (PvNode && moveCount <= ((RootNode && depth <= ONE_PLY) ? MAX_MOVES : 1));
1025 givesCheck = pos.move_gives_check(move, ci);
1026 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1028 // Step 12. Decide the new search depth
1029 ext = extension<PvNode>(pos, move, captureOrPromotion, givesCheck, &dangerous);
1031 // Singular extension search. If all moves but one fail low on a search of
1032 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1033 // is singular and should be extended. To verify this we do a reduced search
1034 // on all the other moves but the ttMove, if result is lower than ttValue minus
1035 // a margin then we extend ttMove.
1036 if ( singularExtensionNode
1038 && pos.pl_move_is_legal(move, ci.pinned)
1041 Value ttValue = value_from_tt(tte->value(), ss->ply);
1043 if (abs(ttValue) < VALUE_KNOWN_WIN)
1045 Value rBeta = ttValue - int(depth);
1046 ss->excludedMove = move;
1047 ss->skipNullMove = true;
1048 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1049 ss->skipNullMove = false;
1050 ss->excludedMove = MOVE_NONE;
1051 ss->bestMove = MOVE_NONE;
1057 // Update current move (this must be done after singular extension search)
1058 newDepth = depth - ONE_PLY + ext;
1060 // Step 13. Futility pruning (is omitted in PV nodes)
1062 && !captureOrPromotion
1066 && !move_is_castle(move))
1068 // Move count based pruning
1069 if ( moveCount >= futility_move_count(depth)
1070 && (!threatMove || !connected_threat(pos, move, threatMove))
1071 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1074 lock_grab(&(sp->lock));
1079 // Value based pruning
1080 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1081 // but fixing this made program slightly weaker.
1082 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
1083 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1084 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1086 if (futilityValueScaled < beta)
1090 lock_grab(&(sp->lock));
1091 if (futilityValueScaled > sp->bestValue)
1092 sp->bestValue = bestValue = futilityValueScaled;
1094 else if (futilityValueScaled > bestValue)
1095 bestValue = futilityValueScaled;
1100 // Prune moves with negative SEE at low depths
1101 if ( predictedDepth < 2 * ONE_PLY
1102 && bestValue > VALUE_MATED_IN_PLY_MAX
1103 && pos.see_sign(move) < 0)
1106 lock_grab(&(sp->lock));
1112 // Check for legality only before to do the move
1113 if (!pos.pl_move_is_legal(move, ci.pinned))
1119 ss->currentMove = move;
1120 if (!SpNode && !captureOrPromotion)
1121 movesSearched[playedMoveCount++] = move;
1123 // Step 14. Make the move
1124 pos.do_move(move, st, ci, givesCheck);
1126 // Step extra. pv search (only in PV nodes)
1127 // The first move in list is the expected PV
1129 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1130 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1133 // Step 15. Reduced depth search
1134 // If the move fails high will be re-searched at full depth.
1135 bool doFullDepthSearch = true;
1137 if ( depth > 3 * ONE_PLY
1138 && !captureOrPromotion
1140 && !move_is_castle(move)
1141 && ss->killers[0] != move
1142 && ss->killers[1] != move
1143 && (ss->reduction = reduction<PvNode>(depth, moveCount)) != DEPTH_ZERO)
1145 Depth d = newDepth - ss->reduction;
1146 alpha = SpNode ? sp->alpha : alpha;
1148 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1149 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1151 ss->reduction = DEPTH_ZERO;
1152 doFullDepthSearch = (value > alpha);
1155 // Step 16. Full depth search
1156 if (doFullDepthSearch)
1158 alpha = SpNode ? sp->alpha : alpha;
1159 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1160 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1162 // Step extra. pv search (only in PV nodes)
1163 // Search only for possible new PV nodes, if instead value >= beta then
1164 // parent node fails low with value <= alpha and tries another move.
1165 if (PvNode && value > alpha && (RootNode || value < beta))
1166 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1167 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1171 // Step 17. Undo move
1172 pos.undo_move(move);
1174 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1176 // Step 18. Check for new best move
1179 lock_grab(&(sp->lock));
1180 bestValue = sp->bestValue;
1184 if (value > bestValue)
1187 ss->bestMove = move;
1192 && value < beta) // We want always alpha < beta
1195 if (SpNode && !thread.cutoff_occurred())
1197 sp->bestValue = value;
1198 sp->ss->bestMove = move;
1200 sp->is_betaCutoff = (value >= beta);
1206 // Finished searching the move. If StopRequest is true, the search
1207 // was aborted because the user interrupted the search or because we
1208 // ran out of time. In this case, the return value of the search cannot
1209 // be trusted, and we break out of the loop without updating the best
1214 // Remember searched nodes counts for this move
1215 RootMove* rm = Rml.find(move);
1216 rm->nodes += pos.nodes_searched() - nodes;
1218 // PV move or new best move ?
1219 if (isPvMove || value > alpha)
1222 rm->pv_score = value;
1223 rm->extract_pv_from_tt(pos);
1225 // We record how often the best move has been changed in each
1226 // iteration. This information is used for time management: When
1227 // the best move changes frequently, we allocate some more time.
1228 if (!isPvMove && MultiPV == 1)
1229 Rml.bestMoveChanges++;
1236 // All other moves but the PV are set to the lowest value, this
1237 // is not a problem when sorting becuase sort is stable and move
1238 // position in the list is preserved, just the PV is pushed up.
1239 rm->pv_score = -VALUE_INFINITE;
1243 // Step 19. Check for split
1246 && depth >= Threads.min_split_depth()
1248 && Threads.available_slave_exists(pos.thread())
1250 && !thread.cutoff_occurred())
1251 Threads.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1252 threatMove, moveCount, &mp, PvNode);
1255 // Step 20. Check for mate and stalemate
1256 // All legal moves have been searched and if there are
1257 // no legal moves, it must be mate or stalemate.
1258 // If one move was excluded return fail low score.
1259 if (!SpNode && !moveCount)
1260 return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1262 // Step 21. Update tables
1263 // If the search is not aborted, update the transposition table,
1264 // history counters, and killer moves.
1265 if (!SpNode && !StopRequest && !thread.cutoff_occurred())
1267 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1268 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1269 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1271 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1273 // Update killers and history only for non capture moves that fails high
1274 if ( bestValue >= beta
1275 && !pos.move_is_capture_or_promotion(move))
1277 if (move != ss->killers[0])
1279 ss->killers[1] = ss->killers[0];
1280 ss->killers[0] = move;
1282 update_history(pos, move, depth, movesSearched, playedMoveCount);
1288 // Here we have the lock still grabbed
1289 sp->is_slave[pos.thread()] = false;
1290 sp->nodes += pos.nodes_searched();
1291 lock_release(&(sp->lock));
1294 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1299 // qsearch() is the quiescence search function, which is called by the main
1300 // search function when the remaining depth is zero (or, to be more precise,
1301 // less than ONE_PLY).
1303 template <NodeType NT>
1304 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1306 const bool PvNode = (NT == PV);
1308 assert(NT == PV || NT == NonPV);
1309 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1310 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1311 assert(PvNode || alpha == beta - 1);
1313 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
1317 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1318 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1321 Value oldAlpha = alpha;
1323 ss->bestMove = ss->currentMove = MOVE_NONE;
1324 ss->ply = (ss-1)->ply + 1;
1326 // Check for an instant draw or maximum ply reached
1327 if (pos.is_draw<true>() || ss->ply > PLY_MAX)
1330 // Decide whether or not to include checks, this fixes also the type of
1331 // TT entry depth that we are going to use. Note that in qsearch we use
1332 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1333 inCheck = pos.in_check();
1334 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1336 // Transposition table lookup. At PV nodes, we don't use the TT for
1337 // pruning, but only for move ordering.
1338 tte = TT.probe(pos.get_key());
1339 ttMove = (tte ? tte->move() : MOVE_NONE);
1341 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1343 ss->bestMove = ttMove; // Can be MOVE_NONE
1344 return value_from_tt(tte->value(), ss->ply);
1347 // Evaluate the position statically
1350 bestValue = futilityBase = -VALUE_INFINITE;
1351 ss->eval = evalMargin = VALUE_NONE;
1352 enoughMaterial = false;
1358 assert(tte->static_value() != VALUE_NONE);
1360 evalMargin = tte->static_value_margin();
1361 ss->eval = bestValue = tte->static_value();
1364 ss->eval = bestValue = evaluate(pos, evalMargin);
1366 // Stand pat. Return immediately if static value is at least beta
1367 if (bestValue >= beta)
1370 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1375 if (PvNode && bestValue > alpha)
1378 // Futility pruning parameters, not needed when in check
1379 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1380 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1383 // Initialize a MovePicker object for the current position, and prepare
1384 // to search the moves. Because the depth is <= 0 here, only captures,
1385 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1387 MovePicker mp(pos, ttMove, depth, H, move_to((ss-1)->currentMove));
1390 // Loop through the moves until no moves remain or a beta cutoff occurs
1391 while ( alpha < beta
1392 && (move = mp.get_next_move()) != MOVE_NONE)
1394 assert(move_is_ok(move));
1396 givesCheck = pos.move_gives_check(move, ci);
1404 && !move_is_promotion(move)
1405 && !pos.move_is_passed_pawn_push(move))
1407 futilityValue = futilityBase
1408 + piece_value_endgame(pos.piece_on(move_to(move)))
1409 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1411 if (futilityValue < alpha)
1413 if (futilityValue > bestValue)
1414 bestValue = futilityValue;
1418 // Prune moves with negative or equal SEE
1419 if ( futilityBase < beta
1420 && depth < DEPTH_ZERO
1421 && pos.see(move) <= 0)
1425 // Detect non-capture evasions that are candidate to be pruned
1426 evasionPrunable = !PvNode
1428 && bestValue > VALUE_MATED_IN_PLY_MAX
1429 && !pos.move_is_capture(move)
1430 && !pos.can_castle(pos.side_to_move());
1432 // Don't search moves with negative SEE values
1434 && (!inCheck || evasionPrunable)
1436 && !move_is_promotion(move)
1437 && pos.see_sign(move) < 0)
1440 // Don't search useless checks
1445 && !pos.move_is_capture_or_promotion(move)
1446 && ss->eval + PawnValueMidgame / 4 < beta
1447 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1449 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1450 bestValue = ss->eval + PawnValueMidgame / 4;
1455 // Check for legality only before to do the move
1456 if (!pos.pl_move_is_legal(move, ci.pinned))
1459 // Update current move
1460 ss->currentMove = move;
1462 // Make and search the move
1463 pos.do_move(move, st, ci, givesCheck);
1464 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1465 pos.undo_move(move);
1467 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1470 if (value > bestValue)
1476 ss->bestMove = move;
1481 // All legal moves have been searched. A special case: If we're in check
1482 // and no legal moves were found, it is checkmate.
1483 if (inCheck && bestValue == -VALUE_INFINITE)
1484 return value_mated_in(ss->ply);
1486 // Update transposition table
1487 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1488 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1490 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1496 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1497 // bestValue is updated only when returning false because in that case move
1500 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1502 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1503 Square from, to, ksq, victimSq;
1506 Value futilityValue, bv = *bestValue;
1508 from = move_from(move);
1510 them = opposite_color(pos.side_to_move());
1511 ksq = pos.king_square(them);
1512 kingAtt = pos.attacks_from<KING>(ksq);
1513 pc = pos.piece_on(from);
1515 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1516 oldAtt = pos.attacks_from(pc, from, occ);
1517 newAtt = pos.attacks_from(pc, to, occ);
1519 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1520 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1522 if (!(b && (b & (b - 1))))
1525 // Rule 2. Queen contact check is very dangerous
1526 if ( piece_type(pc) == QUEEN
1527 && bit_is_set(kingAtt, to))
1530 // Rule 3. Creating new double threats with checks
1531 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1535 victimSq = pop_1st_bit(&b);
1536 futilityValue = futilityBase + piece_value_endgame(pos.piece_on(victimSq));
1538 // Note that here we generate illegal "double move"!
1539 if ( futilityValue >= beta
1540 && pos.see_sign(make_move(from, victimSq)) >= 0)
1543 if (futilityValue > bv)
1547 // Update bestValue only if check is not dangerous (because we will prune the move)
1553 // connected_moves() tests whether two moves are 'connected' in the sense
1554 // that the first move somehow made the second move possible (for instance
1555 // if the moving piece is the same in both moves). The first move is assumed
1556 // to be the move that was made to reach the current position, while the
1557 // second move is assumed to be a move from the current position.
1559 bool connected_moves(const Position& pos, Move m1, Move m2) {
1561 Square f1, t1, f2, t2;
1565 assert(m1 && move_is_ok(m1));
1566 assert(m2 && move_is_ok(m2));
1568 // Case 1: The moving piece is the same in both moves
1574 // Case 2: The destination square for m2 was vacated by m1
1580 // Case 3: Moving through the vacated square
1581 p2 = pos.piece_on(f2);
1582 if ( piece_is_slider(p2)
1583 && bit_is_set(squares_between(f2, t2), f1))
1586 // Case 4: The destination square for m2 is defended by the moving piece in m1
1587 p1 = pos.piece_on(t1);
1588 if (bit_is_set(pos.attacks_from(p1, t1), t2))
1591 // Case 5: Discovered check, checking piece is the piece moved in m1
1592 ksq = pos.king_square(pos.side_to_move());
1593 if ( piece_is_slider(p1)
1594 && bit_is_set(squares_between(t1, ksq), f2))
1596 Bitboard occ = pos.occupied_squares();
1597 clear_bit(&occ, f2);
1598 if (bit_is_set(pos.attacks_from(p1, t1, occ), ksq))
1605 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1606 // "plies to mate from the current ply". Non-mate scores are unchanged.
1607 // The function is called before storing a value to the transposition table.
1609 Value value_to_tt(Value v, int ply) {
1611 if (v >= VALUE_MATE_IN_PLY_MAX)
1614 if (v <= VALUE_MATED_IN_PLY_MAX)
1621 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1622 // the transposition table to a mate score corrected for the current ply.
1624 Value value_from_tt(Value v, int ply) {
1626 if (v >= VALUE_MATE_IN_PLY_MAX)
1629 if (v <= VALUE_MATED_IN_PLY_MAX)
1636 // connected_threat() tests whether it is safe to forward prune a move or if
1637 // is somehow connected to the threat move returned by null search.
1639 bool connected_threat(const Position& pos, Move m, Move threat) {
1641 assert(move_is_ok(m));
1642 assert(threat && move_is_ok(threat));
1643 assert(!pos.move_is_capture_or_promotion(m));
1644 assert(!pos.move_is_passed_pawn_push(m));
1646 Square mfrom, mto, tfrom, tto;
1648 mfrom = move_from(m);
1650 tfrom = move_from(threat);
1651 tto = move_to(threat);
1653 // Case 1: Don't prune moves which move the threatened piece
1657 // Case 2: If the threatened piece has value less than or equal to the
1658 // value of the threatening piece, don't prune moves which defend it.
1659 if ( pos.move_is_capture(threat)
1660 && ( piece_value_midgame(pos.piece_on(tfrom)) >= piece_value_midgame(pos.piece_on(tto))
1661 || piece_type(pos.piece_on(tfrom)) == KING)
1662 && pos.move_attacks_square(m, tto))
1665 // Case 3: If the moving piece in the threatened move is a slider, don't
1666 // prune safe moves which block its ray.
1667 if ( piece_is_slider(pos.piece_on(tfrom))
1668 && bit_is_set(squares_between(tfrom, tto), mto)
1669 && pos.see_sign(m) >= 0)
1676 // ok_to_use_TT() returns true if a transposition table score
1677 // can be used at a given point in search.
1679 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1681 Value v = value_from_tt(tte->value(), ply);
1683 return ( tte->depth() >= depth
1684 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1685 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1687 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1688 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1692 // refine_eval() returns the transposition table score if
1693 // possible otherwise falls back on static position evaluation.
1695 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1699 Value v = value_from_tt(tte->value(), ply);
1701 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1702 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1709 // update_history() registers a good move that produced a beta-cutoff
1710 // in history and marks as failures all the other moves of that ply.
1712 void update_history(const Position& pos, Move move, Depth depth,
1713 Move movesSearched[], int moveCount) {
1715 Value bonus = Value(int(depth) * int(depth));
1717 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1719 for (int i = 0; i < moveCount - 1; i++)
1721 m = movesSearched[i];
1725 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1730 // update_gains() updates the gains table of a non-capture move given
1731 // the static position evaluation before and after the move.
1733 void update_gains(const Position& pos, Move m, Value before, Value after) {
1736 && before != VALUE_NONE
1737 && after != VALUE_NONE
1738 && pos.captured_piece_type() == PIECE_TYPE_NONE
1739 && !move_is_special(m))
1740 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1744 // current_search_time() returns the number of milliseconds which have passed
1745 // since the beginning of the current search.
1747 int current_search_time(int set) {
1749 static int searchStartTime;
1752 searchStartTime = set;
1754 return get_system_time() - searchStartTime;
1758 // score_to_uci() converts a value to a string suitable for use with the UCI
1759 // protocol specifications:
1761 // cp <x> The score from the engine's point of view in centipawns.
1762 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1763 // use negative values for y.
1765 string score_to_uci(Value v, Value alpha, Value beta) {
1767 std::stringstream s;
1769 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1770 s << " score cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1772 s << " score mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1774 s << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1780 // speed_to_uci() returns a string with time stats of current search suitable
1781 // to be sent to UCI gui.
1783 string speed_to_uci(int64_t nodes) {
1785 std::stringstream s;
1786 int t = current_search_time();
1788 s << " nodes " << nodes
1789 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1795 // pv_to_uci() returns a string with information on the current PV line
1796 // formatted according to UCI specification.
1798 string pv_to_uci(const Move pv[], int pvNum, bool chess960) {
1800 std::stringstream s;
1802 s << " multipv " << pvNum << " pv " << set960(chess960);
1804 for ( ; *pv != MOVE_NONE; pv++)
1810 // depth_to_uci() returns a string with information on the current depth and
1811 // seldepth formatted according to UCI specification.
1813 string depth_to_uci(Depth depth) {
1815 std::stringstream s;
1817 // Retrieve max searched depth among threads
1819 for (int i = 0; i < Threads.size(); i++)
1820 if (Threads[i].maxPly > selDepth)
1821 selDepth = Threads[i].maxPly;
1823 s << " depth " << depth / ONE_PLY << " seldepth " << selDepth;
1828 string time_to_string(int millisecs) {
1830 const int MSecMinute = 1000 * 60;
1831 const int MSecHour = 1000 * 60 * 60;
1833 int hours = millisecs / MSecHour;
1834 int minutes = (millisecs % MSecHour) / MSecMinute;
1835 int seconds = ((millisecs % MSecHour) % MSecMinute) / 1000;
1837 std::stringstream s;
1842 s << std::setfill('0') << std::setw(2) << minutes << ':' << std::setw(2) << seconds;
1846 string score_to_string(Value v) {
1848 std::stringstream s;
1850 if (v >= VALUE_MATE_IN_PLY_MAX)
1851 s << "#" << (VALUE_MATE - v + 1) / 2;
1852 else if (v <= VALUE_MATED_IN_PLY_MAX)
1853 s << "-#" << (VALUE_MATE + v) / 2;
1855 s << std::setprecision(2) << std::fixed << std::showpos << float(v) / PawnValueMidgame;
1860 // pretty_pv() creates a human-readable string from a position and a PV.
1861 // It is used to write search information to the log file (which is created
1862 // when the UCI parameter "Use Search Log" is "true").
1864 string pretty_pv(Position& pos, int depth, Value value, int time, Move pv[]) {
1866 const int64_t K = 1000;
1867 const int64_t M = 1000000;
1868 const int startColumn = 28;
1869 const size_t maxLength = 80 - startColumn;
1871 StateInfo state[PLY_MAX_PLUS_2], *st = state;
1874 std::stringstream s;
1877 // First print depth, score, time and searched nodes...
1878 s << set960(pos.is_chess960())
1879 << std::setw(2) << depth
1880 << std::setw(8) << score_to_string(value)
1881 << std::setw(8) << time_to_string(time);
1883 if (pos.nodes_searched() < M)
1884 s << std::setw(8) << pos.nodes_searched() / 1 << " ";
1885 else if (pos.nodes_searched() < K * M)
1886 s << std::setw(7) << pos.nodes_searched() / K << "K ";
1888 s << std::setw(7) << pos.nodes_searched() / M << "M ";
1890 // ...then print the full PV line in short algebraic notation
1891 while (*m != MOVE_NONE)
1893 san = move_to_san(pos, *m);
1894 length += san.length() + 1;
1896 if (length > maxLength)
1898 length = san.length() + 1;
1899 s << "\n" + string(startColumn, ' ');
1903 pos.do_move(*m++, *st++);
1906 // Restore original position before to leave
1907 while (m != pv) pos.undo_move(*--m);
1912 // poll() performs two different functions: It polls for user input, and it
1913 // looks at the time consumed so far and decides if it's time to abort the
1916 void poll(const Position& pos) {
1918 static int lastInfoTime;
1919 int t = current_search_time();
1922 if (input_available())
1924 // We are line oriented, don't read single chars
1927 if (!std::getline(std::cin, command) || command == "quit")
1929 // Quit the program as soon as possible
1930 Limits.ponder = false;
1931 QuitRequest = StopRequest = true;
1934 else if (command == "stop")
1936 // Stop calculating as soon as possible, but still send the "bestmove"
1937 // and possibly the "ponder" token when finishing the search.
1938 Limits.ponder = false;
1941 else if (command == "ponderhit")
1943 // The opponent has played the expected move. GUI sends "ponderhit" if
1944 // we were told to ponder on the same move the opponent has played. We
1945 // should continue searching but switching from pondering to normal search.
1946 Limits.ponder = false;
1948 if (StopOnPonderhit)
1953 // Print search information
1957 else if (lastInfoTime > t)
1958 // HACK: Must be a new search where we searched less than
1959 // NodesBetweenPolls nodes during the first second of search.
1962 else if (t - lastInfoTime >= 1000)
1967 dbg_print_hit_rate();
1969 // Send info on searched nodes as soon as we return to root
1970 SendSearchedNodes = true;
1973 // Should we stop the search?
1977 bool stillAtFirstMove = FirstRootMove
1978 && !AspirationFailLow
1979 && t > TimeMgr.available_time();
1981 bool noMoreTime = t > TimeMgr.maximum_time()
1982 || stillAtFirstMove;
1984 if ( (Limits.useTimeManagement() && noMoreTime)
1985 || (Limits.maxTime && t >= Limits.maxTime)
1986 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1991 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1992 // while the program is pondering. The point is to work around a wrinkle in
1993 // the UCI protocol: When pondering, the engine is not allowed to give a
1994 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1995 // We simply wait here until one of these commands is sent, and return,
1996 // after which the bestmove and pondermove will be printed.
1998 void wait_for_stop_or_ponderhit() {
2002 // Wait for a command from stdin
2003 while ( std::getline(std::cin, command)
2004 && command != "ponderhit" && command != "stop" && command != "quit") {};
2006 if (command != "ponderhit" && command != "stop")
2007 QuitRequest = true; // Must be "quit" or getline() returned false
2011 // When playing with strength handicap choose best move among the MultiPV set
2012 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
2013 void do_skill_level(Move* best, Move* ponder) {
2015 assert(MultiPV > 1);
2019 // Rml list is already sorted by pv_score in descending order
2021 int max_s = -VALUE_INFINITE;
2022 int size = Min(MultiPV, (int)Rml.size());
2023 int max = Rml[0].pv_score;
2024 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
2025 int wk = 120 - 2 * SkillLevel;
2027 // PRNG sequence should be non deterministic
2028 for (int i = abs(get_system_time() % 50); i > 0; i--)
2029 rk.rand<unsigned>();
2031 // Choose best move. For each move's score we add two terms both dependent
2032 // on wk, one deterministic and bigger for weaker moves, and one random,
2033 // then we choose the move with the resulting highest score.
2034 for (int i = 0; i < size; i++)
2036 s = Rml[i].pv_score;
2038 // Don't allow crazy blunders even at very low skills
2039 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
2042 // This is our magical formula
2043 s += ((max - s) * wk + var * (rk.rand<unsigned>() % wk)) / 128;
2048 *best = Rml[i].pv[0];
2049 *ponder = Rml[i].pv[1];
2055 /// RootMove and RootMoveList method's definitions
2057 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2060 bestMoveChanges = 0;
2063 // Generate all legal moves and add them to RootMoveList
2064 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
2066 // If we have a searchMoves[] list then verify the move
2067 // is in the list before to add it.
2068 for (sm = searchMoves; *sm && *sm != ml.move(); sm++) {}
2070 if (sm != searchMoves && *sm != ml.move())
2074 rm.pv.push_back(ml.move());
2075 rm.pv.push_back(MOVE_NONE);
2076 rm.pv_score = -VALUE_INFINITE;
2082 RootMove* RootMoveList::find(const Move& m, int startIndex) {
2084 for (size_t i = startIndex; i < size(); i++)
2085 if ((*this)[i].pv[0] == m)
2091 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2092 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2093 // allow to always have a ponder move even when we fail high at root and also a
2094 // long PV to print that is important for position analysis.
2096 void RootMove::extract_pv_from_tt(Position& pos) {
2098 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2103 assert(m != MOVE_NONE && pos.move_is_pl(m));
2107 pos.do_move(m, *st++);
2109 while ( (tte = TT.probe(pos.get_key())) != NULL
2110 && tte->move() != MOVE_NONE
2111 && pos.move_is_pl(tte->move())
2112 && pos.pl_move_is_legal(tte->move(), pos.pinned_pieces())
2114 && (!pos.is_draw<false>() || ply < 2))
2116 pv.push_back(tte->move());
2117 pos.do_move(tte->move(), *st++);
2120 pv.push_back(MOVE_NONE);
2122 do pos.undo_move(pv[--ply]); while (ply);
2125 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2126 // the PV back into the TT. This makes sure the old PV moves are searched
2127 // first, even if the old TT entries have been overwritten.
2129 void RootMove::insert_pv_in_tt(Position& pos) {
2131 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2134 Value v, m = VALUE_NONE;
2137 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2143 // Don't overwrite existing correct entries
2144 if (!tte || tte->move() != pv[ply])
2146 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
2147 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2149 pos.do_move(pv[ply], *st++);
2151 } while (pv[++ply] != MOVE_NONE);
2153 do pos.undo_move(pv[--ply]); while (ply);
2158 // ThreadsManager::idle_loop() is where the threads are parked when they have no work
2159 // to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2160 // object for which the current thread is the master.
2162 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2164 assert(threadID >= 0 && threadID < MAX_THREADS);
2171 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2172 // master should exit as last one.
2173 if (allThreadsShouldExit)
2176 threads[threadID].state = Thread::TERMINATED;
2180 // If we are not thinking, wait for a condition to be signaled
2181 // instead of wasting CPU time polling for work.
2182 while ( threadID >= activeThreads
2183 || threads[threadID].state == Thread::INITIALIZING
2184 || (useSleepingThreads && threads[threadID].state == Thread::AVAILABLE))
2186 assert(!sp || useSleepingThreads);
2187 assert(threadID != 0 || useSleepingThreads);
2189 if (threads[threadID].state == Thread::INITIALIZING)
2190 threads[threadID].state = Thread::AVAILABLE;
2192 // Grab the lock to avoid races with Thread::wake_up()
2193 lock_grab(&threads[threadID].sleepLock);
2195 // If we are master and all slaves have finished do not go to sleep
2196 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2197 allFinished = (i == activeThreads);
2199 if (allFinished || allThreadsShouldExit)
2201 lock_release(&threads[threadID].sleepLock);
2205 // Do sleep here after retesting sleep conditions
2206 if (threadID >= activeThreads || threads[threadID].state == Thread::AVAILABLE)
2207 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2209 lock_release(&threads[threadID].sleepLock);
2212 // If this thread has been assigned work, launch a search
2213 if (threads[threadID].state == Thread::WORKISWAITING)
2215 assert(!allThreadsShouldExit);
2217 threads[threadID].state = Thread::SEARCHING;
2219 // Copy split point position and search stack and call search()
2220 // with SplitPoint template parameter set to true.
2221 SearchStack ss[PLY_MAX_PLUS_2];
2222 SplitPoint* tsp = threads[threadID].splitPoint;
2223 Position pos(*tsp->pos, threadID);
2225 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2229 search<SplitPointPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2231 search<SplitPointNonPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2233 assert(threads[threadID].state == Thread::SEARCHING);
2235 threads[threadID].state = Thread::AVAILABLE;
2237 // Wake up master thread so to allow it to return from the idle loop in
2238 // case we are the last slave of the split point.
2239 if ( useSleepingThreads
2240 && threadID != tsp->master
2241 && threads[tsp->master].state == Thread::AVAILABLE)
2242 threads[tsp->master].wake_up();
2245 // If this thread is the master of a split point and all slaves have
2246 // finished their work at this split point, return from the idle loop.
2247 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2248 allFinished = (i == activeThreads);
2252 // Because sp->slaves[] is reset under lock protection,
2253 // be sure sp->lock has been released before to return.
2254 lock_grab(&(sp->lock));
2255 lock_release(&(sp->lock));
2257 // In helpful master concept a master can help only a sub-tree, and
2258 // because here is all finished is not possible master is booked.
2259 assert(threads[threadID].state == Thread::AVAILABLE);
2261 threads[threadID].state = Thread::SEARCHING;