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.
61 RootMove(const RootMove& rm) { *this = rm; }
62 RootMove& operator=(const RootMove& rm);
64 // RootMove::operator<() is the comparison function used when
65 // sorting the moves. A move m1 is considered to be better
66 // than a move m2 if it has an higher pv_score
67 bool operator<(const RootMove& m) const { return pv_score < m.pv_score; }
69 void extract_pv_from_tt(Position& pos);
70 void insert_pv_in_tt(Position& pos);
74 Move pv[PLY_MAX_PLUS_2];
77 // RootMoveList struct is mainly a std::vector of RootMove objects
78 struct RootMoveList : public std::vector<RootMove> {
79 void init(Position& pos, Move searchMoves[]);
80 RootMove* find(const Move &m, const int startIndex = 0);
87 // Lookup table to check if a Piece is a slider and its access function
88 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
89 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
93 // Maximum depth for razoring
94 const Depth RazorDepth = 4 * ONE_PLY;
96 // Dynamic razoring margin based on depth
97 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
99 // Maximum depth for use of dynamic threat detection when null move fails low
100 const Depth ThreatDepth = 5 * ONE_PLY;
102 // Step 9. Internal iterative deepening
104 // Minimum depth for use of internal iterative deepening
105 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
107 // At Non-PV nodes we do an internal iterative deepening search
108 // when the static evaluation is bigger then beta - IIDMargin.
109 const Value IIDMargin = Value(0x100);
111 // Step 11. Decide the new search depth
113 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
114 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
115 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
116 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
117 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
119 // Minimum depth for use of singular extension
120 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
122 // Step 12. Futility pruning
124 // Futility margin for quiescence search
125 const Value FutilityMarginQS = Value(0x80);
127 // Futility lookup tables (initialized at startup) and their access functions
128 Value FutilityMargins[16][64]; // [depth][moveNumber]
129 int FutilityMoveCounts[32]; // [depth]
131 inline Value futility_margin(Depth d, int mn) {
133 return d < 7 * ONE_PLY ? FutilityMargins[Max(d, 1)][Min(mn, 63)]
134 : 2 * VALUE_INFINITE;
137 inline int futility_move_count(Depth d) {
139 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
142 // Step 14. Reduced search
144 // Reduction lookup tables (initialized at startup) and their access function
145 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
147 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
149 return (Depth) Reductions[PvNode][Min(d / ONE_PLY, 63)][Min(mn, 63)];
152 // Easy move margin. An easy move candidate must be at least this much
153 // better than the second best move.
154 const Value EasyMoveMargin = Value(0x200);
157 /// Namespace variables
163 int MultiPV, UCIMultiPV, MultiPVIteration;
165 // Time management variables
166 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
171 std::ofstream LogFile;
173 // Skill level adjustment
175 bool SkillLevelEnabled;
177 // Node counters, used only by thread[0] but try to keep in different cache
178 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
179 bool SendSearchedNodes;
181 int NodesBetweenPolls = 30000;
189 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
191 template <NodeType NT>
192 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
194 template <NodeType NT>
195 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
197 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
198 bool connected_moves(const Position& pos, Move m1, Move m2);
199 Value value_to_tt(Value v, int ply);
200 Value value_from_tt(Value v, int ply);
201 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
202 bool connected_threat(const Position& pos, Move m, Move threat);
203 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
204 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
205 void update_gains(const Position& pos, Move move, Value before, Value after);
206 void do_skill_level(Move* best, Move* ponder);
208 int current_search_time(int set = 0);
209 string score_to_uci(Value v, Value alpha, Value beta);
210 string speed_to_uci(int64_t nodes);
211 string pv_to_uci(Move pv[], int pvNum, bool chess960);
212 string pretty_pv(Position& pos, int depth, Value score, int time, Move pv[]);
213 string depth_to_uci(Depth depth);
214 void poll(const Position& pos);
215 void wait_for_stop_or_ponderhit();
217 // MovePickerExt template class extends MovePicker and allows to choose at compile
218 // time the proper moves source according to the type of node. In the default case
219 // we simply create and use a standard MovePicker object.
220 template<NodeType> struct MovePickerExt : public MovePicker {
222 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
223 : MovePicker(p, ttm, d, h, ss, b) {}
226 // In case of a SpNode we use split point's shared MovePicker object as moves source
227 template<> struct MovePickerExt<SplitPointNonPV> : public MovePickerExt<NonPV> {
229 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
230 : MovePickerExt<NonPV>(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
232 Move get_next_move() { return mp->get_next_move(); }
236 template<> struct MovePickerExt<SplitPointPV> : public MovePickerExt<SplitPointNonPV> {
238 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
239 : MovePickerExt<SplitPointNonPV>(p, ttm, d, h, ss, b) {}
242 // Overload operator<<() to make it easier to print moves in a coordinate
243 // notation compatible with UCI protocol.
244 std::ostream& operator<<(std::ostream& os, Move m) {
246 bool chess960 = (os.iword(0) != 0); // See set960()
247 return os << move_to_uci(m, chess960);
250 // When formatting a move for std::cout we must know if we are in Chess960
251 // or not. To keep using the handy operator<<() on the move the trick is to
252 // embed this flag in the stream itself. Function-like named enum set960 is
253 // used as a custom manipulator and the stream internal general-purpose array,
254 // accessed through ios_base::iword(), is used to pass the flag to the move's
255 // operator<<() that will read it to properly format castling moves.
258 std::ostream& operator<< (std::ostream& os, const set960& f) {
260 os.iword(0) = int(f);
264 // extension() decides whether a move should be searched with normal depth,
265 // or with extended depth. Certain classes of moves (checking moves, in
266 // particular) are searched with bigger depth than ordinary moves and in
267 // any case are marked as 'dangerous'. Note that also if a move is not
268 // extended, as example because the corresponding UCI option is set to zero,
269 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
270 template <bool PvNode>
271 FORCE_INLINE Depth extension(const Position& pos, Move m, bool captureOrPromotion,
272 bool moveIsCheck, bool* dangerous) {
273 assert(m != MOVE_NONE);
275 Depth result = DEPTH_ZERO;
276 *dangerous = moveIsCheck;
278 if (moveIsCheck && pos.see_sign(m) >= 0)
279 result += CheckExtension[PvNode];
281 if (piece_type(pos.piece_on(move_from(m))) == PAWN)
283 Color c = pos.side_to_move();
284 if (relative_rank(c, move_to(m)) == RANK_7)
286 result += PawnPushTo7thExtension[PvNode];
289 if (pos.pawn_is_passed(c, move_to(m)))
291 result += PassedPawnExtension[PvNode];
296 if ( captureOrPromotion
297 && piece_type(pos.piece_on(move_to(m))) != PAWN
298 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
299 - piece_value_midgame(pos.piece_on(move_to(m))) == VALUE_ZERO)
300 && !move_is_special(m))
302 result += PawnEndgameExtension[PvNode];
306 return Min(result, ONE_PLY);
312 /// init_search() is called during startup to initialize various lookup tables
316 int d; // depth (ONE_PLY == 2)
317 int hd; // half depth (ONE_PLY == 1)
320 // Init reductions array
321 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
323 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
324 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
325 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
326 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
329 // Init futility margins array
330 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
331 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
333 // Init futility move count array
334 for (d = 0; d < 32; d++)
335 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
339 /// perft() is our utility to verify move generation. All the leaf nodes up to
340 /// the given depth are generated and counted and the sum returned.
342 int64_t perft(Position& pos, Depth depth) {
347 // Generate all legal moves
348 MoveList<MV_LEGAL> ml(pos);
350 // If we are at the last ply we don't need to do and undo
351 // the moves, just to count them.
352 if (depth <= ONE_PLY)
355 // Loop through all legal moves
357 for ( ; !ml.end(); ++ml)
359 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
360 sum += perft(pos, depth - ONE_PLY);
361 pos.undo_move(ml.move());
367 /// think() is the external interface to Stockfish's search, and is called when
368 /// the program receives the UCI 'go' command. It initializes various global
369 /// variables, and calls id_loop(). It returns false when a "quit" command is
370 /// received during the search.
372 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
376 // Initialize global search-related variables
377 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
379 current_search_time(get_system_time());
381 TimeMgr.init(Limits, pos.startpos_ply_counter());
383 // Set output steram in normal or chess960 mode
384 cout << set960(pos.is_chess960());
386 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
388 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
389 else if (Limits.time && Limits.time < 1000)
390 NodesBetweenPolls = 1000;
391 else if (Limits.time && Limits.time < 5000)
392 NodesBetweenPolls = 5000;
394 NodesBetweenPolls = 30000;
396 // Look for a book move
397 if (Options["OwnBook"].value<bool>())
399 if (Options["Book File"].value<string>() != book.name())
400 book.open(Options["Book File"].value<string>());
402 Move bookMove = book.get_move(pos, Options["Best Book Move"].value<bool>());
403 if (bookMove != MOVE_NONE)
406 wait_for_stop_or_ponderhit();
408 cout << "bestmove " << bookMove << endl;
414 UCIMultiPV = Options["MultiPV"].value<int>();
415 SkillLevel = Options["Skill Level"].value<int>();
417 read_evaluation_uci_options(pos.side_to_move());
418 Threads.read_uci_options();
420 // If needed allocate pawn and material hash tables and adjust TT size
421 Threads.init_hash_tables();
422 TT.set_size(Options["Hash"].value<int>());
424 if (Options["Clear Hash"].value<bool>())
426 Options["Clear Hash"].set_value("false");
430 // Do we have to play with skill handicap? In this case enable MultiPV that
431 // we will use behind the scenes to retrieve a set of possible moves.
432 SkillLevelEnabled = (SkillLevel < 20);
433 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
435 // Wake up needed threads and reset maxPly counter
436 for (int i = 0; i < Threads.size(); i++)
438 Threads[i].wake_up();
439 Threads[i].maxPly = 0;
442 // Write to log file and keep it open to be accessed during the search
443 if (Options["Use Search Log"].value<bool>())
445 string name = Options["Search Log Filename"].value<string>();
446 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
448 if (LogFile.is_open())
449 LogFile << "\nSearching: " << pos.to_fen()
450 << "\ninfinite: " << Limits.infinite
451 << " ponder: " << Limits.ponder
452 << " time: " << Limits.time
453 << " increment: " << Limits.increment
454 << " moves to go: " << Limits.movesToGo
458 // We're ready to start thinking. Call the iterative deepening loop function
459 Move ponderMove = MOVE_NONE;
460 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
462 // Write final search statistics and close log file
463 if (LogFile.is_open())
465 int t = current_search_time();
467 LogFile << "Nodes: " << pos.nodes_searched()
468 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
469 << "\nBest move: " << move_to_san(pos, bestMove);
472 pos.do_move(bestMove, st);
473 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
474 pos.undo_move(bestMove); // Return from think() with unchanged position
478 // This makes all the threads to go to sleep
481 // If we are pondering or in infinite search, we shouldn't print the
482 // best move before we are told to do so.
483 if (!StopRequest && (Limits.ponder || Limits.infinite))
484 wait_for_stop_or_ponderhit();
486 // Could be MOVE_NONE when searching on a stalemate position
487 cout << "bestmove " << bestMove;
489 // UCI protol is not clear on allowing sending an empty ponder move, instead
490 // it is clear that ponder move is optional. So skip it if empty.
491 if (ponderMove != MOVE_NONE)
492 cout << " ponder " << ponderMove;
502 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
503 // with increasing depth until the allocated thinking time has been consumed,
504 // user stops the search, or the maximum search depth is reached.
506 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
508 SearchStack ss[PLY_MAX_PLUS_2];
509 Value bestValues[PLY_MAX_PLUS_2];
510 int bestMoveChanges[PLY_MAX_PLUS_2];
511 int depth, aspirationDelta;
512 Value value, alpha, beta;
513 Move bestMove, easyMove, skillBest, skillPonder;
515 // Initialize stuff before a new search
516 memset(ss, 0, 4 * sizeof(SearchStack));
519 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
520 depth = aspirationDelta = 0;
521 value = alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
522 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
524 // Moves to search are verified and copied
525 Rml.init(pos, searchMoves);
527 // Handle special case of searching on a mate/stalemate position
530 cout << "info" << depth_to_uci(DEPTH_ZERO)
531 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW, alpha, beta) << endl;
536 // Iterative deepening loop until requested to stop or target depth reached
537 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
539 Rml.bestMoveChanges = 0;
541 // Remember best moves and values from previous iteration
542 std::vector<Move> prevMoves;
543 std::vector<Value> prevValues;
545 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
547 prevMoves.push_back(Rml[i].pv[0]);
548 prevValues.push_back(Rml[i].pv_score);
551 // MultiPV iteration loop
552 for (MultiPVIteration = 0; MultiPVIteration < Min(MultiPV, (int)Rml.size()); MultiPVIteration++)
554 // Calculate dynamic aspiration window based on previous iterations
555 if (depth >= 5 && abs(prevValues[MultiPVIteration]) < VALUE_KNOWN_WIN)
557 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
558 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
560 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
561 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
563 alpha = Max(prevValues[MultiPVIteration] - aspirationDelta, -VALUE_INFINITE);
564 beta = Min(prevValues[MultiPVIteration] + aspirationDelta, VALUE_INFINITE);
568 alpha = -VALUE_INFINITE;
569 beta = VALUE_INFINITE;
572 // Start with a small aspiration window and, in case of fail high/low,
573 // research with bigger window until not failing high/low anymore.
575 // Search starting from ss+1 to allow calling update_gains()
576 value = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
578 // It is critical that sorting is done with a stable algorithm
579 // because all the values but the first are usually set to
580 // -VALUE_INFINITE and we want to keep the same order for all
581 // the moves but the new PV that goes to head.
582 if (value > alpha && value < beta)
583 sort<RootMove>(Rml.begin(), Rml.end());
585 // In MultiPV mode, sort only the tail of the list
586 // until all fail-highs and fail-lows have been resolved
587 sort<RootMove>(Rml.begin() + MultiPVIteration, Rml.end());
589 // Write PV back to transposition table in case the relevant entries
590 // have been overwritten during the search.
591 for (int i = 0; i <= MultiPVIteration; i++)
592 Rml[i].insert_pv_in_tt(pos);
594 // Value cannot be trusted. Break out immediately!
598 // Send full PV info to GUI if we are going to leave the loop or
599 // if we have a fail high/low and we are deep in the search.
600 if ((value > alpha && value < beta) || current_search_time() > 2000)
601 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
603 bool updated = (i <= MultiPVIteration);
604 bool match = (i == MultiPVIteration);
606 if (!updated && depth == 1)
610 << depth_to_uci((updated ? depth : depth - 1) * ONE_PLY)
611 << score_to_uci(updated ? Rml[i].pv_score : prevValues[i],
612 match ? alpha : -VALUE_INFINITE,
613 match ? beta : VALUE_INFINITE)
614 << speed_to_uci(pos.nodes_searched())
615 << pv_to_uci(updated ? Rml[i].pv : Rml.find(prevMoves[i])->pv,
616 i + 1, pos.is_chess960())
620 // In case of failing high/low increase aspiration window and research,
621 // otherwise exit the fail high/low loop.
624 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
625 aspirationDelta += aspirationDelta / 2;
627 else if (value <= alpha)
629 AspirationFailLow = true;
630 StopOnPonderhit = false;
632 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
633 aspirationDelta += aspirationDelta / 2;
638 } while (abs(value) < VALUE_KNOWN_WIN);
641 // Collect info about search result
642 bestMove = Rml[0].pv[0];
643 *ponderMove = Rml[0].pv[1];
644 bestValues[depth] = value;
645 bestMoveChanges[depth] = Rml.bestMoveChanges;
647 // Do we need to pick now the best and the ponder moves ?
648 if (SkillLevelEnabled && depth == 1 + SkillLevel)
649 do_skill_level(&skillBest, &skillPonder);
651 if (LogFile.is_open())
652 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
654 // Init easyMove after first iteration or drop if differs from the best move
655 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
657 else if (bestMove != easyMove)
658 easyMove = MOVE_NONE;
660 // Check for some early stop condition
661 if (!StopRequest && Limits.useTimeManagement())
663 // Stop search early if one move seems to be much better than the
664 // others or if there is only a single legal move. Also in the latter
665 // case we search up to some depth anyway to get a proper score.
667 && easyMove == bestMove
669 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
670 && current_search_time() > TimeMgr.available_time() / 16)
671 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
672 && current_search_time() > TimeMgr.available_time() / 32)))
675 // Take in account some extra time if the best move has changed
676 if (depth > 4 && depth < 50)
677 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
679 // Stop search if most of available time is already consumed. We probably don't
680 // have enough time to search the first move at the next iteration anyway.
681 if (current_search_time() > (TimeMgr.available_time() * 62) / 100)
684 // If we are allowed to ponder do not stop the search now but keep pondering
685 if (StopRequest && Limits.ponder)
688 StopOnPonderhit = true;
693 // When using skills overwrite best and ponder moves with the sub-optimal ones
694 if (SkillLevelEnabled)
696 if (skillBest == MOVE_NONE) // Still unassigned ?
697 do_skill_level(&skillBest, &skillPonder);
699 bestMove = skillBest;
700 *ponderMove = skillPonder;
707 // search<>() is the main search function for both PV and non-PV nodes and for
708 // normal and SplitPoint nodes. When called just after a split point the search
709 // is simpler because we have already probed the hash table, done a null move
710 // search, and searched the first move before splitting, we don't have to repeat
711 // all this work again. We also don't need to store anything to the hash table
712 // here: This is taken care of after we return from the split point.
714 template <NodeType NT>
715 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
717 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV);
718 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV);
719 const bool RootNode = (NT == Root);
721 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
722 assert(beta > alpha && beta <= VALUE_INFINITE);
723 assert(PvNode || alpha == beta - 1);
724 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
726 Move movesSearched[MAX_MOVES];
731 Move ttMove, move, excludedMove, threatMove;
734 Value bestValue, value, oldAlpha;
735 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
736 bool isPvMove, inCheck, singularExtensionNode, givesCheck, captureOrPromotion, dangerous;
737 int moveCount = 0, playedMoveCount = 0;
738 Thread& thread = Threads[pos.thread()];
739 SplitPoint* sp = NULL;
741 refinedValue = bestValue = value = -VALUE_INFINITE;
743 inCheck = pos.in_check();
744 ss->ply = (ss-1)->ply + 1;
746 // Used to send selDepth info to GUI
747 if (PvNode && thread.maxPly < ss->ply)
748 thread.maxPly = ss->ply;
750 // Step 1. Initialize node and poll. Polling can abort search
753 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
754 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
755 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
761 ttMove = excludedMove = MOVE_NONE;
762 threatMove = sp->threatMove;
763 goto split_point_start;
766 if (pos.thread() == 0 && ++NodesSincePoll > NodesBetweenPolls)
772 // Step 2. Check for aborted search and immediate draw
774 || pos.is_draw<false>()
775 || ss->ply > PLY_MAX) && !RootNode)
778 // Step 3. Mate distance pruning
781 alpha = Max(value_mated_in(ss->ply), alpha);
782 beta = Min(value_mate_in(ss->ply+1), beta);
787 // Step 4. Transposition table lookup
788 // We don't want the score of a partial search to overwrite a previous full search
789 // TT value, so we use a different position key in case of an excluded move.
790 excludedMove = ss->excludedMove;
791 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
792 tte = TT.probe(posKey);
793 ttMove = tte ? tte->move() : MOVE_NONE;
795 // At PV nodes we check for exact scores, while at non-PV nodes we check for
796 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
797 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
798 // we should also update RootMoveList to avoid bogus output.
799 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
800 : ok_to_use_TT(tte, depth, beta, ss->ply)))
803 ss->bestMove = ttMove; // Can be MOVE_NONE
804 return value_from_tt(tte->value(), ss->ply);
807 // Step 5. Evaluate the position statically and update parent's gain statistics
809 ss->eval = ss->evalMargin = VALUE_NONE;
812 assert(tte->static_value() != VALUE_NONE);
814 ss->eval = tte->static_value();
815 ss->evalMargin = tte->static_value_margin();
816 refinedValue = refine_eval(tte, ss->eval, ss->ply);
820 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
821 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
824 // Save gain for the parent non-capture move
825 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
827 // Step 6. Razoring (is omitted in PV nodes)
829 && depth < RazorDepth
831 && refinedValue + razor_margin(depth) < beta
832 && ttMove == MOVE_NONE
833 && abs(beta) < VALUE_MATE_IN_PLY_MAX
834 && !pos.has_pawn_on_7th(pos.side_to_move()))
836 Value rbeta = beta - razor_margin(depth);
837 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
839 // Logically we should return (v + razor_margin(depth)), but
840 // surprisingly this did slightly weaker in tests.
844 // Step 7. Static null move pruning (is omitted in PV nodes)
845 // We're betting that the opponent doesn't have a move that will reduce
846 // the score by more than futility_margin(depth) if we do a null move.
849 && depth < RazorDepth
851 && refinedValue - futility_margin(depth, 0) >= beta
852 && abs(beta) < VALUE_MATE_IN_PLY_MAX
853 && pos.non_pawn_material(pos.side_to_move()))
854 return refinedValue - futility_margin(depth, 0);
856 // Step 8. Null move search with verification search (is omitted in PV nodes)
861 && refinedValue >= beta
862 && abs(beta) < VALUE_MATE_IN_PLY_MAX
863 && pos.non_pawn_material(pos.side_to_move()))
865 ss->currentMove = MOVE_NULL;
867 // Null move dynamic reduction based on depth
868 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
870 // Null move dynamic reduction based on value
871 if (refinedValue - PawnValueMidgame > beta)
874 pos.do_null_move(st);
875 (ss+1)->skipNullMove = true;
876 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
877 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
878 (ss+1)->skipNullMove = false;
879 pos.undo_null_move();
881 if (nullValue >= beta)
883 // Do not return unproven mate scores
884 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
887 if (depth < 6 * ONE_PLY)
890 // Do verification search at high depths
891 ss->skipNullMove = true;
892 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
893 ss->skipNullMove = false;
900 // The null move failed low, which means that we may be faced with
901 // some kind of threat. If the previous move was reduced, check if
902 // the move that refuted the null move was somehow connected to the
903 // move which was reduced. If a connection is found, return a fail
904 // low score (which will cause the reduced move to fail high in the
905 // parent node, which will trigger a re-search with full depth).
906 threatMove = (ss+1)->bestMove;
908 if ( depth < ThreatDepth
910 && threatMove != MOVE_NONE
911 && connected_moves(pos, (ss-1)->currentMove, threatMove))
916 // Step 9. ProbCut (is omitted in PV nodes)
917 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
918 // and a reduced search returns a value much above beta, we can (almost) safely
919 // prune the previous move.
921 && depth >= RazorDepth + ONE_PLY
924 && excludedMove == MOVE_NONE
925 && abs(beta) < VALUE_MATE_IN_PLY_MAX)
927 Value rbeta = beta + 200;
928 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
930 assert(rdepth >= ONE_PLY);
932 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
935 while ((move = mp.get_next_move()) != MOVE_NONE)
936 if (pos.pl_move_is_legal(move, ci.pinned))
938 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
939 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
946 // Step 10. Internal iterative deepening
947 if ( depth >= IIDDepth[PvNode]
948 && ttMove == MOVE_NONE
949 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
951 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
953 ss->skipNullMove = true;
954 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
955 ss->skipNullMove = false;
957 tte = TT.probe(posKey);
958 ttMove = tte ? tte->move() : MOVE_NONE;
961 split_point_start: // At split points actual search starts from here
963 // Initialize a MovePicker object for the current position
964 MovePickerExt<NT> mp(pos, RootNode ? Rml[MultiPVIteration].pv[0] : ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
966 ss->bestMove = MOVE_NONE;
967 futilityBase = ss->eval + ss->evalMargin;
968 singularExtensionNode = !RootNode
970 && depth >= SingularExtensionDepth[PvNode]
971 && ttMove != MOVE_NONE
972 && !excludedMove // Do not allow recursive singular extension search
973 && (tte->type() & VALUE_TYPE_LOWER)
974 && tte->depth() >= depth - 3 * ONE_PLY;
977 lock_grab(&(sp->lock));
978 bestValue = sp->bestValue;
981 // Step 11. Loop through moves
982 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
983 while ( bestValue < beta
984 && (move = mp.get_next_move()) != MOVE_NONE
985 && !thread.cutoff_occurred())
987 assert(move_is_ok(move));
989 if (move == excludedMove)
992 // At root obey the "searchmoves" option and skip moves not listed in Root Move List.
993 // Also in MultiPV mode we skip moves which already have got an exact score
994 // in previous MultiPV Iteration.
995 if (RootNode && !Rml.find(move, MultiPVIteration))
998 // At PV and SpNode nodes we want all moves to be legal since the beginning
999 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
1004 moveCount = ++sp->moveCount;
1005 lock_release(&(sp->lock));
1012 // This is used by time management
1013 FirstRootMove = (moveCount == 1);
1015 // Save the current node count before the move is searched
1016 nodes = pos.nodes_searched();
1018 // If it's time to send nodes info, do it here where we have the
1019 // correct accumulated node counts searched by each thread.
1020 if (SendSearchedNodes)
1022 SendSearchedNodes = false;
1023 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1026 // For long searches send current move info to GUI
1027 if (current_search_time() > 2000)
1028 cout << "info" << depth_to_uci(depth)
1029 << " currmove " << move << " currmovenumber " << moveCount + MultiPVIteration << endl;
1032 // At Root and at first iteration do a PV search on all the moves to score root moves
1033 isPvMove = (PvNode && moveCount <= ((RootNode && depth <= ONE_PLY) ? MAX_MOVES : 1));
1034 givesCheck = pos.move_gives_check(move, ci);
1035 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1037 // Step 12. Decide the new search depth
1038 ext = extension<PvNode>(pos, move, captureOrPromotion, givesCheck, &dangerous);
1040 // Singular extension search. If all moves but one fail low on a search of
1041 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1042 // is singular and should be extended. To verify this we do a reduced search
1043 // on all the other moves but the ttMove, if result is lower than ttValue minus
1044 // a margin then we extend ttMove.
1045 if ( singularExtensionNode
1047 && pos.pl_move_is_legal(move, ci.pinned)
1050 Value ttValue = value_from_tt(tte->value(), ss->ply);
1052 if (abs(ttValue) < VALUE_KNOWN_WIN)
1054 Value rBeta = ttValue - int(depth);
1055 ss->excludedMove = move;
1056 ss->skipNullMove = true;
1057 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1058 ss->skipNullMove = false;
1059 ss->excludedMove = MOVE_NONE;
1060 ss->bestMove = MOVE_NONE;
1066 // Update current move (this must be done after singular extension search)
1067 newDepth = depth - ONE_PLY + ext;
1069 // Step 13. Futility pruning (is omitted in PV nodes)
1071 && !captureOrPromotion
1075 && !move_is_castle(move))
1077 // Move count based pruning
1078 if ( moveCount >= futility_move_count(depth)
1079 && (!threatMove || !connected_threat(pos, move, threatMove))
1080 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1083 lock_grab(&(sp->lock));
1088 // Value based pruning
1089 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1090 // but fixing this made program slightly weaker.
1091 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
1092 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1093 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1095 if (futilityValueScaled < beta)
1099 lock_grab(&(sp->lock));
1100 if (futilityValueScaled > sp->bestValue)
1101 sp->bestValue = bestValue = futilityValueScaled;
1103 else if (futilityValueScaled > bestValue)
1104 bestValue = futilityValueScaled;
1109 // Prune moves with negative SEE at low depths
1110 if ( predictedDepth < 2 * ONE_PLY
1111 && bestValue > VALUE_MATED_IN_PLY_MAX
1112 && pos.see_sign(move) < 0)
1115 lock_grab(&(sp->lock));
1121 // Check for legality only before to do the move
1122 if (!pos.pl_move_is_legal(move, ci.pinned))
1128 ss->currentMove = move;
1129 if (!SpNode && !captureOrPromotion)
1130 movesSearched[playedMoveCount++] = move;
1132 // Step 14. Make the move
1133 pos.do_move(move, st, ci, givesCheck);
1135 // Step extra. pv search (only in PV nodes)
1136 // The first move in list is the expected PV
1138 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1139 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1142 // Step 15. Reduced depth search
1143 // If the move fails high will be re-searched at full depth.
1144 bool doFullDepthSearch = true;
1146 if ( depth > 3 * ONE_PLY
1147 && !captureOrPromotion
1149 && !move_is_castle(move)
1150 && ss->killers[0] != move
1151 && ss->killers[1] != move
1152 && (ss->reduction = reduction<PvNode>(depth, moveCount)) != DEPTH_ZERO)
1154 Depth d = newDepth - ss->reduction;
1155 alpha = SpNode ? sp->alpha : alpha;
1157 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1158 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1160 ss->reduction = DEPTH_ZERO;
1161 doFullDepthSearch = (value > alpha);
1164 // Step 16. Full depth search
1165 if (doFullDepthSearch)
1167 alpha = SpNode ? sp->alpha : alpha;
1168 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1169 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1171 // Step extra. pv search (only in PV nodes)
1172 // Search only for possible new PV nodes, if instead value >= beta then
1173 // parent node fails low with value <= alpha and tries another move.
1174 if (PvNode && value > alpha && (RootNode || value < beta))
1175 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1176 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1180 // Step 17. Undo move
1181 pos.undo_move(move);
1183 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1185 // Step 18. Check for new best move
1188 lock_grab(&(sp->lock));
1189 bestValue = sp->bestValue;
1193 if (value > bestValue)
1196 ss->bestMove = move;
1201 && value < beta) // We want always alpha < beta
1204 if (SpNode && !thread.cutoff_occurred())
1206 sp->bestValue = value;
1207 sp->ss->bestMove = move;
1209 sp->is_betaCutoff = (value >= beta);
1215 // Finished searching the move. If StopRequest is true, the search
1216 // was aborted because the user interrupted the search or because we
1217 // ran out of time. In this case, the return value of the search cannot
1218 // be trusted, and we break out of the loop without updating the best
1223 // Remember searched nodes counts for this move
1224 Rml.find(move)->nodes += pos.nodes_searched() - nodes;
1226 // PV move or new best move ?
1227 if (isPvMove || value > alpha)
1230 Rml.find(move)->pv_score = value;
1231 Rml.find(move)->extract_pv_from_tt(pos);
1233 // We record how often the best move has been changed in each
1234 // iteration. This information is used for time management: When
1235 // the best move changes frequently, we allocate some more time.
1236 if (!isPvMove && MultiPV == 1)
1237 Rml.bestMoveChanges++;
1244 // All other moves but the PV are set to the lowest value, this
1245 // is not a problem when sorting becuase sort is stable and move
1246 // position in the list is preserved, just the PV is pushed up.
1247 Rml.find(move)->pv_score = -VALUE_INFINITE;
1251 // Step 19. Check for split
1254 && depth >= Threads.min_split_depth()
1256 && Threads.available_slave_exists(pos.thread())
1258 && !thread.cutoff_occurred())
1259 Threads.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1260 threatMove, moveCount, &mp, PvNode);
1263 // Step 20. Check for mate and stalemate
1264 // All legal moves have been searched and if there are
1265 // no legal moves, it must be mate or stalemate.
1266 // If one move was excluded return fail low score.
1267 if (!SpNode && !moveCount)
1268 return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1270 // Step 21. Update tables
1271 // If the search is not aborted, update the transposition table,
1272 // history counters, and killer moves.
1273 if (!SpNode && !StopRequest && !thread.cutoff_occurred())
1275 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1276 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1277 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1279 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1281 // Update killers and history only for non capture moves that fails high
1282 if ( bestValue >= beta
1283 && !pos.move_is_capture_or_promotion(move))
1285 if (move != ss->killers[0])
1287 ss->killers[1] = ss->killers[0];
1288 ss->killers[0] = move;
1290 update_history(pos, move, depth, movesSearched, playedMoveCount);
1296 // Here we have the lock still grabbed
1297 sp->is_slave[pos.thread()] = false;
1298 sp->nodes += pos.nodes_searched();
1299 lock_release(&(sp->lock));
1302 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1307 // qsearch() is the quiescence search function, which is called by the main
1308 // search function when the remaining depth is zero (or, to be more precise,
1309 // less than ONE_PLY).
1311 template <NodeType NT>
1312 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1314 const bool PvNode = (NT == PV);
1316 assert(NT == PV || NT == NonPV);
1317 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1318 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1319 assert(PvNode || alpha == beta - 1);
1321 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
1325 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1326 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1329 Value oldAlpha = alpha;
1331 ss->bestMove = ss->currentMove = MOVE_NONE;
1332 ss->ply = (ss-1)->ply + 1;
1334 // Check for an instant draw or maximum ply reached
1335 if (pos.is_draw<true>() || ss->ply > PLY_MAX)
1338 // Decide whether or not to include checks, this fixes also the type of
1339 // TT entry depth that we are going to use. Note that in qsearch we use
1340 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1341 inCheck = pos.in_check();
1342 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1344 // Transposition table lookup. At PV nodes, we don't use the TT for
1345 // pruning, but only for move ordering.
1346 tte = TT.probe(pos.get_key());
1347 ttMove = (tte ? tte->move() : MOVE_NONE);
1349 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1351 ss->bestMove = ttMove; // Can be MOVE_NONE
1352 return value_from_tt(tte->value(), ss->ply);
1355 // Evaluate the position statically
1358 bestValue = futilityBase = -VALUE_INFINITE;
1359 ss->eval = evalMargin = VALUE_NONE;
1360 enoughMaterial = false;
1366 assert(tte->static_value() != VALUE_NONE);
1368 evalMargin = tte->static_value_margin();
1369 ss->eval = bestValue = tte->static_value();
1372 ss->eval = bestValue = evaluate(pos, evalMargin);
1374 // Stand pat. Return immediately if static value is at least beta
1375 if (bestValue >= beta)
1378 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1383 if (PvNode && bestValue > alpha)
1386 // Futility pruning parameters, not needed when in check
1387 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1388 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1391 // Initialize a MovePicker object for the current position, and prepare
1392 // to search the moves. Because the depth is <= 0 here, only captures,
1393 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1395 MovePicker mp(pos, ttMove, depth, H, move_to((ss-1)->currentMove));
1398 // Loop through the moves until no moves remain or a beta cutoff occurs
1399 while ( alpha < beta
1400 && (move = mp.get_next_move()) != MOVE_NONE)
1402 assert(move_is_ok(move));
1404 givesCheck = pos.move_gives_check(move, ci);
1412 && !move_is_promotion(move)
1413 && !pos.move_is_passed_pawn_push(move))
1415 futilityValue = futilityBase
1416 + piece_value_endgame(pos.piece_on(move_to(move)))
1417 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1419 if (futilityValue < alpha)
1421 if (futilityValue > bestValue)
1422 bestValue = futilityValue;
1426 // Prune moves with negative or equal SEE
1427 if ( futilityBase < beta
1428 && depth < DEPTH_ZERO
1429 && pos.see(move) <= 0)
1433 // Detect non-capture evasions that are candidate to be pruned
1434 evasionPrunable = !PvNode
1436 && bestValue > VALUE_MATED_IN_PLY_MAX
1437 && !pos.move_is_capture(move)
1438 && !pos.can_castle(pos.side_to_move());
1440 // Don't search moves with negative SEE values
1442 && (!inCheck || evasionPrunable)
1444 && !move_is_promotion(move)
1445 && pos.see_sign(move) < 0)
1448 // Don't search useless checks
1453 && !pos.move_is_capture_or_promotion(move)
1454 && ss->eval + PawnValueMidgame / 4 < beta
1455 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1457 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1458 bestValue = ss->eval + PawnValueMidgame / 4;
1463 // Check for legality only before to do the move
1464 if (!pos.pl_move_is_legal(move, ci.pinned))
1467 // Update current move
1468 ss->currentMove = move;
1470 // Make and search the move
1471 pos.do_move(move, st, ci, givesCheck);
1472 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1473 pos.undo_move(move);
1475 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1478 if (value > bestValue)
1484 ss->bestMove = move;
1489 // All legal moves have been searched. A special case: If we're in check
1490 // and no legal moves were found, it is checkmate.
1491 if (inCheck && bestValue == -VALUE_INFINITE)
1492 return value_mated_in(ss->ply);
1494 // Update transposition table
1495 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1496 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1498 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1504 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1505 // bestValue is updated only when returning false because in that case move
1508 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1510 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1511 Square from, to, ksq, victimSq;
1514 Value futilityValue, bv = *bestValue;
1516 from = move_from(move);
1518 them = opposite_color(pos.side_to_move());
1519 ksq = pos.king_square(them);
1520 kingAtt = pos.attacks_from<KING>(ksq);
1521 pc = pos.piece_on(from);
1523 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1524 oldAtt = pos.attacks_from(pc, from, occ);
1525 newAtt = pos.attacks_from(pc, to, occ);
1527 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1528 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1530 if (!(b && (b & (b - 1))))
1533 // Rule 2. Queen contact check is very dangerous
1534 if ( piece_type(pc) == QUEEN
1535 && bit_is_set(kingAtt, to))
1538 // Rule 3. Creating new double threats with checks
1539 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1543 victimSq = pop_1st_bit(&b);
1544 futilityValue = futilityBase + piece_value_endgame(pos.piece_on(victimSq));
1546 // Note that here we generate illegal "double move"!
1547 if ( futilityValue >= beta
1548 && pos.see_sign(make_move(from, victimSq)) >= 0)
1551 if (futilityValue > bv)
1555 // Update bestValue only if check is not dangerous (because we will prune the move)
1561 // connected_moves() tests whether two moves are 'connected' in the sense
1562 // that the first move somehow made the second move possible (for instance
1563 // if the moving piece is the same in both moves). The first move is assumed
1564 // to be the move that was made to reach the current position, while the
1565 // second move is assumed to be a move from the current position.
1567 bool connected_moves(const Position& pos, Move m1, Move m2) {
1569 Square f1, t1, f2, t2;
1573 assert(m1 && move_is_ok(m1));
1574 assert(m2 && move_is_ok(m2));
1576 // Case 1: The moving piece is the same in both moves
1582 // Case 2: The destination square for m2 was vacated by m1
1588 // Case 3: Moving through the vacated square
1589 p2 = pos.piece_on(f2);
1590 if ( piece_is_slider(p2)
1591 && bit_is_set(squares_between(f2, t2), f1))
1594 // Case 4: The destination square for m2 is defended by the moving piece in m1
1595 p1 = pos.piece_on(t1);
1596 if (bit_is_set(pos.attacks_from(p1, t1), t2))
1599 // Case 5: Discovered check, checking piece is the piece moved in m1
1600 ksq = pos.king_square(pos.side_to_move());
1601 if ( piece_is_slider(p1)
1602 && bit_is_set(squares_between(t1, ksq), f2))
1604 Bitboard occ = pos.occupied_squares();
1605 clear_bit(&occ, f2);
1606 if (bit_is_set(pos.attacks_from(p1, t1, occ), ksq))
1613 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1614 // "plies to mate from the current ply". Non-mate scores are unchanged.
1615 // The function is called before storing a value to the transposition table.
1617 Value value_to_tt(Value v, int ply) {
1619 if (v >= VALUE_MATE_IN_PLY_MAX)
1622 if (v <= VALUE_MATED_IN_PLY_MAX)
1629 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1630 // the transposition table to a mate score corrected for the current ply.
1632 Value value_from_tt(Value v, int ply) {
1634 if (v >= VALUE_MATE_IN_PLY_MAX)
1637 if (v <= VALUE_MATED_IN_PLY_MAX)
1644 // connected_threat() tests whether it is safe to forward prune a move or if
1645 // is somehow connected to the threat move returned by null search.
1647 bool connected_threat(const Position& pos, Move m, Move threat) {
1649 assert(move_is_ok(m));
1650 assert(threat && move_is_ok(threat));
1651 assert(!pos.move_is_capture_or_promotion(m));
1652 assert(!pos.move_is_passed_pawn_push(m));
1654 Square mfrom, mto, tfrom, tto;
1656 mfrom = move_from(m);
1658 tfrom = move_from(threat);
1659 tto = move_to(threat);
1661 // Case 1: Don't prune moves which move the threatened piece
1665 // Case 2: If the threatened piece has value less than or equal to the
1666 // value of the threatening piece, don't prune moves which defend it.
1667 if ( pos.move_is_capture(threat)
1668 && ( piece_value_midgame(pos.piece_on(tfrom)) >= piece_value_midgame(pos.piece_on(tto))
1669 || piece_type(pos.piece_on(tfrom)) == KING)
1670 && pos.move_attacks_square(m, tto))
1673 // Case 3: If the moving piece in the threatened move is a slider, don't
1674 // prune safe moves which block its ray.
1675 if ( piece_is_slider(pos.piece_on(tfrom))
1676 && bit_is_set(squares_between(tfrom, tto), mto)
1677 && pos.see_sign(m) >= 0)
1684 // ok_to_use_TT() returns true if a transposition table score
1685 // can be used at a given point in search.
1687 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1689 Value v = value_from_tt(tte->value(), ply);
1691 return ( tte->depth() >= depth
1692 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1693 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1695 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1696 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1700 // refine_eval() returns the transposition table score if
1701 // possible otherwise falls back on static position evaluation.
1703 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1707 Value v = value_from_tt(tte->value(), ply);
1709 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1710 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1717 // update_history() registers a good move that produced a beta-cutoff
1718 // in history and marks as failures all the other moves of that ply.
1720 void update_history(const Position& pos, Move move, Depth depth,
1721 Move movesSearched[], int moveCount) {
1723 Value bonus = Value(int(depth) * int(depth));
1725 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1727 for (int i = 0; i < moveCount - 1; i++)
1729 m = movesSearched[i];
1733 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1738 // update_gains() updates the gains table of a non-capture move given
1739 // the static position evaluation before and after the move.
1741 void update_gains(const Position& pos, Move m, Value before, Value after) {
1744 && before != VALUE_NONE
1745 && after != VALUE_NONE
1746 && pos.captured_piece_type() == PIECE_TYPE_NONE
1747 && !move_is_special(m))
1748 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1752 // current_search_time() returns the number of milliseconds which have passed
1753 // since the beginning of the current search.
1755 int current_search_time(int set) {
1757 static int searchStartTime;
1760 searchStartTime = set;
1762 return get_system_time() - searchStartTime;
1766 // score_to_uci() converts a value to a string suitable for use with the UCI
1767 // protocol specifications:
1769 // cp <x> The score from the engine's point of view in centipawns.
1770 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1771 // use negative values for y.
1773 string score_to_uci(Value v, Value alpha, Value beta) {
1775 std::stringstream s;
1777 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1778 s << " score cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1780 s << " score mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1782 s << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1788 // speed_to_uci() returns a string with time stats of current search suitable
1789 // to be sent to UCI gui.
1791 string speed_to_uci(int64_t nodes) {
1793 std::stringstream s;
1794 int t = current_search_time();
1796 s << " nodes " << nodes
1797 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1803 // pv_to_uci() returns a string with information on the current PV line
1804 // formatted according to UCI specification.
1806 string pv_to_uci(Move pv[], int pvNum, bool chess960) {
1808 std::stringstream s;
1810 s << " multipv " << pvNum << " pv " << set960(chess960);
1812 for ( ; *pv != MOVE_NONE; pv++)
1818 // depth_to_uci() returns a string with information on the current depth and
1819 // seldepth formatted according to UCI specification.
1821 string depth_to_uci(Depth depth) {
1823 std::stringstream s;
1825 // Retrieve max searched depth among threads
1827 for (int i = 0; i < Threads.size(); i++)
1828 if (Threads[i].maxPly > selDepth)
1829 selDepth = Threads[i].maxPly;
1831 s << " depth " << depth / ONE_PLY << " seldepth " << selDepth;
1836 string time_to_string(int millisecs) {
1838 const int MSecMinute = 1000 * 60;
1839 const int MSecHour = 1000 * 60 * 60;
1841 int hours = millisecs / MSecHour;
1842 int minutes = (millisecs % MSecHour) / MSecMinute;
1843 int seconds = ((millisecs % MSecHour) % MSecMinute) / 1000;
1845 std::stringstream s;
1850 s << std::setfill('0') << std::setw(2) << minutes << ':' << std::setw(2) << seconds;
1854 string score_to_string(Value v) {
1856 std::stringstream s;
1858 if (v >= VALUE_MATE_IN_PLY_MAX)
1859 s << "#" << (VALUE_MATE - v + 1) / 2;
1860 else if (v <= VALUE_MATED_IN_PLY_MAX)
1861 s << "-#" << (VALUE_MATE + v) / 2;
1863 s << std::setprecision(2) << std::fixed << std::showpos << float(v) / PawnValueMidgame;
1868 // pretty_pv() creates a human-readable string from a position and a PV.
1869 // It is used to write search information to the log file (which is created
1870 // when the UCI parameter "Use Search Log" is "true").
1872 string pretty_pv(Position& pos, int depth, Value value, int time, Move pv[]) {
1874 const int64_t K = 1000;
1875 const int64_t M = 1000000;
1876 const int startColumn = 28;
1877 const size_t maxLength = 80 - startColumn;
1879 StateInfo state[PLY_MAX_PLUS_2], *st = state;
1882 std::stringstream s;
1885 // First print depth, score, time and searched nodes...
1886 s << set960(pos.is_chess960())
1887 << std::setw(2) << depth
1888 << std::setw(8) << score_to_string(value)
1889 << std::setw(8) << time_to_string(time);
1891 if (pos.nodes_searched() < M)
1892 s << std::setw(8) << pos.nodes_searched() / 1 << " ";
1893 else if (pos.nodes_searched() < K * M)
1894 s << std::setw(7) << pos.nodes_searched() / K << "K ";
1896 s << std::setw(7) << pos.nodes_searched() / M << "M ";
1898 // ...then print the full PV line in short algebraic notation
1899 while (*m != MOVE_NONE)
1901 san = move_to_san(pos, *m);
1902 length += san.length() + 1;
1904 if (length > maxLength)
1906 length = san.length() + 1;
1907 s << "\n" + string(startColumn, ' ');
1911 pos.do_move(*m++, *st++);
1914 // Restore original position before to leave
1915 while (m != pv) pos.undo_move(*--m);
1920 // poll() performs two different functions: It polls for user input, and it
1921 // looks at the time consumed so far and decides if it's time to abort the
1924 void poll(const Position& pos) {
1926 static int lastInfoTime;
1927 int t = current_search_time();
1930 if (input_available())
1932 // We are line oriented, don't read single chars
1935 if (!std::getline(std::cin, command) || command == "quit")
1937 // Quit the program as soon as possible
1938 Limits.ponder = false;
1939 QuitRequest = StopRequest = true;
1942 else if (command == "stop")
1944 // Stop calculating as soon as possible, but still send the "bestmove"
1945 // and possibly the "ponder" token when finishing the search.
1946 Limits.ponder = false;
1949 else if (command == "ponderhit")
1951 // The opponent has played the expected move. GUI sends "ponderhit" if
1952 // we were told to ponder on the same move the opponent has played. We
1953 // should continue searching but switching from pondering to normal search.
1954 Limits.ponder = false;
1956 if (StopOnPonderhit)
1961 // Print search information
1965 else if (lastInfoTime > t)
1966 // HACK: Must be a new search where we searched less than
1967 // NodesBetweenPolls nodes during the first second of search.
1970 else if (t - lastInfoTime >= 1000)
1975 dbg_print_hit_rate();
1977 // Send info on searched nodes as soon as we return to root
1978 SendSearchedNodes = true;
1981 // Should we stop the search?
1985 bool stillAtFirstMove = FirstRootMove
1986 && !AspirationFailLow
1987 && t > TimeMgr.available_time();
1989 bool noMoreTime = t > TimeMgr.maximum_time()
1990 || stillAtFirstMove;
1992 if ( (Limits.useTimeManagement() && noMoreTime)
1993 || (Limits.maxTime && t >= Limits.maxTime)
1994 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1999 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2000 // while the program is pondering. The point is to work around a wrinkle in
2001 // the UCI protocol: When pondering, the engine is not allowed to give a
2002 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2003 // We simply wait here until one of these commands is sent, and return,
2004 // after which the bestmove and pondermove will be printed.
2006 void wait_for_stop_or_ponderhit() {
2010 // Wait for a command from stdin
2011 while ( std::getline(std::cin, command)
2012 && command != "ponderhit" && command != "stop" && command != "quit") {};
2014 if (command != "ponderhit" && command != "stop")
2015 QuitRequest = true; // Must be "quit" or getline() returned false
2019 // When playing with strength handicap choose best move among the MultiPV set
2020 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
2021 void do_skill_level(Move* best, Move* ponder) {
2023 assert(MultiPV > 1);
2027 // Rml list is already sorted by pv_score in descending order
2029 int max_s = -VALUE_INFINITE;
2030 int size = Min(MultiPV, (int)Rml.size());
2031 int max = Rml[0].pv_score;
2032 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
2033 int wk = 120 - 2 * SkillLevel;
2035 // PRNG sequence should be non deterministic
2036 for (int i = abs(get_system_time() % 50); i > 0; i--)
2037 rk.rand<unsigned>();
2039 // Choose best move. For each move's score we add two terms both dependent
2040 // on wk, one deterministic and bigger for weaker moves, and one random,
2041 // then we choose the move with the resulting highest score.
2042 for (int i = 0; i < size; i++)
2044 s = Rml[i].pv_score;
2046 // Don't allow crazy blunders even at very low skills
2047 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
2050 // This is our magical formula
2051 s += ((max - s) * wk + var * (rk.rand<unsigned>() % wk)) / 128;
2056 *best = Rml[i].pv[0];
2057 *ponder = Rml[i].pv[1];
2063 /// RootMove and RootMoveList method's definitions
2065 RootMove::RootMove() {
2068 pv_score = -VALUE_INFINITE;
2072 RootMove& RootMove::operator=(const RootMove& rm) {
2074 const Move* src = rm.pv;
2077 // Avoid a costly full rm.pv[] copy
2078 do *dst++ = *src; while (*src++ != MOVE_NONE);
2081 pv_score = rm.pv_score;
2085 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2088 bestMoveChanges = 0;
2091 // Generate all legal moves and add them to RootMoveList
2092 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
2094 // If we have a searchMoves[] list then verify the move
2095 // is in the list before to add it.
2096 for (sm = searchMoves; *sm && *sm != ml.move(); sm++) {}
2098 if (sm != searchMoves && *sm != ml.move())
2102 rm.pv[0] = ml.move();
2103 rm.pv[1] = MOVE_NONE;
2104 rm.pv_score = -VALUE_INFINITE;
2109 RootMove* RootMoveList::find(const Move &m, const int startIndex) {
2111 for (int i = startIndex; i < int(size()); i++)
2113 if ((*this)[i].pv[0] == m)
2120 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2121 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2122 // allow to always have a ponder move even when we fail high at root and also a
2123 // long PV to print that is important for position analysis.
2125 void RootMove::extract_pv_from_tt(Position& pos) {
2127 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2131 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2133 pos.do_move(pv[0], *st++);
2135 while ( (tte = TT.probe(pos.get_key())) != NULL
2136 && tte->move() != MOVE_NONE
2137 && pos.move_is_pl(tte->move())
2138 && pos.pl_move_is_legal(tte->move(), pos.pinned_pieces())
2140 && (!pos.is_draw<false>() || ply < 2))
2142 pv[ply] = tte->move();
2143 pos.do_move(pv[ply++], *st++);
2145 pv[ply] = MOVE_NONE;
2147 do pos.undo_move(pv[--ply]); while (ply);
2150 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2151 // the PV back into the TT. This makes sure the old PV moves are searched
2152 // first, even if the old TT entries have been overwritten.
2154 void RootMove::insert_pv_in_tt(Position& pos) {
2156 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2159 Value v, m = VALUE_NONE;
2162 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2168 // Don't overwrite existing correct entries
2169 if (!tte || tte->move() != pv[ply])
2171 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
2172 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2174 pos.do_move(pv[ply], *st++);
2176 } while (pv[++ply] != MOVE_NONE);
2178 do pos.undo_move(pv[--ply]); while (ply);
2183 // ThreadsManager::idle_loop() is where the threads are parked when they have no work
2184 // to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2185 // object for which the current thread is the master.
2187 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2189 assert(threadID >= 0 && threadID < MAX_THREADS);
2196 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2197 // master should exit as last one.
2198 if (allThreadsShouldExit)
2201 threads[threadID].state = Thread::TERMINATED;
2205 // If we are not thinking, wait for a condition to be signaled
2206 // instead of wasting CPU time polling for work.
2207 while ( threadID >= activeThreads
2208 || threads[threadID].state == Thread::INITIALIZING
2209 || (useSleepingThreads && threads[threadID].state == Thread::AVAILABLE))
2211 assert(!sp || useSleepingThreads);
2212 assert(threadID != 0 || useSleepingThreads);
2214 if (threads[threadID].state == Thread::INITIALIZING)
2215 threads[threadID].state = Thread::AVAILABLE;
2217 // Grab the lock to avoid races with Thread::wake_up()
2218 lock_grab(&threads[threadID].sleepLock);
2220 // If we are master and all slaves have finished do not go to sleep
2221 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2222 allFinished = (i == activeThreads);
2224 if (allFinished || allThreadsShouldExit)
2226 lock_release(&threads[threadID].sleepLock);
2230 // Do sleep here after retesting sleep conditions
2231 if (threadID >= activeThreads || threads[threadID].state == Thread::AVAILABLE)
2232 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2234 lock_release(&threads[threadID].sleepLock);
2237 // If this thread has been assigned work, launch a search
2238 if (threads[threadID].state == Thread::WORKISWAITING)
2240 assert(!allThreadsShouldExit);
2242 threads[threadID].state = Thread::SEARCHING;
2244 // Copy split point position and search stack and call search()
2245 // with SplitPoint template parameter set to true.
2246 SearchStack ss[PLY_MAX_PLUS_2];
2247 SplitPoint* tsp = threads[threadID].splitPoint;
2248 Position pos(*tsp->pos, threadID);
2250 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2254 search<SplitPointPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2256 search<SplitPointNonPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2258 assert(threads[threadID].state == Thread::SEARCHING);
2260 threads[threadID].state = Thread::AVAILABLE;
2262 // Wake up master thread so to allow it to return from the idle loop in
2263 // case we are the last slave of the split point.
2264 if ( useSleepingThreads
2265 && threadID != tsp->master
2266 && threads[tsp->master].state == Thread::AVAILABLE)
2267 threads[tsp->master].wake_up();
2270 // If this thread is the master of a split point and all slaves have
2271 // finished their work at this split point, return from the idle loop.
2272 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2273 allFinished = (i == activeThreads);
2277 // Because sp->slaves[] is reset under lock protection,
2278 // be sure sp->lock has been released before to return.
2279 lock_grab(&(sp->lock));
2280 lock_release(&(sp->lock));
2282 // In helpful master concept a master can help only a sub-tree, and
2283 // because here is all finished is not possible master is booked.
2284 assert(threads[threadID].state == Thread::AVAILABLE);
2286 threads[threadID].state = Thread::SEARCHING;