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/>.
39 #include "ucioption.h"
46 // Different node types, used as template parameter
47 enum NodeType { NonPV, PV };
49 // Set to true to force running with one thread. Used for debugging.
50 const bool FakeSplit = false;
52 // Lookup table to check if a Piece is a slider and its access function
53 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
54 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
56 // RootMove struct is used for moves at the root of the tree. For each root
57 // move, we store two scores, a node count, and a PV (really a refutation
58 // in the case of moves which fail low). Value pv_score is normally set at
59 // -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
60 // according to the order in which moves are returned by MovePicker.
65 RootMove(const RootMove& rm) { *this = rm; }
66 RootMove& operator=(const RootMove& rm);
68 // RootMove::operator<() is the comparison function used when
69 // sorting the moves. A move m1 is considered to be better
70 // than a move m2 if it has an higher pv_score, or if it has
71 // equal pv_score but m1 has the higher non_pv_score. In this way
72 // we are guaranteed that PV moves are always sorted as first.
73 bool operator<(const RootMove& m) const {
74 return pv_score != m.pv_score ? pv_score < m.pv_score
75 : non_pv_score < m.non_pv_score;
78 void extract_pv_from_tt(Position& pos);
79 void insert_pv_in_tt(Position& pos);
80 std::string pv_info_to_uci(Position& pos, int depth, int selDepth,
81 Value alpha, Value beta, int pvIdx);
85 Move pv[PLY_MAX_PLUS_2];
89 // RootMoveList struct is just a vector of RootMove objects,
90 // with an handful of methods above the standard ones.
92 struct RootMoveList : public std::vector<RootMove> {
94 typedef std::vector<RootMove> Base;
96 void init(Position& pos, Move searchMoves[]);
97 void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
98 void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
104 // Overload operator<<() to make it easier to print moves in a coordinate
105 // notation compatible with UCI protocol.
106 std::ostream& operator<<(std::ostream& os, Move m) {
108 bool chess960 = (os.iword(0) != 0); // See set960()
109 return os << move_to_uci(m, chess960);
113 // When formatting a move for std::cout we must know if we are in Chess960
114 // or not. To keep using the handy operator<<() on the move the trick is to
115 // embed this flag in the stream itself. Function-like named enum set960 is
116 // used as a custom manipulator and the stream internal general-purpose array,
117 // accessed through ios_base::iword(), is used to pass the flag to the move's
118 // operator<<() that will read it to properly format castling moves.
121 std::ostream& operator<< (std::ostream& os, const set960& f) {
123 os.iword(0) = int(f);
132 // Maximum depth for razoring
133 const Depth RazorDepth = 4 * ONE_PLY;
135 // Dynamic razoring margin based on depth
136 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
138 // Maximum depth for use of dynamic threat detection when null move fails low
139 const Depth ThreatDepth = 5 * ONE_PLY;
141 // Step 9. Internal iterative deepening
143 // Minimum depth for use of internal iterative deepening
144 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
146 // At Non-PV nodes we do an internal iterative deepening search
147 // when the static evaluation is bigger then beta - IIDMargin.
148 const Value IIDMargin = Value(0x100);
150 // Step 11. Decide the new search depth
152 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
153 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
154 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
155 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
156 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
158 // Minimum depth for use of singular extension
159 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
161 // Step 12. Futility pruning
163 // Futility margin for quiescence search
164 const Value FutilityMarginQS = Value(0x80);
166 // Futility lookup tables (initialized at startup) and their access functions
167 Value FutilityMargins[16][64]; // [depth][moveNumber]
168 int FutilityMoveCounts[32]; // [depth]
170 inline Value futility_margin(Depth d, int mn) {
172 return d < 7 * ONE_PLY ? FutilityMargins[Max(d, 1)][Min(mn, 63)]
173 : 2 * VALUE_INFINITE;
176 inline int futility_move_count(Depth d) {
178 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
181 // Step 14. Reduced search
183 // Reduction lookup tables (initialized at startup) and their access function
184 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
186 template <NodeType PV> inline Depth reduction(Depth d, int mn) {
188 return (Depth) Reductions[PV][Min(d / ONE_PLY, 63)][Min(mn, 63)];
191 // Easy move margin. An easy move candidate must be at least this much
192 // better than the second best move.
193 const Value EasyMoveMargin = Value(0x200);
196 /// Namespace variables
205 int MultiPV, UCIMultiPV;
207 // Time management variables
208 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
213 std::ofstream LogFile;
215 // Skill level adjustment
217 bool SkillLevelEnabled;
220 // Node counters, used only by thread[0] but try to keep in different cache
221 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
222 bool SendSearchedNodes;
224 int NodesBetweenPolls = 30000;
232 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
234 template <NodeType PvNode, bool SpNode, bool Root>
235 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
237 template <NodeType PvNode>
238 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
240 template <NodeType PvNode>
241 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
243 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO)
244 : search<PvNode, false, false>(pos, ss, alpha, beta, depth);
247 template <NodeType PvNode>
248 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool* dangerous);
250 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
251 bool connected_moves(const Position& pos, Move m1, Move m2);
252 Value value_to_tt(Value v, int ply);
253 Value value_from_tt(Value v, int ply);
254 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
255 bool connected_threat(const Position& pos, Move m, Move threat);
256 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
257 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
258 void update_gains(const Position& pos, Move move, Value before, Value after);
259 void do_skill_level(Move* best, Move* ponder);
261 int current_search_time(int set = 0);
262 std::string value_to_uci(Value v);
263 std::string speed_to_uci(int64_t nodes);
264 void poll(const Position& pos);
265 void wait_for_stop_or_ponderhit();
268 // MovePickerExt is an extended MovePicker class used to choose at compile time
269 // the proper move source according to the type of node.
270 template<bool SpNode, bool Root> struct MovePickerExt;
272 // In Root nodes use RootMoveList as source. Score and sort the root moves
273 // before to search them.
274 template<> struct MovePickerExt<false, true> : public MovePicker {
276 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
277 : MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
279 Value score = VALUE_ZERO;
281 // Score root moves using standard ordering used in main search, the moves
282 // are scored according to the order in which they are returned by MovePicker.
283 // This is the second order score that is used to compare the moves when
284 // the first orders pv_score of both moves are equal.
285 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
286 for (rm = Rml.begin(); rm != Rml.end(); ++rm)
287 if (rm->pv[0] == move)
289 rm->non_pv_score = score--;
297 Move get_next_move() {
304 return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
307 RootMoveList::iterator rm;
311 // In SpNodes use split point's shared MovePicker object as move source
312 template<> struct MovePickerExt<true, false> : public MovePicker {
314 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
315 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
317 Move get_next_move() { return mp->get_next_move(); }
319 RootMoveList::iterator rm; // Dummy, needed to compile
323 // Default case, create and use a MovePicker object as source
324 template<> struct MovePickerExt<false, false> : public MovePicker {
326 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
327 : MovePicker(p, ttm, d, h, ss, b) {}
329 RootMoveList::iterator rm; // Dummy, needed to compile
335 /// init_search() is called during startup to initialize various lookup tables
339 int d; // depth (ONE_PLY == 2)
340 int hd; // half depth (ONE_PLY == 1)
343 // Init reductions array
344 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
346 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
347 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
348 Reductions[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
349 Reductions[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
352 // Init futility margins array
353 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
354 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
356 // Init futility move count array
357 for (d = 0; d < 32; d++)
358 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
362 /// perft() is our utility to verify move generation. All the legal moves up to
363 /// given depth are generated and counted and the sum returned.
365 int64_t perft(Position& pos, Depth depth) {
367 MoveStack mlist[MAX_MOVES];
372 // Generate all legal moves
373 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
375 // If we are at the last ply we don't need to do and undo
376 // the moves, just to count them.
377 if (depth <= ONE_PLY)
378 return int(last - mlist);
380 // Loop through all legal moves
382 for (MoveStack* cur = mlist; cur != last; cur++)
385 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
386 sum += perft(pos, depth - ONE_PLY);
393 /// think() is the external interface to Stockfish's search, and is called when
394 /// the program receives the UCI 'go' command. It initializes various global
395 /// variables, and calls id_loop(). It returns false when a "quit" command is
396 /// received during the search.
398 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
400 // Initialize global search-related variables
401 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
403 current_search_time(get_system_time());
405 TimeMgr.init(Limits, pos.startpos_ply_counter());
407 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
409 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
410 else if (Limits.time && Limits.time < 1000)
411 NodesBetweenPolls = 1000;
412 else if (Limits.time && Limits.time < 5000)
413 NodesBetweenPolls = 5000;
415 NodesBetweenPolls = 30000;
417 // Look for a book move, only during games, not tests
418 if (Limits.useTimeManagement() && Options["OwnBook"].value<bool>())
420 if (Options["Book File"].value<std::string>() != OpeningBook.name())
421 OpeningBook.open(Options["Book File"].value<std::string>());
423 Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
424 if (bookMove != MOVE_NONE)
427 wait_for_stop_or_ponderhit();
429 cout << "bestmove " << bookMove << endl;
435 UCIMultiPV = Options["MultiPV"].value<int>();
436 SkillLevel = Options["Skill level"].value<int>();
438 read_evaluation_uci_options(pos.side_to_move());
439 ThreadsMgr.read_uci_options();
441 // If needed allocate pawn and material hash tables and adjust TT size
442 ThreadsMgr.init_hash_tables();
443 TT.set_size(Options["Hash"].value<int>());
445 if (Options["Clear Hash"].value<bool>())
447 Options["Clear Hash"].set_value("false");
451 // Do we have to play with skill handicap? In this case enable MultiPV that
452 // we will use behind the scenes to retrieve a set of possible moves.
453 SkillLevelEnabled = (SkillLevel < 20);
454 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
456 // Wake up needed threads and reset maxPly counter
457 for (int i = 0; i < ThreadsMgr.active_threads(); i++)
459 ThreadsMgr[i].wake_up();
460 ThreadsMgr[i].maxPly = 0;
463 // Write to log file and keep it open to be accessed during the search
464 if (Options["Use Search Log"].value<bool>())
466 std::string name = Options["Search Log Filename"].value<std::string>();
467 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
469 if (LogFile.is_open())
470 LogFile << "\nSearching: " << pos.to_fen()
471 << "\ninfinite: " << Limits.infinite
472 << " ponder: " << Limits.ponder
473 << " time: " << Limits.time
474 << " increment: " << Limits.increment
475 << " moves to go: " << Limits.movesToGo
479 // We're ready to start thinking. Call the iterative deepening loop function
480 Move ponderMove = MOVE_NONE;
481 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
483 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
485 // Write final search statistics and close log file
486 if (LogFile.is_open())
488 int t = current_search_time();
490 LogFile << "Nodes: " << pos.nodes_searched()
491 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
492 << "\nBest move: " << move_to_san(pos, bestMove);
495 pos.do_move(bestMove, st);
496 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
497 pos.undo_move(bestMove); // Return from think() with unchanged position
501 // This makes all the threads to go to sleep
502 ThreadsMgr.set_active_threads(1);
504 // If we are pondering or in infinite search, we shouldn't print the
505 // best move before we are told to do so.
506 if (!StopRequest && (Limits.ponder || Limits.infinite))
507 wait_for_stop_or_ponderhit();
509 // Could be MOVE_NONE when searching on a stalemate position
510 cout << "bestmove " << bestMove;
512 // UCI protol is not clear on allowing sending an empty ponder move, instead
513 // it is clear that ponder move is optional. So skip it if empty.
514 if (ponderMove != MOVE_NONE)
515 cout << " ponder " << ponderMove;
525 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
526 // with increasing depth until the allocated thinking time has been consumed,
527 // user stops the search, or the maximum search depth is reached.
529 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
531 SearchStack ss[PLY_MAX_PLUS_2];
532 Value bestValues[PLY_MAX_PLUS_2];
533 int bestMoveChanges[PLY_MAX_PLUS_2];
534 int depth, selDepth, aspirationDelta;
535 Value value, alpha, beta;
536 Move bestMove, easyMove, skillBest, skillPonder;
538 // Initialize stuff before a new search
539 memset(ss, 0, 4 * sizeof(SearchStack));
542 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
543 depth = aspirationDelta = 0;
544 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
545 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
547 // Moves to search are verified and copied
548 Rml.init(pos, searchMoves);
550 // Handle special case of searching on a mate/stalemate position
553 cout << "info depth 0 score "
554 << value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
560 // Iterative deepening loop until requested to stop or target depth reached
561 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
563 Rml.bestMoveChanges = 0;
564 cout << set960(pos.is_chess960()) << "info depth " << depth << endl;
566 // Calculate dynamic aspiration window based on previous iterations
567 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
569 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
570 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
572 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
573 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
575 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
576 beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
579 // Start with a small aspiration window and, in case of fail high/low,
580 // research with bigger window until not failing high/low anymore.
582 // Search starting from ss+1 to allow calling update_gains()
583 value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY);
585 // Write PV back to transposition table in case the relevant entries
586 // have been overwritten during the search.
587 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
588 Rml[i].insert_pv_in_tt(pos);
590 // Value cannot be trusted. Break out immediately!
594 assert(value >= alpha);
596 // In case of failing high/low increase aspiration window and research,
597 // otherwise exit the fail high/low loop.
600 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
601 aspirationDelta += aspirationDelta / 2;
603 else if (value <= alpha)
605 AspirationFailLow = true;
606 StopOnPonderhit = false;
608 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
609 aspirationDelta += aspirationDelta / 2;
614 } while (abs(value) < VALUE_KNOWN_WIN);
616 // Collect info about search result
617 bestMove = Rml[0].pv[0];
618 *ponderMove = Rml[0].pv[1];
619 bestValues[depth] = value;
620 bestMoveChanges[depth] = Rml.bestMoveChanges;
622 // Do we need to pick now the best and the ponder moves ?
623 if (SkillLevelEnabled && depth == 1 + SkillLevel)
624 do_skill_level(&skillBest, &skillPonder);
626 // Retrieve max searched depth among threads
628 for (int i = 0; i < ThreadsMgr.active_threads(); i++)
629 if (ThreadsMgr[i].maxPly > selDepth)
630 selDepth = ThreadsMgr[i].maxPly;
632 // Send PV line to GUI and to log file
633 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
634 cout << Rml[i].pv_info_to_uci(pos, depth, selDepth, alpha, beta, i) << endl;
636 if (LogFile.is_open())
637 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
639 // Init easyMove after first iteration or drop if differs from the best move
640 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
642 else if (bestMove != easyMove)
643 easyMove = MOVE_NONE;
645 // Check for some early stop condition
646 if (!StopRequest && Limits.useTimeManagement())
648 // Stop search early when the last two iterations returned a mate score
650 && abs(bestValues[depth]) >= VALUE_MATE_IN_PLY_MAX
651 && abs(bestValues[depth - 1]) >= VALUE_MATE_IN_PLY_MAX)
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 PvNode, bool SpNode, bool Root>
706 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
708 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
709 assert(beta > alpha && beta <= VALUE_INFINITE);
710 assert(PvNode || alpha == beta - 1);
711 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
713 Move movesSearched[MAX_MOVES];
718 Move ttMove, move, excludedMove, threatMove;
721 Value bestValue, value, oldAlpha;
722 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
723 bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous, isBadCap;
724 int moveCount = 0, playedMoveCount = 0;
725 int threadID = pos.thread();
726 SplitPoint* sp = NULL;
728 refinedValue = bestValue = value = -VALUE_INFINITE;
730 isCheck = pos.is_check();
731 ss->ply = (ss-1)->ply + 1;
733 // Used to send selDepth info to GUI
734 if (PvNode && ThreadsMgr[threadID].maxPly < ss->ply)
735 ThreadsMgr[threadID].maxPly = ss->ply;
741 ttMove = excludedMove = MOVE_NONE;
742 threatMove = sp->threatMove;
743 goto split_point_start;
748 // Step 1. Initialize node and poll. Polling can abort search
749 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
750 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
751 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
753 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
759 // Step 2. Check for aborted search and immediate draw
761 || ThreadsMgr.cutoff_at_splitpoint(threadID)
763 || ss->ply > PLY_MAX) && !Root)
766 // Step 3. Mate distance pruning
767 alpha = Max(value_mated_in(ss->ply), alpha);
768 beta = Min(value_mate_in(ss->ply+1), beta);
772 // Step 4. Transposition table lookup
773 // We don't want the score of a partial search to overwrite a previous full search
774 // TT value, so we use a different position key in case of an excluded move.
775 excludedMove = ss->excludedMove;
776 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
778 tte = TT.retrieve(posKey);
779 ttMove = tte ? tte->move() : MOVE_NONE;
781 // At PV nodes we check for exact scores, while at non-PV nodes we check for
782 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
783 // smooth experience in analysis mode.
786 && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
787 : ok_to_use_TT(tte, depth, beta, ss->ply)))
790 ss->bestMove = ttMove; // Can be MOVE_NONE
791 return value_from_tt(tte->value(), ss->ply);
794 // Step 5. Evaluate the position statically and update parent's gain statistics
796 ss->eval = ss->evalMargin = VALUE_NONE;
799 assert(tte->static_value() != VALUE_NONE);
801 ss->eval = tte->static_value();
802 ss->evalMargin = tte->static_value_margin();
803 refinedValue = refine_eval(tte, ss->eval, ss->ply);
807 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
808 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
811 // Save gain for the parent non-capture move
812 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
814 // Step 6. Razoring (is omitted in PV nodes)
816 && depth < RazorDepth
818 && refinedValue + razor_margin(depth) < beta
819 && ttMove == MOVE_NONE
820 && abs(beta) < VALUE_MATE_IN_PLY_MAX
821 && !pos.has_pawn_on_7th(pos.side_to_move()))
823 Value rbeta = beta - razor_margin(depth);
824 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
826 // Logically we should return (v + razor_margin(depth)), but
827 // surprisingly this did slightly weaker in tests.
831 // Step 7. Static null move pruning (is omitted in PV nodes)
832 // We're betting that the opponent doesn't have a move that will reduce
833 // the score by more than futility_margin(depth) if we do a null move.
836 && depth < RazorDepth
838 && refinedValue - futility_margin(depth, 0) >= beta
839 && abs(beta) < VALUE_MATE_IN_PLY_MAX
840 && pos.non_pawn_material(pos.side_to_move()))
841 return refinedValue - futility_margin(depth, 0);
843 // Step 8. Null move search with verification search (is omitted in PV nodes)
848 && refinedValue >= beta
849 && abs(beta) < VALUE_MATE_IN_PLY_MAX
850 && pos.non_pawn_material(pos.side_to_move()))
852 ss->currentMove = MOVE_NULL;
854 // Null move dynamic reduction based on depth
855 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
857 // Null move dynamic reduction based on value
858 if (refinedValue - PawnValueMidgame > beta)
861 pos.do_null_move(st);
862 (ss+1)->skipNullMove = true;
863 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
864 (ss+1)->skipNullMove = false;
865 pos.undo_null_move();
867 if (nullValue >= beta)
869 // Do not return unproven mate scores
870 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
873 if (depth < 6 * ONE_PLY)
876 // Do verification search at high depths
877 ss->skipNullMove = true;
878 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
879 ss->skipNullMove = false;
886 // The null move failed low, which means that we may be faced with
887 // some kind of threat. If the previous move was reduced, check if
888 // the move that refuted the null move was somehow connected to the
889 // move which was reduced. If a connection is found, return a fail
890 // low score (which will cause the reduced move to fail high in the
891 // parent node, which will trigger a re-search with full depth).
892 threatMove = (ss+1)->bestMove;
894 if ( depth < ThreatDepth
896 && threatMove != MOVE_NONE
897 && connected_moves(pos, (ss-1)->currentMove, threatMove))
902 // Step 9. Internal iterative deepening
903 if ( depth >= IIDDepth[PvNode]
904 && ttMove == MOVE_NONE
905 && (PvNode || (!isCheck && ss->eval + IIDMargin >= beta)))
907 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
909 ss->skipNullMove = true;
910 search<PvNode>(pos, ss, alpha, beta, d);
911 ss->skipNullMove = false;
913 ttMove = ss->bestMove;
914 tte = TT.retrieve(posKey);
917 split_point_start: // At split points actual search starts from here
919 // Initialize a MovePicker object for the current position
920 MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
922 ss->bestMove = MOVE_NONE;
923 futilityBase = ss->eval + ss->evalMargin;
924 singularExtensionNode = !Root
926 && depth >= SingularExtensionDepth[PvNode]
929 && !excludedMove // Do not allow recursive singular extension search
930 && (tte->type() & VALUE_TYPE_LOWER)
931 && tte->depth() >= depth - 3 * ONE_PLY;
934 lock_grab(&(sp->lock));
935 bestValue = sp->bestValue;
938 // Step 10. Loop through moves
939 // Loop through all legal moves until no moves remain or a beta cutoff occurs
940 while ( bestValue < beta
941 && (move = mp.get_next_move()) != MOVE_NONE
942 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
944 assert(move_is_ok(move));
948 moveCount = ++sp->moveCount;
949 lock_release(&(sp->lock));
951 else if (move == excludedMove)
958 // This is used by time management
959 FirstRootMove = (moveCount == 1);
961 // Save the current node count before the move is searched
962 nodes = pos.nodes_searched();
964 // If it's time to send nodes info, do it here where we have the
965 // correct accumulated node counts searched by each thread.
966 if (SendSearchedNodes)
968 SendSearchedNodes = false;
969 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
972 if (current_search_time() > 2000)
973 cout << "info currmove " << move
974 << " currmovenumber " << moveCount << endl;
977 // At Root and at first iteration do a PV search on all the moves to score root moves
978 isPvMove = (PvNode && moveCount <= (Root ? depth <= ONE_PLY ? 1000 : MultiPV : 1));
979 moveIsCheck = pos.move_is_check(move, ci);
980 captureOrPromotion = pos.move_is_capture_or_promotion(move);
982 // Step 11. Decide the new search depth
983 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, &dangerous);
985 // Singular extension search. If all moves but one fail low on a search of
986 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
987 // is singular and should be extended. To verify this we do a reduced search
988 // on all the other moves but the ttMove, if result is lower than ttValue minus
989 // a margin then we extend ttMove.
990 if ( singularExtensionNode
991 && move == tte->move()
994 Value ttValue = value_from_tt(tte->value(), ss->ply);
996 if (abs(ttValue) < VALUE_KNOWN_WIN)
998 Value rBeta = ttValue - int(depth);
999 ss->excludedMove = move;
1000 ss->skipNullMove = true;
1001 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1002 ss->skipNullMove = false;
1003 ss->excludedMove = MOVE_NONE;
1004 ss->bestMove = MOVE_NONE;
1010 // Update current move (this must be done after singular extension search)
1011 ss->currentMove = move;
1012 newDepth = depth - ONE_PLY + ext;
1014 // Step 12. Futility pruning (is omitted in PV nodes)
1016 && !captureOrPromotion
1020 && !move_is_castle(move))
1022 // Move count based pruning
1023 if ( moveCount >= futility_move_count(depth)
1024 && (!threatMove || !connected_threat(pos, move, threatMove))
1025 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1028 lock_grab(&(sp->lock));
1033 // Value based pruning
1034 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1035 // but fixing this made program slightly weaker.
1036 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1037 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1038 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1040 if (futilityValueScaled < beta)
1044 lock_grab(&(sp->lock));
1045 if (futilityValueScaled > sp->bestValue)
1046 sp->bestValue = bestValue = futilityValueScaled;
1048 else if (futilityValueScaled > bestValue)
1049 bestValue = futilityValueScaled;
1054 // Prune moves with negative SEE at low depths
1055 if ( predictedDepth < 2 * ONE_PLY
1056 && bestValue > VALUE_MATED_IN_PLY_MAX
1057 && pos.see_sign(move) < 0)
1060 lock_grab(&(sp->lock));
1066 // Bad capture detection. Will be used by prob-cut search
1067 isBadCap = depth >= 3 * ONE_PLY
1068 && depth < 8 * ONE_PLY
1069 && captureOrPromotion
1072 && !move_is_promotion(move)
1073 && abs(alpha) < VALUE_MATE_IN_PLY_MAX
1074 && pos.see_sign(move) < 0;
1076 // Step 13. Make the move
1077 pos.do_move(move, st, ci, moveIsCheck);
1079 if (!SpNode && !captureOrPromotion)
1080 movesSearched[playedMoveCount++] = move;
1082 // Step extra. pv search (only in PV nodes)
1083 // The first move in list is the expected PV
1086 // Aspiration window is disabled in multi-pv case
1087 if (Root && MultiPV > 1)
1088 alpha = -VALUE_INFINITE;
1090 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1094 // Step 14. Reduced depth search
1095 // If the move fails high will be re-searched at full depth.
1096 bool doFullDepthSearch = true;
1097 alpha = SpNode ? sp->alpha : alpha;
1099 if ( depth >= 3 * ONE_PLY
1100 && !captureOrPromotion
1102 && !move_is_castle(move)
1103 && ss->killers[0] != move
1104 && ss->killers[1] != move)
1106 ss->reduction = reduction<PvNode>(depth, moveCount);
1109 alpha = SpNode ? sp->alpha : alpha;
1110 Depth d = newDepth - ss->reduction;
1111 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1113 doFullDepthSearch = (value > alpha);
1115 ss->reduction = DEPTH_ZERO; // Restore original reduction
1118 // Probcut search for bad captures. If a reduced search returns a value
1119 // very below beta then we can (almost) safely prune the bad capture.
1122 ss->reduction = 3 * ONE_PLY;
1123 Value rAlpha = alpha - 300;
1124 Depth d = newDepth - ss->reduction;
1125 value = -search<NonPV>(pos, ss+1, -(rAlpha+1), -rAlpha, d);
1126 doFullDepthSearch = (value > rAlpha);
1127 ss->reduction = DEPTH_ZERO; // Restore original reduction
1130 // Step 15. Full depth search
1131 if (doFullDepthSearch)
1133 alpha = SpNode ? sp->alpha : alpha;
1134 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1136 // Step extra. pv search (only in PV nodes)
1137 // Search only for possible new PV nodes, if instead value >= beta then
1138 // parent node fails low with value <= alpha and tries another move.
1139 if (PvNode && value > alpha && (Root || value < beta))
1140 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1144 // Step 16. Undo move
1145 pos.undo_move(move);
1147 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1149 // Step 17. Check for new best move
1152 lock_grab(&(sp->lock));
1153 bestValue = sp->bestValue;
1157 if (value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
1162 sp->bestValue = value;
1164 if (!Root && value > alpha)
1166 if (PvNode && value < beta) // We want always alpha < beta
1174 sp->betaCutoff = true;
1176 if (value == value_mate_in(ss->ply + 1))
1177 ss->mateKiller = move;
1179 ss->bestMove = move;
1182 sp->ss->bestMove = move;
1188 // Finished searching the move. If StopRequest is true, the search
1189 // was aborted because the user interrupted the search or because we
1190 // ran out of time. In this case, the return value of the search cannot
1191 // be trusted, and we break out of the loop without updating the best
1196 // Remember searched nodes counts for this move
1197 mp.rm->nodes += pos.nodes_searched() - nodes;
1199 // PV move or new best move ?
1200 if (isPvMove || value > alpha)
1203 ss->bestMove = move;
1204 mp.rm->pv_score = value;
1205 mp.rm->extract_pv_from_tt(pos);
1207 // We record how often the best move has been changed in each
1208 // iteration. This information is used for time management: When
1209 // the best move changes frequently, we allocate some more time.
1210 if (!isPvMove && MultiPV == 1)
1211 Rml.bestMoveChanges++;
1213 Rml.sort_multipv(moveCount);
1215 // Update alpha. In multi-pv we don't use aspiration window, so
1216 // set alpha equal to minimum score among the PV lines.
1218 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
1219 else if (value > alpha)
1223 mp.rm->pv_score = -VALUE_INFINITE;
1227 // Step 18. Check for split
1230 && depth >= ThreadsMgr.min_split_depth()
1231 && ThreadsMgr.active_threads() > 1
1233 && ThreadsMgr.available_thread_exists(threadID)
1235 && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1236 ThreadsMgr.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1237 threatMove, moveCount, &mp, PvNode);
1240 // Step 19. Check for mate and stalemate
1241 // All legal moves have been searched and if there are
1242 // no legal moves, it must be mate or stalemate.
1243 // If one move was excluded return fail low score.
1244 if (!SpNode && !moveCount)
1245 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1247 // Step 20. Update tables
1248 // If the search is not aborted, update the transposition table,
1249 // history counters, and killer moves.
1250 if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
1252 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1253 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1254 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1256 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1258 // Update killers and history only for non capture moves that fails high
1259 if ( bestValue >= beta
1260 && !pos.move_is_capture_or_promotion(move))
1262 if (move != ss->killers[0])
1264 ss->killers[1] = ss->killers[0];
1265 ss->killers[0] = move;
1267 update_history(pos, move, depth, movesSearched, playedMoveCount);
1273 // Here we have the lock still grabbed
1274 sp->slaves[threadID] = 0;
1275 sp->nodes += pos.nodes_searched();
1276 lock_release(&(sp->lock));
1279 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1284 // qsearch() is the quiescence search function, which is called by the main
1285 // search function when the remaining depth is zero (or, to be more precise,
1286 // less than ONE_PLY).
1288 template <NodeType PvNode>
1289 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1291 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1292 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1293 assert(PvNode || alpha == beta - 1);
1295 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1299 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1300 bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
1303 Value oldAlpha = alpha;
1305 ss->bestMove = ss->currentMove = MOVE_NONE;
1306 ss->ply = (ss-1)->ply + 1;
1308 // Check for an instant draw or maximum ply reached
1309 if (ss->ply > PLY_MAX || pos.is_draw())
1312 // Decide whether or not to include checks, this fixes also the type of
1313 // TT entry depth that we are going to use. Note that in qsearch we use
1314 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1315 isCheck = pos.is_check();
1316 ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1318 // Transposition table lookup. At PV nodes, we don't use the TT for
1319 // pruning, but only for move ordering.
1320 tte = TT.retrieve(pos.get_key());
1321 ttMove = (tte ? tte->move() : MOVE_NONE);
1323 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1325 ss->bestMove = ttMove; // Can be MOVE_NONE
1326 return value_from_tt(tte->value(), ss->ply);
1329 // Evaluate the position statically
1332 bestValue = futilityBase = -VALUE_INFINITE;
1333 ss->eval = evalMargin = VALUE_NONE;
1334 enoughMaterial = false;
1340 assert(tte->static_value() != VALUE_NONE);
1342 evalMargin = tte->static_value_margin();
1343 ss->eval = bestValue = tte->static_value();
1346 ss->eval = bestValue = evaluate(pos, evalMargin);
1348 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1350 // Stand pat. Return immediately if static value is at least beta
1351 if (bestValue >= beta)
1354 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1359 if (PvNode && bestValue > alpha)
1362 // Futility pruning parameters, not needed when in check
1363 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1364 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1367 // Initialize a MovePicker object for the current position, and prepare
1368 // to search the moves. Because the depth is <= 0 here, only captures,
1369 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1371 MovePicker mp(pos, ttMove, depth, H);
1374 // Loop through the moves until no moves remain or a beta cutoff occurs
1375 while ( alpha < beta
1376 && (move = mp.get_next_move()) != MOVE_NONE)
1378 assert(move_is_ok(move));
1380 moveIsCheck = pos.move_is_check(move, ci);
1388 && !move_is_promotion(move)
1389 && !pos.move_is_passed_pawn_push(move))
1391 futilityValue = futilityBase
1392 + pos.endgame_value_of_piece_on(move_to(move))
1393 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1395 if (futilityValue < alpha)
1397 if (futilityValue > bestValue)
1398 bestValue = futilityValue;
1402 // Prune moves with negative or equal SEE
1403 if ( futilityBase < beta
1404 && depth < DEPTH_ZERO
1405 && pos.see(move) <= 0)
1409 // Detect non-capture evasions that are candidate to be pruned
1410 evasionPrunable = isCheck
1411 && bestValue > VALUE_MATED_IN_PLY_MAX
1412 && !pos.move_is_capture(move)
1413 && !pos.can_castle(pos.side_to_move());
1415 // Don't search moves with negative SEE values
1417 && (!isCheck || evasionPrunable)
1419 && !move_is_promotion(move)
1420 && pos.see_sign(move) < 0)
1423 // Don't search useless checks
1428 && !pos.move_is_capture_or_promotion(move)
1429 && ss->eval + PawnValueMidgame / 4 < beta
1430 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1432 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1433 bestValue = ss->eval + PawnValueMidgame / 4;
1438 // Update current move
1439 ss->currentMove = move;
1441 // Make and search the move
1442 pos.do_move(move, st, ci, moveIsCheck);
1443 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1444 pos.undo_move(move);
1446 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1449 if (value > bestValue)
1455 ss->bestMove = move;
1460 // All legal moves have been searched. A special case: If we're in check
1461 // and no legal moves were found, it is checkmate.
1462 if (isCheck && bestValue == -VALUE_INFINITE)
1463 return value_mated_in(ss->ply);
1465 // Update transposition table
1466 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1467 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1469 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1475 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1476 // bestValue is updated only when returning false because in that case move
1479 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1481 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1482 Square from, to, ksq, victimSq;
1485 Value futilityValue, bv = *bestValue;
1487 from = move_from(move);
1489 them = opposite_color(pos.side_to_move());
1490 ksq = pos.king_square(them);
1491 kingAtt = pos.attacks_from<KING>(ksq);
1492 pc = pos.piece_on(from);
1494 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1495 oldAtt = pos.attacks_from(pc, from, occ);
1496 newAtt = pos.attacks_from(pc, to, occ);
1498 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1499 b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
1501 if (!(b && (b & (b - 1))))
1504 // Rule 2. Queen contact check is very dangerous
1505 if ( type_of_piece(pc) == QUEEN
1506 && bit_is_set(kingAtt, to))
1509 // Rule 3. Creating new double threats with checks
1510 b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1514 victimSq = pop_1st_bit(&b);
1515 futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
1517 // Note that here we generate illegal "double move"!
1518 if ( futilityValue >= beta
1519 && pos.see_sign(make_move(from, victimSq)) >= 0)
1522 if (futilityValue > bv)
1526 // Update bestValue only if check is not dangerous (because we will prune the move)
1532 // connected_moves() tests whether two moves are 'connected' in the sense
1533 // that the first move somehow made the second move possible (for instance
1534 // if the moving piece is the same in both moves). The first move is assumed
1535 // to be the move that was made to reach the current position, while the
1536 // second move is assumed to be a move from the current position.
1538 bool connected_moves(const Position& pos, Move m1, Move m2) {
1540 Square f1, t1, f2, t2;
1543 assert(m1 && move_is_ok(m1));
1544 assert(m2 && move_is_ok(m2));
1546 // Case 1: The moving piece is the same in both moves
1552 // Case 2: The destination square for m2 was vacated by m1
1558 // Case 3: Moving through the vacated square
1559 if ( piece_is_slider(pos.piece_on(f2))
1560 && bit_is_set(squares_between(f2, t2), f1))
1563 // Case 4: The destination square for m2 is defended by the moving piece in m1
1564 p = pos.piece_on(t1);
1565 if (bit_is_set(pos.attacks_from(p, t1), t2))
1568 // Case 5: Discovered check, checking piece is the piece moved in m1
1569 if ( piece_is_slider(p)
1570 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1571 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1573 // discovered_check_candidates() works also if the Position's side to
1574 // move is the opposite of the checking piece.
1575 Color them = opposite_color(pos.side_to_move());
1576 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1578 if (bit_is_set(dcCandidates, f2))
1585 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1586 // "plies to mate from the current ply". Non-mate scores are unchanged.
1587 // The function is called before storing a value to the transposition table.
1589 Value value_to_tt(Value v, int ply) {
1591 if (v >= VALUE_MATE_IN_PLY_MAX)
1594 if (v <= VALUE_MATED_IN_PLY_MAX)
1601 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1602 // the transposition table to a mate score corrected for the current ply.
1604 Value value_from_tt(Value v, int ply) {
1606 if (v >= VALUE_MATE_IN_PLY_MAX)
1609 if (v <= VALUE_MATED_IN_PLY_MAX)
1616 // extension() decides whether a move should be searched with normal depth,
1617 // or with extended depth. Certain classes of moves (checking moves, in
1618 // particular) are searched with bigger depth than ordinary moves and in
1619 // any case are marked as 'dangerous'. Note that also if a move is not
1620 // extended, as example because the corresponding UCI option is set to zero,
1621 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1622 template <NodeType PvNode>
1623 Depth extension(const Position& pos, Move m, bool captureOrPromotion,
1624 bool moveIsCheck, bool* dangerous) {
1626 assert(m != MOVE_NONE);
1628 Depth result = DEPTH_ZERO;
1629 *dangerous = moveIsCheck;
1631 if (moveIsCheck && pos.see_sign(m) >= 0)
1632 result += CheckExtension[PvNode];
1634 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1636 Color c = pos.side_to_move();
1637 if (relative_rank(c, move_to(m)) == RANK_7)
1639 result += PawnPushTo7thExtension[PvNode];
1642 if (pos.pawn_is_passed(c, move_to(m)))
1644 result += PassedPawnExtension[PvNode];
1649 if ( captureOrPromotion
1650 && pos.type_of_piece_on(move_to(m)) != PAWN
1651 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1652 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1653 && !move_is_special(m))
1655 result += PawnEndgameExtension[PvNode];
1659 return Min(result, ONE_PLY);
1663 // connected_threat() tests whether it is safe to forward prune a move or if
1664 // is somehow connected to the threat move returned by null search.
1666 bool connected_threat(const Position& pos, Move m, Move threat) {
1668 assert(move_is_ok(m));
1669 assert(threat && move_is_ok(threat));
1670 assert(!pos.move_is_check(m));
1671 assert(!pos.move_is_capture_or_promotion(m));
1672 assert(!pos.move_is_passed_pawn_push(m));
1674 Square mfrom, mto, tfrom, tto;
1676 mfrom = move_from(m);
1678 tfrom = move_from(threat);
1679 tto = move_to(threat);
1681 // Case 1: Don't prune moves which move the threatened piece
1685 // Case 2: If the threatened piece has value less than or equal to the
1686 // value of the threatening piece, don't prune moves which defend it.
1687 if ( pos.move_is_capture(threat)
1688 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1689 || pos.type_of_piece_on(tfrom) == KING)
1690 && pos.move_attacks_square(m, tto))
1693 // Case 3: If the moving piece in the threatened move is a slider, don't
1694 // prune safe moves which block its ray.
1695 if ( piece_is_slider(pos.piece_on(tfrom))
1696 && bit_is_set(squares_between(tfrom, tto), mto)
1697 && pos.see_sign(m) >= 0)
1704 // ok_to_use_TT() returns true if a transposition table score
1705 // can be used at a given point in search.
1707 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1709 Value v = value_from_tt(tte->value(), ply);
1711 return ( tte->depth() >= depth
1712 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1713 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1715 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1716 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1720 // refine_eval() returns the transposition table score if
1721 // possible otherwise falls back on static position evaluation.
1723 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1727 Value v = value_from_tt(tte->value(), ply);
1729 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1730 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1737 // update_history() registers a good move that produced a beta-cutoff
1738 // in history and marks as failures all the other moves of that ply.
1740 void update_history(const Position& pos, Move move, Depth depth,
1741 Move movesSearched[], int moveCount) {
1743 Value bonus = Value(int(depth) * int(depth));
1745 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1747 for (int i = 0; i < moveCount - 1; i++)
1749 m = movesSearched[i];
1753 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1758 // update_gains() updates the gains table of a non-capture move given
1759 // the static position evaluation before and after the move.
1761 void update_gains(const Position& pos, Move m, Value before, Value after) {
1764 && before != VALUE_NONE
1765 && after != VALUE_NONE
1766 && pos.captured_piece_type() == PIECE_TYPE_NONE
1767 && !move_is_special(m))
1768 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1772 // current_search_time() returns the number of milliseconds which have passed
1773 // since the beginning of the current search.
1775 int current_search_time(int set) {
1777 static int searchStartTime;
1780 searchStartTime = set;
1782 return get_system_time() - searchStartTime;
1786 // value_to_uci() converts a value to a string suitable for use with the UCI
1787 // protocol specifications:
1789 // cp <x> The score from the engine's point of view in centipawns.
1790 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1791 // use negative values for y.
1793 std::string value_to_uci(Value v) {
1795 std::stringstream s;
1797 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1798 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1800 s << "mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1806 // speed_to_uci() returns a string with time stats of current search suitable
1807 // to be sent to UCI gui.
1809 std::string speed_to_uci(int64_t nodes) {
1811 std::stringstream s;
1812 int t = current_search_time();
1814 s << " nodes " << nodes
1815 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1822 // poll() performs two different functions: It polls for user input, and it
1823 // looks at the time consumed so far and decides if it's time to abort the
1826 void poll(const Position& pos) {
1828 static int lastInfoTime;
1829 int t = current_search_time();
1832 if (input_available())
1834 // We are line oriented, don't read single chars
1835 std::string command;
1837 if (!std::getline(std::cin, command) || command == "quit")
1839 // Quit the program as soon as possible
1840 Limits.ponder = false;
1841 QuitRequest = StopRequest = true;
1844 else if (command == "stop")
1846 // Stop calculating as soon as possible, but still send the "bestmove"
1847 // and possibly the "ponder" token when finishing the search.
1848 Limits.ponder = false;
1851 else if (command == "ponderhit")
1853 // The opponent has played the expected move. GUI sends "ponderhit" if
1854 // we were told to ponder on the same move the opponent has played. We
1855 // should continue searching but switching from pondering to normal search.
1856 Limits.ponder = false;
1858 if (StopOnPonderhit)
1863 // Print search information
1867 else if (lastInfoTime > t)
1868 // HACK: Must be a new search where we searched less than
1869 // NodesBetweenPolls nodes during the first second of search.
1872 else if (t - lastInfoTime >= 1000)
1877 dbg_print_hit_rate();
1879 // Send info on searched nodes as soon as we return to root
1880 SendSearchedNodes = true;
1883 // Should we stop the search?
1887 bool stillAtFirstMove = FirstRootMove
1888 && !AspirationFailLow
1889 && t > TimeMgr.available_time();
1891 bool noMoreTime = t > TimeMgr.maximum_time()
1892 || stillAtFirstMove;
1894 if ( (Limits.useTimeManagement() && noMoreTime)
1895 || (Limits.maxTime && t >= Limits.maxTime)
1896 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1901 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1902 // while the program is pondering. The point is to work around a wrinkle in
1903 // the UCI protocol: When pondering, the engine is not allowed to give a
1904 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1905 // We simply wait here until one of these commands is sent, and return,
1906 // after which the bestmove and pondermove will be printed.
1908 void wait_for_stop_or_ponderhit() {
1910 std::string command;
1912 // Wait for a command from stdin
1913 while ( std::getline(std::cin, command)
1914 && command != "ponderhit" && command != "stop" && command != "quit") {};
1916 if (command != "ponderhit" && command != "stop")
1917 QuitRequest = true; // Must be "quit" or getline() returned false
1921 // When playing with strength handicap choose best move among the MultiPV set
1922 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1923 void do_skill_level(Move* best, Move* ponder) {
1925 assert(MultiPV > 1);
1927 // Rml list is already sorted by pv_score in descending order
1929 int max_s = -VALUE_INFINITE;
1930 int size = Min(MultiPV, (int)Rml.size());
1931 int max = Rml[0].pv_score;
1932 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
1933 int wk = 120 - 2 * SkillLevel;
1935 // PRNG sequence should be non deterministic
1936 for (int i = abs(get_system_time() % 50); i > 0; i--)
1937 RK.rand<unsigned>();
1939 // Choose best move. For each move's score we add two terms both dependent
1940 // on wk, one deterministic and bigger for weaker moves, and one random,
1941 // then we choose the move with the resulting highest score.
1942 for (int i = 0; i < size; i++)
1944 s = Rml[i].pv_score;
1946 // Don't allow crazy blunders even at very low skills
1947 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
1950 // This is our magical formula
1951 s += ((max - s) * wk + var * (RK.rand<unsigned>() % wk)) / 128;
1956 *best = Rml[i].pv[0];
1957 *ponder = Rml[i].pv[1];
1963 /// RootMove and RootMoveList method's definitions
1965 RootMove::RootMove() {
1968 pv_score = non_pv_score = -VALUE_INFINITE;
1972 RootMove& RootMove::operator=(const RootMove& rm) {
1974 const Move* src = rm.pv;
1977 // Avoid a costly full rm.pv[] copy
1978 do *dst++ = *src; while (*src++ != MOVE_NONE);
1981 pv_score = rm.pv_score;
1982 non_pv_score = rm.non_pv_score;
1986 void RootMoveList::init(Position& pos, Move searchMoves[]) {
1988 MoveStack mlist[MAX_MOVES];
1992 bestMoveChanges = 0;
1994 // Generate all legal moves and add them to RootMoveList
1995 MoveStack* last = generate<MV_LEGAL>(pos, mlist);
1996 for (MoveStack* cur = mlist; cur != last; cur++)
1998 // If we have a searchMoves[] list then verify cur->move
1999 // is in the list before to add it.
2000 for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
2002 if (searchMoves[0] && *sm != cur->move)
2006 rm.pv[0] = cur->move;
2007 rm.pv[1] = MOVE_NONE;
2008 rm.pv_score = -VALUE_INFINITE;
2013 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2014 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2015 // allow to always have a ponder move even when we fail high at root and also a
2016 // long PV to print that is important for position analysis.
2018 void RootMove::extract_pv_from_tt(Position& pos) {
2020 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2024 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2026 pos.do_move(pv[0], *st++);
2028 while ( (tte = TT.retrieve(pos.get_key())) != NULL
2029 && tte->move() != MOVE_NONE
2030 && pos.move_is_legal(tte->move())
2032 && (!pos.is_draw() || ply < 2))
2034 pv[ply] = tte->move();
2035 pos.do_move(pv[ply++], *st++);
2037 pv[ply] = MOVE_NONE;
2039 do pos.undo_move(pv[--ply]); while (ply);
2042 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2043 // the PV back into the TT. This makes sure the old PV moves are searched
2044 // first, even if the old TT entries have been overwritten.
2046 void RootMove::insert_pv_in_tt(Position& pos) {
2048 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2051 Value v, m = VALUE_NONE;
2054 assert(pv[0] != MOVE_NONE && pos.move_is_legal(pv[0]));
2058 tte = TT.retrieve(k);
2060 // Don't overwrite existing correct entries
2061 if (!tte || tte->move() != pv[ply])
2063 v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
2064 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2066 pos.do_move(pv[ply], *st++);
2068 } while (pv[++ply] != MOVE_NONE);
2070 do pos.undo_move(pv[--ply]); while (ply);
2073 // pv_info_to_uci() returns a string with information on the current PV line
2074 // formatted according to UCI specification.
2076 std::string RootMove::pv_info_to_uci(Position& pos, int depth, int selDepth, Value alpha,
2077 Value beta, int pvIdx) {
2078 std::stringstream s;
2080 s << "info depth " << depth
2081 << " seldepth " << selDepth
2082 << " multipv " << pvIdx + 1
2083 << " score " << value_to_uci(pv_score)
2084 << (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
2085 << speed_to_uci(pos.nodes_searched())
2088 for (Move* m = pv; *m != MOVE_NONE; m++)
2097 // ThreadsManager::idle_loop() is where the threads are parked when they have no work
2098 // to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2099 // object for which the current thread is the master.
2101 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2103 assert(threadID >= 0 && threadID < MAX_THREADS);
2110 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2111 // master should exit as last one.
2112 if (allThreadsShouldExit)
2115 threads[threadID].state = THREAD_TERMINATED;
2119 // If we are not thinking, wait for a condition to be signaled
2120 // instead of wasting CPU time polling for work.
2121 while ( threadID >= activeThreads
2122 || threads[threadID].state == THREAD_INITIALIZING
2123 || (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
2125 assert(!sp || useSleepingThreads);
2126 assert(threadID != 0 || useSleepingThreads);
2128 if (threads[threadID].state == THREAD_INITIALIZING)
2129 threads[threadID].state = THREAD_AVAILABLE;
2131 // Grab the lock to avoid races with Thread::wake_up()
2132 lock_grab(&threads[threadID].sleepLock);
2134 // If we are master and all slaves have finished do not go to sleep
2135 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2136 allFinished = (i == activeThreads);
2138 if (allFinished || allThreadsShouldExit)
2140 lock_release(&threads[threadID].sleepLock);
2144 // Do sleep here after retesting sleep conditions
2145 if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
2146 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2148 lock_release(&threads[threadID].sleepLock);
2151 // If this thread has been assigned work, launch a search
2152 if (threads[threadID].state == THREAD_WORKISWAITING)
2154 assert(!allThreadsShouldExit);
2156 threads[threadID].state = THREAD_SEARCHING;
2158 // Copy split point position and search stack and call search()
2159 // with SplitPoint template parameter set to true.
2160 SearchStack ss[PLY_MAX_PLUS_2];
2161 SplitPoint* tsp = threads[threadID].splitPoint;
2162 Position pos(*tsp->pos, threadID);
2164 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2168 search<PV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2170 search<NonPV, true, false>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2172 assert(threads[threadID].state == THREAD_SEARCHING);
2174 threads[threadID].state = THREAD_AVAILABLE;
2176 // Wake up master thread so to allow it to return from the idle loop in
2177 // case we are the last slave of the split point.
2178 if ( useSleepingThreads
2179 && threadID != tsp->master
2180 && threads[tsp->master].state == THREAD_AVAILABLE)
2181 threads[tsp->master].wake_up();
2184 // If this thread is the master of a split point and all slaves have
2185 // finished their work at this split point, return from the idle loop.
2186 for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
2187 allFinished = (i == activeThreads);
2191 // Because sp->slaves[] is reset under lock protection,
2192 // be sure sp->lock has been released before to return.
2193 lock_grab(&(sp->lock));
2194 lock_release(&(sp->lock));
2196 // In helpful master concept a master can help only a sub-tree, and
2197 // because here is all finished is not possible master is booked.
2198 assert(threads[threadID].state == THREAD_AVAILABLE);
2200 threads[threadID].state = THREAD_SEARCHING;