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 two scores, 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, while non_pv_score is computed
58 // according to the order in which moves are returned by MovePicker.
62 RootMove(const RootMove& rm) { *this = rm; }
63 RootMove& operator=(const RootMove& rm);
65 // RootMove::operator<() is the comparison function used when
66 // sorting the moves. A move m1 is considered to be better
67 // than a move m2 if it has an higher pv_score, or if it has
68 // equal pv_score but m1 has the higher non_pv_score. In this way
69 // we are guaranteed that PV moves are always sorted as first.
70 bool operator<(const RootMove& m) const {
71 return pv_score != m.pv_score ? pv_score < m.pv_score
72 : non_pv_score < m.non_pv_score;
75 void extract_pv_from_tt(Position& pos);
76 void insert_pv_in_tt(Position& pos);
81 Move pv[PLY_MAX_PLUS_2];
84 // RootMoveList struct is mainly a std::vector of RootMove objects
85 struct RootMoveList : public std::vector<RootMove> {
86 void init(Position& pos, Move searchMoves[]);
93 // Lookup table to check if a Piece is a slider and its access function
94 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
95 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
99 // Maximum depth for razoring
100 const Depth RazorDepth = 4 * ONE_PLY;
102 // Dynamic razoring margin based on depth
103 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
105 // Maximum depth for use of dynamic threat detection when null move fails low
106 const Depth ThreatDepth = 5 * ONE_PLY;
108 // Step 9. Internal iterative deepening
110 // Minimum depth for use of internal iterative deepening
111 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
113 // At Non-PV nodes we do an internal iterative deepening search
114 // when the static evaluation is bigger then beta - IIDMargin.
115 const Value IIDMargin = Value(0x100);
117 // Step 11. Decide the new search depth
119 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
120 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
121 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
122 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
123 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
125 // Minimum depth for use of singular extension
126 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
128 // Step 12. Futility pruning
130 // Futility margin for quiescence search
131 const Value FutilityMarginQS = Value(0x80);
133 // Futility lookup tables (initialized at startup) and their access functions
134 Value FutilityMargins[16][64]; // [depth][moveNumber]
135 int FutilityMoveCounts[32]; // [depth]
137 inline Value futility_margin(Depth d, int mn) {
139 return d < 7 * ONE_PLY ? FutilityMargins[Max(d, 1)][Min(mn, 63)]
140 : 2 * VALUE_INFINITE;
143 inline int futility_move_count(Depth d) {
145 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
148 // Step 14. Reduced search
150 // Reduction lookup tables (initialized at startup) and their access function
151 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
153 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
155 return (Depth) Reductions[PvNode][Min(d / ONE_PLY, 63)][Min(mn, 63)];
158 // Easy move margin. An easy move candidate must be at least this much
159 // better than the second best move.
160 const Value EasyMoveMargin = Value(0x200);
163 /// Namespace variables
169 int MultiPV, UCIMultiPV;
171 // Time management variables
172 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
177 std::ofstream LogFile;
179 // Skill level adjustment
181 bool SkillLevelEnabled;
183 // Node counters, used only by thread[0] but try to keep in different cache
184 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
185 bool SendSearchedNodes;
187 int NodesBetweenPolls = 30000;
195 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
197 template <NodeType NT>
198 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
200 template <NodeType NT>
201 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
203 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
204 bool connected_moves(const Position& pos, Move m1, Move m2);
205 Value value_to_tt(Value v, int ply);
206 Value value_from_tt(Value v, int ply);
207 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
208 bool connected_threat(const Position& pos, Move m, Move threat);
209 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
210 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
211 void update_gains(const Position& pos, Move move, Value before, Value after);
212 void do_skill_level(Move* best, Move* ponder);
214 int current_search_time(int set = 0);
215 string score_to_uci(Value v, Value alpha, Value beta);
216 string speed_to_uci(int64_t nodes);
217 string pv_to_uci(Move pv[], int pvNum, bool chess960);
218 string pretty_pv(Position& pos, int depth, Value score, int time, Move pv[]);
219 string depth_to_uci(Depth depth);
220 void poll(const Position& pos);
221 void wait_for_stop_or_ponderhit();
223 // MovePickerExt template class extends MovePicker and allows to choose at compile
224 // time the proper moves source according to the type of node. In the default case
225 // we simply create and use a standard MovePicker object.
226 template<NodeType> struct MovePickerExt : public MovePicker {
228 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
229 : MovePicker(p, ttm, d, h, ss, b) {}
231 RootMove& current() { assert(false); return Rml[0]; } // Dummy, needed to compile
234 // In case of a SpNode we use split point's shared MovePicker object as moves source
235 template<> struct MovePickerExt<SplitPointNonPV> : public MovePickerExt<NonPV> {
237 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
238 : MovePickerExt<NonPV>(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
240 Move get_next_move() { return mp->get_next_move(); }
244 template<> struct MovePickerExt<SplitPointPV> : public MovePickerExt<SplitPointNonPV> {
246 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
247 : MovePickerExt<SplitPointNonPV>(p, ttm, d, h, ss, b) {}
250 // In case of a Root node we use RootMoveList as moves source
251 template<> struct MovePickerExt<Root> : public MovePicker {
253 MovePickerExt(const Position&, Move, Depth, const History&, SearchStack*, Value);
254 RootMove& current() { return Rml[cur]; }
255 Move get_next_move() { return ++cur < (int)Rml.size() ? Rml[cur].pv[0] : MOVE_NONE; }
260 // Overload operator<<() to make it easier to print moves in a coordinate
261 // notation compatible with UCI protocol.
262 std::ostream& operator<<(std::ostream& os, Move m) {
264 bool chess960 = (os.iword(0) != 0); // See set960()
265 return os << move_to_uci(m, chess960);
268 // When formatting a move for std::cout we must know if we are in Chess960
269 // or not. To keep using the handy operator<<() on the move the trick is to
270 // embed this flag in the stream itself. Function-like named enum set960 is
271 // used as a custom manipulator and the stream internal general-purpose array,
272 // accessed through ios_base::iword(), is used to pass the flag to the move's
273 // operator<<() that will read it to properly format castling moves.
276 std::ostream& operator<< (std::ostream& os, const set960& f) {
278 os.iword(0) = int(f);
282 // extension() decides whether a move should be searched with normal depth,
283 // or with extended depth. Certain classes of moves (checking moves, in
284 // particular) are searched with bigger depth than ordinary moves and in
285 // any case are marked as 'dangerous'. Note that also if a move is not
286 // extended, as example because the corresponding UCI option is set to zero,
287 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
288 template <bool PvNode>
289 FORCE_INLINE Depth extension(const Position& pos, Move m, bool captureOrPromotion,
290 bool moveIsCheck, bool* dangerous) {
291 assert(m != MOVE_NONE);
293 Depth result = DEPTH_ZERO;
294 *dangerous = moveIsCheck;
296 if (moveIsCheck && pos.see_sign(m) >= 0)
297 result += CheckExtension[PvNode];
299 if (piece_type(pos.piece_on(move_from(m))) == PAWN)
301 Color c = pos.side_to_move();
302 if (relative_rank(c, move_to(m)) == RANK_7)
304 result += PawnPushTo7thExtension[PvNode];
307 if (pos.pawn_is_passed(c, move_to(m)))
309 result += PassedPawnExtension[PvNode];
314 if ( captureOrPromotion
315 && piece_type(pos.piece_on(move_to(m))) != PAWN
316 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
317 - piece_value_midgame(pos.piece_on(move_to(m))) == VALUE_ZERO)
318 && !move_is_special(m))
320 result += PawnEndgameExtension[PvNode];
324 return Min(result, ONE_PLY);
330 /// init_search() is called during startup to initialize various lookup tables
334 int d; // depth (ONE_PLY == 2)
335 int hd; // half depth (ONE_PLY == 1)
338 // Init reductions array
339 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
341 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
342 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
343 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
344 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
347 // Init futility margins array
348 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
349 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
351 // Init futility move count array
352 for (d = 0; d < 32; d++)
353 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
357 /// perft() is our utility to verify move generation. All the leaf nodes up to
358 /// the given depth are generated and counted and the sum returned.
360 int64_t perft(Position& pos, Depth depth) {
365 // Generate all legal moves
366 MoveList<MV_LEGAL> ml(pos);
368 // If we are at the last ply we don't need to do and undo
369 // the moves, just to count them.
370 if (depth <= ONE_PLY)
373 // Loop through all legal moves
375 for ( ; !ml.end(); ++ml)
377 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
378 sum += perft(pos, depth - ONE_PLY);
379 pos.undo_move(ml.move());
385 /// think() is the external interface to Stockfish's search, and is called when
386 /// the program receives the UCI 'go' command. It initializes various global
387 /// variables, and calls id_loop(). It returns false when a "quit" command is
388 /// received during the search.
390 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
394 // Initialize global search-related variables
395 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
397 current_search_time(get_system_time());
399 TimeMgr.init(Limits, pos.startpos_ply_counter());
401 // Set output steram in normal or chess960 mode
402 cout << set960(pos.is_chess960());
404 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
406 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
407 else if (Limits.time && Limits.time < 1000)
408 NodesBetweenPolls = 1000;
409 else if (Limits.time && Limits.time < 5000)
410 NodesBetweenPolls = 5000;
412 NodesBetweenPolls = 30000;
414 // Look for a book move
415 if (Options["OwnBook"].value<bool>())
417 if (Options["Book File"].value<string>() != book.name())
418 book.open(Options["Book File"].value<string>());
420 Move bookMove = book.get_move(pos, Options["Best Book Move"].value<bool>());
421 if (bookMove != MOVE_NONE)
424 wait_for_stop_or_ponderhit();
426 cout << "bestmove " << bookMove << endl;
432 UCIMultiPV = Options["MultiPV"].value<int>();
433 SkillLevel = Options["Skill Level"].value<int>();
435 read_evaluation_uci_options(pos.side_to_move());
436 Threads.read_uci_options();
438 // If needed allocate pawn and material hash tables and adjust TT size
439 Threads.init_hash_tables();
440 TT.set_size(Options["Hash"].value<int>());
442 if (Options["Clear Hash"].value<bool>())
444 Options["Clear Hash"].set_value("false");
448 // Do we have to play with skill handicap? In this case enable MultiPV that
449 // we will use behind the scenes to retrieve a set of possible moves.
450 SkillLevelEnabled = (SkillLevel < 20);
451 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
453 // Wake up needed threads and reset maxPly counter
454 for (int i = 0; i < Threads.size(); i++)
456 Threads[i].wake_up();
457 Threads[i].maxPly = 0;
460 // Write to log file and keep it open to be accessed during the search
461 if (Options["Use Search Log"].value<bool>())
463 string name = Options["Search Log Filename"].value<string>();
464 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
466 if (LogFile.is_open())
467 LogFile << "\nSearching: " << pos.to_fen()
468 << "\ninfinite: " << Limits.infinite
469 << " ponder: " << Limits.ponder
470 << " time: " << Limits.time
471 << " increment: " << Limits.increment
472 << " moves to go: " << Limits.movesToGo
476 // We're ready to start thinking. Call the iterative deepening loop function
477 Move ponderMove = MOVE_NONE;
478 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
480 // Write final search statistics and close log file
481 if (LogFile.is_open())
483 int t = current_search_time();
485 LogFile << "Nodes: " << pos.nodes_searched()
486 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
487 << "\nBest move: " << move_to_san(pos, bestMove);
490 pos.do_move(bestMove, st);
491 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
492 pos.undo_move(bestMove); // Return from think() with unchanged position
496 // This makes all the threads to go to sleep
499 // If we are pondering or in infinite search, we shouldn't print the
500 // best move before we are told to do so.
501 if (!StopRequest && (Limits.ponder || Limits.infinite))
502 wait_for_stop_or_ponderhit();
504 // Could be MOVE_NONE when searching on a stalemate position
505 cout << "bestmove " << bestMove;
507 // UCI protol is not clear on allowing sending an empty ponder move, instead
508 // it is clear that ponder move is optional. So skip it if empty.
509 if (ponderMove != MOVE_NONE)
510 cout << " ponder " << ponderMove;
520 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
521 // with increasing depth until the allocated thinking time has been consumed,
522 // user stops the search, or the maximum search depth is reached.
524 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
526 SearchStack ss[PLY_MAX_PLUS_2];
527 Value bestValues[PLY_MAX_PLUS_2];
528 int bestMoveChanges[PLY_MAX_PLUS_2];
529 int depth, aspirationDelta;
530 Value value, alpha, beta;
531 Move bestMove, easyMove, skillBest, skillPonder;
533 // Initialize stuff before a new search
534 memset(ss, 0, 4 * sizeof(SearchStack));
537 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
538 depth = aspirationDelta = 0;
539 alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
540 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
542 // Moves to search are verified and copied
543 Rml.init(pos, searchMoves);
545 // Handle special case of searching on a mate/stalemate position
548 cout << "info" << depth_to_uci(DEPTH_ZERO)
549 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW, alpha, beta) << endl;
554 // Iterative deepening loop until requested to stop or target depth reached
555 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
557 Rml.bestMoveChanges = 0;
559 // Calculate dynamic aspiration window based on previous iterations
560 if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
562 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
563 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
565 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
566 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
568 alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
569 beta = Min(bestValues[depth - 1] + aspirationDelta, 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 // Write PV back to transposition table in case the relevant entries
579 // have been overwritten during the search.
580 for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
581 Rml[i].insert_pv_in_tt(pos);
583 // Value cannot be trusted. Break out immediately!
587 // Send full PV info to GUI if we are going to leave the loop or
588 // if we have a fail high/low and we are deep in the search.
589 if ((value > alpha && value < beta) || current_search_time() > 2000)
590 for (int i = 0; i < Min(UCIMultiPV, (int)Rml.size()); i++)
592 << depth_to_uci(depth * ONE_PLY)
593 << score_to_uci(Rml[i].pv_score, alpha, beta)
594 << speed_to_uci(pos.nodes_searched())
595 << pv_to_uci(Rml[i].pv, i + 1, pos.is_chess960()) << endl;
597 // In case of failing high/low increase aspiration window and research,
598 // otherwise exit the fail high/low loop.
601 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
602 aspirationDelta += aspirationDelta / 2;
604 else if (value <= alpha)
606 AspirationFailLow = true;
607 StopOnPonderhit = false;
609 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
610 aspirationDelta += aspirationDelta / 2;
615 } while (abs(value) < VALUE_KNOWN_WIN);
617 // Collect info about search result
618 bestMove = Rml[0].pv[0];
619 *ponderMove = Rml[0].pv[1];
620 bestValues[depth] = value;
621 bestMoveChanges[depth] = Rml.bestMoveChanges;
623 // Do we need to pick now the best and the ponder moves ?
624 if (SkillLevelEnabled && depth == 1 + SkillLevel)
625 do_skill_level(&skillBest, &skillPonder);
627 if (LogFile.is_open())
628 LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
630 // Init easyMove after first iteration or drop if differs from the best move
631 if (depth == 1 && (Rml.size() == 1 || Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin))
633 else if (bestMove != easyMove)
634 easyMove = MOVE_NONE;
636 // Check for some early stop condition
637 if (!StopRequest && Limits.useTimeManagement())
639 // Stop search early if one move seems to be much better than the
640 // others or if there is only a single legal move. Also in the latter
641 // case we search up to some depth anyway to get a proper score.
643 && easyMove == bestMove
645 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
646 && current_search_time() > TimeMgr.available_time() / 16)
647 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
648 && current_search_time() > TimeMgr.available_time() / 32)))
651 // Take in account some extra time if the best move has changed
652 if (depth > 4 && depth < 50)
653 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
655 // Stop search if most of available time is already consumed. We probably don't
656 // have enough time to search the first move at the next iteration anyway.
657 if (current_search_time() > (TimeMgr.available_time() * 62) / 100)
660 // If we are allowed to ponder do not stop the search now but keep pondering
661 if (StopRequest && Limits.ponder)
664 StopOnPonderhit = true;
669 // When using skills overwrite best and ponder moves with the sub-optimal ones
670 if (SkillLevelEnabled)
672 if (skillBest == MOVE_NONE) // Still unassigned ?
673 do_skill_level(&skillBest, &skillPonder);
675 bestMove = skillBest;
676 *ponderMove = skillPonder;
683 // search<>() is the main search function for both PV and non-PV nodes and for
684 // normal and SplitPoint nodes. When called just after a split point the search
685 // is simpler because we have already probed the hash table, done a null move
686 // search, and searched the first move before splitting, we don't have to repeat
687 // all this work again. We also don't need to store anything to the hash table
688 // here: This is taken care of after we return from the split point.
690 template <NodeType NT>
691 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
693 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV);
694 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV);
695 const bool RootNode = (NT == Root);
697 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
698 assert(beta > alpha && beta <= VALUE_INFINITE);
699 assert(PvNode || alpha == beta - 1);
700 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
702 Move movesSearched[MAX_MOVES];
707 Move ttMove, move, excludedMove, threatMove;
710 Value bestValue, value, oldAlpha;
711 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
712 bool isPvMove, inCheck, singularExtensionNode, givesCheck, captureOrPromotion, dangerous;
713 int moveCount = 0, playedMoveCount = 0;
714 Thread& thread = Threads[pos.thread()];
715 SplitPoint* sp = NULL;
717 refinedValue = bestValue = value = -VALUE_INFINITE;
719 inCheck = pos.in_check();
720 ss->ply = (ss-1)->ply + 1;
722 // Used to send selDepth info to GUI
723 if (PvNode && thread.maxPly < ss->ply)
724 thread.maxPly = ss->ply;
726 // Step 1. Initialize node and poll. Polling can abort search
729 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
730 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
731 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
737 ttMove = excludedMove = MOVE_NONE;
738 threatMove = sp->threatMove;
739 goto split_point_start;
742 if (pos.thread() == 0 && ++NodesSincePoll > NodesBetweenPolls)
748 // Step 2. Check for aborted search and immediate draw
750 || pos.is_draw<false>()
751 || ss->ply > PLY_MAX) && !RootNode)
754 // Step 3. Mate distance pruning
757 alpha = Max(value_mated_in(ss->ply), alpha);
758 beta = Min(value_mate_in(ss->ply+1), beta);
763 // Step 4. Transposition table lookup
764 // We don't want the score of a partial search to overwrite a previous full search
765 // TT value, so we use a different position key in case of an excluded move.
766 excludedMove = ss->excludedMove;
767 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
768 tte = TT.probe(posKey);
769 ttMove = tte ? tte->move() : MOVE_NONE;
771 // At PV nodes we check for exact scores, while at non-PV nodes we check for
772 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
773 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
774 // we should also update RootMoveList to avoid bogus output.
775 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
776 : ok_to_use_TT(tte, depth, beta, ss->ply)))
779 ss->bestMove = ttMove; // Can be MOVE_NONE
780 return value_from_tt(tte->value(), ss->ply);
783 // Step 5. Evaluate the position statically and update parent's gain statistics
785 ss->eval = ss->evalMargin = VALUE_NONE;
788 assert(tte->static_value() != VALUE_NONE);
790 ss->eval = tte->static_value();
791 ss->evalMargin = tte->static_value_margin();
792 refinedValue = refine_eval(tte, ss->eval, ss->ply);
796 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
797 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
800 // Save gain for the parent non-capture move
801 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
803 // Step 6. Razoring (is omitted in PV nodes)
805 && depth < RazorDepth
807 && refinedValue + razor_margin(depth) < beta
808 && ttMove == MOVE_NONE
809 && abs(beta) < VALUE_MATE_IN_PLY_MAX
810 && !pos.has_pawn_on_7th(pos.side_to_move()))
812 Value rbeta = beta - razor_margin(depth);
813 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
815 // Logically we should return (v + razor_margin(depth)), but
816 // surprisingly this did slightly weaker in tests.
820 // Step 7. Static null move pruning (is omitted in PV nodes)
821 // We're betting that the opponent doesn't have a move that will reduce
822 // the score by more than futility_margin(depth) if we do a null move.
825 && depth < RazorDepth
827 && refinedValue - futility_margin(depth, 0) >= beta
828 && abs(beta) < VALUE_MATE_IN_PLY_MAX
829 && pos.non_pawn_material(pos.side_to_move()))
830 return refinedValue - futility_margin(depth, 0);
832 // Step 8. Null move search with verification search (is omitted in PV nodes)
837 && refinedValue >= beta
838 && abs(beta) < VALUE_MATE_IN_PLY_MAX
839 && pos.non_pawn_material(pos.side_to_move()))
841 ss->currentMove = MOVE_NULL;
843 // Null move dynamic reduction based on depth
844 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
846 // Null move dynamic reduction based on value
847 if (refinedValue - PawnValueMidgame > beta)
850 pos.do_null_move(st);
851 (ss+1)->skipNullMove = true;
852 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
853 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
854 (ss+1)->skipNullMove = false;
855 pos.undo_null_move();
857 if (nullValue >= beta)
859 // Do not return unproven mate scores
860 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
863 if (depth < 6 * ONE_PLY)
866 // Do verification search at high depths
867 ss->skipNullMove = true;
868 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
869 ss->skipNullMove = false;
876 // The null move failed low, which means that we may be faced with
877 // some kind of threat. If the previous move was reduced, check if
878 // the move that refuted the null move was somehow connected to the
879 // move which was reduced. If a connection is found, return a fail
880 // low score (which will cause the reduced move to fail high in the
881 // parent node, which will trigger a re-search with full depth).
882 threatMove = (ss+1)->bestMove;
884 if ( depth < ThreatDepth
886 && threatMove != MOVE_NONE
887 && connected_moves(pos, (ss-1)->currentMove, threatMove))
892 // Step 9. ProbCut (is omitted in PV nodes)
893 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
894 // and a reduced search returns a value much above beta, we can (almost) safely
895 // prune the previous move.
897 && depth >= RazorDepth + ONE_PLY
900 && excludedMove == MOVE_NONE
901 && abs(beta) < VALUE_MATE_IN_PLY_MAX)
903 Value rbeta = beta + 200;
904 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
906 assert(rdepth >= ONE_PLY);
908 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
911 while ((move = mp.get_next_move()) != MOVE_NONE)
912 if (pos.pl_move_is_legal(move, ci.pinned))
914 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
915 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
922 // Step 10. Internal iterative deepening
923 if ( depth >= IIDDepth[PvNode]
924 && ttMove == MOVE_NONE
925 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
927 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
929 ss->skipNullMove = true;
930 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
931 ss->skipNullMove = false;
933 tte = TT.probe(posKey);
934 ttMove = tte ? tte->move() : MOVE_NONE;
937 split_point_start: // At split points actual search starts from here
939 // Initialize a MovePicker object for the current position
940 MovePickerExt<NT> mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
942 ss->bestMove = MOVE_NONE;
943 futilityBase = ss->eval + ss->evalMargin;
944 singularExtensionNode = !RootNode
946 && depth >= SingularExtensionDepth[PvNode]
947 && ttMove != MOVE_NONE
948 && !excludedMove // Do not allow recursive singular extension search
949 && (tte->type() & VALUE_TYPE_LOWER)
950 && tte->depth() >= depth - 3 * ONE_PLY;
953 lock_grab(&(sp->lock));
954 bestValue = sp->bestValue;
957 // Step 11. Loop through moves
958 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
959 while ( bestValue < beta
960 && (move = mp.get_next_move()) != MOVE_NONE
961 && !thread.cutoff_occurred())
963 assert(move_is_ok(move));
965 if (move == excludedMove)
968 // At PV and SpNode nodes we want all moves to be legal since the beginning
969 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
974 moveCount = ++sp->moveCount;
975 lock_release(&(sp->lock));
982 // This is used by time management
983 FirstRootMove = (moveCount == 1);
985 // Save the current node count before the move is searched
986 nodes = pos.nodes_searched();
988 // If it's time to send nodes info, do it here where we have the
989 // correct accumulated node counts searched by each thread.
990 if (SendSearchedNodes)
992 SendSearchedNodes = false;
993 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
996 // For long searches send current move info to GUI
997 if (current_search_time() > 2000)
998 cout << "info" << depth_to_uci(depth)
999 << " currmove " << move << " currmovenumber " << moveCount << endl;
1002 // At Root and at first iteration do a PV search on all the moves to score root moves
1003 isPvMove = (PvNode && moveCount <= (!RootNode ? 1 : depth <= ONE_PLY ? MAX_MOVES : MultiPV));
1004 givesCheck = pos.move_gives_check(move, ci);
1005 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1007 // Step 12. Decide the new search depth
1008 ext = extension<PvNode>(pos, move, captureOrPromotion, givesCheck, &dangerous);
1010 // Singular extension search. If all moves but one fail low on a search of
1011 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1012 // is singular and should be extended. To verify this we do a reduced search
1013 // on all the other moves but the ttMove, if result is lower than ttValue minus
1014 // a margin then we extend ttMove.
1015 if ( singularExtensionNode
1017 && pos.pl_move_is_legal(move, ci.pinned)
1020 Value ttValue = value_from_tt(tte->value(), ss->ply);
1022 if (abs(ttValue) < VALUE_KNOWN_WIN)
1024 Value rBeta = ttValue - int(depth);
1025 ss->excludedMove = move;
1026 ss->skipNullMove = true;
1027 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1028 ss->skipNullMove = false;
1029 ss->excludedMove = MOVE_NONE;
1030 ss->bestMove = MOVE_NONE;
1036 // Update current move (this must be done after singular extension search)
1037 newDepth = depth - ONE_PLY + ext;
1039 // Step 13. Futility pruning (is omitted in PV nodes)
1041 && !captureOrPromotion
1045 && !move_is_castle(move))
1047 // Move count based pruning
1048 if ( moveCount >= futility_move_count(depth)
1049 && (!threatMove || !connected_threat(pos, move, threatMove))
1050 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1053 lock_grab(&(sp->lock));
1058 // Value based pruning
1059 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1060 // but fixing this made program slightly weaker.
1061 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
1062 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1063 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1065 if (futilityValueScaled < beta)
1069 lock_grab(&(sp->lock));
1070 if (futilityValueScaled > sp->bestValue)
1071 sp->bestValue = bestValue = futilityValueScaled;
1073 else if (futilityValueScaled > bestValue)
1074 bestValue = futilityValueScaled;
1079 // Prune moves with negative SEE at low depths
1080 if ( predictedDepth < 2 * ONE_PLY
1081 && bestValue > VALUE_MATED_IN_PLY_MAX
1082 && pos.see_sign(move) < 0)
1085 lock_grab(&(sp->lock));
1091 // Check for legality only before to do the move
1092 if (!pos.pl_move_is_legal(move, ci.pinned))
1098 ss->currentMove = move;
1099 if (!SpNode && !captureOrPromotion)
1100 movesSearched[playedMoveCount++] = move;
1102 // Step 14. Make the move
1103 pos.do_move(move, st, ci, givesCheck);
1105 // Step extra. pv search (only in PV nodes)
1106 // The first move in list is the expected PV
1108 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1109 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1112 // Step 15. Reduced depth search
1113 // If the move fails high will be re-searched at full depth.
1114 bool doFullDepthSearch = true;
1116 if ( depth > 3 * ONE_PLY
1117 && !captureOrPromotion
1119 && !move_is_castle(move)
1120 && ss->killers[0] != move
1121 && ss->killers[1] != move
1122 && (ss->reduction = reduction<PvNode>(depth, moveCount)) != DEPTH_ZERO)
1124 Depth d = newDepth - ss->reduction;
1125 alpha = SpNode ? sp->alpha : alpha;
1127 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1128 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1130 ss->reduction = DEPTH_ZERO;
1131 doFullDepthSearch = (value > alpha);
1134 // Step 16. Full depth search
1135 if (doFullDepthSearch)
1137 alpha = SpNode ? sp->alpha : alpha;
1138 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1139 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1141 // Step extra. pv search (only in PV nodes)
1142 // Search only for possible new PV nodes, if instead value >= beta then
1143 // parent node fails low with value <= alpha and tries another move.
1144 if (PvNode && value > alpha && (RootNode || value < beta))
1145 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1146 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1150 // Step 17. Undo move
1151 pos.undo_move(move);
1153 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1155 // Step 18. Check for new best move
1158 lock_grab(&(sp->lock));
1159 bestValue = sp->bestValue;
1163 if (value > bestValue)
1166 ss->bestMove = move;
1171 && value < beta) // We want always alpha < beta
1174 if (SpNode && !thread.cutoff_occurred())
1176 sp->bestValue = value;
1177 sp->ss->bestMove = move;
1179 sp->is_betaCutoff = (value >= beta);
1185 // Finished searching the move. If StopRequest is true, the search
1186 // was aborted because the user interrupted the search or because we
1187 // ran out of time. In this case, the return value of the search cannot
1188 // be trusted, and we break out of the loop without updating the best
1193 // Remember searched nodes counts for this move
1194 mp.current().nodes += pos.nodes_searched() - nodes;
1196 // PV move or new best move ?
1197 if (isPvMove || value > alpha)
1200 mp.current().pv_score = value;
1201 mp.current().extract_pv_from_tt(pos);
1203 // We record how often the best move has been changed in each
1204 // iteration. This information is used for time management: When
1205 // the best move changes frequently, we allocate some more time.
1206 if (!isPvMove && MultiPV == 1)
1207 Rml.bestMoveChanges++;
1209 // It is critical that sorting is done with a stable algorithm
1210 // because all the values but the first are usually set to
1211 // -VALUE_INFINITE and we want to keep the same order for all
1212 // the moves but the new PV that goes to head.
1213 sort<RootMove>(Rml.begin(), Rml.begin() + moveCount);
1215 // Update alpha. In multi-pv we don't use aspiration window, so set
1216 // alpha equal to minimum score among the PV lines searched so far.
1218 alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score;
1219 else if (value > alpha)
1223 // All other moves but the PV are set to the lowest value, this
1224 // is not a problem when sorting becuase sort is stable and move
1225 // position in the list is preserved, just the PV is pushed up.
1226 mp.current().pv_score = -VALUE_INFINITE;
1230 // Step 19. Check for split
1233 && depth >= Threads.min_split_depth()
1235 && Threads.available_slave_exists(pos.thread())
1237 && !thread.cutoff_occurred())
1238 Threads.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1239 threatMove, moveCount, &mp, PvNode);
1242 // Step 20. Check for mate and stalemate
1243 // All legal moves have been searched and if there are
1244 // no legal moves, it must be mate or stalemate.
1245 // If one move was excluded return fail low score.
1246 if (!SpNode && !moveCount)
1247 return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1249 // Step 21. Update tables
1250 // If the search is not aborted, update the transposition table,
1251 // history counters, and killer moves.
1252 if (!SpNode && !StopRequest && !thread.cutoff_occurred())
1254 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1255 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1256 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1258 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1260 // Update killers and history only for non capture moves that fails high
1261 if ( bestValue >= beta
1262 && !pos.move_is_capture_or_promotion(move))
1264 if (move != ss->killers[0])
1266 ss->killers[1] = ss->killers[0];
1267 ss->killers[0] = move;
1269 update_history(pos, move, depth, movesSearched, playedMoveCount);
1275 // Here we have the lock still grabbed
1276 sp->is_slave[pos.thread()] = false;
1277 sp->nodes += pos.nodes_searched();
1278 lock_release(&(sp->lock));
1281 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1286 // qsearch() is the quiescence search function, which is called by the main
1287 // search function when the remaining depth is zero (or, to be more precise,
1288 // less than ONE_PLY).
1290 template <NodeType NT>
1291 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1293 const bool PvNode = (NT == PV);
1295 assert(NT == PV || NT == NonPV);
1296 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1297 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1298 assert(PvNode || alpha == beta - 1);
1300 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
1304 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1305 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1308 Value oldAlpha = alpha;
1310 ss->bestMove = ss->currentMove = MOVE_NONE;
1311 ss->ply = (ss-1)->ply + 1;
1313 // Check for an instant draw or maximum ply reached
1314 if (pos.is_draw<true>() || ss->ply > PLY_MAX)
1317 // Decide whether or not to include checks, this fixes also the type of
1318 // TT entry depth that we are going to use. Note that in qsearch we use
1319 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1320 inCheck = pos.in_check();
1321 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1323 // Transposition table lookup. At PV nodes, we don't use the TT for
1324 // pruning, but only for move ordering.
1325 tte = TT.probe(pos.get_key());
1326 ttMove = (tte ? tte->move() : MOVE_NONE);
1328 if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ss->ply))
1330 ss->bestMove = ttMove; // Can be MOVE_NONE
1331 return value_from_tt(tte->value(), ss->ply);
1334 // Evaluate the position statically
1337 bestValue = futilityBase = -VALUE_INFINITE;
1338 ss->eval = evalMargin = VALUE_NONE;
1339 enoughMaterial = false;
1345 assert(tte->static_value() != VALUE_NONE);
1347 evalMargin = tte->static_value_margin();
1348 ss->eval = bestValue = tte->static_value();
1351 ss->eval = bestValue = evaluate(pos, evalMargin);
1353 // Stand pat. Return immediately if static value is at least beta
1354 if (bestValue >= beta)
1357 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1362 if (PvNode && bestValue > alpha)
1365 // Futility pruning parameters, not needed when in check
1366 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1367 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1370 // Initialize a MovePicker object for the current position, and prepare
1371 // to search the moves. Because the depth is <= 0 here, only captures,
1372 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1374 MovePicker mp(pos, ttMove, depth, H, move_to((ss-1)->currentMove));
1377 // Loop through the moves until no moves remain or a beta cutoff occurs
1378 while ( alpha < beta
1379 && (move = mp.get_next_move()) != MOVE_NONE)
1381 assert(move_is_ok(move));
1383 givesCheck = pos.move_gives_check(move, ci);
1391 && !move_is_promotion(move)
1392 && !pos.move_is_passed_pawn_push(move))
1394 futilityValue = futilityBase
1395 + piece_value_endgame(pos.piece_on(move_to(move)))
1396 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1398 if (futilityValue < alpha)
1400 if (futilityValue > bestValue)
1401 bestValue = futilityValue;
1405 // Prune moves with negative or equal SEE
1406 if ( futilityBase < beta
1407 && depth < DEPTH_ZERO
1408 && pos.see(move) <= 0)
1412 // Detect non-capture evasions that are candidate to be pruned
1413 evasionPrunable = !PvNode
1415 && bestValue > VALUE_MATED_IN_PLY_MAX
1416 && !pos.move_is_capture(move)
1417 && !pos.can_castle(pos.side_to_move());
1419 // Don't search moves with negative SEE values
1421 && (!inCheck || evasionPrunable)
1423 && !move_is_promotion(move)
1424 && pos.see_sign(move) < 0)
1427 // Don't search useless checks
1432 && !pos.move_is_capture_or_promotion(move)
1433 && ss->eval + PawnValueMidgame / 4 < beta
1434 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1436 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1437 bestValue = ss->eval + PawnValueMidgame / 4;
1442 // Check for legality only before to do the move
1443 if (!pos.pl_move_is_legal(move, ci.pinned))
1446 // Update current move
1447 ss->currentMove = move;
1449 // Make and search the move
1450 pos.do_move(move, st, ci, givesCheck);
1451 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1452 pos.undo_move(move);
1454 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1457 if (value > bestValue)
1463 ss->bestMove = move;
1468 // All legal moves have been searched. A special case: If we're in check
1469 // and no legal moves were found, it is checkmate.
1470 if (inCheck && bestValue == -VALUE_INFINITE)
1471 return value_mated_in(ss->ply);
1473 // Update transposition table
1474 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1475 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1477 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1483 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1484 // bestValue is updated only when returning false because in that case move
1487 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1489 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1490 Square from, to, ksq, victimSq;
1493 Value futilityValue, bv = *bestValue;
1495 from = move_from(move);
1497 them = opposite_color(pos.side_to_move());
1498 ksq = pos.king_square(them);
1499 kingAtt = pos.attacks_from<KING>(ksq);
1500 pc = pos.piece_on(from);
1502 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1503 oldAtt = pos.attacks_from(pc, from, occ);
1504 newAtt = pos.attacks_from(pc, to, occ);
1506 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1507 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1509 if (!(b && (b & (b - 1))))
1512 // Rule 2. Queen contact check is very dangerous
1513 if ( piece_type(pc) == QUEEN
1514 && bit_is_set(kingAtt, to))
1517 // Rule 3. Creating new double threats with checks
1518 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1522 victimSq = pop_1st_bit(&b);
1523 futilityValue = futilityBase + piece_value_endgame(pos.piece_on(victimSq));
1525 // Note that here we generate illegal "double move"!
1526 if ( futilityValue >= beta
1527 && pos.see_sign(make_move(from, victimSq)) >= 0)
1530 if (futilityValue > bv)
1534 // Update bestValue only if check is not dangerous (because we will prune the move)
1540 // connected_moves() tests whether two moves are 'connected' in the sense
1541 // that the first move somehow made the second move possible (for instance
1542 // if the moving piece is the same in both moves). The first move is assumed
1543 // to be the move that was made to reach the current position, while the
1544 // second move is assumed to be a move from the current position.
1546 bool connected_moves(const Position& pos, Move m1, Move m2) {
1548 Square f1, t1, f2, t2;
1552 assert(m1 && move_is_ok(m1));
1553 assert(m2 && move_is_ok(m2));
1555 // Case 1: The moving piece is the same in both moves
1561 // Case 2: The destination square for m2 was vacated by m1
1567 // Case 3: Moving through the vacated square
1568 p2 = pos.piece_on(f2);
1569 if ( piece_is_slider(p2)
1570 && bit_is_set(squares_between(f2, t2), f1))
1573 // Case 4: The destination square for m2 is defended by the moving piece in m1
1574 p1 = pos.piece_on(t1);
1575 if (bit_is_set(pos.attacks_from(p1, t1), t2))
1578 // Case 5: Discovered check, checking piece is the piece moved in m1
1579 ksq = pos.king_square(pos.side_to_move());
1580 if ( piece_is_slider(p1)
1581 && bit_is_set(squares_between(t1, ksq), f2))
1583 Bitboard occ = pos.occupied_squares();
1584 clear_bit(&occ, f2);
1585 if (bit_is_set(pos.attacks_from(p1, t1, occ), ksq))
1592 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1593 // "plies to mate from the current ply". Non-mate scores are unchanged.
1594 // The function is called before storing a value to the transposition table.
1596 Value value_to_tt(Value v, int ply) {
1598 if (v >= VALUE_MATE_IN_PLY_MAX)
1601 if (v <= VALUE_MATED_IN_PLY_MAX)
1608 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1609 // the transposition table to a mate score corrected for the current ply.
1611 Value value_from_tt(Value v, int ply) {
1613 if (v >= VALUE_MATE_IN_PLY_MAX)
1616 if (v <= VALUE_MATED_IN_PLY_MAX)
1623 // connected_threat() tests whether it is safe to forward prune a move or if
1624 // is somehow connected to the threat move returned by null search.
1626 bool connected_threat(const Position& pos, Move m, Move threat) {
1628 assert(move_is_ok(m));
1629 assert(threat && move_is_ok(threat));
1630 assert(!pos.move_is_capture_or_promotion(m));
1631 assert(!pos.move_is_passed_pawn_push(m));
1633 Square mfrom, mto, tfrom, tto;
1635 mfrom = move_from(m);
1637 tfrom = move_from(threat);
1638 tto = move_to(threat);
1640 // Case 1: Don't prune moves which move the threatened piece
1644 // Case 2: If the threatened piece has value less than or equal to the
1645 // value of the threatening piece, don't prune moves which defend it.
1646 if ( pos.move_is_capture(threat)
1647 && ( piece_value_midgame(pos.piece_on(tfrom)) >= piece_value_midgame(pos.piece_on(tto))
1648 || piece_type(pos.piece_on(tfrom)) == KING)
1649 && pos.move_attacks_square(m, tto))
1652 // Case 3: If the moving piece in the threatened move is a slider, don't
1653 // prune safe moves which block its ray.
1654 if ( piece_is_slider(pos.piece_on(tfrom))
1655 && bit_is_set(squares_between(tfrom, tto), mto)
1656 && pos.see_sign(m) >= 0)
1663 // ok_to_use_TT() returns true if a transposition table score
1664 // can be used at a given point in search.
1666 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1668 Value v = value_from_tt(tte->value(), ply);
1670 return ( tte->depth() >= depth
1671 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1672 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1674 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1675 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1679 // refine_eval() returns the transposition table score if
1680 // possible otherwise falls back on static position evaluation.
1682 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1686 Value v = value_from_tt(tte->value(), ply);
1688 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1689 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1696 // update_history() registers a good move that produced a beta-cutoff
1697 // in history and marks as failures all the other moves of that ply.
1699 void update_history(const Position& pos, Move move, Depth depth,
1700 Move movesSearched[], int moveCount) {
1702 Value bonus = Value(int(depth) * int(depth));
1704 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1706 for (int i = 0; i < moveCount - 1; i++)
1708 m = movesSearched[i];
1712 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1717 // update_gains() updates the gains table of a non-capture move given
1718 // the static position evaluation before and after the move.
1720 void update_gains(const Position& pos, Move m, Value before, Value after) {
1723 && before != VALUE_NONE
1724 && after != VALUE_NONE
1725 && pos.captured_piece_type() == PIECE_TYPE_NONE
1726 && !move_is_special(m))
1727 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1731 // current_search_time() returns the number of milliseconds which have passed
1732 // since the beginning of the current search.
1734 int current_search_time(int set) {
1736 static int searchStartTime;
1739 searchStartTime = set;
1741 return get_system_time() - searchStartTime;
1745 // score_to_uci() converts a value to a string suitable for use with the UCI
1746 // protocol specifications:
1748 // cp <x> The score from the engine's point of view in centipawns.
1749 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1750 // use negative values for y.
1752 string score_to_uci(Value v, Value alpha, Value beta) {
1754 std::stringstream s;
1756 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1757 s << " score cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1759 s << " score mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1761 s << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1767 // speed_to_uci() returns a string with time stats of current search suitable
1768 // to be sent to UCI gui.
1770 string speed_to_uci(int64_t nodes) {
1772 std::stringstream s;
1773 int t = current_search_time();
1775 s << " nodes " << nodes
1776 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1782 // pv_to_uci() returns a string with information on the current PV line
1783 // formatted according to UCI specification.
1785 string pv_to_uci(Move pv[], int pvNum, bool chess960) {
1787 std::stringstream s;
1789 s << " multipv " << pvNum << " pv " << set960(chess960);
1791 for ( ; *pv != MOVE_NONE; pv++)
1797 // depth_to_uci() returns a string with information on the current depth and
1798 // seldepth formatted according to UCI specification.
1800 string depth_to_uci(Depth depth) {
1802 std::stringstream s;
1804 // Retrieve max searched depth among threads
1806 for (int i = 0; i < Threads.size(); i++)
1807 if (Threads[i].maxPly > selDepth)
1808 selDepth = Threads[i].maxPly;
1810 s << " depth " << depth / ONE_PLY << " seldepth " << selDepth;
1815 string time_to_string(int millisecs) {
1817 const int MSecMinute = 1000 * 60;
1818 const int MSecHour = 1000 * 60 * 60;
1820 int hours = millisecs / MSecHour;
1821 int minutes = (millisecs % MSecHour) / MSecMinute;
1822 int seconds = ((millisecs % MSecHour) % MSecMinute) / 1000;
1824 std::stringstream s;
1829 s << std::setfill('0') << std::setw(2) << minutes << ':' << std::setw(2) << seconds;
1833 string score_to_string(Value v) {
1835 std::stringstream s;
1837 if (v >= VALUE_MATE_IN_PLY_MAX)
1838 s << "#" << (VALUE_MATE - v + 1) / 2;
1839 else if (v <= VALUE_MATED_IN_PLY_MAX)
1840 s << "-#" << (VALUE_MATE + v) / 2;
1842 s << std::setprecision(2) << std::fixed << std::showpos << float(v) / PawnValueMidgame;
1847 // pretty_pv() creates a human-readable string from a position and a PV.
1848 // It is used to write search information to the log file (which is created
1849 // when the UCI parameter "Use Search Log" is "true").
1851 string pretty_pv(Position& pos, int depth, Value value, int time, Move pv[]) {
1853 const int64_t K = 1000;
1854 const int64_t M = 1000000;
1855 const int startColumn = 28;
1856 const size_t maxLength = 80 - startColumn;
1858 StateInfo state[PLY_MAX_PLUS_2], *st = state;
1861 std::stringstream s;
1864 // First print depth, score, time and searched nodes...
1865 s << set960(pos.is_chess960())
1866 << std::setw(2) << depth
1867 << std::setw(8) << score_to_string(value)
1868 << std::setw(8) << time_to_string(time);
1870 if (pos.nodes_searched() < M)
1871 s << std::setw(8) << pos.nodes_searched() / 1 << " ";
1872 else if (pos.nodes_searched() < K * M)
1873 s << std::setw(7) << pos.nodes_searched() / K << "K ";
1875 s << std::setw(7) << pos.nodes_searched() / M << "M ";
1877 // ...then print the full PV line in short algebraic notation
1878 while (*m != MOVE_NONE)
1880 san = move_to_san(pos, *m);
1881 length += san.length() + 1;
1883 if (length > maxLength)
1885 length = san.length() + 1;
1886 s << "\n" + string(startColumn, ' ');
1890 pos.do_move(*m++, *st++);
1893 // Restore original position before to leave
1894 while (m != pv) pos.undo_move(*--m);
1899 // poll() performs two different functions: It polls for user input, and it
1900 // looks at the time consumed so far and decides if it's time to abort the
1903 void poll(const Position& pos) {
1905 static int lastInfoTime;
1906 int t = current_search_time();
1909 if (input_available())
1911 // We are line oriented, don't read single chars
1914 if (!std::getline(std::cin, command) || command == "quit")
1916 // Quit the program as soon as possible
1917 Limits.ponder = false;
1918 QuitRequest = StopRequest = true;
1921 else if (command == "stop")
1923 // Stop calculating as soon as possible, but still send the "bestmove"
1924 // and possibly the "ponder" token when finishing the search.
1925 Limits.ponder = false;
1928 else if (command == "ponderhit")
1930 // The opponent has played the expected move. GUI sends "ponderhit" if
1931 // we were told to ponder on the same move the opponent has played. We
1932 // should continue searching but switching from pondering to normal search.
1933 Limits.ponder = false;
1935 if (StopOnPonderhit)
1940 // Print search information
1944 else if (lastInfoTime > t)
1945 // HACK: Must be a new search where we searched less than
1946 // NodesBetweenPolls nodes during the first second of search.
1949 else if (t - lastInfoTime >= 1000)
1954 dbg_print_hit_rate();
1956 // Send info on searched nodes as soon as we return to root
1957 SendSearchedNodes = true;
1960 // Should we stop the search?
1964 bool stillAtFirstMove = FirstRootMove
1965 && !AspirationFailLow
1966 && t > TimeMgr.available_time();
1968 bool noMoreTime = t > TimeMgr.maximum_time()
1969 || stillAtFirstMove;
1971 if ( (Limits.useTimeManagement() && noMoreTime)
1972 || (Limits.maxTime && t >= Limits.maxTime)
1973 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1978 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1979 // while the program is pondering. The point is to work around a wrinkle in
1980 // the UCI protocol: When pondering, the engine is not allowed to give a
1981 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1982 // We simply wait here until one of these commands is sent, and return,
1983 // after which the bestmove and pondermove will be printed.
1985 void wait_for_stop_or_ponderhit() {
1989 // Wait for a command from stdin
1990 while ( std::getline(std::cin, command)
1991 && command != "ponderhit" && command != "stop" && command != "quit") {};
1993 if (command != "ponderhit" && command != "stop")
1994 QuitRequest = true; // Must be "quit" or getline() returned false
1998 // When playing with strength handicap choose best move among the MultiPV set
1999 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
2000 void do_skill_level(Move* best, Move* ponder) {
2002 assert(MultiPV > 1);
2006 // Rml list is already sorted by pv_score in descending order
2008 int max_s = -VALUE_INFINITE;
2009 int size = Min(MultiPV, (int)Rml.size());
2010 int max = Rml[0].pv_score;
2011 int var = Min(max - Rml[size - 1].pv_score, PawnValueMidgame);
2012 int wk = 120 - 2 * SkillLevel;
2014 // PRNG sequence should be non deterministic
2015 for (int i = abs(get_system_time() % 50); i > 0; i--)
2016 rk.rand<unsigned>();
2018 // Choose best move. For each move's score we add two terms both dependent
2019 // on wk, one deterministic and bigger for weaker moves, and one random,
2020 // then we choose the move with the resulting highest score.
2021 for (int i = 0; i < size; i++)
2023 s = Rml[i].pv_score;
2025 // Don't allow crazy blunders even at very low skills
2026 if (i > 0 && Rml[i-1].pv_score > s + EasyMoveMargin)
2029 // This is our magical formula
2030 s += ((max - s) * wk + var * (rk.rand<unsigned>() % wk)) / 128;
2035 *best = Rml[i].pv[0];
2036 *ponder = Rml[i].pv[1];
2042 /// RootMove and RootMoveList method's definitions
2044 RootMove::RootMove() {
2047 pv_score = non_pv_score = -VALUE_INFINITE;
2051 RootMove& RootMove::operator=(const RootMove& rm) {
2053 const Move* src = rm.pv;
2056 // Avoid a costly full rm.pv[] copy
2057 do *dst++ = *src; while (*src++ != MOVE_NONE);
2060 pv_score = rm.pv_score;
2061 non_pv_score = rm.non_pv_score;
2065 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2068 bestMoveChanges = 0;
2071 // Generate all legal moves and add them to RootMoveList
2072 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
2074 // If we have a searchMoves[] list then verify the move
2075 // is in the list before to add it.
2076 for (sm = searchMoves; *sm && *sm != ml.move(); sm++) {}
2078 if (sm != searchMoves && *sm != ml.move())
2082 rm.pv[0] = ml.move();
2083 rm.pv[1] = MOVE_NONE;
2084 rm.pv_score = -VALUE_INFINITE;
2089 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2090 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2091 // allow to always have a ponder move even when we fail high at root and also a
2092 // long PV to print that is important for position analysis.
2094 void RootMove::extract_pv_from_tt(Position& pos) {
2096 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2100 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2102 pos.do_move(pv[0], *st++);
2104 while ( (tte = TT.probe(pos.get_key())) != NULL
2105 && tte->move() != MOVE_NONE
2106 && pos.move_is_pl(tte->move())
2107 && pos.pl_move_is_legal(tte->move(), pos.pinned_pieces())
2109 && (!pos.is_draw<false>() || ply < 2))
2111 pv[ply] = tte->move();
2112 pos.do_move(pv[ply++], *st++);
2114 pv[ply] = MOVE_NONE;
2116 do pos.undo_move(pv[--ply]); while (ply);
2119 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2120 // the PV back into the TT. This makes sure the old PV moves are searched
2121 // first, even if the old TT entries have been overwritten.
2123 void RootMove::insert_pv_in_tt(Position& pos) {
2125 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2128 Value v, m = VALUE_NONE;
2131 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2137 // Don't overwrite existing correct entries
2138 if (!tte || tte->move() != pv[ply])
2140 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
2141 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2143 pos.do_move(pv[ply], *st++);
2145 } while (pv[++ply] != MOVE_NONE);
2147 do pos.undo_move(pv[--ply]); while (ply);
2150 // Specializations for MovePickerExt in case of Root node
2151 MovePickerExt<Root>::MovePickerExt(const Position& p, Move ttm, Depth d,
2152 const History& h, SearchStack* ss, Value b)
2153 : MovePicker(p, ttm, d, h, ss, b), cur(-1) {
2155 Value score = VALUE_ZERO;
2157 // Score root moves using standard ordering used in main search, the moves
2158 // are scored according to the order in which they are returned by MovePicker.
2159 // This is the second order score that is used to compare the moves when
2160 // the first orders pv_score of both moves are equal.
2161 while ((move = MovePicker::get_next_move()) != MOVE_NONE)
2162 for (RootMoveList::iterator rm = Rml.begin(); rm != Rml.end(); ++rm)
2163 if (rm->pv[0] == move)
2165 rm->non_pv_score = score--;
2169 sort<RootMove>(Rml.begin(), Rml.end());
2175 // ThreadsManager::idle_loop() is where the threads are parked when they have no work
2176 // to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2177 // object for which the current thread is the master.
2179 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2181 assert(threadID >= 0 && threadID < MAX_THREADS);
2188 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2189 // master should exit as last one.
2190 if (allThreadsShouldExit)
2193 threads[threadID].state = Thread::TERMINATED;
2197 // If we are not thinking, wait for a condition to be signaled
2198 // instead of wasting CPU time polling for work.
2199 while ( threadID >= activeThreads
2200 || threads[threadID].state == Thread::INITIALIZING
2201 || (useSleepingThreads && threads[threadID].state == Thread::AVAILABLE))
2203 assert(!sp || useSleepingThreads);
2204 assert(threadID != 0 || useSleepingThreads);
2206 if (threads[threadID].state == Thread::INITIALIZING)
2207 threads[threadID].state = Thread::AVAILABLE;
2209 // Grab the lock to avoid races with Thread::wake_up()
2210 lock_grab(&threads[threadID].sleepLock);
2212 // If we are master and all slaves have finished do not go to sleep
2213 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2214 allFinished = (i == activeThreads);
2216 if (allFinished || allThreadsShouldExit)
2218 lock_release(&threads[threadID].sleepLock);
2222 // Do sleep here after retesting sleep conditions
2223 if (threadID >= activeThreads || threads[threadID].state == Thread::AVAILABLE)
2224 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2226 lock_release(&threads[threadID].sleepLock);
2229 // If this thread has been assigned work, launch a search
2230 if (threads[threadID].state == Thread::WORKISWAITING)
2232 assert(!allThreadsShouldExit);
2234 threads[threadID].state = Thread::SEARCHING;
2236 // Copy split point position and search stack and call search()
2237 // with SplitPoint template parameter set to true.
2238 SearchStack ss[PLY_MAX_PLUS_2];
2239 SplitPoint* tsp = threads[threadID].splitPoint;
2240 Position pos(*tsp->pos, threadID);
2242 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2246 search<SplitPointPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2248 search<SplitPointNonPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2250 assert(threads[threadID].state == Thread::SEARCHING);
2252 threads[threadID].state = Thread::AVAILABLE;
2254 // Wake up master thread so to allow it to return from the idle loop in
2255 // case we are the last slave of the split point.
2256 if ( useSleepingThreads
2257 && threadID != tsp->master
2258 && threads[tsp->master].state == Thread::AVAILABLE)
2259 threads[tsp->master].wake_up();
2262 // If this thread is the master of a split point and all slaves have
2263 // finished their work at this split point, return from the idle loop.
2264 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2265 allFinished = (i == activeThreads);
2269 // Because sp->slaves[] is reset under lock protection,
2270 // be sure sp->lock has been released before to return.
2271 lock_grab(&(sp->lock));
2272 lock_release(&(sp->lock));
2274 // In helpful master concept a master can help only a sub-tree, and
2275 // because here is all finished is not possible master is booked.
2276 assert(threads[threadID].state == Thread::AVAILABLE);
2278 threads[threadID].state = Thread::SEARCHING;