2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
40 #include "ucioption.h"
48 // Set to true to force running with one thread. Used for debugging
49 const bool FakeSplit = false;
51 // Different node types, used as template parameter
52 enum NodeType { Root, PV, NonPV, SplitPointPV, SplitPointNonPV };
54 // RootMove struct is used for moves at the root of the tree. For each root
55 // move, we store a score, a node count, and a PV (really a refutation
56 // in the case of moves which fail low). Score is normally set at
57 // -VALUE_INFINITE for all non-pv moves.
60 // RootMove::operator<() is the comparison function used when
61 // sorting the moves. A move m1 is considered to be better
62 // than a move m2 if it has an higher score
63 bool operator<(const RootMove& m) const { return score < m.score; }
65 void extract_pv_from_tt(Position& pos);
66 void insert_pv_in_tt(Position& pos);
74 // RootMoveList struct is mainly a std::vector of RootMove objects
75 struct RootMoveList : public std::vector<RootMove> {
77 void init(Position& pos, Move searchMoves[]);
78 RootMove* find(const Move& m, int startIndex = 0);
86 // Lookup table to check if a Piece is a slider and its access function
87 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
88 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
92 // Maximum depth for razoring
93 const Depth RazorDepth = 4 * ONE_PLY;
95 // Dynamic razoring margin based on depth
96 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
98 // Maximum depth for use of dynamic threat detection when null move fails low
99 const Depth ThreatDepth = 5 * ONE_PLY;
101 // Step 9. Internal iterative deepening
103 // Minimum depth for use of internal iterative deepening
104 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
106 // At Non-PV nodes we do an internal iterative deepening search
107 // when the static evaluation is bigger then beta - IIDMargin.
108 const Value IIDMargin = Value(0x100);
110 // Step 11. Decide the new search depth
112 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
113 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
114 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
115 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
116 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
118 // Minimum depth for use of singular extension
119 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
121 // Step 12. Futility pruning
123 // Futility margin for quiescence search
124 const Value FutilityMarginQS = Value(0x80);
126 // Futility lookup tables (initialized at startup) and their access functions
127 Value FutilityMargins[16][64]; // [depth][moveNumber]
128 int FutilityMoveCounts[32]; // [depth]
130 inline Value futility_margin(Depth d, int mn) {
132 return d < 7 * ONE_PLY ? FutilityMargins[Max(d, 1)][Min(mn, 63)]
133 : 2 * VALUE_INFINITE;
136 inline int futility_move_count(Depth d) {
138 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
141 // Step 14. Reduced search
143 // Reduction lookup tables (initialized at startup) and their access function
144 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
146 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
148 return (Depth) Reductions[PvNode][Min(d / ONE_PLY, 63)][Min(mn, 63)];
151 // Easy move margin. An easy move candidate must be at least this much
152 // better than the second best move.
153 const Value EasyMoveMargin = Value(0x200);
156 /// Namespace variables
162 int MultiPV, UCIMultiPV, MultiPVIteration;
164 // Time management variables
165 bool StopOnPonderhit, FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
170 std::ofstream LogFile;
172 // Skill level adjustment
174 bool SkillLevelEnabled;
176 // Node counters, used only by thread[0] but try to keep in different cache
177 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
178 bool SendSearchedNodes;
180 int NodesBetweenPolls = 30000;
188 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
190 template <NodeType NT>
191 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
193 template <NodeType NT>
194 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
196 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
197 bool connected_moves(const Position& pos, Move m1, Move m2);
198 Value value_to_tt(Value v, int ply);
199 Value value_from_tt(Value v, int ply);
200 bool can_return_tt(const TTEntry* tte, Depth depth, Value beta, int ply);
201 bool connected_threat(const Position& pos, Move m, Move threat);
202 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
203 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
204 void update_gains(const Position& pos, Move move, Value before, Value after);
205 void do_skill_level(Move* best, Move* ponder);
207 int current_search_time(int set = 0);
208 string score_to_uci(Value v, Value alpha = -VALUE_INFINITE, Value beta = VALUE_INFINITE);
209 string speed_to_uci(int64_t nodes);
210 string pv_to_uci(const Move pv[], int pvNum, bool chess960);
211 string pretty_pv(Position& pos, int depth, Value score, int time, Move pv[]);
212 string depth_to_uci(Depth depth);
213 void poll(const Position& pos);
214 void wait_for_stop_or_ponderhit();
216 // MovePickerExt template class extends MovePicker and allows to choose at compile
217 // time the proper moves source according to the type of node. In the default case
218 // we simply create and use a standard MovePicker object.
219 template<NodeType> struct MovePickerExt : public MovePicker {
221 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
222 : MovePicker(p, ttm, d, h, ss, b) {}
225 // In case of a SpNode we use split point's shared MovePicker object as moves source
226 template<> struct MovePickerExt<SplitPointNonPV> : 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), mp(ss->sp->mp) {}
231 Move get_next_move() { return mp->get_next_move(); }
235 template<> struct MovePickerExt<SplitPointPV> : public MovePickerExt<SplitPointNonPV> {
237 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
238 : MovePickerExt<SplitPointNonPV>(p, ttm, d, h, ss, b) {}
241 // Overload operator<<() to make it easier to print moves in a coordinate
242 // notation compatible with UCI protocol.
243 std::ostream& operator<<(std::ostream& os, Move m) {
245 bool chess960 = (os.iword(0) != 0); // See set960()
246 return os << move_to_uci(m, chess960);
249 // When formatting a move for std::cout we must know if we are in Chess960
250 // or not. To keep using the handy operator<<() on the move the trick is to
251 // embed this flag in the stream itself. Function-like named enum set960 is
252 // used as a custom manipulator and the stream internal general-purpose array,
253 // accessed through ios_base::iword(), is used to pass the flag to the move's
254 // operator<<() that will read it to properly format castling moves.
257 std::ostream& operator<< (std::ostream& os, const set960& f) {
259 os.iword(0) = int(f);
263 // extension() decides whether a move should be searched with normal depth,
264 // or with extended depth. Certain classes of moves (checking moves, in
265 // particular) are searched with bigger depth than ordinary moves and in
266 // any case are marked as 'dangerous'. Note that also if a move is not
267 // extended, as example because the corresponding UCI option is set to zero,
268 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
269 template <bool PvNode>
270 FORCE_INLINE Depth extension(const Position& pos, Move m, bool captureOrPromotion,
271 bool moveIsCheck, bool* dangerous) {
272 assert(m != MOVE_NONE);
274 Depth result = DEPTH_ZERO;
275 *dangerous = moveIsCheck;
277 if (moveIsCheck && pos.see_sign(m) >= 0)
278 result += CheckExtension[PvNode];
280 if (piece_type(pos.piece_on(move_from(m))) == PAWN)
282 Color c = pos.side_to_move();
283 if (relative_rank(c, move_to(m)) == RANK_7)
285 result += PawnPushTo7thExtension[PvNode];
288 if (pos.pawn_is_passed(c, move_to(m)))
290 result += PassedPawnExtension[PvNode];
295 if ( captureOrPromotion
296 && piece_type(pos.piece_on(move_to(m))) != PAWN
297 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
298 - piece_value_midgame(pos.piece_on(move_to(m))) == VALUE_ZERO)
299 && !move_is_special(m))
301 result += PawnEndgameExtension[PvNode];
305 return Min(result, ONE_PLY);
311 /// init_search() is called during startup to initialize various lookup tables
315 int d; // depth (ONE_PLY == 2)
316 int hd; // half depth (ONE_PLY == 1)
319 // Init reductions array
320 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
322 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
323 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
324 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
325 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
328 // Init futility margins array
329 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
330 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
332 // Init futility move count array
333 for (d = 0; d < 32; d++)
334 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
338 /// perft() is our utility to verify move generation. All the leaf nodes up to
339 /// the given depth are generated and counted and the sum returned.
341 int64_t perft(Position& pos, Depth depth) {
346 // Generate all legal moves
347 MoveList<MV_LEGAL> ml(pos);
349 // If we are at the last ply we don't need to do and undo
350 // the moves, just to count them.
351 if (depth <= ONE_PLY)
354 // Loop through all legal moves
356 for ( ; !ml.end(); ++ml)
358 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
359 sum += perft(pos, depth - ONE_PLY);
360 pos.undo_move(ml.move());
366 /// think() is the external interface to Stockfish's search, and is called when
367 /// the program receives the UCI 'go' command. It initializes various global
368 /// variables, and calls id_loop(). It returns false when a "quit" command is
369 /// received during the search.
371 bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
375 // Initialize global search-related variables
376 StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
378 current_search_time(get_system_time());
380 TimeMgr.init(Limits, pos.startpos_ply_counter());
382 // Set output steram in normal or chess960 mode
383 cout << set960(pos.is_chess960());
385 // Set best NodesBetweenPolls interval to avoid lagging under time pressure
387 NodesBetweenPolls = Min(Limits.maxNodes, 30000);
388 else if (Limits.time && Limits.time < 1000)
389 NodesBetweenPolls = 1000;
390 else if (Limits.time && Limits.time < 5000)
391 NodesBetweenPolls = 5000;
393 NodesBetweenPolls = 30000;
395 // Look for a book move
396 if (Options["OwnBook"].value<bool>())
398 if (Options["Book File"].value<string>() != book.name())
399 book.open(Options["Book File"].value<string>());
401 Move bookMove = book.get_move(pos, Options["Best Book Move"].value<bool>());
402 if (bookMove != MOVE_NONE)
405 wait_for_stop_or_ponderhit();
407 cout << "bestmove " << bookMove << endl;
413 UCIMultiPV = Options["MultiPV"].value<int>();
414 SkillLevel = Options["Skill Level"].value<int>();
416 read_evaluation_uci_options(pos.side_to_move());
417 Threads.read_uci_options();
419 // If needed allocate pawn and material hash tables and adjust TT size
420 Threads.init_hash_tables();
421 TT.set_size(Options["Hash"].value<int>());
423 if (Options["Clear Hash"].value<bool>())
425 Options["Clear Hash"].set_value("false");
429 // Do we have to play with skill handicap? In this case enable MultiPV that
430 // we will use behind the scenes to retrieve a set of possible moves.
431 SkillLevelEnabled = (SkillLevel < 20);
432 MultiPV = (SkillLevelEnabled ? Max(UCIMultiPV, 4) : UCIMultiPV);
434 // Wake up needed threads and reset maxPly counter
435 for (int i = 0; i < Threads.size(); i++)
437 Threads[i].wake_up();
438 Threads[i].maxPly = 0;
441 // Write to log file and keep it open to be accessed during the search
442 if (Options["Use Search Log"].value<bool>())
444 string name = Options["Search Log Filename"].value<string>();
445 LogFile.open(name.c_str(), std::ios::out | std::ios::app);
447 if (LogFile.is_open())
448 LogFile << "\nSearching: " << pos.to_fen()
449 << "\ninfinite: " << Limits.infinite
450 << " ponder: " << Limits.ponder
451 << " time: " << Limits.time
452 << " increment: " << Limits.increment
453 << " moves to go: " << Limits.movesToGo
457 // We're ready to start thinking. Call the iterative deepening loop function
458 Move ponderMove = MOVE_NONE;
459 Move bestMove = id_loop(pos, searchMoves, &ponderMove);
461 // Write final search statistics and close log file
462 if (LogFile.is_open())
464 int t = current_search_time();
466 LogFile << "Nodes: " << pos.nodes_searched()
467 << "\nNodes/second: " << (t > 0 ? pos.nodes_searched() * 1000 / t : 0)
468 << "\nBest move: " << move_to_san(pos, bestMove);
471 pos.do_move(bestMove, st);
472 LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
473 pos.undo_move(bestMove); // Return from think() with unchanged position
477 // This makes all the threads to go to sleep
480 // If we are pondering or in infinite search, we shouldn't print the
481 // best move before we are told to do so.
482 if (!StopRequest && (Limits.ponder || Limits.infinite))
483 wait_for_stop_or_ponderhit();
485 // Could be MOVE_NONE when searching on a stalemate position
486 cout << "bestmove " << bestMove;
488 // UCI protol is not clear on allowing sending an empty ponder move, instead
489 // it is clear that ponder move is optional. So skip it if empty.
490 if (ponderMove != MOVE_NONE)
491 cout << " ponder " << ponderMove;
501 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
502 // with increasing depth until the allocated thinking time has been consumed,
503 // user stops the search, or the maximum search depth is reached.
505 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
507 SearchStack ss[PLY_MAX_PLUS_2];
508 Value bestValues[PLY_MAX_PLUS_2];
509 int bestMoveChanges[PLY_MAX_PLUS_2];
510 int depth, aspirationDelta;
511 Value value, alpha, beta;
512 Move bestMove, easyMove, skillBest, skillPonder;
514 // Initialize stuff before a new search
515 memset(ss, 0, 4 * sizeof(SearchStack));
518 *ponderMove = bestMove = easyMove = skillBest = skillPonder = MOVE_NONE;
519 depth = aspirationDelta = 0;
520 value = alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
521 ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
523 // Moves to search are verified and copied
524 Rml.init(pos, searchMoves);
526 // Handle special case of searching on a mate/stalemate position
529 cout << "info" << depth_to_uci(DEPTH_ZERO)
530 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW, alpha, beta) << endl;
535 // Iterative deepening loop until requested to stop or target depth reached
536 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
538 // Save last iteration's scores, this needs to be done now, because in
539 // the following MultiPV loop Rml moves could be reordered.
540 for (size_t i = 0; i < Rml.size(); i++)
541 Rml[i].prevScore = Rml[i].score;
543 Rml.bestMoveChanges = 0;
545 // MultiPV iteration loop
546 for (MultiPVIteration = 0; MultiPVIteration < Min(MultiPV, (int)Rml.size()); MultiPVIteration++)
548 // Calculate dynamic aspiration window based on previous iterations
549 if (depth >= 5 && abs(Rml[MultiPVIteration].prevScore) < VALUE_KNOWN_WIN)
551 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
552 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
554 aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
555 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
557 alpha = Max(Rml[MultiPVIteration].prevScore - aspirationDelta, -VALUE_INFINITE);
558 beta = Min(Rml[MultiPVIteration].prevScore + aspirationDelta, VALUE_INFINITE);
562 alpha = -VALUE_INFINITE;
563 beta = VALUE_INFINITE;
566 // Start with a small aspiration window and, in case of fail high/low,
567 // research with bigger window until not failing high/low anymore.
569 // Search starting from ss+1 to allow calling update_gains()
570 value = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
572 // It is critical that sorting is done with a stable algorithm
573 // because all the values but the first are usually set to
574 // -VALUE_INFINITE and we want to keep the same order for all
575 // the moves but the new PV that goes to head.
576 sort<RootMove>(Rml.begin() + MultiPVIteration, Rml.end());
578 // In case we have found an exact score reorder the PV moves
579 // before leaving the fail high/low loop, otherwise leave the
580 // last PV move in its position so to be searched again.
581 if (value > alpha && value < beta)
582 sort<RootMove>(Rml.begin(), Rml.begin() + MultiPVIteration);
584 // Write PV back to transposition table in case the relevant entries
585 // have been overwritten during the search.
586 for (int i = 0; i <= MultiPVIteration; i++)
587 Rml[i].insert_pv_in_tt(pos);
589 // Value cannot be trusted. Break out immediately!
593 // Send full PV info to GUI if we are going to leave the loop or
594 // if we have a fail high/low and we are deep in the search.
595 if ((value > alpha && value < beta) || current_search_time() > 2000)
596 for (int i = 0; i < Min(UCIMultiPV, MultiPVIteration + 1); i++)
598 << depth_to_uci(depth * ONE_PLY)
599 << (i == MultiPVIteration ? score_to_uci(Rml[i].score, alpha, beta) :
600 score_to_uci(Rml[i].score))
601 << speed_to_uci(pos.nodes_searched())
602 << pv_to_uci(&Rml[i].pv[0], i + 1, pos.is_chess960())
605 // In case of failing high/low increase aspiration window and research,
606 // otherwise exit the fail high/low loop.
609 beta = Min(beta + aspirationDelta, VALUE_INFINITE);
610 aspirationDelta += aspirationDelta / 2;
612 else if (value <= alpha)
614 AspirationFailLow = true;
615 StopOnPonderhit = false;
617 alpha = Max(alpha - aspirationDelta, -VALUE_INFINITE);
618 aspirationDelta += aspirationDelta / 2;
623 } while (abs(value) < VALUE_KNOWN_WIN);
626 // Collect info about search result
627 bestMove = Rml[0].pv[0];
628 *ponderMove = Rml[0].pv[1];
629 bestValues[depth] = value;
630 bestMoveChanges[depth] = Rml.bestMoveChanges;
632 // Do we need to pick now the best and the ponder moves ?
633 if (SkillLevelEnabled && depth == 1 + SkillLevel)
634 do_skill_level(&skillBest, &skillPonder);
636 if (LogFile.is_open())
637 LogFile << pretty_pv(pos, depth, value, current_search_time(), &Rml[0].pv[0]) << endl;
639 // Init easyMove after first iteration or drop if differs from the best move
640 if (depth == 1 && (Rml.size() == 1 || Rml[0].score > Rml[1].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 if one move seems to be much better than the
649 // others or if there is only a single legal move. Also in the latter
650 // case we search up to some depth anyway to get a proper score.
652 && easyMove == bestMove
654 ||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
655 && current_search_time() > TimeMgr.available_time() / 16)
656 ||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
657 && current_search_time() > TimeMgr.available_time() / 32)))
660 // Take in account some extra time if the best move has changed
661 if (depth > 4 && depth < 50)
662 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
664 // Stop search if most of available time is already consumed. We probably don't
665 // have enough time to search the first move at the next iteration anyway.
666 if (current_search_time() > (TimeMgr.available_time() * 62) / 100)
669 // If we are allowed to ponder do not stop the search now but keep pondering
670 if (StopRequest && Limits.ponder)
673 StopOnPonderhit = true;
678 // When using skills overwrite best and ponder moves with the sub-optimal ones
679 if (SkillLevelEnabled)
681 if (skillBest == MOVE_NONE) // Still unassigned ?
682 do_skill_level(&skillBest, &skillPonder);
684 bestMove = skillBest;
685 *ponderMove = skillPonder;
692 // search<>() is the main search function for both PV and non-PV nodes and for
693 // normal and SplitPoint nodes. When called just after a split point the search
694 // is simpler because we have already probed the hash table, done a null move
695 // search, and searched the first move before splitting, we don't have to repeat
696 // all this work again. We also don't need to store anything to the hash table
697 // here: This is taken care of after we return from the split point.
699 template <NodeType NT>
700 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
702 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV);
703 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV);
704 const bool RootNode = (NT == Root);
706 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
707 assert(beta > alpha && beta <= VALUE_INFINITE);
708 assert(PvNode || alpha == beta - 1);
709 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
711 Move movesSearched[MAX_MOVES];
716 Move ttMove, move, excludedMove, threatMove;
719 Value bestValue, value, oldAlpha;
720 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
721 bool isPvMove, inCheck, singularExtensionNode, givesCheck, captureOrPromotion, dangerous;
722 int moveCount = 0, playedMoveCount = 0;
723 Thread& thread = Threads[pos.thread()];
724 SplitPoint* sp = NULL;
726 refinedValue = bestValue = value = -VALUE_INFINITE;
728 inCheck = pos.in_check();
729 ss->ply = (ss-1)->ply + 1;
731 // Used to send selDepth info to GUI
732 if (PvNode && thread.maxPly < ss->ply)
733 thread.maxPly = ss->ply;
735 // Step 1. Initialize node and poll. Polling can abort search
738 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
739 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
740 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
746 ttMove = excludedMove = MOVE_NONE;
747 threatMove = sp->threatMove;
748 goto split_point_start;
751 if (pos.thread() == 0 && ++NodesSincePoll > NodesBetweenPolls)
757 // Step 2. Check for aborted search and immediate draw
759 || pos.is_draw<false>()
760 || ss->ply > PLY_MAX) && !RootNode)
763 // Step 3. Mate distance pruning
766 alpha = Max(value_mated_in(ss->ply), alpha);
767 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();
777 tte = TT.probe(posKey);
778 ttMove = RootNode ? Rml[MultiPVIteration].pv[0] : tte ? tte->move() : MOVE_NONE;
780 // At PV nodes we check for exact scores, while at non-PV nodes we check for
781 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
782 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
783 // we should also update RootMoveList to avoid bogus output.
784 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
785 : can_return_tt(tte, depth, beta, ss->ply)))
788 ss->bestMove = ttMove; // Can be MOVE_NONE
789 return value_from_tt(tte->value(), ss->ply);
792 // Step 5. Evaluate the position statically and update parent's gain statistics
794 ss->eval = ss->evalMargin = VALUE_NONE;
797 assert(tte->static_value() != VALUE_NONE);
799 ss->eval = tte->static_value();
800 ss->evalMargin = tte->static_value_margin();
801 refinedValue = refine_eval(tte, ss->eval, ss->ply);
805 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
806 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
809 // Save gain for the parent non-capture move
810 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
812 // Step 6. Razoring (is omitted in PV nodes)
814 && depth < RazorDepth
816 && refinedValue + razor_margin(depth) < beta
817 && ttMove == MOVE_NONE
818 && abs(beta) < VALUE_MATE_IN_PLY_MAX
819 && !pos.has_pawn_on_7th(pos.side_to_move()))
821 Value rbeta = beta - razor_margin(depth);
822 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
824 // Logically we should return (v + razor_margin(depth)), but
825 // surprisingly this did slightly weaker in tests.
829 // Step 7. Static null move pruning (is omitted in PV nodes)
830 // We're betting that the opponent doesn't have a move that will reduce
831 // the score by more than futility_margin(depth) if we do a null move.
834 && depth < RazorDepth
836 && refinedValue - futility_margin(depth, 0) >= beta
837 && abs(beta) < VALUE_MATE_IN_PLY_MAX
838 && pos.non_pawn_material(pos.side_to_move()))
839 return refinedValue - futility_margin(depth, 0);
841 // Step 8. Null move search with verification search (is omitted in PV nodes)
846 && refinedValue >= beta
847 && abs(beta) < VALUE_MATE_IN_PLY_MAX
848 && pos.non_pawn_material(pos.side_to_move()))
850 ss->currentMove = MOVE_NULL;
852 // Null move dynamic reduction based on depth
853 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
855 // Null move dynamic reduction based on value
856 if (refinedValue - PawnValueMidgame > beta)
859 pos.do_null_move(st);
860 (ss+1)->skipNullMove = true;
861 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
862 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
863 (ss+1)->skipNullMove = false;
864 pos.undo_null_move();
866 if (nullValue >= beta)
868 // Do not return unproven mate scores
869 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
872 if (depth < 6 * ONE_PLY)
875 // Do verification search at high depths
876 ss->skipNullMove = true;
877 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
878 ss->skipNullMove = false;
885 // The null move failed low, which means that we may be faced with
886 // some kind of threat. If the previous move was reduced, check if
887 // the move that refuted the null move was somehow connected to the
888 // move which was reduced. If a connection is found, return a fail
889 // low score (which will cause the reduced move to fail high in the
890 // parent node, which will trigger a re-search with full depth).
891 threatMove = (ss+1)->bestMove;
893 if ( depth < ThreatDepth
895 && threatMove != MOVE_NONE
896 && connected_moves(pos, (ss-1)->currentMove, threatMove))
901 // Step 9. ProbCut (is omitted in PV nodes)
902 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
903 // and a reduced search returns a value much above beta, we can (almost) safely
904 // prune the previous move.
906 && depth >= RazorDepth + ONE_PLY
909 && excludedMove == MOVE_NONE
910 && abs(beta) < VALUE_MATE_IN_PLY_MAX)
912 Value rbeta = beta + 200;
913 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
915 assert(rdepth >= ONE_PLY);
917 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
920 while ((move = mp.get_next_move()) != MOVE_NONE)
921 if (pos.pl_move_is_legal(move, ci.pinned))
923 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
924 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
931 // Step 10. Internal iterative deepening
932 if ( depth >= IIDDepth[PvNode]
933 && ttMove == MOVE_NONE
934 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
936 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
938 ss->skipNullMove = true;
939 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
940 ss->skipNullMove = false;
942 tte = TT.probe(posKey);
943 ttMove = tte ? tte->move() : MOVE_NONE;
946 split_point_start: // At split points actual search starts from here
948 // Initialize a MovePicker object for the current position
949 MovePickerExt<NT> mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
951 ss->bestMove = MOVE_NONE;
952 futilityBase = ss->eval + ss->evalMargin;
953 singularExtensionNode = !RootNode
955 && depth >= SingularExtensionDepth[PvNode]
956 && ttMove != MOVE_NONE
957 && !excludedMove // Do not allow recursive singular extension search
958 && (tte->type() & VALUE_TYPE_LOWER)
959 && tte->depth() >= depth - 3 * ONE_PLY;
962 lock_grab(&(sp->lock));
963 bestValue = sp->bestValue;
966 // Step 11. Loop through moves
967 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
968 while ( bestValue < beta
969 && (move = mp.get_next_move()) != MOVE_NONE
970 && !thread.cutoff_occurred())
972 assert(move_is_ok(move));
974 if (move == excludedMove)
977 // At root obey the "searchmoves" option and skip moves not listed in Root Move List.
978 // Also in MultiPV mode we skip moves which already have got an exact score
979 // in previous MultiPV Iteration. Finally any illegal move is skipped here.
980 if (RootNode && !Rml.find(move, MultiPVIteration))
983 // At PV and SpNode nodes we want all moves to be legal since the beginning
984 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
989 moveCount = ++sp->moveCount;
990 lock_release(&(sp->lock));
997 // This is used by time management
998 FirstRootMove = (moveCount == 1);
1000 // Save the current node count before the move is searched
1001 nodes = pos.nodes_searched();
1003 // If it's time to send nodes info, do it here where we have the
1004 // correct accumulated node counts searched by each thread.
1005 if (SendSearchedNodes)
1007 SendSearchedNodes = false;
1008 cout << "info" << speed_to_uci(pos.nodes_searched()) << endl;
1011 // For long searches send current move info to GUI
1012 if (current_search_time() > 2000)
1013 cout << "info" << depth_to_uci(depth)
1014 << " currmove " << move
1015 << " currmovenumber " << moveCount + MultiPVIteration << endl;
1018 // At Root and at first iteration do a PV search on all the moves to score root moves
1019 isPvMove = (PvNode && moveCount <= (RootNode && depth <= ONE_PLY ? MAX_MOVES : 1));
1020 givesCheck = pos.move_gives_check(move, ci);
1021 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1023 // Step 12. Decide the new search depth
1024 ext = extension<PvNode>(pos, move, captureOrPromotion, givesCheck, &dangerous);
1026 // Singular extension search. If all moves but one fail low on a search of
1027 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1028 // is singular and should be extended. To verify this we do a reduced search
1029 // on all the other moves but the ttMove, if result is lower than ttValue minus
1030 // a margin then we extend ttMove.
1031 if ( singularExtensionNode
1033 && pos.pl_move_is_legal(move, ci.pinned)
1036 Value ttValue = value_from_tt(tte->value(), ss->ply);
1038 if (abs(ttValue) < VALUE_KNOWN_WIN)
1040 Value rBeta = ttValue - int(depth);
1041 ss->excludedMove = move;
1042 ss->skipNullMove = true;
1043 Value v = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1044 ss->skipNullMove = false;
1045 ss->excludedMove = MOVE_NONE;
1046 ss->bestMove = MOVE_NONE;
1052 // Update current move (this must be done after singular extension search)
1053 newDepth = depth - ONE_PLY + ext;
1055 // Step 13. Futility pruning (is omitted in PV nodes)
1057 && !captureOrPromotion
1061 && !move_is_castle(move))
1063 // Move count based pruning
1064 if ( moveCount >= futility_move_count(depth)
1065 && (!threatMove || !connected_threat(pos, move, threatMove))
1066 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1069 lock_grab(&(sp->lock));
1074 // Value based pruning
1075 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1076 // but fixing this made program slightly weaker.
1077 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
1078 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1079 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1081 if (futilityValueScaled < beta)
1085 lock_grab(&(sp->lock));
1086 if (futilityValueScaled > sp->bestValue)
1087 sp->bestValue = bestValue = futilityValueScaled;
1089 else if (futilityValueScaled > bestValue)
1090 bestValue = futilityValueScaled;
1095 // Prune moves with negative SEE at low depths
1096 if ( predictedDepth < 2 * ONE_PLY
1097 && bestValue > VALUE_MATED_IN_PLY_MAX
1098 && pos.see_sign(move) < 0)
1101 lock_grab(&(sp->lock));
1107 // Check for legality only before to do the move
1108 if (!pos.pl_move_is_legal(move, ci.pinned))
1114 ss->currentMove = move;
1115 if (!SpNode && !captureOrPromotion)
1116 movesSearched[playedMoveCount++] = move;
1118 // Step 14. Make the move
1119 pos.do_move(move, st, ci, givesCheck);
1121 // Step extra. pv search (only in PV nodes)
1122 // The first move in list is the expected PV
1124 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1125 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1128 // Step 15. Reduced depth search
1129 // If the move fails high will be re-searched at full depth.
1130 bool doFullDepthSearch = true;
1132 if ( depth > 3 * ONE_PLY
1133 && !captureOrPromotion
1135 && !move_is_castle(move)
1136 && ss->killers[0] != move
1137 && ss->killers[1] != move
1138 && (ss->reduction = reduction<PvNode>(depth, moveCount)) != DEPTH_ZERO)
1140 Depth d = newDepth - ss->reduction;
1141 alpha = SpNode ? sp->alpha : alpha;
1143 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1144 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1146 ss->reduction = DEPTH_ZERO;
1147 doFullDepthSearch = (value > alpha);
1150 // Step 16. Full depth search
1151 if (doFullDepthSearch)
1153 alpha = SpNode ? sp->alpha : alpha;
1154 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1155 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1157 // Step extra. pv search (only in PV nodes)
1158 // Search only for possible new PV nodes, if instead value >= beta then
1159 // parent node fails low with value <= alpha and tries another move.
1160 if (PvNode && value > alpha && (RootNode || value < beta))
1161 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1162 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1166 // Step 17. Undo move
1167 pos.undo_move(move);
1169 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1171 // Step 18. Check for new best move
1174 lock_grab(&(sp->lock));
1175 bestValue = sp->bestValue;
1179 if (value > bestValue)
1182 ss->bestMove = move;
1187 && value < beta) // We want always alpha < beta
1190 if (SpNode && !thread.cutoff_occurred())
1192 sp->bestValue = value;
1193 sp->ss->bestMove = move;
1195 sp->is_betaCutoff = (value >= beta);
1201 // Finished searching the move. If StopRequest is true, the search
1202 // was aborted because the user interrupted the search or because we
1203 // ran out of time. In this case, the return value of the search cannot
1204 // be trusted, and we break out of the loop without updating the best
1209 // Remember searched nodes counts for this move
1210 RootMove* rm = Rml.find(move);
1211 rm->nodes += pos.nodes_searched() - nodes;
1213 // PV move or new best move ?
1214 if (isPvMove || value > alpha)
1218 rm->extract_pv_from_tt(pos);
1220 // We record how often the best move has been changed in each
1221 // iteration. This information is used for time management: When
1222 // the best move changes frequently, we allocate some more time.
1223 if (!isPvMove && MultiPV == 1)
1224 Rml.bestMoveChanges++;
1231 // All other moves but the PV are set to the lowest value, this
1232 // is not a problem when sorting becuase sort is stable and move
1233 // position in the list is preserved, just the PV is pushed up.
1234 rm->score = -VALUE_INFINITE;
1238 // Step 19. Check for split
1241 && depth >= Threads.min_split_depth()
1243 && Threads.available_slave_exists(pos.thread())
1245 && !thread.cutoff_occurred())
1246 Threads.split<FakeSplit>(pos, ss, &alpha, beta, &bestValue, depth,
1247 threatMove, moveCount, &mp, PvNode);
1250 // Step 20. Check for mate and stalemate
1251 // All legal moves have been searched and if there are
1252 // no legal moves, it must be mate or stalemate.
1253 // If one move was excluded return fail low score.
1254 if (!SpNode && !moveCount)
1255 return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1257 // Step 21. Update tables
1258 // If the search is not aborted, update the transposition table,
1259 // history counters, and killer moves.
1260 if (!SpNode && !StopRequest && !thread.cutoff_occurred())
1262 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1263 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1264 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1266 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1268 // Update killers and history only for non capture moves that fails high
1269 if ( bestValue >= beta
1270 && !pos.move_is_capture_or_promotion(move))
1272 if (move != ss->killers[0])
1274 ss->killers[1] = ss->killers[0];
1275 ss->killers[0] = move;
1277 update_history(pos, move, depth, movesSearched, playedMoveCount);
1283 // Here we have the lock still grabbed
1284 sp->is_slave[pos.thread()] = false;
1285 sp->nodes += pos.nodes_searched();
1286 lock_release(&(sp->lock));
1289 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1294 // qsearch() is the quiescence search function, which is called by the main
1295 // search function when the remaining depth is zero (or, to be more precise,
1296 // less than ONE_PLY).
1298 template <NodeType NT>
1299 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1301 const bool PvNode = (NT == PV);
1303 assert(NT == PV || NT == NonPV);
1304 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1305 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1306 assert(PvNode || alpha == beta - 1);
1308 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
1312 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1313 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1316 Value oldAlpha = alpha;
1318 ss->bestMove = ss->currentMove = MOVE_NONE;
1319 ss->ply = (ss-1)->ply + 1;
1321 // Check for an instant draw or maximum ply reached
1322 if (pos.is_draw<true>() || ss->ply > PLY_MAX)
1325 // Decide whether or not to include checks, this fixes also the type of
1326 // TT entry depth that we are going to use. Note that in qsearch we use
1327 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1328 inCheck = pos.in_check();
1329 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1331 // Transposition table lookup. At PV nodes, we don't use the TT for
1332 // pruning, but only for move ordering.
1333 tte = TT.probe(pos.get_key());
1334 ttMove = (tte ? tte->move() : MOVE_NONE);
1336 if (!PvNode && tte && can_return_tt(tte, ttDepth, beta, ss->ply))
1338 ss->bestMove = ttMove; // Can be MOVE_NONE
1339 return value_from_tt(tte->value(), ss->ply);
1342 // Evaluate the position statically
1345 bestValue = futilityBase = -VALUE_INFINITE;
1346 ss->eval = evalMargin = VALUE_NONE;
1347 enoughMaterial = false;
1353 assert(tte->static_value() != VALUE_NONE);
1355 evalMargin = tte->static_value_margin();
1356 ss->eval = bestValue = tte->static_value();
1359 ss->eval = bestValue = evaluate(pos, evalMargin);
1361 // Stand pat. Return immediately if static value is at least beta
1362 if (bestValue >= beta)
1365 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1370 if (PvNode && bestValue > alpha)
1373 // Futility pruning parameters, not needed when in check
1374 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1375 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1378 // Initialize a MovePicker object for the current position, and prepare
1379 // to search the moves. Because the depth is <= 0 here, only captures,
1380 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1382 MovePicker mp(pos, ttMove, depth, H, move_to((ss-1)->currentMove));
1385 // Loop through the moves until no moves remain or a beta cutoff occurs
1386 while ( alpha < beta
1387 && (move = mp.get_next_move()) != MOVE_NONE)
1389 assert(move_is_ok(move));
1391 givesCheck = pos.move_gives_check(move, ci);
1399 && !move_is_promotion(move)
1400 && !pos.move_is_passed_pawn_push(move))
1402 futilityValue = futilityBase
1403 + piece_value_endgame(pos.piece_on(move_to(move)))
1404 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1406 if (futilityValue < alpha)
1408 if (futilityValue > bestValue)
1409 bestValue = futilityValue;
1413 // Prune moves with negative or equal SEE
1414 if ( futilityBase < beta
1415 && depth < DEPTH_ZERO
1416 && pos.see(move) <= 0)
1420 // Detect non-capture evasions that are candidate to be pruned
1421 evasionPrunable = !PvNode
1423 && bestValue > VALUE_MATED_IN_PLY_MAX
1424 && !pos.move_is_capture(move)
1425 && !pos.can_castle(pos.side_to_move());
1427 // Don't search moves with negative SEE values
1429 && (!inCheck || evasionPrunable)
1431 && !move_is_promotion(move)
1432 && pos.see_sign(move) < 0)
1435 // Don't search useless checks
1440 && !pos.move_is_capture_or_promotion(move)
1441 && ss->eval + PawnValueMidgame / 4 < beta
1442 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1444 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1445 bestValue = ss->eval + PawnValueMidgame / 4;
1450 // Check for legality only before to do the move
1451 if (!pos.pl_move_is_legal(move, ci.pinned))
1454 // Update current move
1455 ss->currentMove = move;
1457 // Make and search the move
1458 pos.do_move(move, st, ci, givesCheck);
1459 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1460 pos.undo_move(move);
1462 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1465 if (value > bestValue)
1471 ss->bestMove = move;
1476 // All legal moves have been searched. A special case: If we're in check
1477 // and no legal moves were found, it is checkmate.
1478 if (inCheck && bestValue == -VALUE_INFINITE)
1479 return value_mated_in(ss->ply);
1481 // Update transposition table
1482 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1483 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
1485 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1491 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1492 // bestValue is updated only when returning false because in that case move
1495 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1497 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1498 Square from, to, ksq, victimSq;
1501 Value futilityValue, bv = *bestValue;
1503 from = move_from(move);
1505 them = opposite_color(pos.side_to_move());
1506 ksq = pos.king_square(them);
1507 kingAtt = pos.attacks_from<KING>(ksq);
1508 pc = pos.piece_on(from);
1510 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1511 oldAtt = pos.attacks_from(pc, from, occ);
1512 newAtt = pos.attacks_from(pc, to, occ);
1514 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1515 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1517 if (!(b && (b & (b - 1))))
1520 // Rule 2. Queen contact check is very dangerous
1521 if ( piece_type(pc) == QUEEN
1522 && bit_is_set(kingAtt, to))
1525 // Rule 3. Creating new double threats with checks
1526 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1530 victimSq = pop_1st_bit(&b);
1531 futilityValue = futilityBase + piece_value_endgame(pos.piece_on(victimSq));
1533 // Note that here we generate illegal "double move"!
1534 if ( futilityValue >= beta
1535 && pos.see_sign(make_move(from, victimSq)) >= 0)
1538 if (futilityValue > bv)
1542 // Update bestValue only if check is not dangerous (because we will prune the move)
1548 // connected_moves() tests whether two moves are 'connected' in the sense
1549 // that the first move somehow made the second move possible (for instance
1550 // if the moving piece is the same in both moves). The first move is assumed
1551 // to be the move that was made to reach the current position, while the
1552 // second move is assumed to be a move from the current position.
1554 bool connected_moves(const Position& pos, Move m1, Move m2) {
1556 Square f1, t1, f2, t2;
1560 assert(m1 && move_is_ok(m1));
1561 assert(m2 && move_is_ok(m2));
1563 // Case 1: The moving piece is the same in both moves
1569 // Case 2: The destination square for m2 was vacated by m1
1575 // Case 3: Moving through the vacated square
1576 p2 = pos.piece_on(f2);
1577 if ( piece_is_slider(p2)
1578 && bit_is_set(squares_between(f2, t2), f1))
1581 // Case 4: The destination square for m2 is defended by the moving piece in m1
1582 p1 = pos.piece_on(t1);
1583 if (bit_is_set(pos.attacks_from(p1, t1), t2))
1586 // Case 5: Discovered check, checking piece is the piece moved in m1
1587 ksq = pos.king_square(pos.side_to_move());
1588 if ( piece_is_slider(p1)
1589 && bit_is_set(squares_between(t1, ksq), f2))
1591 Bitboard occ = pos.occupied_squares();
1592 clear_bit(&occ, f2);
1593 if (bit_is_set(pos.attacks_from(p1, t1, occ), ksq))
1600 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1601 // "plies to mate from the current ply". Non-mate scores are unchanged.
1602 // The function is called before storing a value to the transposition table.
1604 Value value_to_tt(Value v, int ply) {
1606 if (v >= VALUE_MATE_IN_PLY_MAX)
1609 if (v <= VALUE_MATED_IN_PLY_MAX)
1616 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1617 // the transposition table to a mate score corrected for the current ply.
1619 Value value_from_tt(Value v, int ply) {
1621 if (v >= VALUE_MATE_IN_PLY_MAX)
1624 if (v <= VALUE_MATED_IN_PLY_MAX)
1631 // connected_threat() tests whether it is safe to forward prune a move or if
1632 // is somehow connected to the threat move returned by null search.
1634 bool connected_threat(const Position& pos, Move m, Move threat) {
1636 assert(move_is_ok(m));
1637 assert(threat && move_is_ok(threat));
1638 assert(!pos.move_is_capture_or_promotion(m));
1639 assert(!pos.move_is_passed_pawn_push(m));
1641 Square mfrom, mto, tfrom, tto;
1643 mfrom = move_from(m);
1645 tfrom = move_from(threat);
1646 tto = move_to(threat);
1648 // Case 1: Don't prune moves which move the threatened piece
1652 // Case 2: If the threatened piece has value less than or equal to the
1653 // value of the threatening piece, don't prune moves which defend it.
1654 if ( pos.move_is_capture(threat)
1655 && ( piece_value_midgame(pos.piece_on(tfrom)) >= piece_value_midgame(pos.piece_on(tto))
1656 || piece_type(pos.piece_on(tfrom)) == KING)
1657 && pos.move_attacks_square(m, tto))
1660 // Case 3: If the moving piece in the threatened move is a slider, don't
1661 // prune safe moves which block its ray.
1662 if ( piece_is_slider(pos.piece_on(tfrom))
1663 && bit_is_set(squares_between(tfrom, tto), mto)
1664 && pos.see_sign(m) >= 0)
1671 // can_return_tt() returns true if a transposition table score
1672 // can be used to cut-off at a given point in search.
1674 bool can_return_tt(const TTEntry* tte, Depth depth, Value beta, int ply) {
1676 Value v = value_from_tt(tte->value(), ply);
1678 return ( tte->depth() >= depth
1679 || v >= Max(VALUE_MATE_IN_PLY_MAX, beta)
1680 || v < Min(VALUE_MATED_IN_PLY_MAX, beta))
1682 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1683 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1687 // refine_eval() returns the transposition table score if
1688 // possible otherwise falls back on static position evaluation.
1690 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1694 Value v = value_from_tt(tte->value(), ply);
1696 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1697 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1704 // update_history() registers a good move that produced a beta-cutoff
1705 // in history and marks as failures all the other moves of that ply.
1707 void update_history(const Position& pos, Move move, Depth depth,
1708 Move movesSearched[], int moveCount) {
1710 Value bonus = Value(int(depth) * int(depth));
1712 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1714 for (int i = 0; i < moveCount - 1; i++)
1716 m = movesSearched[i];
1720 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1725 // update_gains() updates the gains table of a non-capture move given
1726 // the static position evaluation before and after the move.
1728 void update_gains(const Position& pos, Move m, Value before, Value after) {
1731 && before != VALUE_NONE
1732 && after != VALUE_NONE
1733 && pos.captured_piece_type() == PIECE_TYPE_NONE
1734 && !move_is_special(m))
1735 H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1739 // current_search_time() returns the number of milliseconds which have passed
1740 // since the beginning of the current search.
1742 int current_search_time(int set) {
1744 static int searchStartTime;
1747 searchStartTime = set;
1749 return get_system_time() - searchStartTime;
1753 // score_to_uci() converts a value to a string suitable for use with the UCI
1754 // protocol specifications:
1756 // cp <x> The score from the engine's point of view in centipawns.
1757 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1758 // use negative values for y.
1760 string score_to_uci(Value v, Value alpha, Value beta) {
1762 std::stringstream s;
1764 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1765 s << " score cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1767 s << " score mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1769 s << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1775 // speed_to_uci() returns a string with time stats of current search suitable
1776 // to be sent to UCI gui.
1778 string speed_to_uci(int64_t nodes) {
1780 std::stringstream s;
1781 int t = current_search_time();
1783 s << " nodes " << nodes
1784 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1790 // pv_to_uci() returns a string with information on the current PV line
1791 // formatted according to UCI specification.
1793 string pv_to_uci(const Move pv[], int pvNum, bool chess960) {
1795 std::stringstream s;
1797 s << " multipv " << pvNum << " pv " << set960(chess960);
1799 for ( ; *pv != MOVE_NONE; pv++)
1805 // depth_to_uci() returns a string with information on the current depth and
1806 // seldepth formatted according to UCI specification.
1808 string depth_to_uci(Depth depth) {
1810 std::stringstream s;
1812 // Retrieve max searched depth among threads
1814 for (int i = 0; i < Threads.size(); i++)
1815 if (Threads[i].maxPly > selDepth)
1816 selDepth = Threads[i].maxPly;
1818 s << " depth " << depth / ONE_PLY << " seldepth " << selDepth;
1823 string time_to_string(int millisecs) {
1825 const int MSecMinute = 1000 * 60;
1826 const int MSecHour = 1000 * 60 * 60;
1828 int hours = millisecs / MSecHour;
1829 int minutes = (millisecs % MSecHour) / MSecMinute;
1830 int seconds = ((millisecs % MSecHour) % MSecMinute) / 1000;
1832 std::stringstream s;
1837 s << std::setfill('0') << std::setw(2) << minutes << ':' << std::setw(2) << seconds;
1841 string score_to_string(Value v) {
1843 std::stringstream s;
1845 if (v >= VALUE_MATE_IN_PLY_MAX)
1846 s << "#" << (VALUE_MATE - v + 1) / 2;
1847 else if (v <= VALUE_MATED_IN_PLY_MAX)
1848 s << "-#" << (VALUE_MATE + v) / 2;
1850 s << std::setprecision(2) << std::fixed << std::showpos << float(v) / PawnValueMidgame;
1855 // pretty_pv() creates a human-readable string from a position and a PV.
1856 // It is used to write search information to the log file (which is created
1857 // when the UCI parameter "Use Search Log" is "true").
1859 string pretty_pv(Position& pos, int depth, Value value, int time, Move pv[]) {
1861 const int64_t K = 1000;
1862 const int64_t M = 1000000;
1863 const int startColumn = 28;
1864 const size_t maxLength = 80 - startColumn;
1866 StateInfo state[PLY_MAX_PLUS_2], *st = state;
1869 std::stringstream s;
1872 // First print depth, score, time and searched nodes...
1873 s << set960(pos.is_chess960())
1874 << std::setw(2) << depth
1875 << std::setw(8) << score_to_string(value)
1876 << std::setw(8) << time_to_string(time);
1878 if (pos.nodes_searched() < M)
1879 s << std::setw(8) << pos.nodes_searched() / 1 << " ";
1880 else if (pos.nodes_searched() < K * M)
1881 s << std::setw(7) << pos.nodes_searched() / K << "K ";
1883 s << std::setw(7) << pos.nodes_searched() / M << "M ";
1885 // ...then print the full PV line in short algebraic notation
1886 while (*m != MOVE_NONE)
1888 san = move_to_san(pos, *m);
1889 length += san.length() + 1;
1891 if (length > maxLength)
1893 length = san.length() + 1;
1894 s << "\n" + string(startColumn, ' ');
1898 pos.do_move(*m++, *st++);
1901 // Restore original position before to leave
1902 while (m != pv) pos.undo_move(*--m);
1907 // poll() performs two different functions: It polls for user input, and it
1908 // looks at the time consumed so far and decides if it's time to abort the
1911 void poll(const Position& pos) {
1913 static int lastInfoTime;
1914 int t = current_search_time();
1917 if (input_available())
1919 // We are line oriented, don't read single chars
1922 if (!std::getline(std::cin, command) || command == "quit")
1924 // Quit the program as soon as possible
1925 Limits.ponder = false;
1926 QuitRequest = StopRequest = true;
1929 else if (command == "stop")
1931 // Stop calculating as soon as possible, but still send the "bestmove"
1932 // and possibly the "ponder" token when finishing the search.
1933 Limits.ponder = false;
1936 else if (command == "ponderhit")
1938 // The opponent has played the expected move. GUI sends "ponderhit" if
1939 // we were told to ponder on the same move the opponent has played. We
1940 // should continue searching but switching from pondering to normal search.
1941 Limits.ponder = false;
1943 if (StopOnPonderhit)
1948 // Print search information
1952 else if (lastInfoTime > t)
1953 // HACK: Must be a new search where we searched less than
1954 // NodesBetweenPolls nodes during the first second of search.
1957 else if (t - lastInfoTime >= 1000)
1962 dbg_print_hit_rate();
1964 // Send info on searched nodes as soon as we return to root
1965 SendSearchedNodes = true;
1968 // Should we stop the search?
1972 bool stillAtFirstMove = FirstRootMove
1973 && !AspirationFailLow
1974 && t > TimeMgr.available_time();
1976 bool noMoreTime = t > TimeMgr.maximum_time()
1977 || stillAtFirstMove;
1979 if ( (Limits.useTimeManagement() && noMoreTime)
1980 || (Limits.maxTime && t >= Limits.maxTime)
1981 || (Limits.maxNodes && pos.nodes_searched() >= Limits.maxNodes)) // FIXME
1986 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
1987 // while the program is pondering. The point is to work around a wrinkle in
1988 // the UCI protocol: When pondering, the engine is not allowed to give a
1989 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
1990 // We simply wait here until one of these commands is sent, and return,
1991 // after which the bestmove and pondermove will be printed.
1993 void wait_for_stop_or_ponderhit() {
1997 // Wait for a command from stdin
1998 while ( std::getline(std::cin, command)
1999 && command != "ponderhit" && command != "stop" && command != "quit") {};
2001 if (command != "ponderhit" && command != "stop")
2002 QuitRequest = true; // Must be "quit" or getline() returned false
2006 // When playing with strength handicap choose best move among the MultiPV set
2007 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
2008 void do_skill_level(Move* best, Move* ponder) {
2010 assert(MultiPV > 1);
2014 // Rml list is already sorted by score in descending order
2016 int max_s = -VALUE_INFINITE;
2017 int size = Min(MultiPV, (int)Rml.size());
2018 int max = Rml[0].score;
2019 int var = Min(max - Rml[size - 1].score, PawnValueMidgame);
2020 int wk = 120 - 2 * SkillLevel;
2022 // PRNG sequence should be non deterministic
2023 for (int i = abs(get_system_time() % 50); i > 0; i--)
2024 rk.rand<unsigned>();
2026 // Choose best move. For each move's score we add two terms both dependent
2027 // on wk, one deterministic and bigger for weaker moves, and one random,
2028 // then we choose the move with the resulting highest score.
2029 for (int i = 0; i < size; i++)
2033 // Don't allow crazy blunders even at very low skills
2034 if (i > 0 && Rml[i-1].score > s + EasyMoveMargin)
2037 // This is our magical formula
2038 s += ((max - s) * wk + var * (rk.rand<unsigned>() % wk)) / 128;
2043 *best = Rml[i].pv[0];
2044 *ponder = Rml[i].pv[1];
2050 /// RootMove and RootMoveList method's definitions
2052 void RootMoveList::init(Position& pos, Move searchMoves[]) {
2055 bestMoveChanges = 0;
2058 // Generate all legal moves and add them to RootMoveList
2059 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
2061 // If we have a searchMoves[] list then verify the move
2062 // is in the list before to add it.
2063 for (sm = searchMoves; *sm && *sm != ml.move(); sm++) {}
2065 if (sm != searchMoves && *sm != ml.move())
2069 rm.pv.push_back(ml.move());
2070 rm.pv.push_back(MOVE_NONE);
2071 rm.score = rm.prevScore = -VALUE_INFINITE;
2077 RootMove* RootMoveList::find(const Move& m, int startIndex) {
2079 for (size_t i = startIndex; i < size(); i++)
2080 if ((*this)[i].pv[0] == m)
2086 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2087 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2088 // allow to always have a ponder move even when we fail high at root and also a
2089 // long PV to print that is important for position analysis.
2091 void RootMove::extract_pv_from_tt(Position& pos) {
2093 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2098 assert(m != MOVE_NONE && pos.move_is_pl(m));
2102 pos.do_move(m, *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.push_back(tte->move());
2112 pos.do_move(tte->move(), *st++);
2115 pv.push_back(MOVE_NONE);
2117 do pos.undo_move(pv[--ply]); while (ply);
2120 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2121 // the PV back into the TT. This makes sure the old PV moves are searched
2122 // first, even if the old TT entries have been overwritten.
2124 void RootMove::insert_pv_in_tt(Position& pos) {
2126 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2129 Value v, m = VALUE_NONE;
2132 assert(pv[0] != MOVE_NONE && pos.move_is_pl(pv[0]));
2138 // Don't overwrite existing correct entries
2139 if (!tte || tte->move() != pv[ply])
2141 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
2142 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2144 pos.do_move(pv[ply], *st++);
2146 } while (pv[++ply] != MOVE_NONE);
2148 do pos.undo_move(pv[--ply]); while (ply);
2153 // ThreadsManager::idle_loop() is where the threads are parked when they have no work
2154 // to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2155 // object for which the current thread is the master.
2157 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2159 assert(threadID >= 0 && threadID < MAX_THREADS);
2166 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2167 // master should exit as last one.
2168 if (allThreadsShouldExit)
2171 threads[threadID].state = Thread::TERMINATED;
2175 // If we are not thinking, wait for a condition to be signaled
2176 // instead of wasting CPU time polling for work.
2177 while ( threadID >= activeThreads
2178 || threads[threadID].state == Thread::INITIALIZING
2179 || (useSleepingThreads && threads[threadID].state == Thread::AVAILABLE))
2181 assert(!sp || useSleepingThreads);
2182 assert(threadID != 0 || useSleepingThreads);
2184 if (threads[threadID].state == Thread::INITIALIZING)
2185 threads[threadID].state = Thread::AVAILABLE;
2187 // Grab the lock to avoid races with Thread::wake_up()
2188 lock_grab(&threads[threadID].sleepLock);
2190 // If we are master and all slaves have finished do not go to sleep
2191 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2192 allFinished = (i == activeThreads);
2194 if (allFinished || allThreadsShouldExit)
2196 lock_release(&threads[threadID].sleepLock);
2200 // Do sleep here after retesting sleep conditions
2201 if (threadID >= activeThreads || threads[threadID].state == Thread::AVAILABLE)
2202 cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
2204 lock_release(&threads[threadID].sleepLock);
2207 // If this thread has been assigned work, launch a search
2208 if (threads[threadID].state == Thread::WORKISWAITING)
2210 assert(!allThreadsShouldExit);
2212 threads[threadID].state = Thread::SEARCHING;
2214 // Copy split point position and search stack and call search()
2215 // with SplitPoint template parameter set to true.
2216 SearchStack ss[PLY_MAX_PLUS_2];
2217 SplitPoint* tsp = threads[threadID].splitPoint;
2218 Position pos(*tsp->pos, threadID);
2220 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2224 search<SplitPointPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2226 search<SplitPointNonPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2228 assert(threads[threadID].state == Thread::SEARCHING);
2230 threads[threadID].state = Thread::AVAILABLE;
2232 // Wake up master thread so to allow it to return from the idle loop in
2233 // case we are the last slave of the split point.
2234 if ( useSleepingThreads
2235 && threadID != tsp->master
2236 && threads[tsp->master].state == Thread::AVAILABLE)
2237 threads[tsp->master].wake_up();
2240 // If this thread is the master of a split point and all slaves have
2241 // finished their work at this split point, return from the idle loop.
2242 for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
2243 allFinished = (i == activeThreads);
2247 // Because sp->slaves[] is reset under lock protection,
2248 // be sure sp->lock has been released before to return.
2249 lock_grab(&(sp->lock));
2250 lock_release(&(sp->lock));
2252 // In helpful master concept a master can help only a sub-tree, and
2253 // because here is all finished is not possible master is booked.
2254 assert(threads[threadID].state == Thread::AVAILABLE);
2256 threads[threadID].state = Thread::SEARCHING;