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"
47 std::vector<Move> SearchMoves;
48 Position* RootPosition;
52 // Set to true to force running with one thread. Used for debugging
53 const bool FakeSplit = false;
55 // Different node types, used as template parameter
56 enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
58 // RootMove struct is used for moves at the root of the tree. For each root
59 // move, we store a score, a node count, and a PV (really a refutation
60 // in the case of moves which fail low). Score is normally set at
61 // -VALUE_INFINITE for all non-pv moves.
64 // RootMove::operator<() is the comparison function used when
65 // sorting the moves. A move m1 is considered to be better
66 // than a move m2 if it has an higher score
67 bool operator<(const RootMove& m) const { return score < m.score; }
69 void extract_pv_from_tt(Position& pos);
70 void insert_pv_in_tt(Position& pos);
78 // RootMoveList struct is mainly a std::vector of RootMove objects
79 struct RootMoveList : public std::vector<RootMove> {
81 void init(Position& pos, Move searchMoves[]);
82 RootMove* find(const Move& m, int startIndex = 0);
90 // Lookup table to check if a Piece is a slider and its access function
91 const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
92 inline bool piece_is_slider(Piece p) { return Slidings[p]; }
96 // Maximum depth for razoring
97 const Depth RazorDepth = 4 * ONE_PLY;
99 // Dynamic razoring margin based on depth
100 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
102 // Maximum depth for use of dynamic threat detection when null move fails low
103 const Depth ThreatDepth = 5 * ONE_PLY;
105 // Step 9. Internal iterative deepening
107 // Minimum depth for use of internal iterative deepening
108 const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
110 // At Non-PV nodes we do an internal iterative deepening search
111 // when the static evaluation is bigger then beta - IIDMargin.
112 const Value IIDMargin = Value(0x100);
114 // Step 11. Decide the new search depth
116 // Extensions. Array index 0 is used for non-PV nodes, index 1 for PV nodes
117 const Depth CheckExtension[] = { ONE_PLY / 2, ONE_PLY / 1 };
118 const Depth PawnEndgameExtension[] = { ONE_PLY / 1, ONE_PLY / 1 };
119 const Depth PawnPushTo7thExtension[] = { ONE_PLY / 2, ONE_PLY / 2 };
120 const Depth PassedPawnExtension[] = { DEPTH_ZERO, ONE_PLY / 2 };
122 // Minimum depth for use of singular extension
123 const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
125 // Step 12. Futility pruning
127 // Futility margin for quiescence search
128 const Value FutilityMarginQS = Value(0x80);
130 // Futility lookup tables (initialized at startup) and their access functions
131 Value FutilityMargins[16][64]; // [depth][moveNumber]
132 int FutilityMoveCounts[32]; // [depth]
134 inline Value futility_margin(Depth d, int mn) {
136 return d < 7 * ONE_PLY ? FutilityMargins[std::max(int(d), 1)][std::min(mn, 63)]
137 : 2 * VALUE_INFINITE;
140 inline int futility_move_count(Depth d) {
142 return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
145 // Step 14. Reduced search
147 // Reduction lookup tables (initialized at startup) and their access function
148 int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
150 template <bool PvNode> inline Depth reduction(Depth d, int mn) {
152 return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
155 // Easy move margin. An easy move candidate must be at least this much
156 // better than the second best move.
157 const Value EasyMoveMargin = Value(0x150);
160 /// Namespace variables
166 int MultiPV, UCIMultiPV, MultiPVIdx;
168 // Time management variables
169 volatile bool StopOnPonderhit, FirstRootMove, StopRequest, AspirationFailLow;
172 // Skill level adjustment
174 bool SkillLevelEnabled;
182 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
184 template <NodeType NT>
185 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
187 template <NodeType NT>
188 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth);
190 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
191 bool connected_moves(const Position& pos, Move m1, Move m2);
192 Value value_to_tt(Value v, int ply);
193 Value value_from_tt(Value v, int ply);
194 bool can_return_tt(const TTEntry* tte, Depth depth, Value beta, int ply);
195 bool connected_threat(const Position& pos, Move m, Move threat);
196 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
197 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
198 void do_skill_level(Move* best, Move* ponder);
200 int elapsed_search_time(int set = 0);
201 string score_to_uci(Value v, Value alpha = -VALUE_INFINITE, Value beta = VALUE_INFINITE);
202 string speed_to_uci(int64_t nodes);
203 string pv_to_uci(const Move pv[], int pvNum, bool chess960);
204 string pretty_pv(Position& pos, int depth, Value score, int time, Move pv[]);
205 string depth_to_uci(Depth depth);
207 // MovePickerExt template class extends MovePicker and allows to choose at compile
208 // time the proper moves source according to the type of node. In the default case
209 // we simply create and use a standard MovePicker object.
210 template<bool SpNode> struct MovePickerExt : public MovePicker {
212 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
213 : MovePicker(p, ttm, d, h, ss, b) {}
216 // In case of a SpNode we use split point's shared MovePicker object as moves source
217 template<> struct MovePickerExt<true> : public MovePicker {
219 MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
220 : MovePicker(p, ttm, d, h, ss, b), mp(ss->sp->mp) {}
222 Move get_next_move() { return mp->get_next_move(); }
226 // Overload operator<<() to make it easier to print moves in a coordinate
227 // notation compatible with UCI protocol.
228 std::ostream& operator<<(std::ostream& os, Move m) {
230 bool chess960 = (os.iword(0) != 0); // See set960()
231 return os << move_to_uci(m, chess960);
234 // When formatting a move for std::cout we must know if we are in Chess960
235 // or not. To keep using the handy operator<<() on the move the trick is to
236 // embed this flag in the stream itself. Function-like named enum set960 is
237 // used as a custom manipulator and the stream internal general-purpose array,
238 // accessed through ios_base::iword(), is used to pass the flag to the move's
239 // operator<<() that will read it to properly format castling moves.
242 std::ostream& operator<< (std::ostream& os, const set960& f) {
244 os.iword(0) = int(f);
248 // extension() decides whether a move should be searched with normal depth,
249 // or with extended depth. Certain classes of moves (checking moves, in
250 // particular) are searched with bigger depth than ordinary moves and in
251 // any case are marked as 'dangerous'. Note that also if a move is not
252 // extended, as example because the corresponding UCI option is set to zero,
253 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
254 template <bool PvNode>
255 FORCE_INLINE Depth extension(const Position& pos, Move m, bool captureOrPromotion,
256 bool moveIsCheck, bool* dangerous) {
257 assert(m != MOVE_NONE);
259 Depth result = DEPTH_ZERO;
260 *dangerous = moveIsCheck;
262 if (moveIsCheck && pos.see_sign(m) >= 0)
263 result += CheckExtension[PvNode];
265 if (type_of(pos.piece_on(move_from(m))) == PAWN)
267 Color c = pos.side_to_move();
268 if (relative_rank(c, move_to(m)) == RANK_7)
270 result += PawnPushTo7thExtension[PvNode];
273 if (pos.pawn_is_passed(c, move_to(m)))
275 result += PassedPawnExtension[PvNode];
280 if ( captureOrPromotion
281 && type_of(pos.piece_on(move_to(m))) != PAWN
282 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
283 - PieceValueMidgame[pos.piece_on(move_to(m))] == VALUE_ZERO)
286 result += PawnEndgameExtension[PvNode];
290 return std::min(result, ONE_PLY);
296 /// init_search() is called during startup to initialize various lookup tables
300 int d; // depth (ONE_PLY == 2)
301 int hd; // half depth (ONE_PLY == 1)
304 // Init reductions array
305 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
307 double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
308 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
309 Reductions[1][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
310 Reductions[0][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
313 // Init futility margins array
314 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
315 FutilityMargins[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
317 // Init futility move count array
318 for (d = 0; d < 32; d++)
319 FutilityMoveCounts[d] = int(3.001 + 0.25 * pow(d, 2.0));
323 /// perft() is our utility to verify move generation. All the leaf nodes up to
324 /// the given depth are generated and counted and the sum returned.
326 int64_t perft(Position& pos, Depth depth) {
331 // Generate all legal moves
332 MoveList<MV_LEGAL> ml(pos);
334 // If we are at the last ply we don't need to do and undo
335 // the moves, just to count them.
336 if (depth <= ONE_PLY)
339 // Loop through all legal moves
341 for ( ; !ml.end(); ++ml)
343 pos.do_move(ml.move(), st, ci, pos.move_gives_check(ml.move(), ci));
344 sum += perft(pos, depth - ONE_PLY);
345 pos.undo_move(ml.move());
351 /// think() is the external interface to Stockfish's search, and is called when
352 /// the program receives the UCI 'go' command. It initializes various global
353 /// variables, and calls id_loop(). It returns false when a "quit" command is
354 /// received during the search.
358 static Book book; // Defined static to initialize the PRNG only once
360 Position& pos = *RootPosition;
362 // Save "search start" time and reset elapsed time to zero
363 elapsed_search_time(get_system_time());
365 // Initialize global search-related variables
366 StopOnPonderhit = StopRequest = AspirationFailLow = false;
368 // Set output stream mode: normal or chess960. Castling notation is different
369 cout << set960(pos.is_chess960());
371 // Look for a book move
372 if (Options["OwnBook"].value<bool>())
374 if (Options["Book File"].value<string>() != book.name())
375 book.open(Options["Book File"].value<string>());
377 Move bookMove = book.probe(pos, Options["Best Book Move"].value<bool>());
378 if (bookMove != MOVE_NONE)
380 if (!StopRequest && (Limits.ponder || Limits.infinite))
381 Threads.wait_for_stop_or_ponderhit();
383 cout << "bestmove " << bookMove << endl;
388 // Read UCI options: GUI could change UCI parameters during the game
389 read_evaluation_uci_options(pos.side_to_move());
390 Threads.read_uci_options();
392 // Set a new TT size if changed
393 TT.set_size(Options["Hash"].value<int>());
395 if (Options["Clear Hash"].value<bool>())
397 Options["Clear Hash"].set_value("false");
401 UCIMultiPV = Options["MultiPV"].value<int>();
402 SkillLevel = Options["Skill Level"].value<int>();
404 // Do we have to play with skill handicap? In this case enable MultiPV that
405 // we will use behind the scenes to retrieve a set of possible moves.
406 SkillLevelEnabled = (SkillLevel < 20);
407 MultiPV = (SkillLevelEnabled ? std::max(UCIMultiPV, 4) : UCIMultiPV);
409 // Write current search header to log file
410 if (Options["Use Search Log"].value<bool>())
412 Log log(Options["Search Log Filename"].value<string>());
413 log << "\nSearching: " << pos.to_fen()
414 << "\ninfinite: " << Limits.infinite
415 << " ponder: " << Limits.ponder
416 << " time: " << Limits.time
417 << " increment: " << Limits.increment
418 << " moves to go: " << Limits.movesToGo
422 // Wake up needed threads and reset maxPly counter
423 for (int i = 0; i < Threads.size(); i++)
425 Threads[i].maxPly = 0;
426 Threads[i].wake_up();
429 // Set best timer interval to avoid lagging under time pressure. Timer is
430 // used to check for remaining available thinking time.
431 TimeMgr.init(Limits, pos.startpos_ply_counter());
433 if (TimeMgr.available_time())
434 Threads.set_timer(std::min(100, std::max(TimeMgr.available_time() / 8, 20)));
436 Threads.set_timer(100);
438 // We're ready to start thinking. Call the iterative deepening loop function
439 Move ponderMove = MOVE_NONE;
440 Move bestMove = id_loop(pos, &SearchMoves[0], &ponderMove);
442 // Stop timer, no need to check for available time any more
443 Threads.set_timer(0);
445 // This makes all the slave threads to go to sleep, if not already sleeping
448 // Write current search final statistics to log file
449 if (Options["Use Search Log"].value<bool>())
451 int e = elapsed_search_time();
453 Log log(Options["Search Log Filename"].value<string>());
454 log << "Nodes: " << pos.nodes_searched()
455 << "\nNodes/second: " << (e > 0 ? pos.nodes_searched() * 1000 / e : 0)
456 << "\nBest move: " << move_to_san(pos, bestMove);
459 pos.do_move(bestMove, st);
460 log << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
461 pos.undo_move(bestMove); // Return from think() with unchanged position
464 // When we reach max depth we arrive here even without a StopRequest, but if
465 // we are pondering or in infinite search, we shouldn't print the best move
466 // before we are told to do so.
467 if (!StopRequest && (Limits.ponder || Limits.infinite))
468 Threads.wait_for_stop_or_ponderhit();
470 // Could be MOVE_NONE when searching on a stalemate position
471 cout << "bestmove " << bestMove;
473 // UCI protol is not clear on allowing sending an empty ponder move, instead
474 // it is clear that ponder move is optional. So skip it if empty.
475 if (ponderMove != MOVE_NONE)
476 cout << " ponder " << ponderMove;
484 // id_loop() is the main iterative deepening loop. It calls search() repeatedly
485 // with increasing depth until the allocated thinking time has been consumed,
486 // user stops the search, or the maximum search depth is reached.
488 Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
490 SearchStack ss[PLY_MAX_PLUS_2];
491 Value bestValues[PLY_MAX_PLUS_2];
492 int bestMoveChanges[PLY_MAX_PLUS_2];
493 int depth, aspirationDelta;
494 Value bestValue, alpha, beta;
495 Move bestMove, skillBest, skillPonder;
496 bool bestMoveNeverChanged = true;
498 // Initialize stuff before a new search
499 memset(ss, 0, 4 * sizeof(SearchStack));
502 *ponderMove = bestMove = skillBest = skillPonder = MOVE_NONE;
503 depth = aspirationDelta = 0;
504 bestValue = alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
505 ss->currentMove = MOVE_NULL; // Hack to skip update gains
507 // Moves to search are verified and copied
508 Rml.init(pos, searchMoves);
510 // Handle special case of searching on a mate/stalemate position
513 cout << "info" << depth_to_uci(DEPTH_ZERO)
514 << score_to_uci(pos.in_check() ? -VALUE_MATE : VALUE_DRAW, alpha, beta) << endl;
519 // Iterative deepening loop until requested to stop or target depth reached
520 while (!StopRequest && ++depth <= PLY_MAX && (!Limits.maxDepth || depth <= Limits.maxDepth))
522 // Save now last iteration's scores, before Rml moves are reordered
523 for (size_t i = 0; i < Rml.size(); i++)
524 Rml[i].prevScore = Rml[i].score;
526 Rml.bestMoveChanges = 0;
528 // MultiPV loop. We perform a full root search for each PV line
529 for (MultiPVIdx = 0; MultiPVIdx < std::min(MultiPV, (int)Rml.size()); MultiPVIdx++)
531 // Calculate dynamic aspiration window based on previous iterations
532 if (depth >= 5 && abs(Rml[MultiPVIdx].prevScore) < VALUE_KNOWN_WIN)
534 int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
535 int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
537 aspirationDelta = std::min(std::max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
538 aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
540 alpha = std::max(Rml[MultiPVIdx].prevScore - aspirationDelta, -VALUE_INFINITE);
541 beta = std::min(Rml[MultiPVIdx].prevScore + aspirationDelta, VALUE_INFINITE);
545 alpha = -VALUE_INFINITE;
546 beta = VALUE_INFINITE;
549 // Start with a small aspiration window and, in case of fail high/low,
550 // research with bigger window until not failing high/low anymore.
552 // Search starts from ss+1 to allow referencing (ss-1). This is
553 // needed by update gains and ss copy when splitting at Root.
554 bestValue = search<Root>(pos, ss+1, alpha, beta, depth * ONE_PLY);
556 // Bring to front the best move. It is critical that sorting is
557 // done with a stable algorithm because all the values but the first
558 // and eventually the new best one are set to -VALUE_INFINITE and
559 // we want to keep the same order for all the moves but the new
560 // PV that goes to the front. Note that in case of MultiPV search
561 // the already searched PV lines are preserved.
562 sort<RootMove>(Rml.begin() + MultiPVIdx, Rml.end());
564 // In case we have found an exact score and we are going to leave
565 // the fail high/low loop then reorder the PV moves, otherwise
566 // leave the last PV move in its position so to be searched again.
567 // Of course this is needed only in MultiPV search.
568 if (MultiPVIdx && bestValue > alpha && bestValue < beta)
569 sort<RootMove>(Rml.begin(), Rml.begin() + MultiPVIdx);
571 // Write PV back to transposition table in case the relevant entries
572 // have been overwritten during the search.
573 for (int i = 0; i <= MultiPVIdx; i++)
574 Rml[i].insert_pv_in_tt(pos);
576 // If search has been stopped exit the aspiration window loop,
577 // note that sorting and writing PV back to TT is safe becuase
578 // Rml is still valid, although refers to the previous iteration.
582 // Send full PV info to GUI if we are going to leave the loop or
583 // if we have a fail high/low and we are deep in the search. UCI
584 // protocol requires to send all the PV lines also if are still
585 // to be searched and so refer to the previous search's score.
586 if ((bestValue > alpha && bestValue < beta) || elapsed_search_time() > 2000)
587 for (int i = 0; i < std::min(UCIMultiPV, (int)Rml.size()); i++)
589 bool updated = (i <= MultiPVIdx);
591 if (depth == 1 && !updated)
594 Depth d = (updated ? depth : depth - 1) * ONE_PLY;
595 Value s = (updated ? Rml[i].score : Rml[i].prevScore);
599 << (i == MultiPVIdx ? score_to_uci(s, alpha, beta) : score_to_uci(s))
600 << speed_to_uci(pos.nodes_searched())
601 << pv_to_uci(&Rml[i].pv[0], i + 1, pos.is_chess960())
605 // In case of failing high/low increase aspiration window and
606 // research, otherwise exit the fail high/low loop.
607 if (bestValue >= beta)
609 beta = std::min(beta + aspirationDelta, VALUE_INFINITE);
610 aspirationDelta += aspirationDelta / 2;
612 else if (bestValue <= alpha)
614 AspirationFailLow = true;
615 StopOnPonderhit = false;
617 alpha = std::max(alpha - aspirationDelta, -VALUE_INFINITE);
618 aspirationDelta += aspirationDelta / 2;
623 } while (abs(bestValue) < VALUE_KNOWN_WIN);
626 // Collect info about search result
627 bestMove = Rml[0].pv[0];
628 *ponderMove = Rml[0].pv[1];
629 bestValues[depth] = bestValue;
630 bestMoveChanges[depth] = Rml.bestMoveChanges;
632 // Skills: 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 (Options["Use Search Log"].value<bool>())
638 Log log(Options["Search Log Filename"].value<string>());
639 log << pretty_pv(pos, depth, bestValue, elapsed_search_time(), &Rml[0].pv[0]) << endl;
642 // Filter out startup noise when monitoring best move stability
643 if (depth > 2 && bestMoveChanges[depth])
644 bestMoveNeverChanged = false;
646 // Do we have time for the next iteration? Can we stop searching now?
647 if (!StopRequest && !StopOnPonderhit && Limits.useTimeManagement())
649 // Take in account some extra time if the best move has changed
650 if (depth > 4 && depth < 50)
651 TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth - 1]);
653 // Stop search if most of available time is already consumed. We probably don't
654 // have enough time to search the first move at the next iteration anyway.
655 if (elapsed_search_time() > (TimeMgr.available_time() * 62) / 100)
658 // Stop search early if one move seems to be much better than others
661 && ( bestMoveNeverChanged
662 || elapsed_search_time() > (TimeMgr.available_time() * 40) / 100))
664 Value rBeta = bestValue - EasyMoveMargin;
665 (ss+1)->excludedMove = bestMove;
666 (ss+1)->skipNullMove = true;
667 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth * ONE_PLY) / 2);
668 (ss+1)->skipNullMove = false;
669 (ss+1)->excludedMove = MOVE_NONE;
675 // If we are allowed to ponder do not stop the search now but keep pondering
676 if (StopRequest && Limits.ponder) // FIXME Limits.ponder is racy
679 StopOnPonderhit = true;
684 // When using skills overwrite best and ponder moves with the sub-optimal ones
685 if (SkillLevelEnabled)
687 if (skillBest == MOVE_NONE) // Still unassigned ?
688 do_skill_level(&skillBest, &skillPonder);
690 bestMove = skillBest;
691 *ponderMove = skillPonder;
698 // search<>() is the main search function for both PV and non-PV nodes and for
699 // normal and SplitPoint nodes. When called just after a split point the search
700 // is simpler because we have already probed the hash table, done a null move
701 // search, and searched the first move before splitting, we don't have to repeat
702 // all this work again. We also don't need to store anything to the hash table
703 // here: This is taken care of after we return from the split point.
705 template <NodeType NT>
706 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
708 const bool PvNode = (NT == PV || NT == Root || NT == SplitPointPV || NT == SplitPointRoot);
709 const bool SpNode = (NT == SplitPointPV || NT == SplitPointNonPV || NT == SplitPointRoot);
710 const bool RootNode = (NT == Root || NT == SplitPointRoot);
712 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
713 assert(beta > alpha && beta <= VALUE_INFINITE);
714 assert(PvNode || alpha == beta - 1);
715 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
717 Move movesSearched[MAX_MOVES];
722 Move ttMove, move, excludedMove, threatMove;
725 Value bestValue, value, oldAlpha;
726 Value refinedValue, nullValue, futilityBase, futilityValue;
727 bool isPvMove, inCheck, singularExtensionNode, givesCheck;
728 bool captureOrPromotion, dangerous, doFullDepthSearch;
729 int moveCount = 0, playedMoveCount = 0;
730 Thread& thread = Threads[pos.thread()];
731 SplitPoint* sp = NULL;
733 refinedValue = bestValue = value = -VALUE_INFINITE;
735 inCheck = pos.in_check();
736 ss->ply = (ss-1)->ply + 1;
738 // Used to send selDepth info to GUI
739 if (PvNode && thread.maxPly < ss->ply)
740 thread.maxPly = ss->ply;
742 // Step 1. Initialize node
745 ss->currentMove = ss->bestMove = threatMove = (ss+1)->excludedMove = MOVE_NONE;
746 (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
747 (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
753 ttMove = excludedMove = MOVE_NONE;
754 threatMove = sp->threatMove;
755 goto split_point_start;
758 // Step 2. Check for aborted search and immediate draw
760 || pos.is_draw<false>()
761 || ss->ply > PLY_MAX) && !RootNode)
764 // Step 3. Mate distance pruning
767 alpha = std::max(value_mated_in(ss->ply), alpha);
768 beta = std::min(value_mate_in(ss->ply+1), beta);
773 // Step 4. Transposition table lookup
774 // We don't want the score of a partial search to overwrite a previous full search
775 // TT value, so we use a different position key in case of an excluded move.
776 excludedMove = ss->excludedMove;
777 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
778 tte = TT.probe(posKey);
779 ttMove = RootNode ? Rml[MultiPVIdx].pv[0] : tte ? tte->move() : MOVE_NONE;
781 // At PV nodes we check for exact scores, while at non-PV nodes we check for
782 // a fail high/low. Biggest advantage at probing at PV nodes is to have a
783 // smooth experience in analysis mode. We don't probe at Root nodes otherwise
784 // we should also update RootMoveList to avoid bogus output.
785 if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
786 : can_return_tt(tte, depth, beta, ss->ply)))
789 ss->bestMove = move = ttMove; // Can be MOVE_NONE
790 value = value_from_tt(tte->value(), ss->ply);
794 && !pos.is_capture_or_promotion(move)
795 && move != ss->killers[0])
797 ss->killers[1] = ss->killers[0];
798 ss->killers[0] = move;
803 // Step 5. Evaluate the position statically and update parent's gain statistics
805 ss->eval = ss->evalMargin = VALUE_NONE;
808 assert(tte->static_value() != VALUE_NONE);
810 ss->eval = tte->static_value();
811 ss->evalMargin = tte->static_value_margin();
812 refinedValue = refine_eval(tte, ss->eval, ss->ply);
816 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
817 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
820 // Update gain for the parent non-capture move given the static position
821 // evaluation before and after the move.
822 if ( (move = (ss-1)->currentMove) != MOVE_NULL
823 && (ss-1)->eval != VALUE_NONE
824 && ss->eval != VALUE_NONE
825 && pos.captured_piece_type() == PIECE_TYPE_NONE
826 && !is_special(move))
828 Square to = move_to(move);
829 H.update_gain(pos.piece_on(to), to, -(ss-1)->eval - ss->eval);
832 // Step 6. Razoring (is omitted in PV nodes)
834 && depth < RazorDepth
836 && refinedValue + razor_margin(depth) < beta
837 && ttMove == MOVE_NONE
838 && abs(beta) < VALUE_MATE_IN_PLY_MAX
839 && !pos.has_pawn_on_7th(pos.side_to_move()))
841 Value rbeta = beta - razor_margin(depth);
842 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
844 // Logically we should return (v + razor_margin(depth)), but
845 // surprisingly this did slightly weaker in tests.
849 // Step 7. Static null move pruning (is omitted in PV nodes)
850 // We're betting that the opponent doesn't have a move that will reduce
851 // the score by more than futility_margin(depth) if we do a null move.
854 && depth < RazorDepth
856 && refinedValue - futility_margin(depth, 0) >= beta
857 && abs(beta) < VALUE_MATE_IN_PLY_MAX
858 && pos.non_pawn_material(pos.side_to_move()))
859 return refinedValue - futility_margin(depth, 0);
861 // Step 8. Null move search with verification search (is omitted in PV nodes)
866 && refinedValue >= beta
867 && abs(beta) < VALUE_MATE_IN_PLY_MAX
868 && pos.non_pawn_material(pos.side_to_move()))
870 ss->currentMove = MOVE_NULL;
872 // Null move dynamic reduction based on depth
873 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
875 // Null move dynamic reduction based on value
876 if (refinedValue - PawnValueMidgame > beta)
879 pos.do_null_move<true>(st);
880 (ss+1)->skipNullMove = true;
881 nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
882 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
883 (ss+1)->skipNullMove = false;
884 pos.do_null_move<false>(st);
886 if (nullValue >= beta)
888 // Do not return unproven mate scores
889 if (nullValue >= VALUE_MATE_IN_PLY_MAX)
892 if (depth < 6 * ONE_PLY)
895 // Do verification search at high depths
896 ss->skipNullMove = true;
897 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY);
898 ss->skipNullMove = false;
905 // The null move failed low, which means that we may be faced with
906 // some kind of threat. If the previous move was reduced, check if
907 // the move that refuted the null move was somehow connected to the
908 // move which was reduced. If a connection is found, return a fail
909 // low score (which will cause the reduced move to fail high in the
910 // parent node, which will trigger a re-search with full depth).
911 threatMove = (ss+1)->bestMove;
913 if ( depth < ThreatDepth
915 && threatMove != MOVE_NONE
916 && connected_moves(pos, (ss-1)->currentMove, threatMove))
921 // Step 9. ProbCut (is omitted in PV nodes)
922 // If we have a very good capture (i.e. SEE > seeValues[captured_piece_type])
923 // and a reduced search returns a value much above beta, we can (almost) safely
924 // prune the previous move.
926 && depth >= RazorDepth + ONE_PLY
929 && excludedMove == MOVE_NONE
930 && abs(beta) < VALUE_MATE_IN_PLY_MAX)
932 Value rbeta = beta + 200;
933 Depth rdepth = depth - ONE_PLY - 3 * ONE_PLY;
935 assert(rdepth >= ONE_PLY);
937 MovePicker mp(pos, ttMove, H, pos.captured_piece_type());
940 while ((move = mp.get_next_move()) != MOVE_NONE)
941 if (pos.pl_move_is_legal(move, ci.pinned))
943 pos.do_move(move, st, ci, pos.move_gives_check(move, ci));
944 value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, rdepth);
951 // Step 10. Internal iterative deepening
952 if ( depth >= IIDDepth[PvNode]
953 && ttMove == MOVE_NONE
954 && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
956 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
958 ss->skipNullMove = true;
959 search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);
960 ss->skipNullMove = false;
962 tte = TT.probe(posKey);
963 ttMove = tte ? tte->move() : MOVE_NONE;
966 split_point_start: // At split points actual search starts from here
968 // Initialize a MovePicker object for the current position
969 MovePickerExt<SpNode> mp(pos, ttMove, depth, H, ss, PvNode ? -VALUE_INFINITE : beta);
971 ss->bestMove = MOVE_NONE;
972 futilityBase = ss->eval + ss->evalMargin;
973 singularExtensionNode = !RootNode
975 && depth >= SingularExtensionDepth[PvNode]
976 && ttMove != MOVE_NONE
977 && !excludedMove // Do not allow recursive singular extension search
978 && (tte->type() & VALUE_TYPE_LOWER)
979 && tte->depth() >= depth - 3 * ONE_PLY;
982 lock_grab(&(sp->lock));
983 bestValue = sp->bestValue;
986 // Step 11. Loop through moves
987 // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
988 while ( bestValue < beta
989 && (move = mp.get_next_move()) != MOVE_NONE
990 && !thread.cutoff_occurred())
994 if (move == excludedMove)
997 // At root obey the "searchmoves" option and skip moves not listed in Root
998 // Move List, as a consequence any illegal move is also skipped. In MultiPV
999 // mode we also skip PV moves which have been already searched.
1000 if (RootNode && !Rml.find(move, MultiPVIdx))
1003 // At PV and SpNode nodes we want all moves to be legal since the beginning
1004 if ((PvNode || SpNode) && !pos.pl_move_is_legal(move, ci.pinned))
1009 moveCount = ++sp->moveCount;
1010 lock_release(&(sp->lock));
1017 // This is used by time management
1018 FirstRootMove = (moveCount == 1);
1020 // Save the current node count before the move is searched
1021 nodes = pos.nodes_searched();
1023 // For long searches send current move info to GUI
1024 if (pos.thread() == 0 && elapsed_search_time() > 2000)
1025 cout << "info" << depth_to_uci(depth)
1026 << " currmove " << move
1027 << " currmovenumber " << moveCount + MultiPVIdx << endl;
1030 isPvMove = (PvNode && moveCount <= 1);
1031 givesCheck = pos.move_gives_check(move, ci);
1032 captureOrPromotion = pos.is_capture_or_promotion(move);
1034 // Step 12. Decide the new search depth
1035 ext = extension<PvNode>(pos, move, captureOrPromotion, givesCheck, &dangerous);
1037 // Singular extension search. If all moves but one fail low on a search of
1038 // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
1039 // is singular and should be extended. To verify this we do a reduced search
1040 // on all the other moves but the ttMove, if result is lower than ttValue minus
1041 // a margin then we extend ttMove.
1042 if ( singularExtensionNode
1044 && pos.pl_move_is_legal(move, ci.pinned)
1047 Value ttValue = value_from_tt(tte->value(), ss->ply);
1049 if (abs(ttValue) < VALUE_KNOWN_WIN)
1051 Value rBeta = ttValue - int(depth);
1052 ss->excludedMove = move;
1053 ss->skipNullMove = true;
1054 value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2);
1055 ss->skipNullMove = false;
1056 ss->excludedMove = MOVE_NONE;
1057 ss->bestMove = MOVE_NONE;
1063 // Update current move (this must be done after singular extension search)
1064 newDepth = depth - ONE_PLY + ext;
1066 // Step 13. Futility pruning (is omitted in PV nodes)
1068 && !captureOrPromotion
1072 && !is_castle(move))
1074 // Move count based pruning
1075 if ( moveCount >= futility_move_count(depth)
1076 && (!threatMove || !connected_threat(pos, move, threatMove))
1077 && bestValue > VALUE_MATED_IN_PLY_MAX) // FIXME bestValue is racy
1080 lock_grab(&(sp->lock));
1085 // Value based pruning
1086 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1087 // but fixing this made program slightly weaker.
1088 Depth predictedDepth = newDepth - reduction<PvNode>(depth, moveCount);
1089 futilityValue = futilityBase + futility_margin(predictedDepth, moveCount)
1090 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1092 if (futilityValue < beta)
1096 lock_grab(&(sp->lock));
1097 if (futilityValue > sp->bestValue)
1098 sp->bestValue = bestValue = futilityValue;
1100 else if (futilityValue > bestValue)
1101 bestValue = futilityValue;
1106 // Prune moves with negative SEE at low depths
1107 if ( predictedDepth < 2 * ONE_PLY
1108 && bestValue > VALUE_MATED_IN_PLY_MAX
1109 && pos.see_sign(move) < 0)
1112 lock_grab(&(sp->lock));
1118 // Check for legality only before to do the move
1119 if (!pos.pl_move_is_legal(move, ci.pinned))
1125 ss->currentMove = move;
1126 if (!SpNode && !captureOrPromotion)
1127 movesSearched[playedMoveCount++] = move;
1129 // Step 14. Make the move
1130 pos.do_move(move, st, ci, givesCheck);
1132 // Step 15. Reduced depth search (LMR). If the move fails high will be
1133 // re-searched at full depth.
1134 if ( depth > 3 * ONE_PLY
1136 && !captureOrPromotion
1139 && ss->killers[0] != move
1140 && ss->killers[1] != move)
1142 ss->reduction = reduction<PvNode>(depth, moveCount);
1143 Depth d = newDepth - ss->reduction;
1144 alpha = SpNode ? sp->alpha : alpha;
1146 value = d < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1147 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d);
1149 doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO);
1150 ss->reduction = DEPTH_ZERO;
1153 doFullDepthSearch = !isPvMove;
1155 // Step 16. Full depth search, when LMR is skipped or fails high
1156 if (doFullDepthSearch)
1158 alpha = SpNode ? sp->alpha : alpha;
1159 value = newDepth < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO)
1160 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth);
1163 // Only for PV nodes do a full PV search on the first move or after a fail
1164 // high, in the latter case search only if value < beta, otherwise let the
1165 // parent node to fail low with value <= alpha and to try another move.
1166 if (PvNode && (isPvMove || (value > alpha && (RootNode || value < beta))))
1167 value = newDepth < ONE_PLY ? -qsearch<PV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
1168 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth);
1170 // Step 17. Undo move
1171 pos.undo_move(move);
1173 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1175 // Step 18. Check for new best move
1178 lock_grab(&(sp->lock));
1179 bestValue = sp->bestValue;
1183 // Finished searching the move. If StopRequest is true, the search
1184 // was aborted because the user interrupted the search or because we
1185 // ran out of time. In this case, the return value of the search cannot
1186 // be trusted, and we don't update the best move and/or PV.
1187 if (RootNode && !StopRequest)
1189 // Remember searched nodes counts for this move
1190 RootMove* rm = Rml.find(move);
1191 rm->nodes += pos.nodes_searched() - nodes;
1193 // PV move or new best move ?
1194 if (isPvMove || value > alpha)
1198 rm->extract_pv_from_tt(pos);
1200 // We record how often the best move has been changed in each
1201 // iteration. This information is used for time management: When
1202 // the best move changes frequently, we allocate some more time.
1203 if (!isPvMove && MultiPV == 1)
1204 Rml.bestMoveChanges++;
1207 // All other moves but the PV are set to the lowest value, this
1208 // is not a problem when sorting becuase sort is stable and move
1209 // position in the list is preserved, just the PV is pushed up.
1210 rm->score = -VALUE_INFINITE;
1214 if (value > bestValue)
1217 ss->bestMove = move;
1221 && value < beta) // We want always alpha < beta
1224 if (SpNode && !thread.cutoff_occurred())
1226 sp->bestValue = value;
1227 sp->ss->bestMove = move;
1229 sp->is_betaCutoff = (value >= beta);
1233 // Step 19. Check for split
1235 && depth >= Threads.min_split_depth()
1237 && Threads.available_slave_exists(pos.thread())
1239 && !thread.cutoff_occurred())
1240 bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, depth,
1241 threatMove, moveCount, &mp, NT);
1244 // Step 20. Check for mate and stalemate
1245 // All legal moves have been searched and if there are no legal moves, it
1246 // must be mate or stalemate. Note that we can have a false positive in
1247 // case of StopRequest or thread.cutoff_occurred() are set, but this is
1248 // harmless because return value is discarded anyhow in the parent nodes.
1249 // If we are in a singular extension search then return a fail low score.
1250 if (!SpNode && !moveCount)
1251 return excludedMove ? oldAlpha : inCheck ? value_mated_in(ss->ply) : VALUE_DRAW;
1253 // Step 21. Update tables
1254 // If the search is not aborted, update the transposition table,
1255 // history counters, and killer moves.
1256 if (!SpNode && !StopRequest && !thread.cutoff_occurred())
1258 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1259 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1260 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1262 TT.store(posKey, value_to_tt(bestValue, ss->ply), vt, depth, move, ss->eval, ss->evalMargin);
1264 // Update killers and history only for non capture moves that fails high
1265 if ( bestValue >= beta
1266 && !pos.is_capture_or_promotion(move))
1268 if (move != ss->killers[0])
1270 ss->killers[1] = ss->killers[0];
1271 ss->killers[0] = move;
1273 update_history(pos, move, depth, movesSearched, playedMoveCount);
1279 // Here we have the lock still grabbed
1280 sp->is_slave[pos.thread()] = false;
1281 sp->nodes += pos.nodes_searched();
1282 lock_release(&(sp->lock));
1285 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1290 // qsearch() is the quiescence search function, which is called by the main
1291 // search function when the remaining depth is zero (or, to be more precise,
1292 // less than ONE_PLY).
1294 template <NodeType NT>
1295 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth) {
1297 const bool PvNode = (NT == PV);
1299 assert(NT == PV || NT == NonPV);
1300 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1301 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1302 assert(PvNode || alpha == beta - 1);
1304 assert(pos.thread() >= 0 && pos.thread() < Threads.size());
1308 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1309 bool inCheck, enoughMaterial, givesCheck, evasionPrunable;
1313 Value oldAlpha = alpha;
1315 ss->bestMove = ss->currentMove = MOVE_NONE;
1316 ss->ply = (ss-1)->ply + 1;
1318 // Check for an instant draw or maximum ply reached
1319 if (pos.is_draw<true>() || ss->ply > PLY_MAX)
1322 // Decide whether or not to include checks, this fixes also the type of
1323 // TT entry depth that we are going to use. Note that in qsearch we use
1324 // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
1325 inCheck = pos.in_check();
1326 ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
1328 // Transposition table lookup. At PV nodes, we don't use the TT for
1329 // pruning, but only for move ordering.
1330 tte = TT.probe(pos.get_key());
1331 ttMove = (tte ? tte->move() : MOVE_NONE);
1333 if (!PvNode && tte && can_return_tt(tte, ttDepth, beta, ss->ply))
1335 ss->bestMove = ttMove; // Can be MOVE_NONE
1336 return value_from_tt(tte->value(), ss->ply);
1339 // Evaluate the position statically
1342 bestValue = futilityBase = -VALUE_INFINITE;
1343 ss->eval = evalMargin = VALUE_NONE;
1344 enoughMaterial = false;
1350 assert(tte->static_value() != VALUE_NONE);
1352 evalMargin = tte->static_value_margin();
1353 ss->eval = bestValue = tte->static_value();
1356 ss->eval = bestValue = evaluate(pos, evalMargin);
1358 // Stand pat. Return immediately if static value is at least beta
1359 if (bestValue >= beta)
1362 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1367 if (PvNode && bestValue > alpha)
1370 // Futility pruning parameters, not needed when in check
1371 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1372 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1375 // Initialize a MovePicker object for the current position, and prepare
1376 // to search the moves. Because the depth is <= 0 here, only captures,
1377 // queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
1379 MovePicker mp(pos, ttMove, depth, H, move_to((ss-1)->currentMove));
1382 // Loop through the moves until no moves remain or a beta cutoff occurs
1383 while ( bestValue < beta
1384 && (move = mp.get_next_move()) != MOVE_NONE)
1386 assert(is_ok(move));
1388 givesCheck = pos.move_gives_check(move, ci);
1396 && !is_promotion(move)
1397 && !pos.is_passed_pawn_push(move))
1399 futilityValue = futilityBase
1400 + PieceValueEndgame[pos.piece_on(move_to(move))]
1401 + (is_enpassant(move) ? PawnValueEndgame : VALUE_ZERO);
1403 if (futilityValue < beta)
1405 if (futilityValue > bestValue)
1406 bestValue = futilityValue;
1411 // Prune moves with negative or equal SEE
1412 if ( futilityBase < beta
1413 && depth < DEPTH_ZERO
1414 && pos.see(move) <= 0)
1418 // Detect non-capture evasions that are candidate to be pruned
1419 evasionPrunable = !PvNode
1421 && bestValue > VALUE_MATED_IN_PLY_MAX
1422 && !pos.is_capture(move)
1423 && !pos.can_castle(pos.side_to_move());
1425 // Don't search moves with negative SEE values
1427 && (!inCheck || evasionPrunable)
1429 && !is_promotion(move)
1430 && pos.see_sign(move) < 0)
1433 // Don't search useless checks
1438 && !pos.is_capture_or_promotion(move)
1439 && ss->eval + PawnValueMidgame / 4 < beta
1440 && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
1442 if (ss->eval + PawnValueMidgame / 4 > bestValue)
1443 bestValue = ss->eval + PawnValueMidgame / 4;
1448 // Check for legality only before to do the move
1449 if (!pos.pl_move_is_legal(move, ci.pinned))
1452 // Update current move
1453 ss->currentMove = move;
1455 // Make and search the move
1456 pos.do_move(move, st, ci, givesCheck);
1457 value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
1458 pos.undo_move(move);
1460 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1463 if (value > bestValue)
1466 ss->bestMove = move;
1470 && value < beta) // We want always alpha < beta
1475 // All legal moves have been searched. A special case: If we're in check
1476 // and no legal moves were found, it is checkmate.
1477 if (inCheck && bestValue == -VALUE_INFINITE)
1478 return value_mated_in(ss->ply);
1480 // Update transposition table
1481 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1482 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1483 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1485 TT.store(pos.get_key(), value_to_tt(bestValue, ss->ply), vt, ttDepth, move, ss->eval, evalMargin);
1487 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1493 // check_is_dangerous() tests if a checking move can be pruned in qsearch().
1494 // bestValue is updated only when returning false because in that case move
1497 bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
1499 Bitboard b, occ, oldAtt, newAtt, kingAtt;
1500 Square from, to, ksq, victimSq;
1503 Value futilityValue, bv = *bestValue;
1505 from = move_from(move);
1507 them = flip(pos.side_to_move());
1508 ksq = pos.king_square(them);
1509 kingAtt = pos.attacks_from<KING>(ksq);
1510 pc = pos.piece_on(from);
1512 occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
1513 oldAtt = pos.attacks_from(pc, from, occ);
1514 newAtt = pos.attacks_from(pc, to, occ);
1516 // Rule 1. Checks which give opponent's king at most one escape square are dangerous
1517 b = kingAtt & ~pos.pieces(them) & ~newAtt & ~(1ULL << to);
1519 if (!(b && (b & (b - 1))))
1522 // Rule 2. Queen contact check is very dangerous
1523 if ( type_of(pc) == QUEEN
1524 && bit_is_set(kingAtt, to))
1527 // Rule 3. Creating new double threats with checks
1528 b = pos.pieces(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
1532 victimSq = pop_1st_bit(&b);
1533 futilityValue = futilityBase + PieceValueEndgame[pos.piece_on(victimSq)];
1535 // Note that here we generate illegal "double move"!
1536 if ( futilityValue >= beta
1537 && pos.see_sign(make_move(from, victimSq)) >= 0)
1540 if (futilityValue > bv)
1544 // Update bestValue only if check is not dangerous (because we will prune the move)
1550 // connected_moves() tests whether two moves are 'connected' in the sense
1551 // that the first move somehow made the second move possible (for instance
1552 // if the moving piece is the same in both moves). The first move is assumed
1553 // to be the move that was made to reach the current position, while the
1554 // second move is assumed to be a move from the current position.
1556 bool connected_moves(const Position& pos, Move m1, Move m2) {
1558 Square f1, t1, f2, t2;
1565 // Case 1: The moving piece is the same in both moves
1571 // Case 2: The destination square for m2 was vacated by m1
1577 // Case 3: Moving through the vacated square
1578 p2 = pos.piece_on(f2);
1579 if ( piece_is_slider(p2)
1580 && bit_is_set(squares_between(f2, t2), f1))
1583 // Case 4: The destination square for m2 is defended by the moving piece in m1
1584 p1 = pos.piece_on(t1);
1585 if (bit_is_set(pos.attacks_from(p1, t1), t2))
1588 // Case 5: Discovered check, checking piece is the piece moved in m1
1589 ksq = pos.king_square(pos.side_to_move());
1590 if ( piece_is_slider(p1)
1591 && bit_is_set(squares_between(t1, ksq), f2))
1593 Bitboard occ = pos.occupied_squares();
1594 clear_bit(&occ, f2);
1595 if (bit_is_set(pos.attacks_from(p1, t1, occ), ksq))
1602 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1603 // "plies to mate from the current ply". Non-mate scores are unchanged.
1604 // The function is called before storing a value to the transposition table.
1606 Value value_to_tt(Value v, int ply) {
1608 if (v >= VALUE_MATE_IN_PLY_MAX)
1611 if (v <= VALUE_MATED_IN_PLY_MAX)
1618 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1619 // the transposition table to a mate score corrected for the current ply.
1621 Value value_from_tt(Value v, int ply) {
1623 if (v >= VALUE_MATE_IN_PLY_MAX)
1626 if (v <= VALUE_MATED_IN_PLY_MAX)
1633 // connected_threat() tests whether it is safe to forward prune a move or if
1634 // is somehow connected to the threat move returned by null search.
1636 bool connected_threat(const Position& pos, Move m, Move threat) {
1639 assert(is_ok(threat));
1640 assert(!pos.is_capture_or_promotion(m));
1641 assert(!pos.is_passed_pawn_push(m));
1643 Square mfrom, mto, tfrom, tto;
1645 mfrom = move_from(m);
1647 tfrom = move_from(threat);
1648 tto = move_to(threat);
1650 // Case 1: Don't prune moves which move the threatened piece
1654 // Case 2: If the threatened piece has value less than or equal to the
1655 // value of the threatening piece, don't prune moves which defend it.
1656 if ( pos.is_capture(threat)
1657 && ( PieceValueMidgame[pos.piece_on(tfrom)] >= PieceValueMidgame[pos.piece_on(tto)]
1658 || type_of(pos.piece_on(tfrom)) == KING)
1659 && pos.move_attacks_square(m, tto))
1662 // Case 3: If the moving piece in the threatened move is a slider, don't
1663 // prune safe moves which block its ray.
1664 if ( piece_is_slider(pos.piece_on(tfrom))
1665 && bit_is_set(squares_between(tfrom, tto), mto)
1666 && pos.see_sign(m) >= 0)
1673 // can_return_tt() returns true if a transposition table score
1674 // can be used to cut-off at a given point in search.
1676 bool can_return_tt(const TTEntry* tte, Depth depth, Value beta, int ply) {
1678 Value v = value_from_tt(tte->value(), ply);
1680 return ( tte->depth() >= depth
1681 || v >= std::max(VALUE_MATE_IN_PLY_MAX, beta)
1682 || v < std::min(VALUE_MATED_IN_PLY_MAX, beta))
1684 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1685 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1689 // refine_eval() returns the transposition table score if
1690 // possible otherwise falls back on static position evaluation.
1692 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1696 Value v = value_from_tt(tte->value(), ply);
1698 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1699 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1706 // update_history() registers a good move that produced a beta-cutoff
1707 // in history and marks as failures all the other moves of that ply.
1709 void update_history(const Position& pos, Move move, Depth depth,
1710 Move movesSearched[], int moveCount) {
1712 Value bonus = Value(int(depth) * int(depth));
1714 H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
1716 for (int i = 0; i < moveCount - 1; i++)
1718 m = movesSearched[i];
1722 H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
1727 // current_search_time() returns the number of milliseconds which have passed
1728 // since the beginning of the current search.
1730 int elapsed_search_time(int set) {
1732 static int searchStartTime;
1735 searchStartTime = set;
1737 return get_system_time() - searchStartTime;
1741 // score_to_uci() converts a value to a string suitable for use with the UCI
1742 // protocol specifications:
1744 // cp <x> The score from the engine's point of view in centipawns.
1745 // mate <y> Mate in y moves, not plies. If the engine is getting mated
1746 // use negative values for y.
1748 string score_to_uci(Value v, Value alpha, Value beta) {
1750 std::stringstream s;
1752 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1753 s << " score cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
1755 s << " score mate " << (v > 0 ? VALUE_MATE - v + 1 : -VALUE_MATE - v) / 2;
1757 s << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
1763 // speed_to_uci() returns a string with time stats of current search suitable
1764 // to be sent to UCI gui.
1766 string speed_to_uci(int64_t nodes) {
1768 std::stringstream s;
1769 int t = elapsed_search_time();
1771 s << " nodes " << nodes
1772 << " nps " << (t > 0 ? int(nodes * 1000 / t) : 0)
1779 // pv_to_uci() returns a string with information on the current PV line
1780 // formatted according to UCI specification.
1782 string pv_to_uci(const Move pv[], int pvNum, bool chess960) {
1784 std::stringstream s;
1786 s << " multipv " << pvNum << " pv " << set960(chess960);
1788 for ( ; *pv != MOVE_NONE; pv++)
1795 // depth_to_uci() returns a string with information on the current depth and
1796 // seldepth formatted according to UCI specification.
1798 string depth_to_uci(Depth depth) {
1800 std::stringstream s;
1802 // Retrieve max searched depth among threads
1804 for (int i = 0; i < Threads.size(); i++)
1805 if (Threads[i].maxPly > selDepth)
1806 selDepth = Threads[i].maxPly;
1808 s << " depth " << depth / ONE_PLY << " seldepth " << selDepth;
1813 string time_to_string(int millisecs) {
1815 const int MSecMinute = 1000 * 60;
1816 const int MSecHour = 1000 * 60 * 60;
1818 int hours = millisecs / MSecHour;
1819 int minutes = (millisecs % MSecHour) / MSecMinute;
1820 int seconds = ((millisecs % MSecHour) % MSecMinute) / 1000;
1822 std::stringstream s;
1827 s << std::setfill('0') << std::setw(2) << minutes << ':' << std::setw(2) << seconds;
1831 string score_to_string(Value v) {
1833 std::stringstream s;
1835 if (v >= VALUE_MATE_IN_PLY_MAX)
1836 s << "#" << (VALUE_MATE - v + 1) / 2;
1837 else if (v <= VALUE_MATED_IN_PLY_MAX)
1838 s << "-#" << (VALUE_MATE + v) / 2;
1840 s << std::setprecision(2) << std::fixed << std::showpos << float(v) / PawnValueMidgame;
1846 // pretty_pv() creates a human-readable string from a position and a PV.
1847 // It is used to write search information to the log file (which is created
1848 // when the UCI parameter "Use Search Log" is "true").
1850 string pretty_pv(Position& pos, int depth, Value value, int time, Move pv[]) {
1852 const int64_t K = 1000;
1853 const int64_t M = 1000000;
1854 const int startColumn = 28;
1855 const size_t maxLength = 80 - startColumn;
1857 StateInfo state[PLY_MAX_PLUS_2], *st = state;
1860 std::stringstream s;
1863 // First print depth, score, time and searched nodes...
1864 s << set960(pos.is_chess960())
1865 << std::setw(2) << depth
1866 << std::setw(8) << score_to_string(value)
1867 << std::setw(8) << time_to_string(time);
1869 if (pos.nodes_searched() < M)
1870 s << std::setw(8) << pos.nodes_searched() / 1 << " ";
1871 else if (pos.nodes_searched() < K * M)
1872 s << std::setw(7) << pos.nodes_searched() / K << "K ";
1874 s << std::setw(7) << pos.nodes_searched() / M << "M ";
1876 // ...then print the full PV line in short algebraic notation
1877 while (*m != MOVE_NONE)
1879 san = move_to_san(pos, *m);
1880 length += san.length() + 1;
1882 if (length > maxLength)
1884 length = san.length() + 1;
1885 s << "\n" + string(startColumn, ' ');
1889 pos.do_move(*m++, *st++);
1892 // Restore original position before to leave
1893 while (m != pv) pos.undo_move(*--m);
1899 // When playing with strength handicap choose best move among the MultiPV set
1900 // using a statistical rule dependent on SkillLevel. Idea by Heinz van Saanen.
1902 void do_skill_level(Move* best, Move* ponder) {
1904 assert(MultiPV > 1);
1908 // Rml list is already sorted by score in descending order
1910 int max_s = -VALUE_INFINITE;
1911 int size = std::min(MultiPV, (int)Rml.size());
1912 int max = Rml[0].score;
1913 int var = std::min(max - Rml[size - 1].score, int(PawnValueMidgame));
1914 int wk = 120 - 2 * SkillLevel;
1916 // PRNG sequence should be non deterministic
1917 for (int i = abs(get_system_time() % 50); i > 0; i--)
1918 rk.rand<unsigned>();
1920 // Choose best move. For each move's score we add two terms both dependent
1921 // on wk, one deterministic and bigger for weaker moves, and one random,
1922 // then we choose the move with the resulting highest score.
1923 for (int i = 0; i < size; i++)
1927 // Don't allow crazy blunders even at very low skills
1928 if (i > 0 && Rml[i-1].score > s + EasyMoveMargin)
1931 // This is our magical formula
1932 s += ((max - s) * wk + var * (rk.rand<unsigned>() % wk)) / 128;
1937 *best = Rml[i].pv[0];
1938 *ponder = Rml[i].pv[1];
1944 /// RootMove and RootMoveList method's definitions
1946 void RootMoveList::init(Position& pos, Move searchMoves[]) {
1949 bestMoveChanges = 0;
1952 // Generate all legal moves and add them to RootMoveList
1953 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
1955 // If we have a searchMoves[] list then verify the move
1956 // is in the list before to add it.
1957 for (sm = searchMoves; *sm && *sm != ml.move(); sm++) {}
1959 if (sm != searchMoves && *sm != ml.move())
1963 rm.pv.push_back(ml.move());
1964 rm.pv.push_back(MOVE_NONE);
1965 rm.score = rm.prevScore = -VALUE_INFINITE;
1971 RootMove* RootMoveList::find(const Move& m, int startIndex) {
1973 for (size_t i = startIndex; i < size(); i++)
1974 if ((*this)[i].pv[0] == m)
1981 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
1982 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
1983 // allow to always have a ponder move even when we fail high at root and also a
1984 // long PV to print that is important for position analysis.
1986 void RootMove::extract_pv_from_tt(Position& pos) {
1988 StateInfo state[PLY_MAX_PLUS_2], *st = state;
1993 assert(m != MOVE_NONE && pos.is_pseudo_legal(m));
1997 pos.do_move(m, *st++);
1999 while ( (tte = TT.probe(pos.get_key())) != NULL
2000 && tte->move() != MOVE_NONE
2001 && pos.is_pseudo_legal(tte->move())
2002 && pos.pl_move_is_legal(tte->move(), pos.pinned_pieces())
2004 && (!pos.is_draw<false>() || ply < 2))
2006 pv.push_back(tte->move());
2007 pos.do_move(tte->move(), *st++);
2010 pv.push_back(MOVE_NONE);
2012 do pos.undo_move(pv[--ply]); while (ply);
2016 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2017 // the PV back into the TT. This makes sure the old PV moves are searched
2018 // first, even if the old TT entries have been overwritten.
2020 void RootMove::insert_pv_in_tt(Position& pos) {
2022 StateInfo state[PLY_MAX_PLUS_2], *st = state;
2025 Value v, m = VALUE_NONE;
2028 assert(pv[0] != MOVE_NONE && pos.is_pseudo_legal(pv[0]));
2034 // Don't overwrite existing correct entries
2035 if (!tte || tte->move() != pv[ply])
2037 v = (pos.in_check() ? VALUE_NONE : evaluate(pos, m));
2038 TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
2040 pos.do_move(pv[ply], *st++);
2042 } while (pv[++ply] != MOVE_NONE);
2044 do pos.undo_move(pv[--ply]); while (ply);
2050 // Thread::idle_loop() is where the thread is parked when it has no work to do.
2051 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint object
2052 // for which the thread is the master.
2054 void Thread::idle_loop(SplitPoint* sp) {
2058 // If we are not searching, wait for a condition to be signaled
2059 // instead of wasting CPU time polling for work.
2062 || (Threads.use_sleeping_threads() && !is_searching))
2064 assert((!sp && threadID) || Threads.use_sleeping_threads());
2066 // Slave thread should exit as soon as do_terminate flag raises
2073 // Grab the lock to avoid races with Thread::wake_up()
2074 lock_grab(&sleepLock);
2076 // If we are master and all slaves have finished don't go to sleep
2077 if (sp && Threads.split_point_finished(sp))
2079 lock_release(&sleepLock);
2083 // Do sleep after retesting sleep conditions under lock protection, in
2084 // particular we need to avoid a deadlock in case a master thread has,
2085 // in the meanwhile, allocated us and sent the wake_up() call before we
2086 // had the chance to grab the lock.
2087 if (do_sleep || !is_searching)
2088 cond_wait(&sleepCond, &sleepLock);
2090 lock_release(&sleepLock);
2093 // If this thread has been assigned work, launch a search
2096 assert(!do_terminate);
2098 // Copy split point position and search stack and call search()
2099 SearchStack ss[PLY_MAX_PLUS_2];
2100 SplitPoint* tsp = splitPoint;
2101 Position pos(*tsp->pos, threadID);
2103 memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
2106 if (tsp->nodeType == Root)
2107 search<SplitPointRoot>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2108 else if (tsp->nodeType == PV)
2109 search<SplitPointPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2110 else if (tsp->nodeType == NonPV)
2111 search<SplitPointNonPV>(pos, ss+1, tsp->alpha, tsp->beta, tsp->depth);
2115 assert(is_searching);
2117 is_searching = false;
2119 // Wake up master thread so to allow it to return from the idle loop in
2120 // case we are the last slave of the split point.
2121 if ( Threads.use_sleeping_threads()
2122 && threadID != tsp->master
2123 && !Threads[tsp->master].is_searching)
2124 Threads[tsp->master].wake_up();
2127 // If this thread is the master of a split point and all slaves have
2128 // finished their work at this split point, return from the idle loop.
2129 if (sp && Threads.split_point_finished(sp))
2131 // Because sp->is_slave[] is reset under lock protection,
2132 // be sure sp->lock has been released before to return.
2133 lock_grab(&(sp->lock));
2134 lock_release(&(sp->lock));
2141 // ThreadsManager::wait_for_stop_or_ponderhit() is called when the maximum depth
2142 // is reached while the program is pondering. The point is to work around a wrinkle
2143 // in the UCI protocol: When pondering, the engine is not allowed to give a
2144 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2145 // We simply wait here until one of these commands (that raise StopRequest) is
2146 // sent, and return, after which the bestmove and pondermove will be printed.
2148 void ThreadsManager::wait_for_stop_or_ponderhit() {
2150 StopOnPonderhit = true;
2152 Thread& main = threads[0];
2154 lock_grab(&main.sleepLock);
2156 while (!StopRequest)
2157 cond_wait(&main.sleepCond, &main.sleepLock);
2159 lock_release(&main.sleepLock);
2163 // uci_async_command() is called when a 'cmd' input line is received from the
2164 // GUI while searching.
2166 void uci_async_command(const std::string& cmd) {
2168 if (cmd == "quit" || cmd == "stop")
2171 else if (cmd == "ponderhit")
2173 // The opponent has played the expected move. GUI sends "ponderhit" if
2174 // we were told to ponder on the same move the opponent has played. We
2175 // should continue searching but switching from pondering to normal search.
2176 Limits.ponder = false;
2178 if (StopOnPonderhit)
2184 // do_timer_event() is called by the timer thread when the timer triggers
2186 void do_timer_event() {
2188 static int lastInfoTime;
2189 int e = elapsed_search_time();
2191 // Print debug information every one second
2192 if (!lastInfoTime || get_system_time() - lastInfoTime >= 1000)
2194 lastInfoTime = get_system_time();
2197 dbg_print_hit_rate();
2200 // Should we stop the search?
2204 bool stillAtFirstMove = FirstRootMove
2205 && !AspirationFailLow
2206 && e > TimeMgr.available_time();
2208 bool noMoreTime = e > TimeMgr.maximum_time()
2209 || stillAtFirstMove;
2211 if ( (Limits.useTimeManagement() && noMoreTime)
2212 || (Limits.maxTime && e >= Limits.maxTime)
2213 /* missing nodes limit */ ) // FIXME