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/>.
44 #include "ucioption.h"
50 //// Local definitions
56 enum NodeType { NonPV, PV };
58 // Set to true to force running with one thread.
59 // Used for debugging SMP code.
60 const bool FakeSplit = false;
62 // ThreadsManager class is used to handle all the threads related stuff in search,
63 // init, starting, parking and, the most important, launching a slave thread at a
64 // split point are what this class does. All the access to shared thread data is
65 // done through this class, so that we avoid using global variables instead.
67 class ThreadsManager {
68 /* As long as the single ThreadsManager object is defined as a global we don't
69 need to explicitly initialize to zero its data members because variables with
70 static storage duration are automatically set to zero before enter main()
76 int active_threads() const { return ActiveThreads; }
77 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
79 bool available_thread_exists(int master) const;
80 bool thread_is_available(int slave, int master) const;
81 bool thread_should_stop(int threadID) const;
82 void wake_sleeping_thread(int threadID);
83 void idle_loop(int threadID, SplitPoint* sp);
86 void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
87 Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
91 volatile bool AllThreadsShouldExit;
92 Thread threads[MAX_THREADS];
94 WaitCondition WaitCond[MAX_THREADS];
98 // RootMove struct is used for moves at the root at the tree. For each
99 // root move, we store a score, a node count, and a PV (really a refutation
100 // in the case of moves which fail low).
104 RootMove() : mp_score(0), nodes(0) {}
106 // RootMove::operator<() is the comparison function used when
107 // sorting the moves. A move m1 is considered to be better
108 // than a move m2 if it has a higher score, or if the moves
109 // have equal score but m1 has the higher beta cut-off count.
110 bool operator<(const RootMove& m) const {
112 return score != m.score ? score < m.score : mp_score <= m.mp_score;
119 Move pv[PLY_MAX_PLUS_2];
123 // The RootMoveList class is essentially an array of RootMove objects, with
124 // a handful of methods for accessing the data in the individual moves.
129 RootMoveList(Position& pos, Move searchMoves[]);
131 Move move(int moveNum) const { return moves[moveNum].move; }
132 Move move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
133 int move_count() const { return count; }
134 Value move_score(int moveNum) const { return moves[moveNum].score; }
135 int64_t move_nodes(int moveNum) const { return moves[moveNum].nodes; }
136 void add_move_nodes(int moveNum, int64_t nodes) { moves[moveNum].nodes += nodes; }
137 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
139 void set_move_pv(int moveNum, const Move pv[]);
140 void score_moves(const Position& pos);
142 void sort_multipv(int n);
145 RootMove moves[MOVES_MAX];
150 // When formatting a move for std::cout we must know if we are in Chess960
151 // or not. To keep using the handy operator<<() on the move the trick is to
152 // embed this flag in the stream itself. Function-like named enum set960 is
153 // used as a custom manipulator and the stream internal general-purpose array,
154 // accessed through ios_base::iword(), is used to pass the flag to the move's
155 // operator<<() that will use it to properly format castling moves.
158 std::ostream& operator<< (std::ostream& os, const set960& m) {
160 os.iword(0) = int(m);
169 // Maximum depth for razoring
170 const Depth RazorDepth = 4 * ONE_PLY;
172 // Dynamic razoring margin based on depth
173 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
175 // Maximum depth for use of dynamic threat detection when null move fails low
176 const Depth ThreatDepth = 5 * ONE_PLY;
178 // Step 9. Internal iterative deepening
180 // Minimum depth for use of internal iterative deepening
181 const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
183 // At Non-PV nodes we do an internal iterative deepening search
184 // when the static evaluation is bigger then beta - IIDMargin.
185 const Value IIDMargin = Value(0x100);
187 // Step 11. Decide the new search depth
189 // Extensions. Configurable UCI options
190 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
191 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
192 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
194 // Minimum depth for use of singular extension
195 const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
197 // If the TT move is at least SingularExtensionMargin better then the
198 // remaining ones we will extend it.
199 const Value SingularExtensionMargin = Value(0x20);
201 // Step 12. Futility pruning
203 // Futility margin for quiescence search
204 const Value FutilityMarginQS = Value(0x80);
206 // Futility lookup tables (initialized at startup) and their getter functions
207 Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
208 int FutilityMoveCountArray[32]; // [depth]
210 inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
211 inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
213 // Step 14. Reduced search
215 // Reduction lookup tables (initialized at startup) and their getter functions
216 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
218 template <NodeType PV>
219 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
221 // Common adjustments
223 // Search depth at iteration 1
224 const Depth InitialDepth = ONE_PLY;
226 // Easy move margin. An easy move candidate must be at least this much
227 // better than the second best move.
228 const Value EasyMoveMargin = Value(0x200);
236 // Scores and number of times the best move changed for each iteration
237 Value ValueByIteration[PLY_MAX_PLUS_2];
238 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
240 // Search window management
246 // Time managment variables
247 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
248 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
249 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
254 std::ofstream LogFile;
256 // Multi-threads related variables
257 Depth MinimumSplitDepth;
258 int MaxThreadsPerSplitPoint;
259 ThreadsManager ThreadsMgr;
261 // Node counters, used only by thread[0] but try to keep in different cache
262 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
264 int NodesBetweenPolls = 30000;
271 Value id_loop(Position& pos, Move searchMoves[]);
272 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
274 template <NodeType PvNode, bool SpNode>
275 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
277 template <NodeType PvNode>
278 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
280 template <NodeType PvNode>
281 inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
283 return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
284 : search<PvNode, false>(pos, ss, alpha, beta, depth, ply);
287 template <NodeType PvNode>
288 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
290 bool connected_moves(const Position& pos, Move m1, Move m2);
291 bool value_is_mate(Value value);
292 Value value_to_tt(Value v, int ply);
293 Value value_from_tt(Value v, int ply);
294 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
295 bool connected_threat(const Position& pos, Move m, Move threat);
296 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
297 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
298 void update_killers(Move m, SearchStack* ss);
299 void update_gains(const Position& pos, Move move, Value before, Value after);
301 int current_search_time();
302 std::string value_to_uci(Value v);
303 int nps(const Position& pos);
304 void poll(const Position& pos);
306 void wait_for_stop_or_ponderhit();
307 void init_ss_array(SearchStack* ss, int size);
308 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
309 void insert_pv_in_tt(const Position& pos, Move pv[]);
310 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
312 #if !defined(_MSC_VER)
313 void *init_thread(void *threadID);
315 DWORD WINAPI init_thread(LPVOID threadID);
325 /// init_threads(), exit_threads() and nodes_searched() are helpers to
326 /// give accessibility to some TM methods from outside of current file.
328 void init_threads() { ThreadsMgr.init_threads(); }
329 void exit_threads() { ThreadsMgr.exit_threads(); }
332 /// init_search() is called during startup. It initializes various lookup tables
336 int d; // depth (ONE_PLY == 2)
337 int hd; // half depth (ONE_PLY == 1)
340 // Init reductions array
341 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
343 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
344 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
345 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
346 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
349 // Init futility margins array
350 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
351 FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
353 // Init futility move count array
354 for (d = 0; d < 32; d++)
355 FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
359 /// perft() is our utility to verify move generation is bug free. All the legal
360 /// moves up to given depth are generated and counted and the sum returned.
362 int perft(Position& pos, Depth depth)
364 MoveStack mlist[MOVES_MAX];
369 // Generate all legal moves
370 MoveStack* last = generate_moves(pos, mlist);
372 // If we are at the last ply we don't need to do and undo
373 // the moves, just to count them.
374 if (depth <= ONE_PLY)
375 return int(last - mlist);
377 // Loop through all legal moves
379 for (MoveStack* cur = mlist; cur != last; cur++)
382 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
383 sum += perft(pos, depth - ONE_PLY);
390 /// think() is the external interface to Stockfish's search, and is called when
391 /// the program receives the UCI 'go' command. It initializes various
392 /// search-related global variables, and calls root_search(). It returns false
393 /// when a quit command is received during the search.
395 bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
396 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
398 // Initialize global search variables
399 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
401 SearchStartTime = get_system_time();
402 ExactMaxTime = maxTime;
405 InfiniteSearch = infinite;
406 PonderSearch = ponder;
407 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
409 // Look for a book move, only during games, not tests
410 if (UseTimeManagement && get_option_value_bool("OwnBook"))
412 if (get_option_value_string("Book File") != OpeningBook.file_name())
413 OpeningBook.open(get_option_value_string("Book File"));
415 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
416 if (bookMove != MOVE_NONE)
419 wait_for_stop_or_ponderhit();
421 cout << "bestmove " << bookMove << endl;
426 // Read UCI option values
427 TT.set_size(get_option_value_int("Hash"));
428 if (button_was_pressed("Clear Hash"))
431 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
432 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
433 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
434 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
435 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
436 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
437 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
438 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
439 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
440 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
441 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
442 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
444 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * ONE_PLY;
445 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
446 MultiPV = get_option_value_int("MultiPV");
447 UseLogFile = get_option_value_bool("Use Search Log");
450 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
452 read_weights(pos.side_to_move());
454 // Set the number of active threads
455 int newActiveThreads = get_option_value_int("Threads");
456 if (newActiveThreads != ThreadsMgr.active_threads())
458 ThreadsMgr.set_active_threads(newActiveThreads);
459 init_eval(ThreadsMgr.active_threads());
463 int myTime = time[pos.side_to_move()];
464 int myIncrement = increment[pos.side_to_move()];
465 if (UseTimeManagement)
466 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
468 // Set best NodesBetweenPolls interval to avoid lagging under
469 // heavy time pressure.
471 NodesBetweenPolls = Min(MaxNodes, 30000);
472 else if (myTime && myTime < 1000)
473 NodesBetweenPolls = 1000;
474 else if (myTime && myTime < 5000)
475 NodesBetweenPolls = 5000;
477 NodesBetweenPolls = 30000;
479 // Write search information to log file
481 LogFile << "Searching: " << pos.to_fen() << endl
482 << "infinite: " << infinite
483 << " ponder: " << ponder
484 << " time: " << myTime
485 << " increment: " << myIncrement
486 << " moves to go: " << movesToGo << endl;
488 // We're ready to start thinking. Call the iterative deepening loop function
489 id_loop(pos, searchMoves);
500 // id_loop() is the main iterative deepening loop. It calls root_search
501 // repeatedly with increasing depth until the allocated thinking time has
502 // been consumed, the user stops the search, or the maximum search depth is
505 Value id_loop(Position& pos, Move searchMoves[]) {
507 SearchStack ss[PLY_MAX_PLUS_2];
508 Move pv[PLY_MAX_PLUS_2];
509 Move EasyMove = MOVE_NONE;
510 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
512 // Moves to search are verified, copied, scored and sorted
513 RootMoveList rml(pos, searchMoves);
515 // Handle special case of searching on a mate/stale position
516 if (rml.move_count() == 0)
519 wait_for_stop_or_ponderhit();
521 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
524 // Print RootMoveList startup scoring to the standard output,
525 // so to output information also for iteration 1.
526 cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
527 << "info depth " << 1
528 << "\ninfo depth " << 1
529 << " score " << value_to_uci(rml.move_score(0))
530 << " time " << current_search_time()
531 << " nodes " << pos.nodes_searched()
532 << " nps " << nps(pos)
533 << " pv " << rml.move(0) << "\n";
538 init_ss_array(ss, PLY_MAX_PLUS_2);
539 pv[0] = pv[1] = MOVE_NONE;
540 ValueByIteration[1] = rml.move_score(0);
543 // Is one move significantly better than others after initial scoring ?
544 if ( rml.move_count() == 1
545 || rml.move_score(0) > rml.move_score(1) + EasyMoveMargin)
546 EasyMove = rml.move(0);
548 // Iterative deepening loop
549 while (Iteration < PLY_MAX)
551 // Initialize iteration
553 BestMoveChangesByIteration[Iteration] = 0;
555 cout << "info depth " << Iteration << endl;
557 // Calculate dynamic aspiration window based on previous iterations
558 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
560 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
561 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
563 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
564 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
566 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
567 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
570 // Search to the current depth, rml is updated and sorted, alpha and beta could change
571 value = root_search(pos, ss, pv, rml, &alpha, &beta);
573 // Write PV to transposition table, in case the relevant entries have
574 // been overwritten during the search.
575 insert_pv_in_tt(pos, pv);
578 break; // Value cannot be trusted. Break out immediately!
580 //Save info about search result
581 ValueByIteration[Iteration] = value;
583 // Drop the easy move if differs from the new best move
584 if (pv[0] != EasyMove)
585 EasyMove = MOVE_NONE;
587 if (UseTimeManagement)
590 bool stopSearch = false;
592 // Stop search early if there is only a single legal move,
593 // we search up to Iteration 6 anyway to get a proper score.
594 if (Iteration >= 6 && rml.move_count() == 1)
597 // Stop search early when the last two iterations returned a mate score
599 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
600 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
603 // Stop search early if one move seems to be much better than the others
606 && ( ( rml.move_nodes(0) > (pos.nodes_searched() * 85) / 100
607 && current_search_time() > TimeMgr.available_time() / 16)
608 ||( rml.move_nodes(0) > (pos.nodes_searched() * 98) / 100
609 && current_search_time() > TimeMgr.available_time() / 32)))
612 // Add some extra time if the best move has changed during the last two iterations
613 if (Iteration > 5 && Iteration <= 50)
614 TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
615 BestMoveChangesByIteration[Iteration-1]);
617 // Stop search if most of MaxSearchTime is consumed at the end of the
618 // iteration. We probably don't have enough time to search the first
619 // move at the next iteration anyway.
620 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
626 StopOnPonderhit = true;
632 if (MaxDepth && Iteration >= MaxDepth)
636 // If we are pondering or in infinite search, we shouldn't print the
637 // best move before we are told to do so.
638 if (!AbortSearch && (PonderSearch || InfiniteSearch))
639 wait_for_stop_or_ponderhit();
641 // Print final search statistics
642 cout << "info nodes " << pos.nodes_searched()
643 << " nps " << nps(pos)
644 << " time " << current_search_time() << endl;
646 // Print the best move and the ponder move to the standard output
647 if (pv[0] == MOVE_NONE)
653 assert(pv[0] != MOVE_NONE);
655 cout << "bestmove " << pv[0];
657 if (pv[1] != MOVE_NONE)
658 cout << " ponder " << pv[1];
665 dbg_print_mean(LogFile);
667 if (dbg_show_hit_rate)
668 dbg_print_hit_rate(LogFile);
670 LogFile << "\nNodes: " << pos.nodes_searched()
671 << "\nNodes/second: " << nps(pos)
672 << "\nBest move: " << move_to_san(pos, pv[0]);
675 pos.do_move(pv[0], st);
676 LogFile << "\nPonder move: "
677 << move_to_san(pos, pv[1]) // Works also with MOVE_NONE
680 return rml.move_score(0);
684 // root_search() is the function which searches the root node. It is
685 // similar to search_pv except that it uses a different move ordering
686 // scheme, prints some information to the standard output and handles
687 // the fail low/high loops.
689 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
695 Depth depth, ext, newDepth;
696 Value value, alpha, beta;
697 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
698 int researchCountFH, researchCountFL;
700 researchCountFH = researchCountFL = 0;
703 isCheck = pos.is_check();
704 depth = (Iteration - 2) * ONE_PLY + InitialDepth;
706 // Step 1. Initialize node (polling is omitted at root)
707 ss->currentMove = ss->bestMove = MOVE_NONE;
709 // Step 2. Check for aborted search (omitted at root)
710 // Step 3. Mate distance pruning (omitted at root)
711 // Step 4. Transposition table lookup (omitted at root)
713 // Step 5. Evaluate the position statically
714 // At root we do this only to get reference value for child nodes
715 ss->evalMargin = VALUE_NONE;
716 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
718 // Step 6. Razoring (omitted at root)
719 // Step 7. Static null move pruning (omitted at root)
720 // Step 8. Null move search with verification search (omitted at root)
721 // Step 9. Internal iterative deepening (omitted at root)
723 // Step extra. Fail low loop
724 // We start with small aspiration window and in case of fail low, we research
725 // with bigger window until we are not failing low anymore.
728 // Sort the moves before to (re)search
729 rml.score_moves(pos);
732 // Step 10. Loop through all moves in the root move list
733 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
735 // This is used by time management
736 FirstRootMove = (i == 0);
738 // Save the current node count before the move is searched
739 nodes = pos.nodes_searched();
741 // Pick the next root move, and print the move and the move number to
742 // the standard output.
743 move = ss->currentMove = rml.move(i);
745 if (current_search_time() >= 1000)
746 cout << "info currmove " << move
747 << " currmovenumber " << i + 1 << endl;
749 moveIsCheck = pos.move_is_check(move);
750 captureOrPromotion = pos.move_is_capture_or_promotion(move);
752 // Step 11. Decide the new search depth
753 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
754 newDepth = depth + ext;
756 // Step 12. Futility pruning (omitted at root)
758 // Step extra. Fail high loop
759 // If move fails high, we research with bigger window until we are not failing
761 value = - VALUE_INFINITE;
765 // Step 13. Make the move
766 pos.do_move(move, st, ci, moveIsCheck);
768 // Step extra. pv search
769 // We do pv search for first moves (i < MultiPV)
770 // and for fail high research (value > alpha)
771 if (i < MultiPV || value > alpha)
773 // Aspiration window is disabled in multi-pv case
775 alpha = -VALUE_INFINITE;
777 // Full depth PV search, done on first move or after a fail high
778 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
782 // Step 14. Reduced search
783 // if the move fails high will be re-searched at full depth
784 bool doFullDepthSearch = true;
786 if ( depth >= 3 * ONE_PLY
788 && !captureOrPromotion
789 && !move_is_castle(move))
791 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
794 assert(newDepth-ss->reduction >= ONE_PLY);
796 // Reduced depth non-pv search using alpha as upperbound
797 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
798 doFullDepthSearch = (value > alpha);
801 // The move failed high, but if reduction is very big we could
802 // face a false positive, retry with a less aggressive reduction,
803 // if the move fails high again then go with full depth search.
804 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
806 assert(newDepth - ONE_PLY >= ONE_PLY);
808 ss->reduction = ONE_PLY;
809 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
810 doFullDepthSearch = (value > alpha);
812 ss->reduction = DEPTH_ZERO; // Restore original reduction
815 // Step 15. Full depth search
816 if (doFullDepthSearch)
818 // Full depth non-pv search using alpha as upperbound
819 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
821 // If we are above alpha then research at same depth but as PV
822 // to get a correct score or eventually a fail high above beta.
824 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
828 // Step 16. Undo move
831 // Can we exit fail high loop ?
832 if (AbortSearch || value < beta)
835 // We are failing high and going to do a research. It's important to update
836 // the score before research in case we run out of time while researching.
837 rml.set_move_score(i, value);
839 extract_pv_from_tt(pos, move, pv);
840 rml.set_move_pv(i, pv);
842 // Print information to the standard output
843 print_pv_info(pos, pv, alpha, beta, value);
845 // Prepare for a research after a fail high, each time with a wider window
846 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
849 } // End of fail high loop
851 // Finished searching the move. If AbortSearch is true, the search
852 // was aborted because the user interrupted the search or because we
853 // ran out of time. In this case, the return value of the search cannot
854 // be trusted, and we break out of the loop without updating the best
859 // Remember searched nodes counts for this move
860 rml.add_move_nodes(i, pos.nodes_searched() - nodes);
862 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
863 assert(value < beta);
865 // Step 17. Check for new best move
866 if (value <= alpha && i >= MultiPV)
867 rml.set_move_score(i, -VALUE_INFINITE);
870 // PV move or new best move!
873 rml.set_move_score(i, value);
875 extract_pv_from_tt(pos, move, pv);
876 rml.set_move_pv(i, pv);
880 // We record how often the best move has been changed in each
881 // iteration. This information is used for time managment: When
882 // the best move changes frequently, we allocate some more time.
884 BestMoveChangesByIteration[Iteration]++;
886 // Print information to the standard output
887 print_pv_info(pos, pv, alpha, beta, value);
889 // Raise alpha to setup proper non-pv search upper bound
896 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
898 cout << "info multipv " << j + 1
899 << " score " << value_to_uci(rml.move_score(j))
900 << " depth " << (j <= i ? Iteration : Iteration - 1)
901 << " time " << current_search_time()
902 << " nodes " << pos.nodes_searched()
903 << " nps " << nps(pos)
906 for (int k = 0; rml.move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
907 cout << rml.move_pv(j, k) << " ";
911 alpha = rml.move_score(Min(i, MultiPV - 1));
913 } // PV move or new best move
915 assert(alpha >= *alphaPtr);
917 AspirationFailLow = (alpha == *alphaPtr);
919 if (AspirationFailLow && StopOnPonderhit)
920 StopOnPonderhit = false;
923 // Can we exit fail low loop ?
924 if (AbortSearch || !AspirationFailLow)
927 // Prepare for a research after a fail low, each time with a wider window
928 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
933 // Sort the moves before to return
940 // search<>() is the main search function for both PV and non-PV nodes and for
941 // normal and SplitPoint nodes. When called just after a split point the search
942 // is simpler because we have already probed the hash table, done a null move
943 // search, and searched the first move before splitting, we don't have to repeat
944 // all this work again. We also don't need to store anything to the hash table
945 // here: This is taken care of after we return from the split point.
947 template <NodeType PvNode, bool SpNode>
948 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
950 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
951 assert(beta > alpha && beta <= VALUE_INFINITE);
952 assert(PvNode || alpha == beta - 1);
953 assert(ply > 0 && ply < PLY_MAX);
954 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
956 Move movesSearched[MOVES_MAX];
960 Move ttMove, move, excludedMove, threatMove;
963 Value bestValue, value, oldAlpha;
964 Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
965 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
966 bool mateThreat = false;
968 int threadID = pos.thread();
969 SplitPoint* sp = NULL;
970 refinedValue = bestValue = value = -VALUE_INFINITE;
972 isCheck = pos.is_check();
978 ttMove = excludedMove = MOVE_NONE;
979 threatMove = sp->threatMove;
980 mateThreat = sp->mateThreat;
981 goto split_point_start;
982 } else {} // Hack to fix icc's "statement is unreachable" warning
984 // Step 1. Initialize node and poll. Polling can abort search
985 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
986 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
988 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
994 // Step 2. Check for aborted search and immediate draw
995 if ( AbortSearch || ThreadsMgr.thread_should_stop(threadID)
996 || pos.is_draw() || ply >= PLY_MAX - 1)
999 // Step 3. Mate distance pruning
1000 alpha = Max(value_mated_in(ply), alpha);
1001 beta = Min(value_mate_in(ply+1), beta);
1005 // Step 4. Transposition table lookup
1007 // We don't want the score of a partial search to overwrite a previous full search
1008 // TT value, so we use a different position key in case of an excluded move exists.
1009 excludedMove = ss->excludedMove;
1010 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1012 tte = TT.retrieve(posKey);
1013 ttMove = tte ? tte->move() : MOVE_NONE;
1015 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1016 // This is to avoid problems in the following areas:
1018 // * Repetition draw detection
1019 // * Fifty move rule detection
1020 // * Searching for a mate
1021 // * Printing of full PV line
1022 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1025 ss->bestMove = ttMove; // Can be MOVE_NONE
1026 return value_from_tt(tte->value(), ply);
1029 // Step 5. Evaluate the position statically and
1030 // update gain statistics of parent move.
1032 ss->eval = ss->evalMargin = VALUE_NONE;
1035 assert(tte->static_value() != VALUE_NONE);
1037 ss->eval = tte->static_value();
1038 ss->evalMargin = tte->static_value_margin();
1039 refinedValue = refine_eval(tte, ss->eval, ply);
1043 refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
1044 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
1047 // Save gain for the parent non-capture move
1048 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1050 // Step 6. Razoring (is omitted in PV nodes)
1052 && depth < RazorDepth
1054 && refinedValue < beta - razor_margin(depth)
1055 && ttMove == MOVE_NONE
1056 && (ss-1)->currentMove != MOVE_NULL
1057 && !value_is_mate(beta)
1058 && !pos.has_pawn_on_7th(pos.side_to_move()))
1060 Value rbeta = beta - razor_margin(depth);
1061 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
1063 // Logically we should return (v + razor_margin(depth)), but
1064 // surprisingly this did slightly weaker in tests.
1068 // Step 7. Static null move pruning (is omitted in PV nodes)
1069 // We're betting that the opponent doesn't have a move that will reduce
1070 // the score by more than futility_margin(depth) if we do a null move.
1072 && !ss->skipNullMove
1073 && depth < RazorDepth
1075 && refinedValue >= beta + futility_margin(depth, 0)
1076 && !value_is_mate(beta)
1077 && pos.non_pawn_material(pos.side_to_move()))
1078 return refinedValue - futility_margin(depth, 0);
1080 // Step 8. Null move search with verification search (is omitted in PV nodes)
1082 && !ss->skipNullMove
1085 && refinedValue >= beta
1086 && !value_is_mate(beta)
1087 && pos.non_pawn_material(pos.side_to_move()))
1089 ss->currentMove = MOVE_NULL;
1091 // Null move dynamic reduction based on depth
1092 int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
1094 // Null move dynamic reduction based on value
1095 if (refinedValue - beta > PawnValueMidgame)
1098 pos.do_null_move(st);
1099 (ss+1)->skipNullMove = true;
1100 nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
1101 (ss+1)->skipNullMove = false;
1102 pos.undo_null_move();
1104 if (nullValue >= beta)
1106 // Do not return unproven mate scores
1107 if (nullValue >= value_mate_in(PLY_MAX))
1110 if (depth < 6 * ONE_PLY)
1113 // Do verification search at high depths
1114 ss->skipNullMove = true;
1115 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
1116 ss->skipNullMove = false;
1123 // The null move failed low, which means that we may be faced with
1124 // some kind of threat. If the previous move was reduced, check if
1125 // the move that refuted the null move was somehow connected to the
1126 // move which was reduced. If a connection is found, return a fail
1127 // low score (which will cause the reduced move to fail high in the
1128 // parent node, which will trigger a re-search with full depth).
1129 if (nullValue == value_mated_in(ply + 2))
1132 threatMove = (ss+1)->bestMove;
1133 if ( depth < ThreatDepth
1134 && (ss-1)->reduction
1135 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1140 // Step 9. Internal iterative deepening
1141 if ( depth >= IIDDepth[PvNode]
1142 && ttMove == MOVE_NONE
1143 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1145 Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
1147 ss->skipNullMove = true;
1148 search<PvNode>(pos, ss, alpha, beta, d, ply);
1149 ss->skipNullMove = false;
1151 ttMove = ss->bestMove;
1152 tte = TT.retrieve(posKey);
1155 // Expensive mate threat detection (only for PV nodes)
1157 mateThreat = pos.has_mate_threat();
1159 split_point_start: // At split points actual search starts from here
1161 // Initialize a MovePicker object for the current position
1162 // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
1163 MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1164 MovePicker& mp = SpNode ? *sp->mp : mpBase;
1166 ss->bestMove = MOVE_NONE;
1167 singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
1168 futilityBase = ss->eval + ss->evalMargin;
1169 singularExtensionNode = !SpNode
1170 && depth >= SingularExtensionDepth[PvNode]
1173 && !excludedMove // Do not allow recursive singular extension search
1174 && (tte->type() & VALUE_TYPE_LOWER)
1175 && tte->depth() >= depth - 3 * ONE_PLY;
1178 lock_grab(&(sp->lock));
1179 bestValue = sp->bestValue;
1182 // Step 10. Loop through moves
1183 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1184 while ( bestValue < beta
1185 && (move = mp.get_next_move()) != MOVE_NONE
1186 && !ThreadsMgr.thread_should_stop(threadID))
1188 assert(move_is_ok(move));
1192 moveCount = ++sp->moveCount;
1193 lock_release(&(sp->lock));
1195 else if (move == excludedMove)
1198 movesSearched[moveCount++] = move;
1200 moveIsCheck = pos.move_is_check(move, ci);
1201 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1203 // Step 11. Decide the new search depth
1204 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1206 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1207 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1208 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1209 // lower then ttValue minus a margin then we extend ttMove.
1210 if ( singularExtensionNode
1211 && move == tte->move()
1214 Value ttValue = value_from_tt(tte->value(), ply);
1216 if (abs(ttValue) < VALUE_KNOWN_WIN)
1218 Value b = ttValue - SingularExtensionMargin;
1219 ss->excludedMove = move;
1220 ss->skipNullMove = true;
1221 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1222 ss->skipNullMove = false;
1223 ss->excludedMove = MOVE_NONE;
1224 ss->bestMove = MOVE_NONE;
1230 // Update current move (this must be done after singular extension search)
1231 ss->currentMove = move;
1232 newDepth = depth - ONE_PLY + ext;
1234 // Step 12. Futility pruning (is omitted in PV nodes)
1236 && !captureOrPromotion
1240 && !move_is_castle(move))
1242 // Move count based pruning
1243 if ( moveCount >= futility_move_count(depth)
1244 && !(threatMove && connected_threat(pos, move, threatMove))
1245 && bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
1248 lock_grab(&(sp->lock));
1253 // Value based pruning
1254 // We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
1255 // but fixing this made program slightly weaker.
1256 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1257 futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
1258 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1260 if (futilityValueScaled < beta)
1264 lock_grab(&(sp->lock));
1265 if (futilityValueScaled > sp->bestValue)
1266 sp->bestValue = bestValue = futilityValueScaled;
1268 else if (futilityValueScaled > bestValue)
1269 bestValue = futilityValueScaled;
1275 // Step 13. Make the move
1276 pos.do_move(move, st, ci, moveIsCheck);
1278 // Step extra. pv search (only in PV nodes)
1279 // The first move in list is the expected PV
1280 if (!SpNode && PvNode && moveCount == 1)
1281 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1284 // Step 14. Reduced depth search
1285 // If the move fails high will be re-searched at full depth.
1286 bool doFullDepthSearch = true;
1288 if ( depth >= 3 * ONE_PLY
1289 && !captureOrPromotion
1291 && !move_is_castle(move)
1292 && !(ss->killers[0] == move || ss->killers[1] == move))
1294 ss->reduction = reduction<PvNode>(depth, moveCount);
1297 alpha = SpNode ? sp->alpha : alpha;
1298 Depth d = newDepth - ss->reduction;
1299 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1301 doFullDepthSearch = (value > alpha);
1304 // The move failed high, but if reduction is very big we could
1305 // face a false positive, retry with a less aggressive reduction,
1306 // if the move fails high again then go with full depth search.
1307 if (doFullDepthSearch && ss->reduction > 2 * ONE_PLY)
1309 assert(newDepth - ONE_PLY >= ONE_PLY);
1311 ss->reduction = ONE_PLY;
1312 alpha = SpNode ? sp->alpha : alpha;
1313 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1314 doFullDepthSearch = (value > alpha);
1316 ss->reduction = DEPTH_ZERO; // Restore original reduction
1319 // Step 15. Full depth search
1320 if (doFullDepthSearch)
1322 alpha = SpNode ? sp->alpha : alpha;
1323 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1325 // Step extra. pv search (only in PV nodes)
1326 // Search only for possible new PV nodes, if instead value >= beta then
1327 // parent node fails low with value <= alpha and tries another move.
1328 if (PvNode && value > alpha && value < beta)
1329 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1333 // Step 16. Undo move
1334 pos.undo_move(move);
1336 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1338 // Step 17. Check for new best move
1341 lock_grab(&(sp->lock));
1342 bestValue = sp->bestValue;
1346 if (value > bestValue && !(SpNode && ThreadsMgr.thread_should_stop(threadID)))
1351 sp->bestValue = value;
1355 if (SpNode && (!PvNode || value >= beta))
1356 sp->stopRequest = true;
1358 if (PvNode && value < beta) // We want always alpha < beta
1365 if (value == value_mate_in(ply + 1))
1366 ss->mateKiller = move;
1368 ss->bestMove = move;
1371 sp->parentSstack->bestMove = move;
1375 // Step 18. Check for split
1377 && depth >= MinimumSplitDepth
1378 && ThreadsMgr.active_threads() > 1
1380 && ThreadsMgr.available_thread_exists(threadID)
1382 && !ThreadsMgr.thread_should_stop(threadID)
1384 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1385 threatMove, mateThreat, moveCount, &mp, PvNode);
1388 // Step 19. Check for mate and stalemate
1389 // All legal moves have been searched and if there are
1390 // no legal moves, it must be mate or stalemate.
1391 // If one move was excluded return fail low score.
1392 if (!SpNode && !moveCount)
1393 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1395 // Step 20. Update tables
1396 // If the search is not aborted, update the transposition table,
1397 // history counters, and killer moves.
1398 if (!SpNode && !AbortSearch && !ThreadsMgr.thread_should_stop(threadID))
1400 move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
1401 vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
1402 : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
1404 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
1406 // Update killers and history only for non capture moves that fails high
1407 if ( bestValue >= beta
1408 && !pos.move_is_capture_or_promotion(move))
1410 update_history(pos, move, depth, movesSearched, moveCount);
1411 update_killers(move, ss);
1417 // Here we have the lock still grabbed
1418 sp->slaves[threadID] = 0;
1419 sp->nodes += pos.nodes_searched();
1420 lock_release(&(sp->lock));
1423 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1429 // qsearch() is the quiescence search function, which is called by the main
1430 // search function when the remaining depth is zero (or, to be more precise,
1431 // less than ONE_PLY).
1433 template <NodeType PvNode>
1434 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1436 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1437 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1438 assert(PvNode || alpha == beta - 1);
1440 assert(ply > 0 && ply < PLY_MAX);
1441 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1445 Value bestValue, value, evalMargin, futilityValue, futilityBase;
1446 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1448 Value oldAlpha = alpha;
1450 ss->bestMove = ss->currentMove = MOVE_NONE;
1452 // Check for an instant draw or maximum ply reached
1453 if (pos.is_draw() || ply >= PLY_MAX - 1)
1456 // Transposition table lookup. At PV nodes, we don't use the TT for
1457 // pruning, but only for move ordering.
1458 tte = TT.retrieve(pos.get_key());
1459 ttMove = (tte ? tte->move() : MOVE_NONE);
1461 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1463 ss->bestMove = ttMove; // Can be MOVE_NONE
1464 return value_from_tt(tte->value(), ply);
1467 isCheck = pos.is_check();
1469 // Evaluate the position statically
1472 bestValue = futilityBase = -VALUE_INFINITE;
1473 ss->eval = evalMargin = VALUE_NONE;
1474 deepChecks = enoughMaterial = false;
1480 assert(tte->static_value() != VALUE_NONE);
1482 evalMargin = tte->static_value_margin();
1483 ss->eval = bestValue = tte->static_value();
1486 ss->eval = bestValue = evaluate(pos, evalMargin);
1488 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1490 // Stand pat. Return immediately if static value is at least beta
1491 if (bestValue >= beta)
1494 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
1499 if (PvNode && bestValue > alpha)
1502 // If we are near beta then try to get a cutoff pushing checks a bit further
1503 deepChecks = (depth == -ONE_PLY && bestValue >= beta - PawnValueMidgame / 8);
1505 // Futility pruning parameters, not needed when in check
1506 futilityBase = ss->eval + evalMargin + FutilityMarginQS;
1507 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1510 // Initialize a MovePicker object for the current position, and prepare
1511 // to search the moves. Because the depth is <= 0 here, only captures,
1512 // queen promotions and checks (only if depth == 0 or depth == -ONE_PLY
1513 // and we are near beta) will be generated.
1514 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? DEPTH_ZERO : depth, H);
1517 // Loop through the moves until no moves remain or a beta cutoff occurs
1518 while ( alpha < beta
1519 && (move = mp.get_next_move()) != MOVE_NONE)
1521 assert(move_is_ok(move));
1523 moveIsCheck = pos.move_is_check(move, ci);
1531 && !move_is_promotion(move)
1532 && !pos.move_is_passed_pawn_push(move))
1534 futilityValue = futilityBase
1535 + pos.endgame_value_of_piece_on(move_to(move))
1536 + (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
1538 if (futilityValue < alpha)
1540 if (futilityValue > bestValue)
1541 bestValue = futilityValue;
1546 // Detect non-capture evasions that are candidate to be pruned
1547 evasionPrunable = isCheck
1548 && bestValue > value_mated_in(PLY_MAX)
1549 && !pos.move_is_capture(move)
1550 && !pos.can_castle(pos.side_to_move());
1552 // Don't search moves with negative SEE values
1554 && (!isCheck || evasionPrunable)
1556 && !move_is_promotion(move)
1557 && pos.see_sign(move) < 0)
1560 // Update current move
1561 ss->currentMove = move;
1563 // Make and search the move
1564 pos.do_move(move, st, ci, moveIsCheck);
1565 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
1566 pos.undo_move(move);
1568 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1571 if (value > bestValue)
1577 ss->bestMove = move;
1582 // All legal moves have been searched. A special case: If we're in check
1583 // and no legal moves were found, it is checkmate.
1584 if (isCheck && bestValue == -VALUE_INFINITE)
1585 return value_mated_in(ply);
1587 // Update transposition table
1588 Depth d = (depth == DEPTH_ZERO ? DEPTH_ZERO : DEPTH_ZERO - ONE_PLY);
1589 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1590 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, evalMargin);
1592 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1598 // connected_moves() tests whether two moves are 'connected' in the sense
1599 // that the first move somehow made the second move possible (for instance
1600 // if the moving piece is the same in both moves). The first move is assumed
1601 // to be the move that was made to reach the current position, while the
1602 // second move is assumed to be a move from the current position.
1604 bool connected_moves(const Position& pos, Move m1, Move m2) {
1606 Square f1, t1, f2, t2;
1609 assert(move_is_ok(m1));
1610 assert(move_is_ok(m2));
1612 if (m2 == MOVE_NONE)
1615 // Case 1: The moving piece is the same in both moves
1621 // Case 2: The destination square for m2 was vacated by m1
1627 // Case 3: Moving through the vacated square
1628 if ( piece_is_slider(pos.piece_on(f2))
1629 && bit_is_set(squares_between(f2, t2), f1))
1632 // Case 4: The destination square for m2 is defended by the moving piece in m1
1633 p = pos.piece_on(t1);
1634 if (bit_is_set(pos.attacks_from(p, t1), t2))
1637 // Case 5: Discovered check, checking piece is the piece moved in m1
1638 if ( piece_is_slider(p)
1639 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1640 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1642 // discovered_check_candidates() works also if the Position's side to
1643 // move is the opposite of the checking piece.
1644 Color them = opposite_color(pos.side_to_move());
1645 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1647 if (bit_is_set(dcCandidates, f2))
1654 // value_is_mate() checks if the given value is a mate one eventually
1655 // compensated for the ply.
1657 bool value_is_mate(Value value) {
1659 assert(abs(value) <= VALUE_INFINITE);
1661 return value <= value_mated_in(PLY_MAX)
1662 || value >= value_mate_in(PLY_MAX);
1666 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1667 // "plies to mate from the current ply". Non-mate scores are unchanged.
1668 // The function is called before storing a value to the transposition table.
1670 Value value_to_tt(Value v, int ply) {
1672 if (v >= value_mate_in(PLY_MAX))
1675 if (v <= value_mated_in(PLY_MAX))
1682 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1683 // the transposition table to a mate score corrected for the current ply.
1685 Value value_from_tt(Value v, int ply) {
1687 if (v >= value_mate_in(PLY_MAX))
1690 if (v <= value_mated_in(PLY_MAX))
1697 // extension() decides whether a move should be searched with normal depth,
1698 // or with extended depth. Certain classes of moves (checking moves, in
1699 // particular) are searched with bigger depth than ordinary moves and in
1700 // any case are marked as 'dangerous'. Note that also if a move is not
1701 // extended, as example because the corresponding UCI option is set to zero,
1702 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1703 template <NodeType PvNode>
1704 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1705 bool singleEvasion, bool mateThreat, bool* dangerous) {
1707 assert(m != MOVE_NONE);
1709 Depth result = DEPTH_ZERO;
1710 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1714 if (moveIsCheck && pos.see_sign(m) >= 0)
1715 result += CheckExtension[PvNode];
1718 result += SingleEvasionExtension[PvNode];
1721 result += MateThreatExtension[PvNode];
1724 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1726 Color c = pos.side_to_move();
1727 if (relative_rank(c, move_to(m)) == RANK_7)
1729 result += PawnPushTo7thExtension[PvNode];
1732 if (pos.pawn_is_passed(c, move_to(m)))
1734 result += PassedPawnExtension[PvNode];
1739 if ( captureOrPromotion
1740 && pos.type_of_piece_on(move_to(m)) != PAWN
1741 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1742 - pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
1743 && !move_is_promotion(m)
1746 result += PawnEndgameExtension[PvNode];
1751 && captureOrPromotion
1752 && pos.type_of_piece_on(move_to(m)) != PAWN
1753 && pos.see_sign(m) >= 0)
1755 result += ONE_PLY / 2;
1759 return Min(result, ONE_PLY);
1763 // connected_threat() tests whether it is safe to forward prune a move or if
1764 // is somehow coonected to the threat move returned by null search.
1766 bool connected_threat(const Position& pos, Move m, Move threat) {
1768 assert(move_is_ok(m));
1769 assert(threat && move_is_ok(threat));
1770 assert(!pos.move_is_check(m));
1771 assert(!pos.move_is_capture_or_promotion(m));
1772 assert(!pos.move_is_passed_pawn_push(m));
1774 Square mfrom, mto, tfrom, tto;
1776 mfrom = move_from(m);
1778 tfrom = move_from(threat);
1779 tto = move_to(threat);
1781 // Case 1: Don't prune moves which move the threatened piece
1785 // Case 2: If the threatened piece has value less than or equal to the
1786 // value of the threatening piece, don't prune move which defend it.
1787 if ( pos.move_is_capture(threat)
1788 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1789 || pos.type_of_piece_on(tfrom) == KING)
1790 && pos.move_attacks_square(m, tto))
1793 // Case 3: If the moving piece in the threatened move is a slider, don't
1794 // prune safe moves which block its ray.
1795 if ( piece_is_slider(pos.piece_on(tfrom))
1796 && bit_is_set(squares_between(tfrom, tto), mto)
1797 && pos.see_sign(m) >= 0)
1804 // ok_to_use_TT() returns true if a transposition table score
1805 // can be used at a given point in search.
1807 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1809 Value v = value_from_tt(tte->value(), ply);
1811 return ( tte->depth() >= depth
1812 || v >= Max(value_mate_in(PLY_MAX), beta)
1813 || v < Min(value_mated_in(PLY_MAX), beta))
1815 && ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
1816 || ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
1820 // refine_eval() returns the transposition table score if
1821 // possible otherwise falls back on static position evaluation.
1823 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1827 Value v = value_from_tt(tte->value(), ply);
1829 if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
1830 || ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
1837 // update_history() registers a good move that produced a beta-cutoff
1838 // in history and marks as failures all the other moves of that ply.
1840 void update_history(const Position& pos, Move move, Depth depth,
1841 Move movesSearched[], int moveCount) {
1844 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
1846 for (int i = 0; i < moveCount - 1; i++)
1848 m = movesSearched[i];
1852 if (!pos.move_is_capture_or_promotion(m))
1853 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
1858 // update_killers() add a good move that produced a beta-cutoff
1859 // among the killer moves of that ply.
1861 void update_killers(Move m, SearchStack* ss) {
1863 if (m == ss->killers[0])
1866 ss->killers[1] = ss->killers[0];
1871 // update_gains() updates the gains table of a non-capture move given
1872 // the static position evaluation before and after the move.
1874 void update_gains(const Position& pos, Move m, Value before, Value after) {
1877 && before != VALUE_NONE
1878 && after != VALUE_NONE
1879 && pos.captured_piece_type() == PIECE_TYPE_NONE
1880 && !move_is_special(m))
1881 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
1885 // current_search_time() returns the number of milliseconds which have passed
1886 // since the beginning of the current search.
1888 int current_search_time() {
1890 return get_system_time() - SearchStartTime;
1894 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
1896 std::string value_to_uci(Value v) {
1898 std::stringstream s;
1900 if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
1901 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
1903 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
1908 // nps() computes the current nodes/second count.
1910 int nps(const Position& pos) {
1912 int t = current_search_time();
1913 return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
1917 // poll() performs two different functions: It polls for user input, and it
1918 // looks at the time consumed so far and decides if it's time to abort the
1921 void poll(const Position& pos) {
1923 static int lastInfoTime;
1924 int t = current_search_time();
1929 // We are line oriented, don't read single chars
1930 std::string command;
1932 if (!std::getline(std::cin, command))
1935 if (command == "quit")
1938 PonderSearch = false;
1942 else if (command == "stop")
1945 PonderSearch = false;
1947 else if (command == "ponderhit")
1951 // Print search information
1955 else if (lastInfoTime > t)
1956 // HACK: Must be a new search where we searched less than
1957 // NodesBetweenPolls nodes during the first second of search.
1960 else if (t - lastInfoTime >= 1000)
1967 if (dbg_show_hit_rate)
1968 dbg_print_hit_rate();
1970 cout << "info nodes " << pos.nodes_searched() << " nps " << nps(pos)
1971 << " time " << t << endl;
1974 // Should we stop the search?
1978 bool stillAtFirstMove = FirstRootMove
1979 && !AspirationFailLow
1980 && t > TimeMgr.available_time();
1982 bool noMoreTime = t > TimeMgr.maximum_time()
1983 || stillAtFirstMove;
1985 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
1986 || (ExactMaxTime && t >= ExactMaxTime)
1987 || (Iteration >= 3 && MaxNodes && pos.nodes_searched() >= MaxNodes))
1992 // ponderhit() is called when the program is pondering (i.e. thinking while
1993 // it's the opponent's turn to move) in order to let the engine know that
1994 // it correctly predicted the opponent's move.
1998 int t = current_search_time();
1999 PonderSearch = false;
2001 bool stillAtFirstMove = FirstRootMove
2002 && !AspirationFailLow
2003 && t > TimeMgr.available_time();
2005 bool noMoreTime = t > TimeMgr.maximum_time()
2006 || stillAtFirstMove;
2008 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2013 // init_ss_array() does a fast reset of the first entries of a SearchStack
2014 // array and of all the excludedMove and skipNullMove entries.
2016 void init_ss_array(SearchStack* ss, int size) {
2018 for (int i = 0; i < size; i++, ss++)
2020 ss->excludedMove = MOVE_NONE;
2021 ss->skipNullMove = false;
2022 ss->reduction = DEPTH_ZERO;
2026 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2031 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2032 // while the program is pondering. The point is to work around a wrinkle in
2033 // the UCI protocol: When pondering, the engine is not allowed to give a
2034 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2035 // We simply wait here until one of these commands is sent, and return,
2036 // after which the bestmove and pondermove will be printed (in id_loop()).
2038 void wait_for_stop_or_ponderhit() {
2040 std::string command;
2044 if (!std::getline(std::cin, command))
2047 if (command == "quit")
2052 else if (command == "ponderhit" || command == "stop")
2058 // print_pv_info() prints to standard output and eventually to log file information on
2059 // the current PV line. It is called at each iteration or after a new pv is found.
2061 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2063 cout << "info depth " << Iteration
2064 << " score " << value_to_uci(value)
2065 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2066 << " time " << current_search_time()
2067 << " nodes " << pos.nodes_searched()
2068 << " nps " << nps(pos)
2071 for (Move* m = pv; *m != MOVE_NONE; m++)
2078 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2079 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2081 LogFile << pretty_pv(pos, current_search_time(), Iteration, value, t, pv) << endl;
2086 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2087 // the PV back into the TT. This makes sure the old PV moves are searched
2088 // first, even if the old TT entries have been overwritten.
2090 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2094 Position p(pos, pos.thread());
2095 Value v, m = VALUE_NONE;
2097 for (int i = 0; pv[i] != MOVE_NONE; i++)
2099 tte = TT.retrieve(p.get_key());
2100 if (!tte || tte->move() != pv[i])
2102 v = (p.is_check() ? VALUE_NONE : evaluate(p, m));
2103 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, m);
2105 p.do_move(pv[i], st);
2110 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2111 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2112 // allow to always have a ponder move even when we fail high at root and also a
2113 // long PV to print that is important for position analysis.
2115 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2119 Position p(pos, pos.thread());
2122 assert(bestMove != MOVE_NONE);
2125 p.do_move(pv[ply++], st);
2127 while ( (tte = TT.retrieve(p.get_key())) != NULL
2128 && tte->move() != MOVE_NONE
2129 && move_is_legal(p, tte->move())
2131 && (!p.is_draw() || ply < 2))
2133 pv[ply] = tte->move();
2134 p.do_move(pv[ply++], st);
2136 pv[ply] = MOVE_NONE;
2140 // init_thread() is the function which is called when a new thread is
2141 // launched. It simply calls the idle_loop() function with the supplied
2142 // threadID. There are two versions of this function; one for POSIX
2143 // threads and one for Windows threads.
2145 #if !defined(_MSC_VER)
2147 void* init_thread(void *threadID) {
2149 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2155 DWORD WINAPI init_thread(LPVOID threadID) {
2157 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2164 /// The ThreadsManager class
2167 // idle_loop() is where the threads are parked when they have no work to do.
2168 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2169 // object for which the current thread is the master.
2171 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2173 assert(threadID >= 0 && threadID < MAX_THREADS);
2177 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2178 // master should exit as last one.
2179 if (AllThreadsShouldExit)
2182 threads[threadID].state = THREAD_TERMINATED;
2186 // If we are not thinking, wait for a condition to be signaled
2187 // instead of wasting CPU time polling for work.
2188 while ( threadID >= ActiveThreads
2189 || threads[threadID].state == THREAD_INITIALIZING
2190 || (!sp && threads[threadID].state == THREAD_AVAILABLE))
2193 assert(threadID != 0);
2195 if (AllThreadsShouldExit)
2200 // Retest condition under lock protection
2201 if (!( threadID >= ActiveThreads
2202 || threads[threadID].state == THREAD_INITIALIZING
2203 || (!sp && threads[threadID].state == THREAD_AVAILABLE)))
2205 lock_release(&MPLock);
2209 // Put thread to sleep
2210 threads[threadID].state = THREAD_AVAILABLE;
2211 cond_wait(&WaitCond[threadID], &MPLock);
2212 lock_release(&MPLock);
2215 // If this thread has been assigned work, launch a search
2216 if (threads[threadID].state == THREAD_WORKISWAITING)
2218 assert(!AllThreadsShouldExit);
2220 threads[threadID].state = THREAD_SEARCHING;
2222 // Here we call search() with SplitPoint template parameter set to true
2223 SplitPoint* tsp = threads[threadID].splitPoint;
2224 Position pos(*tsp->pos, threadID);
2225 SearchStack* ss = tsp->sstack[threadID] + 1;
2229 search<PV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2231 search<NonPV, true>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
2233 assert(threads[threadID].state == THREAD_SEARCHING);
2235 threads[threadID].state = THREAD_AVAILABLE;
2238 // If this thread is the master of a split point and all slaves have
2239 // finished their work at this split point, return from the idle loop.
2241 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2243 if (i == ActiveThreads)
2245 // Because sp->slaves[] is reset under lock protection,
2246 // be sure sp->lock has been released before to return.
2247 lock_grab(&(sp->lock));
2248 lock_release(&(sp->lock));
2250 // In helpful master concept a master can help only a sub-tree, and
2251 // because here is all finished is not possible master is booked.
2252 assert(threads[threadID].state == THREAD_AVAILABLE);
2254 threads[threadID].state = THREAD_SEARCHING;
2261 // init_threads() is called during startup. It launches all helper threads,
2262 // and initializes the split point stack and the global locks and condition
2265 void ThreadsManager::init_threads() {
2270 // Initialize global locks
2273 for (i = 0; i < MAX_THREADS; i++)
2274 cond_init(&WaitCond[i]);
2276 // Initialize splitPoints[] locks
2277 for (i = 0; i < MAX_THREADS; i++)
2278 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2279 lock_init(&(threads[i].splitPoints[j].lock));
2281 // Will be set just before program exits to properly end the threads
2282 AllThreadsShouldExit = false;
2284 // Threads will be put all threads to sleep as soon as created
2287 // All threads except the main thread should be initialized to THREAD_INITIALIZING
2288 threads[0].state = THREAD_SEARCHING;
2289 for (i = 1; i < MAX_THREADS; i++)
2290 threads[i].state = THREAD_INITIALIZING;
2292 // Launch the helper threads
2293 for (i = 1; i < MAX_THREADS; i++)
2296 #if !defined(_MSC_VER)
2297 pthread_t pthread[1];
2298 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2299 pthread_detach(pthread[0]);
2301 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2306 cout << "Failed to create thread number " << i << endl;
2307 Application::exit_with_failure();
2310 // Wait until the thread has finished launching and is gone to sleep
2311 while (threads[i].state == THREAD_INITIALIZING) {}
2316 // exit_threads() is called when the program exits. It makes all the
2317 // helper threads exit cleanly.
2319 void ThreadsManager::exit_threads() {
2321 AllThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
2323 // Wake up all the threads and waits for termination
2324 for (int i = 1; i < MAX_THREADS; i++)
2326 wake_sleeping_thread(i);
2327 while (threads[i].state != THREAD_TERMINATED) {}
2330 // Now we can safely destroy the locks
2331 for (int i = 0; i < MAX_THREADS; i++)
2332 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2333 lock_destroy(&(threads[i].splitPoints[j].lock));
2335 lock_destroy(&MPLock);
2337 // Now we can safely destroy the wait conditions
2338 for (int i = 0; i < MAX_THREADS; i++)
2339 cond_destroy(&WaitCond[i]);
2343 // thread_should_stop() checks whether the thread should stop its search.
2344 // This can happen if a beta cutoff has occurred in the thread's currently
2345 // active split point, or in some ancestor of the current split point.
2347 bool ThreadsManager::thread_should_stop(int threadID) const {
2349 assert(threadID >= 0 && threadID < ActiveThreads);
2351 SplitPoint* sp = threads[threadID].splitPoint;
2353 for ( ; sp && !sp->stopRequest; sp = sp->parent) {}
2358 // thread_is_available() checks whether the thread with threadID "slave" is
2359 // available to help the thread with threadID "master" at a split point. An
2360 // obvious requirement is that "slave" must be idle. With more than two
2361 // threads, this is not by itself sufficient: If "slave" is the master of
2362 // some active split point, it is only available as a slave to the other
2363 // threads which are busy searching the split point at the top of "slave"'s
2364 // split point stack (the "helpful master concept" in YBWC terminology).
2366 bool ThreadsManager::thread_is_available(int slave, int master) const {
2368 assert(slave >= 0 && slave < ActiveThreads);
2369 assert(master >= 0 && master < ActiveThreads);
2370 assert(ActiveThreads > 1);
2372 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2375 // Make a local copy to be sure doesn't change under our feet
2376 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2378 // No active split points means that the thread is available as
2379 // a slave for any other thread.
2380 if (localActiveSplitPoints == 0 || ActiveThreads == 2)
2383 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2384 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2385 // could have been set to 0 by another thread leading to an out of bound access.
2386 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2393 // available_thread_exists() tries to find an idle thread which is available as
2394 // a slave for the thread with threadID "master".
2396 bool ThreadsManager::available_thread_exists(int master) const {
2398 assert(master >= 0 && master < ActiveThreads);
2399 assert(ActiveThreads > 1);
2401 for (int i = 0; i < ActiveThreads; i++)
2402 if (thread_is_available(i, master))
2409 // split() does the actual work of distributing the work at a node between
2410 // several available threads. If it does not succeed in splitting the
2411 // node (because no idle threads are available, or because we have no unused
2412 // split point objects), the function immediately returns. If splitting is
2413 // possible, a SplitPoint object is initialized with all the data that must be
2414 // copied to the helper threads and we tell our helper threads that they have
2415 // been assigned work. This will cause them to instantly leave their idle loops and
2416 // call search().When all threads have returned from search() then split() returns.
2418 template <bool Fake>
2419 void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
2420 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2421 bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
2422 assert(pos.is_ok());
2423 assert(ply > 0 && ply < PLY_MAX);
2424 assert(*bestValue >= -VALUE_INFINITE);
2425 assert(*bestValue <= *alpha);
2426 assert(*alpha < beta);
2427 assert(beta <= VALUE_INFINITE);
2428 assert(depth > DEPTH_ZERO);
2429 assert(pos.thread() >= 0 && pos.thread() < ActiveThreads);
2430 assert(ActiveThreads > 1);
2432 int i, master = pos.thread();
2433 Thread& masterThread = threads[master];
2437 // If no other thread is available to help us, or if we have too many
2438 // active split points, don't split.
2439 if ( !available_thread_exists(master)
2440 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2442 lock_release(&MPLock);
2446 // Pick the next available split point object from the split point stack
2447 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2449 // Initialize the split point object
2450 splitPoint.parent = masterThread.splitPoint;
2451 splitPoint.stopRequest = false;
2452 splitPoint.ply = ply;
2453 splitPoint.depth = depth;
2454 splitPoint.threatMove = threatMove;
2455 splitPoint.mateThreat = mateThreat;
2456 splitPoint.alpha = *alpha;
2457 splitPoint.beta = beta;
2458 splitPoint.pvNode = pvNode;
2459 splitPoint.bestValue = *bestValue;
2461 splitPoint.moveCount = moveCount;
2462 splitPoint.pos = &pos;
2463 splitPoint.nodes = 0;
2464 splitPoint.parentSstack = ss;
2465 for (i = 0; i < ActiveThreads; i++)
2466 splitPoint.slaves[i] = 0;
2468 masterThread.splitPoint = &splitPoint;
2470 // If we are here it means we are not available
2471 assert(masterThread.state != THREAD_AVAILABLE);
2473 int workersCnt = 1; // At least the master is included
2475 // Allocate available threads setting state to THREAD_BOOKED
2476 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2477 if (thread_is_available(i, master))
2479 threads[i].state = THREAD_BOOKED;
2480 threads[i].splitPoint = &splitPoint;
2481 splitPoint.slaves[i] = 1;
2485 assert(Fake || workersCnt > 1);
2487 // We can release the lock because slave threads are already booked and master is not available
2488 lock_release(&MPLock);
2490 // Tell the threads that they have work to do. This will make them leave
2491 // their idle loop. But before copy search stack tail for each thread.
2492 for (i = 0; i < ActiveThreads; i++)
2493 if (i == master || splitPoint.slaves[i])
2495 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2497 assert(i == master || threads[i].state == THREAD_BOOKED);
2499 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2501 wake_sleeping_thread(i);
2504 // Everything is set up. The master thread enters the idle loop, from
2505 // which it will instantly launch a search, because its state is
2506 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2507 // idle loop, which means that the main thread will return from the idle
2508 // loop when all threads have finished their work at this split point.
2509 idle_loop(master, &splitPoint);
2511 // We have returned from the idle loop, which means that all threads are
2512 // finished. Update alpha and bestValue, and return.
2515 *alpha = splitPoint.alpha;
2516 *bestValue = splitPoint.bestValue;
2517 masterThread.activeSplitPoints--;
2518 masterThread.splitPoint = splitPoint.parent;
2519 pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
2521 lock_release(&MPLock);
2525 // wake_sleeping_thread() wakes up all sleeping threads when it is time
2526 // to start a new search from the root.
2528 void ThreadsManager::wake_sleeping_thread(int threadID) {
2531 cond_signal(&WaitCond[threadID]);
2532 lock_release(&MPLock);
2536 /// The RootMoveList class
2538 // RootMoveList c'tor
2540 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) {
2542 SearchStack ss[PLY_MAX_PLUS_2];
2543 MoveStack mlist[MOVES_MAX];
2545 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2547 // Initialize search stack
2548 init_ss_array(ss, PLY_MAX_PLUS_2);
2549 ss[0].eval = ss[0].evalMargin = VALUE_NONE;
2552 // Generate all legal moves
2553 MoveStack* last = generate_moves(pos, mlist);
2555 // Add each move to the moves[] array
2556 for (MoveStack* cur = mlist; cur != last; cur++)
2558 bool includeMove = includeAllMoves;
2560 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2561 includeMove = (searchMoves[k] == cur->move);
2566 // Find a quick score for the move
2567 moves[count].move = ss[0].currentMove = moves[count].pv[0] = cur->move;
2568 moves[count].pv[1] = MOVE_NONE;
2569 pos.do_move(cur->move, st);
2570 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
2571 pos.undo_move(cur->move);
2577 // Score root moves using the standard way used in main search, the moves
2578 // are scored according to the order in which are returned by MovePicker.
2580 void RootMoveList::score_moves(const Position& pos)
2584 MovePicker mp = MovePicker(pos, MOVE_NONE, ONE_PLY, H);
2586 while ((move = mp.get_next_move()) != MOVE_NONE)
2587 for (int i = 0; i < count; i++)
2588 if (moves[i].move == move)
2590 moves[i].mp_score = score--;
2595 // RootMoveList simple methods definitions
2597 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2601 for (j = 0; pv[j] != MOVE_NONE; j++)
2602 moves[moveNum].pv[j] = pv[j];
2604 moves[moveNum].pv[j] = MOVE_NONE;
2608 // RootMoveList::sort() sorts the root move list at the beginning of a new
2611 void RootMoveList::sort() {
2613 sort_multipv(count - 1); // Sort all items
2617 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2618 // list by their scores and depths. It is used to order the different PVs
2619 // correctly in MultiPV mode.
2621 void RootMoveList::sort_multipv(int n) {
2625 for (i = 1; i <= n; i++)
2627 RootMove rm = moves[i];
2628 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2629 moves[j] = moves[j - 1];