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 Marco Costalba
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"
44 //// Local definitions
51 // IterationInfoType stores search results for each iteration
53 // Because we use relatively small (dynamic) aspiration window,
54 // there happens many fail highs and fail lows in root. And
55 // because we don't do researches in those cases, "value" stored
56 // here is not necessarily exact. Instead in case of fail high/low
57 // we guess what the right value might be and store our guess
58 // as a "speculated value" and then move on. Speculated values are
59 // used just to calculate aspiration window width, so also if are
60 // not exact is not big a problem.
62 struct IterationInfoType
{
64 IterationInfoType(Value v
= Value(0), Value sv
= Value(0))
65 : value(v
), speculatedValue(sv
) {}
67 Value value
, speculatedValue
;
71 // The BetaCounterType class is used to order moves at ply one.
72 // Apart for the first one that has its score, following moves
73 // normally have score -VALUE_INFINITE, so are ordered according
74 // to the number of beta cutoffs occurred under their subtree during
75 // the last iteration.
77 struct BetaCounterType
{
81 void add(Color us
, Depth d
, int threadID
);
82 void read(Color us
, int64_t& our
, int64_t& their
);
84 int64_t hits
[THREAD_MAX
][2];
88 // The RootMove class is used for moves at the root at the tree. For each
89 // root move, we store a score, a node count, and a PV (really a refutation
90 // in the case of moves which fail low).
95 bool operator<(const RootMove
&); // used to sort
99 int64_t nodes
, cumulativeNodes
;
100 Move pv
[PLY_MAX_PLUS_2
];
101 int64_t ourBeta
, theirBeta
;
105 // The RootMoveList class is essentially an array of RootMove objects, with
106 // a handful of methods for accessing the data in the individual moves.
111 RootMoveList(Position
&pos
, Move searchMoves
[]);
112 inline Move
get_move(int moveNum
) const;
113 inline Value
get_move_score(int moveNum
) const;
114 inline void set_move_score(int moveNum
, Value score
);
115 inline void set_move_nodes(int moveNum
, int64_t nodes
);
116 inline void set_beta_counters(int moveNum
, int64_t our
, int64_t their
);
117 void set_move_pv(int moveNum
, const Move pv
[]);
118 inline Move
get_move_pv(int moveNum
, int i
) const;
119 inline int64_t get_move_cumulative_nodes(int moveNum
) const;
120 inline int move_count() const;
121 Move
scan_for_easy_move() const;
123 void sort_multipv(int n
);
126 static const int MaxRootMoves
= 500;
127 RootMove moves
[MaxRootMoves
];
132 /// Constants and variables initialized from UCI options
134 // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV
136 int LMRPVMoves
, LMRNonPVMoves
;
138 // Depth limit for use of dynamic threat detection
141 // Depth limit for selective search
142 const Depth SelectiveDepth
= 7*OnePly
;
144 // Use internal iterative deepening?
145 const bool UseIIDAtPVNodes
= true;
146 const bool UseIIDAtNonPVNodes
= false;
148 // Internal iterative deepening margin. At Non-PV moves, when
149 // UseIIDAtNonPVNodes is true, we do an internal iterative deepening search
150 // when the static evaluation is at most IIDMargin below beta.
151 const Value IIDMargin
= Value(0x100);
153 // Easy move margin. An easy move candidate must be at least this much
154 // better than the second best move.
155 const Value EasyMoveMargin
= Value(0x200);
157 // Problem margin. If the score of the first move at iteration N+1 has
158 // dropped by more than this since iteration N, the boolean variable
159 // "Problem" is set to true, which will make the program spend some extra
160 // time looking for a better move.
161 const Value ProblemMargin
= Value(0x28);
163 // No problem margin. If the boolean "Problem" is true, and a new move
164 // is found at the root which is less than NoProblemMargin worse than the
165 // best move from the previous iteration, Problem is set back to false.
166 const Value NoProblemMargin
= Value(0x14);
168 // Null move margin. A null move search will not be done if the approximate
169 // evaluation of the position is more than NullMoveMargin below beta.
170 const Value NullMoveMargin
= Value(0x300);
172 // Pruning criterions. See the code and comments in ok_to_prune() to
173 // understand their precise meaning.
174 const bool PruneEscapeMoves
= false;
175 const bool PruneDefendingMoves
= false;
176 const bool PruneBlockingMoves
= false;
178 // Use futility pruning?
179 bool UseQSearchFutilityPruning
, UseFutilityPruning
;
181 // Margins for futility pruning in the quiescence search, and at frontier
182 // and near frontier nodes
183 const Value FutilityMarginQS
= Value(0x80);
185 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
186 const Value FutilityMargins
[12] = { Value(0x100), Value(0x120), Value(0x200), Value(0x220), Value(0x250), Value(0x270),
187 // 4 ply 4.5 ply 5 ply 5.5 ply 6 ply 6.5 ply
188 Value(0x2A0), Value(0x2C0), Value(0x340), Value(0x360), Value(0x3A0), Value(0x3C0) };
190 const Depth RazorDepth
= 4*OnePly
;
192 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
193 const Value RazorMargins
[6] = { Value(0x180), Value(0x300), Value(0x300), Value(0x3C0), Value(0x3C0), Value(0x3C0) };
195 // Remaining depth: 1 ply 1.5 ply 2 ply 2.5 ply 3 ply 3.5 ply
196 const Value RazorApprMargins
[6] = { Value(0x520), Value(0x300), Value(0x300), Value(0x300), Value(0x300), Value(0x300) };
198 // Last seconds noise filtering (LSN)
199 bool UseLSNFiltering
;
200 bool looseOnTime
= false;
201 int LSNTime
; // In milliseconds
204 // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
205 Depth CheckExtension
[2], SingleReplyExtension
[2], PawnPushTo7thExtension
[2];
206 Depth PassedPawnExtension
[2], PawnEndgameExtension
[2], MateThreatExtension
[2];
208 // Search depth at iteration 1
209 const Depth InitialDepth
= OnePly
/*+ OnePly/2*/;
213 int NodesBetweenPolls
= 30000;
215 // Iteration counters
217 BetaCounterType BetaCounter
;
219 // Scores and number of times the best move changed for each iteration:
220 IterationInfoType IterationInfo
[PLY_MAX_PLUS_2
];
221 int BestMoveChangesByIteration
[PLY_MAX_PLUS_2
];
226 // Time managment variables
228 int MaxNodes
, MaxDepth
;
229 int MaxSearchTime
, AbsoluteMaxSearchTime
, ExtraSearchTime
;
234 bool StopOnPonderhit
;
240 bool PonderingEnabled
;
243 // Show current line?
244 bool ShowCurrentLine
;
248 std::ofstream LogFile
;
250 // MP related variables
251 Depth MinimumSplitDepth
;
252 int MaxThreadsPerSplitPoint
;
253 Thread Threads
[THREAD_MAX
];
255 bool AllThreadsShouldExit
= false;
256 const int MaxActiveSplitPoints
= 8;
257 SplitPoint SplitPointStack
[THREAD_MAX
][MaxActiveSplitPoints
];
260 #if !defined(_MSC_VER)
261 pthread_cond_t WaitCond
;
262 pthread_mutex_t WaitLock
;
264 HANDLE SitIdleEvent
[THREAD_MAX
];
270 Value
id_loop(const Position
&pos
, Move searchMoves
[]);
271 Value
root_search(Position
&pos
, SearchStack ss
[], RootMoveList
&rml
, Value alpha
, Value beta
);
272 Value
search_pv(Position
&pos
, SearchStack ss
[], Value alpha
, Value beta
, Depth depth
, int ply
, int threadID
);
273 Value
search(Position
&pos
, SearchStack ss
[], Value beta
, Depth depth
, int ply
, bool allowNullmove
, int threadID
);
274 Value
qsearch(Position
&pos
, SearchStack ss
[], Value alpha
, Value beta
, Depth depth
, int ply
, int threadID
);
275 void sp_search(SplitPoint
*sp
, int threadID
);
276 void sp_search_pv(SplitPoint
*sp
, int threadID
);
277 void init_node(SearchStack ss
[], int ply
, int threadID
);
278 void update_pv(SearchStack ss
[], int ply
);
279 void sp_update_pv(SearchStack
*pss
, SearchStack ss
[], int ply
);
280 bool connected_moves(const Position
&pos
, Move m1
, Move m2
);
281 bool value_is_mate(Value value
);
282 bool move_is_killer(Move m
, const SearchStack
& ss
);
283 Depth
extension(const Position
&pos
, Move m
, bool pvNode
, bool capture
, bool check
, bool singleReply
, bool mateThreat
, bool* dangerous
);
284 bool ok_to_do_nullmove(const Position
&pos
);
285 bool ok_to_prune(const Position
&pos
, Move m
, Move threat
, Depth d
);
286 bool ok_to_use_TT(const TTEntry
* tte
, Depth depth
, Value beta
, int ply
);
287 bool ok_to_history(const Position
&pos
, Move m
);
288 void update_history(const Position
& pos
, Move m
, Depth depth
, Move movesSearched
[], int moveCount
);
289 void update_killers(Move m
, SearchStack
& ss
);
291 bool fail_high_ply_1();
292 int current_search_time();
296 void print_current_line(SearchStack ss
[], int ply
, int threadID
);
297 void wait_for_stop_or_ponderhit();
299 void idle_loop(int threadID
, SplitPoint
*waitSp
);
300 void init_split_point_stack();
301 void destroy_split_point_stack();
302 bool thread_should_stop(int threadID
);
303 bool thread_is_available(int slave
, int master
);
304 bool idle_thread_exists(int master
);
305 bool split(const Position
&pos
, SearchStack
*ss
, int ply
,
306 Value
*alpha
, Value
*beta
, Value
*bestValue
, Depth depth
, int *moves
,
307 MovePicker
*mp
, Bitboard dcCandidates
, int master
, bool pvNode
);
308 void wake_sleeping_threads();
310 #if !defined(_MSC_VER)
311 void *init_thread(void *threadID
);
313 DWORD WINAPI
init_thread(LPVOID threadID
);
320 //// Global variables
323 // The main transposition table
324 TranspositionTable TT
;
327 // Number of active threads:
328 int ActiveThreads
= 1;
330 // Locks. In principle, there is no need for IOLock to be a global variable,
331 // but it could turn out to be useful for debugging.
334 History H
; // Should be made local?
336 // The empty search stack
337 SearchStack EmptySearchStack
;
340 // SearchStack::init() initializes a search stack. Used at the beginning of a
341 // new search from the root.
342 void SearchStack::init(int ply
) {
344 pv
[ply
] = pv
[ply
+ 1] = MOVE_NONE
;
345 currentMove
= threatMove
= MOVE_NONE
;
346 reduction
= Depth(0);
349 void SearchStack::initKillers() {
351 mateKiller
= MOVE_NONE
;
352 for (int i
= 0; i
< KILLER_MAX
; i
++)
353 killers
[i
] = MOVE_NONE
;
361 /// think() is the external interface to Stockfish's search, and is called when
362 /// the program receives the UCI 'go' command. It initializes various
363 /// search-related global variables, and calls root_search()
365 void think(const Position
&pos
, bool infinite
, bool ponder
, int side_to_move
,
366 int time
[], int increment
[], int movesToGo
, int maxDepth
,
367 int maxNodes
, int maxTime
, Move searchMoves
[]) {
369 // Look for a book move
370 if (!infinite
&& !ponder
&& get_option_value_bool("OwnBook"))
373 if (get_option_value_string("Book File") != OpeningBook
.file_name())
376 OpeningBook
.open("book.bin");
378 bookMove
= OpeningBook
.get_move(pos
);
379 if (bookMove
!= MOVE_NONE
)
381 std::cout
<< "bestmove " << bookMove
<< std::endl
;
386 // Initialize global search variables
388 SearchStartTime
= get_system_time();
389 EasyMove
= MOVE_NONE
;
390 for (int i
= 0; i
< THREAD_MAX
; i
++)
392 Threads
[i
].nodes
= 0ULL;
393 Threads
[i
].failHighPly1
= false;
396 InfiniteSearch
= infinite
;
397 PonderSearch
= ponder
;
398 StopOnPonderhit
= false;
404 ExactMaxTime
= maxTime
;
406 // Read UCI option values
407 TT
.set_size(get_option_value_int("Hash"));
408 if (button_was_pressed("Clear Hash"))
411 PonderingEnabled
= get_option_value_bool("Ponder");
412 MultiPV
= get_option_value_int("MultiPV");
414 CheckExtension
[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
415 CheckExtension
[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
417 SingleReplyExtension
[1] = Depth(get_option_value_int("Single Reply Extension (PV nodes)"));
418 SingleReplyExtension
[0] = Depth(get_option_value_int("Single Reply Extension (non-PV nodes)"));
420 PawnPushTo7thExtension
[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
421 PawnPushTo7thExtension
[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
423 PassedPawnExtension
[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
424 PassedPawnExtension
[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
426 PawnEndgameExtension
[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
427 PawnEndgameExtension
[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
429 MateThreatExtension
[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
430 MateThreatExtension
[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
432 LMRPVMoves
= get_option_value_int("Full Depth Moves (PV nodes)") + 1;
433 LMRNonPVMoves
= get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
434 ThreatDepth
= get_option_value_int("Threat Depth") * OnePly
;
436 Chess960
= get_option_value_bool("UCI_Chess960");
437 ShowCurrentLine
= get_option_value_bool("UCI_ShowCurrLine");
438 UseLogFile
= get_option_value_bool("Use Search Log");
440 LogFile
.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out
| std::ios::app
);
442 UseQSearchFutilityPruning
= get_option_value_bool("Futility Pruning (Quiescence Search)");
443 UseFutilityPruning
= get_option_value_bool("Futility Pruning (Main Search)");
445 UseLSNFiltering
= get_option_value_bool("LSN filtering");
446 LSNTime
= get_option_value_int("LSN Time Margin (sec)") * 1000;
447 LSNValue
= value_from_centipawns(get_option_value_int("LSN Value Margin"));
449 MinimumSplitDepth
= get_option_value_int("Minimum Split Depth") * OnePly
;
450 MaxThreadsPerSplitPoint
= get_option_value_int("Maximum Number of Threads per Split Point");
452 read_weights(pos
.side_to_move());
454 int newActiveThreads
= get_option_value_int("Threads");
455 if (newActiveThreads
!= ActiveThreads
)
457 ActiveThreads
= newActiveThreads
;
458 init_eval(ActiveThreads
);
461 // Wake up sleeping threads:
462 wake_sleeping_threads();
464 for (int i
= 1; i
< ActiveThreads
; i
++)
465 assert(thread_is_available(i
, 0));
467 // Set thinking time:
468 int myTime
= time
[side_to_move
];
469 int myIncrement
= increment
[side_to_move
];
471 if (!movesToGo
) // Sudden death time control
475 MaxSearchTime
= myTime
/ 30 + myIncrement
;
476 AbsoluteMaxSearchTime
= Max(myTime
/ 4, myIncrement
- 100);
477 } else { // Blitz game without increment
478 MaxSearchTime
= myTime
/ 30;
479 AbsoluteMaxSearchTime
= myTime
/ 8;
482 else // (x moves) / (y minutes)
486 MaxSearchTime
= myTime
/ 2;
487 AbsoluteMaxSearchTime
= Min(myTime
/ 2, myTime
- 500);
489 MaxSearchTime
= myTime
/ Min(movesToGo
, 20);
490 AbsoluteMaxSearchTime
= Min((4 * myTime
) / movesToGo
, myTime
/ 3);
494 if (PonderingEnabled
)
496 MaxSearchTime
+= MaxSearchTime
/ 4;
497 MaxSearchTime
= Min(MaxSearchTime
, AbsoluteMaxSearchTime
);
500 // Fixed depth or fixed number of nodes?
503 InfiniteSearch
= true; // HACK
508 NodesBetweenPolls
= Min(MaxNodes
, 30000);
509 InfiniteSearch
= true; // HACK
512 NodesBetweenPolls
= 30000;
515 // Write information to search log file:
517 LogFile
<< "Searching: " << pos
.to_fen() << std::endl
518 << "infinite: " << infinite
519 << " ponder: " << ponder
520 << " time: " << myTime
521 << " increment: " << myIncrement
522 << " moves to go: " << movesToGo
<< std::endl
;
525 // We're ready to start thinking. Call the iterative deepening loop
529 Value v
= id_loop(pos
, searchMoves
);
530 looseOnTime
= ( UseLSNFiltering
537 looseOnTime
= false; // reset for next match
538 while (SearchStartTime
+ myTime
+ 1000 > get_system_time())
540 id_loop(pos
, searchMoves
); // to fail gracefully
557 /// init_threads() is called during startup. It launches all helper threads,
558 /// and initializes the split point stack and the global locks and condition
561 void init_threads() {
565 #if !defined(_MSC_VER)
566 pthread_t pthread
[1];
569 for (i
= 0; i
< THREAD_MAX
; i
++)
570 Threads
[i
].activeSplitPoints
= 0;
572 // Initialize global locks:
573 lock_init(&MPLock
, NULL
);
574 lock_init(&IOLock
, NULL
);
576 init_split_point_stack();
578 #if !defined(_MSC_VER)
579 pthread_mutex_init(&WaitLock
, NULL
);
580 pthread_cond_init(&WaitCond
, NULL
);
582 for (i
= 0; i
< THREAD_MAX
; i
++)
583 SitIdleEvent
[i
] = CreateEvent(0, FALSE
, FALSE
, 0);
586 // All threads except the main thread should be initialized to idle state
587 for (i
= 1; i
< THREAD_MAX
; i
++)
589 Threads
[i
].stop
= false;
590 Threads
[i
].workIsWaiting
= false;
591 Threads
[i
].idle
= true;
592 Threads
[i
].running
= false;
595 // Launch the helper threads
596 for(i
= 1; i
< THREAD_MAX
; i
++)
598 #if !defined(_MSC_VER)
599 pthread_create(pthread
, NULL
, init_thread
, (void*)(&i
));
602 CreateThread(NULL
, 0, init_thread
, (LPVOID
)(&i
), 0, iID
);
605 // Wait until the thread has finished launching:
606 while (!Threads
[i
].running
);
609 // Init also the empty search stack
610 EmptySearchStack
.init(0);
611 EmptySearchStack
.initKillers();
615 /// stop_threads() is called when the program exits. It makes all the
616 /// helper threads exit cleanly.
618 void stop_threads() {
620 ActiveThreads
= THREAD_MAX
; // HACK
621 Idle
= false; // HACK
622 wake_sleeping_threads();
623 AllThreadsShouldExit
= true;
624 for (int i
= 1; i
< THREAD_MAX
; i
++)
626 Threads
[i
].stop
= true;
627 while(Threads
[i
].running
);
629 destroy_split_point_stack();
633 /// nodes_searched() returns the total number of nodes searched so far in
634 /// the current search.
636 int64_t nodes_searched() {
638 int64_t result
= 0ULL;
639 for (int i
= 0; i
< ActiveThreads
; i
++)
640 result
+= Threads
[i
].nodes
;
647 // id_loop() is the main iterative deepening loop. It calls root_search
648 // repeatedly with increasing depth until the allocated thinking time has
649 // been consumed, the user stops the search, or the maximum search depth is
652 Value
id_loop(const Position
&pos
, Move searchMoves
[]) {
655 SearchStack ss
[PLY_MAX_PLUS_2
];
657 // searchMoves are verified, copied, scored and sorted
658 RootMoveList
rml(p
, searchMoves
);
663 for (int i
= 0; i
< 3; i
++)
668 IterationInfo
[1] = IterationInfoType(rml
.get_move_score(0), rml
.get_move_score(0));
671 EasyMove
= rml
.scan_for_easy_move();
673 // Iterative deepening loop
674 while (Iteration
< PLY_MAX
)
676 // Initialize iteration
679 BestMoveChangesByIteration
[Iteration
] = 0;
683 std::cout
<< "info depth " << Iteration
<< std::endl
;
685 // Calculate dynamic search window based on previous iterations
688 if (MultiPV
== 1 && Iteration
>= 6)
690 int prevDelta1
= IterationInfo
[Iteration
- 1].speculatedValue
- IterationInfo
[Iteration
- 2].speculatedValue
;
691 int prevDelta2
= IterationInfo
[Iteration
- 2].speculatedValue
- IterationInfo
[Iteration
- 3].speculatedValue
;
693 int delta
= Max(2 * abs(prevDelta1
) + abs(prevDelta2
), ProblemMargin
);
695 alpha
= Max(IterationInfo
[Iteration
- 1].value
- delta
, -VALUE_INFINITE
);
696 beta
= Min(IterationInfo
[Iteration
- 1].value
+ delta
, VALUE_INFINITE
);
700 alpha
= - VALUE_INFINITE
;
701 beta
= VALUE_INFINITE
;
704 // Search to the current depth
705 Value value
= root_search(p
, ss
, rml
, alpha
, beta
);
707 // Write PV to transposition table, in case the relevant entries have
708 // been overwritten during the search.
709 TT
.insert_pv(p
, ss
[0].pv
);
712 break; // Value cannot be trusted. Break out immediately!
714 //Save info about search result
715 Value speculatedValue
;
718 Value delta
= value
- IterationInfo
[Iteration
- 1].value
;
725 speculatedValue
= value
+ delta
;
726 BestMoveChangesByIteration
[Iteration
] += 2; // Allocate more time
728 else if (value
<= alpha
)
730 assert(value
== alpha
);
734 speculatedValue
= value
+ delta
;
735 BestMoveChangesByIteration
[Iteration
] += 3; // Allocate more time
737 speculatedValue
= value
;
739 speculatedValue
= Min(Max(speculatedValue
, -VALUE_INFINITE
), VALUE_INFINITE
);
740 IterationInfo
[Iteration
] = IterationInfoType(value
, speculatedValue
);
742 // Erase the easy move if it differs from the new best move
743 if (ss
[0].pv
[0] != EasyMove
)
744 EasyMove
= MOVE_NONE
;
751 bool stopSearch
= false;
753 // Stop search early if there is only a single legal move:
754 if (Iteration
>= 6 && rml
.move_count() == 1)
757 // Stop search early when the last two iterations returned a mate score
759 && abs(IterationInfo
[Iteration
].value
) >= abs(VALUE_MATE
) - 100
760 && abs(IterationInfo
[Iteration
-1].value
) >= abs(VALUE_MATE
) - 100)
763 // Stop search early if one move seems to be much better than the rest
764 int64_t nodes
= nodes_searched();
768 && EasyMove
== ss
[0].pv
[0]
769 && ( ( rml
.get_move_cumulative_nodes(0) > (nodes
* 85) / 100
770 && current_search_time() > MaxSearchTime
/ 16)
771 ||( rml
.get_move_cumulative_nodes(0) > (nodes
* 98) / 100
772 && current_search_time() > MaxSearchTime
/ 32)))
775 // Add some extra time if the best move has changed during the last two iterations
776 if (Iteration
> 5 && Iteration
<= 50)
777 ExtraSearchTime
= BestMoveChangesByIteration
[Iteration
] * (MaxSearchTime
/ 2)
778 + BestMoveChangesByIteration
[Iteration
-1] * (MaxSearchTime
/ 3);
780 // Stop search if most of MaxSearchTime is consumed at the end of the
781 // iteration. We probably don't have enough time to search the first
782 // move at the next iteration anyway.
783 if (current_search_time() > ((MaxSearchTime
+ ExtraSearchTime
)*80) / 128)
788 //FIXME: Implement fail-low emergency measures
792 StopOnPonderhit
= true;
796 if (MaxDepth
&& Iteration
>= MaxDepth
)
802 // If we are pondering, we shouldn't print the best move before we
805 wait_for_stop_or_ponderhit();
807 // Print final search statistics
808 std::cout
<< "info nodes " << nodes_searched()
810 << " time " << current_search_time()
811 << " hashfull " << TT
.full() << std::endl
;
813 // Print the best move and the ponder move to the standard output
814 if (ss
[0].pv
[0] == MOVE_NONE
)
816 ss
[0].pv
[0] = rml
.get_move(0);
817 ss
[0].pv
[1] = MOVE_NONE
;
819 std::cout
<< "bestmove " << ss
[0].pv
[0];
820 if (ss
[0].pv
[1] != MOVE_NONE
)
821 std::cout
<< " ponder " << ss
[0].pv
[1];
823 std::cout
<< std::endl
;
828 dbg_print_mean(LogFile
);
830 if (dbg_show_hit_rate
)
831 dbg_print_hit_rate(LogFile
);
834 LogFile
<< "Nodes: " << nodes_searched() << std::endl
835 << "Nodes/second: " << nps() << std::endl
836 << "Best move: " << move_to_san(p
, ss
[0].pv
[0]) << std::endl
;
838 p
.do_move(ss
[0].pv
[0], st
);
839 LogFile
<< "Ponder move: " << move_to_san(p
, ss
[0].pv
[1])
840 << std::endl
<< std::endl
;
842 return rml
.get_move_score(0);
846 // root_search() is the function which searches the root node. It is
847 // similar to search_pv except that it uses a different move ordering
848 // scheme (perhaps we should try to use this at internal PV nodes, too?)
849 // and prints some information to the standard output.
851 Value
root_search(Position
&pos
, SearchStack ss
[], RootMoveList
&rml
, Value alpha
, Value beta
) {
853 Value oldAlpha
= alpha
;
855 Bitboard dcCandidates
= pos
.discovered_check_candidates(pos
.side_to_move());
857 // Loop through all the moves in the root move list
858 for (int i
= 0; i
< rml
.move_count() && !AbortSearch
; i
++)
862 // We failed high, invalidate and skip next moves, leave node-counters
863 // and beta-counters as they are and quickly return, we will try to do
864 // a research at the next iteration with a bigger aspiration window.
865 rml
.set_move_score(i
, -VALUE_INFINITE
);
873 RootMoveNumber
= i
+ 1;
876 // Remember the node count before the move is searched. The node counts
877 // are used to sort the root moves at the next iteration.
878 nodes
= nodes_searched();
880 // Reset beta cut-off counters
883 // Pick the next root move, and print the move and the move number to
884 // the standard output.
885 move
= ss
[0].currentMove
= rml
.get_move(i
);
886 if (current_search_time() >= 1000)
887 std::cout
<< "info currmove " << move
888 << " currmovenumber " << i
+ 1 << std::endl
;
890 // Decide search depth for this move
892 ext
= extension(pos
, move
, true, pos
.move_is_capture(move
), pos
.move_is_check(move
), false, false, &dangerous
);
893 newDepth
= (Iteration
- 2) * OnePly
+ ext
+ InitialDepth
;
895 // Make the move, and search it
896 pos
.do_move(move
, st
, dcCandidates
);
900 value
= -search_pv(pos
, ss
, -beta
, -alpha
, newDepth
, 1, 0);
901 // If the value has dropped a lot compared to the last iteration,
902 // set the boolean variable Problem to true. This variable is used
903 // for time managment: When Problem is true, we try to complete the
904 // current iteration before playing a move.
905 Problem
= (Iteration
>= 2 && value
<= IterationInfo
[Iteration
-1].value
- ProblemMargin
);
907 if (Problem
&& StopOnPonderhit
)
908 StopOnPonderhit
= false;
912 value
= -search(pos
, ss
, -alpha
, newDepth
, 1, true, 0);
915 // Fail high! Set the boolean variable FailHigh to true, and
916 // re-search the move with a big window. The variable FailHigh is
917 // used for time managment: We try to avoid aborting the search
918 // prematurely during a fail high research.
920 value
= -search_pv(pos
, ss
, -beta
, -alpha
, newDepth
, 1, 0);
926 // Finished searching the move. If AbortSearch is true, the search
927 // was aborted because the user interrupted the search or because we
928 // ran out of time. In this case, the return value of the search cannot
929 // be trusted, and we break out of the loop without updating the best
934 // Remember the node count for this move. The node counts are used to
935 // sort the root moves at the next iteration.
936 rml
.set_move_nodes(i
, nodes_searched() - nodes
);
938 // Remember the beta-cutoff statistics
940 BetaCounter
.read(pos
.side_to_move(), our
, their
);
941 rml
.set_beta_counters(i
, our
, their
);
943 assert(value
>= -VALUE_INFINITE
&& value
<= VALUE_INFINITE
);
945 if (value
<= alpha
&& i
>= MultiPV
)
946 rml
.set_move_score(i
, -VALUE_INFINITE
);
949 // PV move or new best move!
952 rml
.set_move_score(i
, value
);
954 rml
.set_move_pv(i
, ss
[0].pv
);
958 // We record how often the best move has been changed in each
959 // iteration. This information is used for time managment: When
960 // the best move changes frequently, we allocate some more time.
962 BestMoveChangesByIteration
[Iteration
]++;
964 // Print search information to the standard output:
965 std::cout
<< "info depth " << Iteration
966 << " score " << value_to_string(value
)
967 << " time " << current_search_time()
968 << " nodes " << nodes_searched()
972 for (int j
= 0; ss
[0].pv
[j
] != MOVE_NONE
&& j
< PLY_MAX
; j
++)
973 std::cout
<< ss
[0].pv
[j
] << " ";
975 std::cout
<< std::endl
;
978 LogFile
<< pretty_pv(pos
, current_search_time(), Iteration
, nodes_searched(), value
, ss
[0].pv
)
984 // Reset the global variable Problem to false if the value isn't too
985 // far below the final value from the last iteration.
986 if (value
> IterationInfo
[Iteration
- 1].value
- NoProblemMargin
)
992 for (int j
= 0; j
< Min(MultiPV
, rml
.move_count()); j
++)
995 std::cout
<< "info multipv " << j
+ 1
996 << " score " << value_to_string(rml
.get_move_score(j
))
997 << " depth " << ((j
<= i
)? Iteration
: Iteration
- 1)
998 << " time " << current_search_time()
999 << " nodes " << nodes_searched()
1003 for (k
= 0; rml
.get_move_pv(j
, k
) != MOVE_NONE
&& k
< PLY_MAX
; k
++)
1004 std::cout
<< rml
.get_move_pv(j
, k
) << " ";
1006 std::cout
<< std::endl
;
1008 alpha
= rml
.get_move_score(Min(i
, MultiPV
-1));
1010 } // New best move case
1012 assert(alpha
>= oldAlpha
);
1014 FailLow
= (alpha
== oldAlpha
);
1020 // search_pv() is the main search function for PV nodes.
1022 Value
search_pv(Position
&pos
, SearchStack ss
[], Value alpha
, Value beta
,
1023 Depth depth
, int ply
, int threadID
) {
1025 assert(alpha
>= -VALUE_INFINITE
&& alpha
<= VALUE_INFINITE
);
1026 assert(beta
> alpha
&& beta
<= VALUE_INFINITE
);
1027 assert(ply
>= 0 && ply
< PLY_MAX
);
1028 assert(threadID
>= 0 && threadID
< ActiveThreads
);
1031 return qsearch(pos
, ss
, alpha
, beta
, Depth(0), ply
, threadID
);
1033 // Initialize, and make an early exit in case of an aborted search,
1034 // an instant draw, maximum ply reached, etc.
1035 init_node(ss
, ply
, threadID
);
1037 // After init_node() that calls poll()
1038 if (AbortSearch
|| thread_should_stop(threadID
))
1046 if (ply
>= PLY_MAX
- 1)
1047 return evaluate(pos
, ei
, threadID
);
1049 // Mate distance pruning
1050 Value oldAlpha
= alpha
;
1051 alpha
= Max(value_mated_in(ply
), alpha
);
1052 beta
= Min(value_mate_in(ply
+1), beta
);
1056 // Transposition table lookup. At PV nodes, we don't use the TT for
1057 // pruning, but only for move ordering.
1058 const TTEntry
* tte
= TT
.retrieve(pos
);
1059 Move ttMove
= (tte
? tte
->move() : MOVE_NONE
);
1061 // Go with internal iterative deepening if we don't have a TT move
1062 if (UseIIDAtPVNodes
&& ttMove
== MOVE_NONE
&& depth
>= 5*OnePly
)
1064 search_pv(pos
, ss
, alpha
, beta
, depth
-2*OnePly
, ply
, threadID
);
1065 ttMove
= ss
[ply
].pv
[ply
];
1068 // Initialize a MovePicker object for the current position, and prepare
1069 // to search all moves
1070 MovePicker mp
= MovePicker(pos
, true, ttMove
, ss
[ply
], depth
);
1072 Move move
, movesSearched
[256];
1074 Value value
, bestValue
= -VALUE_INFINITE
;
1075 Bitboard dcCandidates
= mp
.discovered_check_candidates();
1076 Color us
= pos
.side_to_move();
1077 bool isCheck
= pos
.is_check();
1078 bool mateThreat
= pos
.has_mate_threat(opposite_color(us
));
1080 // Loop through all legal moves until no moves remain or a beta cutoff
1082 while ( alpha
< beta
1083 && (move
= mp
.get_next_move()) != MOVE_NONE
1084 && !thread_should_stop(threadID
))
1086 assert(move_is_ok(move
));
1088 bool singleReply
= (isCheck
&& mp
.number_of_moves() == 1);
1089 bool moveIsCheck
= pos
.move_is_check(move
, dcCandidates
);
1090 bool moveIsCapture
= pos
.move_is_capture(move
);
1092 movesSearched
[moveCount
++] = ss
[ply
].currentMove
= move
;
1094 // Decide the new search depth
1096 Depth ext
= extension(pos
, move
, true, moveIsCapture
, moveIsCheck
, singleReply
, mateThreat
, &dangerous
);
1097 Depth newDepth
= depth
- OnePly
+ ext
;
1099 // Make and search the move
1101 pos
.do_move(move
, st
, dcCandidates
);
1103 if (moveCount
== 1) // The first move in list is the PV
1104 value
= -search_pv(pos
, ss
, -beta
, -alpha
, newDepth
, ply
+1, threadID
);
1107 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1108 // if the move fails high will be re-searched at full depth.
1109 if ( depth
>= 2*OnePly
1110 && moveCount
>= LMRPVMoves
1113 && !move_promotion(move
)
1114 && !move_is_castle(move
)
1115 && !move_is_killer(move
, ss
[ply
]))
1117 ss
[ply
].reduction
= OnePly
;
1118 value
= -search(pos
, ss
, -alpha
, newDepth
-OnePly
, ply
+1, true, threadID
);
1121 value
= alpha
+ 1; // Just to trigger next condition
1123 if (value
> alpha
) // Go with full depth non-pv search
1125 ss
[ply
].reduction
= Depth(0);
1126 value
= -search(pos
, ss
, -alpha
, newDepth
, ply
+1, true, threadID
);
1127 if (value
> alpha
&& value
< beta
)
1129 // When the search fails high at ply 1 while searching the first
1130 // move at the root, set the flag failHighPly1. This is used for
1131 // time managment: We don't want to stop the search early in
1132 // such cases, because resolving the fail high at ply 1 could
1133 // result in a big drop in score at the root.
1134 if (ply
== 1 && RootMoveNumber
== 1)
1135 Threads
[threadID
].failHighPly1
= true;
1137 // A fail high occurred. Re-search at full window (pv search)
1138 value
= -search_pv(pos
, ss
, -beta
, -alpha
, newDepth
, ply
+1, threadID
);
1139 Threads
[threadID
].failHighPly1
= false;
1143 pos
.undo_move(move
);
1145 assert(value
> -VALUE_INFINITE
&& value
< VALUE_INFINITE
);
1148 if (value
> bestValue
)
1155 if (value
== value_mate_in(ply
+ 1))
1156 ss
[ply
].mateKiller
= move
;
1158 // If we are at ply 1, and we are searching the first root move at
1159 // ply 0, set the 'Problem' variable if the score has dropped a lot
1160 // (from the computer's point of view) since the previous iteration:
1163 && -value
<= IterationInfo
[Iteration
-1].value
- ProblemMargin
)
1168 if ( ActiveThreads
> 1
1170 && depth
>= MinimumSplitDepth
1172 && idle_thread_exists(threadID
)
1174 && !thread_should_stop(threadID
)
1175 && split(pos
, ss
, ply
, &alpha
, &beta
, &bestValue
, depth
,
1176 &moveCount
, &mp
, dcCandidates
, threadID
, true))
1180 // All legal moves have been searched. A special case: If there were
1181 // no legal moves, it must be mate or stalemate:
1183 return (isCheck
? value_mated_in(ply
) : VALUE_DRAW
);
1185 // If the search is not aborted, update the transposition table,
1186 // history counters, and killer moves.
1187 if (AbortSearch
|| thread_should_stop(threadID
))
1190 if (bestValue
<= oldAlpha
)
1191 TT
.store(pos
, value_to_tt(bestValue
, ply
), VALUE_TYPE_UPPER
, depth
, MOVE_NONE
);
1193 else if (bestValue
>= beta
)
1195 BetaCounter
.add(pos
.side_to_move(), depth
, threadID
);
1196 Move m
= ss
[ply
].pv
[ply
];
1197 if (ok_to_history(pos
, m
)) // Only non capture moves are considered
1199 update_history(pos
, m
, depth
, movesSearched
, moveCount
);
1200 update_killers(m
, ss
[ply
]);
1202 TT
.store(pos
, value_to_tt(bestValue
, ply
), VALUE_TYPE_LOWER
, depth
, m
);
1205 TT
.store(pos
, value_to_tt(bestValue
, ply
), VALUE_TYPE_EXACT
, depth
, ss
[ply
].pv
[ply
]);
1211 // search() is the search function for zero-width nodes.
1213 Value
search(Position
&pos
, SearchStack ss
[], Value beta
, Depth depth
,
1214 int ply
, bool allowNullmove
, int threadID
) {
1216 assert(beta
>= -VALUE_INFINITE
&& beta
<= VALUE_INFINITE
);
1217 assert(ply
>= 0 && ply
< PLY_MAX
);
1218 assert(threadID
>= 0 && threadID
< ActiveThreads
);
1221 return qsearch(pos
, ss
, beta
-1, beta
, Depth(0), ply
, threadID
);
1223 // Initialize, and make an early exit in case of an aborted search,
1224 // an instant draw, maximum ply reached, etc.
1225 init_node(ss
, ply
, threadID
);
1227 // After init_node() that calls poll()
1228 if (AbortSearch
|| thread_should_stop(threadID
))
1236 if (ply
>= PLY_MAX
- 1)
1237 return evaluate(pos
, ei
, threadID
);
1239 // Mate distance pruning
1240 if (value_mated_in(ply
) >= beta
)
1243 if (value_mate_in(ply
+ 1) < beta
)
1246 // Transposition table lookup
1247 const TTEntry
* tte
= TT
.retrieve(pos
);
1248 Move ttMove
= (tte
? tte
->move() : MOVE_NONE
);
1250 if (tte
&& ok_to_use_TT(tte
, depth
, beta
, ply
))
1252 ss
[ply
].currentMove
= ttMove
; // can be MOVE_NONE
1253 return value_from_tt(tte
->value(), ply
);
1256 Value approximateEval
= quick_evaluate(pos
);
1257 bool mateThreat
= false;
1258 bool isCheck
= pos
.is_check();
1264 && !value_is_mate(beta
)
1265 && ok_to_do_nullmove(pos
)
1266 && approximateEval
>= beta
- NullMoveMargin
)
1268 ss
[ply
].currentMove
= MOVE_NULL
;
1271 pos
.do_null_move(st
);
1272 int R
= (depth
>= 5 * OnePly
? 4 : 3); // Null move dynamic reduction
1274 Value nullValue
= -search(pos
, ss
, -(beta
-1), depth
-R
*OnePly
, ply
+1, false, threadID
);
1276 pos
.undo_null_move();
1278 if (value_is_mate(nullValue
))
1280 /* Do not return unproven mates */
1282 else if (nullValue
>= beta
)
1284 if (depth
< 6 * OnePly
)
1287 // Do zugzwang verification search
1288 Value v
= search(pos
, ss
, beta
, depth
-5*OnePly
, ply
, false, threadID
);
1292 // The null move failed low, which means that we may be faced with
1293 // some kind of threat. If the previous move was reduced, check if
1294 // the move that refuted the null move was somehow connected to the
1295 // move which was reduced. If a connection is found, return a fail
1296 // low score (which will cause the reduced move to fail high in the
1297 // parent node, which will trigger a re-search with full depth).
1298 if (nullValue
== value_mated_in(ply
+ 2))
1301 ss
[ply
].threatMove
= ss
[ply
+ 1].currentMove
;
1302 if ( depth
< ThreatDepth
1303 && ss
[ply
- 1].reduction
1304 && connected_moves(pos
, ss
[ply
- 1].currentMove
, ss
[ply
].threatMove
))
1308 // Null move search not allowed, try razoring
1309 else if ( !value_is_mate(beta
)
1310 && depth
< RazorDepth
1311 && approximateEval
< beta
- RazorApprMargins
[int(depth
) - 2]
1312 && ttMove
== MOVE_NONE
1313 && !pos
.has_pawn_on_7th(pos
.side_to_move()))
1315 Value v
= qsearch(pos
, ss
, beta
-1, beta
, Depth(0), ply
, threadID
);
1316 if (v
< beta
- RazorMargins
[int(depth
) - 2])
1320 // Go with internal iterative deepening if we don't have a TT move
1321 if (UseIIDAtNonPVNodes
&& ttMove
== MOVE_NONE
&& depth
>= 8*OnePly
&&
1322 evaluate(pos
, ei
, threadID
) >= beta
- IIDMargin
)
1324 search(pos
, ss
, beta
, Min(depth
/2, depth
-2*OnePly
), ply
, false, threadID
);
1325 ttMove
= ss
[ply
].pv
[ply
];
1328 // Initialize a MovePicker object for the current position, and prepare
1329 // to search all moves:
1330 MovePicker mp
= MovePicker(pos
, false, ttMove
, ss
[ply
], depth
);
1332 Move move
, movesSearched
[256];
1334 Value value
, bestValue
= -VALUE_INFINITE
;
1335 Bitboard dcCandidates
= mp
.discovered_check_candidates();
1336 Value futilityValue
= VALUE_NONE
;
1337 bool useFutilityPruning
= UseFutilityPruning
1338 && depth
< SelectiveDepth
1341 // Loop through all legal moves until no moves remain or a beta cutoff
1343 while ( bestValue
< beta
1344 && (move
= mp
.get_next_move()) != MOVE_NONE
1345 && !thread_should_stop(threadID
))
1347 assert(move_is_ok(move
));
1349 bool singleReply
= (isCheck
&& mp
.number_of_moves() == 1);
1350 bool moveIsCheck
= pos
.move_is_check(move
, dcCandidates
);
1351 bool moveIsCapture
= pos
.move_is_capture(move
);
1353 movesSearched
[moveCount
++] = ss
[ply
].currentMove
= move
;
1355 // Decide the new search depth
1357 Depth ext
= extension(pos
, move
, false, moveIsCapture
, moveIsCheck
, singleReply
, mateThreat
, &dangerous
);
1358 Depth newDepth
= depth
- OnePly
+ ext
;
1361 if ( useFutilityPruning
1364 && !move_promotion(move
))
1366 // History pruning. See ok_to_prune() definition
1367 if ( moveCount
>= 2 + int(depth
)
1368 && ok_to_prune(pos
, move
, ss
[ply
].threatMove
, depth
))
1371 // Value based pruning
1372 if (approximateEval
< beta
)
1374 if (futilityValue
== VALUE_NONE
)
1375 futilityValue
= evaluate(pos
, ei
, threadID
)
1376 + FutilityMargins
[int(depth
) - 2];
1378 if (futilityValue
< beta
)
1380 if (futilityValue
> bestValue
)
1381 bestValue
= futilityValue
;
1387 // Make and search the move
1389 pos
.do_move(move
, st
, dcCandidates
);
1391 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1392 // if the move fails high will be re-searched at full depth.
1393 if ( depth
>= 2*OnePly
1394 && moveCount
>= LMRNonPVMoves
1397 && !move_promotion(move
)
1398 && !move_is_castle(move
)
1399 && !move_is_killer(move
, ss
[ply
]))
1401 ss
[ply
].reduction
= OnePly
;
1402 value
= -search(pos
, ss
, -(beta
-1), newDepth
-OnePly
, ply
+1, true, threadID
);
1405 value
= beta
; // Just to trigger next condition
1407 if (value
>= beta
) // Go with full depth non-pv search
1409 ss
[ply
].reduction
= Depth(0);
1410 value
= -search(pos
, ss
, -(beta
-1), newDepth
, ply
+1, true, threadID
);
1412 pos
.undo_move(move
);
1414 assert(value
> -VALUE_INFINITE
&& value
< VALUE_INFINITE
);
1417 if (value
> bestValue
)
1423 if (value
== value_mate_in(ply
+ 1))
1424 ss
[ply
].mateKiller
= move
;
1428 if ( ActiveThreads
> 1
1430 && depth
>= MinimumSplitDepth
1432 && idle_thread_exists(threadID
)
1434 && !thread_should_stop(threadID
)
1435 && split(pos
, ss
, ply
, &beta
, &beta
, &bestValue
, depth
, &moveCount
,
1436 &mp
, dcCandidates
, threadID
, false))
1440 // All legal moves have been searched. A special case: If there were
1441 // no legal moves, it must be mate or stalemate.
1443 return (pos
.is_check() ? value_mated_in(ply
) : VALUE_DRAW
);
1445 // If the search is not aborted, update the transposition table,
1446 // history counters, and killer moves.
1447 if (AbortSearch
|| thread_should_stop(threadID
))
1450 if (bestValue
< beta
)
1451 TT
.store(pos
, value_to_tt(bestValue
, ply
), VALUE_TYPE_UPPER
, depth
, MOVE_NONE
);
1454 BetaCounter
.add(pos
.side_to_move(), depth
, threadID
);
1455 Move m
= ss
[ply
].pv
[ply
];
1456 if (ok_to_history(pos
, m
)) // Only non capture moves are considered
1458 update_history(pos
, m
, depth
, movesSearched
, moveCount
);
1459 update_killers(m
, ss
[ply
]);
1461 TT
.store(pos
, value_to_tt(bestValue
, ply
), VALUE_TYPE_LOWER
, depth
, m
);
1464 assert(bestValue
> -VALUE_INFINITE
&& bestValue
< VALUE_INFINITE
);
1470 // qsearch() is the quiescence search function, which is called by the main
1471 // search function when the remaining depth is zero (or, to be more precise,
1472 // less than OnePly).
1474 Value
qsearch(Position
&pos
, SearchStack ss
[], Value alpha
, Value beta
,
1475 Depth depth
, int ply
, int threadID
) {
1477 assert(alpha
>= -VALUE_INFINITE
&& alpha
<= VALUE_INFINITE
);
1478 assert(beta
>= -VALUE_INFINITE
&& beta
<= VALUE_INFINITE
);
1480 assert(ply
>= 0 && ply
< PLY_MAX
);
1481 assert(threadID
>= 0 && threadID
< ActiveThreads
);
1483 // Initialize, and make an early exit in case of an aborted search,
1484 // an instant draw, maximum ply reached, etc.
1485 init_node(ss
, ply
, threadID
);
1487 // After init_node() that calls poll()
1488 if (AbortSearch
|| thread_should_stop(threadID
))
1494 // Transposition table lookup, only when not in PV
1495 TTEntry
* tte
= NULL
;
1496 bool pvNode
= (beta
- alpha
!= 1);
1499 tte
= TT
.retrieve(pos
);
1500 if (tte
&& ok_to_use_TT(tte
, depth
, beta
, ply
))
1502 assert(tte
->type() != VALUE_TYPE_EVAL
);
1504 return value_from_tt(tte
->value(), ply
);
1507 Move ttMove
= (tte
? tte
->move() : MOVE_NONE
);
1509 // Evaluate the position statically
1512 bool isCheck
= pos
.is_check();
1513 ei
.futilityMargin
= Value(0); // Manually initialize futilityMargin
1516 staticValue
= -VALUE_INFINITE
;
1518 else if (tte
&& tte
->type() == VALUE_TYPE_EVAL
)
1520 // Use the cached evaluation score if possible
1521 assert(tte
->value() == evaluate(pos
, ei
, threadID
));
1522 assert(ei
.futilityMargin
== Value(0));
1524 staticValue
= tte
->value();
1527 staticValue
= evaluate(pos
, ei
, threadID
);
1529 if (ply
== PLY_MAX
- 1)
1530 return evaluate(pos
, ei
, threadID
);
1532 // Initialize "stand pat score", and return it immediately if it is
1534 Value bestValue
= staticValue
;
1536 if (bestValue
>= beta
)
1538 // Store the score to avoid a future costly evaluation() call
1539 if (!isCheck
&& !tte
&& ei
.futilityMargin
== 0)
1540 TT
.store(pos
, value_to_tt(bestValue
, ply
), VALUE_TYPE_EVAL
, Depth(-127*OnePly
), MOVE_NONE
);
1545 if (bestValue
> alpha
)
1548 // Initialize a MovePicker object for the current position, and prepare
1549 // to search the moves. Because the depth is <= 0 here, only captures,
1550 // queen promotions and checks (only if depth == 0) will be generated.
1551 MovePicker mp
= MovePicker(pos
, pvNode
, ttMove
, EmptySearchStack
, depth
);
1554 Bitboard dcCandidates
= mp
.discovered_check_candidates();
1555 Color us
= pos
.side_to_move();
1556 bool enoughMaterial
= pos
.non_pawn_material(us
) > RookValueMidgame
;
1558 // Loop through the moves until no moves remain or a beta cutoff
1560 while ( alpha
< beta
1561 && (move
= mp
.get_next_move()) != MOVE_NONE
)
1563 assert(move_is_ok(move
));
1566 ss
[ply
].currentMove
= move
;
1569 if ( UseQSearchFutilityPruning
1573 && !move_promotion(move
)
1574 && !pos
.move_is_check(move
, dcCandidates
)
1575 && !pos
.move_is_passed_pawn_push(move
))
1577 Value futilityValue
= staticValue
1578 + Max(pos
.midgame_value_of_piece_on(move_to(move
)),
1579 pos
.endgame_value_of_piece_on(move_to(move
)))
1580 + (move_is_ep(move
) ? PawnValueEndgame
: Value(0))
1582 + ei
.futilityMargin
;
1584 if (futilityValue
< alpha
)
1586 if (futilityValue
> bestValue
)
1587 bestValue
= futilityValue
;
1592 // Don't search captures and checks with negative SEE values
1594 && !move_promotion(move
)
1595 && (pos
.midgame_value_of_piece_on(move_from(move
)) >
1596 pos
.midgame_value_of_piece_on(move_to(move
)))
1597 && pos
.see(move
) < 0)
1600 // Make and search the move.
1602 pos
.do_move(move
, st
, dcCandidates
);
1603 Value value
= -qsearch(pos
, ss
, -beta
, -alpha
, depth
-OnePly
, ply
+1, threadID
);
1604 pos
.undo_move(move
);
1606 assert(value
> -VALUE_INFINITE
&& value
< VALUE_INFINITE
);
1609 if (value
> bestValue
)
1620 // All legal moves have been searched. A special case: If we're in check
1621 // and no legal moves were found, it is checkmate:
1622 if (pos
.is_check() && moveCount
== 0) // Mate!
1623 return value_mated_in(ply
);
1625 assert(bestValue
> -VALUE_INFINITE
&& bestValue
< VALUE_INFINITE
);
1627 // Update transposition table
1628 Move m
= ss
[ply
].pv
[ply
];
1631 Depth d
= (depth
== Depth(0) ? Depth(0) : Depth(-1));
1632 if (bestValue
< beta
)
1633 TT
.store(pos
, value_to_tt(bestValue
, ply
), VALUE_TYPE_UPPER
, d
, MOVE_NONE
);
1635 TT
.store(pos
, value_to_tt(bestValue
, ply
), VALUE_TYPE_LOWER
, d
, m
);
1638 // Update killers only for good check moves
1639 if (alpha
>= beta
&& ok_to_history(pos
, m
)) // Only non capture moves are considered
1640 update_killers(m
, ss
[ply
]);
1646 // sp_search() is used to search from a split point. This function is called
1647 // by each thread working at the split point. It is similar to the normal
1648 // search() function, but simpler. Because we have already probed the hash
1649 // table, done a null move search, and searched the first move before
1650 // splitting, we don't have to repeat all this work in sp_search(). We
1651 // also don't need to store anything to the hash table here: This is taken
1652 // care of after we return from the split point.
1654 void sp_search(SplitPoint
*sp
, int threadID
) {
1656 assert(threadID
>= 0 && threadID
< ActiveThreads
);
1657 assert(ActiveThreads
> 1);
1659 Position pos
= Position(sp
->pos
);
1660 SearchStack
*ss
= sp
->sstack
[threadID
];
1663 bool isCheck
= pos
.is_check();
1664 bool useFutilityPruning
= UseFutilityPruning
1665 && sp
->depth
< SelectiveDepth
1668 while ( sp
->bestValue
< sp
->beta
1669 && !thread_should_stop(threadID
)
1670 && (move
= sp
->mp
->get_next_move(sp
->lock
)) != MOVE_NONE
)
1672 assert(move_is_ok(move
));
1674 bool moveIsCheck
= pos
.move_is_check(move
, sp
->dcCandidates
);
1675 bool moveIsCapture
= pos
.move_is_capture(move
);
1677 lock_grab(&(sp
->lock
));
1678 int moveCount
= ++sp
->moves
;
1679 lock_release(&(sp
->lock
));
1681 ss
[sp
->ply
].currentMove
= move
;
1683 // Decide the new search depth.
1685 Depth ext
= extension(pos
, move
, false, moveIsCapture
, moveIsCheck
, false, false, &dangerous
);
1686 Depth newDepth
= sp
->depth
- OnePly
+ ext
;
1689 if ( useFutilityPruning
1692 && !move_promotion(move
)
1693 && moveCount
>= 2 + int(sp
->depth
)
1694 && ok_to_prune(pos
, move
, ss
[sp
->ply
].threatMove
, sp
->depth
))
1697 // Make and search the move.
1699 pos
.do_move(move
, st
, sp
->dcCandidates
);
1701 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1702 // if the move fails high will be re-searched at full depth.
1704 && moveCount
>= LMRNonPVMoves
1706 && !move_promotion(move
)
1707 && !move_is_castle(move
)
1708 && !move_is_killer(move
, ss
[sp
->ply
]))
1710 ss
[sp
->ply
].reduction
= OnePly
;
1711 value
= -search(pos
, ss
, -(sp
->beta
-1), newDepth
- OnePly
, sp
->ply
+1, true, threadID
);
1714 value
= sp
->beta
; // Just to trigger next condition
1716 if (value
>= sp
->beta
) // Go with full depth non-pv search
1718 ss
[sp
->ply
].reduction
= Depth(0);
1719 value
= -search(pos
, ss
, -(sp
->beta
- 1), newDepth
, sp
->ply
+1, true, threadID
);
1721 pos
.undo_move(move
);
1723 assert(value
> -VALUE_INFINITE
&& value
< VALUE_INFINITE
);
1725 if (thread_should_stop(threadID
))
1729 lock_grab(&(sp
->lock
));
1730 if (value
> sp
->bestValue
&& !thread_should_stop(threadID
))
1732 sp
->bestValue
= value
;
1733 if (sp
->bestValue
>= sp
->beta
)
1735 sp_update_pv(sp
->parentSstack
, ss
, sp
->ply
);
1736 for (int i
= 0; i
< ActiveThreads
; i
++)
1737 if (i
!= threadID
&& (i
== sp
->master
|| sp
->slaves
[i
]))
1738 Threads
[i
].stop
= true;
1740 sp
->finished
= true;
1743 lock_release(&(sp
->lock
));
1746 lock_grab(&(sp
->lock
));
1748 // If this is the master thread and we have been asked to stop because of
1749 // a beta cutoff higher up in the tree, stop all slave threads:
1750 if (sp
->master
== threadID
&& thread_should_stop(threadID
))
1751 for (int i
= 0; i
< ActiveThreads
; i
++)
1753 Threads
[i
].stop
= true;
1756 sp
->slaves
[threadID
] = 0;
1758 lock_release(&(sp
->lock
));
1762 // sp_search_pv() is used to search from a PV split point. This function
1763 // is called by each thread working at the split point. It is similar to
1764 // the normal search_pv() function, but simpler. Because we have already
1765 // probed the hash table and searched the first move before splitting, we
1766 // don't have to repeat all this work in sp_search_pv(). We also don't
1767 // need to store anything to the hash table here: This is taken care of
1768 // after we return from the split point.
1770 void sp_search_pv(SplitPoint
*sp
, int threadID
) {
1772 assert(threadID
>= 0 && threadID
< ActiveThreads
);
1773 assert(ActiveThreads
> 1);
1775 Position pos
= Position(sp
->pos
);
1776 SearchStack
*ss
= sp
->sstack
[threadID
];
1780 while ( sp
->alpha
< sp
->beta
1781 && !thread_should_stop(threadID
)
1782 && (move
= sp
->mp
->get_next_move(sp
->lock
)) != MOVE_NONE
)
1784 bool moveIsCheck
= pos
.move_is_check(move
, sp
->dcCandidates
);
1785 bool moveIsCapture
= pos
.move_is_capture(move
);
1787 assert(move_is_ok(move
));
1789 lock_grab(&(sp
->lock
));
1790 int moveCount
= ++sp
->moves
;
1791 lock_release(&(sp
->lock
));
1793 ss
[sp
->ply
].currentMove
= move
;
1795 // Decide the new search depth.
1797 Depth ext
= extension(pos
, move
, true, moveIsCapture
, moveIsCheck
, false, false, &dangerous
);
1798 Depth newDepth
= sp
->depth
- OnePly
+ ext
;
1800 // Make and search the move.
1802 pos
.do_move(move
, st
, sp
->dcCandidates
);
1804 // Try to reduce non-pv search depth by one ply if move seems not problematic,
1805 // if the move fails high will be re-searched at full depth.
1807 && moveCount
>= LMRPVMoves
1809 && !move_promotion(move
)
1810 && !move_is_castle(move
)
1811 && !move_is_killer(move
, ss
[sp
->ply
]))
1813 ss
[sp
->ply
].reduction
= OnePly
;
1814 value
= -search(pos
, ss
, -sp
->alpha
, newDepth
- OnePly
, sp
->ply
+1, true, threadID
);
1817 value
= sp
->alpha
+ 1; // Just to trigger next condition
1819 if (value
> sp
->alpha
) // Go with full depth non-pv search
1821 ss
[sp
->ply
].reduction
= Depth(0);
1822 value
= -search(pos
, ss
, -sp
->alpha
, newDepth
, sp
->ply
+1, true, threadID
);
1824 if (value
> sp
->alpha
&& value
< sp
->beta
)
1826 // When the search fails high at ply 1 while searching the first
1827 // move at the root, set the flag failHighPly1. This is used for
1828 // time managment: We don't want to stop the search early in
1829 // such cases, because resolving the fail high at ply 1 could
1830 // result in a big drop in score at the root.
1831 if (sp
->ply
== 1 && RootMoveNumber
== 1)
1832 Threads
[threadID
].failHighPly1
= true;
1834 value
= -search_pv(pos
, ss
, -sp
->beta
, -sp
->alpha
, newDepth
, sp
->ply
+1, threadID
);
1835 Threads
[threadID
].failHighPly1
= false;
1838 pos
.undo_move(move
);
1840 assert(value
> -VALUE_INFINITE
&& value
< VALUE_INFINITE
);
1842 if (thread_should_stop(threadID
))
1846 lock_grab(&(sp
->lock
));
1847 if (value
> sp
->bestValue
&& !thread_should_stop(threadID
))
1849 sp
->bestValue
= value
;
1850 if (value
> sp
->alpha
)
1853 sp_update_pv(sp
->parentSstack
, ss
, sp
->ply
);
1854 if (value
== value_mate_in(sp
->ply
+ 1))
1855 ss
[sp
->ply
].mateKiller
= move
;
1857 if(value
>= sp
->beta
)
1859 for(int i
= 0; i
< ActiveThreads
; i
++)
1860 if(i
!= threadID
&& (i
== sp
->master
|| sp
->slaves
[i
]))
1861 Threads
[i
].stop
= true;
1863 sp
->finished
= true;
1866 // If we are at ply 1, and we are searching the first root move at
1867 // ply 0, set the 'Problem' variable if the score has dropped a lot
1868 // (from the computer's point of view) since the previous iteration.
1871 && -value
<= IterationInfo
[Iteration
-1].value
- ProblemMargin
)
1874 lock_release(&(sp
->lock
));
1877 lock_grab(&(sp
->lock
));
1879 // If this is the master thread and we have been asked to stop because of
1880 // a beta cutoff higher up in the tree, stop all slave threads.
1881 if (sp
->master
== threadID
&& thread_should_stop(threadID
))
1882 for (int i
= 0; i
< ActiveThreads
; i
++)
1884 Threads
[i
].stop
= true;
1887 sp
->slaves
[threadID
] = 0;
1889 lock_release(&(sp
->lock
));
1892 /// The BetaCounterType class
1894 BetaCounterType::BetaCounterType() { clear(); }
1896 void BetaCounterType::clear() {
1898 for (int i
= 0; i
< THREAD_MAX
; i
++)
1899 hits
[i
][WHITE
] = hits
[i
][BLACK
] = 0ULL;
1902 void BetaCounterType::add(Color us
, Depth d
, int threadID
) {
1904 // Weighted count based on depth
1905 hits
[threadID
][us
] += int(d
);
1908 void BetaCounterType::read(Color us
, int64_t& our
, int64_t& their
) {
1911 for (int i
= 0; i
< THREAD_MAX
; i
++)
1914 their
+= hits
[i
][opposite_color(us
)];
1919 /// The RootMove class
1923 RootMove::RootMove() {
1924 nodes
= cumulativeNodes
= ourBeta
= theirBeta
= 0ULL;
1927 // RootMove::operator<() is the comparison function used when
1928 // sorting the moves. A move m1 is considered to be better
1929 // than a move m2 if it has a higher score, or if the moves
1930 // have equal score but m1 has the higher node count.
1932 bool RootMove::operator<(const RootMove
& m
) {
1934 if (score
!= m
.score
)
1935 return (score
< m
.score
);
1937 return theirBeta
<= m
.theirBeta
;
1940 /// The RootMoveList class
1944 RootMoveList::RootMoveList(Position
& pos
, Move searchMoves
[]) : count(0) {
1946 MoveStack mlist
[MaxRootMoves
];
1947 bool includeAllMoves
= (searchMoves
[0] == MOVE_NONE
);
1949 // Generate all legal moves
1950 int lm_count
= generate_legal_moves(pos
, mlist
);
1952 // Add each move to the moves[] array
1953 for (int i
= 0; i
< lm_count
; i
++)
1955 bool includeMove
= includeAllMoves
;
1957 for (int k
= 0; !includeMove
&& searchMoves
[k
] != MOVE_NONE
; k
++)
1958 includeMove
= (searchMoves
[k
] == mlist
[i
].move
);
1963 // Find a quick score for the move
1965 SearchStack ss
[PLY_MAX_PLUS_2
];
1967 moves
[count
].move
= mlist
[i
].move
;
1968 pos
.do_move(moves
[count
].move
, st
);
1969 moves
[count
].score
= -qsearch(pos
, ss
, -VALUE_INFINITE
, VALUE_INFINITE
, Depth(0), 1, 0);
1970 pos
.undo_move(moves
[count
].move
);
1971 moves
[count
].pv
[0] = moves
[count
].move
;
1972 moves
[count
].pv
[1] = MOVE_NONE
; // FIXME
1979 // Simple accessor methods for the RootMoveList class
1981 inline Move
RootMoveList::get_move(int moveNum
) const {
1982 return moves
[moveNum
].move
;
1985 inline Value
RootMoveList::get_move_score(int moveNum
) const {
1986 return moves
[moveNum
].score
;
1989 inline void RootMoveList::set_move_score(int moveNum
, Value score
) {
1990 moves
[moveNum
].score
= score
;
1993 inline void RootMoveList::set_move_nodes(int moveNum
, int64_t nodes
) {
1994 moves
[moveNum
].nodes
= nodes
;
1995 moves
[moveNum
].cumulativeNodes
+= nodes
;
1998 inline void RootMoveList::set_beta_counters(int moveNum
, int64_t our
, int64_t their
) {
1999 moves
[moveNum
].ourBeta
= our
;
2000 moves
[moveNum
].theirBeta
= their
;
2003 void RootMoveList::set_move_pv(int moveNum
, const Move pv
[]) {
2005 for(j
= 0; pv
[j
] != MOVE_NONE
; j
++)
2006 moves
[moveNum
].pv
[j
] = pv
[j
];
2007 moves
[moveNum
].pv
[j
] = MOVE_NONE
;
2010 inline Move
RootMoveList::get_move_pv(int moveNum
, int i
) const {
2011 return moves
[moveNum
].pv
[i
];
2014 inline int64_t RootMoveList::get_move_cumulative_nodes(int moveNum
) const {
2015 return moves
[moveNum
].cumulativeNodes
;
2018 inline int RootMoveList::move_count() const {
2023 // RootMoveList::scan_for_easy_move() is called at the end of the first
2024 // iteration, and is used to detect an "easy move", i.e. a move which appears
2025 // to be much bester than all the rest. If an easy move is found, the move
2026 // is returned, otherwise the function returns MOVE_NONE. It is very
2027 // important that this function is called at the right moment: The code
2028 // assumes that the first iteration has been completed and the moves have
2029 // been sorted. This is done in RootMoveList c'tor.
2031 Move
RootMoveList::scan_for_easy_move() const {
2038 // moves are sorted so just consider the best and the second one
2039 if (get_move_score(0) > get_move_score(1) + EasyMoveMargin
)
2045 // RootMoveList::sort() sorts the root move list at the beginning of a new
2048 inline void RootMoveList::sort() {
2050 sort_multipv(count
- 1); // all items
2054 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2055 // list by their scores and depths. It is used to order the different PVs
2056 // correctly in MultiPV mode.
2058 void RootMoveList::sort_multipv(int n
) {
2060 for (int i
= 1; i
<= n
; i
++)
2062 RootMove rm
= moves
[i
];
2064 for (j
= i
; j
> 0 && moves
[j
-1] < rm
; j
--)
2065 moves
[j
] = moves
[j
-1];
2071 // init_node() is called at the beginning of all the search functions
2072 // (search(), search_pv(), qsearch(), and so on) and initializes the search
2073 // stack object corresponding to the current node. Once every
2074 // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
2075 // for user input and checks whether it is time to stop the search.
2077 void init_node(SearchStack ss
[], int ply
, int threadID
) {
2078 assert(ply
>= 0 && ply
< PLY_MAX
);
2079 assert(threadID
>= 0 && threadID
< ActiveThreads
);
2081 Threads
[threadID
].nodes
++;
2085 if(NodesSincePoll
>= NodesBetweenPolls
) {
2092 ss
[ply
+2].initKillers();
2094 if(Threads
[threadID
].printCurrentLine
)
2095 print_current_line(ss
, ply
, threadID
);
2099 // update_pv() is called whenever a search returns a value > alpha. It
2100 // updates the PV in the SearchStack object corresponding to the current
2103 void update_pv(SearchStack ss
[], int ply
) {
2104 assert(ply
>= 0 && ply
< PLY_MAX
);
2106 ss
[ply
].pv
[ply
] = ss
[ply
].currentMove
;
2108 for(p
= ply
+ 1; ss
[ply
+1].pv
[p
] != MOVE_NONE
; p
++)
2109 ss
[ply
].pv
[p
] = ss
[ply
+1].pv
[p
];
2110 ss
[ply
].pv
[p
] = MOVE_NONE
;
2114 // sp_update_pv() is a variant of update_pv for use at split points. The
2115 // difference between the two functions is that sp_update_pv also updates
2116 // the PV at the parent node.
2118 void sp_update_pv(SearchStack
*pss
, SearchStack ss
[], int ply
) {
2119 assert(ply
>= 0 && ply
< PLY_MAX
);
2121 ss
[ply
].pv
[ply
] = pss
[ply
].pv
[ply
] = ss
[ply
].currentMove
;
2123 for(p
= ply
+ 1; ss
[ply
+1].pv
[p
] != MOVE_NONE
; p
++)
2124 ss
[ply
].pv
[p
] = pss
[ply
].pv
[p
] = ss
[ply
+1].pv
[p
];
2125 ss
[ply
].pv
[p
] = pss
[ply
].pv
[p
] = MOVE_NONE
;
2129 // connected_moves() tests whether two moves are 'connected' in the sense
2130 // that the first move somehow made the second move possible (for instance
2131 // if the moving piece is the same in both moves). The first move is
2132 // assumed to be the move that was made to reach the current position, while
2133 // the second move is assumed to be a move from the current position.
2135 bool connected_moves(const Position
&pos
, Move m1
, Move m2
) {
2136 Square f1
, t1
, f2
, t2
;
2138 assert(move_is_ok(m1
));
2139 assert(move_is_ok(m2
));
2144 // Case 1: The moving piece is the same in both moves.
2150 // Case 2: The destination square for m2 was vacated by m1.
2156 // Case 3: Moving through the vacated square:
2157 if(piece_is_slider(pos
.piece_on(f2
)) &&
2158 bit_is_set(squares_between(f2
, t2
), f1
))
2161 // Case 4: The destination square for m2 is attacked by the moving piece
2163 if(pos
.piece_attacks_square(pos
.piece_on(t1
), t1
, t2
))
2166 // Case 5: Discovered check, checking piece is the piece moved in m1:
2167 if(piece_is_slider(pos
.piece_on(t1
)) &&
2168 bit_is_set(squares_between(t1
, pos
.king_square(pos
.side_to_move())),
2170 !bit_is_set(squares_between(t2
, pos
.king_square(pos
.side_to_move())),
2172 Bitboard occ
= pos
.occupied_squares();
2173 Color us
= pos
.side_to_move();
2174 Square ksq
= pos
.king_square(us
);
2175 clear_bit(&occ
, f2
);
2176 if(pos
.type_of_piece_on(t1
) == BISHOP
) {
2177 if(bit_is_set(bishop_attacks_bb(ksq
, occ
), t1
))
2180 else if(pos
.type_of_piece_on(t1
) == ROOK
) {
2181 if(bit_is_set(rook_attacks_bb(ksq
, occ
), t1
))
2185 assert(pos
.type_of_piece_on(t1
) == QUEEN
);
2186 if(bit_is_set(queen_attacks_bb(ksq
, occ
), t1
))
2195 // value_is_mate() checks if the given value is a mate one
2196 // eventually compensated for the ply.
2198 bool value_is_mate(Value value
) {
2200 assert(abs(value
) <= VALUE_INFINITE
);
2202 return value
<= value_mated_in(PLY_MAX
)
2203 || value
>= value_mate_in(PLY_MAX
);
2207 // move_is_killer() checks if the given move is among the
2208 // killer moves of that ply.
2210 bool move_is_killer(Move m
, const SearchStack
& ss
) {
2212 const Move
* k
= ss
.killers
;
2213 for (int i
= 0; i
< KILLER_MAX
; i
++, k
++)
2221 // extension() decides whether a move should be searched with normal depth,
2222 // or with extended depth. Certain classes of moves (checking moves, in
2223 // particular) are searched with bigger depth than ordinary moves and in
2224 // any case are marked as 'dangerous'. Note that also if a move is not
2225 // extended, as example because the corresponding UCI option is set to zero,
2226 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
2228 Depth
extension(const Position
& pos
, Move m
, bool pvNode
, bool capture
, bool check
,
2229 bool singleReply
, bool mateThreat
, bool* dangerous
) {
2231 assert(m
!= MOVE_NONE
);
2233 Depth result
= Depth(0);
2234 *dangerous
= check
|| singleReply
|| mateThreat
;
2237 result
+= CheckExtension
[pvNode
];
2240 result
+= SingleReplyExtension
[pvNode
];
2243 result
+= MateThreatExtension
[pvNode
];
2245 if (pos
.type_of_piece_on(move_from(m
)) == PAWN
)
2247 if (pos
.move_is_pawn_push_to_7th(m
))
2249 result
+= PawnPushTo7thExtension
[pvNode
];
2252 if (pos
.move_is_passed_pawn_push(m
))
2254 result
+= PassedPawnExtension
[pvNode
];
2260 && pos
.type_of_piece_on(move_to(m
)) != PAWN
2261 && ( pos
.non_pawn_material(WHITE
) + pos
.non_pawn_material(BLACK
)
2262 - pos
.midgame_value_of_piece_on(move_to(m
)) == Value(0))
2263 && !move_promotion(m
)
2266 result
+= PawnEndgameExtension
[pvNode
];
2272 && pos
.type_of_piece_on(move_to(m
)) != PAWN
2279 return Min(result
, OnePly
);
2283 // ok_to_do_nullmove() looks at the current position and decides whether
2284 // doing a 'null move' should be allowed. In order to avoid zugzwang
2285 // problems, null moves are not allowed when the side to move has very
2286 // little material left. Currently, the test is a bit too simple: Null
2287 // moves are avoided only when the side to move has only pawns left. It's
2288 // probably a good idea to avoid null moves in at least some more
2289 // complicated endgames, e.g. KQ vs KR. FIXME
2291 bool ok_to_do_nullmove(const Position
&pos
) {
2292 if(pos
.non_pawn_material(pos
.side_to_move()) == Value(0))
2298 // ok_to_prune() tests whether it is safe to forward prune a move. Only
2299 // non-tactical moves late in the move list close to the leaves are
2300 // candidates for pruning.
2302 bool ok_to_prune(const Position
&pos
, Move m
, Move threat
, Depth d
) {
2303 Square mfrom
, mto
, tfrom
, tto
;
2305 assert(move_is_ok(m
));
2306 assert(threat
== MOVE_NONE
|| move_is_ok(threat
));
2307 assert(!move_promotion(m
));
2308 assert(!pos
.move_is_check(m
));
2309 assert(!pos
.move_is_capture(m
));
2310 assert(!pos
.move_is_passed_pawn_push(m
));
2311 assert(d
>= OnePly
);
2313 mfrom
= move_from(m
);
2315 tfrom
= move_from(threat
);
2316 tto
= move_to(threat
);
2318 // Case 1: Castling moves are never pruned.
2319 if (move_is_castle(m
))
2322 // Case 2: Don't prune moves which move the threatened piece
2323 if (!PruneEscapeMoves
&& threat
!= MOVE_NONE
&& mfrom
== tto
)
2326 // Case 3: If the threatened piece has value less than or equal to the
2327 // value of the threatening piece, don't prune move which defend it.
2328 if ( !PruneDefendingMoves
2329 && threat
!= MOVE_NONE
2330 && pos
.move_is_capture(threat
)
2331 && ( pos
.midgame_value_of_piece_on(tfrom
) >= pos
.midgame_value_of_piece_on(tto
)
2332 || pos
.type_of_piece_on(tfrom
) == KING
)
2333 && pos
.move_attacks_square(m
, tto
))
2336 // Case 4: Don't prune moves with good history.
2337 if (!H
.ok_to_prune(pos
.piece_on(move_from(m
)), m
, d
))
2340 // Case 5: If the moving piece in the threatened move is a slider, don't
2341 // prune safe moves which block its ray.
2342 if ( !PruneBlockingMoves
2343 && threat
!= MOVE_NONE
2344 && piece_is_slider(pos
.piece_on(tfrom
))
2345 && bit_is_set(squares_between(tfrom
, tto
), mto
)
2353 // ok_to_use_TT() returns true if a transposition table score
2354 // can be used at a given point in search.
2356 bool ok_to_use_TT(const TTEntry
* tte
, Depth depth
, Value beta
, int ply
) {
2358 Value v
= value_from_tt(tte
->value(), ply
);
2360 return ( tte
->depth() >= depth
2361 || v
>= Max(value_mate_in(100), beta
)
2362 || v
< Min(value_mated_in(100), beta
))
2364 && ( (is_lower_bound(tte
->type()) && v
>= beta
)
2365 || (is_upper_bound(tte
->type()) && v
< beta
));
2369 // ok_to_history() returns true if a move m can be stored
2370 // in history. Should be a non capturing move nor a promotion.
2372 bool ok_to_history(const Position
& pos
, Move m
) {
2374 return !pos
.move_is_capture(m
) && !move_promotion(m
);
2378 // update_history() registers a good move that produced a beta-cutoff
2379 // in history and marks as failures all the other moves of that ply.
2381 void update_history(const Position
& pos
, Move m
, Depth depth
,
2382 Move movesSearched
[], int moveCount
) {
2384 H
.success(pos
.piece_on(move_from(m
)), m
, depth
);
2386 for (int i
= 0; i
< moveCount
- 1; i
++)
2388 assert(m
!= movesSearched
[i
]);
2389 if (ok_to_history(pos
, movesSearched
[i
]))
2390 H
.failure(pos
.piece_on(move_from(movesSearched
[i
])), movesSearched
[i
]);
2395 // update_killers() add a good move that produced a beta-cutoff
2396 // among the killer moves of that ply.
2398 void update_killers(Move m
, SearchStack
& ss
) {
2400 if (m
== ss
.killers
[0])
2403 for (int i
= KILLER_MAX
- 1; i
> 0; i
--)
2404 ss
.killers
[i
] = ss
.killers
[i
- 1];
2409 // fail_high_ply_1() checks if some thread is currently resolving a fail
2410 // high at ply 1 at the node below the first root node. This information
2411 // is used for time managment.
2413 bool fail_high_ply_1() {
2414 for(int i
= 0; i
< ActiveThreads
; i
++)
2415 if(Threads
[i
].failHighPly1
)
2421 // current_search_time() returns the number of milliseconds which have passed
2422 // since the beginning of the current search.
2424 int current_search_time() {
2425 return get_system_time() - SearchStartTime
;
2429 // nps() computes the current nodes/second count.
2432 int t
= current_search_time();
2433 return (t
> 0)? int((nodes_searched() * 1000) / t
) : 0;
2437 // poll() performs two different functions: It polls for user input, and it
2438 // looks at the time consumed so far and decides if it's time to abort the
2443 static int lastInfoTime
;
2444 int t
= current_search_time();
2449 // We are line oriented, don't read single chars
2450 std::string command
;
2451 if (!std::getline(std::cin
, command
))
2454 if (command
== "quit")
2457 PonderSearch
= false;
2460 else if(command
== "stop")
2463 PonderSearch
= false;
2465 else if(command
== "ponderhit")
2468 // Print search information
2472 else if (lastInfoTime
> t
)
2473 // HACK: Must be a new search where we searched less than
2474 // NodesBetweenPolls nodes during the first second of search.
2477 else if (t
- lastInfoTime
>= 1000)
2484 if (dbg_show_hit_rate
)
2485 dbg_print_hit_rate();
2487 std::cout
<< "info nodes " << nodes_searched() << " nps " << nps()
2488 << " time " << t
<< " hashfull " << TT
.full() << std::endl
;
2489 lock_release(&IOLock
);
2490 if (ShowCurrentLine
)
2491 Threads
[0].printCurrentLine
= true;
2493 // Should we stop the search?
2497 bool overTime
= t
> AbsoluteMaxSearchTime
2498 || (RootMoveNumber
== 1 && t
> MaxSearchTime
+ ExtraSearchTime
&& !FailLow
) //FIXME: We are not checking any problem flags, BUG?
2499 || ( !FailHigh
&& !FailLow
&& !fail_high_ply_1() && !Problem
2500 && t
> 6*(MaxSearchTime
+ ExtraSearchTime
));
2502 if ( (Iteration
>= 3 && (!InfiniteSearch
&& overTime
))
2503 || (ExactMaxTime
&& t
>= ExactMaxTime
)
2504 || (Iteration
>= 3 && MaxNodes
&& nodes_searched() >= MaxNodes
))
2509 // ponderhit() is called when the program is pondering (i.e. thinking while
2510 // it's the opponent's turn to move) in order to let the engine know that
2511 // it correctly predicted the opponent's move.
2514 int t
= current_search_time();
2515 PonderSearch
= false;
2516 if(Iteration
>= 3 &&
2517 (!InfiniteSearch
&& (StopOnPonderhit
||
2518 t
> AbsoluteMaxSearchTime
||
2519 (RootMoveNumber
== 1 &&
2520 t
> MaxSearchTime
+ ExtraSearchTime
&& !FailLow
) ||
2521 (!FailHigh
&& !FailLow
&& !fail_high_ply_1() && !Problem
&&
2522 t
> 6*(MaxSearchTime
+ ExtraSearchTime
)))))
2527 // print_current_line() prints the current line of search for a given
2528 // thread. Called when the UCI option UCI_ShowCurrLine is 'true'.
2530 void print_current_line(SearchStack ss
[], int ply
, int threadID
) {
2531 assert(ply
>= 0 && ply
< PLY_MAX
);
2532 assert(threadID
>= 0 && threadID
< ActiveThreads
);
2534 if(!Threads
[threadID
].idle
) {
2536 std::cout
<< "info currline " << (threadID
+ 1);
2537 for(int p
= 0; p
< ply
; p
++)
2538 std::cout
<< " " << ss
[p
].currentMove
;
2539 std::cout
<< std::endl
;
2540 lock_release(&IOLock
);
2542 Threads
[threadID
].printCurrentLine
= false;
2543 if(threadID
+ 1 < ActiveThreads
)
2544 Threads
[threadID
+ 1].printCurrentLine
= true;
2548 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2549 // while the program is pondering. The point is to work around a wrinkle in
2550 // the UCI protocol: When pondering, the engine is not allowed to give a
2551 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2552 // We simply wait here until one of these commands is sent, and return,
2553 // after which the bestmove and pondermove will be printed (in id_loop()).
2555 void wait_for_stop_or_ponderhit() {
2556 std::string command
;
2559 if(!std::getline(std::cin
, command
))
2562 if(command
== "quit") {
2563 OpeningBook
.close();
2568 else if(command
== "ponderhit" || command
== "stop")
2574 // idle_loop() is where the threads are parked when they have no work to do.
2575 // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
2576 // object for which the current thread is the master.
2578 void idle_loop(int threadID
, SplitPoint
*waitSp
) {
2579 assert(threadID
>= 0 && threadID
< THREAD_MAX
);
2581 Threads
[threadID
].running
= true;
2584 if(AllThreadsShouldExit
&& threadID
!= 0)
2587 // If we are not thinking, wait for a condition to be signaled instead
2588 // of wasting CPU time polling for work:
2589 while(threadID
!= 0 && (Idle
|| threadID
>= ActiveThreads
)) {
2590 #if !defined(_MSC_VER)
2591 pthread_mutex_lock(&WaitLock
);
2592 if(Idle
|| threadID
>= ActiveThreads
)
2593 pthread_cond_wait(&WaitCond
, &WaitLock
);
2594 pthread_mutex_unlock(&WaitLock
);
2596 WaitForSingleObject(SitIdleEvent
[threadID
], INFINITE
);
2600 // If this thread has been assigned work, launch a search:
2601 if(Threads
[threadID
].workIsWaiting
) {
2602 Threads
[threadID
].workIsWaiting
= false;
2603 if(Threads
[threadID
].splitPoint
->pvNode
)
2604 sp_search_pv(Threads
[threadID
].splitPoint
, threadID
);
2606 sp_search(Threads
[threadID
].splitPoint
, threadID
);
2607 Threads
[threadID
].idle
= true;
2610 // If this thread is the master of a split point and all threads have
2611 // finished their work at this split point, return from the idle loop:
2612 if(waitSp
!= NULL
&& waitSp
->cpus
== 0)
2616 Threads
[threadID
].running
= false;
2620 // init_split_point_stack() is called during program initialization, and
2621 // initializes all split point objects.
2623 void init_split_point_stack() {
2624 for(int i
= 0; i
< THREAD_MAX
; i
++)
2625 for(int j
= 0; j
< MaxActiveSplitPoints
; j
++) {
2626 SplitPointStack
[i
][j
].parent
= NULL
;
2627 lock_init(&(SplitPointStack
[i
][j
].lock
), NULL
);
2632 // destroy_split_point_stack() is called when the program exits, and
2633 // destroys all locks in the precomputed split point objects.
2635 void destroy_split_point_stack() {
2636 for(int i
= 0; i
< THREAD_MAX
; i
++)
2637 for(int j
= 0; j
< MaxActiveSplitPoints
; j
++)
2638 lock_destroy(&(SplitPointStack
[i
][j
].lock
));
2642 // thread_should_stop() checks whether the thread with a given threadID has
2643 // been asked to stop, directly or indirectly. This can happen if a beta
2644 // cutoff has occured in thre thread's currently active split point, or in
2645 // some ancestor of the current split point.
2647 bool thread_should_stop(int threadID
) {
2648 assert(threadID
>= 0 && threadID
< ActiveThreads
);
2652 if(Threads
[threadID
].stop
)
2654 if(ActiveThreads
<= 2)
2656 for(sp
= Threads
[threadID
].splitPoint
; sp
!= NULL
; sp
= sp
->parent
)
2658 Threads
[threadID
].stop
= true;
2665 // thread_is_available() checks whether the thread with threadID "slave" is
2666 // available to help the thread with threadID "master" at a split point. An
2667 // obvious requirement is that "slave" must be idle. With more than two
2668 // threads, this is not by itself sufficient: If "slave" is the master of
2669 // some active split point, it is only available as a slave to the other
2670 // threads which are busy searching the split point at the top of "slave"'s
2671 // split point stack (the "helpful master concept" in YBWC terminology).
2673 bool thread_is_available(int slave
, int master
) {
2674 assert(slave
>= 0 && slave
< ActiveThreads
);
2675 assert(master
>= 0 && master
< ActiveThreads
);
2676 assert(ActiveThreads
> 1);
2678 if(!Threads
[slave
].idle
|| slave
== master
)
2681 if(Threads
[slave
].activeSplitPoints
== 0)
2682 // No active split points means that the thread is available as a slave
2683 // for any other thread.
2686 if(ActiveThreads
== 2)
2689 // Apply the "helpful master" concept if possible.
2690 if(SplitPointStack
[slave
][Threads
[slave
].activeSplitPoints
-1].slaves
[master
])
2697 // idle_thread_exists() tries to find an idle thread which is available as
2698 // a slave for the thread with threadID "master".
2700 bool idle_thread_exists(int master
) {
2701 assert(master
>= 0 && master
< ActiveThreads
);
2702 assert(ActiveThreads
> 1);
2704 for(int i
= 0; i
< ActiveThreads
; i
++)
2705 if(thread_is_available(i
, master
))
2711 // split() does the actual work of distributing the work at a node between
2712 // several threads at PV nodes. If it does not succeed in splitting the
2713 // node (because no idle threads are available, or because we have no unused
2714 // split point objects), the function immediately returns false. If
2715 // splitting is possible, a SplitPoint object is initialized with all the
2716 // data that must be copied to the helper threads (the current position and
2717 // search stack, alpha, beta, the search depth, etc.), and we tell our
2718 // helper threads that they have been assigned work. This will cause them
2719 // to instantly leave their idle loops and call sp_search_pv(). When all
2720 // threads have returned from sp_search_pv (or, equivalently, when
2721 // splitPoint->cpus becomes 0), split() returns true.
2723 bool split(const Position
&p
, SearchStack
*sstck
, int ply
,
2724 Value
*alpha
, Value
*beta
, Value
*bestValue
, Depth depth
, int *moves
,
2725 MovePicker
*mp
, Bitboard dcCandidates
, int master
, bool pvNode
) {
2728 assert(sstck
!= NULL
);
2729 assert(ply
>= 0 && ply
< PLY_MAX
);
2730 assert(*bestValue
>= -VALUE_INFINITE
&& *bestValue
<= *alpha
);
2731 assert(!pvNode
|| *alpha
< *beta
);
2732 assert(*beta
<= VALUE_INFINITE
);
2733 assert(depth
> Depth(0));
2734 assert(master
>= 0 && master
< ActiveThreads
);
2735 assert(ActiveThreads
> 1);
2737 SplitPoint
*splitPoint
;
2742 // If no other thread is available to help us, or if we have too many
2743 // active split points, don't split:
2744 if(!idle_thread_exists(master
) ||
2745 Threads
[master
].activeSplitPoints
>= MaxActiveSplitPoints
) {
2746 lock_release(&MPLock
);
2750 // Pick the next available split point object from the split point stack:
2751 splitPoint
= SplitPointStack
[master
] + Threads
[master
].activeSplitPoints
;
2752 Threads
[master
].activeSplitPoints
++;
2754 // Initialize the split point object:
2755 splitPoint
->parent
= Threads
[master
].splitPoint
;
2756 splitPoint
->finished
= false;
2757 splitPoint
->ply
= ply
;
2758 splitPoint
->depth
= depth
;
2759 splitPoint
->alpha
= pvNode
? *alpha
: (*beta
- 1);
2760 splitPoint
->beta
= *beta
;
2761 splitPoint
->pvNode
= pvNode
;
2762 splitPoint
->dcCandidates
= dcCandidates
;
2763 splitPoint
->bestValue
= *bestValue
;
2764 splitPoint
->master
= master
;
2765 splitPoint
->mp
= mp
;
2766 splitPoint
->moves
= *moves
;
2767 splitPoint
->cpus
= 1;
2768 splitPoint
->pos
.copy(p
);
2769 splitPoint
->parentSstack
= sstck
;
2770 for(i
= 0; i
< ActiveThreads
; i
++)
2771 splitPoint
->slaves
[i
] = 0;
2773 // Copy the current position and the search stack to the master thread:
2774 memcpy(splitPoint
->sstack
[master
], sstck
, (ply
+1)*sizeof(SearchStack
));
2775 Threads
[master
].splitPoint
= splitPoint
;
2777 // Make copies of the current position and search stack for each thread:
2778 for(i
= 0; i
< ActiveThreads
&& splitPoint
->cpus
< MaxThreadsPerSplitPoint
;
2780 if(thread_is_available(i
, master
)) {
2781 memcpy(splitPoint
->sstack
[i
], sstck
, (ply
+1)*sizeof(SearchStack
));
2782 Threads
[i
].splitPoint
= splitPoint
;
2783 splitPoint
->slaves
[i
] = 1;
2787 // Tell the threads that they have work to do. This will make them leave
2789 for(i
= 0; i
< ActiveThreads
; i
++)
2790 if(i
== master
|| splitPoint
->slaves
[i
]) {
2791 Threads
[i
].workIsWaiting
= true;
2792 Threads
[i
].idle
= false;
2793 Threads
[i
].stop
= false;
2796 lock_release(&MPLock
);
2798 // Everything is set up. The master thread enters the idle loop, from
2799 // which it will instantly launch a search, because its workIsWaiting
2800 // slot is 'true'. We send the split point as a second parameter to the
2801 // idle loop, which means that the main thread will return from the idle
2802 // loop when all threads have finished their work at this split point
2803 // (i.e. when // splitPoint->cpus == 0).
2804 idle_loop(master
, splitPoint
);
2806 // We have returned from the idle loop, which means that all threads are
2807 // finished. Update alpha, beta and bestvalue, and return:
2809 if(pvNode
) *alpha
= splitPoint
->alpha
;
2810 *beta
= splitPoint
->beta
;
2811 *bestValue
= splitPoint
->bestValue
;
2812 Threads
[master
].stop
= false;
2813 Threads
[master
].idle
= false;
2814 Threads
[master
].activeSplitPoints
--;
2815 Threads
[master
].splitPoint
= splitPoint
->parent
;
2816 lock_release(&MPLock
);
2822 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2823 // to start a new search from the root.
2825 void wake_sleeping_threads() {
2826 if(ActiveThreads
> 1) {
2827 for(int i
= 1; i
< ActiveThreads
; i
++) {
2828 Threads
[i
].idle
= true;
2829 Threads
[i
].workIsWaiting
= false;
2831 #if !defined(_MSC_VER)
2832 pthread_mutex_lock(&WaitLock
);
2833 pthread_cond_broadcast(&WaitCond
);
2834 pthread_mutex_unlock(&WaitLock
);
2836 for(int i
= 1; i
< THREAD_MAX
; i
++)
2837 SetEvent(SitIdleEvent
[i
]);
2843 // init_thread() is the function which is called when a new thread is
2844 // launched. It simply calls the idle_loop() function with the supplied
2845 // threadID. There are two versions of this function; one for POSIX threads
2846 // and one for Windows threads.
2848 #if !defined(_MSC_VER)
2850 void *init_thread(void *threadID
) {
2851 idle_loop(*(int *)threadID
, NULL
);
2857 DWORD WINAPI
init_thread(LPVOID threadID
) {
2858 idle_loop(*(int *)threadID
, NULL
);