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stockfish/src/search.cpp
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Marco Costalba 5815718177 Do not special case reductions for MultiPV case 
Note that this introduces an asymmetry in which best move
is searched deeper then others also in MultiPV, but this is
not an error per se.

No functional change when MultiPV = 1

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
2011-02-17 09:08:27 +01:00

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/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
////
//// Includes
////
#include <cassert>
#include <cmath>
#include <cstring>
#include <fstream>
#include <iostream>
#include <sstream>
#include <vector>
#include "book.h"
#include "evaluate.h"
#include "history.h"
#include "misc.h"
#include "move.h"
#include "movegen.h"
#include "movepick.h"
#include "lock.h"
#include "search.h"
#include "timeman.h"
#include "thread.h"
#include "tt.h"
#include "ucioption.h"
using std::cout;
using std::endl;
////
//// Local definitions
////
namespace {
// Types
enum NodeType { NonPV, PV };
// Set to true to force running with one thread.
// Used for debugging SMP code.
const bool FakeSplit = false;
// Fast lookup table of sliding pieces indexed by Piece
const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
inline bool piece_is_slider(Piece p) { return Slidings[p]; }
// ThreadsManager class is used to handle all the threads related stuff in search,
// init, starting, parking and, the most important, launching a slave thread at a
// split point are what this class does. All the access to shared thread data is
// done through this class, so that we avoid using global variables instead.
class ThreadsManager {
/* As long as the single ThreadsManager object is defined as a global we don't
need to explicitly initialize to zero its data members because variables with
static storage duration are automatically set to zero before enter main()
*/
public:
void init_threads();
void exit_threads();
int min_split_depth() const { return minimumSplitDepth; }
int active_threads() const { return activeThreads; }
void set_active_threads(int cnt) { activeThreads = cnt; }
void read_uci_options();
bool available_thread_exists(int master) const;
bool thread_is_available(int slave, int master) const;
bool cutoff_at_splitpoint(int threadID) const;
void wake_sleeping_thread(int threadID);
void idle_loop(int threadID, SplitPoint* sp);
template <bool Fake>
void split(Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
Depth depth, Move threatMove, bool mateThreat, int moveCount, MovePicker* mp, bool pvNode);
private:
Depth minimumSplitDepth;
int maxThreadsPerSplitPoint;
bool useSleepingThreads;
int activeThreads;
volatile bool allThreadsShouldExit;
Thread threads[MAX_THREADS];
Lock mpLock, sleepLock[MAX_THREADS];
WaitCondition sleepCond[MAX_THREADS];
};
// RootMove struct is used for moves at the root at the tree. For each root
// move, we store two scores, a node count, and a PV (really a refutation
// in the case of moves which fail low). Value pv_score is normally set at
// -VALUE_INFINITE for all non-pv moves, while non_pv_score is computed
// according to the order in which moves are returned by MovePicker.
struct RootMove {
RootMove();
RootMove(const RootMove& rm) { *this = rm; }
RootMove& operator=(const RootMove& rm);
// RootMove::operator<() is the comparison function used when
// sorting the moves. A move m1 is considered to be better
// than a move m2 if it has an higher pv_score, or if it has
// equal pv_score but m1 has the higher non_pv_score. In this
// way we are guaranteed that PV moves are always sorted as first.
bool operator<(const RootMove& m) const {
return pv_score != m.pv_score ? pv_score < m.pv_score
: non_pv_score < m.non_pv_score;
}
void extract_pv_from_tt(Position& pos);
void insert_pv_in_tt(Position& pos);
std::string pv_info_to_uci(Position& pos, int depth, Value alpha, Value beta, int pvLine);
int64_t nodes;
Value pv_score;
Value non_pv_score;
Move pv[PLY_MAX_PLUS_2];
};
// RootMoveList struct is essentially a std::vector<> of RootMove objects,
// with an handful of methods above the standard ones.
struct RootMoveList : public std::vector<RootMove> {
typedef std::vector<RootMove> Base;
void init(Position& pos, Move searchMoves[]);
void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n); }
int bestMoveChanges;
};
// When formatting a move for std::cout we must know if we are in Chess960
// or not. To keep using the handy operator<<() on the move the trick is to
// embed this flag in the stream itself. Function-like named enum set960 is
// used as a custom manipulator and the stream internal general-purpose array,
// accessed through ios_base::iword(), is used to pass the flag to the move's
// operator<<() that will use it to properly format castling moves.
enum set960 {};
std::ostream& operator<< (std::ostream& os, const set960& f) {
os.iword(0) = int(f);
return os;
}
// Overload operator << for moves to make it easier to print moves in
// coordinate notation compatible with UCI protocol.
std::ostream& operator<<(std::ostream& os, Move m) {
bool chess960 = (os.iword(0) != 0); // See set960()
return os << move_to_uci(m, chess960);
}
/// Adjustments
// Step 6. Razoring
// Maximum depth for razoring
const Depth RazorDepth = 4 * ONE_PLY;
// Dynamic razoring margin based on depth
inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
// Maximum depth for use of dynamic threat detection when null move fails low
const Depth ThreatDepth = 5 * ONE_PLY;
// Step 9. Internal iterative deepening
// Minimum depth for use of internal iterative deepening
const Depth IIDDepth[2] = { 8 * ONE_PLY /* non-PV */, 5 * ONE_PLY /* PV */};
// At Non-PV nodes we do an internal iterative deepening search
// when the static evaluation is bigger then beta - IIDMargin.
const Value IIDMargin = Value(0x100);
// Step 11. Decide the new search depth
// Extensions. Configurable UCI options
// Array index 0 is used at non-PV nodes, index 1 at PV nodes.
Depth CheckExtension[2], PawnPushTo7thExtension[2], PassedPawnExtension[2];
Depth PawnEndgameExtension[2], MateThreatExtension[2];
// Minimum depth for use of singular extension
const Depth SingularExtensionDepth[2] = { 8 * ONE_PLY /* non-PV */, 6 * ONE_PLY /* PV */};
// If the TT move is at least SingularExtensionMargin better than the
// remaining ones we will extend it.
const Value SingularExtensionMargin = Value(0x20);
// Step 12. Futility pruning
// Futility margin for quiescence search
const Value FutilityMarginQS = Value(0x80);
// Futility lookup tables (initialized at startup) and their getter functions
Value FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
int FutilityMoveCountArray[32]; // [depth]
inline Value futility_margin(Depth d, int mn) { return d < 7 * ONE_PLY ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE; }
inline int futility_move_count(Depth d) { return d < 16 * ONE_PLY ? FutilityMoveCountArray[d] : 512; }
// Step 14. Reduced search
// Reduction lookup tables (initialized at startup) and their getter functions
int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
template <NodeType PV>
inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
// Easy move margin. An easy move candidate must be at least this much
// better than the second best move.
const Value EasyMoveMargin = Value(0x200);
/// Namespace variables
// Book object
Book OpeningBook;
// Root move list
RootMoveList Rml;
// MultiPV mode
int MultiPV;
// Time management variables
int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
bool UseTimeManagement, InfiniteSearch, Pondering, StopOnPonderhit;
bool FirstRootMove, StopRequest, QuitRequest, AspirationFailLow;
TimeManager TimeMgr;
// Log file
bool UseLogFile;
std::ofstream LogFile;
// Multi-threads manager object
ThreadsManager ThreadsMgr;
// Node counters, used only by thread[0] but try to keep in different cache
// lines (64 bytes each) from the heavy multi-thread read accessed variables.
bool SendSearchedNodes;
int NodesSincePoll;
int NodesBetweenPolls = 30000;
// History table
History H;
/// Local functions
Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove);
template <NodeType PvNode, bool SpNode, bool Root>
Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
template <NodeType PvNode>
Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
template <NodeType PvNode>
inline Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
return depth < ONE_PLY ? qsearch<PvNode>(pos, ss, alpha, beta, DEPTH_ZERO, ply)
: search<PvNode, false, false>(pos, ss, alpha, beta, depth, ply);
}
template <NodeType PvNode>
Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool mateThreat, bool* dangerous);
bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bValue);
bool connected_moves(const Position& pos, Move m1, Move m2);
bool value_is_mate(Value value);
Value value_to_tt(Value v, int ply);
Value value_from_tt(Value v, int ply);
bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
bool connected_threat(const Position& pos, Move m, Move threat);
Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
void update_killers(Move m, Move killers[]);
void update_gains(const Position& pos, Move move, Value before, Value after);
void qsearch_scoring(Position& pos, MoveStack* mlist, MoveStack* last);
int current_search_time();
std::string value_to_uci(Value v);
int nps(const Position& pos);
void poll(const Position& pos);
void wait_for_stop_or_ponderhit();
#if !defined(_MSC_VER)
void* init_thread(void* threadID);
#else
DWORD WINAPI init_thread(LPVOID threadID);
#endif
// MovePickerExt is an extended MovePicker used to choose at compile time
// the proper move source according to the type of node.
template<bool SpNode, bool Root> struct MovePickerExt;
// In Root nodes use RootMoveList Rml as source. Score and sort the root moves
// before to search them.
template<> struct MovePickerExt<false, true> : public MovePicker {
MovePickerExt(const Position& p, Move ttm, Depth d, const History& h, SearchStack* ss, Value b)
: MovePicker(p, ttm, d, h, ss, b), firstCall(true) {
Move move;
Value score = VALUE_ZERO;
// Score root moves using the standard way used in main search, the moves
// are scored according to the order in which they are returned by MovePicker.
// This is the second order score that is used to compare the moves when
// the first order pv scores of both moves are equal.
while ((move = MovePicker::get_next_move()) != MOVE_NONE)
for (rm = Rml.begin(); rm != Rml.end(); ++rm)
if (rm->pv[0] == move)
{
rm->non_pv_score = score--;
break;
}
Rml.sort();
rm = Rml.begin();
}
Move get_next_move() {
if (!firstCall)
++rm;
else
firstCall = false;
return rm != Rml.end() ? rm->pv[0] : MOVE_NONE;
}
RootMoveList::iterator rm;
bool firstCall;
};
// In SpNodes use split point's shared MovePicker object as move source
template<> struct MovePickerExt<true, false> : public MovePicker {
MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b),
mp(ss->sp->mp) {}
Move get_next_move() { return mp->get_next_move(); }
RootMoveList::iterator rm; // Dummy, needed to compile
MovePicker* mp;
};
// Default case, create and use a MovePicker object as source
template<> struct MovePickerExt<false, false> : public MovePicker {
MovePickerExt(const Position& p, Move ttm, Depth d, const History& h,
SearchStack* ss, Value b) : MovePicker(p, ttm, d, h, ss, b) {}
RootMoveList::iterator rm; // Dummy, needed to compile
};
} // namespace
////
//// Functions
////
/// init_threads(), exit_threads() and nodes_searched() are helpers to
/// give accessibility to some TM methods from outside of current file.
void init_threads() { ThreadsMgr.init_threads(); }
void exit_threads() { ThreadsMgr.exit_threads(); }
/// init_search() is called during startup. It initializes various lookup tables
void init_search() {
int d; // depth (ONE_PLY == 2)
int hd; // half depth (ONE_PLY == 1)
int mc; // moveCount
// Init reductions array
for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
{
double pvRed = log(double(hd)) * log(double(mc)) / 3.0;
double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(ONE_PLY)) : 0);
ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(ONE_PLY)) : 0);
}
// Init futility margins array
for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
FutilityMarginsMatrix[d][mc] = Value(112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45);
// Init futility move count array
for (d = 0; d < 32; d++)
FutilityMoveCountArray[d] = int(3.001 + 0.25 * pow(d, 2.0));
}
/// perft() is our utility to verify move generation is bug free. All the legal
/// moves up to given depth are generated and counted and the sum returned.
int64_t perft(Position& pos, Depth depth)
{
MoveStack mlist[MOVES_MAX];
StateInfo st;
Move m;
int64_t sum = 0;
// Generate all legal moves
MoveStack* last = generate<MV_LEGAL>(pos, mlist);
// If we are at the last ply we don't need to do and undo
// the moves, just to count them.
if (depth <= ONE_PLY)
return int(last - mlist);
// Loop through all legal moves
CheckInfo ci(pos);
for (MoveStack* cur = mlist; cur != last; cur++)
{
m = cur->move;
pos.do_move(m, st, ci, pos.move_is_check(m, ci));
sum += perft(pos, depth - ONE_PLY);
pos.undo_move(m);
}
return sum;
}
/// think() is the external interface to Stockfish's search, and is called when
/// the program receives the UCI 'go' command. It initializes various
/// search-related global variables, and calls id_loop(). It returns false
/// when a quit command is received during the search.
bool think(Position& pos, bool infinite, bool ponder, int time[], int increment[],
int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
// Initialize global search variables
StopOnPonderhit = StopRequest = QuitRequest = AspirationFailLow = SendSearchedNodes = false;
NodesSincePoll = 0;
SearchStartTime = get_system_time();
ExactMaxTime = maxTime;
MaxDepth = maxDepth;
MaxNodes = maxNodes;
InfiniteSearch = infinite;
Pondering = ponder;
UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
// Look for a book move, only during games, not tests
if (UseTimeManagement && Options["OwnBook"].value<bool>())
{
if (Options["Book File"].value<std::string>() != OpeningBook.name())
OpeningBook.open(Options["Book File"].value<std::string>());
Move bookMove = OpeningBook.get_move(pos, Options["Best Book Move"].value<bool>());
if (bookMove != MOVE_NONE)
{
if (Pondering)
wait_for_stop_or_ponderhit();
cout << "bestmove " << bookMove << endl;
return !QuitRequest;
}
}
// Read UCI option values
TT.set_size(Options["Hash"].value<int>());
if (Options["Clear Hash"].value<bool>())
{
Options["Clear Hash"].set_value("false");
TT.clear();
}
CheckExtension[1] = Options["Check Extension (PV nodes)"].value<Depth>();
CheckExtension[0] = Options["Check Extension (non-PV nodes)"].value<Depth>();
PawnPushTo7thExtension[1] = Options["Pawn Push to 7th Extension (PV nodes)"].value<Depth>();
PawnPushTo7thExtension[0] = Options["Pawn Push to 7th Extension (non-PV nodes)"].value<Depth>();
PassedPawnExtension[1] = Options["Passed Pawn Extension (PV nodes)"].value<Depth>();
PassedPawnExtension[0] = Options["Passed Pawn Extension (non-PV nodes)"].value<Depth>();
PawnEndgameExtension[1] = Options["Pawn Endgame Extension (PV nodes)"].value<Depth>();
PawnEndgameExtension[0] = Options["Pawn Endgame Extension (non-PV nodes)"].value<Depth>();
MateThreatExtension[1] = Options["Mate Threat Extension (PV nodes)"].value<Depth>();
MateThreatExtension[0] = Options["Mate Threat Extension (non-PV nodes)"].value<Depth>();
MultiPV = Options["MultiPV"].value<int>();
UseLogFile = Options["Use Search Log"].value<bool>();
read_evaluation_uci_options(pos.side_to_move());
// Set the number of active threads
ThreadsMgr.read_uci_options();
init_eval(ThreadsMgr.active_threads());
// Wake up needed threads
for (int i = 1; i < ThreadsMgr.active_threads(); i++)
ThreadsMgr.wake_sleeping_thread(i);
// Set thinking time
int myTime = time[pos.side_to_move()];
int myIncrement = increment[pos.side_to_move()];
if (UseTimeManagement)
TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
// Set best NodesBetweenPolls interval to avoid lagging under
// heavy time pressure.
if (MaxNodes)
NodesBetweenPolls = Min(MaxNodes, 30000);
else if (myTime && myTime < 1000)
NodesBetweenPolls = 1000;
else if (myTime && myTime < 5000)
NodesBetweenPolls = 5000;
else
NodesBetweenPolls = 30000;
// Write search information to log file
if (UseLogFile)
{
std::string name = Options["Search Log Filename"].value<std::string>();
LogFile.open(name.c_str(), std::ios::out | std::ios::app);
LogFile << "\nSearching: " << pos.to_fen()
<< "\ninfinite: " << infinite
<< " ponder: " << ponder
<< " time: " << myTime
<< " increment: " << myIncrement
<< " moves to go: " << movesToGo
<< endl;
}
// We're ready to start thinking. Call the iterative deepening loop function
Move ponderMove = MOVE_NONE;
Move bestMove = id_loop(pos, searchMoves, &ponderMove);
// Print final search statistics
cout << "info nodes " << pos.nodes_searched()
<< " nps " << nps(pos)
<< " time " << current_search_time() << endl;
if (UseLogFile)
{
LogFile << "Nodes: " << pos.nodes_searched()
<< "\nNodes/second: " << nps(pos)
<< "\nBest move: " << move_to_san(pos, bestMove);
StateInfo st;
pos.do_move(bestMove, st);
LogFile << "\nPonder move: " << move_to_san(pos, ponderMove) << endl;
pos.undo_move(bestMove); // Return from think() with unchanged position
LogFile.close();
}
// This makes all the threads to go to sleep
ThreadsMgr.set_active_threads(1);
// If we are pondering or in infinite search, we shouldn't print the
// best move before we are told to do so.
if (!StopRequest && (Pondering || InfiniteSearch))
wait_for_stop_or_ponderhit();
// Could be both MOVE_NONE when searching on a stalemate position
cout << "bestmove " << bestMove << " ponder " << ponderMove << endl;
return !QuitRequest;
}
namespace {
// id_loop() is the main iterative deepening loop. It calls search() repeatedly
// with increasing depth until the allocated thinking time has been consumed,
// user stops the search, or the maximum search depth is reached.
Move id_loop(Position& pos, Move searchMoves[], Move* ponderMove) {
SearchStack ss[PLY_MAX_PLUS_2];
Value bestValues[PLY_MAX_PLUS_2];
int bestMoveChanges[PLY_MAX_PLUS_2];
int depth, researchCountFL, researchCountFH, aspirationDelta;
Value value, alpha, beta;
Move bestMove, easyMove;
// Moves to search are verified, scored and sorted
Rml.init(pos, searchMoves);
// Initialize FIXME move before Rml.init()
TT.new_search();
H.clear();
memset(ss, 0, PLY_MAX_PLUS_2 * sizeof(SearchStack));
*ponderMove = bestMove = easyMove = MOVE_NONE;
depth = aspirationDelta = 0;
ss->currentMove = MOVE_NULL; // Hack to skip update_gains()
alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
// Handle special case of searching on a mate/stalemate position
if (Rml.size() == 0)
{
cout << "info depth 0 score "
<< value_to_uci(pos.is_check() ? -VALUE_MATE : VALUE_DRAW)
<< endl;
return MOVE_NONE;
}
// Is one move significantly better than others after initial scoring ?
if ( Rml.size() == 1
|| Rml[0].pv_score > Rml[1].pv_score + EasyMoveMargin)
easyMove = Rml[0].pv[0];
// Iterative deepening loop
while (++depth <= PLY_MAX && (!MaxDepth || depth <= MaxDepth) && !StopRequest)
{
Rml.bestMoveChanges = researchCountFL = researchCountFH = 0;
cout << "info depth " << depth << endl;
// Calculate dynamic aspiration window based on previous iterations
if (MultiPV == 1 && depth >= 5 && abs(bestValues[depth - 1]) < VALUE_KNOWN_WIN)
{
int prevDelta1 = bestValues[depth - 1] - bestValues[depth - 2];
int prevDelta2 = bestValues[depth - 2] - bestValues[depth - 3];
aspirationDelta = Min(Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16), 24);
aspirationDelta = (aspirationDelta + 7) / 8 * 8; // Round to match grainSize
alpha = Max(bestValues[depth - 1] - aspirationDelta, -VALUE_INFINITE);
beta = Min(bestValues[depth - 1] + aspirationDelta, VALUE_INFINITE);
}
// Start with a small aspiration window and, in case of fail high/low,
// research with bigger window until not failing high/low anymore.
while (true)
{
// Search starting from ss+1 to allow calling update_gains()
value = search<PV, false, true>(pos, ss+1, alpha, beta, depth * ONE_PLY, 0);
// Send PV line to GUI and write to transposition table in case the
// relevant entries have been overwritten during the search.
for (int i = 0; i < Min(MultiPV, (int)Rml.size()); i++)
{
Rml[i].insert_pv_in_tt(pos);
cout << set960(pos.is_chess960())
<< Rml[i].pv_info_to_uci(pos, depth, alpha, beta, i) << endl;
}
// Value cannot be trusted. Break out immediately!
if (StopRequest)
break;
assert(value >= alpha);
// In case of failing high/low increase aspiration window and research,
// otherwise exit the fail high/low loop.
if (value >= beta)
{
beta = Min(beta + aspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
researchCountFH++;
}
else if (value <= alpha)
{
AspirationFailLow = true;
StopOnPonderhit = false;
alpha = Max(alpha - aspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
researchCountFL++;
}
else
break;
}
// Collect info about search result
bestMove = Rml[0].pv[0];
bestValues[depth] = value;
bestMoveChanges[depth] = Rml.bestMoveChanges;
if (UseLogFile)
LogFile << pretty_pv(pos, depth, value, current_search_time(), Rml[0].pv) << endl;
// Drop the easy move if differs from the new best move
if (bestMove != easyMove)
easyMove = MOVE_NONE;
if (UseTimeManagement && !StopRequest)
{
// Time to stop?
bool noMoreTime = false;
// Stop search early when the last two iterations returned a mate score
if ( depth >= 5
&& abs(bestValues[depth]) >= abs(VALUE_MATE) - 100
&& abs(bestValues[depth - 1]) >= abs(VALUE_MATE) - 100)
noMoreTime = true;
// Stop search early if one move seems to be much better than the
// others or if there is only a single legal move. In this latter
// case we search up to Iteration 8 anyway to get a proper score.
if ( depth >= 7
&& easyMove == bestMove
&& ( Rml.size() == 1
||( Rml[0].nodes > (pos.nodes_searched() * 85) / 100
&& current_search_time() > TimeMgr.available_time() / 16)
||( Rml[0].nodes > (pos.nodes_searched() * 98) / 100
&& current_search_time() > TimeMgr.available_time() / 32)))
noMoreTime = true;
// Add some extra time if the best move has changed during the last two iterations
if (depth > 4 && depth < 50)
TimeMgr.pv_instability(bestMoveChanges[depth], bestMoveChanges[depth-1]);
// Stop search if most of MaxSearchTime is consumed at the end of the
// iteration. We probably don't have enough time to search the first
// move at the next iteration anyway.
if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
noMoreTime = true;
if (noMoreTime)
{
if (Pondering)
StopOnPonderhit = true;
else
break;
}
}
}
*ponderMove = Rml[0].pv[1];
return bestMove;
}
// search<>() is the main search function for both PV and non-PV nodes and for
// normal and SplitPoint nodes. When called just after a split point the search
// is simpler because we have already probed the hash table, done a null move
// search, and searched the first move before splitting, we don't have to repeat
// all this work again. We also don't need to store anything to the hash table
// here: This is taken care of after we return from the split point.
template <NodeType PvNode, bool SpNode, bool Root>
Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
assert(beta > alpha && beta <= VALUE_INFINITE);
assert(PvNode || alpha == beta - 1);
assert((Root || ply > 0) && ply < PLY_MAX);
assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
Move movesSearched[MOVES_MAX];
int64_t nodes;
StateInfo st;
const TTEntry *tte;
Key posKey;
Move ttMove, move, excludedMove, threatMove;
Depth ext, newDepth;
ValueType vt;
Value bestValue, value, oldAlpha;
Value refinedValue, nullValue, futilityBase, futilityValueScaled; // Non-PV specific
bool isPvMove, isCheck, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
bool mateThreat = false;
int moveCount = 0, playedMoveCount = 0;
int threadID = pos.thread();
SplitPoint* sp = NULL;
refinedValue = bestValue = value = -VALUE_INFINITE;
oldAlpha = alpha;
isCheck = pos.is_check();
if (SpNode)
{
sp = ss->sp;
tte = NULL;
ttMove = excludedMove = MOVE_NONE;
threatMove = sp->threatMove;
mateThreat = sp->mateThreat;
goto split_point_start;
}
else if (Root)
bestValue = alpha;
// Step 1. Initialize node and poll. Polling can abort search
ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
(ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
{
NodesSincePoll = 0;
poll(pos);
}
// Step 2. Check for aborted search and immediate draw
if (( StopRequest
|| ThreadsMgr.cutoff_at_splitpoint(threadID)
|| pos.is_draw()
|| ply >= PLY_MAX - 1) && !Root)
return VALUE_DRAW;
// Step 3. Mate distance pruning
alpha = Max(value_mated_in(ply), alpha);
beta = Min(value_mate_in(ply+1), beta);
if (alpha >= beta)
return alpha;
// Step 4. Transposition table lookup
// We don't want the score of a partial search to overwrite a previous full search
// TT value, so we use a different position key in case of an excluded move.
excludedMove = ss->excludedMove;
posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
tte = TT.retrieve(posKey);
ttMove = tte ? tte->move() : MOVE_NONE;
// At PV nodes we check for exact scores, while at non-PV nodes we check for
// and return a fail high/low. Biggest advantage at probing at PV nodes is
// to have a smooth experience in analysis mode.
if ( !Root
&& tte
&& (PvNode ? tte->depth() >= depth && tte->type() == VALUE_TYPE_EXACT
: ok_to_use_TT(tte, depth, beta, ply)))
{
TT.refresh(tte);
ss->bestMove = ttMove; // Can be MOVE_NONE
return value_from_tt(tte->value(), ply);
}
// Step 5. Evaluate the position statically and
// update gain statistics of parent move.
if (isCheck)
ss->eval = ss->evalMargin = VALUE_NONE;
else if (tte)
{
assert(tte->static_value() != VALUE_NONE);
ss->eval = tte->static_value();
ss->evalMargin = tte->static_value_margin();
refinedValue = refine_eval(tte, ss->eval, ply);
}
else
{
refinedValue = ss->eval = evaluate(pos, ss->evalMargin);
TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);
}
// Save gain for the parent non-capture move
update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
// Step 6. Razoring (is omitted in PV nodes)
if ( !PvNode
&& depth < RazorDepth
&& !isCheck
&& refinedValue < beta - razor_margin(depth)
&& ttMove == MOVE_NONE
&& !value_is_mate(beta)
&& !pos.has_pawn_on_7th(pos.side_to_move()))
{
Value rbeta = beta - razor_margin(depth);
Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO, ply);
if (v < rbeta)
// Logically we should return (v + razor_margin(depth)), but
// surprisingly this did slightly weaker in tests.
return v;
}
// Step 7. Static null move pruning (is omitted in PV nodes)
// We're betting that the opponent doesn't have a move that will reduce
// the score by more than futility_margin(depth) if we do a null move.
if ( !PvNode
&& !ss->skipNullMove
&& depth < RazorDepth
&& !isCheck
&& refinedValue >= beta + futility_margin(depth, 0)
&& !value_is_mate(beta)
&& pos.non_pawn_material(pos.side_to_move()))
return refinedValue - futility_margin(depth, 0);
// Step 8. Null move search with verification search (is omitted in PV nodes)
if ( !PvNode
&& !ss->skipNullMove
&& depth > ONE_PLY
&& !isCheck
&& refinedValue >= beta
&& !value_is_mate(beta)
&& pos.non_pawn_material(pos.side_to_move()))
{
ss->currentMove = MOVE_NULL;
// Null move dynamic reduction based on depth
int R = 3 + (depth >= 5 * ONE_PLY ? depth / 8 : 0);
// Null move dynamic reduction based on value
if (refinedValue - beta > PawnValueMidgame)
R++;
pos.do_null_move(st);
(ss+1)->skipNullMove = true;
nullValue = -search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY, ply+1);
(ss+1)->skipNullMove = false;
pos.undo_null_move();
if (nullValue >= beta)
{
// Do not return unproven mate scores
if (nullValue >= value_mate_in(PLY_MAX))
nullValue = beta;
if (depth < 6 * ONE_PLY)
return nullValue;
// Do verification search at high depths
ss->skipNullMove = true;
Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*ONE_PLY, ply);
ss->skipNullMove = false;
if (v >= beta)
return nullValue;
}
else
{
// The null move failed low, which means that we may be faced with
// some kind of threat. If the previous move was reduced, check if
// the move that refuted the null move was somehow connected to the
// move which was reduced. If a connection is found, return a fail
// low score (which will cause the reduced move to fail high in the
// parent node, which will trigger a re-search with full depth).
if (nullValue == value_mated_in(ply + 2))
mateThreat = true;
threatMove = (ss+1)->bestMove;
if ( depth < ThreatDepth
&& (ss-1)->reduction
&& threatMove != MOVE_NONE
&& connected_moves(pos, (ss-1)->currentMove, threatMove))
return beta - 1;
}
}
// Step 9. Internal iterative deepening
if ( depth >= IIDDepth[PvNode]
&& ttMove == MOVE_NONE
&& (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
{
Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
ss->skipNullMove = true;
search<PvNode>(pos, ss, alpha, beta, d, ply);
ss->skipNullMove = false;
ttMove = ss->bestMove;
tte = TT.retrieve(posKey);
}
// Expensive mate threat detection (only for PV nodes)
if (PvNode)
mateThreat = pos.has_mate_threat();
split_point_start: // At split points actual search starts from here
// Initialize a MovePicker object for the current position
MovePickerExt<SpNode, Root> mp(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
CheckInfo ci(pos);
ss->bestMove = MOVE_NONE;
futilityBase = ss->eval + ss->evalMargin;
singularExtensionNode = !Root
&& !SpNode
&& depth >= SingularExtensionDepth[PvNode]
&& tte
&& tte->move()
&& !excludedMove // Do not allow recursive singular extension search
&& (tte->type() & VALUE_TYPE_LOWER)
&& tte->depth() >= depth - 3 * ONE_PLY;
if (SpNode)
{
lock_grab(&(sp->lock));
bestValue = sp->bestValue;
}
// Step 10. Loop through moves
// Loop through all legal moves until no moves remain or a beta cutoff occurs
while ( bestValue < beta
&& (move = mp.get_next_move()) != MOVE_NONE
&& !ThreadsMgr.cutoff_at_splitpoint(threadID))
{
assert(move_is_ok(move));
if (SpNode)
{
moveCount = ++sp->moveCount;
lock_release(&(sp->lock));
}
else if (move == excludedMove)
continue;
else
moveCount++;
if (Root)
{
// This is used by time management
FirstRootMove = (moveCount == 1);
// Save the current node count before the move is searched
nodes = pos.nodes_searched();
// If it's time to send nodes info, do it here where we have the
// correct accumulated node counts searched by each thread.
if (SendSearchedNodes)
{
SendSearchedNodes = false;
cout << "info nodes " << nodes
<< " nps " << nps(pos)
<< " time " << current_search_time() << endl;
}
if (current_search_time() >= 1000)
cout << "info currmove " << move
<< " currmovenumber " << moveCount << endl;
}
isPvMove = (PvNode && moveCount <= (Root ? MultiPV : 1));
moveIsCheck = pos.move_is_check(move, ci);
captureOrPromotion = pos.move_is_capture_or_promotion(move);
// Step 11. Decide the new search depth
ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, mateThreat, &dangerous);
// Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
// and just one fails high on (alpha, beta), then that move is singular and should be extended.
// To verify this we do a reduced search on all the other moves but the ttMove, if result is
// lower than ttValue minus a margin then we extend ttMove.
if ( singularExtensionNode
&& move == tte->move()
&& ext < ONE_PLY)
{
Value ttValue = value_from_tt(tte->value(), ply);
if (abs(ttValue) < VALUE_KNOWN_WIN)
{
Value b = ttValue - SingularExtensionMargin;
ss->excludedMove = move;
ss->skipNullMove = true;
Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
ss->skipNullMove = false;
ss->excludedMove = MOVE_NONE;
ss->bestMove = MOVE_NONE;
if (v < b)
ext = ONE_PLY;
}
}
// Update current move (this must be done after singular extension search)
ss->currentMove = move;
newDepth = depth - (!Root ? ONE_PLY : DEPTH_ZERO) + ext;
// Step 12. Futility pruning (is omitted in PV nodes)
if ( !PvNode
&& !captureOrPromotion
&& !isCheck
&& !dangerous
&& move != ttMove
&& !move_is_castle(move))
{
// Move count based pruning
if ( moveCount >= futility_move_count(depth)
&& !(threatMove && connected_threat(pos, move, threatMove))
&& bestValue > value_mated_in(PLY_MAX)) // FIXME bestValue is racy
{
if (SpNode)
lock_grab(&(sp->lock));
continue;
}
// Value based pruning
// We illogically ignore reduction condition depth >= 3*ONE_PLY for predicted depth,
// but fixing this made program slightly weaker.
Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
futilityValueScaled = futilityBase + futility_margin(predictedDepth, moveCount)
+ H.gain(pos.piece_on(move_from(move)), move_to(move));
if (futilityValueScaled < beta)
{
if (SpNode)
{
lock_grab(&(sp->lock));
if (futilityValueScaled > sp->bestValue)
sp->bestValue = bestValue = futilityValueScaled;
}
else if (futilityValueScaled > bestValue)
bestValue = futilityValueScaled;
continue;
}
// Prune moves with negative SEE at low depths
if ( predictedDepth < 2 * ONE_PLY
&& bestValue > value_mated_in(PLY_MAX)
&& pos.see_sign(move) < 0)
{
if (SpNode)
lock_grab(&(sp->lock));
continue;
}
}
// Step 13. Make the move
pos.do_move(move, st, ci, moveIsCheck);
if (!SpNode && !captureOrPromotion)
movesSearched[playedMoveCount++] = move;
// Step extra. pv search (only in PV nodes)
// The first move in list is the expected PV
if (isPvMove)
{
// Aspiration window is disabled in multi-pv case
if (Root && MultiPV > 1)
alpha = -VALUE_INFINITE;
value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
}
else
{
// Step 14. Reduced depth search
// If the move fails high will be re-searched at full depth.
bool doFullDepthSearch = true;
if ( depth >= 3 * ONE_PLY
&& !captureOrPromotion
&& !dangerous
&& !move_is_castle(move)
&& ss->killers[0] != move
&& ss->killers[1] != move)
{
ss->reduction = reduction<PvNode>(depth, moveCount);
if (ss->reduction)
{
alpha = SpNode ? sp->alpha : alpha;
Depth d = newDepth - ss->reduction;
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
doFullDepthSearch = (value > alpha);
}
ss->reduction = DEPTH_ZERO; // Restore original reduction
}
// Step 15. Full depth search
if (doFullDepthSearch)
{
alpha = SpNode ? sp->alpha : alpha;
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
// Step extra. pv search (only in PV nodes)
// Search only for possible new PV nodes, if instead value >= beta then
// parent node fails low with value <= alpha and tries another move.
if (PvNode && value > alpha && (Root || value < beta))
value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
}
}
// Step 16. Undo move
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
// Step 17. Check for new best move
if (SpNode)
{
lock_grab(&(sp->lock));
bestValue = sp->bestValue;
alpha = sp->alpha;
}
if (!Root && value > bestValue && !(SpNode && ThreadsMgr.cutoff_at_splitpoint(threadID)))
{
bestValue = value;
if (SpNode)
sp->bestValue = value;
if (value > alpha)
{
if (PvNode && value < beta) // We want always alpha < beta
{
alpha = value;
if (SpNode)
sp->alpha = value;
}
else if (SpNode)
sp->betaCutoff = true;
if (value == value_mate_in(ply + 1))
ss->mateKiller = move;
ss->bestMove = move;
if (SpNode)
sp->parentSstack->bestMove = move;
}
}
if (Root)
{
// To avoid to exit with bestValue == -VALUE_INFINITE
if (value > bestValue)
bestValue = value;
// Finished searching the move. If StopRequest is true, the search
// was aborted because the user interrupted the search or because we
// ran out of time. In this case, the return value of the search cannot
// be trusted, and we break out of the loop without updating the best
// move and/or PV.
if (StopRequest)
break;
// Remember searched nodes counts for this move
mp.rm->nodes += pos.nodes_searched() - nodes;
// Step 17. Check for new best move
if (!isPvMove && value <= alpha)
mp.rm->pv_score = -VALUE_INFINITE;
else
{
// PV move or new best move!
// Update PV
ss->bestMove = move;
mp.rm->pv_score = value;
mp.rm->extract_pv_from_tt(pos);
// We record how often the best move has been changed in each
// iteration. This information is used for time management: When
// the best move changes frequently, we allocate some more time.
if (!isPvMove && MultiPV == 1)
Rml.bestMoveChanges++;
Rml.sort_multipv(moveCount);
// Update alpha. In multi-pv we don't use aspiration window, so
// set alpha equal to minimum score among the PV lines.
if (MultiPV > 1)
alpha = Rml[Min(moveCount, MultiPV) - 1].pv_score; // FIXME why moveCount?
else if (value > alpha)
alpha = value;
} // PV move or new best move
}
// Step 18. Check for split
if ( !Root
&& !SpNode
&& depth >= ThreadsMgr.min_split_depth()
&& ThreadsMgr.active_threads() > 1
&& bestValue < beta
&& ThreadsMgr.available_thread_exists(threadID)
&& !StopRequest
&& !ThreadsMgr.cutoff_at_splitpoint(threadID))
ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
threatMove, mateThreat, moveCount, &mp, PvNode);
}
// Step 19. Check for mate and stalemate
// All legal moves have been searched and if there are
// no legal moves, it must be mate or stalemate.
// If one move was excluded return fail low score.
if (!SpNode && !moveCount)
return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
// Step 20. Update tables
// If the search is not aborted, update the transposition table,
// history counters, and killer moves.
if (!SpNode && !StopRequest && !ThreadsMgr.cutoff_at_splitpoint(threadID))
{
move = bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove;
vt = bestValue <= oldAlpha ? VALUE_TYPE_UPPER
: bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT;
TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ss->evalMargin);
// Update killers and history only for non capture moves that fails high
if ( bestValue >= beta
&& !pos.move_is_capture_or_promotion(move))
{
update_history(pos, move, depth, movesSearched, playedMoveCount);
update_killers(move, ss->killers);
}
}
if (SpNode)
{
// Here we have the lock still grabbed
sp->slaves[threadID] = 0;
sp->nodes += pos.nodes_searched();
lock_release(&(sp->lock));
}
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
return bestValue;
}
// qsearch() is the quiescence search function, which is called by the main
// search function when the remaining depth is zero (or, to be more precise,
// less than ONE_PLY).
template <NodeType PvNode>
Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
assert(PvNode || alpha == beta - 1);
assert(depth <= 0);
assert(ply > 0 && ply < PLY_MAX);
assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
StateInfo st;
Move ttMove, move;
Value bestValue, value, evalMargin, futilityValue, futilityBase;
bool isCheck, enoughMaterial, moveIsCheck, evasionPrunable;
const TTEntry* tte;
Depth ttDepth;
Value oldAlpha = alpha;
ss->bestMove = ss->currentMove = MOVE_NONE;
// Check for an instant draw or maximum ply reached
if (pos.is_draw() || ply >= PLY_MAX - 1)
return VALUE_DRAW;
// Decide whether or not to include checks, this fixes also the type of
// TT entry depth that we are going to use. Note that in qsearch we use
// only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
isCheck = pos.is_check();
ttDepth = (isCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
// Transposition table lookup. At PV nodes, we don't use the TT for
// pruning, but only for move ordering.
tte = TT.retrieve(pos.get_key());
ttMove = (tte ? tte->move() : MOVE_NONE);
if (!PvNode && tte && ok_to_use_TT(tte, ttDepth, beta, ply))
{
ss->bestMove = ttMove; // Can be MOVE_NONE
return value_from_tt(tte->value(), ply);
}
// Evaluate the position statically
if (isCheck)
{
bestValue = futilityBase = -VALUE_INFINITE;
ss->eval = evalMargin = VALUE_NONE;
enoughMaterial = false;
}
else
{
if (tte)
{
assert(tte->static_value() != VALUE_NONE);
evalMargin = tte->static_value_margin();
ss->eval = bestValue = tte->static_value();
}
else
ss->eval = bestValue = evaluate(pos, evalMargin);
update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
// Stand pat. Return immediately if static value is at least beta
if (bestValue >= beta)
{
if (!tte)
TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
return bestValue;
}
if (PvNode && bestValue > alpha)
alpha = bestValue;
// Futility pruning parameters, not needed when in check
futilityBase = ss->eval + evalMargin + FutilityMarginQS;
enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
}
// Initialize a MovePicker object for the current position, and prepare
// to search the moves. Because the depth is <= 0 here, only captures,
// queen promotions and checks (only if depth >= DEPTH_QS_CHECKS) will
// be generated.
MovePicker mp(pos, ttMove, depth, H);
CheckInfo ci(pos);
// Loop through the moves until no moves remain or a beta cutoff occurs
while ( alpha < beta
&& (move = mp.get_next_move()) != MOVE_NONE)
{
assert(move_is_ok(move));
moveIsCheck = pos.move_is_check(move, ci);
// Futility pruning
if ( !PvNode
&& !isCheck
&& !moveIsCheck
&& move != ttMove
&& enoughMaterial
&& !move_is_promotion(move)
&& !pos.move_is_passed_pawn_push(move))
{
futilityValue = futilityBase
+ pos.endgame_value_of_piece_on(move_to(move))
+ (move_is_ep(move) ? PawnValueEndgame : VALUE_ZERO);
if (futilityValue < alpha)
{
if (futilityValue > bestValue)
bestValue = futilityValue;
continue;
}
}
// Detect non-capture evasions that are candidate to be pruned
evasionPrunable = isCheck
&& bestValue > value_mated_in(PLY_MAX)
&& !pos.move_is_capture(move)
&& !pos.can_castle(pos.side_to_move());
// Don't search moves with negative SEE values
if ( !PvNode
&& (!isCheck || evasionPrunable)
&& move != ttMove
&& !move_is_promotion(move)
&& pos.see_sign(move) < 0)
continue;
// Don't search useless checks
if ( !PvNode
&& !isCheck
&& moveIsCheck
&& move != ttMove
&& !pos.move_is_capture_or_promotion(move)
&& ss->eval + PawnValueMidgame / 4 < beta
&& !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
{
if (ss->eval + PawnValueMidgame / 4 > bestValue)
bestValue = ss->eval + PawnValueMidgame / 4;
continue;
}
// Update current move
ss->currentMove = move;
// Make and search the move
pos.do_move(move, st, ci, moveIsCheck);
value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-ONE_PLY, ply+1);
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
// New best move?
if (value > bestValue)
{
bestValue = value;
if (value > alpha)
{
alpha = value;
ss->bestMove = move;
}
}
}
// All legal moves have been searched. A special case: If we're in check
// and no legal moves were found, it is checkmate.
if (isCheck && bestValue == -VALUE_INFINITE)
return value_mated_in(ply);
// Update transposition table
ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, ttDepth, ss->bestMove, ss->eval, evalMargin);
assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
return bestValue;
}
// qsearch_scoring() scores each move of a list using a qsearch() evaluation,
// it is used in RootMoveList to get an initial scoring.
void qsearch_scoring(Position& pos, MoveStack* mlist, MoveStack* last) {
SearchStack ss[PLY_MAX_PLUS_2];
StateInfo st;
memset(ss, 0, 4 * sizeof(SearchStack));
ss[0].eval = ss[0].evalMargin = VALUE_NONE;
for (MoveStack* cur = mlist; cur != last; cur++)
{
ss[0].currentMove = cur->move;
pos.do_move(cur->move, st);
cur->score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
pos.undo_move(cur->move);
}
}
// check_is_dangerous() tests if a checking move can be pruned in qsearch().
// bestValue is updated only when returning false because in that case move
// will be pruned.
bool check_is_dangerous(Position &pos, Move move, Value futilityBase, Value beta, Value *bestValue)
{
Bitboard b, occ, oldAtt, newAtt, kingAtt;
Square from, to, ksq, victimSq;
Piece pc;
Color them;
Value futilityValue, bv = *bestValue;
from = move_from(move);
to = move_to(move);
them = opposite_color(pos.side_to_move());
ksq = pos.king_square(them);
kingAtt = pos.attacks_from<KING>(ksq);
pc = pos.piece_on(from);
occ = pos.occupied_squares() & ~(1ULL << from) & ~(1ULL << ksq);
oldAtt = pos.attacks_from(pc, from, occ);
newAtt = pos.attacks_from(pc, to, occ);
// Rule 1. Checks which give opponent's king at most one escape square are dangerous
b = kingAtt & ~pos.pieces_of_color(them) & ~newAtt & ~(1ULL << to);
if (!(b && (b & (b - 1))))
return true;
// Rule 2. Queen contact check is very dangerous
if ( type_of_piece(pc) == QUEEN
&& bit_is_set(kingAtt, to))
return true;
// Rule 3. Creating new double threats with checks
b = pos.pieces_of_color(them) & newAtt & ~oldAtt & ~(1ULL << ksq);
while (b)
{
victimSq = pop_1st_bit(&b);
futilityValue = futilityBase + pos.endgame_value_of_piece_on(victimSq);
// Note that here we generate illegal "double move"!
if ( futilityValue >= beta
&& pos.see_sign(make_move(from, victimSq)) >= 0)
return true;
if (futilityValue > bv)
bv = futilityValue;
}
// Update bestValue only if check is not dangerous (because we will prune the move)
*bestValue = bv;
return false;
}
// connected_moves() tests whether two moves are 'connected' in the sense
// that the first move somehow made the second move possible (for instance
// if the moving piece is the same in both moves). The first move is assumed
// to be the move that was made to reach the current position, while the
// second move is assumed to be a move from the current position.
bool connected_moves(const Position& pos, Move m1, Move m2) {
Square f1, t1, f2, t2;
Piece p;
assert(m1 && move_is_ok(m1));
assert(m2 && move_is_ok(m2));
// Case 1: The moving piece is the same in both moves
f2 = move_from(m2);
t1 = move_to(m1);
if (f2 == t1)
return true;
// Case 2: The destination square for m2 was vacated by m1
t2 = move_to(m2);
f1 = move_from(m1);
if (t2 == f1)
return true;
// Case 3: Moving through the vacated square
if ( piece_is_slider(pos.piece_on(f2))
&& bit_is_set(squares_between(f2, t2), f1))
return true;
// Case 4: The destination square for m2 is defended by the moving piece in m1
p = pos.piece_on(t1);
if (bit_is_set(pos.attacks_from(p, t1), t2))
return true;
// Case 5: Discovered check, checking piece is the piece moved in m1
if ( piece_is_slider(p)
&& bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
&& !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
{
// discovered_check_candidates() works also if the Position's side to
// move is the opposite of the checking piece.
Color them = opposite_color(pos.side_to_move());
Bitboard dcCandidates = pos.discovered_check_candidates(them);
if (bit_is_set(dcCandidates, f2))
return true;
}
return false;
}
// value_is_mate() checks if the given value is a mate one eventually
// compensated for the ply.
bool value_is_mate(Value value) {
assert(abs(value) <= VALUE_INFINITE);
return value <= value_mated_in(PLY_MAX)
|| value >= value_mate_in(PLY_MAX);
}
// value_to_tt() adjusts a mate score from "plies to mate from the root" to
// "plies to mate from the current ply". Non-mate scores are unchanged.
// The function is called before storing a value to the transposition table.
Value value_to_tt(Value v, int ply) {
if (v >= value_mate_in(PLY_MAX))
return v + ply;
if (v <= value_mated_in(PLY_MAX))
return v - ply;
return v;
}
// value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
// the transposition table to a mate score corrected for the current ply.
Value value_from_tt(Value v, int ply) {
if (v >= value_mate_in(PLY_MAX))
return v - ply;
if (v <= value_mated_in(PLY_MAX))
return v + ply;
return v;
}
// extension() decides whether a move should be searched with normal depth,
// or with extended depth. Certain classes of moves (checking moves, in
// particular) are searched with bigger depth than ordinary moves and in
// any case are marked as 'dangerous'. Note that also if a move is not
// extended, as example because the corresponding UCI option is set to zero,
// the move is marked as 'dangerous' so, at least, we avoid to prune it.
template <NodeType PvNode>
Depth extension(const Position& pos, Move m, bool captureOrPromotion,
bool moveIsCheck, bool mateThreat, bool* dangerous) {
assert(m != MOVE_NONE);
Depth result = DEPTH_ZERO;
*dangerous = moveIsCheck | mateThreat;
if (*dangerous)
{
if (moveIsCheck && pos.see_sign(m) >= 0)
result += CheckExtension[PvNode];
if (mateThreat)
result += MateThreatExtension[PvNode];
}
if (pos.type_of_piece_on(move_from(m)) == PAWN)
{
Color c = pos.side_to_move();
if (relative_rank(c, move_to(m)) == RANK_7)
{
result += PawnPushTo7thExtension[PvNode];
*dangerous = true;
}
if (pos.pawn_is_passed(c, move_to(m)))
{
result += PassedPawnExtension[PvNode];
*dangerous = true;
}
}
if ( captureOrPromotion
&& pos.type_of_piece_on(move_to(m)) != PAWN
&& ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
- pos.midgame_value_of_piece_on(move_to(m)) == VALUE_ZERO)
&& !move_is_promotion(m)
&& !move_is_ep(m))
{
result += PawnEndgameExtension[PvNode];
*dangerous = true;
}
if ( PvNode
&& captureOrPromotion
&& pos.type_of_piece_on(move_to(m)) != PAWN
&& pos.see_sign(m) >= 0)
{
result += ONE_PLY / 2;
*dangerous = true;
}
return Min(result, ONE_PLY);
}
// connected_threat() tests whether it is safe to forward prune a move or if
// is somehow connected to the threat move returned by null search.
bool connected_threat(const Position& pos, Move m, Move threat) {
assert(move_is_ok(m));
assert(threat && move_is_ok(threat));
assert(!pos.move_is_check(m));
assert(!pos.move_is_capture_or_promotion(m));
assert(!pos.move_is_passed_pawn_push(m));
Square mfrom, mto, tfrom, tto;
mfrom = move_from(m);
mto = move_to(m);
tfrom = move_from(threat);
tto = move_to(threat);
// Case 1: Don't prune moves which move the threatened piece
if (mfrom == tto)
return true;
// Case 2: If the threatened piece has value less than or equal to the
// value of the threatening piece, don't prune moves which defend it.
if ( pos.move_is_capture(threat)
&& ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
|| pos.type_of_piece_on(tfrom) == KING)
&& pos.move_attacks_square(m, tto))
return true;
// Case 3: If the moving piece in the threatened move is a slider, don't
// prune safe moves which block its ray.
if ( piece_is_slider(pos.piece_on(tfrom))
&& bit_is_set(squares_between(tfrom, tto), mto)
&& pos.see_sign(m) >= 0)
return true;
return false;
}
// ok_to_use_TT() returns true if a transposition table score
// can be used at a given point in search.
bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
Value v = value_from_tt(tte->value(), ply);
return ( tte->depth() >= depth
|| v >= Max(value_mate_in(PLY_MAX), beta)
|| v < Min(value_mated_in(PLY_MAX), beta))
&& ( ((tte->type() & VALUE_TYPE_LOWER) && v >= beta)
|| ((tte->type() & VALUE_TYPE_UPPER) && v < beta));
}
// refine_eval() returns the transposition table score if
// possible otherwise falls back on static position evaluation.
Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
assert(tte);
Value v = value_from_tt(tte->value(), ply);
if ( ((tte->type() & VALUE_TYPE_LOWER) && v >= defaultEval)
|| ((tte->type() & VALUE_TYPE_UPPER) && v < defaultEval))
return v;
return defaultEval;
}
// update_history() registers a good move that produced a beta-cutoff
// in history and marks as failures all the other moves of that ply.
void update_history(const Position& pos, Move move, Depth depth,
Move movesSearched[], int moveCount) {
Move m;
Value bonus = Value(int(depth) * int(depth));
H.update(pos.piece_on(move_from(move)), move_to(move), bonus);
for (int i = 0; i < moveCount - 1; i++)
{
m = movesSearched[i];
assert(m != move);
H.update(pos.piece_on(move_from(m)), move_to(m), -bonus);
}
}
// update_killers() add a good move that produced a beta-cutoff
// among the killer moves of that ply.
void update_killers(Move m, Move killers[]) {
if (m != killers[0])
{
killers[1] = killers[0];
killers[0] = m;
}
}
// update_gains() updates the gains table of a non-capture move given
// the static position evaluation before and after the move.
void update_gains(const Position& pos, Move m, Value before, Value after) {
if ( m != MOVE_NULL
&& before != VALUE_NONE
&& after != VALUE_NONE
&& pos.captured_piece_type() == PIECE_TYPE_NONE
&& !move_is_special(m))
H.update_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
}
// value_to_uci() converts a value to a string suitable for use with the UCI
// protocol specifications:
//
// cp <x> The score from the engine's point of view in centipawns.
// mate <y> Mate in y moves, not plies. If the engine is getting mated
// use negative values for y.
std::string value_to_uci(Value v) {
std::stringstream s;
if (abs(v) < VALUE_MATE - PLY_MAX * ONE_PLY)
s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to centipawns
else
s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2);
return s.str();
}
// current_search_time() returns the number of milliseconds which have passed
// since the beginning of the current search.
int current_search_time() {
return get_system_time() - SearchStartTime;
}
// nps() computes the current nodes/second count
int nps(const Position& pos) {
int t = current_search_time();
return (t > 0 ? int((pos.nodes_searched() * 1000) / t) : 0);
}
// poll() performs two different functions: It polls for user input, and it
// looks at the time consumed so far and decides if it's time to abort the
// search.
void poll(const Position& pos) {
static int lastInfoTime;
int t = current_search_time();
// Poll for input
if (input_available())
{
// We are line oriented, don't read single chars
std::string command;
if (!std::getline(std::cin, command))
command = "quit";
if (command == "quit")
{
// Quit the program as soon as possible
Pondering = false;
QuitRequest = StopRequest = true;
return;
}
else if (command == "stop")
{
// Stop calculating as soon as possible, but still send the "bestmove"
// and possibly the "ponder" token when finishing the search.
Pondering = false;
StopRequest = true;
}
else if (command == "ponderhit")
{
// The opponent has played the expected move. GUI sends "ponderhit" if
// we were told to ponder on the same move the opponent has played. We
// should continue searching but switching from pondering to normal search.
Pondering = false;
if (StopOnPonderhit)
StopRequest = true;
}
}
// Print search information
if (t < 1000)
lastInfoTime = 0;
else if (lastInfoTime > t)
// HACK: Must be a new search where we searched less than
// NodesBetweenPolls nodes during the first second of search.
lastInfoTime = 0;
else if (t - lastInfoTime >= 1000)
{
lastInfoTime = t;
if (dbg_show_mean)
dbg_print_mean();
if (dbg_show_hit_rate)
dbg_print_hit_rate();
// Send info on searched nodes as soon as we return to root
SendSearchedNodes = true;
}
// Should we stop the search?
if (Pondering)
return;
bool stillAtFirstMove = FirstRootMove
&& !AspirationFailLow
&& t > TimeMgr.available_time();
bool noMoreTime = t > TimeMgr.maximum_time()
|| stillAtFirstMove;
if ( (UseTimeManagement && noMoreTime)
|| (ExactMaxTime && t >= ExactMaxTime)
|| (MaxNodes && pos.nodes_searched() >= MaxNodes)) // FIXME
StopRequest = true;
}
// wait_for_stop_or_ponderhit() is called when the maximum depth is reached
// while the program is pondering. The point is to work around a wrinkle in
// the UCI protocol: When pondering, the engine is not allowed to give a
// "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
// We simply wait here until one of these commands is sent, and return,
// after which the bestmove and pondermove will be printed.
void wait_for_stop_or_ponderhit() {
std::string command;
while (true)
{
// Wait for a command from stdin
if (!std::getline(std::cin, command))
command = "quit";
if (command == "quit")
{
QuitRequest = true;
break;
}
else if (command == "ponderhit" || command == "stop")
break;
}
}
// init_thread() is the function which is called when a new thread is
// launched. It simply calls the idle_loop() function with the supplied
// threadID. There are two versions of this function; one for POSIX
// threads and one for Windows threads.
#if !defined(_MSC_VER)
void* init_thread(void* threadID) {
ThreadsMgr.idle_loop(*(int*)threadID, NULL);
return NULL;
}
#else
DWORD WINAPI init_thread(LPVOID threadID) {
ThreadsMgr.idle_loop(*(int*)threadID, NULL);
return 0;
}
#endif
/// The ThreadsManager class
// read_uci_options() updates number of active threads and other internal
// parameters according to the UCI options values. It is called before
// to start a new search.
void ThreadsManager::read_uci_options() {
maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
minimumSplitDepth = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
useSleepingThreads = Options["Use Sleeping Threads"].value<bool>();
activeThreads = Options["Threads"].value<int>();
}
// idle_loop() is where the threads are parked when they have no work to do.
// The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
// object for which the current thread is the master.
void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
assert(threadID >= 0 && threadID < MAX_THREADS);
int i;
bool allFinished = false;
while (true)
{
// Slave threads can exit as soon as AllThreadsShouldExit raises,
// master should exit as last one.
if (allThreadsShouldExit)
{
assert(!sp);
threads[threadID].state = THREAD_TERMINATED;
return;
}
// If we are not thinking, wait for a condition to be signaled
// instead of wasting CPU time polling for work.
while ( threadID >= activeThreads || threads[threadID].state == THREAD_INITIALIZING
|| (useSleepingThreads && threads[threadID].state == THREAD_AVAILABLE))
{
assert(!sp || useSleepingThreads);
assert(threadID != 0 || useSleepingThreads);
if (threads[threadID].state == THREAD_INITIALIZING)
threads[threadID].state = THREAD_AVAILABLE;
// Grab the lock to avoid races with wake_sleeping_thread()
lock_grab(&sleepLock[threadID]);
// If we are master and all slaves have finished do not go to sleep
for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
allFinished = (i == activeThreads);
if (allFinished || allThreadsShouldExit)
{
lock_release(&sleepLock[threadID]);
break;
}
// Do sleep here after retesting sleep conditions
if (threadID >= activeThreads || threads[threadID].state == THREAD_AVAILABLE)
cond_wait(&sleepCond[threadID], &sleepLock[threadID]);
lock_release(&sleepLock[threadID]);
}
// If this thread has been assigned work, launch a search
if (threads[threadID].state == THREAD_WORKISWAITING)
{
assert(!allThreadsShouldExit);
threads[threadID].state = THREAD_SEARCHING;
// Here we call search() with SplitPoint template parameter set to true
SplitPoint* tsp = threads[threadID].splitPoint;
Position pos(*tsp->pos, threadID);
SearchStack* ss = tsp->sstack[threadID] + 1;
ss->sp = tsp;
if (tsp->pvNode)
search<PV, true, false>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
else
search<NonPV, true, false>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
assert(threads[threadID].state == THREAD_SEARCHING);
threads[threadID].state = THREAD_AVAILABLE;
// Wake up master thread so to allow it to return from the idle loop in
// case we are the last slave of the split point.
if (useSleepingThreads && threadID != tsp->master && threads[tsp->master].state == THREAD_AVAILABLE)
wake_sleeping_thread(tsp->master);
}
// If this thread is the master of a split point and all slaves have
// finished their work at this split point, return from the idle loop.
for (i = 0; sp && i < activeThreads && !sp->slaves[i]; i++) {}
allFinished = (i == activeThreads);
if (allFinished)
{
// Because sp->slaves[] is reset under lock protection,
// be sure sp->lock has been released before to return.
lock_grab(&(sp->lock));
lock_release(&(sp->lock));
// In helpful master concept a master can help only a sub-tree, and
// because here is all finished is not possible master is booked.
assert(threads[threadID].state == THREAD_AVAILABLE);
threads[threadID].state = THREAD_SEARCHING;
return;
}
}
}
// init_threads() is called during startup. It launches all helper threads,
// and initializes the split point stack and the global locks and condition
// objects.
void ThreadsManager::init_threads() {
int i, arg[MAX_THREADS];
bool ok;
// Initialize global locks
lock_init(&mpLock);
for (i = 0; i < MAX_THREADS; i++)
{
lock_init(&sleepLock[i]);
cond_init(&sleepCond[i]);
}
// Initialize splitPoints[] locks
for (i = 0; i < MAX_THREADS; i++)
for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
lock_init(&(threads[i].splitPoints[j].lock));
// Will be set just before program exits to properly end the threads
allThreadsShouldExit = false;
// Threads will be put all threads to sleep as soon as created
activeThreads = 1;
// All threads except the main thread should be initialized to THREAD_INITIALIZING
threads[0].state = THREAD_SEARCHING;
for (i = 1; i < MAX_THREADS; i++)
threads[i].state = THREAD_INITIALIZING;
// Launch the helper threads
for (i = 1; i < MAX_THREADS; i++)
{
arg[i] = i;
#if !defined(_MSC_VER)
pthread_t pthread[1];
ok = (pthread_create(pthread, NULL, init_thread, (void*)(&arg[i])) == 0);
pthread_detach(pthread[0]);
#else
ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&arg[i]), 0, NULL) != NULL);
#endif
if (!ok)
{
cout << "Failed to create thread number " << i << endl;
exit(EXIT_FAILURE);
}
// Wait until the thread has finished launching and is gone to sleep
while (threads[i].state == THREAD_INITIALIZING) {}
}
}
// exit_threads() is called when the program exits. It makes all the
// helper threads exit cleanly.
void ThreadsManager::exit_threads() {
allThreadsShouldExit = true; // Let the woken up threads to exit idle_loop()
// Wake up all the threads and waits for termination
for (int i = 1; i < MAX_THREADS; i++)
{
wake_sleeping_thread(i);
while (threads[i].state != THREAD_TERMINATED) {}
}
// Now we can safely destroy the locks
for (int i = 0; i < MAX_THREADS; i++)
for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
lock_destroy(&(threads[i].splitPoints[j].lock));
lock_destroy(&mpLock);
// Now we can safely destroy the wait conditions
for (int i = 0; i < MAX_THREADS; i++)
{
lock_destroy(&sleepLock[i]);
cond_destroy(&sleepCond[i]);
}
}
// cutoff_at_splitpoint() checks whether a beta cutoff has occurred in
// the thread's currently active split point, or in some ancestor of
// the current split point.
bool ThreadsManager::cutoff_at_splitpoint(int threadID) const {
assert(threadID >= 0 && threadID < activeThreads);
SplitPoint* sp = threads[threadID].splitPoint;
for ( ; sp && !sp->betaCutoff; sp = sp->parent) {}
return sp != NULL;
}
// thread_is_available() checks whether the thread with threadID "slave" is
// available to help the thread with threadID "master" at a split point. An
// obvious requirement is that "slave" must be idle. With more than two
// threads, this is not by itself sufficient: If "slave" is the master of
// some active split point, it is only available as a slave to the other
// threads which are busy searching the split point at the top of "slave"'s
// split point stack (the "helpful master concept" in YBWC terminology).
bool ThreadsManager::thread_is_available(int slave, int master) const {
assert(slave >= 0 && slave < activeThreads);
assert(master >= 0 && master < activeThreads);
assert(activeThreads > 1);
if (threads[slave].state != THREAD_AVAILABLE || slave == master)
return false;
// Make a local copy to be sure doesn't change under our feet
int localActiveSplitPoints = threads[slave].activeSplitPoints;
// No active split points means that the thread is available as
// a slave for any other thread.
if (localActiveSplitPoints == 0 || activeThreads == 2)
return true;
// Apply the "helpful master" concept if possible. Use localActiveSplitPoints
// that is known to be > 0, instead of threads[slave].activeSplitPoints that
// could have been set to 0 by another thread leading to an out of bound access.
if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
return true;
return false;
}
// available_thread_exists() tries to find an idle thread which is available as
// a slave for the thread with threadID "master".
bool ThreadsManager::available_thread_exists(int master) const {
assert(master >= 0 && master < activeThreads);
assert(activeThreads > 1);
for (int i = 0; i < activeThreads; i++)
if (thread_is_available(i, master))
return true;
return false;
}
// split() does the actual work of distributing the work at a node between
// several available threads. If it does not succeed in splitting the
// node (because no idle threads are available, or because we have no unused
// split point objects), the function immediately returns. If splitting is
// possible, a SplitPoint object is initialized with all the data that must be
// copied to the helper threads and we tell our helper threads that they have
// been assigned work. This will cause them to instantly leave their idle loops and
// call search().When all threads have returned from search() then split() returns.
template <bool Fake>
void ThreadsManager::split(Position& pos, SearchStack* ss, int ply, Value* alpha,
const Value beta, Value* bestValue, Depth depth, Move threatMove,
bool mateThreat, int moveCount, MovePicker* mp, bool pvNode) {
assert(pos.is_ok());
assert(ply > 0 && ply < PLY_MAX);
assert(*bestValue >= -VALUE_INFINITE);
assert(*bestValue <= *alpha);
assert(*alpha < beta);
assert(beta <= VALUE_INFINITE);
assert(depth > DEPTH_ZERO);
assert(pos.thread() >= 0 && pos.thread() < activeThreads);
assert(activeThreads > 1);
int i, master = pos.thread();
Thread& masterThread = threads[master];
lock_grab(&mpLock);
// If no other thread is available to help us, or if we have too many
// active split points, don't split.
if ( !available_thread_exists(master)
|| masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
{
lock_release(&mpLock);
return;
}
// Pick the next available split point object from the split point stack
SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
// Initialize the split point object
splitPoint.parent = masterThread.splitPoint;
splitPoint.master = master;
splitPoint.betaCutoff = false;
splitPoint.ply = ply;
splitPoint.depth = depth;
splitPoint.threatMove = threatMove;
splitPoint.mateThreat = mateThreat;
splitPoint.alpha = *alpha;
splitPoint.beta = beta;
splitPoint.pvNode = pvNode;
splitPoint.bestValue = *bestValue;
splitPoint.mp = mp;
splitPoint.moveCount = moveCount;
splitPoint.pos = &pos;
splitPoint.nodes = 0;
splitPoint.parentSstack = ss;
for (i = 0; i < activeThreads; i++)
splitPoint.slaves[i] = 0;
masterThread.splitPoint = &splitPoint;
// If we are here it means we are not available
assert(masterThread.state != THREAD_AVAILABLE);
int workersCnt = 1; // At least the master is included
// Allocate available threads setting state to THREAD_BOOKED
for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
if (thread_is_available(i, master))
{
threads[i].state = THREAD_BOOKED;
threads[i].splitPoint = &splitPoint;
splitPoint.slaves[i] = 1;
workersCnt++;
}
assert(Fake || workersCnt > 1);
// We can release the lock because slave threads are already booked and master is not available
lock_release(&mpLock);
// Tell the threads that they have work to do. This will make them leave
// their idle loop. But before copy search stack tail for each thread.
for (i = 0; i < activeThreads; i++)
if (i == master || splitPoint.slaves[i])
{
memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
assert(i == master || threads[i].state == THREAD_BOOKED);
threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
if (useSleepingThreads && i != master)
wake_sleeping_thread(i);
}
// Everything is set up. The master thread enters the idle loop, from
// which it will instantly launch a search, because its state is
// THREAD_WORKISWAITING. We send the split point as a second parameter to the
// idle loop, which means that the main thread will return from the idle
// loop when all threads have finished their work at this split point.
idle_loop(master, &splitPoint);
// We have returned from the idle loop, which means that all threads are
// finished. Update alpha and bestValue, and return.
lock_grab(&mpLock);
*alpha = splitPoint.alpha;
*bestValue = splitPoint.bestValue;
masterThread.activeSplitPoints--;
masterThread.splitPoint = splitPoint.parent;
pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
lock_release(&mpLock);
}
// wake_sleeping_thread() wakes up the thread with the given threadID
// when it is time to start a new search.
void ThreadsManager::wake_sleeping_thread(int threadID) {
lock_grab(&sleepLock[threadID]);
cond_signal(&sleepCond[threadID]);
lock_release(&sleepLock[threadID]);
}
/// RootMove and RootMoveList method's definitions
RootMove::RootMove() {
nodes = 0;
pv_score = non_pv_score = -VALUE_INFINITE;
pv[0] = MOVE_NONE;
}
RootMove& RootMove::operator=(const RootMove& rm) {
const Move* src = rm.pv;
Move* dst = pv;
// Avoid a costly full rm.pv[] copy
do *dst++ = *src; while (*src++ != MOVE_NONE);
nodes = rm.nodes;
pv_score = rm.pv_score;
non_pv_score = rm.non_pv_score;
return *this;
}
// extract_pv_from_tt() builds a PV by adding moves from the transposition table.
// We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
// allow to always have a ponder move even when we fail high at root and also a
// long PV to print that is important for position analysis.
void RootMove::extract_pv_from_tt(Position& pos) {
StateInfo state[PLY_MAX_PLUS_2], *st = state;
TTEntry* tte;
int ply = 1;
assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
pos.do_move(pv[0], *st++);
while ( (tte = TT.retrieve(pos.get_key())) != NULL
&& tte->move() != MOVE_NONE
&& move_is_legal(pos, tte->move())
&& ply < PLY_MAX
&& (!pos.is_draw() || ply < 2))
{
pv[ply] = tte->move();
pos.do_move(pv[ply++], *st++);
}
pv[ply] = MOVE_NONE;
do pos.undo_move(pv[--ply]); while (ply);
}
// insert_pv_in_tt() is called at the end of a search iteration, and inserts
// the PV back into the TT. This makes sure the old PV moves are searched
// first, even if the old TT entries have been overwritten.
void RootMove::insert_pv_in_tt(Position& pos) {
StateInfo state[PLY_MAX_PLUS_2], *st = state;
TTEntry* tte;
Key k;
Value v, m = VALUE_NONE;
int ply = 0;
assert(pv[0] != MOVE_NONE && move_is_legal(pos, pv[0]));
do {
k = pos.get_key();
tte = TT.retrieve(k);
// Don't overwrite existing correct entries
if (!tte || tte->move() != pv[ply])
{
v = (pos.is_check() ? VALUE_NONE : evaluate(pos, m));
TT.store(k, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[ply], v, m);
}
pos.do_move(pv[ply], *st++);
} while (pv[++ply] != MOVE_NONE);
do pos.undo_move(pv[--ply]); while (ply);
}
// pv_info_to_uci() returns a string with information on the current PV line
// formatted according to UCI specification. It is called at each iteration
// or after a new pv is found.
std::string RootMove::pv_info_to_uci(Position& pos, int depth, Value alpha, Value beta, int pvLine) {
std::stringstream s, l;
Move* m = pv;
while (*m != MOVE_NONE)
l << *m++ << " ";
s << "info depth " << depth
<< " seldepth " << int(m - pv)
<< " multipv " << pvLine + 1
<< " score " << value_to_uci(pv_score)
<< (pv_score >= beta ? " lowerbound" : pv_score <= alpha ? " upperbound" : "")
<< " time " << current_search_time()
<< " nodes " << pos.nodes_searched()
<< " nps " << nps(pos)
<< " pv " << l.str();
return s.str();
}
void RootMoveList::init(Position& pos, Move searchMoves[]) {
MoveStack mlist[MOVES_MAX];
Move* sm;
clear();
bestMoveChanges = 0;
// Generate all legal moves and score them
MoveStack* last = generate<MV_LEGAL>(pos, mlist);
qsearch_scoring(pos, mlist, last);
// Add each move to the RootMoveList's vector
for (MoveStack* cur = mlist; cur != last; cur++)
{
// If we have a searchMoves[] list then verify cur->move
// is in the list before to add it.
for (sm = searchMoves; *sm && *sm != cur->move; sm++) {}
if (searchMoves[0] && *sm != cur->move)
continue;
RootMove rm;
rm.pv[0] = cur->move;
rm.pv[1] = MOVE_NONE;
rm.pv_score = Value(cur->score);
push_back(rm);
}
sort();
}
} // namespace
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