text: /*
    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 "movegen.h"
  #include "movepick.h"
  #include "lock.h"
  #include "san.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(const Position &pos, Value alpha, Value beta, int pvLine = 0);
      
      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;
      
      RootMoveList(Position &pos, Move searchMoves[]);
      
      void set_non_pv_scores(const Position &pos);
      
      void sort() { insertion_sort<RootMove, Base::iterator>(begin(), end()); }
      
      void sort_multipv(int n) { insertion_sort<RootMove, Base::iterator>(begin(), begin() + n + 1); }
    };
    
    
    // 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 &m) {
      
      os.iword(0) = int(m);
      return os;
    }
    
    
    /// 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], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
    Depth PassedPawnExtension[2], 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 then 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)]; }
    
    // Common adjustments
    
    // Search depth at iteration 1
    const Depth InitialDepth = ONE_PLY;
    
    // 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;
    
    // Iteration counter
    int Iteration;
    
    // Scores and number of times the best move changed for each iteration
    Value ValueByIteration[PLY_MAX_PLUS_2];
    int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
    
    // Search window management
    int AspirationDelta;
    
    // MultiPV mode
    int MultiPV;
    
    // Time managment 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);
    
    Value root_search(Position &pos, SearchStack *ss, Value alpha, Value beta, Depth depth, RootMoveList &rml);
    
    template<NodeType PvNode, bool SpNode>
    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>(pos, ss, alpha, beta, depth, ply);
    }
    
    template<NodeType PvNode>
    Depth
    extension(const Position &pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, 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, SearchStack *ss);
    
    void update_gains(const Position &pos, Move move, Value before, Value after);
    
    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();
    
    void init_ss_array(SearchStack *ss, int size);
  
  #if !defined(_MSC_VER)
    
    void *init_thread(void *threadID);
  
  #else
    DWORD WINAPI init_thread(LPVOID threadID);
  #endif
  
  }
  
  
  ////
  //// 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.
  
  int perft(Position &pos, Depth depth) {
    MoveStack mlist[MOVES_MAX];
    StateInfo st;
    Move m;
    int sum = 0;
    
    // Generate all legal moves
    MoveStack *last = generate_moves(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 root_search(). 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.file_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>();
    SingleEvasionExtension[1] = Options["Single Evasion Extension (PV nodes)"].value<Depth>();
    SingleEvasionExtension[0] = Options["Single Evasion 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 << "Searching: " << 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 << "\nNodes: " << 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) // Works also with MOVE_NONE
              << endl;
      
      // Return from think() with unchanged position
      pos.undo_move(bestMove);
      
      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 root_search
    // repeatedly with increasing depth until the allocated thinking time has
    // been consumed, the 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];
      Depth depth;
      Move EasyMove = MOVE_NONE;
      Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
      
      // Moves to search are verified, scored and sorted
      RootMoveList rml(pos, searchMoves);
      
      // Handle special case of searching on a mate/stale position
      if (rml.size() == 0) {
        Value s = (pos.is_check() ? -VALUE_MATE : VALUE_DRAW);
        
        cout << "info depth " << 1
             << " score " << value_to_uci(s) << endl;
        
        return MOVE_NONE;
      }
      
      // Initialize
      TT.new_search();
      H.clear();
      init_ss_array(ss, PLY_MAX_PLUS_2);
      ValueByIteration[1] = rml[0].pv_score;
      Iteration = 1;
      
      // Send initial RootMoveList scoring (iteration 1)
      cout << set960(pos.is_chess960()) // Is enough to set once at the beginning
           << "info depth " << Iteration
           << "\n" << rml[0].pv_info_to_uci(pos, alpha, beta) << endl;
      
      // 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 (Iteration < PLY_MAX) {
        // Initialize iteration
        Iteration++;
        BestMoveChangesByIteration[Iteration] = 0;
        
        cout << "info depth " << Iteration << endl;
        
        // Calculate dynamic aspiration window based on previous iterations
        if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN) {
          int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
          int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
          
          AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
          AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
          
          alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
          beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
        }
        
        depth = (Iteration - 2) * ONE_PLY + InitialDepth;
        
        // Search to the current depth, rml is updated and sorted
        value = root_search(pos, ss, alpha, beta, depth, rml);
        
        if (StopRequest)
          break; // Value cannot be trusted. Break out immediately!
        
        //Save info about search result
        ValueByIteration[Iteration] = value;
        
        // Drop the easy move if differs from the new best move
        if (rml[0].pv[0] != EasyMove)
          EasyMove = MOVE_NONE;
        
        if (UseTimeManagement) {
          // Time to stop?
          bool stopSearch = false;
          
          // Stop search early if there is only a single legal move,
          // we search up to Iteration 6 anyway to get a proper score.
          if (Iteration >= 6 && rml.size() == 1)
            stopSearch = true;
          
          // Stop search early when the last two iterations returned a mate score
          if (Iteration >= 6
              && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
              && abs(ValueByIteration[Iteration - 1]) >= abs(VALUE_MATE) - 100)
            stopSearch = true;
          
          // Stop search early if one move seems to be much better than the others
          if (Iteration >= 8
              && EasyMove == rml[0].pv[0]
              && ((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)))
            stopSearch = true;
          
          // Add some extra time if the best move has changed during the last two iterations
          if (Iteration > 5 && Iteration <= 50)
            TimeMgr.pv_instability(BestMoveChangesByIteration[Iteration],
                                   BestMoveChangesByIteration[Iteration - 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)
            stopSearch = true;
          
          if (stopSearch) {
            if (Pondering)
              StopOnPonderhit = true;
            else
              break;
          }
        }
        
        if (MaxDepth && Iteration >= MaxDepth)
          break;
      }
      
      *ponderMove = rml[0].pv[1];
      return rml[0].pv[0];
    }
    
    
    // root_search() is the function which searches the root node. It is
    // similar to search_pv except that it prints some information to the
    // standard output and handles the fail low/high loops.
    
    Value root_search(Position &pos, SearchStack *ss, Value alpha,
                      Value beta, Depth depth, RootMoveList &rml) {
      StateInfo st;
      CheckInfo ci(pos);
      int64_t nodes;
      Move move;
      Depth ext, newDepth;
      Value value, oldAlpha;
      bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
      int researchCountFH, researchCountFL;
      
      researchCountFH = researchCountFL = 0;
      oldAlpha = alpha;
      isCheck = pos.is_check();
      
      // Step 1. Initialize node (polling is omitted at root)
      ss->currentMove = ss->bestMove = MOVE_NONE;
      
      // Step 2. Check for aborted search (omitted at root)
      // Step 3. Mate distance pruning (omitted at root)
      // Step 4. Transposition table lookup (omitted at root)
      
      // Step 5. Evaluate the position statically
      // At root we do this only to get reference value for child nodes
      ss->evalMargin = VALUE_NONE;
      ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ss->evalMargin);
      
      // Step 6. Razoring (omitted at root)
      // Step 7. Static null move pruning (omitted at root)
      // Step 8. Null move search with verification search (omitted at root)
      // Step 9. Internal iterative deepening (omitted at root)
      
      // Step extra. Fail low loop
      // We start with small aspiration window and in case of fail low, we research
      // with bigger window until we are not failing low anymore.
      while (1) {
        // Sort the moves before to (re)search
        rml.set_non_pv_scores(pos);
        rml.sort();
        
        // Step 10. Loop through all moves in the root move list
        for (int i = 0; i < (int) rml.size() && !StopRequest; i++) {
          // This is used by time management
          FirstRootMove = (i == 0);
          
          // 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;
          }
          
          // Pick the next root move, and print the move and the move number to
          // the standard output.
          move = ss->currentMove = rml[i].pv[0];
          
          if (current_search_time() >= 1000)
            cout << "info currmove " << move
                 << " currmovenumber " << i + 1 << endl;
          
          moveIsCheck = pos.move_is_check(move);
          captureOrPromotion = pos.move_is_capture_or_promotion(move);
          
          // Step 11. Decide the new search depth
          ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
          newDepth = depth + ext;
          
          // Step 12. Futility pruning (omitted at root)
          
          // Step extra. Fail high loop
          // If move fails high, we research with bigger window until we are not failing
          // high anymore.
          value = -VALUE_INFINITE;
          
          while (1) {
            // Step 13. Make the move
            pos.do_move(move, st, ci, moveIsCheck);
            
            // Step extra. pv search
            // We do pv search for first moves (i < MultiPV)
            // and for fail high research (value > alpha)
            if (i < MultiPV || value > alpha) {
              // Aspiration window is disabled in multi-pv case
              if (MultiPV > 1)
                alpha = -VALUE_INFINITE;
              
              // Full depth PV search, done on first move or after a fail high
              value = -search<PV>(pos, ss + 1, -beta, -alpha, newDepth, 1);
            } else {
              // Step 14. Reduced search
              // if the move fails high will be re-searched at full depth
              bool doFullDepthSearch = true;
              
              if (depth >= 3 * ONE_PLY
                  && !dangerous
                  && !captureOrPromotion
                  && !move_is_castle(move)) {
                ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
                if (ss->reduction) {
                  assert(newDepth - ss->reduction >= ONE_PLY);
                  
                  // Reduced depth non-pv search using alpha as upperbound
                  value = -search<NonPV>(pos, ss + 1, -(alpha + 1), -alpha, newDepth - ss->reduction, 1);
                  doFullDepthSearch = (value > alpha);
                }
                ss->reduction = DEPTH_ZERO; // Restore original reduction
              }
              
              // Step 15. Full depth search
              if (doFullDepthSearch) {
                // Full depth non-pv search using alpha as upperbound
                value = -search<NonPV>(pos, ss + 1, -(alpha + 1), -alpha, newDepth, 1);
                
                // If we are above alpha then research at same depth but as PV
                // to get a correct score or eventually a fail high above beta.
                if (value > alpha)
                  value = -search<PV>(pos, ss + 1, -beta, -alpha, newDepth, 1);
              }
            }
            
            // Step 16. Undo move
            pos.undo_move(move);
            
            // Can we exit fail high loop ?
            if (StopRequest || value < beta)
              break;
            
            // We are failing high and going to do a research. It's important to update
            // the score before research in case we run out of time while researching.
            ss->bestMove = move;
            rml[i].pv_score = value;
            rml[i].extract_pv_from_tt(pos);
            
            // Inform GUI that PV has changed
            cout << rml[i].pv_info_to_uci(pos, alpha, beta) << endl;
            
            // Prepare for a research after a fail high, each time with a wider window
            beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
            researchCountFH++;
            
          } // End of fail high loop
          
          // Finished searching the move. If AbortSearch 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
          rml[i].nodes += pos.nodes_searched() - nodes;
          
          assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
          assert(value < beta);
          
          // Step 17. Check for new best move
          if (value <= alpha && i >= MultiPV)
            rml[i].pv_score = -VALUE_INFINITE;
          else {
            // PV move or new best move!
            
            // Update PV
            ss->bestMove = move;
            rml[i].pv_score = value;
            rml[i].extract_pv_from_tt(pos);
            
            // We record how often the best move has been changed in each
            // iteration. This information is used for time managment: When
            // the best move changes frequently, we allocate some more time.
            if (MultiPV == 1 && i > 0)
              BestMoveChangesByIteration[Iteration]++;
            
            // Inform GUI that PV has changed, in case of multi-pv UCI protocol
            // requires we send all the PV lines properly sorted.
            rml.sort_multipv(i);
            
            for (int j = 0; j < Min(MultiPV, (int) rml.size()); j++)
              cout << rml[j].pv_info_to_uci(pos, alpha, beta, j) << endl;
            
            // Update alpha. In multi-pv we don't use aspiration window
            if (MultiPV == 1) {
              // Raise alpha to setup proper non-pv search upper bound
              if (value > alpha)
                alpha = value;
            } else // Set alpha equal to minimum score among the PV lines
              alpha = rml[Min(i, MultiPV - 1)].pv_score;
            
          } // PV move or new best move
          
          assert(alpha >= oldAlpha);
          
          AspirationFailLow = (alpha == oldAlpha);
          
          if (AspirationFailLow && StopOnPonderhit)
            StopOnPonderhit = false;
          
        } // Root moves loop
        
        // Can we exit fail low loop ?
        if (StopRequest || !AspirationFailLow)
          break;
        
        // Prepare for a research after a fail low, each time with a wider window
        oldAlpha = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
        researchCountFL++;
        
      } // Fail low loop
      
      // Sort the moves before to return
      rml.sort();
      
      // Write PV lines 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);
      
      return alpha;
    }
    
    
    // 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>
    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(ply > 0 && ply < PLY_MAX);
      assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
      
      Move movesSearched[MOVES_MAX];
      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 isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
      bool mateThreat = false;
      int moveCount = 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 {} // Hack to fix icc's "statement is unreachable" warning
      
      // 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)
        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 exists.
      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 don't use the TT for pruning, but only for move ordering.
      // This is to avoid problems in the following areas:
      //
      // * Repetition draw detection
      // * Fifty move rule detection
      // * Searching for a mate
      // * Printing of full PV line
      if (!PvNode && tte && 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
      // FIXME currently MovePicker() c'tor is needless called also in SplitPoint
      MovePicker mpBase(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
      MovePicker &mp = SpNode ? *sp->mp : mpBase;
      CheckInfo ci(pos);
      ss->bestMove = MOVE_NONE;
      singleEvasion = !SpNode && isCheck && mp.number_of_evasions() == 1;
      futilityBase = ss->eval + ss->evalMargin;
      singularExtensionNode = !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
          movesSearched[moveCount++] = move;
        
        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, singleEvasion, 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 then 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 - ONE_PLY + 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);
        
        // Step extra. pv search (only in PV nodes)
        // The first move in list is the expected PV
        if (PvNode && moveCount == 1)
          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 && 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 (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;
          }
        }
        
        // Step 18. Check for split
        if (!SpNode
            && depth >= ThreadsMgr.min_split_depth()
            && ThreadsMgr.active_threads() > 1
            && bestValue < beta
            && ThreadsMgr.available_thread_exists(threadID)
            && !StopRequest
            && !ThreadsMgr.cutoff_at_splitpoint(threadID)
            && Iteration <= 99)
          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, moveCount);
          update_killers(move, ss);
        }
      }
      
      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;
    }
    
    
    // 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 singleEvasion, bool mateThreat, bool *dangerous) {
      
      assert(m != MOVE_NONE);
      
      Depth result = DEPTH_ZERO;
      *dangerous = moveIsCheck | singleEvasion | mateThreat;
      
      if (*dangerous) {
        if (moveIsCheck && pos.see_sign(m) >= 0)
          result += CheckExtension[PvNode];
        
        if (singleEvasion)
          result += SingleEvasionExtension[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 coonected 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 move 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;
      
      H.success(pos.piece_on(move_from(move)), move_to(move), depth);
      
      for (int i = 0; i < moveCount - 1; i++) {
        m = movesSearched[i];
        
        assert(m != move);
        
        if (!pos.move_is_capture_or_promotion(m))
          H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
      }
    }
    
    
    // update_killers() add a good move that produced a beta-cutoff
    // among the killer moves of that ply.
    
    void update_killers(Move m, SearchStack *ss) {
      
      if (m == ss->killers[0])
        return;
      
      ss->killers[1] = ss->killers[0];
      ss->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.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
    }
    
    
    // init_ss_array() does a fast reset of the first entries of a SearchStack
    // array and of all the excludedMove and skipNullMove entries.
    
    void init_ss_array(SearchStack *ss, int size) {
      
      for (int i = 0; i < size; i++, ss++) {
        ss->excludedMove = MOVE_NONE;
        ss->skipNullMove = false;
        ss->reduction = DEPTH_ZERO;
        ss->sp = NULL;
        
        if (i < 3)
          ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
      }
    }
    
    
    // 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 (data_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>(pos, ss, tsp->alpha, tsp->beta, tsp->depth, tsp->ply);
          else
            search<NonPV, true>(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 exsisting 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 and eventually writes the info
    // to a log file. It is called at each iteration or after a new pv is found.
    
    std::string RootMove::pv_info_to_uci(const Position &pos, Value alpha, Value beta, int pvLine) {
      
      std::stringstream s, l;
      Move *m = pv;
      
      while (*m != MOVE_NONE)
        l << *m++ << " ";
      
      s << "info depth " << Iteration // FIXME
        << " 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();
      
      if (UseLogFile && pvLine == 0) {
        ValueType t = pv_score >= beta ? VALUE_TYPE_LOWER :
                      pv_score <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
        
        LogFile << pretty_pv(pos, current_search_time(), Iteration, pv_score, t, pv) << endl;
      }
      return s.str();
    }
    
    
    RootMoveList::RootMoveList(Position &pos, Move searchMoves[]) {
      
      SearchStack ss[PLY_MAX_PLUS_2];
      MoveStack mlist[MOVES_MAX];
      StateInfo st;
      Move *sm;
      
      // Initialize search stack
      init_ss_array(ss, PLY_MAX_PLUS_2);
      ss[0].eval = ss[0].evalMargin = VALUE_NONE;
      
      // Generate all legal moves
      MoveStack *last = generate_moves(pos, mlist);
      
      // 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;
        
        // Find a quick score for the move and add to the list
        pos.do_move(cur->move, st);
        
        RootMove rm;
        rm.pv[0] = ss[0].currentMove = cur->move;
        rm.pv[1] = MOVE_NONE;
        rm.pv_score = -qsearch<PV>(pos, ss + 1, -VALUE_INFINITE, VALUE_INFINITE, DEPTH_ZERO, 1);
        push_back(rm);
        
        pos.undo_move(cur->move);
      }
      sort();
    }
    
    // Score root moves using the standard way used in main search, the moves
    // are scored according to the order in which 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.
    
    void RootMoveList::set_non_pv_scores(const Position &pos) {
      Move move;
      Value score = VALUE_ZERO;
      MovePicker mp(pos, MOVE_NONE, ONE_PLY, H);
      
      while ((move = mp.get_next_move()) != MOVE_NONE)
        for (Base::iterator it = begin(); it != end(); ++it)
          if (it->pv[0] == move) {
            it->non_pv_score = score--;
            break;
          }
    }
    
  } // namespace
  