X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=dbbfa022a8920f246f42ed417dca591edc621f50;hp=3ad5423d9d41a7f4600dc97cce32bed306514b2c;hb=54382f8b0765693c7aa5714c94d7d21dc41f1fc4;hpb=f1d982e2c07372627394b83cf24f48e77a34145b

diff --git a/src/search.cpp b/src/search.cpp
index 3ad5423d..dbbfa022 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1,7 +1,7 @@
 /*
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
-  Copyright (C) 2008 Marco Costalba
+  Copyright (C) 2008-2009 Marco Costalba
 
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -28,11 +28,14 @@
 #include <iostream>
 #include <sstream>
 
+#include "bitcount.h"
 #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 "thread.h"
@@ -72,7 +75,8 @@ namespace {
   // Apart for the first one that has its score, following moves
   // normally have score -VALUE_INFINITE, so are ordered according
   // to the number of beta cutoffs occurred under their subtree during
-  // the last iteration.
+  // the last iteration. The counters are per thread variables to avoid
+  // concurrent accessing under SMP case.
 
   struct BetaCounterType {
 
@@ -80,8 +84,6 @@ namespace {
     void clear();
     void add(Color us, Depth d, int threadID);
     void read(Color us, int64_t& our, int64_t& their);
-
-    int64_t hits[THREAD_MAX][2];
   };
 
 
@@ -108,7 +110,7 @@ namespace {
   class RootMoveList {
 
   public:
-    RootMoveList(Position &pos, Move searchMoves[]);
+    RootMoveList(Position& pos, Move searchMoves[]);
     inline Move get_move(int moveNum) const;
     inline Value get_move_score(int moveNum) const;
     inline void set_move_score(int moveNum, Value score);
@@ -129,94 +131,103 @@ namespace {
   };
 
 
-  /// Constants and variables initialized from UCI options
-
-  // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV
-  // nodes
-  int LMRPVMoves, LMRNonPVMoves;
+  /// Constants
 
-  // Depth limit for use of dynamic threat detection
-  Depth ThreatDepth;
+  // Search depth at iteration 1
+  const Depth InitialDepth = OnePly /*+ OnePly/2*/;
 
   // Depth limit for selective search
-  const Depth SelectiveDepth = 7*OnePly;
+  const Depth SelectiveDepth = 7 * OnePly;
 
   // Use internal iterative deepening?
   const bool UseIIDAtPVNodes = true;
   const bool UseIIDAtNonPVNodes = false;
 
-  // Internal iterative deepening margin.  At Non-PV moves, when
-  // UseIIDAtNonPVNodes is true, we do an internal iterative deepening search
-  // when the static evaluation is at most IIDMargin below beta.
+  // Internal iterative deepening margin. At Non-PV moves, when
+  // UseIIDAtNonPVNodes is true, we do an internal iterative deepening
+  // search when the static evaluation is at most IIDMargin below beta.
   const Value IIDMargin = Value(0x100);
 
-  // Easy move margin.  An easy move candidate must be at least this much
+  // Easy move margin. An easy move candidate must be at least this much
   // better than the second best move.
   const Value EasyMoveMargin = Value(0x200);
 
-  // Problem margin.  If the score of the first move at iteration N+1 has
+  // Problem margin. If the score of the first move at iteration N+1 has
   // dropped by more than this since iteration N, the boolean variable
   // "Problem" is set to true, which will make the program spend some extra
   // time looking for a better move.
   const Value ProblemMargin = Value(0x28);
 
-  // No problem margin.  If the boolean "Problem" is true, and a new move
+  // No problem margin. If the boolean "Problem" is true, and a new move
   // is found at the root which is less than NoProblemMargin worse than the
   // best move from the previous iteration, Problem is set back to false.
   const Value NoProblemMargin = Value(0x14);
 
-  // Null move margin.  A null move search will not be done if the approximate
+  // Null move margin. A null move search will not be done if the approximate
   // evaluation of the position is more than NullMoveMargin below beta.
   const Value NullMoveMargin = Value(0x300);
 
-  // Pruning criterions.  See the code and comments in ok_to_prune() to
+  // Pruning criterions. See the code and comments in ok_to_prune() to
   // understand their precise meaning.
-  const bool PruneEscapeMoves = false;
+  const bool PruneEscapeMoves    = false;
   const bool PruneDefendingMoves = false;
-  const bool PruneBlockingMoves = false;
-
-  // Use futility pruning?
-  bool UseQSearchFutilityPruning, UseFutilityPruning;
+  const bool PruneBlockingMoves  = false;
 
   // Margins for futility pruning in the quiescence search, and at frontier
-  // and near frontier nodes
+  // and near frontier nodes.
   const Value FutilityMarginQS = Value(0x80);
 
-   // Remaining depth:                  1 ply         1.5 ply       2 ply         2.5 ply       3 ply         3.5 ply
-   const Value FutilityMargins[12] = { Value(0x100), Value(0x120), Value(0x200), Value(0x220), Value(0x250), Value(0x270),
+  // Remaining depth:                  1 ply         1.5 ply       2 ply         2.5 ply       3 ply         3.5 ply
+  const Value FutilityMargins[12] = { Value(0x100), Value(0x120), Value(0x200), Value(0x220), Value(0x250), Value(0x270),
   //                                   4 ply         4.5 ply       5 ply         5.5 ply       6 ply         6.5 ply
                                       Value(0x2A0), Value(0x2C0), Value(0x340), Value(0x360), Value(0x3A0), Value(0x3C0) };
-   // Razoring
-   const Depth RazorDepth = 4*OnePly;
+  // Razoring
+  const Depth RazorDepth = 4*OnePly;
 
   // Remaining depth:                 1 ply         1.5 ply       2 ply         2.5 ply       3 ply         3.5 ply
   const Value RazorMargins[6]     = { Value(0x180), Value(0x300), Value(0x300), Value(0x3C0), Value(0x3C0), Value(0x3C0) };
 
   // Remaining depth:                 1 ply         1.5 ply       2 ply         2.5 ply       3 ply         3.5 ply
-   const Value RazorApprMargins[6] = { Value(0x520), Value(0x300), Value(0x300), Value(0x300), Value(0x300), Value(0x300) };
+  const Value RazorApprMargins[6] = { Value(0x520), Value(0x300), Value(0x300), Value(0x300), Value(0x300), Value(0x300) };
+
+  // The main transposition table
+  TranspositionTable TT;
+
+
+  /// Variables initialized by UCI options
+
+  // Adjustable playing strength
+  int Slowdown = 0;
+  const int SlowdownArray[32] = {
+    19, 41, 70, 110, 160, 230, 320, 430, 570, 756, 1000, 1300, 1690, 2197,
+    2834, 3600, 4573, 5809, 7700, 9863, 12633, 16181, 20726, 26584, 34005,
+    43557, 55792, 71463, 91536, 117247, 150180, 192363
+  };
+  int Strength;
+  const int MaxStrength = 25;
+
+  // Minimum number of full depth (i.e. non-reduced) moves at PV and non-PV nodes
+  int LMRPVMoves, LMRNonPVMoves; // heavy SMP read access for the latter
+
+  // Depth limit for use of dynamic threat detection
+  Depth ThreatDepth; // heavy SMP read access
 
   // Last seconds noise filtering (LSN)
-  bool UseLSNFiltering;
-  bool looseOnTime = false;
-  int LSNTime; // In milliseconds
-  Value LSNValue;
+  const bool UseLSNFiltering = true;
+  const int LSNTime = 4000; // In milliseconds
+  const Value LSNValue = value_from_centipawns(200);
+  bool loseOnTime = false;
 
   // Extensions. Array index 0 is used at non-PV nodes, index 1 at PV nodes.
+  // There is heavy SMP read access on these arrays
   Depth CheckExtension[2], SingleReplyExtension[2], PawnPushTo7thExtension[2];
   Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
 
-  // Search depth at iteration 1
-  const Depth InitialDepth = OnePly /*+ OnePly/2*/;
-
-  // Node counters
-  int NodesSincePoll;
-  int NodesBetweenPolls = 30000;
-
   // Iteration counters
   int Iteration;
-  BetaCounterType BetaCounter;
+  BetaCounterType BetaCounter; // has per-thread internal data
 
-  // Scores and number of times the best move changed for each iteration:
+  // Scores and number of times the best move changed for each iteration
   IterationInfoType IterationInfo[PLY_MAX_PLUS_2];
   int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
 
@@ -226,19 +237,16 @@ namespace {
   // Time managment variables
   int SearchStartTime;
   int MaxNodes, MaxDepth;
-  int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime;
-  Move EasyMove;
+  int MaxSearchTime, AbsoluteMaxSearchTime, ExtraSearchTime, ExactMaxTime;
   int RootMoveNumber;
   bool InfiniteSearch;
   bool PonderSearch;
   bool StopOnPonderhit;
-  bool AbortSearch;
+  bool AbortSearch; // heavy SMP read access
   bool Quit;
   bool FailHigh;
   bool FailLow;
   bool Problem;
-  bool PonderingEnabled;
-  int ExactMaxTime;
 
   // Show current line?
   bool ShowCurrentLine;
@@ -248,10 +256,12 @@ namespace {
   std::ofstream LogFile;
 
   // MP related variables
+  int ActiveThreads = 1;
   Depth MinimumSplitDepth;
   int MaxThreadsPerSplitPoint;
   Thread Threads[THREAD_MAX];
   Lock MPLock;
+  Lock IOLock;
   bool AllThreadsShouldExit = false;
   const int MaxActiveSplitPoints = 8;
   SplitPoint SplitPointStack[THREAD_MAX][MaxActiveSplitPoints];
@@ -264,29 +274,38 @@ namespace {
   HANDLE SitIdleEvent[THREAD_MAX];
 #endif
 
+  // Node counters, used only by thread[0] but try to keep in different
+  // cache lines (64 bytes each) from the heavy SMP read accessed variables.
+  int NodesSincePoll;
+  int NodesBetweenPolls = 30000;
+
+  // History table
+  History H;
+
 
   /// Functions
 
-  Value id_loop(const Position &pos, Move searchMoves[]);
-  Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta);
-  Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
-  Value search(Position &pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID);
-  Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
-  void sp_search(SplitPoint *sp, int threadID);
-  void sp_search_pv(SplitPoint *sp, int threadID);
-  void init_node(SearchStack ss[], int ply, int threadID);
+  Value id_loop(const Position& pos, Move searchMoves[]);
+  Value root_search(Position& pos, SearchStack ss[], RootMoveList& rml, Value alpha, Value beta);
+  Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
+  Value search(Position& pos, SearchStack ss[], Value beta, Depth depth, int ply, bool allowNullmove, int threadID);
+  Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta, Depth depth, int ply, int threadID);
+  void sp_search(SplitPoint* sp, int threadID);
+  void sp_search_pv(SplitPoint* sp, int threadID);
+  void init_node(const Position& pos, SearchStack ss[], int ply, int threadID);
   void update_pv(SearchStack ss[], int ply);
-  void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply);
-  bool connected_moves(const Position &pos, Move m1, Move m2);
+  void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply);
+  bool connected_moves(const Position& pos, Move m1, Move m2);
   bool value_is_mate(Value value);
   bool move_is_killer(Move m, const SearchStack& ss);
-  Depth extension(const Position &pos, Move m, bool pvNode, bool capture, bool check, bool singleReply, bool mateThreat, bool* dangerous);
-  bool ok_to_do_nullmove(const Position &pos);
-  bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d);
+  Depth extension(const Position& pos, Move m, bool pvNode, bool capture, bool check, bool singleReply, bool mateThreat, bool* dangerous);
+  bool ok_to_do_nullmove(const Position& pos);
+  bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d);
   bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
-  bool ok_to_history(const Position &pos, Move m);
+  bool ok_to_history(const Position& pos, Move m);
   void update_history(const Position& pos, Move m, Depth depth, Move movesSearched[], int moveCount);
   void update_killers(Move m, SearchStack& ss);
+  void slowdown(const Position& pos);
 
   bool fail_high_ply_1();
   int current_search_time();
@@ -296,13 +315,13 @@ namespace {
   void print_current_line(SearchStack ss[], int ply, int threadID);
   void wait_for_stop_or_ponderhit();
 
-  void idle_loop(int threadID, SplitPoint *waitSp);
+  void idle_loop(int threadID, SplitPoint* waitSp);
   void init_split_point_stack();
   void destroy_split_point_stack();
   bool thread_should_stop(int threadID);
   bool thread_is_available(int slave, int master);
   bool idle_thread_exists(int master);
-  bool split(const Position &pos, SearchStack *ss, int ply,
+  bool split(const Position& pos, SearchStack* ss, int ply,
              Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
              MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode);
   void wake_sleeping_threads();
@@ -316,53 +335,16 @@ namespace {
 }
 
 
-////
-//// Global variables
-////
-
-// The main transposition table
-TranspositionTable TT;
-
-
-// Number of active threads:
-int ActiveThreads = 1;
-
-// Locks.  In principle, there is no need for IOLock to be a global variable,
-// but it could turn out to be useful for debugging.
-Lock IOLock;
-
-History H;  // Should be made local?
-
-// The empty search stack
-SearchStack EmptySearchStack;
-
-
-// SearchStack::init() initializes a search stack. Used at the beginning of a
-// new search from the root.
-void SearchStack::init(int ply) {
-
-  pv[ply] = pv[ply + 1] = MOVE_NONE;
-  currentMove = threatMove = MOVE_NONE;
-  reduction = Depth(0);
-}
-
-void SearchStack::initKillers() {
-
-  mateKiller = MOVE_NONE;
-  for (int i = 0; i < KILLER_MAX; i++)
-      killers[i] = MOVE_NONE;
-}
-
-
 ////
 //// Functions
 ////
 
 /// 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()
+/// 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.
 
-void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
+bool think(const Position& pos, bool infinite, bool ponder, int side_to_move,
            int time[], int increment[], int movesToGo, int maxDepth,
            int maxNodes, int maxTime, Move searchMoves[]) {
 
@@ -371,22 +353,19 @@ void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
   {
       Move bookMove;
       if (get_option_value_string("Book File") != OpeningBook.file_name())
-      {
-          OpeningBook.close();
           OpeningBook.open("book.bin");
-      }
+
       bookMove = OpeningBook.get_move(pos);
       if (bookMove != MOVE_NONE)
       {
           std::cout << "bestmove " << bookMove << std::endl;
-          return;
+          return true;
       }
   }
 
   // Initialize global search variables
   Idle = false;
   SearchStartTime = get_system_time();
-  EasyMove = MOVE_NONE;
   for (int i = 0; i < THREAD_MAX; i++)
   {
       Threads[i].nodes = 0ULL;
@@ -406,9 +385,12 @@ void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
   // Read UCI option values
   TT.set_size(get_option_value_int("Hash"));
   if (button_was_pressed("Clear Hash"))
+  {
       TT.clear();
+      loseOnTime = false; // reset at the beginning of a new game
+  }
 
-  PonderingEnabled = get_option_value_bool("Ponder");
+  bool PonderingEnabled = get_option_value_bool("Ponder");
   MultiPV = get_option_value_int("MultiPV");
 
   CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
@@ -429,9 +411,9 @@ void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
   MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
   MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
 
-  LMRPVMoves     = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
-  LMRNonPVMoves  = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
-  ThreatDepth    = get_option_value_int("Threat Depth") * OnePly;
+  LMRPVMoves    = get_option_value_int("Full Depth Moves (PV nodes)") + 1;
+  LMRNonPVMoves = get_option_value_int("Full Depth Moves (non-PV nodes)") + 1;
+  ThreatDepth   = get_option_value_int("Threat Depth") * OnePly;
 
   Chess960 = get_option_value_bool("UCI_Chess960");
   ShowCurrentLine = get_option_value_bool("UCI_ShowCurrLine");
@@ -439,32 +421,41 @@ void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
   if (UseLogFile)
       LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
 
-  UseQSearchFutilityPruning = get_option_value_bool("Futility Pruning (Quiescence Search)");
-  UseFutilityPruning = get_option_value_bool("Futility Pruning (Main Search)");
-
-  UseLSNFiltering = get_option_value_bool("LSN filtering");
-  LSNTime = get_option_value_int("LSN Time Margin (sec)") * 1000;
-  LSNValue = value_from_centipawns(get_option_value_int("LSN Value Margin"));
-
   MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
   MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
 
   read_weights(pos.side_to_move());
 
-  int newActiveThreads = get_option_value_int("Threads");
+  // Set the number of active threads. If UCI_LimitStrength is enabled, never
+  // use more than one thread.
+  int newActiveThreads =
+    get_option_value_bool("UCI_LimitStrength")? 1 : get_option_value_int("Threads");
   if (newActiveThreads != ActiveThreads)
   {
       ActiveThreads = newActiveThreads;
       init_eval(ActiveThreads);
   }
 
-  // Wake up sleeping threads:
+  // Wake up sleeping threads
   wake_sleeping_threads();
 
   for (int i = 1; i < ActiveThreads; i++)
       assert(thread_is_available(i, 0));
 
-  // Set thinking time:
+  // Set playing strength
+  if (get_option_value_bool("UCI_LimitStrength"))
+  {
+      Strength = (get_option_value_int("UCI_Elo") - 2100) / 25;
+      Slowdown =
+        (Strength == MaxStrength)? 0 : SlowdownArray[Max(0, 31-Strength)];
+  }
+  else
+  {
+      Strength = MaxStrength;
+      Slowdown = 0;
+  }
+
+  // Set thinking time
   int myTime = time[side_to_move];
   int myIncrement = increment[side_to_move];
 
@@ -508,33 +499,40 @@ void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
       NodesBetweenPolls = Min(MaxNodes, 30000);
       InfiniteSearch = true; // HACK
   }
+  else if (Slowdown) {
+      if (Slowdown > 50000) NodesBetweenPolls = 30;
+      else if (Slowdown > 10000) NodesBetweenPolls = 100;
+      else if (Slowdown > 1000) NodesBetweenPolls = 500;
+      else if (Slowdown > 100) NodesBetweenPolls = 3000;
+      else NodesBetweenPolls = 15000;
+  }
   else
       NodesBetweenPolls = 30000;
 
-
-  // Write information to search log file:
+  // Write information to search log file
   if (UseLogFile)
       LogFile << "Searching: " << pos.to_fen() << std::endl
-              << "infinite: " << infinite
-              << " ponder: " << ponder
-              << " time: " << myTime
+              << "infinite: "  << infinite
+              << " ponder: "   << ponder
+              << " time: "     << myTime
               << " increment: " << myIncrement
               << " moves to go: " << movesToGo << std::endl;
 
 
-  // We're ready to start thinking.  Call the iterative deepening loop
-  // function:
-  if (!looseOnTime)
+  // We're ready to start thinking. Call the iterative deepening loop function
+  //
+  // FIXME we really need to cleanup all this LSN ugliness
+  if (!loseOnTime)
   {
       Value v = id_loop(pos, searchMoves);
-      looseOnTime = (   UseLSNFiltering
+      loseOnTime = (   UseLSNFiltering
                      && myTime < LSNTime
                      && myIncrement == 0
                      && v < -LSNValue);
   }
   else
   {
-      looseOnTime = false; // reset for next match
+      loseOnTime = false; // reset for next match
       while (SearchStartTime + myTime + 1000 > get_system_time())
           ; // wait here
       id_loop(pos, searchMoves); // to fail gracefully
@@ -543,14 +541,8 @@ void think(const Position &pos, bool infinite, bool ponder, int side_to_move,
   if (UseLogFile)
       LogFile.close();
 
-  if (Quit)
-  {
-      OpeningBook.close();
-      stop_threads();
-      quit_eval();
-      exit(0);
-  }
   Idle = true;
+  return !Quit;
 }
 
 
@@ -569,7 +561,7 @@ void init_threads() {
   for (i = 0; i < THREAD_MAX; i++)
       Threads[i].activeSplitPoints = 0;
 
-  // Initialize global locks:
+  // Initialize global locks
   lock_init(&MPLock, NULL);
   lock_init(&IOLock, NULL);
 
@@ -602,13 +594,9 @@ void init_threads() {
       CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, iID);
 #endif
 
-      // Wait until the thread has finished launching:
+      // Wait until the thread has finished launching
       while (!Threads[i].running);
   }
-
-  // Init also the empty search stack
-  EmptySearchStack.init(0);
-  EmptySearchStack.initKillers();
 }
 
 
@@ -642,6 +630,22 @@ int64_t nodes_searched() {
 }
 
 
+// SearchStack::init() initializes a search stack. Used at the beginning of a
+// new search from the root.
+void SearchStack::init(int ply) {
+
+  pv[ply] = pv[ply + 1] = MOVE_NONE;
+  currentMove = threatMove = MOVE_NONE;
+  reduction = Depth(0);
+}
+
+void SearchStack::initKillers() {
+
+  mateKiller = MOVE_NONE;
+  for (int i = 0; i < KILLER_MAX; i++)
+      killers[i] = MOVE_NONE;
+}
+
 namespace {
 
   // id_loop() is the main iterative deepening loop.  It calls root_search
@@ -649,7 +653,7 @@ namespace {
   // been consumed, the user stops the search, or the maximum search depth is
   // reached.
 
-  Value id_loop(const Position &pos, Move searchMoves[]) {
+  Value id_loop(const Position& pos, Move searchMoves[]) {
 
     Position p(pos);
     SearchStack ss[PLY_MAX_PLUS_2];
@@ -668,7 +672,7 @@ namespace {
     IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
     Iteration = 1;
 
-    EasyMove = rml.scan_for_easy_move();
+    Move EasyMove = rml.scan_for_easy_move();
 
     // Iterative deepening loop
     while (Iteration < PLY_MAX)
@@ -685,7 +689,7 @@ namespace {
         // Calculate dynamic search window based on previous iterations
         Value alpha, beta;
 
-        if (MultiPV == 1 && Iteration >= 6)
+        if (MultiPV == 1 && Iteration >= 6 && abs(IterationInfo[Iteration - 1].value) < VALUE_KNOWN_WIN)
         {
             int prevDelta1 = IterationInfo[Iteration - 1].speculatedValue - IterationInfo[Iteration - 2].speculatedValue;
             int prevDelta2 = IterationInfo[Iteration - 2].speculatedValue - IterationInfo[Iteration - 3].speculatedValue;
@@ -750,7 +754,7 @@ namespace {
             // Time to stop?
             bool stopSearch = false;
 
-            // Stop search early if there is only a single legal move:
+            // Stop search early if there is only a single legal move
             if (Iteration >= 6 && rml.move_count() == 1)
                 stopSearch = true;
 
@@ -848,7 +852,7 @@ namespace {
   // scheme (perhaps we should try to use this at internal PV nodes, too?)
   // and prints some information to the standard output.
 
-  Value root_search(Position &pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta) {
+  Value root_search(Position& pos, SearchStack ss[], RootMoveList &rml, Value alpha, Value beta) {
 
     Value oldAlpha = alpha;
     Value value;
@@ -888,8 +892,9 @@ namespace {
                       << " currmovenumber " << i + 1 << std::endl;
 
         // Decide search depth for this move
+        bool moveIsCapture = pos.move_is_capture(move);
         bool dangerous;
-        ext = extension(pos, move, true, pos.move_is_capture(move), pos.move_is_check(move), false, false, &dangerous);
+        ext = extension(pos, move, true, moveIsCapture, pos.move_is_check(move), false, false, &dangerous);
         newDepth = (Iteration - 2) * OnePly + ext + InitialDepth;
 
         // Make the move, and search it
@@ -897,6 +902,10 @@ namespace {
 
         if (i < MultiPV)
         {
+            // Aspiration window is disabled in multi-pv case
+            if (MultiPV > 1)
+                alpha = -VALUE_INFINITE;
+
             value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
             // If the value has dropped a lot compared to the last iteration,
             // set the boolean variable Problem to true. This variable is used
@@ -909,15 +918,30 @@ namespace {
         }
         else
         {
-            value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
+            if (   newDepth >= 3*OnePly
+                && i >= MultiPV + LMRPVMoves - 2 // Remove -2 and decrease LMRPVMoves instead ?
+                && !dangerous
+                && !moveIsCapture
+                && !move_is_promotion(move)
+                && !move_is_castle(move))
+            {
+                ss[0].reduction = OnePly;
+                value = -search(pos, ss, -alpha, newDepth-OnePly, 1, true, 0);
+            } else
+                value = alpha + 1; // Just to trigger next condition
+
             if (value > alpha)
             {
-                // Fail high! Set the boolean variable FailHigh to true, and
-                // re-search the move with a big window. The variable FailHigh is
-                // used for time managment: We try to avoid aborting the search
-                // prematurely during a fail high research.
-                FailHigh = true;
-                value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
+                value = -search(pos, ss, -alpha, newDepth, 1, true, 0);
+                if (value > alpha)
+                {
+                    // Fail high! Set the boolean variable FailHigh to true, and
+                    // re-search the move with a big window. The variable FailHigh is
+                    // used for time managment: We try to avoid aborting the search
+                    // prematurely during a fail high research.
+                    FailHigh = true;
+                    value = -search_pv(pos, ss, -beta, -alpha, newDepth, 1, 0);
+                }
             }
         }
 
@@ -951,6 +975,7 @@ namespace {
             // Update PV
             rml.set_move_score(i, value);
             update_pv(ss, 0);
+            TT.extract_pv(pos, ss[0].pv);
             rml.set_move_pv(i, ss[0].pv);
 
             if (MultiPV == 1)
@@ -961,9 +986,11 @@ namespace {
                 if (i > 0)
                     BestMoveChangesByIteration[Iteration]++;
 
-                // Print search information to the standard output:
+                // Print search information to the standard output
                 std::cout << "info depth " << Iteration
                           << " score " << value_to_string(value)
+                          << ((value >= beta)?
+                              " lowerbound" : ((value <= alpha)? " upperbound" : ""))
                           << " time " << current_search_time()
                           << " nodes " << nodes_searched()
                           << " nps " << nps()
@@ -1019,7 +1046,7 @@ namespace {
 
   // search_pv() is the main search function for PV nodes.
 
-  Value search_pv(Position &pos, SearchStack ss[], Value alpha, Value beta,
+  Value search_pv(Position& pos, SearchStack ss[], Value alpha, Value beta,
                   Depth depth, int ply, int threadID) {
 
     assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
@@ -1032,7 +1059,7 @@ namespace {
 
     // Initialize, and make an early exit in case of an aborted search,
     // an instant draw, maximum ply reached, etc.
-    init_node(ss, ply, threadID);
+    init_node(pos, ss, ply, threadID);
 
     // After init_node() that calls poll()
     if (AbortSearch || thread_should_stop(threadID))
@@ -1055,7 +1082,7 @@ namespace {
 
     // Transposition table lookup. At PV nodes, we don't use the TT for
     // pruning, but only for move ordering.
-    const TTEntry* tte = TT.retrieve(pos);
+    const TTEntry* tte = TT.retrieve(pos.get_key());
     Move ttMove = (tte ? tte->move() : MOVE_NONE);
 
     // Go with internal iterative deepening if we don't have a TT move
@@ -1067,7 +1094,7 @@ namespace {
 
     // Initialize a MovePicker object for the current position, and prepare
     // to search all moves
-    MovePicker mp = MovePicker(pos, true, ttMove, ss[ply], depth);
+    MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
 
     Move move, movesSearched[256];
     int moveCount = 0;
@@ -1106,11 +1133,11 @@ namespace {
       {
         // Try to reduce non-pv search depth by one ply if move seems not problematic,
         // if the move fails high will be re-searched at full depth.
-        if (    depth >= 2*OnePly
+        if (    depth >= 3*OnePly
             &&  moveCount >= LMRPVMoves
             && !dangerous
             && !moveIsCapture
-            && !move_promotion(move)
+            && !move_is_promotion(move)
             && !move_is_castle(move)
             && !move_is_killer(move, ss[ply]))
         {
@@ -1157,7 +1184,7 @@ namespace {
           }
           // If we are at ply 1, and we are searching the first root move at
           // ply 0, set the 'Problem' variable if the score has dropped a lot
-          // (from the computer's point of view) since the previous iteration:
+          // (from the computer's point of view) since the previous iteration.
           if (   ply == 1
               && Iteration >= 2
               && -value <= IterationInfo[Iteration-1].value - ProblemMargin)
@@ -1178,7 +1205,7 @@ namespace {
     }
 
     // All legal moves have been searched.  A special case: If there were
-    // no legal moves, it must be mate or stalemate:
+    // no legal moves, it must be mate or stalemate.
     if (moveCount == 0)
         return (isCheck ? value_mated_in(ply) : VALUE_DRAW);
 
@@ -1188,7 +1215,7 @@ namespace {
         return bestValue;
 
     if (bestValue <= oldAlpha)
-        TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
+        TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
 
     else if (bestValue >= beta)
     {
@@ -1199,10 +1226,10 @@ namespace {
             update_history(pos, m, depth, movesSearched, moveCount);
             update_killers(m, ss[ply]);
         }
-        TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
+        TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
     }
     else
-        TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
+        TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EXACT, depth, ss[ply].pv[ply]);
 
     return bestValue;
   }
@@ -1210,7 +1237,7 @@ namespace {
 
   // search() is the search function for zero-width nodes.
 
-  Value search(Position &pos, SearchStack ss[], Value beta, Depth depth,
+  Value search(Position& pos, SearchStack ss[], Value beta, Depth depth,
                int ply, bool allowNullmove, int threadID) {
 
     assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
@@ -1222,7 +1249,7 @@ namespace {
 
     // Initialize, and make an early exit in case of an aborted search,
     // an instant draw, maximum ply reached, etc.
-    init_node(ss, ply, threadID);
+    init_node(pos, ss, ply, threadID);
 
     // After init_node() that calls poll()
     if (AbortSearch || thread_should_stop(threadID))
@@ -1244,7 +1271,7 @@ namespace {
         return beta - 1;
 
     // Transposition table lookup
-    const TTEntry* tte = TT.retrieve(pos);
+    const TTEntry* tte = TT.retrieve(pos.get_key());
     Move ttMove = (tte ? tte->move() : MOVE_NONE);
 
     if (tte && ok_to_use_TT(tte, depth, beta, ply))
@@ -1275,11 +1302,7 @@ namespace {
 
         pos.undo_null_move();
 
-        if (value_is_mate(nullValue))
-        {
-            /* Do not return unproven mates */
-        }
-        else if (nullValue >= beta)
+        if (nullValue >= beta)
         {
             if (depth < 6 * OnePly)
                 return beta;
@@ -1309,6 +1332,7 @@ namespace {
     else if (   !value_is_mate(beta)
              && depth < RazorDepth
              && approximateEval < beta - RazorApprMargins[int(depth) - 2]
+             && ss[ply - 1].currentMove != MOVE_NULL
              && ttMove == MOVE_NONE
              && !pos.has_pawn_on_7th(pos.side_to_move()))
     {
@@ -1326,16 +1350,15 @@ namespace {
     }
 
     // Initialize a MovePicker object for the current position, and prepare
-    // to search all moves:
-    MovePicker mp = MovePicker(pos, false, ttMove, ss[ply], depth);
+    // to search all moves.
+    MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
 
     Move move, movesSearched[256];
     int moveCount = 0;
     Value value, bestValue = -VALUE_INFINITE;
     Bitboard dcCandidates = mp.discovered_check_candidates();
     Value futilityValue = VALUE_NONE;
-    bool useFutilityPruning =   UseFutilityPruning
-                             && depth < SelectiveDepth
+    bool useFutilityPruning =   depth < SelectiveDepth
                              && !isCheck;
 
     // Loop through all legal moves until no moves remain or a beta cutoff
@@ -1361,7 +1384,7 @@ namespace {
       if (    useFutilityPruning
           && !dangerous
           && !moveIsCapture
-          && !move_promotion(move))
+          && !move_is_promotion(move))
       {
           // History pruning. See ok_to_prune() definition
           if (   moveCount >= 2 + int(depth)
@@ -1390,11 +1413,11 @@ namespace {
 
       // Try to reduce non-pv search depth by one ply if move seems not problematic,
       // if the move fails high will be re-searched at full depth.
-      if (    depth >= 2*OnePly
+      if (    depth >= 3*OnePly
           &&  moveCount >= LMRNonPVMoves
           && !dangerous
           && !moveIsCapture
-          && !move_promotion(move)
+          && !move_is_promotion(move)
           && !move_is_castle(move)
           && !move_is_killer(move, ss[ply]))
       {
@@ -1448,7 +1471,7 @@ namespace {
         return bestValue;
 
     if (bestValue < beta)
-        TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
+        TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, depth, MOVE_NONE);
     else
     {
         BetaCounter.add(pos.side_to_move(), depth, threadID);
@@ -1458,7 +1481,7 @@ namespace {
             update_history(pos, m, depth, movesSearched, moveCount);
             update_killers(m, ss[ply]);
         }
-        TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
+        TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, depth, m);
     }
 
     assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
@@ -1471,7 +1494,7 @@ namespace {
   // search function when the remaining depth is zero (or, to be more precise,
   // less than OnePly).
 
-  Value qsearch(Position &pos, SearchStack ss[], Value alpha, Value beta,
+  Value qsearch(Position& pos, SearchStack ss[], Value alpha, Value beta,
                 Depth depth, int ply, int threadID) {
 
     assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
@@ -1482,7 +1505,7 @@ namespace {
 
     // Initialize, and make an early exit in case of an aborted search,
     // an instant draw, maximum ply reached, etc.
-    init_node(ss, ply, threadID);
+    init_node(pos, ss, ply, threadID);
 
     // After init_node() that calls poll()
     if (AbortSearch || thread_should_stop(threadID))
@@ -1496,7 +1519,7 @@ namespace {
     bool pvNode = (beta - alpha != 1);
     if (!pvNode)
     {
-        tte = TT.retrieve(pos);
+        tte = TT.retrieve(pos.get_key());
         if (tte && ok_to_use_TT(tte, depth, beta, ply))
         {
             assert(tte->type() != VALUE_TYPE_EVAL);
@@ -1518,7 +1541,6 @@ namespace {
     else if (tte && tte->type() == VALUE_TYPE_EVAL)
     {
         // Use the cached evaluation score if possible
-        assert(tte->value() == evaluate(pos, ei, threadID));
         assert(ei.futilityMargin == Value(0));
 
         staticValue = tte->value();
@@ -1537,7 +1559,7 @@ namespace {
     {
         // Store the score to avoid a future costly evaluation() call
         if (!isCheck && !tte && ei.futilityMargin == 0)
-            TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_EVAL, Depth(-127*OnePly), MOVE_NONE);
+            TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_EVAL, Depth(-127*OnePly), MOVE_NONE);
 
         return bestValue;
     }
@@ -1548,7 +1570,7 @@ namespace {
     // 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 == 0) will be generated.
-    MovePicker mp = MovePicker(pos, pvNode, ttMove, EmptySearchStack, depth);
+    MovePicker mp = MovePicker(pos, ttMove, depth, H);
     Move move;
     int moveCount = 0;
     Bitboard dcCandidates = mp.discovered_check_candidates();
@@ -1566,11 +1588,10 @@ namespace {
       ss[ply].currentMove = move;
 
       // Futility pruning
-      if (    UseQSearchFutilityPruning
-          &&  enoughMaterial
+      if (   enoughMaterial
           && !isCheck
           && !pvNode
-          && !move_promotion(move)
+          && !move_is_promotion(move)
           && !pos.move_is_check(move, dcCandidates)
           && !pos.move_is_passed_pawn_push(move))
       {
@@ -1591,10 +1612,8 @@ namespace {
 
       // Don't search captures and checks with negative SEE values
       if (   !isCheck
-          && !move_promotion(move)
-          && (pos.midgame_value_of_piece_on(move_from(move)) >
-              pos.midgame_value_of_piece_on(move_to(move)))
-          &&  pos.see(move) < 0)
+          && !move_is_promotion(move)
+          &&  pos.see_sign(move) < 0)
           continue;
 
       // Make and search the move.
@@ -1618,7 +1637,7 @@ namespace {
     }
 
     // All legal moves have been searched.  A special case: If we're in check
-    // and no legal moves were found, it is checkmate:
+    // and no legal moves were found, it is checkmate.
     if (pos.is_check() && moveCount == 0) // Mate!
         return value_mated_in(ply);
 
@@ -1630,9 +1649,9 @@ namespace {
     {
         Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
         if (bestValue < beta)
-            TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE);
+            TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_UPPER, d, MOVE_NONE);
         else
-            TT.store(pos, value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, m);
+            TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, d, m);
     }
 
     // Update killers only for good check moves
@@ -1651,18 +1670,17 @@ namespace {
   // also don't need to store anything to the hash table here:  This is taken
   // care of after we return from the split point.
 
-  void sp_search(SplitPoint *sp, int threadID) {
+  void sp_search(SplitPoint* sp, int threadID) {
 
     assert(threadID >= 0 && threadID < ActiveThreads);
     assert(ActiveThreads > 1);
 
     Position pos = Position(sp->pos);
-    SearchStack *ss = sp->sstack[threadID];
+    SearchStack* ss = sp->sstack[threadID];
     Value value;
     Move move;
     bool isCheck = pos.is_check();
-    bool useFutilityPruning =    UseFutilityPruning
-                              && sp->depth < SelectiveDepth
+    bool useFutilityPruning =     sp->depth < SelectiveDepth
                               && !isCheck;
 
     while (    sp->bestValue < sp->beta
@@ -1689,7 +1707,7 @@ namespace {
       if (    useFutilityPruning
           && !dangerous
           && !moveIsCapture
-          && !move_promotion(move)
+          && !move_is_promotion(move)
           &&  moveCount >= 2 + int(sp->depth)
           &&  ok_to_prune(pos, move, ss[sp->ply].threatMove, sp->depth))
         continue;
@@ -1703,7 +1721,7 @@ namespace {
       if (   !dangerous
           &&  moveCount >= LMRNonPVMoves
           && !moveIsCapture
-          && !move_promotion(move)
+          && !move_is_promotion(move)
           && !move_is_castle(move)
           && !move_is_killer(move, ss[sp->ply]))
       {
@@ -1746,7 +1764,7 @@ namespace {
     lock_grab(&(sp->lock));
 
     // If this is the master thread and we have been asked to stop because of
-    // a beta cutoff higher up in the tree, stop all slave threads:
+    // a beta cutoff higher up in the tree, stop all slave threads.
     if (sp->master == threadID && thread_should_stop(threadID))
         for (int i = 0; i < ActiveThreads; i++)
             if (sp->slaves[i])
@@ -1764,16 +1782,16 @@ namespace {
   // the normal search_pv() function, but simpler.  Because we have already
   // probed the hash table and searched the first move before splitting, we
   // don't have to repeat all this work in sp_search_pv().  We also don't
-  // need to store anything to the hash table here:  This is taken care of
+  // need to store anything to the hash table here: This is taken care of
   // after we return from the split point.
 
-  void sp_search_pv(SplitPoint *sp, int threadID) {
+  void sp_search_pv(SplitPoint* sp, int threadID) {
 
     assert(threadID >= 0 && threadID < ActiveThreads);
     assert(ActiveThreads > 1);
 
     Position pos = Position(sp->pos);
-    SearchStack *ss = sp->sstack[threadID];
+    SearchStack* ss = sp->sstack[threadID];
     Value value;
     Move move;
 
@@ -1806,7 +1824,7 @@ namespace {
       if (   !dangerous
           &&  moveCount >= LMRPVMoves
           && !moveIsCapture
-          && !move_promotion(move)
+          && !move_is_promotion(move)
           && !move_is_castle(move)
           && !move_is_killer(move, ss[sp->ply]))
       {
@@ -1825,7 +1843,7 @@ namespace {
           {
               // When the search fails high at ply 1 while searching the first
               // move at the root, set the flag failHighPly1.  This is used for
-              // time managment:  We don't want to stop the search early in
+              // time managment: We don't want to stop the search early in
               // such cases, because resolving the fail high at ply 1 could
               // result in a big drop in score at the root.
               if (sp->ply == 1 && RootMoveNumber == 1)
@@ -1854,10 +1872,10 @@ namespace {
               if (value == value_mate_in(sp->ply + 1))
                   ss[sp->ply].mateKiller = move;
 
-              if(value >= sp->beta)
+              if (value >= sp->beta)
               {
-                  for(int i = 0; i < ActiveThreads; i++)
-                      if(i != threadID && (i == sp->master || sp->slaves[i]))
+                  for (int i = 0; i < ActiveThreads; i++)
+                      if (i != threadID && (i == sp->master || sp->slaves[i]))
                           Threads[i].stop = true;
 
                   sp->finished = true;
@@ -1896,13 +1914,13 @@ namespace {
   void BetaCounterType::clear() {
 
     for (int i = 0; i < THREAD_MAX; i++)
-        hits[i][WHITE] = hits[i][BLACK] = 0ULL;
+        Threads[i].betaCutOffs[WHITE] = Threads[i].betaCutOffs[BLACK] = 0ULL;
   }
 
   void BetaCounterType::add(Color us, Depth d, int threadID) {
 
     // Weighted count based on depth
-    hits[threadID][us] += int(d);
+    Threads[threadID].betaCutOffs[us] += unsigned(d);
   }
 
   void BetaCounterType::read(Color us, int64_t& our, int64_t& their) {
@@ -1910,8 +1928,8 @@ namespace {
     our = their = 0UL;
     for (int i = 0; i < THREAD_MAX; i++)
     {
-        our += hits[i][us];
-        their += hits[i][opposite_color(us)];
+        our += Threads[i].betaCutOffs[us];
+        their += Threads[i].betaCutOffs[opposite_color(us)];
     }
   }
 
@@ -1921,7 +1939,7 @@ namespace {
   // Constructor
 
   RootMove::RootMove() {
-    nodes = cumulativeNodes = 0ULL;
+    nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL;
   }
 
   // RootMove::operator<() is the comparison function used when
@@ -1957,22 +1975,20 @@ namespace {
         for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
             includeMove = (searchMoves[k] == mlist[i].move);
 
-        if (includeMove)
-        {
-            // Find a quick score for the move
-            StateInfo st;
-            SearchStack ss[PLY_MAX_PLUS_2];
-
-            moves[count].move = mlist[i].move;
-            moves[count].nodes = 0ULL;
-            pos.do_move(moves[count].move, st);
-            moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE,
-                                          Depth(0), 1, 0);
-            pos.undo_move(moves[count].move);
-            moves[count].pv[0] = moves[i].move;
-            moves[count].pv[1] = MOVE_NONE; // FIXME
-            count++;
-        }
+        if (!includeMove)
+            continue;
+
+        // Find a quick score for the move
+        StateInfo st;
+        SearchStack ss[PLY_MAX_PLUS_2];
+
+        moves[count].move = mlist[i].move;
+        pos.do_move(moves[count].move, st);
+        moves[count].score = -qsearch(pos, ss, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1, 0);
+        pos.undo_move(moves[count].move);
+        moves[count].pv[0] = moves[count].move;
+        moves[count].pv[1] = MOVE_NONE; // FIXME
+        count++;
     }
     sort();
   }
@@ -2076,25 +2092,30 @@ namespace {
   // NodesBetweenPolls nodes, init_node() also calls poll(), which polls
   // for user input and checks whether it is time to stop the search.
 
-  void init_node(SearchStack ss[], int ply, int threadID) {
+  void init_node(const Position& pos, SearchStack ss[], int ply, int threadID) {
+
     assert(ply >= 0 && ply < PLY_MAX);
     assert(threadID >= 0 && threadID < ActiveThreads);
 
+    if (Slowdown && Iteration >= 3)
+      slowdown(pos);
+
     Threads[threadID].nodes++;
 
-    if(threadID == 0) {
-      NodesSincePoll++;
-      if(NodesSincePoll >= NodesBetweenPolls) {
-        poll();
-        NodesSincePoll = 0;
-      }
+    if (threadID == 0)
+    {
+        NodesSincePoll++;
+        if (NodesSincePoll >= NodesBetweenPolls)
+        {
+            poll();
+            NodesSincePoll = 0;
+        }
     }
-
     ss[ply].init(ply);
     ss[ply+2].initKillers();
 
-    if(Threads[threadID].printCurrentLine)
-      print_current_line(ss, ply, threadID);
+    if (Threads[threadID].printCurrentLine)
+        print_current_line(ss, ply, threadID);
   }
 
 
@@ -2117,7 +2138,7 @@ namespace {
   // difference between the two functions is that sp_update_pv also updates
   // the PV at the parent node.
 
-  void sp_update_pv(SearchStack *pss, SearchStack ss[], int ply) {
+  void sp_update_pv(SearchStack* pss, SearchStack ss[], int ply) {
     assert(ply >= 0 && ply < PLY_MAX);
 
     ss[ply].pv[ply] = pss[ply].pv[ply] = ss[ply].currentMove;
@@ -2134,62 +2155,62 @@ namespace {
   // 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) {
+  bool connected_moves(const Position& pos, Move m1, Move m2) {
     Square f1, t1, f2, t2;
 
     assert(move_is_ok(m1));
     assert(move_is_ok(m2));
 
-    if(m2 == MOVE_NONE)
-      return false;
+    if (m2 == MOVE_NONE)
+        return false;
 
-    // Case 1: The moving piece is the same in both moves.
+    // Case 1: The moving piece is the same in both moves
     f2 = move_from(m2);
     t1 = move_to(m1);
-    if(f2 == t1)
-      return true;
+    if (f2 == t1)
+        return true;
 
-    // Case 2: The destination square for m2 was vacated by m1.
+    // Case 2: The destination square for m2 was vacated by m1
     t2 = move_to(m2);
     f1 = move_from(m1);
-    if(t2 == f1)
-      return true;
+    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))
+    // 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 attacked by the moving piece
-    // in m1:
-    if(pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
-      return true;
+    // Case 4: The destination square for m2 is attacked by the moving piece in m1
+    if (pos.piece_attacks_square(pos.piece_on(t1), t1, t2))
+        return true;
 
-    // Case 5: Discovered check, checking piece is the piece moved in m1:
-    if(piece_is_slider(pos.piece_on(t1)) &&
-       bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())),
-                  f2) &&
-       !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())),
-                   t2)) {
-      Bitboard occ = pos.occupied_squares();
-      Color us = pos.side_to_move();
-      Square ksq = pos.king_square(us);
-      clear_bit(&occ, f2);
-      if(pos.type_of_piece_on(t1) == BISHOP) {
-        if(bit_is_set(bishop_attacks_bb(ksq, occ), t1))
-          return true;
-      }
-      else if(pos.type_of_piece_on(t1) == ROOK) {
-        if(bit_is_set(rook_attacks_bb(ksq, occ), t1))
-          return true;
-      }
-      else {
-        assert(pos.type_of_piece_on(t1) == QUEEN);
-        if(bit_is_set(queen_attacks_bb(ksq, occ), t1))
-          return true;
-      }
+    // Case 5: Discovered check, checking piece is the piece moved in m1
+    if (   piece_is_slider(pos.piece_on(t1))
+        && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
+        && !bit_is_set(squares_between(t2, pos.king_square(pos.side_to_move())), t2))
+    {
+        Bitboard occ = pos.occupied_squares();
+        Color us = pos.side_to_move();
+        Square ksq = pos.king_square(us);
+        clear_bit(&occ, f2);
+        if (pos.type_of_piece_on(t1) == BISHOP)
+        {
+            if (bit_is_set(bishop_attacks_bb(ksq, occ), t1))
+                return true;
+        }
+        else if (pos.type_of_piece_on(t1) == ROOK)
+        {
+            if (bit_is_set(rook_attacks_bb(ksq, occ), t1))
+                return true;
+        }
+        else
+        {
+            assert(pos.type_of_piece_on(t1) == QUEEN);
+            if (bit_is_set(queen_attacks_bb(ksq, occ), t1))
+                return true;
+        }
     }
-
     return false;
   }
 
@@ -2233,16 +2254,19 @@ namespace {
     assert(m != MOVE_NONE);
 
     Depth result = Depth(0);
-    *dangerous = check || singleReply || mateThreat;
+    *dangerous = check | singleReply | mateThreat;
 
-    if (check)
-        result += CheckExtension[pvNode];
+    if (*dangerous)
+    {
+        if (check)
+            result += CheckExtension[pvNode];
 
-    if (singleReply)
-        result += SingleReplyExtension[pvNode];
+        if (singleReply)
+            result += SingleReplyExtension[pvNode];
 
-    if (mateThreat)
-        result += MateThreatExtension[pvNode];
+        if (mateThreat)
+            result += MateThreatExtension[pvNode];
+    }
 
     if (pos.type_of_piece_on(move_from(m)) == PAWN)
     {
@@ -2262,7 +2286,7 @@ namespace {
         && 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(0))
-        && !move_promotion(m)
+        && !move_is_promotion(m)
         && !move_is_ep(m))
     {
         result += PawnEndgameExtension[pvNode];
@@ -2272,7 +2296,7 @@ namespace {
     if (   pvNode
         && capture
         && pos.type_of_piece_on(move_to(m)) != PAWN
-        && pos.see(m) >= 0)
+        && pos.see_sign(m) >= 0)
     {
         result += OnePly/2;
         *dangerous = true;
@@ -2290,10 +2314,9 @@ namespace {
   // probably a good idea to avoid null moves in at least some more
   // complicated endgames, e.g. KQ vs KR.  FIXME
 
-  bool ok_to_do_nullmove(const Position &pos) {
-    if(pos.non_pawn_material(pos.side_to_move()) == Value(0))
-      return false;
-    return true;
+  bool ok_to_do_nullmove(const Position& pos) {
+
+    return pos.non_pawn_material(pos.side_to_move()) != Value(0);
   }
 
 
@@ -2301,23 +2324,24 @@ namespace {
   // non-tactical moves late in the move list close to the leaves are
   // candidates for pruning.
 
-  bool ok_to_prune(const Position &pos, Move m, Move threat, Depth d) {
-    Square mfrom, mto, tfrom, tto;
+  bool ok_to_prune(const Position& pos, Move m, Move threat, Depth d) {
 
     assert(move_is_ok(m));
     assert(threat == MOVE_NONE || move_is_ok(threat));
-    assert(!move_promotion(m));
+    assert(!move_is_promotion(m));
     assert(!pos.move_is_check(m));
     assert(!pos.move_is_capture(m));
     assert(!pos.move_is_passed_pawn_push(m));
     assert(d >= OnePly);
 
+    Square mfrom, mto, tfrom, tto;
+
     mfrom = move_from(m);
     mto = move_to(m);
     tfrom = move_from(threat);
     tto = move_to(threat);
 
-    // Case 1: Castling moves are never pruned.
+    // Case 1: Castling moves are never pruned
     if (move_is_castle(m))
         return false;
 
@@ -2333,10 +2357,10 @@ namespace {
         && (   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 false;
+        return false;
 
-    // Case 4: Don't prune moves with good history.
-    if (!H.ok_to_prune(pos.piece_on(move_from(m)), m, d))
+    // Case 4: Don't prune moves with good history
+    if (!H.ok_to_prune(pos.piece_on(mfrom), mto, d))
         return false;
 
     // Case 5: If the moving piece in the threatened move is a slider, don't
@@ -2345,8 +2369,8 @@ namespace {
         && threat != MOVE_NONE
         && piece_is_slider(pos.piece_on(tfrom))
         && bit_is_set(squares_between(tfrom, tto), mto)
-        && pos.see(m) >= 0)
-            return false;
+        && pos.see_sign(m) >= 0)
+        return false;
 
     return true;
   }
@@ -2373,7 +2397,7 @@ namespace {
 
   bool ok_to_history(const Position& pos, Move m) {
 
-    return !pos.move_is_capture(m) && !move_promotion(m);
+    return !pos.move_is_capture(m) && !move_is_promotion(m);
   }
 
 
@@ -2383,13 +2407,13 @@ namespace {
   void update_history(const Position& pos, Move m, Depth depth,
                       Move movesSearched[], int moveCount) {
 
-    H.success(pos.piece_on(move_from(m)), m, depth);
+    H.success(pos.piece_on(move_from(m)), move_to(m), depth);
 
     for (int i = 0; i < moveCount - 1; i++)
     {
         assert(m != movesSearched[i]);
         if (ok_to_history(pos, movesSearched[i]))
-            H.failure(pos.piece_on(move_from(movesSearched[i])), movesSearched[i]);
+            H.failure(pos.piece_on(move_from(movesSearched[i])), move_to(movesSearched[i]));
     }
   }
 
@@ -2408,14 +2432,31 @@ namespace {
     ss.killers[0] = m;
   }
 
+
+  // slowdown() simply wastes CPU cycles doing nothing useful. It's used
+  // in strength handicap mode.
+
+  void slowdown(const Position &pos) {
+    int i, n;
+    n = Slowdown;
+    for (i = 0; i < n; i++)  {
+        Square s = Square(i&63);
+        if (count_1s(pos.attacks_to(s)) > 63)
+            std::cout << "This can't happen, but I put this string here anyway, in order to prevent the compiler from optimizing away the useless computation." << std::endl;
+    }
+  }
+
+
   // fail_high_ply_1() checks if some thread is currently resolving a fail
   // high at ply 1 at the node below the first root node.  This information
   // is used for time managment.
 
   bool fail_high_ply_1() {
+
     for(int i = 0; i < ActiveThreads; i++)
-      if(Threads[i].failHighPly1)
-        return true;
+        if (Threads[i].failHighPly1)
+            return true;
+
     return false;
   }
 
@@ -2458,13 +2499,14 @@ namespace {
             AbortSearch = true;
             PonderSearch = false;
             Quit = true;
+            return;
         }
-        else if(command == "stop")
+        else if (command == "stop")
         {
             AbortSearch = true;
             PonderSearch = false;
         }
-        else if(command == "ponderhit")
+        else if (command == "ponderhit")
             ponderhit();
     }
     // Print search information
@@ -2513,9 +2555,10 @@ namespace {
   // it correctly predicted the opponent's move.
 
   void ponderhit() {
+
     int t = current_search_time();
     PonderSearch = false;
-    if(Iteration >= 3 &&
+    if (Iteration >= 3 &&
        (!InfiniteSearch && (StopOnPonderhit ||
                             t > AbsoluteMaxSearchTime ||
                             (RootMoveNumber == 1 &&
@@ -2530,20 +2573,23 @@ namespace {
   // thread.  Called when the UCI option UCI_ShowCurrLine is 'true'.
 
   void print_current_line(SearchStack ss[], int ply, int threadID) {
+
     assert(ply >= 0 && ply < PLY_MAX);
     assert(threadID >= 0 && threadID < ActiveThreads);
 
-    if(!Threads[threadID].idle) {
-      lock_grab(&IOLock);
-      std::cout << "info currline " << (threadID + 1);
-      for(int p = 0; p < ply; p++)
-        std::cout << " " << ss[p].currentMove;
-      std::cout << std::endl;
-      lock_release(&IOLock);
+    if (!Threads[threadID].idle)
+    {
+        lock_grab(&IOLock);
+        std::cout << "info currline " << (threadID + 1);
+        for (int p = 0; p < ply; p++)
+            std::cout << " " << ss[p].currentMove;
+
+        std::cout << std::endl;
+        lock_release(&IOLock);
     }
     Threads[threadID].printCurrentLine = false;
-    if(threadID + 1 < ActiveThreads)
-      Threads[threadID + 1].printCurrentLine = true;
+    if (threadID + 1 < ActiveThreads)
+        Threads[threadID + 1].printCurrentLine = true;
   }
 
 
@@ -2555,20 +2601,21 @@ namespace {
   // after which the bestmove and pondermove will be printed (in id_loop()).
 
   void wait_for_stop_or_ponderhit() {
+
     std::string command;
 
-    while(true) {
-      if(!std::getline(std::cin, command))
-        command = "quit";
-
-      if(command == "quit") {
-        OpeningBook.close();
-        stop_threads();
-        quit_eval();
-        exit(0);
-      }
-      else if(command == "ponderhit" || command == "stop")
-        break;
+    while (true)
+    {
+        if (!std::getline(std::cin, command))
+            command = "quit";
+
+        if (command == "quit")
+        {
+            Quit = true;
+            break;
+        }
+        else if (command == "ponderhit" || command == "stop")
+            break;
     }
   }
 
@@ -2577,7 +2624,7 @@ namespace {
   // The parameter "waitSp", if non-NULL, is a pointer to an active SplitPoint
   // object for which the current thread is the master.
 
-  void idle_loop(int threadID, SplitPoint *waitSp) {
+  void idle_loop(int threadID, SplitPoint* waitSp) {
     assert(threadID >= 0 && threadID < THREAD_MAX);
 
     Threads[threadID].running = true;
@@ -2599,7 +2646,7 @@ namespace {
 #endif
       }
 
-      // If this thread has been assigned work, launch a search:
+      // If this thread has been assigned work, launch a search
       if(Threads[threadID].workIsWaiting) {
         Threads[threadID].workIsWaiting = false;
         if(Threads[threadID].splitPoint->pvNode)
@@ -2610,7 +2657,7 @@ namespace {
       }
 
       // If this thread is the master of a split point and all threads have
-      // finished their work at this split point, return from the idle loop:
+      // finished their work at this split point, return from the idle loop.
       if(waitSp != NULL && waitSp->cpus == 0)
         return;
     }
@@ -2649,7 +2696,7 @@ namespace {
   bool thread_should_stop(int threadID) {
     assert(threadID >= 0 && threadID < ActiveThreads);
 
-    SplitPoint *sp;
+    SplitPoint* sp;
 
     if(Threads[threadID].stop)
       return true;
@@ -2722,9 +2769,9 @@ namespace {
   // threads have returned from sp_search_pv (or, equivalently, when
   // splitPoint->cpus becomes 0), split() returns true.
 
-  bool split(const Position &p, SearchStack *sstck, int ply,
-             Value *alpha, Value *beta, Value *bestValue, Depth depth, int *moves,
-             MovePicker *mp, Bitboard dcCandidates, int master, bool pvNode) {
+  bool split(const Position& p, SearchStack* sstck, int ply,
+             Value* alpha, Value* beta, Value* bestValue, Depth depth, int* moves,
+             MovePicker* mp, Bitboard dcCandidates, int master, bool pvNode) {
 
     assert(p.is_ok());
     assert(sstck != NULL);
@@ -2736,24 +2783,24 @@ namespace {
     assert(master >= 0 && master < ActiveThreads);
     assert(ActiveThreads > 1);
 
-    SplitPoint *splitPoint;
+    SplitPoint* splitPoint;
     int i;
 
     lock_grab(&MPLock);
 
     // If no other thread is available to help us, or if we have too many
-    // active split points, don't split:
+    // active split points, don't split.
     if(!idle_thread_exists(master) ||
        Threads[master].activeSplitPoints >= MaxActiveSplitPoints) {
       lock_release(&MPLock);
       return false;
     }
 
-    // Pick the next available split point object from the split point stack:
+    // Pick the next available split point object from the split point stack
     splitPoint = SplitPointStack[master] + Threads[master].activeSplitPoints;
     Threads[master].activeSplitPoints++;
 
-    // Initialize the split point object:
+    // Initialize the split point object
     splitPoint->parent = Threads[master].splitPoint;
     splitPoint->finished = false;
     splitPoint->ply = ply;
@@ -2772,11 +2819,11 @@ namespace {
     for(i = 0; i < ActiveThreads; i++)
       splitPoint->slaves[i] = 0;
 
-    // Copy the current position and the search stack to the master thread:
+    // Copy the current position and the search stack to the master thread
     memcpy(splitPoint->sstack[master], sstck, (ply+1)*sizeof(SearchStack));
     Threads[master].splitPoint = splitPoint;
 
-    // Make copies of the current position and search stack for each thread:
+    // Make copies of the current position and search stack for each thread
     for(i = 0; i < ActiveThreads && splitPoint->cpus < MaxThreadsPerSplitPoint;
         i++)
       if(thread_is_available(i, master)) {
@@ -2806,7 +2853,7 @@ namespace {
     idle_loop(master, splitPoint);
 
     // We have returned from the idle loop, which means that all threads are
-    // finished.  Update alpha, beta and bestvalue, and return:
+    // finished. Update alpha, beta and bestvalue, and return.
     lock_grab(&MPLock);
     if(pvNode) *alpha = splitPoint->alpha;
     *beta = splitPoint->beta;