WebSVN – Games.Chess Giants – Diff – //engine-stockfish/search.cpp

   Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
-  Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
+  Copyright (C) 2015-2019 Marco Costalba, Joona Kiiski, Gary Linscott, 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.
 #include "misc.h"
 #include "movegen.h"
 #include "movepick.h"
 #include "position.h"
 #include "search.h"
-#include "timeman.h"
 #include "thread.h"
+#include "timeman.h"
 #include "tt.h"
 #include "uci.h"
 #include "syzygy/tbprobe.h"
 namespace Search {
   int Cardinality;
   bool RootInTB;
   bool UseRule50;
   Depth ProbeDepth;
-  Value Score;
+}
 namespace TB = Tablebases;
 using std::string;
   // Different node types, used as a template parameter
   enum NodeType { NonPV, PV };
   // Sizes and phases of the skip-blocks, used for distributing search depths across the threads
-  const int skipSize[]  = { 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4 };
+  constexpr int SkipSize[]  = { 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4 };
-  const int skipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 };
+  constexpr int SkipPhase[] = { 0, 1, 0, 1, 2, 3, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 6, 7 };
-  // Razoring and futility margin based on depth
+  // Razor and futility margins
-  const int razor_margin = 600;
+  constexpr int RazorMargin = 600;
-  Value futility_margin(Depth d) { return Value(150 * d / ONE_PLY); }
+  Value futility_margin(Depth d, bool improving) {
+    return Value((175 - 50 * improving) * d / ONE_PLY);
+  }
   // Futility and reductions lookup tables, initialized at startup
   int FutilityMoveCounts[2][16]; // [improving][depth]
   int Reductions[2][2][64][64];  // [pv][improving][depth][moveNumber]
+  }
   // History and stats update bonus, based on depth
   int stat_bonus(Depth depth) {
     int d = depth / ONE_PLY;
-    return d > 17 ? 0 : d * d + 2 * d - 2;
+    return d > 17 ? 0 : 29 * d * d + 138 * d - 134;
+  }
+  // Add a small random component to draw evaluations to keep search dynamic
+  // and to avoid 3fold-blindness.
+  Value value_draw(Depth depth, Thread* thisThread) {
+    return depth < 4 ? VALUE_DRAW
+                     : VALUE_DRAW + Value(2 * (thisThread->nodes.load(std::memory_order_relaxed) % 2) - 1);
+  }
   // Skill structure is used to implement strength limit
   struct Skill {
     explicit Skill(int l) : level(l) {}
     int level;
     Move best = MOVE_NONE;
   };
   template <NodeType NT>
-  Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning);
+  Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
-  template <NodeType NT, bool InCheck>
+  template <NodeType NT>
   Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO);
   Value value_to_tt(Value v, int ply);
   Value value_from_tt(Value v, int ply);
   void update_pv(Move* pv, Move move, Move* childPv);
   void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus);
-  void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, int bonus);
+  void update_quiet_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, int bonus);
   void update_capture_stats(const Position& pos, Move move, Move* captures, int captureCnt, int bonus);
-  bool pv_is_draw(Position& pos);
+  inline bool gives_check(const Position& pos, Move move) {
+    Color us = pos.side_to_move();
+    return  type_of(move) == NORMAL && !(pos.blockers_for_king(~us) & pos.pieces(us))
+          ? pos.check_squares(type_of(pos.moved_piece(move))) & to_sq(move)
+          : pos.gives_check(move);
+  }
   // perft() is our utility to verify move generation. All the leaf nodes up
   // to the given depth are generated and counted, and the sum is returned.
   template<bool Root>
   uint64_t perft(Position& pos, Depth depth) {
+  }
 } // namespace
-/// Search::init() is called during startup to initialize various lookup tables
+/// Search::init() is called at startup to initialize various lookup tables
 void Search::init() {
   for (int imp = 0; imp <= 1; ++imp)
       for (int d = 1; d < 64; ++d)
               Reductions[NonPV][imp][d][mc] = int(std::round(r));
               Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0);
               // Increase reduction for non-PV nodes when eval is not improving
-              if (!imp && Reductions[NonPV][imp][d][mc] >= 2)
+              if (!imp && r > 1.0)
                 Reductions[NonPV][imp][d][mc]++;
+          }
   for (int d = 0; d < 16; ++d)
+  {
   Threads.main()->wait_for_search_finished();
   Time.availableNodes = 0;
   TT.clear();
   Threads.clear();
+  Tablebases::init(Options["SyzygyPath"]); // Free up mapped files
+}
 /// MainThread::search() is called by the main thread when the program receives
 /// the UCI 'go' command. It searches from the root position and outputs the "bestmove".
+  }
   Color us = rootPos.side_to_move();
   Time.init(Limits, us, rootPos.game_ply());
   TT.new_search();
-  int contempt = Options["Contempt"] * PawnValueEg / 100; // From centipawns
-  Eval::Contempt = (us == WHITE ?  make_score(contempt, contempt / 2)
-                                : -make_score(contempt, contempt / 2));
   if (rootMoves.empty())
+  {
       rootMoves.emplace_back(MOVE_NONE);
       sync_cout << "info depth 0 score "
   if (    Options["MultiPV"] == 1
       && !Limits.depth
       && !Skill(Options["Skill Level"]).enabled()
       &&  rootMoves[0].pv[0] != MOVE_NONE)
+  {
+      std::map<Move, int> votes;
+      Value minScore = this->rootMoves[0].score;
+      // Find out minimum score and reset votes for moves which can be voted
-      for (Thread* th : Threads)
+      for (Thread* th: Threads)
+      {
-          Depth depthDiff = th->completedDepth - bestThread->completedDepth;
+          minScore = std::min(minScore, th->rootMoves[0].score);
-          Value scoreDiff = th->rootMoves[0].score - bestThread->rootMoves[0].score;
+          votes[th->rootMoves[0].pv[0]] = 0;
+      }
+      // Vote according to score and depth
+      for (Thread* th : Threads)
+          votes[th->rootMoves[0].pv[0]] +=  int(th->rootMoves[0].score - minScore)
-          // Select the thread with the best score, always if it is a mate
+                                          + int(th->completedDepth);
-          if (    scoreDiff > 0
+      // Select best thread
+      int bestVote = votes[this->rootMoves[0].pv[0]];
+      for (Thread* th : Threads)
+      {
+          if (votes[th->rootMoves[0].pv[0]] > bestVote)
+          {
-              && (depthDiff >= 0 || th->rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY))
+              bestVote = votes[th->rootMoves[0].pv[0]];
               bestThread = th;
+          }
+      }
+  }
   previousScore = bestThread->rootMoves[0].score;
-  // Send new PV when needed
+  // Send again PV info if we have a new best thread
   if (bestThread != this)
       sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl;
   sync_cout << "bestmove " << UCI::move(bestThread->rootMoves[0].pv[0], rootPos.is_chess960());
   Value bestValue, alpha, beta, delta;
   Move  lastBestMove = MOVE_NONE;
   Depth lastBestMoveDepth = DEPTH_ZERO;
   MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
   double timeReduction = 1.0;
+  Color us = rootPos.side_to_move();
+  bool failedLow;
   std::memset(ss-4, 0, 7 * sizeof(Stack));
   for (int i = 4; i > 0; i--)
-     (ss-i)->contHistory = &this->contHistory[NO_PIECE][0]; // Use as sentinel
+     (ss-i)->continuationHistory = &this->continuationHistory[NO_PIECE][0]; // Use as sentinel
   bestValue = delta = alpha = -VALUE_INFINITE;
   beta = VALUE_INFINITE;
   if (mainThread)
-  {
-      mainThread->failedLow = false;
-      mainThread->bestMoveChanges = 0;
+      mainThread->bestMoveChanges = 0, failedLow = false;
-  }
   size_t multiPV = Options["MultiPV"];
   Skill skill(Options["Skill Level"]);
   // When playing with strength handicap enable MultiPV search that we will
   // use behind the scenes to retrieve a set of possible moves.
   if (skill.enabled())
       multiPV = std::max(multiPV, (size_t)4);
   multiPV = std::min(multiPV, rootMoves.size());
+  int ct = int(Options["Contempt"]) * PawnValueEg / 100; // From centipawns
+  // In analysis mode, adjust contempt in accordance with user preference
+  if (Limits.infinite || Options["UCI_AnalyseMode"])
+      ct =  Options["Analysis Contempt"] == "Off"  ? 0
+          : Options["Analysis Contempt"] == "Both" ? ct
+          : Options["Analysis Contempt"] == "White" && us == BLACK ? -ct
+          : Options["Analysis Contempt"] == "Black" && us == WHITE ? -ct
+          : ct;
+  // In evaluate.cpp the evaluation is from the white point of view
+  contempt = (us == WHITE ?  make_score(ct, ct / 2)
+                          : -make_score(ct, ct / 2));
   // Iterative deepening loop until requested to stop or the target depth is reached
   while (   (rootDepth += ONE_PLY) < DEPTH_MAX
          && !Threads.stop
          && !(Limits.depth && mainThread && rootDepth / ONE_PLY > Limits.depth))
+  {
-      // Distribute search depths across the threads
+      // Distribute search depths across the helper threads
-      if (idx)
+      if (idx > 0)
+      {
           int i = (idx - 1) % 20;
-          if (((rootDepth / ONE_PLY + rootPos.game_ply() + skipPhase[i]) / skipSize[i]) % 2)
+          if (((rootDepth / ONE_PLY + SkipPhase[i]) / SkipSize[i]) % 2)
-              continue;
+              continue;  // Retry with an incremented rootDepth
+      }
       // Age out PV variability metric
       if (mainThread)
-          mainThread->bestMoveChanges *= 0.505, mainThread->failedLow = false;
+          mainThread->bestMoveChanges *= 0.517, failedLow = false;
       // Save the last iteration's scores before first PV line is searched and
       // all the move scores except the (new) PV are set to -VALUE_INFINITE.
       for (RootMove& rm : rootMoves)
           rm.previousScore = rm.score;
+      size_t pvFirst = 0;
+      pvLast = 0;
       // MultiPV loop. We perform a full root search for each PV line
-      for (PVIdx = 0; PVIdx < multiPV && !Threads.stop; ++PVIdx)
+      for (pvIdx = 0; pvIdx < multiPV && !Threads.stop; ++pvIdx)
+      {
+          if (pvIdx == pvLast)
+          {
+              pvFirst = pvLast;
+              for (pvLast++; pvLast < rootMoves.size(); pvLast++)
+                  if (rootMoves[pvLast].tbRank != rootMoves[pvFirst].tbRank)
+                      break;
+          }
           // Reset UCI info selDepth for each depth and each PV line
           selDepth = 0;
           // Reset aspiration window starting size
           if (rootDepth >= 5 * ONE_PLY)
+          {
+              Value previousScore = rootMoves[pvIdx].previousScore;
-              delta = Value(18);
+              delta = Value(20);
-              alpha = std::max(rootMoves[PVIdx].previousScore - delta,-VALUE_INFINITE);
+              alpha = std::max(previousScore - delta,-VALUE_INFINITE);
-              beta  = std::min(rootMoves[PVIdx].previousScore + delta, VALUE_INFINITE);
+              beta  = std::min(previousScore + delta, VALUE_INFINITE);
+              // Adjust contempt based on root move's previousScore (dynamic contempt)
+              int dct = ct + 88 * previousScore / (abs(previousScore) + 200);
+              contempt = (us == WHITE ?  make_score(dct, dct / 2)
+                                      : -make_score(dct, dct / 2));
+          }
           // Start with a small aspiration window and, in the case of a fail
-          // high/low, re-search with a bigger window until we're not failing
+          // high/low, re-search with a bigger window until we don't fail
           // high/low anymore.
+          int failedHighCnt = 0;
           while (true)
+          {
+              Depth adjustedDepth = std::max(ONE_PLY, rootDepth - failedHighCnt * ONE_PLY);
-              bestValue = ::search<PV>(rootPos, ss, alpha, beta, rootDepth, false, false);
+              bestValue = ::search<PV>(rootPos, ss, alpha, beta, adjustedDepth, false);
               // Bring the best move to the front. It is critical that sorting
               // is done with a stable algorithm because all the values but the
               // first and eventually the new best one are set to -VALUE_INFINITE
               // and we want to keep the same order for all the moves except the
               // new PV that goes to the front. Note that in case of MultiPV
               // search the already searched PV lines are preserved.
-              std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end());
+              std::stable_sort(rootMoves.begin() + pvIdx, rootMoves.begin() + pvLast);
-              // If search has been stopped, we break immediately. Sorting and
+              // If search has been stopped, we break immediately. Sorting is
-              // writing PV back to TT is safe because RootMoves is still
+              // safe because RootMoves is still valid, although it refers to
-              // valid, although it refers to the previous iteration.
+              // the previous iteration.
               if (Threads.stop)
                   break;
               // When failing high/low give some update (without cluttering
               // the UI) before a re-search.
                   beta = (alpha + beta) / 2;
                   alpha = std::max(bestValue - delta, -VALUE_INFINITE);
                   if (mainThread)
+                  {
+                      failedHighCnt = 0;
-                      mainThread->failedLow = true;
+                      failedLow = true;
                       Threads.stopOnPonderhit = false;
+                  }
+              }
               else if (bestValue >= beta)
+              {
                   beta = std::min(bestValue + delta, VALUE_INFINITE);
+                  if (mainThread)
+                          ++failedHighCnt;
+              }
               else
                   break;
               delta += delta / 4 + 5;
               assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
+          }
           // Sort the PV lines searched so far and update the GUI
-          std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1);
+          std::stable_sort(rootMoves.begin() + pvFirst, rootMoves.begin() + pvIdx + 1);
           if (    mainThread
-              && (Threads.stop || PVIdx + 1 == multiPV || Time.elapsed() > 3000))
+              && (Threads.stop || pvIdx + 1 == multiPV || Time.elapsed() > 3000))
               sync_cout << UCI::pv(rootPos, rootDepth, alpha, beta) << sync_endl;
+      }
       if (!Threads.stop)
           completedDepth = rootDepth;
       // If skill level is enabled and time is up, pick a sub-optimal best move
       if (skill.enabled() && skill.time_to_pick(rootDepth))
           skill.pick_best(multiPV);
       // Do we have time for the next iteration? Can we stop searching now?
-      if (Limits.use_time_management())
+      if (    Limits.use_time_management()
-      {
+          && !Threads.stop
-          if (!Threads.stop && !Threads.stopOnPonderhit)
+          && !Threads.stopOnPonderhit)
+          {
-              // Stop the search if only one legal move is available, or if all
-              // of the available time has been used
-              const int F[] = { mainThread->failedLow,
+              const int F[] = { failedLow,
                                 bestValue - mainThread->previousScore };
-              int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1]));
-              Color us = rootPos.side_to_move();
-              bool thinkHard =    bestValue == VALUE_DRAW
-                               && Limits.time[us] - Time.elapsed() > Limits.time[~us]
+              int improvingFactor = std::max(246, std::min(832, 306 + 119 * F[0] - 6 * F[1]));
-                               && ::pv_is_draw(rootPos);
-              double unstablePvFactor = 1 + mainThread->bestMoveChanges + thinkHard;
+              // If the bestMove is stable over several iterations, reduce time accordingly
+              timeReduction = 1.0;
+              for (int i : {3, 4, 5})
+                  if (lastBestMoveDepth * i < completedDepth)
+                     timeReduction *= 1.25;
-              // if the bestMove is stable over several iterations, reduce time for this move,
-              // the longer the move has been stable, the more.
-              // Use part of the gained time from a previous stable move for the current move.
+              // Use part of the gained time from a previous stable move for the current move
-              timeReduction = 1;
-              for (int i : {3, 4, 5})
-                  if (lastBestMoveDepth * i < completedDepth && !thinkHard)
+              double bestMoveInstability = 1.0 + mainThread->bestMoveChanges;
-                     timeReduction *= 1.3;
-              unstablePvFactor *=  std::pow(mainThread->previousTimeReduction, 0.51) / timeReduction;
+              bestMoveInstability *= std::pow(mainThread->previousTimeReduction, 0.528) / timeReduction;
+              // Stop the search if we have only one legal move, or if available time elapsed
               if (   rootMoves.size() == 1
-                  || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 628)
+                  || Time.elapsed() > Time.optimum() * bestMoveInstability * improvingFactor / 581)
+              {
                   // If we are allowed to ponder do not stop the search now but
                   // keep pondering until the GUI sends "ponderhit" or "stop".
                   if (Threads.ponder)
                       Threads.stopOnPonderhit = true;
                   else
                       Threads.stop = true;
+              }
+          }
-      }
+  }
   if (!mainThread)
       return;
 namespace {
   // search<>() is the main search function for both PV and non-PV nodes
   template <NodeType NT>
-  Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode, bool skipEarlyPruning) {
+  Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
-    const bool PvNode = NT == PV;
+    constexpr bool PvNode = NT == PV;
     const bool rootNode = PvNode && ss->ply == 0;
+    // Check if we have an upcoming move which draws by repetition, or
+    // if the opponent had an alternative move earlier to this position.
+    if (   pos.rule50_count() >= 3
+        && alpha < VALUE_DRAW
+        && !rootNode
+        && pos.has_game_cycle(ss->ply))
+    {
+        alpha = value_draw(depth, pos.this_thread());
+        if (alpha >= beta)
+            return alpha;
+    }
+    // Dive into quiescence search when the depth reaches zero
+    if (depth < ONE_PLY)
+        return qsearch<NT>(pos, ss, alpha, beta);
     assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
     assert(PvNode || (alpha == beta - 1));
     assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
     assert(!(PvNode && cutNode));
     StateInfo st;
     TTEntry* tte;
     Key posKey;
     Move ttMove, move, excludedMove, bestMove;
     Depth extension, newDepth;
-    Value bestValue, value, ttValue, eval, maxValue;
+    Value bestValue, value, ttValue, eval, maxValue, pureStaticEval;
-    bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
+    bool ttHit, inCheck, givesCheck, improving;
     bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture, pvExact;
     Piece movedPiece;
     int moveCount, captureCount, quietCount;
     // Step 1. Initialize node
     Thread* thisThread = pos.this_thread();
     inCheck = pos.checkers();
+    Color us = pos.side_to_move();
     moveCount = captureCount = quietCount = ss->moveCount = 0;
-    ss->statScore = 0;
     bestValue = -VALUE_INFINITE;
     maxValue = VALUE_INFINITE;
     // Check for the available remaining time
     if (thisThread == Threads.main())
         thisThread->selDepth = ss->ply + 1;
     if (!rootNode)
+    {
         // Step 2. Check for aborted search and immediate draw
-        if (Threads.stop.load(std::memory_order_relaxed) || pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
+        if (   Threads.stop.load(std::memory_order_relaxed)
+            || pos.is_draw(ss->ply)
+            || ss->ply >= MAX_PLY)
-            return ss->ply >= MAX_PLY && !inCheck ? evaluate(pos) : VALUE_DRAW;
+            return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos)
+                                                    : value_draw(depth, pos.this_thread());
         // Step 3. Mate distance pruning. Even if we mate at the next move our score
         // would be at best mate_in(ss->ply+1), but if alpha is already bigger because
         // a shorter mate was found upward in the tree then there is no need to search
         // because we will never beat the current alpha. Same logic but with reversed
     assert(0 <= ss->ply && ss->ply < MAX_PLY);
     (ss+1)->ply = ss->ply + 1;
     ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
-    ss->contHistory = &thisThread->contHistory[NO_PIECE][0];
+    ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
     (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
     Square prevSq = to_sq((ss-1)->currentMove);
+    // Initialize statScore to zero for the grandchildren of the current position.
+    // So statScore is shared between all grandchildren and only the first grandchild
+    // starts with statScore = 0. Later grandchildren start with the last calculated
+    // statScore of the previous grandchild. This influences the reduction rules in
+    // LMR which are based on the statScore of parent position.
+    (ss+2)->statScore = 0;
     // Step 4. Transposition table lookup. We don't want the score of a partial
     // search to overwrite a previous full search TT value, so we use a different
     // position key in case of an excluded move.
     excludedMove = ss->excludedMove;
-    posKey = pos.key() ^ Key(excludedMove << 16); // isn't a very good hash
+    posKey = pos.key() ^ Key(excludedMove << 16); // Isn't a very good hash
     tte = TT.probe(posKey, ttHit);
     ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
-    ttMove =  rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0]
+    ttMove =  rootNode ? thisThread->rootMoves[thisThread->pvIdx].pv[0]
             : ttHit    ? tte->move() : MOVE_NONE;
     // At non-PV nodes we check for an early TT cutoff
     if (  !PvNode
         && ttHit
         if (ttMove)
+        {
             if (ttValue >= beta)
+            {
                 if (!pos.capture_or_promotion(ttMove))
-                    update_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth));
+                    update_quiet_stats(pos, ss, ttMove, nullptr, 0, stat_bonus(depth));
                 // Extra penalty for a quiet TT move in previous ply when it gets refuted
                 if ((ss-1)->moveCount == 1 && !pos.captured_piece())
                     update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
+            }
             // Penalty for a quiet ttMove that fails low
             else if (!pos.capture_or_promotion(ttMove))
+            {
                 int penalty = -stat_bonus(depth);
-                thisThread->mainHistory.update(pos.side_to_move(), ttMove, penalty);
+                thisThread->mainHistory[us][from_to(ttMove)] << penalty;
                 update_continuation_histories(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
+            }
+        }
         return ttValue;
+    }
-    // Step 4a. Tablebase probe
+    // Step 5. Tablebases probe
     if (!rootNode && TB::Cardinality)
+    {
         int piecesCount = pos.count<ALL_PIECES>();
         if (    piecesCount <= TB::Cardinality
             &&  pos.rule50_count() == 0
             && !pos.can_castle(ANY_CASTLING))
+        {
             TB::ProbeState err;
             TB::WDLScore wdl = Tablebases::probe_wdl(pos, &err);
+            // Force check of time on the next occasion
+            if (thisThread == Threads.main())
+                static_cast<MainThread*>(thisThread)->callsCnt = 0;
             if (err != TB::ProbeState::FAIL)
+            {
                 thisThread->tbHits.fetch_add(1, std::memory_order_relaxed);
                 if (    b == BOUND_EXACT
                     || (b == BOUND_LOWER ? value >= beta : value <= alpha))
+                {
                     tte->save(posKey, value_to_tt(value, ss->ply), b,
                               std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
-                              MOVE_NONE, VALUE_NONE, TT.generation());
+                              MOVE_NONE, VALUE_NONE);
                     return value;
+                }
                 if (PvNode)
+                }
+            }
+        }
+    }
-    // Step 5. Evaluate the position statically
+    // Step 6. Static evaluation of the position
     if (inCheck)
+    {
-        ss->staticEval = eval = VALUE_NONE;
+        ss->staticEval = eval = pureStaticEval = VALUE_NONE;
-        goto moves_loop;
+        improving = false;
+        goto moves_loop;  // Skip early pruning when in check
+    }
     else if (ttHit)
+    {
         // Never assume anything on values stored in TT
-        if ((ss->staticEval = eval = tte->eval()) == VALUE_NONE)
+        ss->staticEval = eval = pureStaticEval = tte->eval();
+        if (eval == VALUE_NONE)
-            eval = ss->staticEval = evaluate(pos);
+            ss->staticEval = eval = pureStaticEval = evaluate(pos);
         // Can ttValue be used as a better position evaluation?
-        if (   ttValue != VALUE_NONE
+        if (    ttValue != VALUE_NONE
             && (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER)))
             eval = ttValue;
+    }
     else
+    {
+        if ((ss-1)->currentMove != MOVE_NULL)
+        {
-        eval = ss->staticEval =
+            int p = (ss-1)->statScore;
-        (ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
+            int bonus = p > 0 ? (-p - 2500) / 512 :
-                                         : -(ss-1)->staticEval + 2 * Eval::Tempo;
+                        p < 0 ? (-p + 2500) / 512 : 0;
-        tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
+            pureStaticEval = evaluate(pos);
-                  ss->staticEval, TT.generation());
+            ss->staticEval = eval = pureStaticEval + bonus;
+        }
+        else
+            ss->staticEval = eval = pureStaticEval = -(ss-1)->staticEval + 2 * Eval::Tempo;
+        tte->save(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE, pureStaticEval);
+    }
-    if (skipEarlyPruning || !pos.non_pawn_material(pos.side_to_move()))
+    // Step 7. Razoring (~2 Elo)
-        goto moves_loop;
+    if (   depth < 2 * ONE_PLY
+        && eval <= alpha - RazorMargin)
+        return qsearch<NT>(pos, ss, alpha, beta);
-    // Step 6. Razoring (skipped when in check)
-    if (   !PvNode
-        &&  depth < 4 * ONE_PLY
-        &&  eval + razor_margin <= alpha)
+    improving =   ss->staticEval >= (ss-2)->staticEval
-    {
-        if (depth <= ONE_PLY)
-            return qsearch<NonPV, false>(pos, ss, alpha, alpha+1);
-        Value ralpha = alpha - razor_margin;
+               || (ss-2)->staticEval == VALUE_NONE;
-        Value v = qsearch<NonPV, false>(pos, ss, ralpha, ralpha+1);
-        if (v <= ralpha)
-            return v;
-    }
-    // Step 7. Futility pruning: child node (skipped when in check)
+    // Step 8. Futility pruning: child node (~30 Elo)
     if (   !rootNode
         &&  depth < 7 * ONE_PLY
-        &&  eval - futility_margin(depth) >= beta
+        &&  eval - futility_margin(depth, improving) >= beta
-        &&  eval < VALUE_KNOWN_WIN)  // Do not return unproven wins
+        &&  eval < VALUE_KNOWN_WIN) // Do not return unproven wins
         return eval;
-    // Step 8. Null move search with verification search (is omitted in PV nodes)
+    // Step 9. Null move search with verification search (~40 Elo)
     if (   !PvNode
+        && (ss-1)->currentMove != MOVE_NULL
+        && (ss-1)->statScore < 23200
         &&  eval >= beta
-        &&  ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
+        &&  pureStaticEval >= beta - 36 * depth / ONE_PLY + 225
+        && !excludedMove
+        &&  pos.non_pawn_material(us)
-        && (ss->ply >= thisThread->nmp_ply || ss->ply % 2 != thisThread->nmp_odd))
+        && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
+    {
         assert(eval - beta >= 0);
         // Null move dynamic reduction based on depth and value
-        Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min((eval - beta) / PawnValueMg, 3)) * ONE_PLY;
+        Depth R = ((823 + 67 * depth / ONE_PLY) / 256 + std::min(int(eval - beta) / 200, 3)) * ONE_PLY;
         ss->currentMove = MOVE_NULL;
-        ss->contHistory = &thisThread->contHistory[NO_PIECE][0];
+        ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
         pos.do_null_move(st);
-        Value nullValue = depth-R < ONE_PLY ? -qsearch<NonPV, false>(pos, ss+1, -beta, -beta+1)
-                                            : - search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode, true);
+        Value nullValue = -search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
         pos.undo_null_move();
         if (nullValue >= beta)
+        {
             // Do not return unproven mate scores
             if (nullValue >= VALUE_MATE_IN_MAX_PLY)
                 nullValue = beta;
-            if (abs(beta) < VALUE_KNOWN_WIN && (depth < 12 * ONE_PLY || thisThread->nmp_ply))
+            if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 12 * ONE_PLY))
                 return nullValue;
-            // Do verification search at high depths
-            // disable null move pruning for side to move for the first part of the remaining search tree
-            thisThread->nmp_ply = ss->ply + 3 * (depth-R) / 4;
+            assert(!thisThread->nmpMinPly); // Recursive verification is not allowed
-            thisThread->nmp_odd = ss->ply % 2;
-            Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta)
+            // Do verification search at high depths, with null move pruning disabled
+            // for us, until ply exceeds nmpMinPly.
-                                        :  search<NonPV>(pos, ss, beta-1, beta, depth-R, false, true);
+            thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / 4;
+            thisThread->nmpColor = us;
+            Value v = search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
-            thisThread->nmp_odd = thisThread->nmp_ply = 0;
+            thisThread->nmpMinPly = 0;
             if (v >= beta)
                 return nullValue;
+        }
+    }
-    // Step 9. ProbCut (skipped when in check)
+    // Step 10. ProbCut (~10 Elo)
     // If we have a good enough capture and a reduced search returns a value
     // much above beta, we can (almost) safely prune the previous move.
     if (   !PvNode
         &&  depth >= 5 * ONE_PLY
         &&  abs(beta) < VALUE_MATE_IN_MAX_PLY)
+    {
-        Value rbeta = std::min(beta + 200, VALUE_INFINITE);
+        Value rbeta = std::min(beta + 216 - 48 * improving, VALUE_INFINITE);
-        assert(is_ok((ss-1)->currentMove));
         MovePicker mp(pos, ttMove, rbeta - ss->staticEval, &thisThread->captureHistory);
+        int probCutCount = 0;
-        while ((move = mp.next_move()) != MOVE_NONE)
+        while (  (move = mp.next_move()) != MOVE_NONE
+               && probCutCount < 3)
-            if (pos.legal(move))
+            if (move != excludedMove && pos.legal(move))
+            {
+                probCutCount++;
                 ss->currentMove = move;
-                ss->contHistory = &thisThread->contHistory[pos.moved_piece(move)][to_sq(move)];
+                ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)];
                 assert(depth >= 5 * ONE_PLY);
                 pos.do_move(move, st);
+                // Perform a preliminary qsearch to verify that the move holds
+                value = -qsearch<NonPV>(pos, ss+1, -rbeta, -rbeta+1);
+                // If the qsearch held perform the regular search
+                if (value >= rbeta)
-                value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
+                    value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode);
                 pos.undo_move(move);
                 if (value >= rbeta)
                     return value;
+            }
+    }
-    // Step 10. Internal iterative deepening (skipped when in check)
+    // Step 11. Internal iterative deepening (~2 Elo)
-    if (    depth >= 6 * ONE_PLY
+    if (    depth >= 8 * ONE_PLY
-        && !ttMove
+        && !ttMove)
-        && (PvNode || ss->staticEval + 256 >= beta))
+    {
-        Depth d = (3 * depth / (4 * ONE_PLY) - 2) * ONE_PLY;
-        search<NT>(pos, ss, alpha, beta, d, cutNode, true);
+        search<NT>(pos, ss, alpha, beta, depth - 7 * ONE_PLY, cutNode);
         tte = TT.probe(posKey, ttHit);
+        ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
         ttMove = ttHit ? tte->move() : MOVE_NONE;
+    }
-moves_loop: // When in check search starts from here
+moves_loop: // When in check, search starts from here
-    const PieceToHistory* contHist[] = { (ss-1)->contHistory, (ss-2)->contHistory, nullptr, (ss-4)->contHistory };
+    const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr, (ss-4)->continuationHistory };
     Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
-    MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, &thisThread->captureHistory, contHist, countermove, ss->killers);
+    MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
+                                      &thisThread->captureHistory,
+                                      contHist,
+                                      countermove,
+                                      ss->killers);
     value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
-    improving =   ss->staticEval >= (ss-2)->staticEval
-            /* || ss->staticEval == VALUE_NONE Already implicit in the previous condition */
-               ||(ss-2)->staticEval == VALUE_NONE;
-    singularExtensionNode =   !rootNode
-                           &&  depth >= 8 * ONE_PLY
-                           &&  ttMove != MOVE_NONE
-                           &&  ttValue != VALUE_NONE
-                           && !excludedMove // Recursive singular search is not allowed
-                           && (tte->bound() & BOUND_LOWER)
-                           &&  tte->depth() >= depth - 3 * ONE_PLY;
     skipQuiets = false;
-    ttCapture = false;
+    ttCapture = ttMove && pos.capture_or_promotion(ttMove);
     pvExact = PvNode && ttHit && tte->bound() == BOUND_EXACT;
-    // Step 11. Loop through moves
+    // Step 12. Loop through all pseudo-legal moves until no moves remain
-    // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
+    // or a beta cutoff occurs.
     while ((move = mp.next_move(skipQuiets)) != MOVE_NONE)
+    {
       assert(is_ok(move));
       if (move == excludedMove)
           continue;
       // At root obey the "searchmoves" option and skip moves not listed in Root
       // Move List. As a consequence any illegal move is also skipped. In MultiPV
-      // mode we also skip PV moves which have been already searched.
+      // mode we also skip PV moves which have been already searched and those
+      // of lower "TB rank" if we are in a TB root position.
-      if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx,
+      if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->pvIdx,
-                                  thisThread->rootMoves.end(), move))
+                                  thisThread->rootMoves.begin() + thisThread->pvLast, move))
           continue;
       ss->moveCount = ++moveCount;
       if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
           sync_cout << "info depth " << depth / ONE_PLY
                     << " currmove " << UCI::move(move, pos.is_chess960())
-                    << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl;
+                    << " currmovenumber " << moveCount + thisThread->pvIdx << sync_endl;
       if (PvNode)
           (ss+1)->pv = nullptr;
       extension = DEPTH_ZERO;
       captureOrPromotion = pos.capture_or_promotion(move);
       movedPiece = pos.moved_piece(move);
-      givesCheck =  type_of(move) == NORMAL && !pos.discovered_check_candidates()
-                  ? pos.check_squares(type_of(movedPiece)) & to_sq(move)
-                  : pos.gives_check(move);
+      givesCheck = gives_check(pos, move);
       moveCountPruning =   depth < 16 * ONE_PLY
                         && moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];
-      // Step 12. Singular and Gives Check Extensions
+      // Step 13. Extensions (~70 Elo)
-      // Singular extension search. If all moves but one fail low on a search of
+      // Singular extension search (~60 Elo). If all moves but one fail low on a
-      // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
+      // search of (alpha-s, beta-s), and just one fails high on (alpha, beta),
-      // is singular and should be extended. To verify this we do a reduced search
+      // then that move is singular and should be extended. To verify this we do
-      // on all the other moves but the ttMove and if the result is lower than
+      // a reduced search on all the other moves but the ttMove and if the
-      // ttValue minus a margin then we will extend the ttMove.
+      // result is lower than ttValue minus a margin then we will extend the ttMove.
-      if (    singularExtensionNode
+      if (    depth >= 8 * ONE_PLY
           &&  move == ttMove
+          && !rootNode
+          && !excludedMove // Recursive singular search is not allowed
+          &&  ttValue != VALUE_NONE
+          && (tte->bound() & BOUND_LOWER)
+          &&  tte->depth() >= depth - 3 * ONE_PLY
           &&  pos.legal(move))
+      {
           Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
-          Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY;
           ss->excludedMove = move;
-          value = search<NonPV>(pos, ss, rBeta - 1, rBeta, d, cutNode, true);
+          value = search<NonPV>(pos, ss, rBeta - 1, rBeta, depth / 2, cutNode);
           ss->excludedMove = MOVE_NONE;
           if (value < rBeta)
               extension = ONE_PLY;
+      }
-      else if (    givesCheck
+      else if (    givesCheck // Check extension (~2 Elo)
-               && !moveCountPruning
                &&  pos.see_ge(move))
+          extension = ONE_PLY;
+      // Extension if castling
+      else if (type_of(move) == CASTLING)
           extension = ONE_PLY;
       // Calculate new depth for this move
       newDepth = depth - ONE_PLY + extension;
-      // Step 13. Pruning at shallow depth
+      // Step 14. Pruning at shallow depth (~170 Elo)
       if (  !rootNode
-          && pos.non_pawn_material(pos.side_to_move())
+          && pos.non_pawn_material(us)
           && bestValue > VALUE_MATED_IN_MAX_PLY)
+      {
           if (   !captureOrPromotion
               && !givesCheck
               && (!pos.advanced_pawn_push(move) || pos.non_pawn_material() >= Value(5000)))
+          {
-              // Move count based pruning
+              // Move count based pruning (~30 Elo)
               if (moveCountPruning)
+              {
                   skipQuiets = true;
                   continue;
+              }
               // Reduced depth of the next LMR search
               int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;
-              // Countermoves based pruning
+              // Countermoves based pruning (~20 Elo)
-              if (   lmrDepth < 3
+              if (   lmrDepth < 3 + ((ss-1)->statScore > 0)
                   && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
                   && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
                   continue;
-              // Futility pruning: parent node
+              // Futility pruning: parent node (~2 Elo)
               if (   lmrDepth < 7
                   && !inCheck
                   && ss->staticEval + 256 + 200 * lmrDepth <= alpha)
                   continue;
-              // Prune moves with negative SEE
+              // Prune moves with negative SEE (~10 Elo)
-              if (   lmrDepth < 8
-                  && !pos.see_ge(move, Value(-35 * lmrDepth * lmrDepth)))
+              if (!pos.see_ge(move, Value(-29 * lmrDepth * lmrDepth)))
                   continue;
+          }
-          else if (    depth < 7 * ONE_PLY
+          else if (   !extension // (~20 Elo)
-                   && !extension
                    && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY)))
                   continue;
+      }
       // Speculative prefetch as early as possible
       if (!rootNode && !pos.legal(move))
+      {
           ss->moveCount = --moveCount;
           continue;
+      }
-      if (move == ttMove && captureOrPromotion)
-          ttCapture = true;
       // Update the current move (this must be done after singular extension search)
       ss->currentMove = move;
-      ss->contHistory = &thisThread->contHistory[movedPiece][to_sq(move)];
+      ss->continuationHistory = &thisThread->continuationHistory[movedPiece][to_sq(move)];
-      // Step 14. Make the move
+      // Step 15. Make the move
       pos.do_move(move, st, givesCheck);
-      // Step 15. Reduced depth search (LMR). If the move fails high it will be
+      // Step 16. Reduced depth search (LMR). If the move fails high it will be
       // re-searched at full depth.
       if (    depth >= 3 * ONE_PLY
           &&  moveCount > 1
           && (!captureOrPromotion || moveCountPruning))
+      {
           Depth r = reduction<PvNode>(improving, depth, moveCount);
+          // Decrease reduction if opponent's move count is high (~10 Elo)
-          if (captureOrPromotion)
+          if ((ss-1)->moveCount > 15)
-              r -= r ? ONE_PLY : DEPTH_ZERO;
+              r -= ONE_PLY;
-          else
+          if (!captureOrPromotion)
+          {
-              // Decrease reduction if opponent's move count is high
-              if ((ss-1)->moveCount > 15)
-                  r -= ONE_PLY;
-              // Decrease reduction for exact PV nodes
+              // Decrease reduction for exact PV nodes (~0 Elo)
               if (pvExact)
                   r -= ONE_PLY;
-              // Increase reduction if ttMove is a capture
+              // Increase reduction if ttMove is a capture (~0 Elo)
               if (ttCapture)
                   r += ONE_PLY;
-              // Increase reduction for cut nodes
+              // Increase reduction for cut nodes (~5 Elo)
               if (cutNode)
                   r += 2 * ONE_PLY;
               // Decrease reduction for moves that escape a capture. Filter out
               // castling moves, because they are coded as "king captures rook" and
-              // hence break make_move().
+              // hence break make_move(). (~5 Elo)
               else if (    type_of(move) == NORMAL
                        && !pos.see_ge(make_move(to_sq(move), from_sq(move))))
                   r -= 2 * ONE_PLY;
-              ss->statScore =  thisThread->mainHistory[~pos.side_to_move()][from_to(move)]
+              ss->statScore =  thisThread->mainHistory[us][from_to(move)]
                              + (*contHist[0])[movedPiece][to_sq(move)]
                              + (*contHist[1])[movedPiece][to_sq(move)]
                              + (*contHist[3])[movedPiece][to_sq(move)]
                              - 4000;
-              // Decrease/increase reduction by comparing opponent's stat score
+              // Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
               if (ss->statScore >= 0 && (ss-1)->statScore < 0)
                   r -= ONE_PLY;
               else if ((ss-1)->statScore >= 0 && ss->statScore < 0)
                   r += ONE_PLY;
-              // Decrease/increase reduction for moves with a good/bad history
+              // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
-              r = std::max(DEPTH_ZERO, (r / ONE_PLY - ss->statScore / 20000) * ONE_PLY);
+              r -= ss->statScore / 20000 * ONE_PLY;
+          }
-          Depth d = std::max(newDepth - r, ONE_PLY);
+          Depth d = std::max(newDepth - std::max(r, DEPTH_ZERO), ONE_PLY);
-          value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true, false);
+          value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
           doFullDepthSearch = (value > alpha && d != newDepth);
+      }
       else
           doFullDepthSearch = !PvNode || moveCount > 1;
-      // Step 16. Full depth search when LMR is skipped or fails high
+      // Step 17. Full depth search when LMR is skipped or fails high
       if (doFullDepthSearch)
-          value = newDepth <   ONE_PLY ?
-                            givesCheck ? -qsearch<NonPV,  true>(pos, ss+1, -(alpha+1), -alpha)
-                                       : -qsearch<NonPV, false>(pos, ss+1, -(alpha+1), -alpha)
-                                       : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode, false);
+          value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
       // For PV nodes only, do a full PV search on the first move or after a fail
       // high (in the latter case search only if value < beta), otherwise let the
       // parent node fail low with value <= alpha and try another move.
       if (PvNode && (moveCount == 1 || (value > alpha && (rootNode || value < beta))))
+      {
           (ss+1)->pv = pv;
           (ss+1)->pv[0] = MOVE_NONE;
-          value = newDepth <   ONE_PLY ?
-                            givesCheck ? -qsearch<PV,  true>(pos, ss+1, -beta, -alpha)
-                                       : -qsearch<PV, false>(pos, ss+1, -beta, -alpha)
-                                       : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, false, false);
+          value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
+      }
-      // Step 17. Undo move
+      // Step 18. Undo move
       pos.undo_move(move);
       assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
-      // Step 18. Check for a new best move
+      // Step 19. Check for a new best move
       // Finished searching the move. If a stop occurred, the return value of
       // the search cannot be trusted, and we return immediately without
       // updating best move, PV and TT.
       if (Threads.stop.load(std::memory_order_relaxed))
           return VALUE_ZERO;
       if (rootNode)
+      {
           RootMove& rm = *std::find(thisThread->rootMoves.begin(),
                                     thisThread->rootMoves.end(), move);
-          // PV move or new best move ?
+          // PV move or new best move?
           if (moveCount == 1 || value > alpha)
+          {
               rm.score = value;
               rm.selDepth = thisThread->selDepth;
               rm.pv.resize(1);
               if (PvNode && value < beta) // Update alpha! Always alpha < beta
                   alpha = value;
               else
+              {
                   assert(value >= beta); // Fail high
+                  ss->statScore = 0;
                   break;
+              }
+          }
+      }
+      if (move != bestMove)
+      {
-      if (!captureOrPromotion && move != bestMove && quietCount < 64)
+          if (captureOrPromotion && captureCount < 32)
-          quietsSearched[quietCount++] = move;
+              capturesSearched[captureCount++] = move;
-      else if (captureOrPromotion && move != bestMove && captureCount < 32)
+          else if (!captureOrPromotion && quietCount < 64)
-          capturesSearched[captureCount++] = move;
+              quietsSearched[quietCount++] = move;
+      }
+    }
     // The following condition would detect a stop only after move loop has been
     // completed. But in this case bestValue is valid because we have fully
     // searched our subtree, and we can anyhow save the result in TT.
                    :     inCheck ? mated_in(ss->ply) : VALUE_DRAW;
     else if (bestMove)
+    {
         // Quiet best move: update move sorting heuristics
         if (!pos.capture_or_promotion(bestMove))
-            update_stats(pos, ss, bestMove, quietsSearched, quietCount, stat_bonus(depth));
+            update_quiet_stats(pos, ss, bestMove, quietsSearched, quietCount,
+                               stat_bonus(depth + (bestValue > beta + PawnValueMg ? ONE_PLY : DEPTH_ZERO)));
-        else
-            update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth));
+        update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth + ONE_PLY));
         // Extra penalty for a quiet TT move in previous ply when it gets refuted
         if ((ss-1)->moveCount == 1 && !pos.captured_piece())
             update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
+    }
     // Bonus for prior countermove that caused the fail low
-    else if (    depth >= 3 * ONE_PLY
+    else if (   (depth >= 3 * ONE_PLY || PvNode)
              && !pos.captured_piece()
              && is_ok((ss-1)->currentMove))
         update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
     if (PvNode)
     if (!excludedMove)
         tte->save(posKey, value_to_tt(bestValue, ss->ply),
                   bestValue >= beta ? BOUND_LOWER :
                   PvNode && bestMove ? BOUND_EXACT : BOUND_UPPER,
-                  depth, bestMove, ss->staticEval, TT.generation());
+                  depth, bestMove, pureStaticEval);
     assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
     return bestValue;
+  }
   // qsearch() is the quiescence search function, which is called by the main
   // search function with depth zero, or recursively with depth less than ONE_PLY.
-  template <NodeType NT, bool InCheck>
+  template <NodeType NT>
   Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth) {
-    const bool PvNode = NT == PV;
+    constexpr bool PvNode = NT == PV;
-    assert(InCheck == bool(pos.checkers()));
     assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
     assert(PvNode || (alpha == beta - 1));
     assert(depth <= DEPTH_ZERO);
     assert(depth / ONE_PLY * ONE_PLY == depth);
     Move pv[MAX_PLY+1];
     StateInfo st;
     TTEntry* tte;
     Key posKey;
     Move ttMove, move, bestMove;
-    Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
-    bool ttHit, givesCheck, evasionPrunable;
     Depth ttDepth;
+    Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
+    bool ttHit, inCheck, givesCheck, evasionPrunable;
     int moveCount;
     if (PvNode)
+    {
         oldAlpha = alpha; // To flag BOUND_EXACT when eval above alpha and no available moves
         (ss+1)->pv = pv;
         ss->pv[0] = MOVE_NONE;
+    }
-    ss->currentMove = bestMove = MOVE_NONE;
+    Thread* thisThread = pos.this_thread();
     (ss+1)->ply = ss->ply + 1;
+    ss->currentMove = bestMove = MOVE_NONE;
+    ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
+    inCheck = pos.checkers();
     moveCount = 0;
-    // Check for an instant draw or if the maximum ply has been reached
+    // Check for an immediate draw or maximum ply reached
+    if (   pos.is_draw(ss->ply)
-    if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
+        || ss->ply >= MAX_PLY)
-        return ss->ply >= MAX_PLY && !InCheck ? evaluate(pos) : VALUE_DRAW;
+        return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos) : VALUE_DRAW;
     assert(0 <= ss->ply && ss->ply < MAX_PLY);
     // 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.
-    ttDepth = InCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
+    ttDepth = inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS
                                                   : DEPTH_QS_NO_CHECKS;
     // Transposition table lookup
     posKey = pos.key();
     tte = TT.probe(posKey, ttHit);
-    ttMove = ttHit ? tte->move() : MOVE_NONE;
     ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
+    ttMove = ttHit ? tte->move() : MOVE_NONE;
     if (  !PvNode
         && ttHit
         && tte->depth() >= ttDepth
         && ttValue != VALUE_NONE // Only in case of TT access race
-        && (ttValue >= beta ? (tte->bound() &  BOUND_LOWER)
+        && (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
-                            : (tte->bound() &  BOUND_UPPER)))
+                            : (tte->bound() & BOUND_UPPER)))
         return ttValue;
     // Evaluate the position statically
-    if (InCheck)
+    if (inCheck)
+    {
         ss->staticEval = VALUE_NONE;
         bestValue = futilityBase = -VALUE_INFINITE;
+    }
     else
             // Never assume anything on values stored in TT
             if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
                 ss->staticEval = bestValue = evaluate(pos);
             // Can ttValue be used as a better position evaluation?
-            if (   ttValue != VALUE_NONE
+            if (    ttValue != VALUE_NONE
                 && (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER)))
                 bestValue = ttValue;
+        }
         else
             ss->staticEval = bestValue =
         // Stand pat. Return immediately if static value is at least beta
         if (bestValue >= beta)
+        {
             if (!ttHit)
                 tte->save(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER,
-                          DEPTH_NONE, MOVE_NONE, ss->staticEval, TT.generation());
+                          DEPTH_NONE, MOVE_NONE, ss->staticEval);
             return bestValue;
+        }
         if (PvNode && bestValue > alpha)
             alpha = bestValue;
         futilityBase = bestValue + 128;
+    }
+    const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, nullptr, (ss-4)->continuationHistory };
     // 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, &pos.this_thread()->mainHistory, &pos.this_thread()->captureHistory, to_sq((ss-1)->currentMove));
+    MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
+                                      &thisThread->captureHistory,
+                                      contHist,
+                                      to_sq((ss-1)->currentMove));
     // Loop through the moves until no moves remain or a beta cutoff occurs
     while ((move = mp.next_move()) != MOVE_NONE)
+    {
       assert(is_ok(move));
-      givesCheck =  type_of(move) == NORMAL && !pos.discovered_check_candidates()
-                  ? pos.check_squares(type_of(pos.moved_piece(move))) & to_sq(move)
-                  : pos.gives_check(move);
+      givesCheck = gives_check(pos, move);
       moveCount++;
       // Futility pruning
-      if (   !InCheck
+      if (   !inCheck
           && !givesCheck
           &&  futilityBase > -VALUE_KNOWN_WIN
           && !pos.advanced_pawn_push(move))
+      {
           assert(type_of(move) != ENPASSANT); // Due to !pos.advanced_pawn_push
               continue;
+          }
+      }
       // Detect non-capture evasions that are candidates to be pruned
-      evasionPrunable =    InCheck
+      evasionPrunable =    inCheck
                        &&  (depth != DEPTH_ZERO || moveCount > 2)
                        &&  bestValue > VALUE_MATED_IN_MAX_PLY
                        && !pos.capture(move);
       // Don't search moves with negative SEE values
-      if (  (!InCheck || evasionPrunable)
+      if (  (!inCheck || evasionPrunable)
-          &&  !pos.see_ge(move))
+          && !pos.see_ge(move))
           continue;
       // Speculative prefetch as early as possible
       prefetch(TT.first_entry(pos.key_after(move)));
           moveCount--;
           continue;
+      }
       ss->currentMove = move;
+      ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)];
       // Make and search the move
       pos.do_move(move, st, givesCheck);
-      value = givesCheck ? -qsearch<NT,  true>(pos, ss+1, -beta, -alpha, depth - ONE_PLY)
+      value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
-                         : -qsearch<NT, false>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
       pos.undo_move(move);
       assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
       // Check for a new best move
+      {
           bestValue = value;
           if (value > alpha)
+          {
+              bestMove = move;
               if (PvNode) // Update pv even in fail-high case
                   update_pv(ss->pv, move, (ss+1)->pv);
               if (PvNode && value < beta) // Update alpha here!
-              {
                   alpha = value;
-                  bestMove = move;
-              }
+              else
-              else // Fail high
+                  break; // Fail high
-              {
-                  tte->save(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
-                            ttDepth, move, ss->staticEval, TT.generation());
-                  return value;
-              }
+          }
+       }
+    }
     // All legal moves have been searched. A special case: If we're in check
     // and no legal moves were found, it is checkmate.
-    if (InCheck && bestValue == -VALUE_INFINITE)
+    if (inCheck && bestValue == -VALUE_INFINITE)
         return mated_in(ss->ply); // Plies to mate from the root
     tte->save(posKey, value_to_tt(bestValue, ss->ply),
+              bestValue >= beta ? BOUND_LOWER :
-              PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
+              PvNode && bestValue > oldAlpha  ? BOUND_EXACT : BOUND_UPPER,
-              ttDepth, bestMove, ss->staticEval, TT.generation());
+              ttDepth, bestMove, ss->staticEval);
     assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
     return bestValue;
+  }
   void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus) {
     for (int i : {1, 2, 4})
         if (is_ok((ss-i)->currentMove))
-            (ss-i)->contHistory->update(pc, to, bonus);
+            (*(ss-i)->continuationHistory)[pc][to] << bonus;
+  }
   // update_capture_stats() updates move sorting heuristics when a new capture best move is found
                             Move* captures, int captureCnt, int bonus) {
       CapturePieceToHistory& captureHistory =  pos.this_thread()->captureHistory;
       Piece moved_piece = pos.moved_piece(move);
       PieceType captured = type_of(pos.piece_on(to_sq(move)));
+      if (pos.capture_or_promotion(move))
-      captureHistory.update(moved_piece, to_sq(move), captured, bonus);
+          captureHistory[moved_piece][to_sq(move)][captured] << bonus;
       // Decrease all the other played capture moves
       for (int i = 0; i < captureCnt; ++i)
+      {
           moved_piece = pos.moved_piece(captures[i]);
           captured = type_of(pos.piece_on(to_sq(captures[i])));
-          captureHistory.update(moved_piece, to_sq(captures[i]), captured, -bonus);
+          captureHistory[moved_piece][to_sq(captures[i])][captured] << -bonus;
+      }
+  }
-  // update_stats() updates move sorting heuristics when a new quiet best move is found
+  // update_quiet_stats() updates move sorting heuristics when a new quiet best move is found
-  void update_stats(const Position& pos, Stack* ss, Move move,
+  void update_quiet_stats(const Position& pos, Stack* ss, Move move,
-                    Move* quiets, int quietsCnt, int bonus) {
+                          Move* quiets, int quietsCnt, int bonus) {
     if (ss->killers[0] != move)
+    {
         ss->killers[1] = ss->killers[0];
         ss->killers[0] = move;
+    }
-    Color c = pos.side_to_move();
+    Color us = pos.side_to_move();
     Thread* thisThread = pos.this_thread();
-    thisThread->mainHistory.update(c, move, bonus);
+    thisThread->mainHistory[us][from_to(move)] << bonus;
     update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus);
     if (is_ok((ss-1)->currentMove))
+    {
         Square prevSq = to_sq((ss-1)->currentMove);
+    }
     // Decrease all the other played quiet moves
     for (int i = 0; i < quietsCnt; ++i)
+    {
-        thisThread->mainHistory.update(c, quiets[i], -bonus);
+        thisThread->mainHistory[us][from_to(quiets[i])] << -bonus;
         update_continuation_histories(ss, pos.moved_piece(quiets[i]), to_sq(quiets[i]), -bonus);
+    }
+  }
-  // Is the PV leading to a draw position? Assumes all pv moves are legal
-  bool pv_is_draw(Position& pos) {
-    StateInfo st[MAX_PLY];
-    auto& pv = pos.this_thread()->rootMoves[0].pv;
-    for (size_t i = 0; i < pv.size(); ++i)
-        pos.do_move(pv[i], st[i]);
-    bool isDraw = pos.is_draw(pv.size());
-    for (size_t i = pv.size(); i > 0; --i)
-        pos.undo_move(pv[i-1]);
-    return isDraw;
-  }
   // When playing with strength handicap, choose best move among a set of RootMoves
   // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.
   Move Skill::pick_best(size_t multiPV) {
     return best;
+  }
 } // namespace
-  // check_time() is used to print debug info and, more importantly, to detect
+/// MainThread::check_time() is used to print debug info and, more importantly,
-  // when we are out of available time and thus stop the search.
+/// to detect when we are out of available time and thus stop the search.
-  void MainThread::check_time() {
+void MainThread::check_time() {
-    if (--callsCnt > 0)
+  if (--callsCnt > 0)
-        return;
+      return;
-    // At low node count increase the checking rate to about 0.1% of nodes
+  // When using nodes, ensure checking rate is not lower than 0.1% of nodes
-    // otherwise use a default value.
-    callsCnt = Limits.nodes ? std::min(4096, int(Limits.nodes / 1024)) : 4096;
+  callsCnt = Limits.nodes ? std::min(1024, int(Limits.nodes / 1024)) : 1024;
-    static TimePoint lastInfoTime = now();
+  static TimePoint lastInfoTime = now();
-    int elapsed = Time.elapsed();
+  TimePoint elapsed = Time.elapsed();
-    TimePoint tick = Limits.startTime + elapsed;
+  TimePoint tick = Limits.startTime + elapsed;
-    if (tick - lastInfoTime >= 1000)
+  if (tick - lastInfoTime >= 1000)
-    {
+  {
-        lastInfoTime = tick;
+      lastInfoTime = tick;
-        dbg_print();
+      dbg_print();
-    }
+  }
-    // An engine may not stop pondering until told so by the GUI
+  // We should not stop pondering until told so by the GUI
-    if (Threads.ponder)
+  if (Threads.ponder)
-        return;
+      return;
-    if (   (Limits.use_time_management() && elapsed > Time.maximum() - 10)
+  if (   (Limits.use_time_management() && elapsed > Time.maximum() - 10)
-        || (Limits.movetime && elapsed >= Limits.movetime)
+      || (Limits.movetime && elapsed >= Limits.movetime)
-        || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
+      || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
-            Threads.stop = true;
+      Threads.stop = true;
-  }
+}
 /// UCI::pv() formats PV information according to the UCI protocol. UCI requires
 /// that all (if any) unsearched PV lines are sent using a previous search score.
 string UCI::pv(const Position& pos, Depth depth, Value alpha, Value beta) {
   std::stringstream ss;
-  int elapsed = Time.elapsed() + 1;
+  TimePoint elapsed = Time.elapsed() + 1;
   const RootMoves& rootMoves = pos.this_thread()->rootMoves;
-  size_t PVIdx = pos.this_thread()->PVIdx;
+  size_t pvIdx = pos.this_thread()->pvIdx;
   size_t multiPV = std::min((size_t)Options["MultiPV"], rootMoves.size());
   uint64_t nodesSearched = Threads.nodes_searched();
   uint64_t tbHits = Threads.tb_hits() + (TB::RootInTB ? rootMoves.size() : 0);
   for (size_t i = 0; i < multiPV; ++i)
+  {
-      bool updated = (i <= PVIdx && rootMoves[i].score != -VALUE_INFINITE);
+      bool updated = (i <= pvIdx && rootMoves[i].score != -VALUE_INFINITE);
       if (depth == ONE_PLY && !updated)
           continue;
       Depth d = updated ? depth : depth - ONE_PLY;
       Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
       bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
-      v = tb ? TB::Score : v;
+      v = tb ? rootMoves[i].tbScore : v;
       if (ss.rdbuf()->in_avail()) // Not at first line
           ss << "\n";
       ss << "info"
          << " depth "    << d / ONE_PLY
          << " seldepth " << rootMoves[i].selDepth
          << " multipv "  << i + 1
          << " score "    << UCI::value(v);
-      if (!tb && i == PVIdx)
+      if (!tb && i == pvIdx)
           ss << (v >= beta ? " lowerbound" : v <= alpha ? " upperbound" : "");
       ss << " nodes "    << nodesSearched
          << " nps "      << nodesSearched * 1000 / elapsed;
     pos.undo_move(pv[0]);
     return pv.size() > 1;
+}
-void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves) {
+void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) {
     RootInTB = false;
-    UseRule50 = Options["Syzygy50MoveRule"];
+    UseRule50 = bool(Options["Syzygy50MoveRule"]);
-    ProbeDepth = Options["SyzygyProbeDepth"] * ONE_PLY;
+    ProbeDepth = int(Options["SyzygyProbeDepth"]) * ONE_PLY;
-    Cardinality = Options["SyzygyProbeLimit"];
+    Cardinality = int(Options["SyzygyProbeLimit"]);
+    bool dtz_available = true;
-    // Skip TB probing when no TB found: !TBLargest -> !TB::Cardinality
+    // Tables with fewer pieces than SyzygyProbeLimit are searched with
+    // ProbeDepth == DEPTH_ZERO
     if (Cardinality > MaxCardinality)
+    {
         Cardinality = MaxCardinality;
         ProbeDepth = DEPTH_ZERO;
+    }
-    if (Cardinality < popcount(pos.pieces()) || pos.can_castle(ANY_CASTLING))
+    if (Cardinality >= popcount(pos.pieces()) && !pos.can_castle(ANY_CASTLING))
-        return;
+    {
+        // Rank moves using DTZ tables
+        RootInTB = root_probe(pos, rootMoves);
-    // Don't filter any moves if the user requested analysis on multiple
-    if (Options["MultiPV"] != 1)
+        if (!RootInTB)
-        return;
+        {
-    // If the current root position is in the tablebases, then RootMoves
+            // DTZ tables are missing; try to rank moves using WDL tables
-    // contains only moves that preserve the draw or the win.
+            dtz_available = false;
-    RootInTB = root_probe(pos, rootMoves, TB::Score);
+            RootInTB = root_probe_wdl(pos, rootMoves);
+        }
+    }
     if (RootInTB)
-        Cardinality = 0; // Do not probe tablebases during the search
-    else // If DTZ tables are missing, use WDL tables as a fallback
+    {
-        // Filter out moves that do not preserve the draw or the win.
+        // Sort moves according to TB rank
-        RootInTB = root_probe_wdl(pos, rootMoves, TB::Score);
+        std::sort(rootMoves.begin(), rootMoves.end(),
+                  [](const RootMove &a, const RootMove &b) { return a.tbRank > b.tbRank; } );
-        // Only probe during search if winning
+        // Probe during search only if DTZ is not available and we are winning
-        if (RootInTB && TB::Score <= VALUE_DRAW)
+        if (dtz_available || rootMoves[0].tbScore <= VALUE_DRAW)
             Cardinality = 0;
+    }
-    if (RootInTB && !UseRule50)
+    else
-        TB::Score =  TB::Score > VALUE_DRAW ?  VALUE_MATE - MAX_PLY - 1
-                   : TB::Score < VALUE_DRAW ? -VALUE_MATE + MAX_PLY + 1
-                                            :  VALUE_DRAW;
+    {
-    // Since root_probe() and root_probe_wdl() dirty the root move scores,
-    // we reset them to -VALUE_INFINITE
+        // Assign the same rank to all moves
-    for (RootMove& rm : rootMoves)
+        for (auto& m : rootMoves)
-        rm.score = -VALUE_INFINITE;
+            m.tbRank = 0;
+    }
+}

Subversion Repositories Games.Chess Giants

Games.Chess Giants//engine-stockfish/search.cpp – Rev 169 → 185