Retire can_return_tt() and rewirte TT-hit code

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 3793766b9f845e931c52338010add92eba868e65..a3d8781889a690e15e0b91c4044c0243245f90d1 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -55,6 +55,9 @@ namespace {
   // Set to true to force running with one thread. Used for debugging
   const bool FakeSplit = false;
 
   // Set to true to force running with one thread. Used for debugging
   const bool FakeSplit = false;
 

+  // This is the minimum interval in msec between two check_time() calls
+  const int TimerResolution = 5;
+

   // Different node types, used as template parameter
   enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
 
   // Different node types, used as template parameter
   enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
 


@@ -62,28 +65,9 @@ namespace {
   const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
   inline bool piece_is_slider(Piece p) { return Slidings[p]; }
 
   const bool Slidings[18] = { 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1 };
   inline bool piece_is_slider(Piece p) { return Slidings[p]; }
 

-  // Maximum depth for razoring
-  const Depth RazorDepth = 4 * ONE_PLY;
-

   // Dynamic razoring margin based on depth
   inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
 
   // Dynamic razoring margin based on depth
   inline Value razor_margin(Depth d) { return Value(512 + 16 * int(d)); }
 

-  // Maximum depth for use of dynamic threat detection when null move fails low
-  const Depth ThreatDepth = 5 * ONE_PLY;
-
-  // Minimum depth for use of internal iterative deepening
-  const Depth IIDDepth[] = { 8 * ONE_PLY, 5 * ONE_PLY };
-
-  // At Non-PV nodes we do an internal iterative deepening search
-  // when the static evaluation is bigger then beta - IIDMargin.
-  const Value IIDMargin = Value(256);
-
-  // Minimum depth for use of singular extension
-  const Depth SingularExtensionDepth[] = { 8 * ONE_PLY, 6 * ONE_PLY };
-
-  // Futility margin for quiescence search
-  const Value FutilityMarginQS = Value(128);
-

   // Futility lookup tables (initialized at startup) and their access functions
   Value FutilityMargins[16][64]; // [depth][moveNumber]
   int FutilityMoveCounts[32];    // [depth]
   // Futility lookup tables (initialized at startup) and their access functions
   Value FutilityMargins[16][64]; // [depth][moveNumber]
   int FutilityMoveCounts[32];    // [depth]


@@ -94,11 +78,6 @@ namespace {
                            : 2 * VALUE_INFINITE;
   }
 
                            : 2 * VALUE_INFINITE;
   }
 

-  inline int futility_move_count(Depth d) {
-
-    return d < 16 * ONE_PLY ? FutilityMoveCounts[d] : MAX_MOVES;
-  }
-

   // Reduction lookup tables (initialized at startup) and their access function
   int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
 
   // Reduction lookup tables (initialized at startup) and their access function
   int8_t Reductions[2][64][64]; // [pv][depth][moveNumber]
 


@@ -107,14 +86,6 @@ namespace {
     return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
   }
 
     return (Depth) Reductions[PvNode][std::min(int(d) / ONE_PLY, 63)][std::min(mn, 63)];
   }
 

-  // Easy move margin. An easy move candidate must be at least this much better
-  // than the second best move.
-  const Value EasyMoveMargin = Value(0x150);
-
-  // This is the minimum interval in msec between two check_time() calls
-  const int TimerResolution = 5;
-
-

   size_t MultiPV, UCIMultiPV, PVIdx;
   TimeManager TimeMgr;
   int BestMoveChanges;
   size_t MultiPV, UCIMultiPV, PVIdx;
   TimeManager TimeMgr;
   int BestMoveChanges;


@@ -122,7 +93,6 @@ namespace {
   bool SkillLevelEnabled, Chess960;
   History H;
 
   bool SkillLevelEnabled, Chess960;
   History H;
 

-

   template <NodeType NT>
   Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
 
   template <NodeType NT>
   Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
 


@@ -134,36 +104,11 @@ namespace {
   bool connected_moves(const Position& pos, Move m1, Move m2);
   Value value_to_tt(Value v, int ply);
   Value value_from_tt(Value v, int ply);
   bool connected_moves(const Position& pos, Move m1, Move m2);
   Value value_to_tt(Value v, int ply);
   Value value_from_tt(Value v, int ply);

-  bool can_return_tt(const TTEntry* tte, Depth depth, Value ttValue, Value beta);

   bool connected_threat(const Position& pos, Move m, Move threat);
   Value refine_eval(const TTEntry* tte, Value ttValue, Value defaultEval);
   Move do_skill_level();
   string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
 
   bool connected_threat(const Position& pos, Move m, Move threat);
   Value refine_eval(const TTEntry* tte, Value ttValue, Value defaultEval);
   Move do_skill_level();
   string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
 

-  // is_dangerous() checks whether a move belongs to some classes of known
-  // 'dangerous' moves so that we avoid to prune it.
-  FORCE_INLINE bool is_dangerous(const Position& pos, Move m, bool captureOrPromotion) {
-
-    // Castle move?
-    if (type_of(m) == CASTLE)
-        return true;
-
-    // Passed pawn move?
-    if (   type_of(pos.piece_moved(m)) == PAWN
-        && pos.pawn_is_passed(pos.side_to_move(), to_sq(m)))
-        return true;
-
-    // Entering a pawn endgame?
-    if (    captureOrPromotion
-        &&  type_of(pos.piece_on(to_sq(m))) != PAWN
-        &&  type_of(m) == NORMAL
-        && (  pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
-            - PieceValue[Mg][pos.piece_on(to_sq(m))] == VALUE_ZERO))
-        return true;
-
-    return false;
-  }
-

 } // namespace
 
 
 } // namespace
 
 


@@ -229,6 +174,9 @@ void Search::think() {
   Position& pos = RootPosition;
   Chess960 = pos.is_chess960();
   Eval::RootColor = pos.side_to_move();
   Position& pos = RootPosition;
   Chess960 = pos.is_chess960();
   Eval::RootColor = pos.side_to_move();

+  int scaledCF = Eval::ContemptFactor * MaterialTable::game_phase(pos) / PHASE_MIDGAME;
+  Eval::ValueDraw[ Eval::RootColor] = VALUE_DRAW - Value(scaledCF);
+  Eval::ValueDraw[~Eval::RootColor] = VALUE_DRAW + Value(scaledCF);

   TimeMgr.init(Limits, pos.startpos_ply_counter(), pos.side_to_move());
   TT.new_search();
   H.clear();
   TimeMgr.init(Limits, pos.startpos_ply_counter(), pos.side_to_move());
   TT.new_search();
   H.clear();


@@ -469,7 +417,7 @@ namespace {
                 && (   (bestMoveNeverChanged &&  pos.captured_piece_type())
                     || Time::now() - SearchTime > (TimeMgr.available_time() * 40) / 100))
             {
                 && (   (bestMoveNeverChanged &&  pos.captured_piece_type())
                     || Time::now() - SearchTime > (TimeMgr.available_time() * 40) / 100))
             {

-                Value rBeta = bestValue - EasyMoveMargin;
+                Value rBeta = bestValue - 2 * PawnValueMg;

                 (ss+1)->excludedMove = RootMoves[0].pv[0];
                 (ss+1)->skipNullMove = true;
                 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth - 3) * ONE_PLY);
                 (ss+1)->excludedMove = RootMoves[0].pv[0];
                 (ss+1)->skipNullMove = true;
                 Value v = search<NonPV>(pos, ss+1, rBeta - 1, rBeta, (depth - 3) * ONE_PLY);


@@ -528,51 +476,47 @@ namespace {
     Key posKey;
     Move ttMove, move, excludedMove, bestMove, threatMove;
     Depth ext, newDepth;
     Key posKey;
     Move ttMove, move, excludedMove, bestMove, threatMove;
     Depth ext, newDepth;

-    Bound bt;
-    Value bestValue, value, oldAlpha, ttValue;
+    Value bestValue, value, ttValue;

     Value refinedValue, nullValue, futilityValue;
     Value refinedValue, nullValue, futilityValue;

-    bool pvMove, inCheck, singularExtensionNode, givesCheck;
+    bool inCheck, givesCheck, pvMove, singularExtensionNode;

     bool captureOrPromotion, dangerous, doFullDepthSearch;
     int moveCount, playedMoveCount;
 
     bool captureOrPromotion, dangerous, doFullDepthSearch;
     int moveCount, playedMoveCount;
 

+    // Step 1. Initialize node

     Thread* thisThread = pos.this_thread();
     moveCount = playedMoveCount = 0;
     Thread* thisThread = pos.this_thread();
     moveCount = playedMoveCount = 0;

-    oldAlpha = alpha;

     inCheck = pos.in_check();
     inCheck = pos.in_check();

-    ss->ply = (ss-1)->ply + 1;
-
-    // Used to send selDepth info to GUI
-    if (PvNode && thisThread->maxPly < ss->ply)
-        thisThread->maxPly = ss->ply;

 
 

-    // Step 1. Initialize node

     if (SpNode)
     {
     if (SpNode)
     {

+        sp = ss->sp;
+        bestMove   = sp->bestMove;
+        threatMove = sp->threatMove;
+        bestValue  = sp->bestValue;

         tte = NULL;
         ttMove = excludedMove = MOVE_NONE;
         ttValue = VALUE_NONE;
         tte = NULL;
         ttMove = excludedMove = MOVE_NONE;
         ttValue = VALUE_NONE;

-        sp = ss->sp;
-        bestMove = sp->bestMove;
-        threatMove = sp->threatMove;
-        bestValue = sp->bestValue;

 
 

-        assert(bestValue > -VALUE_INFINITE && sp->moveCount > 0);
+        assert(sp->bestValue > -VALUE_INFINITE && sp->moveCount > 0);

 
         goto split_point_start;
     }
 
         goto split_point_start;
     }

-    else
-    {
-        bestValue = -VALUE_INFINITE;
-        ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
-        (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
-        (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
-    }
+
+    bestValue = -VALUE_INFINITE;
+    ss->currentMove = threatMove = (ss+1)->excludedMove = bestMove = MOVE_NONE;
+    ss->ply = (ss-1)->ply + 1;
+    (ss+1)->skipNullMove = false; (ss+1)->reduction = DEPTH_ZERO;
+    (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
+
+    // Used to send selDepth info to GUI
+    if (PvNode && thisThread->maxPly < ss->ply)
+        thisThread->maxPly = ss->ply;

 
     if (!RootNode)
     {
         // Step 2. Check for aborted search and immediate draw
         if (Signals.stop || pos.is_draw<false>() || ss->ply > MAX_PLY)
 
     if (!RootNode)
     {
         // Step 2. Check for aborted search and immediate draw
         if (Signals.stop || pos.is_draw<false>() || ss->ply > MAX_PLY)

-            return VALUE_DRAW;
+            return Eval::ValueDraw[pos.side_to_move()];

 
         // 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
 
         // 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


@@ -599,8 +543,11 @@ namespace {
     // a fail high/low. Biggest advantage at probing at PV nodes is to have a
     // smooth experience in analysis mode. We don't probe at Root nodes otherwise
     // we should also update RootMoveList to avoid bogus output.
     // a fail high/low. Biggest advantage at probing at PV nodes is to have a
     // smooth experience in analysis mode. We don't probe at Root nodes otherwise
     // we should also update RootMoveList to avoid bogus output.

-    if (!RootNode && tte && (PvNode ? tte->depth() >= depth && tte->type() == BOUND_EXACT
-                                    : can_return_tt(tte, depth, ttValue, beta)))
+    if (   !RootNode
+        && tte && tte->depth() >= depth
+        && (           PvNode ?  tte->type() == BOUND_EXACT
+            : ttValue >= beta ? (tte->type() & BOUND_LOWER)
+                              : (tte->type() & BOUND_UPPER)))

     {
         TT.refresh(tte);
         ss->currentMove = ttMove; // Can be MOVE_NONE
     {
         TT.refresh(tte);
         ss->currentMove = ttMove; // Can be MOVE_NONE


@@ -647,7 +594,7 @@ namespace {
 
     // Step 6. Razoring (is omitted in PV nodes)
     if (   !PvNode
 
     // Step 6. Razoring (is omitted in PV nodes)
     if (   !PvNode

-        &&  depth < RazorDepth
+        &&  depth < 4 * ONE_PLY

         && !inCheck
         &&  refinedValue + razor_margin(depth) < beta
         &&  ttMove == MOVE_NONE
         && !inCheck
         &&  refinedValue + razor_margin(depth) < beta
         &&  ttMove == MOVE_NONE


@@ -667,12 +614,12 @@ namespace {
     // the score by more than futility_margin(depth) if we do a null move.
     if (   !PvNode
         && !ss->skipNullMove
     // the score by more than futility_margin(depth) if we do a null move.
     if (   !PvNode
         && !ss->skipNullMove

-        &&  depth < RazorDepth
+        &&  depth < 4 * ONE_PLY

         && !inCheck
         && !inCheck

-        &&  refinedValue - futility_margin(depth, 0) >= beta
+        &&  refinedValue - FutilityMargins[depth][0] >= beta

         &&  abs(beta) < VALUE_MATE_IN_MAX_PLY
         &&  pos.non_pawn_material(pos.side_to_move()))
         &&  abs(beta) < VALUE_MATE_IN_MAX_PLY
         &&  pos.non_pawn_material(pos.side_to_move()))

-        return refinedValue - futility_margin(depth, 0);
+        return refinedValue - FutilityMargins[depth][0];

 
     // Step 8. Null move search with verification search (is omitted in PV nodes)
     if (   !PvNode
 
     // Step 8. Null move search with verification search (is omitted in PV nodes)
     if (   !PvNode


@@ -726,7 +673,7 @@ namespace {
             // parent node, which will trigger a re-search with full depth).
             threatMove = (ss+1)->currentMove;
 
             // parent node, which will trigger a re-search with full depth).
             threatMove = (ss+1)->currentMove;
 

-            if (   depth < ThreatDepth
+            if (   depth < 5 * ONE_PLY

                 && (ss-1)->reduction
                 && threatMove != MOVE_NONE
                 && connected_moves(pos, (ss-1)->currentMove, threatMove))
                 && (ss-1)->reduction
                 && threatMove != MOVE_NONE
                 && connected_moves(pos, (ss-1)->currentMove, threatMove))


@@ -739,7 +686,7 @@ namespace {
     // and a reduced search returns a value much above beta, we can (almost) safely
     // prune the previous move.
     if (   !PvNode
     // and a reduced search returns a value much above beta, we can (almost) safely
     // prune the previous move.
     if (   !PvNode

-        &&  depth >= RazorDepth + ONE_PLY
+        &&  depth >= 5 * ONE_PLY

         && !inCheck
         && !ss->skipNullMove
         &&  excludedMove == MOVE_NONE
         && !inCheck
         && !ss->skipNullMove
         &&  excludedMove == MOVE_NONE


@@ -768,9 +715,9 @@ namespace {
     }
 
     // Step 10. Internal iterative deepening
     }
 
     // Step 10. Internal iterative deepening

-    if (   depth >= IIDDepth[PvNode]
+    if (   depth >= (PvNode ? 5 * ONE_PLY : 8 * ONE_PLY)

         && ttMove == MOVE_NONE
         && ttMove == MOVE_NONE

-        && (PvNode || (!inCheck && ss->eval + IIDMargin >= beta)))
+        && (PvNode || (!inCheck && ss->eval + Value(256) >= beta)))

     {
         Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
 
     {
         Depth d = (PvNode ? depth - 2 * ONE_PLY : depth / 2);
 


@@ -789,7 +736,7 @@ split_point_start: // At split points actual search starts from here
     value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
     singularExtensionNode =   !RootNode
                            && !SpNode
     value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc
     singularExtensionNode =   !RootNode
                            && !SpNode

-                           &&  depth >= SingularExtensionDepth[PvNode]
+                           &&  depth >= (PvNode ? 6 * ONE_PLY : 8 * ONE_PLY)

                            &&  ttMove != MOVE_NONE
                            && !excludedMove // Recursive singular search is not allowed
                            && (tte->type() & BOUND_LOWER)
                            &&  ttMove != MOVE_NONE
                            && !excludedMove // Recursive singular search is not allowed
                            && (tte->type() & BOUND_LOWER)


@@ -797,10 +744,7 @@ split_point_start: // At split points actual search starts from here
 
     // Step 11. Loop through moves
     // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
 
     // Step 11. Loop through moves
     // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs

-    while (    bestValue < beta
-           && (move = mp.next_move<SpNode>()) != MOVE_NONE
-           && !thisThread->cutoff_occurred()
-           && !Signals.stop)
+    while ((move = mp.next_move<SpNode>()) != MOVE_NONE)

     {
       assert(is_ok(move));
 
     {
       assert(is_ok(move));
 


@@ -835,10 +779,17 @@ split_point_start: // At split points actual search starts from here
                         << " currmovenumber " << moveCount + PVIdx << sync_endl;
       }
 
                         << " currmovenumber " << moveCount + PVIdx << sync_endl;
       }
 

+      ext = DEPTH_ZERO;

       captureOrPromotion = pos.is_capture_or_promotion(move);
       givesCheck = pos.move_gives_check(move, ci);
       captureOrPromotion = pos.is_capture_or_promotion(move);
       givesCheck = pos.move_gives_check(move, ci);

-      dangerous = givesCheck || is_dangerous(pos, move, captureOrPromotion);
-      ext = DEPTH_ZERO;
+      dangerous =   givesCheck
+                 || pos.is_passed_pawn_push(move)
+                 || type_of(move) == CASTLE
+                 || (   captureOrPromotion // Entering a pawn endgame?
+                     && type_of(pos.piece_on(to_sq(move))) != PAWN
+                     && type_of(move) == NORMAL
+                     && (  pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
+                         - PieceValue[Mg][pos.piece_on(to_sq(move))] == VALUE_ZERO));

 
       // Step 12. Extend checks and, in PV nodes, also dangerous moves
       if (PvNode && dangerous)
 
       // Step 12. Extend checks and, in PV nodes, also dangerous moves
       if (PvNode && dangerous)


@@ -866,7 +817,7 @@ split_point_start: // At split points actual search starts from here
           ss->excludedMove = MOVE_NONE;
 
           if (value < rBeta)
           ss->excludedMove = MOVE_NONE;
 
           if (value < rBeta)

-              ext = ONE_PLY;
+              ext = rBeta >= beta ? ONE_PLY + ONE_PLY / 2 : ONE_PLY;

       }
 
       // Update current move (this must be done after singular extension search)
       }
 
       // Update current move (this must be done after singular extension search)


@@ -878,10 +829,12 @@ split_point_start: // At split points actual search starts from here
           && !inCheck
           && !dangerous
           &&  move != ttMove
           && !inCheck
           && !dangerous
           &&  move != ttMove

-          && (bestValue > VALUE_MATED_IN_MAX_PLY || bestValue == -VALUE_INFINITE))
+          && (bestValue > VALUE_MATED_IN_MAX_PLY || (   bestValue == -VALUE_INFINITE
+                                                     && alpha > VALUE_MATED_IN_MAX_PLY)))

       {
           // Move count based pruning
       {
           // Move count based pruning

-          if (   moveCount >= futility_move_count(depth)
+          if (   depth < 16 * ONE_PLY
+              && moveCount >= FutilityMoveCounts[depth]

               && (!threatMove || !connected_threat(pos, move, threatMove)))
           {
               if (SpNode)
               && (!threatMove || !connected_threat(pos, move, threatMove)))
           {
               if (SpNode)


@@ -984,7 +937,10 @@ split_point_start: // At split points actual search starts from here
       // was aborted because the user interrupted the search or because we
       // ran out of time. In this case, the return value of the search cannot
       // be trusted, and we don't update the best move and/or PV.
       // was aborted because the user interrupted the search or because we
       // ran out of time. In this case, the return value of the search cannot
       // be trusted, and we don't update the best move and/or PV.

-      if (RootNode && !Signals.stop)
+      if (Signals.stop || thisThread->cutoff_occurred())
+          return bestValue;
+
+      if (RootNode)

       {
           RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
 
       {
           RootMove& rm = *std::find(RootMoves.begin(), RootMoves.end(), move);
 


@@ -1005,82 +961,80 @@ split_point_start: // At split points actual search starts from here
               // is not a problem when sorting becuase sort is stable and move
               // position in the list is preserved, just the PV is pushed up.
               rm.score = -VALUE_INFINITE;
               // is not a problem when sorting becuase sort is stable and move
               // position in the list is preserved, just the PV is pushed up.
               rm.score = -VALUE_INFINITE;

-

       }
 
       if (value > bestValue)
       {
           bestValue = value;
       }
 
       if (value > bestValue)
       {
           bestValue = value;

-          bestMove = move;
-
-          if (   PvNode
-              && value > alpha
-              && value < beta) // We want always alpha < beta
-              alpha = value;
+          if (SpNode) sp->bestValue = value;

 
 

-          if (SpNode && !thisThread->cutoff_occurred())
+          if (value > alpha)

           {
           {

-              sp->bestValue = value;
-              sp->bestMove = move;
-              sp->alpha = alpha;
+              bestMove = move;
+              if (SpNode) sp->bestMove = move;

 
 

-              if (value >= beta)
-                  sp->cutoff = true;
+              if (PvNode && value < beta)
+              {
+                  alpha = value; // Update alpha here! Always alpha < beta
+                  if (SpNode) sp->alpha = value;
+              }
+              else // Fail high
+              {
+                  if (SpNode) sp->cutoff = true;
+                  break;
+              }

           }
       }
 
           }
       }
 

-      // Step 19. Check for split
+      // Step 19. Check for splitting the search

       if (   !SpNode
           &&  depth >= Threads.min_split_depth()
           &&  bestValue < beta
       if (   !SpNode
           &&  depth >= Threads.min_split_depth()
           &&  bestValue < beta

-          &&  Threads.available_slave_exists(thisThread)
-          && !Signals.stop
-          && !thisThread->cutoff_occurred())
+          &&  Threads.available_slave_exists(thisThread))
+      {

           bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,
           bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,

-                                               depth, threatMove, moveCount, &mp, NT);
+                                               depth, threatMove, moveCount, mp, NT);
+          break;
+      }

     }
 
     }
 

+    if (SpNode)
+        return bestValue;
+

     // Step 20. Check for mate and stalemate
     // All legal moves have been searched and if there are no legal moves, it
     // must be mate or stalemate. Note that we can have a false positive in
     // case of Signals.stop or thread.cutoff_occurred() are set, but this is
     // harmless because return value is discarded anyhow in the parent nodes.
     // If we are in a singular extension search then return a fail low score.
     // Step 20. Check for mate and stalemate
     // All legal moves have been searched and if there are no legal moves, it
     // must be mate or stalemate. Note that we can have a false positive in
     // case of Signals.stop or thread.cutoff_occurred() are set, but this is
     // harmless because return value is discarded anyhow in the parent nodes.
     // If we are in a singular extension search then return a fail low score.

+    // A split node has at least one move, the one tried before to be splitted.

     if (!moveCount)
     if (!moveCount)

-        return excludedMove ? oldAlpha : inCheck ? mated_in(ss->ply) : VALUE_DRAW;
+        return excludedMove ? alpha : inCheck ? mated_in(ss->ply) : VALUE_DRAW;

 
     // If we have pruned all the moves without searching return a fail-low score
     if (bestValue == -VALUE_INFINITE)
     {
         assert(!playedMoveCount);
 
 
     // If we have pruned all the moves without searching return a fail-low score
     if (bestValue == -VALUE_INFINITE)
     {
         assert(!playedMoveCount);
 

-        bestValue = oldAlpha;
+        bestValue = alpha;

     }
 
     }
 

-    // Step 21. Update tables
-    // Update transposition table entry, killers and history
-    if (!SpNode && !Signals.stop && !thisThread->cutoff_occurred())
+    if (bestValue >= beta) // Failed high

     {
     {

-        move = bestValue <= oldAlpha ? MOVE_NONE : bestMove;
-        bt   = bestValue <= oldAlpha ? BOUND_UPPER
-             : bestValue >= beta ? BOUND_LOWER : BOUND_EXACT;
-
-        TT.store(posKey, value_to_tt(bestValue, ss->ply), bt, depth, move, ss->eval, ss->evalMargin);
+        TT.store(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER, depth,
+                 bestMove, ss->eval, ss->evalMargin);

 
 

-        // Update killers and history for non capture cut-off moves
-        if (    bestValue >= beta
-            && !pos.is_capture_or_promotion(move)
-            && !inCheck)
+        if (!pos.is_capture_or_promotion(bestMove) && !inCheck)

         {
         {

-            if (move != ss->killers[0])
+            if (bestMove != ss->killers[0])

             {
                 ss->killers[1] = ss->killers[0];
             {
                 ss->killers[1] = ss->killers[0];

-                ss->killers[0] = move;
+                ss->killers[0] = bestMove;

             }
 
             // Increase history value of the cut-off move
             Value bonus = Value(int(depth) * int(depth));
             }
 
             // Increase history value of the cut-off move
             Value bonus = Value(int(depth) * int(depth));

-            H.add(pos.piece_moved(move), to_sq(move), bonus);
+            H.add(pos.piece_moved(bestMove), to_sq(bestMove), bonus);

 
             // Decrease history of all the other played non-capture moves
             for (int i = 0; i < playedMoveCount - 1; i++)
 
             // Decrease history of all the other played non-capture moves
             for (int i = 0; i < playedMoveCount - 1; i++)


@@ -1090,6 +1044,10 @@ split_point_start: // At split points actual search starts from here
             }
         }
     }
             }
         }
     }

+    else // Failed low or PV search
+        TT.store(posKey, value_to_tt(bestValue, ss->ply),
+                 PvNode && bestMove != MOVE_NONE ? BOUND_EXACT : BOUND_UPPER,
+                 depth, bestMove, ss->eval, ss->evalMargin);

 
     assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
 
 
     assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
 


@@ -1108,38 +1066,41 @@ split_point_start: // At split points actual search starts from here
 
     assert(NT == PV || NT == NonPV);
     assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
 
     assert(NT == PV || NT == NonPV);
     assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);

-    assert((alpha == beta - 1) || PvNode);
+    assert(PvNode || (alpha == beta - 1));

     assert(depth <= DEPTH_ZERO);
 
     StateInfo st;
     assert(depth <= DEPTH_ZERO);
 
     StateInfo st;

-    Move ttMove, move, bestMove;
-    Value ttValue, bestValue, value, evalMargin, futilityValue, futilityBase;
-    bool inCheck, enoughMaterial, givesCheck, evasionPrunable;

     const TTEntry* tte;
     const TTEntry* tte;

+    Key posKey;
+    Move ttMove, move, bestMove;
+    Value bestValue, value, ttValue, futilityValue, futilityBase;
+    bool inCheck, givesCheck, enoughMaterial, evasionPrunable;

     Depth ttDepth;
     Depth ttDepth;

-    Bound bt;
-    Value oldAlpha = alpha;

 
 

+    inCheck = pos.in_check();

     ss->currentMove = bestMove = MOVE_NONE;
     ss->ply = (ss-1)->ply + 1;
 
     // Check for an instant draw or maximum ply reached
     if (pos.is_draw<true>() || ss->ply > MAX_PLY)
     ss->currentMove = bestMove = MOVE_NONE;
     ss->ply = (ss-1)->ply + 1;
 
     // Check for an instant draw or maximum ply reached
     if (pos.is_draw<true>() || ss->ply > MAX_PLY)

-        return VALUE_DRAW;
+        return Eval::ValueDraw[pos.side_to_move()];
+
+    // Transposition table lookup. At PV nodes, we don't use the TT for
+    // pruning, but only for move ordering.
+    posKey = pos.key();
+    tte = TT.probe(posKey);
+    ttMove = tte ? tte->move() : MOVE_NONE;
+    ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_NONE;

 
     // 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.
 
     // 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.

-    inCheck = pos.in_check();
-    ttDepth = (inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS);
+    ttDepth = inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS;

 
 

-    // Transposition table lookup. At PV nodes, we don't use the TT for
-    // pruning, but only for move ordering.
-    tte = TT.probe(pos.key());
-    ttMove = (tte ? tte->move() : MOVE_NONE);
-    ttValue = tte ? value_from_tt(tte->value(),ss->ply) : VALUE_ZERO;
-
-    if (!PvNode && tte && can_return_tt(tte, ttDepth, ttValue, beta))
+    if (   tte && tte->depth() >= ttDepth
+        && (           PvNode ?  tte->type() == BOUND_EXACT
+            : ttValue >= beta ? (tte->type() & BOUND_LOWER)
+                              : (tte->type() & BOUND_UPPER)))

     {
         ss->currentMove = ttMove; // Can be MOVE_NONE
         return ttValue;
     {
         ss->currentMove = ttMove; // Can be MOVE_NONE
         return ttValue;


@@ -1148,8 +1109,8 @@ split_point_start: // At split points actual search starts from here
     // Evaluate the position statically
     if (inCheck)
     {
     // Evaluate the position statically
     if (inCheck)
     {

+        ss->eval = ss->evalMargin = VALUE_NONE;

         bestValue = futilityBase = -VALUE_INFINITE;
         bestValue = futilityBase = -VALUE_INFINITE;

-        ss->eval = evalMargin = VALUE_NONE;

         enoughMaterial = false;
     }
     else
         enoughMaterial = false;
     }
     else


@@ -1158,17 +1119,17 @@ split_point_start: // At split points actual search starts from here
         {
             assert(tte->static_value() != VALUE_NONE);
 
         {
             assert(tte->static_value() != VALUE_NONE);
 

-            evalMargin = tte->static_value_margin();

             ss->eval = bestValue = tte->static_value();
             ss->eval = bestValue = tte->static_value();

+            ss->evalMargin = tte->static_value_margin();

         }
         else
         }
         else

-            ss->eval = bestValue = evaluate(pos, evalMargin);
+            ss->eval = bestValue = evaluate(pos, ss->evalMargin);

 
         // Stand pat. Return immediately if static value is at least beta
         if (bestValue >= beta)
         {
             if (!tte)
 
         // Stand pat. Return immediately if static value is at least beta
         if (bestValue >= beta)
         {
             if (!tte)

-                TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, evalMargin);
+                TT.store(pos.key(), value_to_tt(bestValue, ss->ply), BOUND_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, ss->evalMargin);

 
             return bestValue;
         }
 
             return bestValue;
         }


@@ -1176,7 +1137,7 @@ split_point_start: // At split points actual search starts from here
         if (PvNode && bestValue > alpha)
             alpha = bestValue;
 
         if (PvNode && bestValue > alpha)
             alpha = bestValue;
 

-        futilityBase = ss->eval + evalMargin + FutilityMarginQS;
+        futilityBase = ss->eval + ss->evalMargin + Value(128);

         enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMg;
     }
 
         enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMg;
     }
 


@@ -1188,8 +1149,7 @@ split_point_start: // At split points actual search starts from here
     CheckInfo ci(pos);
 
     // Loop through the moves until no moves remain or a beta cutoff occurs
     CheckInfo ci(pos);
 
     // Loop through the moves until no moves remain or a beta cutoff occurs

-    while (   bestValue < beta
-           && (move = mp.next_move<false>()) != MOVE_NONE)
+    while ((move = mp.next_move<false>()) != MOVE_NONE)

     {
       assert(is_ok(move));
 
     {
       assert(is_ok(move));
 


@@ -1256,21 +1216,31 @@ split_point_start: // At split points actual search starts from here
 
       // Make and search the move
       pos.do_move(move, st, ci, givesCheck);
 
       // Make and search the move
       pos.do_move(move, st, ci, givesCheck);

-      value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth-ONE_PLY);
+      value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);

       pos.undo_move(move);
 
       assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
 
       pos.undo_move(move);
 
       assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
 

-      // New best move?
+      // Check for new best move

       if (value > bestValue)
       {
           bestValue = value;
       if (value > bestValue)
       {
           bestValue = value;

-          bestMove = move;

 
 

-          if (   PvNode
-              && value > alpha
-              && value < beta) // We want always alpha < beta
-              alpha = value;
+          if (value > alpha)
+          {
+              if (PvNode && value < beta) // Update alpha here! Always alpha < beta
+              {
+                  alpha = value;
+                  bestMove = move;
+              }
+              else // Fail high
+              {
+                  TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
+                           ttDepth, move, ss->eval, ss->evalMargin);
+
+                  return value;
+              }
+          }

        }
     }
 
        }
     }
 


@@ -1279,12 +1249,9 @@ split_point_start: // At split points actual search starts from here
     if (inCheck && bestValue == -VALUE_INFINITE)
         return mated_in(ss->ply); // Plies to mate from the root
 
     if (inCheck && bestValue == -VALUE_INFINITE)
         return mated_in(ss->ply); // Plies to mate from the root
 

-    // Update transposition table
-    move = bestValue <= oldAlpha ? MOVE_NONE : bestMove;
-    bt   = bestValue <= oldAlpha ? BOUND_UPPER
-         : bestValue >= beta ? BOUND_LOWER : BOUND_EXACT;
-
-    TT.store(pos.key(), value_to_tt(bestValue, ss->ply), bt, ttDepth, move, ss->eval, evalMargin);
+    TT.store(posKey, value_to_tt(bestValue, ss->ply),
+             PvNode && bestMove != MOVE_NONE ? BOUND_EXACT : BOUND_UPPER,
+             ttDepth, bestMove, ss->eval, ss->evalMargin);

 
     assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
 
 
     assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
 


@@ -1457,20 +1424,6 @@ split_point_start: // At split points actual search starts from here
   }
 
 
   }
 
 

-  // can_return_tt() returns true if a transposition table score can be used to
-  // cut-off at a given point in search.
-
-  bool can_return_tt(const TTEntry* tte, Depth depth, Value v, Value beta) {
-
-    return   (   tte->depth() >= depth
-              || v >= std::max(VALUE_MATE_IN_MAX_PLY, beta)
-              || v < std::min(VALUE_MATED_IN_MAX_PLY, beta))
-
-          && (   ((tte->type() & BOUND_LOWER) && v >= beta)
-              || ((tte->type() & BOUND_UPPER) && v < beta));
-  }
-
-

   // refine_eval() returns the transposition table score if possible, otherwise
   // falls back on static position evaluation.
 
   // refine_eval() returns the transposition table score if possible, otherwise
   // falls back on static position evaluation.
 


@@ -1514,7 +1467,7 @@ split_point_start: // At split points actual search starts from here
         int s = RootMoves[i].score;
 
         // Don't allow crazy blunders even at very low skills
         int s = RootMoves[i].score;
 
         // Don't allow crazy blunders even at very low skills

-        if (i > 0 && RootMoves[i-1].score > s + EasyMoveMargin)
+        if (i > 0 && RootMoves[i-1].score > s + 2 * PawnValueMg)

             break;
 
         // This is our magic formula
             break;
 
         // This is our magic formula