Rename yields_to_threat and prevents_threat

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 8dc1f85d9e51a30194f48a3c96d2170aa467259a..085d124ee66b994819a1e8e71e20bf99eb3532cd 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -62,10 +62,6 @@ namespace {
   // 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 };
 

-  // Lookup table to check if a Piece is a slider and its access function
-  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]; }
-

   // 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)); }
 


@@ -100,11 +96,11 @@ namespace {
   Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
 
   void id_loop(Position& pos);
   Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth);
 
   void id_loop(Position& pos);

-  bool check_is_dangerous(Position& pos, Move move, Value futilityBase, Value beta);
-  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);
   Value value_to_tt(Value v, int ply);
   Value value_from_tt(Value v, int ply);

-  bool connected_threat(const Position& pos, Move m, Move threat);
+  bool check_is_dangerous(Position& pos, Move move, Value futilityBase, Value beta);
+  bool allows_move(const Position& pos, Move first, Move second);
+  bool prevents_move(const Position& pos, Move first, Move second);

   string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
 
   struct Skill {
   string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
 
   struct Skill {


@@ -192,7 +188,7 @@ void Search::think() {
   {
       RootMoves.push_back(MOVE_NONE);
       sync_cout << "info depth 0 score "
   {
       RootMoves.push_back(MOVE_NONE);
       sync_cout << "info depth 0 score "

-                << score_to_uci(RootPos.in_check() ? -VALUE_MATE : VALUE_DRAW)
+                << score_to_uci(RootPos.checkers() ? -VALUE_MATE : VALUE_DRAW)

                 << sync_endl;
 
       goto finalize;
                 << sync_endl;
 
       goto finalize;


@@ -212,7 +208,7 @@ void Search::think() {
   if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
   {
       int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns
   if (Options["Contempt Factor"] && !Options["UCI_AnalyseMode"])
   {
       int cf = Options["Contempt Factor"] * PawnValueMg / 100; // From centipawns

-      cf = cf * MaterialTable::game_phase(RootPos) / PHASE_MIDGAME; // Scale down with phase
+      cf = cf * Material::game_phase(RootPos) / PHASE_MIDGAME; // Scale down with phase

       DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
       DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
   }
       DrawValue[ RootColor] = VALUE_DRAW - Value(cf);
       DrawValue[~RootColor] = VALUE_DRAW + Value(cf);
   }


@@ -222,7 +218,7 @@ void Search::think() {
   if (Options["Use Search Log"])
   {
       Log log(Options["Search Log Filename"]);
   if (Options["Use Search Log"])
   {
       Log log(Options["Search Log Filename"]);

-      log << "\nSearching: "  << RootPos.to_fen()
+      log << "\nSearching: "  << RootPos.fen()

           << "\ninfinite: "   << Limits.infinite
           << " ponder: "      << Limits.ponder
           << " time: "        << Limits.time[RootColor]
           << "\ninfinite: "   << Limits.infinite
           << " ponder: "      << Limits.ponder
           << " time: "        << Limits.time[RootColor]


@@ -394,8 +390,9 @@ namespace {
             }
 
             // Sort the PV lines searched so far and update the GUI
             }
 
             // Sort the PV lines searched so far and update the GUI

-            sort<RootMove>(RootMoves.begin(), RootMoves.begin() + PVIdx);
-            sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;
+            sort<RootMove>(RootMoves.begin(), RootMoves.begin() + PVIdx + 1);
+            if (PVIdx + 1 == PVSize || Time::now() - SearchTime > 3000)
+                sync_cout << uci_pv(pos, depth, alpha, beta) << sync_endl;

         }
 
         // Do we need to pick now the sub-optimal best move ?
         }
 
         // Do we need to pick now the sub-optimal best move ?


@@ -488,13 +485,14 @@ namespace {
     Value bestValue, value, ttValue;
     Value eval, nullValue, futilityValue;
     bool inCheck, givesCheck, pvMove, singularExtensionNode;
     Value bestValue, value, ttValue;
     Value eval, nullValue, futilityValue;
     bool inCheck, givesCheck, pvMove, singularExtensionNode;

-    bool captureOrPromotion, dangerous, doFullDepthSearch;
+    bool captureOrPromotion, dangerous, doFullDepthSearch, threatExtension;

     int moveCount, playedMoveCount;
 
     // Step 1. Initialize node
     Thread* thisThread = pos.this_thread();
     moveCount = playedMoveCount = 0;
     int moveCount, playedMoveCount;
 
     // Step 1. Initialize node
     Thread* thisThread = pos.this_thread();
     moveCount = playedMoveCount = 0;

-    inCheck = pos.in_check();
+    threatExtension = false;
+    inCheck = pos.checkers();

 
     if (SpNode)
     {
 
     if (SpNode)
     {


@@ -577,31 +575,17 @@ namespace {
     // Step 5. Evaluate the position statically and update parent's gain statistics
     if (inCheck)
         ss->staticEval = ss->evalMargin = eval = VALUE_NONE;
     // Step 5. Evaluate the position statically and update parent's gain statistics
     if (inCheck)
         ss->staticEval = ss->evalMargin = eval = VALUE_NONE;

-
-    else if (tte)
+    else

     {
     {

-        // Following asserts are valid only in single thread condition because
-        // TT access is always racy and its contents cannot be trusted.
-        assert(tte->static_value() != VALUE_NONE || Threads.size() > 1);
-        assert(ttValue != VALUE_NONE || tte->type() == BOUND_NONE || Threads.size() > 1);
-
-        ss->staticEval = eval = tte->static_value();
-        ss->evalMargin = tte->static_value_margin();
-
-        if (eval == VALUE_NONE || ss->evalMargin == VALUE_NONE) // Due to a race
-            eval = ss->staticEval = evaluate(pos, ss->evalMargin);
+        eval = ss->staticEval = evaluate(pos, ss->evalMargin);

 
         // Can ttValue be used as a better position evaluation?
 
         // Can ttValue be used as a better position evaluation?

-        if (ttValue != VALUE_NONE)
+        if (tte && ttValue != VALUE_NONE)
+        {

             if (   ((tte->type() & BOUND_LOWER) && ttValue > eval)
                 || ((tte->type() & BOUND_UPPER) && ttValue < eval))
                 eval = ttValue;
             if (   ((tte->type() & BOUND_LOWER) && ttValue > eval)
                 || ((tte->type() & BOUND_UPPER) && ttValue < eval))
                 eval = ttValue;

-    }
-    else
-    {
-        eval = ss->staticEval = evaluate(pos, ss->evalMargin);
-        TT.store(posKey, VALUE_NONE, BOUND_NONE, DEPTH_NONE, MOVE_NONE,
-                 ss->staticEval, ss->evalMargin);
+        }

     }
 
     // Update gain for the parent non-capture move given the static position
     }
 
     // Update gain for the parent non-capture move given the static position


@@ -692,16 +676,15 @@ namespace {
             // The null move failed low, which means that we may be faced with
             // some kind of threat. If the previous move was reduced, check if
             // the move that refuted the null move was somehow connected to the
             // The null move failed low, which means that we may be faced with
             // some kind of threat. If the previous move was reduced, check if
             // the move that refuted the null move was somehow connected to the

-            // move which was reduced. If a connection is found, return a fail
-            // low score (which will cause the reduced move to fail high in the
-            // parent node, which will trigger a re-search with full depth).
+            // move which was reduced. If a connection is found extend moves that
+            // defend against threat.

             threatMove = (ss+1)->currentMove;
 
             if (   depth < 5 * ONE_PLY
                 && (ss-1)->reduction
                 && threatMove != MOVE_NONE
             threatMove = (ss+1)->currentMove;
 
             if (   depth < 5 * ONE_PLY
                 && (ss-1)->reduction
                 && threatMove != MOVE_NONE

-                && connected_moves(pos, (ss-1)->currentMove, threatMove))
-                return beta - 1;
+                && allows_move(pos, (ss-1)->currentMove, threatMove))
+                threatExtension = true;

         }
     }
 
         }
     }
 


@@ -797,7 +780,7 @@ split_point_start: // At split points actual search starts from here
       {
           Signals.firstRootMove = (moveCount == 1);
 
       {
           Signals.firstRootMove = (moveCount == 1);
 

-          if (thisThread == Threads.main_thread() && Time::now() - SearchTime > 2000)
+          if (thisThread == Threads.main_thread() && Time::now() - SearchTime > 3000)

               sync_cout << "info depth " << depth / ONE_PLY
                         << " currmove " << move_to_uci(move, pos.is_chess960())
                         << " currmovenumber " << moveCount + PVIdx << sync_endl;
               sync_cout << "info depth " << depth / ONE_PLY
                         << " currmove " << move_to_uci(move, pos.is_chess960())
                         << " currmovenumber " << moveCount + PVIdx << sync_endl;


@@ -819,6 +802,9 @@ split_point_start: // At split points actual search starts from here
       if (PvNode && dangerous)
           ext = ONE_PLY;
 
       if (PvNode && dangerous)
           ext = ONE_PLY;
 

+      else if (threatExtension && prevents_move(pos, move, threatMove))
+          ext = ONE_PLY;
+

       else if (givesCheck && pos.see_sign(move) >= 0)
           ext = ONE_PLY / 2;
 
       else if (givesCheck && pos.see_sign(move) >= 0)
           ext = ONE_PLY / 2;
 


@@ -861,7 +847,7 @@ split_point_start: // At split points actual search starts from here
           // Move count based pruning
           if (   depth < 16 * ONE_PLY
               && moveCount >= FutilityMoveCounts[depth]
           // Move count based pruning
           if (   depth < 16 * ONE_PLY
               && moveCount >= FutilityMoveCounts[depth]

-              && (!threatMove || !connected_threat(pos, move, threatMove)))
+              && (!threatMove || !prevents_move(pos, move, threatMove)))

           {
               if (SpNode)
                   sp->mutex.lock();
           {
               if (SpNode)
                   sp->mutex.lock();


@@ -896,7 +882,7 @@ split_point_start: // At split points actual search starts from here
       }
 
       // Check for legality only before to do the move
       }
 
       // Check for legality only before to do the move

-      if (!pos.pl_move_is_legal(move, ci.pinned))
+      if (!RootNode && !SpNode && !pos.pl_move_is_legal(move, ci.pinned))

       {
           moveCount--;
           continue;
       {
           moveCount--;
           continue;


@@ -1007,8 +993,10 @@ split_point_start: // At split points actual search starts from here
                   alpha = value; // Update alpha here! Always alpha < beta
                   if (SpNode) sp->alpha = value;
               }
                   alpha = value; // Update alpha here! Always alpha < beta
                   if (SpNode) sp->alpha = value;
               }

-              else // Fail high
+              else

               {
               {

+                  assert(value >= beta); // Fail high
+

                   if (SpNode) sp->cutoff = true;
                   break;
               }
                   if (SpNode) sp->cutoff = true;
                   break;
               }


@@ -1018,12 +1006,14 @@ split_point_start: // At split points actual search starts from here
       // Step 19. Check for splitting the search
       if (   !SpNode
           &&  depth >= Threads.min_split_depth()
       // Step 19. Check for splitting the search
       if (   !SpNode
           &&  depth >= Threads.min_split_depth()

-          &&  bestValue < beta

           &&  Threads.available_slave_exists(thisThread))
       {
           &&  Threads.available_slave_exists(thisThread))
       {

+          assert(bestValue < beta);
+

           bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,
                                                depth, threatMove, moveCount, mp, NT);
           bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,
                                                depth, threatMove, moveCount, mp, NT);

-          break;
+          if (bestValue >= beta)
+              break;

       }
     }
 
       }
     }
 


@@ -1051,8 +1041,7 @@ split_point_start: // At split points actual search starts from here
 
     if (bestValue >= beta) // Failed high
     {
 
     if (bestValue >= beta) // Failed high
     {

-        TT.store(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER, depth,
-                 bestMove, ss->staticEval, ss->evalMargin);
+        TT.store(posKey, value_to_tt(bestValue, ss->ply), BOUND_LOWER, depth, bestMove);

 
         if (!pos.is_capture_or_promotion(bestMove) && !inCheck)
         {
 
         if (!pos.is_capture_or_promotion(bestMove) && !inCheck)
         {


@@ -1077,7 +1066,7 @@ 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,
     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->staticEval, ss->evalMargin);
+                 depth, bestMove);

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


@@ -1095,7 +1084,7 @@ split_point_start: // At split points actual search starts from here
     const bool PvNode = (NT == PV);
 
     assert(NT == PV || NT == NonPV);
     const bool PvNode = (NT == PV);
 
     assert(NT == PV || NT == NonPV);

-    assert(InCheck == pos.in_check());
+    assert(InCheck == !!pos.checkers());

     assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
     assert(PvNode || (alpha == beta - 1));
     assert(depth <= DEPTH_ZERO);
     assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
     assert(PvNode || (alpha == beta - 1));
     assert(depth <= DEPTH_ZERO);


@@ -1104,12 +1093,17 @@ split_point_start: // At split points actual search starts from here
     const TTEntry* tte;
     Key posKey;
     Move ttMove, move, bestMove;
     const TTEntry* tte;
     Key posKey;
     Move ttMove, move, bestMove;

-    Value bestValue, value, ttValue, futilityValue, futilityBase;
-    bool givesCheck, enoughMaterial, evasionPrunable;
+    Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
+    bool givesCheck, enoughMaterial, evasionPrunable, fromNull;

     Depth ttDepth;
 
     Depth ttDepth;
 

+    // To flag BOUND_EXACT a node with eval above alpha and no available moves
+    if (PvNode)
+        oldAlpha = alpha;
+

     ss->currentMove = bestMove = MOVE_NONE;
     ss->ply = (ss-1)->ply + 1;
     ss->currentMove = bestMove = MOVE_NONE;
     ss->ply = (ss-1)->ply + 1;

+    fromNull = (ss-1)->currentMove == MOVE_NULL;

 
     // Check for an instant draw or maximum ply reached
     if (pos.is_draw<false, false>() || ss->ply > MAX_PLY)
 
     // Check for an instant draw or maximum ply reached
     if (pos.is_draw<false, false>() || ss->ply > MAX_PLY)


@@ -1147,15 +1141,11 @@ split_point_start: // At split points actual search starts from here
     }
     else
     {
     }
     else
     {

-        if (tte)
+        if (fromNull)

         {
         {

-            assert(tte->static_value() != VALUE_NONE || Threads.size() > 1);
-
-            ss->staticEval = bestValue = tte->static_value();
-            ss->evalMargin = tte->static_value_margin();
-
-            if (ss->staticEval == VALUE_NONE || ss->evalMargin == VALUE_NONE) // Due to a race
-                ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
+            // Approximated score. Real one is slightly higher due to tempo
+            ss->staticEval = bestValue = -(ss-1)->staticEval;
+            ss->evalMargin = VALUE_ZERO;

         }
         else
             ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
         }
         else
             ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);


@@ -1164,8 +1154,7 @@ split_point_start: // At split points actual search starts from here
         if (bestValue >= beta)
         {
             if (!tte)
         if (bestValue >= beta)
         {
             if (!tte)

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

 
             return bestValue;
         }
 
             return bestValue;
         }


@@ -1194,6 +1183,7 @@ split_point_start: // At split points actual search starts from here
       // Futility pruning
       if (   !PvNode
           && !InCheck
       // Futility pruning
       if (   !PvNode
           && !InCheck

+          && !fromNull

           && !givesCheck
           &&  move != ttMove
           &&  enoughMaterial
           && !givesCheck
           &&  move != ttMove
           &&  enoughMaterial


@@ -1206,9 +1196,7 @@ split_point_start: // At split points actual search starts from here
 
           if (futilityValue < beta)
           {
 
           if (futilityValue < beta)
           {

-              if (futilityValue > bestValue)
-                  bestValue = futilityValue;
-
+              bestValue = std::max(bestValue, futilityValue);

               continue;
           }
 
               continue;
           }
 


@@ -1216,7 +1204,10 @@ split_point_start: // At split points actual search starts from here
           if (   futilityBase < beta
               && depth < DEPTH_ZERO
               && pos.see(move) <= 0)
           if (   futilityBase < beta
               && depth < DEPTH_ZERO
               && pos.see(move) <= 0)

+          {
+              bestValue = std::max(bestValue, futilityBase);

               continue;
               continue;

+          }

       }
 
       // Detect non-capture evasions that are candidate to be pruned
       }
 
       // Detect non-capture evasions that are candidate to be pruned


@@ -1272,9 +1263,7 @@ split_point_start: // At split points actual search starts from here
               }
               else // Fail high
               {
               }
               else // Fail high
               {

-                  TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER,
-                           ttDepth, move, ss->staticEval, ss->evalMargin);
-
+                  TT.store(posKey, value_to_tt(value, ss->ply), BOUND_LOWER, ttDepth, move);

                   return value;
               }
           }
                   return value;
               }
           }


@@ -1287,8 +1276,8 @@ split_point_start: // At split points actual search starts from here
         return mated_in(ss->ply); // Plies to mate from the root
 
     TT.store(posKey, value_to_tt(bestValue, ss->ply),
         return mated_in(ss->ply); // Plies to mate from the root
 
     TT.store(posKey, value_to_tt(bestValue, ss->ply),

-             PvNode && bestMove != MOVE_NONE ? BOUND_EXACT : BOUND_UPPER,
-             ttDepth, bestMove, ss->staticEval, ss->evalMargin);
+             PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
+             ttDepth, bestMove);

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


@@ -1357,101 +1346,93 @@ split_point_start: // At split points actual search starts from here
   }
 
 
   }
 
 

-  // connected_moves() tests whether two moves are 'connected' in the sense
-  // that the first move somehow made the second move possible (for instance
-  // if the moving piece is the same in both moves). The first move is assumed
-  // to be the move that was made to reach the current position, while the
-  // second move is assumed to be a move from the current position.
-
-  bool connected_moves(const Position& pos, Move m1, Move m2) {
+  // allows_move() tests whether the move at previous ply (first) somehow makes a
+  // second move possible, for instance if the moving piece is the same in both
+  // moves. Normally the second move is the threat move (the best move returned
+  // from a null search that fails low).

 
 

-    Square f1, t1, f2, t2;
-    Piece p1, p2;
-    Square ksq;
+  bool allows_move(const Position& pos, Move first, Move second) {

 
 

-    assert(is_ok(m1));
-    assert(is_ok(m2));
+    assert(is_ok(first));
+    assert(is_ok(second));
+    assert(color_of(pos.piece_on(from_sq(second))) == ~pos.side_to_move());
+    assert(color_of(pos.piece_on(to_sq(first))) == ~pos.side_to_move());

 
 

-    // Case 1: The moving piece is the same in both moves
-    f2 = from_sq(m2);
-    t1 = to_sq(m1);
-    if (f2 == t1)
-        return true;
+    Square m1from = from_sq(first);
+    Square m2from = from_sq(second);
+    Square m1to = to_sq(first);
+    Square m2to = to_sq(second);

 
 

-    // Case 2: The destination square for m2 was vacated by m1
-    t2 = to_sq(m2);
-    f1 = from_sq(m1);
-    if (t2 == f1)
+    // The piece is the same or second's destination was vacated by the first move
+    if (m1to == m2from || m2to == m1from)

         return true;
 
         return true;
 

-    // Case 3: Moving through the vacated square
-    p2 = pos.piece_on(f2);
-    if (piece_is_slider(p2) && (between_bb(f2, t2) & f1))
+    // Second one moves through the square vacated by first one
+    if (between_bb(m2from, m2to) & m1from)

       return true;
 
       return true;
 

-    // Case 4: The destination square for m2 is defended by the moving piece in m1
-    p1 = pos.piece_on(t1);
-    if (pos.attacks_from(p1, t1, pos.pieces() ^ f2) & t2)
+    // Second's destination is defended by the first move's piece
+    Bitboard m1att = pos.attacks_from(pos.piece_on(m1to), m1to, pos.pieces() ^ m2from);
+    if (m1att & m2to)

         return true;
 
         return true;
 

-    // Case 5: Discovered check, checking piece is the piece moved in m1
-    ksq = pos.king_square(pos.side_to_move());
-    if (    piece_is_slider(p1)
-        && (between_bb(t1, ksq) & f2)
-        && (pos.attacks_from(p1, t1, pos.pieces() ^ f2) & ksq))
+    // Second move gives a discovered check through the first's checking piece
+    if (m1att & pos.king_square(pos.side_to_move()))
+    {
+        assert(between_bb(m1to, pos.king_square(pos.side_to_move())) & m2from);

         return true;
         return true;

+    }

 
     return false;
   }
 
 
 
     return false;
   }
 
 

-  // connected_threat() tests whether it is safe to forward prune a move or if
-  // is somehow connected to the threat move returned by null search.
+  // prevents_move() tests whether a move (first) is able to defend against an
+  // opponent's move (second). In this case will not be pruned. Normally the
+  // second move is the threat move (the best move returned from a null search
+  // that fails low).

 
 

-  bool connected_threat(const Position& pos, Move m, Move threat) {
+  bool prevents_move(const Position& pos, Move first, Move second) {

 
 

-    assert(is_ok(m));
-    assert(is_ok(threat));
-    assert(!pos.is_capture_or_promotion(m));
-    assert(!pos.is_passed_pawn_push(m));
+    assert(is_ok(first));
+    assert(is_ok(second));
+    assert(!pos.is_capture_or_promotion(first));
+    assert(!pos.is_passed_pawn_push(first));

 
 

-    Square mfrom = from_sq(m);
-    Square mto = to_sq(m);
-    Square tfrom = from_sq(threat);
-    Square tto = to_sq(threat);
+    Square m1from = from_sq(first);
+    Square m2from = from_sq(second);
+    Square m1to = to_sq(first);
+    Square m2to = to_sq(second);

 
 

-    // Case 1: Don't prune moves which move the threatened piece
-    if (mfrom == tto)
+    // Don't prune moves of the threatened piece
+    if (m1from == m2to)

         return true;
 
         return true;
 

-    // Case 2: If the threatened piece has value less than or equal to the
-    // value of the threatening piece, don't prune moves which defend it.
-    if (    pos.is_capture(threat)
-        && (   PieceValue[MG][pos.piece_on(tfrom)] >= PieceValue[MG][pos.piece_on(tto)]
-            || type_of(pos.piece_on(tfrom)) == KING))
+    // If the threatened piece has value less than or equal to the value of the
+    // threat piece, don't prune moves which defend it.
+    if (    pos.is_capture(second)
+        && (   PieceValue[MG][pos.piece_on(m2from)] >= PieceValue[MG][pos.piece_on(m2to)]
+            || type_of(pos.piece_on(m2from)) == KING))

     {
         // Update occupancy as if the piece and the threat are moving
     {
         // Update occupancy as if the piece and the threat are moving

-        Bitboard occ = pos.pieces() ^ mfrom ^ mto ^ tfrom;
-        Piece piece = pos.piece_on(mfrom);
+        Bitboard occ = pos.pieces() ^ m1from ^ m1to ^ m2from;
+        Piece piece = pos.piece_on(m1from);

 
         // The moved piece attacks the square 'tto' ?
 
         // The moved piece attacks the square 'tto' ?

-        if (pos.attacks_from(piece, mto, occ) & tto)
+        if (pos.attacks_from(piece, m1to, occ) & m2to)

             return true;
 
         // Scan for possible X-ray attackers behind the moved piece
             return true;
 
         // Scan for possible X-ray attackers behind the moved piece

-        Bitboard xray =  (attacks_bb<  ROOK>(tto, occ) & pos.pieces(color_of(piece), QUEEN, ROOK))
-                       | (attacks_bb<BISHOP>(tto, occ) & pos.pieces(color_of(piece), QUEEN, BISHOP));
+        Bitboard xray =  (attacks_bb<  ROOK>(m2to, occ) & pos.pieces(color_of(piece), QUEEN, ROOK))
+                       | (attacks_bb<BISHOP>(m2to, occ) & pos.pieces(color_of(piece), QUEEN, BISHOP));

 
         // Verify attackers are triggered by our move and not already existing
 
         // Verify attackers are triggered by our move and not already existing

-        if (xray && (xray ^ (xray & pos.attacks_from<QUEEN>(tto))))
+        if (xray && (xray ^ (xray & pos.attacks_from<QUEEN>(m2to))))

             return true;
     }
 
             return true;
     }
 

-    // Case 3: If the moving piece in the threatened move is a slider, don't
-    // prune safe moves which block its ray.
-    if (    piece_is_slider(pos.piece_on(tfrom))
-        && (between_bb(tfrom, tto) & mto)
-        &&  pos.see_sign(m) >= 0)
+    // Don't prune safe moves which block the threat path
+    if ((between_bb(m2from, m2to) & m1to) && pos.see_sign(first) >= 0)

         return true;
 
     return false;
         return true;
 
     return false;


@@ -1564,7 +1545,8 @@ void RootMove::extract_pv_from_tt(Position& pos) {
   do {
       pv.push_back(m);
 
   do {
       pv.push_back(m);
 

-      assert(pos.move_is_legal(pv[ply]));
+      assert(MoveList<LEGAL>(pos).contains(pv[ply]));
+

       pos.do_move(pv[ply++], *st++);
       tte = TT.probe(pos.key());
 
       pos.do_move(pv[ply++], *st++);
       tte = TT.probe(pos.key());
 


@@ -1589,22 +1571,15 @@ void RootMove::insert_pv_in_tt(Position& pos) {
   StateInfo state[MAX_PLY_PLUS_2], *st = state;
   TTEntry* tte;
   int ply = 0;
   StateInfo state[MAX_PLY_PLUS_2], *st = state;
   TTEntry* tte;
   int ply = 0;

-  Value v, m;

 
   do {
       tte = TT.probe(pos.key());
 
       if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries
 
   do {
       tte = TT.probe(pos.key());
 
       if (!tte || tte->move() != pv[ply]) // Don't overwrite correct entries

-      {
-          if (pos.in_check())
-              v = m = VALUE_NONE;
-          else
-              v = evaluate(pos, m);
+          TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply]);

 
 

-          TT.store(pos.key(), VALUE_NONE, BOUND_NONE, DEPTH_NONE, pv[ply], v, m);
-      }
+      assert(MoveList<LEGAL>(pos).contains(pv[ply]));

 
 

-      assert(pos.move_is_legal(pv[ply]));

       pos.do_move(pv[ply++], *st++);
 
   } while (pv[ply] != MOVE_NONE);
       pos.do_move(pv[ply++], *st++);
 
   } while (pv[ply] != MOVE_NONE);