Implement post futility pruning

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index 6232f0cbf3ab8477ff5bc10f5973a3b1a134341b..b653ef9e70f1b33dcde02a8310ea35e24ab6d288 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -703,6 +703,7 @@ namespace {
     // Initialize
     TT.new_search();
     H.clear();
+    MG.clear();
     init_ss_array(ss);
     IterationInfo[1] = IterationInfoType(rml.get_move_score(0), rml.get_move_score(0));
     Iteration = 1;
@@ -894,6 +895,14 @@ namespace {
     Value oldAlpha = alpha;
     Value value = -VALUE_INFINITE;
     CheckInfo ci(pos);
+    bool isCheck = pos.is_check();
+
+    // Evaluate the position statically
+    EvalInfo ei;
+    if (!isCheck)
+        ss[0].eval = evaluate(pos, ei, 0);
+    else
+        ss[0].eval = VALUE_NONE;
 
     // Loop through all the moves in the root move list
     for (int i = 0; i <  rml.move_count() && !AbortSearch; i++)
@@ -1156,9 +1165,25 @@ namespace {
         tte = TT.retrieve(pos.get_key());
     }
 
+    // Evaluate the position statically
+    isCheck = pos.is_check();
+    EvalInfo ei;
+    if (!isCheck)
+    {
+        ss[ply].eval = evaluate(pos, ei, threadID);
+
+        // Store gain statistics
+        Move m = ss[ply - 1].currentMove;
+        if (   m != MOVE_NULL
+            && pos.captured_piece() == NO_PIECE_TYPE
+            && !move_is_castle(m)
+            && !move_is_promotion(m))
+            MG.store(pos.piece_on(move_to(m)), move_from(m), move_to(m), ss[ply - 1].eval, -ss[ply].eval);
+
+    }
+
     // Initialize a MovePicker object for the current position, and prepare
     // to search all moves
-    isCheck = pos.is_check();
     mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
     CheckInfo ci(pos);
     MovePicker mp = MovePicker(pos, ttMove, depth, H, &ss[ply]);
@@ -1394,8 +1419,20 @@ namespace {
         ss[ply].eval = staticValue;
         futilityValue = staticValue + FutilityValueMargin;
         staticValue = refine_eval(tte, staticValue, ply); // Enhance accuracy with TT value if possible
+
+        // Store gain statistics
+        Move m = ss[ply - 1].currentMove;
+        if (   m != MOVE_NULL
+            && pos.captured_piece() == NO_PIECE_TYPE
+            && !move_is_castle(m)
+            && !move_is_promotion(m))
+            MG.store(pos.piece_on(move_to(m)), move_from(m), move_to(m), ss[ply - 1].eval, -ss[ply].eval);
     }
 
+    // Post futility pruning
+    if (staticValue - FutilityValueMargin >= beta)
+        return (staticValue - FutilityValueMargin);
+
     // Null move search
     if (    allowNullmove
         &&  depth > OnePly
@@ -1523,6 +1560,7 @@ namespace {
       if (    useFutilityPruning
           && !dangerous
           && !captureOrPromotion
+          && !move_is_castle(move)
           &&  move != ttMove)
       {
           // Move count based pruning
@@ -1685,6 +1723,19 @@ namespace {
     else
         staticValue = evaluate(pos, ei, threadID);
 
+    if (!isCheck)
+    {
+        ss[ply].eval = staticValue;
+        // Store gain statistics
+        Move m = ss[ply - 1].currentMove;
+        if (   m != MOVE_NULL
+            && pos.captured_piece() == NO_PIECE_TYPE
+            && !move_is_castle(m)
+            && !move_is_promotion(m))
+            MG.store(pos.piece_on(move_to(m)), move_from(m), move_to(m), ss[ply - 1].eval, -ss[ply].eval);
+    }
+
+
     // Initialize "stand pat score", and return it immediately if it is
     // at least beta.
     bestValue = staticValue;
@@ -2464,9 +2515,8 @@ namespace {
 
     Square mfrom, mto, tfrom, tto;
 
-    // Prune if there isn't any threat move and
-    // is not a castling move (common case).
-    if (threat == MOVE_NONE && !move_is_castle(m))
+    // Prune if there isn't any threat move
+    if (threat == MOVE_NONE)
         return true;
 
     mfrom = move_from(m);
@@ -2474,15 +2524,11 @@ namespace {
     tfrom = move_from(threat);
     tto = move_to(threat);
 
-    // Case 1: Castling moves are never pruned
-    if (move_is_castle(m))
-        return false;
-
-    // Case 2: Don't prune moves which move the threatened piece
+    // Case 1: Don't prune moves which move the threatened piece
     if (mfrom == tto)
         return false;
 
-    // Case 3: If the threatened piece has value less than or equal to the
+    // Case 2: If the threatened piece has value less than or equal to the
     // value of the threatening piece, don't prune move which defend it.
     if (   pos.move_is_capture(threat)
         && (   pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
@@ -2490,7 +2536,7 @@ namespace {
         && pos.move_attacks_square(m, tto))
         return false;
 
-    // Case 4: If the moving piece in the threatened move is a slider, don't
+    // Case 3: If the moving piece in the threatened move is a slider, don't
     // prune safe moves which block its ray.
     if (   piece_is_slider(pos.piece_on(tfrom))
         && bit_is_set(squares_between(tfrom, tto), mto)