King-pawn threat bonus for endgames.

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 5a28b286ae0a354c1f01eb6c445fb83fc85eaa13..3099924c0f2be48c2da9fde43c2303c562fcdb2b 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -152,6 +152,8 @@ namespace {
 
   // Hanging contains a bonus for each enemy hanging piece
   const Score Hanging = S(23, 20);
+  const Score KingPawnThreatOne  = S(0, 64);
+  const Score KingPawnThreatMany = S(0, 128);
 
   #undef S
 
@@ -255,7 +257,7 @@ namespace {
             bonus += bonus / 2;
     }
 
-    return make_score(bonus, bonus);
+    return make_score(bonus * 2, bonus / 2);
   }
 
 
@@ -498,6 +500,7 @@ namespace {
 
     Bitboard b, weakEnemies, protectedEnemies;
     Score score = SCORE_ZERO;
+    enum { Minor, Major };
 
     // Protected enemies
     protectedEnemies = (pos.pieces(Them) ^ pos.pieces(Them,PAWN))
@@ -505,7 +508,7 @@ namespace {
                       & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
 
     if(protectedEnemies)
-        score += Threat[0][type_of(pos.piece_on(lsb(protectedEnemies)))];
+        score += Threat[Minor][type_of(pos.piece_on(lsb(protectedEnemies)))];
 
     // Enemies not defended by a pawn and under our attack
     weakEnemies =  pos.pieces(Them)
@@ -517,16 +520,20 @@ namespace {
     {
         b = weakEnemies & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
         if (b)
-            score += Threat[0][type_of(pos.piece_on(lsb(b)))];
+            score += Threat[Minor][type_of(pos.piece_on(lsb(b)))];
 
         b = weakEnemies & (ei.attackedBy[Us][ROOK] | ei.attackedBy[Us][QUEEN]);
         if (b)
-            score += Threat[1][type_of(pos.piece_on(lsb(b)))];
+            score += Threat[Major][type_of(pos.piece_on(lsb(b)))];
 
         b = weakEnemies & ~ei.attackedBy[Them][ALL_PIECES];
         if (b)
             score += more_than_one(b) ? Hanging * popcount<Max15>(b) : Hanging;
-    }
+
+        b = weakEnemies & pos.pieces(Them, PAWN) & ei.attackedBy[Us][KING];
+        if (b)
+            score += more_than_one(b) ? KingPawnThreatMany : KingPawnThreatOne;
+       }
 
     if (Trace)
         Tracing::terms[Us][Tracing::THREAT] = score;
@@ -574,22 +581,18 @@ namespace {
             // If the pawn is free to advance, then increase the bonus
             if (pos.empty(blockSq))
             {
-                squaresToQueen = forward_bb(Us, s);
-
-                // If there is an enemy rook or queen attacking the pawn from behind,
-                // add all X-ray attacks by the rook or queen. Otherwise consider only
-                // the squares in the pawn's path attacked or occupied by the enemy.
-                if (    unlikely(forward_bb(Them, s) & pos.pieces(Them, ROOK, QUEEN))
-                    && (forward_bb(Them, s) & pos.pieces(Them, ROOK, QUEEN) & pos.attacks_from<ROOK>(s)))
-                    unsafeSquares = squaresToQueen;
-                else
-                    unsafeSquares = squaresToQueen & (ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them));
-
-                if (    unlikely(forward_bb(Them, s) & pos.pieces(Us, ROOK, QUEEN))
-                    && (forward_bb(Them, s) & pos.pieces(Us, ROOK, QUEEN) & pos.attacks_from<ROOK>(s)))
-                    defendedSquares = squaresToQueen;
-                else
-                    defendedSquares = squaresToQueen & ei.attackedBy[Us][ALL_PIECES];
+                // If there is a rook or queen attacking/defending the pawn from behind,
+                // consider all the squaresToQueen. Otherwise consider only the squares
+                // in the pawn's path attacked or occupied by the enemy.
+                defendedSquares = unsafeSquares = squaresToQueen = forward_bb(Us, s);
+
+                Bitboard bb = forward_bb(Them, s) & pos.pieces(ROOK, QUEEN) & pos.attacks_from<ROOK>(s);
+
+                if (!(pos.pieces(Us) & bb))
+                    defendedSquares &= ei.attackedBy[Us][ALL_PIECES];
+
+                if (!(pos.pieces(Them) & bb))
+                    unsafeSquares &= ei.attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
 
                 // If there aren't any enemy attacks, assign a big bonus. Otherwise
                 // assign a smaller bonus if the block square isn't attacked.