Unsafe checks

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 0f2744d9e4ec42abd243b45527d2ff16dff0537a..4a52e62658f0deccce3eea3c1287b9d87b3147fa 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -183,7 +183,8 @@ namespace {
   const Score BishopPawns         = S( 8, 12);
   const Score RookOnPawn          = S( 8, 24);
   const Score TrappedRook         = S(92,  0);
-  const Score Checked             = S(20, 20);
+  const Score SafeCheck           = S(20, 20);
+  const Score OtherCheck          = S(10, 10);
   const Score ThreatByHangingPawn = S(71, 61);
   const Score LooseEnemies        = S( 0, 25);
   const Score Hanging             = S(48, 27);
@@ -366,9 +367,10 @@ namespace {
   template<Color Us, bool DoTrace>
   Score evaluate_king(const Position& pos, const EvalInfo& ei) {
 
-    const Color Them = (Us == WHITE ? BLACK : WHITE);
+    const Color Them = (Us == WHITE ? BLACK   : WHITE);
+    const Square  Up = (Us == WHITE ? DELTA_N : DELTA_S);
 
-    Bitboard undefended, b, b1, b2, safe;
+    Bitboard undefended, b, b1, b2, safe, other;
     int attackUnits;
     const Square ksq = pos.square<KING>(Us);
 
@@ -414,27 +416,42 @@ namespace {
             attackUnits += QueenContactCheck * popcount(b);
         }
 
-        // Analyse the enemy's safe distance checks for sliders and knights
-        safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
+        // Analyse the safe enemy's checks which are possible on next move...
+        safe  = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
+
+        // ... and some other potential checks, only requiring the square to be
+        // safe from pawn-attacks, and not being occupied by a blocked pawn.
+        other = ~(   ei.attackedBy[Us][PAWN]
+                  | (pos.pieces(Them, PAWN) & shift_bb<Up>(pos.pieces(PAWN))));
 
-        b1 = pos.attacks_from<ROOK  >(ksq) & safe;
-        b2 = pos.attacks_from<BISHOP>(ksq) & safe;
+        b1 = pos.attacks_from<ROOK  >(ksq);
+        b2 = pos.attacks_from<BISHOP>(ksq);
 
         // Enemy queen safe checks
-        if ((b1 | b2) & ei.attackedBy[Them][QUEEN])
-            attackUnits += QueenCheck, score -= Checked;
+        if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
+            attackUnits += QueenCheck, score -= SafeCheck;
+
+        // Enemy rooks safe and other checks
+        if (b1 & ei.attackedBy[Them][ROOK] & safe)
+            attackUnits += RookCheck, score -= SafeCheck;
+
+        else if (b1 & ei.attackedBy[Them][ROOK] & other)
+            score -= OtherCheck;
+
+        // Enemy bishops safe and other checks
+        if (b2 & ei.attackedBy[Them][BISHOP] & safe)
+            attackUnits += BishopCheck, score -= SafeCheck;
 
-        // Enemy rooks safe checks
-        if (b1 & ei.attackedBy[Them][ROOK])
-            attackUnits += RookCheck, score -= Checked;
+        else if (b2 & ei.attackedBy[Them][BISHOP] & other)
+            score -= OtherCheck;
 
-        // Enemy bishops safe checks
-        if (b2 & ei.attackedBy[Them][BISHOP])
-            attackUnits += BishopCheck, score -= Checked;
+        // Enemy knights safe and other checks
+        b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
+        if (b & safe)
+            attackUnits += KnightCheck, score -= SafeCheck;
 
-        // Enemy knights safe checks
-        if (pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe)
-            attackUnits += KnightCheck, score -= Checked;
+        else if (b & other)
+            score -= OtherCheck;
 
         // Finally, extract the king danger score from the KingDanger[]
         // array and subtract the score from the evaluation.