Undefended King Ring

Rocky640 · zamar · commit e9e5f72c7440 · 2016-04-08T19:22:33.000+01:00
There was already a penalty for squares only defended by King (undefended) This test records a penalty for completely undefended squares in the so called extended king-ring (so if we exclude squares defended by a Kg8 for example, we only look at h6 g6 and f6) We also exclude squares occupied by opponent pieces in this computation, based on the following results Was yellow at STC LLR: -2.97 (-2.94,2.94) [0.00,5.00] Total: 112499 W: 20649 L: 20293 D: 71557 and passed LTC LLR: 2.96 (-2.94,2.94) [0.00,5.00] Total: 36805 W: 5100 L: 4857 D: 26848 Bench: 8430233 Resolves: #619
diff --git a/src/evaluate.cpp b/src/evaluate.cpp
@@ -384,14 +384,17 @@ namespace {
     // Main king safety evaluation
     if (ei.kingAttackersCount[Them])
     {
-        // Find the attacked squares around the king which have no defenders
-        // apart from the king itself.
+        // Find the attacked squares which are defended only by the king...
         undefended =  ei.attackedBy[Them][ALL_PIECES]
                     & ei.attackedBy[Us][KING]
                     & ~(  ei.attackedBy[Us][PAWN]   | ei.attackedBy[Us][KNIGHT]
                         | ei.attackedBy[Us][BISHOP] | ei.attackedBy[Us][ROOK]
                         | ei.attackedBy[Us][QUEEN]);
 
+        // ... and those which are not defended at all in the larger king ring
+        b =   ei.attackedBy[Them][ALL_PIECES] & ~ei.attackedBy[Us][ALL_PIECES] 
+            & ei.kingRing[Us] & ~pos.pieces(Them);
+
         // Initialize the 'attackUnits' variable, which is used later on as an
         // index into the KingDanger[] array. The initial value is based on the
         // number and types of the enemy's attacking pieces, the number of
@@ -400,7 +403,7 @@ namespace {
         attackUnits =  std::min(72, ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them])
                      +  9 * ei.kingAdjacentZoneAttacksCount[Them]
                      + 27 * popcount(undefended)
-                     + 11 * !!ei.pinnedPieces[Us]
+                     + 11 * (popcount(b) + !!ei.pinnedPieces[Us])
                      - 64 * !pos.count<QUEEN>(Them)
                      - mg_value(score) / 8;
 
