Limit king ring to eight squares

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 4351fe2eb7795500b2b44b84c4ffc537f4eb2179..f93e23f66d1ef7b1578e11b50fb740c610846f72 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -88,7 +88,7 @@ namespace {
 
     // kingRing[color] is the zone around the king which is considered
     // by the king safety evaluation. This consists of the squares directly
-    // adjacent to the king, and the three (or two, for a king on an edge file)
+    // adjacent to the king, and (only for a king on its first rank) the
     // squares two ranks in front of the king. For instance, if black's king
     // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,
     // f7, g7, h7, f6, g6 and h6.
@@ -174,14 +174,8 @@ namespace {
     S(-20,-12), S( 1, -8), S( 2, 10), S(  9, 10)
   };
 
-  // Protector[PieceType-2][distance] contains a protecting bonus for our king,
-  // indexed by piece type and distance between the piece and the king.
-  const Score Protector[][8] = {
-    { S(0, 0), S( 7, 9), S( 7, 1), S( 1, 5), S(-10,-4), S( -1,-4), S( -7,-3), S(-16,-10) }, // Knight
-    { S(0, 0), S(11, 8), S(-7,-1), S(-1,-2), S( -1,-7), S(-11,-3), S( -9,-1), S(-16, -1) }, // Bishop
-    { S(0, 0), S(10, 0), S(-2, 2), S(-5, 4), S( -6, 2), S(-14,-3), S( -2,-9), S(-12, -7) }, // Rook
-    { S(0, 0), S( 3,-5), S( 2,-5), S(-4, 0), S( -9,-6), S( -4, 7), S(-13,-7), S(-10, -7) }  // Queen
-  };
+  // KingProtector[PieceType-2] contains a bonus according to distance from king
+  const Score KingProtector[] = { S(-3, -5), S(-4, -3), S(-3, 0), S(-1, 1) };
 
   // Assorted bonuses and penalties used by evaluation
   const Score MinorBehindPawn     = S( 16,  0);
@@ -248,7 +242,10 @@ namespace {
     // Init our king safety tables only if we are going to use them
     if (pos.non_pawn_material(Them) >= QueenValueMg)
     {
-        ei.kingRing[Us] = b | shift<Up>(b);
+        ei.kingRing[Us] = b;
+        if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)
+            ei.kingRing[Us] |= shift<Up>(b);
+
         ei.kingAttackersCount[Them] = popcount(b & ei.pe->pawn_attacks(Them));
         ei.kingAdjacentZoneAttacksCount[Them] = ei.kingAttackersWeight[Them] = 0;
     }
@@ -297,10 +294,10 @@ namespace {
 
         int mob = popcount(b & ei.mobilityArea[Us]);
 
-        mobility[Us] += MobilityBonus[Pt-2][mob];
+        mobility[Us] += MobilityBonus[Pt - 2][mob];
 
         // Bonus for this piece as a king protector
-        score += Protector[Pt-2][distance(s, pos.square<KING>(Us))];
+        score += KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));
 
         if (Pt == BISHOP || Pt == KNIGHT)
         {