Limit king ring to eight squares

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 3bd790bdf4f7f469a2fa9584eb21a556bd049455..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.
@@ -242,7 +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;
     }