From: Alain SAVARD <support@multicim.com>
Date: Fri, 8 Apr 2016 18:19:59 +0000 (+0100)
Subject: Undefended King Ring
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=e9e5f72c7440e6c9162a9578ae59fa2b75faf5f4;hp=29b5842da8d5477c0aea924cfd364c9e619456a2

Undefended King Ring

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
index da4b9c30..d00b862f 100644
--- 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;