From: Stefan Geschwentner <Stefan.Geschwentner@web.de>
Date: Fri, 28 Mar 2014 07:41:50 +0000 (+0100)
Subject: Pinned pieces affect king safety
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=af0c13ba6ad5d51432a8f4531d53c7309484df6b

Pinned pieces affect king safety

Here the new idea is to link pinned pieces
with king safety.

Passed both STC
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 10047 W: 1867 L: 1737 D: 6443

And LTC
LLR: 2.97 (-2.94,2.94) [0.00,6.00]
Total: 10419 W: 1692 L: 1543 D: 7184

bench: 8325087
---

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 99e9f047..8c84ac29 100644
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -204,6 +204,8 @@ namespace {
   const int BishopCheck       = 2;
   const int KnightCheck       = 3;
 
+  const int UnsupportedPinnedPiece = 2;
+
   // KingDanger[Color][attackUnits] contains the actual king danger weighted
   // scores, indexed by color and by a calculated integer number.
   Score KingDanger[COLOR_NB][128];
@@ -693,6 +695,10 @@ Value do_evaluate(const Position& pos) {
         if (b)
             attackUnits += KnightCheck * popcount<Max15>(b);
 
+        // Penalty for pinned pieces not defended by a pawn
+        if (ei.pinnedPieces[Us] & ~ei.attackedBy[Us][PAWN])
+            attackUnits += UnsupportedPinnedPiece;
+
         // To index KingDanger[] attackUnits must be in [0, 99] range
         attackUnits = std::min(99, std::max(0, attackUnits));