From: Gary Linscott <glinscott@gmail.com>
Date: Wed, 21 Mar 2012 06:26:46 +0000 (+0100)
Subject: Penalize undefended minors
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=3c6a4bfbed219b220535bcbaaa76636d3f4879e8;hp=3b7dbc4f6d68928ad97a5d77561509232dd23f78

Penalize undefended minors

Even if not under attack. This seems to be good
especially on openings.

After 12112 games at 10"+0.05
Mod vs Orig 2175 - 1997 - 7940 ELO +5 (+- 3.7)

[Patch series from Gary, little edited by me]

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
---

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index ef52f747..2193eb6b 100644
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -679,12 +679,19 @@ Value do_evaluate(const Position& pos, Value& margin) {
     Bitboard b;
     Score score = SCORE_ZERO;
 
+    // Undefended minors get penalized even if not under attack
+    Bitboard undefended =  pos.pieces(Them)
+                         & (pos.pieces(BISHOP) | pos.pieces(KNIGHT))
+                         & ~ei.attackedBy[Them][0];
+    if (undefended)
+        score += make_score(25, 10) * popcount<Max15>(undefended);
+
     // Enemy pieces not defended by a pawn and under our attack
     Bitboard weakEnemies =  pos.pieces(Them)
                           & ~ei.attackedBy[Them][PAWN]
                           & ei.attackedBy[Us][0];
     if (!weakEnemies)
-        return SCORE_ZERO;
+        return score;
 
     // Add bonus according to type of attacked enemy piece and to the
     // type of attacking piece, from knights to queens. Kings are not