Pawn Center Bind Bonus

Joona Kiiski · zamar · commit e118570038f2 · 2015-02-08T19:28:01.000Z
Bonus for two pawns controlling the same central square STC: LLR: 3.14 (-2.94,2.94) [-1.50,4.50] Total: 15974 W: 3291 L: 3133 D: 9550 LTC: LLR: 3.24 (-2.94,2.94) [0.00,6.00] Total: 10449 W: 1837 L: 1674 D: 6938 Idea from Lyudmil Tsvetkov. Bench: 7699138 Resolves #248
diff --git a/src/pawns.cpp b/src/pawns.cpp
@@ -61,6 +61,14 @@ namespace {
   // Unsupported pawn penalty
   const Score UnsupportedPawnPenalty = S(20, 10);
 
+  // Center bind bonus: Two pawns controlling the same central square
+  const Bitboard CenterBindMask[COLOR_NB] = {
+    (FileDBB | FileEBB) & (Rank5BB | Rank6BB | Rank7BB),
+    (FileDBB | FileEBB) & (Rank4BB | Rank3BB | Rank2BB)
+  };
+
+  const Score CenterBind = S(16, 0);
+
   // Weakness of our pawn shelter in front of the king by [distance from edge][rank]
   const Value ShelterWeakness[][RANK_NB] = {
   { V( 99), V(20), V(26), V(54), V(85), V( 92), V(108) },
@@ -195,6 +203,10 @@ namespace {
     b = e->semiopenFiles[Us] ^ 0xFF;
     e->pawnSpan[Us] = b ? int(msb(b) - lsb(b)) : 0;
 
+    // Center binds: Two pawns controlling the same central square
+    b = shift_bb<Right>(ourPawns) & shift_bb<Left>(ourPawns) & CenterBindMask[Us];
+    score += popcount<Max15>(b) * CenterBind;
+
     return score;
   }
 
