Small tweaks in pawns.cpp

[stockfish] / src / pawns.cpp

diff --git a/src/pawns.cpp b/src/pawns.cpp
index ef456307cafbacb4479a53627a7a1d7b58aa362d..e4c0899ff6d769a9994ab32b6c54ada41f3a3192 100644 (file)
--- 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) },
@@ -130,13 +138,12 @@ namespace {
         e->semiopenFiles[Us] &= ~(1 << f);
 
         // Previous rank
-        p = rank_bb(s - pawn_push(Us));
+        p = rank_bb(s - Up);
 
-        // Flag the pawn as passed, isolated, doubled,
-        // unsupported or connected (but not the backward one).
+        // Flag the pawn
         connected   =   ourPawns   & adjacent_files_bb(f) & (rank_bb(s) | p);
         phalanx     =   connected  & rank_bb(s);
-        unsupported = !(ourPawns   & adjacent_files_bb(f) & p);
+        unsupported = !(connected  & p);
         isolated    = !(ourPawns   & adjacent_files_bb(f));
         doubled     =   ourPawns   & forward_bb(Us, s);
         opposed     =   theirPawns & forward_bb(Us, s);
@@ -144,7 +151,7 @@ namespace {
         lever       =   theirPawns & pawnAttacksBB[s];
 
         // Test for backward pawn.
-        // If the pawn is passed, isolated, connected or a lever it cannot be
+        // If the pawn is passed, isolated, lever or connected it cannot be
         // backward. If there are friendly pawns behind on adjacent files
         // it cannot be backward either.
         if (   (passed | isolated | lever | connected)
@@ -152,7 +159,7 @@ namespace {
             backward = false;
         else
         {
-            // We now know that there are no friendly pawns beside or behind this
+            // We now know there are no friendly pawns beside or behind this
             // pawn on adjacent files. We now check whether the pawn is
             // backward by looking in the forward direction on the adjacent
             // files, and picking the closest pawn there.
@@ -195,6 +202,10 @@ 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;
   }
 
@@ -214,8 +225,8 @@ void init()
       for (int phalanx = 0; phalanx <= 1; ++phalanx)
           for (Rank r = RANK_2; r < RANK_8; ++r)
           {
-              int bonus = Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0);
-              Connected[opposed][phalanx][r] = make_score(bonus / 2, bonus >> opposed);
+              int v = (Seed[r] + (phalanx ? (Seed[r + 1] - Seed[r]) / 2 : 0)) >> opposed;
+              Connected[opposed][phalanx][r] = make_score( 3 * v / 2, v);
           }
 }