⚖️ Passed pawns: bonus for not enemy pieces ahead (#1008)

Replace miscalculated penalty for blocked passers with a bonus for unblocked passers, defining unblocked as no enemy pieces in the passed pawn mask of the square where the pawn is.
lynx-chess · Sep 15, 2024 · 4928f93 · 4928f93
1 parent 3b2b48f
commit 4928f93
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diff --git a/src/Lynx/Model/Position.cs b/src/Lynx/Model/Position.cs
@@ -753,21 +753,20 @@ private int PawnAdditionalEvaluation(int bucket, int squareIndex, int pieceIndex
             packedBonus += IsolatedPawnPenalty;
         }
 
-        if ((PieceBitBoards[(int)Piece.p - pieceIndex] & Masks.PassedPawns[pieceIndex][squareIndex]) == default)    // isPassedPawn
+        ulong passedPawnsMask = Masks.PassedPawns[pieceIndex][squareIndex];
+        if ((PieceBitBoards[(int)Piece.p - pieceIndex] & passedPawnsMask) == default)    // isPassedPawn
         {
             var rank = Constants.Rank[squareIndex];
-            var blockingSquare = squareIndex + 8;
             var oppositeSide = (int)Side.Black;
             if (pieceIndex == (int)Piece.p)
             {
                 rank = 7 - rank;
-                blockingSquare -= 16;
                 oppositeSide = (int)Side.White;
-            }
+            }   
 
-            if (OccupancyBitBoards[oppositeSide].GetBit(blockingSquare))
+            if ((passedPawnsMask & OccupancyBitBoards[oppositeSide]) == 0)
             {
-                packedBonus += PassedPawnBlockedPenalty[bucket][rank];
+                packedBonus += PassedPawnBonusNoEnemiesAheadBonus[bucket][rank];
             }
 
             var friendlyKingDistance = Constants.ChebyshevDistance[squareIndex][sameSideKingSquare];