[Board] Implement EnPassant handling

Board.hpp

@@ -47,7 +47,7 @@ private:
 
     PieceColor mTurn = PieceColor::White;
     CastlingRights mCR = CastlingRights::None;
-    unsigned mEPS = 64;
+    std::optional<Square> mEPS;
 
     enum DefinedBoards : BitBoard {
         AFile = 0x0101010101010101,
@@ -80,6 +80,14 @@ private:
         return (1ULL << i);
     }
 
+    static inline BitBoard genShift(BitBoard x, const int s) {
+        return (s < 0) ? (x >> -s) : (s > 63) ? x : (x << s);
+    }
+
+    static inline BitBoard getRankBB(int r) {
+        return (genShift(1ULL, (r + 1) * 8) - 1) & genShift(~1ULL, r * 8 - 1);
+    }
+
     static inline int toIndex(PieceType t) {
         return static_cast<int>(t);
     }
@@ -118,6 +126,8 @@ private:
     static inline int getLSB(const BitBoard b) {
         return __builtin_ctzll(b);
     }
+
+    void handlePawnDoubleAdvance(const Move &move, BitBoard bb, const Piece &movedPiece);
 };
 
 std::ostream &operator<<(std::ostream &os, const Board &board);