From 55ce07b773b1b57faf65d9591b199b350868a933 Mon Sep 17 00:00:00 2001
From: Tomasz Sobczyk <tomasz.sobczyk1997@gmail.com>
Date: Sat, 3 Apr 2021 16:15:51 +0200
Subject: [PATCH] Add additional checks for en-passant possiblity when fixing
 the erroneus ep flag from a fen.

---
 src/extra/nnue_data_binpack_format.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/extra/nnue_data_binpack_format.h b/src/extra/nnue_data_binpack_format.h
index 453169dd..0b1ac0aa 100644
--- a/src/extra/nnue_data_binpack_format.h
+++ b/src/extra/nnue_data_binpack_format.h
@@ -6116,6 +6116,26 @@ namespace chess
 
     [[nodiscard]] inline bool Position::isEpPossibleColdPath(Square epSquare, Bitboard pawnsAttackingEpSquare, Color sideToMove) const
     {
+        if (pieceAt(epSquare) != Piece::none())
+        {
+            return false;
+        }
+
+        const auto forward =
+            sideToMove == chess::Color::White
+            ? FlatSquareOffset(0, 1)
+            : FlatSquareOffset(0, -1);
+
+        if (pieceAt(epSquare + forward) != Piece::none())
+        {
+            return false;
+        }
+
+        if (pieceAt(epSquare + -forward) != Piece(PieceType::Pawn, !sideToMove))
+        {
+            return false;
+        }
+
         // only set m_epSquare when it matters, ie. when
         // the opposite side can actually capture
         for (Square sq : pawnsAttackingEpSquare)