Fix cross-edge e.p. capture in Cylinder Chess

ApplyMove() did not remove the e.p. victim when an edge-crossing e.p.
capture was made, because e.p. rights are only set to neighboring files
(after checking there is a Pawn there to capture). The e.p. heuristic
has now been changed to also assume e.p. on file-changing Pawn moves
that span a large number of files, assuming that these will be wrapping
moves. Eventually we should change to better e.p. logic that can be
integrated with engine-configured move generation, as the current system
would fail for any Pawn that captures more than just neighbor ranks.

diff --git a/backend.c b/backend.c
index 749bac9..605940e 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -10013,7 +10013,7 @@ ApplyMove (int fromX, int fromY, int toX, int toY, int promoChar, Board board)
             board[toY][toX] = (ChessSquare) (PROMOTED board[toY][toX]);
        board[fromY][fromX] = EmptySquare;
     } else if ((fromY >= BOARD_HEIGHT>>1)
-              && (oldEP == toX || oldEP == EP_UNKNOWN || appData.testLegality)
+              && (oldEP == toX || oldEP == EP_UNKNOWN || appData.testLegality || abs(toX - fromX) > 4)
               && (toX != fromX)
                && gameInfo.variant != VariantXiangqi
                && gameInfo.variant != VariantBerolina
@@ -10074,7 +10074,7 @@ ApplyMove (int fromX, int fromY, int toX, int toY, int promoChar, Board board)
             board[toY][toX] = (ChessSquare) (PROMOTED board[toY][toX]);
        board[fromY][fromX] = EmptySquare;
     } else if ((fromY < BOARD_HEIGHT>>1)
-              && (oldEP == toX || oldEP == EP_UNKNOWN || appData.testLegality)
+              && (oldEP == toX || oldEP == EP_UNKNOWN || appData.testLegality || abs(toX - fromX) > 4)
               && (toX != fromX)
                && gameInfo.variant != VariantXiangqi
                && gameInfo.variant != VariantBerolina