From 7b293fd83e51f0253230381796e24224f314506b Mon Sep 17 00:00:00 2001
From: "Steinar H. Gunderson" <sesse@debian.org>
Date: Sat, 16 Jun 2007 14:31:18 +0200
Subject: [PATCH] Be stricter about the en passent handling in FEN notation;
 unconfuses Rybka.

---
 remoteglot.pl | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/remoteglot.pl b/remoteglot.pl
index 330d47b..7bcbbdf 100644
--- a/remoteglot.pl
+++ b/remoteglot.pl
@@ -190,11 +190,28 @@ sub style12_to_fen {
 	# en passant
 	my $ep = "-";
 	if ($x[10] != -1) {
-		$ep = (qw(a b c d e f g h))[$x[10]];
+		my $col = $x[10];
+		my $nep = (qw(a b c d e f g h))[$col];
+
+		if ($x[9] eq 'B') {
+			$nep .= "3";
+		} else {
+			$nep .= "6";
+		}
+		
+		#
+		# Showing the en passant square when actually no capture can be made
+		# seems to confuse at least Rybka. Thus, check if there's actually
+		# a pawn of the opposite side that can do the en passant move, and if
+		# not, just lie -- it doesn't matter anyway. I'm unsure what's the
+		# "right" thing as per the standard, though.
+		#
 		if ($x[9] eq 'B') {
-			$ep .= "3";
+			$ep = $nep if ($col > 0 && substr($board[4], $col-1, 1) eq 'p');
+			$ep = $nep if ($col < 7 && substr($board[4], $col+1, 1) eq 'p');
 		} else {
-			$ep .= "6";
+			$ep = $nep if ($col > 0 && substr($board[3], $col-1, 1) eq 'P');
+			$ep = $nep if ($col < 7 && substr($board[3], $col+1, 1) eq 'P');
 		}
 	}
 	$fen .= " ";
-- 
2.39.2