From 3011cf5a284746097349db4d9a970cb8b3bf67ab Mon Sep 17 00:00:00 2001
From: binarylab2022-del <binarylab2022@gmail.com>
Date: Thu, 16 Jul 2026 19:12:43 +0100
Subject: [PATCH] Fix square-to-coordinate character conversions

---
 ChessDLL/engine.cpp | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/ChessDLL/engine.cpp b/ChessDLL/engine.cpp
index aaadbee..9394acc 100644
--- a/ChessDLL/engine.cpp
+++ b/ChessDLL/engine.cpp
@@ -3037,12 +3037,15 @@ extern "C" __declspec(dllexport) long long GetDernierTempsRechercheMs()
 }
 
 string caseVersUCI(int casee) {
-    char col = 'a' + (casee % 8);
-    char rng = '1' + (casee / 8);
-    string s = "";
-    s += col;
-    s += rng;
-    return s;
+    // A chess square is encoded from 0 (a1) to 63 (h8).  Validate the
+    // value before converting the numeric file/rank offsets to characters.
+    // The explicit casts also avoid MSVC warning C4244 (int -> char).
+    if (casee < 0 || casee >= 64)
+        return "";
+
+    const char col = static_cast<char>('a' + (casee % 8));
+    const char rng = static_cast<char>('1' + (casee / 8));
+    return string{ col, rng };
 }
 
 string coupVersUCI(int coup) {
@@ -3466,17 +3469,16 @@ extern "C" __declspec(dllexport) const char* GetFEN()
     if (droitRoqueNoirGrand())  roque += 'q';
     if (roque.empty()) roque = "-";
     fen += roque;
-    if (caseEnPassant == -1)
+    if (caseEnPassant < 0 || caseEnPassant >= 64)
     {
+        // The normal sentinel is -1.  Treat any invalid value as no
+        // en-passant target instead of producing malformed FEN text.
         fen += " -";
     }
     else
     {
-        char col = 'a' + (caseEnPassant % 8);
-        char rang = '1' + (caseEnPassant / 8);
         fen += " ";
-        fen += col;
-        fen += rang;
+        fen += caseVersUCI(caseEnPassant);
     }
     fen += " " + to_string(compteurCinquante);
     fen += " " + to_string(numeroCoupComplet);