featuare(fen): validating king counts before accepting fen string

1 files changed, 15 insertions, 0 deletions

diff --git a/src/board/fen.cpp b/src/board/fen.cpp
index e020e78..f44719a 100644
--- a/src/board/fen.cpp
+++ b/src/board/fen.cpp
@@ -2,8 +2,10 @@
 #include "board.hpp"
 #include <cassert>
 #include <cctype>
+#include <cstdint>
 #include <cstdlib>
 #include <cstring>
+#include <iostream>
 #include <print>
 #include <string>
 #include <sys/types.h>
@@ -185,5 +187,18 @@ void setBoardFen(const std::string &fen, Game *g) {
     break;
   }
   g->enPassant = enpassant;
+
   updateBitboards(g);
+
+  int whiteKingCount = __builtin_popcountll(g->PieceBitboards[true][KING]);
+  int blackKingCount = __builtin_popcountll(g->PieceBitboards[false][KING]);
+
+  if (whiteKingCount != 1) {
+    std::cerr << "ERROR: expected exactly one white king\n";
+    exit(1);
+  }
+  if (blackKingCount != 1) {
+    std::cerr << "ERROR: expected exactly one black king\n";
+    exit(1);
+  }
 }