Guard against UB in lsb/msb

[stockfish] / src / bitboard.h

diff --git a/src/bitboard.h b/src/bitboard.h
index 2ad8773634dce967e6cc6b223e68eeb3d4d66f05..77a824ba62106965ba9513803a19c650c092bb4c 100644 (file)
--- a/src/bitboard.h
+++ b/src/bitboard.h
@@ -261,18 +261,27 @@ inline Bitboard attacks_bb(Piece pc, Square s, Bitboard occupied) {
 
 #if defined(__GNUC__)
 
-inline Square lsb(Bitboard b) { return Square(__builtin_ctzll(b)); }
-inline Square msb(Bitboard b) { return Square(63 - __builtin_clzll(b)); }
+inline Square lsb(Bitboard b) {
+  assert(b);
+  return Square(__builtin_ctzll(b));
+}
+
+inline Square msb(Bitboard b) {
+  assert(b);
+  return Square(63 - __builtin_clzll(b));
+}
 
 #elif defined(_WIN64) && defined(_MSC_VER)
 
 inline Square lsb(Bitboard b) {
+  assert(b);
   unsigned long idx;
   _BitScanForward64(&idx, b);
   return (Square) idx;
 }
 
 inline Square msb(Bitboard b) {
+  assert(b);
   unsigned long idx;
   _BitScanReverse64(&idx, b);
   return (Square) idx;