Refactor StartNewLvl

Source/player.cpp

@@ -2680,8 +2680,7 @@ void StartPlrHit(Player &player, int dam, bool forcehit)
 #if defined(__clang__) || defined(__GNUC__)
 __attribute__((no_sanitize("shift-base")))
 #endif
-void
-StartPlayerKill(Player &player, DeathReason deathReason)
+void StartPlayerKill(Player &player, DeathReason deathReason)
 {
 	if (player.hasNoLife() && player._pmode == PM_DEATH) {
 		return;
@@ -2893,11 +2892,7 @@ void RemovePlrMissiles(const Player &player)
 	}
 }
 
-#if defined(__clang__) || defined(__GNUC__)
-__attribute__((no_sanitize("shift-base")))
-#endif
-void
-StartNewLvl(Player &player, interface_mode fom, int lvl)
+void StartNewLvl(Player &player, interface_mode fom, int lvl)
 {
 	InitLevelChange(player);
 
@@ -2914,7 +2909,10 @@ StartNewLvl(Player &player, interface_mode fom, int lvl)
 		player.setLevel(setlvlnum);
 		break;
 	case WM_DIABTWARPUP:
-		MyPlayer->pTownWarps |= 1 << (leveltype - 2);
+		assert(leveltype >= DTYPE_CATACOMBS && leveltype <= DTYPE_HELL);
+		const unsigned warpIndex = static_cast<unsigned>(leveltype - 2);
+		const uint8_t warpMask = static_cast<uint8_t>(1u << warpIndex);
+		MyPlayer->pTownWarps |= warpMask;
 		player.setLevel(lvl);
 		break;
 	case WM_DIABRETOWN: