Fix #157: Integer overflow in town GetNormalGrowthRate

src/town_cmd.cpp

@@ -3727,9 +3727,9 @@ static uint GetNormalGrowthRate(Town *t)
 			return stat.old_max ? ((uint64) (stat.old_act << 15)) / stat.old_max : 1 << 15;
 		};
 		uint32 cargo_ratio_fix16 = calculate_cargo_ratio_fix15(t->supplied[CT_PASSENGERS]) + calculate_cargo_ratio_fix15(t->supplied[CT_MAIL]);
-		uint32 cargo_dependant_part = (((uint64) cargo_ratio_fix16) * ((uint64) inverse_m) * _settings_game.economy.town_growth_cargo_transported) >> 16;
-		uint32 non_cargo_dependant_part = ((uint64) inverse_m) * (100 - _settings_game.economy.town_growth_cargo_transported);
-		uint32 total = (cargo_dependant_part + non_cargo_dependant_part);
+		uint64 cargo_dependant_part = (((uint64) cargo_ratio_fix16) * ((uint64) inverse_m) * _settings_game.economy.town_growth_cargo_transported) >> 16;
+		uint64 non_cargo_dependant_part = ((uint64) inverse_m) * (100 - _settings_game.economy.town_growth_cargo_transported);
+		uint64 total = (cargo_dependant_part + non_cargo_dependant_part);
 		if (total == 0) {
 			ClrBit(t->flags, TOWN_IS_GROWING);
 			return UINT16_MAX;