utx::max_real_t is used to get the lowest maximum type of two real types.
For example, it gets utx::ix64 from utx::u32 and utx::ix16; gets utx::ix32 from utx::ix32 and utx::u8.
However, utx::max_real_t gets utx::overflow_type, if the converter have a chance to make overflow values. Such as it gets utx::overflow_type from utx::u64 and utx::i32.
using target_type = utx::max_real_t<real_type1, real_type2>;