intopt.hpp

#include <cstdint>

template<bool Fits8Bit, bool Fits16Bit, bool Fits32Bit>
struct intopt_helper {
    using signed_type   = std::int64_t;
    using unsigned_type = std::uint64_t;
};

template<>
struct intopt_helper<false, false, true> {
    using signed_type   = std::int32_t;
    using unsigned_type = std::uint32_t;
};

template<>
struct intopt_helper<false, true,  true> {
    using signed_type   = std::int16_t;
    using unsigned_type = std::uint16_t;
};

template<>
struct intopt_helper<true,  true,  true> {
    using signed_type   = std::int8_t;
    using unsigned_type = std::uint8_t;
};

template<std::intmax_t MinValue, std::uintmax_t MaxValue>
struct intopt {
    using type = typename intopt_helper<
        (MinValue >= INT8_MIN  && MaxValue <= INT8_MAX),
        (MinValue >= INT16_MIN && MaxValue <= INT16_MAX),
        (MinValue >= INT32_MIN && MaxValue <= INT32_MAX)
    >::signed_type;
};

template<std::uintmax_t MaxValue>
struct uintopt {
    using type = typename intopt_helper<
        (MaxValue <= UINT8_MAX),
        (MaxValue <= UINT16_MAX),
        (MaxValue <= UINT32_MAX)
    >::unsigned_type;
};

template<std::uintmax_t MaxValue>
struct intopt<0, MaxValue> {
    using type = typename uintopt<MaxValue>::type;
};