conversion.hpp

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/*
 * SPDX-FileCopyrightText: 2024 M5Stack Technology CO LTD
 *
 * SPDX-License-Identifier: MIT
 */
#ifndef M5_UTILITY_CONVERSION_HPP
#define M5_UTILITY_CONVERSION_HPP
 
#include <type_traits>
#include <limits>
#include <cstdint>
#include <cstdint>
#include <cstddef>
 
namespace m5 {
namespace utility {
 
namespace detail {
 
constexpr uint64_t low_bits_mask(const size_t bits)
{
    return (bits >= 64) ? ~uint64_t{0} : ((uint64_t{1} << bits) - 1);
}
 
template <typename T>
constexpr typename std::make_signed<T>::type to_signed_bits(const T v, const size_t bits)
{
    using S = typename std::make_signed<T>::type;
    return (bits == 0)
               ? S{0}
               : ((static_cast<uint64_t>(v) & (uint64_t{1} << (bits - 1)))
                      ? static_cast<S>((static_cast<uint64_t>(v) & low_bits_mask(bits)) - (low_bits_mask(bits) + 1))
                      : static_cast<S>(static_cast<uint64_t>(v) & low_bits_mask(bits)));
}
 
}  // namespace detail
 
template <size_t Bits, typename T>
constexpr auto unsigned_to_signed(const T v) -> typename std::make_signed<T>::type
{
    static_assert(std::is_integral<T>::value && std::is_unsigned<T>::value, "T must be an unsigned integer");
    static_assert(Bits <= sizeof(T) * 8, "Bits must be less than or equal to the number of bits in T");
 
    return detail::to_signed_bits(v, Bits);
}
 
template <typename T>
constexpr auto unsigned_to_signed(const T v, const size_t bits) -> typename std::make_signed<T>::type
{
    static_assert(std::is_integral<T>::value && std::is_unsigned<T>::value, "T must be an unsigned integer");
 
    return detail::to_signed_bits(v, bits);
}
 
template <typename To, typename From>
constexpr To saturate_cast(const From v)
{
    static_assert(std::is_integral<To>::value && std::is_unsigned<To>::value, "To must be an unsigned integer");
    static_assert(std::is_integral<From>::value && std::is_unsigned<From>::value, "From must be an unsigned integer");
 
    return static_cast<To>(static_cast<uintmax_t>(v) > static_cast<uintmax_t>(std::numeric_limits<To>::max())
                               ? std::numeric_limits<To>::max()
                               : v);
}
 
}  // namespace utility
}  // namespace m5
#endif