byteswap.hpp

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/*
 * SPDX-FileCopyrightText: 2024 M5Stack Technology CO LTD
 *
 * SPDX-License-Identifier: MIT
 */
#ifndef M5_UTILITY_STL_BYTESWAP_HPP
#define M5_UTILITY_STL_BYTESWAP_HPP
 
#include <stdint.h>
#include <type_traits>
#include <cstring>  // memcpy
 
namespace m5 {
namespace stl {
 
template <typename U,
          typename std::enable_if<sizeof(U) == 2 && std::is_unsigned<U>::value, std::nullptr_t>::type = nullptr>
inline constexpr U bswap_fixed(U x) noexcept
{
    return static_cast<U>((static_cast<uint16_t>(x >> 8) & 0x00FFu) | (static_cast<uint16_t>(x << 8) & 0xFF00u));
}
 
template <typename U,
          typename std::enable_if<sizeof(U) == 4 && std::is_unsigned<U>::value, std::nullptr_t>::type = nullptr>
inline constexpr U bswap_fixed(U x) noexcept
{
    return static_cast<U>(((static_cast<uint32_t>(x) >> 24)) | ((static_cast<uint32_t>(x) >> 8) & 0x0000FF00u) |
                          ((static_cast<uint32_t>(x) << 8) & 0x00FF0000u) | ((static_cast<uint32_t>(x) << 24)));
}
 
template <typename U,
          typename std::enable_if<sizeof(U) == 8 && std::is_unsigned<U>::value, std::nullptr_t>::type = nullptr>
inline constexpr U bswap_fixed(U x) noexcept
{
    return static_cast<U>(
        ((static_cast<uint64_t>(x) >> 56)) | ((static_cast<uint64_t>(x) >> 40) & 0x000000000000FF00ull) |
        ((static_cast<uint64_t>(x) >> 24) & 0x0000000000FF0000ull) |
        ((static_cast<uint64_t>(x) >> 8) & 0x00000000FF000000ull) |
        ((static_cast<uint64_t>(x) << 8) & 0x000000FF00000000ull) |
        ((static_cast<uint64_t>(x) << 24) & 0x0000FF0000000000ull) |
        ((static_cast<uint64_t>(x) << 40) & 0x00FF000000000000ull) | ((static_cast<uint64_t>(x) << 56)));
}
 
#if defined(__SIZEOF_INT128__)
template <typename U,
          typename std::enable_if<sizeof(U) == 16 && std::is_unsigned<U>::value, std::nullptr_t>::type = nullptr>
inline constexpr U bswap_fixed(U x) noexcept
{
    return ((static_cast<U>(bswap_fixed<uint64_t>(static_cast<uint64_t>(x))) << 64) |
            static_cast<U>(bswap_fixed<uint64_t>(static_cast<uint64_t>(x >> 64))));
}
#endif
 
template <typename U,
          typename std::enable_if<sizeof(U) == 1 && std::is_unsigned<U>::value, std::nullptr_t>::type = nullptr>
inline constexpr U bswap_fixed(U x) noexcept
{
    return x;
}
 
template <typename T, typename std::enable_if<(std::is_integral<T>::value || std::is_enum<T>::value),
                                              std::nullptr_t>::type = nullptr>
inline constexpr T byteswap_constexpr(T v) noexcept
{
    using U = typename std::make_unsigned<T>::type;
    return static_cast<T>(bswap_fixed<U>(static_cast<U>(v)));
}
 
template <typename T, typename std::enable_if<(std::is_integral<T>::value || std::is_enum<T>::value),
                                              std::nullptr_t>::type = nullptr>
inline constexpr T byteswap(T v) noexcept
{
    return byteswap_constexpr(v);
}
 
// If the type is not integral , it is prohibited
template <typename T, typename std::enable_if<!(std::is_integral<T>::value || std::is_enum<T>::value),
                                              std::nullptr_t>::type = nullptr>
T byteswap(T) = delete;
 
}  // namespace stl
}  // namespace m5
 
#endif