endianness.hpp

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/*
 * SPDX-FileCopyrightText: 2024 M5Stack Technology CO LTD
 *
 * SPDX-License-Identifier: MIT
 */
#ifndef M5_UTILITY_STL_ENDIANNESS_HPP
#define M5_UTILITY_STL_ENDIANNESS_HPP
 
#if __cplusplus >= 202002L
// #pragma message("Using std::endian")
#include <bit>
#elif __has_include(<endian.h>)
// #pragma message("Using endian.h")
#include <endian.h>
#elif __has_include(<machine/endian.h>)
// #pragma message("Using machine/endian.h")
#include <machine/endian.h>
#else
// #pragma message("Using hacked")
#include <cstdint>
#endif
 
namespace m5 {
namespace stl {
 
// C++20 or later
#if __cplusplus >= 202002L || DOXYGEN_PROCESS
 
using endian = std::endian;
 
// endian header
#elif __has_include(<endian.h>) || __has_include(<machine/endian.h>)
 
enum class endian {
#if defined(__BYTE_ORDER)
    little = __LITTLE_ENDIAN,
    big    = __BIG_ENDIAN,
    native = __BYTE_ORDER
#elif defined(_BYTE_ORDER)
    little = _LITTLE_ENDIAN,
    big    = _BIG_ENDIAN,
    native = _BYTE_ORDER
#elif defined(BYTE_ORDER)
    little = LITTLE_ENDIAN,
    big    = BIG_ENDIAN,
    native = BYTE_ORDER
#else
    little = 0,
    big    = 0,
    native = 0,
#endif
};
 
#elif defined(__BYTE_ORDER__)
 
enum class endian { little = __ORDER_LITTLE_ENDIAN__, big = __ORDER_BIG_ENDIAN__, native = __BYTE_ORDER__ };
 
// MSVC defines none of the macros above, so say it outright: every target it
// supports (x86, x64, ARM64) is little endian. Without this the runtime
// detection below would be taken, and that one violates strict aliasing.
#elif defined(_MSC_VER)
 
enum class endian { little = 0, big = 1, native = little };
 
#else
#pragma message( \
    "Cannot determine byte order at compile time. Falling back to runtime detection (strict aliasing violation).")
constexpr uint32_t val32 = 0x11223344;
constexpr uint8_t ref8   = static_cast<const uint8_t&>(val32);
enum class endian { little = 0x44, big = 0x11, native = ref8 };
#endif
}  // namespace stl
 
namespace endian {
constexpr bool little = m5::stl::endian::native == m5::stl::endian::little;  
constexpr bool big    = m5::stl::endian::native == m5::stl::endian::big;     
constexpr bool other  = !little && !big;                                     
 
static_assert(little || big || other, "Unable to determine endianness");
static_assert(((int)little + (int)big + (int)other) == 1, "Endian matches more than one");
}  // namespace endian
}  // namespace m5
 
#endif