endian.h

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#pragma once
 
#include "platform.h"
 
#include <cstdint>
 
#if defined(__cpp_lib_endian) && __cpp_lib_endian >= 201907L
#include <bit>
#else // __cpp_lib_endian
#ifndef BS_LITTLE_ENDIAN
// Detect with GCC 4.6's macro.
#if defined(__BYTE_ORDER__)
#if (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
#define BS_LITTLE_ENDIAN true
#elif (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
#define BS_LITTLE_ENDIAN false
#else
#error "Unknown machine byteorder endianness detected. Need to manually define BS_LITTLE_ENDIAN."
#endif
// Detect with GLIBC's endian.h.
#elif defined(__GLIBC__)
#include <endian.h>
#if (__BYTE_ORDER == __LITTLE_ENDIAN)
#define BS_LITTLE_ENDIAN true
#elif (__BYTE_ORDER == __BIG_ENDIAN)
#define BS_LITTLE_ENDIAN false
#else
#error "Unknown machine byteorder endianness detected. Need to manually define BS_LITTLE_ENDIAN."
#endif
// Detect with _LITTLE_ENDIAN and _BIG_ENDIAN macro.
#elif defined(_LITTLE_ENDIAN) && !defined(_BIG_ENDIAN)
#define BS_LITTLE_ENDIAN true
#elif defined(_BIG_ENDIAN) && !defined(_LITTLE_ENDIAN)
#define BS_LITTLE_ENDIAN false
// Detect with architecture macros.
#elif defined(__sparc) || defined(__sparc__) || defined(_POWER) || defined(__powerpc__) || defined(__ppc__) || defined(__hpux) || defined(__hppa) || defined(_MIPSEB) || defined(_POWER) || defined(__s390__)
#define BS_LITTLE_ENDIAN false
#elif defined(__i386__) || defined(__alpha__) || defined(__ia64) || defined(__ia64__) || defined(_M_IX86) || defined(_M_IA64) || defined(_M_ALPHA) || defined(__amd64) || defined(__amd64__) || defined(_M_AMD64) || defined(__x86_64) || defined(__x86_64__) || defined(_M_X64) || defined(__bfin__)
#define BS_LITTLE_ENDIAN true
#elif defined(_MSC_VER) && (defined(_M_ARM) || defined(_M_ARM64))
#define BS_LITTLE_ENDIAN true
#else
#error "Unknown machine byteorder endianness detected. Need to manually define BS_LITTLE_ENDIAN."
#endif
#endif // BS_LITTLE_ENDIAN
#endif // __cpp_lib_endian
 
 
#if defined(_WIN32)
#include <intrin.h>
#endif
 
namespace bitstream::utility
{
    inline constexpr bool little_endian()
    {
#ifdef BS_LITTLE_ENDIAN
#if BS_LITTLE_ENDIAN
        return true;
#else // BS_LITTLE_ENDIAN
        return false;
#endif // BS_LITTLE_ENDIAN
#else // defined(BS_LITTLE_ENDIAN)
        return std::endian::native == std::endian::little;
#endif // defined(BS_LITTLE_ENDIAN)
    }
 
    constexpr inline uint32_t endian_swap32_const(uint32_t value)
    {
        const uint32_t first = (value << 24) & 0xFF000000;
        const uint32_t second = (value << 8) & 0x00FF0000;
        const uint32_t third = (value >> 8) & 0x0000FF00;
        const uint32_t fourth = (value >> 24) & 0x000000FF;
 
        return first | second | third | fourth;
    }
 
    BS_CONSTEXPR inline uint32_t endian_swap32(uint32_t value)
    {
        if BS_CONST_EVALUATED()
        {
            return endian_swap32_const(value);
        }
        else
        {
#if defined(_WIN32)
            return _byteswap_ulong(value);
#elif defined(__linux__)
            return __builtin_bswap32(value);
#else
            return endian_swap32_const(value);
#endif // _WIN32 || __linux__
        }
    }
 
    constexpr inline uint32_t to_big_endian32_const(uint32_t value)
    {
        if constexpr (little_endian())
            return endian_swap32_const(value);
        else
            return value;
    }
 
    BS_CONSTEXPR inline uint32_t to_big_endian32(uint32_t value)
    {
        if constexpr (little_endian())
            return endian_swap32(value);
        else
            return value;
    }
}