mpd/src/util/ByteOrder.hxx

// SPDX-License-Identifier: BSD-2-Clause
// author: Max Kellermann <max.kellermann@gmail.com>

#pragma once

#include <cstdint>

#if defined(__i386__) || defined(__x86_64__) || defined(__ARMEL__)
/* well-known little-endian */
#  define IS_LITTLE_ENDIAN true
#  define IS_BIG_ENDIAN false
#elif defined(__MIPSEB__)
/* well-known big-endian */
#  define IS_LITTLE_ENDIAN false
#  define IS_BIG_ENDIAN true
#elif defined(__APPLE__) || defined(__NetBSD__)
/* compile-time check for MacOS */
#  include <machine/endian.h>
#  if BYTE_ORDER == LITTLE_ENDIAN
#    define IS_LITTLE_ENDIAN true
#    define IS_BIG_ENDIAN false
#  else
#    define IS_LITTLE_ENDIAN false
#    define IS_BIG_ENDIAN true
#  endif
#elif defined(__BYTE_ORDER__)
/* GCC-specific macros */
#  if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
#    define IS_LITTLE_ENDIAN true
#    define IS_BIG_ENDIAN false
#  else
#    define IS_LITTLE_ENDIAN false
#    define IS_BIG_ENDIAN true
#  endif
#else
/* generic compile-time check */
#  include <endian.h>
#  if __BYTE_ORDER == __LITTLE_ENDIAN
#    define IS_LITTLE_ENDIAN true
#    define IS_BIG_ENDIAN false
#  else
#    define IS_LITTLE_ENDIAN false
#    define IS_BIG_ENDIAN true
#  endif
#endif

constexpr bool
IsLittleEndian() noexcept
{
	return IS_LITTLE_ENDIAN;
}

constexpr bool
IsBigEndian() noexcept
{
	return IS_BIG_ENDIAN;
}

constexpr uint16_t
GenericByteSwap16(uint16_t value) noexcept
{
	return (value >> 8) | (value << 8);
}

constexpr uint32_t
GenericByteSwap32(uint32_t value) noexcept
{
	return (value >> 24) | ((value >> 8) & 0x0000ff00) |
		((value << 8) & 0x00ff0000) | (value << 24);
}

constexpr uint64_t
GenericByteSwap64(uint64_t value) noexcept
{
	return uint64_t(GenericByteSwap32(uint32_t(value >> 32)))
		| (uint64_t(GenericByteSwap32(value)) << 32);
}

constexpr uint16_t
ByteSwap16(uint16_t value) noexcept
{
#ifdef __GNUC__
	return __builtin_bswap16(value);
#else
	return GenericByteSwap16(value);
#endif
}

constexpr uint32_t
ByteSwap32(uint32_t value) noexcept
{
#ifdef __GNUC__
	return __builtin_bswap32(value);
#else
	return GenericByteSwap32(value);
#endif
}

constexpr uint64_t
ByteSwap64(uint64_t value) noexcept
{
#ifdef __GNUC__
	return __builtin_bswap64(value);
#else
	return GenericByteSwap64(value);
#endif
}

/**
 * Converts a 16bit value from big endian to the system's byte order
 */
constexpr uint16_t
FromBE16(uint16_t value) noexcept
{
	return IsBigEndian() ? value : ByteSwap16(value);
}

/**
 * Converts a 32bit value from big endian to the system's byte order
 */
constexpr uint32_t
FromBE32(uint32_t value) noexcept
{
	return IsBigEndian() ? value : ByteSwap32(value);
}

/**
 * Converts a 64bit value from big endian to the system's byte order
 */
constexpr uint64_t
FromBE64(uint64_t value) noexcept
{
	return IsBigEndian() ? value : ByteSwap64(value);
}

/**
 * Converts a 16bit value from little endian to the system's byte order
 */
constexpr uint16_t
FromLE16(uint16_t value) noexcept
{
	return IsLittleEndian() ? value : ByteSwap16(value);
}

/**
 * Converts a 32bit value from little endian to the system's byte order
 */
constexpr uint32_t
FromLE32(uint32_t value) noexcept
{
	return IsLittleEndian() ? value : ByteSwap32(value);
}

/**
 * Converts a 64bit value from little endian to the system's byte order
 */
constexpr uint64_t
FromLE64(uint64_t value) noexcept
{
	return IsLittleEndian() ? value : ByteSwap64(value);
}

/**
 * Converts a 16bit value from the system's byte order to big endian
 */
constexpr uint16_t
ToBE16(uint16_t value) noexcept
{
	return IsBigEndian() ? value : ByteSwap16(value);
}

/**
 * Converts a 32bit value from the system's byte order to big endian
 */
constexpr uint32_t
ToBE32(uint32_t value) noexcept
{
	return IsBigEndian() ? value : ByteSwap32(value);
}

/**
 * Converts a 64bit value from the system's byte order to big endian
 */
constexpr uint64_t
ToBE64(uint64_t value) noexcept
{
	return IsBigEndian() ? value : ByteSwap64(value);
}

/**
 * Converts a 16bit value from the system's byte order to little endian
 */
constexpr uint16_t
ToLE16(uint16_t value) noexcept
{
	return IsLittleEndian() ? value : ByteSwap16(value);
}

/**
 * Converts a 32bit value from the system's byte order to little endian
 */
constexpr uint32_t
ToLE32(uint32_t value) noexcept
{
	return IsLittleEndian() ? value : ByteSwap32(value);
}

/**
 * Converts a 64bit value from the system's byte order to little endian
 */
constexpr uint64_t
ToLE64(uint64_t value) noexcept
{
	return IsLittleEndian() ? value : ByteSwap64(value);
}

/**
 * Converts a 16 bit integer from little endian to the host byte order
 * and returns it as a signed integer.
 */
constexpr int16_t
FromLE16S(uint16_t value) noexcept
{
	/* assuming two's complement representation */
	return static_cast<int16_t>(FromLE16(value));
}