musl/include/endian.h

#ifndef _ENDIAN_H
#define _ENDIAN_H

#if __STDC_VERSION__ >= 199901L || defined(__cplusplus)
#define __inline inline
#endif

#define __LITTLE_ENDIAN 1234
#define __BIG_ENDIAN 4321
#define __PDP_ENDIAN 3412

#if defined(__GNUC__) && defined(__BYTE_ORDER__)
#define __BYTE_ORDER __BYTE_ORDER__
#else
#include <bits/endian.h>
#endif

#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)

#define BIG_ENDIAN __BIG_ENDIAN
#define LITTLE_ENDIAN __LITTLE_ENDIAN
#define PDP_ENDIAN __PDP_ENDIAN
#define BYTE_ORDER __BYTE_ORDER

#include <stdint.h>

static __inline uint16_t __bswap16(uint16_t __x)
{
	return __x<<8 | __x>>8;
}

static __inline uint32_t __bswap32(uint32_t __x)
{
	return __x>>24 | __x>>8&0xff00 | __x<<8&0xff0000 | __x<<24;
}

static __inline uint64_t __bswap64(uint64_t __x)
{
	return __bswap32(__x)+0ULL<<32 | __bswap32(__x>>32);
}

#if __BYTE_ORDER == __LITTLE_ENDIAN
#define htobe16(x) __bswap16(x)
#define be16toh(x) __bswap16(x)
#define betoh16(x) __bswap16(x)
#define htobe32(x) __bswap32(x)
#define be32toh(x) __bswap32(x)
#define betoh32(x) __bswap32(x)
#define htobe64(x) __bswap64(x)
#define be64toh(x) __bswap64(x)
#define betoh64(x) __bswap64(x)
#define htole16(x) (uint16_t)(x)
#define le16toh(x) (uint16_t)(x)
#define letoh16(x) (uint16_t)(x)
#define htole32(x) (uint32_t)(x)
#define le32toh(x) (uint32_t)(x)
#define letoh32(x) (uint32_t)(x)
#define htole64(x) (uint64_t)(x)
#define le64toh(x) (uint64_t)(x)
#define letoh64(x) (uint64_t)(x)
#else
#define htobe16(x) (uint16_t)(x)
#define be16toh(x) (uint16_t)(x)
#define betoh16(x) (uint16_t)(x)
#define htobe32(x) (uint32_t)(x)
#define be32toh(x) (uint32_t)(x)
#define betoh32(x) (uint32_t)(x)
#define htobe64(x) (uint64_t)(x)
#define be64toh(x) (uint64_t)(x)
#define betoh64(x) (uint64_t)(x)
#define htole16(x) __bswap16(x)
#define le16toh(x) __bswap16(x)
#define letoh16(x) __bswap16(x)
#define htole32(x) __bswap32(x)
#define le32toh(x) __bswap32(x)
#define letoh32(x) __bswap32(x)
#define htole64(x) __bswap64(x)
#define le64toh(x) __bswap64(x)
#define letoh64(x) __bswap64(x)
#endif

#endif

#endif