byteswap32.c

/* NO-OP for little-endian platforms */
#if defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__)
# if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
#   define BYTESWAP(x) (x)
# endif
/* if __BYTE_ORDER__ is not predefined (like FreeBSD), use arch */
#elif defined(__i386)  || defined(__x86_64) \
  ||  defined(__alpha) || defined(__vax)

# define BYTESWAP(x) (x)
/* use __builtin_bswap32 if available */
#elif defined(__GNUC__) || defined(__clang__)
#ifdef __has_builtin
#if __has_builtin(__builtin_bswap32)
#define BYTESWAP(x) __builtin_bswap32(x)
#endif // __has_builtin(__builtin_bswap32)
#endif // __has_builtin
#endif // defined(__GNUC__) || defined(__clang__)
/* last resort (big-endian w/o __builtin_bswap) */
#ifndef BYTESWAP
# define BYTESWAP(x)   ((((x)&0xFF)<<24) \
         |(((x)>>24)&0xFF) \
         |(((x)&0x0000FF00)<<8)    \
         |(((x)&0x00FF0000)>>8)    )
#endif