FFmpeg/libavcodec/bswap.h

#ifndef __BSWAP_H__
#define __BSWAP_H__

#ifdef HAVE_BYTESWAP_H
#include <byteswap.h>
#else

#include <inttypes.h> /* for __WORDSIZE */
#ifdef ARCH_X86
inline static unsigned short ByteSwap16(unsigned short x)
{
  __asm("xchgb %b0,%h0"	:
        "=q" (x)	:
        "0" (x));
    return x;
}
#define bswap_16(x) ByteSwap16(x)

inline static unsigned int ByteSwap32(unsigned int x)
{
#if __CPU__ > 386
 __asm("bswap	%0":
      "=r" (x)     :
#else
 __asm("xchgb	%b0,%h0\n"
      "	rorl	$16,%0\n"
      "	xchgb	%b0,%h0":
      "=q" (x)		:
#endif
      "0" (x));
  return x;
}
#define bswap_32(x) ByteSwap32(x)

inline static unsigned long long int ByteSwap64(unsigned long long int x)
{
  register union { __extension__ unsigned long long int __ll;
          unsigned long int __l[2]; } __x;
  asm("xchgl	%0,%1":
      "=r"(__x.__l[0]),"=r"(__x.__l[1]):
      "0"(bswap_32((unsigned long)x)),"1"(bswap_32((unsigned long)(x>>32))));
  return __x.__ll;
}
#define bswap_64(x) ByteSwap64(x)

#else

#define bswap_16(x) (((x) & 0x00ff) << 8 | ((x) & 0xff00) >> 8)
			

// code from bits/byteswap.h (C) 1997, 1998 Free Software Foundation, Inc.
#define bswap_32(x) \
     ((((x) & 0xff000000) >> 24) | (((x) & 0x00ff0000) >>  8) | \
      (((x) & 0x0000ff00) <<  8) | (((x) & 0x000000ff) << 24))

#if __WORDSIZE >= 64
# define bswap_64(x) \
     ((((x) & 0xff00000000000000ull) >> 56)				      \
      | (((x) & 0x00ff000000000000ull) >> 40)				      \
      | (((x) & 0x0000ff0000000000ull) >> 24)				      \
      | (((x) & 0x000000ff00000000ull) >> 8)				      \
      | (((x) & 0x00000000ff000000ull) << 8)				      \
      | (((x) & 0x0000000000ff0000ull) << 24)				      \
      | (((x) & 0x000000000000ff00ull) << 40)				      \
      | (((x) & 0x00000000000000ffull) << 56))
#else
#define bswap_64(x) \
     (__extension__						\
      ({ union { __extension__ unsigned long long int __ll;	\
                 unsigned long int __l[2]; } __w, __r;		\
         __w.__ll = (x);					\
         __r.__l[0] = bswap_32 (__w.__l[1]);			\
         __r.__l[1] = bswap_32 (__w.__l[0]);			\
         __r.__ll; }))
#endif
#endif	/* !ARCH_X86 */

#endif	/* !HAVE_BYTESWAP_H */

// be2me ... BigEndian to MachineEndian
// le2me ... LittleEndian to MachineEndian

#ifdef WORDS_BIGENDIAN
#define be2me_16(x) (x)
#define be2me_32(x) (x)
#define be2me_64(x) (x)
#define le2me_16(x) bswap_16(x)
#define le2me_32(x) bswap_32(x)
#define le2me_64(x) bswap_64(x)
#else
#define be2me_16(x) bswap_16(x)
#define be2me_32(x) bswap_32(x)
#define be2me_64(x) bswap_64(x)
#define le2me_16(x) (x)
#define le2me_32(x) (x)
#define le2me_64(x) (x)
#endif

#endif /* __BSWAP_H__ */