byteswap.h

它通过提供glibc兼容使得应用程序移植到较小的c 库时相当得容易. 它能够应用到带虚拟存储的Linux和uClinux上.在大多数带MMU部件的平台上为使它更加紧凑,它也能够编译成共享库.uClib

/*
 * libc/sysdeps/linux/v850/bits/byteswap.h -- Macros to swap the order
 * 	of bytes in integer values
 *
 *  Copyright (C) 2001  NEC Corporation
 *  Copyright (C) 2001  Miles Bader <[e-mail]>
 *  Copyright (C) 1997,1998,2001  Free Software Foundation, Inc.
 *
 * This file is subject to the terms and conditions of the GNU Lesser
 * General Public License.  See the file COPYING.LIB in the main
 * directory of this archive for more details.
 */

#if !defined _BYTESWAP_H && !defined _NETINET_IN_H
# error "Never use <bits/byteswap.h> directly; include <byteswap.h> instead."
#endif

/* Swap bytes in 16 bit value.  */
#define __bswap_constant_16(x) \
  ((((x) >> 8) & 0xff) | (((x) & 0xff) << 8))

#ifdef __GNUC__
# define __bswap_16(x)							      \
    (__extension__							      \
     ({ unsigned long int __bswap_16_v;					      \
        if (__builtin_constant_p (x))					      \
          __bswap_16_v = __bswap_constant_16 (x);			      \
        else								      \
	  __asm__ ("bsh %1, %0" : "=r" (__bswap_16_v) : "r" (x));	      \
	__bswap_16_v; }))
#else
# define __bswap_16(x) __bswap_constant_16 (x)
#endif

/* Swap bytes in 32 bit value.  */
#define __bswap_constant_32(x) \
  ((((x) & 0xff000000) >> 24) | (((x) & 0x00ff0000) >>  8) | \
   (((x) & 0x0000ff00) <<  8) | (((x) & 0x000000ff) << 24))

#ifdef __GNUC__
# define __bswap_32(x)							      \
    (__extension__							      \
     ({ unsigned long int __bswap_32_v;					      \
        if (__builtin_constant_p (x))					      \
          __bswap_32_v = __bswap_constant_32 (x);			      \
        else								      \
	  __asm__ ("bsw %1, %0" : "=r" (__bswap_32_v) : "r" (x));	      \
	__bswap_32_v; }))
#else
# define __bswap_32(x) __bswap_constant_32 (x)
#endif

#if defined __GNUC__ && __GNUC__ >= 2
/* Swap bytes in 64 bit value.  */
# define __bswap_64(x)							      \
     (__extension__							      \
      ({ union { unsigned long long int __ll;				      \
		 unsigned long int __l[2]; } __bswap_64_v, __bswap_64_r;      \
	 __bswap_64_v.__ll = (x);					      \
	 __bswap_64_r.__l[0] = __bswap_32 (__bswap_64_v.__l[1]);	      \
	 __bswap_64_r.__l[1] = __bswap_32 (__bswap_64_v.__l[0]);	      \
	 __bswap_64_r.__ll; }))
#endif