byteorder.h

cygwin, 著名的在win32下模拟unix操作系统的东东

/* asm/byteorder.h

   Copyright 1996, 1998, 2001 Red Hat, Inc.

This file is part of Cygwin.

This software is a copyrighted work licensed under the terms of the
Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
details. */

#ifndef _I386_BYTEORDER_H
#define _I386_BYTEORDER_H

#ifdef __cplusplus
extern "C" {
#endif

#if 0
#undef ntohl
#undef ntohs
#undef htonl
#undef htons
#endif

#ifndef __LITTLE_ENDIAN
#define __LITTLE_ENDIAN 1234
#endif

#ifndef __LITTLE_ENDIAN_BITFIELD
#define __LITTLE_ENDIAN_BITFIELD
#endif

#if 1
extern unsigned long int	ntohl(unsigned long int);
extern unsigned short int	ntohs(unsigned short int);
extern unsigned long int	htonl(unsigned long int);
extern unsigned short int	htons(unsigned short int);

extern __inline__ unsigned long int	__ntohl(unsigned long int);
extern __inline__ unsigned short int	__ntohs(unsigned short int);
extern __inline__ unsigned long int	__constant_ntohl(unsigned long int);
extern __inline__ unsigned short int	__constant_ntohs(unsigned short int);

extern __inline__ unsigned long int
__ntohl(unsigned long int x)
{
	__asm__("xchgb %b0,%h0\n\t"	/* swap lower bytes	*/
		"rorl $16,%0\n\t"	/* swap words		*/
		"xchgb %b0,%h0"		/* swap higher bytes	*/
		:"=q" (x)
		: "0" (x));
	return x;
}

#define __constant_ntohl(x) \
	((unsigned long int)((((unsigned long int)(x) & 0x000000ffU) << 24) | \
			     (((unsigned long int)(x) & 0x0000ff00U) <<  8) | \
			     (((unsigned long int)(x) & 0x00ff0000U) >>  8) | \
			     (((unsigned long int)(x) & 0xff000000U) >> 24)))

extern __inline__ unsigned short int
__ntohs(unsigned short int x)
{
	__asm__("xchgb %b0,%h0"		/* swap bytes		*/
		: "=q" (x)
		:  "0" (x));
	return x;
}

#define __constant_ntohs(x) \
	((unsigned short int)((((unsigned short int)(x) & 0x00ff) << 8) | \
			      (((unsigned short int)(x) & 0xff00) >> 8))) \

#define __htonl(x) __ntohl(x)
#define __htons(x) __ntohs(x)
#define __constant_htonl(x) __constant_ntohl(x)
#define __constant_htons(x) __constant_ntohs(x)

#ifdef  __OPTIMIZE__
#  define ntohl(x) \
(__builtin_constant_p((long)(x)) ? \
 __constant_ntohl((x)) : \
 __ntohl((x)))
#  define ntohs(x) \
(__builtin_constant_p((short)(x)) ? \
 __constant_ntohs((x)) : \
 __ntohs((x)))
#  define htonl(x) \
(__builtin_constant_p((long)(x)) ? \
 __constant_htonl((x)) : \
 __htonl((x)))
#  define htons(x) \
(__builtin_constant_p((short)(x)) ? \
 __constant_htons((x)) : \
 __htons((x)))
#endif
#endif

#ifdef __cplusplus
}
#endif

#endif