swab.c

上一个上传的有问题,这个是好的。visopsys包括系统内核和GUI的全部SOURCE code ,还包括一些基本的docs文档。里面src子目录对应所有SOURCE code.对于想研究操作系统的朋

// 
//  Visopsys
//  Copyright (C) 1998-2007 J. Andrew McLaughlin
//  
//  This library is free software; you can redistribute it and/or modify it
//  under the terms of the GNU Lesser General Public License as published by
//  the Free Software Foundation; either version 2.1 of the License, or (at
//  your option) any later version.
//
//  This library is distributed in the hope that it will be useful, but
//  WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
//  General Public License for more details.
//
//  You should have received a copy of the GNU Lesser General Public License
//  along with this library; if not, write to the Free Software Foundation,
//  Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
//
//  swab.c
//

// This is the standard "swab" function, as found in standard C libraries

#include <unistd.h>


void swab(const void *from, void *to, ssize_t num)
{
  // From the GNU man page:
  // The swab() function copies n bytes from the array pointed to by from to
  // the array pointed to by to, exchanging adjacent even and odd bytes.
  // This function is used to exchange data between machines that have
  // different low/high byte ordering.
  //
  // This function does nothing when n is negative.  When n is positive and
  // odd, it handles n-1 bytes as above, and does something unspecified with
  // the last byte.  (In other words, n should be even.)

  int count;

  if (num < 0)
    return;

  // Make the number even
  num &= ~1;

  if (to != from)
    // Copy data
    for (count = 0; count < num; count ++)
      ((char *) to)[count] = ((const char *) from)[count];

  // Swappem.
  for (count = 0; count < (num - 1); count ++)
    {
      unsigned char tmp = ((char *) to)[count];
      ((char *) to)[count] = ((char *) to)[count + 1];
      ((char *) to)[count + 1] = tmp;
    }

  return;
}