wctomb.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.
//
//  wctomb.c
//

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

#include <stdlib.h>


int wctomb(char *string, wchar_t wc)
{
  // Here's how the Linux man page describes this function:
  //
  // If s is not NULL, the wctomb function converts the wide character wc to
  // its multibyte representation and stores it at the beginning of the
  // character array pointed to by string.  It updates the shift state, which
  // is stored in a static anonymous variable only known to the wctomb func-
  // tion, and returns the length of said multibyte representation, i.e. the
  // number of bytes written at string. The programmer must ensure that there
  // is room for at least MB_CUR_MAX bytes at string.  If string is NULL,
  // the wctomb function resets the shift state, only known to this function,
  // to the initial state, and returns non-zero if the encoding has non-
  // trivial shift state, or zero if the encoding is stateless.
  //
  // We're going to attempt to support UTF-8 as our multibyte standard.

  int numBytes = 1;

  if (string == NULL)
    // Stateless.
    return (0);

  if (wc > 0x0010FFFF)
    // Too large
    return (-1);

  if (wc > 0x7F)
    numBytes += 1;
  if (wc > 0x7FF)
    numBytes += 1;
  if (wc > 0xFFFF)
    numBytes += 1;

  if (numBytes == 1)
    string[0] = (wc & 0x7F);
  else if (numBytes == 2)
    {
      string[0] = (0xC0 | ((wc & 0x07D0) >> 6));
      string[1] = (0x80 | (wc & 0x003F));
    }
  else if (numBytes == 3)
    {
      string[0] = (0xE0 | ((wc & 0xF000) >> 12));
      string[1] = (0x80 | ((wc & 0x0FD0) >> 6));
      string[2] = (0x80 | (wc & 0x003F));
    }
  else if (numBytes == 4)
    {
      string[0] = (0xF0 | ((wc & 0x001D0000) >> 18));
      string[1] = (0x80 | ((wc & 0x0003F000) >> 12));
      string[2] = (0x80 | ((wc & 0x00000FD0) >> 6));
      string[3] = (0x80 | (wc & 0x0000003F));
    }

  return (numBytes);
}