_str2num.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.
//
//  _str2num.c
//

// This is a generic function to interpret a string as a number and return
// the value.

#include <ctype.h>
#include <errno.h>
#include <string.h>
#include <sys/cdefs.h>


unsigned long long _str2num(const char *string, unsigned base, int sign)
{
  unsigned long long result = 0;
  int length = 0;
  int negative = 0;
  int count = 0;

  if (string == NULL)
    {
      errno = ERR_NULLPARAMETER;
      return (0);
    }

  // Get the length of the string
  length = strlen(string);

  if (sign && (string[0] == '-'))
    {
      negative = 1;
      count += 1;
    }

  // Do a loop to iteratively add to the value of 'result'.
  for ( ; count < length; count ++)
    {
      switch (base)
	{
	case 10:
	  if (!isdigit(string[count]))
	    {
	      errno = ERR_INVALID;
	      goto out;
	    }
	  result *= base;
	  result += (string[count] - '0');
	  break;

	case 16:
	  if (!isxdigit(string[count]))
	    {
	      errno = ERR_INVALID;
	      goto out;
	    }
	  result *= base;
	  if ((string[count] >= '0') && (string[count] <= '9'))
	    result += (string[count] - '0');
	  else if ((string[count] >= 'a') && (string[count] <= 'f'))
	    result += ((string[count] - 'a') + 10);
	  else
	    result += ((string[count] - 'A') + 10);
	  break;

	default:
	  errno = ERR_NOTIMPLEMENTED;
	  goto out;
	}
    }

 out:
  
  if (negative)
    result = ((long long) result * -1);
  
  return (result);
}