/*
      NetID 0.2,  Calculates NetID and the number of hosts && nets
                  for a given IP-number and Subnet-mask.
      Copyright © 2002 Kalle Räisänen.

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program 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 General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

      Syntax: NetID ip-number subnet-mask
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int netid[4], ip[4], sub[4];

int countbits(int num)
{
   int ret = 0, i;

   for(i = 0; i < 8; i++)
      if(num & (1<<i))
         ret++;

   return ret;
}

int toip(char *s, int *ip)
{
   int i = 0, j = 0;

   while(s[j])
      {
      if(s[j] == '.')
         {   
         if(ip[i] > 255) return 0;
         i++;
         }
      else if((s[j] >= '0') && (s[j] <= '9'))
         {
         ip[i] *= 10;
         ip[i] += s[j] - '0';
         }
      else
         return 0;
      j++;
      }
   if(ip[i] > 255) return 0;
   return 1;
}

void getnetid(int *netid, int *ip, int *sub)
{
   int i = 0;

   for(; i < 4; i++)
      netid[i] = sub[i] & ip[i];
}

unsigned int nets = 0, hosts = 0;

void getnets(int *subm, int ipcl)
{
   int i = 1, nbit = 0, hbit = 0;

   if(ipcl >= 192)
      i = 3;
   else if(ipcl >= 128)
      i = 2;

   for(;i < 4; i++)
      {
      nbit += countbits(subm[i]);
      hbit += countbits(~subm[i]);
      }
   nets = abs(pow(2, nbit)-2);
   hosts = abs(pow(2, hbit)-2);
}

int main(int argc, char *argv[])
{      
   printf("\nNetID 0.2, Copyright (c) 2002 Kalle Raisanen.\n\n");

   if(argc != 3)
      {
      fprintf(stderr, "\tUsage: %s ip sub\n\n", argv[0]);
      fprintf(stderr, "\tWhere ip is the IP-adress and sub the Subnet-mask.\n");
      return 0;
      }

   if(!toip(argv[1], ip))
      {
      fprintf(stderr, "%s isn't a valid IP-adress!\n", argv[1]);
      return 0;
      }

   if(!toip(argv[2], sub))
      {
      fprintf(stderr, "%s isn't a valid IP-adress!\n", argv[2]);
      return 0;
      }

   getnetid(netid, ip, sub);
   getnets(sub, ip[0]);
   printf("    %d.%d.%d.%d/%d:\n", ip[0], ip[1], ip[2], ip[3],
                               countbits(sub[0]) + countbits(sub[1]) + countbits(sub[2]) + countbits(sub[3]));
   printf("\tNet ID: %d.%d.%d.%d\n", netid[0], netid[1], netid[2], netid[3]);
   printf("\t%d nets, %d hosts.\n\n", nets, hosts);

   return 0;
}