Netmask Calculator

/* (c) Steve Parker 22 July 2004 
 * Written for NetOps staff to help with cluster planning, networking, etc
 */

#include 
#include 
#include 

char vversion[] = __DATE__ " " __TIME__;


struct ip4_addr
{
  unsigned char a, b, c, d;
};

struct ip4_addr IP;
struct ip4_addr MASK;
unsigned char NETMASK;

struct ip4_addr
dotted_quad_to_ip (char *dottedquad)
{
  struct ip4_addr ip;
  int a, b, c, d;

  sscanf (dottedquad, "%d.%d.%d.%d", &a, &b, &c, &d);
  ip.a = a;
  ip.b = b;
  ip.c = c;
  ip.d = d;

  return ip;
}

struct ip4_addr
hex_to_ip (char *hex)
{
  struct ip4_addr ip;
  int a, b, c, d;

  sscanf (hex, "%02x%02x%02x%02x", &a, &b, &c, &d);
  ip.a = a;
  ip.b = b;
  ip.c = c;
  ip.d = d;

  return ip;
}

void
usage ()
{
  printf ("Steve's Netmask Calculator (Build : %s)
", vversion);
  printf ("Usage: netmask [ ip_address ] netmask
");
  printf ("  IP and Netmask can be seperated by space, '/', or both.
");
  printf ("  If only a netmask is provided, the leading '/' is required.
");
  printf ("  Netmask can be provided in any of three formats:
");
  printf ("    /24  or  /255.255.255.0  or  /ffffff00

");
  printf ("e.g.: netmask 192.168.1.1/24
");
  printf ("      netmask 192.168.1.1 255.255.255.0
");
  printf ("      netmask 192.168.1.1 ffffff00
");
  printf ("      netmask /24
");
  printf ("      netmask /255.255.255.0
");
  printf ("      netmask /ffffff00
");
  printf ("
");
  exit (1);
}

int
ip_to_netmask (struct ip4_addr n)
{
  unsigned char i, m = 0;

  for (i = 8; i <= 8; i--)
    {
      if ((n.a & (1 << i)) != 0)
	m++;
      if ((n.b & (1 << i)) != 0)
	m++;
      if ((n.c & (1 << i)) != 0)
	m++;
      if ((n.d & (1 << i)) != 0)
	m++;
    }
  return m;
}

struct ip4_addr
parse_mask (char *mask)
{
  struct ip4_addr netmask;
  unsigned char m, n;
  unsigned char *p;

  if (strchr (mask, '.') != NULL)
    {
      netmask = dotted_quad_to_ip (mask);
      NETMASK = ip_to_netmask (netmask);
    }
  else
    {
      NETMASK = atoi (mask);
      if (NETMASK == 0)
	{
	  // hex format
	  netmask = hex_to_ip (mask);
	  NETMASK = ip_to_netmask (netmask);
	}
      else
	{
	  //    /nn format
	  if (NETMASK > 32)
	    {
	      printf ("ERROR: /nn format must be 1-32
");
	      exit (1);
	    }
	  n = NETMASK;
	  netmask.a = netmask.b = netmask.c = netmask.d = 0;
	  p = &netmask.a;

	  if (n > 23)
	    {
	      netmask.a = netmask.b = netmask.c = 255;
	      n -= 24;
	      p = &netmask.d;
	    }
	  if (n > 15)
	    {
	      netmask.a = netmask.b = 255;
	      n -= 16;
	      p = &netmask.c;
	    }
	  if (n > 7)
	    {
	      netmask.a = 255;
	      n -= 8;
	      p = &netmask.b;
	    }

	  for (m = 7; m <= 8; m--)
	    {
	      if (n > 0)
		{
		  *p += (1 << m);
		  n--;
		}
	    }
	}
    }
  return netmask;
}

void
get_network ()
{
  unsigned char a, b, c, d;

  a = IP.a & MASK.a;
  b = IP.b & MASK.b;
  c = IP.c & MASK.c;
  d = IP.d & MASK.d;
  printf ("Network   = %03d.%03d.%03d.%03d
", a, b, c, d);
}

void
get_broadcast ()
{
  unsigned char a, b, c, d;

  a = IP.a | ~MASK.a;
  b = IP.b | ~MASK.b;
  c = IP.c | ~MASK.c;
  d = IP.d | ~MASK.d;
  printf ("Broadcast = %03d.%03d.%03d.%03d
", a, b, c, d);
}


int
main (int argc, char *argv[])
{
  char *slash;
  char *dot;
  char *mask;

  if ((argc != 2) && (argc != 3))
    usage ();

  slash = strchr (argv[1], '/');
  dot = strchr (argv[1], '.');
  if ((slash == NULL) && (argc == 3))
    {
      slash = argv[2] - sizeof (char);
      if (strchr (argv[2], '/') != NULL)
	slash = strchr (argv[2], '/');
    }
  if (dot > slash)
    dot = NULL;			// "dot" implies an IP address, not an x.x.x.x netmask

  if (slash != NULL)
    {
      mask = (char *) slash + sizeof (char);
      MASK = parse_mask (mask);
      *slash = '';
    }
  if (dot != NULL)
    {
      IP = dotted_quad_to_ip (argv[1]);
    }

  IP = dotted_quad_to_ip (argv[1]);
  if (dot != NULL)
    printf ("IP        = %03d.%03d.%03d.%03d
", IP.a, IP.b, IP.c, IP.d);
  if (slash != NULL)
    printf ("Mask      = %03d.%03d.%03d.%03d (%02x%02x%02x%02x) - aka /%d
",
	    MASK.a, MASK.b, MASK.c, MASK.d, MASK.a, MASK.b, MASK.c, MASK.d,
	    NETMASK);

  if (dot != NULL)
    {
      get_network ();
      get_broadcast ();
    }

  return 0;
}