#include <stdio.h>

#define IPSTRLEN 20


int
ip_str_to_ip_tuple(char ip_str[], int ip_tuple[])
{
	int retval;
	
	if (4!=(retval=sscanf(ip_str, "%d.%d.%d.%d", 
			&ip_tuple[0], &ip_tuple[1], &ip_tuple[2], &ip_tuple[3]))) {
		fprintf(stderr, "Error: sscanf failed, retval was: %d\n", retval);
		return retval;
	}
	
	return 0;
}

int
ip_tuple_to_ip_str(int ip_tuple[], char ip_str[], int ip_str_size)
{	
	int retval;
	
	if (IPSTRLEN<(retval=snprintf(ip_str, ip_str_size, "%d.%d.%d.%d", 
			ip_tuple[3], ip_tuple[2], ip_tuple[1], ip_tuple[0]))) {
		return retval;
	}
	
	return 0;
}

unsigned long
ip_tuple_to_addr(int ip_tuple[])
{
	unsigned long result=0;
	
	for (int i = 0; i < 4; i += 1) {
		result = result<<8;
		result = ip_tuple[i]|result;
	}
	
	return result;
}

int
addr_to_ip_tuple(unsigned long addr, int ip_tuple[])
{
	for (int i = 0; i < 4; i += 1) {
		ip_tuple[i] = (addr>>i*8)&255;
	}
	
	return 0;
}

unsigned long
compute_netmask_for_size(int net_size)
{
	unsigned long netmask = 0xffffffff;
	
	netmask = netmask<<net_size;
	
	return netmask;
}

unsigned long
compute_network_address(unsigned long host_addr, unsigned long netmask)
{
	unsigned long net_addr;
	
	net_addr = host_addr&netmask;
	
	return net_addr;
}

unsigned long
computer_router_address(unsigned long host_addr, unsigned long netmask)
{
	unsigned long router_addr;
	
	router_addr = compute_network_address(host_addr, netmask)+1;
	
	return router_addr;
}

int
addr_to_ip_str(unsigned long addr, char ip_str[], int ip_str_size)
{
	int ip_tuple[4];
	
	addr_to_ip_tuple(addr, ip_tuple);
	
	if (ip_tuple_to_ip_str(ip_tuple, ip_str, ip_str_size)) {
		fprintf(stderr, "Error: IP Address malformed.\n");
	}
	
	return 0;
}


int
main(void)
{
	char the_ip[]="147.142.207.19", new_ip[IPSTRLEN];
	int net_size=8;
	int ip_tuple[4];
	unsigned long ip_addr;
	
	if (ip_str_to_ip_tuple(the_ip, ip_tuple)) {
		fprintf(stderr, "Invalid IP address: %s\n", the_ip);
		return 1;
	}
	ip_addr = ip_tuple_to_addr(ip_tuple);
	printf("IP Address: %lx\n", ip_addr);
	if (addr_to_ip_str(compute_network_address(ip_addr,
			compute_netmask_for_size(net_size)), new_ip, IPSTRLEN)) {
		fprintf(stderr, "Couldn't format network address.\n");
		return 1;
	}
	printf("Network for this host (netmask %lx): %s\n",
		compute_netmask_for_size(net_size), new_ip);
	if (addr_to_ip_str(computer_router_address(ip_addr,
			compute_netmask_for_size(net_size)), new_ip, IPSTRLEN)) {
		fprintf(stderr, "Couldn't format router address.\n");
		return 1;
	}
	printf("Probable router for this host (netmask %lx): %s\n",
		compute_netmask_for_size(net_size), new_ip);

	return 0;
}