subnetting/subnetting.c

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <stdbool.h>
#include "subnetting.h"

enum NetworkClass {CLASS_A, CLASS_B, CLASS_C};

// This section of code consitutes a more Java-like version of finding a preix
// A C programmer is more likely to simply do the binary math.
const unsigned int prefix_map[9] = {0, 128, 192, 224, 240, 248, 252, 254, 255};
const int usable_hosts_map[9] = {254, 126, 62, 30, 14, 6, 2, 0, 0};
const int subnet_multiplyer[4] = {0, 8, 16, 24};

unsigned int* subnet_to_octet_array(unsigned int octets[4], char subnet_mask[16]){
	sscanf(subnet_mask, "%u.%u.%u.%u", &octets[0], &octets[1], &octets[2], &octets[3]);
	return octets;
}

int mask_to_prefix(char mask[16]){
	unsigned int octet[4];
	int pref = 0;
	subnet_to_octet_array(octet, mask);
	for (int i = 0; i < 4; ++i){
		for (int j = 0; j < 9; ++j){
			if (octet[i] == prefix_map[j]){
				pref += j;
				break;
			}
		}
	}
	return pref;
}

char* prefix_to_mask(char subnet_mask[16], unsigned int prefix){
	unsigned int octets[5];
	for (int i = 0; i < 5; ++i){
		for (int j = 8; j >= 0; --j){
			if (prefix >= j){
				prefix -= j;
				octets[i] = prefix_map[j];
				break;
			}
		}
	}
	sprintf(subnet_mask, "%u.%u.%u.%u", octets[0], octets[1], octets[2], octets[3]);
	return subnet_mask;
}

int hosts_for_prefix(int prefix){
	return (int)pow(2.0, (double)(32-prefix));
}

int subnets_for_prefix(int prefix){
	return (int)pow(2.0, (double)(prefix%8));
}

void ui_to_octets(char addr[16], unsigned int subnet_mask){
	int octets[4];
	octets[0] = (subnet_mask >> 24) & 0xFF;
	octets[1] = (subnet_mask >> 16) & 0xFF;
	octets[2] = (subnet_mask >> 8) & 0xFF;
	octets[3] = subnet_mask & 0xFF;
	sprintf(addr, "%d.%d.%d.%d", octets[0], octets[1], octets[2], octets[3]);
}	

int prefix_for_hosts(int hosts_required){
	for (int i = 32; i >= 0; --i){
		if (hosts_for_prefix(i)-2 >= hosts_required){
			return i;
		}
	}
	return -1;
}

char* octet_array_to_string(char subnet_mask[16], char octets[4]){
	sprintf(subnet_mask, "%d.%d.%d.%d", octets[0], octets[1], octets[2], octets[3]);
	return subnet_mask;
}

int network_type_based_on_subnet(int subnet_arr[4]){
	if (subnet_arr[0] != 255){
		return -1;
	} else if (subnet_arr[1] != 255){
		return CLASS_A;
	} else if (subnet_arr[2] != 255){
		return CLASS_B;
	} else if (subnet_arr[3] != 255){
		return CLASS_C;
	} else {
		return -1;
	}
}

char network_class(int subnet_arr[4]){
	if (subnet_arr[0] != 255){
		return '?';
	} else if (subnet_arr[1] != 255){
		return 'A';
	} else if (subnet_arr[2] != 255){
		return 'B';
	} else if (subnet_arr[3] != 255){
		return 'C';
	} else {
		return '?';
	}
}

unsigned int octets_to_ui(char octets[16]){
	int so_s[4];
	unsigned int rv;
	sscanf(octets, "%d.%d.%d.%d", &so_s[0], &so_s[1], &so_s[2], &so_s[3]);
	rv = (so_s[0] << 24) | (so_s[1] << 16) | (so_s[2] << 8) | (so_s[3]);
	return rv;
}

unsigned int bdr_addr(unsigned int ip, unsigned int subnet){
	return ip | ~subnet;
}
unsigned int net_addr(unsigned int ip, unsigned int subnet){
	return ip & subnet;
}

char* network_address(char result[16], char ip[16], char subnet[16]){
	unsigned int num = octets_to_ui(ip) & octets_to_ui(subnet);
	ui_to_octets(result, num);
	return result;
}
char* broadcast_address(char result[16], char ip[16], char subnet[16]){
	unsigned int bdr_add = octets_to_ui(ip) | ~octets_to_ui(subnet);
	ui_to_octets(result, bdr_add);
	return result;
}


char* usable_host_addresses(char result[33], char ip[16], char subnet[16]){
	char slow_addrs[16];
	char shigh_addrs[16];
	unsigned int low_addr = net_addr(octets_to_ui(ip), octets_to_ui(subnet));
	unsigned int high_addr = bdr_addr(octets_to_ui(ip), octets_to_ui(subnet));

	++low_addr;
	--high_addr;

	ui_to_octets(slow_addrs, low_addr);
	ui_to_octets(shigh_addrs, high_addr);
	sprintf(result, "%s-%s", slow_addrs, shigh_addrs);
	return result;
}

int get_ui_class(unsigned int ip){
	unsigned int fo = ip >> 24;
	if (fo >= 1 && fo <= 126){
		return CLASS_A;
	} else if (fo >= 128 && fo <= 191){
		return CLASS_B;
	} else if (fo >= 192 && fo <= 223){
		return CLASS_C;
	}
	return -1;
}