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// SPDX-License-Identifier: GPL-2.0
/*
* iptool.c - Simple IP subnet calculator
*
* Takes an IPv4 address and a prefix length, then calculates:
* - IP class
* - Network address
* - Broadcast address
* - Total hosts
* - Usable hosts
* - Usable IP range
*/
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#define PROGRAM_NAME "iptool"
static uint32_t ip_to_u32(const char *ip_str)
{
int o1, o2, o3, o4;
if (sscanf(ip_str, "%d.%d.%d.%d", &o1, &o2, &o3, &o4) != 4) {
fprintf(stderr, "Invalid IP format: %s\n", ip_str);
exit(1);
}
if (o1 < 0 || o1 > 255 || o2 < 0 || o2 > 255 ||
o3 < 0 || o3 > 255 || o4 < 0 || o4 > 255) {
fprintf(stderr, "IP octet out of range: %s\n", ip_str);
exit(1);
}
return (o1 << 24) | (o2 << 16) | (o3 << 8) | o4;
}
static uint32_t netmask_from_prefix(int prefix)
{
return prefix ? 0xFFFFFFFFU << (32 - prefix) : 0;
}
static uint32_t network_addr(uint32_t ip, uint32_t netmask)
{
return ip & netmask;
}
static uint32_t broadcast_addr(uint32_t ip, uint32_t netmask)
{
return (ip & netmask) | ~netmask;
}
static uint32_t total_hosts(int prefix)
{
return 1U << (32 - prefix);
}
static uint32_t usable_hosts(int prefix)
{
uint32_t th = total_hosts(prefix);
return (th <= 2) ? 0 : th - 2;
}
static char ip_class(uint32_t ip)
{
uint8_t first_octet = ip >> 24;
if (first_octet <= 127)
return 'A';
if (first_octet <= 191)
return 'B';
if (first_octet <= 223)
return 'C';
if (first_octet <= 239)
return 'D';
return 'E';
}
static void print_ip(uint32_t ip)
{
printf("%u.%u.%u.%u",
(ip >> 24) & 0xFF,
(ip >> 16) & 0xFF,
(ip >> 8) & 0xFF,
ip & 0xFF);
}
int main(int argc, char *argv[])
{
uint32_t ip, netmask, network, broadcast;
int prefix;
uint32_t total, usable;
if (argc < 3) {
fprintf(stderr, "Usage: %s <ip> <prefix>\n", PROGRAM_NAME);
return 1;
}
ip = ip_to_u32(argv[1]);
prefix = atoi(argv[2]);
if (prefix < 0 || prefix > 32) {
fprintf(stderr, "Prefix must be 0-32\n");
return 1;
}
netmask = netmask_from_prefix(prefix);
network = network_addr(ip, netmask);
broadcast = broadcast_addr(ip, netmask);
total = total_hosts(prefix);
usable = usable_hosts(prefix);
printf("IP Class: %c\n", ip_class(ip));
printf("Network: "); print_ip(network); printf("\n");
printf("Broadcast: "); print_ip(broadcast); printf("\n");
printf("Total hosts: %u\n", total);
printf("Usable hosts: %u\n", usable);
if (usable > 0) {
printf("Usable IP range: ");
print_ip(network + 1);
printf(" - ");
print_ip(broadcast - 1);
printf("\n");
} else {
printf("No usable IPs in this subnet\n");
}
return 0;
}
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