Initial commit

1 files changed, 130 insertions, 0 deletions

diff --git a/src/iptool.c b/src/iptool.c
new file mode 100644
index 0000000..e940c52
--- /dev/null
+++ b/src/iptool.c
@@ -0,0 +1,130 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * subnet_calc.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>
+
+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", argv[0]);
+		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;
+}
+