3 files changed, 107 insertions, 0 deletions
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..b3d3d4e
--- /dev/null
+++ b/main.c
@@ -0,0 +1,94 @@
+#include <u.h>
+#include <libc.h>
+
+typedef struct IPNet IPNet;
+
+struct IPNet
+{
+	u32int addr;
+	u32int mask;
+	u32int minaddr;
+	u32int maxaddr;
+	u32int bcast;
+	uint nhosts;
+	int cidr;
+};
+
+void
+printip(uint addr)
+{
+	uchar ip4[4];
+
+	ip4[0] = (addr>>24)&0xff;
+	ip4[1] = (addr>>16)&0xff;
+	ip4[2] = (addr>>8)&0xff;
+	ip4[3] = addr&0xff;
+
+	print("%d.%d.%d.%d\n", ip4[0], ip4[1], ip4[2], ip4[3]);
+}
+
+void
+printipnet(IPNet net)
+{
+	print("network "); printip(net.addr);
+	print("netmask "); printip(net.mask);
+	print("minaddr "); printip(net.minaddr);
+	print("maxaddr "); printip(net.maxaddr);
+	print("bcast "); printip(net.bcast);
+	print("hosts %d\n", net.nhosts);
+	print("cidr %d\n", net.cidr);
+}
+
+int
+countones(u32int addr)
+{
+	int cnt, shift;
+
+	for(cnt = 0, shift = 31; cnt < 32 && (addr&(1<<shift)) != 0; cnt++, shift--)
+		;
+	return cnt;
+}
+
+void
+usage(void)
+{
+	fprint(2, "usage: %s addr mask\n", argv0);
+	exits("usage");
+}
+
+void
+main(int argc, char *argv[])
+{
+	IPNet net;
+	uint addr, mask;
+	char *a, *m;
+
+	ARGBEGIN{
+	default: usage();
+	}ARGEND;
+	if(argc != 2)
+		usage();
+
+	a = argv[0];
+	addr = strtoul(a, &a, 10) << 24; a++;
+	addr |= strtoul(a, &a, 10) << 16; a++;
+	addr |= strtoul(a, &a, 10) << 8; a++;
+	addr |= strtoul(a, &a, 10);
+	m = argv[1];
+	mask = strtoul(m, &m, 10) << 24; m++;
+	mask |= strtoul(m, &m, 10) << 16; m++;
+	mask |= strtoul(m, &m, 10) << 8; m++;
+	mask |= strtoul(m, &m, 10);
+
+	net.addr = addr&mask;
+	net.mask = mask;
+	net.bcast = addr|~mask;
+	net.minaddr = net.addr+1;
+	net.maxaddr = net.bcast-1;
+	net.nhosts = net.maxaddr-net.minaddr;
+	net.cidr = countones(net.mask);
+	printipnet(net);
+
+	exits(nil);
+}
+
diff --git a/mkfile b/mkfile
new file mode 100644
index 0000000..97d7a35
--- /dev/null
+++ b/mkfile
@@ -0,0 +1,8 @@
+</$objtype/mkfile
+
+BIN=/$objtype/bin
+TARG=ipcalc
+OFILES=\
+	main.$O
+
+</sys/src/cmd/mkone
diff --git a/readme b/readme
new file mode 100644
index 0000000..9236d2f
--- /dev/null
+++ b/readme
@@ -0,0 +1,5 @@
+# ipcalc(8) for plan 9
+
+What the title says.
+
+It only works with IPv4 networks. Patches to accept IPv6 are welcome.