diff --git a/.gitignore b/.gitignore
index d73bffe..be94685 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 /plag
+/*.o
diff --git a/Makefile b/Makefile
index ac28fb9..7a26ded 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,13 @@
-plag: plag.c config.h
-	cc -O3 -o plag plag.c
+CC=gcc
+CFLAGS= -O3
+
+all: plag
+
+plag: plag.c lib.o lib.h config.h
+	$(CC) $(CFLAGS) -o $@ plag.c lib.o
+
+lib.o: lib.c lib.h
+	$(CC) $(CFLAGS) -o $@ -c lib.c
 
 clean:
-	rm plag
+	rm plag lib.o
diff --git a/config.h b/config.h
index 2751e73..43ab6e8 100644
--- a/config.h
+++ b/config.h
@@ -1,6 +1,11 @@
+#ifndef CONFIG_H
+#define CONFIG_H
+
 #include <stdint.h>
 
 #define SIZE (10 * 1<<20)
 #define BUFLEN 1024
 typedef uint32_t pos_t;
 typedef int mask_t;
+
+#endif /* !CONFIG_H */
diff --git a/lib.c b/lib.c
new file mode 100644
index 0000000..fbca71d
--- /dev/null
+++ b/lib.c
@@ -0,0 +1,99 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <arpa/inet.h>
+#include <error.h>
+#include <errno.h>
+
+#include "config.h"
+#include "lib.h"
+
+void bits2ip4(bits b, mask_t m, char *s, int size) {
+	// convert bits to in4_addr
+	struct in4_addr ip;
+	for (int i = 0; i < 4; ++i) {
+		ip.s4_addr[i] = 0;
+		for (int j = 0; j < 8; ++j) {
+			ip.s4_addr[i] <<= 1;
+			int p = i*8 + j;
+			ip.s4_addr[i] |= (p >= m) ? 0 : b[p];
+		}
+	}
+	// get test representation of ip
+	char s_ip[INET_ADDRSTRLEN];
+	if (!inet_ntop(AF_INET, &ip, s_ip, INET_ADDRSTRLEN)) error(1, errno, "bits2ip4");
+	// print ip with mask to buffer
+	int res = snprintf(s, size, "%s/%d", s_ip, m);
+	// if printing to buffer has failed
+	if (res < 0 || res >= size) error(1, errno, "bits2ip4");
+}
+
+void bits2ip6(bits b, mask_t m, char *s, int size) {
+	// convert bits to in6_addr
+	struct in6_addr ip;
+	for (int i = 0; i < 16; ++i) {
+		ip.s6_addr[i] = 0;
+		for (int j = 0; j < 8; ++j) {
+			ip.s6_addr[i] <<= 1;
+			int p = i*8 + j;
+			ip.s6_addr[i] |= (p >= m) ? 0 : b[p];
+		}
+	}
+	// get test representation of ip
+	char s_ip[INET6_ADDRSTRLEN];
+	if (!inet_ntop(AF_INET6, &ip, s_ip, INET6_ADDRSTRLEN)) error(1, errno, "bits2ip6");
+	// print ip with mask to buffer
+	int res = snprintf(s, size, "%s/%d", s_ip, m);
+	// if printing to buffer has failed
+	if (res < 0 || res >= size) error(1, errno, "bits2ip6");
+}
+
+void ip42bits(char *s, bits b, mask_t *m) {
+	// split ip and mask
+	char *p = strchr(s, '/');
+	if (p) {
+		*p = 0;
+		++p;
+		unsigned long l = strtol(p, &p, 10);
+		if (*p || l > IP4LEN) error(1, errno, "ip42bits: bad mask");
+		*m = l;
+	} else {
+		*m = IP4LEN;
+	}
+	// convert ip to binary
+	struct in4_addr ip;
+	if (!inet_pton(AF_INET, s, &ip)) error(1, errno, "ip42bits");
+	// convert binary ip to bits
+	for (int i = 0; i < 4; ++i) {
+		for (int j = 0; j < 8; ++j) {
+			int p = i*8 + 8-1-j;
+			b[p] = (p > *m) ? 0 : (ip.s4_addr[i] & 1);
+			ip.s4_addr[i] >>= 1;
+		}
+	}
+}
+
+void ip62bits(char *s, bits b, mask_t *m) {
+	// split ip and mask
+	char *p = strchr(s, '/');
+	if (p) {
+		*p = 0;
+		++p;
+		unsigned long l = strtol(p, &p, 10);
+		if (*p || l > IP6LEN) error(1, errno, "ip62bits: bad mask");
+		*m = l;
+	} else {
+		*m = IP6LEN;
+	}
+	// convert ip to binary
+	struct in6_addr ip;
+	if (!inet_pton(AF_INET6, s, &ip)) error(1, errno, "ip62bits");
+	// convert binary ip to bits
+	for (int i = 0; i < 16; ++i) {
+		for (int j = 0; j < 8; ++j) {
+			int p = i*8 + 8-1-j;
+			b[p] = (p > *m) ? 0 : (ip.s6_addr[i] & 1);
+			ip.s6_addr[i] >>= 1;
+		}
+	}
+}
diff --git a/lib.h b/lib.h
new file mode 100644
index 0000000..3a38514
--- /dev/null
+++ b/lib.h
@@ -0,0 +1,23 @@
+#ifndef LIB_H
+#define LIB_H
+
+#include "config.h"
+
+#define IP4LEN 32
+#define IP6LEN 128
+#define IPMAXLEN IP6LEN
+#define IPMAXB (IPMAXLEN/8)
+
+struct in4_addr { unsigned char s4_addr[4]; };
+typedef int bit_t;
+typedef bit_t *bits;
+
+void bits2ip4(bits b, mask_t m, char *s, int size);
+void bits2ip6(bits b, mask_t m, char *s, int size);
+void ip42bits(char *s, bits b, mask_t *m);
+void ip62bits(char *s, bits b, mask_t *m);
+
+#define MIN(a,b) (((a)<(b))?(a):(b))
+#define MAX(a,b) (((a)>(b))?(a):(b))
+
+#endif /* !LIB_H */
diff --git a/plag.c b/plag.c
index fa8f820..7c17bdd 100644
--- a/plag.c
+++ b/plag.c
@@ -1,23 +1,14 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <arpa/inet.h>
 #include <error.h>
 #include <errno.h>
 
 #include "config.h"
-
-#define IP4LEN 32
-#define IP6LEN 128
-#define IPMAXLEN IP6LEN
-
-struct in4_addr {
-	unsigned char s4_addr[4];
-};
+#include "lib.h"
 
 struct node { pos_t a[2]; };
 typedef struct node *iptree;
-typedef int *bits;
 typedef void (*bitsfun)(bits, mask_t);
 
 pos_t maxpos = 0;
@@ -146,103 +137,13 @@ void iptree_traverse_rec(iptree t, bitsfun f, pos_t h, bits b, mask_t m) {
 }
 
 void iptree_traverse(iptree t, pos_t h, bitsfun f) {
-	int b[IPMAXLEN];
+	bit_t b[IPMAXLEN];
 	if (t[h].a[0]) {
 		// tree is not empty
 		iptree_traverse_rec(t, f, t[h].a[0], b, 0);
 	}
 }
 
-void bits2ip4(bits b, mask_t m, char *s, int size) {
-	// convert bits to in4_addr
-	struct in4_addr ip;
-	for (int i = 0; i < 4; ++i) {
-		ip.s4_addr[i] = 0;
-		for (int j = 0; j < 8; ++j) {
-			ip.s4_addr[i] <<= 1;
-			int p = i*8 + j;
-			ip.s4_addr[i] |= (p >= m) ? 0 : b[p];
-		}
-	}
-	// get test representation of ip
-	char s_ip[INET_ADDRSTRLEN];
-	if (!inet_ntop(AF_INET, &ip, s_ip, INET_ADDRSTRLEN)) error(1, errno, "bits2ip4");
-	// print ip with mask to buffer
-	int res = snprintf(s, size, "%s/%d", s_ip, m);
-	// if printing to buffer has failed
-	if (res < 0 || res >= size) error(1, errno, "bits2ip4");
-}
-
-void bits2ip6(bits b, mask_t m, char *s, int size) {
-	// convert bits to in6_addr
-	struct in6_addr ip;
-	for (int i = 0; i < 16; ++i) {
-		ip.s6_addr[i] = 0;
-		for (int j = 0; j < 8; ++j) {
-			ip.s6_addr[i] <<= 1;
-			int p = i*8 + j;
-			ip.s6_addr[i] |= (p >= m) ? 0 : b[p];
-		}
-	}
-	// get test representation of ip
-	char s_ip[INET6_ADDRSTRLEN];
-	if (!inet_ntop(AF_INET6, &ip, s_ip, INET6_ADDRSTRLEN)) error(1, errno, "bits2ip6");
-	// print ip with mask to buffer
-	int res = snprintf(s, size, "%s/%d", s_ip, m);
-	// if printing to buffer has failed
-	if (res < 0 || res >= size) error(1, errno, "bits2ip6");
-}
-
-void ip42bits(char *s, bits b, mask_t *m) {
-	// split ip and mask
-	char *p = strchr(s, '/');
-	if (p) {
-		*p = 0;
-		++p;
-		unsigned long l = strtol(p, &p, 10);
-		if (*p || l > IP4LEN) error(1, errno, "ip42bits: bad mask");
-		*m = l;
-	} else {
-		*m = IP4LEN;
-	}
-	// convert ip to binary
-	struct in4_addr ip;
-	if (!inet_pton(AF_INET, s, &ip)) error(1, errno, "ip42bits");
-	// convert binary ip to bits
-	for (int i = 0; i < 4; ++i) {
-		for (int j = 0; j < 8; ++j) {
-			int p = i*8 + 8-1-j;
-			b[p] = (p > *m) ? 0 : (ip.s4_addr[i] & 1);
-			ip.s4_addr[i] >>= 1;
-		}
-	}
-}
-
-void ip62bits(char *s, bits b, mask_t *m) {
-	// split ip and mask
-	char *p = strchr(s, '/');
-	if (p) {
-		*p = 0;
-		++p;
-		unsigned long l = strtol(p, &p, 10);
-		if (*p || l > IP6LEN) error(1, errno, "ip62bits: bad mask");
-		*m = l;
-	} else {
-		*m = IP6LEN;
-	}
-	// convert ip to binary
-	struct in6_addr ip;
-	if (!inet_pton(AF_INET6, s, &ip)) error(1, errno, "ip62bits");
-	// convert binary ip to bits
-	for (int i = 0; i < 16; ++i) {
-		for (int j = 0; j < 8; ++j) {
-			int p = i*8 + 8-1-j;
-			b[p] = (p > *m) ? 0 : (ip.s6_addr[i] & 1);
-			ip.s6_addr[i] >>= 1;
-		}
-	}
-}
-
 void print4(bits b, mask_t m) {
 	char s_ip[BUFLEN];
 	bits2ip4(b, m, s_ip, BUFLEN);
@@ -260,7 +161,7 @@ double nodes2mb(pos_t n) {
 }
 
 int main(void) {
-	int b[IPMAXLEN];
+	bit_t b[IPMAXLEN];
 	mask_t m;
 	char s[BUFLEN];