ip-address-access: minimize IP address lists

Let's drop redundant items from the IP address list after parsing. Let's
also mask out redundant bits hidden by the prefixlength.

src/basic/in-addr-util.c

@@ -465,6 +465,30 @@ int in_addr_mask(int family, union in_addr_union *addr, unsigned char prefixlen)
         return -EAFNOSUPPORT;
 }
 
+int in_addr_prefix_covers(int family,
+                          const union in_addr_union *prefix,
+                          unsigned char prefixlen,
+                          const union in_addr_union *address) {
+
+        union in_addr_union masked_prefix, masked_address;
+        int r;
+
+        assert(prefix);
+        assert(address);
+
+        masked_prefix = *prefix;
+        r = in_addr_mask(family, &masked_prefix, prefixlen);
+        if (r < 0)
+                return r;
+
+        masked_address = *address;
+        r = in_addr_mask(family, &masked_address, prefixlen);
+        if (r < 0)
+                return r;
+
+        return in_addr_equal(family, &masked_prefix, &masked_address);
+}
+
 int in_addr_parse_prefixlen(int family, const char *p, unsigned char *ret) {
         uint8_t u;
         int r;

src/basic/in-addr-util.h

@@ -60,6 +60,7 @@ struct in_addr* in4_addr_prefixlen_to_netmask(struct in_addr *addr, unsigned cha
 int in4_addr_default_prefixlen(const struct in_addr *addr, unsigned char *prefixlen);
 int in4_addr_default_subnet_mask(const struct in_addr *addr, struct in_addr *mask);
 int in_addr_mask(int family, union in_addr_union *addr, unsigned char prefixlen);
+int in_addr_prefix_covers(int family, const union in_addr_union *prefix, unsigned char prefixlen, const union in_addr_union *address);
 int in_addr_parse_prefixlen(int family, const char *p, unsigned char *ret);
 int in_addr_prefix_from_string(const char *p, int family, union in_addr_union *ret_prefix, unsigned char *ret_prefixlen);
 int in_addr_prefix_from_string_auto(const char *p, int *ret_family, union in_addr_union *ret_prefix, unsigned char *ret_prefixlen);