+struct in_addr* in_addr_prefixlen_to_netmask(struct in_addr *addr, unsigned char prefixlen) {
+ assert(addr);
+ assert(prefixlen <= 32);
+
+ /* Shifting beyond 32 is not defined, handle this specially. */
+ if (prefixlen == 0)
+ addr->s_addr = 0;
+ else
+ addr->s_addr = htobe32((0xffffffff << (32 - prefixlen)) & 0xffffffff);
+
+ return addr;
+}
+