Add V6.link_address_of_mac from RFC 2464. Partially addresses #10.

CHANGES

@@ -6,6 +6,7 @@
 * Add multicast MAC conversions from RFC 1112 and RFC 2464
 * Add to_domain_name conversions to DNS label lists (in-addr.arpa and ip6.arpa)
 * Add V6.interface_routers, V6.site_routers, and V6.Prefix.solicited_node
+* Add V6.link_address_of_mac to convert a MAC into a link local IP address
 
 2.5.0 (2014-05-27):
 * Add `with sexp` (de)serializers to all of the Ipaddr and Macaddr types. (#31)

lib/ipaddr.ml

@@ -811,6 +811,19 @@ module V6 = struct
     else if i = unspecified then Point
     else Global
 
+  let link_address_of_mac =
+    let c b i = Char.code (String.get b i) in
+    fun mac ->
+      let bmac = Macaddr.to_bytes mac in
+      let c_0 = c bmac 0 lxor 2 in
+      let addr = make 0 0 0 0
+        (c_0      lsl 8 + c bmac 1)
+        (c bmac 2 lsl 8 + 0xff    )
+        (0xfe00         + c bmac 3)
+        (c bmac 4 lsl 8 + c bmac 5)
+      in
+      Prefix.(network_address link addr)
+
   let is_global i = (scope i) = Global
   let is_multicast i = Prefix.(mem i multicast)
   let is_private i = (scope i) <> Global

lib/ipaddr.mli

@@ -498,6 +498,13 @@ module V6 : sig
       hierarchy. *)
   val scope : t -> scope
 
+  (** [link_address_of_mac mac] is the link-local address for an
+      Ethernet interface derived by the IEEE MAC -> EUI-64 map with
+      the Universal/Local bit complemented for IPv6.
+      @see <https://tools.ietf.org/html/rfc2464#section-4> RFC 2464
+  *)
+  val link_address_of_mac : Macaddr.t -> t
+
   (** [is_global ipv6] is a predicate indicating whether [ipv6] globally
       addresses a node. *)
   val is_global : t -> bool

lib_test/test_ipaddr.ml

@@ -606,6 +606,13 @@ module Test_v6 = struct
     assert_equal ~msg:"domain_name"
       (String.concat "." (V6.to_domain_name ip)) name
 
+  let test_link_address_of_mac () =
+    let mac = Macaddr.of_string_exn "34-56-78-9A-BC-DE" in
+    let ip_str = V6.(to_string (link_address_of_mac mac)) in
+    let expected = "fe80::3656:78ff:fe9a:bcde" in
+    assert_equal ~msg:("link_address_of_mac "^ip_str^" <> "^expected)
+      ip_str expected
+
   let suite = "Test V6" >::: [
     "string_rt"            >:: test_string_rt;
     "string_rt_bad"        >:: test_string_rt_bad;
@@ -625,6 +632,7 @@ module Test_v6 = struct
     "prefix_map"           >:: test_prefix_map;
     "multicast_mac"        >:: test_multicast_mac;
     "domain_name"          >:: test_domain_name;
+    "link_address_of_mac"  >:: test_link_address_of_mac;
   ]
 end