mirage-tcpip.patch

diff --git a/src/tcpip_checksum/tcpip_checksum.ml b/src/tcpip_checksum/tcpip_checksum.ml
index 2b7abc87..5035ccaa 100644
--- a/src/tcpip_checksum/tcpip_checksum.ml
+++ b/src/tcpip_checksum/tcpip_checksum.ml
@@ -15,6 +15,30 @@
  *)
 
 (** One's complement checksum, RFC1071 *)
-external ones_complement: Cstruct.t -> int = "caml_tcpip_ones_complement_checksum"
+(* external ones_complement: Cstruct.t -> int = "caml_tcpip_ones_complement_checksum" *)
 
-external ones_complement_list: Cstruct.t list -> int = "caml_tcpip_ones_complement_checksum_list"
+(* external ones_complement_list: Cstruct.t list -> int = "caml_tcpip_ones_complement_checksum_list" *)
+
+let ones_complement (buffer: Cstruct.t) =
+  let len = Cstruct.len buffer in
+  let rec finalise_checksum cs =
+    assert (cs >= 0);
+    if cs < 0x10000 then
+      cs
+    else
+      finalise_checksum ((cs land 0xffff) + (cs lsr 16))
+  in
+  let rec do_checksum checksum offset =
+    if offset + 1 < len then (
+      let checksum = checksum + Cstruct.BE.get_uint16 buffer offset in
+      do_checksum checksum (offset + 2)
+    ) else if offset + 1 = len then (
+      let checksum = checksum + (Cstruct.get_uint8 buffer offset lsl 8) in
+      finalise_checksum checksum
+    ) else
+      finalise_checksum checksum
+  in
+  lnot (do_checksum 0 0) land 0xffff
+
+let ones_complement_list buffers =
+  ones_complement (Cstruct.concat buffers)