Erik de Castro Lopo wrote:

>  b) caml_copy_nativeint creates a boxed native int (either Int32.t
>    or Int64.t) not an unboxed Ocaml int. To create an unboxed
>    Ocaml int, Val_int() is the correct macro.
>

caml_copy_nativeint returns a element of the OCaml type 'nativeint':
  http://caml.inria.fr/pub/docs/manual-ocaml/libref/Nativeint.html

The caml_copy_* documentation:
  http://caml.inria.fr/pub/docs/manual-ocaml/manual032.html#htoc238