Big_int disguised as a plain int (Or: how to abuse Ocaml's gc without actually messing it)

big.ml

type real_int =
    | Small of int
    | Big of Big_int.big_int

let pack = function
    | Small v -> v
    | Big v -> (Obj.magic v : int)

let unpack v =
    if Obj.is_int (Obj.repr v) then Small v else Big (Obj.magic v : Big_int.big_int)

let (<+>) a b =
    match unpack a, unpack b with
    | Small a, Small b ->
        let c = a + b in
        if c < a then
            let a = Big_int.big_int_of_int a in
            let b = Big_int.big_int_of_int b in
            (Obj.magic (Big_int.add_big_int a b) : int)
        else
            c
    | Small a, Big b ->
        let a = Big_int.big_int_of_int a in
        (Obj.magic (Big_int.add_big_int a b) : int)
    | Big a, Small b ->
        let b = Big_int.big_int_of_int b in
        (Obj.magic (Big_int.add_big_int a b) : int)
    | Big a, Big b ->
        (Obj.magic (Big_int.add_big_int a b) : int)

let to_string v =
    match unpack v with
    | Small v -> string_of_int v
    | Big v -> Big_int.string_of_big_int v

(* vim: se ts=4 sw=4 et: *)