let until_nul s =
  match String.index_opt s '\x00' with
  | None -> s
  | Some i -> String.sub s 0 i

module type IntType = sig
  type t
  val add : t -> t -> t
  val sub : t -> t -> t
  val mul : t -> t -> t
  val of_int : int -> t
  val to_int : t -> int
end


module IntForInt = struct
  type t = int
  let add = Int.add
  let sub = Int.sub
  let mul = Int.mul
  let of_int x = x
  let to_int x = x
end

let octal_reader (type a) (module I : IntType with type t = a) sin : a =
    let ( + ) = I.add in
    let ( * ) = I.mul in
    let ( - ) = I.sub in
    let s = (until_nul sin) in
    let l = List.init (String.length s) (String.get s) in
    let rec aux a = function
      | c :: rest ->
         if (Char.code c) > (Char.code '7') || (Char.code c) < (Char.code '0') then
           I.of_int 0
         else
         aux ((a * (I.of_int 8)) + (I.of_int (int_of_char c)) - (I.of_int (int_of_char '0'))) rest
      | [] -> a
    in aux (I.of_int 0) l

(* lmao *)
let to_int = octal_reader (module IntForInt)
let to_int64 = octal_reader (module Int64)