type t = {
  mutable data : int array;
  mutable length : int;
  mutable capacity : int;
}


let length a = a.length

let create () =
  { data = Array.create 512 0;
    length = 0;
    capacity = 512
  }

let resize a =
  let ncap = a.capacity lsl 1 in
  let b = Array.create ncap 0 in
  for i = 0 to a.capacity - 1 do
    b.(i) <- a.data.(i)
  done;
  a.data <- b;
  a.capacity <- ncap

let get a i =
  if i >= 0 && i < a.length then a.data.(i)
  else failwith "Invalid array access"

let set a i v =
  if i >= 0 && i < a.length then a.data.(i) <- v
  else failwith "Invalid array access"

let unsafe_get a i = a.data.(i)
let unsafe_set a i v = a.data.(i) <- v


let push_back a v =
  if a.length >= a.capacity then resize a;
  a.data.(a.length) <- v;
  a.length <- a.length + 1

let pack a =
  let b = Array.create a.length 0 in
  Array.blit a.data 0 b 0 a.length;
  b