quick view of a ring buffer as an unordered array

rb_to_array_fast.ml

(* Expose the entire array as fast as possible. Copying is avoided when the array is saturated.
   If non empty, also return the position of the first element. *)  
let to_array_fast b = length b |> function
    | 0 -> A.empty, None
    | len when A.length b.buf = len -> b.buf, Some b.start
    | _ -> to_array b, Some 0