   # alias both SipHash.State/Util
   alias SipHash.State, as: State
   alias SipHash.Util, as: Utils
-
-  # define the (constant) grouping pattern
-  @eighth_group_regex ~r/.{1,8}/
 
   @doc """
   Based on the algorithm as described in https://131002.net/siphash/siphash.pdf,

      iex> SipHash.hash("0123456789ABCDEF", "hello")
      "3D1974E948748CE2"

      iex> SipHash.hash("0123456789ABCDEF", "this is a longer input")
      "C7D6D8A1E7D359DD"

      iex> SipHash.hash("0123456789ABCDEF", "hello", case: :lower)
      "3d1974e948748ce2"

      iex> SipHash.hash_r("hello", "0123456789ABCDEF")
      "3D1974E948748CE2"

  """
  @spec hash_r(binary, binary, [ { atom, atom } ]) :: binary
  def hash_r(input, key, opts \\ []), do: hash(key, input, opts)
