defmodule Fnv1a do
  @doc ~S"""
  Hashes terms using the FNV-1a 32-bit algorithm.

  ## Examples

      iex> Fnv1a.hash({1, 2})
      2761922969
      iex> Fnv1a.hash("this thing")
      891900385
  """

  use Bitwise

  @offset 2166136261
  @prime 16777619

  def hash(term) when is_binary(term) do
    _hash(@offset, 0, term)
  end

  def hash(term) do
    :erlang.term_to_binary(term) |> hash
  end

  defp _hash(hash, byte_offset, bin) when byte_size(bin) == byte_offset do
    hash
  end

  defp _hash(hash, byte_offset, bin) do
    <<_::size(byte_offset) - binary, octet::size(8), _::binary>> = bin
    xord = hash ^^^ octet
    hash = rem((xord * @prime), (2 <<< 31))
    _hash(hash, byte_offset + 1, bin)
  end
end