CRC

[Matt Ludwigs]

We don't need to rely on the CRC package as most of it is not really needed for what we do in Grizzly.

Below is the example code to bring into Grizzly and replace the CRC package.

defmodule NewCRC2.Table do
  use Bitwise
​
  def ccitt_table(poly) do
    table =
      for i <- 0..255 do
        ccitt_entry(i <<< 8, 0, 0, poly)
      end
​
    List.to_tuple(table)
  end
​
  defp ccitt_entry(_, crc, 8, _), do: crc &&& 0xFFFF
​
  defp ccitt_entry(c, crc, bc, poly) do
    next_crc = if (crc ^^^ c &&& 0x8000) > 0, do: (crc <<< 1) ^^^ poly, else: crc <<< 1
​
    ccitt_entry(c <<< 1, next_crc, bc + 1, poly)
  end


defmodule NewCRC2 do
  @compile :native
  @compile {:hipe, [:o3]}
​
  use Bitwise
​
  @table NewCRC2.Table.ccitt_table(0x1021)
​
  @type uint16 :: 0..65535
​
  @doc """
  CRC-16/AUG-CCITT
  """
  @spec crc16_aug_ccitt(binary() | [byte()]) :: uint16
  def crc16_aug_ccitt(data) when is_binary(data) do
    data
    |> :binary.bin_to_list()
    |> crc16_aug_ccitt()
  end
​
  def crc16_aug_ccitt(data) when is_list(data) do
    crc_ccitt(data, 0x1D0F)
  end
​
  defp crc_ccitt([x | rem], crc) do
    index = (crc >>> 8) ^^^ x
    crc = (crc <<< 8) ^^^ elem(@table, index) &&& 0xFFFF
    crc_ccitt(rem, crc)
  end
​
  defp crc_ccitt([], crc), do: crc
end