Add configurable filter size

config/config.exs

@@ -1,6 +1,7 @@
 import Config
 
 config :petal,
+  filter_size: 64,
   hashers: [
     Petal.Hasher.Adler32,
     Petal.Hasher.CRC32

lib/petal/application.ex

@@ -5,15 +5,25 @@ defmodule Petal.Application do
 
   use Application
 
+  import Petal.Bytes, only: [ceil_bits: 1]
+
   @impl true
   def start(_type, _args) do
     children = [
-      {Petal.Worker, size: 64}
+      {Petal.Worker, size: default_filter_size()}
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html
     # for other strategies and supported options
     opts = [strategy: :one_for_one, name: Petal.Supervisor]
     Supervisor.start_link(children, opts)
   end
+
+  # Default size of the filter to use
+  defp default_filter_size() do
+    size = Application.get_env(:petal, :filter_size, _bits = 64)
+
+    # Make sure this is divisible by 8
+    ceil_bits(size)
+  end
 end

lib/petal/bytes.ex

@@ -9,6 +9,12 @@ defmodule Petal.Bytes do
   @spec byte_size_of_field(size :: pos_integer()) :: pos_integer()
   def byte_size_of_field(size), do: div(size, 8)
 
+  @doc """
+  Round up the bits so that they are divisible by 8.
+  """
+  @spec ceil_bits(size :: pos_integer()) :: pos_integer()
+  def ceil_bits(size), do: ceil(size / 8) * 8
+
   @doc ~S"""
   Pad the `encoded` payload to `n` bytes.
 

lib/petal/worker.ex

@@ -51,7 +51,7 @@ defmodule Petal.Worker do
 
   def init(args) do
     # Init the bitfield
-    size_of_field = Keyword.get(args, :size, 64)
+    size_of_field = Keyword.get(args, :size, _bits = 64)
     state = Bitfield.new(size_of_field)
 
     {:ok, state}

test/petal/bytes_test.exs

@@ -8,6 +8,10 @@ defmodule Petal.BytesTest do
     assert Bytes.byte_size_of_field(64) == 8
   end
 
+  test "ceil_bits/1" do
+    assert Bytes.ceil_bits(100) == 104
+  end
+
   test "pad_encoded_payload/2" do
     payload = <<1, 2, 3>>