Replace Bitwise xor with :crypto.exor

[denvaar]

No description provided.

[josevalim]

Hi @denvaar! Have you benchmarked both approaches? A 40 bytes long binary is a reasonable payload to benchmark with. Thanks!

[denvaar]

Here are some results. The difference is quite small, but there is a difference (0.17 μs/op vs 3.11 μs/op) I'm not sure if there are other factors to consider.

iex(1)> input_a = :crypto.strong_rand_bytes(40)
<<11, 71, 42, 174, 69, 99, 233, 48, 182, 46, 122, 189, 246, 94, 59, 227, 217,
  214, 188, 40, 81, 131, 219, 32, 83, 155, 39, 58, 183, 121, 10, 22, 132, 148,
  100, 107, 249, 145, 197, 125>>
iex(2)> input_b = :crypto.strong_rand_bytes(40)
<<223, 157, 121, 169, 104, 218, 32, 1, 97, 157, 49, 2, 47, 165, 18, 13, 148,
  182, 133, 121, 238, 176, 203, 53, 84, 157, 0, 72, 134, 237, 8, 241, 242, 221,
  64, 110, 103, 200, 135, 183>>
iex(3)> Benchwarmer.benchmark [&:crypto.exor/2, &MaskTest.mask/2], [input_a, input_b]
*** &:crypto.exor/2 ***
1.3 sec     8M iterations   0.17 μs/op

*** &MaskTest.mask/2 ***
1.6 sec   524K iterations   3.11 μs/op

Where MaskTest.mask/2 is

defmodule MaskTest do
  use Bitwise

  def mask(left, right) do
    mask(left, right, "")
  end

  defp mask(<<x, left::binary>>, <<y, right::binary>>, acc) do
    mask(left, right, <<acc::binary, x ^^^ y>>)
  end

  defp mask(<<>>, <<>>, acc) do
    acc
  end
end

[josevalim]

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