sub-binary-and-match-context

bench.exs

defmodule MyBinParser1 do
  def valid?(<<length::2, data::binary>>),
    do: byte_size(data) >= length

  def valid?(_), do: false
end

defmodule MyBinParser2 do
  def valid?(<<length::2, _data::binary-size(length), _rest::binary>>),
    do: true

  def valid?(_), do: false
end

data = <<1000::2, :binary.copy("0", 1000)::binary>>

Benchee.run(%{
  mod_1: fn -> MyBinParser1.valid?(data) end,
  mod_2: fn -> MyBinParser2.valid?(data) end
})

# `mod_1` is about 2.6x slower because it creates a sub-binary every time.