jarrodmoldrich/bit_reverse_test.exs

## bit_reverse_test.exs
// Based on a discussion at:
// https://elixirforum.com/t/ingest-a-bitstring-from-least-significant-bit/44265/8

Mix.install([{:benchee, "~> 1.0"}])

use Bitwise

defmodule ReverseStringMap1 do
  def lastbit(bitstring) do
    size = bit_size(bitstring) - 1
    <<_head :: size(size), bit :: 1 >> = bitstring
    bit
  end

  def reverse_string_map(bitstring, so_far \\ [])
  def reverse_string_map(<<>>, so_far), do: Enum.reverse(so_far)
  def reverse_string_map(bitstring, so_far) do
    headsize = bit_size(bitstring) - 1
    <<head :: size(headsize), bit :: 1 >> = bitstring
    reverse_string_map(<<head::size(headsize)>>, [bit | so_far])
  end
end

defmodule ReverseStringMap2 do
  def reverse_string_map(s), do: reverse_string_map(s, [], bit_size(s) - 1)
  def reverse_string_map(<<>>, _, _), do: []
  def reverse_string_map(<<bit::1, _::bits>>, so_far, 0), do: Enum.reverse([bit | so_far])
  def reverse_string_map(s, so_far, prefix) do
    <<_ :: size(prefix), bit::1, _::bits>> = s
    reverse_string_map(s, [bit | so_far], prefix - 1)
  end
end

defmodule ReverseBitString do
  def reverse_bitstring(value) when is_bitstring(value) do
  for << bit::1 <- value >>, reduce: {0, 0} do
    {bits, write_idx} ->
      {(bit <<< write_idx) ||| bits, write_idx + 1}
  end
    |> elem(0)
  end
end

defmodule Simple do
  def reverse_bitstring(value) when is_bitstring(value) do
    (for << bit::1 <- value >>, into: [], do: bit)
      |> Enum.reverse()
  end
end

values =
  for _i <- 1..100,
    do: << (:rand.uniform(65535))::8 >>

Benchee.run(
  %{
    "comprehension and reverse" => fn ->
      for value <- values,
        do: Simple.reverse_bitstring(value)
    end,
    "function style" => fn ->
      for value <- values,
        do: ReverseStringMap1.reverse_string_map(value)
    end,
    "comprehension w/ reduce + bitwise operations" => fn ->
      for value <- values,
        do: ReverseBitString.reverse_bitstring(value)
    end,
    "function style 2" => fn ->
      for value <- values,
        do: ReverseStringMap2.reverse_string_map(value)
    end
  }
)
	// Based on a discussion at:
	// https://elixirforum.com/t/ingest-a-bitstring-from-least-significant-bit/44265/8

	Mix.install([{:benchee, "~> 1.0"}])

	use Bitwise

	defmodule ReverseStringMap1 do
	def lastbit(bitstring) do
	size = bit_size(bitstring) - 1
	<<_head :: size(size), bit :: 1 >> = bitstring
	bit
	end

	def reverse_string_map(bitstring, so_far \\ [])
	def reverse_string_map(<<>>, so_far), do: Enum.reverse(so_far)
	def reverse_string_map(bitstring, so_far) do
	headsize = bit_size(bitstring) - 1
	<<head :: size(headsize), bit :: 1 >> = bitstring
	reverse_string_map(<<head::size(headsize)>>, [bit \| so_far])
	end
	end

	defmodule ReverseStringMap2 do
	def reverse_string_map(s), do: reverse_string_map(s, [], bit_size(s) - 1)
	def reverse_string_map(<<>>, _, _), do: []
	def reverse_string_map(<<bit::1, _::bits>>, so_far, 0), do: Enum.reverse([bit \| so_far])
	def reverse_string_map(s, so_far, prefix) do
	<<_ :: size(prefix), bit::1, _::bits>> = s
	reverse_string_map(s, [bit \| so_far], prefix - 1)
	end
	end

	defmodule ReverseBitString do
	def reverse_bitstring(value) when is_bitstring(value) do
	for << bit::1 <- value >>, reduce: {0, 0} do
	{bits, write_idx} ->
	{(bit <<< write_idx) \|\|\| bits, write_idx + 1}
	end
	\|> elem(0)
	end
	end

	defmodule Simple do
	def reverse_bitstring(value) when is_bitstring(value) do
	(for << bit::1 <- value >>, into: [], do: bit)
	\|> Enum.reverse()
	end
	end

	values =
	for _i <- 1..100,
	do: << (:rand.uniform(65535))::8 >>

	Benchee.run(
	%{
	"comprehension and reverse" => fn ->
	for value <- values,
	do: Simple.reverse_bitstring(value)
	end,
	"function style" => fn ->
	for value <- values,
	do: ReverseStringMap1.reverse_string_map(value)
	end,
	"comprehension w/ reduce + bitwise operations" => fn ->
	for value <- values,
	do: ReverseBitString.reverse_bitstring(value)
	end,
	"function style 2" => fn ->
	for value <- values,
	do: ReverseStringMap2.reverse_string_map(value)
	end
	}
	)