defmodule XXHash do

  use Bitwise

  defmodule Int32 do
    def prime_1, do: 2654435761
    def prime_2, do: 2246822519
    def prime_3, do: 3266489917
    def prime_4, do: 668265263
    def prime_5, do: 374761393

    def add(a, b), do: a + b |> mask
    def sub(a, b), do: a - b |> mask
    def mul(a, b), do: a * b |> mask
    def lshift(a, b), do: a <<< b |> mask
    def rshift(a, b), do: a >>> b
    def xor(a, b), do: a ^^^ b |> mask
    def rotl(a, b), do: lshift(a, b) ||| rshift(a, 32 - b)
    def rshift_xor(a, b), do: a |> xor(rshift(a, b))
    def read(<<a::32>>) when <<1::32-little>> != <<1::32-native>>, do: a
    def read(<<a::32>>), do: byteswap(a)
    defp mask(a), do: a &&& 0xFFFFFFFF
    defp byteswap(a) do <<b::32-big>> = <<a::32-little>>; b end
  end

  defmodule Int64 do
    def prime_1, do: 11400714785074694791
    def prime_2, do: 14029467366897019727
    def prime_3, do: 1609587929392839161
    def prime_4, do: 9650029242287828579
    def prime_5, do: 2870177450012600261

    def add(a, b), do: a + b |> mask
    def sub(a, b), do: a - b |> mask
    def mul(a, b), do: a * b |> mask
    def lshift(a, b), do: a <<< b |> mask
    def rshift(a, b), do: a >>> b
    def xor(a, b), do: a ^^^ b |> mask
    def rotl(a, b), do: lshift(a, b) ||| rshift(a, 64 - b)
    def rshift_xor(a, b), do: a |> xor(rshift(a, b))
    def read(<<a::64>>) when <<1::64-little>> != <<1::64-native>>, do: a
    def read(<<a::64>>), do: byteswap(a)
    defp mask(a), do: a &&& 0xFFFFFFFFFFFFFFFF
    defp byteswap(a) do <<b::64-big>> = <<a::64-little>>; b end
  end

  @spec xxh32(binary | term, non_neg_integer, non_neg_integer) :: non_neg_integer
  def xxh32(input), do: xxh32(input, String.length(input), 0)

  @spec xxh32(binary | term, non_neg_integer) :: non_neg_integer
  def xxh32(input, seed), do: xxh32(input, String.length(input), seed)

  @spec xxh32(binary | term, non_neg_integer, non_neg_integer) :: non_neg_integer
  def xxh32(<<>>, _length, _seed), do: 0

  @spec xxh32(binary | term, non_neg_integer, non_neg_integer) :: non_neg_integer
  def xxh32(input, length, seed) do
    if length >= 16 do
      {h32, buffer} = do_xxh32(0, seed, input)
    else
      {h32, buffer} = {Int32.add(seed, Int32.prime_5), input}
    end

    h32
    |> Int32.add(length)
    |> do_xxh32(seed, buffer)
    |> Int32.rshift_xor(15)
    |> Int32.mul(Int32.prime_2)
    |> Int32.rshift_xor(13)
    |> Int32.mul(Int32.prime_3)
    |> Int32.rshift_xor(16)
  end

  @spec do_xxh32(non_neg_integer, non_neg_integer, binary | term) :: non_neg_integer
  defp do_xxh32(h, seed, <<_a::32, _b::32, _c::32, _d::32, _rest::binary>> = all) do
    v1 = Int32.add(seed, Int32.prime_1) |> Int32.add(Int32.prime_2)
    v2 = Int32.add(seed, Int32.prime_2)
    v3 = Int32.add(seed, 0)
    v4 = Int32.sub(seed, Int32.prime_1)
    do_xxh32(h, seed, all, {v1, v2, v3, v4})
  end

  @spec do_xxh32(non_neg_integer, non_neg_integer, binary | term) :: non_neg_integer
  defp do_xxh32(h, _seed, <<>>), do: h

  @spec do_xxh32(non_neg_integer, non_neg_integer, binary | term) :: non_neg_integer
  defp do_xxh32(h, seed, <<p::32, rest::binary>>) do
    Int32.read(<<p::32>>)
    |> Int32.mul(Int32.prime_3)
    |> Int32.add(h)
    |> Int32.rotl(17)
    |> Int32.mul(Int32.prime_4)
    |> do_xxh32(seed, rest)
  end

  @spec do_xxh32(non_neg_integer, non_neg_integer, binary | term) :: non_neg_integer
  defp do_xxh32(h, seed, <<p::8, rest::binary>>) do
    Int32.mul(p, Int32.prime_5)
    |> Int32.add(h)
    |> Int32.rotl(11)
    |> Int32.mul(Int32.prime_1)
    |> do_xxh32(seed, rest)
  end

  @spec do_xxh32(non_neg_integer, non_neg_integer, binary | term, tuple) :: non_neg_integer
  defp do_xxh32(h, seed, <<a::32, b::32, c::32, d::32, rest::binary>>, {v1, v2, v3, v4}) do
    cv = &(Int32.read(&1) |> Int32.mul(Int32.prime_2) |> Int32.add(&2) |> Int32.rotl(13) |> Int32.mul(Int32.prime_1))
    do_xxh32(h, seed, rest, {cv.(<<a::32>>, v1), cv.(<<b::32>>, v2), cv.(<<c::32>>, v3), cv.(<<d::32>>, v4)})
  end

  @spec do_xxh32(non_neg_integer, non_neg_integer, binary | term, tuple) :: non_neg_integer
  defp do_xxh32(_h, _seed, rest, {v1, v2, v3, v4}) do
    {Int32.rotl(v1, 1) + Int32.rotl(v2, 7) + Int32.rotl(v3, 12) + Int32.rotl(v4, 18), rest}
  end
end