defmodule AlchemyVM.LEB128 do
  @moduledoc false

  @doc """
    Decode an unsigned LEB128 encoded integer from binary, return any
    unused bytes
  """
  @spec decode_unsigned(binary) :: {integer, binary}
  def decode_unsigned(<<n, rest::binary>>) when n < 128, do: {n, rest}
  def decode_unsigned(<<n, rest::binary>>) when n >= 128 do
    {m, rest} = decode_unsigned(rest)
    {n - 128 + 128 * m, rest}
  end

  @doc """
    Decode a signed LEB128 encoded integer from binary, return any
    unused bytes
  """
  @spec decode_signed(binary) :: {integer, binary}
  def decode_signed(<<n, rest::binary>>) when n < 64, do: {n, rest}
  def decode_signed(<<n, rest::binary>>) when n >= 64 and n < 128, do: {n - 128, rest}
  def decode_signed(<<n, rest::binary>>) when n >= 128 do
    {m, rest} = decode_signed(rest)
    {n - 128 + 128 * m, rest}
  end
end