Alternative base62 encoder

[pma]

Hi,

I've been playing with your code and implemented an alternative generator that seems to be a bit faster (6.6 s vs 12.5 s for 1M). The speed-up comes from the base62 encoding. I'm using compiled functions for the base62 encoder and accumulate digits as a list with an iodata_to_binary at the end, instead of binary concatenation. Sharing this in case you want to use any of the ideas in your implementation.

defmodule Ksuid do
  import System, only: [system_time: 1]
  import :crypto, only: [strong_rand_bytes: 1]
  import IO, only: [iodata_to_binary: 1]

  @epoch 1_400_000_000

  def new() do
    encode(<<(system_time(:second) - @epoch)::integer-size(32), strong_rand_bytes(16)::binary-16>>)
  end

  for {encoding, value} <- Enum.with_index('0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz') do
    defp enc(unquote(value)), do: <<unquote(encoding)>>
  end

  defp encode(binary) do
    <<n::size(160)>> = binary
    encode(n, [])
  end

  defp encode(n, r) do
    d = rem(n, 62)
    i = div(n, 62)
    r = [enc(d) | r]

    if i === 0, do: iodata_to_binary(r), else: encode(i, r)
  end
end