iex(2)> <<int::integer-size(2)-unit(8)>> = <<255, 255>>
<<255, 255>>
iex(3)> int
65535

There are 2^n possible values in n bits.

If you’re just doing one number, you can use pattern matching likr this:

<<number::16>> = <<1, 0>>

And that will give you 256. This strategy will work for a 20 byte integer (obviously not with 16). Though if you’re using it as a literal I recommend number=0xFFFFFFFF....FFFFF

Your local thread necromancer checking in.

I am gonna work in my free time on a fairly basic network protocol in Rust, Golang and Elixir, and I am starting with Elixir.

I need to be able to encode and decode unsigned 32-bit integers to/from byte buffers (big endian). While :binary.encode_unsigned(x, :big) works the protocol requires all 4 bytes be sent, and this function always finds the smallest possible representation:

iex(1)> :binary.encode_unsigned 0xFF, :big
<<255>>

Whereas I need <<0, 0, 0, 255>>.

So just to bring visibility in case someone ever needs, encoding is as simple as:

iex(1)> <<255::unsigned-big-integer-32>>
<<0, 0, 0, 255>>

And decoding is done like so:

iex(1)> :binary.decode_unsigned(<<0, 0, 0, 255>>, :big)
255

(Taken from the docs of <<>> and :binary.)

I’d suggest the inverse from encoding, to keep things mirrored/simple:

iex(1)> <<int::unsigned-big-integer-32>> = <<0, 0, 0, 255>>
<<0, 0, 0, 255>>
iex(2)> int
255