How to transform bitstring into iodata?

Questions / Help
,
1

Hi everyone Im facing problems with bitstrings I’m open a folder containing files and have to encode it with Huffman algorithm(huffman | Hex), after encoding I have to save it into an encripted file, but the Huffman.encode functions returns an encoded bitstring and not a binary so I cant save it due to not being an iodata, does anyone have a hint on how to solve this issue

PS I’m using File.write to save a file:
def save_file({encoded, _keys}, filepath, filename) do
IO.inspect(is_bitstring(encoded))
IO.inspect(encoded)
path = filepath <> “/” <> filename <> “.txt”
File.touch!(path)
File.write(path, encoded)
end

Thank you!

2

The biggest difference between a bitstring and a binary is that the former isn’t evenly divisible into bytes - you need to decide how to pad your data (leading zeros? trailing zeros?) to a multiple of 8 bits.

3

Do you have a tip on how can I append zeros to it?

4

You’ll problably need to store the number of bits padded in the file as well, otherwise you won’t be able to reconstruct the original bitstring from the file.

Small example

t = <<3::size(17)>> 
# => <<0, 1, 1::size(1)>>
pad = 8 - (bit_size(t) - (bit_size(t) |> Integer.floor_div(8)) * 8)  
# => 7
<<t::bitstring, 0::size(pad)>>
# => <<0, 1, 128>>

but if that is stored directly to a file, there is no way of knowing how many bits were padded.
So a convention could be to take the first 8-bits to mean the amount of padding that needs
to be removed (as well as the number itself).