Questions & Help>Questions

Binary to integer (no parsing)

#binary
lud

lud

Hi,

Is there a function that would convert <<1>> to 1, <<1, 0>> to 256. I do not mean parsing the binary as a string representation of the integer.

I want to know how bing a 20 bytes integer can be.

b = 1..20 |> Enum.map(fn _ -> 255 end) |> :erlang.list_to_binary
<<255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
  255, 255, 255, 255, 255>>

Thank you.

12 comments
#binary
7159 12

Marked As Solved

voltone

voltone

Try :binary.decode_unsigned/1,2, it does exactly what your code does…

9
Post #7

Also Liked

LostKobrakai

LostKobrakai 

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

NobbZ

There are 2^n possible values in n bits.

3
Post #5
ityonemo

ityonemo

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

1
Post #1

Last Post!

dimitarvp

dimitarvp

Actually yeah, I was just about to post an edit, thank you. :+1:

Guess I really wanted it to be a one-liner but that’s not an important consideration.

0
Post #12

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