Inverse of bitstring(x)

General Usage
1

What function f is f(typeof(x), bitstring(x)) == x ?

2 
f(T, s) = reinterpret(T, parse(Int, s; base = 2))

?

EDIT: This is not general enough (see @rafael.guerra post below). The general answer adopted form @JeffreySarnoff’s solution would look like:

f(T, s) = reinterpret(T, Meta.parse("0b" * s))
2 Likes
3

Not quite, it seems

f(T, s) = reinterpret(T, parse(Int, s; base = 2))
julia> let x =rand(Float16)
       f(typeof(x), bitstring(x)) == x
       end
ERROR: bitcast: argument size does not match size of target type
Stacktrace:
   [1] reinterpret(#unused#::Type{Float16}, x::Int64)
     @ Base ./essentials.jl:438
   [2] f(T::Type, s::String)
     @ Main ./REPL[1]:1
4

Fyi, there is a solution in this other post.

2 Likes
5

I intended to cover this with BitsX.jl, but found it was missing. I added a method to do this.

You can define the function like this:

test_identity(x) = parse_bin(typeof(x), bitstring(x))

Works for many types, including FloatX.

parse_bin is similar to Base.parse(T, s; base=2). But it is much faster and also allows filtering out formatting characters:

julia> s = BitsX.randbitstring(64)
"1100101110101110011000111100111000101101111011101010111100101000"

julia> @btime parse(UInt, $s; base=2);
  197.869 ns (0 allocations: 0 bytes)

julia> @btime parse_bin(UInt, $s);
  53.767 ns (0 allocations: 0 bytes)
2 Likes