Calculating ULP distance between two floating point numbers (quickly)

General Usage
3

Is using isapprox an option? You can give it an absolute or relative allowed difference.

In case it isn’t, the code from your link would look like this in julia:

function ulpsBetween(a::Float64, b::Float64)
    a == b && return 0
    isnan(a) || isnan(b) && return typemax(Int)
    isinf(a) || isinf(b) && return typemax(Int)
    
    a_int = reinterpret(Int64, a)
    b_int = reinterpret(Int64, b)

    (a_int < 0) != (b_int < 0) && return typemax(Int)

    return abs(a_int - b_int)
end

Still, the link discusses precisely why this sort of comparison usually isn’t a good idea (and isapprox is usually the best choice anyway). It’s implemented like this:

function isapprox(x::Number, y::Number;                                                                                          
                  atol::Real=0, rtol::Real=rtoldefault(x,y,atol),                                                                
                  nans::Bool=false, norm::Function=abs)                                                                          
    x == y || (isfinite(x) && isfinite(y) && norm(x-y) <= max(atol, rtol*max(norm(x), norm(y)))) || (nans && isnan(x) && isnan(y)
end

which you can find via @edit isapprox(0.5, 1.0) at base/floatfuncs.jl:360.