# What is the fastest way to obtain an infinity of the correct type?
**URL:** https://discourse.julialang.org/t/what-is-the-fastest-way-to-obtain-an-infinity-of-the-correct-type/88579
**Category:** General Usage
**Tags:** math
**Created:** [October 11, 2022, 2:48pm UTC](https://discourse.julialang.org/t/what-is-the-fastest-way-to-obtain-an-infinity-of-the-correct-type/88579 "2022-10-11T14:48:19Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@jishnub](https://discourse.julialang.org/u/jishnub)
#### Post date: [October 11, 2022, 2:48pm UTC](https://discourse.julialang.org/t/what-is-the-fastest-way-to-obtain-an-infinity-of-the-correct-type/88579/1 "2022-10-11T14:48:19Z")
This is related to [Analogue of zero(T) for infinitiy - #5 by rdeits](https://discourse.julialang.org/t/analogue-of-zero-t-for-infinitiy/7027/5), but the suggestion
```julia
T(Inf)
```
isn’t as fast as expected. In particular,
```julia
julia> @btime convert(Float16, $(Ref(Inf))[]);
9.205 ns (0 allocations: 0 bytes)
```
but I know statically that the answer must be `Inf16`, so ideally this shouldn’t carry out any conversion at all. Is there a faster way to compute this result?
---
### Author:  [@albheim](https://discourse.julialang.org/u/albheim)
#### Post date: [October 11, 2022, 2:56pm UTC](https://discourse.julialang.org/t/what-is-the-fastest-way-to-obtain-an-infinity-of-the-correct-type/88579/2 "2022-10-11T14:56:16Z")
Is that really testing what you want? I’ve never used Refs in timing, have seen it recommended, but I’m not sure exactly what happens behind the scenes. I would do
```julia
julia> @btime convert(Float16, x) setup=(x=Inf)
1.691 ns (0 allocations: 0 bytes)
Inf16
julia> @code_llvm convert(Float16, Inf)
; @ number.jl:7 within `convert`
define half @julia_convert_992(double %0) #0 {
top:
; ┌ @ float.jl:232 within `Float16`
%1 = fptrunc double %0 to half
; └
ret half %1
}
```
which seems fast and comes down to a single llvm instruction.
Wouldn’t `typemax(T)` be a good way to get infinity for the types that support it, and for those that don’t you get the closest approximation?
---
### Author:  [@Elrod](https://discourse.julialang.org/u/Elrod)
#### Post date: [October 11, 2022, 3:03pm UTC](https://discourse.julialang.org/t/what-is-the-fastest-way-to-obtain-an-infinity-of-the-correct-type/88579/3 "2022-10-11T15:03:06Z")
In general, const prop would handle this.
```julia
julia> inf(::Type{T}) where {T} = convert(T, Inf)
inf (generic function with 1 method)
julia> @code_typed inf(Float16)
CodeInfo(
1 ─ return Inf16
) => Float16
```
but yeah, I’d use `typemax(Float16)`.
```julia
julia> @code_typed typemax(Float16)
CodeInfo(
1 ─ return Inf16
) => Float16
```
given it’s already defined and does what you want.