[swift-users] FloatingPoint/BinaryFloatingPoint protocol and concrete FloatingPoint types

Jens Persson jens at bitcycle.com
Sun Dec 3 17:22:52 CST 2017

```I'm not sure what you mean David. That function was just part of my attempt
at presenting a solution to Antonino's question (that particular function
is from Antonino's code).
Below is my solution to Antonino's problem again, including a perhaps
clearer comment in that function:

protocol Float80Convertible : BinaryFloatingPoint {
init(_ value: Float80)
var float80: Float80 { get }
}
extension Double : Float80Convertible {
var float80: Float80 { return Float80(self) }
}
extension Float : Float80Convertible {
var float80: Float80 { return Float80(self) }
}

func maxPrecisionCalculation(input:Float80) -> Float80 {
return inpu
// In the actual use case, this would of course not just
// return input. Instead it would perform some computation
// that (in contrast to just returning input) actually needs
// the high precision of Float80.
}

func someComplexCalculation<T:Float80Convertible>(input: T) -> T {
let input80 = input.float80
let output80 = maxPrecisionCalculation(input: input80)
return T(output80)
}

/Jens

On Fri, Dec 1, 2017 at 11:59 PM, David Sweeris <davesweeris at mac.com> wrote:

>
>
> On Dec 1, 2017, at 13:18, Jens Persson via swift-users <
> swift-users at swift.org> wrote:
>
> func maxPrecisionCalculation(input:Float80) -> Float80 {
>     return input // but something actually reauiring high precision ...
> }
>
>
> AFAIK, Float80 *is* the high precision format on macOS (well, Intel macs,
> anyway... can’t recall if Swift can target OSs old enough to run on PPC
> macs). I’d avoid using it, though. AFAIK it’s an x86-only format (it might
> even be Intel-only... 5-10 minutes of googling didn’t give me a clear
> answer on whether AMD’s CPUs support it).
>
> I don’t know what we do with it on ARM targets, and I’m not at my computer
> to try to figure out.
>
> Unless maybe the x86 or ARM vector extensions support 128 or 256 bit
> floats? I don’t think they do, but I’m not 100% on that.
>
> - Dave Sweeris
>
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