[swift-evolution] [Review #2] SE-0067: Enhanced Floating Point Protocols

[Xiaodi Wu]

I thought you'd mentioned that AbsoluteValuable conformance was removed for
a reason and that the method would be added to FloatingPoint? Otherwise, it
seems like conformance to AbsoluteValuable would be much the same...


On Tue, Apr 26, 2016 at 6:54 PM, Stephen Canon <scanon at apple.com> wrote:

> Do you actually want a method added, or just conformance to
> AbsoluteValuable?
>
> – Steve
>
> On Apr 26, 2016, at 7:41 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>
> Unrelated to this discussion about comparison operators, please remember
> to put back .abs() or .absoluteValue() somewhere in FloatingPoint. Thanks!
>
>
> On Tue, Apr 26, 2016 at 12:07 PM, Nicola Salmoria via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> If performance is the only reasons to have a separate method, perhaps it
>> might make sense to have a note about this in the isLessThanOrEqualTo
>> description, and provide a default implementation that calls down on isLess
>> and isEqual.
>>
>> Nicola
>>
>>
>> On Tue, Apr 26, 2016 at 4:59 PM, Stephen Canon <scanon at apple.com> wrote:
>>
>>> On Apr 26, 2016, at 10:03 AM, Nicola Salmoria via swift-evolution <
>>> swift-evolution at swift.org> wrote:
>>>
>>>
>>> it should be enough to do
>>>
>>> func <= <T: FloatingPoint>(lhs: T, rhs: T) -> Bool
>>> {
>>> return lhs.isLess(than: rhs) || lhs.isEqual(to: rhs)
>>> }
>>>
>>> Or is there some case of x, y where (x <= y) is true but (x < y) and (x
>>> == y) are both false?
>>>
>>>
>>> No, these are always equivalent.
>>>
>>> However, there is a problem with this approach: the compiler knows about
>>> the built-in floating-point types (Float, Double, Float80) and their
>>> aliases (CGFloat, etc) and can fuse the two comparisons into a single
>>> hardware operation.  However, for soft-float types, without a
>>> lessThanOrEqual method, there is no single comparison that the compiler
>>> could fuse these to.
>>>
>>> In some cases, if they are simple enough, the compiler may be able to
>>> actually fuse the bodies of the two comparison operations, but we can’t
>>> reasonably depend on that happening or even being possible in all cases.
>>> So for performance, it’s important that there be an actual less than or
>>> equal to method.
>>>
>>> – Steve
>>>
>>
>>
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>>
>>
>
>
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