[swift-evolution] [Proposal] Add floor() and ceiling() functions to FloatingPoint

[Stephen Canon]

That’s the default rounding mode for arithmetic operations, but these “roundToIntegral” operations are orthogonal from the dynamic rounding mode or its default.

Schoolbook rounding (ties away from zero) is both most people’s naive expectation, and also matches the behavior of the C/C++ round( ) function.  Principle of least surprise makes it the default choice.

– Steve

> On Jun 30, 2016, at 4:52 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
> 
> A question, perhaps Stephen's to answer: apparently IEEE754 defaults to what we're calling `toNearestOrEven`? Should Swift be using that as the default as well?
> 
> 
> On Wed, Jun 29, 2016 at 7:41 PM, Karl Wagner <razielim at gmail.com <mailto:razielim at gmail.com>> wrote:
> OK I’ve incorporated those small things and submitted it for review. We’ve had an initial discussion, incorporated all the feedback, so I think it’s met the bar for a PR 👍
> 
> https://github.com/apple/swift-evolution/pull/394 <https://github.com/apple/swift-evolution/pull/394>
> 
> Karl
> 
>> On 29 Jun 2016, at 20:20, Xiaodi Wu <xiaodi.wu at gmail.com <mailto:xiaodi.wu at gmail.com>> wrote:
>> 
>> On Wed, Jun 29, 2016 at 1:07 PM, Stephen Canon <scanon at apple.com <mailto:scanon at apple.com>> wrote:
>> 
>>> On Jun 29, 2016, at 2:06 PM, Xiaodi Wu <xiaodi.wu at gmail.com <mailto:xiaodi.wu at gmail.com>> wrote:
>>> 
>>> On Wed, Jun 29, 2016 at 12:12 PM, Stephen Canon via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>>> On Jun 29, 2016, at 1:10 PM, Matthew Johnson <matthew at anandabits.com <mailto:matthew at anandabits.com>> wrote:
>>>> 
>>>> My criticism of the 'toNearestOrGreatest' still stands though.  I think this name is misleading given the stated semantics.  The name indicates "greater value" not "greater magnitude" which are opposites in the case of negative numbers.
>>> 
>>> Yup, I agree.  I think I originally suggested `toNearestTiesAway`.  I’m not tied to that name specifically, but we should be clear that ties go away from zero, not up.
>>> 
>>> Agreed; `toNearestOrAwayFromZero` is the most accurate and consistent description.
>> 
>> Worth noting that since this is the defaulted behavior, we can get away with a wordy description.
>> 
>> This is really picking nits, but the most common behavior would be best as the first enum case, no? Maybe go roughly from most-value-preserving to least-value-preserving, like so:
>> 
>> `enum RoundingRule { case toNearestOrAwayFromZero, toNearestOrEven, up, down, towardZero }`
>> 
>>  
>> 
>> – Steve
> 
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20160630/581644e5/attachment.html>