Assuming RawSignificand really is the type you want, I think this does what
you’re looking for?
protocol BinaryFloatingPointWithBitPattern: BinaryFloatingPoint {
init(bitPattern: RawSignificand)
var bitPattern: RawSignificand { get }
}
extension Float: BinaryFloatingPointWithBitPattern { }
extension Double: BinaryFloatingPointWithBitPattern { }
extension BinaryFloatingPointWithBitPattern {
init(unitRangeFromRawSignificand s: RawSignificand) {
self = Self(bitPattern: Self(1).bitPattern | s) - 1
}
}
> On Aug 26, 2016, at 7:38 PM, Stephen Canon via swift-dev
> <swift-dev@swift.org> wrote:
>
> Where does your RawSignificand input come from? Is that really the type that
> you want?
>
> I don’t think you really need very much boilerplate at all here.
>
>> On Aug 26, 2016, at 7:30 PM, Jens Persson <j...@bitcycle.com> wrote:
>>
>> I understand.
>> It's just very tempting to try and use the new static computed properties
>> for eg 23 and 52 etc.
>> I guess I'll just have to write a lot of boilerplate, or perhaps a protocol
>> that is just implemented by Double and Float (that will be very similar to
>> BinaryFloatingPoint in a lot of ways).
>> /Jens
>>
>> On Sat, Aug 27, 2016 at 1:25 AM, Stephen Canon <sca...@apple.com> wrote:
>> This doesn’t really scale up very well, though. BinaryFloatingPoint needs
>> to also be able to model e.g. Float2048 or similar; we generally don't want
>> to require that RawExponent to be the same type as RawSignificand (which I
>> think is what you’re really suggesting), because in typical bignum usage
>> significands are much larger than exponents.
>>
>> It sounds like maybe you actually want to be operating directly on
>> bitPatterns, rather than the abstract fields of the types.
>>
>> – Steve
>>
>>> On Aug 26, 2016, at 7:21 PM, Jens Persson <j...@bitcycle.com> wrote:
>>>
>>> Oh, to more directly answer your question: I don't like having to create a
>>> UInt (UInt64) value when all my bit manipulaton code happens in UInt32 (for
>>> Float) for example.
>>>
>>> The most probable context for using these computed properties and types of
>>> BinaryFloatingPoint is one in which specific fixed width types really
>>> matters a lot (look at the name of the protocol and the properties and
>>> assocated types we are talking about).
>>>
>>> /Jens
>>>
>>>
>>> On Sat, Aug 27, 2016 at 1:15 AM, Jens Persson <j...@bitcycle.com> wrote:
>>> Reason for asking is that I have this:
>>>
>>> extension Double {
>>> init(unitRangeFromRawSignificand s: RawSignificand) {
>>> let bitPattern = s | (1023 << 52)
>>> self = unsafeBitCast(bitPattern, to: Double.self) - 1.0
>>> }
>>> }
>>> extension Float {
>>> init(unitRangeFromRawSignificand s: RawSignificand) {
>>> let bitPattern = s | (127 << 23)
>>> self = unsafeBitCast(bitPattern, to: Float.self) - 1.0
>>> }
>>> }
>>>
>>> But they would be better as:
>>> extension BinaryFloatingPoint {
>>> init(unitRangeFromRawSignificand s: RawSignificand) {
>>> ... problems here, have to try casting things into RawSignificand's
>>> type ...
>>> }
>>> }
>>>
>>> Please have a go at that and perhaps you see what I mean or you will come
>>> up with a nice solution that I have missed. (Speed is very important btw.)
>>>
>>> /Jens
>>>
>>>
>>> On Sat, Aug 27, 2016 at 1:02 AM, Stephen Canon <sca...@apple.com> wrote:
>>> > On Aug 26, 2016, at 6:06 PM, Jens Persson via swift-dev
>>> > <swift-dev@swift.org> wrote:
>>> >
>>> > I can understand why
>>> > Double.RawSignificand is UInt64
>>> > and
>>> > Float.RawSignificand is UInt32
>>> >
>>> > But I can't understand why both
>>> > Double.RawExponent
>>> > and
>>> > Float.RawExponent
>>> > should be UInt.
>>> >
>>> > Why aren't they also just UInt64 and UInt32, resp.?
>>>
>>> Let me flip the question: why would they be UInt64 and UInt32? Absent a
>>> reason to prefer a specific fixed-with type, Swift integers should
>>> generally default to being [U]Int (and ideally Int, but RawExponent is
>>> Unsigned).
>>>
>>> – Steve
>>>
>>>
>>
>>
>
> _______________________________________________
> swift-dev mailing list
> swift-dev@swift.org
> https://lists.swift.org/mailman/listinfo/swift-dev
_______________________________________________
swift-dev mailing list
swift-dev@swift.org
https://lists.swift.org/mailman/listinfo/swift-dev
