Haha ;)
1) Maybe converting the algorithm into a tail-recursive form should be the
first optimization?
func factorial(_ n: Int, multipliedBy m: Int = 1) -> Int {
return n <= 1 ? m : factorial(n-1, multipliedBy: m*n)
}
2) Using a non-recursive algorithm would improve performance even more, I guess.
3) The third is maybe to use precalculation or an efficient algorithm that
doesn't call `factorial` that often. (Assuming that your use-case isn't just
calculating factorial numbers for fun.) (E.g. if you try to calculate (52 over
3) by using the formula (52!/(49!*3!)) it will be inefficient, and btw it will
crash, because 52! does not fit into an Int. The efficient way is 52*51/2*50/3
("*","/": same precedence, left-associative.)) On my 64-bit computer I cannot
go beyond 20!, factorial(21) gives an EXC_BAD_INSTRUCTION a.k.a. integer
overflow. There is no point in optimizing 20!, and there certainly is no point
in optimizing 40!, at least with Int's.
There is really no point in optimizing that anymore beyond that. A silly
SIMD-optimized algorithm is always worse than a well-designed algorithm
compiled with -O0. If you do standard optimization techniques first, the
advantage of SIMD-instructions for factorial become unmeasurable ;)
However, I agree that special optimizations for numeric computations (SIMD and
other extension) would be cool..
-Michael
> Am 02.08.2016 um 18:37 schrieb Muse M via swift-evolution
> <[email protected]>:
>
> I'm concern if simd could improve factorials code and faster timing.
>
> import simd
> func factorial(n: Int) -> Int {
> return n < 1 ? 1 : n * factorial(n: n - 1)
> }
> print(factorial(n: 40))
>
>
> On Wed, Aug 3, 2016 at 12:00 AM, Charlie Monroe <[email protected]>
> wrote:
> That's a good point. :)
>
>> On Aug 2, 2016, at 5:55 PM, Xiaodi Wu <[email protected]> wrote:
>>
>> I'm going to guess, since Musa mentioned science and engineering, that a
>> good chunk of that work is floating point :)
>>
>>
>> On Tue, Aug 2, 2016 at 10:41 AM, Charlie Monroe via swift-evolution
>> <[email protected]> wrote:
>> Are you using the variants of operators without overflow check? I.e.
>>
>> let num = a &+ b // [1]
>>
>> [1]
>> https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/AdvancedOperators.html
>>
>>
>>
>>> On Aug 2, 2016, at 3:01 AM, Muse M <[email protected]> wrote:
>>>
>>> Have always wonder why Maths in Swift is slower than C and Go, it should be
>>> address with priority if Swift is to be adopt for engineering, financial
>>> and science industry.
>>>
>>> On Tue, Aug 2, 2016 at 4:43 AM, Charlie Monroe via swift-evolution
>>> <[email protected]> wrote:
>>> See
>>> https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160725/025711.html
>>>
>>> From what I understand, the discussion should stay focused on the main
>>> topics for Swift 4 that Chris highlighted in
>>> https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160725/025676.html
>>>
>>> I had several ideas in mind, but am postponing them for Swift 5, seeing the
>>> schedule...
>>>
>>>
>>>> On Aug 1, 2016, at 8:48 PM, Anton Zhilin via swift-evolution
>>>> <[email protected]> wrote:
>>>>
>>>> It was stated that 27th of July was the last date for proposal acceptance,
>>>> 29th of July was the last day for implementation, and 1th of August should
>>>> be the starting day of Swift 3.1-related discussions.
>>>> Am I right? Should we begin?
>>>> _______________________________________________
>>>> swift-evolution mailing list
>>>> [email protected]
>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>
>>>
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>>>
>>>
>>
>>
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>
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