Date: Thu, 7 Aug 2025 21:59:27 +0200
> On 7 Aug 2025, at 21:44, Oliver Hunt <oliver_at_[hidden]> wrote:
>
>> On Aug 7, 2025, at 11:45 AM, Hans Åberg <haberg_1_at_[hidden]> wrote:
>>
>> One reason I choose a[] is to avoid overhead given the low programming level. This excludes iterators, as division goes top down, and reverse iterators are offset by one, with lots of hidden additions.
>>
>> Another is that I could not find a good C++ construct that admits switching between dynamic and static allocations. A quick test on std::span shows that problem, but it could be that it can be made to work. Otherwise, I would prefer to keep size and value together, as in std::span.
>
> Adding new pointer based apis just is not something we can reasonably accept at this point, and std::span is exactly equivalent to bounded pointers - can you point to your code (or on godbolt?) showing the difference in codegen?
>
> If there’s a significant difference in codegen that implies an optimizer bug rather than an X-is-bad problem.
I tried changing it in my “div” function, and then the “div32” example I posted failed. So I will have to look at it at some other time.
It is not useful with std::span, because one will always go down to 0. So it is mostly to get a nice interface, but the question is whether it generates an overhead.
>
>> On Aug 7, 2025, at 11:45 AM, Hans Åberg <haberg_1_at_[hidden]> wrote:
>>
>> One reason I choose a[] is to avoid overhead given the low programming level. This excludes iterators, as division goes top down, and reverse iterators are offset by one, with lots of hidden additions.
>>
>> Another is that I could not find a good C++ construct that admits switching between dynamic and static allocations. A quick test on std::span shows that problem, but it could be that it can be made to work. Otherwise, I would prefer to keep size and value together, as in std::span.
>
> Adding new pointer based apis just is not something we can reasonably accept at this point, and std::span is exactly equivalent to bounded pointers - can you point to your code (or on godbolt?) showing the difference in codegen?
>
> If there’s a significant difference in codegen that implies an optimizer bug rather than an X-is-bad problem.
I tried changing it in my “div” function, and then the “div32” example I posted failed. So I will have to look at it at some other time.
It is not useful with std::span, because one will always go down to 0. So it is mostly to get a nice interface, but the question is whether it generates an overhead.
Received on 2025-08-07 19:59:46