Re: [PATCH WIP 2/2] libstdc++: Optimize ranges::distance for segmented iterators [PR123211]

On Tue, 14 Jul 2026 at 05:30, Patrick Palka <[email protected]> wrote:
>
> For segmented iterators, ranges::distance is equivalent to the sum of
> ranges::distance of each of its segments.

There's no [PATCH v2 2/2] that supersedes this, right?

OK for trunk if this is the right one.


>
>         PR libstdc++/123211
>
> libstdc++-v3/ChangeLog:
>
>         * include/bits/ranges_base.h (__distance_fn::operator()): For
>         the non-sized-sentinel overload,
> ---
>  libstdc++-v3/include/bits/ranges_base.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/libstdc++-v3/include/bits/ranges_base.h b/libstdc++-v3/include/bits/ranges_base.h
> index ce1c40fc17f6..7f169feaa6b1 100644
> --- a/libstdc++-v3/include/bits/ranges_base.h
> +++ b/libstdc++-v3/include/bits/ranges_base.h
> @@ -994,6 +994,16 @@ namespace ranges
>        constexpr iter_difference_t<_It>
>        operator()[[nodiscard]](_It __first, _Sent __last) const
>        {
> +       if constexpr (__segmented_iterator<_It> && same_as<_It, _Sent>)
> +         {
> +           iter_difference_t<_It> __n = 0;
> +           std::__for_each_segment(__first, __last, [this, &__n](auto __first, auto __last) {
> +             __n += iter_difference_t<_It>(this->operator()(__first, __last));
> +             return __last;
> +           });
> +           return __n;
> +         }
> +
>         iter_difference_t<_It> __n = 0;
>         while (__first != __last)
>           {
> --
> 2.55.0.141.g55526a1826
>