On Tue, May 20, 2025 at 3:17 PM Tomasz Kaminski <tkami...@redhat.com> wrote:
>
>
> On Tue, May 20, 2025 at 3:07 PM Patrick Palka <ppa...@redhat.com> wrote:
>
>> On Tue, 20 May 2025, Tomasz Kaminski wrote:
>>
>> >
>> >
>> > On Mon, May 19, 2025 at 6:06 PM Patrick Palka <ppa...@redhat.com>
>> wrote:
>> > On Mon, 19 May 2025, Patrick Palka wrote:
>> >
>> > > Changes in v3:
>> > > * Use the forward_range code path for a (non-sized)
>> bidirectional
>> > > haystack, since it's slightly fewer increments/decrements
>> > > overall.
>> > > * Fix wrong iter_difference_t cast in starts_with.
>> > >
>> > > Changes in v2:
>> > > Addressed Tomasz's review comments, namely:
>> > > * Added explicit iter_difference_t casts
>> > > * Made _S_impl member private
>> > > * Optimized sized bidirectional case of ends_with
>> > > * Rearranged control flow of starts_with::_S_impl
>> > >
>> > > Still left to do:
>> > > * Add tests for integer-class types
>> > > * Still working on a better commit description ;)
>> > >
>> > > -- >8 --
>> > >
>> > > libstdc++-v3/ChangeLog:
>> > >
>> > > * include/bits/ranges_algo.h (__starts_with_fn,
>> starts_with):
>> > > Define.
>> > > (__ends_with_fn, ends_with): Define.
>> > > * include/bits/version.def (ranges_starts_ends_with):
>> Define.
>> > > * include/bits/version.h: Regenerate.
>> > > * include/std/algorithm: Provide
>> __cpp_lib_ranges_starts_ends_with.
>> > > * src/c++23/std.cc.in (ranges::starts_with): Export.
>> > > (ranges::ends_with): Export.
>> > > * testsuite/25_algorithms/ends_with/1.cc: New test.
>> > > * testsuite/25_algorithms/starts_with/1.cc: New test.
>> > > ---
>> > > libstdc++-v3/include/bits/ranges_algo.h | 236
>> ++++++++++++++++++
>> > > libstdc++-v3/include/bits/version.def | 8 +
>> > > libstdc++-v3/include/bits/version.h | 10 +
>> > > libstdc++-v3/include/std/algorithm | 1 +
>> > > libstdc++-v3/src/c++23/std.cc.in | 4 +
>> > > .../testsuite/25_algorithms/ends_with/1.cc | 129 ++++++++++
>> > > .../testsuite/25_algorithms/starts_with/1.cc | 128 ++++++++++
>> > > 7 files changed, 516 insertions(+)
>> > > create mode 100644
>> libstdc++-v3/testsuite/25_algorithms/ends_with/1.cc
>> > > create mode 100644
>> libstdc++-v3/testsuite/25_algorithms/starts_with/1.cc
>> > >
>> > > diff --git a/libstdc++-v3/include/bits/ranges_algo.h
>> b/libstdc++-v3/include/bits/ranges_algo.h
>> > > index f36e7dd59911..54646ae62f7e 100644
>> > > --- a/libstdc++-v3/include/bits/ranges_algo.h
>> > > +++ b/libstdc++-v3/include/bits/ranges_algo.h
>> > > @@ -438,6 +438,242 @@ namespace ranges
>> > >
>> > > inline constexpr __search_n_fn search_n{};
>> > >
>> > > +#if __glibcxx_ranges_starts_ends_with // C++ >= 23
>> > > + struct __starts_with_fn
>> > > + {
>> > > + template<input_iterator _Iter1, sentinel_for<_Iter1>
>> _Sent1,
>> > > + input_iterator _Iter2, sentinel_for<_Iter2> _Sent2,
>> > > + typename _Pred = ranges::equal_to,
>> > > + typename _Proj1 = identity, typename _Proj2 =
>> identity>
>> > > + requires indirectly_comparable<_Iter1, _Iter2, _Pred,
>> _Proj1, _Proj2>
>> > > + constexpr bool
>> > > + operator()(_Iter1 __first1, _Sent1 __last1,
>> > > + _Iter2 __first2, _Sent2 __last2, _Pred __pred =
>> {},
>> > > + _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
>> > > + {
>> > > + iter_difference_t<_Iter1> __n1 = -1;
>> > > + iter_difference_t<_Iter2> __n2 = -1;
>> > > + if constexpr (sized_sentinel_for<_Sent1, _Iter1>)
>> > > + __n1 = __last1 - __first1;
>> > > + if constexpr (sized_sentinel_for<_Sent2, _Iter2>)
>> > > + __n2 = __last2 - __first2;
>> > > + return _S_impl(std::move(__first1), __last1, __n1,
>> > > + std::move(__first2), __last2, __n2,
>> > > + std::move(__pred),
>> > > + std::move(__proj1), std::move(__proj2));
>> > > + }
>> > > +
>> > > + template<input_range _Range1, input_range _Range2,
>> > > + typename _Pred = ranges::equal_to,
>> > > + typename _Proj1 = identity, typename _Proj2 =
>> identity>
>> > > + requires indirectly_comparable<iterator_t<_Range1>,
>> iterator_t<_Range2>,
>> > > + _Pred, _Proj1, _Proj2>
>> > > + constexpr bool
>> > > + operator()(_Range1&& __r1, _Range2&& __r2, _Pred __pred
>> = {},
>> > > + _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
>> > > + {
>> > > + range_difference_t<_Range1> __n1 = -1;
>> > > + range_difference_t<_Range1> __n2 = -1;
>> > > + if constexpr (sized_range<_Range1>)
>> > > + __n1 = ranges::size(__r1);
>> > > + if constexpr (sized_range<_Range2>)
>> > > + __n2 = ranges::size(__r2);
>> > > + return _S_impl(ranges::begin(__r1), ranges::end(__r1),
>> __n1,
>> > > + ranges::begin(__r2), ranges::end(__r2),
>> __n2,
>> > > + std::move(__pred),
>> > > + std::move(__proj1), std::move(__proj2));
>> > > + }
>> > > +
>> > > + private:
>> > > + template<typename _Iter1, typename _Sent1, typename
>> _Iter2, typename _Sent2,
>> > > + typename _Pred,
>> > > + typename _Proj1, typename _Proj2>
>> > > + static constexpr bool
>> > > + _S_impl(_Iter1 __first1, _Sent1 __last1,
>> iter_difference_t<_Iter1> __n1,
>> > > + _Iter2 __first2, _Sent2 __last2,
>> iter_difference_t<_Iter2> __n2,
>> > > + _Pred __pred,
>> > > + _Proj1 __proj1, _Proj2 __proj2)
>> > > + {
>> > > + if (__first2 == __last2) [[unlikely]]
>> > > + return true;
>> > > + else if (__n1 == -1 || __n2 == -1)
>> > > + return ranges::mismatch(std::move(__first1), __last1,
>> > > + std::move(__first2), __last2,
>> > > + std::move(__pred),
>> > > + std::move(__proj1),
>> std::move(__proj2)).in2 == __last2;
>> > > + else if (__n1 < __n2)
>> > > + return false;
>> > > + else if constexpr (random_access_iterator<_Iter1>)
>> > > + return ranges::equal(__first1, __first1 +
>> iter_difference_t<_Iter1>(__n2),
>> > > + std::move(__first2), __last2,
>> > > + std::move(__pred),
>> > > + std::move(__proj1),
>> std::move(__proj2));
>> > > + else
>> > > + return
>> ranges::equal(counted_iterator(std::move(__first1),
>> > > +
>> iter_difference_t<_Iter1>(__n2)),
>> > > + default_sentinel,
>> > > + std::move(__first2), __last2,
>> > > + std::move(__pred),
>> > > + std::move(__proj1),
>> std::move(__proj2));
>> > > + }
>> > > + };
>> > > +
>> > > + inline constexpr __starts_with_fn starts_with{};
>> > > +
>> > > + struct __ends_with_fn
>> > > + {
>> > > + template<input_iterator _Iter1, sentinel_for<_Iter1>
>> _Sent1,
>> > > + input_iterator _Iter2, sentinel_for<_Iter2> _Sent2,
>> > > + typename _Pred = ranges::equal_to,
>> > > + typename _Proj1 = identity, typename _Proj2 =
>> identity>
>> > > + requires (forward_iterator<_Iter1> ||
>> sized_sentinel_for<_Sent1, _Iter1>)
>> > > + && (forward_iterator<_Iter2> ||
>> sized_sentinel_for<_Sent2, _Iter2>)
>> > > + && indirectly_comparable<_Iter1, _Iter2, _Pred, _Proj1,
>> _Proj2>
>> > > + constexpr bool
>> > > + operator()(_Iter1 __first1, _Sent1 __last1,
>> > > + _Iter2 __first2, _Sent2 __last2, _Pred __pred =
>> {},
>> > > + _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
>> > > + {
>> > > + iter_difference_t<_Iter1> __n1 = -1;
>> > > + iter_difference_t<_Iter2> __n2 = -1;
>> > > + if constexpr (sized_sentinel_for<_Sent1, _Iter1>)
>> > > + __n1 = __last1 - __first1;
>> > > + if constexpr (sized_sentinel_for<_Sent2, _Iter2>)
>> > > + __n2 = __last2 - __first2;
>> > > + return _S_impl(std::move(__first1), __last1, __n1,
>> > > + std::move(__first2), __last2, __n2,
>> > > + std::move(__pred),
>> > > + std::move(__proj1), std::move(__proj2));
>> > > + }
>> > > +
>> > > + template<input_range _Range1, input_range _Range2,
>> > > + typename _Pred = ranges::equal_to,
>> > > + typename _Proj1 = identity, typename _Proj2 =
>> identity>
>> > > + requires (forward_range<_Range1> || sized_range<_Range1>)
>> > > + && (forward_range<_Range2> || sized_range<_Range2>)
>> > > + && indirectly_comparable<iterator_t<_Range1>,
>> iterator_t<_Range2>,
>> > > + _Pred, _Proj1, _Proj2>
>> > > + constexpr bool
>> > > + operator()(_Range1&& __r1, _Range2&& __r2, _Pred __pred
>> = {},
>> > > + _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const
>> > > + {
>> > > + range_difference_t<_Range1> __n1 = -1;
>> > > + range_difference_t<_Range1> __n2 = -1;
>> > > + if constexpr (sized_range<_Range1>)
>> > > + __n1 = ranges::size(__r1);
>> > > + if constexpr (sized_range<_Range2>)
>> > > + __n2 = ranges::size(__r2);
>> > > + return _S_impl(ranges::begin(__r1), ranges::end(__r1),
>> __n1,
>> > > + ranges::begin(__r2), ranges::end(__r2),
>> __n2,
>> > > + std::move(__pred),
>> > > + std::move(__proj1), std::move(__proj2));
>> > > + }
>> > > +
>> > > + private:
>> > > + template<typename _Iter1, typename _Sent1,
>> > > + typename _Iter2, typename _Sent2,
>> > > + typename _Pred,
>> > > + typename _Proj1, typename _Proj2>
>> > > + static constexpr bool
>> > > + _S_impl(_Iter1 __first1, _Sent1 __last1,
>> iter_difference_t<_Iter1> __n1,
>> > > + _Iter2 __first2, _Sent2 __last2,
>> iter_difference_t<_Iter2> __n2,
>> > > + _Pred __pred,
>> > > + _Proj1 __proj1, _Proj2 __proj2)
>> > > + {
>> > > + if (__first2 == __last2) [[unlikely]]
>> > > + return true;
>> > > +
>> > > + if (__n2 == -1)
>> > > + {
>> > > + if constexpr (forward_iterator<_Iter2>)
>> > > + __n2 = ranges::distance(__first2, __last2);
>> > > + else
>> > > + // Size is known and passed by the caller.
>> > > + __builtin_unreachable();
>> > > + }
>> > > +
>> > > + if (__n1 != -1)
>> > > + {
>> > > + if (__n1 < __n2)
>> > > + return false;
>> > > + if constexpr (random_access_iterator<_Iter1>
>> > > + || !bidirectional_iterator<_Iter1>
>> > > + || !same_as<_Iter1, _Sent1>)
>> >
>> > I begin to wonder what is the benefit of not skipping common
>> bidirectional ranges here?
>> > Code below for random access ranges will call operator- (which is O(1))
>> > and equal. The bidirectional case will decrease the range n2 times.
>> > Should we just check random_access_range?
>>
>> Hmm, but common bidirectional ranges do get skipped in this both-sized
>> code path? The if constexpr condition as written should be true for
>> non-common bidirectional ranges, false for common bidirectional ranges.
>> Common bidirectional ranges currently should always go through the
>> bidirectional_iterator && same_as code path.
>>
> I think I caused misunderstanding, I do not see reason to exclude
> bidirectional
> common ranges here, the random_access_path seem to do more efficient,
> as it's call equal with same arguments, but does only subtraction which is
> O(1)
> instead of n2 decrements.
>
Sorry, I got myself totally confused for a moment by the checks. This only
rejects
bidirectional, common ranges, that are not random access, because them we
can
iterate backwards.
But then iterating backwards is valuable only if n2 < (n1 - n2), and we
could know
that at this point.
And n2 << n1 is fine, if we think of this algorithm as search, but I think
it is closer to
equal.
>> >
>> > Did you mean to optimize bidirectional common not sized ranges, by
>> handling them without computing distance:
>> > i.e. having something like this in beginning (just after first2 ==
>> last2).
>> > if constexpr(bidirectional_iterator<_Iter1> && same_as<_Iter1, _Sent1>
>> > && bidirectional_iterator<_Iter2> && same_as<_Iter2,
>> _Sent2>)
>> > if (n1 != -1 || n2 != -1)
>> > return std::mismatch(make_reverse_iterator(__last1),
>> make_reverse_iterator(__first1),
>> > make_reverse_iterator(__last2),
>> make_reverse_iterator(__first2)).in2.base() == __first2;
>>
>> I didn't consider that but that sounds very worthwhile, I'll try
>> implementing it. I think it should be preferred over the both-sized
>> code path even.
>>
> In that case use starts_with::_S_impl on a reversed iterator. This will
> optimize the sized cases.
>
>>
>> > }
>> > > + {
>> > > + ranges::advance(__first1, __n1 -
>> iter_difference_t<_Iter1>(__n2));
>> > > + return ranges::equal(std::move(__first1), __last1,
>> > > + std::move(__first2), __last2,
>> > > + std::move(__pred),
>> > > + std::move(__proj1),
>> std::move(__proj2));
>> > > + }
>> > > + }
>> > > +
>> > > + if constexpr (bidirectional_iterator<_Iter1> &&
>> same_as<_Iter1, _Sent1>)
>> > > + {
>> > > + _Iter1 __it1 = ranges::next(__first1, __last1);
>> >
>> > We can just initialize __it1 to __last1 now that this code path
>> requires
>> > common-ness.
>> >
>> > > + if (__n1 != -1)
>> > > + ranges::advance(__it1,
>> -iter_difference_t<_Iter1>(__n2), __first1);
>> >
>> > We don't need to use the three-parameter versions of advance here
>> since
>> > we know __n1 >= __n2. Consider these two things fixed
>> >
>> > > + else
>> > > + {
>> > > + // We can't use ranges::advance if the haystack
>> size is
>> > > + // unknown, since we need to detect and return
>> false if
>> > > + // it's smaller than the needle.
>> > > + iter_difference_t<_Iter2> __m = __n2;
>> > > + while (__m != 0 && __it1 != __first1)
>> > > + {
>> > > + --__m;
>> > > + --__it1;
>> > > + }
>> > > + if (__m != 0)
>> > > + return false;
>> > > + }
>> > > + return ranges::equal(__it1, __last1,
>> > > + std::move(__first2), __last2,
>> > > + std::move(__pred),
>> > > + std::move(__proj1),
>> std::move(__proj2));
>> > > + }
>> > > + else if constexpr (forward_iterator<_Iter1>)
>> > > + {
>> > > + _Iter1 __prev_first1;
>> > > + __n1 = 0;
>> > > + while (true)
>> > > + {
>> > > + iter_difference_t<_Iter2> __m = __n2;
>> > > + _Iter1 __it1 = __first1;
>> > > + while (__m != 0 && __it1 != __last1)
>> > > + {
>> > > + ++__n1;
>> > > + --__m;
>> > > + ++__it1;
>> > > + }
>> > > + if (__m != 0)
>> > > + {
>> > > + // __glibcxx_assert(__it1 == __last1);
>> > > + if (__n1 < __n2)
>> > > + return false;
>> > > + __first1 = ranges::next(__prev_first1,
>> > > +
>> iter_difference_t<_Iter1>(__n2 - __m));
>> > > + break;
>> > > + }
>> > > + __prev_first1 = __first1;
>> > > + __first1 = __it1;
>> > > + }
>> > > + return ranges::equal(__first1, __last1,
>> > > + std::move(__first2), __last2,
>> > > + std::move(__pred),
>> > > + std::move(__proj1),
>> std::move(__proj2));
>> > > + }
>> > > + else
>> > > + // If __first1 is non-forward, it must be sized, so it
>> was handled
>> > > + // by the __n1 != -1 case earlier.
>> > > + __builtin_unreachable();
>> > > + }
>> > > +
>> > > + };
>> > > +
>> > > + inline constexpr __ends_with_fn ends_with{};
>> > > +#endif // __glibcxx_ranges_starts_ends_with
>> > > +
>> > > struct __find_end_fn
>> > > {
>> > > template<forward_iterator _Iter1, sentinel_for<_Iter1>
>> _Sent1,
>> > > diff --git a/libstdc++-v3/include/bits/version.def
>> b/libstdc++-v3/include/bits/version.def
>> > > index 6ca148f0488f..8db1967cc184 100644
>> > > --- a/libstdc++-v3/include/bits/version.def
>> > > +++ b/libstdc++-v3/include/bits/version.def
>> > > @@ -1660,6 +1660,14 @@ ftms = {
>> > > };
>> > > };
>> > >
>> > > +ftms = {
>> > > + name = ranges_starts_ends_with;
>> > > + values = {
>> > > + v = 202106;
>> > > + cxxmin = 23;
>> > > + };
>> > > +};
>> > > +
>> > > ftms = {
>> > > name = constexpr_bitset;
>> > > values = {
>> > > diff --git a/libstdc++-v3/include/bits/version.h
>> b/libstdc++-v3/include/bits/version.h
>> > > index 48a090c14a3d..3749528633f2 100644
>> > > --- a/libstdc++-v3/include/bits/version.h
>> > > +++ b/libstdc++-v3/include/bits/version.h
>> > > @@ -1848,6 +1848,16 @@
>> > > #endif /* !defined(__cpp_lib_ranges_find_last) &&
>> defined(__glibcxx_want_ranges_find_last) */
>> > > #undef __glibcxx_want_ranges_find_last
>> > >
>> > > +#if !defined(__cpp_lib_ranges_starts_ends_with)
>> > > +# if (__cplusplus >= 202100L)
>> > > +# define __glibcxx_ranges_starts_ends_with 202106L
>> > > +# if defined(__glibcxx_want_all) ||
>> defined(__glibcxx_want_ranges_starts_ends_with)
>> > > +# define __cpp_lib_ranges_starts_ends_with 202106L
>> > > +# endif
>> > > +# endif
>> > > +#endif /* !defined(__cpp_lib_ranges_starts_ends_with) &&
>> defined(__glibcxx_want_ranges_starts_ends_with) */
>> > > +#undef __glibcxx_want_ranges_starts_ends_with
>> > > +
>> > > #if !defined(__cpp_lib_constexpr_bitset)
>> > > # if (__cplusplus >= 202100L) && _GLIBCXX_HOSTED &&
>> (__cpp_constexpr_dynamic_alloc)
>> > > # define __glibcxx_constexpr_bitset 202202L
>> > > diff --git a/libstdc++-v3/include/std/algorithm
>> b/libstdc++-v3/include/std/algorithm
>> > > index 321a5e22d86b..1563cdf2b17c 100644
>> > > --- a/libstdc++-v3/include/std/algorithm
>> > > +++ b/libstdc++-v3/include/std/algorithm
>> > > @@ -74,6 +74,7 @@
>> > > #define __glibcxx_want_ranges_contains
>> > > #define __glibcxx_want_ranges_find_last
>> > > #define __glibcxx_want_ranges_fold
>> > > +#define __glibcxx_want_ranges_starts_ends_with
>> > > #define __glibcxx_want_robust_nonmodifying_seq_ops
>> > > #define __glibcxx_want_sample
>> > > #define __glibcxx_want_shift
>> > > diff --git a/libstdc++-v3/src/c++23/std.cc.in
>> b/libstdc++-v3/src/c++23/std.cc.in
>> > > index 417c8a1a5626..2e4b3f75234f 100644
>> > > --- a/libstdc++-v3/src/c++23/std.cc.in
>> > > +++ b/libstdc++-v3/src/c++23/std.cc.in
>> > > @@ -506,6 +506,10 @@ export namespace std
>> > > using ranges::find_last;
>> > > using ranges::find_last_if;
>> > > using ranges::find_last_if_not;
>> > > +#endif
>> > > +#if __cpp_lib_ranges_starts_ends_with
>> > > + using ranges::starts_with;
>> > > + using ranges::ends_with;
>> > > #endif
>> > > }
>> > > }
>> > > diff --git
>> a/libstdc++-v3/testsuite/25_algorithms/ends_with/1.cc
>> b/libstdc++-v3/testsuite/25_algorithms/ends_with/1.cc
>> > > new file mode 100644
>> > > index 000000000000..e5714101aecc
>> > > --- /dev/null
>> > > +++ b/libstdc++-v3/testsuite/25_algorithms/ends_with/1.cc
>> > > @@ -0,0 +1,129 @@
>> > > +// { dg-do run { target c++23 } }
>> > > +
>> > > +#include <algorithm>
>> > > +
>> > > +#include <testsuite_hooks.h>
>> > > +#include <testsuite_iterators.h>
>> > > +
>> > > +namespace ranges = std::ranges;
>> > > +
>> > > +template<typename Range1, typename Range2>
>> > > +void
>> > > +test01()
>> > > +{
>> > > + int n[] = {1,2,3,4,5,6,7,8,9,10};
>> > > +
>> > > + Range1 haystack(n, n+10);
>> > > + Range2 needle(n+7, n+10);
>> > > + VERIFY( ranges::ends_with(haystack, needle) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n, n+10);
>> > > + VERIFY( ranges::ends_with(haystack, needle) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+6, n+9);
>> > > + VERIFY( !ranges::ends_with(haystack, needle) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+6, n+9);
>> > > + VERIFY( ranges::ends_with(haystack, needle,
>> > > + [](int n, int m) { return std::abs(n
>> - m) <= 1; }) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+6, n+9);
>> > > + VERIFY( ranges::ends_with(haystack, needle,
>> > > + ranges::equal_to{},
>> > > + [](int n) { return n - 1; }) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+6, n+9);
>> > > + VERIFY( ranges::ends_with(haystack, needle,
>> > > + ranges::equal_to{},
>> > > + std::identity{},
>> > > + [](int n) { return n + 1; }) );
>> > > +
>> > > + haystack = Range1(n, n+5);
>> > > + needle = Range2(n, n+10);
>> > > + VERIFY( !ranges::ends_with(haystack, needle) );
>> > > +}
>> > > +
>> > > +template<typename Range1, typename Range2>
>> > > +void
>> > > +test02()
>> > > +{
>> > > + int n[] = {1,2,3,4,5,6,7,8,9,10};
>> > > +
>> > > + Range1 haystack(n, n+10);
>> > > + Range2 needle(n+7, n+10);
>> > > + VERIFY( ranges::ends_with(haystack.begin(), haystack.end(),
>> > > + needle.begin(), needle.end()) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n, n+10);
>> > > + VERIFY( ranges::ends_with(haystack.begin(), haystack.end(),
>> > > + needle.begin(), needle.end()) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+6, n+9);
>> > > + VERIFY( !ranges::ends_with(haystack.begin(), haystack.end(),
>> > > + needle.begin(), needle.end()) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+6, n+9);
>> > > + VERIFY( ranges::ends_with(haystack.begin(), haystack.end(),
>> > > + needle.begin(), needle.end(),
>> > > + [](int n, int m) { return std::abs(n
>> - m) <= 1; }) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+6, n+9);
>> > > + VERIFY( ranges::ends_with(haystack.begin(), haystack.end(),
>> > > + needle.begin(), needle.end(),
>> > > + ranges::equal_to{},
>> > > + [](int n) { return n - 1; }) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+6, n+9);
>> > > + VERIFY( ranges::ends_with(haystack.begin(), haystack.end(),
>> > > + needle.begin(), needle.end(),
>> > > + ranges::equal_to{},
>> > > + std::identity{},
>> > > + [](int n) { return n + 1; }) );
>> > > +
>> > > + haystack = Range1(n, n+5);
>> > > + needle = Range2(n, n+10);
>> > > + VERIFY( !ranges::ends_with(haystack.begin(), haystack.end(),
>> > > + needle.begin(), needle.end()) );
>> > > +
>> > > + haystack = Range1(n, n+5);
>> > > + needle = Range2(n+10, n+10);
>> > > + VERIFY( ranges::ends_with(haystack.begin(), haystack.end(),
>> > > + needle.begin(), needle.end()) );
>> > > +}
>> > > +
>> > > +int
>> > > +main()
>> > > +{
>> > > + using namespace __gnu_test;
>> > > + using forward = test_forward_range<int>;
>> > > + using input_sized = test_input_sized_range<int>;
>> > > + using input_sized_sent = test_sized_range_sized_sent<int,
>> input_iterator_wrapper>;
>> > > + using random_access = test_random_access_range<int>;
>> > > + using random_access_sized =
>> test_random_access_sized_range<int>;
>> > > + using random_access_sized_sent =
>> test_sized_range_sized_sent<int, random_access_iterator_wrapper>;
>> > > +
>> > > + test01<forward, forward>();
>> > > + test01<random_access, random_access>();
>> > > + test02<forward, forward>();
>> > > + test02<random_access, random_access>();
>> > > +
>> > > + test01<input_sized, input_sized>();
>> > > + test01<random_access_sized, random_access_sized>();
>> > > + // test02<input_sized, input_sized>(); constraint violation
>> > > + test02<random_access_sized, random_access_sized>();
>> > > +
>> > > + test01<input_sized_sent, input_sized_sent>();
>> > > + test01<random_access_sized_sent, random_access_sized_sent>();
>> > > + test02<input_sized_sent, input_sized_sent>();
>> > > + test02<random_access_sized_sent, random_access_sized_sent>();
>> > > +}
>> > > diff --git
>> a/libstdc++-v3/testsuite/25_algorithms/starts_with/1.cc
>> b/libstdc++-v3/testsuite/25_algorithms/starts_with/1.cc
>> > > new file mode 100644
>> > > index 000000000000..805f31ea2b03
>> > > --- /dev/null
>> > > +++ b/libstdc++-v3/testsuite/25_algorithms/starts_with/1.cc
>> > > @@ -0,0 +1,128 @@
>> > > +// { dg-do run { target c++23 } }
>> > > +
>> > > +#include <algorithm>
>> > > +
>> > > +#include <testsuite_hooks.h>
>> > > +#include <testsuite_iterators.h>
>> > > +
>> > > +namespace ranges = std::ranges;
>> > > +
>> > > +template<typename Range1, typename Range2>
>> > > +void
>> > > +test01()
>> > > +{
>> > > + int n[] = {1,2,3,4,5,6,7,8,9,10};
>> > > +
>> > > + Range1 haystack(n, n+10);
>> > > + Range2 needle(n, n+3);
>> > > + VERIFY( ranges::starts_with(haystack, needle) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n, n+10);
>> > > + VERIFY( ranges::starts_with(haystack, needle) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+1, n+4);
>> > > + VERIFY( !ranges::starts_with(haystack, needle) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+1, n+4);
>> > > + VERIFY( ranges::starts_with(haystack, needle,
>> > > + [](int n, int m) { return
>> std::abs(n - m) <= 1; }) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+1, n+4);
>> > > + VERIFY( ranges::starts_with(haystack, needle,
>> > > + ranges::equal_to{},
>> > > + [](int n) { return n + 1; }) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+1, n+4);
>> > > + VERIFY( ranges::starts_with(haystack, needle,
>> > > + ranges::equal_to{},
>> > > + std::identity{},
>> > > + [](int n) { return n - 1; }) );
>> > > +
>> > > + haystack = Range1(n, n+5);
>> > > + needle = Range2(n, n+10);
>> > > + VERIFY( !ranges::starts_with(haystack, needle) );
>> > > +
>> > > + haystack = Range1(n, n+5);
>> > > + needle = Range2(n+10, n+10);
>> > > + VERIFY( ranges::starts_with(haystack, needle) );
>> > > +}
>> > > +
>> > > +template<typename Range1, typename Range2>
>> > > +void
>> > > +test02()
>> > > +{
>> > > + int n[] = {1,2,3,4,5,6,7,8,9,10};
>> > > +
>> > > + Range1 haystack(n, n+10);
>> > > + Range2 needle(n, n+3);
>> > > + VERIFY( ranges::starts_with(haystack.begin(), haystack.end(),
>> > > + needle.begin(), needle.end()) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n, n+10);
>> > > + VERIFY( ranges::starts_with(haystack.begin(), haystack.end(),
>> > > + needle.begin(), needle.end()) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+1, n+4);
>> > > + VERIFY( !ranges::starts_with(haystack.begin(),
>> haystack.end(),
>> > > + needle.begin(), needle.end()) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+1, n+4);
>> > > + VERIFY( ranges::starts_with(haystack.begin(), haystack.end(),
>> > > + needle.begin(), needle.end(),
>> > > + [](int n, int m) { return
>> std::abs(n - m) <= 1; }) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+1, n+4);
>> > > + VERIFY( ranges::starts_with(haystack.begin(), haystack.end(),
>> > > + needle.begin(), needle.end(),
>> > > + ranges::equal_to{},
>> > > + [](int n) { return n + 1; }) );
>> > > +
>> > > + haystack = Range1(n);
>> > > + needle = Range2(n+1, n+4);
>> > > + VERIFY( ranges::starts_with(haystack.begin(), haystack.end(),
>> > > + needle.begin(), needle.end(),
>> > > + ranges::equal_to{},
>> > > + std::identity{},
>> > > + [](int n) { return n - 1; }) );
>> > > +
>> > > + haystack = Range1(n, n+5);
>> > > + needle = Range2(n, n+10);
>> > > + VERIFY( !ranges::starts_with(haystack.begin(),
>> haystack.end(),
>> > > + needle.begin(), needle.end()) );
>> > > +}
>> > > +
>> > > +int
>> > > +main()
>> > > +{
>> > > + using namespace __gnu_test;
>> > > + using input = test_input_range<int>;
>> > > + using input_sized = test_input_sized_range<int>;
>> > > + using input_sized_sent = test_sized_range_sized_sent<int,
>> input_iterator_wrapper>;
>> > > + using random_access = test_random_access_range<int>;
>> > > + using random_access_sized =
>> test_random_access_sized_range<int>;
>> > > + using random_access_sized_sent =
>> test_sized_range_sized_sent<int, random_access_iterator_wrapper>;
>> > > +
>> > > + test01<input, input>();
>> > > + test01<random_access, random_access>();
>> > > + test02<input, input>();
>> > > + test02<random_access, random_access>();
>> > > +
>> > > + test01<input_sized, input_sized>();
>> > > + test01<random_access_sized, random_access_sized>();
>> > > + test02<input_sized, input_sized>();
>> > > + test02<random_access_sized, random_access_sized>();
>> > > +
>> > > + test01<input_sized_sent, input_sized_sent>();
>> > > + test01<random_access_sized_sent, random_access_sized_sent>();
>> > > + test02<input_sized_sent, input_sized_sent>();
>> > > + test02<random_access_sized_sent, random_access_sized_sent>();
>> > > +}
>> > > --
>> > > 2.49.0.608.gcb96e1697a
>> > >
>> > >
>> >
>> >
>> >
>
>
