On Thu, 12 Jun 2025, Patrick Palka wrote:
> Changes in v4:
> * Don't pass a projection function throughout the helpers, instead
> create a pass a composite predicate via __make_comp_proj.
>
> -- >8 --
>
> ranges::push_heap, ranges::pop_heap, ranges::make_heap and
> ranges::sort_heap are currently defined in terms of the corresponding
> STL-style algorithms, but this is incorrect because the STL-style
> algorithms rely on the legacy iterator system, and so misbehave when
> passed a narrowly C++20 random access iterator. The other ranges heap
> algos, ranges::is_heap and ranges::is_heap_until, are implemented
> directly already and have no known issues.
>
> This patch reimplements these ranges:: algos directly instead, based
> closely on the legacy stl_heap.h implementation, with the following
> changes for compatibility with the C++20 iterator system:
>
> - handle non-common ranges by computing the corresponding end iterator
> - use std::__invoke when invoking the comparator
> - use ranges::iter_move instead of std::move(*iter)
> - use iter_value_t / iter_difference_t instead of iterator_traits
>
> Besides these changes, the implementation of these algorithms is
> intended to mirror the stl_heap.h implementations, for ease of
> maintenance and review.
>
> Note that we don't explicitly pass the projection function throughout,
> instead we just create and pass a composite predicate via __make_comp_proj.
>
> PR libstdc++/100795
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/ranges_algo.h (__detail::__push_heap): New,
> based on the stl_heap.h implementation.
> (__push_heap_fn::operator()): Reimplement in terms of the above.
> (__detail::__adjust_heap): New, based on the stl_heap.h
> implementation.
> (__deatil::__pop_heap): Likewise.
> (__pop_heap_fn::operator()): Reimplement in terms of the above.
> (__make_heap_fn::operator()): Likewise.
> (__sort_heap_fn::operator()): Likewise.
> * testsuite/25_algorithms/heap/constrained.cc (test03): New
> test.
> ---
> libstdc++-v3/include/bits/ranges_algo.h | 141 ++++++++++++++++--
> .../25_algorithms/heap/constrained.cc | 46 ++++++
> 2 files changed, 171 insertions(+), 16 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/ranges_algo.h
> b/libstdc++-v3/include/bits/ranges_algo.h
> index a62c3cd3954d..4f10501956a7 100644
> --- a/libstdc++-v3/include/bits/ranges_algo.h
> +++ b/libstdc++-v3/include/bits/ranges_algo.h
> @@ -1881,6 +1881,28 @@ namespace ranges
>
> inline constexpr __shuffle_fn shuffle{};
>
> + namespace __detail
> + {
> + template<typename _Iter, typename _Comp>
> + constexpr void
> + __push_heap(_Iter __first,
> + iter_difference_t<_Iter> __holeIndex,
> + iter_difference_t<_Iter> __topIndex,
> + iter_value_t<_Iter> __value,
> + _Comp __comp)
> + {
> + auto __parent = (__holeIndex - 1) / 2;
> + while (__holeIndex > __topIndex
> + && std::__invoke(__comp, *(__first + __parent), __value))
Oops, these __invoke calls aren't necessary anymore, we can just invoke
__comp directly since the functor returned by __make_comp_proj does
__invoke for us. Fixed below.
-- >8 --
Subject: [PATCH v5 1/2] libstdc++: Directly implement ranges::heap algos
[PR100795]
PR libstdc++/100795
libstdc++-v3/ChangeLog:
* include/bits/ranges_algo.h (__detail::__push_heap): New,
based on the stl_heap.h implementation.
(__push_heap_fn::operator()): Reimplement in terms of the above.
(__detail::__adjust_heap): New, based on the stl_heap.h
implementation.
(__deatil::__pop_heap): Likewise.
(__pop_heap_fn::operator()): Reimplement in terms of the above.
(__make_heap_fn::operator()): Likewise.
(__sort_heap_fn::operator()): Likewise.
* testsuite/25_algorithms/heap/constrained.cc (test03): New
test.
---
libstdc++-v3/include/bits/ranges_algo.h | 140 ++++++++++++++++--
.../25_algorithms/heap/constrained.cc | 46 ++++++
2 files changed, 170 insertions(+), 16 deletions(-)
diff --git a/libstdc++-v3/include/bits/ranges_algo.h
b/libstdc++-v3/include/bits/ranges_algo.h
index a62c3cd3954d..735142a6c702 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -1881,6 +1881,28 @@ namespace ranges
inline constexpr __shuffle_fn shuffle{};
+ namespace __detail
+ {
+ template<typename _Iter, typename _Comp>
+ constexpr void
+ __push_heap(_Iter __first,
+ iter_difference_t<_Iter> __holeIndex,
+ iter_difference_t<_Iter> __topIndex,
+ iter_value_t<_Iter> __value,
+ _Comp __comp)
+ {
+ auto __parent = (__holeIndex - 1) / 2;
+ while (__holeIndex > __topIndex
+ && __comp(*(__first + __parent), __value))
+ {
+ *(__first + __holeIndex) = ranges::iter_move(__first + __parent);
+ __holeIndex = __parent;
+ __parent = (__holeIndex - 1) / 2;
+ }
+ *(__first + __holeIndex) = std::move(__value);
+ }
+ } // namespace __detail
+
struct __push_heap_fn
{
template<random_access_iterator _Iter, sentinel_for<_Iter> _Sent,
@@ -1890,10 +1912,17 @@ namespace ranges
operator()(_Iter __first, _Sent __last,
_Comp __comp = {}, _Proj __proj = {}) const
{
- auto __lasti = ranges::next(__first, __last);
- std::push_heap(__first, __lasti,
- __detail::__make_comp_proj(__comp, __proj));
- return __lasti;
+ if constexpr (!same_as<_Iter, _Sent>)
+ return (*this)(__first, ranges::next(__first, __last),
+ std::move(__comp), std::move(__proj));
+ else
+ {
+ auto __comp_proj = __detail::__make_comp_proj(__comp, __proj);
+ __detail::__push_heap(__first, (__last - __first) - 1,
+ 0, ranges::iter_move(__last - 1),
+ __comp_proj);
+ return __last;
+ }
}
template<random_access_range _Range,
@@ -1909,6 +1938,48 @@ namespace ranges
inline constexpr __push_heap_fn push_heap{};
+ namespace __detail
+ {
+ template<typename _Iter, typename _Comp>
+ constexpr void
+ __adjust_heap(_Iter __first,
+ iter_difference_t<_Iter> __holeIndex,
+ iter_difference_t<_Iter> __len,
+ iter_value_t<_Iter> __value,
+ _Comp __comp)
+ {
+ auto __topIndex = __holeIndex;
+ auto __secondChild = __holeIndex;
+ while (__secondChild < (__len - 1) / 2)
+ {
+ __secondChild = 2 * (__secondChild + 1);
+ if (__comp(*(__first + __secondChild),
+ *(__first + (__secondChild - 1))))
+ __secondChild--;
+ *(__first + __holeIndex) = ranges::iter_move(__first +
__secondChild);
+ __holeIndex = __secondChild;
+ }
+ if ((__len & 1) == 0 && __secondChild == (__len - 2) / 2)
+ {
+ __secondChild = 2 * (__secondChild + 1);
+ *(__first + __holeIndex) = ranges::iter_move(__first +
(__secondChild - 1));
+ __holeIndex = __secondChild - 1;
+ }
+ __detail::__push_heap(__first, __holeIndex, __topIndex,
+ std::move(__value), __comp);
+ }
+
+ template<typename _Iter, typename _Comp>
+ constexpr void
+ __pop_heap(_Iter __first, _Iter __last, _Iter __result, _Comp __comp)
+ {
+ iter_value_t<_Iter> __value = ranges::iter_move(__result);
+ *__result = ranges::iter_move(__first);
+ __detail::__adjust_heap(__first, 0, __last - __first,
+ std::move(__value), __comp);
+ }
+ } // namespace __detail
+
struct __pop_heap_fn
{
template<random_access_iterator _Iter, sentinel_for<_Iter> _Sent,
@@ -1918,10 +1989,18 @@ namespace ranges
operator()(_Iter __first, _Sent __last,
_Comp __comp = {}, _Proj __proj = {}) const
{
- auto __lasti = ranges::next(__first, __last);
- std::pop_heap(__first, __lasti,
- __detail::__make_comp_proj(__comp, __proj));
- return __lasti;
+ if constexpr (!same_as<_Iter, _Sent>)
+ return (*this)(__first, ranges::next(__first, __last),
+ std::move(__comp), std::move(__proj));
+ else
+ {
+ if (__last - __first > 1)
+ {
+ auto __comp_proj = __detail::__make_comp_proj(__comp, __proj);
+ __detail::__pop_heap(__first, __last - 1, __last - 1,
__comp_proj);
+ }
+ return __last;
+ }
}
template<random_access_range _Range,
@@ -1946,10 +2025,29 @@ namespace ranges
operator()(_Iter __first, _Sent __last,
_Comp __comp = {}, _Proj __proj = {}) const
{
- auto __lasti = ranges::next(__first, __last);
- std::make_heap(__first, __lasti,
- __detail::__make_comp_proj(__comp, __proj));
- return __lasti;
+ if constexpr (!same_as<_Iter, _Sent>)
+ return (*this)(__first, ranges::next(__first, __last),
+ std::move(__comp), std::move(__proj));
+ else
+ {
+ const auto __len = __last - __first;
+ if (__len < 2)
+ return __last;
+
+ auto __comp_proj = __detail::__make_comp_proj(__comp, __proj);
+ auto __parent = (__len - 2) / 2;
+ while (true)
+ {
+ iter_value_t<_Iter> __value = ranges::iter_move(__first +
__parent);
+ __detail::__adjust_heap(__first, __parent, __len,
+ std::move(__value),
+ __comp_proj);
+ if (__parent == 0)
+ break;
+ __parent--;
+ }
+ return __last;
+ }
}
template<random_access_range _Range,
@@ -1974,10 +2072,20 @@ namespace ranges
operator()(_Iter __first, _Sent __last,
_Comp __comp = {}, _Proj __proj = {}) const
{
- auto __lasti = ranges::next(__first, __last);
- std::sort_heap(__first, __lasti,
- __detail::__make_comp_proj(__comp, __proj));
- return __lasti;
+ if constexpr (!same_as<_Iter, _Sent>)
+ return (*this)(__first, ranges::next(__first, __last),
+ std::move(__comp), std::move(__proj));
+ else
+ {
+ auto __comp_proj = __detail::__make_comp_proj(__comp, __proj);
+ _Iter __ret = __last;
+ while (__last - __first > 1)
+ {
+ --__last;
+ __detail::__pop_heap(__first, __last, __last, __comp_proj);
+ }
+ return __ret;
+ }
}
template<random_access_range _Range,
diff --git a/libstdc++-v3/testsuite/25_algorithms/heap/constrained.cc
b/libstdc++-v3/testsuite/25_algorithms/heap/constrained.cc
index 8037a2db6b80..5486c8552d03 100644
--- a/libstdc++-v3/testsuite/25_algorithms/heap/constrained.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/heap/constrained.cc
@@ -20,6 +20,7 @@
#include <algorithm>
#include <random>
+#include <ranges>
#include <testsuite_hooks.h>
#include <testsuite_iterators.h>
@@ -97,10 +98,55 @@ test02()
return ok;
}
+constexpr bool
+test03()
+{
+ // PR libstdc++/100795 - ranges::heap algos should not use std::heap directly
+#if __SIZEOF_INT128__
+ auto v = std::views::iota(__int128(0), __int128(20));
+#else
+ auto v = std::views::iota(0ll, 20ll);
+#endif
+
+ int storage[20] = {2,5,4,3,1,6,7,9,10,8,11,14,12,13,15,16,18,0,19,17};
+ auto w = v | std::views::transform([&](auto i) -> int& { return storage[i];
});
+ using type = decltype(w);
+ using cat =
std::iterator_traits<std::ranges::iterator_t<type>>::iterator_category;
+ static_assert( std::same_as<cat, std::output_iterator_tag> );
+ static_assert( std::ranges::random_access_range<type> );
+
+ for (int i = 1; i < 20; i++)
+ ranges::push_heap(w.begin(), w.begin() + i);
+ ranges::sort_heap(w);
+ VERIFY( ranges::equal(w, v) );
+ ranges::make_heap(w);
+ auto it = ranges::pop_heap(w);
+ VERIFY( it[-1] == 19 );
+
+ for (int i = 1; i < 20; i++)
+ ranges::push_heap(w.begin(), w.begin() + i, std::ranges::greater{});
+ ranges::sort_heap(w, std::ranges::greater{});
+ VERIFY( ranges::equal(w, v | std::views::reverse) );
+ ranges::make_heap(w, std::ranges::greater{});
+ it = ranges::pop_heap(w, std::ranges::greater{});
+ VERIFY( it[-1] == 0 );
+
+ for (int i = 1; i < 20; i++)
+ ranges::push_heap(w.begin(), w.begin() + i, std::ranges::greater{},
std::negate{});
+ ranges::sort_heap(w, std::ranges::greater{}, std::negate{});
+ VERIFY( ranges::equal(w, v) );
+ ranges::make_heap(w, std::ranges::greater{}, std::negate{});
+ it = ranges::pop_heap(w, std::ranges::greater{}, std::negate{});
+ VERIFY( it[-1] == 19 );
+
+ return true;
+}
+
int
main()
{
test01<test_range>();
test01<test_container>();
static_assert(test02());
+ static_assert(test03());
}
--
2.50.0.rc2
