[libcxx-commits] [libcxx] [libc++][ranges] Implement `ranges::stride_view`. (PR #65200)

[Christopher Di Bella via libcxx-commits]

================
@@ -0,0 +1,396 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___RANGES_STRIDE_VIEW_H
+#define _LIBCPP___RANGES_STRIDE_VIEW_H
+
+#include "__concepts/relation.h"
+#include "__functional/ranges_operations.h"
+#include "__iterator/indirectly_comparable.h"
+#include <__config>
+
+#include <__compare/three_way_comparable.h>
+#include <__concepts/convertible_to.h>
+#include <__concepts/derived_from.h>
+#include <__concepts/equality_comparable.h>
+#include <__functional/bind_back.h>
+#include <__functional/operations.h>
+#include <__iterator/advance.h>
+#include <__iterator/concepts.h>
+#include <__iterator/default_sentinel.h>
+#include <__iterator/distance.h>
+#include <__iterator/iter_move.h>
+#include <__iterator/iter_swap.h>
+#include <__iterator/iterator_traits.h>
+#include <__ranges/access.h>
+#include <__ranges/all.h>
+#include <__ranges/concepts.h>
+#include <__ranges/range_adaptor.h>
+#include <__ranges/view_interface.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+namespace ranges {
+
+template <class _Value>
+_LIBCPP_HIDE_FROM_ABI constexpr _Value __div_ceil(_Value __left, _Value __right) {
+  _Value __r = __left / __right;
+  if (__left % __right) {
+    __r++;
+  }
+  return __r;
+}
+
+template <input_range _View>
+  requires view<_View>
+class stride_view : public view_interface<stride_view<_View>> {
+  _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View();
+  range_difference_t<_View> __stride_     = 0;
+
+  template <bool _Const>
+  class __iterator;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI constexpr explicit stride_view(_View __base, range_difference_t<_View> __stride)
+      : __base_(std::move(__base)), __stride_(__stride) {
+    _LIBCPP_ASSERT_UNCATEGORIZED(__stride > 0, "The value of stride must be greater than 0");
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
+    requires copy_constructible<_View>
+  {
+    return __base_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr range_difference_t<_View> stride() const noexcept { return __stride_; }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto begin()
+    requires(!__simple_view<_View>)
+  {
+    return __iterator<false>(this, ranges::begin(__base_), 0);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
+    requires range<const _View>
+  {
+    return __iterator<true>(this, ranges::begin(__base_), 0);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto end()
+    requires(!__simple_view<_View>)
+  {
+    if constexpr (common_range<_View> && sized_range<_View> && forward_range<_View>) {
+      auto __missing = (__stride_ - ranges::distance(__base_) % __stride_) % __stride_;
+      return __iterator<false>(this, ranges::end(__base_), __missing);
+    } else if constexpr (common_range<_View> && !bidirectional_range<_View>) {
+      return __iterator<false>(this, ranges::end(__base_), 0);
+    } else {
+      return default_sentinel;
+    }
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
+    requires(range<const _View>)
+  {
+    if constexpr (common_range<const _View> && sized_range<const _View> && forward_range<const _View>) {
+      auto __missing = (__stride_ - ranges::distance(__base_) % __stride_) % __stride_;
+      return __iterator<true>(this, ranges::end(__base_), __missing);
+    } else if constexpr (common_range<_View> && !bidirectional_range<_View>) {
+      return __iterator<true>(this, ranges::end(__base_), 0);
+    } else {
+      return default_sentinel;
+    }
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto size()
+    requires sized_range<_View>
+  {
+    return std::__to_unsigned_like(ranges::__div_ceil(ranges::distance(__base_), __stride_));
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto size() const
+    requires sized_range<const _View>
+  {
+    return std::__to_unsigned_like(ranges::__div_ceil(ranges::distance(__base_), __stride_));
+  }
+}; // class stride_view
+
+template <class _Range>
+stride_view(_Range&&, range_difference_t<_Range>) -> stride_view<views::all_t<_Range>>;
+
+template <class _View>
+struct __stride_iterator_category {};
+
+template <forward_range _View>
+struct __stride_iterator_category<_View> {
+  using _Cat = typename iterator_traits<iterator_t<_View>>::iterator_category;
+  using iterator_category =
+      _If<derived_from<_Cat, random_access_iterator_tag>,
+          random_access_iterator_tag,
+          /* else */ _Cat >;
+};
+
+template <input_range _View>
+  requires view<_View>
+template <bool _Const>
+class stride_view<_View>::__iterator : public __stride_iterator_category<_View> {
+  using _Parent = __maybe_const<_Const, stride_view<_View>>;
+  using _Base   = __maybe_const<_Const, _View>;
+
+  _LIBCPP_NO_UNIQUE_ADDRESS iterator_t<_Base> __current_     = iterator_t<_Base>();
+  _LIBCPP_NO_UNIQUE_ADDRESS ranges::sentinel_t<_Base> __end_ = ranges::sentinel_t<_Base>();
+  range_difference_t<_Base> __stride_                        = 0;
+  range_difference_t<_Base> __missing_                       = 0;
+
+  friend stride_view;
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __iterator(
+      _Parent* __parent, ranges::iterator_t<_Base> __current, range_difference_t<_Base> __missing)
+      : __current_(std::move(__current)),
+        __end_(ranges::end(__parent->__base_)),
+        __stride_(__parent->__stride_),
+        __missing_(__missing) {}
+
+  static consteval auto __get_stride_view_iterator_concept() {
+    if constexpr (random_access_range<_Base>) {
+      return random_access_iterator_tag{};
+    } else if constexpr (bidirectional_range<_Base>) {
+      return bidirectional_iterator_tag{};
+    } else if constexpr (forward_range<_Base>) {
+      return forward_iterator_tag{};
+    } else {
+      return input_iterator_tag{};
+    }
+  }
+
+public:
+  using difference_type  = range_difference_t<_Base>;
+  using value_type       = range_value_t<_Base>;
+  using iterator_concept = decltype(__get_stride_view_iterator_concept());
+  // using iterator_category = inherited;
+
+  _LIBCPP_HIDE_FROM_ABI __iterator()
+    requires default_initializable<iterator_t<_Base>>
+  = default;
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __iterator(__iterator<!_Const> __i)
+    requires _Const && convertible_to<ranges::iterator_t<_View>, iterator_t<_Base>> &&
+                 convertible_to<sentinel_t<_View>, sentinel_t<_Base>>
+      : __current_(std::move(__i.__current_)),
+        __end_(std::move(__i.__end_)),
+        __stride_(__i.__stride_),
+        __missing_(__i.__missing_) {}
+
+  _LIBCPP_HIDE_FROM_ABI constexpr iterator_t<_Base> const& base() const& noexcept { return __current_; }
+  _LIBCPP_HIDE_FROM_ABI constexpr iterator_t<_Base> base() && { return std::move(__current_); }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr decltype(auto) operator*() const {
----------------
cjdb wrote:

Please mark as `_LIBCPP_NODISCARD`.

https://github.com/llvm/llvm-project/pull/65200