1 // Copyright 2019 Hans Dembinski
3 // Distributed under the Boost Software License, Version 1.0.
4 // (See accompanying file LICENSE_1_0.txt
5 // or copy at http://www.boost.org/LICENSE_1_0.txt)
7 #ifndef BOOST_HISTOGRAM_DETAIL_SPAN_HPP
8 #define BOOST_HISTOGRAM_DETAIL_SPAN_HPP
10 #if __cpp_constexpr >= 201603 && __cpp_deduction_guides >= 201703 && \
11 __cpp_lib_nonmember_container_access >= 201411 && __has_include(<span>)
19 } // namespace histogram
22 #else // C++17 span not available, so we use our implementation
24 // to be replaced by boost::span
27 #include <boost/assert.hpp>
28 #include <boost/histogram/detail/non_member_container_access.hpp>
29 #include <initializer_list>
31 #include <type_traits>
37 namespace dtl = ::boost::histogram::detail;
39 static constexpr std::size_t dynamic_extent = ~static_cast<std::size_t>(0);
41 template <class T, std::size_t N>
44 constexpr T* data() noexcept { return begin_; }
45 constexpr const T* data() const noexcept { return begin_; }
46 constexpr std::size_t size() const noexcept { return N; }
49 constexpr span_base(T* b, std::size_t s) noexcept : begin_(b) { BOOST_ASSERT(N == s); }
50 constexpr void set(T* b, std::size_t s) noexcept {
60 class span_base<T, dynamic_extent> {
62 constexpr T* data() noexcept { return begin_; }
63 constexpr const T* data() const noexcept { return begin_; }
64 constexpr std::size_t size() const noexcept { return size_; }
67 constexpr span_base(T* b, std::size_t s) noexcept : begin_(b), size_(s) {}
69 constexpr void set(T* b, std::size_t s) noexcept {
79 template <class T, std::size_t Extent = dynamic_extent>
80 class span : public span_base<T, Extent> {
81 using base = span_base<T, Extent>;
84 using element_type = T;
85 using value_type = std::remove_cv_t<T>;
86 using index_type = std::size_t;
87 using difference_type = std::ptrdiff_t;
89 using const_pointer = const T*;
91 using const_reference = const T&;
92 using iterator = pointer;
93 using const_iterator = const_pointer;
94 using reverse_iterator = std::reverse_iterator<iterator>;
95 using const_reverse_iterator = std::reverse_iterator<const_iterator>;
97 static constexpr std::size_t extent = Extent;
99 template <std::size_t _ = extent,
100 class = std::enable_if_t<(_ == 0 || _ == dynamic_extent)> >
101 constexpr span() noexcept : base(nullptr, 0) {}
103 constexpr span(pointer first, pointer last)
104 : span(first, static_cast<std::size_t>(last - first)) {
105 BOOST_ASSERT(extent == dynamic_extent ||
106 static_cast<difference_type>(extent) == (last - first));
109 constexpr span(pointer ptr, index_type count) : base(ptr, count) {}
111 template <std::size_t N>
112 constexpr span(element_type (&arr)[N]) noexcept : span(dtl::data(arr), N) {
113 static_assert(extent == dynamic_extent || extent == N, "static sizes do not match");
116 template <std::size_t N,
117 class = std::enable_if_t<(extent == dynamic_extent || extent == N)> >
118 constexpr span(std::array<value_type, N>& arr) noexcept : span(dtl::data(arr), N) {}
120 template <std::size_t N,
121 class = std::enable_if_t<(extent == dynamic_extent || extent == N)> >
122 constexpr span(const std::array<value_type, N>& arr) noexcept
123 : span(dtl::data(arr), N) {}
125 template <class Container, class = std::enable_if_t<std::is_convertible<
126 decltype(dtl::size(std::declval<Container>()),
127 dtl::data(std::declval<Container>())),
129 constexpr span(const Container& cont) : span(dtl::data(cont), dtl::size(cont)) {}
131 template <class Container, class = std::enable_if_t<std::is_convertible<
132 decltype(dtl::size(std::declval<Container>()),
133 dtl::data(std::declval<Container>())),
135 constexpr span(Container& cont) : span(dtl::data(cont), dtl::size(cont)) {}
137 template <class U, std::size_t N,
138 class = std::enable_if_t<((extent == dynamic_extent || extent == N) &&
139 std::is_convertible<U, element_type>::value)> >
140 constexpr span(const span<U, N>& s) noexcept : span(s.data(), s.size()) {}
142 template <class U, std::size_t N,
143 class = std::enable_if_t<((extent == dynamic_extent || extent == N) &&
144 std::is_convertible<U, element_type>::value)> >
145 constexpr span(span<U, N>& s) noexcept : span(s.data(), s.size()) {}
147 constexpr span(const span& other) noexcept = default;
149 constexpr iterator begin() { return base::data(); }
150 constexpr const_iterator begin() const { return base::data(); }
151 constexpr const_iterator cbegin() const { return base::data(); }
153 constexpr iterator end() { return base::data() + base::size(); }
154 constexpr const_iterator end() const { return base::data() + base::size(); }
155 constexpr const_iterator cend() const { return base::data() + base::size(); }
157 reverse_iterator rbegin() { return reverse_iterator(end()); }
158 const_reverse_iterator rbegin() const { return reverse_iterator(end()); }
159 const_reverse_iterator crbegin() { return reverse_iterator(end()); }
161 reverse_iterator rend() { return reverse_iterator(begin()); }
162 const_reverse_iterator rend() const { return reverse_iterator(begin()); }
163 const_reverse_iterator crend() { return reverse_iterator(begin()); }
165 constexpr reference front() { *base::data(); }
166 constexpr reference back() { *(base::data() + base::size() - 1); }
168 constexpr reference operator[](index_type idx) const { return base::data()[idx]; }
170 constexpr std::size_t size_bytes() const noexcept {
171 return base::size() * sizeof(element_type);
174 constexpr bool empty() const noexcept { return base::size() == 0; }
176 template <std::size_t Count>
177 constexpr span<element_type, Count> first() const {
178 BOOST_ASSERT(Count <= base::size());
179 return span<element_type, Count>(base::data(), Count);
182 constexpr span<element_type, dynamic_extent> first(std::size_t count) const {
183 BOOST_ASSERT(count <= base::size());
184 return span<element_type, dynamic_extent>(base::data(), count);
187 template <std::size_t Count>
188 constexpr span<element_type, Count> last() const {
189 BOOST_ASSERT(Count <= base::size());
190 return span<element_type, Count>(base::data() + base::size() - Count, Count);
193 constexpr span<element_type, dynamic_extent> last(std::size_t count) const {
194 BOOST_ASSERT(count <= base::size());
195 return span<element_type, dynamic_extent>(base::data() + base::size() - count, count);
198 template <std::size_t Offset, std::size_t Count = dynamic_extent>
199 constexpr span<element_type,
200 (Count != dynamic_extent
202 : (extent != dynamic_extent ? extent - Offset : dynamic_extent))>
204 BOOST_ASSERT(Offset <= base::size());
205 constexpr std::size_t E =
206 (Count != dynamic_extent
208 : (extent != dynamic_extent ? extent - Offset : dynamic_extent));
209 BOOST_ASSERT(E == dynamic_extent || E <= base::size());
210 return span<element_type, E>(base::data() + Offset,
211 Count == dynamic_extent ? base::size() - Offset : Count);
214 constexpr span<element_type, dynamic_extent> subspan(
215 std::size_t offset, std::size_t count = dynamic_extent) const {
216 BOOST_ASSERT(offset <= base::size());
217 const std::size_t s = count == dynamic_extent ? base::size() - offset : count;
218 BOOST_ASSERT(s <= base::size());
219 return span<element_type, dynamic_extent>(base::data() + offset, s);
223 } // namespace detail
224 } // namespace histogram
229 #include <boost/histogram/detail/non_member_container_access.hpp>
233 namespace histogram {
236 namespace dtl = ::boost::histogram::detail;
239 auto make_span(T* begin, T* end) {
240 return dtl::span<T>{begin, end};
244 auto make_span(T* begin, std::size_t size) {
245 return dtl::span<T>{begin, size};
248 template <class Container, class = decltype(dtl::size(std::declval<Container>()),
249 dtl::data(std::declval<Container>()))>
250 auto make_span(const Container& cont) {
251 return make_span(dtl::data(cont), dtl::size(cont));
254 template <class T, std::size_t N>
255 auto make_span(T (&arr)[N]) {
256 return dtl::span<T, N>(arr, N);
259 } // namespace detail
260 } // namespace histogram