| // Copyright 2017 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef THIRD_PARTY_BASE_SPAN_H_ |
| #define THIRD_PARTY_BASE_SPAN_H_ |
| |
| #include <stddef.h> |
| |
| #include <algorithm> |
| #include <array> |
| #include <iterator> |
| #include <type_traits> |
| #include <utility> |
| |
| #include "core/fxcrt/unowned_ptr.h" |
| #include "third_party/base/check.h" |
| |
| namespace pdfium { |
| |
| template <typename T> |
| class span; |
| |
| namespace internal { |
| |
| template <typename T> |
| struct IsSpanImpl : std::false_type {}; |
| |
| template <typename T> |
| struct IsSpanImpl<span<T>> : std::true_type {}; |
| |
| template <typename T> |
| using IsSpan = IsSpanImpl<typename std::decay<T>::type>; |
| |
| template <typename T> |
| struct IsStdArrayImpl : std::false_type {}; |
| |
| template <typename T, size_t N> |
| struct IsStdArrayImpl<std::array<T, N>> : std::true_type {}; |
| |
| template <typename T> |
| using IsStdArray = IsStdArrayImpl<typename std::decay<T>::type>; |
| |
| template <typename From, typename To> |
| using IsLegalSpanConversion = std::is_convertible<From*, To*>; |
| |
| template <typename Container, typename T> |
| using ContainerHasConvertibleData = |
| IsLegalSpanConversion<typename std::remove_pointer<decltype( |
| std::declval<Container>().data())>::type, |
| T>; |
| template <typename Container> |
| using ContainerHasIntegralSize = |
| std::is_integral<decltype(std::declval<Container>().size())>; |
| |
| template <typename From, typename To> |
| using EnableIfLegalSpanConversion = |
| typename std::enable_if<IsLegalSpanConversion<From, To>::value>::type; |
| |
| // SFINAE check if Container can be converted to a span<T>. Note that the |
| // implementation details of this check differ slightly from the requirements in |
| // the working group proposal: in particular, the proposal also requires that |
| // the container conversion constructor participate in overload resolution only |
| // if two additional conditions are true: |
| // |
| // 1. Container implements operator[]. |
| // 2. Container::value_type matches remove_const_t<element_type>. |
| // |
| // The requirements are relaxed slightly here: in particular, not requiring (2) |
| // means that an immutable span can be easily constructed from a mutable |
| // container. |
| template <typename Container, typename T> |
| using EnableIfSpanCompatibleContainer = |
| typename std::enable_if<!internal::IsSpan<Container>::value && |
| !internal::IsStdArray<Container>::value && |
| ContainerHasConvertibleData<Container, T>::value && |
| ContainerHasIntegralSize<Container>::value>::type; |
| |
| template <typename Container, typename T> |
| using EnableIfConstSpanCompatibleContainer = |
| typename std::enable_if<std::is_const<T>::value && |
| !internal::IsSpan<Container>::value && |
| !internal::IsStdArray<Container>::value && |
| ContainerHasConvertibleData<Container, T>::value && |
| ContainerHasIntegralSize<Container>::value>::type; |
| |
| } // namespace internal |
| |
| // A span is a value type that represents an array of elements of type T. Since |
| // it only consists of a pointer to memory with an associated size, it is very |
| // light-weight. It is cheap to construct, copy, move and use spans, so that |
| // users are encouraged to use it as a pass-by-value parameter. A span does not |
| // own the underlying memory, so care must be taken to ensure that a span does |
| // not outlive the backing store. |
| // |
| // span is somewhat analogous to StringPiece, but with arbitrary element types, |
| // allowing mutation if T is non-const. |
| // |
| // span is implicitly convertible from C++ arrays, as well as most [1] |
| // container-like types that provide a data() and size() method (such as |
| // std::vector<T>). A mutable span<T> can also be implicitly converted to an |
| // immutable span<const T>. |
| // |
| // Consider using a span for functions that take a data pointer and size |
| // parameter: it allows the function to still act on an array-like type, while |
| // allowing the caller code to be a bit more concise. |
| // |
| // For read-only data access pass a span<const T>: the caller can supply either |
| // a span<const T> or a span<T>, while the callee will have a read-only view. |
| // For read-write access a mutable span<T> is required. |
| // |
| // Without span: |
| // Read-Only: |
| // // std::string HexEncode(const uint8_t* data, size_t size); |
| // std::vector<uint8_t> data_buffer = GenerateData(); |
| // std::string r = HexEncode(data_buffer.data(), data_buffer.size()); |
| // |
| // Mutable: |
| // // ssize_t SafeSNPrintf(char* buf, size_t N, const char* fmt, Args...); |
| // char str_buffer[100]; |
| // SafeSNPrintf(str_buffer, sizeof(str_buffer), "Pi ~= %lf", 3.14); |
| // |
| // With span: |
| // Read-Only: |
| // // std::string HexEncode(base::span<const uint8_t> data); |
| // std::vector<uint8_t> data_buffer = GenerateData(); |
| // std::string r = HexEncode(data_buffer); |
| // |
| // Mutable: |
| // // ssize_t SafeSNPrintf(base::span<char>, const char* fmt, Args...); |
| // char str_buffer[100]; |
| // SafeSNPrintf(str_buffer, "Pi ~= %lf", 3.14); |
| // |
| // Spans with "const" and pointers |
| // ------------------------------- |
| // |
| // Const and pointers can get confusing. Here are vectors of pointers and their |
| // corresponding spans (you can always make the span "more const" too): |
| // |
| // const std::vector<int*> => base::span<int* const> |
| // std::vector<const int*> => base::span<const int*> |
| // const std::vector<const int*> => base::span<const int* const> |
| // |
| // Differences from the working group proposal |
| // ------------------------------------------- |
| // |
| // https://wg21.link/P0122 is the latest working group proposal, Chromium |
| // currently implements R6. The biggest difference is span does not support a |
| // static extent template parameter. Other differences are documented in |
| // subsections below. |
| // |
| // Differences from [views.constants]: |
| // - no dynamic_extent constant |
| // |
| // Differences in constants and types: |
| // - no element_type type alias |
| // - no index_type type alias |
| // - no different_type type alias |
| // - no extent constant |
| // |
| // Differences from [span.cons]: |
| // - no constructor from a pointer range |
| // - no constructor from std::array |
| // |
| // Differences from [span.sub]: |
| // - no templated first() |
| // - no templated last() |
| // - no templated subspan() |
| // - using size_t instead of ptrdiff_t for indexing |
| // |
| // Differences from [span.obs]: |
| // - using size_t instead of ptrdiff_t to represent size() |
| // |
| // Differences from [span.elem]: |
| // - no operator ()() |
| // - using size_t instead of ptrdiff_t for indexing |
| |
| // [span], class template span |
| template <typename T> |
| class span { |
| public: |
| using value_type = typename std::remove_cv<T>::type; |
| using pointer = T*; |
| using reference = T&; |
| using iterator = T*; |
| using const_iterator = const T*; |
| using reverse_iterator = std::reverse_iterator<iterator>; |
| using const_reverse_iterator = std::reverse_iterator<const_iterator>; |
| |
| // [span.cons], span constructors, copy, assignment, and destructor |
| constexpr span() noexcept : data_(nullptr), size_(0) {} |
| constexpr span(T* data, size_t size) noexcept : data_(data), size_(size) {} |
| |
| // TODO(dcheng): Implement construction from a |begin| and |end| pointer. |
| template <size_t N> |
| constexpr span(T (&array)[N]) noexcept : span(array, N) {} |
| // TODO(dcheng): Implement construction from std::array. |
| // Conversion from a container that provides |T* data()| and |integral_type |
| // size()|. |
| template <typename Container, |
| typename = internal::EnableIfSpanCompatibleContainer<Container, T>> |
| constexpr span(Container& container) |
| : span(container.data(), container.size()) {} |
| template < |
| typename Container, |
| typename = internal::EnableIfConstSpanCompatibleContainer<Container, T>> |
| span(const Container& container) : span(container.data(), container.size()) {} |
| constexpr span(const span& other) noexcept = default; |
| // Conversions from spans of compatible types: this allows a span<T> to be |
| // seamlessly used as a span<const T>, but not the other way around. |
| template <typename U, typename = internal::EnableIfLegalSpanConversion<U, T>> |
| constexpr span(const span<U>& other) : span(other.data(), other.size()) {} |
| span& operator=(const span& other) noexcept = default; |
| ~span() noexcept { |
| if (!size_) { |
| // Empty spans might point to byte N+1 of a N-byte object, legal for |
| // C pointers but not UnownedPtrs. |
| data_.ReleaseBadPointer(); |
| } |
| } |
| |
| // [span.sub], span subviews |
| const span first(size_t count) const { |
| CHECK(count <= size_); |
| return span(data_.Get(), count); |
| } |
| |
| const span last(size_t count) const { |
| CHECK(count <= size_); |
| return span(data_.Get() + (size_ - count), count); |
| } |
| |
| const span subspan(size_t pos, size_t count = -1) const { |
| const auto npos = static_cast<size_t>(-1); |
| CHECK(pos <= size_); |
| CHECK(count == npos || count <= size_ - pos); |
| return span(data_.Get() + pos, count == npos ? size_ - pos : count); |
| } |
| |
| // [span.obs], span observers |
| constexpr size_t size() const noexcept { return size_; } |
| constexpr size_t size_bytes() const noexcept { return size() * sizeof(T); } |
| constexpr bool empty() const noexcept { return size_ == 0; } |
| |
| // [span.elem], span element access |
| T& operator[](size_t index) const noexcept { |
| CHECK(index < size_); |
| return data_.Get()[index]; |
| } |
| |
| constexpr T& front() const noexcept { |
| CHECK(!empty()); |
| return *data(); |
| } |
| |
| constexpr T& back() const noexcept { |
| CHECK(!empty()); |
| return *(data() + size() - 1); |
| } |
| |
| constexpr T* data() const noexcept { return data_.Get(); } |
| |
| // [span.iter], span iterator support |
| constexpr iterator begin() const noexcept { return data_.Get(); } |
| constexpr iterator end() const noexcept { return data_.Get() + size_; } |
| |
| constexpr const_iterator cbegin() const noexcept { return begin(); } |
| constexpr const_iterator cend() const noexcept { return end(); } |
| |
| constexpr reverse_iterator rbegin() const noexcept { |
| return reverse_iterator(end()); |
| } |
| constexpr reverse_iterator rend() const noexcept { |
| return reverse_iterator(begin()); |
| } |
| |
| constexpr const_reverse_iterator crbegin() const noexcept { |
| return const_reverse_iterator(cend()); |
| } |
| constexpr const_reverse_iterator crend() const noexcept { |
| return const_reverse_iterator(cbegin()); |
| } |
| |
| private: |
| UnownedPtr<T> data_; |
| size_t size_; |
| }; |
| |
| // [span.comparison], span comparison operators |
| // Relational operators. Equality is a element-wise comparison. |
| template <typename T> |
| constexpr bool operator==(span<T> lhs, span<T> rhs) noexcept { |
| return lhs.size() == rhs.size() && |
| std::equal(lhs.cbegin(), lhs.cend(), rhs.cbegin()); |
| } |
| |
| template <typename T> |
| constexpr bool operator!=(span<T> lhs, span<T> rhs) noexcept { |
| return !(lhs == rhs); |
| } |
| |
| template <typename T> |
| constexpr bool operator<(span<T> lhs, span<T> rhs) noexcept { |
| return std::lexicographical_compare(lhs.cbegin(), lhs.cend(), rhs.cbegin(), |
| rhs.cend()); |
| } |
| |
| template <typename T> |
| constexpr bool operator<=(span<T> lhs, span<T> rhs) noexcept { |
| return !(rhs < lhs); |
| } |
| |
| template <typename T> |
| constexpr bool operator>(span<T> lhs, span<T> rhs) noexcept { |
| return rhs < lhs; |
| } |
| |
| template <typename T> |
| constexpr bool operator>=(span<T> lhs, span<T> rhs) noexcept { |
| return !(lhs < rhs); |
| } |
| |
| // [span.objectrep], views of object representation |
| template <typename T> |
| span<const uint8_t> as_bytes(span<T> s) noexcept { |
| return {reinterpret_cast<const uint8_t*>(s.data()), s.size_bytes()}; |
| } |
| |
| template <typename T, |
| typename U = typename std::enable_if<!std::is_const<T>::value>::type> |
| span<uint8_t> as_writable_bytes(span<T> s) noexcept { |
| return {reinterpret_cast<uint8_t*>(s.data()), s.size_bytes()}; |
| } |
| |
| // Type-deducing helpers for constructing a span. |
| template <typename T> |
| constexpr span<T> make_span(T* data, size_t size) noexcept { |
| return span<T>(data, size); |
| } |
| |
| template <typename T, size_t N> |
| constexpr span<T> make_span(T (&array)[N]) noexcept { |
| return span<T>(array); |
| } |
| |
| template <typename Container, |
| typename T = typename Container::value_type, |
| typename = internal::EnableIfSpanCompatibleContainer<Container, T>> |
| constexpr span<T> make_span(Container& container) { |
| return span<T>(container); |
| } |
| |
| template < |
| typename Container, |
| typename T = typename std::add_const<typename Container::value_type>::type, |
| typename = internal::EnableIfConstSpanCompatibleContainer<Container, T>> |
| constexpr span<T> make_span(const Container& container) { |
| return span<T>(container); |
| } |
| |
| } // namespace pdfium |
| |
| #endif // THIRD_PARTY_BASE_SPAN_H_ |