| // Copyright 2017 The Chromium Authors |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef BASE_CONTAINERS_SPAN_H_ |
| #define BASE_CONTAINERS_SPAN_H_ |
| |
| #include <stddef.h> |
| #include <stdint.h> |
| |
| #include <array> |
| #include <iterator> |
| #include <limits> |
| #include <type_traits> |
| #include <utility> |
| |
| #include "polyfills/base/check.h" |
| #include "base/compiler_specific.h" |
| #include "base/containers/checked_iterators.h" |
| #include "base/containers/contiguous_iterator.h" |
| #include "base/cxx20_to_address.h" |
| #include "polyfills/base/memory/raw_ptr_exclusion.h" |
| #include "base/numerics/safe_math.h" |
| |
| namespace gurl_base { |
| |
| // [views.constants] |
| constexpr size_t dynamic_extent = std::numeric_limits<size_t>::max(); |
| |
| template <typename T, |
| size_t Extent = dynamic_extent, |
| typename InternalPtrType = T*> |
| class span; |
| |
| namespace internal { |
| |
| template <size_t I> |
| using size_constant = std::integral_constant<size_t, I>; |
| |
| template <typename T> |
| struct ExtentImpl : size_constant<dynamic_extent> {}; |
| |
| template <typename T, size_t N> |
| struct ExtentImpl<T[N]> : size_constant<N> {}; |
| |
| template <typename T, size_t N> |
| struct ExtentImpl<std::array<T, N>> : size_constant<N> {}; |
| |
| template <typename T, size_t N> |
| struct ExtentImpl<gurl_base::span<T, N>> : size_constant<N> {}; |
| |
| template <typename T> |
| using Extent = ExtentImpl<remove_cvref_t<T>>; |
| |
| template <typename T> |
| struct IsSpanImpl : std::false_type {}; |
| |
| template <typename T, size_t Extent> |
| struct IsSpanImpl<span<T, Extent>> : std::true_type {}; |
| |
| template <typename T> |
| using IsNotSpan = std::negation<IsSpanImpl<std::decay_t<T>>>; |
| |
| 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 IsNotStdArray = std::negation<IsStdArrayImpl<std::decay_t<T>>>; |
| |
| template <typename T> |
| using IsNotCArray = std::negation<std::is_array<std::remove_reference_t<T>>>; |
| |
| template <typename From, typename To> |
| using IsLegalDataConversion = std::is_convertible<From (*)[], To (*)[]>; |
| |
| template <typename Iter, typename T> |
| using IteratorHasConvertibleReferenceType = |
| IsLegalDataConversion<std::remove_reference_t<iter_reference_t<Iter>>, T>; |
| |
| template <typename Iter, typename T> |
| using EnableIfCompatibleContiguousIterator = std::enable_if_t< |
| std::conjunction<IsContiguousIterator<Iter>, |
| IteratorHasConvertibleReferenceType<Iter, T>>::value>; |
| |
| template <typename Container, typename T> |
| using ContainerHasConvertibleData = IsLegalDataConversion< |
| std::remove_pointer_t<decltype(std::data(std::declval<Container>()))>, |
| T>; |
| |
| template <typename Container> |
| using ContainerHasIntegralSize = |
| std::is_integral<decltype(std::size(std::declval<Container>()))>; |
| |
| template <typename From, size_t FromExtent, typename To, size_t ToExtent> |
| using EnableIfLegalSpanConversion = |
| std::enable_if_t<(ToExtent == dynamic_extent || ToExtent == FromExtent) && |
| IsLegalDataConversion<From, To>::value>; |
| |
| // SFINAE check if Array can be converted to a span<T>. |
| template <typename Array, typename T, size_t Extent> |
| using EnableIfSpanCompatibleArray = |
| std::enable_if_t<(Extent == dynamic_extent || |
| Extent == internal::Extent<Array>::value) && |
| ContainerHasConvertibleData<Array, T>::value>; |
| |
| // SFINAE check if Container can be converted to a span<T>. |
| template <typename Container, typename T> |
| using IsSpanCompatibleContainer = |
| std::conjunction<IsNotSpan<Container>, |
| IsNotStdArray<Container>, |
| IsNotCArray<Container>, |
| ContainerHasConvertibleData<Container, T>, |
| ContainerHasIntegralSize<Container>>; |
| |
| template <typename Container, typename T> |
| using EnableIfSpanCompatibleContainer = |
| std::enable_if_t<IsSpanCompatibleContainer<Container, T>::value>; |
| |
| template <typename Container, typename T, size_t Extent> |
| using EnableIfSpanCompatibleContainerAndSpanIsDynamic = |
| std::enable_if_t<IsSpanCompatibleContainer<Container, T>::value && |
| Extent == dynamic_extent>; |
| |
| // A helper template for storing the size of a span. Spans with static extents |
| // don't require additional storage, since the extent itself is specified in the |
| // template parameter. |
| template <size_t Extent> |
| class ExtentStorage { |
| public: |
| constexpr explicit ExtentStorage(size_t size) noexcept {} |
| constexpr size_t size() const noexcept { return Extent; } |
| }; |
| |
| // Specialization of ExtentStorage for dynamic extents, which do require |
| // explicit storage for the size. |
| template <> |
| struct ExtentStorage<dynamic_extent> { |
| constexpr explicit ExtentStorage(size_t size) noexcept : size_(size) {} |
| constexpr size_t size() const noexcept { return size_; } |
| |
| private: |
| size_t size_; |
| }; |
| |
| // must_not_be_dynamic_extent prevents |dynamic_extent| from being returned in a |
| // constexpr context. |
| template <size_t kExtent> |
| constexpr size_t must_not_be_dynamic_extent() { |
| static_assert( |
| kExtent != dynamic_extent, |
| "EXTENT should only be used for containers with a static extent."); |
| return kExtent; |
| } |
| |
| } // 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(gurl_base::span<const uint8_t> data); |
| // std::vector<uint8_t> data_buffer = GenerateData(); |
| // std::string r = HexEncode(data_buffer); |
| // |
| // Mutable: |
| // // ssize_t SafeSNPrintf(gurl_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: |
| // |
| // const std::vector<int*> => gurl_base::span<int* const> |
| // std::vector<const int*> => gurl_base::span<const int*> |
| // const std::vector<const int*> => gurl_base::span<const int* const> |
| // |
| // Differences from the C++20 draft |
| // -------------------------------- |
| // |
| // http://eel.is/c++draft/views contains the latest C++20 draft of std::span. |
| // Chromium tries to follow the draft as close as possible. Differences between |
| // the draft and the implementation are documented in subsections below. |
| // |
| // Differences from [span.objectrep]: |
| // - as_bytes() and as_writable_bytes() return spans of uint8_t instead of |
| // std::byte (std::byte is a C++17 feature) |
| // |
| // Differences from [span.cons]: |
| // - Constructing a static span (i.e. Extent != dynamic_extent) from a dynamic |
| // sized container (e.g. std::vector) requires an explicit conversion (in the |
| // C++20 draft this is simply UB) |
| // |
| // Furthermore, all constructors and methods are marked noexcept due to the lack |
| // of exceptions in Chromium. |
| // |
| // Due to the lack of class template argument deduction guides in C++14 |
| // appropriate make_span() utility functions are provided. |
| |
| // [span], class template span |
| template <typename T, size_t Extent, typename InternalPtrType> |
| class GSL_POINTER span : public internal::ExtentStorage<Extent> { |
| private: |
| using ExtentStorage = internal::ExtentStorage<Extent>; |
| |
| public: |
| using element_type = T; |
| using value_type = std::remove_cv_t<T>; |
| using size_type = size_t; |
| using difference_type = ptrdiff_t; |
| using pointer = T*; |
| using const_pointer = const T*; |
| using reference = T&; |
| using const_reference = const T&; |
| using iterator = CheckedContiguousIterator<T>; |
| using reverse_iterator = std::reverse_iterator<iterator>; |
| static constexpr size_t extent = Extent; |
| |
| // [span.cons], span constructors, copy, assignment, and destructor |
| constexpr span() noexcept : ExtentStorage(0), data_(nullptr) { |
| static_assert(Extent == dynamic_extent || Extent == 0, "Invalid Extent"); |
| } |
| |
| template <typename It, |
| typename = internal::EnableIfCompatibleContiguousIterator<It, T>> |
| constexpr span(It first, StrictNumeric<size_t> count) noexcept |
| : ExtentStorage(count), |
| // The use of to_address() here is to handle the case where the iterator |
| // `first` is pointing to the container's `end()`. In that case we can |
| // not use the address returned from the iterator, or dereference it |
| // through the iterator's `operator*`, but we can store it. We must |
| // assume in this case that `count` is 0, since the iterator does not |
| // point to valid data. Future hardening of iterators may disallow |
| // pulling the address from `end()`, as demonstrated by asserts() in |
| // libstdc++: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93960. |
| // |
| // The span API dictates that the `data()` is accessible when size is 0, |
| // since the pointer may be valid, so we cannot prevent storing and |
| // giving out an invalid pointer here without breaking API compatibility |
| // and our unit tests. Thus protecting against this can likely only be |
| // successful from inside iterators themselves, where the context about |
| // the pointer is known. |
| // |
| // We can not protect here generally against an invalid iterator/count |
| // being passed in, since we have no context to determine if the |
| // iterator or count are valid. |
| data_(gurl_base::to_address(first)) { |
| GURL_CHECK(Extent == dynamic_extent || Extent == count); |
| } |
| |
| template < |
| typename It, |
| typename End, |
| typename = internal::EnableIfCompatibleContiguousIterator<It, T>, |
| typename = std::enable_if_t<!std::is_convertible<End, size_t>::value>> |
| constexpr span(It begin, End end) noexcept |
| // Subtracting two iterators gives a ptrdiff_t, but the result should be |
| // non-negative: see GURL_CHECK below. |
| : span(begin, static_cast<size_t>(end - begin)) { |
| // Note: GURL_CHECK_LE is not constexpr, hence regular GURL_CHECK must be used. |
| GURL_CHECK(begin <= end); |
| } |
| |
| template < |
| size_t N, |
| typename = internal::EnableIfSpanCompatibleArray<T (&)[N], T, Extent>> |
| constexpr span(T (&array)[N]) noexcept : span(std::data(array), N) {} |
| |
| template < |
| typename U, |
| size_t N, |
| typename = |
| internal::EnableIfSpanCompatibleArray<std::array<U, N>&, T, Extent>> |
| constexpr span(std::array<U, N>& array) noexcept |
| : span(std::data(array), N) {} |
| |
| template <typename U, |
| size_t N, |
| typename = internal:: |
| EnableIfSpanCompatibleArray<const std::array<U, N>&, T, Extent>> |
| constexpr span(const std::array<U, N>& array) noexcept |
| : span(std::data(array), N) {} |
| |
| // Conversion from a container that has compatible std::data() and integral |
| // std::size(). |
| template < |
| typename Container, |
| typename = |
| internal::EnableIfSpanCompatibleContainerAndSpanIsDynamic<Container&, |
| T, |
| Extent>> |
| constexpr span(Container& container) noexcept |
| : span(std::data(container), std::size(container)) {} |
| |
| template < |
| typename Container, |
| typename = internal::EnableIfSpanCompatibleContainerAndSpanIsDynamic< |
| const Container&, |
| T, |
| Extent>> |
| constexpr span(const Container& container) noexcept |
| : span(std::data(container), std::size(container)) {} |
| |
| constexpr span(const span& other) noexcept = default; |
| |
| // Conversions from spans of compatible types and extents: this allows a |
| // span<T> to be seamlessly used as a span<const T>, but not the other way |
| // around. If extent is not dynamic, OtherExtent has to be equal to Extent. |
| template < |
| typename U, |
| size_t OtherExtent, |
| typename = |
| internal::EnableIfLegalSpanConversion<U, OtherExtent, T, Extent>> |
| constexpr span(const span<U, OtherExtent>& other) |
| : span(other.data(), other.size()) {} |
| |
| constexpr span& operator=(const span& other) noexcept = default; |
| ~span() noexcept = default; |
| |
| // [span.sub], span subviews |
| template <size_t Count> |
| constexpr span<T, Count> first() const noexcept { |
| static_assert(Count <= Extent, "Count must not exceed Extent"); |
| GURL_CHECK(Extent != dynamic_extent || Count <= size()); |
| return {data(), Count}; |
| } |
| |
| template <size_t Count> |
| constexpr span<T, Count> last() const noexcept { |
| static_assert(Count <= Extent, "Count must not exceed Extent"); |
| GURL_CHECK(Extent != dynamic_extent || Count <= size()); |
| return {data() + (size() - Count), Count}; |
| } |
| |
| template <size_t Offset, size_t Count = dynamic_extent> |
| constexpr span<T, |
| (Count != dynamic_extent |
| ? Count |
| : (Extent != dynamic_extent ? Extent - Offset |
| : dynamic_extent))> |
| subspan() const noexcept { |
| static_assert(Offset <= Extent, "Offset must not exceed Extent"); |
| static_assert(Count == dynamic_extent || Count <= Extent - Offset, |
| "Count must not exceed Extent - Offset"); |
| GURL_CHECK(Extent != dynamic_extent || Offset <= size()); |
| GURL_CHECK(Extent != dynamic_extent || Count == dynamic_extent || |
| Count <= size() - Offset); |
| return {data() + Offset, Count != dynamic_extent ? Count : size() - Offset}; |
| } |
| |
| constexpr span<T, dynamic_extent> first(size_t count) const noexcept { |
| // Note: GURL_CHECK_LE is not constexpr, hence regular GURL_CHECK must be used. |
| GURL_CHECK(count <= size()); |
| return {data(), count}; |
| } |
| |
| constexpr span<T, dynamic_extent> last(size_t count) const noexcept { |
| // Note: GURL_CHECK_LE is not constexpr, hence regular GURL_CHECK must be used. |
| GURL_CHECK(count <= size()); |
| return {data() + (size() - count), count}; |
| } |
| |
| constexpr span<T, dynamic_extent> subspan(size_t offset, |
| size_t count = dynamic_extent) const |
| noexcept { |
| // Note: GURL_CHECK_LE is not constexpr, hence regular GURL_CHECK must be used. |
| GURL_CHECK(offset <= size()); |
| GURL_CHECK(count == dynamic_extent || count <= size() - offset); |
| return {data() + offset, count != dynamic_extent ? count : size() - offset}; |
| } |
| |
| // [span.obs], span observers |
| constexpr size_t size() const noexcept { return ExtentStorage::size(); } |
| constexpr size_t size_bytes() const noexcept { return size() * sizeof(T); } |
| [[nodiscard]] constexpr bool empty() const noexcept { return size() == 0; } |
| |
| // [span.elem], span element access |
| constexpr T& operator[](size_t idx) const noexcept { |
| // Note: GURL_CHECK_LT is not constexpr, hence regular GURL_CHECK must be used. |
| GURL_CHECK(idx < size()); |
| return *(data() + idx); |
| } |
| |
| constexpr T& front() const noexcept { |
| static_assert(Extent == dynamic_extent || Extent > 0, |
| "Extent must not be 0"); |
| GURL_CHECK(Extent != dynamic_extent || !empty()); |
| return *data(); |
| } |
| |
| constexpr T& back() const noexcept { |
| static_assert(Extent == dynamic_extent || Extent > 0, |
| "Extent must not be 0"); |
| GURL_CHECK(Extent != dynamic_extent || !empty()); |
| return *(data() + size() - 1); |
| } |
| |
| constexpr T* data() const noexcept { return data_; } |
| |
| // [span.iter], span iterator support |
| constexpr iterator begin() const noexcept { |
| return iterator(data(), data() + size()); |
| } |
| |
| constexpr iterator end() const noexcept { |
| return iterator(data(), data() + size(), data() + size()); |
| } |
| |
| constexpr reverse_iterator rbegin() const noexcept { |
| return reverse_iterator(end()); |
| } |
| |
| constexpr reverse_iterator rend() const noexcept { |
| return reverse_iterator(begin()); |
| } |
| |
| private: |
| // This field is not a raw_ptr<> because it was filtered by the rewriter |
| // for: #constexpr-ctor-field-initializer, #global-scope, #union |
| InternalPtrType data_; |
| }; |
| |
| // span<T, Extent>::extent can not be declared inline prior to C++17, hence this |
| // definition is required. |
| template <class T, size_t Extent, typename InternalPtrType> |
| constexpr size_t span<T, Extent, InternalPtrType>::extent; |
| |
| template <typename It, |
| typename T = std::remove_reference_t<iter_reference_t<It>>> |
| span(It, StrictNumeric<size_t>) -> span<T>; |
| |
| template <typename It, |
| typename End, |
| typename = std::enable_if_t<!std::is_convertible_v<End, size_t>>, |
| typename T = std::remove_reference_t<iter_reference_t<It>>> |
| span(It, End) -> span<T>; |
| |
| template <typename T, size_t N> |
| span(T (&)[N]) -> span<T, N>; |
| |
| template <typename T, size_t N> |
| span(std::array<T, N>&) -> span<T, N>; |
| |
| template <typename T, size_t N> |
| span(const std::array<T, N>&) -> span<const T, N>; |
| |
| template <typename Container, |
| typename T = std::remove_pointer_t< |
| decltype(std::data(std::declval<Container>()))>, |
| size_t X = internal::Extent<Container>::value> |
| span(Container&&) -> span<T, X>; |
| |
| // [span.objectrep], views of object representation |
| template <typename T, size_t X> |
| span<const uint8_t, (X == dynamic_extent ? dynamic_extent : sizeof(T) * X)> |
| as_bytes(span<T, X> s) noexcept { |
| return {reinterpret_cast<const uint8_t*>(s.data()), s.size_bytes()}; |
| } |
| |
| template <typename T, |
| size_t X, |
| typename = std::enable_if_t<!std::is_const<T>::value>> |
| span<uint8_t, (X == dynamic_extent ? dynamic_extent : sizeof(T) * X)> |
| as_writable_bytes(span<T, X> s) noexcept { |
| return {reinterpret_cast<uint8_t*>(s.data()), s.size_bytes()}; |
| } |
| |
| // Type-deducing helpers for constructing a span. |
| template <int&... ExplicitArgumentBarrier, typename It> |
| constexpr auto make_span(It it, StrictNumeric<size_t> size) noexcept { |
| using T = std::remove_reference_t<iter_reference_t<It>>; |
| return span<T>(it, size); |
| } |
| |
| template <int&... ExplicitArgumentBarrier, |
| typename It, |
| typename End, |
| typename = std::enable_if_t<!std::is_convertible_v<End, size_t>>> |
| constexpr auto make_span(It it, End end) noexcept { |
| using T = std::remove_reference_t<iter_reference_t<It>>; |
| return span<T>(it, end); |
| } |
| |
| // make_span utility function that deduces both the span's value_type and extent |
| // from the passed in argument. |
| // |
| // Usage: auto span = gurl_base::make_span(...); |
| template <int&... ExplicitArgumentBarrier, typename Container> |
| constexpr auto make_span(Container&& container) noexcept { |
| using T = |
| std::remove_pointer_t<decltype(std::data(std::declval<Container>()))>; |
| using Extent = internal::Extent<Container>; |
| return span<T, Extent::value>(std::forward<Container>(container)); |
| } |
| |
| // make_span utility functions that allow callers to explicit specify the span's |
| // extent, the value_type is deduced automatically. This is useful when passing |
| // a dynamically sized container to a method expecting static spans, when the |
| // container is known to have the correct size. |
| // |
| // Note: This will GURL_CHECK that N indeed matches size(container). |
| // |
| // Usage: auto static_span = gurl_base::make_span<N>(...); |
| template <size_t N, int&... ExplicitArgumentBarrier, typename It> |
| constexpr auto make_span(It it, StrictNumeric<size_t> size) noexcept { |
| using T = std::remove_reference_t<iter_reference_t<It>>; |
| return span<T, N>(it, size); |
| } |
| |
| template <size_t N, |
| int&... ExplicitArgumentBarrier, |
| typename It, |
| typename End, |
| typename = std::enable_if_t<!std::is_convertible_v<End, size_t>>> |
| constexpr auto make_span(It it, End end) noexcept { |
| using T = std::remove_reference_t<iter_reference_t<It>>; |
| return span<T, N>(it, end); |
| } |
| |
| template <size_t N, int&... ExplicitArgumentBarrier, typename Container> |
| constexpr auto make_span(Container&& container) noexcept { |
| using T = |
| std::remove_pointer_t<decltype(std::data(std::declval<Container>()))>; |
| return span<T, N>(std::data(container), std::size(container)); |
| } |
| |
| } // namespace base |
| |
| // EXTENT returns the size of any type that can be converted to a |gurl_base::span| |
| // with definite extent, i.e. everything that is a contiguous storage of some |
| // sort with static size. Specifically, this works for std::array in a constexpr |
| // context. Note: |
| // * |std::size| should be preferred for plain arrays. |
| // * In run-time contexts, functions such as |std::array::size| should be |
| // preferred. |
| #define EXTENT(x) \ |
| ::gurl_base::internal::must_not_be_dynamic_extent<decltype( \ |
| ::gurl_base::make_span(x))::extent>() |
| |
| #endif // BASE_CONTAINERS_SPAN_H_ |