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-rw-r--r--third_party/base/span.h336
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+// 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 PDFIUM_THIRD_PARTY_BASE_SPAN_H_
+#define PDFIUM_THIRD_PARTY_BASE_SPAN_H_
+
+#include <stddef.h>
+
+#include <algorithm>
+#include <array>
+#include <iterator>
+#include <type_traits>
+#include <utility>
+
+#include "third_party/base/logging.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 from [span.objectrep]:
+// - no as_bytes()
+// - no as_writeable_bytes()
+//
+// 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]:
+// - no size_bytes()
+// - 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 = default;
+
+ // [span.sub], span subviews
+ const span first(size_t count) const {
+ CHECK(count <= size_);
+ return span(data_, count);
+ }
+
+ const span last(size_t count) const {
+ CHECK(count <= size_);
+ return span(data_ + (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_ + pos, count == npos ? size_ - pos : count);
+ }
+
+ // [span.obs], span observers
+ constexpr size_t size() const noexcept { return size_; }
+ constexpr bool empty() const noexcept { return size_ == 0; }
+
+ // [span.elem], span element access
+ const T& operator[](size_t index) const noexcept {
+ CHECK(index < size_);
+ return data_[index];
+ }
+ constexpr T* data() const noexcept { return data_; }
+
+ // [span.iter], span iterator support
+ constexpr iterator begin() const noexcept { return data_; }
+ constexpr iterator end() const noexcept { return data_ + 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:
+ 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);
+}
+
+// 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 // PDFIUM_THIRD_PARTY_BASE_SPAN_H_