blob: bb07f43a0213f23facd90c33a60b533a347c012e [file] [log] [blame]
// 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/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 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* 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_