--- /dev/null
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: fixed_array.h
+// -----------------------------------------------------------------------------
+//
+// A `FixedArray<T>` represents a non-resizable array of `T` where the length of
+// the array can be determined at run-time. It is a good replacement for
+// non-standard and deprecated uses of `alloca()` and variable length arrays
+// within the GCC extension. (See
+// https://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html).
+//
+// `FixedArray` allocates small arrays inline, keeping performance fast by
+// avoiding heap operations. It also helps reduce the chances of
+// accidentally overflowing your stack if large input is passed to
+// your function.
+
+#ifndef ABSL_CONTAINER_FIXED_ARRAY_H_
+#define ABSL_CONTAINER_FIXED_ARRAY_H_
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <cstddef>
+#include <initializer_list>
+#include <iterator>
+#include <limits>
+#include <memory>
+#include <new>
+#include <type_traits>
+
+#include "absl/algorithm/algorithm.h"
+#include "absl/base/dynamic_annotations.h"
+#include "absl/base/internal/throw_delegate.h"
+#include "absl/base/macros.h"
+#include "absl/base/optimization.h"
+#include "absl/base/port.h"
+#include "absl/container/internal/compressed_tuple.h"
+#include "absl/memory/memory.h"
+
+namespace absl {
+
+constexpr static auto kFixedArrayUseDefault = static_cast<size_t>(-1);
+
+// -----------------------------------------------------------------------------
+// FixedArray
+// -----------------------------------------------------------------------------
+//
+// A `FixedArray` provides a run-time fixed-size array, allocating a small array
+// inline for efficiency.
+//
+// Most users should not specify an `inline_elements` argument and let
+// `FixedArray` automatically determine the number of elements
+// to store inline based on `sizeof(T)`. If `inline_elements` is specified, the
+// `FixedArray` implementation will use inline storage for arrays with a
+// length <= `inline_elements`.
+//
+// Note that a `FixedArray` constructed with a `size_type` argument will
+// default-initialize its values by leaving trivially constructible types
+// uninitialized (e.g. int, int[4], double), and others default-constructed.
+// This matches the behavior of c-style arrays and `std::array`, but not
+// `std::vector`.
+//
+// Note that `FixedArray` does not provide a public allocator; if it requires a
+// heap allocation, it will do so with global `::operator new[]()` and
+// `::operator delete[]()`, even if T provides class-scope overrides for these
+// operators.
+template <typename T, size_t N = kFixedArrayUseDefault,
+ typename A = std::allocator<T>>
+class FixedArray {
+ static_assert(!std::is_array<T>::value || std::extent<T>::value > 0,
+ "Arrays with unknown bounds cannot be used with FixedArray.");
+
+ static constexpr size_t kInlineBytesDefault = 256;
+
+ using AllocatorTraits = std::allocator_traits<A>;
+ // std::iterator_traits isn't guaranteed to be SFINAE-friendly until C++17,
+ // but this seems to be mostly pedantic.
+ template <typename Iterator>
+ using EnableIfForwardIterator = absl::enable_if_t<std::is_convertible<
+ typename std::iterator_traits<Iterator>::iterator_category,
+ std::forward_iterator_tag>::value>;
+ static constexpr bool NoexceptCopyable() {
+ return std::is_nothrow_copy_constructible<StorageElement>::value &&
+ absl::allocator_is_nothrow<allocator_type>::value;
+ }
+ static constexpr bool NoexceptMovable() {
+ return std::is_nothrow_move_constructible<StorageElement>::value &&
+ absl::allocator_is_nothrow<allocator_type>::value;
+ }
+ static constexpr bool DefaultConstructorIsNonTrivial() {
+ return !absl::is_trivially_default_constructible<StorageElement>::value;
+ }
+
+ public:
+ using allocator_type = typename AllocatorTraits::allocator_type;
+ using value_type = typename allocator_type::value_type;
+ using pointer = typename allocator_type::pointer;
+ using const_pointer = typename allocator_type::const_pointer;
+ using reference = typename allocator_type::reference;
+ using const_reference = typename allocator_type::const_reference;
+ using size_type = typename allocator_type::size_type;
+ using difference_type = typename allocator_type::difference_type;
+ using iterator = pointer;
+ using const_iterator = const_pointer;
+ using reverse_iterator = std::reverse_iterator<iterator>;
+ using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+
+ static constexpr size_type inline_elements =
+ (N == kFixedArrayUseDefault ? kInlineBytesDefault / sizeof(value_type)
+ : static_cast<size_type>(N));
+
+ FixedArray(
+ const FixedArray& other,
+ const allocator_type& a = allocator_type()) noexcept(NoexceptCopyable())
+ : FixedArray(other.begin(), other.end(), a) {}
+
+ FixedArray(
+ FixedArray&& other,
+ const allocator_type& a = allocator_type()) noexcept(NoexceptMovable())
+ : FixedArray(std::make_move_iterator(other.begin()),
+ std::make_move_iterator(other.end()), a) {}
+
+ // Creates an array object that can store `n` elements.
+ // Note that trivially constructible elements will be uninitialized.
+ explicit FixedArray(size_type n, const allocator_type& a = allocator_type())
+ : storage_(n, a) {
+ if (DefaultConstructorIsNonTrivial()) {
+ memory_internal::ConstructRange(storage_.alloc(), storage_.begin(),
+ storage_.end());
+ }
+ }
+
+ // Creates an array initialized with `n` copies of `val`.
+ FixedArray(size_type n, const value_type& val,
+ const allocator_type& a = allocator_type())
+ : storage_(n, a) {
+ memory_internal::ConstructRange(storage_.alloc(), storage_.begin(),
+ storage_.end(), val);
+ }
+
+ // Creates an array initialized with the size and contents of `init_list`.
+ FixedArray(std::initializer_list<value_type> init_list,
+ const allocator_type& a = allocator_type())
+ : FixedArray(init_list.begin(), init_list.end(), a) {}
+
+ // Creates an array initialized with the elements from the input
+ // range. The array's size will always be `std::distance(first, last)`.
+ // REQUIRES: Iterator must be a forward_iterator or better.
+ template <typename Iterator, EnableIfForwardIterator<Iterator>* = nullptr>
+ FixedArray(Iterator first, Iterator last,
+ const allocator_type& a = allocator_type())
+ : storage_(std::distance(first, last), a) {
+ memory_internal::CopyRange(storage_.alloc(), storage_.begin(), first, last);
+ }
+
+ ~FixedArray() noexcept {
+ for (auto* cur = storage_.begin(); cur != storage_.end(); ++cur) {
+ AllocatorTraits::destroy(storage_.alloc(), cur);
+ }
+ }
+
+ // Assignments are deleted because they break the invariant that the size of a
+ // `FixedArray` never changes.
+ void operator=(FixedArray&&) = delete;
+ void operator=(const FixedArray&) = delete;
+
+ // FixedArray::size()
+ //
+ // Returns the length of the fixed array.
+ size_type size() const { return storage_.size(); }
+
+ // FixedArray::max_size()
+ //
+ // Returns the largest possible value of `std::distance(begin(), end())` for a
+ // `FixedArray<T>`. This is equivalent to the most possible addressable bytes
+ // over the number of bytes taken by T.
+ constexpr size_type max_size() const {
+ return (std::numeric_limits<difference_type>::max)() / sizeof(value_type);
+ }
+
+ // FixedArray::empty()
+ //
+ // Returns whether or not the fixed array is empty.
+ bool empty() const { return size() == 0; }
+
+ // FixedArray::memsize()
+ //
+ // Returns the memory size of the fixed array in bytes.
+ size_t memsize() const { return size() * sizeof(value_type); }
+
+ // FixedArray::data()
+ //
+ // Returns a const T* pointer to elements of the `FixedArray`. This pointer
+ // can be used to access (but not modify) the contained elements.
+ const_pointer data() const { return AsValueType(storage_.begin()); }
+
+ // Overload of FixedArray::data() to return a T* pointer to elements of the
+ // fixed array. This pointer can be used to access and modify the contained
+ // elements.
+ pointer data() { return AsValueType(storage_.begin()); }
+
+ // FixedArray::operator[]
+ //
+ // Returns a reference the ith element of the fixed array.
+ // REQUIRES: 0 <= i < size()
+ reference operator[](size_type i) {
+ assert(i < size());
+ return data()[i];
+ }
+
+ // Overload of FixedArray::operator()[] to return a const reference to the
+ // ith element of the fixed array.
+ // REQUIRES: 0 <= i < size()
+ const_reference operator[](size_type i) const {
+ assert(i < size());
+ return data()[i];
+ }
+
+ // FixedArray::at
+ //
+ // Bounds-checked access. Returns a reference to the ith element of the
+ // fiexed array, or throws std::out_of_range
+ reference at(size_type i) {
+ if (ABSL_PREDICT_FALSE(i >= size())) {
+ base_internal::ThrowStdOutOfRange("FixedArray::at failed bounds check");
+ }
+ return data()[i];
+ }
+
+ // Overload of FixedArray::at() to return a const reference to the ith element
+ // of the fixed array.
+ const_reference at(size_type i) const {
+ if (ABSL_PREDICT_FALSE(i >= size())) {
+ base_internal::ThrowStdOutOfRange("FixedArray::at failed bounds check");
+ }
+ return data()[i];
+ }
+
+ // FixedArray::front()
+ //
+ // Returns a reference to the first element of the fixed array.
+ reference front() { return *begin(); }
+
+ // Overload of FixedArray::front() to return a reference to the first element
+ // of a fixed array of const values.
+ const_reference front() const { return *begin(); }
+
+ // FixedArray::back()
+ //
+ // Returns a reference to the last element of the fixed array.
+ reference back() { return *(end() - 1); }
+
+ // Overload of FixedArray::back() to return a reference to the last element
+ // of a fixed array of const values.
+ const_reference back() const { return *(end() - 1); }
+
+ // FixedArray::begin()
+ //
+ // Returns an iterator to the beginning of the fixed array.
+ iterator begin() { return data(); }
+
+ // Overload of FixedArray::begin() to return a const iterator to the
+ // beginning of the fixed array.
+ const_iterator begin() const { return data(); }
+
+ // FixedArray::cbegin()
+ //
+ // Returns a const iterator to the beginning of the fixed array.
+ const_iterator cbegin() const { return begin(); }
+
+ // FixedArray::end()
+ //
+ // Returns an iterator to the end of the fixed array.
+ iterator end() { return data() + size(); }
+
+ // Overload of FixedArray::end() to return a const iterator to the end of the
+ // fixed array.
+ const_iterator end() const { return data() + size(); }
+
+ // FixedArray::cend()
+ //
+ // Returns a const iterator to the end of the fixed array.
+ const_iterator cend() const { return end(); }
+
+ // FixedArray::rbegin()
+ //
+ // Returns a reverse iterator from the end of the fixed array.
+ reverse_iterator rbegin() { return reverse_iterator(end()); }
+
+ // Overload of FixedArray::rbegin() to return a const reverse iterator from
+ // the end of the fixed array.
+ const_reverse_iterator rbegin() const {
+ return const_reverse_iterator(end());
+ }
+
+ // FixedArray::crbegin()
+ //
+ // Returns a const reverse iterator from the end of the fixed array.
+ const_reverse_iterator crbegin() const { return rbegin(); }
+
+ // FixedArray::rend()
+ //
+ // Returns a reverse iterator from the beginning of the fixed array.
+ reverse_iterator rend() { return reverse_iterator(begin()); }
+
+ // Overload of FixedArray::rend() for returning a const reverse iterator
+ // from the beginning of the fixed array.
+ const_reverse_iterator rend() const {
+ return const_reverse_iterator(begin());
+ }
+
+ // FixedArray::crend()
+ //
+ // Returns a reverse iterator from the beginning of the fixed array.
+ const_reverse_iterator crend() const { return rend(); }
+
+ // FixedArray::fill()
+ //
+ // Assigns the given `value` to all elements in the fixed array.
+ void fill(const value_type& val) { std::fill(begin(), end(), val); }
+
+ // Relational operators. Equality operators are elementwise using
+ // `operator==`, while order operators order FixedArrays lexicographically.
+ friend bool operator==(const FixedArray& lhs, const FixedArray& rhs) {
+ return absl::equal(lhs.begin(), lhs.end(), rhs.begin(), rhs.end());
+ }
+
+ friend bool operator!=(const FixedArray& lhs, const FixedArray& rhs) {
+ return !(lhs == rhs);
+ }
+
+ friend bool operator<(const FixedArray& lhs, const FixedArray& rhs) {
+ return std::lexicographical_compare(lhs.begin(), lhs.end(), rhs.begin(),
+ rhs.end());
+ }
+
+ friend bool operator>(const FixedArray& lhs, const FixedArray& rhs) {
+ return rhs < lhs;
+ }
+
+ friend bool operator<=(const FixedArray& lhs, const FixedArray& rhs) {
+ return !(rhs < lhs);
+ }
+
+ friend bool operator>=(const FixedArray& lhs, const FixedArray& rhs) {
+ return !(lhs < rhs);
+ }
+
+ template <typename H>
+ friend H AbslHashValue(H h, const FixedArray& v) {
+ return H::combine(H::combine_contiguous(std::move(h), v.data(), v.size()),
+ v.size());
+ }
+
+ private:
+ // StorageElement
+ //
+ // For FixedArrays with a C-style-array value_type, StorageElement is a POD
+ // wrapper struct called StorageElementWrapper that holds the value_type
+ // instance inside. This is needed for construction and destruction of the
+ // entire array regardless of how many dimensions it has. For all other cases,
+ // StorageElement is just an alias of value_type.
+ //
+ // Maintainer's Note: The simpler solution would be to simply wrap value_type
+ // in a struct whether it's an array or not. That causes some paranoid
+ // diagnostics to misfire, believing that 'data()' returns a pointer to a
+ // single element, rather than the packed array that it really is.
+ // e.g.:
+ //
+ // FixedArray<char> buf(1);
+ // sprintf(buf.data(), "foo");
+ //
+ // error: call to int __builtin___sprintf_chk(etc...)
+ // will always overflow destination buffer [-Werror]
+ //
+ template <typename OuterT = value_type,
+ typename InnerT = absl::remove_extent_t<OuterT>,
+ size_t InnerN = std::extent<OuterT>::value>
+ struct StorageElementWrapper {
+ InnerT array[InnerN];
+ };
+
+ using StorageElement =
+ absl::conditional_t<std::is_array<value_type>::value,
+ StorageElementWrapper<value_type>, value_type>;
+ using StorageElementBuffer =
+ absl::aligned_storage_t<sizeof(StorageElement), alignof(StorageElement)>;
+
+ static pointer AsValueType(pointer ptr) { return ptr; }
+ static pointer AsValueType(StorageElementWrapper<value_type>* ptr) {
+ return std::addressof(ptr->array);
+ }
+
+ static_assert(sizeof(StorageElement) == sizeof(value_type), "");
+ static_assert(alignof(StorageElement) == alignof(value_type), "");
+
+ struct NonEmptyInlinedStorage {
+ StorageElement* data() {
+ return reinterpret_cast<StorageElement*>(inlined_storage_.data());
+ }
+
+#ifdef ADDRESS_SANITIZER
+ void* RedzoneBegin() { return &redzone_begin_; }
+ void* RedzoneEnd() { return &redzone_end_ + 1; }
+#endif // ADDRESS_SANITIZER
+
+ void AnnotateConstruct(size_type);
+ void AnnotateDestruct(size_type);
+
+ ADDRESS_SANITIZER_REDZONE(redzone_begin_);
+ std::array<StorageElementBuffer, inline_elements> inlined_storage_;
+ ADDRESS_SANITIZER_REDZONE(redzone_end_);
+ };
+
+ struct EmptyInlinedStorage {
+ StorageElement* data() { return nullptr; }
+ void AnnotateConstruct(size_type) {}
+ void AnnotateDestruct(size_type) {}
+ };
+
+ using InlinedStorage =
+ absl::conditional_t<inline_elements == 0, EmptyInlinedStorage,
+ NonEmptyInlinedStorage>;
+
+ // Storage
+ //
+ // An instance of Storage manages the inline and out-of-line memory for
+ // instances of FixedArray. This guarantees that even when construction of
+ // individual elements fails in the FixedArray constructor body, the
+ // destructor for Storage will still be called and out-of-line memory will be
+ // properly deallocated.
+ //
+ class Storage : public InlinedStorage {
+ public:
+ Storage(size_type n, const allocator_type& a)
+ : size_alloc_(n, a), data_(InitializeData()) {}
+
+ ~Storage() noexcept {
+ if (UsingInlinedStorage(size())) {
+ InlinedStorage::AnnotateDestruct(size());
+ } else {
+ AllocatorTraits::deallocate(alloc(), AsValueType(begin()), size());
+ }
+ }
+
+ size_type size() const { return size_alloc_.template get<0>(); }
+ StorageElement* begin() const { return data_; }
+ StorageElement* end() const { return begin() + size(); }
+ allocator_type& alloc() {
+ return size_alloc_.template get<1>();
+ }
+
+ private:
+ static bool UsingInlinedStorage(size_type n) {
+ return n <= inline_elements;
+ }
+
+ StorageElement* InitializeData() {
+ if (UsingInlinedStorage(size())) {
+ InlinedStorage::AnnotateConstruct(size());
+ return InlinedStorage::data();
+ } else {
+ return reinterpret_cast<StorageElement*>(
+ AllocatorTraits::allocate(alloc(), size()));
+ }
+ }
+
+ // `CompressedTuple` takes advantage of EBCO for stateless `allocator_type`s
+ container_internal::CompressedTuple<size_type, allocator_type> size_alloc_;
+ StorageElement* data_;
+ };
+
+ Storage storage_;
+};
+
+template <typename T, size_t N, typename A>
+constexpr size_t FixedArray<T, N, A>::kInlineBytesDefault;
+
+template <typename T, size_t N, typename A>
+constexpr typename FixedArray<T, N, A>::size_type
+ FixedArray<T, N, A>::inline_elements;
+
+template <typename T, size_t N, typename A>
+void FixedArray<T, N, A>::NonEmptyInlinedStorage::AnnotateConstruct(
+ typename FixedArray<T, N, A>::size_type n) {
+#ifdef ADDRESS_SANITIZER
+ if (!n) return;
+ ANNOTATE_CONTIGUOUS_CONTAINER(data(), RedzoneEnd(), RedzoneEnd(), data() + n);
+ ANNOTATE_CONTIGUOUS_CONTAINER(RedzoneBegin(), data(), data(), RedzoneBegin());
+#endif // ADDRESS_SANITIZER
+ static_cast<void>(n); // Mark used when not in asan mode
+}
+
+template <typename T, size_t N, typename A>
+void FixedArray<T, N, A>::NonEmptyInlinedStorage::AnnotateDestruct(
+ typename FixedArray<T, N, A>::size_type n) {
+#ifdef ADDRESS_SANITIZER
+ if (!n) return;
+ ANNOTATE_CONTIGUOUS_CONTAINER(data(), RedzoneEnd(), data() + n, RedzoneEnd());
+ ANNOTATE_CONTIGUOUS_CONTAINER(RedzoneBegin(), data(), RedzoneBegin(), data());
+#endif // ADDRESS_SANITIZER
+ static_cast<void>(n); // Mark used when not in asan mode
+}
+} // namespace absl
+
+#endif // ABSL_CONTAINER_FIXED_ARRAY_H_
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