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inlined_vector.h (39576B)

---

// Copyright 2019 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.

#ifndef ABSL_CONTAINER_INTERNAL_INLINED_VECTOR_H_
#define ABSL_CONTAINER_INTERNAL_INLINED_VECTOR_H_

#include <algorithm>
#include <cstddef>
#include <cstring>
#include <iterator>
#include <limits>
#include <memory>
#include <new>
#include <type_traits>
#include <utility>

#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/internal/identity.h"
#include "absl/base/macros.h"
#include "absl/container/internal/compressed_tuple.h"
#include "absl/memory/memory.h"
#include "absl/meta/type_traits.h"
#include "absl/types/span.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace inlined_vector_internal {

// GCC does not deal very well with the below code
#if !defined(__clang__) && defined(__GNUC__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Warray-bounds"
#endif

template <typename A>
using AllocatorTraits = std::allocator_traits<A>;
template <typename A>
using ValueType = typename AllocatorTraits<A>::value_type;
template <typename A>
using SizeType = typename AllocatorTraits<A>::size_type;
template <typename A>
using Pointer = typename AllocatorTraits<A>::pointer;
template <typename A>
using ConstPointer = typename AllocatorTraits<A>::const_pointer;
template <typename A>
using SizeType = typename AllocatorTraits<A>::size_type;
template <typename A>
using DifferenceType = typename AllocatorTraits<A>::difference_type;
template <typename A>
using Reference = ValueType<A>&;
template <typename A>
using ConstReference = const ValueType<A>&;
template <typename A>
using Iterator = Pointer<A>;
template <typename A>
using ConstIterator = ConstPointer<A>;
template <typename A>
using ReverseIterator = typename std::reverse_iterator<Iterator<A>>;
template <typename A>
using ConstReverseIterator = typename std::reverse_iterator<ConstIterator<A>>;
template <typename A>
using MoveIterator = typename std::move_iterator<Iterator<A>>;

template <typename A>
using IsMoveAssignOk = std::is_move_assignable<ValueType<A>>;
template <typename A>
using IsSwapOk = absl::type_traits_internal::IsSwappable<ValueType<A>>;

template <typename A,
         bool IsTriviallyDestructible =
             absl::is_trivially_destructible<ValueType<A>>::value &&
             std::is_same<A, std::allocator<ValueType<A>>>::value>
struct DestroyAdapter;

template <typename A>
struct DestroyAdapter<A, /* IsTriviallyDestructible */ false> {
 static void DestroyElements(A& allocator, Pointer<A> destroy_first,
                             SizeType<A> destroy_size) {
   for (SizeType<A> i = destroy_size; i != 0;) {
     --i;
     AllocatorTraits<A>::destroy(allocator, destroy_first + i);
   }
 }
};

template <typename A>
struct DestroyAdapter<A, /* IsTriviallyDestructible */ true> {
 static void DestroyElements(A& allocator, Pointer<A> destroy_first,
                             SizeType<A> destroy_size) {
   static_cast<void>(allocator);
   static_cast<void>(destroy_first);
   static_cast<void>(destroy_size);
 }
};

template <typename A>
struct Allocation {
 Pointer<A> data = nullptr;
 SizeType<A> capacity = 0;
};

template <typename A,
         bool IsOverAligned =
             (alignof(ValueType<A>) > ABSL_INTERNAL_DEFAULT_NEW_ALIGNMENT)>
struct MallocAdapter {
 static Allocation<A> Allocate(A& allocator, SizeType<A> requested_capacity) {
   return {AllocatorTraits<A>::allocate(allocator, requested_capacity),
           requested_capacity};
 }

 static void Deallocate(A& allocator, Pointer<A> pointer,
                        SizeType<A> capacity) {
   AllocatorTraits<A>::deallocate(allocator, pointer, capacity);
 }
};

template <typename A, typename ValueAdapter>
void ConstructElements(absl::internal::type_identity_t<A>& allocator,
                      Pointer<A> construct_first, ValueAdapter& values,
                      SizeType<A> construct_size) {
 for (SizeType<A> i = 0; i < construct_size; ++i) {
   ABSL_INTERNAL_TRY { values.ConstructNext(allocator, construct_first + i); }
   ABSL_INTERNAL_CATCH_ANY {
     DestroyAdapter<A>::DestroyElements(allocator, construct_first, i);
     ABSL_INTERNAL_RETHROW;
   }
 }
}

template <typename A, typename ValueAdapter>
void AssignElements(Pointer<A> assign_first, ValueAdapter& values,
                   SizeType<A> assign_size) {
 for (SizeType<A> i = 0; i < assign_size; ++i) {
   values.AssignNext(assign_first + i);
 }
}

template <typename A>
struct StorageView {
 Pointer<A> data;
 SizeType<A> size;
 SizeType<A> capacity;
};

template <typename A, typename Iterator>
class IteratorValueAdapter {
public:
 explicit IteratorValueAdapter(const Iterator& it) : it_(it) {}

 void ConstructNext(A& allocator, Pointer<A> construct_at) {
   AllocatorTraits<A>::construct(allocator, construct_at, *it_);
   ++it_;
 }

 void AssignNext(Pointer<A> assign_at) {
   *assign_at = *it_;
   ++it_;
 }

private:
 Iterator it_;
};

template <typename A>
class CopyValueAdapter {
public:
 explicit CopyValueAdapter(ConstPointer<A> p) : ptr_(p) {}

 void ConstructNext(A& allocator, Pointer<A> construct_at) {
   AllocatorTraits<A>::construct(allocator, construct_at, *ptr_);
 }

 void AssignNext(Pointer<A> assign_at) { *assign_at = *ptr_; }

private:
 ConstPointer<A> ptr_;
};

template <typename A>
class DefaultValueAdapter {
public:
 explicit DefaultValueAdapter() {}

 void ConstructNext(A& allocator, Pointer<A> construct_at) {
   AllocatorTraits<A>::construct(allocator, construct_at);
 }

 void AssignNext(Pointer<A> assign_at) { *assign_at = ValueType<A>(); }
};

template <typename A>
class AllocationTransaction {
public:
 explicit AllocationTransaction(A& allocator)
     : allocator_data_(allocator, nullptr), capacity_(0) {}

 ~AllocationTransaction() {
   if (DidAllocate()) {
     MallocAdapter<A>::Deallocate(GetAllocator(), GetData(), GetCapacity());
   }
 }

 AllocationTransaction(const AllocationTransaction&) = delete;
 void operator=(const AllocationTransaction&) = delete;

 A& GetAllocator() { return allocator_data_.template get<0>(); }
 Pointer<A>& GetData() { return allocator_data_.template get<1>(); }
 SizeType<A>& GetCapacity() { return capacity_; }

 bool DidAllocate() { return GetData() != nullptr; }

 Pointer<A> Allocate(SizeType<A> requested_capacity) {
   Allocation<A> result =
       MallocAdapter<A>::Allocate(GetAllocator(), requested_capacity);
   GetData() = result.data;
   GetCapacity() = result.capacity;
   return result.data;
 }

 [[nodiscard]] Allocation<A> Release() && {
   Allocation<A> result = {GetData(), GetCapacity()};
   Reset();
   return result;
 }

private:
 void Reset() {
   GetData() = nullptr;
   GetCapacity() = 0;
 }

 container_internal::CompressedTuple<A, Pointer<A>> allocator_data_;
 SizeType<A> capacity_;
};

template <typename A>
class ConstructionTransaction {
public:
 explicit ConstructionTransaction(A& allocator)
     : allocator_data_(allocator, nullptr), size_(0) {}

 ~ConstructionTransaction() {
   if (DidConstruct()) {
     DestroyAdapter<A>::DestroyElements(GetAllocator(), GetData(), GetSize());
   }
 }

 ConstructionTransaction(const ConstructionTransaction&) = delete;
 void operator=(const ConstructionTransaction&) = delete;

 A& GetAllocator() { return allocator_data_.template get<0>(); }
 Pointer<A>& GetData() { return allocator_data_.template get<1>(); }
 SizeType<A>& GetSize() { return size_; }

 bool DidConstruct() { return GetData() != nullptr; }
 template <typename ValueAdapter>
 void Construct(Pointer<A> data, ValueAdapter& values, SizeType<A> size) {
   ConstructElements<A>(GetAllocator(), data, values, size);
   GetData() = data;
   GetSize() = size;
 }
 void Commit() && {
   GetData() = nullptr;
   GetSize() = 0;
 }

private:
 container_internal::CompressedTuple<A, Pointer<A>> allocator_data_;
 SizeType<A> size_;
};

template <typename T, size_t N, typename A>
class Storage {
public:
 struct MemcpyPolicy {};
 struct ElementwiseAssignPolicy {};
 struct ElementwiseSwapPolicy {};
 struct ElementwiseConstructPolicy {};

 using MoveAssignmentPolicy = absl::conditional_t<
     // Fast path: if the value type can be trivially move assigned and
     // destroyed, and we know the allocator doesn't do anything fancy, then
     // it's safe for us to simply adopt the contents of the storage for
     // `other` and remove its own reference to them. It's as if we had
     // individually move-assigned each value and then destroyed the original.
     absl::conjunction<absl::is_trivially_move_assignable<ValueType<A>>,
                       absl::is_trivially_destructible<ValueType<A>>,
                       std::is_same<A, std::allocator<ValueType<A>>>>::value,
     MemcpyPolicy,
     // Otherwise we use move assignment if possible. If not, we simulate
     // move assignment using move construction.
     //
     // Note that this is in contrast to e.g. std::vector and std::optional,
     // which are themselves not move-assignable when their contained type is
     // not.
     absl::conditional_t<IsMoveAssignOk<A>::value, ElementwiseAssignPolicy,
                         ElementwiseConstructPolicy>>;

 // The policy to be used specifically when swapping inlined elements.
 using SwapInlinedElementsPolicy = absl::conditional_t<
     // Fast path: if the value type can be trivially relocated, and we
     // know the allocator doesn't do anything fancy, then it's safe for us
     // to simply swap the bytes in the inline storage. It's as if we had
     // relocated the first vector's elements into temporary storage,
     // relocated the second's elements into the (now-empty) first's,
     // and then relocated from temporary storage into the second.
     absl::conjunction<absl::is_trivially_relocatable<ValueType<A>>,
                       std::is_same<A, std::allocator<ValueType<A>>>>::value,
     MemcpyPolicy,
     absl::conditional_t<IsSwapOk<A>::value, ElementwiseSwapPolicy,
                         ElementwiseConstructPolicy>>;

 static SizeType<A> NextCapacity(SizeType<A> current_capacity) {
   return current_capacity * 2;
 }

 static SizeType<A> ComputeCapacity(SizeType<A> current_capacity,
                                    SizeType<A> requested_capacity) {
   return (std::max)(NextCapacity(current_capacity), requested_capacity);
 }

 // ---------------------------------------------------------------------------
 // Storage Constructors and Destructor
 // ---------------------------------------------------------------------------

 Storage() : metadata_(A(), /* size and is_allocated */ 0u) {}

 explicit Storage(const A& allocator)
     : metadata_(allocator, /* size and is_allocated */ 0u) {}

 ~Storage() {
   // Fast path: if we are empty and not allocated, there's nothing to do.
   if (GetSizeAndIsAllocated() == 0) {
     return;
   }

   // Fast path: if no destructors need to be run and we know the allocator
   // doesn't do anything fancy, then all we need to do is deallocate (and
   // maybe not even that).
   if (absl::is_trivially_destructible<ValueType<A>>::value &&
       std::is_same<A, std::allocator<ValueType<A>>>::value) {
     DeallocateIfAllocated();
     return;
   }

   DestroyContents();
 }

 // ---------------------------------------------------------------------------
 // Storage Member Accessors
 // ---------------------------------------------------------------------------

 SizeType<A>& GetSizeAndIsAllocated() { return metadata_.template get<1>(); }

 const SizeType<A>& GetSizeAndIsAllocated() const {
   return metadata_.template get<1>();
 }

 SizeType<A> GetSize() const { return GetSizeAndIsAllocated() >> 1; }

 bool GetIsAllocated() const { return GetSizeAndIsAllocated() & 1; }

 Pointer<A> GetAllocatedData() {
   // GCC 12 has a false-positive -Wmaybe-uninitialized warning here.
#if ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(12, 0)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
#endif
   return data_.allocated.allocated_data;
#if ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(12, 0)
#pragma GCC diagnostic pop
#endif
 }

 ConstPointer<A> GetAllocatedData() const {
   return data_.allocated.allocated_data;
 }

 // ABSL_ATTRIBUTE_NO_SANITIZE_CFI is used because the memory pointed to may be
 // uninitialized, a common pattern in allocate()+construct() APIs.
 // https://clang.llvm.org/docs/ControlFlowIntegrity.html#bad-cast-checking
 // NOTE: When this was written, LLVM documentation did not explicitly
 // mention that casting `char*` and using `reinterpret_cast` qualifies
 // as a bad cast.
 ABSL_ATTRIBUTE_NO_SANITIZE_CFI Pointer<A> GetInlinedData() {
   return reinterpret_cast<Pointer<A>>(data_.inlined.inlined_data);
 }

 ABSL_ATTRIBUTE_NO_SANITIZE_CFI ConstPointer<A> GetInlinedData() const {
   return reinterpret_cast<ConstPointer<A>>(data_.inlined.inlined_data);
 }

 SizeType<A> GetAllocatedCapacity() const {
   return data_.allocated.allocated_capacity;
 }

 SizeType<A> GetInlinedCapacity() const {
   return static_cast<SizeType<A>>(kOptimalInlinedSize);
 }

 StorageView<A> MakeStorageView() {
   return GetIsAllocated() ? StorageView<A>{GetAllocatedData(), GetSize(),
                                            GetAllocatedCapacity()}
                           : StorageView<A>{GetInlinedData(), GetSize(),
                                            GetInlinedCapacity()};
 }

 A& GetAllocator() { return metadata_.template get<0>(); }

 const A& GetAllocator() const { return metadata_.template get<0>(); }

 // ---------------------------------------------------------------------------
 // Storage Member Mutators
 // ---------------------------------------------------------------------------

 ABSL_ATTRIBUTE_NOINLINE void InitFrom(const Storage& other);

 template <typename ValueAdapter>
 void Initialize(ValueAdapter values, SizeType<A> new_size);

 template <typename ValueAdapter>
 void Assign(ValueAdapter values, SizeType<A> new_size);

 template <typename ValueAdapter>
 void Resize(ValueAdapter values, SizeType<A> new_size);

 template <typename ValueAdapter>
 Iterator<A> Insert(ConstIterator<A> pos, ValueAdapter values,
                    SizeType<A> insert_count);

 template <typename... Args>
 Reference<A> EmplaceBack(Args&&... args);

 Iterator<A> Erase(ConstIterator<A> from, ConstIterator<A> to);

 void Reserve(SizeType<A> requested_capacity);

 void ShrinkToFit();

 void Swap(Storage* other_storage_ptr);

 void SetIsAllocated() {
   GetSizeAndIsAllocated() |= static_cast<SizeType<A>>(1);
 }

 void UnsetIsAllocated() {
   GetSizeAndIsAllocated() &= ((std::numeric_limits<SizeType<A>>::max)() - 1);
 }

 void SetSize(SizeType<A> size) {
   GetSizeAndIsAllocated() =
       (size << 1) | static_cast<SizeType<A>>(GetIsAllocated());
 }

 void SetAllocatedSize(SizeType<A> size) {
   GetSizeAndIsAllocated() = (size << 1) | static_cast<SizeType<A>>(1);
 }

 void SetInlinedSize(SizeType<A> size) {
   GetSizeAndIsAllocated() = size << static_cast<SizeType<A>>(1);
 }

 void AddSize(SizeType<A> count) {
   GetSizeAndIsAllocated() += count << static_cast<SizeType<A>>(1);
 }

 void SubtractSize(SizeType<A> count) {
   ABSL_HARDENING_ASSERT(count <= GetSize());

   GetSizeAndIsAllocated() -= count << static_cast<SizeType<A>>(1);
 }

 void SetAllocation(Allocation<A> allocation) {
   data_.allocated.allocated_data = allocation.data;
   data_.allocated.allocated_capacity = allocation.capacity;
 }

 void MemcpyFrom(const Storage& other_storage) {
   // Assumption check: it doesn't make sense to memcpy inlined elements unless
   // we know the allocator doesn't do anything fancy, and one of the following
   // holds:
   //
   //  *  The elements are trivially relocatable.
   //
   //  *  It's possible to trivially assign the elements and then destroy the
   //     source.
   //
   //  *  It's possible to trivially copy construct/assign the elements.
   //
   {
     using V = ValueType<A>;
     ABSL_HARDENING_ASSERT(
         other_storage.GetIsAllocated() ||
         (std::is_same<A, std::allocator<V>>::value &&
          (
              // First case above
              absl::is_trivially_relocatable<V>::value ||
              // Second case above
              (absl::is_trivially_move_assignable<V>::value &&
               absl::is_trivially_destructible<V>::value) ||
              // Third case above
              (absl::is_trivially_copy_constructible<V>::value ||
               absl::is_trivially_copy_assignable<V>::value))));
   }

   GetSizeAndIsAllocated() = other_storage.GetSizeAndIsAllocated();
   data_ = other_storage.data_;
 }

 void DeallocateIfAllocated() {
   if (GetIsAllocated()) {
     MallocAdapter<A>::Deallocate(GetAllocator(), GetAllocatedData(),
                                  GetAllocatedCapacity());
   }
 }

private:
 ABSL_ATTRIBUTE_NOINLINE void DestroyContents();

 using Metadata = container_internal::CompressedTuple<A, SizeType<A>>;

 struct Allocated {
   Pointer<A> allocated_data;
   SizeType<A> allocated_capacity;
 };

 // `kOptimalInlinedSize` is an automatically adjusted inlined capacity of the
 // `InlinedVector`. Sometimes, it is possible to increase the capacity (from
 // the user requested `N`) without increasing the size of the `InlinedVector`.
 static constexpr size_t kOptimalInlinedSize =
     (std::max)(N, sizeof(Allocated) / sizeof(ValueType<A>));

 struct Inlined {
   alignas(ValueType<A>) unsigned char inlined_data[sizeof(
       ValueType<A>[kOptimalInlinedSize])];
 };

 union Data {
   Allocated allocated;
   Inlined inlined;
 };

 void SwapN(ElementwiseSwapPolicy, Storage* other, SizeType<A> n);
 void SwapN(ElementwiseConstructPolicy, Storage* other, SizeType<A> n);

 void SwapInlinedElements(MemcpyPolicy, Storage* other);
 template <typename NotMemcpyPolicy>
 void SwapInlinedElements(NotMemcpyPolicy, Storage* other);

 template <typename... Args>
 ABSL_ATTRIBUTE_NOINLINE Reference<A> EmplaceBackSlow(Args&&... args);

 Metadata metadata_;
 Data data_;
};

template <typename T, size_t N, typename A>
void Storage<T, N, A>::DestroyContents() {
 Pointer<A> data = GetIsAllocated() ? GetAllocatedData() : GetInlinedData();
 DestroyAdapter<A>::DestroyElements(GetAllocator(), data, GetSize());
 DeallocateIfAllocated();
}

template <typename T, size_t N, typename A>
void Storage<T, N, A>::InitFrom(const Storage& other) {
 const SizeType<A> n = other.GetSize();
 ABSL_HARDENING_ASSERT(n > 0);  // Empty sources handled handled in caller.
 ConstPointer<A> src;
 Pointer<A> dst;
 if (!other.GetIsAllocated()) {
   dst = GetInlinedData();
   src = other.GetInlinedData();
 } else {
   // Because this is only called from the `InlinedVector` constructors, it's
   // safe to take on the allocation with size `0`. If `ConstructElements(...)`
   // throws, deallocation will be automatically handled by `~Storage()`.
   SizeType<A> requested_capacity = ComputeCapacity(GetInlinedCapacity(), n);
   Allocation<A> allocation =
       MallocAdapter<A>::Allocate(GetAllocator(), requested_capacity);
   SetAllocation(allocation);
   dst = allocation.data;
   src = other.GetAllocatedData();
 }

 // Fast path: if the value type is trivially copy constructible and we know
 // the allocator doesn't do anything fancy, then we know it is legal for us to
 // simply memcpy the other vector's elements.
 if (absl::is_trivially_copy_constructible<ValueType<A>>::value &&
     std::is_same<A, std::allocator<ValueType<A>>>::value) {
   std::memcpy(reinterpret_cast<char*>(dst),
               reinterpret_cast<const char*>(src), n * sizeof(ValueType<A>));
 } else {
   auto values = IteratorValueAdapter<A, ConstPointer<A>>(src);
   ConstructElements<A>(GetAllocator(), dst, values, n);
 }

 GetSizeAndIsAllocated() = other.GetSizeAndIsAllocated();
}

template <typename T, size_t N, typename A>
template <typename ValueAdapter>
auto Storage<T, N, A>::Initialize(ValueAdapter values,
                                 SizeType<A> new_size) -> void {
 // Only callable from constructors!
 ABSL_HARDENING_ASSERT(!GetIsAllocated());
 ABSL_HARDENING_ASSERT(GetSize() == 0);

 Pointer<A> construct_data;
 if (new_size > GetInlinedCapacity()) {
   // Because this is only called from the `InlinedVector` constructors, it's
   // safe to take on the allocation with size `0`. If `ConstructElements(...)`
   // throws, deallocation will be automatically handled by `~Storage()`.
   SizeType<A> requested_capacity =
       ComputeCapacity(GetInlinedCapacity(), new_size);
   Allocation<A> allocation =
       MallocAdapter<A>::Allocate(GetAllocator(), requested_capacity);
   construct_data = allocation.data;
   SetAllocation(allocation);
   SetIsAllocated();
 } else {
   construct_data = GetInlinedData();
 }

 ConstructElements<A>(GetAllocator(), construct_data, values, new_size);

 // Since the initial size was guaranteed to be `0` and the allocated bit is
 // already correct for either case, *adding* `new_size` gives us the correct
 // result faster than setting it directly.
 AddSize(new_size);
}

template <typename T, size_t N, typename A>
template <typename ValueAdapter>
auto Storage<T, N, A>::Assign(ValueAdapter values,
                             SizeType<A> new_size) -> void {
 StorageView<A> storage_view = MakeStorageView();

 AllocationTransaction<A> allocation_tx(GetAllocator());

 absl::Span<ValueType<A>> assign_loop;
 absl::Span<ValueType<A>> construct_loop;
 absl::Span<ValueType<A>> destroy_loop;

 if (new_size > storage_view.capacity) {
   SizeType<A> requested_capacity =
       ComputeCapacity(storage_view.capacity, new_size);
   construct_loop = {allocation_tx.Allocate(requested_capacity), new_size};
   destroy_loop = {storage_view.data, storage_view.size};
 } else if (new_size > storage_view.size) {
   assign_loop = {storage_view.data, storage_view.size};
   construct_loop = {storage_view.data + storage_view.size,
                     new_size - storage_view.size};
 } else {
   assign_loop = {storage_view.data, new_size};
   destroy_loop = {storage_view.data + new_size, storage_view.size - new_size};
 }

 AssignElements<A>(assign_loop.data(), values, assign_loop.size());

 ConstructElements<A>(GetAllocator(), construct_loop.data(), values,
                      construct_loop.size());

 DestroyAdapter<A>::DestroyElements(GetAllocator(), destroy_loop.data(),
                                    destroy_loop.size());

 if (allocation_tx.DidAllocate()) {
   DeallocateIfAllocated();
   SetAllocation(std::move(allocation_tx).Release());
   SetIsAllocated();
 }

 SetSize(new_size);
}

template <typename T, size_t N, typename A>
template <typename ValueAdapter>
auto Storage<T, N, A>::Resize(ValueAdapter values,
                             SizeType<A> new_size) -> void {
 StorageView<A> storage_view = MakeStorageView();
 Pointer<A> const base = storage_view.data;
 const SizeType<A> size = storage_view.size;
 A& alloc = GetAllocator();
 if (new_size <= size) {
   // Destroy extra old elements.
   DestroyAdapter<A>::DestroyElements(alloc, base + new_size, size - new_size);
 } else if (new_size <= storage_view.capacity) {
   // Construct new elements in place.
   ConstructElements<A>(alloc, base + size, values, new_size - size);
 } else {
   // Steps:
   //  a. Allocate new backing store.
   //  b. Construct new elements in new backing store.
   //  c. Move existing elements from old backing store to new backing store.
   //  d. Destroy all elements in old backing store.
   // Use transactional wrappers for the first two steps so we can roll
   // back if necessary due to exceptions.
   AllocationTransaction<A> allocation_tx(alloc);
   SizeType<A> requested_capacity =
       ComputeCapacity(storage_view.capacity, new_size);
   Pointer<A> new_data = allocation_tx.Allocate(requested_capacity);

   ConstructionTransaction<A> construction_tx(alloc);
   construction_tx.Construct(new_data + size, values, new_size - size);

   IteratorValueAdapter<A, MoveIterator<A>> move_values(
       (MoveIterator<A>(base)));
   ConstructElements<A>(alloc, new_data, move_values, size);

   DestroyAdapter<A>::DestroyElements(alloc, base, size);
   std::move(construction_tx).Commit();
   DeallocateIfAllocated();
   SetAllocation(std::move(allocation_tx).Release());
   SetIsAllocated();
 }
 SetSize(new_size);
}

template <typename T, size_t N, typename A>
template <typename ValueAdapter>
auto Storage<T, N, A>::Insert(ConstIterator<A> pos, ValueAdapter values,
                             SizeType<A> insert_count) -> Iterator<A> {
 StorageView<A> storage_view = MakeStorageView();

 auto insert_index = static_cast<SizeType<A>>(
     std::distance(ConstIterator<A>(storage_view.data), pos));
 SizeType<A> insert_end_index = insert_index + insert_count;
 SizeType<A> new_size = storage_view.size + insert_count;

 if (new_size > storage_view.capacity) {
   AllocationTransaction<A> allocation_tx(GetAllocator());
   ConstructionTransaction<A> construction_tx(GetAllocator());
   ConstructionTransaction<A> move_construction_tx(GetAllocator());

   IteratorValueAdapter<A, MoveIterator<A>> move_values(
       MoveIterator<A>(storage_view.data));

   SizeType<A> requested_capacity =
       ComputeCapacity(storage_view.capacity, new_size);
   Pointer<A> new_data = allocation_tx.Allocate(requested_capacity);

   construction_tx.Construct(new_data + insert_index, values, insert_count);

   move_construction_tx.Construct(new_data, move_values, insert_index);

   ConstructElements<A>(GetAllocator(), new_data + insert_end_index,
                        move_values, storage_view.size - insert_index);

   DestroyAdapter<A>::DestroyElements(GetAllocator(), storage_view.data,
                                      storage_view.size);

   std::move(construction_tx).Commit();
   std::move(move_construction_tx).Commit();
   DeallocateIfAllocated();
   SetAllocation(std::move(allocation_tx).Release());

   SetAllocatedSize(new_size);
   return Iterator<A>(new_data + insert_index);
 } else {
   SizeType<A> move_construction_destination_index =
       (std::max)(insert_end_index, storage_view.size);

   ConstructionTransaction<A> move_construction_tx(GetAllocator());

   IteratorValueAdapter<A, MoveIterator<A>> move_construction_values(
       MoveIterator<A>(storage_view.data +
                       (move_construction_destination_index - insert_count)));
   absl::Span<ValueType<A>> move_construction = {
       storage_view.data + move_construction_destination_index,
       new_size - move_construction_destination_index};

   Pointer<A> move_assignment_values = storage_view.data + insert_index;
   absl::Span<ValueType<A>> move_assignment = {
       storage_view.data + insert_end_index,
       move_construction_destination_index - insert_end_index};

   absl::Span<ValueType<A>> insert_assignment = {move_assignment_values,
                                                 move_construction.size()};

   absl::Span<ValueType<A>> insert_construction = {
       insert_assignment.data() + insert_assignment.size(),
       insert_count - insert_assignment.size()};

   move_construction_tx.Construct(move_construction.data(),
                                  move_construction_values,
                                  move_construction.size());

   for (Pointer<A>
            destination = move_assignment.data() + move_assignment.size(),
            last_destination = move_assignment.data(),
            source = move_assignment_values + move_assignment.size();
        ;) {
     --destination;
     --source;
     if (destination < last_destination) break;
     *destination = std::move(*source);
   }

   AssignElements<A>(insert_assignment.data(), values,
                     insert_assignment.size());

   ConstructElements<A>(GetAllocator(), insert_construction.data(), values,
                        insert_construction.size());

   std::move(move_construction_tx).Commit();

   AddSize(insert_count);
   return Iterator<A>(storage_view.data + insert_index);
 }
}

template <typename T, size_t N, typename A>
template <typename... Args>
auto Storage<T, N, A>::EmplaceBack(Args&&... args) -> Reference<A> {
 StorageView<A> storage_view = MakeStorageView();
 const SizeType<A> n = storage_view.size;
 if (ABSL_PREDICT_TRUE(n != storage_view.capacity)) {
   // Fast path; new element fits.
   Pointer<A> last_ptr = storage_view.data + n;
   AllocatorTraits<A>::construct(GetAllocator(), last_ptr,
                                 std::forward<Args>(args)...);
   AddSize(1);
   return *last_ptr;
 }
 // TODO(b/173712035): Annotate with musttail attribute to prevent regression.
 return EmplaceBackSlow(std::forward<Args>(args)...);
}

template <typename T, size_t N, typename A>
template <typename... Args>
auto Storage<T, N, A>::EmplaceBackSlow(Args&&... args) -> Reference<A> {
 StorageView<A> storage_view = MakeStorageView();
 AllocationTransaction<A> allocation_tx(GetAllocator());
 IteratorValueAdapter<A, MoveIterator<A>> move_values(
     MoveIterator<A>(storage_view.data));
 SizeType<A> requested_capacity = NextCapacity(storage_view.capacity);
 Pointer<A> construct_data = allocation_tx.Allocate(requested_capacity);
 Pointer<A> last_ptr = construct_data + storage_view.size;

 // Construct new element.
 AllocatorTraits<A>::construct(GetAllocator(), last_ptr,
                               std::forward<Args>(args)...);
 // Move elements from old backing store to new backing store.
 ABSL_INTERNAL_TRY {
   ConstructElements<A>(GetAllocator(), allocation_tx.GetData(), move_values,
                        storage_view.size);
 }
 ABSL_INTERNAL_CATCH_ANY {
   AllocatorTraits<A>::destroy(GetAllocator(), last_ptr);
   ABSL_INTERNAL_RETHROW;
 }
 // Destroy elements in old backing store.
 DestroyAdapter<A>::DestroyElements(GetAllocator(), storage_view.data,
                                    storage_view.size);

 DeallocateIfAllocated();
 SetAllocation(std::move(allocation_tx).Release());
 SetIsAllocated();
 AddSize(1);
 return *last_ptr;
}

template <typename T, size_t N, typename A>
auto Storage<T, N, A>::Erase(ConstIterator<A> from,
                            ConstIterator<A> to) -> Iterator<A> {
 StorageView<A> storage_view = MakeStorageView();

 auto erase_size = static_cast<SizeType<A>>(std::distance(from, to));
 auto erase_index = static_cast<SizeType<A>>(
     std::distance(ConstIterator<A>(storage_view.data), from));
 SizeType<A> erase_end_index = erase_index + erase_size;

 // Fast path: if the value type is trivially relocatable and we know
 // the allocator doesn't do anything fancy, then we know it is legal for us to
 // simply destroy the elements in the "erasure window" (which cannot throw)
 // and then memcpy downward to close the window.
 if (absl::is_trivially_relocatable<ValueType<A>>::value &&
     std::is_nothrow_destructible<ValueType<A>>::value &&
     std::is_same<A, std::allocator<ValueType<A>>>::value) {
   DestroyAdapter<A>::DestroyElements(
       GetAllocator(), storage_view.data + erase_index, erase_size);
   std::memmove(
       reinterpret_cast<char*>(storage_view.data + erase_index),
       reinterpret_cast<const char*>(storage_view.data + erase_end_index),
       (storage_view.size - erase_end_index) * sizeof(ValueType<A>));
 } else {
   IteratorValueAdapter<A, MoveIterator<A>> move_values(
       MoveIterator<A>(storage_view.data + erase_end_index));

   AssignElements<A>(storage_view.data + erase_index, move_values,
                     storage_view.size - erase_end_index);

   DestroyAdapter<A>::DestroyElements(
       GetAllocator(), storage_view.data + (storage_view.size - erase_size),
       erase_size);
 }
 SubtractSize(erase_size);
 return Iterator<A>(storage_view.data + erase_index);
}

template <typename T, size_t N, typename A>
auto Storage<T, N, A>::Reserve(SizeType<A> requested_capacity) -> void {
 StorageView<A> storage_view = MakeStorageView();

 if (ABSL_PREDICT_FALSE(requested_capacity <= storage_view.capacity)) return;

 AllocationTransaction<A> allocation_tx(GetAllocator());

 IteratorValueAdapter<A, MoveIterator<A>> move_values(
     MoveIterator<A>(storage_view.data));

 SizeType<A> new_requested_capacity =
     ComputeCapacity(storage_view.capacity, requested_capacity);
 Pointer<A> new_data = allocation_tx.Allocate(new_requested_capacity);

 ConstructElements<A>(GetAllocator(), new_data, move_values,
                      storage_view.size);

 DestroyAdapter<A>::DestroyElements(GetAllocator(), storage_view.data,
                                    storage_view.size);

 DeallocateIfAllocated();
 SetAllocation(std::move(allocation_tx).Release());
 SetIsAllocated();
}

template <typename T, size_t N, typename A>
auto Storage<T, N, A>::ShrinkToFit() -> void {
 // May only be called on allocated instances!
 ABSL_HARDENING_ASSERT(GetIsAllocated());

 StorageView<A> storage_view{GetAllocatedData(), GetSize(),
                             GetAllocatedCapacity()};

 if (ABSL_PREDICT_FALSE(storage_view.size == storage_view.capacity)) return;

 AllocationTransaction<A> allocation_tx(GetAllocator());

 IteratorValueAdapter<A, MoveIterator<A>> move_values(
     MoveIterator<A>(storage_view.data));

 Pointer<A> construct_data;
 if (storage_view.size > GetInlinedCapacity()) {
   SizeType<A> requested_capacity = storage_view.size;
   construct_data = allocation_tx.Allocate(requested_capacity);
   if (allocation_tx.GetCapacity() >= storage_view.capacity) {
     // Already using the smallest available heap allocation.
     return;
   }
 } else {
   construct_data = GetInlinedData();
 }

 ABSL_INTERNAL_TRY {
   ConstructElements<A>(GetAllocator(), construct_data, move_values,
                        storage_view.size);
 }
 ABSL_INTERNAL_CATCH_ANY {
   SetAllocation({storage_view.data, storage_view.capacity});
   ABSL_INTERNAL_RETHROW;
 }

 DestroyAdapter<A>::DestroyElements(GetAllocator(), storage_view.data,
                                    storage_view.size);

 MallocAdapter<A>::Deallocate(GetAllocator(), storage_view.data,
                              storage_view.capacity);

 if (allocation_tx.DidAllocate()) {
   SetAllocation(std::move(allocation_tx).Release());
 } else {
   UnsetIsAllocated();
 }
}

template <typename T, size_t N, typename A>
auto Storage<T, N, A>::Swap(Storage* other_storage_ptr) -> void {
 using std::swap;
 ABSL_HARDENING_ASSERT(this != other_storage_ptr);

 if (GetIsAllocated() && other_storage_ptr->GetIsAllocated()) {
   swap(data_.allocated, other_storage_ptr->data_.allocated);
 } else if (!GetIsAllocated() && !other_storage_ptr->GetIsAllocated()) {
   SwapInlinedElements(SwapInlinedElementsPolicy{}, other_storage_ptr);
 } else {
   Storage* allocated_ptr = this;
   Storage* inlined_ptr = other_storage_ptr;
   if (!allocated_ptr->GetIsAllocated()) swap(allocated_ptr, inlined_ptr);

   StorageView<A> allocated_storage_view{
       allocated_ptr->GetAllocatedData(), allocated_ptr->GetSize(),
       allocated_ptr->GetAllocatedCapacity()};

   IteratorValueAdapter<A, MoveIterator<A>> move_values(
       MoveIterator<A>(inlined_ptr->GetInlinedData()));

   ABSL_INTERNAL_TRY {
     ConstructElements<A>(inlined_ptr->GetAllocator(),
                          allocated_ptr->GetInlinedData(), move_values,
                          inlined_ptr->GetSize());
   }
   ABSL_INTERNAL_CATCH_ANY {
     allocated_ptr->SetAllocation(Allocation<A>{
         allocated_storage_view.data, allocated_storage_view.capacity});
     ABSL_INTERNAL_RETHROW;
   }

   DestroyAdapter<A>::DestroyElements(inlined_ptr->GetAllocator(),
                                      inlined_ptr->GetInlinedData(),
                                      inlined_ptr->GetSize());

   inlined_ptr->SetAllocation(Allocation<A>{allocated_storage_view.data,
                                            allocated_storage_view.capacity});
 }

 swap(GetSizeAndIsAllocated(), other_storage_ptr->GetSizeAndIsAllocated());
 swap(GetAllocator(), other_storage_ptr->GetAllocator());
}

template <typename T, size_t N, typename A>
void Storage<T, N, A>::SwapN(ElementwiseSwapPolicy, Storage* other,
                            SizeType<A> n) {
 std::swap_ranges(GetInlinedData(), GetInlinedData() + n,
                  other->GetInlinedData());
}

template <typename T, size_t N, typename A>
void Storage<T, N, A>::SwapN(ElementwiseConstructPolicy, Storage* other,
                            SizeType<A> n) {
 Pointer<A> a = GetInlinedData();
 Pointer<A> b = other->GetInlinedData();
 // see note on allocators in `SwapInlinedElements`.
 A& allocator_a = GetAllocator();
 A& allocator_b = other->GetAllocator();
 for (SizeType<A> i = 0; i < n; ++i, ++a, ++b) {
   ValueType<A> tmp(std::move(*a));

   AllocatorTraits<A>::destroy(allocator_a, a);
   AllocatorTraits<A>::construct(allocator_b, a, std::move(*b));

   AllocatorTraits<A>::destroy(allocator_b, b);
   AllocatorTraits<A>::construct(allocator_a, b, std::move(tmp));
 }
}

template <typename T, size_t N, typename A>
void Storage<T, N, A>::SwapInlinedElements(MemcpyPolicy, Storage* other) {
 Data tmp = data_;
 data_ = other->data_;
 other->data_ = tmp;
}

template <typename T, size_t N, typename A>
template <typename NotMemcpyPolicy>
void Storage<T, N, A>::SwapInlinedElements(NotMemcpyPolicy policy,
                                          Storage* other) {
 // Note: `destroy` needs to use pre-swap allocator while `construct` -
 // post-swap allocator. Allocators will be swapped later on outside of
 // `SwapInlinedElements`.
 Storage* small_ptr = this;
 Storage* large_ptr = other;
 if (small_ptr->GetSize() > large_ptr->GetSize()) {
   std::swap(small_ptr, large_ptr);
 }

 auto small_size = small_ptr->GetSize();
 auto diff = large_ptr->GetSize() - small_size;
 SwapN(policy, other, small_size);

 IteratorValueAdapter<A, MoveIterator<A>> move_values(
     MoveIterator<A>(large_ptr->GetInlinedData() + small_size));

 ConstructElements<A>(large_ptr->GetAllocator(),
                      small_ptr->GetInlinedData() + small_size, move_values,
                      diff);

 DestroyAdapter<A>::DestroyElements(large_ptr->GetAllocator(),
                                    large_ptr->GetInlinedData() + small_size,
                                    diff);
}

// End ignore "array-bounds"
#if !defined(__clang__) && defined(__GNUC__)
#pragma GCC diagnostic pop
#endif

}  // namespace inlined_vector_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_CONTAINER_INTERNAL_INLINED_VECTOR_H_