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// Copyright (c) 2018 Google LLC
//
// 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
//
// http://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 SOURCE_UTIL_SMALL_VECTOR_H_
#define SOURCE_UTIL_SMALL_VECTOR_H_
#include <array>
#include <cassert>
#include <cstddef>
#include <iostream>
#include <memory>
#include <utility>
#include <vector>
#include "source/util/make_unique.h"
namespace spvtools {
namespace utils {
// The |SmallVector| class is intended to be a drop-in replacement for
// |std::vector|. The difference is in the implementation. A |SmallVector| is
// optimized for when the number of elements in the vector are small. Small is
// defined by the template parameter |small_size|.
//
// Note that |SmallVector| is not always faster than an |std::vector|, so you
// should experiment with different values for |small_size| and compare to
// using and |std::vector|.
//
// TODO: I have implemented the public member functions from |std::vector| that
// I needed. If others are needed they should be implemented. Do not implement
// public member functions that are not defined by std::vector.
template <class T, size_t small_size>
class SmallVector {
public:
using iterator = T*;
using const_iterator = const T*;
SmallVector()
: size_(0),
small_data_(reinterpret_cast<T*>(buffer)),
large_data_(nullptr) {}
SmallVector(const SmallVector& that) : SmallVector() { *this = that; }
SmallVector(SmallVector&& that) : SmallVector() { *this = std::move(that); }
SmallVector(const std::vector<T>& vec) : SmallVector() {
if (vec.size() > small_size) {
large_data_ = MakeUnique<std::vector<T>>(vec);
} else {
size_ = vec.size();
for (uint32_t i = 0; i < size_; i++) {
new (small_data_ + i) T(vec[i]);
}
}
}
template <class InputIt>
SmallVector(InputIt first, InputIt last) : SmallVector() {
insert(end(), first, last);
}
SmallVector(std::vector<T>&& vec) : SmallVector() {
if (vec.size() > small_size) {
large_data_ = MakeUnique<std::vector<T>>(std::move(vec));
} else {
size_ = vec.size();
for (uint32_t i = 0; i < size_; i++) {
new (small_data_ + i) T(std::move(vec[i]));
}
}
vec.clear();
}
SmallVector(std::initializer_list<T> init_list) : SmallVector() {
if (init_list.size() < small_size) {
for (auto it = init_list.begin(); it != init_list.end(); ++it) {
new (small_data_ + (size_++)) T(std::move(*it));
}
} else {
large_data_ = MakeUnique<std::vector<T>>(std::move(init_list));
}
}
SmallVector(size_t s, const T& v) : SmallVector() { resize(s, v); }
virtual ~SmallVector() {
for (T* p = small_data_; p < small_data_ + size_; ++p) {
p->~T();
}
}
SmallVector& operator=(const SmallVector& that) {
assert(small_data_);
if (that.large_data_) {
if (large_data_) {
*large_data_ = *that.large_data_;
} else {
large_data_ = MakeUnique<std::vector<T>>(*that.large_data_);
}
} else {
large_data_.reset(nullptr);
size_t i = 0;
// Do a copy for any element in |this| that is already constructed.
for (; i < size_ && i < that.size_; ++i) {
small_data_[i] = that.small_data_[i];
}
if (i >= that.size_) {
// If the size of |this| becomes smaller after the assignment, then
// destroy any extra elements.
for (; i < size_; ++i) {
small_data_[i].~T();
}
} else {
// If the size of |this| becomes larger after the assignement, copy
// construct the new elements that are needed.
for (; i < that.size_; ++i) {
new (small_data_ + i) T(that.small_data_[i]);
}
}
size_ = that.size_;
}
return *this;
}
SmallVector& operator=(SmallVector&& that) {
if (that.large_data_) {
large_data_.reset(that.large_data_.release());
} else {
large_data_.reset(nullptr);
size_t i = 0;
// Do a move for any element in |this| that is already constructed.
for (; i < size_ && i < that.size_; ++i) {
small_data_[i] = std::move(that.small_data_[i]);
}
if (i >= that.size_) {
// If the size of |this| becomes smaller after the assignment, then
// destroy any extra elements.
for (; i < size_; ++i) {
small_data_[i].~T();
}
} else {
// If the size of |this| becomes larger after the assignement, move
// construct the new elements that are needed.
for (; i < that.size_; ++i) {
new (small_data_ + i) T(std::move(that.small_data_[i]));
}
}
size_ = that.size_;
}
// Reset |that| because all of the data has been moved to |this|.
that.DestructSmallData();
return *this;
}
template <class OtherVector>
friend bool operator==(const SmallVector& lhs, const OtherVector& rhs) {
if (lhs.size() != rhs.size()) {
return false;
}
auto rit = rhs.begin();
for (auto lit = lhs.begin(); lit != lhs.end(); ++lit, ++rit) {
if (*lit != *rit) {
return false;
}
}
return true;
}
// Avoid infinite recursion from rewritten operators in C++20
#if __cplusplus <= 201703L
friend bool operator==(const std::vector<T>& lhs, const SmallVector& rhs) {
return rhs == lhs;
}
#endif
friend bool operator!=(const SmallVector& lhs, const std::vector<T>& rhs) {
return !(lhs == rhs);
}
friend bool operator!=(const std::vector<T>& lhs, const SmallVector& rhs) {
return rhs != lhs;
}
T& operator[](size_t i) {
if (!large_data_) {
return small_data_[i];
} else {
return (*large_data_)[i];
}
}
const T& operator[](size_t i) const {
if (!large_data_) {
return small_data_[i];
} else {
return (*large_data_)[i];
}
}
size_t size() const {
if (!large_data_) {
return size_;
} else {
return large_data_->size();
}
}
iterator begin() {
if (large_data_) {
return large_data_->data();
} else {
return small_data_;
}
}
const_iterator begin() const {
if (large_data_) {
return large_data_->data();
} else {
return small_data_;
}
}
const_iterator cbegin() const { return begin(); }
iterator end() {
if (large_data_) {
return large_data_->data() + large_data_->size();
} else {
return small_data_ + size_;
}
}
const_iterator end() const {
if (large_data_) {
return large_data_->data() + large_data_->size();
} else {
return small_data_ + size_;
}
}
const_iterator cend() const { return end(); }
T* data() { return begin(); }
const T* data() const { return cbegin(); }
T& front() { return (*this)[0]; }
const T& front() const { return (*this)[0]; }
iterator erase(const_iterator pos) { return erase(pos, pos + 1); }
iterator erase(const_iterator first, const_iterator last) {
if (large_data_) {
size_t start_index = first - large_data_->data();
size_t end_index = last - large_data_->data();
auto r = large_data_->erase(large_data_->begin() + start_index,
large_data_->begin() + end_index);
return large_data_->data() + (r - large_data_->begin());
}
// Since C++11, std::vector has |const_iterator| for the parameters, so I
// follow that. However, I need iterators to modify the current container,
// which is not const. This is why I cast away the const.
iterator f = const_cast<iterator>(first);
iterator l = const_cast<iterator>(last);
iterator e = end();
size_t num_of_del_elements = last - first;
iterator ret = f;
if (first == last) {
return ret;
}
// Move |last| and any elements after it their earlier position.
while (l != e) {
*f = std::move(*l);
++f;
++l;
}
// Destroy the elements that were supposed to be deleted.
while (f != l) {
f->~T();
++f;
}
// Update the size.
size_ -= num_of_del_elements;
return ret;
}
void push_back(const T& value) {
if (!large_data_ && size_ == small_size) {
MoveToLargeData();
}
if (large_data_) {
large_data_->push_back(value);
return;
}
new (small_data_ + size_) T(value);
++size_;
}
void push_back(T&& value) {
if (!large_data_ && size_ == small_size) {
MoveToLargeData();
}
if (large_data_) {
large_data_->push_back(std::move(value));
return;
}
new (small_data_ + size_) T(std::move(value));
++size_;
}
void pop_back() {
if (large_data_) {
large_data_->pop_back();
} else {
--size_;
small_data_[size_].~T();
}
}
template <class InputIt>
iterator insert(iterator pos, InputIt first, InputIt last) {
size_t element_idx = (pos - begin());
size_t num_of_new_elements = std::distance(first, last);
size_t new_size = size_ + num_of_new_elements;
if (!large_data_ && new_size > small_size) {
MoveToLargeData();
}
if (large_data_) {
typename std::vector<T>::iterator new_pos =
large_data_->begin() + element_idx;
large_data_->insert(new_pos, first, last);
return begin() + element_idx;
}
// Move |pos| and all of the elements after it over |num_of_new_elements|
// places. We start at the end and work backwards, to make sure we do not
// overwrite data that we have not moved yet.
for (iterator i = begin() + new_size - 1, j = end() - 1; j >= pos;
--i, --j) {
if (i >= begin() + size_) {
new (i) T(std::move(*j));
} else {
*i = std::move(*j);
}
}
// Copy the new elements into position.
iterator p = pos;
for (; first != last; ++p, ++first) {
if (p >= small_data_ + size_) {
new (p) T(*first);
} else {
*p = *first;
}
}
// Update the size.
size_ += num_of_new_elements;
return pos;
}
bool empty() const {
if (large_data_) {
return large_data_->empty();
}
return size_ == 0;
}
void clear() {
if (large_data_) {
large_data_->clear();
} else {
DestructSmallData();
}
}
template <class... Args>
void emplace_back(Args&&... args) {
if (!large_data_ && size_ == small_size) {
MoveToLargeData();
}
if (large_data_) {
large_data_->emplace_back(std::forward<Args>(args)...);
} else {
new (small_data_ + size_) T(std::forward<Args>(args)...);
++size_;
}
}
void resize(size_t new_size, const T& v) {
if (!large_data_ && new_size > small_size) {
MoveToLargeData();
}
if (large_data_) {
large_data_->resize(new_size, v);
return;
}
// If |new_size| < |size_|, then destroy the extra elements.
for (size_t i = new_size; i < size_; ++i) {
small_data_[i].~T();
}
// If |new_size| > |size_|, the copy construct the new elements.
for (size_t i = size_; i < new_size; ++i) {
new (small_data_ + i) T(v);
}
// Update the size.
size_ = new_size;
}
private:
// Moves all of the element from |small_data_| into a new std::vector that can
// be access through |large_data|.
void MoveToLargeData() {
assert(!large_data_);
large_data_ = MakeUnique<std::vector<T>>();
for (size_t i = 0; i < size_; ++i) {
large_data_->emplace_back(std::move(small_data_[i]));
}
DestructSmallData();
}
// Destroys all of the elements in |small_data_| that have been constructed.
void DestructSmallData() {
for (size_t i = 0; i < size_; ++i) {
small_data_[i].~T();
}
size_ = 0;
}
// The number of elements in |small_data_| that have been constructed.
size_t size_;
// A type with the same alignment and size as T, but will is POD.
struct alignas(T) PodType {
std::array<int8_t, sizeof(T)> data;
};
// The actual data used to store the array elements. It must never be used
// directly, but must only be accessed through |small_data_|.
PodType buffer[small_size];
// The pointed used to access the array of elements when the number of
// elements is small.
T* small_data_;
// A pointer to a vector that is used to store the elements of the vector when
// this size exceeds |small_size|. If |large_data_| is nullptr, then the data
// is stored in |small_data_|. Otherwise, the data is stored in
// |large_data_|.
std::unique_ptr<std::vector<T>> large_data_;
}; // namespace utils
} // namespace utils
} // namespace spvtools
#endif // SOURCE_UTIL_SMALL_VECTOR_H_