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// Copyright 2018 the V8 project 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 V8_BASE_SMALL_VECTOR_H_
#define V8_BASE_SMALL_VECTOR_H_
#include <algorithm>
#include <type_traits>
#include <utility>
#include "src/base/bits.h"
#include "src/base/macros.h"
namespace v8 {
namespace base {
// Minimal SmallVector implementation. Uses inline storage first, switches to
// malloc when it overflows.
template <typename T, size_t kSize>
class SmallVector {
// Currently only support trivially copyable and trivially destructible data
// types, as it uses memcpy to copy elements and never calls destructors.
ASSERT_TRIVIALLY_COPYABLE(T);
STATIC_ASSERT(std::is_trivially_destructible<T>::value);
public:
static constexpr size_t kInlineSize = kSize;
SmallVector() = default;
explicit SmallVector(size_t size) { resize_no_init(size); }
SmallVector(const SmallVector& other) V8_NOEXCEPT { *this = other; }
SmallVector(SmallVector&& other) V8_NOEXCEPT { *this = std::move(other); }
SmallVector(std::initializer_list<T> init) {
resize_no_init(init.size());
memcpy(begin_, init.begin(), sizeof(T) * init.size());
}
~SmallVector() {
if (is_big()) free(begin_);
}
SmallVector& operator=(const SmallVector& other) V8_NOEXCEPT {
if (this == &other) return *this;
size_t other_size = other.size();
if (capacity() < other_size) {
// Create large-enough heap-allocated storage.
if (is_big()) free(begin_);
begin_ = reinterpret_cast<T*>(malloc(sizeof(T) * other_size));
end_of_storage_ = begin_ + other_size;
}
memcpy(begin_, other.begin_, sizeof(T) * other_size);
end_ = begin_ + other_size;
return *this;
}
SmallVector& operator=(SmallVector&& other) V8_NOEXCEPT {
if (this == &other) return *this;
if (other.is_big()) {
if (is_big()) free(begin_);
begin_ = other.begin_;
end_ = other.end_;
end_of_storage_ = other.end_of_storage_;
other.reset();
} else {
DCHECK_GE(capacity(), other.size()); // Sanity check.
size_t other_size = other.size();
memcpy(begin_, other.begin_, sizeof(T) * other_size);
end_ = begin_ + other_size;
}
return *this;
}
T* data() { return begin_; }
const T* data() const { return begin_; }
T* begin() { return begin_; }
const T* begin() const { return begin_; }
T* end() { return end_; }
const T* end() const { return end_; }
size_t size() const { return end_ - begin_; }
bool empty() const { return end_ == begin_; }
size_t capacity() const { return end_of_storage_ - begin_; }
T& back() {
DCHECK_NE(0, size());
return end_[-1];
}
const T& back() const {
DCHECK_NE(0, size());
return end_[-1];
}
T& operator[](size_t index) {
DCHECK_GT(size(), index);
return begin_[index];
}
const T& at(size_t index) const {
DCHECK_GT(size(), index);
return begin_[index];
}
const T& operator[](size_t index) const { return at(index); }
template <typename... Args>
void emplace_back(Args&&... args) {
T* end = end_;
if (V8_UNLIKELY(end == end_of_storage_)) end = Grow();
new (end) T(std::forward<Args>(args)...);
end_ = end + 1;
}
void pop_back(size_t count = 1) {
DCHECK_GE(size(), count);
end_ -= count;
}
void resize_no_init(size_t new_size) {
// Resizing without initialization is safe if T is trivially copyable.
ASSERT_TRIVIALLY_COPYABLE(T);
if (new_size > capacity()) Grow(new_size);
end_ = begin_ + new_size;
}
// Clear without freeing any storage.
void clear() { end_ = begin_; }
// Clear and go back to inline storage.
void reset() {
begin_ = inline_storage_begin();
end_ = begin_;
end_of_storage_ = begin_ + kInlineSize;
}
private:
T* begin_ = inline_storage_begin();
T* end_ = begin_;
T* end_of_storage_ = begin_ + kInlineSize;
typename std::aligned_storage<sizeof(T) * kInlineSize, alignof(T)>::type
inline_storage_;
// Grows the backing store by a factor of two. Returns the new end of the used
// storage (this reduces binary size).
V8_NOINLINE T* Grow() { return Grow(0); }
// Grows the backing store by a factor of two, and at least to {min_capacity}.
V8_NOINLINE T* Grow(size_t min_capacity) {
size_t in_use = end_ - begin_;
size_t new_capacity =
base::bits::RoundUpToPowerOfTwo(std::max(min_capacity, 2 * capacity()));
T* new_storage = reinterpret_cast<T*>(malloc(sizeof(T) * new_capacity));
memcpy(new_storage, begin_, sizeof(T) * in_use);
if (is_big()) free(begin_);
begin_ = new_storage;
end_ = new_storage + in_use;
end_of_storage_ = new_storage + new_capacity;
return end_;
}
bool is_big() const { return begin_ != inline_storage_begin(); }
T* inline_storage_begin() { return reinterpret_cast<T*>(&inline_storage_); }
const T* inline_storage_begin() const {
return reinterpret_cast<const T*>(&inline_storage_);
}
};
} // namespace base
} // namespace v8
#endif // V8_BASE_SMALL_VECTOR_H_
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