// 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 <type_traits> #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 kInlineSize> 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: SmallVector() = default; SmallVector(const SmallVector& other) V8_NOEXCEPT { *this = other; } SmallVector(SmallVector&& other) V8_NOEXCEPT { *this = std::move(other); } ~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() const { return begin_; } T* begin() const { return begin_; } 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]; } T& operator[](size_t index) { DCHECK_GT(size(), index); return begin_[index]; } const T& operator[](size_t index) const { DCHECK_GT(size(), index); return begin_[index]; } template <typename... Args> void emplace_back(Args&&... args) { if (V8_UNLIKELY(end_ == end_of_storage_)) Grow(); new (end_) T(std::forward<Args>(args)...); ++end_; } 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_; void Grow(size_t min_capacity = 0) { 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; } 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_