88 lines
1.7 KiB
C
88 lines
1.7 KiB
C
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#pragma once
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#include <array>
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#include <cstddef>
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#include <cstdint>
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#include <type_traits>
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/** Helper class for allocating temporary fixed size arrays with SBO.
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*
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* This is intentionally much simpler than SmallVector, to improve performance
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* at the expense of many features:
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* - No zero-initialization for numeric types
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* - No resizing after construction
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* - No copy/move
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* - No non-trivial types
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*/
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namespace c10 {
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template <typename T, size_t N>
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class SmallBuffer {
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static_assert(std::is_trivial_v<T>, "SmallBuffer is intended for POD types");
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std::array<T, N> storage_;
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size_t size_{};
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T* data_{};
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public:
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SmallBuffer(size_t size) : size_(size) {
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if (size > N) {
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data_ = new T[size];
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} else {
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data_ = &storage_[0];
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}
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}
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SmallBuffer(const SmallBuffer&) = delete;
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SmallBuffer& operator=(const SmallBuffer&) = delete;
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// move constructor is needed in function return
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SmallBuffer(SmallBuffer&& rhs) noexcept : size_{rhs.size_} {
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rhs.size_ = 0;
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if (size_ > N) {
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data_ = rhs.data_;
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rhs.data_ = nullptr;
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} else {
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storage_ = std::move(rhs.storage_);
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data_ = &storage_[0];
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}
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}
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SmallBuffer& operator=(SmallBuffer&&) = delete;
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~SmallBuffer() {
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if (size_ > N) {
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delete[] data_;
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}
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}
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T& operator[](size_t idx) {
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return data()[idx];
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}
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const T& operator[](size_t idx) const {
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return data()[idx];
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}
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T* data() {
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return data_;
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}
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const T* data() const {
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return data_;
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}
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size_t size() const {
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return size_;
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}
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T* begin() {
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return data_;
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}
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const T* begin() const {
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return data_;
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}
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T* end() {
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return data_ + size_;
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}
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const T* end() const {
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return data_ + size_;
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}
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};
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} // namespace c10
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