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