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stack_allocator_vec.hpp
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stack_allocator_vec.hpp
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#pragma once
#include <memory>
#include <type_traits>
#include <cassert>
#include "utils.hpp"
template <typename T, size_t Capacity>
class StackAllocatorVector : public std::allocator<T> {
public:
using pointer = typename std::allocator<T>::pointer;
using size_type = typename std::allocator<T>::size_type;
struct ReservedMemory {
using AlignedStorage =
typename std::aligned_storage<sizeof(T), alignof(T)>::type;
ReservedMemory() = default;
T* Data() { return reinterpret_cast<T*>(buffer_); }
bool in_use_ = false;
AlignedStorage buffer_[Capacity];
};
template <typename U>
struct rebind {
using other = StackAllocatorVector<U, Capacity>;
};
StackAllocatorVector(const StackAllocatorVector<T, Capacity>& other)
: std::allocator<T>(), reserved_memory_(other.reserved_memory_) {}
template <typename U, size_type OtherCapacity>
StackAllocatorVector(const StackAllocatorVector<U, OtherCapacity>& other)
: reserved_memory_(nullptr) {}
StackAllocatorVector(ReservedMemory* reserved) : reserved_memory_(reserved) {}
StackAllocatorVector() = default;
pointer allocate(size_type n, void* hint = 0) {
if (reserved_memory_ != nullptr && !reserved_memory_->in_use_ &&
n <= Capacity) {
reserved_memory_->in_use_ = true;
return reserved_memory_->Data();
}
return std::allocator<T>::allocate(n, hint);
}
bool use_stack_memory() {
return reserved_memory_ != nullptr && reserved_memory_->in_use_;
}
void deallocate(pointer p, size_type n) {
if (reserved_memory_ != nullptr && p == reserved_memory_->Data()) {
reserved_memory_->in_use_ = false;
} else {
std::allocator<T>::deallocate(p, n);
}
}
private:
ReservedMemory* reserved_memory_ = nullptr;
};
template <typename T, size_t Capacity>
inline bool operator==(const StackAllocatorVector<T, Capacity>& lhs,
const StackAllocatorVector<T, Capacity>& rhs) {
return false;
}