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/*
* Copyright (c) 2020 Samsung Electronics Co., Ltd. All rights reserved.
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#ifndef VSTACK_ALLOCATOR_H
#define VSTACK_ALLOCATOR_H
#include <cstddef>
#include <cassert>
template <std::size_t N, std::size_t alignment = alignof(std::max_align_t)>
class arena
{
alignas(alignment) char buf_[N];
char* ptr_;
public:
~arena() {ptr_ = nullptr;}
arena() noexcept : ptr_(buf_) {}
arena(const arena&) = delete;
arena& operator=(const arena&) = delete;
template <std::size_t ReqAlign> char* allocate(std::size_t n);
void deallocate(char* p, std::size_t n) noexcept;
static constexpr std::size_t size() noexcept {return N;}
std::size_t used() const noexcept {return static_cast<std::size_t>(ptr_ - buf_);}
void reset() noexcept {ptr_ = buf_;}
private:
static
std::size_t
align_up(std::size_t n) noexcept
{return (n + (alignment-1)) & ~(alignment-1);}
bool
pointer_in_buffer(char* p) noexcept
{return buf_ <= p && p <= buf_ + N;}
};
template <std::size_t N, std::size_t alignment>
template <std::size_t ReqAlign>
char*
arena<N, alignment>::allocate(std::size_t n)
{
static_assert(ReqAlign <= alignment, "alignment is too small for this arena");
assert(pointer_in_buffer(ptr_) && "stack_alloc has outlived arena");
auto const aligned_n = align_up(n);
if (static_cast<decltype(aligned_n)>(buf_ + N - ptr_) >= aligned_n)
{
char* r = ptr_;
ptr_ += aligned_n;
return r;
}
static_assert(alignment <= alignof(std::max_align_t), "you've chosen an "
"alignment that is larger than alignof(std::max_align_t), and "
"cannot be guaranteed by normal operator new");
return static_cast<char*>(::operator new(n));
}
template <std::size_t N, std::size_t alignment>
void
arena<N, alignment>::deallocate(char* p, std::size_t n) noexcept
{
assert(pointer_in_buffer(ptr_) && "stack_alloc has outlived arena");
if (pointer_in_buffer(p))
{
n = align_up(n);
if (p + n == ptr_)
ptr_ = p;
}
else
::operator delete(p);
}
template <class T, std::size_t N, std::size_t Align = alignof(std::max_align_t)>
class stack_alloc
{
public:
using value_type = T;
static auto constexpr alignment = Align;
static auto constexpr size = N;
using arena_type = arena<size, alignment>;
private:
arena_type& a_;
public:
stack_alloc(const stack_alloc&) = default;
stack_alloc& operator=(const stack_alloc&) = delete;
stack_alloc(arena_type& a) noexcept : a_(a)
{
static_assert(size % alignment == 0,
"size N needs to be a multiple of alignment Align");
}
template <class U>
stack_alloc(const stack_alloc<U, N, alignment>& a) noexcept
: a_(a.a_) {}
template <class _Up> struct rebind {using other = stack_alloc<_Up, N, alignment>;};
T* allocate(std::size_t n)
{
return reinterpret_cast<T*>(a_.template allocate<alignof(T)>(n*sizeof(T)));
}
void deallocate(T* p, std::size_t n) noexcept
{
a_.deallocate(reinterpret_cast<char*>(p), n*sizeof(T));
}
template <class T1, std::size_t N1, std::size_t A1,
class U, std::size_t M, std::size_t A2>
friend
bool
operator==(const stack_alloc<T1, N1, A1>& x, const stack_alloc<U, M, A2>& y) noexcept;
template <class U, std::size_t M, std::size_t A> friend class stack_alloc;
};
template <class T, std::size_t N, std::size_t A1, class U, std::size_t M, std::size_t A2>
inline
bool
operator==(const stack_alloc<T, N, A1>& x, const stack_alloc<U, M, A2>& y) noexcept
{
return N == M && A1 == A2 && &x.a_ == &y.a_;
}
template <class T, std::size_t N, std::size_t A1, class U, std::size_t M, std::size_t A2>
inline
bool
operator!=(const stack_alloc<T, N, A1>& x, const stack_alloc<U, M, A2>& y) noexcept
{
return !(x == y);
}
#endif // VSTACK_ALLOCATOR_H
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