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/*
// The MIT License (MIT)
//
// Copyright (c) 2015 Howard Hinnant
//
// 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 STACK_ALLOC_HPP
#define STACK_ALLOC_HPP
/*
* Based on Howard Hinnants awesome allocator boilerplate code
* https://howardhinnant.github.io/short_alloc.h
*/
#include <cstddef>
#include <cassert>
namespace jwt {
/*
*/
template <
/// Size of the stack allocated byte buffer.
size_t N,
/// The alignment required for the buffer.
size_t alignment = alignof(std::max_align_t)
>
class Arena
{
public: // 'tors
Arena() noexcept
: ptr_(buf_)
{
static_assert (alignment <= alignof(std::max_align_t),
"Alignment chosen is more than the maximum supported alignment");
}
/// Non copyable and assignable
Arena(const Arena&) = delete;
Arena& operator=(const Arena&) = delete;
~Arena()
{
ptr_ = nullptr;
}
public: // Public APIs
/*
* Reserves space within the buffer of size atleast 'n'
* bytes.
* More bytes maybe reserved based on the alignment requirements.
*
* Returns:
* 1. The pointer within the storage buffer where the object can be constructed.
* 2. nullptr if space cannot be reserved for requested number of bytes
* (+ alignment padding if applicable)
*/
template <
/// The requested alignment for this allocation.
/// Must be less than or equal to the 'alignment'.
size_t requested_alignment
>
char* allocate(size_t n) noexcept;
/*
* Free back the space pointed by p within the storage buffer.
*/
void deallocate(char* p, size_t n) noexcept;
/*
* The size of the internal storage buffer.
*/
constexpr static size_t size() noexcept
{
return N;
}
/*
* Returns number of remaining bytes within the storage buffer
* that can be used for further allocation requests.
*/
size_t used() const noexcept
{
return static_cast<size_t>(ptr_ - buf_);
}
private: // Private member functions
/*
* A check to determine if the pointer 'p'
* points to a region within storage.
*/
bool pointer_in_storage(char* p) const noexcept
{
return (buf_ <= p) && (p <= (buf_ + N));
}
/*
* Rounds up the number to the next closest number
* as per the alignment.
*/
constexpr static size_t align_up(size_t n) noexcept
{
return (n + (alignment - 1)) & ~(alignment - 1);
}
private: // data members
/// Storage
alignas(alignment) char buf_[N];
/// Current allocation pointer within storage
char* ptr_ = nullptr;
};
/*
*/
template <
/// The allocator for type T
typename T,
/// Number of bytes for the arena
size_t N,
/// Alignment of the arena
size_t align = alignof(std::max_align_t)
>
class stack_alloc
{
public: // typedefs
using value_type = T;
using arena_type = Arena<N, align>;
static auto constexpr alignment = align;
static auto constexpr size = N;
public: // 'tors
stack_alloc(arena_type& a)
: arena_(a)
{
}
stack_alloc(const stack_alloc&) = default;
stack_alloc& operator=(const stack_alloc&) = delete;
template <typename U>
stack_alloc(const stack_alloc<U, N, alignment>& other)
: arena_(other.arena_)
{
}
template <typename U>
struct rebind {
using other = stack_alloc<U, N, alignment>;
};
public: // Exposed APIs
/*
* Allocate memory of 'n' bytes for object
* of type 'T'
*/
T* allocate(size_t n) noexcept;
/*
* Deallocate the storage reserved for the object
* of type T pointed by pointer 'p'
*/
void deallocate(T* p, size_t n) noexcept;
private: // Private APIs
private: // Private data members
/// The arena
arena_type& arena_;
};
} // END namespace jwt
#include "jwt/impl/stack_alloc.ipp"
#endif
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