sso_allocator.h

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP_SSO_ALLOCATOR_H
#define _LIBCPP_SSO_ALLOCATOR_H

#include <__config>
#include <cstddef>
#include <memory>
#include <new>
#include <type_traits>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

template <class _Tp, size_t _Np>
class _LIBCPP_HIDDEN __sso_allocator;

template <size_t _Np>
class _LIBCPP_HIDDEN __sso_allocator<void, _Np> {
public:
  typedef const void* const_pointer;
  typedef void value_type;
};

template <class _Tp, size_t _Np>
class _LIBCPP_HIDDEN __sso_allocator {
  alignas(_Tp) std::byte buf_[sizeof(_Tp) * _Np];
  bool __allocated_;

public:
  typedef size_t size_type;
  typedef _Tp* pointer;
  typedef _Tp value_type;

  template <class U>
  struct rebind {
    using other = __sso_allocator<U, _Np>;
  };

  _LIBCPP_HIDE_FROM_ABI __sso_allocator() throw() : __allocated_(false) {}
  _LIBCPP_HIDE_FROM_ABI __sso_allocator(const __sso_allocator&) throw() : __allocated_(false) {}
  template <class _Up>
  _LIBCPP_HIDE_FROM_ABI __sso_allocator(const __sso_allocator<_Up, _Np>&) throw() : __allocated_(false) {}

private:
  __sso_allocator& operator=(const __sso_allocator&);

public:
  _LIBCPP_HIDE_FROM_ABI pointer allocate(size_type __n, typename __sso_allocator<void, _Np>::const_pointer = nullptr) {
    if (!__allocated_ && __n <= _Np) {
      __allocated_ = true;
      return (pointer)&buf_;
    }
    return allocator<_Tp>().allocate(__n);
  }
  _LIBCPP_HIDE_FROM_ABI void deallocate(pointer __p, size_type __n) {
    if (__p == (pointer)&buf_)
      __allocated_ = false;
    else
      allocator<_Tp>().deallocate(__p, __n);
  }
  _LIBCPP_HIDE_FROM_ABI size_type max_size() const throw() { return size_type(~0) / sizeof(_Tp); }

  _LIBCPP_HIDE_FROM_ABI bool operator==(const __sso_allocator& __a) const { return &buf_ == &__a.buf_; }
  _LIBCPP_HIDE_FROM_ABI bool operator!=(const __sso_allocator& __a) const { return &buf_ != &__a.buf_; }
};

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP_SSO_ALLOCATOR_H