1// -*- C++ -*-
2//===----------------------------------------------------------------------===//
3//
4// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5// See https://llvm.org/LICENSE.txt for license information.
6// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7//
8//===----------------------------------------------------------------------===//
9
10#ifndef _LIBCPP_SSO_ALLOCATOR_H
11#define _LIBCPP_SSO_ALLOCATOR_H
12
13#include <__config>
14#include <cstddef>
15#include <memory>
16#include <new>
17#include <type_traits>
18
19#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
20# pragma GCC system_header
21#endif
22
23_LIBCPP_BEGIN_NAMESPACE_STD
24
25template <class _Tp, size_t _Np>
26class _LIBCPP_HIDDEN __sso_allocator;
27
28template <size_t _Np>
29class _LIBCPP_HIDDEN __sso_allocator<void, _Np> {
30public:
31 typedef const void* const_pointer;
32 typedef void value_type;
33};
34
35template <class _Tp, size_t _Np>
36class _LIBCPP_HIDDEN __sso_allocator {
37 alignas(_Tp) std::byte buf_[sizeof(_Tp) * _Np];
38 bool __allocated_;
39
40public:
41 typedef size_t size_type;
42 typedef _Tp* pointer;
43 typedef _Tp value_type;
44
45 template <class U>
46 struct rebind {
47 using other = __sso_allocator<U, _Np>;
48 };
49
50 _LIBCPP_HIDE_FROM_ABI __sso_allocator() throw() : __allocated_(false) {}
51 _LIBCPP_HIDE_FROM_ABI __sso_allocator(const __sso_allocator&) throw() : __allocated_(false) {}
52 template <class _Up>
53 _LIBCPP_HIDE_FROM_ABI __sso_allocator(const __sso_allocator<_Up, _Np>&) throw() : __allocated_(false) {}
54
55private:
56 __sso_allocator& operator=(const __sso_allocator&);
57
58public:
59 _LIBCPP_HIDE_FROM_ABI pointer allocate(size_type __n, typename __sso_allocator<void, _Np>::const_pointer = nullptr) {
60 if (!__allocated_ && __n <= _Np) {
61 __allocated_ = true;
62 return (pointer)&buf_;
63 }
64 return allocator<_Tp>().allocate(__n);
65 }
66 _LIBCPP_HIDE_FROM_ABI void deallocate(pointer __p, size_type __n) {
67 if (__p == (pointer)&buf_)
68 __allocated_ = false;
69 else
70 allocator<_Tp>().deallocate(__p, __n);
71 }
72 _LIBCPP_HIDE_FROM_ABI size_type max_size() const throw() { return size_type(~0) / sizeof(_Tp); }
73
74 _LIBCPP_HIDE_FROM_ABI bool operator==(const __sso_allocator& __a) const { return &buf_ == &__a.buf_; }
75 _LIBCPP_HIDE_FROM_ABI bool operator!=(const __sso_allocator& __a) const { return &buf_ != &__a.buf_; }
76};
77
78_LIBCPP_END_NAMESPACE_STD
79
80#endif // _LIBCPP_SSO_ALLOCATOR_H
81

source code of libcxx/src/include/sso_allocator.h