libcxx/src/include/sso_allocator.h

   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 <memory>
  15 #include <new>
  16 #include <type_traits>
  17
  18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  19 #pragma GCC system_header
  20 #endif
  21
  22 _LIBCPP_BEGIN_NAMESPACE_STD
  23
  24 template <class _Tp, size_t _Np> class _LIBCPP_HIDDEN __sso_allocator;
  25
  26 template <size_t _Np>
  27 class _LIBCPP_HIDDEN __sso_allocator<void, _Np>
  28 {
  29 public:
  30     typedef const void*       const_pointer;
  31     typedef void              value_type;
  32 };
  33
  34 template <class _Tp, size_t _Np>
  35 class _LIBCPP_HIDDEN __sso_allocator
  36 {
  37     typename aligned_storage<sizeof(_Tp) * _Np>::type buf_;
  38     bool __allocated_;
  39 public:
  40     typedef size_t            size_type;
  41     typedef _Tp*              pointer;
  42     typedef _Tp               value_type;
  43
  44     template <class U>
  45     struct rebind {
  46         using other = __sso_allocator<U, _Np>;
  47     };
  48
  49     _LIBCPP_INLINE_VISIBILITY __sso_allocator() throw() : __allocated_(false) {}
  50     _LIBCPP_INLINE_VISIBILITY __sso_allocator(const __sso_allocator&) throw() : __allocated_(false) {}
  51     template <class _Up> _LIBCPP_INLINE_VISIBILITY __sso_allocator(const __sso_allocator<_Up, _Np>&) throw()
  52          : __allocated_(false) {}
  53 private:
  54     __sso_allocator& operator=(const __sso_allocator&);
  55 public:
  56     _LIBCPP_INLINE_VISIBILITY pointer allocate(size_type __n, typename __sso_allocator<void, _Np>::const_pointer = nullptr)
  57     {
  58         if (!__allocated_ && __n <= _Np)
  59         {
  60             __allocated_ = true;
  61             return (pointer)&buf_;
  62         }
  63         return allocator<_Tp>().allocate(__n);
  64     }
  65     _LIBCPP_INLINE_VISIBILITY void deallocate(pointer __p, size_type __n)
  66     {
  67         if (__p == (pointer)&buf_)
  68             __allocated_ = false;
  69         else
  70             allocator<_Tp>().deallocate(__p, __n);
  71     }
  72     _LIBCPP_INLINE_VISIBILITY size_type max_size() const throw() {return size_type(~0) / sizeof(_Tp);}
  73
  74     _LIBCPP_INLINE_VISIBILITY
  75     bool operator==(const __sso_allocator& __a) const {return &buf_ == &__a.buf_;}
  76     _LIBCPP_INLINE_VISIBILITY
  77     bool operator!=(const __sso_allocator& __a) const {return &buf_ != &__a.buf_;}
  78 };
  79
  80 _LIBCPP_END_NAMESPACE_STD
  81
  82 #endif // _LIBCPP_SSO_ALLOCATOR_H