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 <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
  25 template <class _Tp, size_t _Np>
  26 class _LIBCPP_HIDDEN __sso_allocator;
  27
  28 template <size_t _Np>
  29 class _LIBCPP_HIDDEN __sso_allocator<void, _Np> {
  30 public:
  31   typedef const void* const_pointer;
  32   typedef void value_type;
  33 };
  34
  35 template <class _Tp, size_t _Np>
  36 class _LIBCPP_HIDDEN __sso_allocator {
  37   alignas(_Tp) std::byte buf_[sizeof(_Tp) * _Np];
  38   bool __allocated_;
  39
  40 public:
  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
  55 private:
  56   __sso_allocator& operator=(const __sso_allocator&);
  57
  58 public:
  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