bits/new_allocator.h

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// Allocator that wraps operator new -*- C++ -*-
 
// Copyright (C) 2001-2026 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
 
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
 
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
 
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.
 
/** @file bits/new_allocator.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{memory}
 */
 
#ifndef _STD_NEW_ALLOCATOR_H
#define _STD_NEW_ALLOCATOR_H 1
 
#include <bits/c++config.h>
#include <new>
#include <bits/new_throw.h>
#include <bits/move.h>
#if __cplusplus >= 201103L
#include <type_traits>
#endif
#include <bits/memoryfwd.h>
 
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
 
  /**
   * @brief  An allocator that uses global `new`, as per C++03 [20.4.1].
   * @ingroup allocators
   *
   * This is precisely the allocator defined in the C++ Standard.
   *   - all allocation calls `operator new`
   *   - all deallocation calls `operator delete`
   *
   * This is the default base-class implementation of `std::allocator`,
   * and is also the base-class of the `__gnu_cxx::new_allocator` extension.
   * You should use either `std::allocator` or `__gnu_cxx::new_allocator`
   * instead of using this directly.
   *
   * @tparam  _Tp  Type of allocated object.
   *
   * @headerfile memory
   */
  template<typename _Tp>
    class __new_allocator
    {
    public:
      typedef _Tp        value_type;
      typedef std::size_t     size_type;
      typedef std::ptrdiff_t  difference_type;
#if __cplusplus <= 201703L
      typedef _Tp*       pointer;
      typedef const _Tp* const_pointer;
      typedef _Tp&       reference;
      typedef const _Tp& const_reference;
 
      template<typename _Tp1>
        struct rebind
        { typedef __new_allocator<_Tp1> other; };
#endif
 
#if __cplusplus >= 201103L
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 2103. propagate_on_container_move_assignment
      typedef std::true_type propagate_on_container_move_assignment;
#endif
 
      __attribute__((__always_inline__))
      _GLIBCXX20_CONSTEXPR
      __new_allocator() _GLIBCXX_USE_NOEXCEPT { }
 
      __attribute__((__always_inline__))
      _GLIBCXX20_CONSTEXPR
      __new_allocator(const __new_allocator&) _GLIBCXX_USE_NOEXCEPT { }
 
      template<typename _Tp1>
        __attribute__((__always_inline__))
        _GLIBCXX20_CONSTEXPR
        __new_allocator(const __new_allocator<_Tp1>&) _GLIBCXX_USE_NOEXCEPT { }
 
#if __cplusplus >= 201103L
      __new_allocator& operator=(const __new_allocator&) = default;
#endif
 
#if __cplusplus <= 201703L
      ~__new_allocator() _GLIBCXX_USE_NOEXCEPT { }
 
      pointer
      address(reference __x) const _GLIBCXX_NOEXCEPT
      { return std::__addressof(__x); }
 
      const_pointer
      address(const_reference __x) const _GLIBCXX_NOEXCEPT
      { return std::__addressof(__x); }
#endif
 
#if __has_builtin(__builtin_operator_new) >= 201802L
# define _GLIBCXX_OPERATOR_NEW __builtin_operator_new
# define _GLIBCXX_OPERATOR_DELETE __builtin_operator_delete
#else
# define _GLIBCXX_OPERATOR_NEW ::operator new
# define _GLIBCXX_OPERATOR_DELETE ::operator delete
#endif
 
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wc++17-extensions" // if constexpr
 
      __attribute__((__always_inline__))
      _GLIBCXX20_CONSTEXPR static void
      _S_check_allocation_limit(size_t __n)
      {
        if (__builtin_expect(__n > _S_max_size(), false))
          {
            // _GLIBCXX_RESOLVE_LIB_DEFECTS
            // 3190. allocator::allocate sometimes returns too little storage
            if (__n > (std::size_t(-1) / sizeof(_Tp)))
              std::__throw_bad_array_new_length();
            std::__throw_bad_alloc();
          }
      }
 
      // NB: __n is permitted to be 0.  The C++ standard says nothing
      // about what the return value is when __n == 0.
      _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR _Tp*
      allocate(size_type __n, const void* = static_cast<const void*>(0))
      {
#if __cplusplus >= 201103L
        // _GLIBCXX_RESOLVE_LIB_DEFECTS
        // 3308. std::allocator<void>().allocate(n)
#if ! __cpp_concepts
        static_assert(sizeof(_Tp) != 0, "cannot allocate incomplete types");
#else
        static_assert(requires { sizeof(_Tp); },
          "cannot allocate incomplete types");
 
        if constexpr (!requires { sizeof(_Tp); })
          return nullptr; // static_assert already failed
        else
#endif
#endif
          {
            _S_check_allocation_limit(__n);
#if __cpp_aligned_new && __cplusplus >= 201103L
            if constexpr (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
              {
                std::align_val_t __al = std::align_val_t(alignof(_Tp));
                return static_cast<_Tp*>(
                  _GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp), __al));
              }
            else
#endif
              return static_cast<_Tp*>(
                _GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp)));
          }
      }
 
#ifdef __glibcxx_allocate_at_least  // C++23
      [[nodiscard]] constexpr std::allocation_result<_Tp*, size_t>
      allocate_at_least(size_t __n)
      {
#if __cpp_aligned_new
        if ! consteval
          {
            if constexpr (requires { sizeof(_Tp); })
            if constexpr (alignof(_Tp) <= __STDCPP_DEFAULT_NEW_ALIGNMENT__)
            if constexpr ( sizeof(_Tp) <  __STDCPP_DEFAULT_NEW_ALIGNMENT__)
              {
                _S_check_allocation_limit(__n);
                size_t __bytes = __n * sizeof(_Tp);
                const size_t __mask = __STDCPP_DEFAULT_NEW_ALIGNMENT__ - 1;
                size_t __max = (__bytes + __mask) & ~__mask;
                // Avoid seeming to ask for 2^63 bytes (PR108377):
                __max -= __max >> (__SIZE_WIDTH__ - 1);
                auto __spare = static_cast<unsigned>(__max - __bytes);
                if constexpr (sizeof(_Tp) < (__mask + 1) / 2)
                  {
                    auto __bonus = __spare / sizeof(_Tp);
                    __n += __bonus;
                    __bytes += __bonus * sizeof(_Tp);
                  }
                else if (sizeof(_Tp) <= __spare)
                  {
                    __n += 1;
                    __bytes += sizeof(_Tp);
                  }
                void* __p = _GLIBCXX_OPERATOR_NEW(__bytes);
                return { static_cast<_Tp*>(__p), __n };
              }
          }
#endif
        return { allocate(__n), __n };
      }
#endif
 
      // __p is not permitted to be a null pointer.
      _GLIBCXX20_CONSTEXPR void
      deallocate(_Tp* __p, size_type __n __attribute__ ((__unused__)))
      {
#if __cpp_sized_deallocation
# define _GLIBCXX_SIZED_DEALLOC(p, n) (p), (n) * sizeof(_Tp)
#else
# define _GLIBCXX_SIZED_DEALLOC(p, n) (p)
#endif
 
#if __cpp_aligned_new && __cplusplus >= 201103L
        if constexpr (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
          {
            _GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(__p, __n),
                                     std::align_val_t(alignof(_Tp)));
          }
        else
#endif
          _GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(__p, __n));
      }
 
#pragma GCC diagnostic pop
#undef _GLIBCXX_SIZED_DEALLOC
#undef _GLIBCXX_OPERATOR_DELETE
#undef _GLIBCXX_OPERATOR_NEW
 
#if __cplusplus <= 201703L
      __attribute__((__always_inline__))
      size_type
      max_size() const _GLIBCXX_USE_NOEXCEPT
      { return _S_max_size(); }
 
#if __cplusplus >= 201103L
      template<typename _Up, typename... _Args>
        __attribute__((__always_inline__))
        void
        construct(_Up* __p, _Args&&... __args)
        noexcept(__is_nothrow_new_constructible<_Up, _Args...>)
        { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
 
      template<typename _Up>
        __attribute__((__always_inline__))
        void
        destroy(_Up* __p)
        noexcept(std::is_nothrow_destructible<_Up>::value)
        { __p->~_Up(); }
#else
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 402. wrong new expression in [some_] allocator::construct
      __attribute__((__always_inline__))
      void
      construct(pointer __p, const _Tp& __val)
      { ::new((void *)__p) _Tp(__val); }
 
      __attribute__((__always_inline__))
      void
      destroy(pointer __p) { __p->~_Tp(); }
#endif
#endif // ! C++20
 
      template<typename _Up>
        friend __attribute__((__always_inline__)) _GLIBCXX20_CONSTEXPR bool
        operator==(const __new_allocator&, const __new_allocator<_Up>&)
        _GLIBCXX_NOTHROW
        { return true; }
 
#if __cpp_impl_three_way_comparison < 201907L
      template<typename _Up>
        friend __attribute__((__always_inline__)) _GLIBCXX20_CONSTEXPR bool
        operator!=(const __new_allocator&, const __new_allocator<_Up>&)
        _GLIBCXX_NOTHROW
        { return false; }
#endif
 
    private:
      __attribute__((__always_inline__))
      _GLIBCXX_CONSTEXPR static size_type
      _S_max_size() _GLIBCXX_USE_NOEXCEPT
      {
#if __PTRDIFF_MAX__ < __SIZE_MAX__
        return std::size_t(__PTRDIFF_MAX__) / sizeof(_Tp);
#else
        return std::size_t(-1) / sizeof(_Tp);
#endif
      }
    };
 
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
 
#endif