malloc_allocator.h

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// Allocator that wraps "C" malloc -*- C++ -*-
 
// Copyright (C) 2001-2023 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 ext/malloc_allocator.h
 *  This file is a GNU extension to the Standard C++ Library.
 */
 
#ifndef _MALLOC_ALLOCATOR_H
#define _MALLOC_ALLOCATOR_H 1
 
#include <bits/requires_hosted.h> // malloc
 
#include <cstdlib>
#include <cstddef>
#include <new>
#include <bits/functexcept.h>
#include <bits/move.h>
#if __cplusplus >= 201103L
#include <type_traits>
#endif
 
namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
 
  /**
   *  @brief  An allocator that uses malloc.
   *  @ingroup allocators
   *
   *  This is precisely the allocator defined in the C++ Standard. 
   *    - all allocation calls malloc
   *    - all deallocation calls free
   */
  template<typename _Tp>
    class malloc_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 malloc_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
 
      _GLIBCXX20_CONSTEXPR
      malloc_allocator() _GLIBCXX_USE_NOEXCEPT { }
 
      _GLIBCXX20_CONSTEXPR
      malloc_allocator(const malloc_allocator&) _GLIBCXX_USE_NOEXCEPT { }
 
      template<typename _Tp1>
        _GLIBCXX20_CONSTEXPR
        malloc_allocator(const malloc_allocator<_Tp1>&)
        _GLIBCXX_USE_NOEXCEPT { }
 
#if __cplusplus <= 201703L
      ~malloc_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
 
      // NB: __n is permitted to be 0.  The C++ standard says nothing
      // about what the return value is when __n == 0.
      _GLIBCXX_NODISCARD _Tp*
      allocate(size_type __n, const void* = 0)
      {
#if __cplusplus >= 201103L
        // _GLIBCXX_RESOLVE_LIB_DEFECTS
        // 3308. std::allocator<void>().allocate(n)
        static_assert(sizeof(_Tp) != 0, "cannot allocate incomplete types");
#endif
 
        if (__builtin_expect(__n > this->_M_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();
          }
 
        _Tp* __ret = 0;
#if __cpp_aligned_new
#if __cplusplus > 201402L && _GLIBCXX_HAVE_ALIGNED_ALLOC
        if (alignof(_Tp) > alignof(std::max_align_t))
          {
            __ret = static_cast<_Tp*>(::aligned_alloc(alignof(_Tp),
                                                      __n * sizeof(_Tp)));
          }
#else
# define _GLIBCXX_CHECK_MALLOC_RESULT
#endif
#endif
        if (!__ret)
          __ret = static_cast<_Tp*>(std::malloc(__n * sizeof(_Tp)));
        if (!__ret)
          std::__throw_bad_alloc();
#ifdef _GLIBCXX_CHECK_MALLOC_RESULT
#undef _GLIBCXX_CHECK_MALLOC_RESULT
          if (reinterpret_cast<std::size_t>(__ret) % alignof(_Tp))
            {
              // Memory returned by malloc is not suitably aligned for _Tp.
              deallocate(__ret, __n);
              std::__throw_bad_alloc();
            }
#endif
        return __ret;
      }
 
      // __p is not permitted to be a null pointer.
      void
      deallocate(_Tp* __p, size_type)
      { std::free(static_cast<void*>(__p)); }
 
#if __cplusplus <= 201703L
      size_type
      max_size() const _GLIBCXX_USE_NOEXCEPT 
      { return _M_max_size(); }
 
#if __cplusplus >= 201103L
      template<typename _Up, typename... _Args>
        void
        construct(_Up* __p, _Args&&... __args)
        noexcept(std::is_nothrow_constructible<_Up, _Args...>::value)
        { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
 
      template<typename _Up>
        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
      void
      construct(pointer __p, const _Tp& __val)
      { ::new((void *)__p) value_type(__val); }
 
      void
      destroy(pointer __p) { __p->~_Tp(); }
#endif
#endif // ! C++20
 
      template<typename _Up>
        friend _GLIBCXX20_CONSTEXPR bool
        operator==(const malloc_allocator&, const malloc_allocator<_Up>&)
        _GLIBCXX_NOTHROW
        { return true; }
 
#if __cpp_impl_three_way_comparison < 201907L
      template<typename _Up>
        friend _GLIBCXX20_CONSTEXPR bool
        operator!=(const malloc_allocator&, const malloc_allocator<_Up>&)
        _GLIBCXX_NOTHROW
        { return false; }
#endif
 
    private:
      _GLIBCXX_CONSTEXPR size_type
      _M_max_size() const _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