libstdc++-v3/include/bits/stl_tempbuf.h

// Temporary buffer implementation -*- 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/>.

/*
 *
 * Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 * Copyright (c) 1996,1997
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 */

/** @file bits/stl_tempbuf.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{memory}
 */

#ifndef _STL_TEMPBUF_H
#define _STL_TEMPBUF_H 1

#include <new>
#include <bits/exception_defines.h>
#include <bits/stl_construct.h>
#include <bits/stl_pair.h>
#include <ext/numeric_traits.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

#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

  namespace __detail
  {
    // Equivalent to std::get_temporary_buffer but won't return a smaller size.
    // It either returns a buffer of __len elements, or a null pointer.
    template<typename _Tp>
      inline _Tp*
      __get_temporary_buffer(ptrdiff_t __len) _GLIBCXX_NOTHROW
      {
	if (__builtin_expect(size_t(__len) > (size_t(-1) / sizeof(_Tp)), 0))
	  return 0;

#if __cpp_aligned_new && __cplusplus >= 201103L
	if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
	  return (_Tp*) _GLIBCXX_OPERATOR_NEW(__len * sizeof(_Tp),
					      align_val_t(alignof(_Tp)),
					      nothrow_t());
#endif
	return (_Tp*) _GLIBCXX_OPERATOR_NEW(__len * sizeof(_Tp), nothrow_t());
      }

    // Equivalent to std::return_temporary_buffer but with a size argument.
    // The size is the number of elements, not the number of bytes.
    template<typename _Tp>
      inline void
      __return_temporary_buffer(_Tp* __p,
				size_t __len __attribute__((__unused__)))
      {
#if __cpp_sized_deallocation
# define _GLIBCXX_SIZED_DEALLOC(T, p, n) (p), (n) * sizeof(T)
#else
# define _GLIBCXX_SIZED_DEALLOC(T, p, n) (p)
#endif

#if __cpp_aligned_new && __cplusplus >= 201103L
	if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
	  {
	    _GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(_Tp, __p, __len),
				     align_val_t(alignof(_Tp)));
	    return;
	  }
#endif
	_GLIBCXX_OPERATOR_DELETE(_GLIBCXX_SIZED_DEALLOC(_Tp, __p, __len));
      }
#undef _GLIBCXX_SIZED_DEALLOC
  }

  /**
   *  @brief Allocates a temporary buffer.
   *  @param  __len  The number of objects of type Tp.
   *  @return See full description.
   *
   *  Reinventing the wheel, but this time with prettier spokes!
   *
   *  This function tries to obtain storage for @c __len adjacent Tp
   *  objects.  The objects themselves are not constructed, of course.
   *  A pair<> is returned containing <em>the buffer's address and
   *  capacity (in the units of sizeof(_Tp)), or a pair of 0 values if
   *  no storage can be obtained.</em>  Note that the capacity obtained
   *  may be less than that requested if the memory is unavailable;
   *  you should compare len with the .second return value.
   *
   * Provides the nothrow exception guarantee.
   */
  template<typename _Tp>
    _GLIBCXX17_DEPRECATED
    pair<_Tp*, ptrdiff_t>
    get_temporary_buffer(ptrdiff_t __len) _GLIBCXX_NOEXCEPT
    {
      const ptrdiff_t __max =
	__gnu_cxx::__numeric_traits<ptrdiff_t>::__max / sizeof(_Tp);
      if (__len > __max)
	__len = __max;

      while (__len > 0)
	{
	  if (_Tp* __tmp = __detail::__get_temporary_buffer<_Tp>(__len))
	    return pair<_Tp*, ptrdiff_t>(__tmp, __len);
	  __len = __len == 1 ? 0 : ((__len + 1) / 2);
	}
      return pair<_Tp*, ptrdiff_t>();
    }

  /**
   *  @brief The companion to get_temporary_buffer().
   *  @param  __p  A buffer previously allocated by get_temporary_buffer.
   *
   *  Frees the memory pointed to by __p.
   */
  template<typename _Tp>
    _GLIBCXX17_DEPRECATED
    inline void
    return_temporary_buffer(_Tp* __p)
    {
#if __cpp_aligned_new && __cplusplus >= 201103L
      if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
	_GLIBCXX_OPERATOR_DELETE(__p, align_val_t(alignof(_Tp)));
      else
#endif
      _GLIBCXX_OPERATOR_DELETE(__p);
    }

#undef _GLIBCXX_OPERATOR_DELETE
#undef _GLIBCXX_OPERATOR_NEW

  /**
   *  This class is used in two places: stl_algo.h and ext/memory,
   *  where it is wrapped as the temporary_buffer class.  See
   *  temporary_buffer docs for more notes.
   */
  template<typename _ForwardIterator, typename _Tp>
    class _Temporary_buffer
    {
      // concept requirements
      __glibcxx_class_requires(_ForwardIterator, _ForwardIteratorConcept)

    public:
      typedef _Tp         value_type;
      typedef value_type* pointer;
      typedef pointer     iterator;
      typedef ptrdiff_t   size_type;

    protected:
      size_type  _M_original_len;
      struct _Impl
      {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
	explicit
	_Impl(ptrdiff_t __original_len)
	{
	  pair<pointer, size_type> __p(
	    std::get_temporary_buffer<value_type>(__original_len));
	  _M_len = __p.second;
	  _M_buffer = __p.first;
	}
#pragma GCC diagnostic pop

	~_Impl()
	{ std::__detail::__return_temporary_buffer(_M_buffer, _M_len); }

	size_type  _M_len;
	pointer    _M_buffer;
      } _M_impl;

    public:
      /// As per Table mumble.
      size_type
      size() const
      { return _M_impl._M_len; }

      /// Returns the size requested by the constructor; may be >size().
      size_type
      _M_requested_size() const
      { return _M_original_len; }

      /// As per Table mumble.
      iterator
      begin()
      { return _M_impl._M_buffer; }

      /// As per Table mumble.
      iterator
      end()
      { return _M_impl._M_buffer + _M_impl._M_len; }

      /**
       * Constructs a temporary buffer of a size somewhere between
       * zero and the given length.
       */
      _Temporary_buffer(_ForwardIterator __seed, size_type __original_len);

      ~_Temporary_buffer()
      { std::_Destroy(_M_impl._M_buffer, _M_impl._M_buffer + _M_impl._M_len); }

    private:
      // Disable copy constructor and assignment operator.
      _Temporary_buffer(const _Temporary_buffer&);

      void
      operator=(const _Temporary_buffer&);
    };


  template<bool>
    struct __uninitialized_construct_buf_dispatch
    {
      template<typename _Pointer, typename _ForwardIterator>
        static void
        __ucr(_Pointer __first, _Pointer __last,
	      _ForwardIterator __seed)
        {
	  if (__builtin_expect(__first == __last, 0))
	    return;

	  _Pointer __cur = __first;
	  __try
	    {
	      std::_Construct(std::__addressof(*__first),
			      _GLIBCXX_MOVE(*__seed));
	      _Pointer __prev = __cur;
	      ++__cur;
	      for(; __cur != __last; ++__cur, ++__prev)
		std::_Construct(std::__addressof(*__cur),
				_GLIBCXX_MOVE(*__prev));
	      *__seed = _GLIBCXX_MOVE(*__prev);
	    }
	  __catch(...)
	    {
	      std::_Destroy(__first, __cur);
	      __throw_exception_again;
	    }
	}
    };

  template<>
    struct __uninitialized_construct_buf_dispatch<true>
    {
      template<typename _Pointer, typename _ForwardIterator>
        static void
        __ucr(_Pointer, _Pointer, _ForwardIterator) { }
    };

  // Constructs objects in the range [first, last).
  // Note that while these new objects will take valid values,
  // their exact value is not defined. In particular they may
  // be 'moved from'.
  //
  // While *__seed may be altered during this algorithm, it will have
  // the same value when the algorithm finishes, unless one of the
  // constructions throws.
  //
  // Requirements:
  // _Tp is move constructible and constructible from std::move(*__seed).
  template<typename _Tp, typename _ForwardIterator>
    inline void
    __uninitialized_construct_buf(_Tp* __first, _Tp* __last,
				  _ForwardIterator __seed)
    {
      std::__uninitialized_construct_buf_dispatch<
	__has_trivial_constructor(_Tp)>::
	  __ucr(__first, __last, __seed);
    }

  template<typename _ForwardIterator, typename _Tp>
    _Temporary_buffer<_ForwardIterator, _Tp>::
    _Temporary_buffer(_ForwardIterator __seed, size_type __original_len)
    : _M_original_len(__original_len), _M_impl(__original_len)
    {
      std::__uninitialized_construct_buf(begin(), end(), __seed);
    }

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif /* _STL_TEMPBUF_H */