libstdc++
stl_tempbuf.h
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00001 // Temporary buffer implementation -*- C++ -*-
00002 
00003 // Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
00004 // Free Software Foundation, Inc.
00005 //
00006 // This file is part of the GNU ISO C++ Library.  This library is free
00007 // software; you can redistribute it and/or modify it under the
00008 // terms of the GNU General Public License as published by the
00009 // Free Software Foundation; either version 3, or (at your option)
00010 // any later version.
00011 
00012 // This library is distributed in the hope that it will be useful,
00013 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00014 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00015 // GNU General Public License for more details.
00016 
00017 // Under Section 7 of GPL version 3, you are granted additional
00018 // permissions described in the GCC Runtime Library Exception, version
00019 // 3.1, as published by the Free Software Foundation.
00020 
00021 // You should have received a copy of the GNU General Public License and
00022 // a copy of the GCC Runtime Library Exception along with this program;
00023 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00024 // <http://www.gnu.org/licenses/>.
00025 
00026 /*
00027  *
00028  * Copyright (c) 1994
00029  * Hewlett-Packard Company
00030  *
00031  * Permission to use, copy, modify, distribute and sell this software
00032  * and its documentation for any purpose is hereby granted without fee,
00033  * provided that the above copyright notice appear in all copies and
00034  * that both that copyright notice and this permission notice appear
00035  * in supporting documentation.  Hewlett-Packard Company makes no
00036  * representations about the suitability of this software for any
00037  * purpose.  It is provided "as is" without express or implied warranty.
00038  *
00039  *
00040  * Copyright (c) 1996,1997
00041  * Silicon Graphics Computer Systems, Inc.
00042  *
00043  * Permission to use, copy, modify, distribute and sell this software
00044  * and its documentation for any purpose is hereby granted without fee,
00045  * provided that the above copyright notice appear in all copies and
00046  * that both that copyright notice and this permission notice appear
00047  * in supporting documentation.  Silicon Graphics makes no
00048  * representations about the suitability of this software for any
00049  * purpose.  It is provided "as is" without express or implied warranty.
00050  */
00051 
00052 /** @file bits/stl_tempbuf.h
00053  *  This is an internal header file, included by other library headers.
00054  *  Do not attempt to use it directly. @headername{memory}
00055  */
00056 
00057 #ifndef _STL_TEMPBUF_H
00058 #define _STL_TEMPBUF_H 1
00059 
00060 #include <bits/stl_algobase.h>
00061 #include <bits/stl_construct.h>
00062 
00063 namespace std _GLIBCXX_VISIBILITY(default)
00064 {
00065 _GLIBCXX_BEGIN_NAMESPACE_VERSION
00066 
00067   /**
00068    *  @brief Allocates a temporary buffer.
00069    *  @param  len  The number of objects of type Tp.
00070    *  @return See full description.
00071    *
00072    *  Reinventing the wheel, but this time with prettier spokes!
00073    *
00074    *  This function tries to obtain storage for @c len adjacent Tp
00075    *  objects.  The objects themselves are not constructed, of course.
00076    *  A pair<> is returned containing <em>the buffer s address and
00077    *  capacity (in the units of sizeof(Tp)), or a pair of 0 values if
00078    *  no storage can be obtained.</em>  Note that the capacity obtained
00079    *  may be less than that requested if the memory is unavailable;
00080    *  you should compare len with the .second return value.
00081    *
00082    * Provides the nothrow exception guarantee.
00083    */
00084   template<typename _Tp>
00085     pair<_Tp*, ptrdiff_t>
00086     get_temporary_buffer(ptrdiff_t __len)
00087     {
00088       const ptrdiff_t __max =
00089     __gnu_cxx::__numeric_traits<ptrdiff_t>::__max / sizeof(_Tp);
00090       if (__len > __max)
00091     __len = __max;
00092       
00093       while (__len > 0) 
00094     {
00095       _Tp* __tmp = static_cast<_Tp*>(::operator new(__len * sizeof(_Tp), 
00096                             std::nothrow));
00097       if (__tmp != 0)
00098         return std::pair<_Tp*, ptrdiff_t>(__tmp, __len);
00099       __len /= 2;
00100     }
00101       return std::pair<_Tp*, ptrdiff_t>(static_cast<_Tp*>(0), 0);
00102     }
00103 
00104   /**
00105    *  @brief The companion to get_temporary_buffer().
00106    *  @param  p  A buffer previously allocated by get_temporary_buffer.
00107    *  @return   None.
00108    *
00109    *  Frees the memory pointed to by p.
00110    */
00111   template<typename _Tp>
00112     inline void
00113     return_temporary_buffer(_Tp* __p)
00114     { ::operator delete(__p, std::nothrow); }
00115 
00116 
00117   /**
00118    *  This class is used in two places: stl_algo.h and ext/memory,
00119    *  where it is wrapped as the temporary_buffer class.  See
00120    *  temporary_buffer docs for more notes.
00121    */
00122   template<typename _ForwardIterator, typename _Tp>
00123     class _Temporary_buffer
00124     {
00125       // concept requirements
00126       __glibcxx_class_requires(_ForwardIterator, _ForwardIteratorConcept)
00127 
00128     public:
00129       typedef _Tp         value_type;
00130       typedef value_type* pointer;
00131       typedef pointer     iterator;
00132       typedef ptrdiff_t   size_type;
00133 
00134     protected:
00135       size_type  _M_original_len;
00136       size_type  _M_len;
00137       pointer    _M_buffer;
00138 
00139     public:
00140       /// As per Table mumble.
00141       size_type
00142       size() const
00143       { return _M_len; }
00144 
00145       /// Returns the size requested by the constructor; may be >size().
00146       size_type
00147       requested_size() const
00148       { return _M_original_len; }
00149 
00150       /// As per Table mumble.
00151       iterator
00152       begin()
00153       { return _M_buffer; }
00154 
00155       /// As per Table mumble.
00156       iterator
00157       end()
00158       { return _M_buffer + _M_len; }
00159 
00160       /**
00161        * Constructs a temporary buffer of a size somewhere between
00162        * zero and the size of the given range.
00163        */
00164       _Temporary_buffer(_ForwardIterator __first, _ForwardIterator __last);
00165 
00166       ~_Temporary_buffer()
00167       {
00168     std::_Destroy(_M_buffer, _M_buffer + _M_len);
00169     std::return_temporary_buffer(_M_buffer);
00170       }
00171 
00172     private:
00173       // Disable copy constructor and assignment operator.
00174       _Temporary_buffer(const _Temporary_buffer&);
00175 
00176       void
00177       operator=(const _Temporary_buffer&);
00178     };
00179 
00180 
00181   template<bool>
00182     struct __uninitialized_construct_buf_dispatch
00183     {
00184       template<typename _ForwardIterator, typename _Tp>
00185         static void
00186         __ucr(_ForwardIterator __first, _ForwardIterator __last,
00187           _Tp& __value)
00188         {
00189       if(__first == __last)
00190         return;
00191 
00192       _ForwardIterator __cur = __first;
00193       __try
00194         {
00195           std::_Construct(std::__addressof(*__first),
00196                   _GLIBCXX_MOVE(__value));
00197           _ForwardIterator __prev = __cur;
00198           ++__cur;
00199           for(; __cur != __last; ++__cur, ++__prev)
00200         std::_Construct(std::__addressof(*__cur),
00201                 _GLIBCXX_MOVE(*__prev));
00202           __value = _GLIBCXX_MOVE(*__prev);
00203         }
00204       __catch(...)
00205         {
00206           std::_Destroy(__first, __cur);
00207           __throw_exception_again;
00208         }
00209     }
00210     };
00211 
00212   template<>
00213     struct __uninitialized_construct_buf_dispatch<true>
00214     {
00215       template<typename _ForwardIterator, typename _Tp>
00216         static void
00217         __ucr(_ForwardIterator, _ForwardIterator, _Tp&) { }
00218     };
00219 
00220   // Constructs objects in the range [first, last).
00221   // Note that while these new objects will take valid values,
00222   // their exact value is not defined. In particular they may
00223   // be 'moved from'.
00224   //
00225   // While __value may altered during this algorithm, it will have
00226   // the same value when the algorithm finishes, unless one of the
00227   // constructions throws.
00228   //
00229   // Requirements: _ForwardIterator::value_type(_Tp&&) is valid.
00230   template<typename _ForwardIterator, typename _Tp>
00231     inline void
00232     __uninitialized_construct_buf(_ForwardIterator __first,
00233                   _ForwardIterator __last,
00234                   _Tp& __value)
00235     {
00236       typedef typename std::iterator_traits<_ForwardIterator>::value_type
00237     _ValueType;
00238 
00239       std::__uninitialized_construct_buf_dispatch<
00240         __has_trivial_constructor(_ValueType)>::
00241       __ucr(__first, __last, __value);
00242     }
00243 
00244   template<typename _ForwardIterator, typename _Tp>
00245     _Temporary_buffer<_ForwardIterator, _Tp>::
00246     _Temporary_buffer(_ForwardIterator __first, _ForwardIterator __last)
00247     : _M_original_len(std::distance(__first, __last)),
00248       _M_len(0), _M_buffer(0)
00249     {
00250       __try
00251     {
00252       std::pair<pointer, size_type> __p(std::get_temporary_buffer<
00253                         value_type>(_M_original_len));
00254       _M_buffer = __p.first;
00255       _M_len = __p.second;
00256       if(_M_buffer)
00257         std::__uninitialized_construct_buf(_M_buffer, _M_buffer + _M_len,
00258                            *__first);
00259     }
00260       __catch(...)
00261     {
00262       std::return_temporary_buffer(_M_buffer);
00263       _M_buffer = 0;
00264       _M_len = 0;
00265       __throw_exception_again;
00266     }
00267     }
00268 
00269 _GLIBCXX_END_NAMESPACE_VERSION
00270 } // namespace
00271 
00272 #endif /* _STL_TEMPBUF_H */
00273