gslice.h

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// The template and inlines for the -*- C++ -*- gslice class.

// Copyright (C) 1997, 1998, 1999, 2000, 2001, 2004
// 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 2, 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.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
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// the GNU General Public License.

// Written by Gabriel Dos Reis <Gabriel.Dos-Reis@DPTMaths.ENS-Cachan.Fr>

/** @file gslice.h
 *  This is an internal header file, included by other library headers.
 *  You should not attempt to use it directly.
 */

#ifndef _GSLICE_H
#define _GSLICE_H 1

#pragma GCC system_header

namespace std {

  /**
   *  @brief  Class defining multi-dimensional subset of an array.
   *
   *  The slice class represents a multi-dimensional subset of an array,
   *  specified by three parameter sets: start offset, size array, and stride
   *  array.  The start offset is the index of the first element of the array
   *  that is part of the subset.  The size and stride array describe each
   *  dimension of the slice.  Size is the number of elements in that
   *  dimension, and stride is the distance in the array between successive
   *  elements in that dimension.  Each dimension's size and stride is taken
   *  to begin at an array element described by the previous dimension.  The
   *  size array and stride array must be the same size.
   *
   *  For example, if you have offset==3, stride[0]==11, size[1]==3,
   *  stride[1]==3, then slice[0,0]==array[3], slice[0,1]==array[6],
   *  slice[0,2]==array[9], slice[1,0]==array[14], slice[1,1]==array[17],
   *  slice[1,2]==array[20].
   */
    class gslice
    {
    public:
      ///  Construct an empty slice.
      gslice ();

      /**
       *  @brief  Construct a slice.
       *
       *  Constructs a slice with as many dimensions as the length of the @a l
       *  and @a s arrays.
       *
       *  @param  o  Offset in array of first element.
       *  @param  l  Array of dimension lengths.
       *  @param  s  Array of dimension strides between array elements.
       */
      gslice(size_t, const valarray<size_t>&, const valarray<size_t>&);

      // XXX: the IS says the copy-ctor and copy-assignment operators are
      //      synthetized by the compiler but they are just unsuitable
      //      for a ref-counted semantic
      ///  Copy constructor.
      gslice(const gslice&);

      ///  Destructor.
      ~gslice();

      // XXX: See the note above.
      ///  Assignment operator.
      gslice& operator=(const gslice&);

      ///  Return array offset of first slice element.
      size_t           start() const;

      ///  Return array of sizes of slice dimensions.
      valarray<size_t> size() const;

      ///  Return array of array strides for each dimension.
      valarray<size_t> stride() const;

    private:
      struct _Indexer {
    size_t _M_count;
    size_t _M_start;
    valarray<size_t> _M_size;
    valarray<size_t> _M_stride;
    valarray<size_t> _M_index; // Linear array of referenced indices
    _Indexer(size_t, const valarray<size_t>&,
         const valarray<size_t>&);
    void _M_increment_use() { ++_M_count; }
    size_t _M_decrement_use() { return --_M_count; }
      };

      _Indexer* _M_index;

      template<typename _Tp> friend class valarray;
    };

    inline size_t
    gslice::start () const
    { return _M_index ? _M_index->_M_start : 0; }

    inline valarray<size_t>
    gslice::size () const
    { return _M_index ? _M_index->_M_size : valarray<size_t>(); }

    inline valarray<size_t>
    gslice::stride () const
    { return _M_index ? _M_index->_M_stride : valarray<size_t>(); }

    inline gslice::gslice () : _M_index(0) {}

    inline
    gslice::gslice(size_t __o, const valarray<size_t>& __l,
                   const valarray<size_t>& __s)
            : _M_index(new gslice::_Indexer(__o, __l, __s)) {}

    inline
    gslice::gslice(const gslice& __g) : _M_index(__g._M_index)
    { if (_M_index) _M_index->_M_increment_use(); }

    inline
    gslice::~gslice()
    { if (_M_index && _M_index->_M_decrement_use() == 0) delete _M_index; }

    inline gslice&
    gslice::operator= (const gslice& __g)
    {
        if (__g._M_index) __g._M_index->_M_increment_use();
        if (_M_index && _M_index->_M_decrement_use() == 0) delete _M_index;
        _M_index = __g._M_index;
        return *this;
    }


} // std::


#endif /* _GSLICE_H */

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