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[EDIT] FILE: mask_array.h

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

// Copyright (C) 1997-2018 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/mask_array.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{valarray}
 */

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

#ifndef _MASK_ARRAY_H
#define _MASK_ARRAY_H 1

#pragma GCC system_header

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

/**
   * @addtogroup numeric_arrays
   * @{
   */

/**
   *  @brief  Reference to selected subset of an array.
   *
   *  A mask_array is a reference to the actual elements of an array specified
   *  by a bitmask in the form of an array of bool.  The way to get a
   *  mask_array is to call operator[](valarray<bool>) on a valarray.  The
   *  returned mask_array then permits carrying operations out on the
   *  referenced subset of elements in the original valarray.
   *
   *  For example, if a mask_array is obtained using the array (false, true,
   *  false, true) as an argument, the mask array has two elements referring
   *  to array[1] and array[3] in the underlying array.
   *
   *  @param  Tp  Element type.
   */
  template <class _Tp>
    class mask_array
    {
    public:
      typedef _Tp value_type;

// _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 253. valarray helper functions are almost entirely useless

///  Copy constructor.  Both slices refer to the same underlying array.
      mask_array (const mask_array&);
      
      ///  Assignment operator.  Assigns elements to corresponding elements
      ///  of @a a.
      mask_array& operator=(const mask_array&);

void operator=(const valarray<_Tp>&) const;
      ///  Multiply slice elements by corresponding elements of @a v.
      void operator*=(const valarray<_Tp>&) const;
      ///  Divide slice elements by corresponding elements of @a v.
      void operator/=(const valarray<_Tp>&) const;
      ///  Modulo slice elements by corresponding elements of @a v.
      void operator%=(const valarray<_Tp>&) const;
      ///  Add corresponding elements of @a v to slice elements.
      void operator+=(const valarray<_Tp>&) const;
      ///  Subtract corresponding elements of @a v from slice elements.
      void operator-=(const valarray<_Tp>&) const;
      ///  Logical xor slice elements with corresponding elements of @a v.
      void operator^=(const valarray<_Tp>&) const;
      ///  Logical and slice elements with corresponding elements of @a v.
      void operator&=(const valarray<_Tp>&) const;
      ///  Logical or slice elements with corresponding elements of @a v.
      void operator|=(const valarray<_Tp>&) const;
      ///  Left shift slice elements by corresponding elements of @a v.
      void operator<<=(const valarray<_Tp>&) const;
      ///  Right shift slice elements by corresponding elements of @a v.
      void operator>>=(const valarray<_Tp>&) const;
      ///  Assign all slice elements to @a t.
      void operator=(const _Tp&) const;

//        ~mask_array ();

template<class _Dom>
        void operator=(const _Expr<_Dom,_Tp>&) const;
      template<class _Dom>
        void operator*=(const _Expr<_Dom,_Tp>&) const;
      template<class _Dom>
        void operator/=(const _Expr<_Dom,_Tp>&) const;
      template<class _Dom>
        void operator%=(const _Expr<_Dom,_Tp>&) const;
      template<class _Dom>
        void operator+=(const _Expr<_Dom,_Tp>&) const;
      template<class _Dom>
        void operator-=(const _Expr<_Dom,_Tp>&) const;
      template<class _Dom>
        void operator^=(const _Expr<_Dom,_Tp>&) const;
      template<class _Dom>
        void operator&=(const _Expr<_Dom,_Tp>&) const;
      template<class _Dom>
        void operator|=(const _Expr<_Dom,_Tp>&) const;
      template<class _Dom>
        void operator<<=(const _Expr<_Dom,_Tp>&) const;
      template<class _Dom>
        void operator>>=(const _Expr<_Dom,_Tp>&) const;

private:
      mask_array(_Array<_Tp>, size_t, _Array<bool>);
      friend class valarray<_Tp>;

const size_t       _M_sz;
      const _Array<bool> _M_mask;
      const _Array<_Tp>  _M_array;

// not implemented
      mask_array();
    };

template<typename _Tp>
    inline mask_array<_Tp>::mask_array(const mask_array<_Tp>& __a)
    : _M_sz(__a._M_sz), _M_mask(__a._M_mask), _M_array(__a._M_array) {}

template<typename _Tp>
    inline
    mask_array<_Tp>::mask_array(_Array<_Tp> __a, size_t __s, _Array<bool> __m)
    : _M_sz(__s), _M_mask(__m), _M_array(__a) {}

template<typename _Tp>
    inline mask_array<_Tp>&
    mask_array<_Tp>::operator=(const mask_array<_Tp>& __a)
    {
      std::__valarray_copy(__a._M_array, __a._M_mask,
			   _M_sz, _M_array, _M_mask);
      return *this;
    }

template<typename _Tp>
    inline void
    mask_array<_Tp>::operator=(const _Tp& __t) const
    { std::__valarray_fill(_M_array, _M_sz, _M_mask, __t); }

template<typename _Tp>
    inline void
    mask_array<_Tp>::operator=(const valarray<_Tp>& __v) const
    { std::__valarray_copy(_Array<_Tp>(__v), __v.size(), _M_array, _M_mask); }

template<typename _Tp>
    template<class _Ex>
      inline void
      mask_array<_Tp>::operator=(const _Expr<_Ex, _Tp>& __e) const
      { std::__valarray_copy(__e, __e.size(), _M_array, _M_mask); }

#undef _DEFINE_VALARRAY_OPERATOR
#define _DEFINE_VALARRAY_OPERATOR(_Op, _Name)				\
  template<typename _Tp>						\
    inline void								\
    mask_array<_Tp>::operator _Op##=(const valarray<_Tp>& __v) const	\
    {									\
      _Array_augmented_##_Name(_M_array, _M_mask,			\
			       _Array<_Tp>(__v), __v.size());		\
    }									\
									\
  template<typename _Tp>                                                \
    template<class _Dom>			                        \
      inline void							\
      mask_array<_Tp>::operator _Op##=(const _Expr<_Dom, _Tp>& __e) const\
      {									\
	_Array_augmented_##_Name(_M_array, _M_mask, __e, __e.size());   \
      }

_DEFINE_VALARRAY_OPERATOR(*, __multiplies)
_DEFINE_VALARRAY_OPERATOR(/, __divides)
_DEFINE_VALARRAY_OPERATOR(%, __modulus)
_DEFINE_VALARRAY_OPERATOR(+, __plus)
_DEFINE_VALARRAY_OPERATOR(-, __minus)
_DEFINE_VALARRAY_OPERATOR(^, __bitwise_xor)
_DEFINE_VALARRAY_OPERATOR(&, __bitwise_and)
_DEFINE_VALARRAY_OPERATOR(|, __bitwise_or)
_DEFINE_VALARRAY_OPERATOR(<<, __shift_left)
_DEFINE_VALARRAY_OPERATOR(>>, __shift_right)

#undef _DEFINE_VALARRAY_OPERATOR

// @} group numeric_arrays

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

#endif /* _MASK_ARRAY_H */

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