StrideIterator.h

#ifndef _theplu_yat_utility_stride_iterator_
#define _theplu_yat_utility_stride_iterator_

// $Id: StrideIterator.h 4207 2022-08-26 04:36:28Z peter $

/*
  Copyright (C) 2007, 2008 Jari Häkkinen, Peter Johansson
  Copyright (C) 2010, 2015, 2016, 2022 Peter Johansson

  This file is part of the yat library, http://dev.thep.lu.se/yat

  The yat 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 of the
  License, or (at your option) any later version.

  The yat 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 yat. If not, see <http://www.gnu.org/licenses/>.
*/

#include <boost/concept_check.hpp>
#include <boost/iterator/iterator_adaptor.hpp>
#include <boost/iterator/iterator_concepts.hpp>

namespace theplu {
namespace yat {
namespace utility {

  template<typename RandomAccessIterator>
  class StrideIterator
    : public boost::iterator_adaptor<StrideIterator<RandomAccessIterator>
                                     , RandomAccessIterator>
  {
    typedef boost::iterator_adaptor<StrideIterator<RandomAccessIterator>,
                                    RandomAccessIterator>
    super_t;

  public:
    typedef RandomAccessIterator iterator_type;

    explicit StrideIterator(size_t stride=1)
      : StrideIterator::iterator_adaptor_(), stride_(stride)
    {
      using boost_concepts::RandomAccessTraversal;
      using boost_concepts::ReadableIterator;
      BOOST_CONCEPT_ASSERT((ReadableIterator<RandomAccessIterator>));
      BOOST_CONCEPT_ASSERT((RandomAccessTraversal<RandomAccessIterator>));
    }

    explicit StrideIterator(RandomAccessIterator p, size_t stride=1)
      : StrideIterator::iterator_adaptor_(p), stride_(stride) {}


    StrideIterator(const StrideIterator& other)
      : StrideIterator::iterator_adaptor_(other.base()), stride_(other.stride())
    {}

    template<typename I2>
    StrideIterator(StrideIterator<I2> other,
                   typename boost::enable_if_convertible<I2
                   , RandomAccessIterator>::type* = 0 )
      : StrideIterator::iterator_adaptor_(other.base()),
        stride_(other.stride()) {}

    StrideIterator& operator=(const StrideIterator& rhs)
    {
      stride_ = rhs.stride();
      this->base_reference() = rhs.base();
      return *this;
    }

    inline size_t stride(void) const { return stride_; }

  private:
    // to give base class access to private parts
    friend class boost::iterator_core_access;

    size_t stride_;

    //typedef typename StrideIterator::iterator_adaptor_::difference_type
    typedef typename StrideIterator::iterator_adaptor_::difference_type
    difference_t;

    void advance(typename super_t::difference_type n)
    { this->base_reference() += stride_*n; }

    void decrement(void) { this->base_reference()-=stride_; }

    template <class OtherIterator>
    typename super_t::difference_type
    distance_to(const StrideIterator<OtherIterator>& other) const
    {
      // casting to int to avoid loss of sign in numerator
      return (other.base() - this->base() )/static_cast<int>(stride_);
    }

    void increment(void) { this->base_reference()+=stride_; }
  };

}}} // of namespace utility, yat, and theplu

#endif