median_h.hh

// Copyright (C) 2007, 2008, 2009 EPITA Research and Development Laboratory (LRDE)
//
// This file is part of Olena.
//
// Olena 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, version 2 of the License.
//
// Olena 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 Olena.  If not, see <http://www.gnu.org/licenses/>.
//
// As a special exception, you may use this file as part of a free
// software project without restriction.  Specifically, if other files
// instantiate templates or use macros or inline functions from this
// file, or you compile this file and link it with other files to produce
// an executable, this file does not by itself cause the resulting
// executable to be covered by the GNU General Public License.  This
// exception does not however invalidate any other reasons why the
// executable file might be covered by the GNU General Public License.

#ifndef MLN_ACCU_STAT_MEDIAN_H_HH
# define MLN_ACCU_STAT_MEDIAN_H_HH


# include <mln/accu/internal/base.hh>
# include <mln/accu/histo.hh>
# include <mln/value/set.hh>


namespace mln
{

  namespace accu
  {

    namespace stat
    {

      // Forward declaration.
      template <typename V>
      struct median_h;

    } // end of namespace mln::accu::stat

    namespace meta
    {

      namespace stat
      {

        struct median_h : public Meta_Accumulator< median_h >
        {
          template <typename V>
          struct with
          {
            typedef accu::stat::median_h<V> ret;
          };
        };

      } // end of namespace mln::accu::meta::stat

    } // end of namespace mln::accu::meta

    namespace stat
    {

      template <typename V>
      struct median_h : public mln::accu::internal::base< const V&, median_h<V> >
      {
        typedef V argument;

        median_h();

        void init();
        void   take(const argument& t);
        void   take(const median_h<V>& other);
        void untake(const argument& t);

        unsigned card() const { return h_.sum(); }

        const argument& to_result() const;

        const accu::histo<V>& histo() const;

        bool is_valid() const;

      protected:

        mutable accu::histo<V> h_;
        const value::set<V>& s_;        // derived from h_

        mutable unsigned sum_minus_, sum_plus_;

        mutable bool valid_;
        mutable unsigned i_;    // the median_h index
        mutable argument t_;    // the median_h value

        // Auxiliary methods
        void update_() const;
        void go_minus_() const;
        void go_plus_() const;
      };

# ifndef MLN_INCLUDE_ONLY

      template <typename V>
      inline
      median_h<V>::median_h()
        : h_(),
          s_(h_.vset())
      {
        init();
      }

      template <typename V>
      inline
      void
      median_h<V>::take(const argument& t)
      {
        h_.take(t);

        if (t < t_)
          ++sum_minus_;
        else if (t > t_)
          ++sum_plus_;

        if (valid_)
          valid_ = false;
      }

      template <typename V>
      inline
      void
      median_h<V>::take(const median_h<V>& other)
      {
        // h_
        h_.take(other.h_);

        // sum_minus_
        for (unsigned i = 0; i < i_; ++i)
          sum_minus_ += other.h_[i];

        // sum_plus_
        for (unsigned i = i_ + 1; i < h_.nvalues(); ++i)
          sum_plus_ += other.h_[i];

        if (valid_)
          valid_ = false;
      }

      template <typename V>
      inline
      void
      median_h<V>::untake(const argument& t)
      {
        mln_precondition(h_(t) != 0);
        h_.untake(t);

        if (t < t_)
          --sum_minus_;
        else if (t > t_)
          --sum_plus_;

        if (valid_)
          valid_ = false;
      }

      template <typename V>
      inline
      void
      median_h<V>::update_() const
      {
        valid_ = true;

        if (h_.sum() == 0)
          return;

        if (2 * sum_minus_ > h_.sum())
          go_minus_();
        else
          if (2 * sum_plus_ > h_.sum())
            go_plus_();
          else
            if (h_[i_] == 0)
              {
                // go to the heaviest side
                if (sum_plus_ > sum_minus_)
                  go_plus_();
                else
                  go_minus_(); // default when both sides are balanced
              }
      }

      template <typename V>
      inline
      void
      median_h<V>::go_minus_() const
      {
        do
          {
            sum_plus_ += h_[i_];
            do
              --i_;
            while (h_[i_] == 0);
            sum_minus_ -= h_[i_];
          }
        while (2 * sum_minus_ > h_.sum());
        t_ = s_[i_];
      }

      template <typename V>
      inline
      void
      median_h<V>::go_plus_() const
      {
        do
          {
            sum_minus_ += h_[i_];
            do
              ++i_;
            while (h_[i_] == 0);
            sum_plus_ -= h_[i_];
          }
        while (2 * sum_plus_ > h_.sum());
        t_ = s_[i_];
      }

      template <typename V>
      inline
      void
      median_h<V>::init()
      {
        h_.init();
        sum_minus_ = 0;
        sum_plus_ = 0;
        i_ = (s_.index_of(mln_max(argument))
              - s_.index_of(mln_min(argument))) / 2;
        t_ = s_[i_];
        valid_ = true;
      }

      template <typename V>
      inline
      const typename median_h<V>::argument&
      median_h<V>::to_result() const
      {
        if (! valid_)
          update_();
        return t_;
      }

      template <typename V>
      inline
      const accu::histo<V>&
      median_h<V>::histo() const
      {
        return h_;
      }

      template <typename V>
      inline
      bool
      median_h<V>::is_valid() const
      {
        return true;
      }

# endif // ! MLN_INCLUDE_ONLY

    } // end of namespace mln::accu::stat

  } // end of namespace mln::accu

} // end of namespace mln

#endif // ! MLN_ACCU_STAT_MEDIAN_H_HH

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