round.h

#ifndef _theplu_yat_utility_round_
#define _theplu_yat_utility_round_

// $Id: round.h 4059 2021-04-20 02:28:38Z peter $

/*
  Copyright (C) 2021 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 <cmath>
#include <map>

namespace theplu {
namespace yat {
namespace utility {

  template<typename InputIterator, typename ForwardIterator>
  void round(InputIterator first, InputIterator last,
             ForwardIterator result)
  {
    std::multimap<double, ForwardIterator> map;
    double result_sum = 0;
    double input_sum = 0;
    for (auto it = first; it != last; ++it) {
      // copy value here in case result and first point to same value
      double x = *it;
      input_sum += x;
      *result = std::floor(x);
      map.insert(std::make_pair(*result - x, result));
      result_sum += *result;
      ++result;
    }
    double rounded_sum = std::round(input_sum);

    for (auto it = map.begin(); result_sum<rounded_sum; ++it) {
      YAT_ASSERT(it != map.end());
      *it->second += 1.0;
      result_sum += 1.0;
    }
  }

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

#endif