sample24.cpp

Example for finding bit-vector ranges with the specifed number of ON bitsThe use case here:

• search algorithm runs a query, the result set represented as a bit-vector
• second stage needs to calculate statistics (or run a sub-query) on each element of a result set and we want to do it in-parallel so we need to create batches (or jobs) with approximately equal complexity

• we assume that each found element in the bitset has approximately same complexity, so to model the situation we need to find range boundaries with the specifed population count

  See also

  bm::rank_range_split

  bm::bvector::get_enumerator

  bm::bvector::enumerator

  /*
  Copyright(c) 2002-2017 Anatoliy Kuznetsov(anatoliy_kuznetsov at yahoo.com)
   
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
   
      http://www.apache.org/licenses/LICENSE-2.0
   
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
   
  For more information please visit:  http://bitmagic.io
  */
   
  /** \example sample24.cpp
  @brief Example for finding bit-vector ranges with the specifed number of ON bits
   
  The use case here:
     - search algorithm runs a query, the result set represented as a bit-vector
   
     - second stage needs to calculate statistics (or run a sub-query) on each
       element of a result set and we want to do it in-parallel so we need to
       create batches (or jobs) with approximately equal complexity
   
     - we assume that each found element in the bitset has approximately same
       complexity, so to model the situation we need to find range boundaries with
       the specifed population count
   
      @sa bm::rank_range_split
      @sa bm::bvector::get_enumerator
      @sa bm::bvector::enumerator
   
  */
   
  /*! \file sample24.cpp
      \brief Example: demo for bm::rank_range_split
  */
   
  #include <stdlib.h>
  #include <iostream>
  #include <vector>
  #include <utility>
   
  #include "bm.h"
  #include "bmalgo.h"
  #include "bmundef.h" /* clear the pre-proc defines from BM */
   
  using namespace std;
   
  typedef bm::bvector<>::size_type bv_size_type;
  typedef std::vector<std::pair<bv_size_type, bv_size_type> > bv_ranges_vector;
   
  int main(void)
  {
      try
      {
          const unsigned ranges = 3; // split into 3 ranges
          bm::bvector<>   bv { 10, 20, 100, 200, 300, 655000, bm::id_max-1 };
   
   
          bv_size_type cnt = bv.count();
          bv_size_type split_rank = cnt / ranges; // target population count
   
          bv_ranges_vector pair_vect;
   
          // run the search for splits, traget bin size is split_rank
   
          cout << "Target split rank:" << split_rank << endl;
   
          bm::rank_range_split(bv, split_rank, pair_vect);
   
          // go through each range and print all bit values
          for (size_t k = 0; k < pair_vect.size(); ++k)
          {
              const auto& p = pair_vect[k];
              cout << k << ": [" << p.first << ".." << p.second << "] ";
   
              // find and print bits in the target range with bvector<>::enumerator
              bm::bvector<>::enumerator en = bv.get_enumerator(p.first);
              for (; en.valid(); ++en)
              {
                  auto v = *en;
                  if (v > p.second)
                      break;
                  cout << v << ", ";
              } // for en
              cout << endl;
          } // for k
   
      }
      catch(std::exception& ex)
      {
          std::cerr << ex.what() << std::endl;
          return 1;
      }
      
   
      return 0;
  }