sample24.cpp

Example for finding bit-vector ranges with the specifed number of ON bits.

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;
  }
  bm.h
  Compressed bit-vector bvector<> container, set algebraic methods, traversal iterators.
  bmalgo.h
  Algorithms for bvector<> (main include).
  bmundef.h
  pre-processor un-defines to avoid global space pollution (internal)
  bm::bvector::enumerator
  Constant iterator designed to enumerate "ON" bits.
  Definition bm.h:603
  bm::bvector::iterator_base::valid
  bool valid() const BMNOEXCEPT
  Checks if iterator is still valid.
  Definition bm.h:283
  bm::bvector
  Bitvector Bit-vector container with runtime compression of bits.
  Definition bm.h:115
  bm::bvector::count
  size_type count() const BMNOEXCEPT
  population count (count of ON bits)
  Definition bm.h:2401
  bm::bvector::size_type
  bvector_size_type size_type
  Definition bm.h:121
  bm::bvector::get_enumerator
  enumerator get_enumerator(size_type pos) const
  Returns enumerator pointing on specified or the next available bit.
  Definition bm.h:1883
  bm::rank_range_split
  void rank_range_split(const BV &bv, typename BV::size_type rank, PairVect &target_v)
  Algorithm to identify bit-vector ranges (splits) for the rank.
  Definition bmalgo.h:394
  bm::id_max
  const unsigned id_max
  Definition bmconst.h:109
  main
  int main(void)
  Definition sample1.cpp:43
  bv_size_type
  bm::bvector ::size_type bv_size_type
  Definition sample24.cpp:54
  bv_ranges_vector
  std::vector< std::pair< bv_size_type, bv_size_type > > bv_ranges_vector
  Definition sample24.cpp:55