text: // Copyright (c) 2018, ETH Zurich and UNC Chapel Hill.
  // All rights reserved.
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are met:
  //
  //     * Redistributions of source code must retain the above copyright
  //       notice, this list of conditions and the following disclaimer.
  //
  //     * Redistributions in binary form must reproduce the above copyright
  //       notice, this list of conditions and the following disclaimer in the
  //       documentation and/or other materials provided with the distribution.
  //
  //     * Neither the name of ETH Zurich and UNC Chapel Hill nor the names of
  //       its contributors may be used to endorse or promote products derived
  //       from this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  // ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
  // LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  // CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  // SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  // CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  // POSSIBILITY OF SUCH DAMAGE.
  //
  // Author: Johannes L. Schoenberger (jsch-at-demuc-dot-de)
  
  #ifndef COLMAP_SRC_RETRIEVAL_INVERTED_FILE_ENTRY_H_
  #define COLMAP_SRC_RETRIEVAL_INVERTED_FILE_ENTRY_H_
  
  #include <bitset>
  #include <fstream>
  
  #include "retrieval/geometry.h"
  
  namespace colmap {
  namespace retrieval {
  
  // An inverted file entry. The template defines the dimensionality of the binary
  // string used to approximate the descriptor in the Hamming space.
  // This class is based on an original implementation by Torsten Sattler.
  template <int N>
  struct InvertedFileEntry {
    void Read(std::istream* ifs);
    void Write(std::ostream* ofs) const;
  
    // The identifier of the image this entry is associated with.
    int image_id = -1;
  
    // The index of the feature within the image's keypoints list.
    int feature_idx = -1;
  
    // The geometry of the feature, used for spatial verification.
    FeatureGeometry geometry;
  
    // The binary signature in the Hamming embedding.
    std::bitset<N> descriptor;
  };
  
  ////////////////////////////////////////////////////////////////////////////////
  // Implementation
  ////////////////////////////////////////////////////////////////////////////////
  
  template <int N>
  void InvertedFileEntry<N>::Read(std::istream* ifs) {
    static_assert(N <= 64, "Dimensionality too large");
    static_assert(sizeof(unsigned long long) >= 8,
                  "Expected unsigned long to be at least 8 byte");
    static_assert(sizeof(FeatureGeometry) == 16, "Geometry type size mismatch");
  
    int32_t image_id_data = 0;
    ifs->read(reinterpret_cast<char*>(&image_id_data), sizeof(int32_t));
    image_id = static_cast<int>(image_id_data);
  
    int32_t feature_idx_data = 0;
    ifs->read(reinterpret_cast<char*>(&feature_idx_data), sizeof(int32_t));
    feature_idx = static_cast<int>(feature_idx_data);
  
    ifs->read(reinterpret_cast<char*>(&geometry), sizeof(FeatureGeometry));
  
    uint64_t descriptor_data = 0;
    ifs->read(reinterpret_cast<char*>(&descriptor_data), sizeof(uint64_t));
    descriptor = std::bitset<N>(descriptor_data);
  }
  
  template <int N>
  void InvertedFileEntry<N>::Write(std::ostream* ofs) const {
    static_assert(N <= 64, "Dimensionality too large");
    static_assert(sizeof(unsigned long long) >= 8,
                  "Expected unsigned long to be at least 8 byte");
    static_assert(sizeof(FeatureGeometry) == 16, "Geometry type size mismatch");
  
    const int32_t image_id_data = image_id;
    ofs->write(reinterpret_cast<const char*>(&image_id_data), sizeof(int32_t));
  
    const int32_t feature_idx_data = feature_idx;
    ofs->write(reinterpret_cast<const char*>(&feature_idx_data), sizeof(int32_t));
  
    ofs->write(reinterpret_cast<const char*>(&geometry), sizeof(FeatureGeometry));
  
    const uint64_t descriptor_data =
        static_cast<uint64_t>(descriptor.to_ullong());
    ofs->write(reinterpret_cast<const char*>(&descriptor_data), sizeof(uint64_t));
  }
  
  }  // namespace retrieval
  }  // namespace colmap
  
  #endif  // COLMAP_SRC_RETRIEVAL_INVERTED_FILE_ENTRY_H_
  