text: // Copyright 2020 Google LLC
  //
  // 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
  //
  //     https://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.
  //
  // -----------------------------------------------------------------------------
  // File: xor_filter.h
  // -----------------------------------------------------------------------------
  
  #ifndef CI_XOR_FILTER_H_
  #define CI_XOR_FILTER_H_
  
  #include <iostream>
  #include <vector>
  
  #include "absl/strings/str_cat.h"
  #include "xor_singleheader/include/xorfilter.h"
  
  namespace ci {
  
  // A wrapper for the Xor filter with 8-bit fingerprints. This filter uses close
  // to 10 bits per element and achieves a false positive probability of ~0.3%.
  //
  // Adapted from https://github.com/FastFilter/xor_singleheader.
  class Xor8 {
   public:
    // `keys` has to be duplicate free.
    explicit Xor8(const std::vector<uint64_t>& keys) {
      if (!xor8_allocate(keys.size(), &filter_)) {
        std::cerr << "Couldn't allocate Xor filter." << std::endl;
        exit(EXIT_FAILURE);
      }
      if (!xor8_buffered_populate(reinterpret_cast<const uint64_t*>(keys.data()),
                                  keys.size(), &filter_)) {
        std::cerr << "Couldn't populate Xor filter." << std::endl;
        exit(EXIT_FAILURE);
      }
    }
  
    // Forbid copying and moving.
    Xor8(const Xor8&) = delete;
    Xor8& operator=(const Xor8&) = delete;
    Xor8(Xor8&&) = delete;
    Xor8& operator=(Xor8&&) = delete;
  
    ~Xor8() { xor8_free(&filter_); }
  
    inline bool Contains(const uint64_t key) const {
      return xor8_contain(key, &filter_);
    }
  
    std::string Data() const {
      std::string data;
      absl::StrAppend(&data, filter_.seed);
      absl::StrAppend(&data, filter_.blockLength);
      const size_t num_fingerprints = 3 * filter_.blockLength;
      for (size_t i = 0; i < num_fingerprints; ++i)
        absl::StrAppend(&data, filter_.fingerprints[i]);
      return data;
    }
  
    size_t SizeInBytes() const { return xor8_size_in_bytes(&filter_); }
  
   private:
    xor8_s filter_;
  };
  
  }  // namespace ci
  
  #endif  // CI_XOR_FILTER_H_
  