text: /**
   *    Copyright (C) 2018-present MongoDB, Inc.
   *
   *    This program is free software: you can redistribute it and/or modify
   *    it under the terms of the Server Side Public License, version 1,
   *    as published by MongoDB, Inc.
   *
   *    This program 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
   *    Server Side Public License for more details.
   *
   *    You should have received a copy of the Server Side Public License
   *    along with this program. If not, see
   *    <http://www.mongodb.com/licensing/server-side-public-license>.
   *
   *    As a special exception, the copyright holders give permission to link the
   *    code of portions of this program with the OpenSSL library under certain
   *    conditions as described in each individual source file and distribute
   *    linked combinations including the program with the OpenSSL library. You
   *    must comply with the Server Side Public License in all respects for
   *    all of the code used other than as permitted herein. If you modify file(s)
   *    with this exception, you may extend this exception to your version of the
   *    file(s), but you are not obligated to do so. If you do not wish to do so,
   *    delete this exception statement from your version. If you delete this
   *    exception statement from all source files in the program, then also delete
   *    it in the license file.
   */
  
  #pragma once
  
  #include <cstddef>
  #include <cstdint>
  
  #include "mongo/base/data_type.h"
  #include "mongo/base/status.h"
  
  namespace mongo {
  /**
   * Methods to compress and decompress 64-bit integers into variable integers
   *
   * Uses a technique described here:
   * S. Buttcher, C. L. A. Clarke, and G. V. Cormack.
   *  Information Retrieval: Implementing and Evaluating Search Engines. MIT Press, Cambridge, MA,
   *  2010
   */
  struct FTDCVarInt {
      /**
       * Maximum number of bytes an integer can compress to
       */
      static const std::size_t kMaxSizeBytes64 = 10;
  
      FTDCVarInt() = default;
      FTDCVarInt(std::uint64_t t) : _value(t) {}
  
      operator std::uint64_t() const {
          return _value;
      }
  
  private:
      std::uint64_t _value{0};
  };
  
  template <>
  struct DataType::Handler<FTDCVarInt> {
      /**
       * Compress a 64-bit integer and return the new buffer position.
       *
       * end should be the byte after the end of the buffer.
       *
       * Return nullptr for bad encoded data.
       */
      static Status load(FTDCVarInt* t,
                         const char* ptr,
                         size_t length,
                         size_t* advanced,
                         std::ptrdiff_t debug_offset);
  
      /**
       * Compress a 64-bit integer and return the new buffer position
       */
      static Status store(const FTDCVarInt& t,
                          char* ptr,
                          size_t length,
                          size_t* advanced,
                          std::ptrdiff_t debug_offset);
  
      static FTDCVarInt defaultConstruct() {
          return 0;
      }
  };
  
  }  // namespace mongo
  