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/**
* Copyright (C) 2015 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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
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