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RocksDB for Erlang

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rocksdb c_src counter_merge_operator.cc
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c_src/counter_merge_operator.cc 

// Copyright (c) 2018 Benoit Chesneau

//

// This file is provided to you 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.



#include <iostream>

#include <string>

#include <memory>

#include <list>

#include <algorithm>

#include <assert.h>



#include "rocksdb/slice.h"

#include "rocksdb/merge_operator.h"



#include "erl_nif.h"

#include "util.h"

#include "counter_merge_operator.h"



namespace erocksdb {



    CounterMergeOperator::CounterMergeOperator() {}



    bool CounterMergeOperator::Merge(

            const rocksdb::Slice& /*key*/,

            const rocksdb::Slice* existing_value,

            const rocksdb::Slice& value,

            std::string* new_value,

            rocksdb::Logger* /*logger*/) const {



        int counter = 0;

        if (existing_value != nullptr) {

            try {

                counter = std::stoi(existing_value->ToString());

            } catch (...) {

                return false;

            }

        }



        int oper;

        try {

            oper = std::stoi(value.ToString());

        } catch(...) {

            return false;

        }

        auto new_counter = counter + oper;

        *new_value = std::to_string(new_counter);

        return true;

    }



    const char* CounterMergeOperator::Name() const  {

        return "CounterMergeOperator";

    }



    std::shared_ptr<CounterMergeOperator> CreateCounterMergeOperator() {

        return std::make_shared<CounterMergeOperator>();

    }

}