Merge "Use bitset for BloomFilter."

        dic_nodes_cache.cpp) \

    $(addprefix suggest/core/dictionary/, \

        bigram_dictionary.cpp \

        bloom_filter.cpp \

        dictionary.cpp \

        digraph_utils.cpp \

        error_type_utils.cpp \

/*

 * Copyright (C) 2013, The Android Open Source Project

 *

 * 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

 *

 *     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 "suggest/core/dictionary/bloom_filter.h"

namespace latinime {

// Must be smaller than BIGRAM_FILTER_BYTE_SIZE * 8, and preferably prime. 1021 is the largest

// prime under 128 * 8.

const int BloomFilter::BIGRAM_FILTER_MODULO = 1021;

} // namespace latinime

#ifndef LATINIME_BLOOM_FILTER_H

#define LATINIME_BLOOM_FILTER_H

#include <cstdint>

#include <cstring>

#include <bitset>

#include "defines.h"

//   Total 148603.14 (sum of others 148579.90)

class BloomFilter {

 public:

    BloomFilter() {

        ASSERT(BIGRAM_FILTER_BYTE_SIZE * 8 >= BIGRAM_FILTER_MODULO);

        memset(mFilter, 0, sizeof(mFilter));

    }

    BloomFilter() : mFilter() {}

    // TODO: uint32_t position

    AK_FORCE_INLINE void setInFilter(const int32_t position) {

        const uint32_t bucket = static_cast<uint32_t>(position % BIGRAM_FILTER_MODULO);

        mFilter[bucket >> 3] |= static_cast<uint8_t>(1 << (bucket & 0x7));

    AK_FORCE_INLINE void setInFilter(const int position) {

        mFilter.set(getIndex(position));

    }

    // TODO: uint32_t position

    AK_FORCE_INLINE bool isInFilter(const int32_t position) const {

        const uint32_t bucket = static_cast<uint32_t>(position % BIGRAM_FILTER_MODULO);

        return (mFilter[bucket >> 3] & static_cast<uint8_t>(1 << (bucket & 0x7))) != 0;

    AK_FORCE_INLINE bool isInFilter(const int position) const {

        return mFilter.test(getIndex(position));

    }

 private:

    DISALLOW_ASSIGNMENT_OPERATOR(BloomFilter);

    // Size, in bytes, of the bloom filter index for bigrams

    // 128 gives us 1024 buckets. The probability of false positive is (1 - e ** (-kn/m))**k,

    AK_FORCE_INLINE size_t getIndex(const int position) const {

        return static_cast<size_t>(position) % BIGRAM_FILTER_MODULO;

    }

    // Size, in bits, of the bloom filter index for bigrams

    // The probability of false positive is (1 - e ** (-kn/m))**k,

    // where k is the number of hash functions, n the number of bigrams, and m the number of

    // bits we can test.

    // At the moment 100 is the maximum number of bigrams for a word with the current

    // At the moment 100 is the maximum number of bigrams for a word with the current main

    // dictionaries, so n = 100. 1024 buckets give us m = 1024.

    // With 1 hash function, our false positive rate is about 9.3%, which should be enough for

    // our uses since we are only using this to increase average performance. For the record,

    // k = 2 gives 3.1% and k = 3 gives 1.6%. With k = 1, making m = 2048 gives 4.8%,

    // and m = 4096 gives 2.4%.

    // This is assigned here because it is used for array size.

    static const int BIGRAM_FILTER_BYTE_SIZE = 128;

    static const int BIGRAM_FILTER_MODULO;

    uint8_t mFilter[BIGRAM_FILTER_BYTE_SIZE];

    // This is assigned here because it is used for bitset size.

    // 1021 is the largest prime under 1024.

    static const size_t BIGRAM_FILTER_MODULO = 1021;

    std::bitset<BIGRAM_FILTER_MODULO> mFilter;

};

} // namespace latinime

#endif // LATINIME_BLOOM_FILTER_H