Add DynamicLanguageModelProbabilityUtils.

        ver4_patricia_trie_writing_helper.cpp \

        ver4_pt_node_array_reader.cpp) \

    $(addprefix suggest/policyimpl/dictionary/structure/v4/content/, \

        dynamic_language_model_probability_utils.cpp \

        language_model_dict_content.cpp \

        language_model_dict_content_global_counters.cpp \

        shortcut_dict_content.cpp \

/*

 * Copyright (C) 2014, 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/policyimpl/dictionary/structure/v4/content/dynamic_language_model_probability_utils.h"

namespace latinime {

// These counts are used to provide stable probabilities even if the user's input count is small.

const int DynamicLanguageModelProbabilityUtils::ASSUMED_MIN_COUNT_FOR_UNIGRAMS = 8192;

const int DynamicLanguageModelProbabilityUtils::ASSUMED_MIN_COUNT_FOR_BIGRAMS = 2;

const int DynamicLanguageModelProbabilityUtils::ASSUMED_MIN_COUNT_FOR_TRIGRAMS = 2;

// These are encoded backoff weights.

// Note that we give positive value for trigrams that means the weight is more than 1.

// TODO: Apply backoff for main dictionaries and quit giving a positive backoff weight.

const int DynamicLanguageModelProbabilityUtils::ENCODED_BACKOFF_WEIGHT_FOR_UNIGRAMS = -32;

const int DynamicLanguageModelProbabilityUtils::ENCODED_BACKOFF_WEIGHT_FOR_BIGRAMS = 0;

const int DynamicLanguageModelProbabilityUtils::ENCODED_BACKOFF_WEIGHT_FOR_TRIGRAMS = 8;

// This value is used to remove too old entries from the dictionary.

const int DynamicLanguageModelProbabilityUtils::DURATION_TO_DISCARD_ENTRY_IN_SECONDS =

        300 * 24 * 60 * 60; // 300 days

} // namespace latinime

/*

 * Copyright (C) 2014, 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.

 */

#ifndef LATINIME_DYNAMIC_LANGUAGE_MODEL_PROBABILITY_UTILS_H

#define LATINIME_DYNAMIC_LANGUAGE_MODEL_PROBABILITY_UTILS_H

#include <algorithm>

#include "defines.h"

#include "suggest/core/dictionary/property/historical_info.h"

#include "utils/time_keeper.h"

namespace latinime {

class DynamicLanguageModelProbabilityUtils {

 public:

    static float computeRawProbabilityFromCounts(const int count, const int contextCount,

            const int matchedWordCountInContext) {

        int minCount = 0;

        switch (matchedWordCountInContext) {

            case 1:

                minCount = ASSUMED_MIN_COUNT_FOR_UNIGRAMS;

                break;

            case 2:

                minCount = ASSUMED_MIN_COUNT_FOR_BIGRAMS;

                break;

            case 3:

                minCount = ASSUMED_MIN_COUNT_FOR_TRIGRAMS;

                break;

            default:

                AKLOGE("computeRawProbabilityFromCounts is called with invalid "

                        "matchedWordCountInContext (%d).", matchedWordCountInContext);

                ASSERT(false);

                return 0.0f;

        }

        return static_cast<float>(count) / static_cast<float>(std::max(contextCount, minCount));

    }

    static float backoff(const int ngramProbability, const int matchedWordCountInContext) {

        int probability = NOT_A_PROBABILITY;

        switch (matchedWordCountInContext) {

            case 1:

                probability = ngramProbability + ENCODED_BACKOFF_WEIGHT_FOR_UNIGRAMS;

                break;

            case 2:

                probability = ngramProbability + ENCODED_BACKOFF_WEIGHT_FOR_BIGRAMS;

                break;

            case 3:

                probability = ngramProbability + ENCODED_BACKOFF_WEIGHT_FOR_TRIGRAMS;

                break;

            default:

                AKLOGE("backoff is called with invalid matchedWordCountInContext (%d).",

                        matchedWordCountInContext);

                ASSERT(false);

                return NOT_A_PROBABILITY;

        }

        return std::min(std::max(probability, NOT_A_PROBABILITY), MAX_PROBABILITY);

    }

    static int getDecayedProbability(const int probability, const HistoricalInfo historicalInfo) {

        const int elapsedTime = TimeKeeper::peekCurrentTime() - historicalInfo.getTimestamp();

        if (elapsedTime < 0) {

            AKLOGE("The elapsed time is negatime value. Timestamp overflow?");

            return NOT_A_PROBABILITY;

        }

        // TODO: Improve this logic.

        // We don't modify probability depending on the elapsed time.

        return probability;

    }

    static int shouldRemoveEntryDuringGC(const HistoricalInfo historicalInfo) {

        // TODO: Improve this logic.

        const int elapsedTime = TimeKeeper::peekCurrentTime() - historicalInfo.getTimestamp();

        return elapsedTime > DURATION_TO_DISCARD_ENTRY_IN_SECONDS;

    }

    static int getPriorityToPreventFromEviction(const HistoricalInfo historicalInfo) {

        // TODO: Improve this logic.

        // More recently input entries get higher priority.

        return historicalInfo.getTimestamp();

    }

private:

    DISALLOW_IMPLICIT_CONSTRUCTORS(DynamicLanguageModelProbabilityUtils);

    static_assert(MAX_PREV_WORD_COUNT_FOR_N_GRAM <= 2, "Max supported Ngram is Trigram.");

    static const int ASSUMED_MIN_COUNT_FOR_UNIGRAMS;

    static const int ASSUMED_MIN_COUNT_FOR_BIGRAMS;

    static const int ASSUMED_MIN_COUNT_FOR_TRIGRAMS;

    static const int ENCODED_BACKOFF_WEIGHT_FOR_UNIGRAMS;

    static const int ENCODED_BACKOFF_WEIGHT_FOR_BIGRAMS;

    static const int ENCODED_BACKOFF_WEIGHT_FOR_TRIGRAMS;

    static const int DURATION_TO_DISCARD_ENTRY_IN_SECONDS;

};

} // namespace latinime

#endif /* LATINIME_DYNAMIC_LANGUAGE_MODEL_PROBABILITY_UTILS_H */