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/*
* 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 "dictionary/utils/multi_bigram_map.h"
#include <cstddef>
#include <unordered_map>
namespace latinime {
// Max number of bigram maps (previous word contexts) to be cached. Increasing this number
// could improve bigram lookup speed for multi-word suggestions, but at the cost of more memory
// usage. Also, there are diminishing returns since the most frequently used bigrams are
// typically near the beginning of the input and are thus the first ones to be cached. Note
// that these bigrams are reset for each new composing word.
const size_t MultiBigramMap::MAX_CACHED_PREV_WORDS_IN_BIGRAM_MAP = 25;
// Most common previous word contexts currently have 100 bigrams
const int MultiBigramMap::BigramMap::DEFAULT_HASH_MAP_SIZE_FOR_EACH_BIGRAM_MAP = 100;
// Look up the bigram probability for the given word pair from the cached bigram maps.
// Also caches the bigrams if there is space remaining and they have not been cached already.
int MultiBigramMap::getBigramProbability(
const DictionaryStructureWithBufferPolicy *const structurePolicy,
const WordIdArrayView prevWordIds, const int nextWordId,
const int unigramProbability) {
if (prevWordIds.empty() || prevWordIds[0] == NOT_A_WORD_ID) {
return structurePolicy->getProbability(unigramProbability, NOT_A_PROBABILITY);
}
const auto mapPosition = mBigramMaps.find(prevWordIds[0]);
if (mapPosition != mBigramMaps.end()) {
return mapPosition->second.getBigramProbability(structurePolicy, nextWordId,
unigramProbability);
}
if (mBigramMaps.size() < MAX_CACHED_PREV_WORDS_IN_BIGRAM_MAP) {
addBigramsForWord(structurePolicy, prevWordIds);
return mBigramMaps[prevWordIds[0]].getBigramProbability(structurePolicy,
nextWordId, unigramProbability);
}
return readBigramProbabilityFromBinaryDictionary(structurePolicy, prevWordIds,
nextWordId, unigramProbability);
}
void MultiBigramMap::BigramMap::init(
const DictionaryStructureWithBufferPolicy *const structurePolicy,
const WordIdArrayView prevWordIds) {
structurePolicy->iterateNgramEntries(prevWordIds, this /* listener */);
}
int MultiBigramMap::BigramMap::getBigramProbability(
const DictionaryStructureWithBufferPolicy *const structurePolicy,
const int nextWordId, const int unigramProbability) const {
int bigramProbability = NOT_A_PROBABILITY;
if (mBloomFilter.isInFilter(nextWordId)) {
const auto bigramProbabilityIt = mBigramMap.find(nextWordId);
if (bigramProbabilityIt != mBigramMap.end()) {
bigramProbability = bigramProbabilityIt->second;
}
}
return structurePolicy->getProbability(unigramProbability, bigramProbability);
}
void MultiBigramMap::BigramMap::onVisitEntry(const int ngramProbability, const int targetWordId) {
if (targetWordId == NOT_A_WORD_ID) {
return;
}
mBigramMap[targetWordId] = ngramProbability;
mBloomFilter.setInFilter(targetWordId);
}
void MultiBigramMap::addBigramsForWord(
const DictionaryStructureWithBufferPolicy *const structurePolicy,
const WordIdArrayView prevWordIds) {
mBigramMaps[prevWordIds[0]].init(structurePolicy, prevWordIds);
}
int MultiBigramMap::readBigramProbabilityFromBinaryDictionary(
const DictionaryStructureWithBufferPolicy *const structurePolicy,
const WordIdArrayView prevWordIds, const int nextWordId, const int unigramProbability) {
const int bigramProbability = structurePolicy->getProbabilityOfWord(prevWordIds, nextWordId);
if (bigramProbability != NOT_A_PROBABILITY) {
return bigramProbability;
}
return structurePolicy->getProbability(unigramProbability, NOT_A_PROBABILITY);
}
} // namespace latinime
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