Add spellcheck and word suggestion to the prediction service

third_party/android_prediction/suggest/core/dictionary/multi_bigram_map.cpp

Index: third_party/android_prediction/suggest/core/dictionary/multi_bigram_map.cpp
diff --git a/third_party/android_prediction/suggest/core/dictionary/multi_bigram_map.cpp b/third_party/android_prediction/suggest/core/dictionary/multi_bigram_map.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..8ddfbb44d52ea8952a04310b92cf16b97bf43770
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+++ b/third_party/android_prediction/suggest/core/dictionary/multi_bigram_map.cpp
@@ -0,0 +1,107 @@
+/*
+ * 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 "third_party/android_prediction/suggest/core/dictionary/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 int *const prevWordsPtNodePos, const int nextWordPosition,
+        const int unigramProbability) {
+    if (!prevWordsPtNodePos || prevWordsPtNodePos[0] == NOT_A_DICT_POS) {
+        return structurePolicy->getProbability(unigramProbability, NOT_A_PROBABILITY);
+    }
+    std::unordered_map<int, BigramMap>::const_iterator mapPosition =
+            mBigramMaps.find(prevWordsPtNodePos[0]);
+    if (mapPosition != mBigramMaps.end()) {
+        return mapPosition->second.getBigramProbability(structurePolicy, nextWordPosition,
+                unigramProbability);
+    }
+    if (mBigramMaps.size() < MAX_CACHED_PREV_WORDS_IN_BIGRAM_MAP) {
+        addBigramsForWordPosition(structurePolicy, prevWordsPtNodePos);
+        return mBigramMaps[prevWordsPtNodePos[0]].getBigramProbability(structurePolicy,
+                nextWordPosition, unigramProbability);
+    }
+    return readBigramProbabilityFromBinaryDictionary(structurePolicy, prevWordsPtNodePos,
+            nextWordPosition, unigramProbability);
+}
+
+void MultiBigramMap::BigramMap::init(
+        const DictionaryStructureWithBufferPolicy *const structurePolicy,
+        const int *const prevWordsPtNodePos) {
+    structurePolicy->iterateNgramEntries(prevWordsPtNodePos, this /* listener */);
+}
+
+int MultiBigramMap::BigramMap::getBigramProbability(
+        const DictionaryStructureWithBufferPolicy *const structurePolicy,
+        const int nextWordPosition, const int unigramProbability) const {
+    int bigramProbability = NOT_A_PROBABILITY;
+    if (mBloomFilter.isInFilter(nextWordPosition)) {
+        const std::unordered_map<int, int>::const_iterator bigramProbabilityIt =
+                mBigramMap.find(nextWordPosition);
+        if (bigramProbabilityIt != mBigramMap.end()) {
+            bigramProbability = bigramProbabilityIt->second;
+        }
+    }
+    return structurePolicy->getProbability(unigramProbability, bigramProbability);
+}
+
+void MultiBigramMap::BigramMap::onVisitEntry(const int ngramProbability,
+        const int targetPtNodePos) {
+    if (targetPtNodePos == NOT_A_DICT_POS) {
+        return;
+    }
+    mBigramMap[targetPtNodePos] = ngramProbability;
+    mBloomFilter.setInFilter(targetPtNodePos);
+}
+
+void MultiBigramMap::addBigramsForWordPosition(
+        const DictionaryStructureWithBufferPolicy *const structurePolicy,
+        const int *const prevWordsPtNodePos) {
+    if (prevWordsPtNodePos) {
+        mBigramMaps[prevWordsPtNodePos[0]].init(structurePolicy, prevWordsPtNodePos);
+    }
+}
+
+int MultiBigramMap::readBigramProbabilityFromBinaryDictionary(
+        const DictionaryStructureWithBufferPolicy *const structurePolicy,
+        const int *const prevWordsPtNodePos, const int nextWordPosition,
+        const int unigramProbability) {
+    const int bigramProbability = structurePolicy->getProbabilityOfPtNode(prevWordsPtNodePos,
+            nextWordPosition);
+    if (bigramProbability != NOT_A_PROBABILITY) {
+        return bigramProbability;
+    }
+    return structurePolicy->getProbability(unigramProbability, NOT_A_PROBABILITY);
+}
+
+} // namespace latinime