Add spellcheck and word suggestion to the prediction service

third_party/android_prediction/suggest/core/dictionary/bloom_filter.h

Index: third_party/android_prediction/suggest/core/dictionary/bloom_filter.h
diff --git a/third_party/android_prediction/suggest/core/dictionary/bloom_filter.h b/third_party/android_prediction/suggest/core/dictionary/bloom_filter.h
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+/*
+ * Copyright (C) 2012 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_BLOOM_FILTER_H
+#define LATINIME_BLOOM_FILTER_H
+
+#include <bitset>
+
+#include "third_party/android_prediction/defines.h"
+
+namespace latinime {
+
+// This bloom filter is used for optimizing bigram retrieval.
+// Execution times with previous word "this" are as follows:
+//  without bloom filter (use only hash_map):
+//   Total 147792.34 (sum of others 147771.57)
+//  with bloom filter:
+//   Total 145900.64 (sum of others 145874.30)
+//  always read binary dictionary:
+//   Total 148603.14 (sum of others 148579.90)
+class BloomFilter {
+ public:
+    BloomFilter() : mFilter() {}
+
+    AK_FORCE_INLINE void setInFilter(const int position) {
+        mFilter.set(getIndex(position));
+    }
+
+    AK_FORCE_INLINE bool isInFilter(const int position) const {
+        return mFilter.test(getIndex(position));
+    }
+
+ private:
+    DISALLOW_ASSIGNMENT_OPERATOR(BloomFilter);
+
+    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 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 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