Use bloom filter in multi bigram map.

Evaluated with previous word "this".
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)

Bug: 8592527
Change-Id: I821dc39454543826adb73b9eeeef6408fad8ae28

6 files changed, 122 insertions, 47 deletions

diff --git a/native/jni/Android.mk b/native/jni/Android.mk
index 9db50473d..fb60139d3 100644
--- a/native/jni/Android.mk
+++ b/native/jni/Android.mk
@@ -57,9 +57,11 @@ LATIN_IME_CORE_SRC_FILES := \
         binary_dictionary_format_utils.cpp \
         binary_dictionary_header.cpp \
         binary_dictionary_header_reading_utils.cpp \
+        bloom_filter.cpp \
         byte_array_utils.cpp \
         dictionary.cpp \
-        digraph_utils.cpp) \
+        digraph_utils.cpp \
+        multi_bigram_map.cpp) \
     $(addprefix suggest/core/layout/, \
         additional_proximity_chars.cpp \
         proximity_info.cpp \
diff --git a/native/jni/src/defines.h b/native/jni/src/defines.h
index a3cf6a4b4..e349aedb1 100644
--- a/native/jni/src/defines.h
+++ b/native/jni/src/defines.h
@@ -300,33 +300,6 @@ static inline void prof_out(void) {
 #define DIC_NODES_CACHE_INITIAL_QUEUE_ID_CACHE_FOR_CONTINUOUS_SUGGESTION 3
 #define DIC_NODES_CACHE_PRIORITY_QUEUES_SIZE 4
 
-// 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,
-// 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
-// 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%.
-#define BIGRAM_FILTER_BYTE_SIZE 128
-// Must be smaller than BIGRAM_FILTER_BYTE_SIZE * 8, and preferably prime. 1021 is the largest
-// prime under 128 * 8.
-#define BIGRAM_FILTER_MODULO 1021
-#if BIGRAM_FILTER_BYTE_SIZE * 8 < BIGRAM_FILTER_MODULO
-#error "BIGRAM_FILTER_MODULO is larger than BIGRAM_FILTER_BYTE_SIZE"
-#endif
-
-// 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.
-#define MAX_CACHED_PREV_WORDS_IN_BIGRAM_MAP 25
-// Most common previous word contexts currently have 100 bigrams
-#define DEFAULT_HASH_MAP_SIZE_FOR_EACH_BIGRAM_MAP 100
-
 template<typename T> AK_FORCE_INLINE const T &min(const T &a, const T &b) { return a < b ? a : b; }
 template<typename T> AK_FORCE_INLINE const T &max(const T &a, const T &b) { return a > b ? a : b; }
 
diff --git a/native/jni/src/suggest/core/dictionary/bloom_filter.cpp b/native/jni/src/suggest/core/dictionary/bloom_filter.cpp
new file mode 100644
index 000000000..4ae474e0c
--- /dev/null
+++ b/native/jni/src/suggest/core/dictionary/bloom_filter.cpp
@@ -0,0 +1,25 @@
+/*
+ * 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
diff --git a/native/jni/src/suggest/core/dictionary/bloom_filter.h b/native/jni/src/suggest/core/dictionary/bloom_filter.h
index bcce1f7ea..5205456a8 100644
--- a/native/jni/src/suggest/core/dictionary/bloom_filter.h
+++ b/native/jni/src/suggest/core/dictionary/bloom_filter.h
@@ -23,16 +23,48 @@
 
 namespace latinime {
 
-// TODO: uint32_t position
-static inline void setInFilter(uint8_t *filter, const int32_t position) {
-    const uint32_t bucket = static_cast<uint32_t>(position % BIGRAM_FILTER_MODULO);
-    filter[bucket >> 3] |= static_cast<uint8_t>(1 << (bucket & 0x7));
-}
-
-// TODO: uint32_t position
-static inline bool isInFilter(const uint8_t *filter, const int32_t position) {
-    const uint32_t bucket = static_cast<uint32_t>(position % BIGRAM_FILTER_MODULO);
-    return filter[bucket >> 3] & static_cast<uint8_t>(1 << (bucket & 0x7));
-}
+// 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() {
+        ASSERT(BIGRAM_FILTER_BYTE_SIZE * 8 >= BIGRAM_FILTER_MODULO);
+    }
+
+    // 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));
+    }
+
+    // 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;
+    }
+
+ private:
+    // 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,
+    // 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
+    // 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];
+};
 } // namespace latinime
 #endif // LATINIME_BLOOM_FILTER_H
diff --git a/native/jni/src/suggest/core/dictionary/multi_bigram_map.cpp b/native/jni/src/suggest/core/dictionary/multi_bigram_map.cpp
new file mode 100644
index 000000000..b1d2f4b4d
--- /dev/null
+++ b/native/jni/src/suggest/core/dictionary/multi_bigram_map.cpp
@@ -0,0 +1,33 @@
+/*
+ * 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/multi_bigram_map.h"
+
+#include <cstddef>
+
+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;
+
+} // namespace latinime
diff --git a/native/jni/src/suggest/core/dictionary/multi_bigram_map.h b/native/jni/src/suggest/core/dictionary/multi_bigram_map.h
index b380e9727..60169f80e 100644
--- a/native/jni/src/suggest/core/dictionary/multi_bigram_map.h
+++ b/native/jni/src/suggest/core/dictionary/multi_bigram_map.h
@@ -17,10 +17,13 @@
 #ifndef LATINIME_MULTI_BIGRAM_MAP_H
 #define LATINIME_MULTI_BIGRAM_MAP_H
 
+#include <cstddef>
+
 #include "defines.h"
 #include "suggest/core/dictionary/binary_dictionary_bigrams_iterator.h"
 #include "suggest/core/dictionary/binary_dictionary_info.h"
 #include "suggest/core/dictionary/binary_format.h"
+#include "suggest/core/dictionary/bloom_filter.h"
 #include "utils/hash_map_compat.h"
 
 namespace latinime {
@@ -60,7 +63,7 @@ class MultiBigramMap {
 
     class BigramMap {
      public:
-        BigramMap() : mBigramMap(DEFAULT_HASH_MAP_SIZE_FOR_EACH_BIGRAM_MAP) {}
+        BigramMap() : mBigramMap(DEFAULT_HASH_MAP_SIZE_FOR_EACH_BIGRAM_MAP), mBloomFilter() {}
         ~BigramMap() {}
 
         void init(const BinaryDictionaryInfo *const binaryDictionaryInfo, const int nodePos) {
@@ -73,24 +76,30 @@ class MultiBigramMap {
                     bigramsIt.hasNext(); /* no-op */) {
                 bigramsIt.next();
                 mBigramMap[bigramsIt.getBigramPos()] = bigramsIt.getProbability();
+                mBloomFilter.setInFilter(bigramsIt.getBigramPos());
             }
         }
 
         AK_FORCE_INLINE int getBigramProbability(
                 const int nextWordPosition, const int unigramProbability) const {
-            const hash_map_compat<int, int>::const_iterator bigramProbabilityIt =
-                    mBigramMap.find(nextWordPosition);
-            if (bigramProbabilityIt != mBigramMap.end()) {
-                const int bigramProbability = bigramProbabilityIt->second;
-                return ProbabilityUtils::computeProbabilityForBigram(
-                        unigramProbability, bigramProbability);
+            if (mBloomFilter.isInFilter(nextWordPosition)) {
+                const hash_map_compat<int, int>::const_iterator bigramProbabilityIt =
+                        mBigramMap.find(nextWordPosition);
+                if (bigramProbabilityIt != mBigramMap.end()) {
+                    const int bigramProbability = bigramProbabilityIt->second;
+                    return ProbabilityUtils::computeProbabilityForBigram(
+                            unigramProbability, bigramProbability);
+                }
             }
             return ProbabilityUtils::backoff(unigramProbability);
         }
 
      private:
-        // Note: Default copy constructor needed for use in hash_map.
+        // NOTE: The BigramMap class doesn't use DISALLOW_COPY_AND_ASSIGN() because its default
+        // copy constructor is needed for use in hash_map.
+        static const int DEFAULT_HASH_MAP_SIZE_FOR_EACH_BIGRAM_MAP;
         hash_map_compat<int, int> mBigramMap;
+        BloomFilter mBloomFilter;
     };
 
     AK_FORCE_INLINE void addBigramsForWordPosition(
@@ -117,6 +126,7 @@ class MultiBigramMap {
         return ProbabilityUtils::backoff(unigramProbability);
     }
 
+    static const size_t MAX_CACHED_PREV_WORDS_IN_BIGRAM_MAP;
     hash_map_compat<int, BigramMap> mBigramMaps;
 };
 } // namespace latinime