Enable Quadgram for personalized dicts.

Before:
Total words: 1134659, Success Num: 944709, Success Percentage: 83.259%
Bad Failures, with auto-correction (typed word == expected word, output word != expected word): 1258, Bad Failure Percentage: 0.111%
Failures, with auto-correction (F-C): 28013, F-C Percentage: 2.469%
Max Keystrokes: 6072844, Min Keystrokes: 3347332, Keystroke Saving Percentage:44.880%

After:
Total words: 1134665, Success Num: 945026, Success Percentage: 83.287%
Bad Failures, with auto-correction (typed word == expected word, output word != expected word): 1271, Bad Failure Percentage: 0.112%
Failures, with auto-correction (F-C): 27756, F-C Percentage: 2.446%
Max Keystrokes: 6072850, Min Keystrokes: 3290996, Keystroke Saving Percentage:45.808%

Change-Id: I16af52a3e9c371b95fd6f0741f45ee6b2443bea6

common/src/com/android/inputmethod/latin/common/Constants.java

@@ -179,7 +179,7 @@ public final class Constants {
 
     // (MAX_PREV_WORD_COUNT_FOR_N_GRAM + 1)-gram is supported in Java side. Needs to modify
     // MAX_PREV_WORD_COUNT_FOR_N_GRAM in native/jni/src/defines.h for suggestions.
-    public static final int MAX_PREV_WORD_COUNT_FOR_N_GRAM = 2;
+    public static final int MAX_PREV_WORD_COUNT_FOR_N_GRAM = 3;
 
     // Key events coming any faster than this are long-presses.
     public static final int LONG_PRESS_MILLISECONDS = 200;

native/jni/src/defines.h

@@ -275,7 +275,7 @@ static inline void showStackTrace() {
 #define MAX_POINTER_COUNT_G 2
 
 // (MAX_PREV_WORD_COUNT_FOR_N_GRAM + 1)-gram is supported.
-#define MAX_PREV_WORD_COUNT_FOR_N_GRAM 2
+#define MAX_PREV_WORD_COUNT_FOR_N_GRAM 3
 
 #define DISALLOW_DEFAULT_CONSTRUCTOR(TypeName) \
   TypeName() = delete

native/jni/src/suggest/policyimpl/dictionary/header/header_policy.cpp

@@ -31,10 +31,11 @@ const char *const HeaderPolicy::IS_DECAYING_DICT_KEY = "USES_FORGETTING_CURVE";
 const char *const HeaderPolicy::DATE_KEY = "date";
 const char *const HeaderPolicy::LAST_DECAYED_TIME_KEY = "LAST_DECAYED_TIME";
 const char *const HeaderPolicy::NGRAM_COUNT_KEYS[] =
-        {"UNIGRAM_COUNT", "BIGRAM_COUNT", "TRIGRAM_COUNT"};
+        {"UNIGRAM_COUNT", "BIGRAM_COUNT", "TRIGRAM_COUNT", "QUADGRAM_COUNT"};
 const char *const HeaderPolicy::MAX_NGRAM_COUNT_KEYS[] =
-        {"MAX_UNIGRAM_ENTRY_COUNT", "MAX_BIGRAM_ENTRY_COUNT", "MAX_TRIGRAM_ENTRY_COUNT"};
+        {"MAX_UNIGRAM_ENTRY_COUNT", "MAX_BIGRAM_ENTRY_COUNT", "MAX_TRIGRAM_ENTRY_COUNT",
-const int HeaderPolicy::DEFAULT_MAX_NGRAM_COUNTS[] = {10000, 30000, 30000};
+                "MAX_QUADGRAM_ENTRY_COUNT"};
+const int HeaderPolicy::DEFAULT_MAX_NGRAM_COUNTS[] = {10000, 30000, 30000, 30000};
 const char *const HeaderPolicy::EXTENDED_REGION_SIZE_KEY = "EXTENDED_REGION_SIZE";
 // Historical info is information that is needed to support decaying such as timestamp, level and
 // count.

native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/dynamic_language_model_probability_utils.cpp

@@ -19,12 +19,13 @@
 namespace latinime {
 
 // Used to provide stable probabilities even if the user's input count is small.
-const int DynamicLanguageModelProbabilityUtils::ASSUMED_MIN_COUNTS[] = {8192, 2, 2};
+const int DynamicLanguageModelProbabilityUtils::ASSUMED_MIN_COUNTS[] = {8192, 2, 2, 1};
 
 // Encoded backoff weights.
-// Note that we give positive value for trigrams that means the weight is more than 1.
+// Note that we give positive values for trigrams and quadgrams 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_WEIGHTS[] = {-32, 0, 8};
+const int DynamicLanguageModelProbabilityUtils::ENCODED_BACKOFF_WEIGHTS[] = {-32, -4, 2, 8};
 
 // This value is used to remove too old entries from the dictionary.
 const int DynamicLanguageModelProbabilityUtils::DURATION_TO_DISCARD_ENTRY_IN_SECONDS =

native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/dynamic_language_model_probability_utils.h

@@ -66,7 +66,7 @@ class DynamicLanguageModelProbabilityUtils {
 private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(DynamicLanguageModelProbabilityUtils);
 
-    static_assert(MAX_PREV_WORD_COUNT_FOR_N_GRAM <= 2, "Max supported Ngram is Trigram.");
+    static_assert(MAX_PREV_WORD_COUNT_FOR_N_GRAM <= 3, "Max supported Ngram is Quadgram.");
 
     static const int ASSUMED_MIN_COUNTS[];
     static const int ENCODED_BACKOFF_WEIGHTS[];

native/jni/src/suggest/policyimpl/dictionary/utils/entry_counters.h

@@ -27,7 +27,7 @@ namespace latinime {
 // Copyable but immutable
 class EntryCounts final {
  public:
-    EntryCounts() : mEntryCounts({{0, 0, 0}}) {}
+    EntryCounts() : mEntryCounts({{0, 0, 0, 0}}) {}
 
     explicit EntryCounts(const std::array<int, MAX_PREV_WORD_COUNT_FOR_N_GRAM + 1> &counters)
             : mEntryCounts(counters) {}

native/jni/src/utils/ngram_utils.h

@@ -25,6 +25,7 @@ enum class NgramType : int {
     Unigram = 0,
     Bigram = 1,
     Trigram = 2,
+    Quadgram = 3,
     NotANgramType = -1,
 };