Calibrate the scores of the proximity chars according to the distances.

+1      75
-1      27
+2       0
-2       0
+3       0
-3       0
+4      30
-4      48
+5      37
-5      27
+6       4
-6      35
+7       9
-7      18

Change-Id: I3c6ab06a0084c18ab595147c36c2ff4b1e961a7b

native/src/correction.cpp

@@ -118,7 +118,6 @@ bool Correction::initProcessState(const int outputIndex) {
     mInputIndex = mCorrectionStates[outputIndex].mInputIndex;
     mNeedsToTraverseAllNodes = mCorrectionStates[outputIndex].mNeedsToTraverseAllNodes;
 
-    mSumOfDistance = mCorrectionStates[outputIndex].mSumOfDistance;
     mEquivalentCharCount = mCorrectionStates[outputIndex].mEquivalentCharCount;
     mProximityCount = mCorrectionStates[outputIndex].mProximityCount;
     mTransposedCount = mCorrectionStates[outputIndex].mTransposedCount;
@@ -174,7 +173,6 @@ void Correction::incrementOutputIndex() {
     mCorrectionStates[mOutputIndex].mInputIndex = mInputIndex;
     mCorrectionStates[mOutputIndex].mNeedsToTraverseAllNodes = mNeedsToTraverseAllNodes;
 
-    mCorrectionStates[mOutputIndex].mSumOfDistance = mSumOfDistance;
     mCorrectionStates[mOutputIndex].mEquivalentCharCount = mEquivalentCharCount;
     mCorrectionStates[mOutputIndex].mProximityCount = mProximityCount;
     mCorrectionStates[mOutputIndex].mTransposedCount = mTransposedCount;
@@ -227,20 +225,26 @@ Correction::CorrectionType Correction::processCharAndCalcState(
     // TODO: Change the limit if we'll allow two or more corrections
     const bool noCorrectionsHappenedSoFar = correctionCount == 0;
     const bool canTryCorrection = noCorrectionsHappenedSoFar;
+    int proximityIndex = 0;
+    mDistances[mOutputIndex] = NOT_A_DISTANCE;
 
     if (mNeedsToTraverseAllNodes || isQuote(c)) {
         bool incremented = false;
         if (mLastCharExceeded && mInputIndex == mInputLength - 1) {
             // TODO: Do not check the proximity if EditDistance exceeds the threshold
             const ProximityInfo::ProximityType matchId =
-                    mProximityInfo->getMatchedProximityId(mInputIndex, c, true);
+                    mProximityInfo->getMatchedProximityId(mInputIndex, c, true, &proximityIndex);
             if (isEquivalentChar(matchId)) {
                 mLastCharExceeded = false;
                 --mExcessiveCount;
+                mDistances[mOutputIndex] =
+                        mProximityInfo->getNormalizedSquaredDistance(mInputIndex, 0);
             } else if (matchId == ProximityInfo::NEAR_PROXIMITY_CHAR) {
                 mLastCharExceeded = false;
                 --mExcessiveCount;
                 ++mProximityCount;
+                mDistances[mOutputIndex] =
+                        mProximityInfo->getNormalizedSquaredDistance(mInputIndex, proximityIndex);
             }
             incrementInputIndex();
             incremented = true;
@@ -301,7 +305,8 @@ Correction::CorrectionType Correction::processCharAndCalcState(
     const bool checkProximityChars = noCorrectionsHappenedSoFar ||  mProximityCount == 0;
     ProximityInfo::ProximityType matchedProximityCharId = secondTransposing
             ? ProximityInfo::EQUIVALENT_CHAR
-            : mProximityInfo->getMatchedProximityId(mInputIndex, c, checkProximityChars);
+            : mProximityInfo->getMatchedProximityId(
+                    mInputIndex, c, checkProximityChars, &proximityIndex);
 
     if (ProximityInfo::UNRELATED_CHAR == matchedProximityCharId) {
         if (canTryCorrection && mOutputIndex > 0
@@ -323,8 +328,8 @@ Correction::CorrectionType Correction::processCharAndCalcState(
             // Here, we are doing something equivalent to matchedProximityCharId,
             // but we already know that "excessive char correction" just happened
             // so that we just need to check "mProximityCount == 0".
-            matchedProximityCharId =
-                    mProximityInfo->getMatchedProximityId(mInputIndex, c, mProximityCount == 0);
+            matchedProximityCharId = mProximityInfo->getMatchedProximityId(
+                    mInputIndex, c, mProximityCount == 0, &proximityIndex);
         }
     }
 
@@ -399,17 +404,12 @@ Correction::CorrectionType Correction::processCharAndCalcState(
     } else if (isEquivalentChar(matchedProximityCharId)) {
         mMatching = true;
         ++mEquivalentCharCount;
-        if (mSumOfDistance != NOT_A_DISTANCE) {
-            const int distance = mProximityInfo->getNormalizedSquaredDistance(mInputIndex);
-            if (distance != NOT_A_DISTANCE) {
-                mSumOfDistance += distance;
-            } else {
-                mSumOfDistance = NOT_A_DISTANCE;
-            }
-        }
+        mDistances[mOutputIndex] = mProximityInfo->getNormalizedSquaredDistance(mInputIndex, 0);
     } else if (ProximityInfo::NEAR_PROXIMITY_CHAR == matchedProximityCharId) {
         mProximityMatching = true;
         ++mProximityCount;
+        mDistances[mOutputIndex] =
+                mProximityInfo->getNormalizedSquaredDistance(mInputIndex, proximityIndex);
     }
 
     mWord[mOutputIndex] = c;
@@ -583,8 +583,6 @@ int Correction::RankingAlgorithm::calculateFinalFreq(const int inputIndex, const
     const int transposedCount = correction->mTransposedCount / 2;
     const int excessiveCount = correction->mExcessiveCount + correction->mTransposedCount % 2;
     const int proximityMatchedCount = correction->mProximityCount;
-    const int mSumOfDistance = correction->mSumOfDistance;
-    const int mEquivalentCharCount = correction->mEquivalentCharCount;
     const bool lastCharExceeded = correction->mLastCharExceeded;
     const bool useFullEditDistance = correction->mUseFullEditDistance;
     const int outputLength = outputIndex + 1;
@@ -684,47 +682,50 @@ int Correction::RankingAlgorithm::calculateFinalFreq(const int inputIndex, const
         }
     }
 
-    // Promotion for a word with proximity characters
-    for (int i = 0; i < adjustedProximityMatchedCount; ++i) {
-        // A word with proximity corrections
-        if (DEBUG_DICT_FULL) {
-            LOGI("Found a proximity correction.");
+    // Score calibration by touch coordinates is being done only for pure-fat finger typing error
+    // cases.
+    // TODO: Remove this constraint.
+    if (CALIBRATE_SCORE_BY_TOUCH_COORDINATES && proximityInfo->touchPositionCorrectionEnabled()
+            && skippedCount == 0 && excessiveCount == 0 && transposedCount == 0) {
+        for (int i = 0; i < outputLength; ++i) {
+            const int squaredDistance = correction->mDistances[i];
+            if (i < adjustedProximityMatchedCount) {
+                multiplyIntCapped(typedLetterMultiplier, &finalFreq);
+            }
+            if (squaredDistance >= 0) {
+                // Promote or demote the score according to the distance from the sweet spot
+                static const float A = ZERO_DISTANCE_PROMOTION_RATE / 100.0f;
+                static const float B = 1.0f;
+                static const float C = 0.5f;
+                static const float R1 = NEUTRAL_SCORE_SQUARED_RADIUS;
+                static const float R2 = HALF_SCORE_SQUARED_RADIUS;
+                const float x = (float)squaredDistance
+                        / ProximityInfo::NORMALIZED_SQUARED_DISTANCE_SCALING_FACTOR;
+                const float factor = (x < R1)
+                    ? (A * (R1 - x) + B * x) / R1
+                    : (B * (R2 - x) + C * (x - R1)) / (R2 - R1);
+                // factor is piecewise linear function like:
+                // A -_                  .
+                //     ^-_               .
+                // B      \              .
+                //         \             .
+                // C        \            .
+                //   0   R1 R2
+                multiplyRate((int)(factor * 100), &finalFreq);
+            } else if (squaredDistance == PROXIMITY_CHAR_WITHOUT_DISTANCE_INFO) {
+                multiplyRate(WORDS_WITH_PROXIMITY_CHARACTER_DEMOTION_RATE, &finalFreq);
+            }
+        }
+    } else {
+        // Promotion for a word with proximity characters
+        for (int i = 0; i < adjustedProximityMatchedCount; ++i) {
+            // A word with proximity corrections
+            if (DEBUG_DICT_FULL) {
+                LOGI("Found a proximity correction.");
+            }
+            multiplyIntCapped(typedLetterMultiplier, &finalFreq);
+            multiplyRate(WORDS_WITH_PROXIMITY_CHARACTER_DEMOTION_RATE, &finalFreq);
         }
-        multiplyIntCapped(typedLetterMultiplier, &finalFreq);
-        multiplyRate(WORDS_WITH_PROXIMITY_CHARACTER_DEMOTION_RATE, &finalFreq);
-    }
-
-    if (CALIBRATE_SCORE_BY_TOUCH_COORDINATES
-            && mEquivalentCharCount > 0 && mSumOfDistance != NOT_A_DISTANCE) {
-        // Let (x, y) be the coordinate of a user's touch, and let c be a key.
-        // Assuming users' touch distribution is gauss distribution, the conditional probability of
-        // the user touching (x, y) given he or she intends to hit c is:
-        //   p(x, y | c) = exp(-(x - m_x) / (2 * s^2)) / (sqrt(2 * pi) * s)
-        //               * exp(-(y - m_y) / (2 * s^2)) / (sqrt(2 * pi) * s)
-        // where (m_x, m_y) is a mean of touches of c, and s is a variance of touches of c.
-        // If user touches c1, c2, .., cn, the joint distribution is
-        //   p(x1, y1 | c1) * p(x2, y2 | c2) * ... * p(xn, yn | cn)
-        // We consider the logarithm of this value, that is
-        //     sum_i log p(x_i, y_i | c_i) + const
-        //   = sum_i ((x_i - m_x)^2 + (y_i - m_y)^2) / (2 * s^2) + const
-        // Thus, we use the sum of squared distance as a score of the word.
-        static const int UPPER = WORDS_WITH_EQUIVALENT_CHAR_STRONGEST_PROMOTION_RATE;
-        static const int LOWER = WORDS_WITH_EQUIVALENT_CHAR_WEAKEST_DEMOTION_RATE;
-        static const int MIDDLE = 100;
-        static const int SHIFT = ProximityInfo::NORMALIZED_SQUARED_DISTANCE_SCALING_FACTOR_LOG_2;
-        const int expected = mEquivalentCharCount << SHIFT;
-        // factor is a function as described below:
-        // U\            .
-        //   \           .
-        // M  \          .
-        //     \         .
-        // L    \------- .
-        //  0 e
-        // (x-axis is mSumOfDistance, y-axis is rate,
-        //  and e, U, M, L are expected, UPPER, MIDDLE, LOWER respectively.
-        const int factor =
-                max((UPPER * expected - (UPPER - MIDDLE) * mSumOfDistance) / expected, LOWER);
-        multiplyRate(factor, &finalFreq);
     }
 
     const int errorCount = adjustedProximityMatchedCount > 0

native/src/correction.h

@@ -115,7 +115,11 @@ private:
     int mMissingSpacePos;
     int mTerminalInputIndex;
     int mTerminalOutputIndex;
+
+    // The following arrays are state buffer.
     unsigned short mWord[MAX_WORD_LENGTH_INTERNAL];
+    int mDistances[MAX_WORD_LENGTH_INTERNAL];
+
     // Edit distance calculation requires a buffer with (N+1)^2 length for the input length N.
     // Caveat: Do not create multiple tables per thread as this table eats up RAM a lot.
     int mEditDistanceTable[(MAX_WORD_LENGTH_INTERNAL + 1) * (MAX_WORD_LENGTH_INTERNAL + 1)];
@@ -128,7 +132,6 @@ private:
     int mInputIndex;
 
     int mEquivalentCharCount;
-    int mSumOfDistance;
     int mProximityCount;
     int mExcessiveCount;
     int mTransposedCount;

native/src/correction_state.h

@@ -29,7 +29,6 @@ struct CorrectionState {
     uint16_t mChildCount;
     uint8_t mInputIndex;
 
-    int32_t mSumOfDistance;
     uint8_t mEquivalentCharCount;
     uint8_t mProximityCount;
     uint8_t mTransposedCount;
@@ -65,7 +64,6 @@ inline static void initCorrectionState(CorrectionState *state, const int rootPos
     state->mExcessivePos = -1;
     state->mSkipPos = -1;
 
-    state->mSumOfDistance = 0;
     state->mEquivalentCharCount = 0;
     state->mProximityCount = 0;
     state->mTransposedCount = 0;

native/src/defines.h

@@ -163,6 +163,9 @@ static void dumpWord(const unsigned short* word, const int length) {
 #define NOT_VALID_WORD -99
 #define NOT_A_CHARACTER -1
 #define NOT_A_DISTANCE -1
+#define EQUIVALENT_CHAR_WITHOUT_DISTANCE_INFO -2
+#define PROXIMITY_CHAR_WITHOUT_DISTANCE_INFO -3
+#define NOT_A_INDEX -1
 
 #define KEYCODE_SPACE ' '
 
@@ -181,8 +184,6 @@ static void dumpWord(const unsigned short* word, const int length) {
 #define WORDS_WITH_EXCESSIVE_CHARACTER_DEMOTION_RATE 75
 #define WORDS_WITH_EXCESSIVE_CHARACTER_OUT_OF_PROXIMITY_DEMOTION_RATE 75
 #define WORDS_WITH_TRANSPOSED_CHARACTERS_DEMOTION_RATE 60
-#define WORDS_WITH_EQUIVALENT_CHAR_STRONGEST_PROMOTION_RATE 110
-#define WORDS_WITH_EQUIVALENT_CHAR_WEAKEST_DEMOTION_RATE 90
 #define FULL_MATCHED_WORDS_PROMOTION_RATE 120
 #define WORDS_WITH_PROXIMITY_CHARACTER_DEMOTION_RATE 90
 #define WORDS_WITH_MATCH_SKIP_PROMOTION_RATE 105
@@ -191,6 +192,9 @@ static void dumpWord(const unsigned short* word, const int length) {
 #define INPUT_EXCEEDS_OUTPUT_DEMOTION_RATE 70
 #define FIRST_CHAR_DIFFERENT_DEMOTION_RATE 96
 #define TWO_WORDS_CAPITALIZED_DEMOTION_RATE 50
+#define ZERO_DISTANCE_PROMOTION_RATE 110
+#define NEUTRAL_SCORE_SQUARED_RADIUS 8.0f
+#define HALF_SCORE_SQUARED_RADIUS 32.0f
 
 // This should be greater than or equal to MAX_WORD_LENGTH defined in BinaryDictionary.java
 // This is only used for the size of array. Not to be used in c functions.

native/src/proximity_info.cpp

@@ -44,13 +44,21 @@ ProximityInfo::ProximityInfo(const int maxProximityCharsSize, const int keyboard
           CELL_WIDTH((keyboardWidth + gridWidth - 1) / gridWidth),
           CELL_HEIGHT((keyboardHeight + gridHeight - 1) / gridHeight),
           KEY_COUNT(min(keyCount, MAX_KEY_COUNT_IN_A_KEYBOARD)),
-          mInputXCoordinates(NULL), mInputYCoordinates(NULL) {
+          HAS_TOUCH_POSITION_CORRECTION_DATA(keyCount > 0 && keyXCoordinates && keyYCoordinates
+                  && keyWidths && keyHeights && keyCharCodes && sweetSpotCenterXs
+                  && sweetSpotCenterYs && sweetSpotRadii),
+          mInputXCoordinates(NULL), mInputYCoordinates(NULL),
+          mTouchPositionCorrectionEnabled(false) {
     const int len = GRID_WIDTH * GRID_HEIGHT * MAX_PROXIMITY_CHARS_SIZE;
     mProximityCharsArray = new uint32_t[len];
+    mNormalizedSquaredDistances = new int[len];
     if (DEBUG_PROXIMITY_INFO) {
         LOGI("Create proximity info array %d", len);
     }
     memcpy(mProximityCharsArray, proximityCharsArray, len * sizeof(mProximityCharsArray[0]));
+    for (int i = 0; i < len; ++i) {
+        mNormalizedSquaredDistances[i] = NOT_A_DISTANCE;
+    }
 
     copyOrFillZero(mKeyXCoordinates, keyXCoordinates, KEY_COUNT * sizeof(mKeyXCoordinates[0]));
     copyOrFillZero(mKeyYCoordinates, keyYCoordinates, KEY_COUNT * sizeof(mKeyYCoordinates[0]));
@@ -79,6 +87,7 @@ void ProximityInfo::initializeCodeToKeyIndex() {
 }
 
 ProximityInfo::~ProximityInfo() {
+    delete[] mNormalizedSquaredDistances;
     delete[] mProximityCharsArray;
 }
 
@@ -109,52 +118,61 @@ void ProximityInfo::setInputParams(const int* inputCodes, const int inputLength,
     mInputCodes = inputCodes;
     mInputXCoordinates = xCoordinates;
     mInputYCoordinates = yCoordinates;
+    mTouchPositionCorrectionEnabled =
+            HAS_TOUCH_POSITION_CORRECTION_DATA && xCoordinates && yCoordinates;
     mInputLength = inputLength;
     for (int i = 0; i < inputLength; ++i) {
         mPrimaryInputWord[i] = getPrimaryCharAt(i);
     }
     mPrimaryInputWord[inputLength] = 0;
     for (int i = 0; i < mInputLength; ++i) {
-        float normalizedSquaredDistance = calculateNormalizedSquaredDistance(i);
-        if (normalizedSquaredDistance >= 0.0f) {
-            mNormalizedSquaredDistance[i] =
-                (int)(normalizedSquaredDistance * NORMALIZED_SQUARED_DISTANCE_SCALING_FACTOR);
-        } else {
-            mNormalizedSquaredDistance[i] = NOT_A_DISTANCE;
+        const int *proximityChars = getProximityCharsAt(i);
+        for (int j = 0; j < MAX_PROXIMITY_CHARS_SIZE && proximityChars[j] > 0; ++j) {
+            const int currentChar = proximityChars[j];
+            const int keyIndex = getKeyIndex(currentChar);
+            const float squaredDistance = calculateNormalizedSquaredDistance(keyIndex, i);
+            if (squaredDistance >= 0.0f) {
+                mNormalizedSquaredDistances[i * MAX_PROXIMITY_CHARS_SIZE + j] =
+                        (int)(squaredDistance * NORMALIZED_SQUARED_DISTANCE_SCALING_FACTOR);
+            } else {
+                mNormalizedSquaredDistances[i * MAX_PROXIMITY_CHARS_SIZE + j] = (j == 0)
+                        ? EQUIVALENT_CHAR_WITHOUT_DISTANCE_INFO
+                        : PROXIMITY_CHAR_WITHOUT_DISTANCE_INFO;
+            }
         }
     }
 }
 
 inline float square(const float x) { return x * x; }
 
-float ProximityInfo::calculateNormalizedSquaredDistance(int index) const {
+float ProximityInfo::calculateNormalizedSquaredDistance(
+        const int keyIndex, const int inputIndex) const {
     static const float NOT_A_DISTANCE_FLOAT = -1.0f;
-    if (KEY_COUNT == 0 || !mInputXCoordinates || !mInputYCoordinates) {
-        // We do not have the coordinate data
+    if (keyIndex == NOT_A_INDEX) {
         return NOT_A_DISTANCE_FLOAT;
     }
-    const int currentChar = getPrimaryCharAt(index);
-    const unsigned short baseLowerC = Dictionary::toBaseLowerCase(currentChar);
-    if (baseLowerC > MAX_CHAR_CODE) {
+    if (!hasSweetSpotData(keyIndex)) {
         return NOT_A_DISTANCE_FLOAT;
     }
-    const int keyIndex = mCodeToKeyIndex[baseLowerC];
-    if (keyIndex < 0) {
-        return NOT_A_DISTANCE_FLOAT;
+    const float squaredDistance = calculateSquaredDistanceFromSweetSpotCenter(keyIndex, inputIndex);
+    const float squaredRadius = square(mSweetSpotRadii[keyIndex]);
+    return squaredDistance / squaredRadius;
+}
+
+int ProximityInfo::getKeyIndex(const int c) const {
+    if (KEY_COUNT == 0 || !mInputXCoordinates || !mInputYCoordinates) {
+        // We do not have the coordinate data
+        return NOT_A_INDEX;
     }
-    const float radius = mSweetSpotRadii[keyIndex];
-    if (radius <= 0.0) {
-        // When there are no calibration data for a key,
-        // the radius of the key is assigned to zero.
-        return NOT_A_DISTANCE;
+    const unsigned short baseLowerC = Dictionary::toBaseLowerCase(c);
+    if (baseLowerC > MAX_CHAR_CODE) {
+        return NOT_A_INDEX;
     }
-    const float squaredRadius = square(radius);
-    const float squaredDistance = calculateSquaredDistanceFromSweetSpotCenter(keyIndex, index);
-    return squaredDistance / squaredRadius;
+    return mCodeToKeyIndex[baseLowerC];
 }
 
 float ProximityInfo::calculateSquaredDistanceFromSweetSpotCenter(
-        int keyIndex, int inputIndex) const {
+        const int keyIndex, const int inputIndex) const {
     const float sweetSpotCenterX = mSweetSpotCenterXs[keyIndex];
     const float sweetSpotCenterY = mSweetSpotCenterYs[keyIndex];
     const float inputX = (float)mInputXCoordinates[inputIndex];
@@ -202,11 +220,13 @@ bool ProximityInfo::existsAdjacentProximityChars(const int index) const {
 // then the word contains at that position a character close to what the user
 // typed.
 // What the user typed is actually the first character of the array.
+// proximityIndex is a pointer to the variable where getMatchedProximityId returns
+// the index of c in the proximity chars of the input index.
 // Notice : accented characters do not have a proximity list, so they are alone
 // in their list. The non-accented version of the character should be considered
 // "close", but not the other keys close to the non-accented version.
-ProximityInfo::ProximityType ProximityInfo::getMatchedProximityId(
-        const int index, const unsigned short c, const bool checkProximityChars) const {
+ProximityInfo::ProximityType ProximityInfo::getMatchedProximityId(const int index,
+        const unsigned short c, const bool checkProximityChars, int *proximityIndex) const {
     const int *currentChars = getProximityCharsAt(index);
     const int firstChar = currentChars[0];
     const unsigned short baseLowerC = Dictionary::toBaseLowerCase(c);
@@ -227,9 +247,14 @@ ProximityInfo::ProximityType ProximityInfo::getMatchedProximityId(
 
     // Not an exact nor an accent-alike match: search the list of close keys
     int j = 1;
-    while (currentChars[j] > 0 && j < MAX_PROXIMITY_CHARS_SIZE) {
+    while (j < MAX_PROXIMITY_CHARS_SIZE && currentChars[j] > 0) {
         const bool matched = (currentChars[j] == baseLowerC || currentChars[j] == c);
-        if (matched) return NEAR_PROXIMITY_CHAR;
+        if (matched) {
+            if (proximityIndex) {
+                *proximityIndex = j;
+            }
+            return NEAR_PROXIMITY_CHAR;
+        }
         ++j;
     }
 

native/src/proximity_info.h

@@ -28,6 +28,8 @@ class Correction;
 class ProximityInfo {
 public:
     static const int NORMALIZED_SQUARED_DISTANCE_SCALING_FACTOR_LOG_2 = 10;
+    static const int NORMALIZED_SQUARED_DISTANCE_SCALING_FACTOR =
+            1 << NORMALIZED_SQUARED_DISTANCE_SCALING_FACTOR_LOG_2;
 
     // Used as a return value for character comparison
     typedef enum {
@@ -53,19 +55,20 @@ public:
     unsigned short getPrimaryCharAt(const int index) const;
     bool existsCharInProximityAt(const int index, const int c) const;
     bool existsAdjacentProximityChars(const int index) const;
-    ProximityType getMatchedProximityId(
-            const int index, const unsigned short c, const bool checkProximityChars) const;
-    int getNormalizedSquaredDistance(int index) const {
-        return mNormalizedSquaredDistance[index];
+    ProximityType getMatchedProximityId(const int index, const unsigned short c,
+            const bool checkProximityChars, int *proximityIndex = NULL) const;
+    int getNormalizedSquaredDistance(const int inputIndex, const int proximityIndex) const {
+        return mNormalizedSquaredDistances[inputIndex * MAX_PROXIMITY_CHARS_SIZE + proximityIndex];
     }
     bool sameAsTyped(const unsigned short *word, int length) const;
     const unsigned short* getPrimaryInputWord() const {
         return mPrimaryInputWord;
     }
+    bool touchPositionCorrectionEnabled() const {
+        return mTouchPositionCorrectionEnabled;
+    }
 
 private:
-    static const int NORMALIZED_SQUARED_DISTANCE_SCALING_FACTOR =
-            1 << NORMALIZED_SQUARED_DISTANCE_SCALING_FACTOR_LOG_2;
     // The max number of the keys in one keyboard layout
     static const int MAX_KEY_COUNT_IN_A_KEYBOARD = 64;
     // The upper limit of the char code in mCodeToKeyIndex
@@ -73,8 +76,15 @@ private:
 
     int getStartIndexFromCoordinates(const int x, const int y) const;
     void initializeCodeToKeyIndex();
-    float calculateNormalizedSquaredDistance(int index) const;
-    float calculateSquaredDistanceFromSweetSpotCenter(int keyIndex, int inputIndex) const;
+    float calculateNormalizedSquaredDistance(const int keyIndex, const int inputIndex) const;
+    float calculateSquaredDistanceFromSweetSpotCenter(
+            const int keyIndex, const int inputIndex) const;
+    int getKeyIndex(const int c) const;
+    bool hasSweetSpotData(const int keyIndex) const {
+        // When there are no calibration data for a key,
+        // the radius of the key is assigned to zero.
+        return mSweetSpotRadii[keyIndex] > 0.0;
+    }
 
     const int MAX_PROXIMITY_CHARS_SIZE;
     const int KEYBOARD_WIDTH;
@@ -84,10 +94,13 @@ private:
     const int CELL_WIDTH;
     const int CELL_HEIGHT;
     const int KEY_COUNT;
+    const bool HAS_TOUCH_POSITION_CORRECTION_DATA;
     const int *mInputCodes;
     const int *mInputXCoordinates;
     const int *mInputYCoordinates;
+    bool mTouchPositionCorrectionEnabled;
     uint32_t *mProximityCharsArray;
+    int *mNormalizedSquaredDistances;
     int32_t mKeyXCoordinates[MAX_KEY_COUNT_IN_A_KEYBOARD];
     int32_t mKeyYCoordinates[MAX_KEY_COUNT_IN_A_KEYBOARD];
     int32_t mKeyWidths[MAX_KEY_COUNT_IN_A_KEYBOARD];
@@ -96,7 +109,6 @@ private:
     float mSweetSpotCenterXs[MAX_KEY_COUNT_IN_A_KEYBOARD];
     float mSweetSpotCenterYs[MAX_KEY_COUNT_IN_A_KEYBOARD];
     float mSweetSpotRadii[MAX_KEY_COUNT_IN_A_KEYBOARD];
-    int mNormalizedSquaredDistance[MAX_WORD_LENGTH_INTERNAL];
     int mInputLength;
     unsigned short mPrimaryInputWord[MAX_WORD_LENGTH_INTERNAL];
     int mCodeToKeyIndex[MAX_CHAR_CODE + 1];