Improve gesture input scoring method 2.

Align next key to path bases its scoring method on probabilities.

Change-Id: I5247c965b92c0052bfdab8a9b1027bc86eb33218

native/jni/src/geometry_utils.h

@@ -90,8 +90,8 @@ static inline float pointToLineSegSquaredDistanceFloat(
 struct NormalDistribution {
     NormalDistribution(const float u, const float sigma)
             : mU(u), mSigma(sigma),
-              mPreComputedNonExpPart(1.0f / sqrtf(2.0f * M_PI_F * sigma * sigma)),
+              mPreComputedNonExpPart(1.0f / sqrtf(2.0f * M_PI_F * SQUARE_FLOAT(sigma))),
-              mPreComputedExponentPart(-1.0f / (2.0f * sigma * sigma)) {}
+              mPreComputedExponentPart(-1.0f / (2.0f * SQUARE_FLOAT(sigma))) {}
 
     float getProbabilityDensity(const float x) {
         const float shiftedX = x - mU;

native/jni/src/proximity_info.cpp

@@ -239,6 +239,9 @@ int ProximityInfo::getKeyIndexOf(const int c) const {
         // We do not have the coordinate data
         return NOT_AN_INDEX;
     }
+    if (c == NOT_A_CODE_POINT) {
+        return NOT_AN_INDEX;
+    }
     const int lowerCode = static_cast<int>(toLowerCase(c));
     hash_map_compat<int, int>::const_iterator mapPos = mCodeToKeyMap.find(lowerCode);
     if (mapPos != mCodeToKeyMap.end()) {
@@ -296,9 +299,7 @@ int ProximityInfo::getKeyCenterYOfKeyIdG(int keyId) const {
     return 0;
 }
 
-int ProximityInfo::getKeyKeyDistanceG(int key0, int key1) const {
+int ProximityInfo::getKeyKeyDistanceG(const int keyId0, const int keyId1) const {
-    const int keyId0 = getKeyIndexOf(key0);
-    const int keyId1 = getKeyIndexOf(key1);
     if (keyId0 >= 0 && keyId1 >= 0) {
         return mKeyKeyDistancesG[keyId0][keyId1];
     }

native/jni/src/proximity_info.h

@@ -109,7 +109,7 @@ class ProximityInfo {
     int getKeyCenterYOfCodePointG(int charCode) const;
     int getKeyCenterXOfKeyIdG(int keyId) const;
     int getKeyCenterYOfKeyIdG(int keyId) const;
-    int getKeyKeyDistanceG(int key0, int key1) const;
+    int getKeyKeyDistanceG(int keyId0, int keyId1) const;
 
  private:
     DISALLOW_IMPLICIT_CONSTRUCTORS(ProximityInfo);

native/jni/src/proximity_info_state.cpp

@@ -105,6 +105,7 @@ void ProximityInfoState::initInputParams(const int pointerId, const float maxPoi
         mLengthCache.clear();
         mDistanceCache.clear();
         mNearKeysVector.clear();
+        mSearchKeysVector.clear();
         mRelativeSpeeds.clear();
         mCharProbabilities.clear();
     }
@@ -132,6 +133,10 @@ void ProximityInfoState::initInputParams(const int pointerId, const float maxPoi
         NearKeysDistanceMap *currentNearKeysDistances = &nearKeysDistances[0];
         NearKeysDistanceMap *prevNearKeysDistances = &nearKeysDistances[1];
         NearKeysDistanceMap *prevPrevNearKeysDistances = &nearKeysDistances[2];
+        // "sumAngle" is accumulated by each angle of input points. And when "sumAngle" exceeds
+        // the threshold we save that point, reset sumAngle. This aims to keep the figure of
+        // the curve.
+        float sumAngle = 0.0f;
 
         for (int i = pushTouchPointStartIndex; i <= lastInputIndex; ++i) {
             // Assuming pointerId == 0 if pointerIds is null.
@@ -144,9 +149,18 @@ void ProximityInfoState::initInputParams(const int pointerId, const float maxPoi
                 const int x = proximityOnly ? NOT_A_COORDINATE : xCoordinates[i];
                 const int y = proximityOnly ? NOT_A_COORDINATE : yCoordinates[i];
                 const int time = times ? times[i] : -1;
+
+                if (i > 1) {
+                    const float prevAngle = getAngle(xCoordinates[i - 2], yCoordinates[i - 2],
+                            xCoordinates[i - 1], yCoordinates[i - 1]);
+                    const float currentAngle =
+                            getAngle(xCoordinates[i - 1], yCoordinates[i - 1], x, y);
+                    sumAngle += getAngleDiff(prevAngle, currentAngle);
+                }
+
                 if (pushTouchPoint(i, c, x, y, time, isGeometric /* do sampling */,
-                        i == lastInputIndex, currentNearKeysDistances, prevNearKeysDistances,
+                        i == lastInputIndex, sumAngle, currentNearKeysDistances,
-                        prevPrevNearKeysDistances)) {
+                        prevNearKeysDistances, prevPrevNearKeysDistances)) {
                     // Previous point information was popped.
                     NearKeysDistanceMap *tmp = prevNearKeysDistances;
                     prevNearKeysDistances = currentNearKeysDistances;
@@ -156,6 +170,7 @@ void ProximityInfoState::initInputParams(const int pointerId, const float maxPoi
                     prevPrevNearKeysDistances = prevNearKeysDistances;
                     prevNearKeysDistances = currentNearKeysDistances;
                     currentNearKeysDistances = tmp;
+                    sumAngle = 0.0f;
                 }
             }
         }
@@ -163,6 +178,7 @@ void ProximityInfoState::initInputParams(const int pointerId, const float maxPoi
     }
 
     if (mInputSize > 0 && isGeometric) {
+        // Relative speed calculation.
         const int sumDuration = mTimes.back() - mTimes.front();
         const int sumLength = mLengthCache.back() - mLengthCache.front();
         const float averageSpeed = static_cast<float>(sumLength) / static_cast<float>(sumDuration);
@@ -174,7 +190,7 @@ void ProximityInfoState::initInputParams(const int pointerId, const float maxPoi
 
             // Calculate velocity by using distances and durations of
             // NUM_POINTS_FOR_SPEED_CALCULATION points for both forward and backward.
-            static const int NUM_POINTS_FOR_SPEED_CALCULATION = 1;
+            static const int NUM_POINTS_FOR_SPEED_CALCULATION = 2;
             for (int j = index; j < min(inputSize - 1, index + NUM_POINTS_FOR_SPEED_CALCULATION);
                     ++j) {
                 if (i < mInputSize - 1 && j >= mInputIndice[i + 1]) {
@@ -202,12 +218,21 @@ void ProximityInfoState::initInputParams(const int pointerId, const float maxPoi
         }
     }
 
+    if (DEBUG_GEO_FULL) {
+        for (int i = 0; i < mInputSize; ++i) {
+            AKLOGI("Sampled(%d): x = %d, y = %d, time = %d", i, mInputXs[i], mInputYs[i],
+                    mTimes[i]);
+        }
+    }
+
     if (mInputSize > 0) {
         const int keyCount = mProximityInfo->getKeyCount();
         mNearKeysVector.resize(mInputSize);
+        mSearchKeysVector.resize(mInputSize);
         mDistanceCache.resize(mInputSize * keyCount);
         for (int i = lastSavedInputSize; i < mInputSize; ++i) {
             mNearKeysVector[i].reset();
+            mSearchKeysVector[i].reset();
             static const float NEAR_KEY_NORMALIZED_SQUARED_THRESHOLD = 4.0f;
             for (int k = 0; k < keyCount; ++k) {
                 const int index = i * keyCount + k;
@@ -217,25 +242,28 @@ void ProximityInfoState::initInputParams(const int pointerId, const float maxPoi
                         mProximityInfo->getNormalizedSquaredDistanceFromCenterFloatG(k, x, y);
                 mDistanceCache[index] = normalizedSquaredDistance;
                 if (normalizedSquaredDistance < NEAR_KEY_NORMALIZED_SQUARED_THRESHOLD) {
-                    mNearKeysVector[i].set(k, 1);
+                    mNearKeysVector[i][k] = true;
                 }
             }
         }
+        if (isGeometric) {
+            // updates probabilities of skipping or mapping each key for all points.
+            updateAlignPointProbabilities(lastSavedInputSize);
 
             static const float READ_FORWORD_LENGTH_SCALE = 0.95f;
             const int readForwordLength = static_cast<int>(
                     hypotf(mProximityInfo->getKeyboardWidth(), mProximityInfo->getKeyboardHeight())
                             * READ_FORWORD_LENGTH_SCALE);
             for (int i = 0; i < mInputSize; ++i) {
-            if (DEBUG_GEO_FULL) {
+                if (i >= lastSavedInputSize) {
-                AKLOGI("Sampled(%d): x = %d, y = %d, time = %d", i, mInputXs[i], mInputYs[i],
+                    mSearchKeysVector[i].reset();
-                        mTimes[i]);
                 }
-            for (int j = max(i + 1, lastSavedInputSize); j < mInputSize; ++j) {
+                for (int j = max(i, lastSavedInputSize); j < mInputSize; ++j) {
                     if (mLengthCache[j] - mLengthCache[i] >= readForwordLength) {
                         break;
                     }
-                mNearKeysVector[i] |= mNearKeysVector[j];
+                    mSearchKeysVector[i] |= mNearKeysVector[j];
+                }
             }
         }
     }
@@ -307,10 +335,6 @@ void ProximityInfoState::initInputParams(const int pointerId, const float maxPoi
     if (DEBUG_GEO_FULL) {
         AKLOGI("ProximityState init finished: %d points out of %d", mInputSize, inputSize);
     }
-    if (isGeometric && mInputSize > 0) {
-        // updates probabilities of skipping or mapping each key for all points.
-        updateAlignPointProbabilities();
-    }
 }
 
 bool ProximityInfoState::checkAndReturnIsContinuationPossible(const int inputSize,
@@ -329,7 +353,7 @@ bool ProximityInfoState::checkAndReturnIsContinuationPossible(const int inputSiz
 // the given point and the nearest key position.
 float ProximityInfoState::updateNearKeysDistances(const int x, const int y,
         NearKeysDistanceMap *const currentNearKeysDistances) {
-    static const float NEAR_KEY_THRESHOLD = 1.7f;
+    static const float NEAR_KEY_THRESHOLD = 2.0f;
 
     currentNearKeysDistances->clear();
     const int keyCount = mProximityInfo->getKeyCount();
@@ -350,7 +374,7 @@ float ProximityInfoState::updateNearKeysDistances(const int x, const int y,
 bool ProximityInfoState::isPrevLocalMin(const NearKeysDistanceMap *const currentNearKeysDistances,
         const NearKeysDistanceMap *const prevNearKeysDistances,
         const NearKeysDistanceMap *const prevPrevNearKeysDistances) const {
-    static const float MARGIN = 0.03f;
+    static const float MARGIN = 0.01f;
 
     for (NearKeysDistanceMap::const_iterator it = prevNearKeysDistances->begin();
         it != prevNearKeysDistances->end(); ++it) {
@@ -367,47 +391,33 @@ bool ProximityInfoState::isPrevLocalMin(const NearKeysDistanceMap *const current
 // Calculating a point score that indicates usefulness of the point.
 float ProximityInfoState::getPointScore(
         const int x, const int y, const int time, const bool lastPoint, const float nearest,
-        const NearKeysDistanceMap *const currentNearKeysDistances,
+        const float sumAngle, const NearKeysDistanceMap *const currentNearKeysDistances,
         const NearKeysDistanceMap *const prevNearKeysDistances,
         const NearKeysDistanceMap *const prevPrevNearKeysDistances) const {
     static const int DISTANCE_BASE_SCALE = 100;
-    static const int SAVE_DISTANCE_SCALE = 500;
+    static const float NEAR_KEY_THRESHOLD = 0.6f;
-    static const int SKIP_DISTANCE_SCALE = 10;
+    static const int CORNER_CHECK_DISTANCE_THRESHOLD_SCALE = 25;
-    static const float NEAR_KEY_THRESHOLD = 1.0f;
-    static const int CHECK_LOCALMIN_DISTANCE_THRESHOLD_SCALE = 100;
-    static const int STRAIGHT_SKIP_DISTANCE_THRESHOLD_SCALE = 200;
-    static const int CORNER_CHECK_DISTANCE_THRESHOLD_SCALE = 20;
-    static const float SAVE_DISTANCE_SCORE = 2.0f;
-    static const float SKIP_DISTANCE_SCORE = -1.0f;
     static const float NOT_LOCALMIN_DISTANCE_SCORE = -1.0f;
-    static const float LOCALMIN_DISTANCE_AND_NEAR_TO_KEY_SCORE = 2.0f;
+    static const float LOCALMIN_DISTANCE_AND_NEAR_TO_KEY_SCORE = 1.0f;
-    static const float STRAIGHT_ANGLE_THRESHOLD = M_PI_F / 36.0f;
+    static const float CORNER_ANGLE_THRESHOLD = M_PI_F * 2.0f / 3.0f;
-    static const float STRAIGHT_SKIP_NEAREST_DISTANCE_THRESHOLD = 0.5f;
+    static const float CORNER_SUM_ANGLE_THRESHOLD = M_PI_F / 4.0f;
-    static const float STRAIGHT_SKIP_SCORE = -1.0f;
-    static const float CORNER_ANGLE_THRESHOLD = M_PI_F / 6.0f;
     static const float CORNER_SCORE = 1.0f;
 
-    const std::size_t size = mInputXs.size();
+    const size_t size = mInputXs.size();
-    if (size <= 1) {
+    // If there is only one point, add this point. Besides, if the previous point's distance map
+    // is empty, we re-compute nearby keys distances from the current point.
+    // Note that the current point is the first point in the incremental input that needs to
+    // be re-computed.
+    if (size <= 1 || prevNearKeysDistances->empty()) {
         return 0.0f;
     }
+
     const int baseSampleRate = mProximityInfo->getMostCommonKeyWidth();
-    const int distNext = getDistanceInt(x, y, mInputXs.back(), mInputYs.back())
-            * DISTANCE_BASE_SCALE;
     const int distPrev = getDistanceInt(mInputXs.back(), mInputYs.back(),
             mInputXs[size - 2], mInputYs[size - 2]) * DISTANCE_BASE_SCALE;
     float score = 0.0f;
 
-    // Sum of distances
-    if (distPrev + distNext > baseSampleRate * SAVE_DISTANCE_SCALE) {
-        score +=  SAVE_DISTANCE_SCORE;
-    }
-    // Distance
-    if (distPrev < baseSampleRate * SKIP_DISTANCE_SCALE) {
-        score += SKIP_DISTANCE_SCORE;
-    }
     // Location
-    if (distPrev < baseSampleRate * CHECK_LOCALMIN_DISTANCE_THRESHOLD_SCALE) {
     if (!isPrevLocalMin(currentNearKeysDistances, prevNearKeysDistances,
         prevPrevNearKeysDistances)) {
         score += NOT_LOCALMIN_DISTANCE_SCORE;
@@ -415,21 +425,15 @@ float ProximityInfoState::getPointScore(
         // Promote points nearby keys
         score += LOCALMIN_DISTANCE_AND_NEAR_TO_KEY_SCORE;
     }
-    }
     // Angle
     const float angle1 = getAngle(x, y, mInputXs.back(), mInputYs.back());
     const float angle2 = getAngle(mInputXs.back(), mInputYs.back(),
             mInputXs[size - 2], mInputYs[size - 2]);
     const float angleDiff = getAngleDiff(angle1, angle2);
-    // Skip straight
+
-    if (nearest > STRAIGHT_SKIP_NEAREST_DISTANCE_THRESHOLD
-            && distPrev < baseSampleRate * STRAIGHT_SKIP_DISTANCE_THRESHOLD_SCALE
-            && angleDiff < STRAIGHT_ANGLE_THRESHOLD) {
-        score += STRAIGHT_SKIP_SCORE;
-    }
     // Save corner
     if (distPrev > baseSampleRate * CORNER_CHECK_DISTANCE_THRESHOLD_SCALE
-            && angleDiff > CORNER_ANGLE_THRESHOLD) {
+            && (sumAngle > CORNER_SUM_ANGLE_THRESHOLD || angleDiff > CORNER_ANGLE_THRESHOLD)) {
         score += CORNER_SCORE;
     }
     return score;
@@ -438,18 +442,17 @@ float ProximityInfoState::getPointScore(
 // Sampling touch point and pushing information to vectors.
 // Returning if previous point is popped or not.
 bool ProximityInfoState::pushTouchPoint(const int inputIndex, const int nodeChar, int x, int y,
-        const int time, const bool sample, const bool isLastPoint,
+        const int time, const bool sample, const bool isLastPoint, const float sumAngle,
         NearKeysDistanceMap *const currentNearKeysDistances,
         const NearKeysDistanceMap *const prevNearKeysDistances,
         const NearKeysDistanceMap *const prevPrevNearKeysDistances) {
     static const int LAST_POINT_SKIP_DISTANCE_SCALE = 4;
-    static const int LAST_AND_NOT_NEAREST_POINT_SKIP_DISTANCE_SCALE = 2;
 
     size_t size = mInputXs.size();
     bool popped = false;
     if (nodeChar < 0 && sample) {
         const float nearest = updateNearKeysDistances(x, y, currentNearKeysDistances);
-        const float score = getPointScore(x, y, time, isLastPoint, nearest,
+        const float score = getPointScore(x, y, time, isLastPoint, nearest, sumAngle,
                 currentNearKeysDistances, prevNearKeysDistances, prevPrevNearKeysDistances);
         if (score < 0) {
             // Pop previous point because it would be useless.
@@ -461,9 +464,8 @@ bool ProximityInfoState::pushTouchPoint(const int inputIndex, const int nodeChar
         }
         // Check if the last point should be skipped.
         if (isLastPoint && size > 0) {
-            const int lastPointsDistance = getDistanceInt(x, y, mInputXs.back(), mInputYs.back());
+            if (getDistanceInt(x, y, mInputXs.back(), mInputYs.back())
-            if (lastPointsDistance * LAST_POINT_SKIP_DISTANCE_SCALE
+                    * LAST_POINT_SKIP_DISTANCE_SCALE < mProximityInfo->getMostCommonKeyWidth()) {
-                    < mProximityInfo->getMostCommonKeyWidth()) {
                 // This point is not used because it's too close to the previous point.
                 if (DEBUG_GEO_FULL) {
                     AKLOGI("p0: size = %zd, x = %d, y = %d, lx = %d, ly = %d, dist = %d, "
@@ -473,28 +475,6 @@ bool ProximityInfoState::pushTouchPoint(const int inputIndex, const int nodeChar
                                    / LAST_POINT_SKIP_DISTANCE_SCALE);
                 }
                 return popped;
-            } else if (lastPointsDistance * LAST_AND_NOT_NEAREST_POINT_SKIP_DISTANCE_SCALE
-                    < mProximityInfo->getMostCommonKeyWidth()) {
-                int nearestChar = 0;
-                float nearestCharDistance = mMaxPointToKeyLength;
-                for (NearKeysDistanceMap::const_iterator it = currentNearKeysDistances->begin();
-                        it != currentNearKeysDistances->end(); ++it) {
-                    if (nearestCharDistance > it->second) {
-                        nearestChar = it->first;
-                        nearestCharDistance = it->second;
-                    }
-                }
-                NearKeysDistanceMap::const_iterator itPP =
-                        prevNearKeysDistances->find(nearestChar);
-                if (itPP != prevNearKeysDistances->end() && nearestCharDistance > itPP->second) {
-                    // The nearest key of the penultimate point is same as the nearest key of the
-                    // last point. So, we don't need to use the last point.
-                    if (DEBUG_GEO_FULL) {
-                        AKLOGI("p1: char = %c, minDist = %f, prevNear key minDist = %f",
-                                nearestChar, itPP->second, nearestCharDistance);
-                    }
-                    return popped;
-                }
             }
         }
     }
@@ -550,11 +530,16 @@ int ProximityInfoState::getDuration(const int index) const {
 }
 
 float ProximityInfoState::getPointToKeyLength(const int inputIndex, const int codePoint) const {
+    const int keyId = mProximityInfo->getKeyIndexOf(codePoint);
+    if (keyId != NOT_AN_INDEX) {
+        const int index = inputIndex * mProximityInfo->getKeyCount() + keyId;
+        return min(mDistanceCache[index], mMaxPointToKeyLength);
+    }
     if (isSkippableChar(codePoint)) {
         return 0.0f;
     }
-    const int keyId = mProximityInfo->getKeyIndexOf(codePoint);
+    // If the char is not a key on the keyboard then return the max length.
-    return getPointToKeyByIdLength(inputIndex, keyId);
+    return MAX_POINT_TO_KEY_LENGTH;
 }
 
 float ProximityInfoState::getPointToKeyByIdLength(const int inputIndex, const int keyId) const {
@@ -587,8 +572,9 @@ int32_t ProximityInfoState::getAllPossibleChars(
         return filterSize;
     }
     int newFilterSize = filterSize;
-    for (int j = 0; j < mProximityInfo->getKeyCount(); ++j) {
+    const int keyCount = mProximityInfo->getKeyCount();
-        if (mNearKeysVector[index].test(j)) {
+    for (int j = 0; j < keyCount; ++j) {
+        if (mSearchKeysVector[index].test(j)) {
             const int32_t keyCodePoint = mProximityInfo->getCodePointOf(j);
             bool insert = true;
             // TODO: Avoid linear search
@@ -606,6 +592,12 @@ int32_t ProximityInfoState::getAllPossibleChars(
     return newFilterSize;
 }
 
+bool ProximityInfoState::isKeyInSerchKeysAfterIndex(const int index, const int keyId) const {
+    ASSERT(keyId >= 0);
+    ASSERT(index >= 0 && index < mInputSize);
+    return mSearchKeysVector[index].test(keyId);
+}
+
 void ProximityInfoState::popInputData() {
     mInputXs.pop_back();
     mInputYs.pop_back();
@@ -614,18 +606,26 @@ void ProximityInfoState::popInputData() {
     mInputIndice.pop_back();
 }
 
+float ProximityInfoState::getDirection(const int index0, const int index1) const {
+    if (index0 < 0 || index0 > mInputSize - 1) {
+        return 0.0f;
+    }
+    if (index1 < 0 || index1 > mInputSize - 1) {
+        return 0.0f;
+    }
+    const int x1 = mInputXs[index0];
+    const int y1 = mInputYs[index0];
+    const int x2 = mInputXs[index1];
+    const int y2 = mInputYs[index1];
+    return getAngle(x1, y1, x2, y2);
+}
+
 float ProximityInfoState::getPointAngle(const int index) const {
     if (index <= 0 || index >= mInputSize - 1) {
         return 0.0f;
     }
-    const int x = mInputXs[index];
+    const float previousDirection = getDirection(index - 1, index);
-    const int y = mInputYs[index];
+    const float nextDirection = getDirection(index, index + 1);
-    const int nextX = mInputXs[index + 1];
-    const int nextY = mInputYs[index + 1];
-    const int previousX = mInputXs[index - 1];
-    const int previousY = mInputYs[index - 1];
-    const float previousDirection = getAngle(previousX, previousY, x, y);
-    const float nextDirection = getAngle(x, y, nextX, nextY);
     const float directionDiff = getAngleDiff(previousDirection, nextDirection);
     return directionDiff;
 }
@@ -641,190 +641,354 @@ float ProximityInfoState::getPointsAngle(
     if (index2 < 0 || index2 > mInputSize - 1) {
         return 0.0f;
     }
-    const int x0 = mInputXs[index0];
+    const float previousDirection = getDirection(index0, index1);
-    const int y0 = mInputYs[index0];
+    const float nextDirection = getDirection(index1, index2);
-    const int x1 = mInputXs[index1];
+    return getAngleDiff(previousDirection, nextDirection);
-    const int y1 = mInputYs[index1];
+}
-    const int x2 = mInputXs[index2];
+
-    const int y2 = mInputYs[index2];
+float ProximityInfoState::getLineToKeyDistance(
-    const float previousDirection = getAngle(x0, y0, x1, y1);
+        const int from, const int to, const int keyId, const bool extend) const {
-    const float nextDirection = getAngle(x1, y1, x2, y2);
+    if (from < 0 || from > mInputSize - 1) {
-    const float directionDiff = getAngleDiff(previousDirection, nextDirection);
+        return 0.0f;
-    return directionDiff;
+    }
+    if (to < 0 || to > mInputSize - 1) {
+        return 0.0f;
+    }
+    const int x0 = mInputXs[from];
+    const int y0 = mInputYs[from];
+    const int x1 = mInputXs[to];
+    const int y1 = mInputYs[to];
+
+    const int keyX = mProximityInfo->getKeyCenterXOfKeyIdG(keyId);
+    const int keyY = mProximityInfo->getKeyCenterYOfKeyIdG(keyId);
+
+    return pointToLineSegSquaredDistanceFloat(keyX, keyY, x0, y0, x1, y1, extend);
 }
 
 // Updates probabilities of aligning to some keys and skipping.
 // Word suggestion should be based on this probabilities.
-void ProximityInfoState::updateAlignPointProbabilities() {
+void ProximityInfoState::updateAlignPointProbabilities(const int start) {
-    static const float MIN_PROBABILITY = 0.00001f;
+    static const float MIN_PROBABILITY = 0.000001f;
+    static const float MAX_SKIP_PROBABILITY = 0.95f;
     static const float SKIP_FIRST_POINT_PROBABILITY = 0.01f;
     static const float SKIP_LAST_POINT_PROBABILITY = 0.1f;
-    static const float ANGLE_RATE = 0.8f;
+    static const float MIN_SPEED_RATE_FOR_SKIP_PROBABILITY = 0.15f;
-    static const float DEEP_CORNER_ANGLE_THRESHOLD = M_PI_F * 0.5f;
+    static const float SPEED_WEIGHT_FOR_SKIP_PROBABILITY = 0.9f;
-    static const float SKIP_DEEP_CORNER_PROBABILITY = 0.3f;
+    static const float SLOW_STRAIGHT_WEIGHT_FOR_SKIP_PROBABILITY = 0.6f;
-    static const float CORNER_ANGLE_THRESHOLD = M_PI_F * 35.0f / 180.0f;
+    static const float NEAREST_DISTANCE_WEIGHT = 0.5f;
+    static const float NEAREST_DISTANCE_BIAS = 0.5f;
+    static const float NEAREST_DISTANCE_WEIGHT_FOR_LAST = 0.6f;
+    static const float NEAREST_DISTANCE_BIAS_FOR_LAST = 0.4f;
+
+    static const float ANGLE_WEIGHT = 0.90f;
+    static const float DEEP_CORNER_ANGLE_THRESHOLD = M_PI_F * 60.0f / 180.0f;
+    static const float SKIP_DEEP_CORNER_PROBABILITY = 0.1f;
+    static const float CORNER_ANGLE_THRESHOLD = M_PI_F * 30.0f / 180.0f;
     static const float STRAIGHT_ANGLE_THRESHOLD = M_PI_F * 15.0f / 180.0f;
-    static const float SKIP_CORNER_PROBABILITY = 0.5f;
+    static const float SKIP_CORNER_PROBABILITY = 0.4f;
-    static const float SLOW_STRAIGHT_WEIGHT = 0.8f;
+    static const float SPEED_MARGIN = 0.1f;
     static const float CENTER_VALUE_OF_NORMALIZED_DISTRIBUTION = 0.0f;
 
+    const int keyCount = mProximityInfo->getKeyCount();
     mCharProbabilities.resize(mInputSize);
     // Calculates probabilities of using a point as a correlated point with the character
     // for each point.
-    for (int i = 0; i < mInputSize; ++i) {
+    for (int i = start; i < mInputSize; ++i) {
-        // First, calculates skip probability. Starts form 100%.
+        mCharProbabilities[i].clear();
+        // First, calculates skip probability. Starts form MIN_SKIP_PROBABILITY.
         // Note that all values that are multiplied to this probability should be in [0.0, 1.0];
-        float skipProbability = 1.0f;
+        float skipProbability = MAX_SKIP_PROBABILITY;
-        const float speed = getRelativeSpeed(i);
+
+        const float currentAngle = getPointAngle(i);
+        const float relativeSpeed = getRelativeSpeed(i);
+
+        float nearestKeyDistance = static_cast<float>(MAX_POINT_TO_KEY_LENGTH);
+        for (int j = 0; j < keyCount; ++j) {
+            if (mNearKeysVector[i].test(j)) {
+                const float distance = getPointToKeyByIdLength(i, j);
+                if (distance < nearestKeyDistance) {
+                    nearestKeyDistance = distance;
+                }
+            }
+        }
 
-        // Adjusts skip probability by a rate depending on speed.
-        skipProbability *= min(1.0f, speed);
         if (i == 0) {
+            skipProbability *= min(1.0f, nearestKeyDistance * NEAREST_DISTANCE_WEIGHT
+                    + NEAREST_DISTANCE_BIAS);
+            // Promote the first point
             skipProbability *= SKIP_FIRST_POINT_PROBABILITY;
         } else if (i == mInputSize - 1) {
+            skipProbability *= min(1.0f, nearestKeyDistance * NEAREST_DISTANCE_WEIGHT_FOR_LAST
+                    + NEAREST_DISTANCE_BIAS_FOR_LAST);
+            // Promote the last point
             skipProbability *= SKIP_LAST_POINT_PROBABILITY;
         } else {
-            const float currentAngle = getPointAngle(i);
+            // If the current speed is relatively slower than adjacent keys, we promote this point.
+            if (getRelativeSpeed(i - 1) - SPEED_MARGIN > relativeSpeed
+                    && relativeSpeed < getRelativeSpeed(i + 1) - SPEED_MARGIN) {
+                if (currentAngle < CORNER_ANGLE_THRESHOLD) {
+                    skipProbability *= min(1.0f, relativeSpeed
+                            * SLOW_STRAIGHT_WEIGHT_FOR_SKIP_PROBABILITY);
+                } else {
+                    // If the angle is small enough, we promote this point more. (e.g. pit vs put)
+                    skipProbability *= min(1.0f, relativeSpeed * SPEED_WEIGHT_FOR_SKIP_PROBABILITY
+                            + MIN_SPEED_RATE_FOR_SKIP_PROBABILITY);
+                }
+            }
+
+            skipProbability *= min(1.0f, relativeSpeed * nearestKeyDistance *
+                    NEAREST_DISTANCE_WEIGHT + NEAREST_DISTANCE_BIAS);
 
             // Adjusts skip probability by a rate depending on angle.
             // ANGLE_RATE of skipProbability is adjusted by current angle.
-            skipProbability *= max((M_PI_F - currentAngle) / M_PI_F, 0.0f) * ANGLE_RATE +
+            skipProbability *= (M_PI_F - currentAngle) / M_PI_F * ANGLE_WEIGHT
-                    (1.0f - ANGLE_RATE);
+                    + (1.0f - ANGLE_WEIGHT);
             if (currentAngle > DEEP_CORNER_ANGLE_THRESHOLD) {
                 skipProbability *= SKIP_DEEP_CORNER_PROBABILITY;
             }
-            const float prevAngle = getPointsAngle(i, i - 1, i - 2);
+            // We assume the angle of this point is the angle for point[i], point[i - 2]
-            if (prevAngle < STRAIGHT_ANGLE_THRESHOLD && currentAngle > CORNER_ANGLE_THRESHOLD) {
+            // and point[i - 3]. The reason why we don't use the angle for point[i], point[i - 1]
+            // and point[i - 2] is this angle can be more affected by the noise.
+            const float prevAngle = getPointsAngle(i, i - 2, i - 3);
+            if (i >= 3 && prevAngle < STRAIGHT_ANGLE_THRESHOLD
+                    && currentAngle > CORNER_ANGLE_THRESHOLD) {
                 skipProbability *= SKIP_CORNER_PROBABILITY;
             }
-            if (currentAngle < STRAIGHT_ANGLE_THRESHOLD) {
-                // Adjusts skip probability by speed.
-                skipProbability *= min(1.0f, speed * SLOW_STRAIGHT_WEIGHT);
-            }
         }
 
-        // probabilities must be in [0.0, 1.0];
+        // probabilities must be in [0.0, MAX_SKIP_PROBABILITY];
         ASSERT(skipProbability >= 0.0f);
-        ASSERT(skipProbability <= 1.0f);
+        ASSERT(skipProbability <= MAX_SKIP_PROBABILITY);
-
         mCharProbabilities[i][NOT_AN_INDEX] = skipProbability;
+
         // Second, calculates key probabilities by dividing the rest probability
         // (1.0f - skipProbability).
         const float inputCharProbability = 1.0f - skipProbability;
-        // Summing up probability densities of all near keys.
+
-        float sumOfProbabilityDensityOfNearKeys = 0.0f;
+        // TODO: The variance is critical for accuracy; thus, adjusting these parameter by machine
-        const float sigma = speed;
+        // learning or something would be efficient.
+        static const float SPEEDxANGLE_WEIGHT_FOR_STANDARD_DIVIATION = 0.3f;
+        static const float MAX_SPEEDxANGLE_RATE_FOR_STANDERD_DIVIATION = 0.25f;
+        static const float SPEEDxNEAREST_WEIGHT_FOR_STANDARD_DIVIATION = 0.5f;
+        static const float MAX_SPEEDxNEAREST_RATE_FOR_STANDERD_DIVIATION = 0.15f;
+        static const float MIN_STANDERD_DIVIATION = 0.37f;
+
+        const float speedxAngleRate = min(relativeSpeed * currentAngle / M_PI_F
+                * SPEEDxANGLE_WEIGHT_FOR_STANDARD_DIVIATION,
+                        MAX_SPEEDxANGLE_RATE_FOR_STANDERD_DIVIATION);
+        const float speedxNearestKeyDistanceRate = min(relativeSpeed * nearestKeyDistance
+                * SPEEDxNEAREST_WEIGHT_FOR_STANDARD_DIVIATION,
+                        MAX_SPEEDxNEAREST_RATE_FOR_STANDERD_DIVIATION);
+        const float sigma = speedxAngleRate + speedxNearestKeyDistanceRate + MIN_STANDERD_DIVIATION;
+
         NormalDistribution distribution(CENTER_VALUE_OF_NORMALIZED_DISTRIBUTION, sigma);
-        for (int j = 0; j < mProximityInfo->getKeyCount(); ++j) {
+        static const float PREV_DISTANCE_WEIGHT = 0.5f;
+        static const float NEXT_DISTANCE_WEIGHT = 0.6f;
+        // Summing up probability densities of all near keys.
+        float sumOfProbabilityDensities = 0.0f;
+        for (int j = 0; j < keyCount; ++j) {
             if (mNearKeysVector[i].test(j)) {
-                const float distance = sqrtf(getPointToKeyByIdLength(i, j));
+                float distance = sqrtf(getPointToKeyByIdLength(i, j));
-                sumOfProbabilityDensityOfNearKeys += distribution.getProbabilityDensity(distance);
+                if (i == 0 && i != mInputSize - 1) {
+                    // For the first point, weighted average of distances from first point and the
+                    // next point to the key is used as a point to key distance.
+                    const float nextDistance = sqrtf(getPointToKeyByIdLength(i + 1, j));
+                    if (nextDistance < distance) {
+                        // The distance of the first point tends to bigger than continuing
+                        // points because the first touch by the user can be sloppy.
+                        // So we promote the first point if the distance of that point is larger
+                        // than the distance of the next point.
+                        distance = (distance + nextDistance * NEXT_DISTANCE_WEIGHT)
+                                / (1.0f + NEXT_DISTANCE_WEIGHT);
+                    }
+                } else if (i != 0 && i == mInputSize - 1) {
+                    // For the first point, weighted average of distances from last point and
+                    // the previous point to the key is used as a point to key distance.
+                    const float previousDistance = sqrtf(getPointToKeyByIdLength(i - 1, j));
+                    if (previousDistance < distance) {
+                        // The distance of the last point tends to bigger than continuing points
+                        // because the last touch by the user can be sloppy. So we promote the
+                        // last point if the distance of that point is larger than the distance of
+                        // the previous point.
+                        distance = (distance + previousDistance * PREV_DISTANCE_WEIGHT)
+                                / (1.0f + PREV_DISTANCE_WEIGHT);
                     }
                 }
-        for (int j = 0; j < mProximityInfo->getKeyCount(); ++j) {
+                // TODO: Promote the first point when the extended line from the next input is near
+                // from a key. Also, promote the last point as well.
+                sumOfProbabilityDensities += distribution.getProbabilityDensity(distance);
+            }
+        }
+
+        // Split the probability of an input point to keys that are close to the input point.
+        for (int j = 0; j < keyCount; ++j) {
             if (mNearKeysVector[i].test(j)) {
-                const float distance = sqrtf(getPointToKeyByIdLength(i, j));
+                float distance = sqrtf(getPointToKeyByIdLength(i, j));
-                const float probabilityDessity = distribution.getProbabilityDensity(distance);
+                if (i == 0 && i != mInputSize - 1) {
-                // inputCharProbability divided to the probability for each near key.
+                    // For the first point, weighted average of distances from the first point and
-                const float probability = inputCharProbability * probabilityDessity
+                    // the next point to the key is used as a point to key distance.
-                        / sumOfProbabilityDensityOfNearKeys;
+                    const float prevDistance = sqrtf(getPointToKeyByIdLength(i + 1, j));
-                if (probability > MIN_PROBABILITY) {
+                    if (prevDistance < distance) {
+                        distance = (distance + prevDistance * NEXT_DISTANCE_WEIGHT)
+                                / (1.0f + NEXT_DISTANCE_WEIGHT);
+                    }
+                } else if (i != 0 && i == mInputSize - 1) {
+                    // For the first point, weighted average of distances from last point and
+                    // the previous point to the key is used as a point to key distance.
+                    const float prevDistance = sqrtf(getPointToKeyByIdLength(i - 1, j));
+                    if (prevDistance < distance) {
+                        distance = (distance + prevDistance * PREV_DISTANCE_WEIGHT)
+                                / (1.0f + PREV_DISTANCE_WEIGHT);
+                    }
+                }
+                const float probabilityDensity = distribution.getProbabilityDensity(distance);
+                const float probability = inputCharProbability * probabilityDensity
+                        / sumOfProbabilityDensities;
                 mCharProbabilities[i][j] = probability;
             }
         }
     }
-    }
 
-    // Decrease key probabilities of points which don't have the highest probability of that key
-    // among nearby points. Probabilities of the first point and the last point are not suppressed.
-    for (int i = 1; i < mInputSize - 1; ++i) {
-        // forward
-        for (int j = i + 1; j < mInputSize; ++j) {
-            if (suppressCharProbabilities(i, j)) {
-                break;
-            }
-        }
-        // backward
-        for (int j = i - 1; j >= 0; --j) {
-            if (suppressCharProbabilities(i, j)) {
-                break;
-            }
-        }
-    }
 
     if (DEBUG_POINTS_PROBABILITY) {
         for (int i = 0; i < mInputSize; ++i) {
             std::stringstream sstream;
             sstream << i << ", ";
+            sstream << "("<< mInputXs[i] << ", ";
+            sstream << ", "<< mInputYs[i] << "), ";
+            sstream << "Speed: "<< getRelativeSpeed(i) << ", ";
+            sstream << "Angle: "<< getPointAngle(i) << ", \n";
+
             for (hash_map_compat<int, float>::iterator it = mCharProbabilities[i].begin();
                     it != mCharProbabilities[i].end(); ++it) {
+                if (it->first == NOT_AN_INDEX) {
+                    sstream << it->first
+                            << "(skip):"
+                            << it->second
+                            << "\n";
+                } else {
                     sstream << it->first
                             << "("
                             << static_cast<char>(mProximityInfo->getCodePointOf(it->first))
                             << "):"
                             << it->second
-                        << ", ";
+                            << "\n";
+                }
             }
             AKLOGI("%s", sstream.str().c_str());
         }
     }
+
+    // Decrease key probabilities of points which don't have the highest probability of that key
+    // among nearby points. Probabilities of the first point and the last point are not suppressed.
+    for (int i = max(start, 1); i < mInputSize; ++i) {
+        for (int j = i + 1; j < mInputSize; ++j) {
+            if (!suppressCharProbabilities(i, j)) {
+                break;
+            }
+        }
+        for (int j = i - 1; j >= max(start, 0); --j) {
+            if (!suppressCharProbabilities(i, j)) {
+                break;
+            }
+        }
     }
 
-// Decreases char probabilities of index0 by checking probabilities of a near point (index1).
+    // Converting from raw probabilities to log probabilities to calculate spatial distance.
+    for (int i = start; i < mInputSize; ++i) {
+        for (int j = 0; j < keyCount; ++j) {
+            hash_map_compat<int, float>::iterator it = mCharProbabilities[i].find(j);
+            if (it == mCharProbabilities[i].end()){
+                mNearKeysVector[i].reset(j);
+            } else if(it->second < MIN_PROBABILITY) {
+                // Erases from near keys vector because it has very low probability.
+                mNearKeysVector[i].reset(j);
+                mCharProbabilities[i].erase(j);
+            } else {
+                it->second = -logf(it->second);
+            }
+        }
+        mCharProbabilities[i][NOT_AN_INDEX] = -logf(mCharProbabilities[i][NOT_AN_INDEX]);
+    }
+}
+
+// Decreases char probabilities of index0 by checking probabilities of a near point (index1) and
+// increases char probabilities of index1 by checking probabilities of index0.
 bool ProximityInfoState::suppressCharProbabilities(const int index0, const int index1) {
     ASSERT(0 <= index0 && index0 < mInputSize);
     ASSERT(0 <= index1 && index1 < mInputSize);
+
     static const float SUPPRESSION_LENGTH_WEIGHT = 1.5f;
+    static const float MIN_SUPPRESSION_RATE = 0.1f;
+    static const float SUPPRESSION_WEIGHT = 0.5f;
+    static const float SUPPRESSION_WEIGHT_FOR_PROBABILITY_GAIN = 0.1f;
+    static const float SKIP_PROBABALITY_WEIGHT_FOR_PROBABILITY_GAIN = 0.3f;
+
     const float keyWidthFloat = static_cast<float>(mProximityInfo->getMostCommonKeyWidth());
     const float diff = fabsf(static_cast<float>(mLengthCache[index0] - mLengthCache[index1]));
     if (diff > keyWidthFloat * SUPPRESSION_LENGTH_WEIGHT) {
         return false;
     }
-    // Summing up decreased amount of probabilities from 0%.
+    const float suppressionRate = MIN_SUPPRESSION_RATE
-    float sumOfAdjustedProbabilities = 0.0f;
+            + diff / keyWidthFloat / SUPPRESSION_LENGTH_WEIGHT * SUPPRESSION_WEIGHT;
-    const float suppressionRate = diff / keyWidthFloat / SUPPRESSION_LENGTH_WEIGHT;
     for (hash_map_compat<int, float>::iterator it = mCharProbabilities[index0].begin();
             it != mCharProbabilities[index0].end(); ++it) {
-        hash_map_compat<int, float>::const_iterator it2 =
+        hash_map_compat<int, float>::iterator it2 =  mCharProbabilities[index1].find(it->first);
-                mCharProbabilities[index1].find(it->first);
         if (it2 != mCharProbabilities[index1].end() && it->second < it2->second) {
             const float newProbability = it->second * suppressionRate;
-            sumOfAdjustedProbabilities += it->second - newProbability;
+            const float suppression = it->second - newProbability;
             it->second = newProbability;
+            // mCharProbabilities[index0][NOT_AN_INDEX] is the probability of skipping this point.
+            mCharProbabilities[index0][NOT_AN_INDEX] += suppression;
+
+            // Add the probability of the same key nearby index1
+            const float probabilityGain = min(suppression * SUPPRESSION_WEIGHT_FOR_PROBABILITY_GAIN,
+                    mCharProbabilities[index1][NOT_AN_INDEX]
+                            * SKIP_PROBABALITY_WEIGHT_FOR_PROBABILITY_GAIN);
+            it2->second += probabilityGain;
+            mCharProbabilities[index1][NOT_AN_INDEX] -= probabilityGain;
         }
     }
-    // All decreased amount of probabilities are added to the probability of skipping.
-    mCharProbabilities[index0][NOT_AN_INDEX] += sumOfAdjustedProbabilities;
     return true;
 }
 
 // Get a word that is detected by tracing highest probability sequence into charBuf and returns
 // probability of generating the word.
 float ProximityInfoState::getHighestProbabilitySequence(uint16_t *const charBuf) const {
-    int buf[mInputSize];
+    static const float LOG_PROBABILITY_MARGIN = 0.2f;
-    // Maximum probabilities of each point are multiplied to 100%.
+    int index = 0;
-    float probability = 1.0f;
+    float sumLogProbability = 0.0f;
     // TODO: Current implementation is greedy algorithm. DP would be efficient for many cases.
-    for (int i = 0; i < mInputSize; ++i) {
+    for (int i = 0; i < mInputSize && index < MAX_WORD_LENGTH_INTERNAL - 1; ++i) {
-        float maxProbability = 0.0f;
+        float minLogProbability = static_cast<float>(MAX_POINT_TO_KEY_LENGTH);
+        int character = NOT_AN_INDEX;
         for (hash_map_compat<int, float>::const_iterator it = mCharProbabilities[i].begin();
                 it != mCharProbabilities[i].end(); ++it) {
-            if (it->second > maxProbability) {
+            const float logProbability = (it->first != NOT_AN_INDEX)
-                maxProbability = it->second;
+                    ? it->second + LOG_PROBABILITY_MARGIN : it->second;
-                buf[i] = it->first;
+            if (logProbability < minLogProbability) {
+                minLogProbability = logProbability;
+                character = it->first;
             }
         }
-        probability *= maxProbability;
+        if (character != NOT_AN_INDEX) {
-    }
+            charBuf[index] = mProximityInfo->getCodePointOf(character);
-    int index = 0;
-    for (int i = 0; i < mInputSize && index < MAX_WORD_LENGTH_INTERNAL - 1; ++i) {
-        if (buf[i] != NOT_AN_INDEX) {
-            charBuf[index] = mProximityInfo->getCodePointOf(buf[i]);
             index++;
         }
+        sumLogProbability += minLogProbability;
     }
     charBuf[index] = '\0';
-    return probability;
+    return sumLogProbability;
+}
+
+// Returns a probability of mapping index to keyIndex.
+float ProximityInfoState::getProbability(const int index, const int keyIndex) const {
+    ASSERT(0 <= index && index < mInputSize);
+    hash_map_compat<int, float>::const_iterator it = mCharProbabilities[index].find(keyIndex);
+    if (it != mCharProbabilities[index].end()) {
+        return it->second;
+    }
+    return static_cast<float>(MAX_POINT_TO_KEY_LENGTH);
 }
 
 } // namespace latinime

native/jni/src/proximity_info_state.h

@@ -56,7 +56,8 @@ class ProximityInfoState {
               mKeyCount(0), mCellHeight(0), mCellWidth(0), mGridHeight(0), mGridWidth(0),
               mIsContinuationPossible(false), mInputXs(), mInputYs(), mTimes(), mInputIndice(),
               mDistanceCache(), mLengthCache(), mRelativeSpeeds(), mCharProbabilities(),
-              mNearKeysVector(), mTouchPositionCorrectionEnabled(false), mInputSize(0) {
+              mNearKeysVector(), mSearchKeysVector(),
+              mTouchPositionCorrectionEnabled(false), mInputSize(0) {
         memset(mInputCodes, 0, sizeof(mInputCodes));
         memset(mNormalizedSquaredDistances, 0, sizeof(mNormalizedSquaredDistances));
         memset(mPrimaryInputWord, 0, sizeof(mPrimaryInputWord));
@@ -214,7 +215,6 @@ class ProximityInfoState {
     }
 
     float getPointToKeyLength(const int inputIndex, const int charCode) const;
-
     float getPointToKeyByIdLength(const int inputIndex, const int keyId) const;
 
     int getSpaceY() const;
@@ -226,11 +226,21 @@ class ProximityInfoState {
         return mRelativeSpeeds[index];
     }
 
+    // get xy direction
+    float getDirection(const int x, const int y) const;
+
     float getPointAngle(const int index) const;
     // Returns angle of three points. x, y, and z are indices.
     float getPointsAngle(const int index0, const int index1, const int index2) const;
 
     float getHighestProbabilitySequence(uint16_t *const charBuf) const;
+
+    float getProbability(const int index, const int charCode) const;
+
+    float getLineToKeyDistance(
+            const int from, const int to, const int keyId, const bool extend) const;
+
+    bool isKeyInSerchKeysAfterIndex(const int index, const int keyId) const;
  private:
     DISALLOW_COPY_AND_ASSIGN(ProximityInfoState);
     typedef hash_map_compat<int, float> NearKeysDistanceMap;
@@ -243,7 +253,7 @@ class ProximityInfoState {
             const int keyIndex, const int inputIndex) const;
 
     bool pushTouchPoint(const int inputIndex, const int nodeChar, int x, int y, const int time,
-            const bool sample, const bool isLastPoint,
+            const bool sample, const bool isLastPoint, const float sumAngle,
             NearKeysDistanceMap *const currentNearKeysDistances,
             const NearKeysDistanceMap *const prevNearKeysDistances,
             const NearKeysDistanceMap *const prevPrevNearKeysDistances);
@@ -267,13 +277,13 @@ class ProximityInfoState {
             const NearKeysDistanceMap *const prevPrevNearKeysDistances) const;
     float getPointScore(
             const int x, const int y, const int time, const bool last, const float nearest,
-            const NearKeysDistanceMap *const currentNearKeysDistances,
+            const float sumAngle, const NearKeysDistanceMap *const currentNearKeysDistances,
             const NearKeysDistanceMap *const prevNearKeysDistances,
             const NearKeysDistanceMap *const prevPrevNearKeysDistances) const;
     bool checkAndReturnIsContinuationPossible(const int inputSize, const int *const xCoordinates,
             const int *const yCoordinates, const int *const times);
     void popInputData();
-    void updateAlignPointProbabilities();
+    void updateAlignPointProbabilities(const int start);
     bool suppressCharProbabilities(const int index1, const int index2);
 
     // const
@@ -298,7 +308,15 @@ class ProximityInfoState {
     std::vector<float> mRelativeSpeeds;
     // probabilities of skipping or mapping to a key for each point.
     std::vector<hash_map_compat<int, float> > mCharProbabilities;
+    // The vector for the key code set which holds nearby keys for each sampled input point
+    // 1. Used to calculate the probability of the key
+    // 2. Used to calculate mSearchKeysVector
     std::vector<NearKeycodesSet> mNearKeysVector;
+    // The vector for the key code set which holds nearby keys of some trailing sampled input points
+    // for each sampled input point. These nearby keys contain the next characters which can be in
+    // the dictionary. Specifically, currently we are looking for keys nearby trailing sampled
+    // inputs including the current input point.
+    std::vector<NearKeycodesSet> mSearchKeysVector;
     bool mTouchPositionCorrectionEnabled;
     int32_t mInputCodes[MAX_PROXIMITY_CHARS_SIZE_INTERNAL * MAX_WORD_LENGTH_INTERNAL];
     int mNormalizedSquaredDistances[MAX_PROXIMITY_CHARS_SIZE_INTERNAL * MAX_WORD_LENGTH_INTERNAL];