Calculate edit distances incrementally.

Change-Id: I3ee734b9b71351523dc8658cba33d6c8435e348e

native/src/correction.cpp

@@ -27,6 +27,87 @@
 
 namespace latinime {
 
+/////////////////////////////
+// edit distance funcitons //
+/////////////////////////////
+
+#if 0 /* no longer used */
+inline static int editDistance(
+        int* editDistanceTable, const unsigned short* input,
+        const int inputLength, const unsigned short* output, const int outputLength) {
+    // dp[li][lo] dp[a][b] = dp[ a * lo + b]
+    int* dp = editDistanceTable;
+    const int li = inputLength + 1;
+    const int lo = outputLength + 1;
+    for (int i = 0; i < li; ++i) {
+        dp[lo * i] = i;
+    }
+    for (int i = 0; i < lo; ++i) {
+        dp[i] = i;
+    }
+
+    for (int i = 0; i < li - 1; ++i) {
+        for (int j = 0; j < lo - 1; ++j) {
+            const uint32_t ci = Dictionary::toBaseLowerCase(input[i]);
+            const uint32_t co = Dictionary::toBaseLowerCase(output[j]);
+            const uint16_t cost = (ci == co) ? 0 : 1;
+            dp[(i + 1) * lo + (j + 1)] = min(dp[i * lo + (j + 1)] + 1,
+                    min(dp[(i + 1) * lo + j] + 1, dp[i * lo + j] + cost));
+            if (i > 0 && j > 0 && ci == Dictionary::toBaseLowerCase(output[j - 1])
+                    && co == Dictionary::toBaseLowerCase(input[i - 1])) {
+                dp[(i + 1) * lo + (j + 1)] = min(
+                        dp[(i + 1) * lo + (j + 1)], dp[(i - 1) * lo + (j - 1)] + cost);
+            }
+        }
+    }
+
+    if (DEBUG_EDIT_DISTANCE) {
+        LOGI("IN = %d, OUT = %d", inputLength, outputLength);
+        for (int i = 0; i < li; ++i) {
+            for (int j = 0; j < lo; ++j) {
+                LOGI("EDIT[%d][%d], %d", i, j, dp[i * lo + j]);
+            }
+        }
+    }
+    return dp[li * lo - 1];
+}
+#endif
+
+inline static void initEditDistance(int *editDistanceTable) {
+    for (int i = 0; i <= MAX_WORD_LENGTH_INTERNAL; ++i) {
+        editDistanceTable[i] = i;
+    }
+}
+
+inline static void calcEditDistanceOneStep(int *editDistanceTable, const unsigned short *input,
+        const int inputLength, const unsigned short *output, const int outputLength) {
+    // Let dp[i][j] be editDistanceTable[i * (inputLength + 1) + j].
+    // Assuming that dp[0][0] ... dp[outputLength - 1][inputLength] are already calculated,
+    // and calculate dp[ouputLength][0] ... dp[outputLength][inputLength].
+    int *const current = editDistanceTable + outputLength * (inputLength + 1);
+    const int *const prev = editDistanceTable + (outputLength - 1) * (inputLength + 1);
+    const int *const prevprev =
+            outputLength >= 2 ? editDistanceTable + (outputLength - 2) * (inputLength + 1) : NULL;
+    current[0] = outputLength;
+    const uint32_t co = Dictionary::toBaseLowerCase(output[outputLength - 1]);
+    const uint32_t prevCO =
+            outputLength >= 2 ? Dictionary::toBaseLowerCase(output[outputLength - 2]) : 0;
+    for (int i = 1; i <= inputLength; ++i) {
+        const uint32_t ci = Dictionary::toBaseLowerCase(input[i - 1]);
+        const uint16_t cost = (ci == co) ? 0 : 1;
+        current[i] = min(current[i - 1] + 1, min(prev[i] + 1, prev[i - 1] + cost));
+        if (i >= 2 && prevprev && ci == prevCO
+                && co == Dictionary::toBaseLowerCase(input[i - 2])) {
+            current[i] = min(current[i], prevprev[i - 2] + 1);
+        }
+    }
+}
+
+inline static int getCurrentEditDistance(
+        int *editDistanceTable, const int inputLength, const int outputLength) {
+    return editDistanceTable[(inputLength + 1) * (outputLength + 1) - 1];
+}
+
 //////////////////////
 // inline functions //
 //////////////////////
@@ -43,6 +124,7 @@ inline bool Correction::isQuote(const unsigned short c) {
 
 Correction::Correction(const int typedLetterMultiplier, const int fullWordMultiplier)
         : TYPED_LETTER_MULTIPLIER(typedLetterMultiplier), FULL_WORD_MULTIPLIER(fullWordMultiplier) {
+    initEditDistance(mEditDistanceTable);
 }
 
 void Correction::initCorrection(const ProximityInfo *pi, const int inputLength,
@@ -197,13 +279,21 @@ void Correction::startToTraverseAllNodes() {
 }
 
 bool Correction::needsToPrune() const {
+    // TODO: use edit distance here
     return mOutputIndex - 1 >= mMaxDepth || mProximityCount > mMaxEditDistance;
 }
 
+void Correction::addCharToCurrentWord(const int32_t c) {
+    mWord[mOutputIndex] = c;
+    const unsigned short *primaryInputWord = mProximityInfo->getPrimaryInputWord();
+    calcEditDistanceOneStep(mEditDistanceTable, primaryInputWord, mInputLength,
+            mWord, mOutputIndex + 1);
+}
+
 // TODO: inline?
 Correction::CorrectionType Correction::processSkipChar(
         const int32_t c, const bool isTerminal, const bool inputIndexIncremented) {
-    mWord[mOutputIndex] = c;
+    addCharToCurrentWord(c);
     if (needsToTraverseAllNodes() && isTerminal) {
         mTerminalInputIndex = mInputIndex - (inputIndexIncremented ? 1 : 0);
         mTerminalOutputIndex = mOutputIndex;
@@ -412,7 +502,7 @@ Correction::CorrectionType Correction::processCharAndCalcState(
                 mProximityInfo->getNormalizedSquaredDistance(mInputIndex, proximityIndex);
     }
 
-    mWord[mOutputIndex] = c;
+    addCharToCurrentWord(c);
 
     // 4. Last char excessive correction
     mLastCharExceeded = mExcessiveCount == 0 && mSkippedCount == 0 && mTransposedCount == 0
@@ -526,47 +616,6 @@ inline static bool isUpperCase(unsigned short c) {
      return false;
 }
 
-/* static */
-inline static int editDistance(
-        int* editDistanceTable, const unsigned short* input,
-        const int inputLength, const unsigned short* output, const int outputLength) {
-    // dp[li][lo] dp[a][b] = dp[ a * lo + b]
-    int* dp = editDistanceTable;
-    const int li = inputLength + 1;
-    const int lo = outputLength + 1;
-    for (int i = 0; i < li; ++i) {
-        dp[lo * i] = i;
-    }
-    for (int i = 0; i < lo; ++i) {
-        dp[i] = i;
-    }
-
-    for (int i = 0; i < li - 1; ++i) {
-        for (int j = 0; j < lo - 1; ++j) {
-            const uint32_t ci = Dictionary::toBaseLowerCase(input[i]);
-            const uint32_t co = Dictionary::toBaseLowerCase(output[j]);
-            const uint16_t cost = (ci == co) ? 0 : 1;
-            dp[(i + 1) * lo + (j + 1)] = min(dp[i * lo + (j + 1)] + 1,
-                    min(dp[(i + 1) * lo + j] + 1, dp[i * lo + j] + cost));
-            if (i > 0 && j > 0 && ci == Dictionary::toBaseLowerCase(output[j - 1])
-                    && co == Dictionary::toBaseLowerCase(input[i - 1])) {
-                dp[(i + 1) * lo + (j + 1)] = min(
-                        dp[(i + 1) * lo + (j + 1)], dp[(i - 1) * lo + (j - 1)] + cost);
-            }
-        }
-    }
-
-    if (DEBUG_EDIT_DISTANCE) {
-        LOGI("IN = %d, OUT = %d", inputLength, outputLength);
-        for (int i = 0; i < li; ++i) {
-            for (int j = 0; j < lo; ++j) {
-                LOGI("EDIT[%d][%d], %d", i, j, dp[i * lo + j]);
-            }
-        }
-    }
-    return dp[li * lo - 1];
-}
-
 //////////////////////
 // RankingAlgorithm //
 //////////////////////
@@ -612,9 +661,7 @@ int Correction::RankingAlgorithm::calculateFinalFreq(const int inputIndex, const
     // TODO: Optimize this.
     // TODO: Ignoring edit distance for transposed char, for now
     if (transposedCount == 0 && (proximityMatchedCount > 0 || skipped || excessiveCount > 0)) {
-        const unsigned short* primaryInputWord = proximityInfo->getPrimaryInputWord();
+        ed = getCurrentEditDistance(editDistanceTable, inputLength, outputIndex + 1);
-        ed = editDistance(editDistanceTable, primaryInputWord,
-                inputLength, word, outputIndex + 1);
         const int matchWeight = powerIntCapped(typedLetterMultiplier,
                 max(inputLength, outputIndex + 1) - ed);
         multiplyIntCapped(matchWeight, &finalFreq);

native/src/correction.h

@@ -102,6 +102,7 @@ private:
     inline bool isQuote(const unsigned short c);
     inline CorrectionType processSkipChar(
             const int32_t c, const bool isTerminal, const bool inputIndexIncremented);
+    inline void addCharToCurrentWord(const int32_t c);
 
     const int TYPED_LETTER_MULTIPLIER;
     const int FULL_WORD_MULTIPLIER;