Add spellcheck and word suggestion to the prediction service

third_party/android_prediction/utils/autocorrection_threshold_utils.cpp

+/*
+ * 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 "third_party/android_prediction/utils/autocorrection_threshold_utils.h"
+
+#include <algorithm>
+#include <cmath>
+
+#include "third_party/android_prediction/defines.h"
+#include "third_party/android_prediction/suggest/policyimpl/utils/edit_distance.h"
+#include "third_party/android_prediction/suggest/policyimpl/utils/damerau_levenshtein_edit_distance_policy.h"
+
+namespace latinime {
+
+const int AutocorrectionThresholdUtils::MAX_INITIAL_SCORE = 255;
+const int AutocorrectionThresholdUtils::TYPED_LETTER_MULTIPLIER = 2;
+const int AutocorrectionThresholdUtils::FULL_WORD_MULTIPLIER = 2;
+
+/* static */ int AutocorrectionThresholdUtils::editDistance(const int *before,
+        const int beforeLength, const int *after, const int afterLength) {
+    const DamerauLevenshteinEditDistancePolicy daemaruLevenshtein(
+            before, beforeLength, after, afterLength);
+    return static_cast<int>(EditDistance::getEditDistance(&daemaruLevenshtein));
+}
+
+// In dictionary.cpp, getSuggestion() method,
+// When USE_SUGGEST_INTERFACE_FOR_TYPING is true:
+//
+//   // TODO: Revise the following logic thoroughly by referring to the logic
+//   // marked as "Otherwise" below.
+//   SUGGEST_INTERFACE_OUTPUT_SCALE was multiplied to the original suggestion scores to convert
+//   them to integers.
+//     score = (int)((original score) * SUGGEST_INTERFACE_OUTPUT_SCALE)
+//   Undo the scaling here to recover the original score.
+//     normalizedScore = ((float)score) / SUGGEST_INTERFACE_OUTPUT_SCALE
+//
+// Otherwise: suggestion scores are computed using the below formula.
+// original score
+//  := powf(mTypedLetterMultiplier (this is defined 2),
+//         (the number of matched characters between typed word and suggested word))
+//     * (individual word's score which defined in the unigram dictionary,
+//         and this score is defined in range [0, 255].)
+// Then, the following processing is applied.
+//     - If the dictionary word is matched up to the point of the user entry
+//       (full match up to min(before.length(), after.length())
+//       => Then multiply by FULL_MATCHED_WORDS_PROMOTION_RATE (this is defined 1.2)
+//     - If the word is a true full match except for differences in accents or
+//       capitalization, then treat it as if the score was 255.
+//     - If before.length() == after.length()
+//       => multiply by mFullWordMultiplier (this is defined 2))
+// So, maximum original score is powf(2, min(before.length(), after.length())) * 255 * 2 * 1.2
+// For historical reasons we ignore the 1.2 modifier (because the measure for a good
+// autocorrection threshold was done at a time when it didn't exist). This doesn't change
+// the result.
+// So, we can normalize original score by dividing powf(2, min(b.l(),a.l())) * 255 * 2.
+
+/* static */ float AutocorrectionThresholdUtils::calcNormalizedScore(const int *before,
+        const int beforeLength, const int *after, const int afterLength, const int score) {
+    if (0 == beforeLength || 0 == afterLength) {
+        return 0.0f;
+    }
+    const int distance = editDistance(before, beforeLength, after, afterLength);
+    int spaceCount = 0;
+    for (int i = 0; i < afterLength; ++i) {
+        if (after[i] == KEYCODE_SPACE) {
+            ++spaceCount;
+        }
+    }
+
+    if (spaceCount == afterLength) {
+        return 0.0f;
+    }
+
+    if (score <= 0 || distance >= afterLength) {
+        // normalizedScore must be 0.0f (the minimum value) if the score is less than or equal to 0,
+        // or if the edit distance is larger than or equal to afterLength.
+        return 0.0f;
+    }
+    // add a weight based on edit distance.
+    const float weight = 1.0f - static_cast<float>(distance) / static_cast<float>(afterLength);
+
+    // TODO: Revise the following logic thoroughly by referring to...
+    if (true /* USE_SUGGEST_INTERFACE_FOR_TYPING */) {
+        return (static_cast<float>(score) / SUGGEST_INTERFACE_OUTPUT_SCALE) * weight;
+    }
+    // ...this logic.
+    const float maxScore = score >= S_INT_MAX ? static_cast<float>(S_INT_MAX)
+            : static_cast<float>(MAX_INITIAL_SCORE)
+                    * powf(static_cast<float>(TYPED_LETTER_MULTIPLIER),
+                            static_cast<float>(std::min(beforeLength, afterLength - spaceCount)))
+                    * static_cast<float>(FULL_WORD_MULTIPLIER);
+
+    return (static_cast<float>(score) / maxScore) * weight;
+}
+
+} // namespace latinime