refactor distance cache
Change-Id: I21b54b356641a63d7be17fd34b9ede7a63ec738a
diff --git a/native/jni/src/suggest_utils.h b/native/jni/src/suggest_utils.h
new file mode 100644
index 0000000..a3b3c12
--- /dev/null
+++ b/native/jni/src/suggest_utils.h
@@ -0,0 +1,53 @@
+/*
+ * 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.
+ */
+
+#ifndef LATINIME_SUGGEST_UTILS_H
+#define LATINIME_SUGGEST_UTILS_H
+
+#include "defines.h"
+
+namespace latinime {
+class SuggestUtils {
+ public:
+ static float getDistanceScalingFactor(float normalizedSquaredDistance) {
+ if (normalizedSquaredDistance < 0.0f) {
+ return -1.0f;
+ }
+ // 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 MIN = 0.3f;
+ static const float R1 = NEUTRAL_SCORE_SQUARED_RADIUS;
+ static const float R2 = HALF_SCORE_SQUARED_RADIUS;
+ const float x = static_cast<float>(normalizedSquaredDistance)
+ / ProximityInfoState::NORMALIZED_SQUARED_DISTANCE_SCALING_FACTOR;
+ const float factor = max((x < R1)
+ ? (A * (R1 - x) + B * x) / R1
+ : (B * (R2 - x) + C * (x - R1)) / (R2 - R1), MIN);
+ // factor is a piecewise linear function like:
+ // A -_ .
+ // ^-_ .
+ // B \ .
+ // \_ .
+ // C ------------.
+ // .
+ // 0 R1 R2 .
+ return factor;
+ }
+};
+} // namespace latinime
+#endif // LATINIME_SUGGEST_UTILS_H