native/jni/src/suggest_utils.h

/*
 * 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