/*

 * Copyright 2016 Google Inc.

 *

 * 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 "guetzli/score.h"

#include <cmath>

namespace guetzli {

double ScoreJPEG(double butteraugli_distance, int size,

                 double butteraugli_target) {

  constexpr double kScale = 50;

  constexpr double kMaxExponent = 10;

  constexpr double kLargeSize = 1e30;

  // TODO(user): The score should also depend on distance below target (and be

  // smooth).

  double diff = butteraugli_distance - butteraugli_target;

  if (diff <= 0.0) {

    return size;

  } else {

    double exponent = kScale * diff;

    if (exponent > kMaxExponent) {

      return kLargeSize * std::exp(kMaxExponent) * diff + size;

    } else {

      return std::exp(exponent) * size;

    }

  }

}

}  // namespace guetzli