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/*
* Copyright (C) 2016 The CyanogenMod 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.
*/
package org.lineageos.internal.util;
public final class MathUtils {
/**
* Given a range of values which change continuously in a non-linear way,
* we can map back and forth to a linear scale using some quadratic equations.
*
* The linear scale ranges from 0 -> 1. This method will calculate the
* coefficients needed to solve the conversion functions in the next two methods.
*
* lower = actual value when linear value = 0
* mid = actual value when linear value = .5
* upper actual value when linear value = 1
*
* @param lower
* @param mid
* @param upper
* @return array of coefficients
*/
public static double[] powerCurve(double lower, double mid, double upper) {
final double[] curve = new double[3];
curve[0] = ((lower * upper) - (mid * mid)) / (lower - (2 * mid) + upper);
curve[1] = Math.pow((mid - lower), 2) / (lower - (2 * mid) + upper);
curve[2] = 2 * Math.log((upper - mid) / (mid - lower));
return curve;
}
/**
* Map a value on a power curve to a linear value
*
* @param curve obtained from powerCurve()
* @param value to convert to linear scale
* @return linear value from 0 -> 1
*/
public static double powerCurveToLinear(final double[] curve, double value) {
return Math.log((value - curve[0]) / curve[1]) / curve[2];
}
/**
* Map a value on a linear scale to a value on a power curve
*
* @param curve obtained from powerCurve()
* @param value from 0 -> 1 to map onto power curve
* @return actual value on the given curve
*/
public static double linearToPowerCurve(final double[] curve, double value) {
return curve[0] + curve[1] * Math.exp(curve[2] * value);
}
}
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