xref: /external/parameter-framework/upstream/parameter/LogarithmicParameterAdaptation.h

/*
 * Copyright (c) 2011-2015, Intel Corporation
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 * 2. Redistributions in binary form must reproduce the above copyright notice,
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 * may be used to endorse or promote products derived from this software without
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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#pragma once

#include "LinearParameterAdaptation.h"
#include <cmath>
#include <limits>

/**
 * This class is used to perform a logarithmic adapation of type:
 * (slopeNumerator / slopeDenominator) * log(parameter) + offset
 * Since log(x) == -INFINITY , we can define FloorValue as a
 *       x -> 0
 * a lower bound limit for the adaptation
 */
class CLogarithmicParameterAdaptation : public CLinearParameterAdaptation
{
public:
    CLogarithmicParameterAdaptation();

    /**
     * Conversions must satisfy the following: f(f'(a)) = a
     * Let f=fromUserValue and f'=toUserValue
     * if y = f(log(x)/log(base)), then
     * f'(y) * log(base) = log (x)
     * exp(f'(y)*log(base)) = x
     */
    virtual int64_t fromUserValue(double dValue) const;
    virtual double toUserValue(int64_t iValue) const;

    virtual void showProperties(std::string &strResult) const;

    virtual bool fromXml(const CXmlElement &xmlElement, CXmlSerializingContext &serializingContext);

private:
    /**
     * _dLogarithmBase characterizes the new logarithm logB(x) with
     * the following property: logB(x) = log(x) / log(_dLogarithmBase).
     * log being the base-e logarithm.
     *
     * std::exp(1) == e^1 == e == natural logarithm base
     * Make sure there is no precision lose by using std::exp overload that
     * return the same type as _dLogarithmBase
     */
    double _dLogarithmBase{std::exp(decltype(_dLogarithmBase){1})};
    /**
     * _dFloorValue reflects the lower bound for volume attenuation
     */
    double _dFloorValue{-std::numeric_limits<double>::infinity()};
};