tetrees/Plugins/Wwise/Source/AkAudio/Classes/GTE/Mathematics/LogEstimate.h

// David Eberly, Geometric Tools, Redmond WA 98052
// Copyright (c) 1998-2020
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt
// https://www.geometrictools.com/License/Boost/LICENSE_1_0.txt
// Version: 4.0.2019.12.23

#pragma once

#include <Mathematics/Log2Estimate.h>

// Minimax polynomial approximations to log2(x).  The polynomial p(x) of
// degree D minimizes the quantity maximum{|log2(x) - p(x)| : x in [1,2]}
// over all polynomials of degree D.  The natural logarithm is computed
// using log(x) = log2(x)/log2(e) = log2(x)*log(2).

namespace WwiseGTE
{
    template <typename Real>
    class LogEstimate
    {
    public:
        // The input constraint is x in [1,2].  For example,
        //   float x; // in [1,2]
        //   float result = LogEstimate<float>::Degree<3>(x);
        template <int D>
        inline static Real Degree(Real x)
        {
            return Log2Estimate<Real>::Degree<D>(x) * (Real)GTE_C_LN_2;
        }

        // The input constraint is x > 0.  Range reduction is used to generate
        // a value y in (0,1], call Degree(y), and add the exponent for the
        // power of two in the binary scientific representation of x.  For
        // example,
        //   float x;  // x > 0
        //   float result = LogEstimate<float>::DegreeRR<3>(x);
        template <int D>
        inline static Real DegreeRR(Real x)
        {
            return Log2Estimate<Real>::DegreeRR<D>(x) * (Real)GTE_C_LN_2;
        }
    };
}