juce_Polynomial.h

/*
  ==============================================================================
 
   This file is part of the JUCE library.
   Copyright (c) 2022 - Raw Material Software Limited
 
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   licensing.
 
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   www.gnu.org/licenses).
 
   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
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  ==============================================================================
*/
 
namespace juce::dsp
{

template <typename FloatingType>
class Polynomial
{
public:
    //==============================================================================
    Polynomial()
    {
        coeffs.add (0);
    }

    Polynomial (const FloatingType* coefficients, int numCoefficients)
        : coeffs (coefficients, numCoefficients)
    {
        jassert (! coeffs.isEmpty());
    }

    Polynomial (const Polynomial&) = default;

    Polynomial (Polynomial&&) = default;

    Polynomial& operator= (const Polynomial&) = default;

    Polynomial& operator= (Polynomial&&) = default;

    template <typename... Values>
    Polynomial (Values... items)  : coeffs (items...)
    {
        jassert (! coeffs.isEmpty());
    }
 
    //==============================================================================
    FloatingType operator[] (int index) const noexcept              { return coeffs.getUnchecked (index); }

    FloatingType& operator[] (int index) noexcept                   { return coeffs.getReference (index); }

    FloatingType operator() (FloatingType x) const noexcept
    {
        // Horner's method
        FloatingType y (0);
 
        for (int i = coeffs.size(); --i >= 0;)
            y = (x * y) + coeffs.getUnchecked (i);
 
        return y;
    }

    int getOrder() noexcept
    {
        return coeffs.size() - 1;
    }
 
    //==============================================================================
    Polynomial<FloatingType> withGain (double gain) const
    {
        auto result = *this;
 
        for (auto& c : result.coeffs)
            c *= gain;
 
        return result;
    }

    Polynomial<FloatingType> getSumWith (const Polynomial<FloatingType>& other) const
    {
        if (coeffs.size() < other.coeffs.size())
            return other.getSumWith (*this);
 
        auto result = *this;
 
        for (int i = 0; i < other.coeffs.size(); ++i)
            result[i] += other[i];
 
        return result;
    }

    Polynomial<FloatingType> getProductWith (const Polynomial<FloatingType>& other) const
    {
        Polynomial<FloatingType> result;
        result.coeffs.clearQuick();
 
        auto N1 = coeffs.size();
        auto N2 = other.coeffs.size();
        auto Nmax = jmax (N1, N2);
 
        auto N = N1 + N2 - 1;
 
        for (int i = 0; i < N; ++i)
        {
            FloatingType value (0);
 
            for (int j = 0; j < Nmax; ++j)
                if (j >= 0 && j < N1 && i - j >= 0 && i - j < N2)
                    value = value + (*this)[j] * other[i - j];
 
            result.coeffs.add (value);
        }
 
        return result;
    }
 
private:
    //==============================================================================
    Array<FloatingType> coeffs;
 
    JUCE_LEAK_DETECTOR (Polynomial)
};
 
} // namespace juce::dsp