/*
  ==============================================================================

   This file is part of the JUCE 6 technical preview.
   Copyright (c) 2020 - Raw Material Software Limited

   You may use this code under the terms of the GPL v3
   (see www.gnu.org/licenses).

   For this technical preview, this file is not subject to commercial licensing.

   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.

  ==============================================================================
*/

namespace juce
{
namespace dsp
{

/**
    This class contains various fast mathematical function approximations.

    @tags{DSP}
*/
struct FastMathApproximations
{
    /** Provides a fast approximation of the function cosh(x) using a Pade approximant
        continued fraction, calculated sample by sample.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -5 and +5 for limiting the error.
    */
    template <typename FloatType>
    static FloatType cosh (FloatType x) noexcept
    {
        auto x2 = x * x;
        auto numerator = -(39251520 + x2 * (18471600 + x2 * (1075032 + 14615 * x2)));
        auto denominator = -39251520 + x2 * (1154160 + x2 * (-16632 + 127 * x2));
        return numerator / denominator;
    }

    /** Provides a fast approximation of the function cosh(x) using a Pade approximant
        continued fraction, calculated on a whole buffer.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -5 and +5 for limiting the error.
    */
    template <typename FloatType>
    static void cosh (FloatType* values, size_t numValues) noexcept
    {
        for (size_t i = 0; i < numValues; ++i)
            values[i] = FastMathApproximations::cosh (values[i]);
    }

    /** Provides a fast approximation of the function sinh(x) using a Pade approximant
        continued fraction, calculated sample by sample.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -5 and +5 for limiting the error.
    */
    template <typename FloatType>
    static FloatType sinh (FloatType x) noexcept
    {
        auto x2 = x * x;
        auto numerator = -x * (11511339840 + x2 * (1640635920 + x2 * (52785432 + x2 * 479249)));
        auto denominator = -11511339840 + x2 * (277920720 + x2 * (-3177720 + x2 * 18361));
        return numerator / denominator;
    }

    /** Provides a fast approximation of the function sinh(x) using a Pade approximant
        continued fraction, calculated on a whole buffer.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -5 and +5 for limiting the error.
    */
    template <typename FloatType>
    static void sinh (FloatType* values, size_t numValues) noexcept
    {
        for (size_t i = 0; i < numValues; ++i)
            values[i] = FastMathApproximations::sinh (values[i]);
    }

    /** Provides a fast approximation of the function tanh(x) using a Pade approximant
        continued fraction, calculated sample by sample.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -5 and +5 for limiting the error.
    */
    template <typename FloatType>
    static FloatType tanh (FloatType x) noexcept
    {
        auto x2 = x * x;
        auto numerator = x * (135135 + x2 * (17325 + x2 * (378 + x2)));
        auto denominator = 135135 + x2 * (62370 + x2 * (3150 + 28 * x2));
        return numerator / denominator;
    }

    /** Provides a fast approximation of the function tanh(x) using a Pade approximant
        continued fraction, calculated on a whole buffer.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -5 and +5 for limiting the error.
    */
    template <typename FloatType>
    static void tanh (FloatType* values, size_t numValues) noexcept
    {
        for (size_t i = 0; i < numValues; ++i)
            values[i] = FastMathApproximations::tanh (values[i]);
    }

    //==============================================================================
    /** Provides a fast approximation of the function cos(x) using a Pade approximant
        continued fraction, calculated sample by sample.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -pi and +pi for limiting the error.
    */
    template <typename FloatType>
    static FloatType cos (FloatType x) noexcept
    {
        auto x2 = x * x;
        auto numerator = -(-39251520 + x2 * (18471600 + x2 * (-1075032 + 14615 * x2)));
        auto denominator = 39251520 + x2 * (1154160 + x2 * (16632 + x2 * 127));
        return numerator / denominator;
    }

    /** Provides a fast approximation of the function cos(x) using a Pade approximant
        continued fraction, calculated on a whole buffer.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -pi and +pi for limiting the error.
    */
    template <typename FloatType>
    static void cos (FloatType* values, size_t numValues) noexcept
    {
        for (size_t i = 0; i < numValues; ++i)
            values[i] = FastMathApproximations::cos (values[i]);
    }

    /** Provides a fast approximation of the function sin(x) using a Pade approximant
        continued fraction, calculated sample by sample.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -pi and +pi for limiting the error.
    */
    template <typename FloatType>
    static FloatType sin (FloatType x) noexcept
    {
        auto x2 = x * x;
        auto numerator = -x * (-11511339840 + x2 * (1640635920 + x2 * (-52785432 + x2 * 479249)));
        auto denominator = 11511339840 + x2 * (277920720 + x2 * (3177720 + x2 * 18361));
        return numerator / denominator;
    }

    /** Provides a fast approximation of the function sin(x) using a Pade approximant
        continued fraction, calculated on a whole buffer.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -pi and +pi for limiting the error.
    */
    template <typename FloatType>
    static void sin (FloatType* values, size_t numValues) noexcept
    {
        for (size_t i = 0; i < numValues; ++i)
            values[i] = FastMathApproximations::sin (values[i]);
    }

    /** Provides a fast approximation of the function tan(x) using a Pade approximant
        continued fraction, calculated sample by sample.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -pi/2 and +pi/2 for limiting the error.
    */
    template <typename FloatType>
    static FloatType tan (FloatType x) noexcept
    {
        auto x2 = x * x;
        auto numerator = x * (-135135 + x2 * (17325 + x2 * (-378 + x2)));
        auto denominator = -135135 + x2 * (62370 + x2 * (-3150 + 28 * x2));
        return numerator / denominator;
    }

    /** Provides a fast approximation of the function tan(x) using a Pade approximant
        continued fraction, calculated on a whole buffer.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -pi/2 and +pi/2 for limiting the error.
    */
    template <typename FloatType>
    static void tan (FloatType* values, size_t numValues) noexcept
    {
        for (size_t i = 0; i < numValues; ++i)
            values[i] = FastMathApproximations::tan (values[i]);
    }

    //==============================================================================
    /** Provides a fast approximation of the function exp(x) using a Pade approximant
        continued fraction, calculated sample by sample.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -6 and +4 for limiting the error.
    */
    template <typename FloatType>
    static FloatType exp (FloatType x) noexcept
    {
        auto numerator = 1680 + x * (840 + x * (180 + x * (20 + x)));
        auto denominator = 1680 + x *(-840 + x * (180 + x * (-20 + x)));
        return numerator / denominator;
    }

    /** Provides a fast approximation of the function exp(x) using a Pade approximant
        continued fraction, calculated on a whole buffer.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -6 and +4 for limiting the error.
    */
    template <typename FloatType>
    static void exp (FloatType* values, size_t numValues) noexcept
    {
        for (size_t i = 0; i < numValues; ++i)
            values[i] = FastMathApproximations::exp (values[i]);
    }

    /** Provides a fast approximation of the function log(x+1) using a Pade approximant
        continued fraction, calculated sample by sample.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -0.8 and +5 for limiting the error.
    */
    template <typename FloatType>
    static FloatType logNPlusOne (FloatType x) noexcept
    {
        auto numerator = x * (7560 + x * (15120 + x * (9870 + x * (2310 + x * 137))));
        auto denominator = 7560 + x * (18900 + x * (16800 + x * (6300 + x * (900 + 30 * x))));
        return numerator / denominator;
    }

    /** Provides a fast approximation of the function log(x+1) using a Pade approximant
        continued fraction, calculated on a whole buffer.

        Note: This is an approximation which works on a limited range. You are
        advised to use input values only between -0.8 and +5 for limiting the error.
    */
    template <typename FloatType>
    static void logNPlusOne (FloatType* values, size_t numValues) noexcept
    {
        for (size_t i = 0; i < numValues; ++i)
            values[i] = FastMathApproximations::logNPlusOne (values[i]);
    }
};

} // namespace dsp
} // namespace juce