log.h

#pragma once

#include <funcy/concepts.h>
#include <funcy/util/chainer.h>
#include <funcy/util/exceptions.h>
#include <funcy/util/macros.h>

#include <cmath>

namespace funcy
{
    struct LN : Chainer< LN >
    {
        explicit LN( double x = 1. ) FUNCY_NOEXCEPT
        {
            update( x );
        }

        void update( double x ) FUNCY_NOEXCEPT
        {
#ifdef FUNCY_ENABLE_EXCEPTIONS
            if ( x <= 0 )
                throw OutOfDomainException( "LN", "]0,inf[", x, __FILE__, __LINE__ );
#endif
            x_inv = 1. / x;
            value = ::log( x );
        }

        [[nodiscard]] double d0() const noexcept
        {
            return value;
        }

        [[nodiscard]] double d1( double dx = 1. ) const noexcept
        {
            return x_inv * dx;
        }

        [[nodiscard]] double d2( double dx = 1., double dy = 1. ) const noexcept
        {
            return -x_inv * x_inv * dx * dy;
        }

        [[nodiscard]] double d3( double dx = 1., double dy = 1., double dz = 1. ) const noexcept
        {
            return 2 * x_inv * x_inv * x_inv * dx * dy * dz;
        }

    private:
        double value = 0., x_inv = 1.;
    };

    struct Log10 : Chainer< Log10 >
    {
        explicit Log10( double x = 1. ) FUNCY_NOEXCEPT
        {
            update( x );
        }

        void update( double x ) FUNCY_NOEXCEPT
        {
#ifdef FUNCY_ENABLE_EXCEPTIONS
            if ( x <= 0 )
                throw OutOfDomainException( "Log10", "]0,inf[", x, __FILE__, __LINE__ );
#endif
            x_inv = 1. / x;
            value = ::log10( x );
        }

        [[nodiscard]] double d0() const noexcept
        {
            return value;
        }

        [[nodiscard]] double d1( double dx = 1. ) const noexcept
        {
            return ln10inv * x_inv * dx;
        }

        [[nodiscard]] double d2( double dx = 1., double dy = 1. ) const noexcept
        {
            return -ln10inv * x_inv * x_inv * dx * dy;
        }

        [[nodiscard]] double d3( double dx = 1., double dy = 1., double dz = 1. ) const noexcept
        {
            return 2 * ln10inv * x_inv * x_inv * x_inv * dx * dy * dz;
        }

    private:
        double value = 0., x_inv = 1., ln10inv = 1 / log( 10. );
    };

    struct Log2 : Chainer< Log2 >
    {
        explicit Log2( double x = 1. ) FUNCY_NOEXCEPT
        {
            update( x );
        }

        void update( double x ) FUNCY_NOEXCEPT
        {
#ifdef FUNCY_ENABLE_EXCEPTIONS
            if ( x <= 0 )
                throw OutOfDomainException( "Log2", "]0,inf[", x, __FILE__, __LINE__ );
#endif
            x_inv = 1. / x;
            value = ::log2( x );
        }

        [[nodiscard]] double d0() const noexcept
        {
            return value;
        }

        [[nodiscard]] double d1( double dx = 1. ) const noexcept
        {
            return ln2inv * x_inv * dx;
        }

        [[nodiscard]] double d2( double dx = 1., double dy = 1. ) const noexcept
        {
            return -ln2inv * x_inv * x_inv * dx * dy;
        }

        [[nodiscard]] double d3( double dx = 1., double dy = 1., double dz = 1. ) const noexcept
        {
            return 2 * ln2inv * x_inv * x_inv * x_inv * dx * dy * dz;
        }

    private:
        double value = 0., x_inv = 1., ln2inv = 1 / log( 2. );
    };

    [[nodiscard]] inline auto ln( double x )
    {
        return LN( x )();
    }

    template < Function F >
    [[nodiscard]] auto ln( const F& f )
    {
        return LN()( f );
    }

    template < Function F >
    [[nodiscard]] auto log10( const F& f )
    {
        return Log10()( f );
    }

    template < Function F >
    [[nodiscard]] auto log2( const F& f )
    {
        return Log2()( f );
    }
} // namespace funcy