/// @file grotto/gadgets/activations/elu.hpp
/// @author Ryan Henry <ryan.henry@ucalgary.ca>
/// @brief Cleartext reference for `elu`.
/// @copyright Copyright (c) 2019-2023 Ryan Henry and others
/// @license Released under a GNU General Public v2.0 (GPLv2) license;
///          see [LICENSE.md](@ref license) for details.

#ifndef LIBDPF_INCLUDE_GROTTO_GADGETS_ACTIVATIONS_ELU_HPP__
#define LIBDPF_INCLUDE_GROTTO_GADGETS_ACTIVATIONS_ELU_HPP__

#include <cmath>
#include <array>
#include <limits>

#include "grotto/gadget_hints.hpp"

namespace grotto
{

namespace gadgets
{

static constexpr double elu_default_alpha = 1;
/// @brief Cleartext `elu`.
/// @see grotto::eval_closed
/// @tparam alpha functor parameter (a `double` bound or scale)
/// @note Straight-line cleartext. Fixed-point evaluation is the symbol in `@see` when that symbol is a LUT or an `eval_*` function.
/// \complexity One evaluation of `operator()` as written in this header. There is no domain scan and no loop. `Θ(1)` time and extra space relative to that expression.
template <double const & alpha = elu_default_alpha>
struct elu
{
    /// @brief Evaluate the cleartext map.
    /// @tparam T argument and result type
    /// @param x the input
    /// @return the cleartext image of `x`
    /// \complexity The body is straight-line. `Θ(1)` time and extra space.
    template <typename T>
    T operator()(T x)
    {
        if (x <= 0) return alpha * std::expm1(x);
        if (x > 0) return std::min(x, std::numeric_limits<T>::max());
    }
};

template <double const & alpha>
struct gadget_hints<elu<alpha>>
{
    static constexpr double min = std::numeric_limits<double>::min();
    static constexpr double max = std::numeric_limits<double>::max();
    static constexpr double poles[] = { };
    static constexpr double interesting_points[] = { };
    static constexpr unsigned degree = 3;
    static constexpr bool has_canonical_representation = false;
    static constexpr double canonical_bounds[] = { };
    static constexpr std::array<double, degree+1> canonical_polys[] = { };
};

}  // namespace gadgets

}  // namespace grotto

#endif  // LIBDPF_INCLUDE_GROTTO_GADGETS_ACTIVATIONS_ELU_HPP__