libcruft-util/cruft/util/polynomial.hpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2015 Danny Robson <danny@nerdcruft.net>
 */

#ifndef CRUFT_UTIL_POLYNOMIAL_HPP
#define CRUFT_UTIL_POLYNOMIAL_HPP

#include <array>
#include <cstdlib>

namespace cruft::polynomial {
    // Invalid solutions are represented by NaN. They are guaranteed to
    // be at the end of the solution list, so they are safe to skip on the
    // first instance.
    template <size_t S>
    std::array<float,S>
    roots (std::array<float,S+1>);

    template <size_t S, typename T, typename U>
    T
    eval (std::array<T,S> coeffs, U x)
    {
        U x_ = 1.f;
        T sum {0.f};

        for (size_t i = 0; i < S; ++i) {
            sum += coeffs[S-i-1] * x_;
            x_ *= x;
        }

        return sum;
    }
}

#endif