numeric.hpp

//
// Copyright 2019 Olzhas Zhumabek <anonymous.from.applecity@gmail.com>
//
// Use, modification and distribution are subject to the Boost Software License,
// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//
#ifndef BOOST_GIL_IMAGE_PROCESSING_NUMERIC_HPP
#define BOOST_GIL_IMAGE_PROCESSING_NUMERIC_HPP

#include <boost/gil/detail/math.hpp>
#include <cmath>

namespace boost { namespace gil {

inline double normalized_sinc(double x)
{
    return std::sin(x * boost::gil::pi) / (x * boost::gil::pi);
}

inline double lanczos(double x, std::ptrdiff_t a)
{
    // means == but <= avoids compiler warning
    if (0 <= x && x <= 0)
        return 1;

    if (-a < x && x < a)
        return normalized_sinc(x) / normalized_sinc(x / static_cast<double>(a));

    return 0;
}

}} // namespace boost::gil

#endif