portapack-mayhem/firmware/baseband/linear_resampler.hpp

/*
 * Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
 *
 * This file is part of PortaPack.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#ifndef __LINEAR_RESAMPLER_H__
#define __LINEAR_RESAMPLER_H__

namespace dsp {
namespace interpolation {

class LinearResampler {
   public:
    void configure(
        const float input_rate,
        const float output_rate) {
        phase_increment = calculate_increment(input_rate, output_rate);
    }

    template <typename InterpolatedSampleHandler>
    void operator()(
        const float sample,
        InterpolatedSampleHandler interpolated_sample_handler) {
        const float sample_delta = sample - last_sample;
        while (phase < 1.0f) {
            const float interpolated_value = last_sample + phase * sample_delta;
            interpolated_sample_handler(interpolated_value);
            phase += phase_increment;
        }
        last_sample = sample;
        phase -= 1.0f;
    }

    void advance(const float fraction) {
        phase += (fraction * phase_increment);
    }

   private:
    float last_sample{0.0f};
    float phase{0.0f};
    float phase_increment{0.0f};

    static constexpr float calculate_increment(const float input_rate, const float output_rate) {
        return input_rate / output_rate;
    }
};

} /* namespace interpolation */
} /* namespace dsp */

#endif /*__LINEAR_RESAMPLER_H__*/