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:
	constexpr LinearResampler(
		const float input_rate,
		const float output_rate
	) : last_sample { 0.0f },
		phase { 0.0f },
		phase_increment { calculate_increment(input_rate, output_rate) }
	{
	}

	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);
			advance();
		}
		last_sample = sample;
		phase -= 1.0f;
	}

	void advance(const float fraction = 1.0f) {
		phase += (fraction * phase_increment);
	}

private:
	float last_sample;
	float phase;
	float phase_increment;

	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__*/