Add LinearResampler implementation for clock recovery.

firmware/baseband/linear_resampler.hpp

@@ -0,0 +1,78 @@
+/*
+ * 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__*/