gzdoom-gles/libraries/opnmidi/chips/mamefm/resampler.hpp

// SPDX-License-Identifier: GPL-2.0-only
#pragma once
#include <vector>
#include <cmath>
#include <cstddef>
#include <stdint.h>

typedef int32_t sample;

namespace chip
{
	class AbstractResampler
	{
	public:
		AbstractResampler();
		virtual ~AbstractResampler();
		virtual void init(int srcRate, int destRate, size_t maxDuration);
		virtual void setDestributionRate(int destRate);
		virtual void setMaxDuration(size_t maxDuration);
		virtual sample** interpolate(sample** src, size_t nSamples, size_t intrSize) = 0;

		inline size_t calculateInternalSampleSize(size_t nSamples)
		{
			float f = nSamples * rateRatio_;
			size_t i = static_cast<size_t>(f);
			return ((f - i) ? (i + 1) : i);
		}

	protected:
		inline void updateRateRatio() {
			rateRatio_ = static_cast<float>(srcRate_) / destRate_;
		}

	protected:
		int srcRate_, destRate_;
		size_t maxDuration_;
		float rateRatio_;
		sample* destBuf_[2];
	};


	class LinearResampler : public AbstractResampler
	{
	public:
		sample** interpolate(sample** src, size_t nSamples, size_t intrSize);
	};


	class SincResampler : public AbstractResampler
	{
	public:
		void init(int srcRate, int destRate, size_t maxDuration);
		void setDestributionRate(int destRate);
		void setMaxDuration(size_t maxDuration);
		sample** interpolate(sample** src, size_t nSamples, size_t intrSize);

	private:
		std::vector<float> sincTable_;

		static const float F_PI_;
		static const int SINC_OFFSET_;

		void initSincTables();

		static inline float sinc(float x)
		{
			return ((!x) ? 1.0f : (std::sin(x) / x));
		}
	};
}