premiere-libtorrent/include/libtorrent/timestamp_history.hpp

/*

Copyright (c) 2009-2016, Arvid Norberg
All rights reserved.

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      from this software without specific prior written permission.

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*/

#ifndef TIMESTAMP_HISTORY_HPP
#define TIMESTAMP_HISTORY_HPP

#include <cstdint>

#include "libtorrent/config.hpp"
#include "libtorrent/assert.hpp"

namespace libtorrent {

// timestamp history keeps a history of the lowest timestamps we've
// seen in the last 20 minutes
struct TORRENT_EXTRA_EXPORT timestamp_history
{
	static constexpr int history_size = 20;

	timestamp_history() : m_base(0), m_index(0), m_num_samples(not_initialized) {}
	bool initialized() const { return m_num_samples != not_initialized; }

	// add a sample to the timestamp history. If step is true, it's been
	// a minute since the last step
	std::uint32_t add_sample(std::uint32_t sample, bool step);
	std::uint32_t base() const { TORRENT_ASSERT(initialized()); return m_base; }
	void adjust_base(int change);

private:

	// this is a circular buffer
	std::uint32_t m_history[history_size];

	// this is the lowest sample seen in the
	// last 'history_size' minutes
	std::uint32_t m_base;

	// and this is the index we're currently at
	// in the circular buffer
	std::uint16_t m_index;

	static constexpr std::uint16_t not_initialized = 0xffff;

	// this is the number of samples since the
	// last time we stepped one minute. If we
	// don't have enough samples, we won't step
	// if this is set to 'not_initialized' we
	// have bit seen any samples at all yet
	// and m_base is not initialized yet
	std::uint16_t m_num_samples;
};

}

#endif