premiere-libtorrent/src/timestamp_history.cpp

/*

Copyright (c) 2009-2018, Arvid Norberg
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in
      the documentation and/or other materials provided with the distribution.
    * Neither the name of the author nor the names of its
      contributors may be used to endorse or promote products derived
      from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

*/


#include "libtorrent/timestamp_history.hpp"
#include "libtorrent/aux_/numeric_cast.hpp"

namespace libtorrent {

constexpr std::uint32_t TIME_MASK = 0xffffffff;

// defined in utp_stream.cpp
bool compare_less_wrap(std::uint32_t lhs, std::uint32_t rhs
	, std::uint32_t mask);

std::uint32_t timestamp_history::add_sample(std::uint32_t sample, bool step)
{
	if (!initialized())
	{
		m_history.fill(sample);
		m_base = sample;
		m_num_samples = 0;
	}

	// don't let the counter wrap
	if (m_num_samples < 0xfffe) ++m_num_samples;

	// if sample is less than base, update the base
	// and update the history entry (because it will
	// be less than that too)
	if (compare_less_wrap(sample, m_base, TIME_MASK))
	{
		m_base = sample;
		m_history[m_index] = sample;
	}
	// if sample is less than our history entry, update it
	else if (compare_less_wrap(sample, m_history[m_index], TIME_MASK))
	{
		m_history[m_index] = sample;
	}

	std::uint32_t ret = sample - m_base;

	// don't step base delay history unless we have at least 120
	// samples. Anything less would suggest that the connection is
	// essentially idle and the samples are probably not very reliable
	if (step && m_num_samples > 120)
	{
		m_num_samples = 0;
		m_index = (m_index + 1) % history_size;

		m_history[m_index] = sample;
		// update m_base
		m_base = sample;
		for (auto& h : m_history)
		{
			if (compare_less_wrap(h, m_base, TIME_MASK))
				m_base = h;
		}
	}
	return ret;
}

void timestamp_history::adjust_base(int change)
{
	TORRENT_ASSERT(initialized());
	m_base += aux::numeric_cast<std::uint32_t>(change);
	// make sure this adjustment sticks by updating all history slots
	for (auto& h : m_history)
	{
		if (compare_less_wrap(h, m_base, TIME_MASK))
			h = m_base;
	}
}

}