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45 lines
1.4 KiB
45 lines
1.4 KiB
// Copyright 2019 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "cast/streaming/ssrc.h"
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#include <random>
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#include "platform/api/time.h"
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namespace openscreen {
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namespace cast {
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namespace {
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// These ranges are arbitrary, but have been used for several years (in prior
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// implementations of Cast Streaming).
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constexpr int kHigherPriorityMin = 1;
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constexpr int kHigherPriorityMax = 50000;
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constexpr int kNormalPriorityMin = 50001;
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constexpr int kNormalPriorityMax = 100000;
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} // namespace
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Ssrc GenerateSsrc(bool higher_priority) {
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// Use a statically-allocated generator, instantiated upon first use, and
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// seeded with the current time tick count. This generator was chosen because
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// it is light-weight and does not need to produce unguessable (nor
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// crypto-secure) values.
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static std::minstd_rand generator(static_cast<std::minstd_rand::result_type>(
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Clock::now().time_since_epoch().count()));
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std::uniform_int_distribution<int> distribution(
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higher_priority ? kHigherPriorityMin : kNormalPriorityMin,
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higher_priority ? kHigherPriorityMax : kNormalPriorityMax);
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return static_cast<Ssrc>(distribution(generator));
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}
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int ComparePriority(Ssrc ssrc_a, Ssrc ssrc_b) {
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return static_cast<int>(ssrc_a) - static_cast<int>(ssrc_b);
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}
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} // namespace cast
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} // namespace openscreen
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