1 /* Copyright 2016, Ableton AG, Berlin. All rights reserved.
2  *
3  *  This program is free software: you can redistribute it and/or modify
4  *  it under the terms of the GNU General Public License as published by
5  *  the Free Software Foundation, either version 2 of the License, or
6  *  (at your option) any later version.
7  *
8  *  This program is distributed in the hope that it will be useful,
9  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
10  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
11  *  GNU General Public License for more details.
12  *
13  *  You should have received a copy of the GNU General Public License
14  *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
15  *
16  *  If you would like to incorporate Link into a proprietary software application,
17  *  please contact <link-devs@ableton.com>.
18  */
19 
20 #pragma once
21 
22 #include <ableton/link/LinearRegression.hpp>
23 #include <chrono>
24 #include <vector>
25 
26 namespace ableton
27 {
28 namespace link
29 {
30 
31 template <class T>
32 class HostTimeFilter
33 {
34   static const std::size_t kNumPoints = 512;
35   using Points = std::vector<std::pair<double, double>>;
36   using PointIt = typename Points::iterator;
37 
38 public:
HostTimeFilter()39   HostTimeFilter()
40     : mIndex(0)
41   {
42     mPoints.reserve(kNumPoints);
43   }
44 
45   ~HostTimeFilter() = default;
46 
reset()47   void reset()
48   {
49     mIndex = 0;
50     mPoints.clear();
51   }
52 
sampleTimeToHostTime(const double sampleTime)53   std::chrono::microseconds sampleTimeToHostTime(const double sampleTime)
54   {
55     const auto micros = static_cast<double>(mHostTimeSampler.micros().count());
56     const auto point = std::make_pair(sampleTime, micros);
57 
58     if (mPoints.size() < kNumPoints)
59     {
60       mPoints.push_back(point);
61     }
62     else
63     {
64       mPoints[mIndex] = point;
65     }
66     mIndex = (mIndex + 1) % kNumPoints;
67 
68     const auto result = linearRegression(mPoints.begin(), mPoints.end());
69 
70     const auto hostTime = (result.first * sampleTime) + result.second;
71 
72     return std::chrono::microseconds(llround(hostTime));
73   }
74 
75 private:
76   std::size_t mIndex;
77   Points mPoints;
78   T mHostTimeSampler;
79 };
80 
81 } // namespace link
82 } // namespace ableton
83