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[Profiler] Compare fixed and Poisson threshold allocation sampling/upscaling (#4016)
* Add Poisson sampling/upscaling strategy * Compare Poisson and fixed threshold sampling/upscaling results
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12 files changed

+329
-43
lines changed

12 files changed

+329
-43
lines changed

‎profiler/src/Tools/AllocSimulator/BinaryFileAllocProvider.cs‎

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@@ -139,7 +139,6 @@ private void ReadAllocations(FileStream fileStream, ref int pos)
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pos += 8; // skip the read 2 x 4 bytes
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}
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}
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}
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}
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}

‎profiler/src/Tools/AllocSimulator/Engine.cs‎

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@@ -9,18 +9,18 @@ namespace AllocSimulator
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{
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public class Engine : IEngine
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{
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private const long Threshold = 100 * 1024;
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private IAllocProvider _provider;
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private ISampler _sampler;
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private IUpscaler _upscaler;
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private long _cumulatedSize;
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private IDictionary<string, AllocInfo> _allocations;
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// TODO support a list of ISampler to compare non upscaled and upscaled for example
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public Engine(IAllocProvider provider, ISampler sampler)
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public Engine(IAllocProvider provider, ISampler sampler, IUpscaler upscaler)
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{
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_provider = provider;
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_sampler = sampler;
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_upscaler = upscaler;
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_cumulatedSize = 0;
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_allocations = new Dictionary<string, AllocInfo>();
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}
@@ -61,21 +61,16 @@ public void Run()
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info.Size = info.Size + alloc.Size;
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info.Count = info.Count + alloc.Count;
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_cumulatedSize += alloc.Size;
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if (ShouldSample(alloc.Size))
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if (_sampler.ShouldSample(alloc.Size))
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{
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_sampler.OnAllocationTick(alloc.Type, alloc.Key, alloc.Size, _cumulatedSize);
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_upscaler.OnAllocationTick(alloc.Type, alloc.Key, alloc.Size, _cumulatedSize);
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_cumulatedSize = 0;
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}
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}
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}
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}
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private bool ShouldSample(long size)
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{
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_cumulatedSize += size;
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return (_cumulatedSize >= Threshold);
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}
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}
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}
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‎profiler/src/Tools/AllocSimulator/FixedSampler.cs‎

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// <copyright file="FixedSampler.cs" company="Datadog">
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// Unless explicitly stated otherwise all files in this repository are licensed under the Apache 2 License.
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// This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2022 Datadog, Inc.
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// </copyright>
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namespace AllocSimulator
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{
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public class FixedSampler : ISampler
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{
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// the current .NET fixed threshold for AllocationTick is 100 KB
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private const long Threshold = 100 * 1024;
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private long _totalAllocatedAmount;
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public bool ShouldSample(long size)
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{
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_totalAllocatedAmount += size;
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var shouldSample = _totalAllocatedAmount > Threshold;
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if (shouldSample)
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{
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_totalAllocatedAmount = 0;
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}
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return shouldSample;
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}
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}
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}

‎profiler/src/Tools/AllocSimulator/FixedUpscaler.cs‎

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// <copyright file="FixedUpscaler.cs" company="Datadog">
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// Unless explicitly stated otherwise all files in this repository are licensed under the Apache 2 License.
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// This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2022 Datadog, Inc.
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// </copyright>
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namespace AllocSimulator
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{
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public class FixedUpscaler : UpscalerBase
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{
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protected override void OnUpscale(AllocInfo sampled, ref AllocInfo upscaled)
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{
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upscaled.Size = (long)((sampled.Size * _totalAllocatedAmount) / _totalSampledSize);
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upscaled.Count = (int)((sampled.Count * _totalAllocatedAmount) / _totalSampledSize);
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}
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}
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}

‎profiler/src/Tools/AllocSimulator/ISampler.cs‎

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Original file line numberDiff line numberDiff line change
@@ -7,8 +7,6 @@ namespace AllocSimulator
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{
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public interface ISampler
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{
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public void OnAllocationTick(string type, int key, long size, long allocationsAmount);
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public IEnumerable<AllocInfo> GetAllocs();
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public bool ShouldSample(long size);
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}
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}

‎profiler/src/Tools/AllocSimulator/IUpscaler.cs‎

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// <copyright file="IUpscaler.cs" company="Datadog">
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// Unless explicitly stated otherwise all files in this repository are licensed under the Apache 2 License.
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// This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2022 Datadog, Inc.
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// </copyright>
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namespace AllocSimulator
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{
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public interface IUpscaler
9+
{
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public void OnAllocationTick(string type, int key, long size, long allocationsAmount);
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public IEnumerable<AllocInfo> GetAllocs();
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}
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}

‎profiler/src/Tools/AllocSimulator/JavaPoissonSampler.cs‎

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// <copyright file="JavaPoissonSampler.cs" company="Datadog">
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// Unless explicitly stated otherwise all files in this repository are licensed under the Apache 2 License.
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// This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2022 Datadog, Inc.
4+
// </copyright>
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namespace AllocSimulator
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{
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// from https://github.com/openjdk/jdk/blob/master/src/hotspot/share/runtime/threadHeapSampler.cpp
9+
public class JavaPoissonSampler : ISampler
10+
{
11+
private const ulong MeanSamplingSize = 512 * 1024; // 512 KB is the mean of the distribution
12+
private const double MinusLog2 = -0.6931471805599453; // = - ln(2)
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// for fast randomizer
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private const ulong PrngMult = 0x5DEECE66D;
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private const ulong PrngAdd = 0xB;
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private const ulong PrngModMask = (1 << 48) - 1;
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private ulong _totalAllocatedAmount;
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private ulong _threshold; // number of bytes until the next sample
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private ulong _random;
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public JavaPoissonSampler()
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{
25+
_random = (ulong)Random.Shared.NextInt64(1, 281474976710656); // from 1 to 2^48
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_threshold = GetNextThreshold();
27+
}
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public bool ShouldSample(long size)
30+
{
31+
_totalAllocatedAmount += (ulong)size;
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var shouldSample = _totalAllocatedAmount > _threshold;
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34+
if (shouldSample)
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{
36+
_totalAllocatedAmount = 0;
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_threshold = GetNextThreshold();
38+
}
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40+
return shouldSample;
41+
}
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43+
// Generates a geometric variable with the specified mean (512K by default).
44+
// This is done by generating a random number between 0 and 1 and applying
45+
// the inverse cumulative distribution function for an exponential.
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// Specifically: Let m be the inverse of the sample interval, then
47+
// the probability distribution function is m*exp(-mx) so the CDF is
48+
// p = 1 - exp(-mx), so
49+
// q = 1 - p = exp(-mx)
50+
// log_e(q) = -mx
51+
// -log_e(q)/m = x
52+
// log_2(q) * (-log_e(2) * 1/m) = x
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// In the code, q is actually in the range 1 to 2**26, hence the -26 below
54+
private ulong GetNextThreshold()
55+
{
56+
_random = GetNextRandom(_random);
57+
58+
// Take the top 26 bits as the random number
59+
// (This plus a 1<<58 sampling bound gives a max possible step of
60+
// 5194297183973780480 bytes. In this case,
61+
// for sample_parameter = 1<<19, max possible step is
62+
// 9448372 bytes (24 bits).
63+
64+
// 48 is the number of bits in prng
65+
// The uint32_t cast is to prevent a (hard-to-reproduce) NAN
66+
// under piii debug for some binaries.
67+
double q = (uint)(_random >> (48 - 26)) + 1.0;
68+
// Put the computed p-value through the CDF of a geometric.
69+
// For faster performance (save ~1/20th exec time), replace
70+
// min(0.0, FastLog2(q) - 26) by (Fastlog2(q) - 26.000705)
71+
// The value 26.000705 is used rather than 26 to compensate
72+
// for inaccuracies in FastLog2 which otherwise result in a
73+
// negative answer.
74+
double log_val = (Log2(q) - 26);
75+
if (log_val > 0.0)
76+
{
77+
log_val = 0.0;
78+
}
79+
80+
double result = (log_val * (MinusLog2 * (MeanSamplingSize))) + 1;
81+
ulong interval = (ulong)result;
82+
_threshold = interval;
83+
return _threshold;
84+
}
85+
86+
// Returns the next prng value.
87+
// pRNG is: aX+b mod c with a = 0x5DEECE66D, b = 0xB, c = 1<<48
88+
// This is the lrand64 generator.
89+
private ulong GetNextRandom(ulong random)
90+
{
91+
return ((PrngMult * random) + PrngAdd) & PrngModMask;
92+
}
93+
94+
private double Log2(double d)
95+
{
96+
return Math.Log2(d);
97+
}
98+
}
99+
}

‎profiler/src/Tools/AllocSimulator/PoissonSampler.cs‎

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// <copyright file="PoissonSampler.cs" company="Datadog">
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// Unless explicitly stated otherwise all files in this repository are licensed under the Apache 2 License.
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// This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2022 Datadog, Inc.
4+
// </copyright>
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namespace AllocSimulator
7+
{
8+
public class PoissonSampler : ISampler
9+
{
10+
private Random _randomizer = new Random(DateTime.Now.Millisecond);
11+
private ulong _totalAllocatedAmount;
12+
private ulong _threshold; // number of bytes until the next sample
13+
private float _meanPoisson;
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15+
public PoissonSampler(int meanPoisson)
16+
{
17+
_meanPoisson = meanPoisson * 1024;
18+
_threshold = GetNextThreshold();
19+
}
20+
21+
public bool ShouldSample(long size)
22+
{
23+
_totalAllocatedAmount += (ulong)size;
24+
var shouldSample = _totalAllocatedAmount > _threshold;
25+
26+
if (shouldSample)
27+
{
28+
_totalAllocatedAmount = 0;
29+
_threshold = GetNextThreshold();
30+
}
31+
32+
return shouldSample;
33+
}
34+
35+
public ulong GetNextThreshold()
36+
{
37+
var q = _randomizer.NextDouble();
38+
39+
ulong next = (ulong)((-Math.Log(1 - q)) * _meanPoisson) + 1;
40+
return next;
41+
}
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}
43+
}

‎profiler/src/Tools/AllocSimulator/PoissonUpscaler.cs‎

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// <copyright file="PoissonUpscaler.cs" company="Datadog">
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// Unless explicitly stated otherwise all files in this repository are licensed under the Apache 2 License.
3+
// This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2022 Datadog, Inc.
4+
// </copyright>
5+
6+
namespace AllocSimulator
7+
{
8+
public class PoissonUpscaler : UpscalerBase
9+
{
10+
private float _meanPoisson;
11+
12+
public PoissonUpscaler(int meanPoisson)
13+
{
14+
_meanPoisson = meanPoisson * 1024;
15+
}
16+
17+
protected override void OnUpscale(AllocInfo sampled, ref AllocInfo upscaled)
18+
{
19+
var averageSize = (double)sampled.Size / (double)sampled.Count;
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var scale = 1 / (1 - Math.Exp(-averageSize / _meanPoisson));
21+
22+
upscaled.Size = (long)((float)sampled.Size * scale);
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upscaled.Count = (int)((float)sampled.Count * scale);
24+
}
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}
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}

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