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Improve RGB Min Max evaluation performance by using 2 or 3 comparison… #50622

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merged 5 commits into from
Apr 6, 2021
Merged

Improve RGB Min Max evaluation performance by using 2 or 3 comparison… #50622

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7a0fabe
Improve RGB Min Max evaluation performance by using 2 or 3 comparison…
L2 Apr 1, 2021
59d5387
Conform trailing braces to .NET style guide
L2 Apr 1, 2021
8341fe2
Add missing functional test cases for MinMaxRgb
L2 Apr 2, 2021
03644b6
Use ternary conditional operator and out var initialization
L2 Apr 2, 2021
5c109b7
Simplify by removing nested conditionals
L2 Apr 5, 2021
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40 changes: 34 additions & 6 deletions src/libraries/System.Drawing.Primitives/src/System/Drawing/Color.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -487,12 +487,42 @@ private void GetRgbValues(out int r, out int g, out int b)
b = (int)(value & ARGBBlueMask) >> ARGBBlueShift;
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
private void MinMaxRgb(out int min, out int max, int r, int g, int b)
{
if (b < g)
{
if (b < r)
{
min = b;
max = r < g ? g : r;
}
else
{
min = r;
max = g;
}
}
else
{
if (r < b)
{
max = b;
min = g < r ? g : r;
}
else
{
max = r;
min = g;
}
}
}
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This can be simplified to instead be:

Suggested change
private void MinMaxRgb(out int min, out int max, int r, int g, int b)
{
if (b < g)
{
if (b < r)
{
min = b;
max = r < g ? g : r;
}
else
{
min = r;
max = g;
}
}
else
{
if (r < b)
{
max = b;
min = g < r ? g : r;
}
else
{
max = r;
min = g;
}
}
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static void MinMaxRgb(out int min, out int max, int r, int g, int b)
{
if (r > g)
{
max = r;
min = g;
}
else
{
max = g;
min = r;
}
if (b > max)
{
max = b;
}
else if (b < min)
{
min = b;
}
}

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Thanks @stephentoub , I ran the perf_color microbenchmarks against 1) before this PR changeset, 2) the current PR's changeset, 3) proposed simplification

**.NET6 Before VS .NET6 with current PR changeset: Run1** summary: better: 3, geomean: 1.151 total diff: 3

No Slower results for the provided threshold = 2% and noise filter = 25ns.

Faster base/diff Base Median (ns) Diff Median (ns) Modality
System.Drawing.Tests.Perf_Color.GetBrightness 1.23 1549.96 1259.50
System.Drawing.Tests.Perf_Color.GetHue 1.18 1753.24 1484.57
System.Drawing.Tests.Perf_Color.GetSaturation 1.05 1451.59 1383.79
**.NET6 Before VS .NET6 with current PR changeset: Run2** summary: better: 3, geomean: 1.208 total diff: 3

No Slower results for the provided threshold = 2% and noise filter = 25ns.

Faster base/diff Base Median (ns) Diff Median (ns) Modality
System.Drawing.Tests.Perf_Color.GetBrightness 1.23 1543.19 1259.71
System.Drawing.Tests.Perf_Color.GetSaturation 1.22 1682.03 1384.17
System.Drawing.Tests.Perf_Color.GetHue 1.18 1758.68 1485.53
**.NET6 Before VS .NET6 with current PR changeset: Run3** summary: better: 3, geomean: 1.189 total diff: 3

No Slower results for the provided threshold = 2% and noise filter = 25ns.

Faster base/diff Base Median (ns) Diff Median (ns) Modality
System.Drawing.Tests.Perf_Color.GetSaturation 1.22 1682.42 1384.03
System.Drawing.Tests.Perf_Color.GetBrightness 1.19 1497.18 1259.28
System.Drawing.Tests.Perf_Color.GetHue 1.16 1725.25 1483.41
**.NET6 Before VS .NET6 with proposed simplification: Run1** summary: better: 2, geomean: 1.123 total diff: 2

No Slower results for the provided threshold = 2% and noise filter = 25ns.

Faster base/diff Base Median (ns) Diff Median (ns) Modality
System.Drawing.Tests.Perf_Color.GetBrightness 1.13 1549.96 1375.52
System.Drawing.Tests.Perf_Color.GetHue 1.12 1753.24 1565.75
**.NET6 Before VS .NET6 with proposed simplification: Run2** summary: better: 3, geomean: 1.135 total diff: 3

No Slower results for the provided threshold = 2% and noise filter = 25ns.

Faster base/diff Base Median (ns) Diff Median (ns) Modality
System.Drawing.Tests.Perf_Color.GetSaturation 1.16 1682.03 1448.45
System.Drawing.Tests.Perf_Color.GetHue 1.12 1758.68 1566.17
System.Drawing.Tests.Perf_Color.GetBrightness 1.12 1543.19 1375.17
**.NET6 Before VS .NET6 with proposed simplification: Run3** summary: better: 2, geomean: 1.132 worse: 1, geomean: 1.050 total diff: 3
Slower diff/base Base Median (ns) Diff Median (ns) Modality
System.Drawing.Tests.Perf_Color.GetBrightness 1.05 1497.18 1572.36
Faster base/diff Base Median (ns) Diff Median (ns) Modality
System.Drawing.Tests.Perf_Color.GetSaturation 1.16 1682.42 1446.59
System.Drawing.Tests.Perf_Color.GetHue 1.10 1725.25 1565.42
---------------------- ----------------------

Some of the benchmarks seem to get a bit slower on average after the simplification. I think what is happening may be two causes:

  1. There are paths with an extra store (we store max & min in the first conditional and then if the second conditional is taken one of these is overwritten).
  2. Just my guess, but processor pipelining with branch prediction may find it easier to go through each of the conditionals in the current implementation as there are no dependencies. The simplification introduces a dependency on the second conditional as it needs the values from the first? Just a guess here.

I will follow yours and @safern 's recommendation on which to keep. Thanks again.

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I didn't look at the disassembly but there might be an aliasing complication also, if the JIT compiler has to account for the possibility that min and max refer to the same location. Although perhaps it can disprove that after inlining.

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I actually see them get faster on my machine. Regardless, though, I'd rather keep the code smaller, especially with it triplicated due to the aggressive inlining.

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One more possible improvement - using local valiables instead of out parameters:

		private static void MinMaxRgb(out int min, out int max, int r, int g, int b)
		{
			int minLoc, maxLoc;
			if (r > g)
			{
				maxLoc = r;
				minLoc = g;
			}
			else
			{
				maxLoc = g;
				minLoc = r;
			}

			if (b > maxLoc)
			{
				maxLoc = b;
			}
			else if (b < minLoc)
			{
				minLoc = b;
			}

			max = maxLoc;
			min = minLoc;
		}

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@L2 L2 Apr 5, 2021 •
edited
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I actually see them get faster on my machine. Regardless, though, I'd rather keep the code smaller, especially with it triplicated due to the aggressive inlining.

Sounds good @stephentoub , I've updated it with the requested changes. (I'm not sure how crediting works in this project as this is my second pull request, so I've added your username to the commit details as the originator of the simplification).

One more possible improvement - using local valiables instead of out parameters:

Thanks @hypeartist, I'm wondering if these local variables will be eliminated due to inlining, so performance will be about the same?

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I'm not sure how crediting works in this project as this is my second pull request, so I've added your username to the commit details as the originator of the simplification

Thanks, but not necessary... I comment on a lot of PRs :)


public float GetBrightness()
{
GetRgbValues(out int r, out int g, out int b);

int min = Math.Min(Math.Min(r, g), b);
int max = Math.Max(Math.Max(r, g), b);
MinMaxRgb(out int min, out int max, r, g, b);

return (max + min) / (byte.MaxValue * 2f);
}
Expand All @@ -504,8 +534,7 @@ public float GetHue()
if (r == g && g == b)
return 0f;

int min = Math.Min(Math.Min(r, g), b);
int max = Math.Max(Math.Max(r, g), b);
MinMaxRgb(out int min, out int max, r, g, b);

float delta = max - min;
float hue;
Expand All @@ -531,8 +560,7 @@ public float GetSaturation()
if (r == g && g == b)
return 0f;

int min = Math.Min(Math.Min(r, g), b);
int max = Math.Max(Math.Max(r, g), b);
MinMaxRgb(out int min, out int max, r, g, b);

int div = max + min;
if (div > byte.MaxValue)
Expand Down
6 changes: 6 additions & 0 deletions src/libraries/System.Drawing.Primitives/tests/ColorTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -390,6 +390,12 @@ private void CheckRed(Color color)
[InlineData(51, 255, 51, 0.6f)]
[InlineData(51, 51, 255, 0.6f)]
[InlineData(51, 51, 51, 0.2f)]
[InlineData(0, 51, 255, 0.5f)]
[InlineData(51, 255, 0, 0.5f)]
[InlineData(0, 255, 51, 0.5f)]
[InlineData(255, 0, 51, 0.5f)]
[InlineData(51, 0, 255, 0.5f)]
[InlineData(255, 51, 0, 0.5f)]
public void GetBrightness(int r, int g, int b, float expected)
{
Assert.Equal(expected, Color.FromArgb(r, g, b).GetBrightness());
Expand Down