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Merged
MihaZupan merged 3 commits into from
Nov 4, 2022
Merged

Vectorize {Last}IndexOfAny{Except} for ASCII needles #76740

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69743df
Vectorize {Last}IndexOfAny{Except} for ASCII needles
MihaZupan Oct 26, 2022
08b4285
Add a ShouldUseSimpleLoop helper
MihaZupan Oct 31, 2022
e9ded14
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MihaZupan Nov 3, 2022
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Vectorize {Last}IndexOfAny{Except} for ASCII needles
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@MihaZupan
MihaZupan committed Nov 3, 2022
commit 69743df25c0b8425b9d6d155b28864509970e617
66 changes: 66 additions & 0 deletions src/libraries/System.Memory/tests/Span/IndexOfAny.char.cs
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Expand Up @@ -3,6 +3,7 @@

using System.Linq;
using System.Numerics;
using System.Runtime.InteropServices;
using System.Text;
using Xunit;

Expand Down Expand Up @@ -772,5 +773,70 @@ public static void MakeSureNoChecksGoOutOfRangeMany_Char()
Assert.Equal(-1, index);
}
}

[Fact]
public static void TestIndexOfAny_RandomInputs_Char()
{
IndexOfAnyCharTestHelper.TestRandomInputs(
expected: IndexOfAnyReferenceImpl,
actual: (searchSpace, values) => searchSpace.IndexOfAny(values));

static int IndexOfAnyReferenceImpl(ReadOnlySpan<char> searchSpace, ReadOnlySpan<char> values)
{
for (int i = 0; i < searchSpace.Length; i++)
{
if (values.Contains(searchSpace[i]))
{
return i;
}
}

return -1;
}
}
}

public static class IndexOfAnyCharTestHelper
{
public delegate int IndexOfAnySearchDelegate(ReadOnlySpan<char> searchSpace, ReadOnlySpan<char> values);

public static void TestRandomInputs(IndexOfAnySearchDelegate expected, IndexOfAnySearchDelegate actual)
{
TestRandomInputs(127, expected, actual);
TestRandomInputs(char.MaxValue, expected, actual);
}

private static void TestRandomInputs(int maxNeedleValue, IndexOfAnySearchDelegate expected, IndexOfAnySearchDelegate actual)
{
maxNeedleValue++;

Span<char> needleSpace = stackalloc char[8];
Span<char> haystackSpace = stackalloc char[40];
var rng = new Random();
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@stephentoub stephentoub Nov 2, 2022

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To make this reproducable, we should include a seed here.

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@MihaZupan MihaZupan Nov 2, 2022 •
edited
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If I remember correctly, I removed it because the RNG part represents a significant portion of the test execution time, with the non-explicit-seed ctor using the faster impl AFAIK.

For reproducibility, I made sure to emit the exact inputs that failed as part of the error message. Does that address your concerns here?

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@stephentoub stephentoub Nov 3, 2022 •
edited
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Does that address your concerns here?

Only partially. There are two concerns:

  1. That a test could fail and you not know why or be able to trigger it again.
  2. That two runs of the same test suite might be non-deterministic.

Outputting the exact inputs addresses (1) but not (2). And (2) in general contributes to test flakiness.

If this test is about randomly stressing the implementation, then I don't believe it belongs in the functional test suite. If it's about using pseudo-randomness to try out thousands of inputs without having to manually code them all and be creative enough to ensure a reasonable spread of inputs, then it should be done in a way that runs the same tests every time, which means using a seed.

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@MihaZupan MihaZupan Nov 3, 2022

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I changed it to waste less time in Random and use a constant seed.

It was extremely useful when working on the initial implementation to get rid of all the edge-case bugs. Some were so odd that I don't believe we would have come up with test cases for otherwise.

I increased the number of iterations so it now takes about a second of CPU time to run through them, so I moved these to outerloop.
Outerloop already takes ~4 minutes on my machine so I'm gonna assume that's acceptable.


for (int iterations = 0; iterations < 100_000; iterations++)
{
Span<char> needle = needleSpace.Slice(0, rng.Next(needleSpace.Length + 1));
Span<char> haystack = haystackSpace.Slice(0, rng.Next(haystackSpace.Length + 1));

for (int i = 0; i < needle.Length; i++)
{
needle[i] = (char)rng.Next(0, maxNeedleValue);
}

rng.NextBytes(MemoryMarshal.Cast<char, byte>(haystack));

int expectedIndex = expected(haystack, needle);
int actualIndex = actual(haystack, needle);

if (expectedIndex != actualIndex)
{
string readableNeedle = string.Join(", ", needle.ToString().Select(c => (int)c));
string readableHaystack = string.Join(", ", haystack.ToString().Select(c => (int)c));

Assert.True(false, $"Expected {expectedIndex}, got {actualIndex} for needle='{readableNeedle}', haystack='{readableHaystack}'");
}
}
}
}
}
42 changes: 42 additions & 0 deletions src/libraries/System.Memory/tests/Span/IndexOfAnyExcept.T.cs
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Expand Up @@ -53,6 +53,48 @@ public void SearchingNulls(string[] input, string[] targets, int expected)
break;
}
}

[Fact]
public static void TestIndexOfAnyExcept_RandomInputs_Char()
{
IndexOfAnyCharTestHelper.TestRandomInputs(
expected: IndexOfAnyExceptReferenceImpl,
actual: (searchSpace, values) => searchSpace.IndexOfAnyExcept(values));

static int IndexOfAnyExceptReferenceImpl(ReadOnlySpan<char> searchSpace, ReadOnlySpan<char> values)
{
for (int i = 0; i < searchSpace.Length; i++)
{
if (!values.Contains(searchSpace[i]))
{
return i;
}
}

return -1;
}
}

[Fact]
public static void TestLastIndexOfAnyExcept_RandomInputs_Char()
{
IndexOfAnyCharTestHelper.TestRandomInputs(
expected: LastIndexOfAnyExceptReferenceImpl,
actual: (searchSpace, values) => searchSpace.LastIndexOfAnyExcept(values));

static int LastIndexOfAnyExceptReferenceImpl(ReadOnlySpan<char> searchSpace, ReadOnlySpan<char> values)
{
for (int i = searchSpace.Length - 1; i >= 0; i--)
{
if (!values.Contains(searchSpace[i]))
{
return i;
}
}

return -1;
}
}
}

public record SimpleRecord(int Value);
Expand Down
21 changes: 21 additions & 0 deletions src/libraries/System.Memory/tests/Span/LastIndexOfAny.T.cs
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Expand Up @@ -951,5 +951,26 @@ public static void LastIndexOfAnyNullSequence_String(string[] spanInput, string[
}
}
}

[Fact]
public static void TestLastIndexOfAny_RandomInputs_Char()
{
IndexOfAnyCharTestHelper.TestRandomInputs(
expected: LastIndexOfAnyReferenceImpl,
actual: (searchSpace, values) => searchSpace.LastIndexOfAny(values));

static int LastIndexOfAnyReferenceImpl(ReadOnlySpan<char> searchSpace, ReadOnlySpan<char> values)
{
for (int i = searchSpace.Length - 1; i >= 0; i--)
{
if (values.Contains(searchSpace[i]))
{
return i;
}
}

return -1;
}
}
}
}
1 change: 1 addition & 0 deletions src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
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Expand Up @@ -414,6 +414,7 @@
<Compile Include="$(MSBuildThisFileDirectory)System\IFormatProvider.cs" />
<Compile Include="$(MSBuildThisFileDirectory)System\IFormattable.cs" />
<Compile Include="$(MSBuildThisFileDirectory)System\Index.cs" />
<Compile Include="$(MSBuildThisFileDirectory)System\IndexOfAnyAsciiSearcher.cs" />
<Compile Include="$(MSBuildThisFileDirectory)System\IndexOutOfRangeException.cs" />
<Compile Include="$(MSBuildThisFileDirectory)System\InsufficientExecutionStackException.cs" />
<Compile Include="$(MSBuildThisFileDirectory)System\InsufficientMemoryException.cs" />
Expand Down
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