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Stop RingBuffer.Resample's index mapping overflowing for large buffers #76

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Merged
matt-edmondson merged 1 commit into from
Sep 26, 2026
Merged

Stop RingBuffer.Resample's index mapping overflowing for large buffers #76

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23 changes: 23 additions & 0 deletions Containers.Test/RingBufferTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -290,6 +290,29 @@ public void Resize_NonPositiveLength_Throws()
Assert.ThrowsExactly<ArgumentOutOfRangeException>(() => buffer.Resize(-1));
}

[TestMethod]
public void Resample_LargeBufferToSameLength_KeepsContents()
{
const int length = 50_000;
RingBuffer<int> buffer = new(Enumerable.Range(0, length), length);

buffer.Resample(length);

Assert.AreSequenceEqual(Enumerable.Range(0, length), buffer);
}

[TestMethod]
public void Resample_UpsampleToMillionsOfElements_Succeeds()
{
RingBuffer<int> buffer = new(Enumerable.Range(0, 1000), 1000);

buffer.Resample(3_000_000);

Assert.HasCount(3_000_000, buffer);
Assert.AreEqual(0, buffer.Front());
Assert.AreEqual(999, buffer.Back());
}

[TestMethod]
public void Resample_NonPositiveLength_Throws()
{
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3 changes: 2 additions & 1 deletion Containers/RingBuffer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -267,7 +267,8 @@ public void Resample(int length)
for (int i = 0; i < length; i++)
{
// Map the new index to the old data range
double oldIndex = i * (oldCount - 1) / (double)Math.Max(length - 1, 1);
// Multiply in double: the int product overflows once length * oldCount passes int.MaxValue
double oldIndex = (double)i * (oldCount - 1) / Math.Max(length - 1, 1);
int index = (int)Math.Round(oldIndex);

// Ensure we don't go out of bounds
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