Test failure: TensorTests.TensorExtensionsSpanInSpanOut<Single> Exp10M1 returns +∞ instead of a finite value near float.MaxValue

[lewing]

Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1619756
Build error leg or test failing: net11.0-linux-Debug-arm64-Mono_Minijit_Debug-(AzureLinux.3.0.ArmArch.Open)-System.Numerics.Tensors.Tests.TensorTests.TensorExtensionsSpanInSpanOut
Pull request: #134959

KBE authoring guidance (ci-failure-scan)

• Error Details is for readers. Paste the full exception, stack trace, or build error excerpt so the failure is understandable without opening the raw log.
• Build Analysis parses only the single JSON block under Error Message.
• ErrorMessage is a case-sensitive ordinal String.Contains substring copied verbatim from the failing log.
• Set BuildRetry to true only for a clear infrastructure retry case. ExcludeConsoleLog disables Helix console-log scanning.

Error Details

System.Numerics.Tensors.Tests.TensorTests.TensorExtensionsSpanInSpanOut<Single>(tensorPrimitivesOperation: PerformCalculationSpanInSpanOut`1 { Method = Single Exp10M1(Single), Target = null }, tensorOperation: PerformSpanInSpanOut`1 { Method = System.Numerics.Tensors.Tensor`1[System.Single] Exp10M1[Single](System.Numerics.Tensors.ReadOnlyTensorSpan`1[System.Single] ByRef), Target = null }, tolerance: 9.99999975E-06) [FAIL]
  Assert.All() Failure: 1 out of 12 items in the collection did not pass.
  [10]: Item:  [4, 4, 4, 4, 4]
        Error: Assert.Equal() Failure: Values differ
               Expected: 3.40280805E+38
               Actual:           +∞
  Stack Trace:
    /_/src/libraries/System.Numerics.Tensors/tests/TensorTests.cs(102,0): at System.Numerics.Tensors.Tests.TensorTests.TensorExtensionsSpanInSpanOut[Single](PerformCalculationSpanInSpanOut`1 tensorPrimitivesOperation, PerformSpanInSpanOut`1 tensorOperation, Nullable`1 tolerance)
       at System.Object.InvokeStub_TensorTests.TensorExtensionsSpanInSpanOut(Object, Span`1)
    /_/src/libraries/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.cs(136,0): at System.Reflection.MethodBaseInvoker.InvokeWithFewArgs(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)

Analysis:

• FillTensor<T> fills the inputs with Random.Shared.NextSingle() * 100 - 50. When an input lands just below log10(float.MaxValue) ≈ 38.53, scalar float.Exp10M1 returns a finite value close to float.MaxValue, but Tensor.Exp10M1 overflows to +∞. A tolerance doesn't help when one side is infinite.
• Fix Tensor correctness and accelerate contiguous operations #134914, merged 2026-09-30, routes dense Tensor elementwise operations through TensorPrimitives and added the tolerance for this case. The failing build's merge commit includes that change, so Tensor.Exp10M1 probably now uses the vectorized TensorPrimitives path, which overflows slightly earlier than the scalar implementation.
• The failure is rare because the input is random; Build Analysis reports a 0.02% failure rate.
• It isn't related to [wasi] Make File.Copy metadata copy best effort #134959, which only changes WASI code in pal_io.c.

Error Message

{
  "ErrorMessage": [
    "Method = Single Exp10M1(Single), Target = null }, tensorOperation: PerformSpanInSpanOut`1",
    "Actual:           +∞"
  ],
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Agentic workflow metadata (ci-failure-scan)

Workflow artifact: ci-failure-scan
Artifact kind: kbe-verification
Verified match count: 1 hits in failure.log

Note

This issue was created with the help of GitHub Copilot.

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1619756
Error message validated: [Method = Single Exp10M1(Single), Target = null }, tensorOperation: PerformSpanInSpanOut1 Actual: +∞`]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 10/1/2026 9:16:58 PM UTC

Report

Build	Repository	Test	Pull Request
1626316	dotnet/runtime	System.Numerics.Tensors.Tests.TensorTests.TensorExtensionsSpanInSpanOut	#135278
1626097	dotnet/runtime	System.Numerics.Tensors.Tests.TensorTests.TensorExtensionsSpanInSpanOut	#135277
1622992	dotnet/runtime	System.Numerics.Tensors.Tests.TensorTests.TensorExtensionsSpanInSpanOut	#135167
1620583	dotnet/runtime	System.Numerics.Tensors.Tests.TensorTests.TensorExtensionsSpanInSpanOut	#134260
1619756	dotnet/runtime	System.Numerics.Tensors.Tests.TensorTests.TensorExtensionsSpanInSpanOut	#134959

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
2	5	5

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