Fix NIndex/NRange ToString truncation on 64-bit: cast to nuint instead of uint by Copilot · Pull Request #124294 · dotnet/runtime

Copilot · 2026-02-11T20:15:48Z

Description

NIndex.ToStringFromEnd() and NRange.ToString() cast nint values to uint before formatting, truncating values exceeding uint.MaxValue on 64-bit platforms:

var ni = NIndex.FromEnd(unchecked((nint)(1L + uint.MaxValue)));
Console.WriteLine(ni.ToString()); // Prints "^0" instead of "^4294967296"

Fix

NIndex.cs: (uint)Value → (nuint)Value in ToStringFromEnd()
NRange.cs: (uint)Start.Value → (nuint)Start.Value and (uint)End.Value → (nuint)End.Value in ToString()

Tests

Replaced [Fact] ToStringTest with [Theory] + [InlineData] for both NIndexTests and NRangeTests
Added [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.Is64BitProcess))] tests exercising values above uint.MaxValue

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…int, add Theory tests Co-authored-by: vcsjones <[email protected]>

dotnet-policy-service · 2026-02-11T20:49:43Z

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Pull request overview

Fixes incorrect string formatting for NIndex/NRange on 64-bit platforms where values larger than uint.MaxValue were being truncated due to casts to uint during formatting.

Changes:

Update NIndex.ToStringFromEnd() to format using (nuint)Value rather than (uint)Value.
Update NRange.ToString() to format start/end using (nuint)Start.Value / (nuint)End.Value rather than uint.
Expand/adjust unit tests to cover 64-bit values above uint.MaxValue, converting prior [Fact] coverage into [Theory] + [InlineData] and adding 64-bit conditional cases.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/libraries/System.Numerics.Tensors/src/System/Buffers/NIndex.cs	Fixes 64-bit truncation in `ToStringFromEnd()` by formatting via `nuint`.
src/libraries/System.Numerics.Tensors/src/System/Buffers/NRange.cs	Fixes 64-bit truncation in `ToString()` by formatting start/end via `nuint`.
src/libraries/System.Numerics.Tensors/tests/NIndexTests.cs	Adds theory-based coverage and conditional 64-bit test cases for large values.
src/libraries/System.Numerics.Tensors/tests/NRangeTests.cs	Adds theory-based coverage and conditional 64-bit test cases for large range endpoints.

vcsjones · 2026-02-11T21:08:43Z

@copilot please invoke the code-review skill and post your analysis/results as a comment on this PR.

Copilot · 2026-02-11T21:16:09Z

@copilot please invoke the code-review skill and post your analysis/results as a comment on this PR.

🤖 Copilot Code Review

Holistic Assessment

Motivation: The bug is real and clearly reproducible — (uint) casts truncate nint values exceeding uint.MaxValue on 64-bit platforms, causing NIndex.FromEnd(1L + uint.MaxValue).ToString() to return ^0 instead of ^4294967296. The buffer comment on line 177 ("20 for longest possible nuint value") confirms the original intent was nuint.

Approach: Changing (uint) → (nuint) is the minimal correct fix. The tests use [Theory]/[InlineData] and [ConditionalTheory] with PlatformDetection.Is64BitProcess appropriately, consistent with patterns used in NFloatTests.cs and elsewhere in the test project.

Summary: ✅ LGTM. The three cast fixes are correct, minimal, and well-tested. All findings below are positive confirmations or out-of-scope observations.

Detailed Findings

✅ Correctness — Cast fix is correct in all three locations

NIndex.cs:178: (uint)Value → (nuint)Value in ToStringFromEnd()
NRange.cs:73: (uint)Start.Value → (nuint)Start.Value in ToString()
NRange.cs:84: (uint)End.Value → (nuint)End.Value in ToString()

The Value property returns nint (always non-negative for valid NIndex values), so the nuint cast is safe. The stackalloc buffer was already sized for nuint (21 chars = 1 for ^ + 20 digits for max nuint on 64-bit). The non-FromEnd path (NIndex.ToString() line 172) uses Value.ToString() which calls nint.ToString() directly — no truncation issue there.

✅ Test quality — Good coverage with appropriate conditional attributes

The tests cover both fromStart and fromEnd paths, use boundary values (int.MaxValue, uint.MaxValue + 1, long.MaxValue), and correctly gate 64-bit-specific cases with [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.Is64BitProcess))]. PlatformDetection is already used in other tests in this project (TensorPrimitives.Generic.cs, TensorPrimitivesTests.cs).

💡 Out-of-scope observation — `NRange.GetOffsetAndLength` has a similar `(uint)` cast on `nint`

NRange.cs:113 uses (uint)end > (uint)length || (uint)start > (uint)end — this truncates nint values on 64-bit, which could cause incorrect bounds validation for large collections. However, this is mirrored from Range.GetOffsetAndLength (which uses int → uint, which is correct for that type) and is a separate issue from the ToString fix.

tannergooding · 2026-02-11T21:26:37Z

💡 Out-of-scope observation — NRange.GetOffsetAndLength has a similar (uint) cast on nint

@copilot can you open a separate PR to address this.

Copilot · 2026-02-11T21:30:01Z

💡 Out-of-scope observation — NRange.GetOffsetAndLength has a similar (uint) cast on nint

@copilot can you open a separate PR to address this.

I'm not able to open new PRs. Could you open an issue for tracking the (uint) truncation in NRange.GetOffsetAndLength (line 113) so it can be picked up separately? The fix there would be changing (uint) to (nuint) for the bounds checks on end, length, and start.

vcsjones · 2026-02-11T21:32:57Z

I will open a separate PR for the offset / length issue.

tannergooding · 2026-02-12T15:26:00Z

This one should be backported, yes?

vcsjones · 2026-02-12T15:34:50Z

@tannergooding Up to you, but there are a couple of things you may want to back port when things are merged.

tannergooding · 2026-02-12T15:37:04Z

I'm fine with taking them all together, but I do think we should take them for bar check at least. -- CC. @jeffhandley

…nt (#124300) ## Description `NRange.GetOffsetAndLength` casts its `nint` parameters to `uint` for range validation. On 64-bit platforms, this truncates values larger than `uint.MaxValue`, allowing invalid ranges to pass validation silently. ```csharp // Before: truncates upper 32 bits on 64-bit platforms if ((uint)end > (uint)length || (uint)start > (uint)end) // After: correct comparison for all nint values if ((nuint)end > (nuint)length || (nuint)start > (nuint)end) ``` For example, `start = 0x1_0000_0001` and `end = 2` with `length = 0x1_0000_0003`: the `(uint)` cast truncates start to `1`, making `1 > 2` false and incorrectly passing validation. **Note:** Other `(uint)` conversion issues in `NRange` (e.g., `ToString`) are intentionally not addressed here — those are covered by #124294. ### Tests - Converted existing `GetOffsetAndLengthTest` `[Fact]` to `[Theory]` with `[InlineData]` - Split success and exception cases into separate theory methods - Added `[ConditionalTheory(Is64BitProcess)]` tests exercising values above `uint.MaxValue`, including a case that directly catches the truncation bug  --- 💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more [Copilot coding agent tips](https://gh.io/copilot-coding-agent-tips) in the docs. --------- Co-authored-by: copilot-swe-agent[bot] <[email protected]> Co-authored-by: vcsjones <[email protected]>

Initial plan

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Fix NIndex and NRange ToString truncation: cast to nuint instead of u…

9295a87

…int, add Theory tests Co-authored-by: vcsjones <[email protected]>

Copilot AI changed the title ~~[WIP] Fix NIndex formatting for end index conversion~~ Fix NIndex/NRange ToString truncation on 64-bit: cast to nuint instead of uint Feb 11, 2026

Copilot AI requested a review from vcsjones February 11, 2026 20:43

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vcsjones added area-System.Numerics.Tensors and removed needs-area-label An area label is needed to ensure this gets routed to the appropriate area owners labels Feb 11, 2026

vcsjones marked this pull request as ready for review February 11, 2026 20:51

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Copilot AI mentioned this pull request Feb 11, 2026

Fix NRange.GetOffsetAndLength truncation: cast to nuint instead of uint #124300

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tannergooding merged commit de90299 into main Feb 12, 2026
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vcsjones deleted the copilot/fix-nindex-to-string-issue branch February 12, 2026 04:06

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System.Security.Cryptography.CryptographicException : m_safeCertContext is an invalid handle. #124279

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[main] Source code updates from dotnet/runtime dotnet/dotnet#4839

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Fix NIndex/NRange ToString truncation on 64-bit: cast to nuint instead of uint#124294

Fix NIndex/NRange ToString truncation on 64-bit: cast to nuint instead of uint#124294
tannergooding merged 2 commits intomainfrom
copilot/fix-nindex-to-string-issue

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Description

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Tests

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Pull request overview

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Copilot AI commented Feb 11, 2026

🤖 Copilot Code Review

Holistic Assessment

Detailed Findings

✅ Correctness — Cast fix is correct in all three locations

✅ Test quality — Good coverage with appropriate conditional attributes

💡 Out-of-scope observation — NRange.GetOffsetAndLength has a similar (uint) cast on nint

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Copilot AI commented Feb 11, 2026 •

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💡 Out-of-scope observation — `NRange.GetOffsetAndLength` has a similar `(uint)` cast on `nint`