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Add BinaryWriter benchmarks for _useFastUtf8 true and false code paths by Copilot · Pull Request #5121 · dotnet/performance · GitHub
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Add BinaryWriter benchmarks for _useFastUtf8 true and false code paths - #5121

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Add BinaryWriter benchmarks for _useFastUtf8 true and false code paths#5121
jeffhandley with Copilot wants to merge 5 commits into
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copilot/augment-binary-writer-tests

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Copilot AI commented Feb 16, 2026 •
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  • Analyze the _useFastUtf8 condition in BinaryWriter (true for UTF-8 encoding, false for non-UTF-8)
  • Review existing benchmark coverage (only covers _useFastUtf8 = true path via default UTF-8 encoding, ASCII only)
  • Add benchmarks to cover both _useFastUtf8 = true and _useFastUtf8 = false paths
    • BinaryWriterExtendedTests: Added WriteNonAsciiCharArray and WriteNonAsciiString benchmarks (UTF-8, _useFastUtf8 = true with multi-byte chars)
    • BinaryWriterUnicodeEncodingTests: New class using Encoding.Unicode for Write(string) and Write(char[]) (_useFastUtf8 = false)
    • BinaryWriterUnicodeEncodingCharTests: New class using Encoding.Unicode for Write(char) (_useFastUtf8 = false)
  • Add comments explaining the significance of '\u00E0' character selection (2-byte UTF-8 encoding)
  • Run code review (no issues found)
  • Run CodeQL security check (timed out - expected for benchmark-only changes with no security implications)

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@jeffhandley jeffhandley mentioned this pull request Feb 16, 2026
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Add BinaryWriter benchmarks for _useFastUtf8 true and false code paths
22dfd09 
Co-authored-by: jeffhandley <1031940+jeffhandley@users.noreply.github.com>
Copilot AI changed the title [WIP] Augment BinaryWriterTests benchmark coverage Add BinaryWriter benchmarks for _useFastUtf8 true and false code paths Feb 16, 2026
Copilot AI requested a review from jeffhandley February 16, 2026 02:26
jeffhandley
jeffhandley requested changes Feb 16, 2026
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Comment thread src/benchmarks/micro/libraries/System.IO/BinaryWriterExtendedTests.cs Resolved
Comment thread src/benchmarks/micro/libraries/System.IO/BinaryWriterExtendedTests.cs Resolved
Comment thread src/benchmarks/micro/libraries/System.IO/BinaryWriterTests.cs Resolved
@jeffhandley
Add comments explaining significance of '\u00E0' character selection
c0cca99 
Co-authored-by: jeffhandley <1031940+jeffhandley@users.noreply.github.com>
Copilot AI requested a review from jeffhandley February 16, 2026 02:42
@jeffhandley
jeffhandley marked this pull request as ready for review February 16, 2026 03:02
Copilot AI review requested due to automatic review settings June 26, 2026 10:50
Copilot AI reviewed Jun 26, 2026
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Pull request overview

Adds additional microbenchmarks for BinaryWriter to cover both UTF-8 and non-UTF-8 encoding paths, with new scenarios targeting Unicode (UTF-16) and non-ASCII input.

Changes:

  • Expanded existing UTF-8 benchmarks to include non-ASCII string and char[] inputs.
  • Added new Encoding.Unicode benchmarks to exercise non-UTF-8 code paths for Write(string), Write(char[]), and Write(char).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File Description
src/benchmarks/micro/libraries/System.IO/BinaryWriterExtendedTests.cs Adds non-ASCII UTF-8 benchmarks and a new Encoding.Unicode benchmark class for string/char[] writes.
src/benchmarks/micro/libraries/System.IO/BinaryWriterTests.cs Adds a new Encoding.Unicode benchmark class for Write(char).

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Comment thread src/benchmarks/micro/libraries/System.IO/BinaryWriterTests.cs Resolved
Comment thread src/benchmarks/micro/libraries/System.IO/BinaryWriterTests.cs Resolved
Comment thread src/benchmarks/micro/libraries/System.IO/BinaryWriterExtendedTests.cs Resolved
Comment thread src/benchmarks/micro/libraries/System.IO/BinaryWriterExtendedTests.cs Resolved
@build-analysis build-analysis Bot mentioned this pull request Jun 26, 2026
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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Copilot AI review requested due to automatic review settings July 9, 2026 18:28
Copilot AI reviewed Jul 9, 2026
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Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

Comment thread src/benchmarks/micro/libraries/System.IO/BinaryWriterTests.cs
Comment on lines +83 to +86
/// <summary>
/// Benchmarks for BinaryWriter using a non-UTF-8 encoding (Encoding.Unicode),
/// exercising the non-UTF-8 path used by Write(char).
/// </summary>
Comment thread src/benchmarks/micro/libraries/System.IO/BinaryWriterExtendedTests.cs
_inputAsChars = _input.ToCharArray();
_asciiInput = new string('x', StringLengthInChars);
_asciiInputAsChars = _asciiInput.ToCharArray();
// '\u00E0' (à) encodes to 2 bytes in UTF-8, exercising multi-byte encoding paths
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@adamsitnik adamsitnik Awaiting requested review from adamsitnik
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