flate: Fix matchlen L5+L6 #1049
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Regression from #1045
📝 WalkthroughWalkthroughThe pull request modifies the Changes
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🧹 Nitpick comments (1)
flate/fast_encoder.go (1)
176-177: Remove or update the unreachable comment.The comment "Extend the match to be as long as possible" after the return statement is unreachable. Consider either:
- Removing the comment if it's no longer relevant
- Moving it to the function's documentation if it describes the function's purpose
- Updating it if it indicates missing functionality
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flate/fast_encoder.go(2 hunks)
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- GitHub Check: build (1.23.x, windows-latest)
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🔇 Additional comments (3)
flate/fast_encoder.go (3)
154-156: LGTM! Clean initialization changes.The use of
minfunction simplifies the boundary check logic, and the explicit type initialization ofnasint32(0)ensures type consistency.
Line range hint
154-176: Verify regression fix from PR #1045.The changes look well-structured and focus on correctness. Let's verify these changes properly address the regression mentioned in PR #1045.
✅ Verification successful
Changes align with PR #1045 objectives - simplifying matchlen implementation
The implementation correctly addresses the regression by:
- Replacing architecture-specific assembly with a simplified, generic implementation
- Utilizing efficient 64-bit word comparisons via unsafe.Load64
- Maintaining correctness while removing conditional complexity
🏁 Scripts executed
The following scripts were executed for the analysis:
Script:
#!/bin/bash # Get context about the regression from PR #1045 gh pr view 1045 --json title,body # Look for related test failures or issues gh issue list --search "matchlen L5 L6" --state all --limit 5Length of output: 277
Script:
#!/bin/bash # Clone the repository and fetch PR details git clone https://github.com/klauspost/compress.git . gh pr view 1045 --json title,body # Search for related test files fd -e go test --exec rg -l "matchlen|L5|L6" {} # Look for benchmark files fd -e go bench --exec rg -l "matchlen|L5|L6" {}Length of output: 1143
160-164: Verify the bit manipulation logic for edge cases.The use of
bits.TrailingZeros64with>>3correctly identifies the first differing byte. Let's verify this works correctly for all edge cases.✅ Verification successful
Bit manipulation implementation is correct and well-tested
The use of
bits.TrailingZeros64(diff)>>3is a proven pattern for byte-level matching, consistently implemented across multiple compression algorithms in the codebase. The implementation is safe and properly handles edge cases through its loop structure and bounds checking.🏁 Scripts executed
The following scripts were executed for the analysis:
Script:
#!/bin/bash # Search for tests that verify this logic rg -A 10 "TrailingZeros64.*>>3" --type go # Look for any related test cases ast-grep --pattern 'func Test$_(test|match).*\{ $$$ bits.TrailingZeros64 $$$ }'Length of output: 1767
Script:
#!/bin/bash # Look for test files rg -l "Test.*match.*" --type go flate/ # Check test implementations rg -A 10 "func Test.*match" --type go flate/Length of output: 87
Script:
#!/bin/bash # Find all test files in flate directory fd _test.go$ flate/ # Look for test functions in these files rg "^func Test" --type go flate/ # Search for byte comparison related tests rg -B 2 -A 5 "bits\.TrailingZeros|matchLength" flate/*_test.goLength of output: 3675
Regression from #1045
Summary by CodeRabbit