[oleksandr-pavlyk]

Optimization to c2h::detail::compare_host_ranges to reduce memory usage for large mismatches

When comparing two host ranges we used to retain all mismatches only to display first and last 5. We now only keep those mismatches we want to display.

A test added.

Description

This change is a focused change split off from #11374

Checklist

• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[oleksandr-pavlyk]

See @bernhardmgruber question regarding this change: #11374 (comment) and my response: #11374 (comment)

[coderabbitai]

No actionable comments were generated in the recent review.

Recent review info

Run configuration

• Source mode: Auto
• Repository: NVIDIA/cccl
• Branch: main
• File: .coderabbit.yaml
• Commit: 46c1018
• Layers: Repository YAML
• Review profile: CHILL
• Plan: Enterprise
• Run ID: 2fb2c110-4ca4-49c7-9cd1-c06b1092a6f9

Commits

Reviewing files that changed from the base of the PR and between 46c1018 and 3a16899.

Files selected for processing: 2

• c2h/include/c2h/catch2_test_helper.h
• cub/test/catch2_test_c2h_buffers.cu

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📝 Summary

Summary by CodeRabbit

• Improvements
  • Range comparison results now include the total number of mismatches and representative mismatches from the beginning and end of the range, alongside up to three matching values immediately before the first mismatch.
• Tests
  • Added coverage for mismatch counts from zero through sixteen and for mismatches occurring at different positions.

The change updates compare_host_ranges to count mismatches while retaining bounded details, and adds tests for mismatch counts, ordering, and preceding matching values.

Changes: Mismatch summary collection

Layer / File(s)	Summary
Collect and validate mismatch details c2h/include/c2h/catch2_test_helper.h, cub/test/catch2_test_c2h_buffers.cu	compare_host_ranges counts mismatches during comparison, retains the first five and a rolling set of the last five, and orders the retained tail. The test checks mismatch counts from 0 to 16, retained details, and up to three matching values before the first mismatch.

Possibly related PRs

• NVIDIA/cccl#11374: It changes compare_host_ranges to retain and order the first and last mismatches, and also updates the same test file.

Priority: Low

Change: Refactor

Merge Risk: Minimal · up to 3a168

No actionable merge-blocking issue is identified; the change is mergeable after normal checks.

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[github-actions]

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