KF-26 add tests for timsort

[Kellesi]

Task: https://jira.dev.local/jira/browse/KF-26

[Copilot]

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[Copilot]

Pull Request Overview

Adds comprehensive test coverage for the timsort algorithm implementation by creating a new test file with extensive unit tests for all timsort functions.

• Added a new test file TimsortTest.cpp with 1523 lines of comprehensive test cases
• Tests cover all utility functions (cmp, clzll, compute_minrun) and core algorithm functions
• Integrated the test file into the CMake build system

Reviewed Changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 8 comments.

File	Description
test/TimsortTest.cpp	New comprehensive test suite covering all timsort functions with edge cases and normal operations
test/CMakeLists.txt	Added TimsortTest.cpp to the test build configuration
include/kf/algorithm/timsort.h	Minor code improvements and bug fixes discovered during testing

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[Copilot]

This line will cause undefined behavior when arr.size() is 0. The expression arr.size() - 1 will underflow to a very large number since size() returns an unsigned type. Consider adding a check for empty arrays or using a different approach.

Suggested change

	reverse_elements(arr.data(), 0, arr.size() - 1);
	// Avoid underflow: only call if array is non-empty
	if (arr.size() > 0) {
	reverse_elements(arr.data(), 0, arr.size() - 1);
	}

[Kellesi]

Here some functions have unusual or unintuitive usage.
For example, reverse_elements expects end to be the last element instead of the array’s end,
and binary_insertion_sort_start starts at 1 instead of the usual 0.
Might be worth rewriting them in a more standard way to avoid confusion if these functions get used outside of Timsort?

[belyshevdenis]

Here some functions have unusual or unintuitive usage. For example, reverse_elements expects end to be the last element instead of the array’s end, and binary_insertion_sort_start starts at 1 instead of the usual 0. Might be worth rewriting them in a more standard way to avoid confusion if these functions get used outside of Timsort?

Definitely we should fix the logical mistakes in code using logical tests, instead cover illogical functionality.

[Kellesi]

I've fixed small issues and incorrect behavior, but fixing the full logic would take more time because all these functions depend on each other, and I guess I also need approval to do this. And another task for it