A C++ implementation of TimSort, an O(n log n) stable sorting algorithm, ported from Python's and OpenJDK's.

See also the following links for a detailed description of TimSort:

• http://svn.python.org/projects/python/trunk/Objects/listsort.txt
• http://en.wikipedia.org/wiki/Timsort

This version of the library requires at least C++20. Older versions of the library, available in different branches, offer support for older standards though implement fewer features:

• Branch 2.x.y is compatible with C++11, and is slightly more permissive in some reagard due to the lack of concepts to constrain its interface (it notaby supports iterators without postfix operator++/--).
• Branch 1.x.y is compatible with C++03. Older versions are not actively maintained anymore. If you need extended support for those, please open specific issues for the problems you want solved.

According to the benchmarks, gfx::timsort is slower than std::ranges::sort on randomized sequences, but faster on partially-sorted ones. It can be used as a drop-in replacement for std::ranges::stable_sort, with the difference that it can't fall back to a O(n log² n) algorithm when there isn't enough extra heap memory available.

Merging sorted ranges efficiently is an important part of the TimSort algorithm. This library exposes gfx::timmerge in the public API, a drop-in replacement for std::ranges::inplace_merge with the difference that it can't fall back to a O(n log n) algorithm when there isn't enough extra heap memory available. According to the benchmarks, gfx::timmerge is slower than std::ranges::inplace_merge on heavily/randomly overlapping subranges of simple elements, but it is faster for complex elements such as std::string, and on sparsely overlapping subranges.

The ibrary exposes the following functions in namespace gfx:

// timsort template < std::random_access_iterator Iterator, std::sentinel_for<Iterator> Sentinel, typename Compare = std::ranges::less, typename Projection = std::identity > requires std::sortable<Iterator, Compare, Projection> auto timsort(Iterator first, Sentinel last, Compare compare={}, Projection projection={}) -> Iterator; template < std::ranges::random_access_range Range, typename Compare = std::ranges::less, typename Projection = std::identity > requires std::sortable<std::ranges::iterator_t<Range>, Compare, Projection> auto timsort(Range &range, Compare compare={}, Projection projection={}) -> std::ranges::borrowed_iterator_t<Range>; // timmerge template < std::random_access_iterator Iterator, std::sentinel_for<Iterator> Sentinel, typename Compare = std::ranges::less, typename Projection = std::identity > requires std::sortable<Iterator, Compare, Projection> auto timmerge(Iterator first, Iterator middle, Sentinel last, Compare compare={}, Projection projection={}) -> Iterator; template < std::ranges::random_access_range Range, typename Compare = std::ranges::less, typename Projection = std::identity > requires std::sortable<std::ranges::iterator_t<Range>, Compare, Projection> auto timmerge(Range &&range, std::ranges::iterator_t<Range> middle, Compare compare={}, Projection projection={}) -> std::ranges::borrowed_iterator_t<Range>;

Example of using timsort with a defaulted comparison function and a projection function to sort a vector of strings by length:

#include <string> #include <vector> #include <gfx/timsort.hpp> size_t len(const std::string& str) { return str.size(); } // Sort a vector of strings by length std::vector<std::string> collection = { /* ... */ }; gfx::timsort(collection, {}, &len);

The library is tested with the following compilers:

• Ubuntu: GCC 10, Clang 11
• Windows: MSVC 19.37.32826.1, MinGW-w64 GCC 12
• MacOS: GCC 10, Clang 17

The library can be installed on the system via CMake (at least 3.14) with the following commands:

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release cmake --install build

Alternatively the library is also available Conan Center and can be directly installed in your local Conan cache with the following command:

conan install --requires=timsort/3.0.1

The following configuration macros allow gfx::timsort and gfx::timmerge to emit diagnostics, which can be helpful to diagnose issues:

• Defining GFX_TIMSORT_ENABLE_ASSERT light inserts assertions in key locations in the algorithm to avoid logic errors.
• Defining GFX_TIMSORT_ENABLE_AUDIT inserts assertions that verify pre- and postconditions. These verifications can slow the algorithm down significantly. Enable the audits only while testing or debugging. Enabling audits automatically enables lighter assertions too.
• Defining GFX_TIMSORT_ENABLE_LOG inserts logs in key locations, which allow to follow more closely the flow of the algorithm.

cpp-TimSort follows semantic versioning and provides the following macros to retrieve the current major, minor and patch versions:

GFX_TIMSORT_VERSION_MAJOR GFX_TIMSORT_VERSION_MINOR GFX_TIMSORT_VERSION_PATCH

The tests are written with Catch2 and can be compiled with CMake and run through CTest.

When using the project's main CMakeLists.txt, the CMake option BUILD_TESTING is ON by default unless the project is included as a subdirectory. The following CMake options are available to change the way the tests are built with CMake:

• GFX_TIMSORT_USE_VALGRIND: if ON, the tests will be run through Valgrind (OFF by default)
• GFX_TIMSORT_SANITIZE: this variable takes a comma-separated list of sanitizers options to run the tests (empty by default)

Benchmarks are available in the benchmarks subdirectory, and can be constructed directly by passing the option -DBUILD_BENCHMARKS=ON to CMake during the configuration step.

Example bench_sort output (timing scale: sec.):

c++ -v Apple LLVM version 7.0.0 (clang-700.0.72) Target: x86_64-apple-darwin14.5.0 Thread model: posix c++ -I. -Wall -Wextra -g -DNDEBUG -O2 -std=c++11 example/bench.cpp -o .bin/bench ./.bin/bench RANDOMIZED SEQUENCE [int] size	100000 std::sort 0.695253 std::stable_sort 0.868916 timsort 1.255825 [std::string] size	100000 std::sort 3.438217 std::stable_sort 4.122629 timsort 5.791845 REVERSED SEQUENCE [int] size	100000 std::sort 0.045461 std::stable_sort 0.575431 timsort 0.019139 [std::string] size	100000 std::sort 0.586707 std::stable_sort 2.715778 timsort 0.345099 SORTED SEQUENCE [int] size	100000 std::sort 0.021876 std::stable_sort 0.087993 timsort 0.008042 [std::string] size	100000 std::sort 0.402458 std::stable_sort 2.436326 timsort 0.298639 

Example bench_merge output (timing scale: milliseconds; omitted detailed results for different middle iterator positions, reformatted to improve readability):

c++ -v Using built-in specs. ... Target: x86_64-pc-linux-gnu ... gcc version 10.2.0 (GCC) c++ -I ../include -Wall -Wextra -g -DNDEBUG -O2 -std=c++11 bench_merge.cpp -o bench_merge ./bench_merge size	100000 element type\algorithm:	std::inplace_merge	timmerge RANDOMIZED SEQUENCE [int] approx. average 33.404430 37.047990 [std::string] approx. average	324.964249	210.297207 REVERSED SEQUENCE [int] approx. average 11.441404 4.017482 [std::string] approx. average	305.649503	114.773898 SORTED SEQUENCE [int] approx. average 4.291098 0.105571 [std::string] approx. average	158.238114 0.273858 

Detailed bench_merge results for different middle iterator positions can be found at https://github.com/timsort/cpp-TimSort/wiki/Benchmark-results