A stable adapative mergesort implementation

This is a lightweight library offering two high performance sort functions:

• sortArrayBy sorts a GHC MutableArray# of boxed elements in place.
• sortIntArrayBy sorts a GHC MutableByteArray# of Int#s in place.

There are no dependencies outside of base. This means that this library is not tied to array abstractions from any particular library. This also means that you may need to write a few lines of code to get a MutableArray# or MutableByteArray# from your data, which can then be sorted. See HOWTO.md for a guide.

If you need to use this library in an environment where you cannot depend on other packages, you may simply copy the lone source file src/Data/SamSort.hs to your project.

• The sort is a comparison-based $O(n \log n)$ mergesort.
• The sort is stable, i.e. the order of equal elements in the input is preserved.
• The sort is adaptive, i.e. the sort identifies and uses ascending and descending runs of elements occuring in the input to perform less work. As a result, the sort is $O(n)$ for already sorted inputs.
• The sort is the fastest among implementations from other libraries in most scenarios. See the benchmarks for details.

Ideally, this library would offer only an algorithm, capable of sorting arrays of any flavor. To support different arrays we would need to rely on some abstraction, either from another library (like vector), or created here. We cannot do either of those while also keeping the library as lightweight as it is now.

Questions, bug reports, documentation improvements, code contributions welcome! Please open an issue as the first step. Slow performance counts as a bug!