https://elixir.bootlin.com/glibc/glibc-2.40.9000/source/stdlib/qsort.c

It uses quicksort with optimizations and fallback to insertion sort for small partitions.

overall time complexity is:

• Average Case: O(n log n)
• Worst Case: O(n²)
• Best Case: O(n log n)

space complexity:

• O(log n)