This module implements various algorithms based on the introsort algorithm, originally described by David R. Musser in the paper /Introspective Sorting and Selection Algorithms/. It is also in widespread practical use, as the standard unstable sort used in the C++ Standard Template Library.

Introsort is at its core a quicksort. The version implemented here has the following optimizations that make it perform better in practice:

• Small segments of the array are left unsorted until a final insertion sort pass. This is faster than recursing all the way down to one-element arrays.
• The pivot for segment [l,u) is chosen as the median of the elements at l, u-1 and (u+l)/2. This yields good behavior on mostly sorted (or reverse-sorted) arrays.
• The algorithm tracks its recursion depth, and if it decides it is taking too long (depth greater than 2 * lg n), it switches to a heap sort to maintain O(n lg n) worst case behavior. (This is what makes the algorithm introsort).