Perl 5.6 and earlier used a quicksort algorithm to implement
               sort.  That algorithm was not stable, and could go quadratic.
               (A stable sort preserves the input order of elements that
               compare equal.  Although quicksort’s run time is O(NlogN) when
               averaged over all arrays of length N, the time can be O(N**2),
               quadratic behavior, for some inputs.)  In 5.7, the quicksort
               implementation was replaced with a stable mergesort algorithm
               whose worst-case behavior is O(NlogN).  But benchmarks
               indicated that for some inputs, on some platforms, the original
               quicksort was faster.  5.8 has a sort pragma for limited
               control of the sort.  Its rather blunt control of the
               underlying algorithm may not persist into future Perls, but the
               ability to characterize the input or output in implementation
               independent ways quite probably will.  See sort.

I see you used

perldoc -f sort | grep -C5 algo
[download]

:)

Considering that the first line of my quote contains the word 'algorithm', you're obviously very, very wrong.