Replace O(n^2) list sort with an O(n log n) merge sort.
The merge sort is based on the solution suggested in:
http://cslibrary.stanford.edu/105/LinkedListProblems.pdf
Tested sort_rules() improvement:
100K rules: O(n^2): 31382 milliseconds; O(n log n): 10 milliseconds
259K rules: O(n^2): 133753 milliseconds; O(n log n): 22 milliseconds
Signed-off-by: Mark Smith <marsmith@akamai.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
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