It looks easy enough to me to code up an order independent version that will actually work. I would initialize adds[] and dels[] with old & new berval pointers, iterate through dels[] and adds[] (nested), and clear both on match. The code is easier to follow and empirically I see one fewer matches in the cases I tested it on. But that's just a test of the algorithm - I haven't sorted out what needs to be done at the end of the function where mcur etc. are modified depending on i == j.