gh-119105: Differ.compare is too slow [for degenerate cases] #119492
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…window of 10 lines, and picks "the first" pair within the current window with a ratio > cutoff to synch on. This should make cubic-time cases impossible. It may change results in some cases, but I don't think I care - difflib is fundamentally opposed to synching on lines "far apart", and using a window enforces a notion of locality.
Stop tresting junk lines specially - if we synch on junk, so be it - it almost never occurs in real life anyway.
estyxx
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…ython#119492) ``_fancy_replace()`` is no longer recursive. and a single call does a worst-case linear number of ratio() computations instead of quadratic. This renders toothless a universe of pathological cases. Some inputs may produce different output, but that's rare, and I didn't find a case where the final diff appeared to be of materially worse quality. To the contrary, by refusing to even consider synching on lines "far apart", there was more easy-to-digest locality in the output.
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Make it impossible for
Differ.compare()to degenerate to cubic-time. This may change results in some cases, but no natural ones come to mind, and I don't care about contrived cases.