Takes hours for finish a 300kb diff file about diff2html

[rtfpessoa]

@escitalopram I did some debugging and the Rematch.distance(amod, bmod) algorithm is taking too long, and maybe getting an infinite loop or something.
Do you have any idea?

[escitalopram]

I'll have a look

[escitalopram]

The problem seems to be triggered by large blocks of changes, like OASIS.csproj having 2,2k lines added and removed in one block. The algorithm is O(nm) time with n lines added and m lines removed in a single block, starting almost 5 million levenshtein distance calculations, which are in turn O(op) time with o,p being the line lengths. I'd suggest we'll just disable the line matching on blocks larger than say n*m=2500 (and maybe make that limit configurable).

The memory hunger will probably go away with that, too, because there is some cache for distance function results. If that isn't enough, maybe I could also introduce some hash function for the cache keys.

[rtfpessoa]

I think that is a great idea. Can you make a PR?

[escitalopram]

Which branch should I base it on?

[rtfpessoa]

master

[rtfpessoa]

Fixed by #68 in release 2.0.0-beta10