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Thu, 20 Jan 2011

Blunder's PGN-to-FEN converter nearing completion

The minor re-design, or major refactoring, of Blunder's PGN-to-FEN converter was finished three days after my last blog post about it. It went very well, the new code which replaced the old code is more abstract and flexible, looks better and works better. Funny how these things go together - it seems good coding practices solve a lot of the headaches of coding and things begin working automagically.

I mentioned problems in Lutz Tautenhahn's PGN-to-FEN converter in my last blog post. After writing it, I decided to e-mail him a bug report. Within 14 hours he fixed the bug and posted new code, which I tested, and both problems were fixed. So Lutz's converter is now working without problem, as far as I can see.

I've fixed many things in the PGN-to-FEN converter since the redesign/refactor. I check in every (?) manner if a move would put the king in check. I now handle many (all?) en passant scenarios. I also now deal with PGNs where a FEN position in the middle of a game is given, and where the subsequent moves are from that position (i.e. we start in the middle of the game). I made other changes as well.

I just made my most satisfying commit since the redesign/refactoring. It was the fruit of other commits before. First I began marking games on the linked list as I went, not all in the beginning (which caused an initial delay when parsing large PGNs with many games). Then I pushed code into the Game class that I had wanted to push there for a while. All of this allowed me to do the latest commit.

I was reading the entire PGN into a linked list in the PGN class, and then pushing the entire linked list into other classes like Game. As Game only needs one game, I created a second, short linked list with only one game, and pushed that to Game. As the original data on the first, long list is no longer needed, I removed it. I am always dealing with the head of the linked list in these cases. Anyhow, this process of dealing only with the head of the larger linked list, and shrinking it as the program goes, has made the program over ten times faster.

So what more is there to do? People have their own bizarre implementations of the PGN format. I handle many of them, but there are a few more out there I might do. All of the code is working, but I might clean up some of it so that it is easier to read and cleaner. I also might work on a user interface other than running the jar file from the command line. I might also discover some edge cases of the en passant sort that I am not dealing with. I have tested tens of thousands of games, and have been looking over FIDE chess rules, the specifications and so forth, so I don't think there will be much more of this type. The program is in decent enough shape right now, I guess I just want to deal with a few more of the oddball PGN implementations, and fix up the UI a little bit, before I feel this is fully formed in its first generation. But it is working pretty well as it is.

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