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Subject: Re: Improvements in BF makes my MoveGen suck =(

Author: Christophe Theron

Date: 12:02:40 06/27/03

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On June 27, 2003 at 08:13:53, Albert Bertilsson wrote:

>Just wanted to share my latest findings and warn you from making the same
>mistake (or maybe I just point out the obvious).
>I've always been proud to have a very fast movegen, doing perft calculations
>very fast. I optimized the movegen alot, and always saw playing strength
>increasing. I use a legal move generator and always saw the cost of verifying
>legality to be minor. Lately however I've noticed that the engine performance
>isn't that great (compared to other engines) inspite of the fast movegen. So I
>started digging today and the numbers struck me as lightning...
>As I've improved moveordering very much with hashtable/iterative deepening,
>killer moves and history tables the effective BF is now much lower. The lower BF
>now means that very few moves of all the generated ones are actually ever made.
>This means that the cost of generating legal moves have increased incredibly
>It's really anoying to notice that something you though was very good now is on
>the list of improvements again =(.
>/Regards Albert

You have just discovered something that took me years to understand:

>>> in a chess program, do not compute something if you do not have an immediate need for it. <<<


>>> Do not compute something that you are going to use later if there is the slightest chance that you will not use it. <<<

That's why I think that basically the idea of generating lists of legal moves
only is flawed. You are wasting time computing something that in general you are
not going to use.

Generating lists of moves in general is sub-optimal. It's much better to
generate move lists incrementally (moves should be generated on demand, a
complete list is never generated).

I have the same opinion about attack tables, but it depends on what you are


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