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Subject: Re: How to extend if only one reply?

Author: Robert Hyatt

Date: 18:34:17 01/23/01

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On January 23, 2001 at 14:59:40, Severi Salminen wrote:

>Hi!
>
>I want my engine to also solve these mate in 3871 positions fast :) So: how do
>you guys extend if there is only one legal reply in node. Obviously you have to
>check the legality before trying that move. So do you allways when the king is
>in check check the legality of all moves and if that results one legal move you
>extend? Are there another ways to do this?
>
>Severi


I do this, yes.  Because if you know you are in check, most of the moves a
normal move generator will produce are illegal.  It is faster to simply not
generate them.  This has the added convenience of giving you a real easy way
of detecting the case where you have only one legal move so you can extend.

I didn't do this in Cray Blitz so there is an alternative.  Do the normal
search, but each time you search a legal move, inc a counter.  When you are
done searching all moves, if the counter == 1, there was only one legal one
to search.  Search it _again_ but one ply deeper...




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