Author: Robert Hyatt
Date: 18:50:05 07/16/04
Go up one level in this thread
On July 16, 2004 at 16:04:28, Volker Böhm wrote:
>Hi,
>
>I am currently refining time control and want to use shorter time when a
>recapture is the only good move.
>I looked at crafty code to get some hints and found to "strange" piece of code.
>
>1.
>Crafty calls quiescense for all root moves and sort the moves according the
>quiescense value returned. If the best move is more than two pawns better than
>the second best move then it is an "easy-move" if a second condition holds true.
>I do not understand the second condition:
>it is:
>(Value[first_move] < PawnValue) || (IsRecapture(first_move). Why does crafty
>handle moves with value < PawnValue different here?
>
Here is the actual code, I've inserted comments to make it clearer:
/* if the first move has a value at least 2 pawns better than the second, then
the first move is sort of "obvious". The idea here is that there is exactly
_one_ good capture to play or else this "easy move" idea won't work. */
if (sort_value[0] > sort_value[1] + 200 &&
/* the move has to be a recapture. IE the To square of the first root move has
to be the same as the To square for the last opponent move. If it isn't a
recapture, I don't trust it. For example try the position given later where an
older version of Cray Blitz thought that taking the knight was "easy" when it
was a blunder. */
((To(rmoves[0]) == To(last_opponent_move) &&
/* What I am capturing must also be the piece the opponent last moved. I am not
sure why this is there as it appears to be redundant. IE if To = To, then piece
must = piece. */
Captured(rmoves[0]) == Piece(last_opponent_move)) ||
sort_value[0] < PAWN_VALUE))
/* This is the "non-recapture" exception. IE You take my knight at h2, I take
your knight at g7. The value says we are equal (score doesn't suggest we are
winning something which needs a full search to be sure it is safe.) */
easy_move = 1;
Here is a test position to see what I mean:
Came from the Cray Blitz vs Belle game at the 1981 ACM NACCC tournament:
[D]5r1k/6p1/1n2Q2p/4p3/8/7P/PP4PK/R1B1q3 w - - 0 1
>2.
>Another question on another aspect of time control. Crafty terminates search if
>time runs low and currently searching the first move of ply 1.
>I have implemented the opposit in Spike. I do not stop searching when currently
>searching the first move of ply 1 because I whant to prove that my current best
>move does not drop in value one depth later. If the value drops I continue
>searching with more time.
>Am I wrong?
If the score is going to drop, it drops quickly. Fail lows are much faster to
search than normal or fail high positions. Here's the reason I do that.
Suppose my opponent takes a _long_ time to make a move, and I get deep into the
search and start a new iteration. Do I want to spend an hour to search the
first move, or should I give up quickly?
>
>Grettings and Thanks
>
>Volker
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