Computer Chess Club Archives




Subject: Re: Fail Soft question

Author: Chan Rasjid

Date: 11:31:29 02/18/06

Go up one level in this thread

On February 18, 2006 at 07:52:10, David B Weller wrote:

>Hi Vincent,
>Yes. That is what I am doing. Will try and remove those.
>Let me make sure I understand perfectly:
>If a hash entry is LOWER or UPPER bound AND exceeds current search bounds, just
>return bounds. Do NOT return hashed value.

Hello David,

I am surprised you understand Vincent. I have a hard time as he gives only
subtle hints.

I have done TT and fail-soft many times over and still have no inkling if there
should be things to take special care of.

If I am right, fail-soft is always better. When a node FL, best may be < alpha
and we hash best and not the bound alpha. When it is FH, best is likely > beta
and we hash best and not beta.The lower/upper in TT will always be more useful
when the bounds are as "tight" as we get; ie smallest upper or greatest lower.

Following a strict coding usually prevents mistakes. eg.

v = hashProbe(&bound);//etc....

case lower:
 if (v >= beta)
 return v;//FH
case upper:
 if (v <= alpha)
 return v;//FL- search dont get better

Best regards

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