Author: Sune Fischer
Date: 15:43:29 06/18/02
Go up one level in this thread
On June 18, 2002 at 17:56:58, Robert Hyatt wrote:
>On June 18, 2002 at 16:02:45, Sune Fischer wrote:
>
>>On June 18, 2002 at 12:11:57, Robert Hyatt wrote:
>>>
>>>OK... define "MATE" as 32768, for now.
>>>
>>>If you find a move at the root that leads to a mate in 4, the score
>>>will typically be 32768 - 8 since you find you are mated at ply=8 and
>>>you return MATE-ply (I do, anyway). Therefore, the root score that
>>>gets backed up will be 32760, and so far, all is well. That means that
>>>the "mate score" that gets returned from ply = 8 has to be - ( MATE - PLY )
>>>so that - is bad for the side on move at ply=8.
>>>
>>>Note that you have 4 moves for the program in the path, the move at
>>>ply=1, 3, 5 and 7. When you store a hash table entry at ply=7, you
>>>should store MATE-1, since the move at ply 7 will result in a MATE at
>>>ply=8. At ply 5, you should store MATE-3, at ply 3 you should store MATE-5
>>>and if you want to store the entry at the root, it would be MATE-7.
>>>
>>>All this means is that at any point in the path that terminates in a mate
>>>score of any kind, you have to adjust the score so that it is a mate-in-N
>>>from the current ply, not from the root. Because the root score is wrong
>>>at the current ply, since we are _closer_ to the final mate than we were at
>>>the root of the search.
>>>
>>>If that isn't clear enough, ask again. You can find how I return a mate score
>>>by looking at the bottom of search.c in Crafty (look for string MATE). You can
>>>find how I adjust the mate score before I store it in the hash table by looking
>>>at hash.c, module Store()...
>>>
>>>Bob
>>
>>I think that _is_ what I'm doing!?
>>
>>#define CHECKMATE 100000
>>#define CMSCORE 99000
>>
>>search() {
>>..
>> if (!movesfound) {
>> if (InCheck(wtm))
>> score=-CHECKMATE+depthroot;
>> else
>> score=DRAWSCORE;
>> }
>>...
>>}
>>
>>hasprobe() {
>>...
>> switch (phash->flag) {
>> case HASH_EXACT:
>> if (abs(score)>CMSCORE){
>> if (score>0)
>> score-=depthroot;
>> else
>> score+=depthroot;
>> }
>>...
>>}
>>
>>hashstore() {
>>...
>> if (abs(score)>CMSCORE){
>> if (score>0)
>> score+=depthroot;
>> else
>> score-=depthroot;
>> }
>>...
>>}
>>
>>"depthroot" is just distance to the root position we are searching, I assume it
>>is identical to yours "ply" variable.
>>
>>Something must be wrong, I get weird results, it does work fine, it seems, but
>>when I look at the log I'm worried.
>
>One last thing: when you store the score, how do you do that? IE I use N
>bits for the score, and to avoid sign-extension for negative numbers, I add a
>constant larger than any possible negative score and then store the sum. If
>you do that, you aren't suffering from an overflow??? IE 1 bit can make a big
>difference.
No overflow, I'm using a full 4 byte signed integer for the score.
That's because I'm using milipawns, so two bytes is not enough.
Three bytes would be enough, but that's just an optimization I can play with
later.
>>
>>This position was from a quick test game, it's mate in 3, but I get mate in 1
>>three times in a row, but it doesn't have a problem playing the right moves,
>>really strange...
>>[D]1r2qrk1/n5p1/1p1p2P1/p2p2P1/2P1pPK1/P1PB2P1/2Q5/1R5R w - - 0 1
>>
>>-S.
>
>
>I get a mate in 3. I make a move, get mate in 2, make a move and get
>mate. All from the hash table after the mate in 3 is found...
...but you couldn't find anything wrong with what I pasted?
I don't see anything wrong with it either, matescore is first adjusted for
distance to root, then when recorded to hash it is readjusted to be the distance
from where I save to the mate, and when I probe it's adjusted again by adding
the current distance to root.
Why tha' heck isn't that working??
-S.
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