Author: Robert Hyatt
Date: 14:56:58 06/18/02
Go up one level in this thread
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.
>
>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...
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