Mate scores from IID

[ZirconiumX]

I was looking through the Stockfish source code, and noticed that it simply discards the search result. Which, to be fair, seems to be the common thing to do.

But say you get a mate score from IID. Since you're searching with the same window, the score should still be valid, right? So wouldn't it make sense to simply cutoff from this instead of going for a full depth search?

[Dann Corbit]

I was looking through the Stockfish source code, and noticed that it simply discards the search result. Which, to be fair, seems to be the common thing to do.

But say you get a mate score from IID. Since you're searching with the same window, the score should still be valid, right? So wouldn't it make sense to simply cutoff from this instead of going for a full depth search?

It's already in the hash table. I guess the real search will find it in a snap

[hgm]

But the IID result will not have enough depth to satisfy the real search. Unless you correct the draft of mate scores you are certain of to infinite. And you should do that on probing when you use the draft for a depth-preferred replacement scheme, or the whole table would be poisoned with mate scores.

But it should be safe to correct the draft of a mate-in-N score to infinity when it originally was >= 2*N-1, before you compare it with the requested depth.

[ZirconiumX]

I was looking through the Stockfish source code, and noticed that it simply discards the search result. Which, to be fair, seems to be the common thing to do.

But say you get a mate score from IID. Since you're searching with the same window, the score should still be valid, right? So wouldn't it make sense to simply cutoff from this instead of going for a full depth search?

It's already in the hash table. I guess the real search will find it in a snap

Perhaps so, but the cutoff will still save effort of things like evaluations, pruning and search stack setup. It probably won't save much effort, but it should still be worth something.

[hgm]

The IID search should have already done these things, or you would also waste that effort every time IID does not return a mate score.

[jdart]

I set an EXACT flag in the node structure when a search returns an exact score, including mate, stalemate, tablebase hit.

IID searches that return with this flag set return a score immediately and don't search further.

--Jon