Remove Zobrist::noPawns which is no longer necessary #4344
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This Zobrist key is only used once, to initialize a `Position`'s `si->pawnKey`. The `si->pawnKey` is then updated with pawn information as board state is changed. The `si->pawnKey` is itself only used in one place: `Entry::probe`, where it is used to look into the current thread's `pawnsTable`. This is likewise the only place that the thread's `pawnsTable` is used. As a result of the above, we can be confident that this particular key can be removed. It's only ever mixed into a key once, and that key is only ever used to index into a hash table that no other key is used for. Therefore its removal cannot possibly lead to colliding with another key from another source. Bench: 4106793
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This 9eccba7 commit and the mentioned bugs may be of interest. |
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So, I guess that needs some more checking to see if this is a problem with this commit. |
Fascinating! If indeed this PR turns out to not be mergeable, that means then that the code is more than a little bit under commented -- we should add this documentation as an alternative to this PR. |
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After 18fdc2d was merged, Zobrist::noPawns is no longer used anywhere. This should be merged. |
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Merged via 027713c, thanks! |
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This Zobrist key is only used once, to initialize a
Position'ssi->pawnKey. Thesi->pawnKeyis then updated with pawn information as board state is changed.The
si->pawnKeyis itself only used in one place:Entry::probe, where it is used to look into the current thread'spawnsTable. This is likewise the only place that the thread'spawnsTableis used.As a result of the above, we can be confident that this particular key can be removed. It's only ever mixed into a key once, and that key is only ever used to index into a hash table that no other key is used for. Therefore its removal cannot possibly lead to colliding with another key from another source.
Bench: 4106793
https://tests.stockfishchess.org/tests/view/63c5cb8418c20f4929c5fd7e