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The Hash Move is a Move Ordering related issue.
The Hash Move is a move probed from the transposition table, either a best move of a stored PV-node - a PV-move, or a good enough refutation move to cause a cutoff. This move should most importantly searched first 1 2. One may save the move generation at all, if the hash move actually fails high. To guard against rare TT key collisions, one may apply a legality test of the hash move 3. __FORCETOC__
See also
- Best Move
- Internal Iterative Deepening
- Killer Move
- Mate Killers
- Move Ordering
- Null Move
- Pseudo-Legal Move
- PV-Move
- Refutation Move
- Threat Move from null move refutations
- Transposition Table
Forum Posts
- TTMove legality checking ? & Killers Move Format? by Mahmoud Uthman, CCC, February 08, 2017 » Killer Move
- tt move vs null move by Erin Dame, CCC, May 27, 2017 » Null Move, Null Move Pruning
- Marginal hash move by Harm Geert Muller, CCC, September 16, 2017
- Hash move ordering vs. Hash cuts: savings in number of nodes visited by Marcel Vanthoor, CCC, March 16, 2021
- Best move from previous iteration first: still needed with TT? by Marcel Vanthoor, CCC, March 16, 2021 » PV-Move
- PV-move ordering necessary if you have TT-move ordering? by Marcel Vanthoor, CCC, July 01, 2021
References
but usually after trying the Null Move of the Null Move Heuristic↩︎
tt move vs null move by Erin Dame, CCC, May 27, 2017↩︎
Robert Hyatt, Anthony Cozzie (2005). The Effect of Hash Signature Collisions in a Chess Program. ICGA Journal, Vol. 28., No. 3↩︎