Author: Tony Werten
Date: 02:57:14 10/19/00
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On October 18, 2000 at 09:54:25, Robert Hyatt wrote: >On October 18, 2000 at 08:06:23, David Rasmussen wrote: > >>I was wondering about a potential "bug" or at least "unwanted feature" of the >>way hashing and extensions affect eachother in, say, Crafty. >> >>The problem is basically this: >> >>In Crafty, whenever depth is used for other purposes than searching (that is >>hashing and nullmove), the extension factor isn't included. That means that a >>search that essentially asked for a depth=5 + extensions=3 == 8 ply search, will >>return with success from the hashprobe if the draft is just 6 or 7. Shouldn't >>the depth parameter ALWAYS be used with relevant extensions for the search to be >>(at least more) theoretically correct ? >> >>Am I making sense? > > >You are missing an important point. > >Extensions happen _after_ a move is made. Hashing happens at the start of a >ply. If extensions were added in at any previous ply, they are certainly >factored into the hash probe. But there is no way to factor in extensions >triggered by a move, when the hash probe is done _before_ any move is made. > >IE if an in-check extension is done, it is added in at the _previous_ >ply, rather than at the current ply. Which means it is _always_ done. >The only exception is that the one-reply extension isn't done until crafty >discovers that there is only one legal move. But this is perfectly >consistent... How about threat extensions. In the previous search you did a nullmove and found out you're about to be checkmated and so you get an extension. Next search hashtable lookup >= current depth so you abort. I solve this by setting a "got a threat extensions last search" flag. Tony > >Don't forget that the hash entry will be the result of searching _all_ >moves at this ply, which _does_ factor in the extensions for each move as >appropriate...
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