Author: Tord Romstad
Date: 02:39:24 03/08/06
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On March 07, 2006 at 21:42:15, Robert Hyatt wrote: >On March 07, 2006 at 16:01:57, Dann Corbit wrote: > >>Fruit uses late move reductions, and yet the search is perfectly symmetrical. > >Same number of nodes at same depth in all 4 positions? No, not even from the initial position, as you can see from my reply to Dann. >I don't see how he does it, but then again, bitboard programs have different >issues. I have FirstOne() and LastOne(). But if you flip the board >horizontally, I can't flip the way those two functions find the first 1 bit, >so my moves are generated in a different order. Even if a program has perfectly symmetrical move ordering (which Fruit does not have, by the way), the search will not be symmetrical, because of the hash table. When sufficiently many of the lower order bits of the Zobrist keys of two different positions match, they will be stored to the same address in the transposition table. The lower order bits of the two corresponding mirrored positions will of course generally not resemble each other at all, and the positions will no longer be stored to the same address. This means that the search can never be symmetrical, as long as a transposition table is used. Tord
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