Author: Christophe Theron
Date: 16:51:15 08/20/03
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On August 20, 2003 at 13:36:59, Sune Fischer wrote: >On August 20, 2003 at 13:05:17, Christophe Theron wrote: >>>Copying a struct does take time, and it can easily be pinpointed. Saving and >>>restoring and unupdating also takes time, but is harder to identify. Especially >>>since the stress on code cache and branch prediction don't show up in a run time >>>profile. >>> >>>... Johan >> >> >> >>I'm not surprised by Bob results on this issue, as Crafty has a *lot* of things >>to save/restore, and all of them are rather big structures. >> >>In a non-bitboard program like Chess Tiger, saving/restoring is probably faster. >>At least it is in Chess Tiger. >> >>I do not know if you are using bitboards in The King. Do you? >> >>Actually I'm using a mix of undo and restore: I do not save the chessboard >>itself because undoing a move involves very few read/write operations. So I undo >>the move "manually" on the chessboard but restore with a memcpy a single >>structure that holds the rest of the chessboard and a part of the search state. >>I seem to remember that this structure is less than 40 bytes big, so restoring >>it is really no problem, and as you pointed out most of the time the data to be >>restored still lies in the L1 cache. >> >>In any case I cannot imagine that restoring the hash key for the current >>position from memory could be slower than computing it again by undoing a >>sequence of XORs (at least 2) on a 64 bits integer... > >Actually I think you are doing the same as Crafty, Crafty is using a mix of >copying and undoing as well. >The expensive stuff, hash key and rotated boards are copied back. >The piece bitboards don't all need accessing, perhaps just 1 or 2 out of ~20, so >for this undoing is faster. > >-S. Oh well... Last time I glanced at Crafty I think it was version 9.2 or something... :) Christophe
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