Author: Johan de Koning
Date: 00:59:38 08/20/03
Go up one level in this thread
On August 19, 2003 at 22:11:14, Robert Hyatt wrote: >On August 19, 2003 at 20:06:58, Mathieu Pagé wrote: > >>Hi, >> >>The fact: >> >>I have this question i read at some place that it is faster to unmake a move >>than to save the state of the game before moving then restoring it when we want >>to unmake the move. >> >>For the moment my engines did not implement unmake() (it is still buggy). >> >>My thougth: >> >>Since bitboard computation are slow (on 32 hardware) i think that it can be >>slower to unmake the move than to save the state. I friend of me that is lot >>better than me at optimizing code also think that. >> >>My questions: >> >>Are you all using unmake() function or there is some of you that found that >>saving the state is better ? > > > >read the comments from Crafty in main.c. I started out using what is >commonly called "copy/make" as that worked well in Cray Blitz. But it >didn't work well in the PC. The PC has very limited memory bandwidth, >when you compare the speed of memory to the speed/demands of current >processors. If you keep the board in cache, and update it there, it is >more efficient than to copy it from real memory to real memory... I hate to play Vincent here, but real memory is not an issue. If you manage to keep the deepest few plies worth of position structs in L1 cache, then bandwith is pretty decent on the PC. And it has been ever since them PCs were endowed with cache. 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
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