Author: Omid David Tabibi
Date: 02:28:59 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... > >> >>In the case that unmake is better. by wich factor ? > > > >For me, just faster. Not 300% or any such number, but at least 25% if >not more. > > Up until now almost all my data was global, updated in make_move and takeback. However, the more data structures I add, the more costly takeback becomes. Now I'm trying to dynamically update my attack tables in make_move, which is a very costly operation. Even though the attack tablea are about 256 bytes, I think copying them will be far cheaper than resotorig in take_back. So, it seems that one should experiment with each piece of data to find out whether resotring in takeback is cheaper than copying the structure. > > >> >>Thanks for your help. >> >>Mathieu Pagé
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