Author: Robert Hyatt
Date: 17:23:04 12/23/02
Go up one level in this thread
On December 23, 2002 at 19:21:57, Uri Blass wrote: >On December 23, 2002 at 18:31:03, Dieter Buerssner wrote: > >>On December 23, 2002 at 18:08:15, Martin Bauer wrote: >> >>>Hello, >>> >>>i have a queastion about move ordering. There are many sources with move >>>ordering heuristics like killer heuristic, history and so on... >>> >>>But I found no description _how_ to program the move ordering in an _efficient_ >>>way. In my own enginge I use an integer value together with the move and put it >>>on the move stack. Moves that should be searched first, become a high value and >>>the less important moves a low one. Then there is a function named >>>"NextBestMove" that that looks for the highest value at the actual searchdepth >>>on the movestack. Therefore it must look at all possible moves in the actual >>>position. When the best move is found, the value is set to -Matescore, so it can >>>not get the best move the next time the function is called. >> >>This is the normal way to do it, I think. Instead of giving a "marker score", to >>not search the move again, you could shift the move to the start or to the end >>of the array, and remember the new bounds (incrementing a pointer may be enough >>for this). This will save a few CPU cycles. It is essentially the inner loop of >>a normal selection sort. >> >>>This algorithm must have a look at all possible moves in the position at the >>>actual depth, even if the frist 10 best moves are searched. This look not >>>efficient to me, because it is an O(n) algorithm in reading the best move and >>>O(1) in storing the best move. >> >>I think, there is no practical better way. Sorting the whole move list can >>easily be done faster (especially, when it has some considerable length, so not >>just relpy to check). But often, the work will be done for nothing, because one >>move will be enough for a cutoff. I experimented a bit with the following idea: >>Try to guess, when we expect a fail high node: use the selection sort method >>above. Whe expecting a fail low node, do a qsort (the Standard C-language qsort >>would probably be a bit slow for this, because of all the calls to the compare >>function, I had written my own). But, I really could not measure any performance >>increase, so I gave up on the idea. It just made the code bigger ... > >If you expect a fail low move you can simply not care about order of moves. >Latest movei does not continue to sort the moves if the first 10 moves did not >give a fail high(I do not know if 10 is the best number but the gain that I may >get from changing it is small because movei is not a fast searcher). > >Uri I've done this in crafty for many years. I try the hash move, the good capture moves, the killer moves (2), and then if the first 4 history moves don't produce a fail high, I just take the remaining moves in the order they were generated. saves time.
This page took 0.01 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.