Author: John Lowe
Date: 02:41:50 12/24/02
Go up one level in this thread
On December 24, 2002 at 05:32:06, Uri Blass wrote: >On December 24, 2002 at 04:16:11, John Lowe wrote: > >>On December 23, 2002 at 20:23:04, Robert Hyatt wrote: >> >>>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. >> >>I have understood good capture, killer and history but could you expand "hash >>move" a little. (Terra incognita for me) > >hash move is a move that you remember from the hash tables and caused a fail >high in the same position in previous search. > >Uri That's what I thought but why "try" again - have some parameters changed?
This page took 0 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.