Author: Uri Blass
Date: 23:12:42 03/24/04
Go up one level in this thread
On March 24, 2004 at 20:16:26, Tom Likens wrote: >On March 24, 2004 at 16:59:57, Dieter Buerssner wrote: > >>On March 24, 2004 at 14:26:04, Tom Likens wrote: >> >>>How do you handle extensions? Currently, most of my extensions are >>>set after the engine moves and since the extensions affect the draft >>>(which in turn affects the validity of the hash match) it seems like this is >>>a problem. This might be workable (in my current scheme) if I started >>>tracking the extensions that were triggered by a move in the hash >>>table. >> >>I don't get it. How could you track the extensions that were triggered by a >move in the hash? We are speaking about the situation (current position) is >>already after that move. > >I'll try to explain what I was referring to in my previous post. Hopefully, >I won't mess it up too badly (although I make no guarantees). According to >my reading of Plaat and Schaeffer's original ETC forumlation the order things >occur in is roughly: > >1. When first entering a node, check the transposition table for a match. > If found then handle it (return up the tree etc.), otherwise... >2. Generate all the moves for this node >3. Make the first (next) move in the move list >4. Check this new position for a hash match (this is the ETC part) >5. If we find a match then handle it and return back up the tree, > if appropriate >6. Goto 3 and repeat until all moves are exhausted > >Most implementations that I know of, don't actually perform step 3 but instead >simply update the hash key without making the move. But we still need to >recreate the extensions for this move in order to determine if the draft is >OK (and hence if the match is valid). We need to recreate the extensions only in case that there is a match and in most cases it is easy to find that there is no match. making moves only when there is a match and you are not sure if to prune should be clearly cheaper than making moves for all legal moves Uri
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