🚀 go-pugleaf

In article <3AF5BEF5.AA663175@wretched.demon.co.uk>, 
Simon@wretched.demon.co.uk wrote:

> Dan Oetting wrote:
> > 
> > In the later versions of Gnu Chess 4.0 I had implemented transposition
> > aging so that the transposition table did not need to be cleared between
> > moves. Without aging, the hash table would eventually be filled with
> > unreachable positions from previous moves making hash hits less likely
> > and the damage from hash collisions more severe. Aging has not been
> > carried into Gnu Chess 5 yet.
> 
> Is there a better explanation of this than the gnuchess4
> source code? I need to get my hand into some real coding,
> rather than just fiddling around the edges.

Most of the work was done in the Mac version of the code and I don't 
recall how much transfered back into the main branch. Along with aging I 
added locking so you don't need to search for an entry a second time to 
update the position. With all nodes on the current path locked you also 
get repetition detection free with each probe.

Crafty now uses a much simpler version of aging used in 
> How big a difference did this make to gnuchess 4?

Just clearing the old table was causing a noticable delay. I don't know 
how much was gained by saving the table between moves since the standard 
tests use isolated moves.

> 
> All this talk of saving between moves got me thinking,
> especially as I have been looking carefully at "sort" after
> I discovered some minor tweaks to the program had huge
> repercussions through minor changes to the move ordering.
> 
> Should I expect changes to SortRoot to have much effect? I
> tried changing it to reflex the comments (it doesn't have
> some stuff that the normal move sort has for no obvious
> reason), and the results were promising but inconclusive -
> same test scores in same time, 5% less Nodes examined (I'd
> hoped it would find some more solutions, but it just found
> the same ones with less effort AFAICT.)

It's all about sort and move order. Alpha-Beta allows you to search 
twice as deep in the same number of nodes if you always search the best 
move first so you get all of the cutoffs. Changing the sort should not 
change the final result but can get you there sooner.

-- Dan Oetting