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Subject: Re: Move ordering - How do I know if I have played this move already?

Author: Bruce Moreland

Date: 10:49:49 04/08/99

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On April 08, 1999 at 12:45:42, Steve Maughan wrote:

>>>
>>>Nope, I've never done this.

>>This is really surprising!

>Yes indeed it is!  Bruce - I assume you have tried the "play the hash move
>before generating other moves" idea and not found a benefit, yet I cann't see
>any situation where this wouldn't be an easy win.
>
>I'm puzzled!

I use a move table.  A move is described as a pointer into the move table.  At
the time I originally wrote the program, I didn't have enough space in the move
table for a pointer back to the source square.

So if I had a pointer to the move table, I knew I had something that described a
unique move, but I didn't know which piece was doing the moving, I had to store
that seperately.

I put one of these pointers in my hash table when I failed high, to remember
what the best move was, and when I encountered this node later, I could figure
out if I was trying to execute the same move that was in the hash table, and if
so, order it highly.

But I couldn't reconstruct the whole move itself from the pointer.  All I knew
was, for instance, that a white knight was coming from some unique place and
going to e5.  I had no idea that the knight was coming from f3.

So for me, incremental move generation of this sort was not an option.

That was back in the 16-bit world.  I had to have that move table element as
small as possible, since I jammed it into my code segment.

My program is now a 32-bit program and that table is now about half a megabyte.
But I still don't have the source square in the move table.

If I put the source square in the move table and did incremental move
generation, it might be a good thing, I could save quite a few move generations.
 But on the other hand, I would have to deal with the topic of this thread, and
I would have to mess up a few loops and write some move verification code that
would be a little icky given how rarely it is executed.

That's the story.

bruce



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