Questions on Updating the Killer Moves Heuristic

[StackFish5]

I understand how the killer moves heuristic functions. But I do not know how to properly implement it in search. The main problem I'm having isn't scoring them but is how to update the heuristic during a beta-cutoff. Help would be greatly appreciated and so would some code examples on how to do so.

Thanks.

[tcusr]

I understand how the killer moves heuristic functions. But I do not know how to properly implement it in search. The main problem I'm having isn't scoring them but is how to update the heuristic during a beta-cutoff. Help would be greatly appreciated and so would some code examples on how to do so.

Thanks.

update your table with the current move before returning beta.

[hgm]

If(move != killer1[ply]) { killer2[ply] = killer1[ply]; killer1[ply] = move; }

[StackFish5]

If(move != killer1[ply]) { killer2[ply] = killer1[ply]; killer1[ply] = move; }

Killer1 would be scored higher compared to killer2 right?

[lithander]

If(move != killer1[ply]) { killer2[ply] = killer1[ply]; killer1[ply] = move; }

Killer1 would be scored higher compared to killer2 right?

Yes. You can also defer generating the quiet moves and just check the killers for legality and play them. Maybe you get a cutoff and save generating the quiet moves entirely. Then you will never have to score them for sorting

[StackFish5]

Thank you all for the advice on how to update the killer move heuristic. It really helped me a lot.

[j.t.]

I also have, additionally to the two traditional killermoves, a third killer move for each color that is valid through all heights (opposed to the normal killermoves which are only used/updated on their specific tree height).

[hgm]

How do you set that 3rd killer?

[j.t.]

How do you set that 3rd killer?

Basically always, whenever the normal killers are updated, too:

Code: Select all

struct KillerTable{
  Move table[MAX_PLY][2];
  Move goodMove[2];
  
  void update(Ply height, Move move){
    goodMove[height % 2] = move;
    if(table[height][0] != move){
      table[height][1] = table[height][0];
      table[height][0] = move;
    }    
  }
};

(real code)