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Subject: Futility Prune question

Author: Stuart Cracraft

Date: 09:07:24 10/17/04


Futility prune at depth == 1, extended futility prune at depth == 2, and razor
at depth == 3....

Are the above depths *before* or *after* the makemove?

I implemented the above (with depths calculated before the makemove)
and although my total nodes is reduced 30%, for me it is about the
same runtime and result.

Not sure why this is so as I took extra care to avoid any extra calls to
incheck(). My eval() is simply lazy-eval level so nothing expensive there
either.

I profiled both runs and there are not more incheck()'s in any amount
in the version with futility pruning turned on vs. not.

Note -- my Extensions() routine calculates whether the move is a checking
move but does this last and only if all the extensions together don't
add up to 1.

Likewise Reductions() which calculates Futility pruning initial status (parent
in check, depth = 1 2 3, whether futility, extended, or razor, and alpha status
in relation to evaluation+MARGIN) only calculates incheck() status if
not already done.

A profiled run shows no great difference in incheck() calls. My
Futility pruning implementation must simply be wrong. Plese have
a look.

Here is the code:

int Reductions(int alpha, int depth, int *bd)
{
  int reduction=0;
  if (FUTIL_R != 0.0) {
    if (depth == 1) {
      if (parentincheck || alpha < eval(bd,QUIET)+3000)
        reduction = 0;
      else
        reduction = 1;
    }
    else if (depth == 2) {
      if (parentincheck || alpha < eval(bd,QUIET)+5000)
        reduction = 0;
      else
        reduction=1;
    }
    else if (depth == 3) {
      if (parentincheck || alpha < eval(bd,QUIET)+9000)
        reduction = 0;
      else
        reduction=1;
    }
  }
  return(reduction);
}

mainsearch()
:
:
  parentincheck=incheck(bd);
:
  reduction=Reductions(alpha, depth, bd);
:
  make first move
:
    extension=Extensions(alpha,depth,bd,sml[mvi],threat,bmext,&checked,ply,qentr
y);
  ^^ perhaps the above alpha should be -beta?
      prune = 1;
      if (extension || !reduction || sml[mvi].cap) prune = 0;
      else {
        if (checked status not yet known) checked=incheck(bd);
        if (checked) prune = 0;
      }
      if (!prune)
        best = -search(bd,depth-1+extension, ply+1,-beta,-alpha);
:
  for main move loop
  :
  similar to above
:

Thanks,

Stuart



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