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Less aggressive razoring

Use a margin to compare with beta so that positions
that after the verifying qsearch have gained a lot of points
are not discarded just becasue not above beta.

Also remove the second condition on depth <= OnePly, it
was too risky and added only a 2% more of pruned nodes.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
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1 parent b58ad35 commit 96d05017354fa838462a7f8f6e25b8731e2ec400 @mcostalba committed Dec 21, 2008
Showing with 3 additions and 3 deletions.
  1. +3 −3 src/search.cpp
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6 src/search.cpp
@@ -1237,11 +1237,11 @@ namespace {
}
// Null move search not allowed, try razoring
else if ( !value_is_mate(beta)
- && ( (approximateEval < beta - RazorMargin && depth < RazorDepth)
- ||(approximateEval < beta - PawnValueMidgame && depth <= OnePly)))
+ && approximateEval < beta - RazorMargin
+ && depth < RazorDepth)
{
Value v = qsearch(pos, ss, beta-1, beta, Depth(0), ply, threadID);
- if (v < beta)
+ if (v < beta - RazorMargin / 2)
return v;
}

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