From: Marco Costalba <mcostalba@gmail.com>
Date: Sun, 21 Dec 2008 09:42:39 +0000 (+0100)
Subject: Less aggressive razoring
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=96d05017354fa838462a7f8f6e25b8731e2ec400;hp=b58ad355ca6b3d81795563da3b5172efaf6cc941

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>
---

diff --git a/src/search.cpp b/src/search.cpp
index c3f96e13..054ef45d 100644
--- a/src/search.cpp
+++ b/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;
     }