From: Marco Costalba <mcostalba@gmail.com>
Date: Sat, 18 Jul 2009 10:28:09 +0000 (+0100)
Subject: Correctly set mateThreat in search()
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=1cc44bcaaecf254063138f801271629a81566ee4

Correctly set mateThreat in search()

We do not accept null search returned mate values,
but we always do a full search in those cases.

So the variable mateThreat that is set only if null move
search returns a mate value is always false.

Restore the functionality of mateThreat moving the
assignement where it can be triggered.

After 999 games at 1+0

Mod vs Orig +253 =517 -229 51.20%  +8 ELO

Bug reported by xiaozhi

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
---

diff --git a/src/search.cpp b/src/search.cpp
index de343144..75b6bd0c 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1251,6 +1251,9 @@ namespace {
 
         if (value_is_mate(nullValue))
         {
+            if (nullValue == value_mated_in(ply + 2))
+                mateThreat = true;
+
             /* Do not return unproven mates */
         }
         else if (nullValue >= beta)
@@ -1269,9 +1272,6 @@ namespace {
             // move which was reduced. If a connection is found, return a fail
             // low score (which will cause the reduced move to fail high in the
             // parent node, which will trigger a re-search with full depth).
-            if (nullValue == value_mated_in(ply + 2))
-                mateThreat = true;
-
             ss[ply].threatMove = ss[ply + 1].currentMove;
             if (   depth < ThreatDepth
                 && ss[ply - 1].reduction