Remove useless mate value special handling in null search

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index c8c8d4bda672a45fba916c8ad48168e9c3bcba30..252b4299239e5e039e3bb90a4ba04ed0cef5b49d 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1080,7 +1080,7 @@ namespace {
       {
         // Try to reduce non-pv search depth by one ply if move seems not problematic,
         // if the move fails high will be re-searched at full depth.
-        if (    depth >= 2*OnePly
+        if (    depth >= 3*OnePly
             &&  moveCount >= LMRPVMoves
             && !dangerous
             && !moveIsCapture
@@ -1243,16 +1243,13 @@ namespace {
 
         StateInfo st;
         pos.do_null_move(st);
+        int R = (depth >= 5 * OnePly ? 4 : 3); // Null move dynamic reduction
 
-        Value nullValue = -search(pos, ss, -(beta-1), depth-4*OnePly, ply+1, false, threadID);
+        Value nullValue = -search(pos, ss, -(beta-1), depth-R*OnePly, ply+1, false, threadID);
 
         pos.undo_null_move();
 
-        if (value_is_mate(nullValue))
-        {
-            /* Do not return unproven mates */
-        }
-        else if (nullValue >= beta)
+        if (nullValue >= beta)
         {
             if (depth < 6 * OnePly)
                 return beta;
@@ -2201,16 +2198,19 @@ namespace {
     assert(m != MOVE_NONE);
 
     Depth result = Depth(0);
-    *dangerous = check || singleReply || mateThreat;
+    *dangerous = check | singleReply | mateThreat;
 
-    if (check)
-        result += CheckExtension[pvNode];
+    if (*dangerous)
+    {
+        if (check)
+            result += CheckExtension[pvNode];
 
-    if (singleReply)
-        result += SingleReplyExtension[pvNode];
+        if (singleReply)
+            result += SingleReplyExtension[pvNode];
 
-    if (mateThreat)
-        result += MateThreatExtension[pvNode];
+        if (mateThreat)
+            result += MateThreatExtension[pvNode];
+    }
 
     if (pos.type_of_piece_on(move_from(m)) == PAWN)
     {