Use increased LMR horizont only after a null move

Revert to LMR horizont of 2 plies. Only if parent move
is a null move increase to 3 so to avoid the bad combination
of null move reduction + LMR reduction. This is a more
aggressive patch then previous one, but it seems we are
going in the wromg direction.

After 531 games result is not good:

Mod vs Orig  +123/=265/-143 48.12%  255.5/531  -13 ELO

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

diff --git a/src/search.cpp b/src/search.cpp
index c8c8d4bda672a45fba916c8ad48168e9c3bcba30..08e3a997c4d3c63365e24040e1803d298e8b3075 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1363,7 +1363,7 @@ 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 >= 3*OnePly
+      if (    depth >= (ss[ply-1].currentMove == MOVE_NULL ? 3 : 2) * OnePly
           &&  moveCount >= LMRNonPVMoves
           && !dangerous
           && !moveIsCapture