NMP Tweaks

Tweak again the null move pruning preconditions.

STC:
LLR: 2.96 (-2.94,2.94) [0.50,4.50]
Total: 19675 W: 4430 L: 4169 D: 11076
http://tests.stockfishchess.org/tests/view/5d52bc0e0ebc5925cf108300

LTC:
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 73895 W: 12496 L: 12114 D: 49285
http://tests.stockfishchess.org/tests/view/5d52dcbc0ebc5925cf108552

Closes https://github.com/official-stockfish/Stockfish/pull/2268

Bench: 3690065

diff --git a/src/search.cpp b/src/search.cpp
index 7a16ef8cfc08af9da7ab9e374d5baf338a5d8026..f0fa6f05132522d5ca043e3a56e51841ab2c16a2 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -799,7 +799,8 @@ namespace {
         && (ss-1)->currentMove != MOVE_NULL
         && (ss-1)->statScore < 22661
         &&  eval >= beta
         && (ss-1)->currentMove != MOVE_NULL
         && (ss-1)->statScore < 22661
         &&  eval >= beta

-        &&  ss->staticEval >= beta - 33 * depth / ONE_PLY + 299
+        &&  eval >= ss->staticEval
+        &&  ss->staticEval >= beta - 33 * depth / ONE_PLY + 299 - improving * 30

         && !excludedMove
         &&  pos.non_pawn_material(us)
         && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
         && !excludedMove
         &&  pos.non_pawn_material(us)
         && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))