ProbCutCount limit dependancy to cutNode

Use the ProbCutCount limit `2 + 2 * cutNode` instead of constant 3.

STC
LLR: -2.95 (-2.94,2.94) [0.50,4.50]
Total: 61812 W: 13599 L: 13459 D: 34754
http://tests.stockfishchess.org/tests/view/5c6d19240ebc5925cffca07a

LTC
LLR: 2.96 (-2.94,2.94) [0.00,3.50]
Total: 27549 W: 4614 L: 4363 D: 18572
http://tests.stockfishchess.org/tests/view/5c6d45c10ebc5925cffca7a6

Closes https://github.com/official-stockfish/Stockfish/pull/2015

Bench: 3368889

diff --git a/src/search.cpp b/src/search.cpp
index dbfb94696ac3d60f92f2a0c22fcc52deb8b4f819..6bb1e1dfdbf54c6bbce8f7c9572f58e810403bec 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -830,7 +830,7 @@ namespace {
         int probCutCount = 0;
 
         while (  (move = mp.next_move()) != MOVE_NONE
         int probCutCount = 0;
 
         while (  (move = mp.next_move()) != MOVE_NONE

-               && probCutCount < 3)
+                && probCutCount < 2 + 2 * cutNode)

             if (move != excludedMove && pos.legal(move))
             {
                 probCutCount++;
             if (move != excludedMove && pos.legal(move))
             {
                 probCutCount++;