From: Jerry Donald Watson <j1.donald1@gmail.com>
Date: Tue, 13 Mar 2018 09:15:42 +0000 (+0000)
Subject: Simplify condition for ProbCut move count pruning
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=b605103a34be5bea7815ab3f6d4a21d487d0182b

Simplify condition for ProbCut move count pruning

We retire depth-dependence in ProbCut move count pruning,
the move count limit condition is now : "probCutCount < 3"

STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 33895 W: 6995 L: 6897 D: 20003
http://tests.stockfishchess.org/tests/view/5aa6eaba0ebc59029781009d

LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 28959 W: 4441 L: 4333 D: 20185
http://tests.stockfishchess.org/tests/view/5aa73dfa0ebc5902978100be

Ideas for future work:

• Is a flat move count limit in ProbCut ideal? Depth dependence, or
  dependence on some other variable, could possibly be reintroduced.

• The move count limit 3 is untuned and a better value may exist.

Closes https://github.com/official-stockfish/Stockfish/pull/1486

Bench: 5741807
---

diff --git a/src/search.cpp b/src/search.cpp
index b2622ab3..0f599fc2 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -766,7 +766,7 @@ namespace {
         int probCutCount = 0;
 
         while (  (move = mp.next_move()) != MOVE_NONE
-               && probCutCount < depth / ONE_PLY - 3)
+               && probCutCount < 3)
             if (pos.legal(move))
             {
                 probCutCount++;