From: Joona Kiiski <joona.kiiski@gmail.com>
Date: Thu, 25 Sep 2014 19:42:25 +0000 (+0100)
Subject: Cap evaluation based null move extra reduction to three plies
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=7ed15af371be19a4d261df87fa33df0a94fdc930

Cap evaluation based null move extra reduction to three plies

It's a zero elo patch, and a reasonable safeguard against uncontrolled extreme reductions.

STC:
ELO: -0.08 +-2.0 (95%) LOS: 46.9%
Total: 40000 W: 6728 L: 6737 D: 26535

LTC:
ELO: -0.14 +-1.8 (95%) LOS: 44.0%
Total: 40000 W: 5557 L: 5573 D: 28870

Bench: 7201830
---

diff --git a/src/search.cpp b/src/search.cpp
index 05e3de51..6215b083 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -567,8 +567,7 @@ namespace {
         // Null move dynamic reduction based on depth and value
         Depth R =  3 * ONE_PLY
                  + depth / 4
-                 + (abs(beta) < VALUE_KNOWN_WIN ? int(eval - beta) / PawnValueMg * ONE_PLY
-                                                : DEPTH_ZERO);
+                 + std::min(int(eval - beta) / PawnValueMg, 3) * ONE_PLY;
 
         pos.do_null_move(st);
         (ss+1)->skipNullMove = true;