From: Marco Costalba <mcostalba@gmail.com>
Date: Fri, 29 Mar 2013 21:55:07 +0000 (+0100)
Subject: Set IID half way between d/2 and d-4
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=7d42d02ec77a03c4c1e1b399df30ef8b363c1237;ds=sidebyside

Set IID half way between d/2 and d-4

Master IID formula is depth / 2
Previous patch is depth - 4 * ONE_PLY

This one is the middle way:

(dept/2 + depth-4*ONE_PLY)/2  -> depth-2*ONE_PLY-depth/4

After 16000 games at 60+0.05 th 1
ELO: 4.08 +-3.1 (95%) LOS: 99.5%
Total: 16000 W: 2742 L: 2554 D: 10704

bench: 4781239
---

diff --git a/src/search.cpp b/src/search.cpp
index 9ab8c800..ed029b4c 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -745,7 +745,7 @@ namespace {
         && ttMove == MOVE_NONE
         && (PvNode || (!inCheck && ss->staticEval + Value(256) >= beta)))
     {
-        Depth d = (PvNode ? depth - 2 * ONE_PLY : depth - 4 * ONE_PLY);
+        Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4);
 
         ss->skipNullMove = true;
         search<PvNode ? PV : NonPV>(pos, ss, alpha, beta, d);