From: Lucas Braesch <lucas.braesch@gmail.com>
Date: Thu, 26 Sep 2013 10:25:27 +0000 (+0800)
Subject: Simplify extensions
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=bc6faf633e7f4d2c998f434a41ecfc9b80047607

Simplify extensions

Unify extensions between PV and not PV nodes
and remove all but check extensions.

This is a simplification so tested at fixed number
of games where proved to not regress.

About 45k games at 15+0.05
ELO: 1.23 +-2.0 (95%) LOS: 88.5%
Total: 45643 W: 9107 L: 8946 D: 27590

About 45k games at 60+0.05
ELO: 1.07 +-1.8 (95%) LOS: 87.8%
Total: 46786 W: 7728 L: 7584 D: 31474

bench: 3172206
---

diff --git a/src/search.cpp b/src/search.cpp
index 0b87b456..789492fd 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -829,13 +829,10 @@ moves_loop: // When in check and at SpNode search starts from here
                  || pos.is_passed_pawn_push(move)
                  || type_of(move) == CASTLE;
 
-      // Step 12. Extend checks and, in PV nodes, also dangerous moves
-      if (PvNode && dangerous)
+      // Step 12. Extend checks
+      if (givesCheck && pos.see_sign(move) >= 0)
           ext = ONE_PLY;
 
-      else if (givesCheck && pos.see_sign(move) >= 0)
-          ext = inCheck || ss->staticEval <= alpha ? ONE_PLY : ONE_PLY / 2;
-
       // Singular extension search. If all moves but one fail low on a search of
       // (alpha-s, beta-s), and just one fails high on (alpha, beta), then that move
       // is singular and should be extended. To verify this we do a reduced search