From: Joseph Ellis <jhellis3@gmail.com>
Date: Wed, 13 Oct 2021 16:10:50 +0000 (-0500)
Subject: Simplify multi-cut condition
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=673841301b0cc6ed78c4db3e6ec2a0b9a010c8cb;hp=c8459b18ba2d6ddc76d6db90d6eab346ed682e69;ds=sidebyside

Simplify multi-cut condition

Now that the multi-cut condition is safer, we can avoid the cost of the sub-search.

STC:
https://tests.stockfishchess.org/tests/view/6165fd9283dd501a05b0b2fe
LLR: 2.93 (-2.94,2.94) <-2.50,0.50>
Total: 18648 W: 4745 L: 4600 D: 9303
Ptnml(0-2): 47, 2111, 4887, 2208, 71

LTC:
https://tests.stockfishchess.org/tests/view/616629ea83dd501a05b0b320
LLR: 2.96 (-2.94,2.94) <-2.50,0.50>
Total: 41704 W: 10407 L: 10302 D: 20995
Ptnml(0-2): 35, 4425, 11823, 4538, 31

closes https://github.com/official-stockfish/Stockfish/pull/3738

Bench: 5905086
---

diff --git a/src/search.cpp b/src/search.cpp
index 73fc8a55..28049e87 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1123,18 +1123,9 @@ moves_loop: // When in check, search starts here
           else if (singularBeta >= beta)
               return singularBeta;
 
-          // If the eval of ttMove is greater than beta we try also if there is another
-          // move that pushes it over beta, if so the position also has probably multiple
-          // moves giving fail highs. We will then reduce the ttMove (negative extension).
+          // If the eval of ttMove is greater than beta, we reduce it (negative extension)
           else if (ttValue >= beta)
-          {
-              ss->excludedMove = move;
-              value = search<NonPV>(pos, ss, beta - 1, beta, (depth + 3) / 2, cutNode);
-              ss->excludedMove = MOVE_NONE;
-
-              if (value >= beta)
-                  extension = -2;
-          }
+              extension = -2;
       }
 
       // Capture extensions for PvNodes and cutNodes