From 21ad356c0900c9eba9b7b1f7453f934eab80f303 Mon Sep 17 00:00:00 2001
From: Michael Chaly <Vizvezdenec@gmail.com>
Date: Sun, 26 Sep 2021 06:39:27 +0200
Subject: [PATCH] Extend quiet tt moves at PvNodes

Idea is to extend some quiet ttMoves if a lot of things indicate that
the transposition table move is going to be a good move:

1) move being a killer - so being the best move in nearby node;
2) reply continuation history is really good.

This is basically saying that move is good "in general" in this position,
that it is a good reply to the opponent move and that it was the best in
this position somewhere in search - so extending it makes a lot of sense.
In general in past year we had a lot of extensions of different types,
maybe there is something more in it :)

passed STC
LLR: 2.96 (-2.94,2.94) <-0.50,2.50>
Total: 42944 W: 10932 L: 10695 D: 21317
Ptnml(0-2): 141, 4869, 11210, 5116, 136
https://tests.stockfishchess.org/tests/view/614cca8e7bdc23e77ceb89f0

passed LTC
LLR: 2.93 (-2.94,2.94) <0.50,3.50>
Total: 156848 W: 39473 L: 38893 D: 78482
Ptnml(0-2): 125, 16327, 44913, 16961, 98
https://tests.stockfishchess.org/tests/view/614cf93d7bdc23e77ceb8a13

closes https://github.com/official-stockfish/Stockfish/pull/3719

Bench: 5714575
---
 src/search.cpp | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index 8db295f1fd8..48694cb2ded 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1147,7 +1147,14 @@ namespace {
       // Check extensions
       else if (   givesCheck
                && depth > 6
-               && abs(ss->staticEval) > Value(100))
+               && abs(ss->staticEval) > 100)
+          extension = 1;
+
+      // Quiet ttMove extensions
+      else if (   PvNode
+               && move == ttMove
+               && move == ss->killers[0]
+               && (*contHist[0])[movedPiece][to_sq(move)] >= 10000)
           extension = 1;
 
       // Add extension to new depth
@@ -1223,11 +1230,10 @@ namespace {
           // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
           r -= ss->statScore / 14721;
 
-          // In general we want to cap the LMR depth search at newDepth. But if
-          // reductions are really negative and movecount is low, we allow this move
-          // to be searched deeper than the first move in specific cases (note that
-          // this may lead to hidden double extensions if newDepth got it own extension
-          // before).
+          // In general we want to cap the LMR depth search at newDepth. But if reductions
+          // are really negative and movecount is low, we allow this move to be searched
+          // deeper than the first move (this may lead to hidden double extensions if
+          // newDepth got its own extension before).
           int deeper =   r >= -1               ? 0
                        : noLMRExtension        ? 0
                        : moveCount <= 5        ? 1