From 5dda4037c73ead63b145c9a77f1dbb41422e058f Mon Sep 17 00:00:00 2001
From: rn5f107s2 <clemens.lerchl@gmail.com>
Date: Wed, 5 Jun 2024 18:56:25 +0200
Subject: [PATCH] Simplify razor changes

Remove razoring changes from
https://github.com/official-stockfish/Stockfish/pull/5360

The mentioned patch introduced the usage of futility_margin into
razoring alongside a tune to futility_margin. It seems the elo gained in
this patch comes from the tune of futility_margin and not the
introduction of futility_margin to razoring, so simplify it away here.

Passed Non-regression STC:
https://tests.stockfishchess.org/tests/view/66606581c340c8eed7757bc8
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 169056 W: 43922 L: 43848 D: 81286
Ptnml(0-2): 438, 20288, 43034, 20298, 470

Passed Non-regression LTC:
https://tests.stockfishchess.org/tests/view/66607764c340c8eed7757c58
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 157134 W: 39805 L: 39723 D: 77606
Ptnml(0-2): 74, 17444, 43461, 17502, 86

Passed rebased Non-regression LTC:
https://tests.stockfishchess.org/tests/view/6660c696c340c8eed77580c0
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 135984 W: 34427 L: 34324 D: 67233
Ptnml(0-2): 67, 15063, 37615, 15194, 53

closes https://github.com/official-stockfish/Stockfish/pull/5366

Bench: 1150518
---
 src/search.cpp | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index 2cbc7677..e0a49dba 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -554,7 +554,7 @@ Value Search::Worker::search(
     bool     givesCheck, improving, priorCapture, opponentWorsening;
     bool     capture, moveCountPruning, ttCapture;
     Piece    movedPiece;
-    int      moveCount, captureCount, quietCount, futilityMargin;
+    int      moveCount, captureCount, quietCount;
     Bound    singularBound;
 
     // Step 1. Initialize node
@@ -762,12 +762,10 @@ Value Search::Worker::search(
 
     opponentWorsening = ss->staticEval + (ss - 1)->staticEval > 2;
 
-    futilityMargin = futility_margin(depth, cutNode && !ss->ttHit, improving, opponentWorsening);
-
     // Step 7. Razoring (~1 Elo)
     // If eval is really low check with qsearch if it can exceed alpha, if it can't,
     // return a fail low.
-    if (eval < alpha - 465 - futilityMargin * depth * 33 / 32)
+    if (eval < alpha - 512 - 293 * depth * depth)
     {
         value = qsearch<NonPV>(pos, ss, alpha - 1, alpha);
         if (value < alpha)
@@ -776,7 +774,10 @@ Value Search::Worker::search(
 
     // Step 8. Futility pruning: child node (~40 Elo)
     // The depth condition is important for mate finding.
-    if (!ss->ttPv && depth < 13 && eval - futilityMargin - (ss - 1)->statScore / 263 >= beta
+    if (!ss->ttPv && depth < 13
+        && eval - futility_margin(depth, cutNode && !ss->ttHit, improving, opponentWorsening)
+               - (ss - 1)->statScore / 263
+             >= beta
         && eval >= beta && eval < VALUE_TB_WIN_IN_MAX_PLY && (!ttMove || ttCapture))
         return beta > VALUE_TB_LOSS_IN_MAX_PLY ? beta + (eval - beta) / 3 : eval;