From: Michael Chaly <Vizvezdenec@gmail.com>
Date: Thu, 1 Jun 2023 12:24:13 +0000 (+0300)
Subject: Move internal iterative reduction before probcut
X-Git-Url: https://git.sesse.net/?a=commitdiff_plain;ds=sidebyside;h=8dea070538dcad790de3c5b9720bdbb836a32440;p=stockfish

Move internal iterative reduction before probcut

This patch moves IIR before probcut which allows probcut
to be produced at lower depths. Comments in IIR are also slightly updated.

Passed STC:
https://tests.stockfishchess.org/tests/view/6472d604d29264e4cfa749fd
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 387616 W: 103295 L: 102498 D: 181823
Ptnml(0-2): 976, 42322, 106381, 43187, 942

Passed LTC:
https://tests.stockfishchess.org/tests/view/6475eb8c4a36543c4c9f42e8
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 202836 W: 54901 L: 54281 D: 93654
Ptnml(0-2): 85, 19609, 61422, 20205, 97

closes https://github.com/official-stockfish/Stockfish/pull/4597

bench 2551691
---

diff --git a/src/search.cpp b/src/search.cpp
index 4365b215..0e82f04e 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -822,9 +822,24 @@ namespace {
         }
     }
 
+    // Step 10. If the position doesn't a have ttMove, decrease depth by 2
+    // (or by 4 if the TT entry for the current position was hit and the stored depth is greater than or equal to the current depth).
+    // Use qsearch if depth is equal or below zero (~9 Elo)
+    if (    PvNode
+        && !ttMove)
+        depth -= 2 + 2 * (ss->ttHit && tte->depth() >= depth);
+
+    if (depth <= 0)
+        return qsearch<PV>(pos, ss, alpha, beta);
+
+    if (    cutNode
+        &&  depth >= 8
+        && !ttMove)
+        depth -= 2;
+
     probCutBeta = beta + 168 - 61 * improving;
 
-    // Step 10. ProbCut (~10 Elo)
+    // Step 11. ProbCut (~10 Elo)
     // If we have a good enough capture (or queen promotion) and a reduced search returns a value
     // much above beta, we can (almost) safely prune the previous move.
     if (   !PvNode
@@ -875,20 +890,6 @@ namespace {
         Eval::NNUE::hint_common_parent_position(pos);
     }
 
-    // Step 11. If the position is not in TT, decrease depth by 2 (or by 4 if the TT entry for the current position was hit and the stored depth is greater than or equal to the current depth).
-    // Use qsearch if depth is equal or below zero (~9 Elo)
-    if (    PvNode
-        && !ttMove)
-        depth -= 2 + 2 * (ss->ttHit && tte->depth() >= depth);
-
-    if (depth <= 0)
-        return qsearch<PV>(pos, ss, alpha, beta);
-
-    if (    cutNode
-        &&  depth >= 8
-        && !ttMove)
-        depth -= 2;
-
 moves_loop: // When in check, search starts here
 
     // Step 12. A small Probcut idea, when we are in check (~4 Elo)