From 53968f5116694b6fd7da3fed970abc69debe1662 Mon Sep 17 00:00:00 2001
From: PikaCat <Pika-Cat@qq.com>
Date: Sat, 24 Feb 2024 22:01:14 +0800
Subject: [PATCH] Simplify IIR

Simplified depth reduction for PV nodes without a ttMove to 3.
---
 src/search.cpp | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index 4ee38683..c55391b9 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -705,13 +705,11 @@ Value Search::Worker::search(
     }
 
     // Step 9. Internal iterative reductions (~9 Elo)
-    // For PV nodes without a ttMove, we decrease depth by 2,
-    // or by 4 if the current position is present in the TT and
-    // the stored depth is greater than or equal to the current depth.
-    // Use qsearch if depth <= 0.
+    // For PV nodes without a ttMove, we decrease depth by 3.
     if (PvNode && !ttMove)
-        depth -= 2 + 2 * (ss->ttHit && tte->depth() >= depth);
+        depth -= 3;
 
+    // Use qsearch if depth <= 0.
     if (depth <= 0)
         return qsearch<PV>(pos, ss, alpha, beta);