From 299c6d6dee96a50f9366955192f922d449d11f20 Mon Sep 17 00:00:00 2001
From: eug-vs <eugene@eug-vs.xyz>
Date: Mon, 22 Jan 2024 01:30:47 +0100
Subject: feat: store PV in a separate table

---
 src/grossmeister/ttable.rs | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

(limited to 'src/grossmeister/ttable.rs')

diff --git a/src/grossmeister/ttable.rs b/src/grossmeister/ttable.rs
index b1eeec3..b40bac1 100644
--- a/src/grossmeister/ttable.rs
+++ b/src/grossmeister/ttable.rs
@@ -62,8 +62,12 @@ impl TranspositionTable {
 
 #[derive(Debug, Default, Clone)]
 pub struct MasterTable {
+    /// Always contains the most recent transposition
     always_replace: TranspositionTable,
+    /// Stores highest-depth entries
     depth_preferred: TranspositionTable,
+    /// Used to collect Principal Variation. Not used in search
+    pv: TranspositionTable,
 }
 
 impl Grossmeister {
@@ -81,6 +85,26 @@ impl Grossmeister {
         } {
             self.transposition_table.depth_preferred.set(self.board.hash, transposition)
         }
+
+        // Store PV/Cut nodes in PV table
+        // Note: Cut nodes are probably only relevant in close-to-mate situations
+        if match transposition.node_type {
+            NodeType::PV => true, // Always replace PV nodes
+            NodeType::Cut => {
+                match self.transposition_table.pv.get(self.board.hash) {
+                    Some(existing_transposition) => existing_transposition.node_type != NodeType::PV,
+                    None => true,
+                }
+            }
+            _ => false,
+        } {
+            self.transposition_table.pv.set(self.board.hash, transposition)
+        }
+    }
+
+    /// Extract current node information from PV table
+    pub fn pv(&self) -> Option<&TranspositionTableItem> {
+        self.transposition_table.pv.get(self.board.hash)
     }
 
     pub fn table_full(&self) -> u64 {
-- 
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