Do TT cutoffs before LMP, use TT move as starting best_move and readability changes

src/search/transposition_table.rs

@@ -10,11 +10,11 @@ pub struct TranspositionTable {
 
 impl TranspositionTable {
     pub fn new() -> Self {
-        Self::new_with_mb_size(TT_SIZE_IN_MB)
+        Self::with_capacity(TT_SIZE_IN_MB)
     }
 
-    pub fn new_with_mb_size(size_in_mega_bytes: usize) -> Self {
-        let size_in_bytes = size_in_mega_bytes * 1024 * 1024;
+    pub fn with_capacity(size_in_mb: usize) -> Self {
+        let size_in_bytes = size_in_mb * 1024 * 1024;
         let num_of_entries = size_in_bytes / std::mem::size_of::<TTEntry>();
 
         Self {
@@ -23,19 +23,19 @@ impl TranspositionTable {
         }
     }
 
-    pub fn lookup(&self, zobrist_hash: ZobristHash) -> Option<&TTEntry> {
+    pub fn lookup(&self, zobrist_hash: ZobristHash) -> Option<TTEntry> {
         self.positions
             .get((zobrist_hash.0 % self.size) as usize)
-            .and_then(|entry| entry.as_ref())
+            .and_then(|entry| *entry)
     }
 
-    pub fn insert(&mut self, tt_entry: TTEntry) {
-        let idx = (tt_entry.hash.0 % self.size) as usize;
-        self.positions[idx] = Some(tt_entry);
+    pub fn insert(&mut self, entry: TTEntry) {
+        let idx = (entry.hash.0 % self.size) as usize;
+        self.positions[idx] = Some(entry);
     }
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct TTEntry {
     pub hash: ZobristHash,
     pub mv: Option<Move>,
@@ -62,13 +62,21 @@ impl TTEntry {
     }
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum NodeType {
     Exact,
     LowerBound,
     UpperBound,
 }
 
+impl NodeType {
+    pub fn cutoff_eligible(self, score: i16, alpha: i16, beta: i16) -> bool {
+        self == Self::Exact
+            || self == Self::LowerBound && score >= beta
+            || self == Self::UpperBound && score <= alpha
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::{
@@ -96,14 +104,14 @@ mod tests {
         dbg!(time_info.instant.elapsed());
 
         let will_be_hash = from_fen(FEN_POSSIBLE).unwrap().hash;
-        let tt_entry = game.tt.lookup(will_be_hash);
+        let entry = game.tt.lookup(will_be_hash);
 
-        assert!(tt_entry.is_some());
+        assert!(entry.is_some());
 
         let wont_be_hash = from_fen(FEN_IMPOSSIBLE).unwrap().hash;
-        let tt_entry = game.tt.lookup(wont_be_hash);
+        let entry = game.tt.lookup(wont_be_hash);
 
-        assert!(tt_entry.is_none());
+        assert!(entry.is_none());
 
         Ok(())
     }