fix: Add forgotten files

src/chess/zobrist.rs

@@ -0,0 +1,86 @@
+//! Implements Zobrist hashing and [Transposition Table] functionality.
+//!
+//! [Transposition Table](https://www.chessprogramming.org/Transposition_Table
+
+// TODO: Migrate to RawTable instead for better performance?
+use std::collections::HashMap;
+use std::hash::{Hash, Hasher};
+
+use super::position::Position;
+
+/// Zobrist key is a 64-bit integer.
+pub type Key = u64;
+
+pub(crate) struct RepetitionTable {
+    table: HashMap<Key, u8>,
+}
+
+impl RepetitionTable {
+    pub(crate) fn new() -> Self {
+        Self {
+            table: HashMap::new(),
+        }
+    }
+
+    pub(crate) fn clear(&mut self) {
+        self.table.clear();
+    }
+
+    /// Returns true if the position has occurred 3 times.
+    pub(crate) fn record(&mut self, key: Key) -> bool {
+        let count = self.table.entry(key).or_insert(0);
+        *count += 1;
+        *count == 3
+    }
+
+    /// Reduces the number of times a position has occurred by one.
+    pub(crate) fn remove(&mut self, key: Key) {
+        let count = self.table.entry(key).or_insert(0);
+        match count {
+            1 => {
+                let _ = self.table.remove_entry(&key);
+            },
+            2 | 3 => {
+                *count -= 1;
+            },
+            _ => {
+                unreachable!("can not call remove on position that has not occurred yet")
+            },
+        }
+    }
+}
+
+mod test {
+    use super::*;
+    use crate::chess::core::Move;
+
+    #[test]
+    fn repetition_table() {
+        let mut table = RepetitionTable::new();
+
+        let mut position = Position::starting();
+        assert!(!table.record(position.compute_hash()));
+
+        position.make_move(&Move::from_uci("g1f3").expect("valid move"));
+        assert!(!table.record(position.compute_hash()));
+        position.make_move(&Move::from_uci("g8f6").expect("valid move"));
+        assert!(!table.record(position.compute_hash()));
+
+        position.make_move(&Move::from_uci("f3g1").expect("valid move"));
+        assert!(!table.record(position.compute_hash()));
+        // Two-fold repetition.
+        position.make_move(&Move::from_uci("f6g8").expect("valid move"));
+        assert!(!table.record(position.compute_hash()));
+
+        position.make_move(&Move::from_uci("g1f3").expect("valid move"));
+        assert!(!table.record(position.compute_hash()));
+        position.make_move(&Move::from_uci("g8f6").expect("valid move"));
+        assert!(!table.record(position.compute_hash()));
+
+        position.make_move(&Move::from_uci("f3g1").expect("valid move"));
+        assert!(!table.record(position.compute_hash()));
+       // Three-fold repetition.
+        position.make_move(&Move::from_uci("f6g8").expect("valid move"));
+        assert!(table.record(position.compute_hash()));
+    }
+}

src/search/transposition.rs

@@ -0,0 +1,33 @@
+//! Implements Zobrist hashing and [Transposition Table] functionality.
+//!
+//! [Transposition Table](https://www.chessprogramming.org/Transposition_Table
+
+use crate::chess::position::Position;
+use core::hash;
+use std::hash::{Hash, Hasher};
+
+pub type Key = u64;
+
+pub(super) struct Entry {}
+
+pub(super) struct TranspositionTable {}
+
+impl TranspositionTable {
+    #[must_use]
+    pub(super) fn new() -> Self {
+        todo!()
+    }
+
+    pub(super) fn clear(&mut self) {
+        todo!()
+    }
+
+    #[must_use]
+    pub(super) fn probe(&self, key: u64) -> Option<&Entry> {
+        todo!()
+    }
+
+    pub(super) fn store(&mut self, key: u64, entry: Entry) {
+        todo!()
+    }
+}