tic tac toe

Cargo.toml

@@ -9,4 +9,7 @@ edition = "2021"
 
 
 [profile.dev]
-opt-level = 3
+opt-level = 3
+
+[profile.release]
+debug = true

build.rs

@@ -1,3 +1,25 @@
+//! Builds the board state table
+//! 
+//! The board is encoded as an 18 bit integer, two bits for each position.
+//! The position are in the bits row by row with the first position being the
+//! least significant two bits.
+//! ```text
+//! 0 => X
+//! 1 => O
+//! 2 => Empty
+//! 3 => INVALID
+//! ```
+//! 
+//! Then, this integer is used as an index into the winner table.
+//! Each byte of the winner table contains the information about the game state.
+//! ```text
+//! 0 => X
+//! 1 => O
+//! 2 => In Progress
+//! 3 => Draw
+//! _ => INVALID
+//! ```
+
 use std::{fs::File, io::Write, path::PathBuf};
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -69,7 +91,7 @@ impl Board {
         let mut i = 0;
         let this = self.clone();
         std::iter::from_fn(move || {
-            let result = (i < 8).then(|| this.get(i));
+            let result = (i < 9).then(|| this.get(i));
             i += 1;
             result
         })

src/board.rs

@@ -58,24 +58,21 @@ impl Board {
         Self(0x0002AAAA)
     }
 
-    #[cfg(not(debug_assertions))]
-    fn validate(&self) {}
-
-    #[cfg(debug_assertions)]
     fn validate(&self) {
-        let board = self.0;
-        for i in 0..16 {
-            let next_step = board >> (i * 2);
-            let mask = 0b11;
-            let pos = next_step & mask;
-            if pos >= 3 {
-                panic!("Invalid bits, self: {board:0X}, bits: {pos:0X}");
+        if cfg!(debug_assertions) {
+            let board = self.0;
+            for i in 0..16 {
+                let next_step = board >> (i * 2);
+                let mask = 0b11;
+                let pos = next_step & mask;
+                if pos >= 3 {
+                    panic!("Invalid bits, self: {board:0X}, bits: {pos:0X}");
+                }
             }
         }
     }
 
     pub fn get(&self, index: usize) -> Option<Player> {
-        self.validate();
         debug_assert!(index < 9);
 
         let board = self.0;
@@ -83,7 +80,13 @@ impl Board {
         let shifted = board >> (index * 2);
         let masked = shifted & 0b11;
 
-        Player::from_u8(masked as u8).unwrap()
+        // SAFETY: So uh, this is a bit unlucky.
+        // You see, there are two entire bits of information at our disposal for each position.
+        // This is really bad. We only have three valid states. So we need to do _something_ if it's invalid.
+        // We just hope that it will never be invalid which it really shouldn't be and also have a debug assertion
+        // here to make sure that it really is valid and then if it's not invalid we just mov it out and are happy.
+        self.validate();
+        unsafe { Player::from_u8(masked as u8).unwrap_unchecked() }
     }
 
     pub fn set(&mut self, index: usize, value: Option<Player>) {
@@ -106,7 +109,7 @@ impl Board {
         let mut i = 0;
         let this = self.clone();
         std::iter::from_fn(move || {
-            let result = (i < 8).then(|| this.get(i));
+            let result = (i < 9).then(|| this.get(i));
             i += 1;
             result
         })
@@ -121,7 +124,7 @@ mod win_table {
     use super::{Board, Player, State};
 
     const WIN_TABLE_SIZE: usize = 2usize.pow(2 * 9);
-    const WIN_TABLE: &[u8; WIN_TABLE_SIZE] = include_bytes!(concat!(env!("OUT_DIR"), "/win_table"));
+    static WIN_TABLE: &[u8; WIN_TABLE_SIZE] = include_bytes!(concat!(env!("OUT_DIR"), "/win_table"));
 
     pub fn result(board: &Board) -> State {
         match WIN_TABLE[board.0 as usize] {

src/game.rs

@@ -4,14 +4,18 @@ use crate::{
 };
 
 impl Board {
-    pub fn play<A: GamePlayer, B: GamePlayer>(&mut self, a: &mut A, b: &mut B) -> Option<Player> {
+    pub fn default_play<X: GamePlayer, O: GamePlayer>() -> Option<Player> {
+        Self::empty().play(&mut X::default(), &mut O::default())
+    }
+
+    pub fn play<A: GamePlayer, B: GamePlayer>(&mut self, x: &mut A, o: &mut B) -> Option<Player> {
         let mut current_player = Player::X;
 
         for _ in 0..9 {
             if current_player == Player::X {
-                a.next_move(self, current_player);
+                x.next_move(self, current_player);
             } else {
-                b.next_move(self, current_player);
+                o.next_move(self, current_player);
             }
 
             match self.result() {

src/lib.rs

@@ -1,17 +1,17 @@
 mod board;
 mod game;
-mod minmax;
+mod perfect;
 
 use std::io::Write;
 
 pub use board::{Board, Player, State};
-pub use minmax::PerfectPlayer;
+pub use perfect::PerfectPlayer;
 
-pub trait GamePlayer {
+pub trait GamePlayer: Default {
     fn next_move(&mut self, board: &mut Board, this_player: Player);
 }
 
-#[derive(Clone)]
+#[derive(Clone, Default)]
 pub struct GreedyPlayer;
 
 impl GamePlayer for GreedyPlayer {
@@ -21,7 +21,7 @@ impl GamePlayer for GreedyPlayer {
     }
 }
 
-#[derive(Clone)]
+#[derive(Clone, Default)]
 pub struct HumanPlayer;
 
 impl GamePlayer for HumanPlayer {
@@ -51,7 +51,7 @@ impl GamePlayer for HumanPlayer {
     }
 }
 
-#[derive(Clone)]
+#[derive(Clone, Default)]
 pub struct RandomPlayer;
 
 fn fun_random() -> u64 {
@@ -75,3 +75,34 @@ impl GamePlayer for RandomPlayer {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::{Board, GamePlayer, GreedyPlayer, PerfectPlayer, Player, RandomPlayer};
+
+    fn assert_win_ratio<X: GamePlayer, O: GamePlayer>(runs: u64, x_win_ratio: f64) {
+        let mut results = [0u64, 0, 0];
+
+        for _ in 0..runs {
+            let result = Board::default_play::<X, O>();
+            let idx = Player::as_u8(result);
+            results[idx as usize] += 1;
+        }
+
+        let total = results.iter().copied().sum::<u64>();
+
+        let ratio = (total as f64) / (results[0] as f64);
+        println!("{ratio} >= {x_win_ratio}");
+        assert!(ratio >= x_win_ratio);
+    }
+
+    #[test]
+    fn perfect_always_beats_greedy() {
+        assert_win_ratio::<PerfectPlayer, GreedyPlayer>(20, 1.0);
+    }
+
+    #[test]
+    fn perfect_beats_random() {
+        assert_win_ratio::<PerfectPlayer, RandomPlayer>(10, 0.95);
+    }
+}

src/main.rs

@@ -9,8 +9,8 @@ fn main() {
 
     let start = SystemTime::now();
 
-    for _ in 0..10_000 {
-        let result = play_round(PerfectPlayer::new(), PerfectPlayer::new(), false);
+    for _ in 0..1000 {
+        let result = play_round::<PerfectPlayer, GreedyPlayer>(false);
         let idx = Player::as_u8(result);
         results[idx as usize] += 1;
     }
@@ -25,21 +25,21 @@ fn main() {
     println!("Completed in {}ms", time.as_millis());
 }
 
-fn play_round<A: GamePlayer, B: GamePlayer>(mut a: A, mut b: B, print: bool) -> Option<Player> {
+fn play_round<X: GamePlayer, O: GamePlayer>(print: bool) -> Option<Player> {
     let mut board = Board::empty();
-    let result = board.play(&mut a, &mut b);
+    let result = board.play(&mut X::default(), &mut O::default());
     if print {
-        println!("{board}");
+        //println!("{board}");
     }
     match result {
         Some(winner) => {
             if print {
-                println!("player {winner} won!");
+                //println!("player {winner} won!");
             }
         }
         None => {
             if print {
-                println!("a draw...")
+                //println!("a draw...")
             }
         }
     }

src/perfect.rs

@@ -1,16 +1,40 @@
+use std::ops::Neg;
+
 use crate::{
     board::{Player, State},
     Board, GamePlayer,
 };
 
-#[derive(PartialEq, Eq, PartialOrd, Ord)]
-struct Score(isize);
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
+enum Score {
+    Lost = -1,
+    Tie = 0,
+    Won = 1,
+}
+
+impl Neg for Score {
+    type Output = Self;
+
+    fn neg(self) -> Self::Output {
+        match self {
+            Self::Lost => Self::Won,
+            Self::Tie => Self::Tie,
+            Self::Won => Self::Lost,
+        }
+    }
+}
 
 #[derive(Clone)]
 pub struct PerfectPlayer {
     best_move: usize,
 }
 
+impl Default for PerfectPlayer {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl PerfectPlayer {
     pub fn new() -> Self {
         Self {
@@ -19,17 +43,31 @@ impl PerfectPlayer {
     }
 
     fn minmax(&mut self, board: &mut Board, player: Player, depth: usize) -> Score {
+        if depth < 2 {
+            //print!("{board}{}| playing {player}: ", " ".repeat(depth));
+        }
         match board.result() {
             State::Winner(winner) => {
+                if depth < 2 {
+                    //println!("   a winner {winner}");
+                }
                 if winner == player {
-                    Score(1)
+                    Score::Won
                 } else {
-                    Score(-1)
+                    Score::Lost
                 }
             }
-            State::Draw => Score(0),
+            State::Draw => {
+                if depth < 2 {
+                    //println!("this is gonna be a draw");
+                }
+                Score::Tie
+            }
             State::InProgress => {
-                let mut max_value = Score(isize::MIN);
+                if depth < 2 {
+                    //println!("not done yet");
+                }
+                let mut max_value = Score::Lost;
 
                 debug_assert!(
                     !board.iter().all(|x| x.is_some()),
@@ -42,7 +80,15 @@ impl PerfectPlayer {
                     }
 
                     board.set(i, Some(player));
-                    let value = self.minmax(board, player.opponent(), depth + 1);
+                    let value = -self.minmax(board, player.opponent(), depth + 1);
+
+                    if depth < 2 {
+                        if i == 8 {
+                            //println!("AAA\n{board}AAAA");
+                        }
+                        //println!("{}^| {i} {player} -> {:?}", " ".repeat(depth), value);
+                    }
+
                     board.set(i, None);
 
                     if value > max_value {