ai implemented, needs some perf tuning

Cargo.lock

@@ -244,6 +244,7 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "criterion",
+ "regex",
 ]
 
 [[package]]

Cargo.toml

@@ -8,11 +8,12 @@ name = "othello"
 path = "src/lib.rs"
 
 [[bin]]
-name = "othello-gui"
+name = "othello-cli"
 path = "src/main.rs"
 
 [dependencies]
 anyhow = "1.0.100"
+regex = "1.12.2"
 
 [dev-dependencies]
 criterion = "0.7.0"

src/ai.rs

@@ -0,0 +1,81 @@
+use crate::{
+    board::{Board, explode_board},
+    game::{Game, Team},
+};
+
+/// Using alpha-beta pruning and the minimax algorithm, determine the best move
+/// for a game with a recursion depth of `depth`.
+pub fn alphabeta(game: Game, depth: u8, mut alpha: i8, mut beta: i8) -> (Board, i8) {
+    if depth == 0 {
+        return (0, game.score().diff());
+    }
+    let moves = game.available();
+    if moves == 0 {
+        return (0, game.score().diff());
+    }
+
+    let mut best_move: Board = 0;
+    // I just establish a convention of maximizing for black and minimizing for white.
+    // I'm not sure if that's conventional or not, but it's what I chose.
+    match game.current_team {
+        Team::Black => {
+            for mv in explode_board(moves) {
+                let mut g = game.clone();
+                g.play(mv);
+                // maximize for the evaluation of subsequent moves
+                let evaluation = alphabeta(g, depth - 1, alpha, beta).1;
+                if evaluation > alpha {
+                    alpha = evaluation;
+                    best_move = mv;
+                };
+                if beta <= alpha {
+                    break;
+                }
+            }
+            (best_move, alpha)
+        }
+        Team::White => {
+            for mv in explode_board(moves) {
+                let mut g = game.clone();
+                g.play(mv);
+                // maximize for the evaluation of subsequent moves
+                let evaluation = alphabeta(g, depth - 1, alpha, beta).1;
+                if evaluation < beta {
+                    beta = evaluation;
+                    best_move = mv;
+                };
+                if beta <= alpha {
+                    break;
+                }
+            }
+            (best_move, beta)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::board::view::View;
+    use crate::board::{BitBoard, squares::*};
+    use crate::game::Game;
+
+    #[test]
+    // just a sanity check to ensure that my AI performs up to snuff with another popular engine
+    fn opening() {
+        let mut game = Game::default();
+
+        println!("{}", game.board().render(View::RankAsc, vec![]));
+        game.play(D3);
+        let (best_move, _) = alphabeta(game.clone(), 12, i8::MIN + 1, i8::MAX - 1);
+        println!(
+            "dis:\n{}",
+            BitBoard {
+                boards: [0, best_move]
+            }
+        );
+        game.play(best_move);
+        println!("{}", game.board().render(View::RankAsc, vec![]));
+        assert_eq!(best_move, C3);
+    }
+}

src/board/mod.rs

@@ -12,6 +12,64 @@ pub mod view;
 
 pub type Board = u64;
 
+/// Represents the score at a given moment in the game. It is computed as
+/// the number of black discs vs white discs. Structured as (black, white)
+#[derive(Debug, PartialEq)]
+pub struct Score(pub u8, pub u8);
+impl Score {
+    /// Get black's current score
+    pub fn black(&self) -> u8 {
+        self.0
+    }
+    /// Get white's current score
+    pub fn white(&self) -> u8 {
+        self.1
+    }
+
+    /// Compute diff of evaluation. Useful for easily comparing a bunch of scores.
+    pub fn diff(&self) -> i8 {
+        self.0 as i8 - self.1 as i8
+    }
+}
+
+/// Explode a single board into an iterator over all of its excited one-hot
+/// boards.
+///
+/// For example:
+/// `0b1010` will explode into an iterator over `[0b0010, 0b1000]`.
+///
+/// The boards will be sorted by rank-ascending.
+#[inline]
+pub fn explode_board(mut b: Board) -> impl Iterator<Item = Board> {
+    // a naive solution would be to simply start at the rightmost bit and
+    // shift until we reach an excited bit, AND it for result, and store
+    // the current shift + 1 for the next iteration until `b` is zero. This
+    // is a bit wasteful, as we can abuse a handful of modular relationships
+    // with negation.
+    //
+    // we do this using the `u64::wrapping_neg` method.
+    // In two's-complement, negation can be used to isolate the least
+    // significant excited bit in a signed integer. For example,
+    // if `Board` were defined as `i64` instead, we could define LSB as
+    // `lsb = b & -b`. Since we're using `u64`, we can mimic this using
+    // `u64::wrapping_neg`.
+    std::iter::from_fn(move || {
+        // if we have no more excited bits, return None
+        if b == 0 {
+            None
+        } else {
+            // if we have more, continue isolating the LSB
+            let lsb = b & b.wrapping_neg();
+            // If you're skeptical of the claim above about these being
+            // equivalent, comment out the line above this and uncomment
+            // the line below this. They both pass the test.
+            // let lsb = (b as i64 & -(b as i64)) as u64;
+            b &= b - 1;
+            Some(lsb)
+        }
+    })
+}
+
 // Directions:
 //  7  8  9
 // -1  0  1
@@ -380,11 +438,14 @@ impl BitBoard {
     }
 
     /// Compute the score (B, W) by counting the excited bits in each board.
-    pub fn score(&self) -> (u32, u32) {
+    pub fn score(&self) -> Score {
         // `u64::count_ones()` is implemented `unsafe` and makes use of primitives in the
         // low-level implementation of the language itself for maximum performance. Better
         // to use this than implement myself.
-        (self.boards[0].count_ones(), self.boards[1].count_ones())
+        Score(
+            self.boards[0].count_ones() as u8,
+            self.boards[1].count_ones() as u8,
+        )
     }
 }
 
@@ -610,7 +671,6 @@ mod tests {
     fn test_available_no_moves_surrounded() {
         // Black piece at b7 completely surrounded by white
         let bb = BitBoard::from_jon("www/wbw/www////").expect("Valid board");
-        println!("dis:\n{}", bb);
         // Black should have three moves in this position: d7, b5, and d5
         assert_eq!(bb.available(Team::Black), D7 | B5 | D5);
     }
@@ -619,7 +679,6 @@ mod tests {
     fn test_available_long_capture() {
         // Black at a4, white at b4-f4, empty g4, black at h4
         let bb = BitBoard::from_jon("////bwwwww1b///").expect("Valid board");
-        println!("dis:\n{}", bb);
         // Black can play at g4 to capture entire row of white pieces
         assert_eq!(bb.available(Team::Black), G4);
     }
@@ -692,18 +751,27 @@ mod tests {
     #[test]
     fn play_works() {
         let mut bb = BitBoard::default();
-        assert_eq!(bb.score(), (2, 2));
+        assert_eq!(bb.score(), Score(2, 2));
         bb.play(Team::Black, E6);
         assert_eq!(bb, BitBoard::new(D5 | E6 | E5 | E4, D4));
-        assert_eq!(bb.score(), (4, 1));
+        assert_eq!(bb.score(), Score(4, 1));
         bb.play(Team::White, F4);
         assert_eq!(bb, BitBoard::new(D5 | E6 | E5, D4 | E4 | F4));
-        assert_eq!(bb.score(), (3, 3));
+        assert_eq!(bb.score(), Score(3, 3));
         bb.play(Team::Black, G3);
         assert_eq!(bb, BitBoard::new(D5 | E6 | E5 | G3 | F4, D4 | E4));
-        assert_eq!(bb.score(), (5, 2));
+        assert_eq!(bb.score(), Score(5, 2));
         bb.play(Team::White, E7);
         assert_eq!(bb, BitBoard::new(D5 | G3 | F4, D4 | E4 | E5 | E6 | E7));
-        assert_eq!(bb.score(), (3, 5));
+        assert_eq!(bb.score(), Score(3, 5));
+    }
+
+    #[test]
+    fn explode_works() {
+        let bb = BitBoard::default();
+        assert_eq!(
+            explode_board(bb.available(Team::Black)).collect::<Vec<Board>>(),
+            vec![D3, C4, F5, E6] // they are sorted in rank-ascending
+        );
     }
 }

src/cli/mod.rs

@@ -1,18 +1,97 @@
-use othello::{board::view::Overlay, game::Game};
+use std::io;
+
+use othello::{
+    ai::alphabeta,
+    board::{
+        Board, Score,
+        view::{Overlay, View},
+    },
+    game::Game,
+};
+
+use anyhow::Context;
+use regex::Regex;
+
+enum Action {
+    Play(Board),
+    Skip,
+    Ai,
+}
+
+const PLAY_RE: &str = r"^(play - )?([abcdefghABCDEFGH])(\d)$";
 
 pub fn run() -> anyhow::Result<()> {
     let mut game = Game::default();
+    let mut board_changed = true;
 
+    let play_re = Regex::new(PLAY_RE).unwrap();
+
+    while !game.is_complete() {
+        let legal_moves = game.available();
+        if board_changed {
+            let Score(b, w) = game.score();
+            println!("Score: (Black: {} , White: {}", b, w);
             println!(
                 "{}",
                 game.board().render(
-            game.current_team,
+                    View::RankAsc,
-            vec![Overlay(
+                    vec![Overlay(legal_moves, "\x1b[95m*\x1b[37m")]
-                game.board().available(game.current_team),
-                "\x1b[95m*\x1b[37m"
-            )]
                 )
             );
+            board_changed = false;
+        }
+
+        let choice = loop {
+            println!("Please choose your action: [play - (move), skip, ai]");
+            let mut raw_input = String::new();
+            io::stdin()
+                .read_line(&mut raw_input)
+                .context("Failed to read input")?;
+            if let Some(captures) = play_re.captures(&raw_input.trim()) {
+                let file = captures.get(2).context("Failed to get file capture")?;
+                let rank = captures
+                    .get(3)
+                    .context("Failed to get rank capture")?
+                    .as_str()
+                    .parse::<u8>()
+                    .context("Failed to parse rank")?;
+                break Action::Play(create_move(file.as_str(), rank));
+            }
+
+            match raw_input.as_str().trim() {
+                "skip" => break Action::Skip,
+                "ai" => break Action::Ai,
+                _ => println!("Invalid input"),
+            }
+        };
+
+        match choice {
+            Action::Play(mv) => {
+                if mv & legal_moves == 0 {
+                    println!(
+                        "Attempted illegal moves. Legal moves are indicated by asterisks (*)."
+                    );
+                } else {
+                    game.play(mv);
+                    board_changed = true;
+                }
+            }
+            Action::Skip => {
+                if legal_moves != 0 {
+                    println!("Cannot skip with legal moves available. Must choose `play` or `ai`.");
+                } else {
+                    game.skip()
+                }
+            }
+            Action::Ai => {
+                let (mv, eval) = alphabeta(game.clone(), 12, i8::MIN + 1, i8::MAX - 1);
+                println!("beep. boop. eval = {eval}");
+                game.play(mv);
+                board_changed = true;
+            }
+        }
+    }
+
     game.play(othello::board::squares::E6);
     println!();
     println!(
@@ -28,3 +107,36 @@ pub fn run() -> anyhow::Result<()> {
 
     Ok(())
 }
+
+/// Convert a file and rank into an actual board
+fn create_move(file: &str, rank: u8) -> Board {
+    1 << (match file {
+        "a" => 0,
+        "b" => 1,
+        "c" => 2,
+        "d" => 3,
+        "e" => 4,
+        "f" => 5,
+        "g" => 6,
+        "h" => 7,
+        _ => unreachable!("impossible file"),
+    } + (rank - 1) * 8) as Board
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use othello::board::squares::*;
+    #[test]
+    fn create_move_works() {
+        assert_eq!(create_move("a", 1), A1);
+        assert_eq!(create_move("d", 3), D3);
+        assert_eq!(create_move("h", 8), H8);
+    }
+
+    #[test]
+    fn re_works() {
+        let play_re = Regex::new(PLAY_RE).unwrap();
+        assert!(play_re.is_match("play - d3"));
+    }
+}

src/game.rs

@@ -1,4 +1,4 @@
-use crate::board::{BitBoard, Board};
+use crate::board::{BitBoard, Board, Score};
 
 #[repr(u8)]
 #[derive(Copy, Clone, Debug, PartialEq, Default)]
@@ -19,7 +19,8 @@ impl Team {
     }
 }
 
-#[derive(Default)]
+#[derive(Default, Clone)]
+// TODO: Look into potentially better memory alignment for this
 pub struct Game {
     pub current_team: Team,
     board: BitBoard,
@@ -42,9 +43,31 @@ impl Game {
         Ok(())
     }
 
+    /// Skip the current player
+    pub fn skip(&mut self) {
+        self.current_team = self.current_team.next();
+    }
+
+    /// Copy the board
     pub fn board(&self) -> BitBoard {
         self.board
     }
+
+    /// Compute the available moves
+    pub fn available(&self) -> Board {
+        self.board.available(self.current_team)
+    }
+
+    /// Compute the score of the game
+    pub fn score(&self) -> Score {
+        self.board.score()
+    }
+
+    /// Determine whether or not the game has concluded
+    pub fn is_complete(&self) -> bool {
+        let score = self.board.score();
+        score.0 + score.1 == 64
+    }
 }
 
 #[cfg(test)]

src/lib.rs

@@ -1,2 +1,3 @@
+pub mod ai;
 pub mod board;
 pub mod game;