player

build.rs

@@ -0,0 +1,108 @@
+use std::{fs::File, io::Write, path::PathBuf};
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum Player {
+    X,
+    O,
+}
+
+impl Player {
+    fn from_u8(num: u8) -> Option<Self> {
+        match num {
+            0 => Some(Player::X),
+            1 => Some(Player::O),
+            2 => None,
+            _ => panic!("Invalid value {num}"),
+        }
+    }
+
+    fn as_u8(this: Option<Player>) -> u8 {
+        match this {
+            Some(Player::X) => 0,
+            Some(Player::O) => 1,
+            None => 2,
+        }
+    }
+}
+
+#[derive(Clone, Copy)]
+struct Board(u32);
+
+impl Board {
+    fn new(num: u32) -> Option<Board> {
+        for i in 0..16 {
+            let next_step = num >> (i * 2);
+            let mask = 0b11;
+            let pos = next_step & mask;
+            if pos == 3 {
+                return None;
+            }
+        }
+
+        Some(Self(num))
+    }
+
+    fn get(&self, index: usize) -> Option<Player> {
+        debug_assert!(index < 9);
+
+        let shifted = self.0 >> (index * 2);
+        let masked = shifted & 0b11;
+        Player::from_u8(masked as u8)
+    }
+}
+
+fn winner(board: Board) -> Option<Player> {
+    fn won_row(a: Option<Player>, b: Option<Player>, c: Option<Player>) -> Option<Player> {
+        if a == Some(Player::X) && b == Some(Player::X) && c == Some(Player::X) {
+            Some(Player::X)
+        } else if a == Some(Player::O) && b == Some(Player::O) && c == Some(Player::O) {
+            Some(Player::O)
+        } else {
+            None
+        }
+    }
+
+    macro_rules! test_row {
+        ($a:literal, $b:literal, $c:literal) => {
+            match won_row(board.get($a), board.get($b), board.get($c)) {
+                Some(player) => return Some(player),
+                None => {}
+            }
+        };
+    }
+
+    test_row!(0, 1, 2);
+    test_row!(3, 4, 5);
+    test_row!(6, 7, 8);
+
+    test_row!(0, 3, 6);
+    test_row!(1, 4, 7);
+    test_row!(2, 5, 8);
+
+    test_row!(0, 4, 8);
+    test_row!(2, 4, 6);
+    None
+}
+
+fn calculate_win_table(file: &mut impl Write) {
+    for board in 0..(2u32.pow(18)) {
+        let byte = match Board::new(board) {
+            Some(board) => {
+                let winner = winner(board);
+                Player::as_u8(winner)
+            }
+            None => 0,
+        };
+        file.write_all(&[byte]).expect("write file");
+    }
+}
+
+fn main() {
+    let out_dir = std::env::var("OUT_DIR").expect("OUT_DIR");
+    let win_table_path = PathBuf::from(out_dir).join("win_table");
+    let mut win_table_file = File::create(win_table_path).expect("create win table file");
+
+    calculate_win_table(&mut win_table_file);
+
+    win_table_file.flush().expect("flushing file");
+}