board optimizations

src/repr/board.rs

@@ -227,22 +227,26 @@ impl Board {
 
     /// Return a modified [`Board`] with the piece placed at a position
     /// Returns None if the move was invalid
-    pub fn what_if(&self, coord: CoordPair, piece: Piece) -> Result<Self, &'static str> {
+    pub const fn what_if(&self, coord: CoordPair, piece: Piece) -> Option<Self> {
         // extract check here to avoid copy
         if self.get(coord).is_some() {
-            return Err("position is occupied");
+            return None;
         }
 
         let mut self_copy = *self;
-        self_copy.place(coord, piece).map(|_| self_copy)
+        if let Ok(_) = self_copy.place(coord, piece) {
+            Some(self_copy)
+        } else {
+            None
+        }
     }
 
     /// Returns a bool which represents whether or not a move would propegate and be valid
-    pub fn would_prop(&self, coord: CoordPair, piece: Piece) -> bool {
+    pub const fn would_prop(&self, coord: CoordPair, piece: Piece) -> bool {
         self.get(coord).is_none() && !self.propegate_from_dry(coord, piece).is_empty()
     }
 
-    pub fn place(&mut self, coord: CoordPair, piece: Piece) -> Result<(), &'static str> {
+    pub const fn place(&mut self, coord: CoordPair, piece: Piece) -> Result<(), &'static str> {
         if self.get(coord).is_some() {
             return Err("position is occupied");
         }
@@ -257,7 +261,7 @@ impl Board {
 
     /// Propegate the board and captures starting from a specific position
     /// returns true if flips occurred
-    fn propegate_from(&mut self, coord: CoordPair, starting_color: Piece) -> bool {
+    const fn propegate_from(&mut self, coord: CoordPair, starting_color: Piece) -> bool {
         let flip_mask = self.propegate_from_dry(coord, starting_color);
         let did_flip = !flip_mask.is_empty();
 
@@ -267,40 +271,52 @@ impl Board {
         did_flip
     }
 
-    fn apply_flip_mask(&mut self, color: Piece, flip_mask: BitBoard) {
+    const fn apply_flip_mask(&mut self, color: Piece, flip_mask: BitBoard) {
+        // did some investigation, seems using xor actually decreases
+        // performance over the branchfull impl? 3.2-3.5% slower
         get_board!(mut self, color).bitor_assign(flip_mask);
-        get_board!(mut self, color.flip()).bitand_assign(!flip_mask);
+        get_board!(mut self, color.flip()).bitand_assign(flip_mask.not());
     }
 
     /// Propegate piece captures originating from (i, j)
     /// DO NOT USE THIS ALONE, this should be called as a part of
     /// [`Board::place`] or [`Board::place_and_prop_unchecked`]
-    fn propegate_from_dry(&self, coords: CoordPair, starting_color: Piece) -> BitBoard {
+    const fn propegate_from_dry(&self, coords: CoordPair, starting_color: Piece) -> BitBoard {
         let player_board = get_board!(self, starting_color);
         let opponent_board = get_board!(self, starting_color.flip());
 
         let mut flip_mask = BitBoard::new();
         let seed = BitBoard::from_coord(coords);
 
-        for dir in BitBoard::DIRECTIONS {
-            let mut current = seed;
-            let mut temp_flips = BitBoard::new();
+        macro_rules! apply_dir {
+            ($base:expr, $sum_mask:expr, $dir:expr) => {
+                let mut current = $base;
+                let mut temp_flips = BitBoard::new();
 
-            // Expand in direction until edge or non-opponent piece
-            loop {
-                current = dir(&current, 1);
-                if current.is_empty() || !current.intersects(*opponent_board) {
-                    break;
+                // Expand in direction until edge or non-opponent piece
+                loop {
+                    current = $dir(&current, 1);
+                    if current.is_empty() || !current.intersects(*opponent_board) {
+                        break;
+                    }
+                    temp_flips.bitor_assign(current);
                 }
-                temp_flips |= current;
-            }
 
-            // If terminated on a player piece, keep the flips
-            if current.intersects(*player_board) {
-                flip_mask |= temp_flips;
-            }
+                // If terminated on a player piece, keep the flips
+                if current.intersects(*player_board) {
+                    $sum_mask.bitor_assign(temp_flips);
+                }
+            };
         }
 
+        apply_dir!(seed, flip_mask, BitBoard::east);
+        apply_dir!(seed, flip_mask, BitBoard::west);
+        apply_dir!(seed, flip_mask, BitBoard::north);
+        apply_dir!(seed, flip_mask, BitBoard::south);
+        apply_dir!(seed, flip_mask, BitBoard::northeast);
+        apply_dir!(seed, flip_mask, BitBoard::northwest);
+        apply_dir!(seed, flip_mask, BitBoard::southeast);
+        apply_dir!(seed, flip_mask, BitBoard::southwest);
         flip_mask
     }