get rid of OptionSquare

src/board.rs

@@ -434,52 +434,6 @@ impl core::str::FromStr for Square {
     }
 }
 
-#[rustfmt::skip]
-#[allow(unused)]
-#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
-#[repr(u8)]
-pub(crate) enum OptionSquare {
-    A1, B1, C1, D1, E1, F1, G1, H1,
-    A2, B2, C2, D2, E2, F2, G2, H2,
-    A3, B3, C3, D3, E3, F3, G3, H3,
-    A4, B4, C4, D4, E4, F4, G4, H4,
-    A5, B5, C5, D5, E5, F5, G5, H5,
-    A6, B6, C6, D6, E6, F6, G6, H6,
-    A7, B7, C7, D7, E7, F7, G7, H7,
-    A8, B8, C8, D8, E8, F8, G8, H8,
-    None,
-}
-
-impl OptionSquare {
-    #[inline]
-    pub(crate) fn new(square: Option<Square>) -> OptionSquare {
-        match square {
-            Some(square) => Self::from_square(square),
-            None => Self::None,
-        }
-    }
-
-    #[inline]
-    pub(crate) fn try_into_square(self) -> Option<Square> {
-        unsafe {
-            match self {
-                Self::None => None,
-                _ => Some(Square::new_unchecked(self as u8)),
-            }
-        }
-    }
-
-    #[inline]
-    pub(crate) fn from_square(square: Square) -> Self {
-        unsafe { core::mem::transmute(square) }
-    }
-
-    #[inline]
-    pub(crate) fn bitboard(&self) -> Bitboard {
-        Bitboard(1 << (*self as u8))
-    }
-}
-
 /// A type of piece.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 #[repr(u8)]

src/position.rs

@@ -94,7 +94,7 @@ impl Position {
             ],
             turn: Color::White,
             castling_rights: CastlingRights::full(),
-            en_passant: OptionSquare::None,
+            en_passant: None,
         })
     }
 
@@ -164,7 +164,7 @@ impl Position {
     /// Returns `true` if taking en passant is legal on the position.
     #[must_use]
     pub fn en_passant_is_legal(&self) -> bool {
-        if self.as_setup().en_passant == OptionSquare::None {
+        if self.as_setup().en_passant == None {
             return false;
         }
         struct MoveGenImpl {
@@ -192,7 +192,11 @@ impl Position {
             }
         }
         let mut moves = MoveGenImpl {
-            to: self.as_setup().en_passant.bitboard(),
+            to: self
+                .as_setup()
+                .en_passant
+                .map(|square| square.bitboard())
+                .unwrap_or(Bitboard::new()),
         };
         self.generate_moves(&mut moves).is_break()
     }
@@ -204,7 +208,7 @@ impl Position {
     /// passant before calling this function.
     #[inline]
     pub fn remove_en_passant_target_square(&mut self) {
-        self.0.en_passant = OptionSquare::None;
+        self.0.en_passant = None
     }
 
     /// Removes the castling rights for the given color and side, if any.
@@ -255,7 +259,7 @@ impl Position {
         checkers.is_empty().then(|| {
             Self(Setup {
                 turn: !turn,
-                en_passant: OptionSquare::None,
+                en_passant: None,
                 ..self.0.clone()
             })
         })
@@ -801,7 +805,7 @@ impl Position {
                 ),
             )?;
             // en passant
-            if let Some(to) = en_passant.try_into_square() {
+            if let Some(to) = en_passant {
                 if global_mask_to.contains(to) {
                     let capture_square = unsafe {
                         // SAFETY: the position is legal
@@ -907,7 +911,7 @@ impl Position {
     pub(crate) unsafe fn play_unchecked(&mut self, m: RawMove) {
         let Self(setup) = self;
 
-        setup.en_passant = OptionSquare::None;
+        setup.en_passant = None;
 
         let RawMove {
             kind,
@@ -927,13 +931,13 @@ impl Position {
             MoveType::PawnAttackPromotion => aux_play_normal(setup, role, from, to),
             MoveType::PawnDoubleAdvance => {
                 aux_play_pawn_advance(setup, Role::Pawn, from, to);
-                setup.en_passant = OptionSquare::new(Some(Square::from_coords(
+                setup.en_passant = Some(Square::from_coords(
                     from.file(),
                     match setup.turn {
                         Color::White => Rank::Third,
                         Color::Black => Rank::Sixth,
                     },
-                )));
+                ));
             }
             MoveType::EnPassant => {
                 let direction = !setup.turn.forward();

src/setup.rs

@@ -32,7 +32,7 @@ pub struct Setup {
     /// bitboards = [pawns | bishops | queens, knights | bishops | kings, rooks | queens | kings, black]
     pub(crate) bitboards: [Bitboard; 4],
     pub(crate) turn: Color,
-    pub(crate) en_passant: OptionSquare,
+    pub(crate) en_passant: Option<Square>,
     pub(crate) castling_rights: CastlingRights,
 }
 
@@ -43,7 +43,7 @@ impl Setup {
         Self {
             bitboards: [Bitboard(0); 4],
             turn: Color::White,
-            en_passant: OptionSquare::None,
+            en_passant: None,
             castling_rights: CastlingRights::new(),
         }
     }
@@ -208,7 +208,7 @@ impl Setup {
 
         w.write_char(' ')?;
 
-        match self.en_passant.try_into_square() {
+        match self.en_passant {
             Some(sq) => {
                 w.write_char(sq.file().to_char())?;
                 w.write_char(sq.rank().to_char())?;
@@ -245,7 +245,7 @@ impl Setup {
     /// Returns the optional en passant target square.
     #[inline]
     pub fn en_passant_target_square(&self) -> Option<Square> {
-        self.en_passant.try_into_square()
+        self.en_passant
     }
 
     /// Sets the occupancy of a square.
@@ -307,7 +307,7 @@ impl Setup {
     /// Sets the en passant target square.
     #[inline]
     pub fn set_en_passant_target_square(&mut self, square: Option<Square>) {
-        self.en_passant = OptionSquare::new(square);
+        self.en_passant = square;
     }
 
     /// Returns the quad-bitboard representation of the board.
@@ -341,11 +341,7 @@ impl Setup {
                 (black ^ (p_b_q | n_b_k | r_q_k)).mirror(),
             ],
             turn: !self.turn,
-            en_passant: self
+            en_passant: self.en_passant.map(|square| square.mirror()),
-                .en_passant
-                .try_into_square()
-                .map(|square| OptionSquare::from_square(square.mirror()))
-                .unwrap_or(OptionSquare::None),
             castling_rights: self.castling_rights.mirror(),
         }
     }
@@ -460,7 +456,7 @@ impl Setup {
             reasons.add(IllegalPositionReason::InvalidCastlingRights);
         }
 
-        if self.en_passant.try_into_square().is_some_and(|en_passant| {
+        if self.en_passant.is_some_and(|en_passant| {
             let (target_rank, pawn_rank) = match self.turn {
                 Color::White => (Rank::Sixth, Rank::Fifth),
                 Color::Black => (Rank::Third, Rank::Fourth),
@@ -473,7 +469,7 @@ impl Setup {
             reasons.add(IllegalPositionReason::InvalidEnPassant);
         }
 
-        if self.en_passant.try_into_square().is_some_and(|en_passant| {
+        if self.en_passant.is_some_and(|en_passant| {
             let blockers = blockers
                 & !en_passant.bitboard().trans(match self.turn {
                     Color::White => Direction::South,