chessfriend/bitboard/src/library.rs

// Eryn Wells <eryn@erynwells.me>

use crate::BitBoard;
use chessfriend_core::{Color, Direction, Square};
use std::sync::OnceLock;

pub(crate) const RANKS: [BitBoard; 8] = [
    BitBoard(0xFF << 0 * 8),
    BitBoard(0xFF << 1 * 8),
    BitBoard(0xFF << 2 * 8),
    BitBoard(0xFF << 3 * 8),
    BitBoard(0xFF << 4 * 8),
    BitBoard(0xFF << 5 * 8),
    BitBoard(0xFF << 6 * 8),
    BitBoard(0xFF << 7 * 8),
];

pub(crate) const FILES: [BitBoard; 8] = [
    BitBoard(0x0101010101010101 << 0),
    BitBoard(0x0101010101010101 << 1),
    BitBoard(0x0101010101010101 << 2),
    BitBoard(0x0101010101010101 << 3),
    BitBoard(0x0101010101010101 << 4),
    BitBoard(0x0101010101010101 << 5),
    BitBoard(0x0101010101010101 << 6),
    BitBoard(0x0101010101010101 << 7),
];

/// Bitboards representing the kingside of the board, per color.
pub(crate) const KINGSIDES: [BitBoard; 2] =
    [BitBoard(0xF0F0F0F0F0F0F0F0), BitBoard(0x0F0F0F0F0F0F0F0F)];

/// Bitboards representing the queenside of the board, per color.
pub(crate) const QUEENSIDES: [BitBoard; 2] =
    [BitBoard(0x0F0F0F0F0F0F0F0F), BitBoard(0xF0F0F0F0F0F0F0F0)];

/// A bitboard representing the light squares.
pub(crate) const LIGHT_SQUARES: BitBoard =
    BitBoard(0x5555 | 0x5555 << 16 | 0x5555 << 32 | 0x5555 << 48);

/// A bitboad representing the dark squares
pub(crate) const DARK_SQUARES: BitBoard = BitBoard(!LIGHT_SQUARES.0);

pub(super) fn library() -> &'static MoveLibrary {
    static mut MOVE_LIBRARY: OnceLock<MoveLibrary> = OnceLock::new();

    unsafe {
        MOVE_LIBRARY.get_or_init(|| {
            let mut library = MoveLibrary::new();
            library.init();

            library
        })
    }
}

macro_rules! library_getter {
    ($name:ident) => {
        pub(super) fn $name(&self, sq: Square) -> BitBoard {
            self.$name[sq as usize]
        }
    };
}

#[derive(Debug)]
pub(super) struct MoveLibrary {
    // Rays
    rays: [[BitBoard; 8]; Square::NUM],

    // Piecewise move tables
    pawn_attacks: [[BitBoard; 64]; 2],
    pawn_pushes: [[BitBoard; 64]; 2],
    knight_moves: [BitBoard; 64],
    bishop_moves: [BitBoard; 64],
    rook_moves: [BitBoard; 64],
    queen_moves: [BitBoard; 64],
    king_moves: [BitBoard; 64],
}

impl MoveLibrary {
    const fn new() -> MoveLibrary {
        MoveLibrary {
            rays: [[BitBoard::empty(); 8]; Square::NUM],
            pawn_attacks: [[BitBoard::empty(); 64]; 2],
            pawn_pushes: [[BitBoard::empty(); 64]; 2],
            knight_moves: [BitBoard::empty(); 64],
            bishop_moves: [BitBoard::empty(); 64],
            rook_moves: [BitBoard::empty(); 64],
            queen_moves: [BitBoard::empty(); 64],
            king_moves: [BitBoard::empty(); 64],
        }
    }

    fn init(&mut self) {
        for sq in Square::ALL {
            self.init_pawn_moves(sq);
            self.init_orthogonal_rays(sq);
            self.init_diagonal_rays(sq);
            self.init_knight_moves(sq as usize);
            self.init_bishop_moves(sq);
            self.init_rook_moves(sq);
            self.init_queen_moves(sq);
            self.init_king_moves(sq as usize);
        }
    }

    fn init_orthogonal_rays(&mut self, sq: Square) {
        let sq_bb: BitBoard = sq.into();
        let rays = &mut self.rays[sq as usize];
        rays[Direction::North as usize] = Self::generate_ray(sq_bb, BitBoard::shift_north_one);
        rays[Direction::South as usize] = Self::generate_ray(sq_bb, BitBoard::shift_south_one);
        rays[Direction::East as usize] = Self::generate_ray(sq_bb, BitBoard::shift_east_one);
        rays[Direction::West as usize] = Self::generate_ray(sq_bb, BitBoard::shift_west_one);
    }

    fn init_diagonal_rays(&mut self, sq: Square) {
        let sq_bb: BitBoard = sq.into();
        let rays = &mut self.rays[sq as usize];
        rays[Direction::NorthEast as usize] =
            Self::generate_ray(sq_bb, BitBoard::shift_north_east_one);
        rays[Direction::NorthWest as usize] =
            Self::generate_ray(sq_bb, BitBoard::shift_north_west_one);
        rays[Direction::SouthWest as usize] =
            Self::generate_ray(sq_bb, BitBoard::shift_south_west_one);
        rays[Direction::SouthEast as usize] =
            Self::generate_ray(sq_bb, BitBoard::shift_south_east_one);
    }

    fn init_king_moves(&mut self, idx: usize) {
        let king = BitBoard::new(1 << idx);
        let mut attacks = king.shift_east_one() | king.shift_west_one();

        let king = king | attacks;
        attacks |= king.shift_north_one() | king.shift_south_one();

        self.king_moves[idx] = attacks;
    }

    /// Calculate bitboards representing knight moves from each square on the
    /// board. The algorithm is described on the [Chess Programming Wiki][cpw].
    ///
    /// [cpw]: https://www.chessprogramming.org/Knight_Pattern
    fn init_knight_moves(&mut self, idx: usize) {
        let knight = BitBoard::new(1 << idx);

        let east = knight.shift_east_one();
        let west = knight.shift_west_one();

        let mut attacks = (east | west).shift_north(2);
        attacks |= (east | west).shift_south(2);

        let east = east.shift_east_one();
        let west = west.shift_west_one();

        attacks |= (east | west).shift_north_one();
        attacks |= (east | west).shift_south_one();

        self.knight_moves[idx] = attacks;
    }

    fn init_bishop_moves(&mut self, sq: Square) {
        let rays = self.rays[sq as usize];
        self.bishop_moves[sq as usize] = rays[Direction::NorthWest as usize]
            | rays[Direction::NorthEast as usize]
            | rays[Direction::SouthEast as usize]
            | rays[Direction::SouthWest as usize];
    }

    fn init_rook_moves(&mut self, sq: Square) {
        let rays = self.rays[sq as usize];
        self.rook_moves[sq as usize] = rays[Direction::North as usize]
            | rays[Direction::East as usize]
            | rays[Direction::South as usize]
            | rays[Direction::West as usize];
    }

    fn init_queen_moves(&mut self, sq: Square) {
        let rook_moves = self.rook_moves[sq as usize];
        let bishop_moves = self.bishop_moves[sq as usize];
        self.queen_moves[sq as usize] = rook_moves | bishop_moves;
    }

    fn init_pawn_moves(&mut self, sq: Square) {
        let bitboard: BitBoard = sq.into();

        self.pawn_attacks[Color::White as usize][sq as usize] =
            bitboard.shift_north_west_one() | bitboard.shift_north_east_one();
        self.pawn_attacks[Color::Black as usize][sq as usize] =
            bitboard.shift_south_west_one() | bitboard.shift_south_east_one();

        self.pawn_pushes[Color::White as usize][sq as usize] = {
            let mut push = bitboard.shift_north_one();
            if !(bitboard & RANKS[1]).is_empty() {
                push |= push.shift_north_one();
            }

            push
        };

        self.pawn_pushes[Color::Black as usize][sq as usize] = {
            let mut push = bitboard.shift_south_one();
            if !(bitboard & RANKS[6]).is_empty() {
                push |= push.shift_south_one();
            }

            push
        };
    }

    #[inline]
    fn generate_ray(sq: BitBoard, shift: fn(&BitBoard) -> BitBoard) -> BitBoard {
        let mut ray = BitBoard::empty();

        let mut iter = shift(&sq);
        while !iter.is_empty() {
            ray |= iter;
            iter = shift(&iter);
        }

        ray
    }

    pub(super) fn ray(&self, sq: Square, dir: Direction) -> &BitBoard {
        &self.rays[sq as usize][dir as usize]
    }

    pub(super) fn pawn_pushes(&self, sq: Square, color: Color) -> BitBoard {
        self.pawn_pushes[color as usize][sq as usize]
    }

    pub(super) fn pawn_attacks(&self, sq: Square, color: Color) -> BitBoard {
        self.pawn_attacks[color as usize][sq as usize]
    }

    library_getter!(knight_moves);
    library_getter!(bishop_moves);
    library_getter!(rook_moves);
    library_getter!(queen_moves);
    library_getter!(king_moves);
}