chessfriend/board/src/bitboard.rs

// Eryn Wells <eryn@erynwells.me>

use crate::square::Square;
use std::ops::{BitAnd, BitOr, Not};

#[derive(Clone, Copy, Debug, Default, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct BitBoard(u64);

impl BitBoard {
    pub fn empty() -> BitBoard {
        BitBoard(0)
    }

    pub fn from_bit_field(bits: u64) -> BitBoard {
        BitBoard(bits)
    }

    fn is_empty(&self) -> bool {
        self.0 == 0
    }

    fn has_piece_at(&self, sq: &Square) -> bool {
        (self.0 & (1 << sq.index)) > 0
    }

    fn place_piece_at(&mut self, sq: &Square) {
        self.0 |= 1 << sq.index
    }

    fn remove_piece_at(&mut self, sq: &Square) {
        self.0 &= !(1 << sq.index)
    }

    #[cfg(target_arch = "arm")]
    fn _arm_count_leading_zeros(&self) -> u8 {
        let mut number_of_leading_zeros: u8 = 0;
        unsafe {
            asm!(
                "clz {count}, {bitfield}",
                count = out(reg) number_of_leading_zeros,
                bitfield = in(reg) self.0,
            );
        }

        number_of_leading_zeros
    }
}

impl BitAnd for BitBoard {
    type Output = BitBoard;

    #[inline]
    fn bitand(self, rhs: Self) -> Self {
        BitBoard(self.0 & rhs.0)
    }
}

impl BitAnd<&BitBoard> for BitBoard {
    type Output = BitBoard;

    #[inline]
    fn bitand(self, rhs: &Self) -> Self {
        BitBoard(self.0 & rhs.0)
    }
}

impl Not for BitBoard {
    type Output = BitBoard;

    #[inline]
    fn not(self) -> Self::Output {
        BitBoard(!self.0)
    }
}

impl Not for &BitBoard {
    type Output = BitBoard;

    #[inline]
    fn not(self) -> Self::Output {
        BitBoard(!self.0)
    }
}

impl BitOr for BitBoard {
    type Output = BitBoard;

    #[inline]
    fn bitor(self, rhs: Self) -> Self {
        BitBoard(self.0 | rhs.0)
    }
}

impl BitOr<&BitBoard> for BitBoard {
    type Output = BitBoard;

    #[inline]
    fn bitor(self, rhs: &Self) -> Self {
        BitBoard(self.0 | rhs.0)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::square::Square;

    #[test]
    fn is_empty() {
        assert!(BitBoard(0).is_empty());
    }

    #[test]
    fn has_piece_at() {
        let bb = BitBoard(0b1001100);

        assert!(bb.has_piece_at(
            &Square::from_algebraic_string("a3").expect("Unable to get square for 'a3'")
        ));
        assert!(!bb.has_piece_at(
            &Square::from_algebraic_string("a2").expect("Unable to get square for 'a2'")
        ));
    }

    #[test]
    fn place_piece_at() {
        let sq = Square::from_index(34).expect("Invalid square index");

        let mut bb = BitBoard(0b1001100);
        bb.place_piece_at(&sq);
        assert!(bb.has_piece_at(&sq));
    }

    #[test]
    fn remove_piece_at() {
        let sq = Square::from_index(2).expect("Invalid square index");

        let mut bb = BitBoard(0b1001100);
        bb.remove_piece_at(&sq);
        assert!(!bb.has_piece_at(&sq));
    }

    #[cfg(target_arch = "arm")]
    #[test]
    fn arm_count_leading_zeros() {
        assert_eq!(BitBoard(0)._arm_count_leading_zeros(), 0);
        assert_eq!(BitBoard(0b10)._arm_count_leading_zeros(), 62);
        assert_eq!(BitBoard(0b1010)._arm_count_leading_zeros(), 60);
        assert_eq!(BitBoard(0x80000000)._arm_count_leading_zeros(), 0);
    }
}