//! Bitwise AND via the [`BitAnd`] trait.
use super::U512;
use core::ops::BitAnd;

/// Computes the bitwise AND of two 512-bit integers, producing a
/// result where each bit is set only if both corresponding input bits
/// are set.
///
/// Applied independently to each of the eight `u64` limbs.
///
/// # Examples
///
/// ```
/// use cnfy_uint::u512::U512;
///
/// let a = U512::from_be_limbs([0xFF; 8]);
/// let b = U512::from_be_limbs([0x0F; 8]);
/// assert_eq!(a & b, U512::from_be_limbs([0x0F; 8]));
/// ```
impl BitAnd for U512 {
    type Output = U512;

    #[inline]
    fn bitand(self, rhs: U512) -> U512 {
        U512([
            self.0[0] & rhs.0[0],
            self.0[1] & rhs.0[1],
            self.0[2] & rhs.0[2],
            self.0[3] & rhs.0[3],
            self.0[4] & rhs.0[4],
            self.0[5] & rhs.0[5],
            self.0[6] & rhs.0[6],
            self.0[7] & rhs.0[7],
        ])
    }
}

#[cfg(test)]
mod ai_tests {
    use super::*;

    /// AND with self is identity.
    #[test]
    fn self_identity() {
        let a = U512::from_be_limbs([0x1234, 0x5678, 0x9ABC, 0xDEF0, 1, 2, 3, 4]);
        assert_eq!(a & a, a);
    }

    /// AND with zero is zero.
    #[test]
    fn and_zero() {
        let a = U512::from_be_limbs([0x1234, 0x5678, 0x9ABC, 0xDEF0, 1, 2, 3, 4]);
        assert_eq!(a & U512::ZERO, U512::ZERO);
    }

    /// AND with MAX is identity.
    #[test]
    fn and_max() {
        let a = U512::from_be_limbs([0x1234, 0x5678, 0x9ABC, 0xDEF0, 1, 2, 3, 4]);
        assert_eq!(a & U512::MAX, a);
    }

    /// Masking extracts specific bits.
    #[test]
    fn mask() {
        let a = U512::from_be_limbs([0xFF00, 0, 0, 0, 0, 0, 0, 0]);
        let mask = U512::from_be_limbs([0x0F00, 0, 0, 0, 0, 0, 0, 0]);
        assert_eq!(a & mask, U512::from_be_limbs([0x0F00, 0, 0, 0, 0, 0, 0, 0]));
    }

    /// AND is commutative.
    #[test]
    fn commutative() {
        let a = U512::from_be_limbs([1, 2, 3, 4, 5, 6, 7, 8]);
        let b = U512::from_be_limbs([8, 7, 6, 5, 4, 3, 2, 1]);
        assert_eq!(a & b, b & a);
    }
}
