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

/// Computes the bitwise XOR of two 512-bit integers, producing a
/// result where each bit is set if exactly one of the corresponding
/// input bits is set.
///
/// Applied independently to each of the eight `u64` limbs.
///
/// # Examples
///
/// ```
/// use cnfy_uint::u512::U512;
///
/// let a = U512::from_be_limbs([0, 0, 0, 0, 0, 0, 0, 0xFF]);
/// let b = U512::from_be_limbs([0, 0, 0, 0, 0, 0, 0, 0x0F]);
/// assert_eq!(a ^ b, U512::from_be_limbs([0, 0, 0, 0, 0, 0, 0, 0xF0]));
/// ```
impl BitXor for U512 {
    type Output = U512;

    #[inline]
    fn bitxor(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::*;

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

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

    /// XOR with MAX flips all bits.
    #[test]
    fn xor_max() {
        let a = U512::from_be_limbs([0x1234, 0x5678, 0x9ABC, 0xDEF0, 1, 2, 3, 4]);
        assert_eq!(a ^ U512::MAX, !a);
    }

    /// XOR 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);
    }

    /// Double XOR is identity.
    #[test]
    fn double_xor() {
        let a = U512::from_be_limbs([0xAB, 0xCD, 0xEF, 0x42, 1, 2, 3, 4]);
        let b = U512::from_be_limbs([0x11, 0x22, 0x33, 0x44, 5, 6, 7, 8]);
        assert_eq!((a ^ b) ^ b, a);
    }
}
