//! Bitwise XOR via the [`BitXor`] trait.
use super::U256;
use core::ops::BitXor;

/// Computes the bitwise exclusive OR of two 256-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 four `u64` limbs.
///
/// # Examples
///
/// ```
/// use cnfy_uint::u256::U256;
///
/// let a = U256::from_be_limbs([0xFF, 0, 0, 0]);
/// let b = U256::from_be_limbs([0x0F, 0, 0, 0]);
/// assert_eq!(a ^ b, U256::from_be_limbs([0xF0, 0, 0, 0]));
/// ```
impl BitXor for U256 {
    type Output = U256;

    #[inline]
    fn bitxor(self, rhs: U256) -> U256 {
        U256([
            self.0[0] ^ rhs.0[0],
            self.0[1] ^ rhs.0[1],
            self.0[2] ^ rhs.0[2],
            self.0[3] ^ rhs.0[3],
        ])
    }
}

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

    /// XOR with self is zero.
    #[test]
    fn self_cancellation() {
        let a = U256::from_be_limbs([0x1234, 0x5678, 0x9ABC, 0xDEF0]);
        assert_eq!(a ^ a, U256::ZERO);
    }

    /// XOR with zero is identity.
    #[test]
    fn xor_zero() {
        let a = U256::from_be_limbs([0x1234, 0x5678, 0x9ABC, 0xDEF0]);
        assert_eq!(a ^ U256::ZERO, a);
    }

    /// XOR with MAX flips all bits.
    #[test]
    fn xor_max() {
        let a = U256::from_be_limbs([0, 0, 0, 0xFF]);
        assert_eq!(
            a ^ U256::MAX,
            U256::from_be_limbs([u64::MAX, u64::MAX, u64::MAX, u64::MAX ^ 0xFF]),
        );
    }

    /// Double XOR is identity.
    #[test]
    fn double_xor() {
        let a = U256::from_be_limbs([0x1234, 0x5678, 0x9ABC, 0xDEF0]);
        let b = U256::from_be_limbs([0xAAAA, 0xBBBB, 0xCCCC, 0xDDDD]);
        assert_eq!((a ^ b) ^ b, a);
    }

    /// XOR is commutative.
    #[test]
    fn commutative() {
        let a = U256::from_be_limbs([1, 2, 3, 4]);
        let b = U256::from_be_limbs([5, 6, 7, 8]);
        assert_eq!(a ^ b, b ^ a);
    }
}
