//! Conversion from [`U256`] into a `[u64; 4]` big-endian limb array.
use super::U256;

/// Converts a [`U256`] into its four `u64` limbs in big-endian order:
/// `[w0, w1, w2, w3]` where `w0` is the most significant.
///
/// This is the inverse of `From<[u64; 4]> for U256` and equivalent to
/// calling [`U256::to_be_limbs`].
///
/// # Examples
///
/// ```
/// use cnfy_uint::u256::U256;
///
/// let v = U256::from_be_limbs([1, 2, 3, 4]);
/// let arr: [u64; 4] = v.into();
/// assert_eq!(arr, [1, 2, 3, 4]);
/// ```
impl From<U256> for [u64; 4] {
    #[inline]
    fn from(value: U256) -> Self {
        [value.0[3], value.0[2], value.0[1], value.0[0]]
    }
}

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

    /// Round-trip from limbs through U256 back to limbs.
    #[test]
    fn round_trip() {
        let arr = [0xA, 0xB, 0xC, 0xD];
        let v = U256::from_be_limbs(arr);
        let back: [u64; 4] = v.into();
        assert_eq!(back, arr);
    }

    /// Zero converts to all-zero limbs.
    #[test]
    fn zero() {
        let arr: [u64; 4] = U256::ZERO.into();
        assert_eq!(arr, [0, 0, 0, 0]);
    }

    /// MAX converts to all-max limbs.
    #[test]
    fn max() {
        let arr: [u64; 4] = U256::MAX.into();
        assert_eq!(arr, [u64::MAX; 4]);
    }
}
