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//! Conversion from `u128` into [`U256`].
use super::U256;
/// Creates a [`U256`] from a `u128` value, placing the high 64 bits in
/// limb `w2` and the low 64 bits in limb `w3`, with the upper two limbs
/// set to zero.
///
/// # Examples
///
/// ```
/// use cnfy_uint::u256::U256;
///
/// let v = U256::from(0x1_0000_0000_0000_0000u128);
/// assert_eq!(v, U256::from_be_limbs([0, 0, 1, 0]));
/// ```
impl From<u128> for U256 {
#[inline]
fn from(value: u128) -> Self {
Self::from_be_limbs([0, 0, (value >> 64) as u64, value as u64])
}
}
#[cfg(test)]
mod ai_tests {
use super::*;
/// Converting zero produces U256::ZERO.
#[test]
fn zero() {
assert_eq!(U256::from(0u128), U256::ZERO);
}
/// Converting one produces U256::ONE.
#[test]
fn one() {
assert_eq!(U256::from(1u128), U256::ONE);
}
/// Converting u128::MAX fills the lower two limbs.
#[test]
fn max_u128() {
assert_eq!(
U256::from(u128::MAX),
U256::from_be_limbs([0, 0, u64::MAX, u64::MAX]),
);
}
/// Value spanning both u64 halves of the u128.
#[test]
fn cross_limb() {
let v = U256::from(((5u128) << 64) | 7);
assert_eq!(v, U256::from_be_limbs([0, 0, 5, 7]));
}
/// Low 128 bits round-trip correctly.
#[test]
fn round_trip_low() {
let n: u128 = 0xABCD_1234_5678_9ABC_DEF0_1234_5678_9ABC;
let v = U256::from(n);
assert_eq!(v.low_u128(), n);
assert_eq!(v.high_u128(), 0);
}
}