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//! Checked addition for [`U512`].
use super::U512;
impl U512 {
/// Checked 512-bit addition, returning `None` on overflow.
///
/// Computes `self + other` via [`overflowing_add`](U512::overflowing_add).
/// Returns `Some(result)` if the sum fits in 512 bits, or `None` if
/// the addition would overflow.
///
/// # Examples
///
/// ```
/// use cnfy_uint::u512::U512;
///
/// let a = U512::from_be_limbs([0, 0, 0, 0, 0, 0, 0, 10]);
/// let b = U512::from_be_limbs([0, 0, 0, 0, 0, 0, 0, 20]);
/// assert_eq!(a.checked_add(&b), Some(U512::from_be_limbs([0, 0, 0, 0, 0, 0, 0, 30])));
/// assert_eq!(U512::MAX.checked_add(&U512::ONE), None);
/// ```
#[inline]
pub const fn checked_add(&self, other: &U512) -> Option<U512> {
let (result, overflow) = self.overflowing_add(other);
if overflow {
None
} else {
Some(result)
}
}
}
#[cfg(test)]
mod ai_tests {
use super::*;
/// Small values add without overflow.
#[test]
fn small_add() {
let a = U512::from_be_limbs([0, 0, 0, 0, 0, 0, 0, 100]);
let b = U512::from_be_limbs([0, 0, 0, 0, 0, 0, 0, 200]);
assert_eq!(
a.checked_add(&b),
Some(U512::from_be_limbs([0, 0, 0, 0, 0, 0, 0, 300])),
);
}
/// MAX + 1 overflows to None.
#[test]
fn max_plus_one() {
assert_eq!(U512::MAX.checked_add(&U512::ONE), None);
}
/// MAX + MAX overflows to None.
#[test]
fn max_plus_max() {
assert_eq!(U512::MAX.checked_add(&U512::MAX), None);
}
/// Zero is the additive identity.
#[test]
fn additive_identity() {
let a = U512::from_be_limbs([0x1234, 0x5678, 0x9ABC, 0xDEF0, 1, 2, 3, 4]);
assert_eq!(a.checked_add(&U512::ZERO), Some(a));
}
/// Carry across all limbs without overflow.
#[test]
fn carry_no_overflow() {
let a = U512::from_be_limbs([0, u64::MAX, u64::MAX, u64::MAX, u64::MAX, u64::MAX, u64::MAX, u64::MAX]);
let b = U512::ONE;
assert_eq!(
a.checked_add(&b),
Some(U512::from_be_limbs([1, 0, 0, 0, 0, 0, 0, 0])),
);
}
/// Just below overflow boundary succeeds.
#[test]
fn just_below_overflow() {
let a = U512::from_be_limbs([u64::MAX, u64::MAX, u64::MAX, u64::MAX, u64::MAX, u64::MAX, u64::MAX, u64::MAX - 1]);
assert_eq!(a.checked_add(&U512::ONE), Some(U512::MAX));
}
}