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//! Checked subtraction for [`U384`].
use super::U384;
impl U384 {
/// Computes `self - other`, returning `None` if the subtraction would
/// underflow (i.e., `self < other`).
///
/// # Examples
///
/// ```
/// use cnfy_uint::u384::U384;
///
/// let a = U384::from_be_limbs([0, 0, 0, 0, 0, 10]);
/// let b = U384::from_be_limbs([0, 0, 0, 0, 0, 3]);
/// assert_eq!(a.checked_sub(&b), Some(U384::from_be_limbs([0, 0, 0, 0, 0, 7])));
///
/// assert_eq!(U384::ZERO.checked_sub(&U384::ONE), None);
/// ```
#[inline]
pub const fn checked_sub(&self, other: &U384) -> Option<U384> {
let (result, underflow) = self.overflowing_sub(other);
if underflow {
None
} else {
Some(result)
}
}
}
#[cfg(test)]
mod ai_tests {
use super::*;
/// Small subtraction succeeds.
#[test]
fn small() {
let a = U384::from_be_limbs([0, 0, 0, 0, 0, 10]);
let b = U384::from_be_limbs([0, 0, 0, 0, 0, 3]);
assert_eq!(
a.checked_sub(&b),
Some(U384::from_be_limbs([0, 0, 0, 0, 0, 7])),
);
}
/// 0 - 1 returns None.
#[test]
fn underflow() {
assert_eq!(U384::ZERO.checked_sub(&U384::ONE), None);
}
/// Subtracting zero always succeeds.
#[test]
fn zero() {
let a = U384::from_be_limbs([0x1234, 0x5678, 0x9ABC, 0xDEF0, 0x1111, 0x2222]);
assert_eq!(a.checked_sub(&U384::ZERO), Some(a));
}
/// Self minus self returns zero.
#[test]
fn self_sub() {
let a = U384::from_be_limbs([1, 2, 3, 4, 5, 6]);
assert_eq!(a.checked_sub(&a), Some(U384::ZERO));
}
}